Interleukin-10 alleviates inflammatory responses after acute tendon injury

Abstract

BACKGROUND: During the repair process following tendon injury, an excessive inflammatory response can cause tendon cell apoptosis, thereby leading to a reduction in the biomechanical properties of the tendon. Meanwhile, a persistent inflammatory response can also trigger tissue fibrosis and adhesion. Studies have confirmed that interleukin-10 exerts an inflammatory regulatory role in connective tissue cells such as fibroblasts and can block inflammatory responses produced in various models. OBJECTIVE: To explore the effect of interleukin-10 against inflammatory responses following acute tendon injury. METHODS: Forty-two Sprague-Dawley rats were randomly divided into a normal group (n=6), model group (n=12), control group (n=12), and intervention group (n=12). Except for the normal group, the other three groups underwent acute Achilles tendon injury modeling via intra-tendinous injection of type I collagenase solution (the model was successfully established after 3 days). On the day of modeling, the control and intervention groups were subjected to daily injections of PBS and interleukin-10 protein solution, respectively, at the 1 cm points on both sides of the hind limb midline and abdominal midline intersection. Injections were given once daily for 4 consecutive days. On day 3 after successful modeling, ultrasound examination of the Achilles tendon was performed. On days 3 and 7 after successful modeling, tissue samples were collected for hematoxylin-eosin staining to observe pathological changes, immunohistochemical staining to detect phosphorylated nuclear factor kappa B (p-NF-κB) and tumor necrosis factor alpha (TNF-α) protein expression, RT-PCR to detect NF-κB, TNF-α, and cyclooxygenase-2 (COX-2) mRNA expression, and western blot to detect p-NF-κB, TNF-α, and COX-2 protein expression. RESULTS AND CONCLUSION: Ultrasound showed that the model group had blurred tendon boundaries and increased thickness, while the intervention group had clearer boundaries and thickness close to normal. Hematoxylin-eosin staining on day 3 showed that the model and control groups had disordered collagen fibers, massive inflammatory cell infiltration, and round nuclei concentrated; the intervention group had reduced fiber disorder, fewer inflammatory cells, and more elongated spindle-shaped tenocytes. On day 7, the model and control groups showed significantly improved collagen fiber arrangement, reduced inflammatory infiltration, and tenocytes transitioning from round to spindle shape with mostly aligned nuclei; the intervention group showed parallel and orderly collagen fibers approaching normal, further reduced inflammatory infiltration, and mostly elongated spindle-shaped tenocytes. Immunohistochemistry showed that on days 3 and 7, the model group had higher p-NF-κB and TNF-α protein expression than the normal and intervention groups (P < 0.05). RT-PCR showed that on days 3 and 7, the model group had higher NF-κB, TNF-α, and COX-2 mRNA expression than the normal and intervention groups (P < 0.05). Western blot showed that on days 3 and 7, the model group had higher p-NF-κB, TNF-α, and COX-2 protein expression than the normal group (P < 0.05); on day 3, the intervention group had lower p-NF-κB, TNF-α, and COX-2 protein expression than the model group (P < 0.05). These findings indicate that interleukin-10 can alleviate inflammatory responses during acute tendon injury repair.

1. Introduction

When tendons are subjected to long-term overuse, excessive load, or repeated stretching, they undergo pathological changes in cells and extracellular matrix, including increased proteoglycan content and disruption of collagen fiber structure, leading to tendon injury. The injured tendon site exhibits pain, exudation, redness, and functional impairment, which are typical manifestations of early inflammatory responses. Moderate inflammation is beneficial for wound or tissue healing, but persistent inflammation can lead to excessive extracellular matrix deposition, tissue fibrosis, and inhibition of extracellular matrix-degrading enzymes, ultimately resulting in an imbalance between synthesis and degradation of the extracellular matrix and the formation of hypertrophic scars. Currently, treatment for inflammation in tendon injuries often involves oral non-steroidal anti-inflammatory drugs and corticosteroid injections, but long-term use of these drugs increases the risk of tendon rupture.

Interleukin-10 is one of the most studied anti-inflammatory cytokines. It inhibits the antigen-presenting capacity of antigen-presenting cells, thereby effectively suppressing the synthesis and expression of inflammatory cytokines and mediators, providing a finely tuned regulatory mechanism for the immune system. Studies have shown that IL-10 reduces the activity of nuclear factor kappa B (NF-κB) to block persistent inflammatory responses in dermal fibroblasts, thereby alleviating skin tissue fibrosis. KIERAN et al. demonstrated that IL-10 promotes skin soft tissue healing and reduces scar formation by inhibiting inflammatory responses. Based on this background, the authors hypothesized that IL-10 may also exert anti-inflammatory effects during tendon injury repair. Therefore, this experiment explored the effect of IL-10 on inflammatory responses after acute tendon injury, providing experimental and theoretical basis for clinical treatment of acute tendon injuries.