Regulation of BileAcid Synthesis by a alpha1-AT Peptide

说明(申请人提供)：胆汁酸合成在维持胆固醇动态平衡方面起着至关重要的作用，因为它负责体内排泄的超过50%的胆固醇的分解代谢。高胆固醇往往导致动脉粥样硬化，这是慢性炎症的一种形式。作为对炎症的反应，α1-抗胰蛋白酶(α1-AT)的合成速率增加。α1-抗胰蛋白酶是一种血清蛋白水解酶抑制物，在肝脏中合成，其合成速度因炎症而增加。这种α1-AT合成的增加会导致多肽的增加，比如它的羧基末端C-36肽，这是由于蛋白酶对α1-AT的切割造成的。由于血浆胆固醇水平、炎症和α-AT合成率之间的这种相关性，我们研究了C-36丝氨酸肽对肝脏胆汁酸生物合成的影响，结果表明，C-36通过抑制胆固醇7α-羟基酶/细胞色素P7A1(7α-羟基酶)和固醇12α-羟基酶/细胞色素P8B1(12α-羟基酶)启动子，是胆汁酸合成的强大和特异的转录下调因子。这种抑制似乎是通过与甲胎蛋白转录因子(FTF)特异性地相互作用而实现的，FTF是胆汁酸生物合成中的一个关键的正转录因子。我们假设C-36肽与FTF特异地相互作用，这种相互作用抑制了7α和12α-羟基酶的启动子活性。实验被用来验证这一假说，并研究这两个分子--FTF蛋白和α1-AT衍生的C-36肽之间相互作用的分子机制。本建议的具体目的是：1.确定A1-AT衍生C-36肽对动物胆汁酸生物合成的影响。2.测定α1-AT衍生C-36肽在培养细胞和动物体内的亚细胞靶向性。3.α1-AT衍生C-36肽对7α和12α-羟基酶基因转录调控作用机制的研究4.α1-AT启动子的特性及其受C-36肽的自我调节这个项目的成功完成可能会在胆固醇稳态和炎症之间提供一个重要的联系。

DESCRIPTION (provided by applicant): Bile acid synthesis plays a crucial role in maintaining cholesterol homeostasis since it is responsible for the catabolism of more than 50% of the cholesterol excreted from the body. High plasma cholesterol often results in atherosclerosis, which is a form of chronic inflammation. In response to inflammation, the rate of synthesis of alpha1-antitrypsin (alpha1 -AT) increases. Alpha1-antitrypsin is a serum protease inhibitor that is synthesized in the liver and its rate of synthesis increases in response to inflammation. This increase in alpha1-AT synthesis gives rise to an increase in peptides, like its carboxy-terminal C-36 peptide, resulting from alpha1-AT cleavage by proteases. Because of this correlation between plasma cholesterol levels, inflammation and alpha1-AT rate of synthesis, we investigated the effect of the C-36 serpin peptide on hepatic bile acid biosynthesis and showed that C-36 is a powerful and specific transcriptional down-regulator of bile acid synthesis through inhibition of the cholesterol 7alpha-hydroxylase/CYP7A1 (7alpha-hydroxylase) and sterol12alpha-hydroxylase/CYP8B1 (12alpha-hydroxylase) promoters. This inhibition appears to be mediated by specifically interacting with alpha1-fetoprotein transcriptional factor (FTF), a positive transcriptional factor key in bile acid biosynthesis. We hypothesize that the C-36 peptide specifically interacts with FTF, and this interaction suppresses 7alpha- and 12alpha-hydroxylase promoter activities. Experiments are proposed to validate this hypothesis and to study the molecular mechanisms involved in the interaction between these two molecules, the FTF protein and the alpha1-AT-derived C-36 peptide. The specific aims of this proposal are: 1. Determine the effect of the a1-AT derived C-36 peptide on bile acid biosynthesis in animals. 2. Determine the subcellular targeting of the alpha1-AT derived C-36 peptide in both culture cells and animals. 3. Characterization of the mechanism of action involved in the regulation of 7alpha- and 12alpha-hydroxylase gene transcription by the alpha1-AT derived C-36 peptide. 4. Characterization of the alpha1-AT promoter and its self-regulation by the C-36 peptide. The successful completion of this project may provide an important link between cholesterol homeostasis and inflammation.