Abstract
Purpose: :
The S334ter rhodopsin (Rho) rat (line 4) bears the rhodopsin gene with an early termination codon at residue 334 that is similar to the one found in human patients with autosomal dominant retinitis pigmentosa (ADRP). The Unfolded Protein Response (UPR) or Endoplasmic Reticulum (ER) 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.
Methods: :
We have collected retinas of SD (control) and S334ter Rho (Experimental) rat and RT-PCR was performed on CDNA prepared from these retinas to evaluate the gene expression profiles for postnatal day (P)10, P12, P15, P18 and P21 stages of the development and progression of ADRP in S334ter Rho photoreceptors. We have also performed Western Blots for few proteins to confirm the results.
Results: :
We found that during the P12-P15 period, ER stress-related genes are strongly upregulated in transgenic retinas resulting in the activation of the unfolded protein response (UPR) that was confirmed using western blot analysis. The activation of UPR was associated with the increased expression of JNK, Bik, Bim, Bid, Noxa and Puma genes that together with activated calpains compromise the integrity of the mitochondrial MPTP(Mitochondrial permeability transition pore), leading to the release of pro-apoptotic AIF1 into the cytosol of S334ter Rho photoreceptor cells.
Conclusions: :
Two major cross-talking pathways, the UPR and mitochondrial MPTP pathways communicate closely with each other in S334ter Rho retinas and eventually promote the death of the photoreceptor cells.
Keywords: retinal degenerations: cell biology • stress response • gene/expression