Serval - A growth hormone-releasing peptide that binds scavenger receptor CD36 and ghrelin receptor up-regulates sterol transporters and cholesterol efflux in macrophages through a peroxisome proliferator-activated receptor gamma-dependent pathway.
serval:BIB_30E62DF3CF17
Avallone R., Demers A., Rodrigue-Way A., Bujold K., Harb D., Anghel S., Wahli W., Marleau S., Ong H., Tremblay A.
Macrophages play a central role in the pathogenesis of atherosclerosis by accumulating cholesterol through increased uptake of oxidized low-density lipoproteins by scavenger receptor CD36, leading to foam cell formation. Here we demonstrate the ability of hexarelin, a GH-releasing peptide, to enhance the expression of ATP-binding cassette A1 and G1 transporters and cholesterol efflux in macrophages. These effects were associated with a transcriptional activation of nuclear receptor peroxisome proliferator-activated receptor (PPAR)gamma in response to binding of hexarelin to CD36 and GH secretagogue-receptor 1a, the receptor for ghrelin. The hormone binding domain was not required to mediate PPARgamma activation by hexarelin, and phosphorylation of PPARgamma was increased in THP-1 macrophages treated with hexarelin, suggesting that the response to hexarelin may involve PPARgamma activation function-1 activity. However, the activation of PPARgamma by hexarelin did not lead to an increase in CD36 expression, as opposed to liver X receptor (LXR)alpha, suggesting a differential regulation of PPARgamma-targeted genes in response to hexarelin. Chromatin immunoprecipitation assays showed that, in contrast to a PPARgamma agonist, the occupancy of the CD36 promoter by PPARgamma was not increased in THP-1 macrophages treated with hexarelin, whereas the LXRalpha promoter was strongly occupied by PPARgamma in the same conditions. Treatment of apolipoprotein E-null mice maintained on a lipid-rich diet with hexarelin resulted in a significant reduction in atherosclerotic lesions, concomitant with an enhanced expression of PPARgamma and LXRalpha target genes in peritoneal macrophages. The response was strongly impaired in PPARgamma(+/-) macrophages, indicating that PPARgamma was required to mediate the effect of hexarelin. These findings provide a novel mechanism by which the beneficial regulation of PPARgamma and cholesterol metabolism in macrophages could be regulated by CD36 and ghrelin receptor downstream effects.
ATP-Binding Cassette Transporters/metabolism, Animals, Antigens, CD36/genetics, Antigens, CD36/metabolism, Apolipoproteins E/genetics, Atherosclerosis/genetics, Atherosclerosis/prevention & control, Cells, Cultured, Cholesterol/metabolism, DNA-Binding Proteins/genetics, Humans, Lipoproteins/metabolism, Macrophages, Peritoneal/drug effects, Macrophages, Peritoneal/metabolism, Mice, Mice, Knockout, Oligopeptides/pharmacology, Orphan Nuclear Receptors, PPAR gamma/metabolism, Phosphorylation, Promoter Regions, Genetic, Receptors, Cytoplasmic and Nuclear/genetics, Receptors, G-Protein-Coupled/genetics, Receptors, Ghrelin, Transcription, Genetic, Up-Regulation
oai:serval.unil.ch:BIB_30E62DF3CF17