Effects Of Endurance Exercise And HIIT On FoxO Ssignal Pathway And GDF8 Signal In Skeletal Muscle

Background and Objective:Different patterns of exercise have different effects on skeletal muscle mass,and skeletal muscle mass depends on the balance between skeletal muscle protein synthesis and breakdown.Forkhead transcription factor O(FoxOs)plays an important role in the skeletal muscle breakdown.It is believed that FoxOs can upregulate the ubiquitin ligases MAFbx/Atrogin-1 and MuRF1 which cause skeletal muscle atrophy directly.In addition myostatin(GDF8)and its receptor(Activin ? B)can inhibit skeletal muscle hypertrophy and also play an important role in the regulation of skeletal muscle mass.In general,high intensity endurance exercise is more effective than low/moderate endurance exercise to promote skeletal muscle hypertrophy.High-intensity Interval Training(HIIT)is a short-bout,highly effective exercise training that enhances cardiorespiratory endurance and skeletal muscle performance.This study aims to investigate the effects of two different exercise patterns on skeletal muscles mass and explored the changes of FoxOs signal pathways and GDF8/Activin?B.Material and Method:8-week-old young SD rats were randomly divided into normal sedentary control group(group N),moderate endurance exercise group(group M)and HIIT group(group H).Rats were housed under controlled temperature and lighting with free access to water and diets.Group M and group H used tail electrostimulation and manual drive to carry out treadmill exercise with a slope of 0.Both groups were trained six days a week and rest on Sunday.At the end of the experiment,all animals were fasted for12-16 h and 24 h after their last exercise.Rats were sacrificed by intraperitoneal injection of 20% wulaisu(5 ml/kg).The extensor digitorum longus muscle(EDL)and soleus muscles(SOL)of both sides of the rat were quickly removed and weighted.The cross-sectional area of skeletal muscle cells was calculated by hematoxylin-eosin(HE)staining.The gene expression and protein levels of FoxO1,FoxO3,MuRF1,MAFbx/Atrogin-1,GDF8 and Activin?B were detected by fluorescence quantitative PCR and western blotting respectively.All data were processed with SPSS16.0software and one-way analysis of variance was performed on each group of data(significant P<0.05).Result:1.Compared with normal rats,12-week moderate intensity endurance exercise increased the relative mass of rat SOL and EDL(p<0.05),and increased its cell cross-sectional area(p<0.05),but 12-week high-intensity interval training did not significantly affect the relative skeletal muscle mass and cell size(p> 0.05).2.Both 12-week moderate intensity endurance exercise and 12-week HIIT increased expression of FoxO1 mRNA in EDL(p<0.01),while FoxO3 mRNA significantly increased in EDL and SOL(p<0.05),but FoxO1,FoxO3 phosphorylated FoxO protein expression levels were not significantly changed(p>0.05);12-week moderate strength endurance exercise and 12-week HIIT increased MuRF1 mRNA expression in EDL(p<0.01),and was higher than the 12-week endurance exercise group.In the 12-week HIIT group(p<0.01),MAFbx mRNA had no significant changes in the EDL and SOL(p>0.05),and there was no significant change in the expression of MuRF1 and MAFbx protein(p>0.05).3.There was no significant change in the expression of GDF8 mRNA,ActivinIIB mRNA and protein in 12-weeks moderate strength endurance exercise and12-weeks HIIT(p>0.05).Conclusion:1.Compared with normal rats,moderate intensity endurance exercise at 12 weeks increase the relative mass of fast muscle,but 12 weeks HIIT has no significant effect.2.12-weeks moderate intensity endurance exercise and 12-weeks HIIT result in an increase of FoxO3 mRNA in skeletal muscle,and an increase of FoxO1/MuRF1 mRNA in EDL.