1. Introduction {#sec1-brainsci-07-00020}
===============

Age-related cognitive decline is a common problem for many elderly people, yet its cause is poorly understood. Over 99% of investigational drugs, participating in over 200 clinical trials, failed to receive approval for the treatment of Alzheimer's disease \[[@B1-brainsci-07-00020]\]. Even the success of a few approved drugs provides only minimal patient improvement. There is a need for new, safe, and effective therapeutics with extensive safety and efficacy data that can be developed for use in humans within the next few years.

GHK (glycyl-[l]{.smallcaps}-histidyl-[l]{.smallcaps}-lysine) is a human plasma copper-binding peptide with a stunning array of actions that appear to counter aging-associated diseases and conditions. GHK was isolated in 1973 as an activity bound to human albumin that caused aged human liver tissue to synthesize proteins like younger tissue \[[@B2-brainsci-07-00020]\]. It has a strong affinity for copper and readily forms the complex GHK-Cu. It was first proposed that GHK-Cu functions by modulating copper intake into cells \[[@B3-brainsci-07-00020]\]. Since then, it has been established that the GHK peptide has stimulating and growth-promoting effects on many cells and tissues such as chondrocytes \[[@B4-brainsci-07-00020]\], liver cells and human fibroblasts \[[@B5-brainsci-07-00020]\]. It increases stemness and stimulates integrin secretion in human epidermal basal keratinocytes \[[@B6-brainsci-07-00020]\], as well as has a strong wound-healing and tissue-repairing effect \[[@B7-brainsci-07-00020]\]. GHK has also been shown to improve wound healing in controlled experiments using animals, such as rats, dogs, and rabbits \[[@B8-brainsci-07-00020],[@B9-brainsci-07-00020],[@B10-brainsci-07-00020]\].

In 2010, Hong et al. using the Broad Institute's Connectivity Map (cMap), a compendium of transcriptional responses to compounds, identified GHK as the most active of 1309 bioactive substances, uniquely capable of reversing the expression of 54 genes in a metastatic-prone signature for aggressive early stage mismatch-repair colorectal cancer. GHK was active at a very low concentration of 1 µM \[[@B11-brainsci-07-00020]\].

Another study, which also used the cMap to identify genes affected by GHK, was conducted in 2012 when Campbell et al. identified 127 genes whose expression levels were associated with regional severity of chronic obstructive pulmonary disease (COPD). Emphysema and chronic bronchitis, the two main conditions of COPD, cause both small airway obstruction and significant loss of lung function over time. The cMap predicted that GHK would reverse the aberrant gene-expression signature associated with emphysematous destruction and induce expression patterns consistent with healing and repair. These finding were supported by laboratory experiments. GHK, at 10 nM, added to cultured fibroblasts from the affected lung areas of patients, changed gene expression patterns from tissue destruction to tissue repair. This led to the organization of the actin cytoskeleton, elevated the expression of integrin beta 1, and restored collagen contraction \[[@B12-brainsci-07-00020]\].

In addition to topping the list of 1309 biologically active molecules as the computer-recommended treatment for both human COPD (chronic obstructive pulmonary disease) and aggressive metastatic colon cancer, GHK has been recommended as a treatment for inflammations, acute lung injury, activation of stem cells, regeneration of aged skin, wound healing and tissue regeneration (skin, hair follicles, stomach and intestinal linings, hair growth, and boney tissue). It is also widely used in anti-aging skin products \[[@B13-brainsci-07-00020]\].

Even though it is not always possible to link gene expression data to biological actions, it is important to notice that GHK is highest in very healthy young people. Unfortunately, GHK declines with age. In studies at the University of California at San Francisco, young (age 20--25), male medical students were found to have about 200 nanograms/mL of GHK in their blood plasma, while the healthy, male medical school faculty (average age of 60) had only 80 nanograms/mL \[[@B7-brainsci-07-00020]\].

Our previous publication reviewed the biological effects of GHK relevant to neurodegeneration and cognitive health \[[@B14-brainsci-07-00020]\]. This paper will discuss the effect of GHK on gene expression relevant to nervous system functions and cognitive decline as well as review genetic and laboratory data relevant to nerve outgrowth, copper transport into cells, anxiety and pain, DNA repair, the ubiquitin proteasome system, the anti-oxidant system, changes in gene expression for glial cells, astrocytes, brain cells, dendrites, ganglia, motor neurons, Schwann cells, and sensory cells. It will also present possible methods for the use of therapeutic GHK in the treatment of nerve diseases.

2. Materials and Methods {#sec2-brainsci-07-00020}
========================

The cMap was used to acquire the gene expression data. It is a large database that contains more than 7000 gene expression profiles of 5 human cell lines treated with 1309 distinct small molecules. Three GHK profiles are contained in this repository. The profiles are the result of cell lines treated with GHK at 1 micromolar which is around the concentration where many of GHK's cellular effects occur \[[@B15-brainsci-07-00020]\]. These profiles were created using the GeneChip HT Human Genome U133A Array. Among the 5 cell lines used by the Connectivity Map only 2 were treated with GHK. Two of the profiles were created using the PC3 cell line - human prostate cancer cells, while the third used the MCF7 cell line -- human breast cancer cells. Our studies utilized all three gene expression profiles.

GenePattern, a publicly available computational biology open-source software package developed for the analysis of genomic data, was used to analyze the gene data obtained from the cMap. The CEL files (data files used by Affymetrix software, used by the Broad Institute) were processed with MAS5 (Microarray Analysis Suite 5 software, Affymetrix, Santa Clara, CA, USA) and background correction. Files were then uploaded to the ComparativeMarkerSelectionViewer module in order to view fold changes for each probe set. Gene abbreviations appearing throughout the paper are consistent with the NCBI Gene database \[[@B16-brainsci-07-00020]\].

Due to multiple probe sets mapping to the same gene, the fold changes in m-RNA production produced by GenePattern were converted to percentages, and then all probe sets representing the same gene were averaged. It was determined that the 22,277 probe sets in the Broad data represent 13,424 genes. This ratio (1.66) was used to calculate the overall number of genes that affect GHK at various cutoff points (rather than probe sets).

The percentage of genes stimulated or suppressed by GHK with a change greater than or equal to 50% was estimated to be 31.2% \[[@B17-brainsci-07-00020]\]. Listed in the article are the gene expression effects of GHK on over 700 human genes associated with various nerve cell types. For well-defined systems where animal and cell cultures exist, such as anti-pain and anti-oxidation, relevant genes were manually chosen. For other systems, each gene's Gene Ontology description was searched, using terms such as "neuron" or "glial". The Gene Ontology consortium provides controlled vocabularies for the description of the molecular function, biological process, and cellular component of gene products. \[[@B18-brainsci-07-00020]\]. For most systems, gene expression numbers were given from 100% + or − and larger.

The cMap data was proven to be predictive of biological actions in most cases. In 2010, cMap predicted the anti-cancer actions of GHK. Subsequent work found GHK at 1 to 10 nanomolar reset the programmed cell death system on human nerve cancer cells and inhibited their growth in culture, while having the same effect on sarcoma cell growth in mice; it changed the gene expression of over 80 genes in an anti-growth manner \[[@B17-brainsci-07-00020]\]. Data from cMap also led to experiments that found GHK at 10 nanomolar caused human COPD-afflicted lung cells to switch cell expression from tissue destruction to repair and remodeling. For anti-oxidant actions, cMap has been very predictive of actions in mammals. However, gene expression numbers can vary widely at times and are not always predictable. For example, the cMap gives NGF (nerve growth factor) as a −243% decrease, yet in vivo rat studies have found NGF to be increased and two in vitro cell culture studies have found GHK to increase nerve outgrowth, an effect usually attributed to NGF.

Below, we cover GHK's relationship with the following. Nerve OutgrowthCopper Lack in Nerve DiseasesAnti-Anxiety and Anti-PainAnti-Oxidant Biological and Gene Expression DataDNA Repair Data and Gene Expression DNA RepairRestoring Regeneration after Cortisone TreatmentGene Expression---Clearing Damaged Protein with the Ubiquitin Proteasome System (UPS)Gene Expression---NeuronsGene Expression---Motor neuronsGene Expression---Glial cellsGene Expression---AstrocytesGene Expression---SchwannGene Expression---MyelinGene Expression---DendriteGene Expression---Oligodendrocyte cellsGene Expression---Schwann cellsGene Expression---SpinalPossible methods of therapeutic use of GHK for nerve disease

3. Results {#sec3-brainsci-07-00020}
==========

3.1. Nerve Outgrowth {#sec3dot1-brainsci-07-00020}
--------------------

The lack of nerve outgrowth growth is considered a major factor in dementia \[[@B19-brainsci-07-00020],[@B20-brainsci-07-00020],[@B21-brainsci-07-00020]\].

GHK was discovered in 1973 as a growth factor for cultured hepatocytes. In 1975, Sensenbrenner and colleagues reported that GHK induced the formation chick embryonic neurons while suppressing glial cells. See [Figure 1](#brainsci-07-00020-f001){ref-type="fig"} \[[@B22-brainsci-07-00020]\].

Lindner and colleagues found that explants from chick embryo PNS (ganglion trigeminale) and from CNS of embryonal rats (hippocampus) and dissociated cells from chick embryo cerebral hemispheres that 0.01 microgram GHK per ml of medium stimulated the outgrowth of neuronal processes. Again, GHK promoted neuronal growth but not glial cells \[[@B23-brainsci-07-00020]\].

In studies of rats, severed sciatic nerves (axotomy) were inserted into a collagen prosthesis to which GHK was bonded. These were re-inserted into the rat, then removed after 10 days. GHK enhanced the production of trophic factors (Nerve Growth Factor, Neurotrophins 3 and 4) and recruited hematogenous cells and Schwann cells, which in turn help in the secretion of certain vital trophic and tropic factors essential for early regeneration. This improved nerve regeneration following axotomy \[[@B24-brainsci-07-00020]\]. Surprisingly, GHK's gene expression data gives suppression of NGF (−243%) and NGFR (nerve growth factor receptor) (−132%). Thus, the biological system within wounded rat's nervous tissue is more complex and probably due to other nerve stimulatory molecules.

3.2. Copper Deficiency, Dementia, and Nerve Dysfunction {#sec3dot2-brainsci-07-00020}
-------------------------------------------------------

Copper is an essential component of important anti-oxidant proteins such as SOD (copper zinc superoxide dismutase), ceruloplasmin, and Atox1 (human antioxidant protein 1). Copper deficiency has been postulated as a causative factor in a variety of gene diseases such as Alzheimer's \[[@B25-brainsci-07-00020],[@B26-brainsci-07-00020],[@B27-brainsci-07-00020],[@B28-brainsci-07-00020],[@B29-brainsci-07-00020],[@B30-brainsci-07-00020]\], myelopathy \[[@B31-brainsci-07-00020]\], motor neuron diseases and amyotrophic lateral sclerosis \[[@B32-brainsci-07-00020]\], Huntington's \[[@B33-brainsci-07-00020]\], Lewy bodies and Creutzfeldt Jakob diseases \[[@B34-brainsci-07-00020]\].

More importantly, analysis of actual human brains from deceased patients with dementia has found the damaged areas to have very little cellular copper. In plaques from persons with Alzheimer's disease, iron and aluminum appear to cause plaque formation while copper and zinc may be protective \[[@B26-brainsci-07-00020],[@B27-brainsci-07-00020],[@B28-brainsci-07-00020],[@B35-brainsci-07-00020],[@B36-brainsci-07-00020],[@B37-brainsci-07-00020]\].

Copper deficiency caused by bariatric surgery or gastrointestinal bleeding led to myelopathy (human swayback), paralysis, blindness and behavioral and cognitive changes. Mice born and maintained on a copper deficient diet had 80% reduction in brain copper level at 6-8 weeks and had neuronal and glial changes typical for neurodegenerative disorders \[[@B25-brainsci-07-00020],[@B31-brainsci-07-00020],[@B38-brainsci-07-00020],[@B39-brainsci-07-00020]\].

### 3.2.1. Supplying Copper to Nerve Cells {#sec3dot2dot1-brainsci-07-00020}

Though copper deficiency appears linked to major nerve diseases, the use of copper supplements as a treatment has been disappointing. A placebo-controlled study of 68 Alzheimer's patients (34 control, 34 copper) with a treatment of 8 mgs of daily copper (a high level) for 1 year produced no negative findings. This seems to rule out excessive copper levels as a causative agent for the development of Alzheimer's. The predictive protein marker, CSF Abeta42, is lower in persons developing Alzheimer's. Subjects given extra copper supplementation maintained this protein at a higher level, a possible positive effect, but there was minimal improvement in the disease \[[@B40-brainsci-07-00020]\].

One small copper complex chelator, CuATSM (diacetyl-bis(4-methylthiosemicarbazonato)copper 2+), has given indications of ameliorating the effects of ALS (familial amyotrophic lateral sclerosis) in a strain of genetically modified mice that develop a form of ALS. CuATSM extends life in such mice by up to 25%. The motor neuron disease can be restarted and then stopped by controlling CuATSM treatment. The treatment increases the amount of active superoxide dismutase in the mice \[[@B41-brainsci-07-00020]\]. The safety of CuATSM is largely unknown. The safety data sheet states the following: "Material may be irritating to the mucous membranes and upper respiratory tract. May be harmful by inhalation, ingestion, or skin absorption. May cause eye, skin, or respiratory system irritation. To the best of our knowledge, the toxicological properties have not been thoroughly investigated."

GHK-Copper 2+ increased superoxide dismutase (SOD) activity in mice as detailed below in [Section 4](#sec4-brainsci-07-00020){ref-type="sec"} \[[@B42-brainsci-07-00020]\].

### 3.2.2. Albumin, GHK and Copper Transport {#sec3dot2dot2-brainsci-07-00020}

Both albumin and GHK transport copper 2+ to cells and tissues. However, in human blood, there are 700 albumin molecules for each GHK molecule, so albumin is the major source of copper for tissue use. GHK and albumin have high and very similar binding constants for copper 2+ (Albumin = pK binding log 10 \|16.2\|; GHK = pK binding log 10 \|16.4\|). Human plasma contains about 15 micromolar copper and 12% (1.8 micromolar) of this is bound to albumin. But GHK-Cu is maximally active on most cells around one nanomolar or less. Aqueous dialysis studies established that GHK can obtain copper 2+ from albumin. We assume that this also occurs in cell culture and within mammals and that GHK has adequate copper for biological actions.

Our studies over the past 39 years have indicated that virtually all biological GHK effects require the presence of copper 2+ chelated to the tripeptide. Strong copper chelators such as bathocuproine abolish GHK actions. GHK alone is often effective in murine wound healing or hair growth models, but GHK-Cu always produced much stronger responses. GHK attached to radioactive copper-64 increases copper uptake into cultured hepatoma cells \[[@B7-brainsci-07-00020]\].

The intravenous injection of tritiated copper-free GHK into mice was found, after 4 h, to concentrate most densely within the animals' kidneys and brain. See [Figure 2](#brainsci-07-00020-f002){ref-type="fig"} \[[@B43-brainsci-07-00020]\].

The best evidence that GHK can obtain copper 2+ from body fluids was from a study that used biotinylated GHK bound to collagen films placed over wounds in rats. The GHK pads raised the copper concentration by ninefold at the wound site when compared to non-GHK collagen films. Such biotinylated GHK collagen films also increased wound healing, cell proliferation, and increased the expression of antioxidant enzymes in the treated group \[[@B9-brainsci-07-00020]\].

Most importantly, GHK activates numerous regenerative and protective genes. Albumin will not mimic the GHK activated systems. So GHK must act through a separate pathway, not the albumin pathway. Albumin's copper feeds cells; GHK's copper activates regenerative and protective genes.

GHK-Cu's regenerative and protective actions on tissue are very similar to those found by John R Sorenson throughout his 33 years of work on various copper salicylates. See [Table 1](#brainsci-07-00020-t001){ref-type="table"}. It appears that GHK-Copper and Sorenson's DIPS-Cu (diisopropylsalicylate-copper 2+) both activate the same pathway, a pathway strongly associated with tissue health and repair. GHK-copper 2+ (molecular weight 404) and Sorenson's DIPS-Cu (molecular weight 506) are both very small molecules while albumin is much larger (molecular weight 64,000). Hence, they are likely to use different cell receptor systems \[[@B44-brainsci-07-00020],[@B45-brainsci-07-00020],[@B46-brainsci-07-00020],[@B47-brainsci-07-00020],[@B48-brainsci-07-00020],[@B49-brainsci-07-00020]\]. See [Figure 3](#brainsci-07-00020-f003){ref-type="fig"}.

3.3. Anti-Anxiety (Anxiolytic) and Anti-Pain {#sec3dot3-brainsci-07-00020}
--------------------------------------------

Anxiety and pain are serious issues in patients with dementia and other disabling mental conditions. Opiate peptides often possess both anti-pain and wound healing properties \[[@B50-brainsci-07-00020]\]. When healthy human males were fed a low copper diet (1 mg/day of copper) for 11 weeks, their plasma opiate levels dropped by 80%. As soon as copper was restored (with a diet containing 3 mg/day of copper), the levels returned to normal \[[@B51-brainsci-07-00020]\].

GHK has been found to possess analgesic and anxiolytic effects (anti-anxiety) in animal experiments. GHK reduced pain after thermal injury to rats at a dose of 0.5 milligrams/kg. Within 12 min after intraperitoneal injection, it also increased the amount of time the rats spent exploring more open areas of the maze and decreased time spent immobile (the freeze reaction), which indicated reduction of fear and anxiety. These effects were observed at 0.5 micrograms/kg \[[@B52-brainsci-07-00020],[@B53-brainsci-07-00020]\].

These effects also prove that GHK rapidly affects the brain perception and function. This is an area where GHK could be used on patients today.

A manual search of genes affected by GHK found that seven anti-pain genes increased and two genes decreased. See [Table 2](#brainsci-07-00020-t002){ref-type="table"} and [Table 3](#brainsci-07-00020-t003){ref-type="table"}.

3.4. Antioxidant Activity of the GHK Peptide {#sec3dot4-brainsci-07-00020}
--------------------------------------------

High metabolic activity found in the brains of both humans and animals results in elevated oxygen consumption and constant production of reactive oxygen species (ROS) in mitochondria. At the same time, the brain tissue is rich in unsaturated fatty acids and transition metal ions, yet has relatively fewer antioxidants compared to other organs, creating favorable conditions for oxidative damage. Since the blood-brain barrier prevents many dietary antioxidants from entering the brain, it largely relays on endogenous antioxidants such as Cu and Zn dependent superoxide dismutase (Cu, Zn SOD1). This enzyme requires the metal ions copper and zinc in order to be active. Hence, copper deficiency can lead to reduced SOD activity and increased oxidative brain damage. When pregnant rats were fed a copper deficient diet, the embryos displayed low SOD activity, increased super oxide anion radical level, and higher incidence of DNA damage and malformations \[[@B54-brainsci-07-00020]\].

GHK has broad and powerful anti-oxidation properties in both mammals and cell culture, and it is known to increase anti-oxidant gene expression. Tissue oxidation has been postulated as a causative factor in Parkinson's disease and other various nerve diseases of aging \[[@B55-brainsci-07-00020],[@B56-brainsci-07-00020],[@B57-brainsci-07-00020],[@B58-brainsci-07-00020],[@B59-brainsci-07-00020]\].

Diminished copper has been found in cells expressing SOD1 mutations postulated to cause ALS in mice and increase memory loss \[[@B60-brainsci-07-00020],[@B61-brainsci-07-00020]\].

A peptidomimetic inhibitor (P6), based on GHK, interacts with amyloid beta (Aβ) peptide and its aggregates. P6 prevents the formation of toxic Aβ oligomeric species, fibrillar aggregates and DNA damage. It is a potential therapeutic candidate to ameliorate the multifaceted Aβ toxicity in Alzheimer's \[[@B62-brainsci-07-00020]\].

### 3.4.1. GHK's Anti-Oxidant Effects in Mammals and Cell Culture {#sec3dot4dot1-brainsci-07-00020}

The use of GHK-Cu in mice protected their lung tissue from lipopolysaccharide-induced acute lung injury (ALI). When GHK-Cu was used by mice with LPS-induced ALI, it attenuated related histological alterations in the lungs and suppressed the infiltration of inflammatory cells into the lung parenchyma. The GHK-Cu also increased superoxide dismutase (SOD) activity while decreasing TNF-α and IL-6 production through the suppression of the phosphorylation of NF-κB p65 and p38 MAPK in the nucleus of lung cells \[[@B42-brainsci-07-00020]\].

P38 mitogen-activated protein kinases are responsive to stress stimuli, such as cytokines, ultraviolet irradiation, heat shock, and osmotic shock, and are involved in cell differentiation, apoptosis, and autophagy. NF-κB/RELA p65 activation has been found to be correlated with cancer development, suggesting the potential of RELA as a cancer biomarker. Specific modification patterns of RELA have also been observed in many cancer types.

Multiple antioxidant actions of GHK have been demonstrated in vitro and in animal wound healing studies. They include inhibiting the formation of reactive carbonyl species (RCS), detoxifying toxic products of lipid peroxidation such as acrolein, protecting keratinocytes from lethal UVB radiation, and preventing hepatic damage by dichloromethane radicals.

The ability of GHK to prevent oxidative stress was tested in vitro using Cu(2+)-dependent oxidation of low-density lipoproteins (LDL). LDL were treated with 5 μM Cu(2+) for 18 h in either phosphate buffered saline (PBS) or Ham's F-10 medium. There was increased production of thiobarbituric acid reactive substances (TBARSs), which indicated increased oxidation. GHK and histidine "entirely blocked" (quoted from the article) the in vitro Cu(2+)-dependent oxidation of low-density lipoproteins (LDL). In comparison, superoxide dismutase (SOD1) provided only 20% reduction of oxidation \[[@B63-brainsci-07-00020]\].

Acrolein, a well-known carbonyl toxin, is produced by lipid peroxidation of polyunsaturated fatty acids. GHK effectively reduces the formation of both acrolein and another product of oxidation, 4-hydroxynonenal. GHK also blocks lethal ultraviolet radiation damage to cultured skin keratinocytes by binding and inactivating reactive carbonyl species such as 4-hydroxynoneal, acrolein, malondialdehyde, and glyoxal \[[@B64-brainsci-07-00020],[@B65-brainsci-07-00020],[@B66-brainsci-07-00020]\].

The intraperitoneal injection of 1.5 mg/kg of GHK into rats for five days before dichloromethane poisoning and five days thereafter provided protection of the functional activity of hepatocytes and immunological responsiveness. Dichloromethane is toxic to hepatic tissue via the formation of a dichloromethane free radical that induces acute toxic damage \[[@B67-brainsci-07-00020]\].

In rats with experimental bone fractures peptides, GHK (0.5 μg/kg), dalargin (1.2 μg/kg), and thymogen (0.5 μg/kg) were injected intraperitoneally. Within 10 days, there was a decrease of malonic dialdehyde and an increase of catalase activity in blood. There was also a marked increase of reparative activity. Each combination of peptides was more potent than any of the studied peptides injected separately. The synergetic action of peptides Gly-His-Lys, thymogen, and dalargin was proposed for stimulation of reparative osteogenesis \[[@B68-brainsci-07-00020]\].

GHK-Cu reduced iron release from ferritin by 87%. Iron has also been shown to have a direct role in the initiation of lipid peroxidation. An Fe(2+)/Fe(3+) complex can serve as an initiator of lipid oxidation. In addition, many iron complexes can catalyze the decomposition of lipid hydroperoxides to the corresponding lipid alkoxy radicals. The major storage site for iron in serum and tissue is ferritin. Ferritin in blood plasma can store up to 4500 atoms of iron per protein molecule, and superoxide anions can promote the mobilization of iron from ferritin. This free iron may then catalyze lipid peroxidation and the conversion of a superoxide anion to the more damaging hydroxyl radical \[[@B69-brainsci-07-00020]\].

### 3.4.2. Synthesis of GHK-Cu Analogs with Higher Anti-ROS Activity {#sec3dot4dot2-brainsci-07-00020}

GHK-Cu has, on a molar basis, about 1% to 3% of the activity of the Cu, Zn superoxide dismutase protein. By simple modifications to the peptide, it is possible to raise the SOD-mimetic activity up 223-fold. Given the broad range of the antioxidant actions of GHK, it is likely that modifications will increase its countering reactive species such as RCS and dichloromethane radicals. See [Table 4](#brainsci-07-00020-t004){ref-type="table"} \[[@B70-brainsci-07-00020]\].

### 3.4.3. Antioxidant Gene Expression Analysis {#sec3dot4dot3-brainsci-07-00020}

A manual search of antioxidant associated genes effected by GHK yielded 18 genes with significant antioxidant activity. See [Table 5](#brainsci-07-00020-t005){ref-type="table"} and [Table 6](#brainsci-07-00020-t006){ref-type="table"}.

3.5. DNA Repair, Cell Culture, and Gene Expression {#sec3dot5-brainsci-07-00020}
--------------------------------------------------

A lack of adequate DNA repair may be related to neurological degeneration in the aging population \[[@B90-brainsci-07-00020],[@B91-brainsci-07-00020],[@B92-brainsci-07-00020],[@B93-brainsci-07-00020]\].

DNA damage is a major problem in the life cycle of biological cells. Normal cellular metabolism releases compounds that damage DNA such as reactive oxygen species, reactive nitrogen species, reactive carbonyl species, lipid peroxidation products and alkylating agents, among others, while hydrolysis cleaves chemical bonds in DNA. It is estimated that each normally functioning cell in the human body suffers at least 10,000 DNA damaging incidents daily \[[@B94-brainsci-07-00020]\].

Radiation therapy is believed to stop cell replication by damaging cellular DNA. A study of cultured primary human dermal fibroblast cell lines from patients who had undergone radiation therapy for head and neck cancer found that the procedure slowed the population doubling times for the cells. But treatment with one nanomolar GHK-Cu restored population doubling times to normal. Irradiated cells treated with GHK-Cu also produced significantly more basic fibroblast growth factor and vascular endothelial growth factor than untreated irradiated cells \[[@B5-brainsci-07-00020]\].

GHK is primarily stimulatory for gene expression of DNA Repair genes (47 UP, 5 DOWN), suggesting an increased DNA repair activity. Here we searched the Gene Ontology descriptions for "DNA Repair". See [Table 7](#brainsci-07-00020-t007){ref-type="table"} and [Table 8](#brainsci-07-00020-t008){ref-type="table"}.

3.6. Restoring Regeneration After Cortisone Treatment {#sec3dot6-brainsci-07-00020}
-----------------------------------------------------

Steroid dementia syndrome describes the signs and symptoms of hippocampal and prefrontal cortical dysfunction, such as deficits in memory, attention, and executive function, induced by glucocorticoids. Dementia-like symptoms have been found in some individuals who have been exposed to glucocorticoid medication, often dispensed in the form of asthma, arthritis, and anti-inflammatory steroid medications. The condition reverses, but not always completely, within months after steroid treatment is stopped \[[@B95-brainsci-07-00020]\].

In the human body, cortisone and cortisol are easily interconvertible and have similar anti-inflammatory actions. They also profoundly inhibit tissue regeneration, such as wound repair. DHEA (dehydroepiandrosterone) is an androgenic hormone. It is a precursor for testosterone and the estrogens. DHEA antagonizes the effects of cortisol but decreases about 80% from age 20 to age 80 while cortisone/cortisol levels remain high. It has been proposed that many of the deleterious effects of aging are due to excessive cortisol that is not balanced by DHEA.

GHK-Cu, when administered systemically to mice, rats, and pigs, counters the wound healing inhibition of cortisone throughout the animal \[[@B96-brainsci-07-00020]\].

3.7. Gene Expression---Clearing Damaged Protein---Ubiquitin Proteasome System {#sec3dot7-brainsci-07-00020}
-----------------------------------------------------------------------------

The ubiquitin proteasome system (UPS) clears damaged proteins. Insufficient activity of this system is postulated to produce an accumulation of toxic protein oligomers which start the neurodegenerative process. During aging, there is decreased activity of the ubiquitin proteasome system. To date, no effective therapies have been developed that can specifically increase the UPS activity \[[@B97-brainsci-07-00020],[@B98-brainsci-07-00020],[@B99-brainsci-07-00020],[@B100-brainsci-07-00020]\].

GHK strongly stimulates the gene expression of the UPS system with 41 genes increased and 1 gene suppressed. Here we searched gene title for "ubiquitin" or "proteasome". See [Table 9](#brainsci-07-00020-t009){ref-type="table"} and [Table 10](#brainsci-07-00020-t010){ref-type="table"}.

3.8. Gene Expression---Neurons {#sec3dot8-brainsci-07-00020}
------------------------------

Neurons are cells that carry messages between the brain and other parts of the body; they are the basic units of the nervous system.

GHK is primarily stimulatory for gene expression of neuron related genes. Here we searched the Gene Ontology descriptions for "Neuron". See [Table 11](#brainsci-07-00020-t011){ref-type="table"} and [Table 12](#brainsci-07-00020-t012){ref-type="table"}.

3.9. Motor Neurons {#sec3dot9-brainsci-07-00020}
------------------

Motor neurons are nerve cells forming part of a pathway along which impulses pass from the brain or spinal cord to a muscle or gland.

Here we searched Gene Ontology descriptions for "motor neuron". See [Table 13](#brainsci-07-00020-t013){ref-type="table"} and [Table 14](#brainsci-07-00020-t014){ref-type="table"}.

3.10. Gene Expression---Glial Cells {#sec3dot10-brainsci-07-00020}
-----------------------------------

Glial cells are non-neuronal cells that maintain homeostasis, form myelin, and provide support and protection for neurons in the central and peripheral nervous systems.

Here we searched Gene Ontology descriptions for "glial". See [Table 15](#brainsci-07-00020-t015){ref-type="table"} and [Table 16](#brainsci-07-00020-t016){ref-type="table"}.

3.11. Astrocyte {#sec3dot11-brainsci-07-00020}
---------------

Astrocytes are characteristic star-shaped glial cells in the brain and spinal cord. The astrocyte proportion varies by region and ranges from 20% to 40% of all glial cells. They perform many functions, including biochemical support of endothelial cells that form the blood--brain barrier, provision of nutrients to the nervous tissue, maintenance of extracellular ion balance, and a role in the repair and scarring process of the brain and spinal cord following traumatic injuries.

Here we searched Gene Ontology descriptions for "astrocyte". See [Table 17](#brainsci-07-00020-t017){ref-type="table"} and [Table 18](#brainsci-07-00020-t018){ref-type="table"}.

3.12. Schwann Cells {#sec3dot12-brainsci-07-00020}
-------------------

Schwann cells are cells of the peripheral nervous system that wrap around a nerve fiber, jelly-roll fashion, forming the myelin sheath.

Here we searched Gene Ontology descriptions for "Schwann". See [Table 19](#brainsci-07-00020-t019){ref-type="table"} and [Table 20](#brainsci-07-00020-t020){ref-type="table"}.

3.13. Myelin {#sec3dot13-brainsci-07-00020}
------------

Myelin is a mixture of proteins and phospholipids that form a whitish insulating sheath around many nerve fibers, increasing the speed at which impulses are conducted.

Here we searched Gene Ontology descriptions for "myelin". See [Table 21](#brainsci-07-00020-t021){ref-type="table"} and [Table 22](#brainsci-07-00020-t022){ref-type="table"}.

3.14. Gene Expression---Dendrites {#sec3dot14-brainsci-07-00020}
---------------------------------

Dendrites are short branched extensions of a nerve cell, along which impulses received from other cells at synapses are transmitted to the cell body.

Here we searched Gene Ontology descriptions for "dendrite". See [Table 23](#brainsci-07-00020-t023){ref-type="table"} and [Table 24](#brainsci-07-00020-t024){ref-type="table"}.

3.15. Gene Expression---Oligodendrocytes {#sec3dot15-brainsci-07-00020}
----------------------------------------

Oligodendrocytes are glial cells similar to astrocytes, but with fewer protuberances, which are concerned with the production of myelin in the central nervous system.

Here we searched Gene Ontology descriptions for "oligodendrocyte". See [Table 25](#brainsci-07-00020-t025){ref-type="table"} and [Table 26](#brainsci-07-00020-t026){ref-type="table"}.

3.16. Gene Expression---Sensory Nerve cells {#sec3dot16-brainsci-07-00020}
-------------------------------------------

Sensory neurons are nerves that transmit sensory information (sight, sound, feeling, etc.). They are activated by sensory input and send projections to other elements of the nervous system, ultimately conveying sensory information to the brain or spinal cord.

Here we searched Gene Ontology descriptions for "sensory". See [Table 27](#brainsci-07-00020-t027){ref-type="table"} and [Table 28](#brainsci-07-00020-t028){ref-type="table"}.

3.17. Spinal Nerve Cells {#sec3dot17-brainsci-07-00020}
------------------------

Spinal nerve cells transfer information, which travels down the spinal cord, as a conduit for sensory information in the reverse direction, and finally as a center for coordinating certain reflexes.

Here we searched Gene Ontology descriptions for "spinal". See [Table 29](#brainsci-07-00020-t029){ref-type="table"} and [Table 30](#brainsci-07-00020-t030){ref-type="table"}.

4. Possible Methods of Therapeutic Use of GHK for Nerve Diseases {#sec4-brainsci-07-00020}
================================================================

4.1. Mode of Administering GHK-Cu to Patients {#sec4dot1-brainsci-07-00020}
---------------------------------------------

### 4.1.1. Skin Cream or Patch {#sec4dot1dot1-brainsci-07-00020}

GHK-Cu has an unexpectedly rapid passage through skin's stratum corneum. When tested by Howard Maibach's group (Univerisity of California at San Francisco), 0.68% GHK-Cu was applied to dermatomed skin. Over 48 h, 136 micrograms of GHK-Cu passed through the skin per centimeter squared. This is a significant amount of GHK-Cu, and a transdermal patch of a several centimeters squared may pass therapeutically effective amounts throughout the human body \[[@B101-brainsci-07-00020]\].

Russian studies reported that 0.5 micrograms/kg reduced anxiety in rats. Scaled up for a human weight of 70 kg, this would be 35 micrograms in a human \[[@B52-brainsci-07-00020]\]. Our studies on activation of systemic healing in mice, rats, and pigs suggest that about 50 milligrams of GHK-Cu would be effective throughout the human body, although dose-ranging to determine the minimum active dosage was never performed.

### 4.1.2. Liposomal Encapsulated Oral Tablet {#sec4dot1dot2-brainsci-07-00020}

Alternately, the use of encapsulated liposomal GHK-Cu would allow its oral administration at relatively high dosages. Some sellers of an encapsulated liposomal tripeptide glutathione claim that 60% of the orally administrated peptide enters the human blood stream \[[@B102-brainsci-07-00020]\]. Direct administration in a regular pill form is unlikely to work because of GHK's extreme sensitivity to breakdown by intestinal carboxypeptidase \[[@B103-brainsci-07-00020]\].

GHK-Cu costs about \$8/gram in kilogram amounts. For a 50 mg dosage, the GHK-Cu would cost about \$0.40. It is possible that GHK alone would be effective in humans and be able to obtain sufficient amounts of copper 2+ from albumin. If so, this would simplify its therapeutic use. The minimum effective dosage of GHK-Cu for various uses is unknown since such studies were never performed.

GHK-Cu does lower blood pressure, but the LD50 (Lethal Dose for 50% of mice) for such effects would be about a single dosage of 23,000 mgs of GHK-Cu in a 70 kg human. In GHK-Cu's long history of use in cosmetics, no health issues have ever arisen. We were never able to find an LD 50 for GHK without copper.

In our studies, equimolar mixtures of GHK-Cu and GHK (no copper) are often used to avoid any release of loosely bound copper. Also, copper chelators such as penicillamine have been reported to cause psychosis in humans \[[@B104-brainsci-07-00020]\].

5. Conclusions {#sec5-brainsci-07-00020}
==============

Given all the failed attempts to develop effective treatment methods for nerve degeneration, it is suggested that researchers must take a very broad view of the possible factors causing neurodegenerative diseases and not focus on limited possible causes. It is sensible to concentrate research efforts on the reversion of affected tissues to a healthier condition more characteristic of younger humans. GHK gene studies have increasingly led to the conclusion that the conditions and diseases of aging cannot be scientifically treated without understanding the extensive changes in overall gene activity during aging.

There are three sources of evidence on GHK actions: The best data is in vivo mammalian data, including human clinical studies. As reviewed in this paper, these studies give overwhelming evidence of GHK's effects on cells and tissue growth, as well as anti-cancer, anti-oxidant, wound-healing, anti-inflammation, anti-pain, anti-anxiety and skin regeneration actions.A second form of data is in vitro cell culture and organ culture results. Culture results give evidence about the effect of GHK on cellular production of collagen and other structural proteins, the effect on stem cell function, the recovery of cellular function after anticancer radiation or ultraviolet radiation, and sensitivity of cells to oxidative molecules.A third source of data is in Human Gene expression. Data analysis found that GHK induces a 50% or greater (plus or minus) change of expression in 31.2% of human genes, affecting genes linked to multiple biochemical pathways in many organs and tissue, including the nervous system.

Many studies highlight gene expression effects of various molecules. Given today's advances in computer modeling, it is not that difficult to find substances which affect gene expression in one way or another. However, in most cases, computer-based predictions do not have the same supporting evidence of in vivo and in vitro laboratory data as GHK has. Also, in many cases, the safety and cost of the proposed treatments are a big concern. GHK is safe, inexpensive, and can be used in humans today.

The future research should be focused on further making sense of the very extensive gene data, which has to be paralleled with laboratory and clinical studies. GHK has a wealth of biological data in the areas of wound healing, hair and skin regeneration, intestinal tract and bone repair. However, there is a surprising lack of GHK research in the area of neurodegeneration and cognitive health. We hope that our gene data will encourage researchers to take a better look at biological actions and significance of GHK in connection with cognitive health and nervous system function.

The best administration method, in our opinion, would be GHK-Cu incorporated into liposomes, then administered as an enteric capsule for oral use. A dosage of 10 mgs per dose would be a good starting point, at least for safety studies, but inducing positive actions will most likely require a higher dosage.

We would like to thank Germaine Emilie Pugh and Cassia McClain for their invaluable work in the manuscript preparation.

The authors have equally contributed to the writing and revision of this article.

The authors declare no conflict of interest.

![(**Top**)---Control; (**Bottom**)---Addition of 200 ng/mL of GHK to culture media (Phase contrast ×250, photo micrographs used with permission of John Wiley and Sons).](brainsci-07-00020-g001){#brainsci-07-00020-f001}

![Uptake of glycyl-[l]{.smallcaps}-histidyl-[l]{.smallcaps}-lysine (GHK) into various mouse tissues. (Reprinted from Pickart, L. \[[@B43-brainsci-07-00020]\]).](brainsci-07-00020-g002){#brainsci-07-00020-f002}

![Proposed cell receptor for GHK-Cu.](brainsci-07-00020-g003){#brainsci-07-00020-f003}

brainsci-07-00020-t001_Table 1

###### 

Similarity of Actions of GHK-Copper and Diisopropylsalicylate-Copper.

  Action                             GHK-Copper 2+   Diisopropylsalicylate-Copper 2+
  ---------------------------------- --------------- ---------------------------------
  Wound Healing                      Yes             Yes
  Inhibit Cancer Growth              Yes             Yes
  Anti-Ulcer                         Yes             Yes
  Anti-Pain                          Yes             Yes
  Improve Recovery After Radiation   Yes             Yes
  Increase Stem Cell Activity        Yes             Yes

brainsci-07-00020-t002_Table 2

###### 

Distribution of Genes Affected by GHK and Associated with Pain.

  Percent Change in Gene Expression   Genes UP   Genes DOWN
  ----------------------------------- ---------- ------------
  50%--99%                            0          0
  100%--199%                          5          2
  200%--299%                          1          0
  300%--399%                          0          0
  400%--499%                          0          0
  500%+                               1          0
  Total                               7          2

brainsci-07-00020-t003_Table 3

###### 

GHK and Genes Associated with Pain.

  ---------- -------------- --------------------------------------- -----------------------------------------------------------------------------------------------------
  **UP**     **Gene**       **Percent Change in Gene Expression**   **Comments**
  1          OPRMI          1294                                    Opioid mu 1-High Affinity for enkephalins and beta-endorphins
  2          OPRL1          246                                     Receptor for neuropeptide nociceptin
  3          CCKAR          190                                     Cholecystokinin A receptor, cholecystokinin affects satiety, release of beta-endorphin and dopamine
  4          CNR1           172                                     Cannabinoid receptor, pain-reducing
  5          SIGMAR1        155                                     Non-opioid receptor
  6          PNOC           150                                     Prepronociceptin, complex interactions with pain and anxiety induction
  7          OXT            136                                     Ocytocin, bonding protein---gene also increases human chorionic gonadotropin
  **DOWN**   **Gene**       **Percent Change in Gene Expression**   **Comments**
  1          AMPA 3/GRIA3   −126.00%                                Glutamate receptor, retrograde endocannaboid signaling, nervous system
  2          OPRK1          −119.00%                                Reduced cocaine effects
  ---------- -------------- --------------------------------------- -----------------------------------------------------------------------------------------------------

brainsci-07-00020-t004_Table 4

###### 

Superoxide Dismutase Mimetic Activity of GHK and Analogs.

  Molecule                         Superoxide Dismutase Mimetic Activity
  -------------------------------- ---------------------------------------
  Gly-His-Lys:Cu(2+)               100
  Lys-His-Gly-Amide:Cu(2+)         21
  Gly-His-Lys-Ala-Phe-Ala:Cu(2+)   561
  Ala-His-Lys:Cu(2+)               563
  Gly-His-Lys-Octyl Ester:Cu(2+)   810
  Gly-His-Caprolactam:Cu(2+)       4500
  His-Gly-Lys:Cu(2+)               22,300

brainsci-07-00020-t005_Table 5

###### 

Distribution of Genes Affected by GHK with Antioxidant Activity.

  Percent Change in Gene Expression   Genes UP   Genes DOWN
  ----------------------------------- ---------- ------------
  50%--99%                            2          0
  100%--199%                          7          1
  200%--299%                          2          0
  300%--399%                          1          0
  400%--499%                          1          0
  500%+                               3          1
  Total                               16         2

brainsci-07-00020-t006_Table 6

###### 

GHK and Genes Associate with Antioxidant Activity.

  ---------- ----------- --------------------------------------- -------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------
  **UP**     **Genes**   **Percent Change in Gene Expression**   **Comments**
  1          TLE1        762                                     Inhibits the oxidative/inflammatory gene NF-κB \[[@B71-brainsci-07-00020]\].
  2          SPRR2C      721                                     This proline-rich, antioxidant protein protects outer skin cells from oxidative damage from reactive oxygen species (ROS). When the ROS level is low, the protein remains in the outer cell membrane, but when the ROS level is high, the protein clusters around the cell's DNA to protect it \[[@B72-brainsci-07-00020],[@B73-brainsci-07-00020]\].
  3          ITGB4       609                                     Up-regulation of ITGB4 promotes wound repair ability and antioxidative ability \[[@B74-brainsci-07-00020]\].
  4          APOM        403                                     Binds oxidized phospholipids and increases the antioxidant effect of high-density lipoproteins (HDL) \[[@B75-brainsci-07-00020]\].
  5          PON3        319                                     Absence of PON3 (paraoxonase 3) in mice resulted in increased rates of early fetal and neonatal death. Knockdown of PON3 in human cells reduced cell proliferation and total antioxidant capacity \[[@B76-brainsci-07-00020]\].
  6          IL18BP      295                                     The protein encoded by this gene is an inhibitor of the pro-inflammatory cytokine IL18. IL18BP abolished IL18 induction of interferon-gamma (IFN gamma), IL8, and activation of NF-κB in vitro. Blocks neutrophil oxidase activity \[[@B77-brainsci-07-00020]\].
  7          HEPH        217                                     Inhibits the conversion of Fe(2+) to Fe(3+). HEPH increases iron efflux, lowers cellular iron levels, suppresses reactive oxygen species production, and restores mitochondrial transmembrane potential \[[@B78-brainsci-07-00020]\].
  8          GPSM3       193                                     Acts as a direct negative regulator of NLRP3. NLRP3 triggers the maturation of the pro-inflammatory cytokines IL-1β and IL-18 \[[@B79-brainsci-07-00020]\].
  9          FABP1       186                                     Reduces intracellular ROS level. Plays a significant role in reduction of oxidative stress \[[@B80-brainsci-07-00020],[@B81-brainsci-07-00020]\].
  10         AGTR2       171                                     AGTR2 exerts an anti-inflammatory response in macrophages via enhanced IL-10 production and ERK1/2 phosphorylation, which may have protective roles in hypertension and associated tissue injury \[[@B82-brainsci-07-00020]\].
  11         PON1        149                                     PON1 (paraoxonase 1) is a potent antioxidant and a major anti-atherosclerotic component of HDL \[[@B83-brainsci-07-00020]\].
  12         MT3         142                                     Metallothioneins (MTs) display in vitro free radical scavenging capacity, suggesting that they may specifically neutralize hydroxyl radicals. Metallothioneins and metallothionein-like proteins isolated from mouse brain act as neuroprotective agents by scavenging superoxide radicals \[[@B84-brainsci-07-00020],[@B85-brainsci-07-00020]\].
  13         PTGS2       120                                     Produces cyclooxygenase-II (COX-II), which has antioxidant activities \[[@B86-brainsci-07-00020]\].
  14         SLC2A9      117                                     The p53-SLC2A9 pathway is a novel antioxidant mechanism. During oxidative stress, SLC2A9 undergoes p53-dependent induction, and functions as an antioxidant by suppressing ROS, DNA damage, and cell death \[[@B87-brainsci-07-00020]\].
  **DOWN**   **Genes**   **Percent Change in Gene Expression**   **Comments**
  1          IL17A       −1018                                   This cytokine can stimulate the expression of IL6 and cyclooxygenase-2 (PTGS2/COX-2), as well as enhance the production of nitric oxide (NO). High levels of this cytokine are associated with several chronic inflammatory diseases including rheumatoid arthritis, psoriasis, and multiple sclerosis (\[[@B88-brainsci-07-00020]\]).
  2          TNF         −115                                    GHK suppresses this pro-oxidant TNF gene \[[@B89-brainsci-07-00020]\].
  ---------- ----------- --------------------------------------- -------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------

brainsci-07-00020-t007_Table 7

###### 

Distribution of Genes Affected by GHK and Associated with DNA Repair.

  Percent Change in Gene Expression   Genes UP   Genes DOWN
  ----------------------------------- ---------- ------------
  50%--100%                           41         4
  100%--150%                          2          1
  150%--200%                          1          0
  200%--250%                          2          0
  250%--300%                          1          0
  Total                               47         5

brainsci-07-00020-t008_Table 8

###### 

GHK and Genes Associate with DNA Repair.

  ---------- ------------------------------------------------------ ---------------------------------------
  **UP**     **Gene Title**                                         **Percent Change in Gene Expression**
  1          poly (ADP-ribose) polymerase family, member 3, PARP3   253
  2          polymerase (DNA directed), mu, POLM                    225
  3          MRE11 meiotic recombination 11 homolog A MRE11A        212
  4          RAD50 homolog (S. cerevisiae), RAD50                   175
  5          eyes absent homolog 3 (Drosophila), EYA3               128
  6          retinoic acid receptor, alpha, RARA                    123
  **DOWN**   **Gene Title**                                         **Percent Change in Gene Expression**
  1          cholinergic receptor, nicotinic, alpha 4, CHRNA4       −105
  ---------- ------------------------------------------------------ ---------------------------------------

brainsci-07-00020-t009_Table 9

###### 

Distribution of Genes Affected by GHK and Associated with the Ubiquitin Proteasome System.

  Percent Change in Gene Expression   Genes UP   Genes DOWN
  ----------------------------------- ---------- ------------
  50%--99%                            31         1
  100%--199%                          7          0
  200%--299%                          0          0
  300%--399%                          1          0
  400%--499%                          1          0
  500%+                               1          0
  Total                               41         1

brainsci-07-00020-t010_Table 10

###### 

GHK and Genes Associated with the Ubiquitin Proteasome System.

  UP   Gene Title                                                                     Percent Change
  ---- ------------------------------------------------------------------------------ ----------------
  1    ubiquitin specific peptidase 29, USP29                                         1056
  2    ubiquitin protein ligase E3 component n-recognin 2, UBR2                       455
  3    gamma-aminobutyric acid (GABA) B receptor, 1 /// ubiquitin D, GABBR1 /// UBD   310
  4    ubiquitin specific peptidase 34, USP34                                         195
  5    parkinson protein 2, E3 ubiquitin protein ligase (parkin), PARK2               169
  6    ubiquitin-conjugating enzyme E2I (UBC9 homolog, yeast), UBE2I                  150
  7    ubiquitin protein ligase E3 component n-recognin 4, UBR4                       146
  8    ubiquitin protein ligase E3B, UBE3B                                            116
  9    ubiquitin specific peptidase 2, USP2                                           104
  10   ubiquitin-like modifier activating enzyme 6, UBA6                              104

brainsci-07-00020-t011_Table 11

###### 

Distribution of Genes Affected by GHK and Associated with Neurons.

  Percent Change in Gene Expression   Genes UP   Genes DOWN
  ----------------------------------- ---------- ------------
  50%--99%                            230        80
  100%--199%                          99         80
  200%--299%                          45         35
  300%--399%                          19         14
  400%--499%                          9          10
  500%+                               6          11
  Total                               408        230

brainsci-07-00020-t012_Table 12

###### 

GHK and Genes Associated with Neurons.

  ---------- ------------------------------------------------------------------------------------------------------------------------------------------------ --------------------
  **UP**     **Gene Title**                                                                                                                                   **Percent Change**
  1          opioid receptor, mu 1, OPRM1                                                                                                                     1294
  2          tumor protein p73, TP73                                                                                                                          938
  3          potassium voltage-gated channel, Shal-related subfamily, member 1, KCND1                                                                         845
  4          solute carrier family 8 (sodium/calcium exchanger), member 2, SLC8A2                                                                             737
  5          contactin associated protein-like 2, CNTNAP2                                                                                                     581
  6          stathmin-like 3, STMN3                                                                                                                           500
  7          latrophilin 3, LPHN3                                                                                                                             494
  8          angiopoietin 1, ANGPT1                                                                                                                           487
  9          synapsin III, SYN3                                                                                                                               478
  10         dipeptidyl-peptidase 6, DPP6                                                                                                                     448
  11         somatostatin receptor 2, SSTR2                                                                                                                   442
  12         G protein-coupled receptor, family C, group 5, member B, GPRC5B                                                                                  431
  13         sodium channel, voltage-gated, type III, alpha subunit, SCN3A                                                                                    423
  14         smoothened homolog (Drosophila), SMO                                                                                                             415
  15         tryptophan hydroxylase 1, TPH1                                                                                                                   409
  16         caspase 8, apoptosis-related cysteine peptidase, CASP8                                                                                           399
  17         gamma-aminobutyric acid (GABA) A receptor, alpha 5 /// gamma-aminobutyric acid receptor subunit alpha-5-like, GABRA5 /// LOC100509612            392
  18         transcription factor 7 (T-cell specific, HMG-box), TCF7                                                                                          372
  19         solute carrier family 17 (sodium-dependent inorganic phosphate cotransporter), member 6, SLC17A6                                                 369
  20         doublecortin-like kinase 1, DCLK1                                                                                                                365
  21         p21 protein (Cdc42/Rac)-activated kinase 1, PAK1                                                                                                 363
  22         neurogenic differentiation 4, NEUROD4                                                                                                            362
  23         zinc finger protein 335, ZNF335                                                                                                                  358
  24         wingless-type MMTV integration site family, member 3, WNT3                                                                                       352
  25         ADAM metallopeptidase domain 8, ADAM8                                                                                                            352
  26         neuropeptide Y, NPY                                                                                                                              346
  27         potassium voltage-gated channel, Shaw-related subfamily, member 3, KCNC3                                                                         332
  28         EPH receptor B1, EPHB1                                                                                                                           330
  29         LIM domain kinase 1, LIMK1                                                                                                                       322
  30         myeloid/lymphoid or mixed-lineage leukemia (trithorax homolog, Drosophila), MLL                                                                  318
  31         growth associated protein 43, GAP43                                                                                                              305
  32         FBJ murine osteosarcoma viral oncogene homolog, FOS                                                                                              305
  33         sal-like 1 (Drosophila), SALL1                                                                                                                   302
  34         synovial sarcoma, X breakpoint 2 /// synovial sarcoma, X breakpoint 2B, SSX2 /// SSX2B                                                           301
  35         inositol 1,4,5-triphosphate receptor, type 3, ITPR3                                                                                              298
  36         bone morphogenetic protein receptor, type IB, BMPR1B                                                                                             298
  37         synuclein, gamma (breast cancer-specific protein 1), SNCG                                                                                        292
  38         calcium channel, voltage-dependent, P/Q type, alpha 1A subunit, CACNA1A                                                                          286
  39         capping protein (actin filament) muscle Z-line, beta, CAPZB                                                                                      285
  40         plexin C1, PLXNC1                                                                                                                                282
  41         nuclear factor I/B, NFIB                                                                                                                         279
  42         islet amyloid polypeptide, IAPP                                                                                                                  276
  43         nephroblastoma overexpressed gene, NOV                                                                                                           275
  44         hyperpolarization activated cyclic nucleotide-gated potassium channel 4, HCN4                                                                    269
  45         calsyntenin 2, CLSTN2                                                                                                                            268
  46         potassium intermediate/small conductance calcium-activated channel, subfamily N, member 1, KCNN1                                                 266
  47         sodium channel, voltage-gated, type II, alpha subunit, SCN2A                                                                                     264
  48         neuroligin 1, NLGN1                                                                                                                              261
  49         ELKS/RAB6-interacting/CAST family member 2, ERC2                                                                                                 261
  50         scratch homolog 1, zinc finger protein (Drosophila), SCRT1                                                                                       252
  51         low density lipoprotein receptor-related protein 1, LRP1                                                                                         249
  52         hypothetical protein LOC728392 /// NLR family, pyrin domain containing 1, LOC728392 /// NLRP1                                                    249
  53         opiate receptor-like 1, OPRL1                                                                                                                    246
  54         myosin, heavy chain 14, non-muscle, MYH14                                                                                                        243
  55         nitric oxide synthase 1 (neuronal), NOS1                                                                                                         240
  56         wingless-type MMTV integration site family, member 2B, WNT2B                                                                                     238
  57         glutamate receptor, metabotropic 1, GRM1                                                                                                         231
  58         glutamate receptor interacting protein 1, GRIP1                                                                                                  230
  59         myelin associated glycoprotein, MAG                                                                                                              229
  60         chemokine (C-C motif) ligand 3 /// chemokine (C-C motif) ligand 3-like 1 /// chemokine (C-C motif) ligand 3-like 3, CCL3 /// CCL3L1 /// CCL3L3   228
  61         family with sequence similarity 162, member A, FAM162A                                                                                           228
  62         sphingosine-1-phosphate receptor 5, S1PR5                                                                                                        227
  63         protein tyrosine phosphatase, receptor type, R, PTPRR                                                                                            225
  64         IKAROS family zinc finger 1 (Ikaros), IKZF1                                                                                                      225
  65         potassium intermediate/small conductance calcium-activated channel, subfamily N, member 3, KCNN3                                                 221
  66         solute carrier family 18 (vesicular monoamine), member 2, SLC18A2                                                                                219
  67         glutamate receptor, ionotropic, *N*-methyl [d]{.smallcaps}-aspartate 1, GRIN1                                                                    216
  68         v-src sarcoma (Schmidt-Ruppin A-2) viral oncogene homolog (avian), SRC                                                                           216
  69         jagged 1, JAG1                                                                                                                                   215
  70         adenylate cyclase activating polypeptide 1 (pituitary), ADCYAP1                                                                                  215
  71         ATPase, Ca++ transporting, plasma membrane 2, ATP2B2                                                                                             214
  72         tripartite motif-containing 2, TRIM2                                                                                                             213
  73         netrin 1, NTN1                                                                                                                                   212
  74         paired related homeobox 1, PRRX1                                                                                                                 209
  75         purinergic receptor P2X, ligand-gated ion channel, 3, P2RX3                                                                                      207
  76         inhibitor of DNA binding 4, dominant negative helix-loop-helix protein, ID4                                                                      203
  77         solute carrier family 5 (choline transporter), member 7, SLC5A7                                                                                  202
  78         empty spiracles homeobox 1, EMX1                                                                                                                 202
  79         muscle, skeletal, receptor tyrosine kinase, MUSK                                                                                                 200
  80         GATA binding protein 2, GATA2                                                                                                                    193
  81         cadherin 13, H-cadherin (heart), CDH13                                                                                                           192
  82         Rho/Rac guanine nucleotide exchange factor (GEF) 2, ARHGEF2                                                                                      191
  83         anaplastic lymphoma receptor tyrosine kinase, ALK                                                                                                191
  84         cholecystokinin A receptor, CCKAR                                                                                                                190
  85         GLI family zinc finger 2, GLI2                                                                                                                   183
  86         cholinergic receptor, nicotinic, beta 1 (muscle), CHRNB1                                                                                         182
  87         NK2 homeobox 2, NKX2-2                                                                                                                           181
  88         purinergic receptor P2X, ligand-gated ion channel, 4, P2RX4                                                                                      180
  89         gamma-aminobutyric acid (GABA) receptor, rho 2, GABRR2                                                                                           179
  90         PDZ and LIM domain 5, PDLIM5                                                                                                                     177
  91         plasminogen activator, urokinase, PLAU                                                                                                           172
  92         cannabinoid receptor 1 (brain), CNR1                                                                                                             172
  93         chondrolectin, CHODL                                                                                                                             172
  94         neurexin 2, NRXN2                                                                                                                                171
  95         parkinson protein 2, E3 ubiquitin protein ligase (parkin), PARK2                                                                                 169
  96         calcium channel, voltage-dependent, L type, alpha 1F subunit, CACNA1F                                                                            168
  97         neuregulin 1, NRG1                                                                                                                               164
  98         zinc finger protein 536, ZNF536                                                                                                                  162
  99         endothelin 3, EDN3                                                                                                                               161
  100        paired box 7, PAX7                                                                                                                               161
  101        calcium/calmodulin-dependent protein kinase II beta, CAMK2B                                                                                      161
  102        solute carrier family 30 (zinc transporter), member 3, SLC30A3                                                                                   160
  103        ciliary neurotrophic factor /// zinc finger protein 91 homolog (mouse) /// ZFP91-CNTF readthrough transcript, CNTF /// ZFP91 /// ZFP91-CNTF      159
  104        calcium channel, voltage-dependent, T type, alpha 1I subunit, CACNA1I                                                                            156
  105        membrane associated guanylate kinase, WW and PDZ domain containing 2, MAGI2                                                                      155
  106        sigma non-opioid intracellular receptor 1, SIGMAR1                                                                                               155
  107        leptin, LEP                                                                                                                                      152
  108        microtubule-associated protein tau, MAPT                                                                                                         150
  109        erythropoietin receptor, EPOR                                                                                                                    147
  110        frizzled homolog 8 (Drosophila), FZD8                                                                                                            147
  111        nuclear mitotic apparatus protein 1, NUMA1                                                                                                       147
  112        ninjurin 2, NINJ2                                                                                                                                144
  113        probable transcription factor PML-like /// promyelocytic leukemia, LOC652346 /// PML                                                             144
  114        fasciculation and elongation protein zeta 1 (zygin I), FEZ1                                                                                      143
  115        ribonucleotide reductase M1, RRM1                                                                                                                142
  116        retinoic acid receptor, beta, RARB                                                                                                               142
  117        metallothionein 3, MT3                                                                                                                           142
  118        vascular endothelial growth factor A, VEGFA                                                                                                      141
  119        glycoprotein M6A, GPM6A                                                                                                                          140
  120        runt-related transcription factor 1, RUNX1                                                                                                       136
  121        cholinergic receptor, nicotinic, delta, CHRND                                                                                                    135
  122        testis specific, 10, TSGA10                                                                                                                      135
  123        growth hormone secretagogue receptor, GHSR                                                                                                       135
  124        guanine nucleotide binding protein (G protein), beta polypeptide 3, GNB3                                                                         134
  125        glycine receptor, beta, GLRB                                                                                                                     132
  126        runt-related transcription factor 1; translocated to, 1 (cyclin D-related), RUNX1T1                                                              131
  127        synaptotagmin V, SYT5                                                                                                                            131
  128        bridging integrator 1, BIN1                                                                                                                      130
  129        general transcription factor IIi, GTF2I                                                                                                          128
  130        mitogen-activated protein kinase kinase 7, MAP2K7                                                                                                127
  131        peroxisome proliferator-activated receptor gamma, coactivator 1 alpha, PPARGC1A                                                                  126
  132        v-erb-a erythroblastic leukemia viral oncogene homolog 4 (avian), ERBB4                                                                          125
  133        retinoic acid receptor, alpha, RARA                                                                                                              123
  134        baculoviral IAP repeat-containing protein 1-like /// NLR family, apoptosis inhibitory protein, LOC100510692 /// NAIP                             123
  135        myosin VA (heavy chain 12, myoxin), MYO5A                                                                                                        122
  136        heat shock protein 90kDa alpha (cytosolic), class B member 1, HSP90AB1                                                                           121
  137        voltage-dependent anion channel 1, VDAC1                                                                                                         120
  138        prostaglandin-endoperoxide synthase 2 (prostaglandin G/H synthase and cyclooxygenase), PTGS2                                                     120
  139        spectrin, beta, non-erythrocytic 1, SPTBN1                                                                                                       120
  140        tubulin, beta 2A /// tubulin, beta 2B, TUBB2A /// TUBB2B                                                                                         119
  141        misshapen-like kinase 1, MINK1                                                                                                                   119
  142        neural cell adhesion molecule 1, NCAM1                                                                                                           119
  143        kelch-like 1 (Drosophila), KLHL1                                                                                                                 119
  144        sperm associated antigen 9, SPAG9                                                                                                                118
  145        gonadotropin-releasing hormone 1 (luteinizing-releasing hormone), GNRH1                                                                          116
  146        cholinergic receptor, nicotinic, beta 3, CHRNB3                                                                                                  115
  147        neuralized homolog (Drosophila), NEURL                                                                                                           115
  148        SRY (sex determining region Y)-box 14, SOX14                                                                                                     115
  149        purinergic receptor P2X, ligand-gated ion channel, 1, P2RX1                                                                                      112
  150        transcription factor 4, TCF4                                                                                                                     112
  151        lysozyme, LYZ                                                                                                                                    111
  152        MYC associated factor X, MAX                                                                                                                     111
  153        synaptojanin 1, SYNJ1                                                                                                                            108
  154        ret proto-oncogene, RET                                                                                                                          108
  155        cadherin 2, type 1, N-cadherin (neuronal), CDH2                                                                                                  108
  156        AXL receptor tyrosine kinase, AXL                                                                                                                108
  157        ataxia telangiectasia mutated, ATM                                                                                                               107
  158        parvalbumin, PVALB                                                                                                                               107
  159        glyceraldehyde-3-phosphate dehydrogenase, GAPDH                                                                                                  107
  160        Rap guanine nucleotide exchange factor (GEF) 1, RAPGEF1                                                                                          106
  161        protein kinase C, gamma, PRKCG                                                                                                                   106
  162        neurofibromin 2 (merlin), NF2                                                                                                                    105
  163        serrate RNA effector molecule homolog (Arabidopsis), SRRT                                                                                        105
  164        syntaxin 3, STX3                                                                                                                                 105
  165        X-box binding protein 1, XBP1                                                                                                                    104
  166        potassium large conductance calcium-activated channel, subfamily M, beta member 2, KCNMB2                                                        104
  167        chemokine (C-X3-C motif) receptor 1, CX3CR1                                                                                                      104
  168        aldehyde dehydrogenase 1 family, member A2, ALDH1A2                                                                                              103
  169        drebrin 1, DBN1                                                                                                                                  103
  170        UDP glycosyltransferase 8, UGT8                                                                                                                  103
  171        achaete-scute complex homolog 1 (Drosophila), ASCL1                                                                                              103
  172        POU class 4 homeobox 3, POU4F3                                                                                                                   102
  173        neurofibromin 1, NF1                                                                                                                             102
  174        steroidogenic acute regulatory protein, STAR                                                                                                     101
  175        histamine receptor H3, HRH3                                                                                                                      101
  176        nuclear receptor subfamily 2, group F, member 6, NR2F6                                                                                           100
  177        transforming growth factor, beta 1, TGFB1                                                                                                        100
  178        homeobox D3, HOXD3                                                                                                                               100
  **DOWN**   **Gene Title**                                                                                                                                   **Percent Change**
  81         5-hydroxytryptamine (serotonin) receptor 3A, HTR3A                                                                                               −100
  82         neuroligin 3, NLGN3                                                                                                                              −101
  83         aquaporin 1 (Colton blood group), AQP1                                                                                                           −101
  84         SH3 and multiple ankyrin repeat domains 2, SHANK2                                                                                                −102
  85         neurochondrin, NCDN                                                                                                                              −102
  86         astrotactin 1, ASTN1                                                                                                                             −102
  87         mitogen-activated protein kinase 8 interacting protein 2, MAPK8IP2                                                                               −103
  88         limbic system-associated membrane protein, LSAMP                                                                                                 −103
  89         calcium binding protein 1, CABP1                                                                                                                 −106
  90         integrin, beta 1 (fibronectin receptor, beta polypeptide, antigen CD29 includes MDF2, MSK12), ITGB1                                              −107
  91         discs, large (Drosophila) homolog-associated protein 2, DLGAP2                                                                                   −108
  92         doublecortin, DCX                                                                                                                                −108
  93         colony stimulating factor 3 (granulocyte), CSF3                                                                                                  −108
  94         advanced glycosylation end product-specific receptor, AGER                                                                                       −108
  95         corticotropin releasing hormone receptor 1, CRHR1                                                                                                −109
  96         neuropeptides B/W receptor 2, NPBWR2                                                                                                             −109
  97         even-skipped homeobox 1, EVX1                                                                                                                    −110
  98         retinoid X receptor, gamma, RXRG                                                                                                                 −110
  99         cytoplasmic polyadenylation element binding protein 3, CPEB3                                                                                     −112
  100        alpha tubulin acetyltransferase 1, ATAT1                                                                                                         −113
  101        paralemmin, PALM                                                                                                                                 −115
  102        tumor necrosis factor, TNF                                                                                                                       −115
  103        fatty acid binding protein 7, brain, FABP7                                                                                                       −118
  104        olfactory marker protein, OMP                                                                                                                    −118
  105        Amphiregulin, AREG                                                                                                                               −118
  106        opioid receptor, kappa 1, OPRK1                                                                                                                  −119
  107        calbindin 2, CALB2                                                                                                                               −119
  108        phosphodiesterase 10A, PDE10A                                                                                                                    −121
  109        early growth response 1, EGR1                                                                                                                    −121
  110        cell cycle exit and neuronal differentiation 1, CEND1                                                                                            −123
  111        5-hydroxytryptamine (serotonin) receptor 3B, HTR3B                                                                                               −123
  112        synaptosomal-associated protein, 23kDa, SNAP23                                                                                                   −123
  113        sodium channel, voltage-gated, type XI, alpha subunit, SCN11A                                                                                    −124
  114        growth arrest-specific 7, GAS7                                                                                                                   −124
  115        contactin 1, CNTN1                                                                                                                               −125
  116        neuroligin 4, X-linked, NLGN4X                                                                                                                   −128
  117        gamma-aminobutyric acid (GABA) A receptor, alpha 1, GABRA1                                                                                       −130
  118        leucine zipper, putative tumor suppressor 1, LZTS1                                                                                               −130
  119        mesenchyme homeobox 2, MEOX2                                                                                                                     −131
  120        TYRO3 protein tyrosine kinase, TYRO3                                                                                                             −131
  121        synaptophysin, SYP                                                                                                                               −132
  122        coiled-coil domain containing 64, CCDC64                                                                                                         −132
  123        leucine-rich, glioma inactivated 1, LGI1                                                                                                         −132
  124        nerve growth factor receptor, NGFR                                                                                                               −132
  125        cholinergic receptor, nicotinic, beta 4, CHRNB4                                                                                                  −135
  126        5-hydroxytryptamine (serotonin) receptor 2A, HTR2A                                                                                               −135
  127        myocyte enhancer factor 2C, MEF2C                                                                                                                −138
  128        cholinergic receptor, nicotinic, alpha 4, CHRNA4                                                                                                 −139
  129        prodynorphin, PDYN                                                                                                                               −142
  130        discs, large homolog 2 (Drosophila), DLG2                                                                                                        −142
  131        neurexin 1, NRXN1                                                                                                                                −144
  132        secretin, SCT                                                                                                                                    −148
  133        serpin peptidase inhibitor, clade F (alpha-2 antiplasmin, pigment epithelium derived factor), member 1, SERPINF1                                 −148
  134        tachykinin receptor 3, TACR3                                                                                                                     −150
  135        Ras homolog enriched in brain, RHEB                                                                                                              −150
  136        PARK2 co-regulated, PACRG                                                                                                                        −153
  137        glutamate receptor, ionotropic, kainate 5, GRIK5                                                                                                 −159
  138        bone morphogenetic protein 2, BMP2                                                                                                               −159
  139        choline O-acetyltransferase, CHAT                                                                                                                −160
  140        sodium channel, voltage-gated, type I, alpha subunit, SCN1A                                                                                      −162
  141        TOX high mobility group box family member 3, TOX3                                                                                                −163
  142        gastric inhibitory polypeptide, GIP                                                                                                              −164
  143        corticotropin releasing hormone receptor 2, CRHR2                                                                                                −165
  144        kinesin family member 1A, KIF1A                                                                                                                  −165
  145        RAB35, member RAS oncogene family, RAB35                                                                                                         −166
  146        protein kinase C, theta, PRKCQ                                                                                                                   −167
  147        cell adhesion molecule with homology to L1CAM (close homolog of L1), CHL1                                                                        −171
  148        unc-51-like kinase 4 (C. elegans), ULK4                                                                                                          −172
  149        wingless-type MMTV integration site family, member 4, WNT4                                                                                       −175
  150        thyroid stimulating hormone receptor, TSHR                                                                                                       −175
  151        potassium voltage-gated channel, Shal-related subfamily, member 3, KCND3                                                                         −175
  152        contactin 2 (axonal), CNTN2                                                                                                                      −180
  153        glutamate receptor, ionotropic, N-methyl D-aspartate 2A, GRIN2A                                                                                  −180
  154        fibronectin leucine rich transmembrane protein 1, FLRT1                                                                                          −183
  155        gamma-aminobutyric acid (GABA) A receptor, gamma 3, GABRG3                                                                                       −186
  156        calcium/calmodulin-dependent protein kinase IG, CAMK1G                                                                                           −187
  157        interleukin 6 receptor, IL6R                                                                                                                     −190
  158        calsyntenin 3, CLSTN3                                                                                                                            −191
  159        vesicle-associated membrane protein 1 (synaptobrevin 1), VAMP1                                                                                   −193
  160        promyelocytic leukemia, PML                                                                                                                      −196
  161        ATPase, H+ transporting, lysosomal accessory protein 2, ATP6AP2                                                                                  −209
  162        mitogen-activated protein kinase 8 interacting protein 3, MAPK8IP3                                                                               −209
  163        estrogen receptor 2 (ER beta), ESR2                                                                                                              −216
  164        cytochrome b-245, beta polypeptide, CYBB                                                                                                         −217
  165        purinergic receptor P2Y, G-protein coupled, 11 /// PPAN-P2RY11 readthrough, P2RY11 /// PPAN-P2RY11                                               −219
  166        sonic hedgehog, SHH                                                                                                                              −220
  167        growth differentiation factor 11, GDF11                                                                                                          −221
  168        protein tyrosine phosphatase, receptor type, D, PTPRD                                                                                            −221
  169        ELK1, member of ETS oncogene family, ELK1                                                                                                        −224
  170        regulating synaptic membrane exocytosis 1, RIMS1                                                                                                 −225
  171        hairy/enhancer-of-split related with YRPW motif-like, HEYL                                                                                       −228
  172        neurotrophic tyrosine kinase, receptor, type 3, NTRK3                                                                                            −230
  173        potassium voltage-gated channel, Shab-related subfamily, member 2, KCNB2                                                                         −233
  174        regulator of G-protein signaling 6, RGS6                                                                                                         −235
  175        glycine receptor, alpha 3, GLRA3                                                                                                                 −235
  176        potassium voltage-gated channel, shaker-related subfamily, beta member 1, KCNAB1                                                                 −235
  177        guanine nucleotide binding protein (G protein), alpha transducing activity polypeptide 1, GNAT1                                                  −242
  178        proprotein convertase subtilisin/kexin type 2, PCSK2                                                                                             −242
  179        nerve growth factor (beta polypeptide), NGF                                                                                                      −243
  180        corticotropin releasing hormone, CRH                                                                                                             −243
  181        laminin, alpha 1, LAMA1                                                                                                                          −245
  182        cyclic nucleotide gated channel alpha 3, CNGA3                                                                                                   −249
  183        glutamate receptor, ionotropic, kainate 1, GRIK1                                                                                                 −254
  184        lin-28 homolog A (C. elegans), LIN28A                                                                                                            −259
  185        empty spiracles homeobox 2, EMX2                                                                                                                 −260
  186        cyclin-dependent kinase 5, regulatory subunit 1 (p35), CDK5R1                                                                                    −260
  187        agrin, AGRN                                                                                                                                      −264
  188        T-box, brain, 1, TBR1                                                                                                                            −272
  189        stathmin-like 2, STMN2                                                                                                                           −274
  190        microcephalin 1, MCPH1                                                                                                                           −275
  191        ELAV (embryonic lethal, abnormal vision, Drosophila)-like 4 (Hu antigen D), ELAVL4                                                               −282
  192        mitogen-activated protein kinase 8 interacting protein 1, MAPK8IP1                                                                               −289
  193        calcium channel, voltage-dependent, N type, alpha 1B subunit, CACNA1B                                                                            −290
  194        FEZ family zinc finger 2, FEZF2                                                                                                                  −295
  195        dopamine receptor D4, DRD4                                                                                                                       −296
  196        zinc finger E-box binding homeobox 1, ZEB1                                                                                                       −300
  197        T-cell leukemia homeobox 1, TLX1                                                                                                                 −311
  198        sterile alpha motif domain containing 4A, SAMD4A                                                                                                 −315
  199        opioid binding protein/cell adhesion molecule-like, OPCML                                                                                        −333
  200        fibroblast growth factor receptor 2, FGFR2                                                                                                       −337
  201        SRY (sex determining region Y)-box 1, SOX1                                                                                                       −337
  202        neurogenin 1, NEUROG1                                                                                                                            −345
  203        PTK2B protein tyrosine kinase 2 beta, PTK2B                                                                                                      −348
  204        somatostatin receptor 5, SSTR5                                                                                                                   −353
  205        myelin basic protein, MBP                                                                                                                        −361
  206        EPH receptor A7, EPHA7                                                                                                                           −365
  207        G protein-coupled receptor 173, GPR173                                                                                                           −373
  208        S100 calcium binding protein A5, S100A5                                                                                                          −374
  209        acyl-CoA synthetase long-chain family member 6, ACSL6                                                                                            −384
  210        family with sequence similarity 107, member A, FAM107A                                                                                           −407
  211        Kv channel interacting protein 1, KCNIP1                                                                                                         −413
  212        Fas apoptotic inhibitory molecule 2, FAIM2                                                                                                       −416
  213        bradykinin receptor B1, BDKRB1                                                                                                                   −426
  214        discs, large homolog 4 (Drosophila), DLG4                                                                                                        −452
  215        adenylate cyclase 10 (soluble), ADCY10                                                                                                           −460
  216        cyclin-dependent kinase 5, regulatory subunit 2 (p39), CDK5R2                                                                                    −481
  217        EPH receptor A3, EPHA3                                                                                                                           −485
  218        phosphodiesterase 1A, calmodulin-dependent, PDE1A                                                                                                −485
  219        chemokine (C-X-C motif) receptor 4, CXCR4                                                                                                        −496
  220        membrane metallo-endopeptidase, MME                                                                                                              −540
  221        paired-like homeodomain 3, PITX3                                                                                                                 −541
  222        notch 3, NOTCH3                                                                                                                                  −547
  223        discs, large (Drosophila) homolog-associated protein 1, DLGAP1                                                                                   −547
  224        slit homolog 1 (Drosophila), SLIT1                                                                                                               −553
  225        bassoon (presynaptic cytomatrix protein), BSN                                                                                                    −563
  226        cadherin, EGF LAG seven-pass G-type receptor 1 (flamingo homolog, Drosophila), CELSR1                                                            −647
  227        calcium channel, voltage-dependent, beta 4 subunit, CACNB4                                                                                       −672
  228        necdin homolog (mouse), NDN                                                                                                                      −729
  229        endothelin receptor type B, EDNRB                                                                                                                −768
  230        cholinergic receptor, muscarinic 2, CHRM2                                                                                                        −1049
  ---------- ------------------------------------------------------------------------------------------------------------------------------------------------ --------------------

brainsci-07-00020-t013_Table 13

###### 

Distribution of Genes Affected by GHK and Associated with Motor Neurons.

  Percent Change in Gene Expression   Genes UP   Genes DOWN
  ----------------------------------- ---------- ------------
  50%--99%                            9          5
  100%--199%                          2          0
  200%--299%                          2          1
  300%--399%                          0          0
  400%--499%                          0          2
  500%+                               0          1
  Total                               13         9

brainsci-07-00020-t014_Table 14

###### 

GHK and Genes Associate with Motor Neurons.

  ---------- ------------------------------------------------------------------------- --------------------
  **UP**     **Gene Title**                                                            **Percent Change**
  1          calcium channel, voltage-dependent, P/Q type, alpha 1A subunit, CACNA1A   286
  2          plexin C1, PLXNC1                                                         282
  3          GLI family zinc finger 2, GLI2                                            183
  4          NK2 homeobox 2, NKX2-2                                                    181
  **DOWN**   **Gene Title**                                                            **Percent Change**
  1          slit homolog 1 (Drosophila), SLIT1                                        −553
  2          chemokine (C-X-C motif) receptor 4, CXCR4                                 −496
  3          EPH receptor A3, EPHA3                                                    −485
  4          sonic hedgehog, SHH                                                       −220
  ---------- ------------------------------------------------------------------------- --------------------

brainsci-07-00020-t015_Table 15

###### 

Distribution of Genes Affected by GHK and Associated with Glial Cells.

  Percent Change in Gene Expression   Genes UP   Genes DOWN
  ----------------------------------- ---------- ------------
  50%--99%                            11         4
  100%--199%                          7          3
  200%--299%                          4          4
  300%--399%                          2          1
  400%--499%                          0          1
  500%+                               0          2
  Total                               24         15

brainsci-07-00020-t016_Table 16

###### 

GHK and Genes Associated with Glial Cells.

  ---------- ------------------------------------------------------------------------------------------------------------ --------------------
  **UP**     **Gene Title**                                                                                               **Percent Change**
  1          neurogenic differentiation 4, NEUROD4                                                                        362
  2          growth associated protein 43, GAP43                                                                          305
  3          nuclear factor I/B, NFIB                                                                                     279
  4          caspase 1, apoptosis-related cysteine peptidase (interleukin 1, beta, convertase), CASP1                     257
  5          Kruppel-like factor 15, KLF15                                                                                238
  6          adenylate cyclase activating polypeptide 1 (pituitary), ADCYAP1                                              215
  7          neuregulin 1, NRG1                                                                                           164
  8          versican, VCAN                                                                                               134
  9          protein kinase C, eta, PRKCH                                                                                 124
  10         SWI/SNF related, matrix associated, actin dependent regulator of chromatin, subfamily a, member 4, SMARCA4   107
  11         chemokine (C-X3-C motif) receptor 1, CX3CR1                                                                  104
  12         achaete-scute complex homolog 1 (Drosophila), ASCL1                                                          103
  13         neurofibromin 1, NF1                                                                                         102
  **DOWN**   **Gene Title**                                                                                               **Percent Change**
  1          necdin homolog (mouse), NDN                                                                                  −729
  2          insulin-like growth factor 1 (somatomedin C), IGF1                                                           −522
  3          forkhead box D4 /// forkhead box D4-like 1, FOXD4 /// FOXD4L1                                                −498
  4          PTK2B protein tyrosine kinase 2 beta, PTK2B                                                                  −348
  5          pleiomorphic adenoma gene 1, PLAG1                                                                           −276
  6          lin-28 homolog A (C. elegans), LIN28A                                                                        −259
  7          sonic hedgehog, SHH                                                                                          −220
  8          forkhead box E1 (thyroid transcription factor 2), FOXE1                                                      −204
  9          allograft inflammatory factor 1, AIF1                                                                        −144
  10         GDNF family receptor alpha 2, GFRA2                                                                          −141
  11         chondroitin sulfate proteoglycan 4, CSPG4                                                                    −113
  ---------- ------------------------------------------------------------------------------------------------------------ --------------------

brainsci-07-00020-t017_Table 17

###### 

Distribution of Gene Affected by GHK and Associated with Astrocytes.

  Percent Change in Gene Expression   Genes UP   Genes DOWN
  ----------------------------------- ---------- ------------
  50%--99%                            8          3
  100%--199%                          5          2
  200%--299%                          2          1
  300%--399%                          0          0
  400%--499%                          0          0
  500%+                               0          0
  Total                               15         6

brainsci-07-00020-t018_Table 18

###### 

GHK and Genes Associated with Astrocytes.

  ---------- ------------------------------------------------------------------------------------------------------------------------------------------------ --------------------
  **UP**     **Gene Title**                                                                                                                                   **Percent Change**
  1          chemokine (C-C motif) ligand 3 /// chemokine (C-C motif) ligand 3-like 1 /// chemokine (C-C motif) ligand 3-like 3, CCL3 /// CCL3L1 /// CCL3L3   228
  2          inhibitor of DNA binding 4, dominant negative helix-loop-helix protein, ID4                                                                      203
  3          NK2 homeobox 2, NKX2-2                                                                                                                           181
  4          metallothionein 3, MT3                                                                                                                           142
  5          bridging integrator 1, BIN1                                                                                                                      130
  6          matrix metallopeptidase 14 (membrane-inserted), MMP14                                                                                            114
  7          neurofibromin 1, NF1                                                                                                                             102
  **DOWN**   **Gene Title**                                                                                                                                   **Percent Change**
  1          neurotrophic tyrosine kinase, receptor, type 3, NTRK3                                                                                            −230
  2          contactin 2 (axonal), CNTN2                                                                                                                      −180
  3          bone morphogenetic protein 2, BMP2                                                                                                               −159
  ---------- ------------------------------------------------------------------------------------------------------------------------------------------------ --------------------

brainsci-07-00020-t019_Table 19

###### 

Distribution of Genes Affected by GHK and Associated with Schwann Cells.

  Percent Change in Gene Expression   Genes UP   Genes DOWN
  ----------------------------------- ---------- ------------
  50%--99%                            5          1
  100%--199%                          2          0
  200%--299%                          0          0
  300%--399%                          1          1
  400%--499%                          0          0
  500%+                               0          0
  Total                               8          2

brainsci-07-00020-t020_Table 20

###### 

GHK and Genes Associated with Schwann Cells.

  ---------- ----------------------------------------------------------------- --------------------
  **UP**     **Gene Title**                                                    **Percent Change**
  1          Mediator complex subunit 12, MED12                                393
  2          neurofibromin 2 (merlin), NF2                                     105
  3          neurofibromin 1, NF1                                              102
  **DOWN**   **Gene Title**                                                    **Percent Change**
  1          cytochrome P450, family 11, subfamily A, polypeptide 1, CYP11A1   −393
  ---------- ----------------------------------------------------------------- --------------------

brainsci-07-00020-t021_Table 21

###### 

Distribution of Genes Affected by GHK and Associated with Myelin.

  Percent Change in Gene Expression   Genes UP   Genes DOWN
  ----------------------------------- ---------- ------------
  50%--99%                            24         5
  100%--199%                          8          8
  200%--299%                          4          0
  300%--399%                          0          3
  400%--499%                          0          2
  500%+                               0          0
  Total                               36         18

brainsci-07-00020-t022_Table 22

###### 

GHK and Genes Associated with Myelin.

  ---------- ----------------------------------------------------------------------------------------------------- --------------------
  **UP**     **Gene Title**                                                                                        **Percent Change**
  1          inositol 1,4,5-triphosphate receptor, type 3, ITPR3                                                   298
  2          sodium channel, voltage-gated, type II, alpha subunit, SCN2A                                          264
  3          myelin associated glycoprotein, MAG                                                                   229
  4          inhibitor of DNA binding 4, dominant negative helix-loop-helix protein, ID4                           203
  5          aspartoacylase, ASPA                                                                                  195
  6          probable transcription factor PML-like /// promyelocytic leukemia, LOC652346 /// PML                  144
  7          retinoic acid receptor, beta, RARB                                                                    142
  8          retinoic acid receptor, alpha, RARA                                                                   123
  9          myosin VA (heavy chain 12, myoxin), MYO5A                                                             122
  10         neurofibromin 1, NF1                                                                                  102
  11         histamine receptor H3, HRH3                                                                           101
  12         transforming growth factor, beta 1, TGFB1                                                             100
  **DOWN**   **Gene Title**                                                                                        **Percent Change**
  1          chemokine (C-X-C motif) receptor 4, CXCR4                                                             −496
  2          gap junction protein, gamma 2, 47kDa, GJC2                                                            −428
  3          lethal giant larvae homolog 1 (Drosophila), LLGL1                                                     −393
  4          myelin basic protein, MBP                                                                             −361
  5          chromosome 11 open reading frame 9, C11orf9                                                           −342
  6          promyelocytic leukemia, PML                                                                           −196
  7          myelin protein zero, MPZ                                                                              −180
  8          contactin 2 (axonal), CNTN2                                                                           −180
  9          toll-like receptor 2, TLR2                                                                            −169
  10         laminin, alpha 2, LAMA2                                                                               −150
  11         retinoid X receptor, gamma, RXRG                                                                      −110
  12         integrin, beta 1 (fibronectin receptor, beta polypeptide, antigen CD29 includes MDF2, MSK12), ITGB1   −107
  13         thyroglobulin, TG                                                                                     −100
  ---------- ----------------------------------------------------------------------------------------------------- --------------------

brainsci-07-00020-t023_Table 23

###### 

Distribution of Genes Affected by GHK and Associated with Dendrites.

  Percent Change in Gene Expression   Genes UP   Genes DOWN
  ----------------------------------- ---------- ------------
  50%--99%                            47         14
  100%--199%                          19         31
  200%--299%                          11         15
  300%--399%                          8          3
  400%--499%                          0          3
  500%+                               2          2
  Total                               87         68

brainsci-07-00020-t024_Table 24

###### 

GHK and Genes Associated with Dendrites.

  ---------- --------------------------------------------------------------------------------------------------------------------------------------- --------------------
  **UP**     **Gene Title**                                                                                                                          **Percent Change**
  1          potassium voltage-gated channel, Shal-related subfamily, member 1, KCND1                                                                845
  2          contactin associated protein-like 2, CNTNAP2                                                                                            581
  3          leukocyte specific transcript 1, LST1                                                                                                   395
  4          gamma-aminobutyric acid (GABA) A receptor, alpha 5 /// gamma-aminobutyric acid receptor subunit alpha-5-like, GABRA5 /// LOC100509612   392
  5          chemokine (C-C motif) ligand 19, CCL19                                                                                                  378
  6          doublecortin-like kinase 1, DCLK1                                                                                                       365
  7          p21 protein (Cdc42/Rac)-activated kinase 1, PAK1                                                                                        363
  8          potassium voltage-gated channel, Shaw-related subfamily, member 3, KCNC3                                                                332
  9          EPH receptor B1, EPHB1                                                                                                                  330
  10         gamma-aminobutyric acid (GABA) B receptor, 1 /// ubiquitin D, GABBR1 /// UBD                                                            310
  11         calcium channel, voltage-dependent, P/Q type, alpha 1A subunit, CACNA1A                                                                 286
  12         nephroblastoma overexpressed gene, NOV                                                                                                  275
  13         obscurin-like 1, OBSL1                                                                                                                  263
  14         neuroligin 1, NLGN1                                                                                                                     261
  15         low density lipoprotein receptor-related protein 1, LRP1                                                                                249
  16         glutamate receptor, ionotropic, kainate 3, GRIK3                                                                                        246
  17         RNA binding protein, fox-1 homolog (*C. elegans*) 2, RBFOX2                                                                             245
  18         glutamate receptor, metabotropic 1, GRM1                                                                                                231
  19         glutamate receptor interacting protein 1, GRIP1                                                                                         230
  20         glutamate receptor, ionotropic, *N*-methyl [d]{.smallcaps}-aspartate 1, GRIN1                                                           216
  21         MCF.2 cell line derived transforming sequence, MCF2                                                                                     202
  22         purinergic receptor P2X, ligand-gated ion channel, 4, P2RX4                                                                             180
  23         synapsin I, SYN1                                                                                                                        170
  24         Abl-interactor 2, ABI2                                                                                                                  168
  25         calcium channel, voltage-dependent, L type, alpha 1F subunit, CACNA1F                                                                   168
  26         membrane associated guanylate kinase, WW and PDZ domain containing 2, MAGI2                                                             155
  27         ubiquitin-conjugating enzyme E2I (UBC9 homolog, yeast), UBE2I                                                                           150
  28         nuclear mitotic apparatus protein 1, NUMA1                                                                                              147
  29         glutamate receptor, ionotropic, *N*-methyl [d]{.smallcaps}-aspartate 2C, GRIN2C                                                         146
  30         probable transcription factor PML-like /// promyelocytic leukemia, LOC652346 /// PML                                                    144
  31         fasciculation and elongation protein zeta 1 (zygin I), FEZ1                                                                             143
  32         glutamate receptor, metabotropic 7, GRM7                                                                                                140
  33         acetylcholinesterase, ACHE                                                                                                              131
  34         retinoic acid receptor, alpha, RARA                                                                                                     123
  35         misshapen-like kinase 1, MINK1                                                                                                          119
  36         kelch-like 1 (Drosophila), KLHL1                                                                                                        119
  37         neuralized homolog (Drosophila), NEURL                                                                                                  115
  38         protein kinase C, gamma, PRKCG                                                                                                          106
  39         drebrin 1, DBN1                                                                                                                         103
  40         neurofibromin 1, NF1                                                                                                                    102
  **DOWN**   **Gene Title**                                                                                                                          **Percent Change**
  1          bassoon (presynaptic cytomatrix protein), BSN                                                                                           −563
  2          membrane metallo-endopeptidase, MME                                                                                                     −540
  3          adenylate cyclase 10 (soluble), ADCY10                                                                                                  −460
  4          discs, large homolog 4 (Drosophila), DLG4                                                                                               −452
  5          Kv channel interacting protein 1, KCNIP1                                                                                                −413
  6          EPH receptor A7, EPHA7                                                                                                                  −365
  7          PTK2B protein tyrosine kinase 2 beta, PTK2B                                                                                             −348
  8          sterile alpha motif domain containing 4A, SAMD4A                                                                                        −315
  9          dopamine receptor D4, DRD4                                                                                                              −296
  10         FEZ family zinc finger 2, FEZF2                                                                                                         −295
  11         calcium channel, voltage-dependent, N type, alpha 1B subunit, CACNA1B                                                                   −290
  12         mitogen-activated protein kinase 8 interacting protein 1, MAPK8IP1                                                                      −289
  13         regulator of G-protein signaling 11, RGS11                                                                                              −266
  14         cyclin-dependent kinase 5, regulatory subunit 1 (p35), CDK5R1                                                                           −260
  15         glutamate receptor, ionotropic, kainate 1, GRIK1                                                                                        −254
  16         thyroid hormone receptor, alpha (erythroblastic leukemia viral (v-erb-a) oncogene homolog, avian), THRA                                 −253
  17         cyclic nucleotide gated channel alpha 3, CNGA3                                                                                          −249
  18         adenylate cyclase 2 (brain), ADCY2                                                                                                      −247
  19         proprotein convertase subtilisin/kexin type 2, PCSK2                                                                                    −242
  20         Rho guanine nucleotide exchange factor (GEF) 15, ARHGEF15                                                                               −230
  21         potassium voltage-gated channel, Shal-related subfamily, member 3, KCND3                                                                −224
  22         protein tyrosine phosphatase, receptor type, D, PTPRD                                                                                   −221
  23         cytochrome b-245, beta polypeptide, CYBB                                                                                                −217
  24         GABA(A) receptors associated protein like 3, pseudogene, GABARAPL3                                                                      −197
  25         neutrophil cytosolic factor 1C pseudogene, NCF1C                                                                                        −196
  26         promyelocytic leukemia, PML                                                                                                             −196
  27         C-reactive protein, pentraxin-related, CRP                                                                                              −182
  28         glutamate receptor, ionotropic, *N*-methyl [d]{.smallcaps}-aspartate 2A, GRIN2A                                                         −180
  29         tubby like protein 1, TULP1                                                                                                             −176
  30         Mitogen-activated protein kinase 8 interacting protein 3, MAPK8IP3                                                                      −174
  31         cell adhesion molecule with homology to L1CAM (close homolog of L1), CHL1                                                               −171
  32         choline *O*-acetyltransferase, CHAT                                                                                                     −160
  33         glutamate receptor, ionotropic, kainate 5, GRIK5                                                                                        −159
  34         glutamate receptor, ionotropic, kainate 4, GRIK4                                                                                        −155
  35         5-hydroxytryptamine (serotonin) receptor 6, HTR6                                                                                        −150
  36         tachykinin receptor 3, TACR3                                                                                                            −150
  37         5-hydroxytryptamine (serotonin) receptor 5A, HTR5A                                                                                      −149
  38         protease, serine, 12 (neurotrypsin, motopsin), PRSS12                                                                                   −141
  39         cholinergic receptor, nicotinic, alpha 4, CHRNA4                                                                                        −139
  40         5-hydroxytryptamine (serotonin) receptor 2A, HTR2A                                                                                      −135
  41         leucine zipper, putative tumor suppressor 1, LZTS1                                                                                      −130
  42         neuroligin 4, X-linked, NLGN4X                                                                                                          −128
  43         glutamate receptor, ionotrophic, AMPA 3, GRIA3                                                                                          −126
  44         glutamate receptor, metabotropic 6, GRM6                                                                                                −120
  45         paralemmin, PALM                                                                                                                        −115
  46         copine VI (neuronal), CPNE6                                                                                                             −114
  47         cytoplasmic polyadenylation element binding protein 3, CPEB3                                                                            −112
  48         corticotropin releasing hormone receptor 1, CRHR1                                                                                       −109
  49         doublecortin, DCX                                                                                                                       −108
  50         regulator of G-protein signaling 14, RGS14                                                                                              −108
  51         apolipoprotein E, APOE                                                                                                                  −107
  52         calcium binding protein 1, CABP1                                                                                                        −106
  53         mitogen-activated protein kinase 8 interacting protein 2, MAPK8IP2                                                                      −103
  54         neurochondrin, NCDN                                                                                                                     −102
  ---------- --------------------------------------------------------------------------------------------------------------------------------------- --------------------

brainsci-07-00020-t025_Table 25

###### 

Distribution of Genes Affected by GHK and Associated with Oligodendrocytes.

  Percent Change in Gene Expression   Genes UP   Genes DOWN
  ----------------------------------- ---------- ------------
  50%--99%                            6          4
  100%--199%                          6          3
  200%--299%                          3          1
  300%--399%                          0          1
  400%--499%                          0          1
  500%+                               1          0
  Total                               16         10

brainsci-07-00020-t026_Table 26

###### 

GHK and Genes Associated with Oligodendrocytes.

  ---------- ----------------------------------------------------------------------------- --------------------
  **UP**     **Gene Title**                                                                **Percent Change**
  1          tumor protein p73, TP73                                                       938
  2          adenylate cyclase activating polypeptide 1 (pituitary), ADCYAP1               215
  3          gelsolin, GSN                                                                 214
  4          inhibitor of DNA binding 4, dominant negative helix-loop-helix protein, ID4   203
  5          aspartoacylase, ASPA                                                          195
  6          NK2 homeobox 2, NKX2-2                                                        181
  7          dopamine receptor D3, DRD3                                                    164
  8          histone deacetylase 11, HDAC11                                                105
  9          achaete-scute complex homolog 1 (Drosophila), ASCL1                           103
  10         neurofibromin 1, NF1                                                          102
  **DOWN**   **Gene Title**                                                                **Percent Change**
  1          chemokine (C-X-C motif) receptor 4, CXCR4                                     −496
  2          chromosome 11 open reading frame 9, C11orf9                                   −342
  3          sonic hedgehog, SHH                                                           −220
  4          zinc finger protein 287, ZNF287                                               −143
  5          early growth response 1, EGR1                                                 −121
  6          apolipoprotein E, APOE                                                        −107
  ---------- ----------------------------------------------------------------------------- --------------------

brainsci-07-00020-t027_Table 27

###### 

Distribution of Genes Affected by GHK and Associated with Sensory Nerve Cells.

  Percent Change in Gene Expression   Genes UP   Genes DOWN
  ----------------------------------- ---------- ------------
  50%--99%                            45         25
  100%--199%                          24         36
  200%--299%                          18         6
  300%--399%                          7          1
  400%--499%                          1          3
  500%+                               2          4
  Total                               97         75

brainsci-07-00020-t028_Table 28

###### 

GHK and Gene Associate with Sensory Nerve Cells.

  ---------- ------------------------------------------------------------------------------------------------------------------------------------------------ --------------------
  **UP**     **Gene Title**                                                                                                                                   **Percent Change**
  1          opioid receptor, mu 1, OPRM1                                                                                                                     1294
  2          T-box 1, TBX1                                                                                                                                    553
  3          adrenergic, beta-1-, receptor, ADRB1                                                                                                             477
  4          gamma-aminobutyric acid (GABA) A receptor, alpha 5 /// gamma-aminobutyric acid receptor subunit alpha-5-like, GABRA5 /// LOC100509612            392
  5          calcium channel, voltage-dependent, L type, alpha 1D subunit, CACNA1D                                                                            372
  6          olfactory receptor, family 2, subfamily W, member 1, OR2W1                                                                                       370
  7          guanine nucleotide binding protein (G protein), alpha activating activity polypeptide, olfactory type, GNAL                                      366
  8          olfactory receptor, family 2, subfamily B, member 6, OR2B6                                                                                       345
  9          cyclic nucleotide gated channel beta 1, CNGB1                                                                                                    330
  10         EPH receptor B1, EPHB1                                                                                                                           330
  11         inositol 1,4,5-triphosphate receptor, type 3, ITPR3                                                                                              298
  12         olfactory receptor, family 7, subfamily A, member 17, OR7A17                                                                                     285
  13         nuclear factor I/B, NFIB                                                                                                                         279
  14         islet amyloid polypeptide, IAPP                                                                                                                  276
  15         opiate receptor-like 1, OPRL1                                                                                                                    246
  16         potassium voltage-gated channel, KQT-like subfamily, member 4, KCNQ4                                                                             245
  17         myosin, heavy chain 14, non-muscle, MYH14                                                                                                        243
  18         taste receptor, type 2, member 13, TAS2R13                                                                                                       237
  19         olfactory receptor, family 2, subfamily F, member 2, OR2F2                                                                                       232
  20         glutamate receptor, metabotropic 1, GRM1                                                                                                         231
  21         chemokine (C-C motif) ligand 3 /// chemokine (C-C motif) ligand 3-like 1 /// chemokine (C-C motif) ligand 3-like 3, CCL3 /// CCL3L1 /// CCL3L3   228
  22         polycystic kidney disease 2-like 1, PKD2L1                                                                                                       225
  23         glutamate receptor, ionotropic, *N*-methyl [d]{.smallcaps}-aspartate 1, GRIN1                                                                    216
  24         adenylate cyclase activating polypeptide 1 (pituitary), ADCYAP1                                                                                  215
  25         ATPase, Ca++ transporting, plasma membrane 2, ATP2B2                                                                                             214
  26         olfactory receptor, family 7, subfamily C, member 1, OR7C1                                                                                       207
  27         purinergic receptor P2X, ligand-gated ion channel, 3, P2RX3                                                                                      207
  28         neuropeptide Y receptor Y1, NPY1R                                                                                                                201
  29         family with sequence similarity 38, member B, FAM38B                                                                                             193
  30         olfactory receptor, family 1, subfamily A, member 1, OR1A1                                                                                       189
  31         taste receptor, type 2, member 14, TAS2R14                                                                                                       181
  32         purinergic receptor P2X, ligand-gated ion channel, 4, P2RX4                                                                                      180
  33         receptor accessory protein 2, REEP2                                                                                                              174
  34         endothelin receptor type A, EDNRA                                                                                                                173
  35         cannabinoid receptor 1 (brain), CNR1                                                                                                             172
  36         melanocortin 1 receptor (alpha melanocyte stimulating hormone receptor), MC1R                                                                    164
  37         olfactory receptor, family 12, subfamily D, member 3 /// olfactory receptor, family 5, subfamily V, member 1, OR12D3 /// OR5V1                   163
  38         odorant binding protein 2A /// odorant binding protein 2B, OBP2A /// OBP2B                                                                       162
  39         prepronociceptin, PNOC                                                                                                                           150
  40         phospholipase C, beta 2, PLCB2                                                                                                                   148
  41         glutamate receptor, metabotropic 7, GRM7                                                                                                         140
  42         oxytocin, prepropeptide, OXT                                                                                                                     136
  43         WD repeat domain 1, WDR1                                                                                                                         127
  44         olfactory receptor, family 1, subfamily D, member 4 (gene/pseudogene) /// olfactory receptor, family 1, subfamily D, member 5, OR1D4 /// OR1D5   125
  45         UDP glucuronosyltransferase 2 family, polypeptide A1 /// UDP glucuronosyltransferase 2 family, polypeptide A2, UGT2A1 /// UGT2A2                 121
  46         prostaglandin-endoperoxide synthase 2 (prostaglandin G/H synthase and cyclooxygenase), PTGS2                                                     120
  47         taste receptor, type 2, member 4, TAS2R4                                                                                                         118
  48         lysozyme, LYZ                                                                                                                                    111
  49         protein kinase C, gamma, PRKCG                                                                                                                   106
  50         collagen, type XI, alpha 1, COL11A1                                                                                                              103
  51         POU class 4 homeobox 3, POU4F3                                                                                                                   102
  52         nuclear receptor subfamily 2, group F, member 6, NR2F6                                                                                           100
  **DOWN**   **Gene Title**                                                                                                                                   **Percent Change**
  1          taste receptor, type 2, member 9, TAS2R9                                                                                                         −1494
  2          endothelin receptor type B, EDNRB                                                                                                                −768
  3          necdin homolog (mouse), NDN                                                                                                                      −729
  4          membrane metallo-endopeptidase, MME                                                                                                              −540
  5          EPH receptor A3, EPHA3                                                                                                                           −485
  6          arachidonate lipoxygenase 3, ALOXE3                                                                                                              −461
  7          bradykinin receptor B1, BDKRB1                                                                                                                   −426
  8          gap junction protein, beta 4, 30.3kDa, GJB4                                                                                                      −317
  9          nerve growth factor (beta polypeptide), NGF                                                                                                      −243
  10         guanine nucleotide binding protein (G protein), alpha transducing activity polypeptide 1, GNAT1                                                  −242
  11         olfactory receptor, family 3, subfamily A, member 1, OR3A1                                                                                       −234
  12         apelin receptor, APLNR                                                                                                                           −230
  13         olfactory receptor, family 2, subfamily F, member 1 /// olfactory receptor, family 2, subfamily F, member 2, OR2F1 /// OR2F2                     −212
  14         olfactory receptor, family 12, subfamily D, member 3, OR12D3                                                                                     −201
  15         olfactory receptor, family 6, subfamily A, member 2, OR6A2                                                                                       −199
  16         cholecystokinin B receptor, CCKBR                                                                                                                −198
  17         carbonic anhydrase VI, CA6                                                                                                                       −192
  18         olfactory receptor, family 5, subfamily I, member 1, OR5I1                                                                                       −191
  19         collagen, type XI, alpha 2, COL11A2                                                                                                              −186
  20         olfactory receptor, family 10, subfamily H, member 3, OR10H3                                                                                     −182
  21         glutamate receptor, ionotropic, N-methyl D-aspartate 2A, GRIN2A                                                                                  −180
  22         protein phosphatase, EF-hand calcium binding domain 2, PPEF2                                                                                     −178
  23         sodium channel, nonvoltage-gated 1 alpha, SCNN1A                                                                                                 −175
  24         trace amine associated receptor 5, TAAR5                                                                                                         −168
  25         gastric inhibitory polypeptide, GIP                                                                                                              −164
  26         olfactory receptor, family 2, subfamily H, member 1, OR2H1                                                                                       −156
  27         olfactory receptor, family 2, subfamily J, member 2, OR2J2                                                                                       −155
  28         otoferlin, OTOF                                                                                                                                  −155
  29         discs, large homolog 2 (Drosophila), DLG2                                                                                                        −142
  30         cholinergic receptor, nicotinic, alpha 4, CHRNA4                                                                                                 −139
  31         5-hydroxytryptamine (serotonin) receptor 2A, HTR2A                                                                                               −135
  32         tectorin alpha, TECTA                                                                                                                            −126
  33         sodium channel, voltage-gated, type XI, alpha subunit, SCN11A                                                                                    −124
  34         olfactory receptor, family 7, subfamily C, member 2, OR7C2                                                                                       −120
  35         taste receptor, type 2, member 16, TAS2R16                                                                                                       −120
  36         glutamate receptor, metabotropic 6, GRM6                                                                                                         −120
  37         opioid receptor, kappa 1, OPRK1                                                                                                                  −119
  38         ATPase, H+ transporting, lysosomal 56/58kDa, V1 subunit B1, ATP6V1B1                                                                             −118
  39         olfactory marker protein, OMP                                                                                                                    −118
  40         contactin 5, CNTN5                                                                                                                               −116
  41         cysteinyl leukotriene receptor 2, CYSLTR2                                                                                                        −113
  42         olfactory receptor, family 2, subfamily H, member 2, OR2H2                                                                                       −110
  43         rhodopsin, RHO                                                                                                                                   −108
  44         interleukin 10, IL10                                                                                                                             −107
  45         olfactory receptor, family 11, subfamily A, member 1, OR11A1                                                                                     −107
  46         polymeric immunoglobulin receptor, PIGR                                                                                                          −107
  47         guanine nucleotide binding protein (G protein), gamma 13, GNG13                                                                                  −106
  48         tubby homolog (mouse), TUB                                                                                                                       −101
  49         glutamate receptor, metabotropic 8, GRM8                                                                                                         −101
  50         cystatin S, CST4                                                                                                                                 −101
  ---------- ------------------------------------------------------------------------------------------------------------------------------------------------ --------------------

brainsci-07-00020-t029_Table 29

###### 

Distribution of Genes Affected by GHK and Associated with Spinal Nerve Cells.

  Percent Change in Gene Expression   Genes UP   Genes DOWN
  ----------------------------------- ---------- ------------
  50%--99%                            8          6
  100%--199%                          9          3
  200%--299%                          1          2
  300%--399%                          0          1
  400%--499%                          1          0
  500%+                               1          1
  Total                               20         13

brainsci-07-00020-t030_Table 30

###### 

GHK and Genes Associated with Spinal Nerve Cells.

  ---------- --------------------------------------------------------------------------------- --------------------
  **UP**     **Gene Title**                                                                    **Percent Change**
  1          tumor protein p73, TP73                                                           938
  2          smoothened homolog (Drosophila), SMO                                              415
  3          calcium channel, voltage-dependent, P/Q type, alpha 1A subunit, CACNA1A           286
  4          GATA binding protein 2, GATA2                                                     193
  5          GLI family zinc finger 2, GLI2                                                    183
  6          NK2 homeobox 2, NKX2-2                                                            181
  7          dopamine receptor D3, DRD3                                                        164
  8          paired box 7, PAX7                                                                161
  9          slit homolog 3 (Drosophila), SLIT3                                                154
  10         polycystic kidney disease 1 (autosomal dominant), PKD1                            137
  11         achaete-scute complex homolog 1 (Drosophila), ASCL1                               103
  12         neurofibromin 1, NF1                                                              102
  **DOWN**   **Gene Title**                                                                    **Percent Change**
  1          slit homolog 1 (Drosophila), SLIT1                                                −553
  2          SRY (sex determining region Y)-box 1, SOX1                                        −337
  3          growth differentiation factor 11, GDF11                                           −221
  4          sonic hedgehog, SHH                                                               −220
  5          glutamate receptor, ionotropic, *N*-methyl [d]{.smallcaps}-aspartate 2A, GRIN2A   −180
  6          even-skipped homeobox 1, EVX1                                                     −110
  7          aquaporin 1 (Colton blood group), AQP1                                            −101
  ---------- --------------------------------------------------------------------------------- --------------------
