Down-regulation of a few post-receptor insulin signaling transducers in skeletal muscle of type 2 diabetic mice

Objective To investigate the insulin-stimulated regulation of the expression and phosphorylation of a few post-receptor key transducers:insulin receptor substrates-1(IRS-1),phosphatidylinositol 3-kinase(PI3-K) and protein kinase B(PKB).Methods Thirty female C57BL/6J mice were divided into two groups,control group were fed normal commercial diet,type 2 diabetes (T2DM) group was given high fat and sugar diet(fat:355 g/kg,amount for 58%,primarily lard;carbohydrate:36.6 g/kg,primarily sucrose),after 16 weeks,intact skeletal muscle strips of the mice were obtained. These strips were incubationinmediumcontaininginsulin(10~ -7 mol/L)respectivelyfor 0,2,15,or 30 min,thenthe protein expression of IRS-1,PI3-K ,PKB and PKB serine-473 phosphorylation.IRS-1were measured by Western blot analysis,and the phosphorylation of IRS-1 were measured by immunoprecipitate procedures.Results The expression amount of IRS-1 and PKB protein in skeletal muscle cell was not found different between control group and T2DM group.The expression of PI3-K protein in T2DM group was significant lower than in control group (P0.05).T2DM mice had similar level of phosphoproteins in based state and considerably decreased IRS-1 tyrosine phosphorylation and PKB serine-473 phosphorylation response curves after insulin-stimulation as compared with the control group.Conclusion There is a down-regulation in insulin signaling system of skeletal muscle from type 2 diabetic mice,and the degradation of post-receptor steps is associated with reduced activation of IRS-1,PKB and low expression of PI3-K protein.