Effects Of Hypoxia And Exercise On PKB/mTOR Signaling Pathway In Skeletal Muscle

Aims:To study the effect and mechanism of hypoxic exercise on protein synthesis in skeletal muscle,it tested the effect of exercise and hypoxia on IGF-1 and Myostatin expression which are positive and negative regulating factor of muscle growth,and the influence on PKB/mTOR signal pathway.Materials and methods:SD rats were randomly divided into four groups: normoxia control group,normoxic exercise group,hypoxic exposure group, living high training low(HiLo) group.Hypoxic exposure treatment consisted of intermittent hypoxia with 13.6%concentrations of oxygen for 12 h/day under normobaric conditions in hypoxic chamber,and the training protocol consisted of treadmill running with 5°incline,20 m/min,1 h/day,1 time/day,6 days/wk.One hour after the exercise under normoxic condition,the HiLo group rats were exposed to hypoxia under normobaric condition for 12 h.1 day,28 days of exercise and(or) intermittent hypoxia exposure,7 days of reoxygen and exercise are carried out in the HiLo group and the normoxic exercise group.IGF-1,Myostatin,PKB,mTOR,p70S6E expression in gastrocnemius muscle were tested with the method of RT-PCR,ELISA,western blot.Results:(1) After exercise and hypoxia exposure for 28 days,the HiLo group rats body weight,muscle mass and total protein content had been the decreased tendency;(2) After exercise and hypoxic exposure for 28 days,IGF-1 protein expression in muscle decreased significantly, myostatin protein expression increased significantly in the HiLo group (p＜0.05);(3) After 28 days exercise,phosphorylated PKB protein,mTOR and p70S6K protein expression in muscle increased significantly; (4)After living high training low for 28 days,mTOR protein expression in muscle had no change,but increased significantly after 7 days reoxygen.Conclusions:(1) Exercise followed by hypoxia repress muscle protein synthesis,and its mechanism may be the way of regulation of mTOR signal in skeletal muscle by exercise and hypoxia.(2) In the condition of exercise and hypoxia,IGF-1 and Myostatin expression have complete contrast changes and involed in the regulation of growth of muscle and metabolism of muscle protein by exercise and hypoxia together.(3) It maybe the PKB/mTOR signaling pathway involved in IGF-1 and others pathway not involved in IGF-1 that exercise and hypoxia regulate mTOR signal.