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Yogesh Bhootada, Clark Gully, Marina S Gorbatyuk; Controlling PERK-ATF4-CHOP branch of the UPR is the key to reverse retinal degeneration of T17M Retina. Invest. Ophthalmol. Vis. Sci. 2015;56(7 ):5409.
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© ARVO (1962-2015); The Authors (2016-present)
Class I & II rhodopsin gene (RHO) mutations cause endoplasmic reticulum (ER) stress that in turn activates the unfolded protein response (UPR) and results in cell death. Previously, we have shown that down regulation of a downstream mediator of the PERK branch, ATF4, completely rescues one-month-old degenerating retinas expressing the T17M rhodopsin protein. We hypothesized that simultaneous down regulation of two PERK mediators, ATF4 and CHOP, would give long term preservation to autosomal dominant retinitis pigmentosa (ADRP) mutations as compared to a single ATF4 knockdown.
T17M RHO ATF4+/- (single knockdown), T17M RHO ATF4+/- CHOP+/- (double knockdown), T17M RHO ATF4+/+ CHOP+/+ (T17M) and C57Bl/6 mice were used in the study. All groups were subjected to electroretinogram (ERG) at postnatal (P) day 30, P90 and P180. Proteins were extracted from retina at P30 to perform western blot analysis.
A single knockdown rescued vision of P30 T17M mice and resulted in significant retardation of retinal degeneration at P90. In single ATF4 knockdown animals, a- and b- wave amplitudes of the scotopic ERG were higher (215% and 131%, respectively) than T17M mice, and lower (55% and 24%, respectively) than C57BL6 mice. Double knockdown of the PERK mediators resulted in a higher therapeutic effect than was provided by a single knockdown. At P90, these mice had an even greater increase in amplitudes of a- and b- waves (359% and 151%, respectively). This effect was sustained, lasted at least 6 months and lead to a dramatic reduction in the rate of retinal degeneration. The a-and b-wave amplitudes in P180 animals were 55% and 80% respectively of those found in the wild type retinas suggesting a preservation of physiological function of T17M photoreceptors. The therapeutic mechanism of ATF4-deficeincy in P30 T17M retinas was found to be associated with attenuation of UPR markers pEIF2A, pATF6 and CHOP by 70%, 32% and 72% respectively. Interestingly, reduction of ATF4 produced a significant 2.5-fold increase in both mouse and human rhodopsin expression as compared to T17M retinas which demonstrated significant inhibition of rhodopsin expression machinery.
ATF4 and CHOP deficiency dramatically preserves a loss of photoreceptors and their physiological function in T17M RHO retina suggesting that the PERK branch could be a viable therapeutic target for the treatment of ADRP.
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