BILE ACID METABOLISM AND PLASMA CHOLESTEROL REGULATION

胆汁酸代谢和血浆胆固醇调节

• 批准号: 2223749
• 负责人: DAVID K SPADY
• 金额: $ 20.74万
• 依托单位: UT SOUTHWESTERN MEDICAL CENTER
• 依托单位国家: 美国
• 财政年份: 1993
• 资助国家: 美国
• 起止时间: 1993-09-01 至 1996-08-31
• 项目状态: 已结题
• 来源: https://reporter.nih.gov/project-details/2223749
• 关键词: HMG coA reductases; blood lipoprotein metabolism; cholanate compound; cholesterol; dietary lipid; enzyme activity; fatty acids; gene expression; hamsters; laboratory rat; liver metabolism; low density lipoprotein; nucleic acid sequence; nutrition related tag; oxygenases; receptor; receptor binding; steroid metabolism; transcription factor; transfection

Dietary cholesterol suppresses receptor-dependent uptake of low density lipoprotein (LDL) by the liver and raises LDL cholesterol levels. However, the response to a given level of dietary cholesterol varies greatly among different species and among different individuals of the same species. The overall goal. of the proposed research is to understand the mechanistic basis for the marked variability in response to dietary cholesterol, using the rat and hamster as animal models that span the range of responses seen in humans. Potential mechanisms by which the liver may compensate for changes in net sterol input include induction of bile acid synthesis, suppression of de novo sterol synthesis and suppression of receptor- dependent LDL uptake. The first major group of studies will determine the mechanisms whereby dietary lipids regulate these three pathways in the hamster in vivo. Specifically, the transcriptional and/or post- transcriptional events involved in the regulation of these pathways by cholesterol, bile acids and fatty acids will be examined. In particular, mRNA and protein levels of 7alpha-hydroxylase, LDL receptor and 3-hydroxy- 3-methylglutaryl coenzyme A (HMG-CoA) reductase will be measured and correlated with assays of bile acid output, receptor-dependent LDL uptake, HMG-CoA reductase activity and absolute rates of sterol synthesis. Preliminary studies indicate that transcriptional regulation of 7alpha- hydroxylase by cholesterol differs in the rat and hamster. The possibility that other differences in the regulation of hepatic sterol metabolism also contribute to the overall response to dietary lipids will thus be addressed in the first group of studies. The second group of studies will be undertaken to determine the molecular mechanisms that control 7alpha- hydroxylase gene expression in the rat and hamster. The 5 '-flanking regions of the rat and hamster genes have been isolated and will be evaluated using a combination of transfection analysis, in vitro transcriptional analysis and transgenic approaches to identify the putative regulatory sequences that confer sensitivity to sterols and bile acids and the trans-acting factors that interact with these sequences. In particular, these studies will seek to identify the basis for differences in sensitivity to cholesterol-mediated induction of gene expression in the rat and hamster. Overall, these detailed experiments should provide information on the molecular mechanisms involved in the regulation of the major pathways that determine sterol balance across the liver and plasma LDL concentrations.

膳食胆固醇抑制受体依赖性低密度胆固醇的摄取 肝脏中的脂蛋白（LDL）会升高 LDL 胆固醇水平。然而， 不同人群对特定膳食胆固醇水平的反应差异很大 不同物种之间以及同一物种的不同个体之间。这 总体目标。拟议研究的目的是了解其机制 饮食胆固醇反应显着差异的基础，使用 大鼠和仓鼠作为动物模型，涵盖了所观察到的反应范围 在人类中。肝脏补偿的潜在机制 净甾醇输入的变化包括诱导胆汁酸合成， 抑制甾醇从头合成和抑制受体- 依赖性 LDL 摄取。第一个主要研究组将确定 膳食脂质调节这三种途径的机制 仓鼠体内。具体来说，转录和/或后 转录事件参与这些途径的调节 将检查胆固醇、胆汁酸和脂肪酸。尤其， 7α-羟化酶、LDL 受体和 3-羟基- 的 mRNA 和蛋白质水平 将测量 3-甲基戊二酰辅酶 A (HMG-CoA) 还原酶并 与胆汁酸输出、受体依赖性 LDL 摄取测定相关， HMG-CoA 还原酶活性和甾醇合成的绝对速率。 初步研究表明7α-的转录调控 胆固醇羟化酶在大鼠和仓鼠中是不同的。可能性 肝脏甾醇代谢调节的其他差异也 因此，有助于对膳食脂质的总体反应 在第一组研究中得到解决。第二组研究将 确定控制7α-的分子机制 大鼠和仓鼠中羟化酶基因的表达。 5'-侧翼 大鼠和仓鼠基因的区域已经被分离出来，并将被 使用体外转染分析相结合进行评估 转录分析和转基因方法来鉴定 假定的调节序列赋予对甾醇和胆汁的敏感性 酸和与这些序列相互作用的反式作用因子。在 特别是，这些研究将寻求找出差异的基础 对胆固醇介导的基因表达诱导的敏感性 老鼠和仓鼠。总的来说，这些详细的实验应该提供 有关调节的分子机制的信息 决定肝脏和血浆甾醇平衡的主要途径 低密度脂蛋白浓度。