Abstract 5478: P2Y 13 ADP-Receptor Regulates Plasma HDL Clearance, Biliary Cholesterol and Bile Acids Secretions In Vivo

Abstract

Plasma high density lipoprotein (HDL) protects against atherosclerosis, in part through the removal of cholesterol from peripheral tissues and its delivery to the liver for metabolism and bile excretion. Thus understanding of the molecular event implicated in HDL-cholesterol uptake by the liver is critical to the development of therapeutic strategies to enhance HDL catabolism. The scavenger receptor (SR)-BI modulates plasma HDL level and contributes to cholesteryl ester uptake from HDL in mice but a distinct pathway for holo-HDL particle uptake (protein + lipid) has been recently identified in human hepatocytes. This pathway which strictly depends on extracellular ADP level involves different cell surface partners: ADP generated from the activation by apo AI (the main HDL apolipoprotein) of a cell surface F 1 -ATPase, activates the P2Y 13 ADP-receptor and subsequent HDL endocytosis through an unknown low-affinity HDL receptor. To evaluate the physiological relevance of this P2Y 13 -mediated HDL endocytosis pathway in vivo in mice, P2Y 13 receptor was activated by treating C57BL/6 and liver specific SR-BI-KO mice (SR-BI-KO liver ) with the specific agonist (AR-C69931MX, 8nmol/kg, intra-orbital injection). Expression of P2Y 13 protein in liver was also disrupted by siRNA adenovirus (10 9 vp/mice, intra-orbital injection) and in P2Y 13 KO mice. Plasma clearance of 125 I-labeled HDL was rapidly enhanced under AR-C69931MX treatment in SR-BI-KO liver mouse. Conversely, HDL clearance was decreased in P2Y 13 KO mice but no modification was observed in plasma lipids profile versus control mice, suggesting a mechanism of modulation of plasma HDL turnover rather than a simply disruption of HDL uptake. Furthermore, biliary lipids content was decreased under P2Y 13 extinction in mice (bile acids: −60%, cholesterol: −30%), whereas it was dramatically increased under stimulation of P2Y 13 by AR-C69931MX treatment in C57BL/6 mice (bile acids: +85%, cholesterol: +50%,). These results indicate that P2Y 13 has an important role in hepatic HDL metabolism in controlling circulating HDL turnover and biliary lipids elimination, and thus may have an impact on the development of atherosclerosis.