[Study on anti-adhesion effect and mechanism of dynamic and static stress stimulation during early healing process of rat Achilles tendon injury].

Objective: To investigate the anti-adhesive effect and underlying mechanism of dynamic and static stress stimulation on the early healing process of rat Achilles tendon injury.

Methods: Achilles tendon tissues of 15 male Sprague Dawley (SD) rats aged 4-6 weeks were isolated and cultured by enzyme digestion method. Rat Achilles tendon cells were treated with tumor necrosis factor α to construct the Achilles tendon injury cell model, and dynamic stress stimulation (dynamic group) and static stress stimulation (static group) were applied respectively, while the control group was not treated. Live/dead cell double staining was used to detect cell activity, ELISA assay was used to detect the expression of α smooth muscle actin (α-SMA), and real-time fluorescence quantitative PCR was used to detect the mRNA expression of collagen type Ⅰ (COL1A1), collagen type Ⅲ (COL3A1), and Scleraxis (SCX). Thirty male SD rats aged 4-6 weeks underwent Achilles tendon suture and were randomly divided into dynamic group (treated by dynamic stress stimulation), static group (treated by static stress stimulation), and control group (untreated), with 10 rats in each group. HE staining and scoring were performed to evaluate the healing of Achilles tendon at 8 days after operation. COL1A1 and COL3A1 protein expressions were detected by immunohistochemical staining, α-SMA and SCX protein expressions were detected by Western blot, and maximum tendon breaking force and tendon stiffness were detected by biomechanical stretching test.

Results: In vitro cell experiment, when compared to the static group, the number of living cells in the dynamic group was higher, the expression of α-SMA protein was decreased, the relative expression of COL3A1 mRNA was decreased, and the relative expression of SCX mRNA was increased, and the differences were all significant ( P<0.05). In the in vivo animal experiment, when compared to the static group, the tendon healing in the dynamic group was better, the HE staining score was lower, the expression of COL1A1 protein was increased, the expression of COL3A1 protein was decreased, the relative expression of SCX protein was increased, the relative expression of α-SMA protein was decreased, and the tendon stiffness was increased, the differences were all significant ( P<0.05).

Conclusion: Compared with static stress stimulation, the dynamic stress stimulation improves the fibrosis of the scar tissue of the rat Achilles tendon, promote the recovery of the biomechanical property of the Achilles tendon, and has obvious anti-adhesion effect.