Regulation of cholesterol catabolism by bile acids

描述（由申请人提供）：本项目的总体目标是了解胆汁酸作为最近公认的控制综合代谢和能量平衡的关键信号分子的作用，以及该调节途径在肥胖和相关疾病中的功能障碍。肥胖是一种全球性的流行病。脂肪肝（脂肪变性）在肥胖人群中发展会增加糖尿病，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信号如何整合以控制肝脏代谢知之甚少。小异源二聚体伴侣（SHP）已被认为是BA信号通路中的关键参与者。响应胆汁酸信号，SHP介导的表观遗传阻遏Cyp7a1，限速胆汁酸生物合成基因，协调招募组蛋白修饰蛋白（组蛋白甲基化酶和脱乙酰酶）的启动子。此外，SHP本身的翻译后修饰（PTM）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解决 SHP的PTM和表观遗传组蛋白修饰如何响应于BA信号传导而调节以及这种调节如何在病理学中改变的关键问题，例如脂肪肝疾病。解决这些问题是本提案的具体目标。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活性以响应胆汁酸信号传导，这对于SHP抑制活性是关键的，并且是控制其稳定性和活性的SHP的其它已知PTM上游的关键事件。尤其是PKC？是肥胖诱导的炎症和肝脂肪变性的负调节剂，因此，PKC磷酸化SHP？可能与胆汁酸调节的肝脏代谢密切相关。基于这些研究，我们假设SHP在胆汁酸调节的肝代谢中起关键的表观遗传协调者的作用，胆汁酸信号传导诱导的SHP的PTM，特别是PKC？磷酸化，对肝脏功能至关重要，但在肥胖症中，SHP的PTM和SHP介导的表观遗传调节失调，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）确定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？2)确定SHP是否作为胆汁酸响应性肝脏基因的关键表观遗传协调者发挥作用，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）研究脂肪肝中SHP的PTM、全局SHP结合位点和SHP介导的表观遗传事件是否改变，从而导致肥胖症的代谢异常。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.