Melanoma Differentiation-Associated Gene 5 Positively Modulates TNF-α-Induced CXCL10 Expression in Cultured HuH-7 and HLE Cells

The molecular mechanisms of innate immunity are closely associated with the development of non-alcoholic fatty liver disease (NAFLD). TNF-α is a key cytokine involved in the pathogenesis of metabolic inflammation like NAFLD. Melanoma differentiation-associated gene 5 (MDA5) is a member of the intracellular RNA helicase family proteins that play a pivotal role in an antiviral immune response. Previous studies have demonstrated that TNF-α induces the expression of MDA5 in some types of cells. However, the correlation between TNF-α and the expression of MDA5 in hepatocytes remains unknown. In the present study, we used two human hepatocellular carcinoma cell lines, HuH-7 and HLE, and examined the expression of MDA5 in these cells upon stimulation with TNF-α. The expression of MDA5 induced by TNF-α was analyzed by quantitative real-time RT-PCR and western blotting. Next, RNA interference against MDA5 was performed and the expressions of CXCL10 and STAT1 were examined. We found that the expression of MDA5 had increased upon stimulation with TNF-α in a concentration-dependent manner. Gene silencing against MDA5 suppressed the expression of TNF-α-induced CXCL10 in both cells. In HLE cells, gene silencing of MDA5 impaired STAT1 phosphorylation 24 h after stimulation with TNF-α. On the other hand, TNF-α-induced STAT1 phosphorylation was not detected in HuH-7 cells. These results indicated that MDA5 positively modulated the TNF-α-induced expression of CXCL10 in both STAT1-dependent and -independent manner and may be associated with metabolic inflammation in the liver.