Equine Bone Marrow–Derived MSCs and Their EVs Exhibit Different Immunomodulatory Effects on Cartilage Explants in an In Vitro Osteoarthritis Model

Objective To compare the effects of equine MSCs and their extracellular vesicles (EV) on stimulated cartilage explants and assess how serum type influences EV production and cartilage inflammation. Methods EVs were isolated from bone marrow–derived MSCs cultured in equine serum (ES) or fetal bovine serum (FBS) media and concentrated via ultracentrifugation. Cartilage explants were stimulated with IL-1β and TNF-α and treated with MSCs, EVs, or left untreated. Cartilage explants were analyzed for cytokine concentration and examined for gene expression, glycosaminoglycan depletion, and histology. Results EVs produced by MSCs cultured in ES or FBS had similar characteristics. Cartilage explants treated with MSCs in ES media had decreased concentrations of IL-1β and increased concentrations of IL-6 in the supernatant compared to cartilage explants alone. Treatment with EVs did not significantly alter supernatant mediators. Cartilage explants cultured in ES had higher levels of IL-1β, IL-6, and TNF-α, while cartilage explants cultured in FBS had higher levels of PGE2. Treatment of stimulated cartilage explants with either MSCs or EVs did not alter gene expression or support extracellular matrix (ECM) degradation. Conclusion Equine MSCs appear to have enhanced immunomodulatory properties compared to EVs when used to treat stimulated cartilage explants. While some beneficial alterations in culture supernatants were detected, ECM degradation was not affected by treatment.