Expression and mechanism of N6-methyladenosine methylation-related factors in the repair of skeletal muscle injury in mice
Objective To investigate the dynamic expression with the time change of N6-methyladenosine(m6A)methylation-related factors in the repair process of skeletal muscle injury and its mechanism in the inflammatory response of macrophage in the injure process.Methods In vivo mice models of BaCl2 injury in the gastrocnemius were established.Four mice per group in the control group and injury group.Gastrocnemius tissues were harvested at day 1,3,5,7,and 9 after injury for experiments.Primary gastrocnemius muscle tissue cells,muscle satellite cells,muscle cells,and cell line C2C12 cells were treated with dexamethasone(DEX,50 μmol/L)to mimic injury.Lipopolysaccharide(LPS,100 μg/L)induced RAW264.7 cell lines to mimic the inflammatory response after skeletal muscle injury,and STM2457(30 μmol/L)was added to inhibit the effect of methyltransferase 3(Mettl3)before LPS treatment.The expression of m6A methylation-related factors(Writers,Erasers,Readers)and inflammation factors were detected by Real-time PCR and Western blotting.Results The muscle fibers were dissolved and then gradually repaired with the extension of injury time,the number of monocytes/macrophages increased first and then decreased,and the Pax7 mRNA level increased first and then decreased with the change of injury time.Compared with the control group,the mRNA and protein levels of m6A methylation-related factors in gastrocnemius did not change significantly on the injury-1 day.However,they were significantly increased on the injury-3 days compared with the control group(P＜0.05),and then obviously decreased on the injury-5 days group compared with the injury-3 days group(P＜0.05).Compared with the control group,they were no significant differences on the injury-7 days group and-9 days group.In vitro DEX decreased the mRNA levels of m6A methyltransferase factors in primary muscle satellite cells and C2C12 cells and increased the mRNA expression level of methylation-recognition enzyme factors(P＜0.05).The mRNA levels of m6A methylation-related factors increased significantly in skeletal muscle tissue cells and myocytes after DEX treatment(P＜0.05).After LPS treatment,the mRNA and protein expression levels of m6A methylation-related factors and the mRNA expression levels of inflammatory factors interleukin(IL)-6 and IL-1β in macrophages increased significantly(P＜0.05),while the levels of IL-6 and IL-1β mRNA in macrophages decreased significantly when the Mettl3 was inhibited(P＜0.05).Conclusion m6A methylation-related factors primarily is activated in the damaged muscle cells and inflammation response of macrophages.Inhibition of m6A methyltransferase can reduce the inflammatory response of macrophages.
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