I. Pinilla, Y. Sauvé, N. Cuenca, E. Abecia, R. D. Lund

Purpose:

To examine the effect of preventive subretinal cell injections in the RCS rat on the outer retina and synaptic connectivity between photoreceptors and their target neurons.

Methods:

Eight rats received subretinal injections of a human RPE cell line (ARPE19) at age P22; they were sacrificed at P90 (n=4) and P120 (n=4). Controls consisted of 6 unoperated rats sacrificed at the same time points (n=3) and 3 non-dystrophic RCS rats at P30. All animals were immunosuppressed with oral cyclosporine. The outer plexiform layer (OPL), outer nuclear layer (ONL), inner nuclear layer (INL) and inner plexiform layer (IPL) were studied immunohistochemically and retinal function examined with the electroretinogram (ERG).

Results:

In areas preserved by injected cells, maintained organization was evident in all the studied layers. Photoreceptors were clearly preserved, with maintained cone morphology, expressing both blue and green-red opsins. Bipolar cells were well organized in the optimal rescue area with normal dendritic branching. Synapses were well preserved with respect to rod terminal/bipolar pairing and clear cone synaptic sites. The number of cells and their synapses became less numerous away from the rescue area. Some sprouting of horizontal and bipolar dendrites could be seen in areas away the transplant, related to the loss of photoreceptors, always less frequent than in dystrophic untreated eyes. The transplant showed an improvement on the connectivity at the IPL, using synaptophysin. ERG recordings showed at best the persistence of both a- and b-waves, which reflected the level of anatomical preservation achieved in treated animals.

Conclusion:

Photoreceptor rescue following hRPE cell injections is accompanied with the maintenance of synaptic connectivity and preservation of ERG.

Take-home message:

hRPE transplantation in animal models of retinal degeneration can delay anatomical and functional lost.