BILE ACID METABOLISM AND PLASMA CHOLESTEROL REGULATION

膳食胆固醇抑制受体依赖的低密度摄取 低密度脂蛋白（LDL）是由肝脏和提高低密度脂蛋白胆固醇水平。然而，在这方面， 对给定水平的饮食胆固醇的反应在 不同的物种和同一物种的不同个体之间。的 总体目标。研究的目的是了解 饮食胆固醇反应的显著变异性的基础，使用 大鼠和仓鼠作为动物模型， 在人类身上。肝脏可能补偿的潜在机制 净甾醇输入的变化包括胆汁酸合成的诱导， 抑制甾醇从头合成和抑制受体- 依赖LDL摄取。第一组主要研究将确定 膳食脂质调节这三种途径的机制， 仓鼠体内。具体地，转录和/或后表达的蛋白质可以被转录和/或后表达。 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。特别是， 7 α-羟化酶、LDL受体和3-羟基-β-D-半乳糖苷酶的mRNA和蛋白水平 3-将测量甲基戊二酰辅酶A（HMG-CoA）还原酶， 与胆汁酸排出、受体依赖性LDL摄取、 HMG-CoA还原酶活性和甾醇合成的绝对速率。 初步研究表明，转录调控7 α- 胆固醇对羟化酶的影响在大鼠和仓鼠中不同。的可能性 肝固醇代谢调节的其他差异也 因此，对膳食脂质的总体反应的贡献 在第一组研究中。第二组研究将 进行，以确定控制7 α- 羟化酶基因在大鼠和仓鼠中的表达。5 '-侧翼 大鼠和仓鼠基因的区域已经被分离出来， 使用体外转染分析的组合进行评价 转录分析和转基因方法，以确定 赋予对固醇和胆汁敏感性的假定调节序列 酸和与这些序列相互作用的反式作用因子。在 特别是，这些研究将寻求确定差异的基础， 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 信息的分子机制参与的调节， 决定肝脏和血浆中固醇平衡的主要途径 LDL浓度。

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.