The role of light in the pathogenesis of rhodopsin retinitis pigmentosa

Abstract

Purpose : Autosomal dominant Retinitis Pigmentosa (adRP) is an inherited retinal degenerative disease that initially affects rod photoreceptors function and survival. The first gene identified to cause adRP was RHO, which encodes for rhodopsin, a G-protein coupled receptor involved in the detection of low level light and the consequent activation of rods phototransduction cascade. We focused our attention on a common UK pathogenic rhodopsin amino acid substitution, RHO^M39R. Here we have investigated the effect of light on retinal function and degeneration in both RHO^M39R and Rho^M39R models.

Methods : To investigate the role of light in retinal degeneration, we used two different models: Rho^M39R knock-in (KI) mice and RHO^M39R/+ human iPSC-derived retinal organoids (hROs). Different levels of light exposure were investigated as a modifier of disease. Optic Coherence Tomography (OCT) and Electroretinogram (ERG) were performed on mice to characterise mouse retina thickness and activity, respectively. Electron microscopy was performed to characterise the ultrastructure of the retina. Rhodopsin protein levels were analysed by western blotting. RNAseq was performed to evaluate changes in the retinal transcriptome, while immunohistochemistry was used to analyse rhodopsin localization and retina degeneration in both mouse retina and hROs.

Results : 3 weeks old Rho^M39R/+ KI mice reared in ambient light had impaired retinal function by ERG, while the thickness of the outer nuclear layer (ONL) was comparable to control Rho^+/+. By contrast, rearing in reduced ambient light exposure, protected the ERG function of Rho^M39R/+ animals. Exposure to bright light (max intensity: 30 cd*s/m²) through repeated ERG, caused a progressive decrease in ONL thickness and in retinal activity. 3 week old Rho^M39R/M39R KI mice raised in ambient light showed severely compromised retinal function, reduced ONL thickness and altered outer segment (OS) morphology. Moreover, a single exposure to bright light significantly decreased the ONL thickness of Rho^M39R/M39R KI retina within 24h, while inducing the expression of apoptotic genes by 3h. 170-200 days old RHO^M39R/+ hROs showed signs of retinal degeneration and mistrafficking of rhodopsin compared to control RHO^+/+ hROs.

Conclusions : The combined study in both KI mice and human ROs can provide insights into the role of light in sector RP in mammalian models and the ability to develop new therapies to treat RP patients.

This abstract was presented at the 2022 ARVO Annual Meeting, held in Denver, CO, May 1-4, 2022, and virtually.