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）描述了一系列病理学， 可逆性肝脏脂肪蓄积（脂肪变性）进展为脂肪性肝炎伴纤维化， 更复杂的代谢疾病的风险。NAFLD患病率预计将从2015年的约8300万增加 到2030年仅在美国就将达到1.01亿。越来越多的证据表明，环境污染物 在NAFLD发展和进展中的作用未被充分认识。许多化学物质诱发脂肪肝，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， 最大的潜力。大多数（如果不是全部）TCDD诱导的效应是由芳烃介导的 受体（AHR）。我们已经证明，TCDD诱导脂肪变性发展为脂肪性肝炎（非肝性）。 酒精性脂肪性肝炎（NASH）伴纤维化，但其潜在机制尚不清楚 除了AHR激活和随后的基因表达变化之外。我们整合了初步的RNAseq 代谢组学数据表明，多种AHR介导的效应会导致肝毒性 以及NAFLD样病理学的进展，包括肝脂肪酸氧化的抑制， 胆汁酸水平升高，免疫细胞浸润和血清钴胺素（Cbl，又名维生素B12）降低 程度.该提案将检验AHR激活重新编程脂肪酸代谢导致 导致肝毒性和脂肪变性进展的毒性中间体的积累， 脂肪性肝炎伴纤维化体内和体外遗传学和药理学方法将进一步 研究辛烯酰辅酶A、丙烯酰辅酶A和二羧酸（DCA）的作用。具体目标1将使用小说 肝细胞特异性AHR无效小鼠，以显示肝辛烯酰-CoA、丙烯酰-CoA和DCA有助于 肝毒性和NAFLD病理学严重程度。具体目标2将使用（i）Cbl补充剂来防止 肝毒性和NALF进展和（ii）Acod 1敲除小鼠，以研究衣康酸盐（Ita）在 降低Cbl水平。特异性目标3将使用人HepaRG细胞来确定AHR介导的 代谢重编程和有毒中间代谢物的积累。这些结果将建立一个 机制涉及AHR介导的差异基因表达，代谢重编程和 在某些实施方案中，NAFLD是导致肝毒性和NAFLD进展的毒性代谢物的生物合成。我们将展示 补充Cbl可以保护免受AHR介导的肝毒性。CBL补充剂也将 证明是保护易受AHR介导的暴露人群的有效对策 肝毒性，这也可能有利于NAFLD的治疗和管理。

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.