PPARγ Represses Apolipoprotein A-I Gene but Impedes TNFα-Mediated ApoA-I Downregulation in HepG2 Cells.

Apolipoprotein A-I (ApoA-I) is the main anti-atherogenic component of human high-density lipoproteins (HDL). ApoA-I gene expression is regulated by several nuclear receptors, which are the sensors for metabolic changes during development of cardiovascular diseases. Activation of nuclear receptor PPAR has been shown to impact lipid metabolism as well as inflammation. Here, we have shown that synthetic PPAR agonist GW1929 decreases both ApoA-I mRNA and protein levels in HepG2 cells and the effect of GW1929 on apoA-I gene transcription depends on PPAR. PPAR binds to the sites A and C within the hepatic enhancer of apoA-I gene and the negative regulation of apoA-I gene transcription by PPAR appears to be realized via the site C (-134 to -119). Ligand activation of PPAR leads to an increase of LXR and a decrease of PPAR binding to the apoA-I gene hepatic enhancer in HepG2 cells. GW1929 abolishes the TNF-mediated decrease of ApoA-I mRNA expression in both HepG2 and Caco-2 cells but does not block TNF-mediated inhibition of ApoA-I protein secretion by HepG2 cells. These data demonstrate that complex of PPAR with GW1929 is a negative regulator involved in the control of ApoA-I expression and secretion in human hepatocyte- and enterocyte-like cells. J. Cell. Biochem. 117: 2010-2022, 2016. (c) 2016 Wiley Periodicals, Inc.