Regulation of Cholesterol Catabolism by Bile Acids

摘要 肥胖已经成为一种全球流行病，并极大地增加了患糖尿病、心血管疾病、 和非酒精性脂肪性肝病(NAFLD)。近80%的肥胖者会患上NAFLD， 进展为脂肪性肝炎(NASH)，并进一步发展为终末期肝病，如纤维化、肝硬变和 肝癌，但治疗非酒精性脂肪肝的好的治疗方案尚不存在。NAFLD的标志是 由于脂肪代谢失调，甘油三酯(TG)在肝脏中异常堆积。胆汁酸 (Bas)是最近认识到的信号分子，它深刻地影响新陈代谢并中和 肥胖。BA诱导的肠道激素，FGF15/19(mFGF15。HFGF19)，受到了极大的关注 因为它的降脂和胰岛素增敏作用，因此，它的治疗潜力 肥胖和糖尿病。然而，关于FGF15/19是如何控制脂代谢的，人们知之甚少。整体而言 本申请的目的是确定孤儿核受体小杂二聚体伙伴(SHP， NR0B2)通过对肝脏脂肪代谢的表观遗传调节来调节FGF15/19的餐后作用。 我们有初步数据显示，FGF19处理诱导了DNA甲基转移酶-3a的重新启动 (DNMT3A)以SHP依赖的方式与关键的致脂基因结合，以及SHP或SHP的肝脏特异性下调 DNMT3A导致这些基因5-甲基胞嘧啶(5mC)DNA水平降低，肝脏甘油三酯(TG)升高 提示SHP和DNMT3a在肝脏脂肪生成中具有新的功能。基于这些令人兴奋的 初步数据，我们假设SHP生理上介导了肝脏的表观遗传抑制。 在美联储后期，通过招募DNMT3a来响应FGF15信号的脂肪生成，但这个FGF15- SHP-DNMT3a调节轴在肥胖中被扰乱。为了检验这一假设，我们将1)确定 以及FGF15-SHP-DNMT3a调节轴如何调节表观遗传学的潜在机制 抑制肝脏生脂基因，然后，2)研究肝脏SHP的体内功能和 DNMT3A在调节肝脏脂代谢中的作用，重点是新生脂肪生成及其失调 通过分析NAFLD的肝脏样本确定小鼠肥胖的调节轴及其与人类的相关性 病人。为了实现这些目标，多方面的方法，包括分子/生化、代谢、 表观遗传学研究和全球基因组分析将用于SHP-LKO和FGF15-KO小鼠，以及 病毒介导的蛋白质表达和下调所产生的小鼠模型。 影响：我们在核转录和表观遗传控制肝脏脂肪代谢方面的专业知识 受体使我们有资格执行这一项目。该提案将测试SHP和DNMT3a 介导FGF15/19在肝脂代谢中的作用，并可能揭示开发的有效途径 NAFLD的新治疗靶点和监测其进展的诊断生物标记物。

Summary Obesity has become a global epidemic and greatly increases the risk for diabetes, cardiovascular disease, and non-alcoholic fatty liver disease (NAFLD). Nearly 80% of obese people develop NAFLD, which progresses to steatohepatitis (NASH) and further to end-stage liver diseases, such as fibrosis, cirrhosis, and liver cancer, but good therapeutic options to treat NAFLD are not available. The hallmark of NAFLD is abnormal accumulation of triglyceride (TG) in the liver due to dysregulated lipid metabolism. Bile acids (BAs) are recently recognized signaling molecules that profoundly impact metabolism and counteract obesity. The BA-induced intestinal hormone, FGF15/19 (mFGF15. hFGF19), has received great attention because its lipid-lowering and insulin-sensitizing effects and, thus, its therapeutic potential in treating obesity and diabetes. However, little is known about how FGF15/19 controls lipid metabolism. The overall goal of this application is to determine how an orphan nuclear receptor Small Heterodimer Partner (SHP, NR0B2) mediates postprandial actions of FGF15/19 by epigenetic regulation of hepatic lipid metabolism. We have preliminary data showing that FGF19 treatment induced recruitment of DNA methyltransferase-3a (DNMT3a) to key lipogenic genes in a SHP-dependent manner, and liver-specific downregulation of SHP or DNMT3a led to decreased 5-methyl cytosine (5mC) DNA levels at these genes and increased liver TG levels, suggesting a novel function of SHP and DNMT3a in hepatic lipogenesis. Based these exciting preliminary data, we hypothesize that SHP physiologically mediates epigenetic repression of hepatic lipogenesis by recruiting DNMT3a, in response to FGF15 signaling in the late fed-state, but this FGF15- SHP-DNMT3a regulatory axis is disrupted in obesity. To test this hypothesis, we will 1) determine the role and the underlying mechanisms of how the FGF15-SHP-DNMT3a regulatory axis mediates epigenetic repression of hepatic lipogenic genes, and then, 2) investigate the in vivo function of hepatic SHP and DNMT3a in regulation of liver lipid metabolism, focusing on de novo lipogenesis, and dysregulation of this regulatory axis in obesity in mice and determine human relevance by analysis of liver samples from NAFLD patients. To achieve these goals, multifaceted approaches, including molecular/biochemical, metabolic, and epigenetic studies and global genomic analyses, will be utilized in SHP-LKO and FGF15-KO mice, and mouse models generated by viral-mediated expression and downregulation of proteins. Impact: Our expertise on transcriptional and epigenetic control of liver lipid metabolism by nuclear receptors uniquely qualifies us to carry out this project. This proposal will test whether SHP and DNMT3a mediate FGF15/19 actions in hepatic lipid metabolism, and may reveal effective approaches for developing new therapeutic targets for NAFLD and diagnostic biomarkers to monitor its progression.