Mesenchymal stem cells (MSCs) have potential applications in regenerative medicine and tissue engineering and may represent an attractive option for tendon repair and regeneration. Thus far the ability of MSCs to differentiate into tenocytes in vitro has not been investigated. Experiments were performed with and without growth factors (IGF-1, TGF-β1, IGF-1/TGF-β1, PDGF-BB, and BMP-12), in co-cultures of tenocytes and MSCs mixed in different ratios and by culturing MSCs with spent media obtained from primary tenocytes. Tenogenesis was induced in MSCs through a combination of treatment with IGF-1 and TGF-β1, in high-density co-cultures and through cultivation with the spent media from primary tenocytes. Electron microscopy and immunoblotting were used to demonstrate up-regulation of collagen I/III, decorin, tenomodulin, β1-Integrin, MAPKinase pathway (Shc, Erk1/2), and scleraxis in the co-cultures and provide simultaneous evidence for the inhibition of apoptosis. In monolayer co-cultures extensive intercellular contacts between MSCs and tenocytes were observed. Cells actively exchanged vesicles, which were labeled by using immunofluorescence and immunogold techniques, suggesting the uptake and interchange of soluble factors produced by the MSCs and/or tenocytes. We conclude that MSCs possess tenogenic differentiation potential when provided with relevant stimuli and a suitable microenvironment. This approach may prove to be of practical benefit in future tissue engineering and tendon regenerative medicine research.
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