芳香烃受体激活导致的脂肪酸转位酶表达增加在高同型半胱氨酸血症所致脂肪肝中的作用

Hyperhomocysteinemia (HHcy) and non-alcoholic fatty liver disease (NAFLD) are metabolic disorders globally. The role of HHcy in NAFLD and the underlying mechanisms are still unknown. CD36 mediates uptake and intracellular transport of long-chain fatty acids and contributes to the pathogenesis of fatty liver disease. As a ligand-activated transcription factor, activation of aryl hydrocarbon receptor（AhR）in mice induced the expression of its target gene CD36 and resulted in increased lipid deposition in liver. In the preliminary study, we found that the HHcy mouse model displayed hepatic steatosis, increased CD36 expression and activation of AhR in liver. Based on those data, the hypothesis of the current project is that HHcy can induce hepatic steatosis by activating AhR/CD36 pathway via increasing AhR ligands. By approaches of molecular biology and metabolomics, we will elucidate the mechanisms of AhR activation and consequent induction of CD36 expression by HHcy, and further search for the ligands of AhR increased by HHcy. This study may extend our knowledge of the mechanisms of NAFLD induced by HHcy and potentially contribute to the development of novel therapeutic approaches to it.

高同型半胱氨酸血症（HHcy）及非酒精性脂肪肝（NAFLD）是世界范围内重要的代谢紊乱性疾病，二者的相互关系以及机制尚未阐明。脂肪酸转位酶CD36可通过促进肝脏脂质摄取参与NAFLD的发生。芳香烃受体（AhR）是配体激活的转录因子，它的激活也可引起NAFLD，而CD36是AhR的靶基因。预实验结果发现，HHcy小鼠肝脏中脂质沉积增加，CD36的表达显著上调并且AhR被激活。因此，本项目的科学假说为：HHcy通过增加AhR的内源性配体激活AhR，进而增加CD36的表达促进肝脏的脂质摄取，最终导致NAFLD的发生。本项目拟在动物及细胞水平，运用分子生物学及代谢组学手段研究：HHcy在肝脏中激活AhR，进而增加CD36表达的机制以及其在HHcy所致NAFLD中的作用，同时寻找HHcy增加的AhR内源性配体。以期进一步揭示HHcy引起NAFLD发生的分子机制，并为其治疗提供新的潜在性靶点。

非酒精性脂肪肝（non-alcoholic fatty liver disease, NAFLD）是世界范围内重要的代谢紊乱性疾病。高同型半胱氨酸血症（Hyperhomocysteinemia, HHcy）是NAFLD的独立危险因素，但HHcy引起NAFLD的机制尚未明确。本项目通过动物实验、细胞实验以及分子生物学实验研究了HHcy引起NAFLD发生的分子机制。本项目在高蛋氨酸饮食引起的HHcy小鼠肝脏中发现肝脏脂质沉积增加，并且介导脂质摄取的关键分子脂肪酸转位酶CD36的mRNA以及蛋白质表达水平均显著上调。进一步研究发现，同型半胱氨酸（Homocysteine, Hcy）处理原代肝细胞可增加CD36的表达，敲减CD36则改善了Hcy导致的肝细胞脂质摄取和脂质沉积增加。CD36是由多种转录因子调控的靶点。为了明确HHcy引起CD36表达上调的机制，我们筛选了参与CD36表达调控并且和肝脏的脂质代谢密切相关的转录因子及其靶基因的表达。发现HHcy激活了肝脏中芳香烃受体（Aryl hydrocarbon receptor, AhR）。在原代肝细胞上发现Hcy增加了AhR与CD36启动子的结合，通过敲减AhR证明Hcy通过激活AhR增加基因CD36的表达和肝细胞脂质沉积。AhR是由配体激活的转录因子，多个花生四烯酸的代谢产物是AhR的内源性配体。靶向代谢组学研究发现HHcy增加了肝脏中LXA4的水平，LXA4作为AhR的内源性配体通过激活AhR促进了CD36的表达。并且AhR的抑制剂可降低HHcy小鼠肝脏中CD36的表达、改善其肝脏脂质沉积。本项目明确了AhR 激活导致的CD36 表达增加是HHcy 引起肝脏脂质沉积的关键机制，为减轻HHcy引起的肝脏脂质沉积提供了新的治疗思路和靶点。在本项目的资助下，于Hepatology、British journal of phamarcology、Cell Mol Gastroenterol Hepatol发表论文4篇。