Metformin ameliorates PA-induced skeletal muscle insulin resistance by suppressing SREBP-1c / 中国药理学通报

ABSTRACT

Aim Metformin has been the first-line oral agent for the treatment of type 2 diabetes. The results from preliminary studies suggested that sterol regulatory element binding protein-1c( SREBP-1c) inhibited the transcription of insulin receptor substrate-1 ( IRS-1), which plays a key role in PA-induced skeletal muscle insulin resistance. In the current study, we investiga-ted the role and mechanism of SREBP-1c in metformin ameliorating PA-induced skeletal muscle insulin resist-ance. Methods L6 cells were treated with metformin (1,10 mmol·L - 1 ) for 24h in 500 μmol·L - 1 PA-in-duced insulin-resistant state and then harvested for pro-tein and glucose uptake assay. Glucose uptake was performed by 2-NBDG method. The protein expression of SREBP-1c, FAS, p-IRS-1 ( Tyr608 / 612), IRS-1, p-AKT ( Ser473 ) and AKT was detected by western blot. The effects of metformin on SREBP-1c and IRS-1 gene transcription were assessed by a dual-luciferase reporter assay. CHIP assay was performed to examine the binding of SREBP-1c protein to the IRS-1 promoter region by metformin treatment. Results PA treatment decreased glucose uptake in L6 myotubes. The protein expression of SREBP-1c and its downstream molecule FAS was increased significantly after exposure to PA. By contrast, the proteins related to insulin signaling pathway including IRS-1, p-IRS-1( Tyr608 / 612) and p-AKT ( Ser473) / AKT were decreased significantly. Metformin increased glucose uptake in a dose-depend-ent manner compared to PA-cultured L6 cells. The SREBP-1c and FAS protein levels were decreased by metformin treatment. Correspondingly, p-IRS-1 (Tyr608 / 612), IRS-1, p-AKT(Ser473) / AKT protein levels were increased significantly. The results from dual-luciferase reporter assay indicated metformin sup-pressed SREBP-1c promoter activity and enhanced IRS-1 promoter. The results from CHIP assay showed that metformin decreased binding of SREBP-1c protein to the IRS-1 promoter region (about 30% ). Conclu-sion Metformin can improve PA-induced muscular in-sulin resistance by suppressing SREBP-1c.