the prevalence of obesity has tripled in the united states over the past three decades . as a result ,
the burden of obesity - related morbidity has increased dramatically , generating an urgent need to understand the mechanisms that promote metabolic disease .
substantial evidence supports the contribution of obesity - induced inflammation ( metainflammation ) to diseases such as diabetes and cardiovascular disease via the pro - inflammatory activation of leukocytes in mice [ 24 ] and humans [ 57 ] . in humans and animal models ,
obesity is associated with a pro - inflammatory activation profile of macrophages in a wide variety of tissues that include the liver , adipose tissue , skeletal muscle , pancreatic islets , and the hypothalamus .
a major site of leukocyte activation is visceral adipose tissue where a pro - inflammatory population of cd11c adipose tissue macrophages ( atms ) accumulates with progressive obesity [ 810 ] .
cd11c atms secrete pro - inflammatory cytokines and promote an m1-like activation profile in adipose tissue that contributes to adipocyte dysfunction and insulin resistance .
activated macrophages have also been implicated in metabolic dysfunction in the liver , pancreas , and central nervous system .
numerous studies in mice have shown that suppression of this macrophage activation can uncouple obesity from metabolic disease and the development of insulin resistance [ 1618 ] .
the processes that govern the accumulation of pro - inflammatory macrophages in diverse tissues in response to obesity are not fully understood .
obesity - induced atm accumulation is dependent on the trafficking of monocytes to adipose tissue where they are differentiate into macrophages and surround dead and dying adipocytes [ 1923 ] .
consistent with this , obesity triggers an expansion of the pool of circulating classical blood monocytes ( ccr2 ly6c ) in mice .
similar observations are seen in obese humans as an increase in the frequency of circulating neutrophils and cd14 cd16 monocytes is seen in obese insulin resistant patients   and is suppressed with weight loss .
these observations suggest that myeloid cell production and activation may be an important regulated step in generating metainflammation and a biomarker of obesity - induced inflammation .
while atherosclerosis prone mice have been shown to harbor a reservoir of ly6c monocytes within the spleen , the primary site of monocyte production is the bone marrow ( bm ) compartment where they are generated from hematopoietic stem cells ( hscs ) .
hscs are active participants in peripheral inflammatory responses and can alter their cellular output depending on environmental cues . in sepsis , lipopolysaccharide ( lps ) can  push  hscs to increase production of myeloid cells by direct   and indirect   action on hscs in order to potentiate peripheral immune responses .
consistent with this , clinical studies have identified an increase in circulating hematopoietic progenitors in obese patients suggesting that obesogenic cues can trigger the activation of hscs .
diabetes associated hyperglycemia has been identified as one potential signal that increases myeloid cell production from the bm .
many studies have supported a role for myd88 and tlr signaling in the development of obesity - associated metainflammation .
activation of these pathways within adipose tissue have been implicated in potentiating hsc activation toward myelopoiesis .
these pathways have also been implicated in the activation of myelopoiesis in other inflammatory settings .
it remains unclear how tlr / myd88 on hematopoietic stem cells may contribute to high fat diet - induced inflammation .
based on these observations , we examined the hypothesis that myeloid cell production by hscs is potentiated by high fat diet induced obesity and plays a crucial role in the generation of pro - inflammatory tissue macrophages . using mouse models of obesity
, we found that obesity induces qualitative and quantitative changes in myeloid bm progenitors that amplify the generation of cd11c atms .
serial transplantation experiments demonstrate that long term self - renewing hscs ( lt - hsc ) retain this property in a cell autonomous fashion .
competitive reconstitution experiments demonstrate that the capacity of hscs to activate myelopoiesis is dependent on myd88 for the generation of cd11c atms in visceral adipose depots .
mice used in these experiments were male c57bl/6j , cd45.1 cd57 bl/6j mice ( b6.sjl-ptprca pepcb / boyj ) , tlr4 and myd88 ( jackson laboratories ) .
mice were fed ad lib either a control normal diet ( nd ) consisting of 4.5% fat ( 5001 ; labdiet ) or a high fat diet ( hfd ) of 60% of calories from fat ( research diets , inc . , d12492 ) starting at 68 weeks of age for 16 weeks unless specified . in all experiments animals were age matched by purchase or less then one week apart in date of birth .
animals were housed in a specific pathogen - free facility with a 12  h light/12  h dark cycle and given free access to food and water .
all animal use was in compliance with the institute of laboratory animal research guide for the care and use of laboratory animals and approved by the university committee on use and care of animals at the university of michigan ( animal welfare assurance number a3114 - 01 ) .
peritoneal macrophages were elicited by 2  ml of 3% thioglycollate injection as previously described .
after rbc lysis , cells were plated at 1.5    10  cells / ml prior to differentiation into bm derived macrophages ( bmmp , 20% l929 conditioned media ) or bm derived dendritic cells ( bmdc , gm - csf ) for 6 days as previously described . differentiation was confirmed by demonstrating cd11c and mhcii expression in bmdc by flow cytometry .
cells were then placed in 10% serum media for 24  h prior to treatment with lps ( 10100  ng / ml ) for 1824  h. cells were sorted by fluorescent activated cell sorting in the university of michigan core facility for cd11c live bmdc or bmmp .
rt reactions were performed and real - time pcr analysis was performed normalized to gapdh ( sybr green , abi prism 7200 sequence detection system ; applied biosystems ) .
relative expression was assessed by the comparative ct method correcting for amplification efficiency of the primers and performed in duplicate as previously described .
rna was amplified and rna prepared as previously described before hybridization to mouse affymetrix 430 2.0 gene strip array .
after quality control assessments probe sets with unadjusted p - value of 0.05 or less were identified .
genes with significant differences from lean and obese cells were analyzed using david and conceptgen .
analysis was performed through the university of michigan microarray core using affy , limma , and affy plm packages of bioconductor implemented in the r statistical environment .
whole adipose tissue was digested in collagenase ( 1  mg / ml ) and svf fraction pelleted .
after red blood cell lysis cells were stained with cd64 pe , cd45.1 pecy7 , cd45.2 e450 , f4/80-apc , cd11b - apc - cy7 , and cd11c - pe - cy7 ( ebioscience ) .
macrophages were identified as f4/80 cd11b or cd64 cells in the cd45 gate and then differentiated based on cd11c expression as shown in supplementary figure  1 .
bm from one femur was flushed with pbs , made into single cell suspension with a syringe , and centrifuged .
pellet with then treated with rbc lysis solution for 5  min . after re - suspension in pbs and washing cells were stained with lineage markers on apc ( cd4 , cd5 , cd8 , cd11b , b220 ( cd45r ) , gr1 , ter119 , cd41 ) ( ebioscience ) , cd117 apccy7 ( ebioscience ) , sca 1 pecy7 ( ebioscience ) , cd150 pe ( biolegend ) , endoglin pacific blue ( biolegend ) , cd16/32 percp5.5 ( ebioscience ) and gating as described by pronk et  al . .
initial gating identified lineage ( cd4 , cd5 , cd8 , cd11b , b220 , gr1 , ter119 , cd41 ) negative singlet cells .
cells were classified as lin sca kit ( lsk ) or lin kit ( lk ) .
lsk cells were further subdivided between endoglin cd150 multipotent progenitors ( mpp ) or endoglin cd150 long term hematopoietic stem cells ( lt - hsc ) .
lk cells were further subdivided between cd16/32 cd150 granulocyte macrophage progenitors ( gmp ) or cd16/32 cd150endoglin pre - granulocyte macrophage ( pre - gm ) cells .
in competitive bmts cd45.1 and cd45.2 stains were used for determining donors in the blood and svf . within the bm compartment and hsc staining cd45.2 staining
cells were then re - suspended in methocult media and plated at 10,000 cells per plate per protocol ( stem cell technology ) .
bm cells were isolated from donor groups   and injected retro - orbitally into lethally irradiated ( 900 rad ) 6 week old recipient mice ( 10  million cells / mouse ) .
lsk bmts were performed with 4000 sorted lsk cells with 0.5    10 whole bm from a cd45 1.2 mouse .
competitive bmts were performed with 5  million cells from each donor mouse ( cd45.1 and cd45.2 ) per recipient .
animals were treated with antibiotics ( polymyxin and neomycin ) for 4 weeks post bm transplantation .
blood flow analysis was performed to assess reconstitution two weeks after bone marrow transplantation . following two weeks of normal chow diet ,
glucose tolerance testing was performed as described   after 6  h of fasting with intraperitoneal injection of 0.7 
statistical analyses were conducted using a 2-sample student 's t - test , with significance set at p - value < 0.05 . for competitive bmt experiments the ratio from donor groups was compared to 1 using one - sample t - test .
results with multiple groups were first assessed with one - way or two - way anova as appropriate followed by confirmatory analysis .
the activation profile of macrophages is the result of a combination of the tissue microenvironment and the potential of myeloid progenitors and monocytes from which they are derived . to examine the hypothesis that obesity modifies the profile of bm derived myeloid cells , bm dendritic cells ( bmdc )
were generated from c57bl/6 mice fed a normal ( nd ) or 60% high fat diet ( hfd ) for 12 weeks .
these cells were chosen given the similarities between bmdcs and obesity - associated atms in terms of the induction of cd11c and apc function .
after 7 days of ex  vivo differentiation in gm - csf , unstimulated bmdcs from hfd mice had significantly higher tnf , il6 , and nos2 gene expression compared to bmdc from nd mice ( figure  1a ) . with lps stimulation , bmdcs from obese mice had a higher induction of il6 and nos2 compared to bmdcs from lean mice ( figure  1b ) .
similar , gene expression changes were seen in bm derived macrophages from lean and obese mice .
flow cytometry analysis showed that bm from obese mice produced more mature mhcii cd11c bmdcs compared to lean mice , suggesting that bm cells from obese mice have a propensity toward a mature dc profile independent of stimulation ( figure  1c and d ) .
gene expression microarray analysis of unstimulated bmdcs derived from lean and obese mice identified 520 genes with increased expression in obese bmdcs and 84 genes with decreased expression in obese bmdcs compared to lean bmdcs .
pathway analysis identified  regulation of cell proliferation  and  immune system development  as gene sets that were most significantly increased in hfd derived bmdcs ( supplementary tables  1 and 2 , figure  1e ) .
these observations demonstrate that diet induced obesity ( dio ) promotes a pro - inflammatory profile in bm derived myeloid cells that persists even after removal from the obesogenic environment . to assess whether obesity primes bm - derived myeloid cells for a pro - inflammatory response in  vivo , we examined macrophage activation in a competitive mixed chimera model .
nd ( cd45.1 ) and hfd ( cd45.2 ) bm was mixed in a 1:1 ratio prior to injected into lethally irradiated lean mice ( cd45.1 ) ( figure  2a ) .
after reconstitution , animals were injected ip with pbs or thioglycollate ( thio ) to induce peritoneal macrophage ( pm ) accumulation ( figure  2b ) .
pms were collected by lavage and cd45 chimerism assessed by flow cytometry to evaluate the differential contribution of bm precursors from nd and hfd mice to pms ( figure  2c ) .
pms from control pbs injected mice had a cd45.2/cd45.1 ratio of hfd to nd derived cells significantly less than 1 that was similar to blood leukocyte chimerism ( figure  2d ) .
this represents the baseline reconstitution of the myeloid compartment in this experimental paradigm . with thio administration the cd45.2/cd45.1 ratio of pms
was significantly increased demonstrating the preferential accumulation of macrophages derived from the hfd bm in the peritoneum with this inflammatory stimulus ( figure  2d ) .
this is in contrast to the peritoneal neutrophils ( pmns ) in the peritoneum where there was no change in the hfd / nd ratio indicating equal contributions of pmns in the thio treatment group . to examine the properties of the pms derived from the different bm progenitors , hfd and nd derived pms
cd45.2 pms derived from hfd donors produced more tnf after lps stimulation compared to cd45.1 pms from nd donors ( figure  2e ) . in summary , these observations support the in  vitro studies and suggest that bm progenitors from obese mice are primed to generate macrophages with an increased capacity to traffic to inflammatory sites and maintain a proinflammatory profile .
flow cytometry was used to quantify stem cell progenitors in the bm in mice fed either a nd chow or long - term hfd ( 816 weeks ) .
hfd - fed animals had more fat mass , were glucose intolerant , and had increased ly6c blood monocytes and cd11c atms in perigonadal adipose tissue ( supplementary figure  2a  d ) . compared to nd controls
, hfd increased the number of long term repopulating ( lt ) hsc ( lsk cd150 ) as well as all myeloid progenitor populations ( mpp , gmp , pre - gm ) in the bm   ( figure  3a  e ) .
consistent with this result bm from hfd mice generated more granulocyte and macrophage cfu ( figure  3f ) .
we did not observe a significant increase in the lt - hscs or gmp populations in the spleen of hfd fed mice ( figure  3 g ) .
this demonstrates that hfd promotes the quantitative expansion of hscs and generation of myeloid progenitors in the bm compartment .
our previous experiments suggest that hfd leads to sustained changes in the production of myeloid cells from bm precursors . to examine this longitudinally
, hfd fed mice ( 12 weeks ) were switched off of hfd chow to nd chow for 8 weeks to induce weight loss .
this diet switch led to a significant decrease in body weight to match those of age - matched nd controls ( supplementary figure  2e ) and a normalization of glycemic control based on glucose tolerance tests ( supplementary figure  2f ) . in the bm , while the number of lt - hscs normalized , the quantity of pre - gms and lin cells remained elevated in the bm despite weight loss and normalization of glucose tolerance ( figure  3h ) .
this suggests that while the expansion of lt - hsc by dio may be reversible , an increase in the production of some myeloid progenitors persists after removal of obesogenic stimuli . to examine the effect of short term hfd feeding on bm hscs
one week of hfd feeding did not lead to significant differences in body weight ( nd 30.35    2.9  g and 1 week hfd 30.04    3.9  g ) but a rapid expansion of fat pad weight ( nd 0.27    0.11  g vs 1 week 0.70    0.12  g , p  <  0.0001 ) .
gmp and pre - gm myeloid progenitors in the bm declined after one - week of hfd exposure and then increased by 4 weeks ( figure  3i ) .
this suggests that rapid fat expansion with short term hfd exposure triggers a transient depletion of lt - hscs followed by a later increase in the generation of myeloid bm progenitors . to compare the myeloid cell output between hscs from lean and obese mice , bm from nd and hfd mouse donors ( cd45.2 )
consistent with a continued myeloid bias after bmt , colony forming unit ( cfu ) assays from the chimeras showed that bm from h    n mice generated more granulocyte and myeloid colonies (
cfu - g / m / gm ) compared to mice reconstituted with nd donors n 
evaluation of atms demonstrated that h    n mice had an increased number of cd11c atms in visceral fat compared to n    n controls ( figure  4c ) .
hfd increase the number of atms in gonadal fat to a similar degree in both donor groups .
however , mice receiving hfd donor bm ( h    h ) had a higher percentage of cd11c atms in visceral adipose tissue compared to those receiving bm from nd fed donors ( n    h ) .
this generated an overall increase in the ratio of cd11c to cd11c atms in h    h mice .
evaluation of adipose tissue t cells showed an increase in cd8 t cells in fat with obesity , but no differences were seen between donor groups ( figure  4d ) .
cd4 t cells in fat were induced with obesity but were decreased in h    h compared to n    h. analysis of adipose tissue regulatory t cells ( treg ; cd4
foxp3 ) showed a marginally significant decrease in tregs in mice that received hfd bm .
hfd challenged mice reconstituted with hfd bm were more insulin resistant than those receiving nd marrow based on elevated fasting insulin levels ( figure  4e ) and glucose tolerance testing primarily during phase 2 ( figure  4f ) .
no differences in glucose tolerance were seen between donor groups in lean nd fed mice . to confirm that the effects were due to differences at the level of hscs , another bmt experiment was performed using equal numbers ( 4000 ) of facs sorted donor lsk cells from nd and hfd mice .
4 weeks after bmt , animals reconstituted with hfd lsk cells had more monocytes and more ly6c monocytes in circulation ( figure  4 g ) .
after hfd feeding , cfu assays from bm cells demonstrated a significant increase in cfu - g / m / gm in hfd chimeras compared to nd chimeras ( figure  4 g ) . to perform the most stringent test for obesity - induced alterations in lt - hsc function
, a serial bmt experiment was performed starting with hfd and nd bm donor cells ( figure  5a ) .
after the first transplant , recipient mice were maintained on a nd for 16 weeks prior to a second round of bmt using these mice as donors .
no differences in body weight or adipose tissue weight were seen based on donor origin ( figure  5b and supplementary figure  3a ) .
after the second transplant , lean mice did not show any significant differences in the quantity of hscs , myeloid progenitors , or atms based on the original donor source ( data not shown ) .
compared to mice derived from nd bm ( n    h ) , obese mice that originally received hfd bm ( h    h ) had similar numbers of lt - hscs , but had more bm lin and lsk cells as well as an increase in pre - gm and mpp myeloid progenitors ( figure  5c ) .
h    h mice demonstrated an increase in cd11c bm cells as well as total atms , and cd11c atms in visceral adipose tissue ( figure  5d ) .
consistent with this , immunofluorescence imaging of the adipose tissue demonstrated in increase in the number of crown - like structures ( cls ) that correlate with inflammatory atm accumulation ( figure  5e ) .
t - cells ( cd3 total and cd4 and cd8 positive sub - sets ) were not different in the spleen and adipose tissue amongst all groups .
glucose tolerance testing did not demonstrate any significant differences in fasting glucose or glucose tolerance after serial bmt by donor ( figure  5 g ) . as anticipated , obese mice did have higher glucose levels compared to lean mice .
lean mice derived from hfd bm ( h    n ) had higher fasting insulin levels ( figure  5f ) .
obese mice derived from hfd donors ( h    h ) demonstrated elevated fed insulin levels compared to those derived from a nd donor .
gene expression analysis showed that inflammatory gene expression did not differ based on donor source , however adiponectin expression was lower in h    h mice compared to n    h ( supplementary figure  3b ) .
this data show that sustained changes in lt - hscs induced by hfd can potentiate myeloid output , the generation of cd11c atms , and influence adipokine signaling .
since tlr / myd88 signals have been implicated in hsc activation in response to microbial infection , we examined the contribution of these pathways to hfd induced myeloid cell production in a long - term competitive reconstitution model .
donor bm from myd88 ( cd45.2 ) and wt ( cd45.1 ) mice were mixed in a 1:1 ratio prior to injection into irradiated wt recipients .
chimeras were fed a hfd for 16 weeks prior to analysis of the ratio of myd88 ( cd45.2 ) to wt ( cd45.1 ) cells .
bm was stained and progenitors were analyzed by gating lineage negative cells for lsk , gmp , and hsc populations as shown in figure  6a .
myd88 and wt donors contributed similarly to lt - hscs suggesting that myd88 is not required for the reconstitution or maintenance of lt - hscs .
however , compared to wt cells , fewer myd88 cells contributed to either lin progenitors or gmps ( cd45.2/cd45.1 ratio < 1 ) consistent with impairment in myelopoiesis in cells lacking myd88 ( figure  6b ) .
the preferential contribution of wt donors relative to myd88 donors ( cd45.2/cd45.1 ratio < 1 ) was observed in blood monocytes and total atms from visceral adipose tissue .
stratification of atms based on cd11c expression demonstrated the preferential accumulation of wt cd11c atms over myd88 cd11c atms , without a significant difference in the donor contributions to cd11c resident atms .
these results suggest that myd88 regulates the generation activated cd11c atms with obesogenic stimuli at the level of myeloid progenitor production . to examine
if tlr4 contributes to the same process , a similar long - term reconstitution model was performed with chimeras generated from donor bm from an equal ratio of tlr4 ( cd45.2 ) and wt ( cd45.1 ) bm fed a hfd for 16 weeks ( figure  6c ) .
in contrast to myd88 chimeras , there was a decrease in tlr4 lt - hscs relative to wt demonstrating that tlr4 hscs have a competitive disadvantage in reconstitution compared to wt cells .
tlr4 derived cells contributed more to gmps suggesting that tlr4 may inhibit the generation of myeloid precursors in the bm after long - term hfd .
overall , our results suggest the myd88 is required for maximal myeloid production in the setting of hfd and while tlr4 is required for lt - hsc expansion it is not required for the increased myeloid cell production .
an increase in peripheral leukocytes of the myeloid lineage ( monocytes and neutrophils ) is a common feature of obesity in children   and adults . more importantly ,
leukocytosis is a biomarker for risk of obesity - associated diseases such as diabetes and atherosclerosis .
this study demonstrates that high fat diet induced obesity leads to alterations in the bm pool of hscs that contributes to 1 ) quantitative expansion of the hsc pool in the bm , 2 ) increased production of myeloid precursors from hscs , and 3 ) qualitative changes at the level of bm progenitors that potentiate the generation of pro - inflammatory macrophages .
however , the increased capacity for obese hscs to generate activated myeloid cells is sustained and amplified by hfd in mouse bmt models .
myd88 in hscs contributes to myelopoiesis with hfd that ultimately impairs the generation of cd11c atms .
our results support the growing evidence that hscs are not passive bystanders in inflammatory responses and can alter their output in response to a range of inflammatory and nutritional stimuli .
dio has been shown to increase hematopoiesis and lymphopoiesis in mice but progenitors were not examined in this study .
hscs from diabetic db / db mice demonstrate markers of inflammatory activation and upregulation of adhesion molecules suggesting that leptin signaling may play a role in hsc regulation .
cholesterol metabolism is also critical to the proper maintenance of hsc proliferation and production of myeloid cells from committed progenitors .
the atherosclerosis - prone phenotype of apoe deficient mice is directly linked to defective cholesterol efflux in hscs that amplifies myeloid cell production and activation and promotes atherosclerosis .
recent studies have found a suppression of b cell lymphopoiesis after hfd , which is consistent with our findings of myeloid activation which could lead to such lymphoid differentiation .
our findings that myd88 is critical for atm accumulation and development is consistent with the recent findings that myd88 in mature macrophages and endothelial cells is important for obesity - induced inflammation .
given recent studies showing the contribution of committed myeloid progenitors in the spleen to the production of ly6c monocytes in atherogenesis   we investigated this and found that with high fat diet induced there was no significant quantitative induction of splenic progenitors .
a consistent finding in several of our bm chimera experiments is an increased generation of cd11c atms generated from hscs from obese mouse donors .
this matches our in  vitro observations of a potentiation of inflammatory capacity of bm derived macrophages from obese mice
. this may also relate to alterations in atm proliferation and differentiation into cd11c atms .
however , the weight of evidence still supports an important role of monocyte trafficking to adipose tissue as the mechanism of obesity - induced cd11c atm accumulation .
overall , our serial bm transplant studies support the concept that obesity can durably reprogram the output of bm progenitors and that this is taking place at the level of long term repopulating ( lt ) hscs .
we hypothesize that obesity - induced epigenetic changes may play a role in generating this phenotype as this has been shown to influence macrophage activation states after chronic and acute inflammatory stimuli .
the preferential accumulation of cd11c atms and crown - like structures was not associated with any significant derangements in glucose metabolism in lean or obese conditions in the serial transplant .
this may be due to physiologic changes related to the conditioning irradiation known to influence weight gain after bmt .
it may also relate to compensatory protective changes in other adipose tissue leukocyte populations such as regulator t cells that we have found to be radio - resistant to standard conditioning regimens .
our results have implication for interpretation of bm chimeras in the study of obesity - induced inflammation .
most of these have focused primarily on mature macrophage responses and have not taken into account the important role innate immune signals such as tlrs and nlrs play in hsc function and myeloid progenitor from the bm pool .
our studies suggest that myd88 in hscs controls the generation of myeloid progenitors in the setting of hfd while tlr4 itself is not required for this process .
the competitive advantage wt cells have over myd88ko cells extends outside of the bm compartment and extends toward the generation of cd11c atms .
this study suggests that obesity may have life - long effects on inflammatory responses by altering hsc function .
this view is supported by epidemiologic data linking rapid early growth to an increase in leukocyte counts that tracks throughout childhood and into adulthood .
it is also consistent with the importance of the duration of obesity on diabetes risk and the observation that adults who were obese as children retain an increased risk of insulin resistance .
our observations may explain the data that adipose tissue inflammation and fibrosis are not resolved even after returning to normal weight after weight loss .
this has implications not only towards effects of childhood obesity , but also toward the impact of obesity on other obesity - associated diseases with an inflammatory component that includes cancer , kidney disease , and liver disease [ 6365 ] .
our studies demonstrate that obesity - induces changes at the level of hscs and early bm myeloid progenitors that expand myeloid cell production and potentiate the production of pro - inflammatory macrophages .
myd88 dependent generation of myeloid precursors contributes to the generation of cd11c adipose tissue macrophages .
 obesity is associated with an activated macrophage phenotype in multiple tissues that contributes to tissue inflammation and metabolic disease . to evaluate the mechanisms by which obesity potentiates myeloid activation 
 , we evaluated the hypothesis that obesity activates myeloid cell production from bone marrow progenitors to potentiate inflammatory responses in metabolic tissues . 
 high fat diet - induced obesity generated both quantitative increases in myeloid progenitors as well as a potentiation of inflammation in macrophages derived from these progenitors . in  vivo , hematopoietic stem cells from obese mice demonstrated the sustained capacity to preferentially generate inflammatory cd11c+ adipose tissue macrophages after serial bone marrow transplantation . 
 we identified that hematopoietic myd88 was important for the accumulation of cd11c+ adipose tissue macrophage accumulation by regulating the generation of myeloid progenitors from hscs . 
 these findings demonstrate that obesity and metabolic signals potentiate leukocyte production and that dietary priming of hematopoietic progenitors contributes to adipose tissue inflammation . 
Introduction
Materials and methods
Results
Discussion
Conclusions