Changes of fibrotic factors in the recovery process of skeletal muscle strain / 中国组织工程研究

ABSTRACT

BACKGROUND: Skeletal muscle injury is the most common sports injury, which can develop fibrosis and then impair muscle function. Varieties of fibrotic factors are involved in the repair of skeletal muscle and effectively regulate the process of tissue fibrosis. OBJECTIVE: To establish a rat model of acute gastrocnemius strain, observe the changes of fibrotic factors in the recovery of injury and explore the possible roles of fibrotic factors. METHODS: Totally 112 male Sprague-Dawley rats were randomly divided into control group (n=56) and injury group (n=56). The left gastrocnemius muscle was injured by a rat gastrocnemius pull-off device in the injury group. Each group was further subdivided into immediately group, 2 days group, 4 days group, 7 days group, 14 days group, 21 days group and 28 days group depending on the sampling time points. There were eight rats in each subgroup. The control group did not receive any intervention. The left gastrocnemius muscle of the injury group was strained by specialized equipment. Muscle fiber injury and inflammation were observed by hematoxylin-eosin staining. The expression of transforming growth factor β1 (TGF-β1), connective tissue growth factor (CTGF), matrix metalloproteinase-1 (MMP-1), and matrix metalloproteinase tissue inhibitor 1 (TIMP-1) were detected by western blot. The experiment was approved by the Sports Science Experimental Ethics Committee of Beijing Sport University. RESULTS AND CONCLUSION: Hematoxylin-eosin staining results showed that the muscle fibers of the gastrocnemius muscle arranged disorderedly and inflammatory cells were aggregated in the injury group. Compared with the control group, protein expression levels of TGF-β1 and CTGF significantly increased in the injury group from the 2nd day throughout the recovery (P 0.05). TIMP-1 expression significantly increased from the 7th day until the 28th day (P < 0.05). These findings indicate that TGF-β1/CTGF signal pathway may be successively activated during the recovery of skeletal muscle strain, triggering the occurrence and development of skeletal muscle fibrosis. Meanwhile, MMP-1 and TIMP-1 protein may be activated to participate in the recovery of injury.