Study of the functional integrity of the retinal pigment epithelium with a new technique in two models of inherited retinal degeneration

Introduction Retinal pigment epithelium (RPE) is a cell layer located between the neurosensory retina and the choroid. RPE has many functions that are essential for photoreceptor nutrition and renewal, among others. To understand the pathogenesis of retinal degenerations, it is crucial to study the integrity, morphology and functionality of this layer. Material and methods Dystrophic young and old adult female albino P23H‐1 (rhodopsin mutation) and Royal College of Surgeon, (RCS, RPE mutation that impairs phagocytosis), rats were used in this experiment. Control strains were Sprague‐Dawley (SD) and Pievald Virol Glaxo (PVG). To label the RPE, 1.5 µl of 3% Fluorogold (FG) diluted in saline was administered intravitreally under general anaesthesia. RPE in‐vivo analysis were performed with SD‐OCT and by eye fundus observation; for ex‐vivo analysis flat mounted RPE and cryostat cross‐sections were used. Results In‐vivo analysis of the dystrophic strains showed an overexpression of lipofuscin in the RPE and a reduction of the retinal thickness, both pathological conditions increased with time. Ex‐vivo analysis in cross sections revealed that in control SD and PVG rats, RPE was labelled with FG showing its typical cubic morphology. The retinal structure and RPE morphology however, was altered in the dystrophic strains. In flat mounts we observed that FG accumulates inside the somas of RPE cells in SD, PVG and young P23H‐1 rats, indicating that the RPE has a correct function. However, in old P23H‐1 rats, FG was found inside and outside the RPE somas, which in addition were bigger and unstructured. When analysing RCS rats, we observed that FG accumulated outside the RPE somas, indicative of the phagocytosis malfunction that characterises this strain. Conclusions Intraocular injection of FG is a reliable technique to label functional RPE. In both models of inhered retinal degeneration RPE functional integrity was affected by the evolution of degeneration.