Molecular Biology of Bile Acid Synthesis

项目摘要 胆汁酸信号通过FXR和TGR5在控制代谢和炎症中发挥关键作用 肝脏。大量有毒胆汁酸的积累会导致肝脏炎症和损伤，从而导致 慢性非酒精性脂肪性肝病(NAFLD)、糖尿病和肥胖的发病机制。这些炎症性疾病 肝脏代谢性疾病在美国人群中已达到流行状态，NAFLD的发病率较高 男性患病率高于女性。在过去的二十年里，过多的胆汁酸研究揭示了一种 整合胆汁酸激活的法尼醇X受体(FXR)和胆汁酸的复杂通路网络-- 激活的G蛋白偶联受体TGR5信号调节脂、糖和能量代谢 动态平衡。胆汁酸的合成受到抑制转录的负反馈机制的严格调控 编码胆固醇7α羟基酶(CYP7A1)的基因，它是限速合成酶和甾醇 在经典的胆汁酸合成途径中，胆酸合成所需的12α-羟基酶(CYP8B1)是胆酸合成所必需的。这个 另一条途径是由氧固醇7羟基酶(α7B1)调节的。肠道微生物区系调节胆汁酸 胆汁池大小、胆汁酸组成和胆汁酸的肝-肠循环。胆汁的抗炎作用 近年来，酸激活受体已被认识到。然而，胆汁的潜在分子机制 酸性信号在肝脏代谢动态平衡和炎症调节中的作用尚不完全清楚。 在本资助期间，我们使用Cyp7a1-/-、FXR-/-和TGR5-/-小鼠来研究胆汁酸的作用 代谢调节中的信号传递。肠道FXR的激活重塑了肠道微生物区系，激活了TGR5， 刺激胰升糖素样肽1(GLP-1)分泌，促进白色脂肪组织褐变，改善 肥胖和糖尿病小鼠的胰岛素敏感性和糖耐量。我们已经成功地培育出FXR和TGR5 双基因敲除(DKO)小鼠。DKO小鼠胆汁酸合成和池大小增加，并诱导 牛磺胆酸激活的鞘氨醇-1-磷酸受体2(S1PR2)在肝脏中的作用 新陈代谢还不是很清楚。我们设计了两个特定的目标来1)研究胆汁酸的作用机制 信号在调节肝脏胆汁酸合成和代谢动态平衡中的作用 胆汁酸信号转导在NAFLD发病机制中的作用。代谢组学，16S RNA-测序 肠道微生物组和转录组的RNA测序将用于研究胆汁酸的合成和 雄性和雌性FXR-/-、TGR5-/-和DKO小鼠的肝脏代谢。这项研究具有非常重要的意义 阐明胆汁酸合成和脂类动态平衡调节的分子机制 影响美国大量人群的肝脏相关代谢性疾病的机制发病机制 以及世界范围内。

Project Summary Bile acid signaling through FXR and TGR5 plays a critical role in the control of metabolism and inflammation in the liver. Accumulation of high levels of toxic bile acids causes liver inflammation and injury, contributing to the pathogenesis of chronic non-alcoholic fatty liver disease (NAFLD), diabetes and obesity. These inflammatory liver metabolic diseases have reached epidemic status in the U.S. population, and NAFLD occurs with a higher prevalence in males than females. A plethora of bile acid research in the last two decades has unveiled a complex network of pathways that integrate bile acid-activated farnesoid X receptor (FXR) and the bile acid- activated G protein-coupled receptor TGR5 signaling to regulate lipid, glucose, and energy metabolism and homeostasis. Bile acid synthesis is tightly regulated by a negative feedback mechanism to inhibit transcription of the gene encoding cholesterol 7α-hydroxylase (CYP7A1), the rate-limiting synthesis enzyme, and sterol 12α-hydroxylase (CYP8B1), required for cholic acid synthesis, in the classic bile acid synthesis pathway. The alternative pathway is regulated by oxysterol 7α-hydroxylase (CYP7B1). The gut microbiota regulates bile acid pool size, bile acid composition and enterohepatic circulation of bile acids. The anti-inflammatory action of bile acid-activated receptors has been recognized recently. However, the underlying molecular mechanisms of bile acid signaling in the regulation of hepatic metabolic homeostasis and inflammation are not fully understood. During the current funding period, we have used Cyp7a1-/-, Fxr-/- and Tgr5-/- mice to study the role of bile acid signaling in metabolic regulation. Activation of intestinal FXR reshaped the gut microbiota to activate TGR5, stimulating glucagon-like-peptide 1 (GLP-1) secretion, promoting white adipose tissue browning, and improving insulin sensitivity and glucose tolerance in obese and diabetic mice. We have successfully bred Fxr and Tgr5 double knockout (DKO) mice. DKO mice have increased bile acid synthesis and pool size and induction of the taurocholic acid-activated sphingosine-1-phosphate receptor 2 (S1PR2), the role of which in hepatic metabolism is not understood. Two specific aims are designed to 1) study the mechanisms of bile acid signaling in the regulation of hepatic bile acid synthesis and metabolic homeostasis, and 2) to study the role and mechanism of bile acid signaling in the pathogenesis of NAFLD. Metabolomics, 16S RNA-sequencing of the gut microbiome, and RNA-sequencing of the transcriptome will be used to study bile acid synthesis and hepatic metabolism in both male and female Fxr-/-, Tgr5-/- and DKO mice. This study is highly significant in elucidating the molecular mechanism of the regulation of bile acid synthesis and lipid homeostasis, and the mechanistic pathogenesis of liver-related metabolic diseases affecting a large population in the United States and worldwide.