BACKGROUND:A high-load exercise can trigger the degradation of titin,leading to skeletal muscle damage.MyoD participates in skeletal muscle generation and plays an important role in the repair of skeletal muscle damage. OBJECTIVE:To observe the expression changes of MyoD,BMAL1 and titin in skeletal muscles at different times during a high-load exercise,as to clarify the role of MyoD and BMAL1 in exercise-induced skeletal muscle damage. METHODS:Twenty-four 8-week-old Sprague-Dawley rats were randomly divided into a control group(n=4)and an exercise group(n=20).Rats in the exercise group were subjected to downhill running(90 minutes).Soleus muscle samples were collected at 0,12,24,48,and 72 hours after exercise.The mRNA expressions of BMAL1 and MyoD were measured by real-time fluorescence quantitative PCR.The ultrastructure of skeletal muscle fibers was observed by transmission electron microscope.Immunofluorescence was used to observe the co-localization of MyoD and BMAL1 as well as BMAL1 and titin. RESULTS AND CONCLUSION:After the single high-load centrifugal exercise,the sarcomere of the soleus muscle was widened and the Z-line was blurred and water wave-like,both of which were most serious at 12 hours after exercise and basically recovered at 72 hours.The results of real-time fluorescent quantitative PCR showed that BMAL1 mRNA expression in the exercise group increased first and then tended to normal,while the mRNA expression of MyoD decreased first and then increased.Immunofluorescence co-localization observation indicated that the co-localization of BMAL1 and MyoD was obviously observed at 12 and 24 hours after exercise,and the co-localization of BMAL1 and titin was observed at 0,12,and 24 hours.All the findings indicate that MyoD and BMAL1 are jointly involved in the repair of exercise-induced skeletal muscle damage probably via titin.

Objective To explore the potential regulatory mechanism of resistance exercise in senescence accelerated-prone 8 mice(SAMP8)by evaluating the effects of exercise on the expression of long non-coding RNA(lncRNA)and mRNA in quadriceps muscles by RNA-sequencing(RNA-seq)technology.Methods Twenty-eight-week-old male SAMP8 mice were divided into a model group(M group)and resistance-exercise group(R group)(n=6 mice per group).Another eight normally aging SAMR1 mice of the same age were used as the control group(C group).Mice in R group received 8 weeks of increasing weight climbing exercise training.Relative grip strength was measured every week and the rotarod test was performed every 2 weeks.Histological changes in the right quadriceps femoris were observed by hematoxylin-eosin staining and the left quadriceps was used for RNA-seq.Differentially expressed lncRNA and mRNA were screened and analyzed for enrichment by Gene Ontology(GO)and Kyoto Encyclopedia of Genes and Genomes(KEGG)analyses.Finally,key differentially expressed genes were analyzed by quantitative reverse transcription-polymerase chain reaction to verify the accuracy of the RNA-seq result.Results(1)Relative grip strength and rotarod test time were significantly decreased in M group compared with C group(P＜0.01),but were significantly increased after 8 weeks of Rgroup compared with M group(P＜0.01).(2)The cross-sectional area of the muscle fibers was significantly lower in M group compared with C group,as shown by HE staining(P＜0.01),while the cross-sectional area of the muscle fibers was significantly increased in the R group compared with M group(P＜0.01).(3)Differential expression analysis identified 182 upregulated and 218 downregulated lncRNA,and 454 upregulated and 289 downregulated mRNA between M group and R group.The KEGG pathways of lncRNA target genes that were differentially expressed between M group and R group were significantly enriched in intestinal immune network for IgA production,nuclear factor-kappa B signaling pathway,and inflammatory bowel disease.Conclusions(1)This study demonstrated that resistance exercise can improve skeletal muscle function in SAMP8 mice with sarcopenia.We identified lncRNA and mRNA that were differentially expressed as a result of resistance exercise,and which might be potential targets of sarcopenia therapy.(2)Furthermore,analyzing the biological functions of the target genes of the differentially expressed lncRNA and mRNA may further our understanding of the mechanism of resistance exercise for improving sarcopenia.