Mechanism of O-GlcNAcylation regulating liver lipid synthesis in mice through FASN

Nonalcoholic fatty liver disease (NAFLD) has become one of the most common chronic liver diseases. O-Linked attachment of beta-N-acetylglucosamine (O-GlcNAc) are ubiquitous post-translational modifications of proteins as "nutrient sensors" and "stress receptors" in the body that are involved in maintaining normal cellular physiological functions. Increased levels of O-GlcNAcylation have been found in the liver samples of patients with NAFLD and nonalcoholic steatohepatitis. However, the role of O-GlcNAcylation in the development and pathogenesis of NAFLD remains unclear. Here, we sought to determine the specific role of O-GlcNAcylation in NAFLD. In this study, the results demonstrated that inhibition of O-GlcNAc transferase (OGT) led to decreased expression of liver lipid synthesis genes and proteins in vitro. In addition, we showed that fatty acid synthase (FASN) expression was positively correlated with O-GlcNAcylation levels. Immunoprecipitation and pulldown assays confirmed the interaction between FASN and OGT at the serine 1483 of FASN, to inhibit K48-linked ubiquitination and degradation of FASN, thereby promoting hepatic lipid accumulation and the development of NAFLD. Administration of the OGT inhibitor OSMI-1 to ob/ob mice led to decreased liver lipid accumulation, further confirming our in vitro experimental results. Finally, we used liver-specific Ogt gene knockout mice fed a high-fat diet to elucidate the specific mechanism of O-GlcNAcylation on NAFLD and found that knockdown of the Ogt gene led to decreased liver lipid accumulation. In conclusion, our findings show that inhibiting the O-GlcNAcylation of FASN at the S1483 site promotes the K48-linked ubiquitination and degradation of FASN and leads to inhibition of lipid accumulation in the liver. Treatment with the OGT inhibitor OSMI-1 leads to decreased lipid accumulation in the liver, suggesting that targeting O-GlcNAcylation sites could be a potential therapeutic strategy for alleviating NAFLD.