| Objective: Skeletal muscle is an important exercise organ and tissue for glucose and lipid metabolism in the body.It is composed of two types of muscle fibers,including slow-twitch fibers with aerobic oxidative metabolism and fast-twitch fibers with glycolytic metabolism.The differences in mitochondrial homeostasis in different muscle fibers result in differences in muscle fiber morphology and function.The two types of muscle fibers have different responses to exercise.Slow muscle fibers mainly respond to aerobic exercise,while fast muscle fibers mainly respond to resistance exercise.There is a type switch between the two types of muscle fibers during exercise response,but the mechanism is still unclear.In this study,rat mixed muscles(gastrocnemius)were used as the research object.Aerobic exercise training models were established to activate slow-twitch fibers,and resistance exercise training models were established to activate fast-twitch fibers.From the perspective of the epigenetic modification of myosin heavy chain subtypes and mitochondrial homeostasis-related proteins,the biological differences of the two types of muscle fibers are explored,in order to initially reveal the biological mechanism of muscle fiber type conversion.Method: In this study,24 8-week-old Wistar rats were selected and randomly divided into the control group(C),aerobic exercise group(E),and resistance exercise group(R).The aerobic exercise group performed moderate-intensity treadmill training(20m/min)for 8 weeks,5 days a week,and the duration of each training session was 40 minutes.The resistance exercise group performed ladder training for 8 weeks,5 days a week,with one training session in the morning and afternoon each day,with 3 groups each,5 times in each group,and 1 minute rest between each group.The climbing gradient is 85°,and the initial weight-bearing is 20% of the rat's body weight,and the increase is 10% every two weeks,and the final weight is 50% of the rat's body weight.After the rats were sacrificed,the bilateral gastrocnemius muscles were separated,and the ratio of the two types of muscle fibers was detected by immunofluorescence;RT-PCR and Western-blotting methods were used to detect slow muscle fiber marker MYH7,fast muscle fiber marker MYH4,and mitochondrial biosynthesis expression of control factor PGC-1?,mitochondrial unfolded protein response master factor ATF5,mitochondrial autophagy-related factors PINK1 and BNIP3 at the transcription level and translation level;chromatin immunoprecipitation(Ch IP)method to detect myosin heavy chain subtypes and mitochondrial homeostasis-related protein coding H3K27me3 and H3K4me3 histone methylation modification levels at gene promoters.Results:(1)The difference in the ratio of slow-twitch and fast-twitch fibers after different sports training interventions.After aerobic exercise intervention,the content of type IIb muscle fibers corresponding to myosin heavy chain 4(MYH4)in rat skeletal muscle was significantly decreased(p<0.001),and the content of type IIb muscle fibers corresponding to myosin heavy chain 7(MYH7)in rat Gastrocnemius was significantly increased(p<0.001),suggesting a decrease in the ratio of fast muscles and an increase in the ratio of slow muscles.After resistance exercise intervention,the content of type IIb muscle fibers in the skeletal muscle of rats was significantly increased(p<0.001),and the content of type I muscle fibers in the skeletal muscle of the resistance exercise group was significantly decreased(p<0.001).In the skeletal muscle,the ratio of fast muscles decreases and the ratio of slow muscles increases.Compared with the aerobic exercise group,the content of type I muscle fiber in the skeletal muscle of the resistance exercise group was significantly decreased(p<0.001),and the content of type IIb muscle fiber was significantly increased(p<0.001).(2)Differences in gastrocnemius(mixed muscle)myosin heavy chain subtypes and mitochondrial homeostasis-related protein expression after different exercise training interventions After aerobic exercise intervention,the expression levels of MYH7,PGC-1?,PINK1,BNIP3 m RNA and protein in rat gastrocnemius increased significantly(p<0.05~0.001);ATF5m RNA levels increased significantly(p<0.05);MYH4 gene transcription level Significantly decreased(p<0.05).After resistance exercise intervention,the expression levels of MYH4 and PGC-1?m RNA and protein in the gastrocnemius of rats increased significantly(p<0.05~0.001);the level of BNIP3 m RNA increased significantly(p<0.05);the level of MYH7 m RNA decreased significantly(p<0.05)),but its protein expression level increased significantly(p<0.05).Compared with the aerobic exercise group,the expression levels of MYH7,PGC-1?,Pink1 m RNA and protein in the gastrocnemius of the resistance exercise group increased significantly(p<0.05~0.001);the expression level of BNIP3 protein decreased significantly(p<0.05));ATF5m RNA levels were significantly decreased(p<0.05);MYH4 gene transcription and protein expression levels were significantly increased(p<0.001;p<0.001).(3)Differences in epigenetic modification of gastrocnemius(mixed muscle)myosin heavy chain subtypes and mitochondrial homeostasis-related protein coding genes after different exercise training interventions After aerobic exercise intervention,the enrichment rate of promotive H3K4me3 on MYH7,PGC-1a,PINK1 and ATF5 promoters in rat gastrocnemius increased significantly(p < 0.01-0.001),while the enrichment rate of inhibitory H3K27me3 on MYH7,PGC-1a,PINK1 and BNIP3 promoters in rat skeletal muscle decreased significantly(p < 0.05-0.001).After the intervention of resistance exercise,the enrichment rate of promotive H3K4me3 on MYH4,PGC-1a,PINK1 and MYH7 promoters in rat gastrocnemius increased significantly(p < 0.05-0.01),while the enrichment rate of inhibitory H3K27me3 on MYH4,PGC-1a,PINK1 and BNIP3 promoters in rat skeletal muscle decreased significantly(p < 0.05-0.001).Compared with the aerobic exercise group,the enrichment rate of H3K4me3 promoted by the promoters of MYH7,PGC-1a,PINK1 and ATF5 in the gastrocnemius of the resistance exercise group was significantly decreased(p <0.05-0.001),while the enrichment rate of the inhibitory H3K27me3 on the MYH7 and PGC-1a promoters in the skeletal muscle of the rats was significantly increased(p < 0.05).The enrichment rate of H3K4me3 promoted by MYH4 promoter in rat gastrocnemius was significantly increased(p < 0.001),while the enrichment rate of inhibitory H3K27me3 was significantly decreased(p < 0.05).Conclusions: In this study,rat mixed muscle(gastrocnemius)was used as the research object.Aerobic exercise training was used to activate slow-twitch muscle fibers,and resistance exercise training was used to activate fast-twitch muscle fibers,and from myosin heavy chain subtypes and mitochondrial homeostasis-related protein histones.From the perspective of methylation modification,the biological differences between the two types of muscle fibers were discussed,and the following conclusions were initially obtained:(1)Aerobic exercise up-regulates the enrichment rate of type I muscle fiber heavy chain myosin MYH7 promoter H3K4me3(transcription activation effect),and down-regulates the enrichment rate of its promoter H3K27me3(transcription inhibition effect),thereby promoting the increase in the proportion of slow muscle fibers.Resistance exercise up-regulates the H3K4me3 enrichment rate of type IIb muscle fiber heavy chain myosin MYH4 promoter(transcription activation effect),and down-regulates the enrichment rate of its promoter H3K27me3(transcription inhibition effect),thereby promoting the increase of muscle fiber ratio.(2)Compared with resistance exercise,aerobic exercise has more significant effects on the up-regulation of mitochondrial homeostasis-related gene promoter H3K4me3 enrichment rate(transcription activation effect)and the down-regulation of H3K27me3 enrichment rate(transcription repressive effect).The two exercise modes may affect the expression of mitochondrial homeostasis-related proteins by regulating epigenetic modification to meet the metabolic needs of the two types of muscle fibers.(3)The above suggests that the epigenetic modification of histone methylation mediated by H3K4me3 and H3K27me3 is involved in the regulation of the difference in myosin heavy chain and mitochondrial homeostasis of slow-twitch and fast-twitch fibers. |
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