Neurogenic Potential of Retinal Precursor Cells (Rpcs) Transplanted into a Model of Terminal Stages of Retinitis Pigmentosa

Abstract

Abstract: : Purpose: To investigate the fate of in vitro expanded RPCs transplanted into a degenerating (early VPP) or a fully degenerated (late VPP) retina in order to characterize the potential of these cells to integrate the photoreceptor layer. Methods: RPCs were isolated either from DBA2J newborn mice and labeled with the PKH26 dye prior transplantation or from mice expressing GFP and cultured in EGF and FGF2 for an extensive period of time. After expansion, cells were transplanted subretinally or intravitreally into the eye of adult wild–type, transgenic mice undergoing slow retinal degeneration (VPP strain) or rapid retinal degeneration (rd1 strain). Retinas were studied at different time–points after transplantation. Results: In healthy retinas (n=20), grafted cells do not migrate or differentiate except in rare cases. In late VPP and rd1 (n=10 and 13 respectively), intravitreally grafted cells showed no or only slight migration and stayed in close vicinity to the GCL in a cluster form. After subretinal injection (n=9), transplanted cells massively migrated into the ganglion cell layer (GCL) of late VPP and, at 1 and 3 weeks, expressed neuronal and glial markers, such as ß–Tub III, NeuN, Brn3b or GFAP with marked preference for the glial phenotype. In early VPP (n=5), the grafted cells behaved similarly. In some occasions grafted cells stayed in the remaining ONL. These cells were, in rare cases, positive for recoverin, a specific marker for photoreceptors. Moreover the engraftment seems to be accompanied by an increased glial activity. Conclusions: These results indicate that RPCs retained the capacity to differentiate into retinal cells in a region–specific manner, by exhibiting migratory and differentiation preferences. It also appeared that the retina, either during or at a late stage of degeneration, does not provide signals to induce massive differentiation of RPCs into photoreceptors. This suggests that RPCs transplantation may not be sufficient to restore the function of a diseased retina and thus photoreceptors transplantation may be more suitable than RPCs to integrate the ONL.

Keywords: retina • transplantation • retinitis