Hypoxic Training-mediated Autophagy Benefits For The Control Of Body Weight And Improvement Of Swimming Performance Of Mice

Objective: Hypoxic training is an effective strategy for exercise training. The stimuli under the low-oxygen environment combined with regular exercise training or regular physical activity can stimulate a series of physiological responses to adapt to hypoxic conditions, thus achieving the optimization of body compositions, the enhancement of muscle adaptation to exercise, and the improvement of exercise performance. In the present study, we have adopted the method of “Living high-training low” and established a hypoxic carbin with oxygen concentration of 15%( 2500 m environment above sea level) for mice to explore the effect of living in hypoxic environment and training in normoxic environment on exerice capacity and its underlying molecular mechanisms.Methods: Totally 60 Kunming mice with the age of 8 weeks old were randomly divided into normoxia control(NC), normoxia exercise(NE) and hypoxia exercise(HE) groups with20 mice in each group. The mice from NE group were subjected to the living and swimming training under the environment with normal oxygen concentration, but the mice from HE group were provided with the living in a carbin with oxygen concentration of 15% coupled with swimming training at normal oxygen condition. These mice were provided with swimming training from Monday to Friday according to the designated time for 45 min each day within 5 days a week. The mice from NC groups lived in the normal oxygen environment without swimming training as the control. After 8 weeks swimming training, some mice of each group were randomly selected for the exhaustive swimming to evaluate their exercise capacity. The other mice were sarficed immediately, and the blood, myocardial, soleus and gastrocnemius samples were harvested to determine SOD activity and MDA content through ELISA, and evaluate the expression of autophagy-related proteins such as Beclin1, p62, LC-3,AMPK and p-AMPK as well as the expression of anti-apoptotic protein such as Bcl-2 through Western blotting.Results:1. Compared with NC group, the body weights of the mice from HE and NE groups revealed a significant decrease(P < 0.05). Meanwhile, the average body weight of the mice from HE group was much lower than that from NE group(P < 0.05).2. Compared with NC group, the exhaustive swimming time of the mice from HE and NE groups was significantly prolonged(P < 0.05). Similarly, the exhaustive swimming time of the mice from HE group was significantly longer than that from NE group(P < 0.05).3. Compared with NC group, the SOD activity in soleus and gastrocnemius of the mice from NE and HE groups revealed a significant enhancement(P < 0.05), and the SOD activity in soleus and gastrocnemius of the mice from HE group exhibited more enhancement(P < 0.05); on the other hand, the MDA contents in soleus and gastrocnemius of the mice from NE and HE groups were significantly reduced.4. Compared with NC group, the SOD activity in myocardium of the mice from NE and HE groups was also significantly higher(P < 0.05), but no significant difference in MDA content in myocardium of the mice from each group was observed.5. Compared with NC group, AMPK, p-AMPK, Beclin1, LC3-I, LC3-II and LC3-II/LC3-I in myocardial, soleus and gastrocnemius samples revealed a significant up-regulation(P < 0.05), and the expression of these proteins in these samples from HE group exhibited more obvious up-regulation when compared with NE group(P < 0.05).Similarly, compared with NC group, the expression of p62 in HE and NE groups was significantly reduced(P < 0.05), with the more reduction in HE group when compared with NE group(P < 0.05).6. Compared with NC group, the expression of Bcl-2 in soleus and gastrocnemius samples from HE group was significantly increased(P < 0.05). However, the expression of Bcl-2 protein only in myocardial and soleus samples from NE groups was higher than that in NC group(P < 0.05).Conclusion: Appropriate hypoxic exposure coupled with regular exercise training could effectively realize the loss or control of body weights, the optimization of body compositions and the enhancement of muscular adaptation to exercise as well as the improvement of exercise capacity. Correspondingly, all of these functional improvements are highly required for the activation of autophagy, which is benefit for the metabolism and utilization of energy,the clearance of metabolic wastes, and the maintanence of cellular homostatsis. Moreover,hypoxic exposure has an obvious synergistic effect on exercise training.