ER Stress in Retinal Degeneration in S334ter Rho Rats

Vishal M Shinde,Jonathan H Lin,Matthew M Lavail,Olga S Sizova,Marina S Gorbatyuk,Demetrios Vavvas

doi:10.1371/journal.pone.0033266

Abstract

The S334ter rhodopsin (Rho) rat (line 4) bears the rhodopsin gene with an early termination codon at residue 334 that is a model for several such mutations found in human patients with autosomal dominant retinitis pigmentosa (ADRP). The Unfolded Protein Response (UPR) is implicated in the pathophysiology of several retinal disorders including ADRP in P23H Rho rats. The aim of this study was to examine the onset of UPR gene expression in S334ter Rho retinas to determine if UPR is activated in ADRP animal models and to investigate how the activation of UPR molecules leads to the final demise of S334ter Rho photoreceptors. RT-PCR was performed to evaluate the gene expression profiles for the P10, P12, P15, and P21 stages of the development and progression of ADRP in S334ter Rho photoreceptors. We determined that during the P12–P15 period, ER stress-related genes are strongly upregulated in transgenic retinas, resulting in the activation of the UPR that was confirmed using western blot analysis and RT-PCR. The activation of UPR was associated with the increased expression of JNK, Bik, Bim, Bid, Noxa, and Puma genes and cleavage of caspase-12 that together with activated calpains presumably compromise the integrity of the mitochondrial MPTP, leading to the release of pro-apoptotic AIF1 into the cytosol of S334ter Rho photoreceptor cells. Therefore, two major cross-talking pathways, the UPR and mitochondrial MPTP occur in S334ter-4 Rho retina concomitantly and eventually promote the death of the photoreceptor cells.

Highlights

Retinitis pigmentosa (RP) is an inherited retinal disorder that is caused by the progressive loss of rod and cone photoreceptors with clinical hallmarks that include sensitivity to dim light, abnormal visual function and characteristic bone spicule deposits of pigment in the retina [1]
A number of investigators have dedicated their research to the elucidation of the mechanism of retinal degeneration in autosomal dominant retinitis pigmentosa (ADRP), and some of these studies have focused on ADRP progression in S334ter-4 Rho rats
Despite the progression in our understanding of the cellular mechanisms leading to the decline of S334ter-4 Rho photoreceptors, the essential link that connects endoplasmic reticulum (ER) stress, Unfolded Protein Response (UPR), and calpain activation with mitochondria-induced apoptosis has not been elucidated

Summary

Introduction

Retinitis pigmentosa (RP) is an inherited retinal disorder that is caused by the progressive loss of rod and cone photoreceptors with clinical hallmarks that include sensitivity to dim light, abnormal visual function and characteristic bone spicule deposits of pigment in the retina [1]. S334ter rhodopsin (Rho) rats (line 4) express rhodopsin gene containing an early termination codon at residue 334 and is a model of a number of Rho truncation mutations in human RP patients (http://www.ask.com/wiki/Retinal_Degeneration_(Rhodopsin_Mutation). This mutation results in the expression of a rhodopsin protein that lacks the 15 C-terminal amino acids that are involved in rhodopsin trafficking to the photoreceptor outer segments and in the deactivation of the rhodopsin protein after light absorption. The primary cause of degeneration in the S334ter-4 Rho photoreceptors has been identified, the precise mechanism responsible for triggering the apoptotic cascade remains unknown

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