REGULATION OF BILE ACID SYNTHESIS

胆汁酸合成的调节

• 批准号: 5210584
• 负责人: Z. R VLAHCEVIC
• 金额: --
• 依托单位国家: 美国
• 资助国家: 美国
• 起止时间: 至
• 项目状态: 未结题
• 来源: https://reporter.nih.gov/project-details/5210584
• 关键词: HMG coA reductases; cholanate compound; cholesterol; dexamethasone; enzyme activity; estrogens; hydroxysteroid dehydrogenases; laboratory rat; liver cells; liver metabolism; microsomes; nucleic acid hybridization; oxygenases; steroid biosynthesis; tissue /cell culture

Hepatic cholesterol and bile acid synthesis are coordinated, since under most physiologic and experimental conditions the activities of HMG-C0A reductase (HMG-CoA-R) and cholesterol 7alpha-hydroxylase (C7alphaH), change in tandem. Both enzymes are subject to end product feedback regulation; HMG -CoA-R by cholesterol or oxidation products of cholesterol, and C7alphaH activity by bile salts. Recent data also show that hydrophobic bile salts down-regulate HMG-CoA-R, and cholesterol feeding, up-regulates C7alphaH activities. The molecular mechanism by which HMG-CoA-R and C7alphaH are regulated by bile salts have not been fully elucidated, nor is it known how the levels of microsomal cholesterol regulate C7alphaH. Recently, we obtained specific antibodies and cDNA probes for HMG-CoA-R and C7alphaH which will enable us to study the regulation of both enzymes simultaneously. Specific questions to be addressed in this grant proposal are: 1) What is the mechanism by which bile salts and cholesterol regulate C7alphaH? 2) What is the time course and concentration dependency of repression of C7alphaH and HMG-CoA-R by naturally occurring bile salts? 3) Is down regulation of C7alphaH by cholic acid secondary to its intestinal biotransformation to deoxycholic acid? 4) Is the mechanism of regulation of HMG-CoA-R by bile salts due to direct (post- transcriptional) or indirect effects of bile salts i.e. by facilitation of intestinal cholesterol absorption? 5) What is the role of steroid hormones (estrogen, dexamethasone) in the regulation of C7alphaH? 6) Can cultured hepatocytes, prepared by new and modified methods, be used to study regulation of C7alphaH and HMG-CoA-R? In addition, in collaboration with Drs. Chiang and Hylemon, we will study the regulation of 3beta-hydroxy-delta5-C27-steroid dehydrogenase/isomerase (3beta-HSD), and 12alpha-hydroxylase (12alphaH), two key enzymes in the bile acid biosynthetic pathway. The information obtained from these studies will be relevant to our understanding of factors responsible for the regulation of C7alphaH, the key enzyme in cholesterol degradation pathway and the mechanism by which cholesterol homeostasis is maintained in the liver.

肝脏胆固醇和胆汁酸的合成是协调的，因为在 HMG-C0A活性的大多数生理和实验条件 还原酶(HMG-CoA-R)和胆固醇7α-羟基酶(C7αH)， 一步步改变。这两种酶都受到最终产物反馈的影响。 胆固醇或氧化产物对HMG-CoA-R的调节 胆固醇和胆盐对C7AlphaH活性的影响。最近的数据还显示 疏水性胆盐下调HMG-CoA-R和胆固醇 摄食，上调C7alphaH的活性。分子机制是通过 胆盐对哪些HMG-CoA-R和C7alphaH的调节作用尚未得到证实 完全阐明，也不知道微粒体的水平是如何 胆固醇调节C7alphaH。最近，我们获得了特异性抗体。 以及HMG-CoA-R和C7alphaH的cDNA探针，这将使我们能够研究 同时对两种酶的调节。 在这项赠款提案中要解决的具体问题是：1)什么是 胆盐和胆固醇调节C7αH？2的机制 压抑的时间进程和浓度依赖是什么 天然胆盐产生的C7AlphaH和HMG-CoA-R？下降了 继发性胆酸对C7AlphaH的调节作用 生物转化为脱氧胆酸？4)是 胆盐对HMG-CoA-R的直接(后)调节作用 转录)或胆盐的间接作用，即通过促进 肠道胆固醇的吸收？5)类固醇的作用是什么 调节C7AlphaH？6的激素(雌激素、地塞米松)可以 用新的和改进的方法制备的培养的肝细胞可用于 研究C7AlphaH和HMG-CoA-R？此外，在 与江博士和希尔蒙博士合作，我们将研究这一规定 3β-羟基-5-C27-类固醇脱氢酶/异构酶(3β-HSD)， 和12Alpha-羟基酶(12AlphaH)，这是胆汁酸的两种关键酶 生物合成途径。从这些研究中获得的信息将 与我们对导致以下问题的因素的理解相关 胆固醇降解途径中的关键酶C7AlphaH的调控 以及维持体内胆固醇动态平衡的机制 肝脏。