Scavenger receptor CD36 mediates inhibition of cholesterol synthesis via activation of the PPARγ/PGC-1α pathway and Insig1/2 expression in hepatocytes

The scavenger receptor CD36 plays a central role in lipid metabolism by promoting macrophage cholesterol efflux with the potential to reduce atherosclerotic lesions. However, the effect of CD36 on de novo cholesterol synthesis is not known. Here, we describe the cellular mechanism by which CD36 activation induces cholesterol depletion in HepG2 cells. Using the CD36 ligand hexarelin, we found a rapid phosphorylation of HMG-CoA reductase Ser-872 in treated cells, resulting in inactivation of the rate-limiting enzyme in sterol synthesis. Degradation of HMG-CoA reductase by the ubiquitin-proteasome pathway was also enhanced by hexarelin, through an increased recruitment of the anchor proteins insulin-induced gene (Insig)-1 and Insig-2. Genes encoding key enzymes involved in cholesterol synthesis and under the control of transcription factor sterol regulatory element-binding protein (SREBP)-2 remained unresponsive to sterol depletion, due to retention of the SREBP-2 escort protein Scap by Insig-1/2. Insig1 and Insig2 gene expression was also increased through activation of nuclear receptor peroxisome-proliferator activating receptor gamma (PPAR gamma) by CD36, which lifted the inhibitory effect of PPAR gamma 1 Ser-84 phosphorylation. Recruitment of coactivator peroxisome proliferator-activated receptor-gamma coactivator 1 alpha (PGC1 alpha) to activated AMPK alpha was also promoted, resulting in PGC-1 alpha transcriptional activation through Sirt1-mediated deacetylation, increased recruitment of PPAR gamma, and up-regulation of Insig-1/2, revealing a regulatory role of CD36 on PGC-1 alpha signaling. Our data identify CD36 as a novel regulator of HMG-CoA reductase function and Insig-1/2 expression, 2 critical steps regulating cholesterol synthesis in hepatocytes.-Rodrigue-Way, A., Caron, V., Bilodeau, S., Keil, S., Hassan, M., Levy, E., Mitchell, G. A., Tremblay, A. Scavenger receptor CD36 mediates inhibition of cholesterol synthesis via activation of the PPAR gamma/PGC-1 alpha pathway and Insig1/2 expression in hepatocytes.