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

Abstract 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.