Genetic deficiency of norrin and LRP5 results in RPE dysmorphia in mice

Abstract

Purpose : RPE, a continuous monolayer of pigmented cells, nourishes photoreceptors and plays a crucial role in maintaining visual cycle. Wnt signaling plays a crucial role in RPE development, regulating adhesion, pigmentation and morphogenesis. Previously we and others have demonstrated that absence of Wnt/β-catenin signaling results in abnormal retinal vasculature and increased vascular permeability with disrupted inner blood retinal barrier integrity in mice deficient of Wnt ligand Norrin (Ndp^y/-) and co-receptor low-density lipoprotein receptor-related protein (Lrp5^-/-), models for two rare hereditary diseases, Norrie disease and familial exudative vitreoretinopathy (FEVR). Yet, whether norrin and LRP5 pathway regulates RPE morphology and function remains unclear. In the current study, we investigated the morphology of RPE in both Ndp^y/- and Lrp5^-/- mice.

Methods : Retinal pigment epithelium (RPE) morphology was assessed in young adult (3-month old) Lrp5^-/- and Ndp^y/- mice and their respective age-matched wild-type (WT) and Ndp^y/+ controls, using RPE flat mounts and eye cross-sections. RPE were immunostained for tight junction protein ZO-1 and adherent junction proteins b-catenin and P-cadherin. Changes in RPE cell morphology were analyzed quantitatively for cell shape & size.

Results : Both Lrp5^-/- and Ndp^y/- RPE flat mounts showed abnormal distribution of tight junction protein, ZO-1 and adherent junction proteins, b-catenin and P-cadherin, with all of which showed reduced cell membrane localization and enhanced cytoplasmic accumulation. Moreover, RPE of both Lrp5^-/- and Ndp^y/- mice demonstrated significant alterations in cell shape & size. In contrast to WT RPE cells with the characteristic honeycomb pattern and intact junctions, Lrp5^-/- and Ndp^y/- RPE demonstrated substantially enlarged size and deformed cell shape with dislocated junction staining pattern.

Conclusions : Our findings suggest that loss of canonical Wnt signaling in Lrp5^-/- and Ndp^y/- mice results in RPE dysmorphia with disrupted cell membrane localization of tight and adherent junction proteins, suggesting the involvement of Wnt/β-catenin pathway in regulating RPE structure and potentially function.

This abstract was presented at the 2023 ARVO Annual Meeting, held in New Orleans, LA, April 23-27, 2023.