Hepatic Cholesterol Transport Mediated by SR-BI

描述(由申请人提供) 肝脏是控制体内胆固醇动态平衡的关键器官，通过胆固醇反向转运途径的最后一步：胆固醇从血浆高密度脂蛋白进入胆汁。该途径的功能受控于肝脏B型清道夫受体I(SR-BI)的表达和活性。SR-BI是一种多脂蛋白受体，介导对高密度脂蛋白胆固醇的选择性摄取。对小鼠的活体研究，包括SR-BI在肝脏的过表达和SR-BI纯合零突变的分析，表明肝脏SR-BI的表达在决定血浆高密度脂蛋白水平、肝细胞对高密度脂蛋白的摄取及其有效分泌到胆汁中起着关键作用。在生理条件下，SR-BI可能通过促进肝细胞肝窦表面血浆脂蛋白胆固醇的摄取而增加肝内胆固醇的利用率，从而促进胆汁胆固醇的分泌。由于SR-BI可介导胆固醇外流，并且已在SR-BI过表达的肝细胞的小管膜上发现，因此SR-BI也可能直接参与小管膜上胆汁胆固醇的分泌。然而，决定其肝脏质膜分布及其在肝脏胆固醇转运中的功能的SR-BI的确切结构特征仍不清楚。这一建议的总体目标是：1)阐明SR-BI在体内肝脏质膜极化分布的生化和结构基础；2)建立SR-BI的结构决定因素，这些决定因素支持SR-BI调节胆固醇从血浆通过肝脏进入胆汁的功能活性。将产生不同的SR-BI突变形式，用于重组腺病毒的制备，并测试它们对感染这些重组腺病毒的小鼠的极化质膜定位、血浆高密度脂蛋白水平和肝脏胆汁胆固醇分泌的影响。这项拟议的工作将有助于确定SR-BI介导的高密度脂蛋白在肝脏中转运的关键分子和细胞机制，并可能为动脉粥样硬化和胆石病的发病机制和治疗提供新的见解，这两种疾病与肝脏高密度脂蛋白代谢异常相关。这项研究将由阿蒂里奥·里戈蒂主要在智利进行，作为美国国立卫生研究院#HL64737和HL52212号补助金的延伸。

DESCRIPTION (provided by applicant) The liver is a key organ controlling body cholesterol homeostasis through the last step of reverse cholesterol transport pathway: the movement of cholesterol from plasma HDL into bile. The function of this pathway is under control of the hepatic expression and activity of the scavenger receptor class B type I (SR-BI). SR-BI is a multilipoprotein receptor that mediates selective uptake of HDL cholesterol. In vivo studies with mice, including overexpression of SR-BI in the liver and analysis of SR-BI homozygous null mutants, have shown that hepatic SR-BI expression plays a key role in determining plasma levels of HDL cholesterol, its uptake by liver cells and its efficient secretion into bile. Under physiological conditions, SR-BI might facilitate biliary cholesterol secretion by increasing intrahepatic cholesterol availability as a consequence of facilitated hepatic uptake of plasma lipoprotein cholesterol at the sinusoidal surface of hepatocytes. Because SR-BI can mediate cholesterol efflux and has been found in the canalicular membrane of SR-BI over-expressing liver cells, it might also be directly participating in biliary cholesterol secretion from the canalicular membrane. However, the precise structural features of SR-BI that determine its hepatic plasma membrane distribution and its function in hepatic cholesterol trafficking remain mostly unknown. The overall goals of this proposal are: 1) to elucidate the biochemical and structural bases for the polarized distribution of SR-BI in liver plasma membranes in vivo, and 2) to establish the structural determinants of SR-BI that underlie its functional activity in regulating the transport of cholesterol from plasma through the liver into bile. Various SR-BI mutant forms will be generated, utilized for recombinant adenoviral preparation, and tested for their effects on polarized plasma membrane localization and plasma HDL cholesterol levels and biliary cholesterol secretion in livers of mice infected with these recombinant adenoviruses. The proposed work will help to determine the key molecular and cellular mechanisms involved in SR-BI-mediated HDL cholesterol trafficking in the liver, and may provide new insights into the pathogenesis and treatment of atherosclerosis and gallstone disease, two frequent conditions associated with abnormal hepatic HDL metabolism. This research will be done by Attilio Rigotti primarily in Chile as an extension of NIH Grants # HL64737 and HL52212.