O-GlcNAcylation promotes the progression of nonalcoholic fatty liver disease by upregulating the expression and function of CD36

Abstract

Background and aims: Nonalcoholic fatty liver disease (NAFLD) and its progressive variant, nonalcoholic steatohepatitis (NASH), constitute a burgeoning worldwide epidemic with no FDA-approved pharmacotherapies. The multifunctional immunometabolic receptor, fatty acid translocase CD36 (CD36), plays an important role in the progression of hepatic steatosis. O-GlcNAcylation is a crucial posttranslational modification that mediates the distribution and function of CD36, but its involvement in NAFLD remains poorly understood.

Methods: O-GlcNAcylation and CD36 expression were evaluated in human liver tissues obtained from NASH patients and normal control. Mice with hepatocyte-specific CD36 knockout were administered adeno-associated viral vectors expressing wild-type CD36 (WT-CD36) or CD36 O-GlcNAcylation site mutants (S468A&T470A-CD36) and were provided with a high-fat/high-cholesterol (HFHC) diet for 3 months. RT-qPCR analysis, immunoblotting, dual-luciferase reporter assays, chromatin immunoprecipitation, and coimmunoprecipitation were performed to explore the mechanisms by which O-GlcNAcylation regulates CD36 expression. Membrane protein extraction, immunofluorescence analysis, site-directed mutagenesis, and fatty acid uptake assays were conducted to elucidate the impact of O-GlcNAcylation on CD36 function.

Results: O-GlcNAcylation and CD36 expression were significantly increased in patients with NASH, mouse models of NASH, and palmitic acid-stimulated hepatocytes. Mechanistically, the increase in O-GlcNAcylation facilitated the transcription of CD36 via the NF-κB signalling pathway and stabilized the CD36 protein by inhibiting its ubiquitination, thereby promoting CD36 expression. On the other hand, O-GlcNAcylation facilitated the membrane localization of CD36, fatty acid uptake, and lipid accumulation. However, site-directed mutagenesis of residues S468 and T470 of CD36 reversed these effects. Furthermore, compared with their WT-CD36 counterparts, HFHC-fed S468A&T470A-CD36 mice exhibited decreases in systemic insulin resistance, steatosis severity, inflammation and fibrosis. Pharmacological inhibition of O-GlcNAcylation and CD36 also mitigated the progression of NASH.

Conclusions: O-GlcNAcylation promotes the progression of NAFLD by upregulating CD36 expression and function. Inhibition of CD36 O-GlcNAcylation protects against NASH, highlighting a potentially effective therapeutic approach for individuals with NASH.

Keywords: CD36; Hepatocyte; NAFLD; O-GlcNAcylation; PTM.