Potential function of Scx+/Sox9+ cells as progenitor cells in rotator cuff tear repair in rats

Suramin enhances proliferation, migration, and tendon gene expression of human supraspinatus tenocytes

Rotator cuff tendinopathy is a common musculoskeletal disorder with limited pharmacological treatment strategies. This study aimed to investigate tenocytes' functional in vitro response from a ruptured supraspinatus tendon to suramin administration and to elucidate whether suramin can enhance tendon repair and modulate the inflammatory response to injury. Tenocytes were obtained from human supraspinatus tendons (n = 6). We investigated the effect of suramin on LPS-induced inflammatory responses and the underlying molecular mechanisms in THP-1 macrophages. Suramin enhanced the proliferation, cell viability, and migration of tenocytes. It also increased the protein expression of PCNA and Ki-67. Suramin-treated tenocytes exhibited increased expression of COL1A1, COL3A1, TNC, SCX, and VEGF. Suramin significantly reduced LPS-induced iNOS, COX2 synthesis, inflammatory cytokine TNF-α production, and inflammatory signaling by influencing the NF-κB pathways in THP-1 cells. Our results suggest that suramin holds great promise as a therapeutic option for treating rotator cuff tendinopathy.

Aging negatively affects postoperative recovery of biomechanical strength through decreased recruitment of scleraxis+/SRY-box-containing gene 9+ enthesis-related progenitors after rotator cuff repair in rats

BACKGROUND

Although older adult patients have a higher retear rate after rotator cuff (RC) repair, the influence of aging on the healing process remains unclear. During mouse enthesis development, a multipotent progenitor coexpressing scleraxis (Scx) and SRY-box 9 (Sox9) contributes to enthesis formation. Scx+/Sox9+ cells may act as enthesis progenitors even during postnatal healing, and their number decreases with maturation. However, the pathophysiology of decreased RC healing ability due to aging remains unclear. We aimed to evaluate the effects of aging on tendon-to-bone healing after surgical RC repair in rats through biomechanical and histological analyses of Scx+ and Sox9+ progenitors in a ScxGFP transgenic rat model.

METHODS

This was a controlled laboratory study. Adult Sprague-Dawley rats (n = 111) underwent unilateral surgery for supraspinatus tendon repair immediately after transection. The rats were divided into aged (95 week old) and control (12 week old) groups. The effects of aging were assessed using biomechanical tests at 6 weeks postoperatively and histologically at 2 and 6 weeks postoperatively. ScxGFP transgenic rats were used for the immunohistochemical assessment of Scx- and Sox9-expressing progenitors during the repair process. Sox9, Scx, and tenomodulin expression was assessed using real-time reverse transcription polymerase chain reaction.

RESULTS

In the biomechanical test at 6 weeks postoperatively, the aged group had lower ultimate load to failure (control: 20.4 ± 6.1 N, aged: 14.9 ± 6.6 N, P = .007), stiffness (control: 16.1 ± 6.2 N/mm, aged: 12.6 ± 5.5 N/mm, P = .023), and ultimate stress to failure (control: 6.0 ± 3.4 N/mm2, aged: 3.4 ± 2.5 N/mm2, P < .001) than the control group. The total histological score of the aged group was lower than that of the control group at 6 weeks postoperatively (control: 8.8 ± 0.8, aged: 5.8 ± 0.4, P = .029). Immunohistochemistry tests showed that the percentages of Sox9+ (control: 6.6 ± 1.1, aged: 2.0 ± 1.0, P = .029) and Scx+/Sox9+ (control: 3.6 ± 0.8, aged: 1.1 ± 0.6, P = .029) cells at the reparative site were lower in the aged group than in the control group at 2 weeks postoperatively.

CONCLUSION

In a rat RC tendon-to-bone healing model, the decreased recruitment of Scx+/Sox9+ enthesis-related progenitor cells in the early phase may be associated with delayed reparative tissue remodeling in aging animals. These findings encourage the development of therapeutic strategies that biologically promote healing and reduce postoperative retears in older adult patients.

Optimizing Tissue Engineering for Clinical Relevance in Rotator Cuff Repair

Rotator cuff tear (RCT) is the most common cause of disability in the upper extremity. It results in 4.5 million physician visits in the United States every year and is the most common etiology of shoulder conditions evaluated by orthopedic surgeons. Over 460,000 RCT repair surgeries are performed in the United States annually. Rotator cuff (RC) retear and failure to heal remain significant postoperative complications. Literature suggests that the retear rates can range from 29.5% to as high as 94%. Weakened and irregular enthesis regeneration is a crucial factor in postsurgical failure. Although commercially available RC repair grafts have been introduced to augment RC enthesis repair, they have been associated with mixed clinical outcomes. These grafts lack appropriate biological cues such as stem cells and signaling molecules at the bone-tendon interface. In addition, they do little to prevent fibrovascular scar tissue formation, which causes the RC to be susceptible to retear. Advances in tissue engineering have demonstrated that mesenchymal stem cells (MSCs) and growth factors (GFs) enhance RC enthesis regeneration in animal models. These models show that delivering MSCs and GFs to the site of RCT enhances native enthesis repair and leads to greater mechanical strength. In addition, these models demonstrate that MSCs and GFs may be delivered through a variety of methods including direct injection, saturation of repair materials, and loaded microspheres. Grafts that incorporate MSCs and GFs enhance anti-inflammation, osteogenesis, angiogenesis, and chondrogenesis in the RC repair process. It is crucial that the techniques that have shown success in animal models are incorporated into the clinical setting. A gap currently exists between the promising biological factors that have been investigated in animal models and the RC repair grafts that can be used in the clinical setting. Future RC repair grafts must allow for stable implantation and fixation, be compatible with current arthroscopic techniques, and have the capability to deliver MSCs and/or GFs.