Inhibition of metabotropic glutamate receptor-5 alleviates hepatic steatosis by enhancing autophagy via activation of the AMPK signaling pathway

Background: The global prevalence of metabolic dysfunction-associated steatotic liver disease (MASLD) has continued to increase annually. Recent studies have indicated that inhibition of metabotropic glutamate receptor 5 (mGluR5) may alleviate hepatic steatosis. However, the precise mechanism warrants further exploration.

Aim: To investigate the potential mechanism by which mGluR5 attenuates hepatocyte steatosis in vitro and in vivo.

Methods: Free fatty acids (FFAs)-stimulated HepG2 cells were treated with the mGluR5 Antagonist MPEP and the mGluR5 Agonist CHPG. Oil Red O staining and a triglyceride assay kit were used to evaluate lipid content. Western blot analysis was conducted to detect the expression of the autophagy-associated proteins p62 and LC3-II, as well as the expression of the key signaling molecules AMPK and ULK1, in the treated cells. To further elucidate the contributions of Autophagy and AMPK, we used chloroquine (CQ) to inhibit Autophagy and compound C (CC) to inhibit AMPK activity. In parallel, wild-type mice and mGluR5 knockout (KO) mice fed a normal chow diet or a high-fat diet (HFD) were used to evaluate the effect of mGluR5 inhibition in vivo.

Results: mGluR5 inhibition by MPEP attenuated hepatocellular steatosis and increased LC3-II and p62 protein expression. The Autophagy inhibitor CQ reversed the effects of MPEP. In addition, MPEP promoted AMPK and ULK1 expression in HepG2 cells exposed to FFAs. MPEP treatment led to the nuclear translocation of transcription factor EB, which is known to promote p62 expression. This effect was negated by the AMPK Inhibitor CC. mGluR5 KO mice presented reduced body weight, improved glucose tolerance and reduced hyperlipidemia when fed a HFD. Additionally, the livers of HFD-fed mGluR5 KO mice presented increases in LC3-II and p62.

Conclusion: Our results suggest that mGluR5 inhibition promoted Autophagy and reduced hepatocyte steatosis through activation of the AMPK signaling pathway. These findings reveal a new functional mechanism of mGluR5 as a target in the treatment of MASLD.

AMPK; Autophagy; Hepatic steatosis; Metabolic dysfunction-associated steatotic liver disease; Metabotropic glutamate receptor 5.