Lipoproteins in Cardiovascular Biology and Pathology

高密度脂蛋白受体，即B型清道夫受体(SR-BI)，通过以下途径介导高密度脂蛋白的细胞传递 选择性脂质摄取，一种不同于经典受体介导的内吞作用的机制。此外，SR-BI还可以 结合低密度脂蛋白和极低密度脂蛋白，既能介导细胞摄取非脂蛋白胆固醇，又能刺激细胞 胆固醇外流。通过对小鼠的活体研究，我们发现SR-BI在决定 高密度脂蛋白的结构及血浆高密度脂蛋白和胆汁胆固醇的水平，2)在调节递送中的作用 高密度脂蛋白-胆固醇对类固醇生成组织和肝脏的作用，以及3)防止动脉粥样硬化。vt.在.上 饲料喂养的载脂蛋白E基因敲除(KO)遗传背景(自发性动脉粥样硬化的标准小鼠模型)， SR-BI基因的纯合子零突变(SR-BI KO)会显著加速动脉粥样硬化。在……里面 此外，这些双KO小鼠(‘dKO’)表现出在人类致命冠状动脉中常见的多种特征 心脏病(CHD)和心力衰竭，包括高胆固醇血症、闭塞性动脉粥样硬化、心肌梗死 梗塞(毫升)、心功能不全和肥厚、泵衰竭和过早死亡(5-8周龄， 6周时死亡率为50%)。将各种转基因或靶基因缺失导入dKO小鼠或治疗 他们的药物有助于阐明CHD的发病机制，并提供了 更多证据表明，该系统可能成为人类CHD的有力模型。通过交叉SR-BI单 KO小鼠与携带载脂蛋白E亚型等位基因(ApoeR61-h/h)的小鼠，我们产生了SR-BI KO/ApoeR61-h/h小鼠 当喂食食物时，这看起来是正常的，但当喂食致动脉粥样硬化的食物时，就会发生致命的闭塞 与饮食喂养的dKO小鼠几乎相同的CHD(发病后32+/-6天死亡率为50%) 致动脉粥样硬化饮食)。停用致动脉粥样硬化的饮食可用于研究疾病的消退/恢复。 (动脉粥样硬化，ML，心力衰竭)。对这两种CHD小鼠模型的分析应该会提供新的 机制洞察力和初步分析新的治疗或预防战略的平台。 该项目的两个目标是：1)表征早发冠心病和死亡的机制 在dKO和SR-BI KO/ApoeR61-h/h小鼠中，评估和改进这些小鼠作为模型的有效性 人类冠心病，以及ii)使用体细胞遗传学在细胞水平上鉴定基因产物和 SR-BI活动所需的功能以及SR-BI对心血管的深刻影响 系统。广泛的分子、细胞、生理、成像、遗传、基因组和药理学 这些办法将与其他项目和核心密切结合使用。例如，1)使用 小鼠遗传学和生理学核心我们将继续开发一个名为Hermes to Acquired的系统，网络 实时广播和分析幼崽(因此体型较小)的连续鸡蛋测量结果 DKO小鼠，这将使我们能够将心功能与生化、基因(包括microRNA)联系起来 表达和心脏形态。我们将与项目II和项目V合作，以评估 黏附分子、血小板和止血，以及冠心病的炎症，3)与项目III一起探讨 关键能量代谢激素脂联素在冠心病中的作用，以及4)项目III使用逆转录病毒 技术和体细胞遗传学，以确定SR-BI活动所需的细胞基因。正如我们所确定的 体细胞遗传学可能对心血管疾病有重大贡献的其他基因 病理生理学，我们将评估这些基因的遗传变异对临床的贡献。 表型。我们将测试以下假设：1)我们现有的基于SR-BI基因改良的小鼠 系统是人类CHD的有效模型，可以用来阐明疾病的潜在机制， 2)在培养细胞中鉴定SR-BI功能所需的基因将有助于揭示SR-BI特异性 以及膜蛋白加工和功能的全球重要机制。建议数 这项工作应该有助于阐明心血管功能和 病理生理学。

The HDL receptor, scavenger receptor class B type I (SR-BI), mediates cellular delivery of HDL cholesterol by selective lipid uptake, a mechanism distinct from classic receptor-mediated endocytosis. In addition, SR-BI can bind LDL and VLDL and can mediate both cellular uptake of non-lipoprotein cholesterol and stimulate cellular cholesterol efflux. Using in vivo studies with mice, we have shown that SR-BI plays a key role 1) in determining the structure of HDL and levels of both plasma HDL and biliary cholesterol, 2) in mediating the regulated delivery of HDL-cholesterol to steroidogenic tissues and the liver, and 3) in protecting against atherosclerosis. On a chow-fed apoE knockout (KO) genetic background (standard murine model of spontaneous atherosclerosis), homozygous null mutations in the SR-BI gene (SR-BI KO) cause dramatically accelerated atherosclerosis. In addition, these double KO mice ('dKO') express multiple characteristics commonly seen in human fatal coronary heart disease (CHD) and heart failure, including hypercholesterolemia, occlusive atherosclerosis, myocardial infarction (Ml), cardiac dysfunction and hypertrophy, pump failure and premature death (5-8 weeks of age, 50% mortality at 6 weeks). Crossing various transgenes or targeted gene deletions into dKO mice or treating them with pharmacologic agents is helping to elucidate the mechanisms underlying CHD and has provided additional evidence that this system may serve as a powerful model for human CHD. By crossing SR-BI single KO mice with mice carrying a hypomorphic apoE allele (ApoeR61-h/h), we generated SR-BI KO/ApoeR61-h/h mice that appear normal when fed a chow diet, but when fed an atherogenic ('Paigen') diet develop fatal occlusive CHD that is virtually identical to that in chow-fed dKO mice (50% mortality 32+/-6 days after initiation of the atherogenic diet). Withdrawal of the atherogenic diet can be used to study regression/recovery of disease (atherosclerosis, Ml, heart failure). Analysis of these two murine models of CHD should provide new mechanistic insights and a platform for preliminary analysis of new treatment or prevention strategies. The twin goals of this Project are I) to characterize the mechanisms underlying early onset CHD and death in dKO and SR-BI KO/ApoeR61-h/h mice and assess and improve the validity of these mice as models for human CHD, and II) to use somatic cell genetics to identify at the cellular level the gene products and functions that are required for SR-BI activity and underlie SR-BI's profound effects on the cardiovascular system. A wide array of molecular, cellular, physiologic, imaging, genetic, genomic and pharmacologic approaches will be used in close conjunction with the other Projects and Cores. For example, 1) with the Murine Genetics and Physiology Core we will continue to develop a system called HERMES to acquire, web broadcast and analyze in real time continuous EGG measurements from the very young (and thus small) dKO mice, which will allow us to correlate cardiac function with biochemistry, gene (including microRNA) expression and cardiac morphology. We will collaborate 2) with Projects II and V to evaluate the roles of adhesion molecules, platelets and hemostasis, and inflammation on CHD, 3) with Project III to explore the role of the key energy metabolism hormone adiponectin on CHD, and 4) with Project III in using retroviral technologies and somatic cell genetics to identify cellular genes required for SR-BI activity. As we identify additional genes by somatic cell genetics that are potentially significant contributors to cardiovascular pathophysiology, we will assess the contributions of genetic variation in these genes to clinical phenotypes. We will test the hypotheses that 1) our current and genetically improved SR-BI-based murine systems are valid models for human CHD and can be used to elucidate mechanisms underlying disease, and 2) identification of genes required for SR-BI function in cultured cells will help uncover both SR-BI-specific and globally important mechanisms of membrane protein processing and function. The proposed work should help elucidate key biological mechanisms underlying cardiovascular function and pathophysiology.