200 Section - Tissue-reparative hUC-MSCs Subpopulation Mediate Tendon Repair by Regulating Macrophages and Tendon Stem Progenitor Cells in the Injured Microenvironment

Achilles tendon rupture, characterized by limited regenerative capacity, significantly compromises motor function and quality of life. Human umbilical cord mesenchymal stem cells (hUC-MSCs) offer regenerative potential for tendon repair, but their functional heterogeneity and precise interactions with cells during healing remain poorly characterized, contributing to inconsistent therapeutic outcomes. This study aims to systematically investigate hUC-MSCs-mediated dynamic changes in cellular subpopulations during tendon repair, delineate the differentiation trajectories of reparative hUC-MSCs subpopulations, and elucidate their interactive mechanisms within the injury microenvironment.

Design:

This study established a rat model of Achilles tendon rupture to evaluate the therapeutic effects of hUC-MSCs. Multimodal assessments were performed on postoperative days 7, 14, and 28, including gait analysis, histopathological examination, and gene expression profiling to systematically evaluate immunomodulation, tendon regeneration, and extracellular matrix (ECM) remodeling. Single-cell RNA sequencing (scRNA-seq) was conducted to characterize dynamic cellular changes within the injured microenvironment and identify tissue-resident hUC-MSCs subpopulations with distinct molecular signatures.

Results:

hUC-MSCs transplantation promoted early and sustained functional recovery in rats with Achilles tendon rupture. Histopathological and single-cell analysis revealed that hUC-MSCs promoted macrophage polarization toward an anti-inflammatory phenotype, with decreased iNOS⁺ and increased CD206⁺ macrophages. Concurrently, hUC-MSCs enhanced tenocyte maturation, showing expanded Tppp3⁺Pdgfra⁺ tendon stem/progenitor cells (TSPCs) and Scx⁺ cells with organized alignment and improved collagen restructuring with elevated Tnmd, Fmod, and Thbs4 expression. Pseudotime analysis revealed that transplanted hUC-MSCs rapidly transitioned from proliferative towards tissue-reparative subpopulations within 4 days. Cell-cell communication analysis revealed that tissue-reparative hUC-MSCs specifically modulated macrophages and TSPCs via MDK-LRP1 and PDGFD-PDGFR signaling axes.

Conclusion:

This study delineates the microenvironmental cellular landscape during MSC-mediated Achilles tendon repair. We demonstrate that transplanted hUC-MSCs form dynamically evolving subpopulations during the healing process, and identify a specialized tissue-reparative hUC-MSCs subpopulation that coordinates tendon regeneration through dual regulation of macrophage polarization and TSPC differentiation.