Introduction: Tendon injuries are among the most common and challenging orthopedic conditions. Many patients suffer from long-term pain and reduced function primarily due to an imbalanced healing response with excessive inflammation and inadequate regeneration. We found that extracellular vesicles produced by inflammation-primed adipose stem cells (iEV) can attenuate inflammation. It remains to be determined if iEV can also promote tendon regeneration and functional recovery and the cellular and molecular mechanisms of iEV action during tendon healing. Therefore, this study investigated the mechanistic roles of iEV in tendon healing using a mouse Achilles tendon injury and repair model combined with cell-based assays.
Methods: iEV were prepared from conditioned medium of IFNγ-primed adipose stem cell culture and applied locally in mice subjected to 2/3 right Achilles tendon transection and repair. Tendon responses were assessed using live bioluminescence imaging, ankle function test, and gene expression and histological analyses. iEV cargos and functions were determined via RNA-seq and Taqman PCR analyses and cell-based assays.
Results: iEV dose-dependently reduced injury-site NF-κB activity at 1-week post-injury (wpi) and increased anti-inflammatory gene expression at 4 wpi. iEV enhanced ankle function by 64%, reduced postoperative complications by 35%, and improved repair-site collagen deposition at 4 wpi. iEV also blocked macrophage TLR4/NF-κB signaling and promoted tendon cell proliferation, anabolic gene expression, and type I collagen release. Consistently, iEV were enriched in an anti-inflammatory miRNA that blocks macrophage NF-κB activity. iEV also carried substantial mRNAs that promote cell proliferation and survival. The combined results demonstrated that iEV can both reduce inflammation and promote tendon regeneration and the effects of iEV are associated with their abilities in inhibiting macrophage inflammatory response and promoting tendon cell proliferation and collagen production via transferring regulatory miRNAs and mRNAs.
Impact: This is a critical proof-of-concept study toward clinical application of EV-based therapy for tendon injuries, which will benefit millions of patients.
Organization – Washington University in St. Louis
Shen H, Lane R, Ray RB