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 大多数生理和实验条件下 HMG-C0A 的活性 还原酶 (HMG-CoA-R) 和胆固醇 7α-羟化酶 (C7αH)， 串联变化。 两种酶均受到最终产品反馈的影响 规定; HMG-CoA-R由胆固醇或氧化产物组成 胆固醇和胆汁盐的 C7alphaH 活性。 近期数据还显示 疏水性胆汁盐下调 HMG-CoA-R 和胆固醇 喂养，上调 C7alphaH 活性。 其分子机制为 其中 HMG-CoA-R 和 C7alphaH 受胆汁盐调节尚未被证实 已完全阐明，也不知道微粒体的水平如何 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 同时调节两种酶。 本拨款提案要解决的具体问题是： 1) 什么是 胆汁盐和胆固醇调节 C7alphaH 的机制是什么？ 2） 抑制的时间进程和浓度依赖性是多少？ C7alphaH 和 HMG-CoA-R 是天然存在的胆汁盐吗？ 3）下降了 胆酸对 C7αH 的调节继发于肠道 生物转化为脱氧胆酸？ 4）其机制是 胆汁盐对 HMG-CoA-R 的调节由于直接（后 胆汁盐的转录）或间接影响，即通过促进 影响小肠胆固醇的吸收？ 5）类固醇的作用是什么 激素（雌激素、地塞米松）对 C7αH 的调节？ 6) 可以 通过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 的调节？ 此外，在 与博士的合作。蒋和海勒蒙，我们将研究规定 3β-羟基-δ5-C27-类固醇脱氢酶/异构酶(3β-HSD)， 和 12α-羟化酶 (12αH)，胆汁酸中的两种关键酶 生物合成途径。 从这些研究中获得的信息将 与我们对影响因素的理解相关 胆固醇降解途径关键酶 C7alphaH 的调节 以及维持胆固醇稳态的机制 肝。