MODULATORS OF ALCOHOLIC LIPIDEMIA & STEATOSIS:KEY ROLE OF SCAVENGER RECEPTOR B I

描述(申请人提供)：基本原理：肝脏清道夫受体B类，I型受体(SRBI)是一种高度糖化的82 kDa蛋白质，主要负责肝脏从高密度脂蛋白(HDL)中摄取胆固醇酯，这一过程被称为反向胆固醇运输(RCT)。Pi的中心假设是，SRBI是一个迄今尚未探索的潜在靶点，可用于慢性酒精诱导的RCT缺陷，其原因是相应的SRB1表达受损和/或翻译后修饰，这反过来可能影响其细胞内转运。最终结果将是伴随而来的酒精性高脂血症。因此，阐明酒精对SRB1功能的影响及其与酒精性高脂血症的关系具有重要的临床意义。同样，由于饮食甜菜碱对血浆和肝脏有显著的降脂作用，研究甜菜碱是否通过调节SRB1的表达、翻译后修饰和功能而产生降血脂作用也同样重要。初步结果：PI有以下初步数据支持这一建议：1.与酒精喂养大鼠的肝细胞相比，正常高密度脂蛋白对肝脏对胆固醇的摄取减少了48%(p&lt；0.05)。2.乙醇可使肝脏SRB1基因表达下调51%(p&lt；0.05)。3.乙醇能抑制肝脏SRB1的相对糖化率41%(p&lt；0.05)。4.膳食甜菜碱可减弱乙醇的上述作用。基于这些数据和我们的新假设，我们希望实现以下特定目的：1.慢性乙醇和甜菜碱对SRB_1和高密度脂蛋白在调节RCT中的协同作用的可能作用及其与血脂和脂蛋白、肝脂和肝组织病理学的关系。特定目的2.慢性乙醇和甜菜碱在转录和转录后调控SRB1表达中的可能作用/S。具体目的3.慢性乙醇和甜菜碱在调节肝脏相对合成糖化速率和SRB1转运中的可能作用/S因此，R21拨款申请的主要重点将是确立SRB1作为慢性酒精暴露的新靶点的核心作用，并可能从潜在和逻辑上导致更详细的R01申请，说明SRB1在酒精性高脂血症发病机制中的地位和功能。最后，测试饮食甜菜碱是否可以通过恢复正常的SRB1状态和功能来减轻乙醇的有害行为，这在治疗上是有意义的。方法：我们将使用活体动物模型&应用分子生物学、免疫组织化学和生化方法的肝细胞系统来实现我们的特定目标。PI有一个强大的分子生物学和生化小组，在这项提议的所有方面都有专业知识。 与公共健康相关：这项探索性拨款申请的目标是确定长期接触乙醇会影响SRB1的胆固醇吸收功能，SRB1是导致酒精性脂肪变性的高密度脂蛋白胆固醇的特异性受体。如果是这样的话，验证这种缺陷是否是由于SRB1基因的表达受损、其翻译后修饰及其处置具有重要的临床意义。

DESCRIPTION (provided by applicant): Rationale: Hepatic Scavenger Receptor Class B, Type I receptor (SRBI), a highly glycosylated 82 kDa protein, is primarily responsible for hepatic cholesterol ester uptake from high density lipoproteins (HDL), a process termed Reverse Cholesterol Transport (RCT). PI's central hypothesis is that SRBI is a, hitherto unexplored, potential target for chronic alcohol-induced defective RCT that is due to corresponding impaired SRB1 expression and/or post-translational modifications, which in turn, could affect its intracellular trafficking. The net result would be the concomitant onset of alcoholic hyperlipidemia. Therefore, it is important and clinically relevant to delineate the actions of alcohol on SRB1 function and status in relation to alcoholic hyperlipidemia. Similarly, since dietary betaine has significant lowering effects on plasma and liver lipids, it is equally important to investigate whether betaine elicits its hypolipidemic actions by regulating the expression, post-translational modification and function of SRB1. Preliminary Results: PI has the following preliminary data in support of this proposal: 1. Liver uptake of cholesterol from normal HDL is decreased by 48% (p<0.05) when tested with hepatocytes from alcohol-fed rats compared to the control group. 2. Ethanol down regulates liver SRB1 gene expression by 51% (p<0.05). 3. Ethanol inhibits hepatic relative glycosylation rate of SRB1 by 41% (p<0.05). 4. These effects of ethanol are attenuated by dietary betaine. Based on these data and our novel hypotheses, we wish to accomplish the following specific aims: Specific Aim 1. Possible action/s of chronic ethanol and betaine on the synergistic functions of SRB1 and HDL in the regulation of RCT and correlation with plasma lipids & lipoproteins, liver lipids and liver histopathology. Specific Aim 2. Possible action/s of chronic ethanol and betaine in the transcriptional and post- transcriptional regulation of SRB1 expression. Specific Aim 3. Possible action/s of chronic ethanol and betaine in the regulation of hepatic relative synthetic & glycosylation rates and trafficking of SRB1. Thus, the major emphasis on this R21 grant application will be to establish a central role for SRB1 as a new target of chronic alcohol exposure and can potentially and logically lead to a more detailed R01 application on this novel role of SRB1 status and function in the pathogenesis of alcoholic hyperlipidemia. Finally, it is therapeutically pertinent to test whether dietary betaine can attenuate deleterious actions of ethanol by restoring the normal SRB1 status & function. Methods of Approach: We will accomplish our specific aims using an in vivo animal model & liver cell systems applying molecular biology, immuno-histochemistry and biochemical approaches. PI has a strong molecular biology & biochemical group with expertise in all aspects of this proposal. PUBLIC HEALTH RELEVANCE: It is goal of this exploratory grant application to establish that chronic ethanol exposure affects the cholesterol uptake function of SRB1, a specific receptor for HDL cholesterol leading to alcoholic steatosis. If so, it is clinically important to verify whether this defect is due to impaired SRB1 gene expression, its post-translational modification and its disposition.