Research On Mitochondrial Adaptation To Endurance Training Or Sprint Interval Training In Skeletal Muscle And Related Gene Response To Exercise Program

The insulin resistance syndrome (IRS)is a trait cluster composed of risk factors forthe future development of cardiovascular disease,obesity and/or type 2 diabetes.Impaired mitochondrial function is related to common insulin resistance in skeletalmuscle.Mitochondrial adaptation to long-term exercise training is redarded as a keyfactor for exercise to prevent cardiovascular disease,obesity and/or type 2 diabetes.Exercise-induced mitochondrial adaptations in muscle are highly specific and aredependent upon the type of exercise (i.e.resistance vs endurance)as well as itsintensity,frequency and duration.These adaptations include changes in mito-biogenesis,mito-fusion/fission,mitochondrial metabolism and ATP production.However,at the present time,most of the mechanisms underlying the mitochondrialadaptation of skeletal muscle to specific exercise still remain to be unclear.Little isknown about the regulatory factors directly modulating the expression ofexercise-responsive genes.Purpose:Exercise programs of endurance training and sprint interval training werefounded in the study,one of the purposes was to determine the molecular difference ofmitochondrial adaptations in muscle between the two training programs and providesome evidence for execise to prevent metabolic disease.Muscle disuse modelcharacterized by muscle unloading was also selected as a negative control group,another purpose was to investigate mechanisms underlying muscle disuse-inducedatrophy,and to support some conclusions about exercise adaptation.Methods:40 male Sprague-Dawley rats were distributed into four groups:sedentary(C,n=10),hindlimb suspension(D,n=8),sprint interval training(S,n=12)orendurance training(E,n= 10).Sprint interval training consisted of 9-10 repeats of a 10s"all out"treadmill test((?)42m/min)with 30-60s recovery between repeats,6 days/wk.Endurance training consisted of 30-60min of continuous treadmill exercise at a lowerintensity((?)16.7m/min)per day,6 days/wk.Group D were administered similarly toGroup C in the 1～5wk,hindlimb suspension was implemented in the 6～8wk bykeeping the rat's hindlimb 1～2cm away from the ground.After 8 weeks of eithersprint interval or endurance training,all rats were decapitated 24h after the lasttreadmill test.Blood was collected from heart,blood glucose,insulin,leptin andtriglyceride were detected.The content ofpyruvate and lactate,the enzyme activity ofhexokinase(HK),pyruvate kinase(PK)and malate dehydrogenase(MDH)ingastrocnemius homogenate were measured by spectrophotometric assays.Thecapacity of citrate synthase(CS)andβ-hydroxyacyl-CoA dehydrogenase(HCD)wasdetermined in mitochondrial extact from gastrocnemius.Real-time PCR was used todetermine the mRNA content of GLUT4,AMPKα2,PDK4,CPT-1β,PGC-1α,ERRα,NRF-2α,Mfnl,Mfn2,OPAl,Drpl,Fisl in gastrocnemius.Western blot was used todetermine the protein content of PDK4,CPT-1β,Mfn2,Drpl in mitochondria andPGC-1,ERRαin nuclear extract.ELISA was used to determine the content ofcytochrome c in mitonchondria and cytoplasm. Results:(1)Hindlimb suspension and exercise program in the study had no negative effects onphysiological homeostasis in an organism.However,endurance training decreasedblood triglyceride,sprint interval training and hindlimb suspension had no markedeffects on blood triglyceride,suggesting that endurance training differed in bloodtriglyceride from sprint interval training.(2)Both endurance training and sprint interval training increased pyruvate level inresting muscle,but it was only sprint interval training that increased lactate level inresting muscle,suggesting that sprint interval training activated anerobic metabolismin resting muscle.Hindlimb suspension and the two exercise programs in the studyhad no marked effects on the activities of HK,PK,MDH,mito-HCD,but sprintinterval training elevated the capacity ofmito-CS.(3)Endurance training in the study had no marked effect on mRNA content ofGLUT4,sprint interval training induced the upregulation of GLUT4mRNA.Endurance training in the study induced a downregulation of AMPKα2 mRNA,suggesting that AMPK signalling in resting muscle may be attenuated after endurancetraining.Endurance training in the study had no marked effect on mRNA and proteincontent of CPT-1,and induced a decrease only in PDK4mRNA.Sprint intervaltraining in the study induced a marked decrease in mRNA and protein content ofPDK4.Hindlimb suspension had a very similar effect to sprint interval training onregulating gene expression of PDK4,CPT-1.(4)Hindlimb suspension and the two exercise programs in the study had no markedeffects on NRF-2αmRNA.The synchronization of mRNA and protein content wasvery poor in PGC-1\ERRαgene expression.The two exercise programs in the studywere likely to induce a"labor-saving"transcription of PGC-1αand ERRor.PGC-1αprotein was in linear correlation with ERRαin nuclear extract.Hindlimb suspensionhad a very similar effect to endurance training on regulating mRNA transcription ofPGC-1/ERRα/NRF-2,and had a very similar effect to sprint interval training onregulating protein expression of PGC-1/ERRα.(5)Endurance training in the study upregulated Mfn1 mRNA,but Mfn2 kept silenceto endurance training in transcriptional level and mitochondrial localization.Sprintinterval training induced a decrease in Mfn2 mRNA and an increase in mito-Mfn2protein.Sprint interval training maybe increased the stability of Mfn2 mRNA andprotein,and induced a"labor-saving"transcription of Mfn2.The two exerciseprograms in the study had no marked effects on Fisl mRNA.Sprint interval traininginduced an increase in Drpl mRNA and a decrease in mito-Drpl protein,but DrplmRNA and protein expression kept silence to endurance training.(6)Hindlimb suspension induced an increase in cytoplasmic CytC and had no markedeffect on mito-CytC.Endurance training induced an increase in cytoplasmic CytC andmito-CytC,Sprint interval training induced an increase in mito-CytC and had nomarked effect on cytoplasmic CytC. Conlusions:(1)There may be an interdependent stability among blood glucose,insulin and leptin,exercise training maybe have positive effects on maintaining the interdependence.Ourdata indicated that sprint interval training might be used as an efficient program toenhance oxidative capacity and increase the conversion of pyruvate to lactate inresting muscle.(2)The downregulation of PDK4 protein maybe attenuate the inhibitory effect ofPDK4 on mitochondrial oxidation of carbohydrate and contribute to glycogenoxidation.These changes were a favorable metabolic adaptation to sprint intervaltraining.PGC-1 coordinated likely the activation of metabolic genes with ERRαinnuclei of muscle,sprint interval training in the study probably induced more intensivetranscriptional activation than endurance training.(3)Endurance training in the study had less effect on muscle glycogen oxidation andmito-fusion than sprint interval training.The latter exercise program could inducemito-fusin and decrease mito-fission.Elevation of mito-Mfn2 protein with decrease inmito-PDK4 and Drpl protein maybe enhance mito-fusion and glycogen oxidation inmuscle.The present data suggested that sprint interval training was more likely toincrease mito-fusion than endurance training.(4)Muscle disuse in the study might decrease myofiber number by apoptosis,notdecrease mitochondrial density in muscle fiber.Mitochondrial density and oxidativecapacity in muscle fiber maybe increased dramatically after endurance training.Sprintinterval training was more likely to prevent muscular apoptosis and atrophy andmaintain muscle mass than endurance training,gastrocnemius adaptation to sprintinterval training showed mixed and transitive.(5)The similarity between exercise-and disuse-induced muscle suggested that musclecells were not necessary to response dissimilarly to muscle overloading or unloading.Hindlimb suspension and sprint interval training in the study had much rnore intensiveeffects on mitochondrial homeostasis than endurance training.Endurance trainingcould be used as a better program to keep healthy homeostasis.Sprint interval trainingcould be used as a timesaving program to enhance mitochondrial function and preventmitochondrial related diseases.