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受其细胞在细胞凋亡之前处理过剩胆固醇的能力的调节。巨噬细胞是人类和小鼠早期斑块的主要细胞类型，可以利用几种途径内化脂蛋白和外流胆固醇。由于胆固醇外流是通过向LXR运送脂蛋白衍生的氧固醇来激活的，所以不同的内化受体可能会诱导不同的巨噬细胞对相同的胆固醇负荷做出不同的反应。载脂蛋白E是一种由巨噬细胞高度表达的多功能蛋白，受LXR调控，具有很强的抗动脉粥样硬化作用，其抗动脉粥样硬化作用可通过与内化受体LDLR和LRP1或与胆固醇外流试剂ABCA1和PLTP的相互作用而实现。在这笔赠款的前一个周期中，我们发现从巨噬细胞中删除LRP1会导致apoE合成增加，并且令人惊讶的是，增加病变的形成。这表明，如果没有LRP1，apoE就不能发挥其有益的作用。我们还鉴定了apoE和LRP1之间控制巨噬细胞apoE分泌效率的功能相互作用，并确定巨噬细胞表达的人apoE变异体与LRP1结合不同，在动脉粥样硬化形成中具有截然不同的作用。最后，我们为载脂蛋白E在巨噬细胞胆固醇外流中的作用提供了证据，即使在过量的载脂蛋白AI存在的情况下，载脂蛋白AI是高密度脂蛋白途径的典型激活剂。我们的结果与apoE和LRP1在一个功能轴上工作，以最大限度地提高动脉粥样硬化泡沫细胞对动脉内膜巨大胆固醇负荷的适应性反应的情景是一致的。在这项新的提议中，我们计划：1)证明巨噬细胞中apoE和LRP1之间的相互作用影响动脉粥样硬化小鼠模型的病变形成；2)检验LRP1介导的富含apoE的脂蛋白内化可以改善胆固醇向外排可及的间隔室的转运并增强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在巨噬细胞中参与抗炎和促生存的反调节。我们的研究旨在解锁从病变巨噬细胞到高密度脂蛋白途径的胆固醇释放的基本调节，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。我们的研究集中在导致动脉粥样硬化斑块中胆固醇积聚和清除的机制，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低密度脂蛋白水平来减少胆固醇在斑块中的积累，但还没有可用的治疗方法来诱导胆固醇从斑块中排出。我们已经发现了两种蛋白质(apoE和LRP1)之间的功能联系，它可以改善斑块巨噬细胞中胆固醇的处置，并可能导致冠状动脉斑块消退的新药的开发。

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.