Regulation of cholesterol catabolism by bile acids

描述(申请人提供)：本项目的总体目标是了解胆汁酸作为最近发现的控制综合代谢和能量平衡的关键信号分子的作用，以及这一调控途径在肥胖和相关疾病中的功能障碍。肥胖在全球范围内是一种日益流行的疾病。脂肪肝(脂肪变性)在肥胖人群中发展，会增加患糖尿病、心脏病甚至肝癌的风险。胰岛素在代谢调节中的作用已被广泛研究，但对BA信号如何整合来控制肝脏代谢知之甚少。小异二聚体(SHP)被认为是BA信号通路中的关键分子。作为对胆汁酸信号的响应，SHP通过协调募集组蛋白修饰蛋白(组蛋白甲基酶和脱乙酰酶)到启动子来介导胆汁酸生物合成限速基因Cyp7a1的表观遗传抑制。此外，SHP的翻译后修饰(PTM)本身调节其在肝脏中的水平和活性。然而，这些先前的研究并没有涉及 关键问题是如何调节SHP的PTM和表观遗传组蛋白修饰以响应BA信号，以及这种调节在病理上如何改变，如脂肪肝疾病。回答这些问题是当前提案的具体目标。令人惊讶的是，初步研究揭示了蛋白激酶C-Zeta(PKC？)通过磷酸化SHP的Thr-55来调节SHP的活性以响应胆汁酸信号，这是SHP抑制活性的关键，也是SHP的其他已知PTM的上游控制其稳定性和活性的关键事件。值得注意的是，PKC？是肥胖引起的炎症和肝脏脂肪变性的负调节因子，从而使蛋白激酶C磷酸化SHP吗？可能在胆汁酸调节的肝脏代谢中起关键作用。在这些研究的基础上，我们假设SHP在胆汁酸调节的肝脏代谢中起着关键的表观遗传协调器的作用，胆汁酸信号诱导的SHP的PTMS，特别是PKC？的磷酸化对其肝功能是至关重要的，但在肥胖中，SHP的PTMS和SHP介导的表观遗传调节是失调的，导致肝脏代谢异常。为了验证这一假设，我们将利用转基因和肥胖小鼠模型、培养的肝细胞和人类肝细胞或正常或脂肪肝患者的组织进行体外和体内研究。我们的具体目标是：1)明确BA信号(BA或FGF19)诱导的SHP的PTM在正常肝脏代谢中的作用，重点是PKC的磷酸化？？2)确定SHP是否作为胆汁酸反应的肝基因的关键表观遗传协调者，包括分析SHP的全局基因组结合位点和胆汁酸介导的表观遗传基因调控，以及3)研究SHP的PTM、全局SHP结合位点以及SHP介导的表观遗传事件是否在脂肪肝中发生改变，从而导致肥胖的代谢异常。这些研究将阐明SHP如何在表观遗传学上控制BA调节的肝功能，并确定代谢性疾病的新的潜在诊断和/或治疗靶点。

DESCRIPTION (provided by applicant): The overall goal of this project is to understand the role of bile acids as recently recognized key signaling molecules that control integrative metabolism and energy balance and the dysfunction of this regulatory pathway in obesity and related diseases. Obesity is a growing epidemic worldwide. Fatty liver (steatosis) that develops in obese people increases the risk for diabetes, heart disease, and even, liver cancer. The role of insulin in the regulation of metabolism has been extensively studied, but little is known about how BA signaling is integrated to control hepatic metabolism. Small Heterodimer Partner (SHP) has been implicated as a key player in BA signaling pathways. In response to bile acid signaling, SHP mediates the epigenetic repression of Cyp7a1, the rate-limiting bile acid biosynthetic gene, by coordinately recruiting histone-modifying proteins (histone methylases and deacetylases) to the promoter. Further, post-translational modifications (PTMs) of SHP itself regulates its level and activity in the liver. These previous studies, however, did not address the key questions of how the PTM of SHP and the epigenetic histone modifications are regulated in response to BA signaling and how this regulation is altered in pathology, such as fatty liver disease. Answering these questions is the specific goal of the current proposal. Surprisingly, preliminary studies have revealed a role for protein kinase C-zeta (PKC?) in regulating SHP activity in response to bile acid signaling by phosphorylating Thr-55 of SHP which is critical for SHP-repression activity and is a key event upstream of other known PTMs of SHP that control its stability and activity. Notably, PKC? is a negative regulator of obesity-induced inflammation and hepatic steatosis, thus, phosphorylation of SHP by PKC? may be critically involved in bile acid-regulated hepatic metabolism. Based on these studies, we hypothesize that SHP functions as a key epigenetic coordinator in bile acid-regulated hepatic metabolism and that bile acid signaling-induced PTMs of SHP, particularly phosphorylation by PKC?, are critical to its hepatic functions, but, in obesity, PTMs of SHP and SHP-mediated epigenetic regulation are dysregulated, contributing to abnormal hepatic metabolism. To test this hypothesis, we will utilize in vitro and in vivo studies using transgenic and obese mouse models, cultured hepatic cells, and human liver hepatocyes or tissue from normal or fatty liver disease patients. Our specific aims are to: 1) define the role of PTMs of SHP induced by BA signaling (BA or FGF19) in normal hepatic metabolism, focusing on phosphorylation by PKC?? 2) determine whether SHP functions as a key epigenetic coordinator of bile acid responsive hepatic genes, including analyzing global genomic binding sites of SHP and bile acid-mediated epigenetic gene regulation, and 3) investigate whether PTMs of SHP, global SHP binding sites, and SHP-mediated epigenetic events are altered in fatty livers, contributing to metabolic abnormalities in obesity. These studies will elucidate how SHP epigenetically controls BA-regulated hepatic functions, and identify novel potential diagnostic and/or therapeutic targets for metabolic diseases.