Abstract
Purpose:
The T17M mutation within the rhodopsin gene (RHO) causes protein misfolding, endoplasmic reticulum (ER) stress, and activation of the unfolded protein response (UPR) leading to autosomal dominant retinitis pigmentosa (ADRP). The activation of the UPR in T17M RHO retina occurs through induction of the PERK UPR signaling and leads to up-regulation of phosphorylated eIF2a, ATF4, and pro-apoptotic CHOP. Our long term goal is to reverse retinal degeneration in T17M RHO mice. Therefore, we hypothesize that the modulation of the PERK signaling could prevent or slow down the rate of retinal degeneration in T17M RHO mice.
Methods:
T17M RHO ATF4+/-, T17M RHO ATF4+/+, ATF4+/- and ATF4+/+ (C57Bl/6) mice were used in the study. All groups were subjected to electroretinogram (ERG) and spectral domain optical coherent tomography (SD-OCT) analysis at postnatal (P) day 30, P60 and P90 of retinal degeneration. RNA and protein were extracted from retina in all the four groups of mice at P30 to perform qRT-PCR and western blot analysis.
Results:
An analysis of the scotopic ERG response demonstrated that the a- and b-wave amplitudes were dramatically increased in ATF4-deficient T17M RHO retinas by 392% and 207%, respectively at P30 compared to T17M RHO ATF4+/+and reached the level of the ERG amplitudes measured in C57Bl6 mice. At P90 the increase was only 172% and 125%, respectively compared to T17M RHO ATF4+/+ and was lower compared to one measured in C57Bl6 retina pointing a slow loss of physiological function. The thickness of the outer nuclear layer (ONL) in the superior (S) and the inferior (I) regions of the T17M RHO ATF4+/- retina was dramatically increased by 141% and 145%, respectively compared to control ADRP mice and was compatible with the length of the ONL in C57Bl6 retina. However, at P90 we observed a 204% and 224% increase in the thickness of the ONL for S and I , respectively compared to T17M RHO ATF4+/+ mice pointing out a slow loss of photoreceptors in ADRP retina. QPCR and protein analysis of P30 retinas revealed a lack of activation of the UPR in the T17M RHO retina deficient in ATF4 suggesting the presence of a link between the activated UPR in T17M RHO retina and the progression of ADRP.
Conclusions:
ATF4 deficiency dramatically slows down a loss of physiological function and photoreceptors in T17M RHO retina suggesting that the ATF4 gene could be a viable therapeutic target for the treatment of ADRP.
Keywords: 702 retinitis •
695 retinal degenerations: cell biology •
648 photoreceptors