A negative feedback loop between microRNA-378 and Nrf1 promotes the development of hepatosteatosis in mice treated with a high fat diet

Backgrounds: The incidence of nonalcoholic fatty liver disease (NAFLD) is rapidly increasing due to the prevalence of obesity. NAFLD is a major risk factor of hepatocellular carcinoma (HCC). Even with successful surgical removal, the presence of NAFLD is associated with an increased recurrence of HCC. Despite the extensive study of NAFLD, its underlying mechanism(s) remains essentially unknown and there are no FDA-approved drugs for its treatment. Alterations in microRNA (miR) expression have been observed in human fatty livers. However, regulatory mechanism(s) of miRNA biogenesis and their role in regulating the development of NAFLD is poorly described. Methods: We used immunohistochemistry, luciferase assays and immunoblotting to study the regulatory mechanism of miR-378 biogenesis. 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 was significantly increased in fatty livers of dietary obese mice and human hepatoma HepG2 cells with accumulated lipid. Further studies identified NRFI (Nuclear receptor factor 1), a key regulator of fatty acid oxidation (FAD), as a direct target of miR-378. Overexpression of miR-378 impaired FAO and promoted lipid accumulation in murine hepatoma Hepal-6 cells. In contrast, knockdown of miR-378 using its ASO (anti-sense oligo) improved FAO and reduced intracellular lipid content in Hepal-6 cells. Liver-specific expression of miR-378 impaired FAO, which subsequently promoted the development of hepatosteatosis. Antagonizing miR-378 via injecting miR-378-ASO into HFD-treated mice led to increased expression of Nrf1, improved FAO and decreased hepatosteatosis. Additional knockdown of up-regulated Nrfl offset the effects of miR-378-ASO, suggesting that MD mediated the inhibitory effect of miR-378-ASO on hepatosteatosis. Furthermore, Nrfl was identified as a transcriptional repressor of miR-378. Ablation of Nip using its shRNA in livers led to increased miR-378, which subsequently resulted in reduced FAO and elevated hepatic lipid content. Conclusions: These findings identified a negative feedback loop between miR-378 and Nrfl that promotes the pathogenesis of hepatosteatosis, and suggests the use of miR-378 as a potential therapeutic target for NAFLD. (C) 2018 The Authors. Published by Elsevier Inc.