The activation of innate immune system is essential for the pathogenesis of nonalcoholic steatohepatitis (NASH). Among pattern recognition receptors, it is well-characterized that toll-like receptors (TLRs) are deeply involved in the development of NASH to reflect exposure of the liver to gut-driven endotoxins. In contrast, it has not been elucidated whether retinoic acid-inducible gene-I (RIG-I)-like receptors (RLRs) are similarly implicated in the disease progression. In the present study, we examined the expression of melanoma differentiation-associated antigen 5 (MDA5), known to be a member of RLRs, in a diet-induced murine model of NASH. The liver tissues were collected from C57BL/6 J mice at 1, 3, and 6 weeks after choline-deficient l-amino acid-defined high-fat diet (CDAHFD), and the expression of MDA5 was analyzed by western blotting, immunofluorescence (IF), and real-time quantitative PCR (qPCR). The results of western blotting showed that hepatic expression of MDA5 was increased at 3 and 6 weeks. In IF, MDA5-positive cells co-expressed F4/80 and CD11b, indicating they were activated macrophages, and these cells began to appear at 1 week after CDAHFD. The mRNA expression of MDA5 was significantly upregulated at 1 week. Additionally, we performed IF using liver biopsy specimens collected from 11 patients with nonalcoholic fatty liver diseases (NAFLD), and found that MDA5-positive macrophages were detected in eight out of eleven patients. In an in vitro study, MDA5 was induced upon stimulation with lipopolysaccharide in murine bone marrow-derived macrophages and THP-1 cells. Our findings suggest that MDA5 may be involved in the inflammation of NASH.

先天免疫系统的激活对于非酒精性脂肪性肝炎 (NASH) 的发病机制至关重要。在模式识别受体中，Toll 样受体 (TLR) 深入参与 NASH 的发展以反映肝脏对肠道驱动的内毒素的暴露，这是一个很好的特征。相反，尚未阐明视黄酸诱导基因-I (RIG-I) 样受体 (RLR) 是否与疾病进展类似。在本研究中，我们在饮食诱导的 NASH 小鼠模型中检测了已知为 RLR 成员的黑色素瘤分化相关抗原 5 (MDA5) 的表达。在胆碱缺乏l后 1、3 和 6 周从 C57BL/6 J 小鼠收集肝组织-氨基酸确定的高脂饮食（CDAHFD），通过蛋白质印迹、免疫荧光（IF）和实时定量PCR（qPCR）分析MDA5的表达。免疫印迹结果显示，MDA5的肝脏表达在3周和6周时增加。IF中，MDA5阳性细胞共表达F4/80和CD11b，表明它们是活化的巨噬细胞，这些细胞在CDAHFD后1周开始出现。MDA5的mRNA表达在1周时显着上调。此外，我们使用从 11 名非酒精性脂肪性肝病 (NAFLD) 患者收集的肝活检标本进行 IF，发现 11 名患者中有 8 名检测到 MDA5 阳性巨噬细胞。在一项体外研究中，在小鼠骨髓来源的巨噬细胞和 THP-1 细胞中用脂多糖刺激后可诱导 MDA5。