Study On The Effect And Mechanism Of Eccentric Exercise On Protein Synthesis Of Skeletal Muscle

Objective:To explore the effect and potential mechanism of eccentric exercise on skeletal muscle protein synthesis.Methods:Twenty-four 3-month-old Sprague Dawley（SD）rats were randomly divided into blank control group（Control,C,n=8）,2-week downhill eccentric exercise group（2 Weeks Exercise,2E,n=8）and 4-week downhill eccentric exercise group（4 Weeks Exercise,4E,n=8）.After adaptive training,rats were given 2 or 4weeks of formal downhill running eccentric exercise intervention.The exercise program was:slope-16°,running speed 16 m/min,training time 90 min,training 5days a week.The rats in group C were not arranged to exercise,but allowed to move freely.All rats in the exercise group were killed 48 hours after the last training and the gastrocnemius muscle was taken.The co-localization and quantity of Lamp2-mTOR were detected by immunofluorescence double labeling method,the protein expression of MHC Ⅱb and LRS and the phosphorylation rate of mTOR^Ser2448,p70S6K^Thr389and4E-BP1^Thr37/46were measured by protein immunoblotting method,the protein synthesis rate of gastrocnemius muscle was measured by purinomycin surface labeling translation method,and the cross-sectional area and diameter of muscle fibers were measured by H&E staining.Results:Compared with group C rats,the total protein content,myofibril protein content,sarcoplasmic protein content,gastrocnemius protein synthesis rate,fiber cross-sectional area and diameter of gastrocnemius muscle and gastrocnemius weight in group 2E and 4E rats showed an upward trend,and the differences between groups were statistically significant;The protein expression of MHC Ⅱb and LRS,the amount of co-localization of Lamp2 and mTOR,and the phosphorylation rate of mTOR^Ser2448,p70S6K^Thr389and 4E-BP1^Thr37/46were all increased,and the difference between groups was statistically significant.Similar changes were also observed in the comparison between 4E group and 2E group.Conclusions:（1）eccentric exercise can promote the protein synthesis of gastrocnemius muscle,and the effect of relatively long training period is more significant in the short-term exercise period;（2）eccentric exercise can up-regulate the expression of LRS,thus promoting the translocation of mTOR to lysosomal membrane and activation,and up-regulate the rate of protein synthesis through mTOR-p70S6K-4E-BP1 signal transduction pathway,thus inducing adaptive skeletal muscle hypertrophy response.