LncRNA MEG3 up-regulates SIRT6 by ubiquitinating EZH2 and alleviates nonalcoholic fatty liver disease

Nonalcoholic fatty liver disease (NAFLD) is a global health threat. Here, we presented the significant role of a novel signaling axis comprising long non-coding RNA maternally expressed gene 3 (MEG3), enhancer of zeste homolog 2 (EZH2), and sirtuin 6 (SIRT6) in controlling lipid accumulation, inflammation, and the progression of NAFLD. Mice fed with high-fat diet (HFD) were established as in vitro and in vivo NAFLD models, respectively. Lipid accumulation was measured by oil red O staining and assays for triglycerides or cholesterol. Inflammation was examined by ELISA for pro-inflammatory cytokines. Gene expressions were examined by RT-qPCR or Western blot. Interactions between key signaling molecules were examined by combining expressional analysis, RNA immunoprecipitation, cycloheximide stability assay, co-immunoprecipitation, and chromatin immunoprecipitation. MEG3 level was reduced in FFA-challenged hepatocytes or liver from HFD-fed mice, and the reduction paralleled the severity of NAFLD in clinic. Overexpressing MEG3 suppressed FFA-induced lipid accumulation or inflammation in hepatocytes. By promoting the ubiquitination and degradation of EZH2, MEG3 upregulated SIRT6, an EZH2 target. SIRT6 essentially mediated the protective effects of MEG3 in hepatocytes. Consistently, overexpressing MEG3 alleviated HFD-induced NAFLD in vivo. By controlling the expressions of genes involved in lipid metabolism and inflammation, the MEG3/EZH2/SIRT6 axis significantly suppressed lipid accumulation and inflammation in vitro, and NAFLD development in vivo. Therefore, boosting MEG3 level may benefit the treatment of NAFLD.