Effects Of High-intensity Interval Training On Mitochondrial Quality Control Systems And Glucose Catabolism Related Enzymes In Skeletal Muscle Of Mice

Objective:The expression of proteins related to mitochondrial quality control system has an adaptive response to exercise training.It has been found that aerobic exercise can enhance the expression of mitochondrial function and related proteins.However,as for high-intensity interval training,There are few studies on the effects of HIIT on the proteins related to the mitochondrial quality control system(mitochondrial biogenesis,mitochondrial fusion,mitochondrial fission and mitophagy)in skeletal muscle of mice.During body exercise,sugar is the main energy substance,and the activity of enzymes related to glucose catabolism plays an important role in the performance of HIIT.The mitochondrial quality control system plays a key role in mitochondrial oxidative phosphorylation.In this study,the expression levels of proteins related to mitochondrial quality control system and enzymes related to glucose catabolism in skeletal muscle of mice were measured by HIIT at 6 weeks,and the expressions of oxphos-related genes NDUFS8,SDHb,Uqcrc1,COX5 b and Atp5 a in skeletal muscle of mice were detected.To investigate the effects of 6-week HIIT on mitochondrial quality control system related proteins,OXPHOS related genes and glucose catabolism related enzymes in skeletal muscle of mice.Method:Twelve C57BL/6J(male,7-week-old)mice were reared in cages,with 4 mice in each cage,and previously fed in the laboratory for one week to adapt to the new environment and reduce stress response.Then they were randomly divided into Control group(n=6)and HIIT group(n=6).Then,mice in group CON rested quietly for a week,and mice in group HIIT underwent adaptive training for 5 days a week before formal training: warm-up exercise for 10 minutes + HIIT for 5 groups,and training at a fixed time every day.Each group of HIIT was 6 minutes,with 4 minutes of high intensity(20m/min)and 2 minutes of low intensity(10m/min).After the adaptive training,formal training began for 6 weeks,5 days a week: 10 minutes warm-up exercise(10m/min)+10 sets of HIIT.At this time,each group of HIIT was performed for 6 minutes,4 minutes of high intensity(80-90% maximum speed)+2minutes of low intensity(40-50% maximum speed),and the training was performed for 1h at a fixed time every day.The test of maximum speed was conducted at three time points after the training of 0week,2week and 4week,to detect the change of the mice’s motor ability with the training intensity,and adjust the training program timely.In particular,the incline of the platform is 0 degrees for both adaptive training and formal training.In addition,blood samples from tail vein were collected immediately after 2week,4week,and 6week of training to detect blood lactate level.The mice were anesthetized 24 h after 6 weeks of exercise,and the quadriceps femoris muscle was taken on ice.Protein expression of PGC-1α,TFAM,NRF1,NRF2,MFN1,MFN2,OPA1,DRP1,FIS1,PARKIN,PINK1,CS,OGDH,SDHA,HK,LDHA,LDHB,GAPDH were detected by Western Blot,real-time PCR was used to detect the gene expression of Atp5a1,COX5 b,Uqcrc1,SDHb,NDUFS8 in skeletal muscle of mice.Results:(1)After 2,4 and 6 weeks,the blood lactic acid level of HIIT group was significantly higher than that of Control group(P<0.01),indicating that glycolysis may be the main energy supply for HIIT.(2)6 weeks of HIIT did not significantly increase the expression of MFN1,a mitochondrial fusion-related protein(P>0.05),but the expression of MFN2 was significantly increased(P<0.05)and OPA1 was highly significantly increased(P<0.01),suggesting that 6 weeks of HIIT may have an enhancing effect on skeletal muscle mitochondrial fusion.(3)6 weeks of HIIT significantly increased the expression levels of FIS1(P<0.01)and DRP1(P<0.01).These results suggest that 6 weeks HIIT may cause enhanced mitochondrial fision in skeletal muscle(4)6 weeks of HIIT significantly increased the expression level of mitochondrial biogenesis related protein NRF2(P<0.01),significantly increased the expression level of PGC-1α(P<0.01).There were no significant changes in TFAM and NRF1expression(P>0.05).These results suggest that 6 weeks HIIT may cause enhanced mitochondrial biogenesis in skeletal muscle.(5)6 weeks HIIT significantly decreased the expression level of mitophagy related protein PINK1(P<0.05),and very significantly reduced the expression levels of PARKIN(P<0.01),suggesting that 6 weeks HIIT may cause the decrease of mitophagy in skeletal muscle.(6)6 weeks HIIT had no significant effect on the expression levels of the glycolytic metabolizing enzymes HK and LDHB(P>0.05),but the expression level of LDHA was significantly reduced(P<0.05),indicating that the ability to convert pyruvate to lactate in skeletal muscle of mice was diminished.(7)6 weeks HIIT significantly increased the expression levels of oxygenation-related proteins CS,SDHA(P<0.01),but there were no significant changes in thr expression level of OGDH(P>0.05),suggesting that HIIT may improve the aerobic oxidation capacity of skeletal muscle in mice.(8)6 weeks HIIT had a highly significant increase in the gene expression levels of COX5b(P<0.01),Uqcrc1 and Atp5a1(P<0.05),and no significant effect on NDUFS8 and SDHb gene expression(P>0.05),suggesting that HIIT may enhance mitochondrial oxidative phosphorylation in skeletal muscle of mice at the genetic level.Conclusion:(i)HIIT promoted mitochondrial biogenesis,fission and fusion in skeletal muscle of mice,attenuated mitophagy and improved the mitochondrial quality control system.(ii)HIIT enhanced aerobic oxidation levels in skeletal muscle of mice.(iii)HIIT increased mitochondrial content and improved mitochondrial oxidative phosphorylation in skeletal muscle of mice.