Abstract
Osteoarthritis (OA) is a degenerative disease with a strong inflammatory component. Intra-articular (IA) injections of mesenchymal stem cells (MSCs) modulate local inflammation, although the lack of engraftment suggests that they undergo apoptosis. The aim of this study is to investigate the fate of IA-delivered MSCs in an animal model of OA and to assess the role of apoptosis in vitro. Collagenase-induced OA (CIOA) was performed on C57BL/6 mice and 2×10∧5 GFP+ MSCs were IA-injected in the animals. 3 days later, knee joints were digested into a single-cell suspension and MSCs retrieved by cell sorting. Conditioned medium (CM) of retrieved cells was tested on murine macrophages and cytokine secretion was measured. Apoptosis of MSCs was induced in vitro with staurosporine (STS) and evaluated by Annexin V/Sytox Blue staining; activation of caspases was measured by FLICA assays. Murine lymphocytes were cocultured with apoptotic MSCs and their proliferation measured by quantification of Cell Trace Violet. 1.63% of injected cells were retrieved and proliferated in culture. Their CM significantly modulated activation of macrophages, with greater effects from OA-induced MSCs. STS induced apoptosis with activation of Caspase 3/7. Apoptotic MSCs significantly prevented the proliferation of murine lymphocytes. MSCs can be administered and retrieved from murine knees. Retrieval yield is low, consistent with previous studies. MSCs were licensed from the OA joint to produce an immunosuppressive milieu that modulated macrophages ex vivo. In vitro, apoptosis increased the immunomodulatory potential of MSCs. This suggests that apoptosis may contribute to the therapeutic effects of MSCs in OA.
