Effects Of Cell-Free Conditioned Media on Healing of Rat Achilles Tendon

Tendon injuries are common musculoskeletal conditions that impose significant challenges to medical professionals, pain and debilitation of patients, and financial burdens to the healthcare system. Due to limited natural healing capacity, tendons typically undergo scar-mediated repair that compromises biomechanical integrity and increases the risk of reinjury. Despite a variety of therapeutic strategies, functional tendon healing remains a major clinical challenge. Mesenchymal stem cells (MSCs) represent an attractive strategy to improve tendon healing, largely due to their paracrine activity via the release of the secretome, a set of bioactive molecules that are known to mimic the immunomodulatory and regenerative properties of their parental cells. More recently, acellular approaches using MSC-secretome derivatives, including conditioned media (CM) and exosomes, have been largely explored for tendon healing. This work begins with a review of the literature surrounding the therapeutic potential of MSC secretome to improve tendon healing, highlighting advantages of MSC secretome over MSC-based therapies, proposed mechanisms of action, manufacturing considerations, and the current state of research. Building on this foundation, it then evaluates the effects of CM derived from TGFβ-3-primed tendon stem cells (TSCs) in an acute rat Achilles tendon injury model. In vitro, CM from TGF-β3-primed and unprimed TSCs was profiled by proteomics and functionally characterized using cell proliferation/viability and immunofluorescence assays. In vivo, the effects of CM on Achilles tendon healing were assessed via intralesional administration of CM, blended with fibrin gel for controlled delivery, in a rat Achilles tendon injury model. Overall, TGFβ-3 priming of TSCs produced a matrix-organizing secretome that accelerated tenogenic marker expression in vitro, provided cytoprotection under nutrient stress conditions, and improved gross tendon repair quality in vivo.