Extracellular Vesicles from Inflammation-Primed Adipose-Derived Stem Cells Enhance Achilles Tendon Repair by Reducing Inflammation and Promoting Intrinsic Healing

Achilles tendon rupture is a common sports-related tendon injury. Even with advanced clinical treatments, many patients suffer from long-term pain and reduced function. These unsatisfactory outcomes result primarily from an imbalanced injury response with excessive inflammation and inadequate regeneration. Prior studies showed that extracellular vesicles from inflammation-primed adipose-derived stem cells (iEVs) can attenuate inflammation in the early phase of tendon healing. However, the effect of iEVs on tendon inflammation and regeneration in the later phases of tendon healing and the underlying mechanism remain to be determined. Accordingly, this study investigated the mechanistic roles of iEVs in regulating tendon response to injury using a mouse Achilles tendon injury and repair model in vivo and iEV-macrophage and iEV-tendon cell co-culture models in vitro. Results showed that iEVs promoted tendon anti-inflammatory gene expression and reduced mononuclear cell infiltration in the remodeling phase of tendon healing. iEVs also increased injury site collagen deposition and promoted tendon structural recovery. As such, mice treated with iEVs showed less peritendinous scar formation, much lower incidence of postoperative tendon gap or rupture, and faster functional recovery compared to untreated mice. Further in vitro study revealed that iEVs both inhibited macrophage inflammatory response and increased tendon cell proliferation and collagen production. The iEV effects were partially mediated by miR-147-3p, which blocks the toll-like receptor 4/NF-κB signaling pathway that activates macrophage M1 polarization. The combined results demonstrated that iEVs are a promising therapeutic agent, which can enhance tendon repair by attenuating inflammation and promoting intrinsic healing. Significance statement Using a clinically relevant mouse Achilles tendon injury and repair model, this study revealed that iEVs, a biological product generated from inflammation-primed adipose-derived stem cells, can directly target both macrophages and tendon cells and enhance tendon structural and functional recovery by limiting inflammation and promoting intrinsic healing. Results further identified miR-147-3p as one of the active components of iEVs that modulate macrophage inflammatory response by inhibiting toll-like receptor 4/NF-κB signaling pathway. These promising findings paved the road toward clinical application of iEVs in the treatment of tendon injury and other related disorders.