Functional and structural characteristics of photoreceptor cells rescued in RPE-cell grafted retinas of RCS dystrophic rats.

In this study retinas of pink-eyed 26 day-old RCS dystrophic rats were injected with normal, melanotic retinal pigment epithelial (RPE) cells into the subretinal space. The areas containing underlying photoreceptor cells were subsequently investigated by electron microscopy at 60 days and light microscopy immunocytochemistry at 60 and 120 days. Retinal regions containing viable RPE-cell grafts exhibited melanin-contained RPE cell transplants attached to Bruch's membrane and containing shed rod outer segments (ROS). Also, the ROS of these photoreceptor cells exhibited a normal-appearing structural relationship with apical membrane projections of these RPE cells. The debris zone, prominent in retinas of 60 day-old RCS dystrophic rats, was much reduced in RPE-cell grafted regions. By at least 3 months after RPE transplantation, immunostaining for Na+,K+-ATPase was demonstrated along inner segments (IS) of photoreceptor cells in grafted regions, as was also shown in control retinas, but not in non-grafted regions. Opsin immunostaining in RPE-cell grafted regions and in control retinas was detected along ROS and rod inner segments (RIS) and at the periphery of cell bodies in the outer nuclear layer. This study has shown that transplanted normal RPE cells in retinas of RCS dystrophic rats appear to have normal functional and structural characteristics at least three months after transplantation. Furthermore, the rescued PRC's exhibited a normal distribution of and immunostaining density for the membrane-bound enzyme Na+,K+-ATPase and the photo-pigment opsin.