Abstract
Osteoarthritis (OA) represents a significant global health burden without a known disease modifying agent thereby necessitating pursuit of innovative therapeutic approaches. The infrapatellar fat pad (IFP) serves as a reservoir of mesenchymal stem/stromal cells (MSC), and with adjacent synovium plays key roles in joint disease affecting local inflammatory responses. Therapeutically, IFP-MSC have garnered attention for their potential in OA treatment due to their immunomodulatory and regenerative properties. However, optimizing their therapeutic efficacy necessitates a comprehensive understanding of how growth medium and inflammatory/hormonal priming influence their behavior. In this study, we isolated and expanded IFP-MSC in three different growth media: DMEM + 10% fetal bovine serum (FBS), DMEM + 10% human platelet lysate (HPL), and xeno-/serum-free synthetic (XFSF) medium. Subsequently, cells were induced with an inflammatory/fibrotic cocktail (TIC) with or without oxytocin (OXT). We evaluated various parameters including growth kinetics, phenotype, immunomodulatory capacity, gene expression, and macrophage polarization capacity. Our results revealed significant differences in the behavior of MSC cultured in different media. IFP-MSC cultured in HPL and XFSF exhibited superior growth kinetics and colony-forming abilities compared to those cultured in FBS. Furthermore, both HPL and XFSF media enhanced the expression of MSC markers (> 90%) and potentiated their immunomodulatory properties. Notably, XFSF-conditioned IFP-MSC demonstrated the highest attenuation of peripheral blood mononuclear cell (PBMC) proliferation, indicating their robust immunosuppressive capacity. Additionally, TIC priming further augmented the immunomodulatory functionality of MSC, with IFP-MSC exhibiting enhanced suppression of PBMC proliferation upon TIC priming. Of particular interest, gene expression analysis revealed distinct patterns in TIC + OXT induced MSC compared to TIC only induced, with upregulation of genes associated with immunomodulatory and regenerative functions. Furthermore, TIC + OXT priming promoted M2 polarization in macrophages, suggesting a potential therapeutic strategy for immune-mediated inflammatory joint conditions including OA. Our findings highlight the critical influence of growth medium and inflammatory/hormonal priming on MSC behavior and therapeutic potential. XFSF and HPL media offer promising alternatives to FBS, enhancing MSC growth and immunomodulatory properties. Moreover, TIC + OXT priming represents a novel approach to augment MSC immunomodulation and promote M2 polarization, providing insights into potential therapeutic strategies for OA and other immune-mediated inflammatory conditions.