Retinal regeneration and stem cell therapy in retinitis pigmentosa

Retinitis pigmentosa (RP) is the leading cause of hereditary blindness, and there is currently no available treatment that can either significantly slow the progression of this disease or restore lost vision. Amphibians and birds exhibit different strategies for retinal regeneration, including the proliferation of cells in the ciliary margin and transdifferentiation of the retinal pigment epithelium (RPE) and Muller glia. The mammalian retina does not have the innate ability to regenerate damaged retina, but research is actively exploring pathways that promote endogenous regeneration. Because the inner retinal architecture is largely preserved, even in advanced cases of RP, an alternative is to replace the degenerated photoreceptor cells, thereby replenishing the photoreceptor population. The transplantation of embryonic stem cells, induced pluripotent stem cells, embryonic retinal progenitors (postmitotic photoreceptor precursors), and hippocampal neuronal progenitors have been investigated for this purpose. The encouraging results demonstrate the integration and possible functional connection between the transplanted cells and the inner retinal circuitry of the host. In this review, we summarize recent advancements in this field and their potential for the treatment of RP and other retinal degenerations.