Regulation of Tendon Repair with Stem Cell-Derived Extracellular Vesicles

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PROJECT SUMMARY/ABSTRACT Tendon and ligament injuries are among the most common and challenging orthopedic conditions. Many patients suffer from long-term pain and reduced function after injury. Substantial evidence indicates that these unsatisfactory outcomes result primarily from an imbalanced healing response with excessive and/or sustained inflammation and inadequate tendon regeneration. We discovered that extracellular vesicles produced by inflammation-primed adipose-derived stem cells (iEV) could potentially restore balanced healing by attenuating inflammation mediated by macrophages and stimulating regeneration driven by tendon cells. However, bulk iEV are heterogeneous. Differentially generated iEV carry different mRNA and microRNA molecules, which determine iEV functions. There is strong evidence that only a fraction of iEV carry the active molecules that balance the injury responses of macrophages and tendon cells, whereas many other iEV could potentially compromise tendon healing or cause unwanted side effects. Therefore, it is necessary to identify the iEV subpopulation and active cargo molecules specific for tendon repair and use them to develop disease-specific therapy to greatly enhance tendon repair. To achieve this goal, bulk iEV will be sorted into hierarchically organized subgroups based on vesicle generation and cargo sorting machineries that determine vesicle cargo composition. The subpopulation and active cargo molecules that specifically enhance tendon healing will be identified by their potency in regulating tendon cell and macrophage activities and functions. The therapeutic efficacy of identified iEV and cargo molecules for tendon repair will be examined in a preclinical mouse Achilles tendon injury and repair model. We anticipate that removal of functionally non-specific iEV or selective enrichment of functionally specific cargo molecules in bulk iEV will greatly increase the therapeutic efficacy and avoid potential adverse side effects of bulk iEV for tendon injury treatments. This study is a critical proof-of- concept analysis toward clinical application of extracellular vesicle (EV)-based therapy for tendon and ligament injuries, which will benefit millions of patients. This study also will discover the mechanism of iEV action for tendon injuries, and mechanisms underlying the molecular regulation of tendon cell and macrophage activities and functions. Knowledge gained about the active molecules, surface markers, and biogenesis of the iEV subpopulation specific for tendon repair will be used to increase the yield and release of these iEV by parent cells and scale up iEV production via immunoaffinity-based method. Our established approaches can be used for the future development of EV-based and disease-specific therapies for other medical conditions, which will improve the quality of life and outcomes of more patients.