Functional Hierarchy of Remnant Lipoprotein Receptors

描述（由申请人提供）：动脉粥样硬化斑块的演变是由其细胞在凋亡发生前处理多余胆固醇的能力调节的。巨噬细胞是人类和小鼠早期斑块的主要细胞类型，可以利用几种途径进行脂蛋白内化和胆固醇外排。由于胆固醇外排是通过脂蛋白衍生的氧甾醇传递到LXR而激活的，因此不同的内化受体可能会对相同的胆固醇负荷诱导不同的巨噬细胞反应。载脂蛋白（apo）E是一种由巨噬细胞高度表达并受LXR控制的多功能蛋白，具有很强的抗动脉粥样硬化作用，可通过其与内化受体（如LDLR和LRP1）或胆固醇外排剂（如ABCA1和PLTP）的相互作用介导。在本研究的前一个周期中，我们发现巨噬细胞的LRP1缺失导致apoE合成增加，令人惊讶的是，病变形成增加。这表明如果没有LRP1， apoE就无法发挥其有益作用。我们还发现了apoE和LRP1之间的功能相互作用，控制巨噬细胞apoE的分泌效率，并确定巨噬细胞表达的人类apoE变体与LRP1的关联不同，对动脉粥样硬化的影响也截然不同。最后，我们提供了apoE在巨噬细胞胆固醇外排中的作用的证据，即使存在过量的apoAI （HDL途径的典型激活剂）。我们的结果与apoE和LRP1在一个功能轴上工作以最大化动脉内膜中巨大胆固醇负担的动脉粥样硬化泡沫细胞的适应性反应的情况相一致。在这个新的提案中，我们计划：1)证明巨噬细胞中apoE和LRP1的相互作用影响小鼠动脉粥样硬化模型的病变形成；2)验证lrp1介导的apoe富集脂蛋白内化促进胆固醇向外排可及的腔室运输并增强LXR反应的假设；3)确定LRP1信号是否通过胆固醇依赖和独立的机制参与巨噬细胞的抗炎和促生存拮抗调节。我们的研究旨在揭示胆固醇从病变巨噬细胞释放到HDL通路的基本调控，作为开发斑块消退和控制缺血性心脏病的治疗方法的平台。我们的研究重点是导致胆固醇从动脉粥样硬化斑块中积累和去除的机制，这是心脏病发作和中风的常见原因。虽然目前的药物可以通过降低血浆LDL水平来减少斑块中胆固醇的积累，但目前还没有治疗方法可以诱导胆固醇从斑块中排出。我们已经发现了两种蛋白（apoE和LRP1）之间的功能联系，可以改善斑块巨噬细胞中的胆固醇处置，并可能导致开发新的冠状动脉斑块消退药物。

DESCRIPTION (provided by applicant): The evolution of the atherosclerotic plaque is regulated by the ability of its cells to dispose of excess cholesterol before apoptosis ensues. Macrophages are the dominant cell type of early plaques in humans and mice, and can utilize several pathways for lipoprotein internalization and for cholesterol efflux. Because cholesterol efflux is activated by delivery of lipoprotein-derived oxysterols to LXR, it is possible that different internalizing receptors may induce different macrophage responses to the same cholesterol load. Apolipoprotein (apo)E, a multifunctional protein highly expressed by macrophages and under LXR control, has strong anti-atherogenic effects that can be mediated by its interactions with internalizing receptors, such LDLR and LRP1, or with agents of cholesterol efflux, such as ABCA1 and PLTP. In the previous cycle of this grant, we discovered that LRP1 deletion from macrophages leads to increased apoE synthesis and, surprisingly, increased lesion formation. This suggests that apoE cannot exert its beneficial effects without LRP1. We also identified a functional interaction between apoE and LRP1 controlling the secretory efficiency of macrophage apoE, and determined that human apoE variants expressed by macrophages associate differently with LRP1 and have profoundly different effects on atherogenesis. Finally, we provided evidence for a role of apoE in macrophage cholesterol efflux even in the presence of excess amounts of apoAI, the canonical activator of the HDL pathway. Our results are compatible with a scenario where apoE and LRP1 work in a functional axis to maximize the adaptive responses of atheroma foam cells to the tremendous cholesterol burden in the arterial intima. In this new proposal, we plan to: 1) Demonstrate that the interaction between apoE and LRP1 in macrophages influences lesion formation in mouse models of atherosclerosis; 2) Test the hypothesis that LRP1-mediated internalization of apoE-enriched lipoproteins improves trafficking of cholesterol to efflux- accessible compartments and enhances LXR response; 3) Determine whether LRP1 signaling is responsible for anti-inflammatory and pro-survival counter-regulation in macrophages through cholesterol-dependent and independent mechanisms. Our studies aim at unlocking the fundamental regulation of cholesterol release from lesion macrophages into the HDL pathway as a platform for the development of therapeutics for plaque regression and control of ischemic heart disease. Our studies focus on the mechanisms leading to the accumulation and removal of cholesterol from the atherosclerotic plaque, which is the common cause of heart attacks and strokes. Whereas current medications can reduce the accumulation of cholesterol in the plaque by reducing plasma LDL levels, no therapies are available to induce exit of cholesterol from the plaque. We have discovered a functional connection between two proteins (apoE and LRP1) that improves cholesterol disposal in plaque macrophages, and may lead to development of new drugs for regression of coronary plaques.