Role of Star Proteins in Bile Acid and Cholesterol Metabolism

胆固醇体内平衡通过胆固醇摄取的协调调节来维持， 合成、运输、酯化、分泌和降解。最近的进展导致了一个 更全面地了解胆固醇的分类和运输方式有助于 维持胆固醇稳态。然而，许多细胞内胆固醇的作用- 体内各种细胞内的结合蛋白及其对胆固醇的影响 代谢/降解，仍然未知。本申请的总体目标是 阐明两个START结构域蛋白（StarD4，StarD5）在胆固醇和 使用体外和体内方法研究肝细胞和巨噬细胞中的胆汁酸稳态 模型私家侦探的实验室最近显示胆固醇运输到体内 线粒体膜代表了控制胆汁酸合成的速率决定步骤， “酸性”途径，并且“酸性”途径能够控制已知的 调节性氧固醇、27-羟基胆固醇、25-羟基胆固醇和至少一种新的 硫酸氧化甾醇除了StarD1之外，还存在含有StarD1的蛋白质家族。 同源结构域，其潜在地能够在细胞内结合和转运固醇。所有 该家族中的蛋白质具有类似的结构脂质结合域，称为StarD1- 脂质转运相关结构域（START）。最近，他们还显示了以下内容：1）a StarD1、27-羟基胆固醇和StarD5水平的协调反应; 2） StarD5蛋白从高尔基体到质膜的细胞内再分布 胆固醇; 3）胆固醇是StarD4和StarD5的配体;后者也结合25- 羟基胆固醇;和，4）胆汁酸合成和胆固醇酯形成增加 StarD4过表达。在本申请提出的研究中，体外和体内 模型将用于研究StarD4和StarD5的调节和生理功能， 肝细胞和巨噬细胞中。具体而言，研究建议：1）表征 StarD4和StarD5在巨噬细胞和肝细胞中的调节和亚细胞运动 （StarD 4）对胆固醇的反应; 2）表征StarD 4和StarD 5在胆固醇中的功能 巨噬细胞和肝细胞（StarD4）; 3）表征StarD4在 体内胆固醇稳态。了解调节的机制， 肝细胞和巨噬细胞中的胆固醇稳态与理解 动脉硬化和心脏病的发展。

Cholesterol homeostasis is maintained through the coordinated regulation of cholesterol uptake, synthesis, transport, esterification, secretion, and degradation. Recent advances have led to a more complete understanding of the way cholesterol's sorting and transport contribute to the maintenance of cholesterol homeostasis. However, the role of many intracellular cholesterol- binding proteins within various cells in the body, and their effect on cholesterol metabolism/degradation, remains unknown. The overall aim of this application is to elucidate the role of two START domain proteins (StarD4, StarD5) play in cholesterol and bile acid homeostasis in hepatocytes and macrophages using both in vitro and in vivo models. The P.I.s' labs have recently shown that cholesterol transport to the inner mitochondrial membrane represents the rate-determining step controlling bile acid synthesis via the 'acidic' pathway, and that the 'acidic' pathway is able to control nuclear levels of the known regulatory oxysterols, 27-hydroxycholesterol, 25-hydroxycholesterol, and at least one novel sulfated oxysterol. In addition to StarD1, there exists a family of proteins containing a StarD1 homologue domain that potentially is capable of binding and transporting sterols within cells. All proteins in this family have a similar structural lipid-binding domain referred to as the StarD1- related lipid transfer (START) domain. Most recently, they have also shown the following: 1) a coordinated response in the levels of StarD1, 27-hydroxycholesterol, and StarD5; 2) an intracellular redistribution of StarD5 protein from the Golgi to the plasma membrane in response to cholesterol; 3) that cholesterol is a ligand for both StarD4 and StarD5; the later also binds 25- hydroxycholesterol; and, 4) an increase in bile acid synthesis and cholesterol ester formation following StarD4 overexpression. In the studies proposed in this application, in vitro and in vivo models will be used to study the regulation, and physiological function of StarD4, and StarD5 in hepatocytes and in macrophages. Specifically, studies are proposed to: 1) characterize the regulation and subcellular movement of StarD4 and StarD5 in macrophages and hepatocytes (StarD4) in response to cholesterol; 2) characterize the function of StarD4, and StarD5 in macrophages and hepatocytes (StarD4); 3) characterize the physiological role(s) of StarD4 in cholesterol homeostasis in vivo. An understanding of the mechanisms of regulation of cholesterol homeostasis in hepatocytes and macrophages is very relevant to the understanding of the development of arteriosclerosis and heart disease in humans.