Carboxyl Ester Lipase Affects Hepatic HDL Metabolism

描述(申请人提供)：反向胆固醇转运(RCT)是指多余的胆固醇从周围组织转移到肝脏，以胆汁胆固醇和胆汁酸的形式处置。近年来，许多研究都集中在寻找加强这一过程的方法，从而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。这项建议的总体目标是更好地了解肝细胞选择性地从高密度脂蛋白中去除和水解胆固醇酯并将游离胆固醇输送到胆汁或首先将其代谢成胆汁酸的机制。重点研究了负责这些胆固醇酯的水解酶(S)，以及如果这种水解酶没有发生的话所引起的新陈代谢变化。羧基酯脂肪酶(CEL)又称胆固醇酯酶和胆盐刺激脂肪酶，由肝脏合成和分泌。来自培养细胞和CEL缺失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发挥作用。提出了三个具体目标。1)表征CEL缺失的生理后果，并探讨CEL影响肝脏胆固醇代谢的机制。胆固醇和胆汁酸的合成以及脂蛋白代谢将在CEL缺失的小鼠中进行研究。2)利用肝脏CEL表达升高的转基因小鼠，验证肝脏CEL表达增加将增加对高密度脂蛋白胆固醇的选择性摄取和向胆汁的转运的假设。3)测试这样一种假设：从表达CETP(胆固醇酯：甘油三酯转移蛋白)的小鼠体内去除CEL将增加高密度脂蛋白和富含甘油三酯的脂蛋白之间的脂肪交换，并导致后者更快地从循环中清除。CETP基因将通过与表达猴CETP转基因的小鼠杂交而转移到CEL缺失的小鼠。与公众健康相关：拟议的实验结果将提供关于高密度脂蛋白功能和肝脏胆固醇代谢的有价值的信息，这些信息可能有助于确定增加胆固醇分解和排泄的新药物靶点，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.