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Vishal M Shinde, Austin Lenox, Marina S Gorbatyuk; Calcium-Induced Apoptosis in retinal degeneration of S334terRho and P23H Rho Rats. Invest. Ophthalmol. Vis. Sci. 2014;55(13):2962.
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The S334ter-4 rhodopsin (Rho) and the P23H-3 Rho rats bear mutant rhodopsin transgenes with an early termination codon at residue 334 and a point mutation substituting Proline to Histidene at position 23, correspondingly. Expression of S334ter RHO (Class 1) and P23H RHO (Class II) is known to activate the Unfolded Protein Response (UPR) and to trigger the photoreceptor cell death through apoptosis. However, the ADRP progression in the S334ter RHO rats is more rapid compared to P23H RHO. It is generally known that the persistent UPR is capable of provoking a cytosolic Ca+2 release from the Endoplasmic Reticulum (ER), thus inducing a cell death. Therefore, the goal of this study is to investigate whether the ADRP photoreceptors have a raise in the cytosolic Ca2+ and whether the progression of retinal degeneration in ADRP retina is associated with Ca2+-induced apoptosis.
The RNA and protein extracts were obtained from ADRP and Sprague Dawley (SD) retinas at different time points: P13, P21, P30, P41, and P60. QRT-PCR and western blotting were performed to analyze expression of Ca2+-sensing genes and proteins from different cellular compartments including the ER, cytosol and the mitochondria.
We found that expression levels of the ER residents, BAX Inhibitor-1 and calreticulin proteins was steady increased during the ADRP progression in both rat models starting at P21. However, this increase was more prominent in P23H RHO retina. Both ADRP models demonstrated an elevated expression of the ER Ca2+releasing channel, the IP3R mRNA starting at P13 and a transient up-regulation of the SERCA2b mRNA in P21 retina. The level of the cytosolic calpastatin mRNA was significantly higher in both ADRP models compared to SD but the expression was higher in the P23H RHO than in the S334ter retina. Western blotting analysis confirmed the up-regulation of the IP3R protein and revealed no changes in the SERCA 2b protein in both ADRP retinas.
Results of the study indicate a potential rise in the intracellular Ca2+ concentration and suggest that Ca2+ signaling might be involved in the ADRP photoreceptor cell death
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