TGF-β3 regulates adhesion formation through the JNK/c-Jun pathway during flexor tendon healing

BACKGROUND: The injured flexor tendon has poor healing ability, which is easy to cause tendon adhesion. It can affect the recovery of tendon function, which is still a long-term and difficult task for surgeons. Transforming growth factor β (TGF-β) has been widely considered to play an important role in flexor tendon repair in recent years. AIM: This work was to investigate the anti-adhesion and anti-inflammatory effects of TGF-β3 on flexor digitorum longus (FDL) tendon repair rats. METHOD: Anastomosis models of tendon laceration in the flexion toes of rats were delivered with no treatment, vehicle, or TGF-β3 -overexpressed adenovirus vector (ad-TGF-β3) locally to the injured tendon area from day 3 to 8. Subsequently, the expression of TGF-β3, TGF-β1/2, Smad3, Smad7, JNK, phosphorylation (p)-JNK, c-Jun, and phosphorylation (p)-c-Jun were detected by western blot, the expression of Mmp9 and Mmp2 by RT-qPCR, the Range of motion (ROM) and gliding resistance by adhesion formation testing, the mechanical strength of tendon healing by biomechanical testing, the pathologic changes of flexor tendon tissues by HE staining, the expression of collagen type III by immunohistochemical staining, and the levels of IL-6, TNF-α, COX2 and IL-1β in serum by ELISA, respectively. RESULTS: Rat models treated with no treatment showed a lower elevation of TGF-β3 and Smad7 expression, and a higher elevation of TGF-β1/2 and Smad3 expression, during day 14 to day 28. Besides, under the treatment of ad-TGF-β3, a significantly increase was reflected in the expression of TGF-β3 and Smad7, ROM, as well as mechanical strength of flexor tendon, whereas significantly reduction was shown in gliding resistance, the content of inflammatory cytokines, the ratio of p-JNK/JNK, p-c-Jun/c-Jun, as well as the expression of TGF-β1/2, Smad3, Mmp9, and Mmp2 genes, as compared to those from vehicle treatment. Meanwhile, TGF-β3 demonstrated a better pathologic recovery process with no obvious necrosis or fracture of collagen fibers. Besides, TGF-β3 revealed a significant reduction of collagen type-III expression in the flexor tendon healing tissues. CONCLUSION: These findings suggested that TGF-β3 effectively protected against flexor tendon injury via regulating adhesion formation.