Priming-Dependent Modulation of Secretome in Placenta- and Adipose-Derived Mesenchymal Stromal/Stem Cells: Toward Cell-Free Immunoregenerative Therapies for Osteochondral and Degenerative Joint Diseases

Age-related joint diseases are driven by structural deterioration, chronic inflammation, and impaired regenerative capacity. Mesenchymal stromal/stem cells (MSCs) have emerged as promising therapeutic candidates due to their immunomodulatory and regenerative effects, largely mediated by their secretome and extracellular vesicles (EVs). However, the therapeutic efficacy of MSC-derived products depends on both the cell source and the conditioning stimuli to which MSCs are exposed. In this study, we characterized secretomes derived from placenta-derived MSCs (PDSCs) and adipose-derived MSCs (ASCs) by performing a comparative proteomic and exosomal microRNA (miRNA) profiling. Moreover, the impact of different priming strategies, including hypoxia, interferon-gamma (IFN gamma), and interleukin-1 beta (IL1 beta), on the paracrine properties of these cells was assessed. Proteomic analysis identified over 7,000 proteins, with PDSC secretome enriched in pathways related to osteogenesis, chondrogenesis, extracellular matrix organization, angiogenesis, and immune regulation, whereas ASC secretome displayed limited enrichment in these processes. Functional scoring highlighted IL1 beta priming as the most effective strategy to enhance osteochondral and immunomodulatory protein signatures in PDSCs. Differently, IFN gamma priming selectively expanded the repertoire of exosomal miRNAs, with enrichment in signalling networks including Wnt/beta-catenin, TGF-beta, NF-kappa B, and T cell receptor pathways, underscoring its role in fine-tuning immune and regenerative functions. Together, our findings revealed that PDSCs secrete a broader and more functionally relevant spectrum of bioactive molecules for osteochondral applications compared with ASCs. Moreover, distinct priming strategies showed to differentially regulate cell paracrine outputs. In particular, while IL1 beta primarily enhances protein-driven regenerative and immunomodulatory activity, IFN gamma promotes a functionally enriched exosomal miRNA cargo. These results indicate PDSC-derived secretomes as versatile candidates for next-generation, cell-free therapies in joint diseases.