Mice received a dose of 1.5 μg/g MC-TTR-miR-378 or MC-TTR-miR-378-MM complexed with in vivo-jetPEI weekly for 9 weeks via tail vein injection.

BACKGROUND AND AIMS: The progression of hepatosteatosis to non-alcoholic steatohepatitis (NASH) is a critical step in the pathogenesis of hepatocellular cancer. However, the underlying mechanism(s) for this progression is essentially unknown. This study was designed to determine the role of miR-378 in regulating NASH progression. METHODS: We used immunohistochemistry, luciferase assays and immunoblotting to study the role of miR-378 in modulating an inflammatory pathway. Wild-type mice kept on a high fat diet (HFD) were injected with miR-378 inhibitors or a mini-circle expression system containing miR-378 to study loss and gain-of functions of miR-378. RESULTS: MiR-378 expression is increased in livers of dietary obese mice and NASH patients. Further studies revealed that miR-378 directly targeted Prkag2 that encodes AMP-activated protein kinase gamma 2 (AMPKgamma2). AMPK signaling is a negative regulator of NFkappaB-TNFalpha inflammatory axis by increasing deacetylase activity of Sirtuin 1. By targeting Prkag2, miR-378 reduced Sirtuin1 activity and facilitated an inflammatory pathway involving NFkappaB-TNFalpha. In contrast, miR-378 knockdown using its inhibitor induced expression of Prkag2, increased Sirtuin1 activity and blocked NFkappaB-TNFalpha axis. Additional knockdown of increased Prkag2 offset the inhibitory effects of miR-378 inhibitor on the NFkappaB-TNFalpha axis, suggesting that AMPK signaling mediates the role of miR-378 in facilitating this inflammatory pathway. Liver-specific expression of miR-378 triggered the development of NASH and fibrosis by activating TNFalpha signaling. Ablation of TNFalpha in miR-378-treated mice impaired the ability of miR-378 to facilitate hepatic inflammation and fibrosis, suggesting that TNFalpha signaling is required for miR-378 to promote NASH. CONCLUSION: MiR-378 plays a key role in the development of hepatic inflammation and fibrosis by facilitating NFkappaB-TNFalpha axis; and might act as a potential therapeutic target for the treatment of NASH. Lay summary The recent epidemic increase in obesity has been associated with a sharp rise in the incidence of non-alcoholic fatty liver disease (NAFLD). However, the underlying mechanism(s) remains poorly described and effective therapeutic approaches against NAFLD are lacking. The results establish that miR-378 facilitates the development of hepatic inflammation and fibrosis and suggest the therapeutic potential of microRNA-378 inhibitor for the treatment of NAFLD.