Abstract 13229: Varying ABCG1 Expression is Associated With Macrophage Apoptosis&Phagocytosis

Abstract

Introduction: ATP-binding cassette transporter G1(ABCG1)is a transmembrane protein mediated efflux of cellular cholesterol to HDL, which plays a vital part in macrophage lipid homeostasis, but the role of ABCG1 in atherosclerosis still remains controversial. Our previous study demonstrated that human ABCG1 -367 G>A polymorphism in promoter region, which leads to lower ABCG1 protein expression, was associated with a reduced risk of CAD. However, the mechanism behind is not fully understood. Hypothesis: Oxysterols, the oxidized derivatives of cholesterol, whose efflux are mediated by ABCG1, exert cytotoxic effect on macrophage and accelerate cell apoptosis. Low ABCG1 expression induces excess oxysterols accumulation in macrophage, which augments the inflammatory response and accelerates apoptosis. Since defective apoptotic macrophage clearance in late lesions promotes atherosclerosis progression, we hypothesize that macrophage with lower ABCG1 expression may remove apoptotic cells more efficiently, thereby generating an antiatherogenic effect. Methods: To investigate the effect of ABCG1 expression on macrophage, we established ABCG1 knockdown cell line by means of lentivirus mediated shRNA. Apoptosis was determined by flow cytometry (FCM). Fluorescence labeled apoptotic model was generated and macrophage phagocytosis was evaluated. The inflammatory factors level and phagocytosis associated gene expression were measured by ELISA and realtime PCR. Results: Compared with control group, macrophage with lower ABCG1 expression had a higher secretion level of Inflammatory factors, such as TNF-α and IL-1β, showing an increased expression of classic inflammatory M1 phenotype markers,such as CD86 and TGF-β, and a down-regulation of CD163,Arg and IL-6 expression, which are markers of anti-inflammatory M2 phenotype macrophage. The apoptosis was significantly accelerated and the phagocytic clearance was enhanced after ABCG1 expression decreased, which means apoptotic cells could be removed more quickly. Both CD36 and Mertk showed a higher mRNA level in ABCG1 knockdown group. Conclusions: Decreased expression of macrophage ABCG1 may exert antiatherogenic function through accelerating apoptosis and enhancing phagocytosis.