Genetic deletion of S-opsin prevents rapid cone degeneration in a mouse model of Leber congenital amaurosis

Abstract

Purpose: Retinoid isomerase (RPE65) and lecithin-retinol acyltransferase (LRAT) are critical in recycling 11-cis-retinal in retinal pigment epithelium (RPE). Mutations in either gene lead to Leber congenital amaurosis (LCA), an inherited retinal degenerative disease characterized by severe loss of vision in childhood and early degeneration of cones. We recently showed that the short-wavelength (SW) opsins are more prone to aggregation than the medium- and long-wavelength (MW/LW) opsins in the absence of 11-cis-retinal. The accumulation of SW opsin triggers endoplasmic reticulum (ER) stress and rapid cone degeneration. The purpose of this study is to determine the role of mouse S opsin in cone degeneration in Lrat-/- mice by genetically deleting S-opsin.

Methods: We bred Lrat-/- mice with S-opsin-/- mice to generate Lrat-/-S-opsin-/- mice, which express only M-opsin without chromophore in their cones. We compared the cone density and morphology between Lrat-/-S-opsin-/- and three control mouse lines (Lrat-/-, S-opsin-/-, and WT) by cone density analysis and histology. We analyzed the expression and subcellular localization of cone specific proteins by western blotting and immunohistochemistry, respectively.

Results: Deletion of S-opsin significantly reduced ER stress and prevented apoptosis in Lrat-/- retina. Although majority of cones degenerated in the central and ventral regions of Lrat-/- mice, deletion of S-opsin completely prevented the rapid cone degeneration in all regions of Lrat-/- retina at 1 month of age. However, deletion of S-opsin neither prevented M-opsin mistrafficking nor prevented the degradation of membrane associated proteins in cones.

Conclusions: Our results suggest that S-opsin aggregation is responsible for the rapid cone degeneration in Lrat-/- mice.

Keywords: 695 retinal degenerations: cell biology • 625 opsins • 648 photoreceptors