Background:Though the mechanisms of skeletal muscle regeneration are deeply understood,those involved in muscle contusion,one of the most common muscle injuries in sports medicine clinics,are not.The objective of this study is to explore the mechanisms involved in muscle regeneration after contusion injury.Methods:In this study,a total of 72 mice were used.Eight of them were randomly chosen for the control group,while the rest were subjected to muscle contusion.Subsequently,their gastrocnemius muscles were harvested at different time points.The changes in muscle morphology were assessed by hematoxylin and eosin(HE) stain.In addition,the gene expression was analyzed by real-time polymerase chain reaction.Results:The data showed that the expression of many genes,i.e.,specific markers of immune cells and satellite cells,regulatory factors for muscle regeneration,cytokines,and chemokines,increased in the early stages of recovery,especially in the first 3 days.Furthermore,there were strict rules in the expression of these genes.However,almost all the genes returned to normal at 14 days post-injury.Conclusion:The sequence of immune cells invaded after muscle contusion was neutrophils,M1 macrophages and M2 macrophages.Some CC(CCL2,CCL3,and CCL4) and CXC(CXCL10) chemokines may be involved in the chemotaxis of these immune cells.HGF may be the primary factor to activate the satellite cells after muscle contusion.Moreover,2 weeks are needed to recover when acute contusion happens as used in this study.
