JSES - 2026-04-01 - Journal Article
Enthesis-related progenitors recruited from the subacromial bursa contribute to rotator cuff healing in rats.
Tanimura S, Tokunaga T, Kawakami J, Tian X, Goshogawa H, Tsuyama T, Karasugi T, Yamagata K, Miyamoto T
Topics
Key Takeaway
SAB-preserved rotator cuff repair achieved 2.1× higher ultimate load to failure at 3 weeks compared to SAB-resected repair (6.8 N vs. 3.3 N, P=.0004) in a rat supraspinatus transection model.
Summary Depth
Choose how much analysis to show on this article page.
Summary
This study investigated whether subacromial bursa (SAB) preservation affects enthesis progenitor cell recruitment and tendon-to-bone healing quality in a rat supraspinatus repair model using four surgical groups. Single-cell RNA sequencing identified PDGFRα+/CD34+ mesenchymal progenitors as the origin of Scx+ and Scx+/Sox9+ enthesis progenitors, with these cells localizing to the SAB layer in intact tissue and to the reparative enthesis after repair. SAB-preserved repairs demonstrated superior early biomechanical properties (ultimate load 6.8 vs. 3.3 N, P=.0004; ultimate stress 1.1 vs. 0.5 N/mm², P=.0001) and better collagen fiber orientation by second harmonic generation imaging at 3 weeks.
Key Limitation
The study evaluates only early healing endpoints (3 and 6 weeks) in rats, providing no data on whether the biomechanical advantage of SAB preservation persists through remodeling phases or translates to reduced retear rates.
Original Abstract
BACKGROUND
Understanding the origin and regulatory mechanisms of enthesis-related progenitor cells expressing scleraxis (Scx) and SRY-box-containing gene 9 (Sox9) may help develop therapeutic approaches to improve endogenous rotator cuff (RC) tendon-to-bone healing capabilities. This study explores the characteristics of Scx + /Sox9 + cells during RC healing. The effects of subacromial bursa (SAB) preservation on Scx + and Scx + /Sox9 + progenitor cell recruitment and the histological and biomechanical maturation of postoperative RC tendon-to-bone healing are evaluated in rats.
METHODS
Twelve-week-old wild-type Sprague-Dawley rats (n = 71) and ScxGFP transgenic rats (n = 6) underwent unilateral surgery for supraspinatus tendon repair immediately after transection. Four in vivo models were used: intact, SAB injury-only, SAB-preserved RC repair, and SAB-resected RC repair. Cells isolated from reparative entheses 1 week postoperative and intact entheses were analyzed via single-cell RNA sequencing. Progenitor marker (CD34, PDGFRα, Scx, and Sox9) expression was assessed by immunostaining. The SAB-preserved and SAB-resected RC repair groups were compared through histological and biomechanical analysis 3 and 6 weeks postoperatively.
RESULTS
Single-cell RNA sequencing identified 17 transcriptionally distinct cell clusters isolated from the intact and SAB-preserved groups. After reclustering the mesenchymal population, 4 distinct clusters were identified: Pdgfra +/ Cd34 + mesenchymal progenitors, tendon progenitors, Scx + tendon fibroblasts, and Scx + /Sox9 + enthesis progenitors. Lineage analysis revealed that Scx + and Scx + /Sox9 + cells differentiated from Pdgfra + /Cd34 + mesenchymal progenitors. In immunostained intact entheses, PDGFRα + and CD34 + cells were localized on the surface of the supraspinatus tendon, and humeral greater tuberosity in the area assumed to be the SAB layer. In reparative entheses, Scx + and Scx + /Sox9 + cells were within the reparative tissue between the bone and supraspinatus tendon, near the SAB, and sparser in the SAB-resected group. The second harmonic generation signal revealed that the SAB-resected group exhibited less collagen fiber orientation and inferior biomechanical properties. At 3 weeks postoperatively, the SAB-preserved RC repair group exhibited higher ultimate load to failure (SAB-preserved: 6.8 ± 1.9 N vs. SAB-resected: 3.3 ± 2.2 N, P = .0004) and ultimate stress to failure (SAB-preserved: 1.1 ± 0.4 N/mm 2 vs. SAB-resected: 0.5 ± 0.3 N/mm 2 , P = .0001).
CONCLUSIONS
During the RC repair process, Scx + and Scx + /Sox9 + enthesis-related progenitors may be associated with endogenous PDGFRα + and CD34 + mesenchymal stem/progenitors in the SAB near the tendon-bone repair site. SAB preservation positively impacts early histological and mechanical maturation after RC tendon-bone repair.