BILE ACID SIGNALING & HEPATIC CHOLESTEROL METABOLISM

胆汁酸可能通过调节胆汁酸生物合成酶和磷脂转运蛋白基因的表达，帮助协调调节肝细胞的胆固醇和磷脂代谢。胆汁酸如何协调这些基因的表达以维持胆固醇的动态平衡，以及将特定比例的胆固醇：胆汁酸：磷脂分泌到胆汁中的机制尚不清楚，但可能在胆固醇结石形成、高胆固醇血症和胆汁淤积性肝病的发病机制中具有重要意义。本拨款申请的目的是：(1)确定肝细胞内胆汁酸激活的信号级联反应，并确定这种激活是通过蛋白激酶C依赖还是独立途径发生的；(2)确定胆汁酸是否激活原代肝细胞中的受体蛋白酪氨酸激酶(RPTK)以及激活所需的胆汁酸结构；(3)确定胆汁酸激活的下游信号级联反应(S)调节参与维持肝细胞胆固醇和磷脂稳态的基因，包括：细胞色素P7a1、细胞色素P8b1、低密度脂蛋白受体、中性胆固醇酯水解酶和mdr2磷脂转运体；(4)确定在JNK-1和JNK-2基因敲除小鼠中胆汁酸和胆固醇代谢对CYP7a1的调节是否发生改变，以及在胆汁酸喂养的大鼠和慢性胆瘘大鼠模型中，显性阴性的JNK-1或c-jun的过度表达是否改变胆汁酸对CYP7a1的调节。将努力确定胆汁酸是否激活了信号通路与核受体，即也被胆汁酸激活的法尼醇X受体。

Bile acids may help to coordinately regulate cholesterol and phospholipid metabolism in the hepatocyte by modulating the expression of genes encoding bile acid biosynthetic enzymes and phospholipid transport proteins. The mechanisms by which bile acids coordinate the expression of these genes in order to maintain cholesterol homeostasis and the secretion of a specific ratio of cholesterol: bile acids: phospholipids into bile is unclear, but may have important implications in the pathogenesis of cholesterol gallstone formation, hypercholesterolemia, and cholestatic liver diseases. The objectives of the present grant application are: (1) To identify bile acid-activated signaling cascades within the hepatocyte and determine if the activation occurs via a protein kinase C-dependent or independent pathway; (2) To determine if bile acids activate receptor protein tyrosine kinases (RPTK) in primary hepatocytes and the bile acid structural requirements for activation; (3) To determine which bile acid-activated down-stream signaling cascade(s) regulate genes involved in maintaining cholesterol and phospholipid homeostasis in the hepatocyte, including: CYP7a1, CYP8b1, LDL receptor, neutral cholesterol ester hydrolase (CEH) and mdr2 phospholipid transporter; (4) To determine if the regulation of CYP7a1 by bile acids and cholesterol metabolism is altered in JNK-1 and JNK-2 knock-out mice and if over-expression of a dominant negative JNK-1 or c-Jun alters CYP7a1 regulation by bile acids in bile acid fed rats and in a chronic bile fistula rat model. Efforts will be made to determine if bile acids activated signaling pathways "cross-talk" with nuclear receptors i.e. farnesoid X receptor that are also activated by bile acids.