Effect Of Exercise Training On Autophagy Of Skeletal Muscle In Naturally-Aged Mice And Its Association With Sarcopenia

Objective: This study aims to investigate the relationship between autophagy and senile muscular atrophy in 10-month-old SPF KM mice under the conditions of natural rearing,and exercise intervention such as ladder-climbing ladder exercise with same intensity;to explore the effect of exercise intervention on the regulation of autophagy signal pathway in the improvement of senile amyotrophic atrophy(sarcopenia),and to validate the determinant role of autophagy functional status in the regulation of sarcopenia;and to provide the reference or basis for the elderly to improve their quality of life through scientific exercise training.Methods: Thirty-two 10-month-old male KM mice were randomly divided into three groups including senior control group(SC group),senior ladder-climbing group(SL group),and senior chloroquine administration group(CQ group),and chloroquine administration plus ladder-climbing group(CQL group).Each group has 8 mice.In addition,8 young mice at the age of 3 months were used as the young control group(YC group).The mice from CQ and CQL groups were intraperitoneally injected with CQ at the dose of 40 mg/kg each day;The mice from SL and CQL groups were subjected to 8-week ladder-climbing exercise intervention with 3 times each week.After exercise intervention for 24 hours,all mice were sacrificed.The histological changes in skeletal muscles of all mice were observed by HE staining and TUNEL staining.The expression of Bcl-2,Beclin1,p62 and LC3 proteins associated with autophagy was evaluated by Western blot.Results:1.Compared with YC group,the gastrocnemius muscle wet weight ratio of the mice from SC group was significantly decreased(p < 0.01),while the ratio between the skeletal muscle weight of the mice from SL group was significantly higher than that of the mice from SC group(p < 0.01).The ratio between gastrocnemius muscle weight and body weight of the mice from CQ group was significantly decreased(p < 0.001).Compared with CQ group,the gastrocnemius muscle wet weight ratio of the mice from CQL group still showed a downward trend,and there was no significant difference.2.HE staining: compared with YC group,the atrophied cells in skeletal muscle of themice from SC group revealed an obvious increase,while the number of atrophied cells in skeletal muscle of the mice from SL group was lower than that of SC group;at the same time,compared with YC group,the muscle atrophy and translocation of the cells in mice from CQ group exhibited a significant increase.In contrast,compared with CQ group,the number of nucleus migration in skeletal muscle of the mice from CQL group was decreased.3.TUNEL staining: Compared with YC group,the number of positive cells in skeletal muscle of the mice from SC group increased,while the number of positive cells in skeletal muscle of the mice from SL group decreased when compared with SC group;meanwhile,compared with YC group,the number of positive cells in skeletal muscle of the mice from CQ group still increased;in contrast,compared with CQ group,the number of positive cells in skeletal muscle of the mice from CQL group did not decrease.4.Western blot results: Compared with YC group,the expression of Beclin1 and Bcl-2 in skeletal muscle of the mice from SC group was significantly decreased(p < 0.01),and the expression of p62 was significantly increased(p < 0.001),although LC3-II/LC3-I ratio did not reveal obvious change;compared with SC group,the expression of Beclin1 and Bcl-2expression in skeletal muscle of the mice from SL group was significantly increased(p <0.001),but the expression of p62 and LC3-II/LC3-I ratio was significantly decreased(p <0.001)(p < 0.001).Compared with YC group,the expression of Beclin1,Bcl-2 and LC3-II/LC3-I ratio in skeletal muscle of the mice from CQ group was significantly decreased(p < 0.001),and p62 expression was significantly increased(p < 0.05);compared with CQ group,CQL group revealed the lower level of Bcl-2 expression in rat skeletal muscle(p < 0.001),significantly increased p62 expression(p < 0.001),reduced Beclin-1expression(p < 0.001),and decreased LC3-II/LC3-I ratio.Conclusion:1.The 12-month-old KM mice revealed the enhanced apoptosis and inhibited autophagy of skeletal muscle cells,thereby inducing the atrophy of skeletal muscle.2.Exercise training such as ladder-climbing exercise intervention can effectively activate autophagy of skeletal muscle cells,thereby alleviating the atrophy of skeletal muscle.3.Once autophagy signal pathway is blocked,exercise training does not accomplish autophagy activation of skeletal muscle cells to alleviate skeletal muscle atrophy;in contrast,exercise training can partially aggravate the atrophy of skeletal muscle.In summary,moderate exercise intervention can activate autophagy of skeletal muscle cells,inhibit apoptosis and protein degradation,maintain skeletal muscle mass,alleviate the occurrence of sarcopenia.On the other hand,exercise training can aggravate the atrophy of skeletal muscle in the presence of drug-induced or gene-induced deficiency of autophagy.These studies provide a novel direction for exploring the function status of autophagy in the prevention of aging-associated diseases such as sarcopenia and health promotion as well as the enhancement of quality of life.