HIIT/MICT Activated The Expression Of NAMPT During Mitochondrial Autophagy In Skeletal Muscle Of Rats With High Fat Diet

Objective:Long-term high-fat diet and physical inactivity can lead to the decrease of aerobic capacity of skeletal muscle and damage to mitochondrial homeostasis,thereby inducing a variety of chronic diseases.Exercise can regulate skeletal muscle mitochondrial homeostasis,maintain normal cellular and body functions,and affect skeletal muscle aerobic capacity,but the specific mechanism has not been fully elucidated.Nampt can maintain homeostasis by regulating mitochondrial autophagy in skeletal muscle and prevent the decrease of aerobic capacity of skeletal muscle.A large number of studies have found that both high intensity interval exercise（HIIT）and moderate intensity sustained exercise（MICT）can improve the aerobic working capacity of skeletal muscle,but the differences and similarities of their effects have not been reported.Therefore,this study to SD male rats as the research object,observe the HIIT and MICT efforts to prevent a high-fat diet rats skeletal muscle aerobic ability of different effect,and detect the expression of skeletal muscle AMPK,Nampt,which discuss long-term high fat diet led to the decrease of the skeletal muscle aerobic work ability and exercise regimens prevention effect of similarities and differences of the two possible mechanisms.Methods:After adaptive feeding for one week,5-week-old SD male rats（164.1±8.9g）were randomly divided into 4 groups:normal diet quiet group（CC group,n=8）,high fat diet quiet group（FC group,n=8）,high fat diet HIIT group（FH group,n=8）,and high fat diet MITT group（FM group,n=8）.All the normal feed and high fat feed were purchased from Liaoning Changsheng Biotechnology Co.,Ltd.FH and FM groups were not only fed with high-fat diet,but also received 12-week exercise intervention.FH group alternately exercised on the running platform with exercise intensity of 40%-45%V O₂max and 95%-99%V O₂max.In the FM group,the intensity of warm-up exercise was 40%-50%V O₂max,the intensity of continuous running on the platform was 70%V O₂max,and the intensity of recovery was40%-50%V O₂max.The movement distance of rats in FH group and FM group was ensured to be approximately equal.Before the formal exercise intervention,and after the 6th and 12th week of the intervention,the maximum exhaustive exercise time of the four groups of rats was tested respectively.During the experiment,food intake was measured daily and body weight was measured once every three days.The ultrastructure of mitochondria and autophagosomes in soleus muscle was observed by transmission electron microscopy after the12-week intervention experiment.The expression levels of Nampt and AMPK in rat soleus muscle mitochondria were detected by western blot.The citrate synthase activity test kit was used to detect the citrate synthase activity of rat soleus muscle.SPSS 20.0 was used for statistical analysis of the experimental data.Independent sample T test was used for comparison between CC group and FC group,one-way analysis of variance was used for comparison between FC group,FH group and FM group,and one-way Repeated analysis of variance was used for comparison between adjacent time nodes of the same group.P<0.05was the standard of significant difference,and P<0.01 was the standard of very significant difference.Results:1 There was no statistical difference in the initial body weight among all groups（P>0.05）,suggesting that the experimental rats were from the same sample group.At the end of the 12-week intervention experiment,the average body weight of rats in each group was statistically different,the average body weight of rats in the FC group was higher than that in the CC group,the difference was very significant（P<0.01）,and the average body weight of rats in the FH and FM groups was lower than that in the FC group,the difference was very significant（P<0.01）.There was no significant difference in average body weight between FH group and FM group（P>0.05）.During the 12-week intervention experiment,the weight of rats in each group increased,indicating that the experimental intervention did not affect the growth and development of rats.The weight gain rate of rats in CC group slowed down with time,and the weight gain reached 145.98%at the end of the experiment（P<0.01）.The trend of weight gain in FC group was the same as that in CC group,but the rate of weight gain was significantly higher than that in CC group,suggesting that high fat diet could accelerate the rate of weight gain in rats.The weight gain rate of FC group was significantly higher than that of FH group and FM group,suggesting that exercise could resist the rapid weight gain of excessive high-fat diet,and the weight gain of FC group reached 204.36%at the end of the experiment（P<0.01）.The change trend of Lee’s index and body weight of rats in all groups was the same.There was statistical difference in the initial food intake of rats in all experimental groups.The initial food intake of rats in FC group was higher than that in CC group,and the difference was very significant（P<0.01）,suggesting that rats had different preferences for ordinary diet and high-fat diet.The initial food intake of rats in FH group and FM group was lower than that in FC group,and the difference was significant（P<0.01）,suggesting that exercise intervention affected the appetite of rats in FH group and FM group for high-fat diet.There was no significant difference in the initial food intake between FH group and FM group（P>0.05）,suggesting that HIIT and MICT had the same effect on the appetite of rats.During the 12-week experiment,the total food intake of CC group was higher than that of FC group,and the total food intake of FC group was higher than that of FM group and FH group.The energy intake of rats in the FC group was significantly higher than that in the CC group（P<0.01）,suggesting that the rats had different preferences for the ordinary feed and the high-fat feed,and the energy density of the high-fat feed was higher than that of the ordinary feed.The energy intake of rats in FH and FM groups was lower than that in FC group,and the difference was significant（P<0.05）.It was suggested that exercise intervention affected the appetite of rats in FH group and FM group to high fat diet.There was no significant difference in thermal energy intake between FH group and FM group（P>0.05）,suggesting that HIIT and MICT had the same effect on appetite.During the 12-week experiment,the total energy intake of rats in FC group was higher than that in CC group,and the total energy intake of rats in FC group was higher than that in FH and FM group.2 During the whole experiment period,rats in all experimental groups underwent three tests of maximum exercise exhaustion time.The results before formal exercise intervention showed that the exercise ability of rats in CC group was lower than that of rats in FH group,and the difference was significant（P<0.05）,suggesting that the exercise ability of rats in CC group was poor,while that of rats in FH group was better.The results of two tests in the middle and late stages of exercise intervention showed that the exercise ability of rats in FC group was lower than that in FH group and FM group,and the difference was very significant（P<0.01）,suggesting that exercise intervention had an effect on the aerobic capacity of rats fed with high fat diet.There was no significant difference in exercise ability between the FH group and the FM group（P>0.05）,suggesting that there was no difference in the effect of HIIT and MICT.3 Transmission electron microscopy results of soleus muscle of rats showed that the accumulation degree of oil in FC group>CC group,FC group>FM group>FH group;About the number of mitochondria and their morphological integrity,the CC group>FC group,FC group=FM group>FH group;About the arrangement regularity and integrity of skeletal muscle filaments,CC group>FC group,FM group>FC group>FH group;In general comparison,CC group>FC group,FC group>FM group>FH group.Regarding the presence of autophagosomes,the CC group,FC group,FM group and FH group all had autophagosomes.The quality control of soleus mitochondria in the CC group was better than that in the FC group,suggesting that long-term intervention of high-fat diet and lack of physical activity resulted in the accumulation of soleus lipid and the reduction of mitochondrial morphology in the FC group.The quality control of soleus mitochondria in the FM group was better than that in the FH group,suggesting that the intervention effect of MICT was better than that of HIIT.4 The protein expression levels of Nampt and AMPK in CC group were significantly lower than those in FC group（P<0.01）,suggesting that high fat diet could promote the high expression of Nampt and AMPK.The protein expression levels of Nampt and AMPK in FH and FM groups were higher than those in FC group,and the differences were significant（P<0.01）,indicating that exercise promoted the high expression of Nampt and AMPK.The protein expression levels of Nampt and AMPK in the FM group were higher than those in the FH group,and the difference was very significant（P<0.01）,indicating that MICT had a better effect on promoting the high expression of Nampt and AMPK than HIIT.5 The results of citrate synthase activity showed that there was no significant difference in CS activity of soleus muscle among CC group,FC group,FC group,FH group and FM group（P>0.05）.The activity of CS in the soleus muscle of rats reflected the number of mitochondria in the soleus muscle of rats to some extent,and there was no significant difference in the number of mitochondria in the soleus muscle of rats in the CC group,FC group,FC group,FH group and FM group（P>0.05）.Conclusions:12 weeks of high-fat diet did not cause significant changes in aerobic capacity and CS activity,and the expression of AMPK and Nampt in soleus muscle increased compensatively,but mitochondrial homeostasis was disrupted.HIIT and MICT can be effectively prevented with different effects,and the mechanism may be that the two exercise programs further enhance the expression of AMPK and Nampt in skeletal muscle of high-fat diet rats,and regulate mitochondrial homeostasis,and MICT has a better effect.