CRB2 Loss in Rod Photoreceptors Is Associated with Progressive Loss of Retinal Contrast Sensitivity.

C Henrique Alves,Jan Wijnholds,Abraham J Koster,Nanda Boon,Aat A Mulder,Carolina R Jost

doi:10.3390/ijms20174069

Abstract

Variations in the Crumbs homolog-1 (CRB1) gene are associated with a wide variety of autosomal recessive retinal dystrophies, including early onset retinitis pigmentosa (RP) and Leber congenital amaurosis (LCA). CRB1 belongs to the Crumbs family, which in mammals includes CRB2 and CRB3. Here, we studied the specific roles of CRB2 in rod photoreceptor cells and whether ablation of CRB2 in rods exacerbates the Crb1-disease. Therefore, we assessed the morphological, retinal, and visual functional consequences of specific ablation of CRB2 from rods with or without concomitant loss of CRB1. Our data demonstrated that loss of CRB2 in mature rods resulted in RP. The retina showed gliosis and disruption of the subapical region and adherens junctions at the outer limiting membrane. Rods were lost at the peripheral and central superior retina, while gross retinal lamination was preserved. Rod function as measured by electroretinography was impaired in adult mice. Additional loss of CRB1 exacerbated the retinal phenotype leading to an early reduction of the dark-adapted rod photoreceptor a-wave and reduced contrast sensitivity from 3-months-of-age, as measured by optokinetic tracking reflex (OKT) behavior testing. The data suggest that CRB2 present in rods is required to prevent photoreceptor degeneration and vision loss.

Highlights

The Crumbs protein complex is essential for polarity establishment and adhesion of the retinal neural epithelium
Variations in the Crumbs homolog-1 (CRB1) gene are associated with a wide variety of autosomal recessive retinal dystrophies, including retinitis pigmentosa (RP), Leber congenital amaurosis (LCA), cone-rod dystrophy, isolated macular dystrophy, and foveal retinoschisis [9,10]
We previously showed proof-of-concept for AAV9-CMV-CRB2, reintroduction of CRB2 into photoreceptors and Müller glial cells (MGCs) rescued the phenotype of Crb2flox/floxChx10Cre and Crb1Crb2F/+Chx10Cre mouse retinas [24]

Summary

Introduction

The Crumbs protein complex is essential for polarity establishment and adhesion of the retinal neural epithelium. CRB1 and CRB2 have a large extracellular domain with epidermal growth-factor-like and laminin-A globular domains, a single transmembrane domain, and an intracellular C-terminal domain of 37 amino acids; CRB3 lacks the extracellular domain [1]. The intracellular domain has a single C-terminal PDZ protein-binding motif and a single FERM-protein-binding motif juxtaposing the transmembrane domain [1]. In the developing mouse retina, the Crumbs proteins localize at the subapical region adjacent to the adherens junctions between retinal progenitor cells [4]. The Crumbs proteins are present in photoreceptors and Müller glial cells (MGCs) [5,6]. CRB2 protein is present in photoreceptors and MGCs, whereas CRB1 protein is present only in MGCs [7,8]

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Discussion

Conclusion