SR-BI and SR-BII recycling and selective lipid uptake

描述(申请人提供)：高密度脂蛋白水平与冠状动脉疾病呈负相关。高密度脂蛋白受体SR-BI在高密度脂蛋白代谢中起着关键作用。SR-BI结合高密度脂蛋白并调节选择性脂质摄取的过程，其机制尚不清楚。各种研究表明，SR-BI在某些细胞中的选择性摄取是通过非内吞过程发生在细胞表面的。然而，最近的研究报道，在肝细胞中，SR-BI介导完整的高密度脂蛋白颗粒的内化，并提示选择性脂质摄取涉及细胞内高密度脂蛋白的内化和循环。我们已经证明，SR-BII是SR-BI的一个变体，它在细胞转运和高密度脂蛋白的内吞方面与SR-BI有显著不同。这一理论的核心假设是，SR-BI和SR-BII在细胞内胆固醇转运中的作用与细胞内受体/配体循环相耦合，SR-BI和SR-BII遵循不同的内化和再循环途径，不同地影响细胞内胆固醇的运输和调节。其具体目的是：1)确定高密度脂蛋白内化和细胞内循环在SR-BI和SR-BII介导的选择性脂质摄取过程中的作用。2)阐明SR-BI和SR-BII内化和循环高密度脂蛋白的机制。将研究SR-BI和SR-BII使用的内吞和循环途径(S)，并将确定SR-BI和SR-BII C末端负责受体靶向的蛋白质基序；3)确定SR-BI和SR-BII对高密度脂蛋白细胞内靶向的差异如何影响细胞胆固醇的调节和运输。我们将确定通过SR-BI和SR-BII选择性摄取脂肪对细胞中调节类固醇的池和胆固醇外流的影响，以及4)使用同种异型特异性敲入小鼠评估SR-BI和SR-BII在体内高密度脂蛋白代谢和动脉粥样硬化形成中的作用。将产生同工型特异性的敲入小鼠，并研究每种受体对血浆脂蛋白、高密度脂蛋白代谢和动脉粥样硬化的影响。

DESCRIPTION (provided by applicant): HDL levels are inversely related to coronary artery disease. The HDL receptor, SR-BI, plays a key role in HDL metabolism. SR-BI binds HDL and mediates the process known as selective lipid uptake, the mechanism of which is not understood. Various studies have indicated that selective uptake by SR-BI in certain cells occurs at the cell surface by a non-endocytic process. However, recent studies have reported that in hepatocytes SR-BI mediates the internalization of intact HDL particles and suggest that selective lipid uptake involves HDL internalization and recycling in cells. We have shown that SR-BII, a variant of SR-BI, differs markedly from SR-BI in its cellular trafficking and endocytosis of HDL. The central hypothesis of this proposal is that the functions of SR-BI and SR-BII in intracellular cholesterol trafficking are coupled to receptor/ligand recycling in cells and that SR-BI and SR-BII follow different internalization and recycling routes and differentially affect cellular cholesterol trafficking and regulation. The specific aims are: 1) determine the contribution of HDL internalization and intracellular recycling to the selective lipid uptake process mediated by SR-BI and SR-BII. HDL recycling by each of the two receptors will be quantified in hepatocytes and other cells, 2) elucidate the mechanisms responsible for HDL internalization and recycling by SR-BI and SR-BII. Endocytic and recycling pathway(s) used by SR-BI and SR-BII will be studied and protein motifs in the C-terminal tails of SR-BI and SR-BII that are responsible for receptor targeting will be identified, 3) determine how differences in the intracellular targeting of HDL by SR-BI and SR-BII influence cellular cholesterol regulation and trafficking. We will determine the effects of selective lipid uptake via SR-BI and SR-BII on the pool of regulatory sterols in cells and on cholesterol efflux and 4) assess the roles of SR-BI and SR-BII in HDL metabolism and atherogenesis in vivo using isoform-specific knock-in mice. Isoform-specific knock-in mice will be generated and the effects of each receptor on plasma lipoproteins, HDL metabolism and atherogenesis studied.