Effects of Aerobic Training in Combination with Leucine Supplementation on Protein Metabolism in Skeletal Muscle of Pre-Senescent Mice

Objective: To investigate the effect and mechanism of aerobic training in combination with leucine supplementation on muscle protein synthesis and protein degradation. Methods: Thirteen-month-old male CD-1^® mice were randomly divided into sedentary control, aerobic training control, dietary leucine supplementation, and aerobic training in combination with leucine supplementation. Leucine was supplemented with 5% dosage. Mice in training group received 45 min swimming training with 3% body weight workload for 8 weeks (6 days/wk) . Protein content were measured with Bradford kit. The expression and phosphorylation rate of protein were determined by using Western blotting. The concentration of serum inflammatory cytokines were measured with ELISA kit. The profile of free amino acids in muscle was detected with an amino acids analyzer. The activity of chymotrypsin-like enzyme was determined by using fluorescence method. Results: Both aerobic training and 5% leucine supplementation did not change the body weight, and food intake. Myofibrillar, sarcoplasmic and total protein content, the phosphorylation rate of mTORSer2448, 4 E-BP1 Thr37/46, p70 S6 KThr389 and the expression of MHCⅡ were significantly elevated, while the expression of Ubiquitin, Atrogin-1 and Mu RF-1, and the concentration of pro-inflammatory cytokines in serum were decreased obviously. Besides, leucine supplementation induced a significant decrease of chymotrypsin-like enzyme activity, and increases of leucine, isoleucine and valine in skeletal muscle. The combination of aerobic training and leucine supplementation leaded more significant effects when in comparison with training or leucine supplementation alone. Conclusion: Moderate aerobic training in combination with 5% leucine supplementation promotes post-prandial protein synthesis in skeletal muscle of pre-senescent mice, and inhibits protein degradation, which may be correlated with elevated functional expression of mTOR-p70 S6 K/4 E-BP1 pathway and decreased activity of ubiquitin-proteasome system.