Behavioral and Electrophysiological Evaluation of Long-term Functionality of hESC Derived RPE Monolayer Implanted in RCS Rats

Abstract

Purpose: : Long-term evaluation of human embryonic stem cell (hESC) derived retinal pigment epithelial (RPE) cells cultured on the biocompatible polymer parylene as a monolayer transplanted into the subretinal space of Royal College of Surgeon (RCS) rats using optokinetic testing and superior colliculus (SC) electrophysiology.

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 RCS rats (n=6). Rats that received parylene sheets alone (without hESC-RPE) served as the control group (n=3). All animals were administered with oral cyclosporine A (CyA in drinking water, 210mg/l) from one day prior to surgery and maintained for the entire period of study. An intraperitoneal injection of dexamethasone was given for the initial two weeks (1.6mg/kg/day) after surgery. Post-operative examinations were performed using spectral-domain optical coherence tomography (OCT) and optokinetic testing. Electrophysiological mapping of the SC was performed at 6 months post-implantation.

Results: : OCT examination confirmed the placement of the hESC-RPE graft in the rat’s subretinal space. Optokinetic testing demonstrated considerably higher visual activity only in the hESC-RPE transplanted eye and was maintained throughout the study period. Electrophysiological testing revealed that visual responses recorded from transplanted rats under low level light stimulation (threshold = -1.0 log cd/m²) was confined to a small area on the surface of the SC. Fundus imaging data confirmed that the location of the hESC-RPE graft inside the eye is corresponding to the area of visual preservation in the SC.

Conclusions: : Based on optokinetic testing and SC mapping studies, hESC-RPE cultured on parylene substrates contributed to the preservation of the visual responses in RCS rats.This study suggests that hESC-RPE seeded parylene implants may be considered for treatment strategies to slow the progression of dry-type age-related macular degeneration.

Keywords: retinal pigment epithelium • age-related macular degeneration • transplantation