Regulation of low density lipoprotein receptor-related protein gene expression, and, Cholesteryl ester transfer protein-mediated HDL selective uptake in the liver.

摘要

Disordered lipoprotein metabolism is a major risk factor for coronary artery disease (CAD). This thesis focuses on two proteins that may exert protective effects against CAD: (1) the regulation of LDL receptor-related protein (LRP) gene expression and (2) hepatic cholesteryl ester transfer protein (CETP)-mediated selective uptake.; LRP is a large multifunctional receptor, which is implicated in numerous biologically important processes including lipoprotein metabolism, cell signal transduction and atherosclerosis. Despite this, regulation of LRP gene expression remains largely unknown. We have identified a novel transcriptional regulatory element, known as a peroxisome proliferator response element (PPRE), at position -1185 to -1173 in the 5'-flanking region of the human LRP gene. The PPRE is transactivated by peroxisome proliferator activated receptors (PPAR) alpha and gamma when activated by ligands such as long chain fatty acids, rosiglitazone (PPARgamma-specific) and fenofibric acid (PPARalpha-specific). This results in upregulation of LRP expression and function in several cell types including adipocytes (PPARgamma-expressing) and hepatocytes (PPARalpha-expressing). These data suggest that LRP gene expression could be preferentially modulated by the use of PPAR-selective agonists and may have important implications for the regulation of human preadipocyte differentiation and triglyceride-rich lipoprotein metabolism in adipocytes and hepatocytes.; CETP is a hydrophobic glycoprotein that plays a central role in human high-density lipoprotein (HDL) metabolism. We have examined the role of CETP in HDL-cholesteryl ester (CE) selective uptake in primary mouse hepatocytes expressing CETP via adenovirus-mediated gene transfer (ad-CETP) or incubated in CETP-containing media. These studies demonstrate that CETP mediates hepatocyte selective uptake of HDL-derived CE independently of other known lipoprotein receptors. Furthermore, CETP-mediated selective uptake occurs by two pathways, only one of which requires CETP transfer activity. Hepatic expression of ad-CETP in vivo resulted in an acute drop in plasma cholesterol in particles in the HDL density range. Finally, CETP-mediated selective uptake in vivo was only partially inhibited by concomitant administration of torcetrapib, a compound which inhibits CETP neutral lipid transfer activity. Taken together, these studies demonstrate a novel and important role for CETP in the selective uptake of HDL-derived CE by hepatocytes, findings which are of fundamental importance to human lipoprotein metabolism.