Selective Uptake and Hydrolysis of Cholesteryl Ester by SR-BI

 性状（由申请方提供）：I型B类清道夫受体（SR-BI）和HDL的受体-配体复合物负责通过胆固醇逆向转运（RCT）从体内清除胆固醇，并且在预防功能障碍性HDL形成和动脉粥样硬化中至关重要。我们研究的长期目标是了解调节SR-BI介导的胆固醇酯（CE）从HDL到肝脏排泄的机制。该提议由两个主要目的组成，其将检验通过RCT的胆固醇通量取决于“功能性”HDL颗粒与高度结构化SR-BI的低聚组装体的接合的总体假设。目的1旨在确定SR-BI跨膜（TM）结构域的寡聚体组织及其在促进HDL-CE选择性摄取中的作用。首先，我们将使用尖端的NMR策略来确定SR-BI的TM结构域的高分辨率结构和二聚化性质。接下来，我们将设计SR-BI的结构导向突变体，以确定在HDL-CE的选择性摄取中SR-BI的TM结构域的邻近和方向的配体诱导变化的要求。总之，这些研究将测试SR-BI的TM结构域的结构组织和构象灵活性在介导HDL-CE选择性摄取到质膜中至关重要的假设。在目标2中，我们将使用一系列基于细胞的测定和体内实验来确定受损的HDL/SR-BI相互作用的下游后果。首先，我们将确定氧化修饰HDL阻止HDL-CE有效选择性摄取的机制。其次，我们将确定是否SR-BI缺乏症产生功能障碍的HDL颗粒在体内。最后，我们将确定SCARB 1（人类SR-BI基因）的人类突变体对RCT和动脉粥样硬化的影响。这组实验将帮助我们检验以下假设：破坏性受体/配体相互作用通过SR-BI介导的选择性摄取和RCT阻止HDL清除，并导致促进动脉粥样硬化形成的功能障碍性HDL颗粒的形成。总之，这些研究将确定（i）HDL诱导的与SR-BI低聚复合物相关的构象变化促进选择性摄取过程的机制，以及（ii）受损的受体/配体相互作用如何阻碍选择性摄取过程并降低RCT，从而导致功能障碍性致动脉粥样硬化HDL颗粒的形成。我们预计这些研究的结果将有助于确定治疗高胆固醇血症及其相关病理学（如动脉粥样硬化）的新治疗策略。

 DESCRIPTION (provided by applicant): The receptor-ligand complex of scavenger receptor class B type I (SR-BI) and HDL is responsible for cholesterol disposal from the body via reverse cholesterol transport (RCT) and is critical in the prevention of dysfunctional HDL formation and atherosclerosis. The long-term objective of our research is to understand the mechanisms that regulate SR-BI-mediated delivery of cholesteryl ester (CE) from HDL to the liver for excretion. This proposal consists of two primary objectives that will test the overall hypothesis that cholesterol flux via RCT is dependent on the engagement of "functional" HDL particles with an oligomeric assembly of highly- structured SR-BI. Aim 1 is designed to determine the oligomeric organization of the transmembrane (TM) domains of SR-BI and their role in facilitating the selective uptake of HDL-CE. First, we will use cutting-edge NMR strategies to determine the high-resolution structures and dimerization properties of the TM domains of SR-BI. Next, we will design structure-guided mutants of SR-BI to define the requirement of ligand-induced changes in proximity and orientation of the TM domains of SR-BI in the selective uptake of HDL-CE. Together, these studies will test the hypothesis that the structural organization and conformational flexibility of the TM domains of SR-BI are critical in mediating the selective uptake of HDL-CE into the plasma membrane. In Aim 2, we will use a series of cell-based assays and in vivo experiments to determine the downstream consequences of an impaired HDL/SR-BI interaction. First, we will determine the mechanisms by which oxidatively-modified HDL prevents efficient selective uptake of HDL-CE. Second, we will determine whether SR-BI deficiency produces dysfunctional HDL particles in vivo. Finally, we will determine the effects of human mutants of SCARB1 (the human SR-BI gene) on RCT and atherosclerosis. This set of experiments will help us test the hypothesis that disruptive receptor/ligand interactions prevent HDL clearance via SR-BI-mediated selective uptake and RCT, and result in the formation of dysfunctional HDL particles that promote atherogenesis. Together, these studies will identify (i) the mechanisms by which HDL-induced conformational changes associated with the SR-BI oligomeric complex facilitate the selective uptake process and (ii) how impaired receptor/ligand interactions impede the selective uptake process and decrease RCT, resulting in the formation of dysfunctional, atherogenic HDL particles. We anticipate the findings from these studies will help identify novel therapeutic strategies for treating hypercholesterolemia and its associated pathologies such as atherosclerosis.