Histological correlation of superior collicus response to light preserved by transplantation of hESC derived RPE monolayer in RCS rats

Abstract

Purpose: Histological evaluation of the retina of Royal College of Surgeon (RCS) rats that received subretinal implantation of human embryonic stem cell (hESC) derived retinal pigment epithelial (RPE) cells cultured on the biocompatible polymer parylene as a monolayer and its correlation with visual functional preservation in the superior colliculus (SC).

Methods: Polarized hESC-RPE cells (H9) were cultured for 4 weeks on parylene sheets. Rectangular pieces (0.4mm x 0.9mm) of parylene were seeded with RPE cells, which formed a confluent monolayer. These grafts were implanted into the subretinal space of postnatal (P) 28 RCS rats (n=16). All animals were maintained under immunosuppression for the entire period of study. Histological evaluation was performed based on immunostaining. In selected animals, electrophysiological mapping of the SC using various light intensity stimulus was performed at 2 months post-implantation.

Results: At P90, immunostaining demonstrated robust photoreceptor (rod and or cone) survival in an area overlying the hESC-RPE implant. In non-treated dystrophic RCS eyes, photoreceptor survival at this age was negligible. Long-term (6 months post-implantation) evaluation confirmed the preservation of rod and cone photoreceptors in the implant area. In all hESC-RPE implanted animals, at threshold stimulus level, responses in the SC could be recorded only from an area corresponding to the implant location in the eye. Immunostaining revealed better rod preservation (4.25±0.59 layers) among rats that responded to low level light stimulation (-5.4 log cd/m²). Rats that responded only at higher light stimulation (>-4.4 log cd/m²) showed less rod survival (2.25±1.1 layers) and majority of these rods were inferior in appearance. No such differences between two luminance measurement groups were observed in the degree of cone survival.

Conclusions: hESC-RPE cultured on parylene substrates implanted into the RCS retina is capable of preserving rod and cone photoreceptors up to P180. Histological correlation of SC luminance measurement suggests preservation of functional rod and cone photoreceptors. The results support the use of such implants for therapeutic approaches aimed at slowing the progression of outer retinal dystrophies such as age-related macular degeneration (AMD).

Keywords: 701 retinal pigment epithelium • 508 electrophysiology: non-clinical • 687 regeneration