Si-Ni-San improves the deposition of lipid droplets in MAFLD through modulating the FXR-GPAT4 axis

Background Metabolic-associated fatty liver disease (MAFLD) is a common metabolic disease with complex pathogenesis and a lack of effective treatment. Si-Ni-San (SNS), a traditional Chinese medicine, has emerged as a promising candidate for MAFLD treatment. However, its mechanism of action remains unclear. Methods C57BL/6 mice were fed a high-fat diet (HFD) for 12 weeks to establish a mouse model of MAFLD. Second, an MAFLD cell model was established by inducing HepG2 cells with oleic acid. The effects of SNS and the positive drug obeticholic acid on hepatic lipid droplet deposition in MAFLD mice and cell models were evaluated. The expression levels of farnesoid X receptor (FXR) and glycerol 3-phosphate acyltransferase 4 (GPAT4) were detected by Western Blot assay. siRNA assay and Dual-Luciferase reporter assay were used to detect the interaction between FXR and GPAT4. Active components in the aqueous decoction of SNS were screened by HPLC, and their binding to targets was further validated by molecular docking and molecular dynamics simulations. Results SNS ameliorates hepatic lipid droplet deposition in both the MAFLD mouse and cell models. It activates hepatic FXR, inhibits hepatic GPAT4, and regulates proteins related to hepatic lipolysis and lipophagy. FXR reduces lipid droplet accumulation by inhibiting GPAT4. The Dual-Luciferase reporter assay confirms that FXR transcriptionally regulates and inhibits GPAT4 expression. Seven active components in SNS were detected by HPLC, and their binding to FXR and GPAT4 was confirmed through molecular docking and molecular dynamics simulations. Conclusion This study provides a new mechanistic exploration for FXR in improving MAFLD and broadens the research direction on the mechanisms by which SNS reduces hepatic lipid droplet deposition. It also offers a molecular dynamics basis for subsequent studies on how active components in SNS exert their effects through binding to FXR.