Transdifferentiated Mesenchymal Stem Cells as Alternative Therapy in Supporting Nerve Regeneration and Myelination

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Abstract
1. Aims: Demyelination plays a crucial role in neurodegenerative processes and traumatic disorders. One possibility to achieve remyelination and subsequent restoration of neuronal function is to provide an exogenous source of myelinating cells via transplantation. In this context, mesenchymal stem cells (MSCs) have attracted interest. They are multipotent stem cells that differentiate into cells of the mesodermal lineage like bone, cartilage, fat, and muscle. Although adult, their differentiation potential is remarkable, and they are able to transdifferentiate. 2. Methods: We transformed cultivated rat MSCs into myelinating cells by using a cytokine cocktail. Transdifferentiated MSCs were characterized by an enhanced expression of LNGF-receptor, Krox20, and CD104, and a decreased expression of BMP receptor-1A as compared to untreated MSCs. The myelinating capacity was evaluated in vitro and in vivo. Therefore, PC12 cells, normally unmyelinated, were cocultivated with MSCs, transdifferentiated MSCs, and Schwann cells, or the respective cells were grafted into an autologous muscle conduit bridging a 2-cm gap in the rat sciatic nerve. Myelination of PC12 cells was demonstrated by electron microscopy. In vivo, after 3 and 6 weeks regeneration including myelination was monitored histologically and morphometrically. Autologous nerves and cell-free muscle grafts were used as control. 3. Results: Schwann cells and transdifferentiated MSCs were able to myelinate PC12 cells after 14 days in vitro. In vivo, autologous nerve grafts demonstrated the best results in all regenerative parameters. An appropriate myelination was noted in the Schwann cell groups and, albeit with restrictions, in the transdifferentiated MSC groups, while regeneration in the MSC groups and in the cell-free groups was impaired. 4. Conclusion: Our findings demonstrate that it may be possible to differentiate MSCs into therapeutically useful cells for clinical applications in myelin defects.