Photoreceptor rescue in the RCS rat without pigment epithelium transplantation

Abstract

Transplantation of normal retinal pigment epithelium (RPE) to the subretinal space has been reported to rescue photoreceptors in the RCS rat. Moreover, the rescue effect was surprisingly large considering the relatively small number of RPE cells transplanted. The reason for this widespread rescue of photoreceptors is not known, nor is the mechanism for outer segment phagocytosis in photoreceptors not apposed to the transplanted RPE cells. This suggests that the rescue effect may not be solely mediated by the transplanted cells. We therefore wished to test whether the transplantation surgery itself might contribute to the rescue of RCS photoreceptors. For these control experiments, we performed the surgery on juvenile RCS rats as described by others for the transplantation of RPE but instead of injecting RPE, we injected saline. We sacrificed the RCS control operates two months following surgery. In the area of the surgery (superior retinal quadrant) the outer nuclear layer (ONL) was up to 8–10 photoreceptor cells thick, while at the extreme inferior margin of the retina the ONL was almost eliminated. To investigate the role of temporary retinal detachment in photoreceptor rescue we repeated the above experiment using our trans-corneal approach to the subretinal space. This procedure results in a large temporary retinal detachment and little or no damage to the choroid and sclera. In these cases we found extensive preservation of the ONL extending across both the superior and inferior aspects of the retina. The degree of rescue of photoreceptors that we obtained in these experiments was comparable to (with saline injections) or greater than (with gelatin insertion) that obtained with the RPE cell injection technique. It therefore appears that the rescue of photoreceptors in this animal for at least 2 months (a post surgical time comparable to previous RPE transplantation reports) does not require transplantation of normal RPE cells, but only the surgical manipulation for such transplantation. Furthermore, it appears that temporary retinal detachment alone can induce photoreceptor rescue in the RCS rat.