Cells Processing High Density Lipoproteins

描述（由申请人提供）：清道夫受体B类I型（SR-BI）通过一个过程促进胆固醇酯（CE）从脂蛋白颗粒如高密度脂蛋白（HDL）中的选择性摄取，在该过程中HDL核心-CE被摄入细胞，而HDL颗粒本身没有平行摄取和降解。该SR-BI介导的“选择性”途径代表了将CE递送至啮齿动物和人类的肝脏和类固醇生成组织以分别生物合成胆汁酸和类固醇激素的主要途径。除了促进选择性CE转运外，SR-BI还促进胆固醇逆向转运（RCT）并发挥动脉粥样硬化保护作用。虽然对SR-BI的这些不同功能了解很多，但控制SR-BI功能表达的细胞机制尚未完全建立。这种竞争性更新应用的总体目标是阐明某些正性和负性调节剂调节SR-BI在肝脏、肾上腺和性腺中的表达和功能的机制。具体而言，我们建议确定SF-1/LRH-1和NHERF 1/2和SIK-1对SR-BI表达、SR-BI介导的选择性CE转运以及肝脏和类固醇生成组织中胆汁酸和类固醇合成的刺激和抑制作用。该提案的具体目的是：1）表征和确定LRH-1和SF-1在完整的肝和类固醇生成组织和分离的细胞中的类固醇诱导的SR-BI表达和功能中的作用; 2）确定NHERF 1和NHERF 2如何潜在地影响SR-BI表达，其细胞定位和SR-BI介导的选择性HDL-CE摄取在体外和体内使用肝和类固醇生成细胞和遗传小鼠模型;和3）鉴定在体内和体外在肝和类固醇生成细胞模型系统中，SIK-I抑制SR-BI依赖性选择性HDL-CE摄取的潜在机制。该方案利用最先进的分子、细胞、生物化学和生物物理学方法以及独特的细胞和动物模型来剖析介导核受体SF-1和LRH-1、含PDZ结构域的蛋白NHERF 1/2和细胞调节的SIK-1蛋白的调节作用的分子事件。成功完成拟议的研究可能会确定新的目标，可用于开发新的疗法来治疗胆汁酸和类固醇激素相关疾病。在更广泛的范围内，由于SR-BI具有动脉粥样硬化保护作用，因此目前的研究也可能有助于开发心血管疾病临床管理中的新治疗和预防策略。 公共卫生相关性：胆汁酸和类固醇激素是分别由肝脏和肾上腺/性腺产生的化学物质，并且是许多正常生理过程所必需的。胆汁酸在促进脂质消化和吸收中起重要作用，并且也是肝和肠功能的重要调节剂。同样，肾上腺类固醇影响碳水化合物，脂质和蛋白质代谢，盐和水平衡，以及炎症，免疫力和血压，而性腺类固醇对第二性征，生殖以及肌肉和骨骼生长至关重要。胆汁酸和类固醇都是由SR-BI介导的选择性递送胆固醇合成的，因此强调了理解控制SR-BI功能表达的细胞机制的相关性。

DESCRIPTION (provided by applicant): Scavenger receptor class B, type I (SR-BI) facilitates selective uptake of cholesteryl ester (CE) from lipoprotein particles such as high-density lipoprotein (HDL) by a process in which HDL core-CE is taken into cells without a parallel uptake and degradation of the HDL particle itself. This SR-BI-mediated 'selective' pathway represents a major route for the delivery of CEs to the liver and steroidogenic tissues of rodents and humans for the biosynthesis of bile acids and steroid hormones, respectively. Besides facilitating selective CE transport, SR-BI also promotes reverse cholesterol transport (RCT) and exerts atheroprotective actions. Although much is known about these various functions of SR-BI, the cellular mechanisms controlling functional expression of SR-BI are not fully established. The overall goal of this competitive renewal application is to elucidate mechanisms by which certain positive and negative modulators regulate the expression and function of SR-BI in the liver, adrenal and gonads. Specifically, we propose to determine the stimulatory and inhibitory actions of SF-1/LRH-1 and NHERF1/2 and SIK-1 on SR-BI expression, SR-BI mediated selective CE transport and bile acid and steroid synthesis in liver and steroidogenic tissues. The specific aims of the proposal are to: 1) characterize and establish the roles of LRH-1 and SF-1 in hormone-induced SR-BI expression and function in intact hepatic and steroidogenic tissues and isolated cells; 2) determine how NHERF1 and NHERF2 potentially impact SR-BI expression, its cellular localization and SR-BI-mediated selective HDL-CE uptake in vitro and in vivo using hepatic and steroidogenic cells and genetic mouse models; and 3) identify underlying mechanisms by which SIK-1 inhibits SR-BI-dependent selective HDL-CE uptake in vivo and in hepatic and steroidogenic cell model systems in vitro. This proposal utilizes state-of-the-art molecular, cellular and biochemical and biophysical approaches and unique cell and animal models to dissect the molecular events mediating the modulatory actions of nuclear receptors SF-1 and LRH-1, PDZ-domain containing proteins NHERF1/2 and hormone-regulated SIK-1 protein. Successful completion of the proposed studies is likely to identify novel targets that can be exploited for the development of new therapies to treat bile acids and steroid hormone related diseases. On a broader scope, since SR-BI is atheroprotective, the current studies may also aid in the development of new therapeutic and preventive strategies in the clinical management of cardiovascular disease. PUBLIC HEALTH RELEVANCE: Bile acids and steroid hormones are chemicals produced by the liver and adrenal/gonads, respectively, and are essential for a multitude of normal physiological processes. Bile acids play essential roles in facilitating lipid digestion and absorption, and also serve as important regulators of hepatic and intestinal function. Likewise, adrenal steroids influence carbohydrate, lipid, and protein metabolism, and salt and water balance, as well as inflammation, immunity and blood pressure, whereas gonadal steroids are critical for secondary sex characteristics, reproduction and muscle and bone growth. Both bile acids and steroids are synthesized from SR-BI-mediated selectively delivered cholesterol, thus underscoring the relevance of understanding the cellular mechanisms controlling the functional expression of SR-BI.