Carboxyl Ester Lipase Affects Hepatic HDL Metabolism

描述（由申请人提供）：胆固醇逆向转运（RCT）是指将多余的胆固醇从外周组织转移到肝脏，以胆胆固醇和胆汁酸的形式处理。近年来，许多研究都集中在寻找增强这一过程的方法，以预防和治疗心血管疾病。高密度脂蛋白（HDL）是RCT的主要载体，主要以胆固醇酯的形式运输胆固醇。本建议的总体目标是更好地了解肝细胞选择性地从HDL中去除和水解胆固醇酯并将游离胆固醇传递到胆汁或首先将其代谢为胆汁酸的机制。特别的重点是研究负责水解这些胆固醇酯的酶和代谢变化，如果这种水解不发生。羧基酯脂肪酶（CEL），又称胆固醇酯酶和胆汁盐刺激脂肪酶，由肝脏产生和分泌。培养细胞和CEL-null小鼠的初步结果表明，该酶在高密度脂蛋白胆固醇酯的选择性摄取和随后的水解中起作用。提出了三个具体目标。1)描述CEL缺失的生理后果，并研究CEL影响肝脏胆固醇代谢的机制。将在CEL-null小鼠中研究胆固醇和胆汁酸合成以及脂蛋白代谢。2)利用转基因小鼠提高肝脏的CEL表达，验证增加肝脏的CEL表达会增加高密度脂蛋白胆固醇的选择性摄取和传递到胆汁的假设。3)验证从表达CETP（胆固醇酯：甘油三酯转移蛋白）的小鼠体内去除CEL会增加高密度脂蛋白和富含甘油三酯的脂蛋白之间的脂质交换，并导致后者更快地从循环中清除。CETP基因将通过与表达类人猿CETP转基因的小鼠杂交，转移到CEL-null小鼠身上。与公共卫生的相关性：拟议的实验结果将提供有关HDL功能和肝脏胆固醇代谢的有价值信息，可能有助于确定增加胆固醇分解和排泄的新药理学靶点，从而降低心血管疾病的风险和进展。

DESCRIPTION (provided by applicant): Reverse Cholesterol Transport (RCT) is the movement of excess cholesterol from peripheral tissues to the liver for disposal as biliary cholesterol and bile acids. In recent years, much research has focused on finding ways to enhance this process so as to both prevent and treat cardiovascular disease. High density lipoproteins (HDL) are the primary vehicles for RCT and transport the cholesterol primarily as cholesteryl esters. The overall goal of this proposal is to better understand the mechanisms by which hepatocytes selectively remove and hydrolyze cholesteryl esters from HDL and deliver the free cholesterol to bile or first metabolize it to bile acids. Particular focus is given to study of the enzyme(s) responsible for hydrolyzing these cholesteryl esters and the metabolic changes that ensue if this hydrolysis does not occur. Carboxyl ester lipase (CEL), also called cholesterol esterase and bile salt-stimulated lipase, is made and secreted by the liver. Preliminary results from cultured cells and CEL-null mice show that this enzyme plays a role in both the selective uptake and the subsequent hydrolysis of HDL cholesteryl esters. Three specific aims are proposed. 1) Characterize the physiological consequences of the absence of CEL and investigate the mechanism by which CEL affects hepatic cholesterol metabolism. Cholesterol and bile acid synthesis as well as lipoprotein metabolism will be studied in CEL-null mice. 2) Test the hypothesis that increasing hepatic CEL expression will increase selective uptake and delivery of HDL cholesterol to the bile using transgenic mice with elevated liver expression of CEL. 3) Test the hypothesis that removing CEL from mice that express CETP (cholesteryl ester:triglyceride transfer protein) will increase lipid exchange between HDL and triglyceride-rich lipoproteins and result in more rapid removal of the latter from the circulation. The CETP gene will be transferred to CEL-null mice by cross-breeding with mice that express a simian CETP transgene. Relevance to Public Health: The results of the proposed experiments will provide valuable information about HDL function and liver cholesterol metabolism that may help identify new pharmacologic targets for increasing cholesterol breakdown and excretion, thereby reducing the risk for and progression of cardiovascular disease.