Extracellular Vesicle-Educated Macrophages Promote Early Achilles Tendon Healing

Abstract

Tendon healing follows a complex series of coordinated events, which ultimately produces a mechanically inferior tissue more scar‐like than native tendon. More regenerative healing occurs when anti‐inflammatory M2 macrophages play a more dominant role. Mesenchymal stromal/stem cells (MSCs) are able to polarize macrophages to an M2 immunophenotype via paracrine mechanisms. We previously reported that coculture of CD14+ macrophages (MQs) with MSCs resulted in a unique M2‐like macrophage. More recently, we generated M2‐like macrophages using only extracellular vesicles (EVs) isolated from MSCs creating “EV‐educated macrophages” (also called exosome‐educated macrophages [EEMs]), thereby foregoing direct use of MSCs. For the current study, we hypothesized that cell therapy with EEMs would improve in vivo tendon healing by modulating tissue inflammation and endogenous macrophage immunophenotypes. We evaluated effects of EEMs using a mouse Achilles tendon rupture model and compared results to normal tendon healing (without any biologic intervention), MSCs, MQs, or EVs. We found that exogenous administration of EEMs directly into the wound promoted a healing response that was significantly more functional and more regenerative. Injured tendons treated with exogenous EEMs exhibited (a) improved mechanical properties, (b) reduced inflammation, and (c) earlier angiogenesis. Treatment with MSC‐derived EVs alone were less effective functionally but stimulated a biological response as evidenced by an increased number of endothelial cells and decreased M1/M2 ratio. Because of their regenerative and immunomodulatory effects, EEM treament could provide a novel strategy to promote wound healing in this and various other musculoskeletal injuries or pathologies where inflammation and inadequate healing is problematic. Stem Cells 2019;37:652–662

Stem cell‐derived extracellular vesicles attenuate the early inflammatory response after tendon injury and repair

“…Our in vitro results further demonstrated that EVs can directly target macrophages and can block the inflammatory NF‐κB signaling in these cells. Consistent with these findings, a recent study showed that MSC‐derived EVs can drive macrophage differentiation toward the anti‐inflammatory M2 phenotype and that implantation of EV‐educated M2 macrophages can promote early tendon healing . In addition to macrophages, this study found that some ASC EVs were co‐localized with tenocytes near the injury center.…”

“…Although nearly all cells can produce EVs, the composition and function of EVs are cell‐type specific. MSC EVs from several origins including adipose tissue have recently been reported to modulate the macrophage inflammatory response and the function of MSC EVs may be further enhanced by priming MSCs with such inflammatory cytokine as interferon γ (IFNγ) . Therefore, EVs produced by ASCs may provide an alternative to ASCs as a new potent therapeutic agent for tendon injury.…”

Extracellular vesicles from rat-bone-marrow mesenchymal stromal/stem cells improve tendon repair in rat Achilles tendon injury model in dose-dependent manner: A pilot study

“…Higher concentrations of MSC-derived EVs performed better than low concentrations and better than MSCs alone. As already shown [9,10,11], three studies have already been published on this topic, but direct comparisons with the present investigations are difficult given the different focus. The three previous studies focused largely on inflammatory mechanisms, and used different methodologies and different types of injury over different time periods.…”

“…Cell-free delivery of bioactive cargos by EV induces the same beneficial responses as stemcell transplantation, offering remarkable benefits over conventional cell-therapy: for example, EVs avoid the risk of tumorigenesis, and heterotopic ossification and calcification [3,4] and are immunologically unresponsive agents [7,8]. Finally EVs play a role in tendon-healing by modulating inflammatory responses [9,10,11].…”

Extracellular Vesicles from Mesenchymal Stem Cells as Novel Treatments for Musculoskeletal Diseases

“…Another possible strategy consists of polarizing macrophages to an M2 phenotype by incubating these cells with EVs from human BM-MSCs. These M2 macrophages may increase angiogenesis and repair in the above model of tendon transection [155].…”