A Novel Role of the Aryl Hydrocarbon Receptor in Hepatic Steatosis

芳基烃受体在肝脂肪变性中的新作用

• 批准号: 8248808
• 负责人: Wen Xie
• 金额: $ 31.12万
• 依托单位: UNIVERSITY OF PITTSBURGH AT PITTSBURGH
• 依托单位国家: 美国
• 财政年份: 2010
• 资助国家: 美国
• 起止时间: 2010-05-01 至 2015-03-31
• 项目状态: 已结题
• 来源: https://reporter.nih.gov/project-details/8248808
• 关键词: ARNT protein; Affect; Agonist; Aryl Hydrocarbon Receptor; Autopsy; Backcrossings; Binding; Biological Assay; CD36 Antigens; CD36 gene; Chemistry; DNA Binding; Data; Development; Diet; Dioxins; Enzymatic Biochemistry; Enzymes; Esterification; Exhibits; Fatty Acids; Fatty Liver; Fatty acid glycerol esters; Fibrosis; Gene Expression; Gene Expression Regulation; Gene Targeting; Generations; Genes; Genetic; Goals; Hepatic; Hepatocyte; Histology; Human; Individual; Inflammation; Knock-out; Link; Liver; Liver diseases; Medical; Metabolic; Metabolic syndrome; Modeling; Molecular; Mus; Nonesterified Fatty Acids; Patients; Phenotype; Physiology; Population; Regulation; Reporter Genes; Response Elements; Rodent; Role; Serum; Testing; Tetrachlorodibenzodioxin; Tetracyclines; Tissues; Transgenes; Transgenic Mice; Transgenic Organisms; Triglycerides; Very low density lipoprotein; Wild Type Mouse; Xenobiotics; aryl hydrocarbon receptor ligand; base; chromatin immunoprecipitation; fatty acid oxidation; feeding; gain of function; glucose tolerance; hepatoma cell; human ARNT protein; insulin sensitivity; loss of function; mouse Ahr protein; new therapeutic target; non-alcoholic fatty liver; novel; oxidation; prevent; promoter; public health relevance; receptor; toxicant; translocase; uptake; very low density lipoprotein triglyceride

DESCRIPTION (provided by applicant): Hepatic steatosis, or fatty liver, is strongly associated with metabolic syndrome. Understanding the mechanism of hepatic steatosis will help to prevent and treat this common medical problem. The aryl hydrocarbon receptor (AhR), highly expressed in the liver, is a transcriptional factor originally cloned as a "xenobiotic receptor." AhR regulates the expression of xenobiotic enzymes by binding to the dioxin response elements (DREs) present in target gene promoters. Subsequent studies suggest that AhR may also have endobiotic functions by affecting physiology, but the molecular mechanism for the endobiotic function of AhR remains largely unknown. Our preliminary results showed that: (1) Transgenic mice expressing the constitutively activated AhR (CA-AhR) exhibited hepatic steatosis when maintained in chow diet, a phenotype that has been recapitulated in wild type mice treated with the AhR agonist; (2) Activation of AhR in transgenic mice induced the expression of CD36/FAT, a fatty acid transporter important for hepatic fatty acid uptake and steatosis; (3) Activation of CD36 gene expression was also seen in wild type mice treated with the AhR agonist and this activation was abolished in AhR-/- mice; (4) Treatment of human hepatoma cells with AhR agonist induced the expression of CD36 and increased the uptake of free fatty acids; (5) The mouse and human CD36 gene promoters were activated by AhR; (6) Activation of AhR inhibited very-low density lipoprotein (VLDL)-triglyceride secretion; (7) Activation of AhR suppressed peroxisomal fatty acid 2-oxidation; and 8) CA-AhR transgenic mice in third generation of backcross to C57BL/6J showed spontaneous steatosis and signs of compromised glucose tolerance. Based on our preliminary data, we hypothesize that activation of AhR promotes hepatic steatosis through multiple mechanisms, including the activation of fatty acid transporter CD36, suppression of fatty acid oxidation, and inhibition of export of triglycerides. By using the "gain-of-function" CA-AhR transgenic, "loss-of-function" AhR-/- and CD36-/-, and AhR ligand-treated wild type mice, we propose four specific aims: (1) To determine whether activation of AhR is sufficient and necessary to induce hepatic steatosis; (2) To characterize AhR-induced hepatic steatosis; (3) To determine whether the fatty acid transporter CD36 is necessary for the steatotic effect of AhR; and (4) To determine the molecular mechanism by which AhR regulates the expression of CD36. To our knowledge, the current study represents the first attempt to determine the pathophysiological role of AhR in hepatic steatosis and associated metabolic abnormalities. The tetracycline inducible AhR transgenic mice, exhibiting fatty liver even when maintained in chow diet, represent a novel, convenient and reversible model of nonalcoholic fatty liver disease (NAFLD). It is hoped that results from this study may help to establish AhR and its target fatty acid transporter as novel therapeutic targets for fatty liver in human patients. PUBLIC HEALTH RELEVANCE: The aryl hydrocarbon receptor (AhR) is a transcriptional factor originally cloned as a "xenobiotic receptor" to sense xenobiotic toxicants. The goal of this study is to determine whether AhR has an endobiotic role in promoting hepatic steatosis. Hepatic steatosis, or fatty liver, is a common medical problem strongly associated with metabolic syndrome. It is hoped that results from this study may help to establish AhR as a novel therapeutic target for fatty liver in human patients.

描述（由申请人提供）：肝脂肪变性或脂肪肝与代谢综合征密切相关。了解肝脂肪变性的机制将有助于预防和治疗这一常见的医学问题。芳基碳氢化合物受体（AhR）在肝脏中高度表达，是一种转录因子，最初被克隆为“异生素受体”。 AhR 通过与靶基因启动子中存在的二恶英反应元件 (DRE) 结合来调节外源酶的表达。后续研究表明AhR也可能通过影响生理学而具有内生功能，但AhR内生功能的分子机制仍然很大程度上未知。我们的初步结果表明：（1）表达组成型激活的AhR（CA-AhR）的转基因小鼠在维持饲料饮食时表现出肝脂肪变性，这种表型已在用AhR激动剂治疗的野生型小鼠中重现； (2) 转基因小鼠中AhR的激活诱导了CD36/FAT的表达，CD36/FAT是一种对肝脏脂肪酸摄取和脂肪变性很重要的脂肪酸转运蛋白； (3)在用AhR激动剂处理的野生型小鼠中也观察到CD36基因表达的激活，并且这种激活在AhR-/-小鼠中被消除； (4)AhR激动剂处理人肝癌细胞诱导CD36表达并增加游离脂肪酸的摄取； (5) AhR激活小鼠和人CD36基因启动子； (6)AhR的激活抑制极低密度脂蛋白(VLDL)-甘油三酯的分泌； (7) AhR的激活抑制过氧化物酶体脂肪酸2-氧化； 8)与C57BL/6J回交的第三代CA-AhR转基因小鼠表现出自发性脂肪变性和葡萄糖耐量受损的迹象。根据我们的初步数据，我们假设 AhR 的激活通过多种机制促进肝脂肪变性，包括激活脂肪酸转运蛋白 CD36、抑制脂肪酸氧化和抑制甘油三酯的输出。通过使用“功能获得”CA-AhR 转基因小鼠、“功能丧失”AhR-/- 和 CD36-/- 以及 AhR 配体处理的野生型小鼠，我们提出了四个具体目标：(1)确定AhR的激活对于诱导肝脂肪变性是否是充分和必要的； (2) 表征AhR诱导的肝脂肪变性； (3) 确定脂肪酸转运蛋白CD36对于AhR的脂肪变性作用是否是必需的； (4)探讨AhR调节CD36表达的分子机制。据我们所知，目前的研究首次尝试确定 AhR 在肝脂肪变性和相关代谢异常中的病理生理学作用。四环素诱导的 AhR 转基因小鼠即使维持正常饮食也表现出脂肪肝，代表了一种新颖、方便且可逆的非酒精性脂肪肝疾病 (NAFLD) 模型。希望这项研究的结果有助于将 AhR 及其靶脂肪酸转运蛋白确立为人类脂肪肝的新治疗靶点。 公共健康相关性：芳基碳氢化合物受体 (AhR) 是一种转录因子，最初被克隆为“异生物质受体”，用于感知异生物质毒物。本研究的目的是确定 AhR 是否具有促进肝脂肪变性的内生作用。肝脂肪变性或脂肪肝是与代谢综合征密切相关的常见医学问题。希望这项研究的结果有助于将 AhR 确立为人类脂肪肝的新治疗靶点。