Title: Mitofusin-2 ameliorates high-fat diet-induced insulin resistance in liver of rats
Abstract: AIM:To investigate the effects of mitofusin-2 (MFN2) on insulin sensitivity and its potential targets in the liver of rats fed with a high-fat diet (HFD). METHODS:Rats were fed with a control or HFD for 4 or 8 wk, and were then infected with a control or an MFN2 expressing adenovirus once a week for 3 wk starting from the 9 th wk.Blood glucose (BG), plasma insulin and insulin sensitivity of rats were determined at end of the 4 th and 8 th wk, and after treatment with different amounts of MFN2 expressing adenovirus (10 8 , 10 9 or 10 10 vp/kg body weight).BG levels were measured by Accu-chek Active Meter.Plasma insulin levels were analyzed by using a Rat insulin enzyme-linked immunosorbent assay kit.Insulin resistance was evaluated by measuring the glucose infusion rate (GIR) using a hyperinsulinemic euglycemic clamp technique.The expression or phosphorylation levels of MFN2 and essential molecules in the insulin signaling pathway, such as insulin receptor (INSR), insulin receptor substrate 2 (IRS2), phosphoinositide-3-kinase (PI3K), protein kinase beta (AKT2) and glucose transporter type 2 (GLUT2) was assayed by quantitative real-time polymerase chain reaction and Western-blotting. RESULTS:After the end of 8 wk, the body weight of rats receiving the normal control diet (ND) and the HFD was not significantly different (P > 0.05).Compared with the ND group, GIR in the HFD group was significantly decreased (P < 0.01), while the levels of BG, triglycerides (TG), total cholesterol (TC) and insulin in the HFD group were significantly higher than those in the ND group (P < 0.05).Expression of MFN2 mRNA and protein in liver of rats was significantly downregulated in the HFD group (P < 0.01) after 8 wk of HFD feeding.The expression of INSR, IRS2 and GLUT2 were down-regulated markedly (P < 0.01).Although there were no changes in PI3K-P85 and AKT2 expression, their phosphorylation levels were decreased significantly (P < 0.01).After intervention with MFN2 expressing adenovirus for 3 wk, the expression of MFN2 mRNA and protein levels were up-regulated (P < 0.01).There was no difference in body weight of rats between the groups.The levels of BG, TG, TC and insulin in rats were lower than those in the Ad group (P < 0.05), but GIR in rats infected with Ad-MFN2 was significantly increased (P < 0.01), compared with the Ad group.The expression of INSR, IRS2 and GLUT2 was increased, while phosphorylation levels of PI3K-P85 and AKT2 were increased (P < 0.01), compared with the Ad group. CONCLUSION:HFDs induce insulin resistance, and this can be reversed by MFN2 over-expression targeting the insulin signaling pathway.