A Study On Changes Of Pericyte Number In Relation To Posttraumatic Interval During Repair Of Skeletal Muscle Contusion In Mice

Objective:Skeletal muscle contusion is one of the most common types of soft tissue injuries in human body on forensic practice.Healing of injured skeletal muscle is a multi-factor regulated inflammatory healing process.Pericytes promote post-natal myofiber growth.Transplanted pericytes can spontaneously fuse together with myoblasts to form myotubes and participate in muscle regeneration in skeletal muscle injuries and diseases.It is still unclear whether there is a definitely expression pattern for pericytes after injury of skeletal muscle.It is possible to provide a new candidate to wound age estimation in skeletal muscle and new thoughts on skeletal muscle therapies by investigating the time-dependent expression of pericytes after skeletal contusion.Methods:An animal model of skeletal muscle contusion was established in C57B6/L male mice.Samples were taken at 1,3,5,7,9,14,28 days post-injury,respectively(5mice in each posttraumatic interval).Morphological and number changes of pericytes were investigated by multiple immunofluorescence staining.Data were expressed as mean±standard deviation(?±)with Ratio test and analyzed using GraphPad Prism6.0 software.The one-way ANOVA followed by Tukey test and Fisher's exact test were used for data analysis between two groups.Difference associated with P<0.05 was considered as statistically significant.Results:1.In sections stained with H-E,hemorrhage,edema and degeneration were observed in mice contused skeletal muscles.2.Double indirect immunofluorescence analyses for NG2 and PDGFR?showed apparent ballooning of pericytes from 1 day post-injury compared to normal skeletal muscle pericytes in mice.In the central contusion area,a large number of NG2~+/PDGFR?~+newly born myotubes can be observed.There is a time-dependent express of pericytes'number after skeletal muscle contusion and it has a unimodal distribution as the injury time increases.The number of pericytes in central contusion area peaked at 5 days post-injury,while the ratio of pericytes in central contused area peaked at 5 and 7 days post-injury.In adjacent contused area,number of pericytes peaked at 5 and 7 days post-injury and the ratio of pericytes peaked at 7 days post-injury.3.Triple indirect immunofluorescence analyses for NG2,PDGFR?and Pax7 of MyoD1 showed partial pericytes in contused area express the marker of satellite cells,Pax7 or MyoD1.Conclusion:1.The number of pericytes varies time-dependently after skeletal muscle contusion and might be a potential parameter for muscle wound age estimation on forensic practice.2.Part of pericytes were found to express satellite cell markers and considerable number of newly born myotubes were detected to express pericytes markers,suggesting that pericytes might be involved in formation of myotubes during repair of muscle injury.