Metformin ameliorates insulin resistance in L6 rat skeletal muscle cells through upregulation of SIRT3

Background SIRT3 is an important regulator in cell metabolism, and recent studies have shown that it may be involved in the pharmacological effects of metformin. However, the molecular mechanisms underlying this process are unclear. Methods The effects of SIRT3 on the regulation of oxidative stress and insulin resistance in skeletal muscle were evaluated in vitro. Differentiated L6 skeletal muscle cells were treated with 750 mu mol/L palmitic acid to induce insulin resistance. SIRT3 was knocked down and overexpressed in L6 cells. SIRT3, nuclear factor kappa-light-chain-enhancer of activated B cells (NF-kappa B) p65, c-Jun N-terminal kinase 1 (JNK1), and superoxide dismutase 2 (SOD2) were evaluated by Western blotting. Results Over expression of SIRT3 increased glucose. uptake and decreased ROS production in L6-IR cells as well as in L6 cells. Knock-down of SIRT3 induced increased production of ROS while decreased glucose uptake in both L6 and L6-IR cells, and these effects were reversed by N-acetyl-L-cysteine (NAC). Metformin increased the expression of SIRT3 (1.5-fold) and SOD2 (2-fold) while down regulating NF-kappa B p65 (1.5-fold) and JNK1 (1.5-fold). Knockdown of SIRT3 (P<0.05) reversed the metformin-induced decreases in NF-kappa B p65 and JNK1 and the metformin-induced increase in SOD2 (P<0.05). Conclusions Upregulated SIRT3 is involved in the pharmacological mechanism by which metformin promotes glucose uptake. Additionally, SIRT3 may function as an important regulator of oxidative stress and a new alternative approach for targeting insulin resistance-related diseases.