FMO2 ameliorates nonalcoholic fatty liver disease by suppressing ER-to-Golgi transport of SREBP1

Background and Aims:Nonalcoholic fatty liver disease (NAFLD), comprises a spectrum of liver disorders with the initial abnormal accumulation of lipids in hepatocytes called nonalcoholic fatty liver (NAFL), progressing to the more serious non-alcoholic steatohepatitis (NASH) in a subset of individuals. Our previous study revealed that global flavin-containing monooxygenase 2 (FMO2) knockout causes higher liver weight in rats. However, the role of FMO2 in NAFLD remains unclear. Herein, we aimed to determine the function and mechanism of FMO2 in liver steatosis and steatohepatitis.Approach and Results:The expression of FMO2 was significantly downregulated in NAFL/NASH patients and mouse model. Both global and hepatocyte-specific knockout of FMO2 resulted in increased lipogenesis and severer hepatic steatosis, inflammation, and fibrosis, whereas FMO2 overexpression in mice improved NAFL/NASH. RNA sequencing showed that hepatic FMO2 deficiency is associated with impaired lipogenesis in response to metabolic challenges. Mechanistically, FMO2 directly interacts with SREBP1 at amino acids 217-296 competitively with SREBP cleavage-activating protein (SCAP) and inhibits SREBP1 translocation from the endoplasmic reticulum (ER) to the Golgi apparatus (GA) and its subsequent activation, thus suppressing de novo lipogenesis (DNL) and improving NAFL/NASH.Conclusion:In hepatocytes, FMO2 is a novel molecule that protects against the progression of NAFL/NASH independent of enzyme activity. FMO2 impairs lipogenesis in HFD or CDAHFD-induced steatosis, inflammation and fibrosis by directly binding to SREBP1 and preventing its organelle translocation and subsequent activation. FMO2 thus is a promising molecule for targeting the activation of SREBP1 and for the treatment of NAFL/NASH.

Automated summary

FMO2 deficiency is associated with increased lipogenesis and worsened hepatic steatosis, inflammation, and fibrosis in NAFL/NASH, whereas FMO2 overexpression improves these conditions. Mechanistically, FMO2 interacts with SREBP1 competitively with SCAP to inhibit lipogenesis, making it a promising target for NAFL/NASH treatment.