Effect Of IGF-1 And Exercise On 4E-BP1 Protein Expression And Phosphorylation In Rat Skeletal Muscle

Objective:To study the effect and regulating mechanism of IGF-1 and exercise on protein synthesis in skeletal muscle,it investigated changes of 4E-BP1 protein expression and phosphorylation of 4E-BPlThr37/46 through exercise and injection of IGF-1 and LY294002—one kind of blocking agents of PI3K. As we know,4E-BP1 is one typical downstream targets of mTOR(mammalian target of rapamycin) signaling pathway.Methods:9-week male Sprague-Dawley rats were randomly divided into eight groups as follow:Sedentary group(S), Sedentary and Injection of IGF-1 group (SI), Sedentary and Injection of LY294002 group (SL), Sedentary and Injection of both IGF-1 and LY294002 group(SIL), Exercise Group(E),Exercise and Injection of IGF-1 group(EI), Exercise and Injection of LY294002(EL), Exercise and Injection of both IGF-1 and LY294002 group(SIL),each one with 6 rats. After all the groups had been adapted for one week, the rats of four exercise groups performed closely monitored formal training in treadmills (gradient of 10%, at the speed of 20m/min and duration of 60min/day) for one week. All the injection groups were injected at the same time immediately after exercise every day. On the 7th day of formal training, the injected gastrocnemius muscles were collected at the 6th hour after the last exercise. Protein content of gastrocnemius muscle was assessed with Bradford, phosphorylation of 4E-BPlThr37/46 and protein expression of 4E-BP1 were determined by Western Blot.Results:(1)One-week IGF-1 injection increased the wet gastrocnemius muscle weight significantly(p<0.05);(2)One-week endurance exercise enhanced the protein content of gastrocnemius muscle significantly(p<0.05);(3)One-week endurance exercise promoted 4E-BP1 protein expression(p<0.05) and phosphorylation of 4E-BPlThr37/46 (p<0.01) at the 6th hour of recovery period;(4)One-week IGF-1 injection also promoted 4E-BP1 protein expression(p<0.01) and phosphorylation of 4E-BPlThr37/46(p<0.01) at the 6th hour of recovery period;(5)One-week LY294002 injection inhibited 4E-BP1 protein expression(p<0.05) and phosphorylation of 4E-BP1Thr37/46(p>0.05) at the 6th hour of recovery period.Conclusions:(1)Both one-week IGF-1 injection and endurance exercise could promoted the protein expression and phosphorylation of 4E-BP1 in skeletal muscle. (2)One-week injection of IGF-1 or exercise could weaken the inhibition of 4E-BP1 protein expression and phosphorylation by LY. Moreover, the combination of IGF-1 and exercise could have accumulated and/or congenerous effect on promoting 4E-BP1 signaling expression. (3)Both IGF-1 and exercise promoted the protein expression and phosphorylation of 4E-BP1 in skeletal muscle probably via PI3K/Akt/mTOR pathway, but other non-PI3K pathways maybe also existed.