Different anti-inflammatory effects of extracellular vesicles from adipose-derived mesenchymal stem cell or keratinocyte cell line on osteoarthritic cartilage

Background: Osteoarthritis (OA) is a joint condition associated with articular cartilage loss, low-grade synovitis and alterations in subchondral bone and periarticular tissues. In OA, the interest for mesenchymal stem cell (MSC)-EV therapeutic applications has increased. However, there is an increasing concern about the reproducibility of recent EV publications. We have assessed the immunomodulary properties of adipose-derived MSCs (AD-MSCs) microvesicles (MV) and exosomes (EX) in OA chondrocytes and compared their effects with EVs from a different biological source. Methods: AD-MSCs from abdominoplasty fat and immortalized keratinocytes (HaCaT) were cultured with appropriate media supplemented with EV free human serum. EVs were isolated from conditioned media by differential centrifugation and characterized by resistive pulse sensing. Cartilage explants and primary chondrocytes were obtained from knee specimens of advanced OA. Both were stimulated with interleukin (IL)1ß (10 ng/mL) and treated with MSC- or HaCaT-MV (3.6 x 107 particles (p)/mL) or EX (7.2 x 107 p/mL) for 24 h. Then, levels of IL-6, IL-10 and TNFα were measured. Results: RPS revealed distinct size and concentration EV signatures from AD-MSCs (MV: 317 ± 54 nm and 8 x 109 p/mL; EX: 151 ± 27 nm and 4 x 1010 p/mL) or HaCaT (MV: 281 ± 2 nm and 7 x 1010 p/mL; EX: 105 ± 1 nm and 1.1 x 1012 p/mL). MSC-EV treatment of OA cartilage explants and chondrocyte cultures reduced the inflammatory cytokines IL-6 and TNFα with respect to those solely stimulated IL-1β. The anti-inflammatory cytokine IL-10 increased with respect to explants or cells solely stimulated with IL-1β. On the contrary, the levels of the same cytokines were not affected by treatment with HaCaT-EVs. Summary/Conclusion: Administration of EV may have potential pharmacological applications in OA. However, experimental procedures to avoid data artefacts are currently lacking; in this regard, the use of nonrelated EVs as negative controls has proven useful. Interestingly, cell line HaCaT EVs had less deviation in size, and were obtained in higher concentrations, compared to EVs from primary cell cultures. Further studies on EV properties may lead to new and more specific therapeutic targets based on the interaction between AD-MSC-EVs and cells.