Secretome from human placenta-derived mesenchymal stem cells repairs mechanically induced meniscus injury in mice by activating the proliferation and suppressing the apoptosis of endogenous meniscus progenitor cells.

BACKGROUND: Meniscus diseases present certain therapeutic limitations. Although meniscectomy is the primary treatment option for meniscus injury (MI), this approach may accelerate the development of osteoarthritis and other degenerative joint diseases, and its therapeutic efficacy remains controversial. While human mesenchymal stem cells (MSCs) have emerged as a promising treatment option for MI, particularly in promoting cell proliferation and preventing apoptosis, their effect on activating endogenous meniscus progenitor cells (MPCs) to ameliorate MI and the underlying mechanisms remain unclear. METHODS: The secretome was collected from human placenta-derived MSCs (pcMSCs). A cellular model of MI was established by challenging mouse MPCs with H2O2. Male C57BL/6 mouse model of MI was established by mechanically destabilizing the medial meniscus (DMM). Protein expression was analyzed through Western blotting, flow cytometry, and immunohistochemistry staining. After secretome administration, behavioral activity was assessed through gait analysis and rotarod tests. Key secretome factors were identified through cytokine arrays and microRNA (miRNA) analysis. RESULTS: The pcMSC secretome significantly mitigated MI in both cellular and mouse models, as indicated by gait analysis (P < 0.05), rotarod tests (P < 0.01), histological analysis (safranin-O staining, P < 0.001), and immunohistochemical staining for apoptosis marker (Caspase-3) and MPC proliferation markers (Gli-1, Sca-1, and Ki67). Cytokine arrays revealed several factors associated with immunomodulation (MCP1 and MCP3), regeneration and angiogenesis (IGF-1, ANG, and VEGFA), osteogenesis (OPG and OPN), and extracellular matrix preservation (TIMP1 and TIMP2). Furthermore, exosomal miRNA analysis revealed target genes involved in endogenous stem cell activation (SUFU and RUNX2), apoptosis regulation (Caspase-3), anti-inflammatory responses (IL-1β, IL-6, and PTEN), ECM formation (TRAF6 and MMPs), anti-cartilage matrix degradation (mTOR, AKT2, AKT3, and COL10A1), and cell migration (ADAM family). CONCLUSIONS: To the best of our knowledge, this is the first study demonstrating that the human pcMSC secretome promotes meniscus regeneration through activating endogenous meniscus progenitor cells both in vivo and in vitro. Our findings suggest that these regenerative effects are mediated by growth factors and exosomal miRNAs in the pcMSC secretome. The potential exosomal miRNAs effectively modulated ECM formation, anti-apoptosis, anti-inflammation, and anti-cartilage matrix degradation to mitigate MPCs injury. Overall, this study provides valuable insights into potential stem cell-derived secretome cell-free therapies for patients with exercise-induced meniscus injuries.