Research On Androgen And Exercise Regulating MTOR Pathway Of Skeletal Muscle Mediated By IGF-I

Objective:In the present study, we focused on the mechanism of androgen regulating mTOR pathway mediated by IGF-I, and investigated the changing characteristics and regular pattern of AR, MAPK pathway and mTOR pathway of skeletal muscle by exercise with various intensities and exogenous IGF-I and androgen.Methods:Experiment1:The following exercises were applied to male SD ratswith two different exercise intensities (20m/min and26m/min at10%slope) with fixed time (60mins). White gastrocnemius was isolated at time point of immediately,6and12hrs after exercise. Experiment2:Intramscular injection exogenous IGF-I was applied to male SD ratsand white gastrocnemius was isolated at time point of20,60and120mins after injection. Experiment3:Male SD rat were divided into the following four groups:control (S), exercise (E), subcutaneous(sc) implant of DHT (D), and combination of exercise and sc implant of DHT (ED). For DHT administration, each animal received an subcutaneous implant of a DHT-containing pellet (Innovative Research of America, Sarasota, FL), which was designed to deliver50mg5α-DHT over a period of21days. The others had sham operation. E and ED groups were applied following exercise(20m/min at10%slope,60mins). All groups were divided into groups(3days and10days). White gastrocnemius was isolated at12h after last exercise. The protein concentration of skeletal muscle was determined by BCA assay. The AR and IGF-I mRNA were analyzed by real-time fluorescence quantitative RT-PCR assay. The protein expression of MHC and the phosphorylation expression of AR, MEK, ERK, p90RSK, mTOR, p70S6K and4EBP1of skeletal muscle were examined by western blotting analysis.Results:1) The increase in phosphorylated of AR, MAPK pathway and mTOR pathway had intensity-dependent manner to acute exercise. The peak phosphorylation of MAPK pathway emerged at immediately after exercise, and AR and mTOR pathway at6h after exercise.2) The phosphorylated of AR were up--regulated by intramscular injection exogenous IGF-I, and the peak occured at60min after injection.3) The cross-sectional areas, wet weight and MHC of skeletal muscle were increased by sc implant of DHT-containing pellet. Exercise had synergetic enhancement effect on exogenous androgen on skeletal muscle.4) The content of musclar IGF-I was significantly increased by DHT in three days which had synergetic enhancement effect on musclar IGF-I combination of exercise.5) The phosphorylated of MAPK pathway and mTOR pathway were significantly increased by DHT.Conclusions:1) The increase on bioactivity of AR, MAPK pathway and mTOR pathway had intensity-dependent manner to exercise. The peak of MAPK pathway occured more early than the AR and mTOR pathway's.2) Androgen promoted muscular hypertrophy, so as the biosynthesis of musclar IGF-I. Exercise had synergistic effect of DHT on these effects. The bioactivity of AR, MAPK pathway and mTOR pathway could enhanced by IGF-I.3) MAPK pathway was one of upstreams signaling of mTOR pathway during nongenomic androgen actions of skeletal muscle.