Sonic hedgehog promotes the generation of myelin proteins by transplanted oligosphere-derived cells.

The generation of large numbers of functionally relevant cells for transplantation remains central to the use of cell replacement as a therapeutic strategy for neurodegenerative diseases. In this study we have analyzed the effect of sonic hedgehog (Shh) pretreatment on the myelinating potential of transplanted oligosphere-derived cells. The retina was chosen as a model for assessing this myelinating capability because 1) there is a lack of endogenous myelin in the normal rodent retina and 2) the retinal ganglion cell (RGC) axons are receptive to myelination, once myelinating cells have access to the retinal nerve fiber layer. Initially, oligospheres were generated in the presence of B104 CM but without the addition of Shh. After transplantation, 60% of the animals developed tumors in the eye that had received the transplant and were not analyzed for the presence of myelin. In the remaining retinas, the transplanted oligosphere-derived cells were not myelin competent, as indicated by the absence of myelin proteins in the retinal nerve fiber layer. In contrast, when B104 CM oligospheres were generated in the presence of Shh, myelin proteins were found in the nerve fiber layer after transplantation. In addition, the amount of myelin proteins synthesized increased with time posttransplantation, with the majority of the nerve fiber layer immunoreactive for these proteins in some retinas after 2 months. This study has demonstrated that growth as oligospheres and endogenously derived growth/differentiation factors alone are not sufficient to induce the differentiation of B104-treated oligosphere-derived cells and that pretreating the oligospheres by growth in the presence of Shh before transplantation is essential to induce their myelinating competence.