Toxic lipid intermediate accumulation and cobalamin depletion promote AHR-mediated hepatotoxicity and the progression of non-alcoholic fatty liver disease (NAFLD)-like pathologies

摘要： 非酒精性脂肪性肝病(NAFLD)描述了一系列的病理，通常涉及简单的， 可逆性肝脂肪堆积(脂肪变性)进展为脂肪性肝炎伴纤维化，增加 更复杂的代谢性疾病的风险。非酒精性脂肪肝的患病率预计将从2015年的约8300万上升 到2030年，仅在美国就达到1.01亿人。越来越多的证据表明，环境污染物对 在非酒精性脂肪肝的发展和进展中的作用被低估。许多化学物质会导致脂肪肝，但 环境污染物2，3，7，8-四氯二苯并对二恶英(TCDD)和相关化合物 最强大的力量。TCDD引起的大部分效应(如果不是全部的话)是由芳烃介导的。 受体(AHR)。我们已经证明TCDD诱导脂肪变性进展为脂肪性肝炎(非脂肪性肝炎)。 酒精性脂肪性肝炎(NASH)合并纤维化，但其潜在机制尚不清楚 超越AHR的激活和随后基因表达的变化。我们对初步RNAseq的整合 代谢组学数据表明，多种AHR介导的效应汇聚在一起，导致肝脏毒性 以及NAFLD样病理的进展，包括抑制肝脏脂肪酸氧化， 胆汁酸水平升高，免疫细胞浸润，血清钴胺(Cbl，又名维生素B12)降低 级别。这项提议将检验AHR激活重新编程脂肪酸代谢导致 导致肝脏毒性和脂肪变性进展的有毒中间体积聚 脂肪性肝炎伴纤维化。体内和体外遗传和药理学方法将进一步 研究辛烯基辅酶A、丙烯酰辅酶A和二元酸(DCA)的作用。《特定目标1》将使用小说 肝细胞特异性AHR缺失小鼠表明肝脏辛烯酰辅酶A、丙烯酰辅酶A和DCAs有助于 肝毒性和非酒精性脂肪肝病理严重程度。特殊目标2将使用(I)Cbl补充剂来预防 肝毒性与NAFLF进展及(Ii)Acod1基因缺失小鼠研究衣康酸(Ita)在肝损伤中的作用 降低Cbl水平。特定目标3将使用人HepaRG细胞来确定AHR介导的相关性 代谢重新编程和有毒中间代谢物的积累。这些结果将建立一个 涉及AHR介导的差异基因表达、代谢重编程和 导致肝脏毒性和NAFLD进展的有毒代谢物的生物合成。我们会展示的 补充Cbl对AHR介导的肝毒性有保护作用。CBL补充也将 事实证明，这是保护易受AHR介导的暴露人群的有效对策 肝毒性，在治疗和管理非酒精性脂肪肝方面也可能是有益的。

Abstract: Non-alcoholic fatty liver disease (NAFLD) describes a spectrum of pathologies which typically involves simple, reversible hepatic fat accumulation (steatosis) progressing into steatohepatitis with fibrosis that increases the risk for more complex metabolic diseases. NAFLD prevalence is projected to increase from ~83 million in 2015 to ~101 million by 2030 in the US alone. Accumulating evidence suggests environmental contaminants play an underappreciated role in NAFLD development and progression. Many chemicals induce fatty liver, but the environmental contaminant, 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD), and related compounds, exhibit the greatest potency. Most, if not all, of the effects induced by TCDD are mediated by the aryl hydrocarbon receptor (AHR). We have shown that TCDD induces the progression of steatosis to steatohepatitis (non- alcoholic steatohepatitis (NASH)) with fibrosis, however the underlying mechanisms are poorly understood beyond AHR activation and subsequent changes in gene expression. Our integration of preliminary RNAseq and metabolomics data suggests multiple AHR-mediated effects converge to cause to cause hepatotoxicity and the progression of NAFLD-like pathologies including the repression of hepatic fatty acid oxidation, increased bile acid levels, immune cell infiltration and decreased serum cobalamin (Cbl, aka Vitamin B12) levels. This proposal will test the hypothesis that AHR activation reprograms fatty acid metabolism causing the accumulation of toxic intermediates that contribute to hepatotoxicity and the progression of steatosis to steatohepatitis with fibrosis. In vivo and in vitro genetic and pharmacological approaches will be to further investigate the role of octenoyl-CoA, acrylyl-CoA and dicarboxylic acids (DCAs). Specific Aim 1 will use novel hepatocyte-specific AHR null mice to show that hepatic octenoyl-CoA, acrylyl-CoA and DCAs contribute to hepatotoxicity and NAFLD pathology severity. Specific Aim 2 will use (i) Cbl supplementation to protect against hepatotoxicity and NAFLF progression and (ii) Acod1 null mice to investigate the role of itaconate (Ita) in reducing Cbl levels. Specific Aim 3 will use human HepaRG cells to determine the relevance of AHR-mediated metabolic reprogramming and the accumulation of toxic intermediate metabolites. These results will establish a mechanism that involves AHR-mediated differential gene expression, metabolic reprograming and the biosynthesis of toxic metabolites that contribute to the hepatotoxicity and NAFLD progression. We will show that Cbl supplementation can protect against AHR-mediated hepatotoxicity. Cbl supplementation will also prove to be an effective countermeasure to protect exposed populations susceptible to AHR-mediated hepatotoxicity that may also be beneficial in the treatment and management of NAFLD.