Deletion of Tribbles Pseudokinase-3 Ameliorates Retinal Function in CEP290^RD16 Mice

Abstract

Purpose : CEP290^RD16 mice expressing truncated CEP290 (Centrosomal protein 290) mimic Leber congenital amaurosis (LCA) in humans, a severe inherited retinal dystrophy with early onset of photoreceptor degeneration. Cellular mechanisms involved in retinal pathogenesis of CEP290^RD16 mouse retinas include activation of Integrated Stress Response, endoplasmic reticulum (ER) stress markers, tribbles pseudokinase-3 (TRB3) gene by p-eIF2α→ ATF4→ CHOP signaling, and inhibition of phosphorylated (p) serine/threonine-protein kinase AKT and mechanistic target of rapamycin (mTOR). Moreover, reduction in p-AKT→p-mTOR arm in CEP290^RD16 retinas is known to be associated with reduced rate of protein synthesis. Therefore, the purpose of this study was to evaluate the impact of TRB3 deletion on progression of retinal degeneration in CEP290^RD16 mice.

Methods : CEP290^RD16 were bred with TRB3-/- mice. Retinal functions of CEP290^RD16 TRB3-/-; CEP290^RD16; TRB3 -/- and C57BL6 mice were evaluated by registration of a- and b-wave amplitudes of the scotopic ERGs at postnatal (P) day 18. Number of rows of photoreceptor nuclei were counted in H&E stained mouse retinas at P18. At P15, we isolated retinal protein extracts to detect phosphorylation of AKT→mTOR and eIF2α signaling in all four groups of animals. Statistical analysis was done using one-way ANOVA software in all groups.

Results : Analysis of the scotopic ERGs revealed dramatic increase in both a- and b-wave amplitudes in CEP290^RD16 TRB3-/- by 133.56% and 268.64%, respectively as compared to CEP290^RD16 mice. These data correlated with the increase in the number of photoreceptor nuclei in CEP290^RD16 TRB3-/- (6.45 rows vs 4.29 rows in CEP290^RD16 mice) at P18. In addition, we found that levels of p-mTOR was elevated in CEP290^RD16 TRB3 ablated retinas by 66.45% and the p-eIF2α level was decreased by 35.79% as compared to CEP290^RD16. These data indicate a potential increase in the rate of protein synthesis and decrease in ER stress, respectively.

Conclusions : Our results depict that deletion of TRB3 gene in CEP290^RD16 mouse model of retina degeneration improves the overall retinal structure and function resulting in increase in the ERG amplitudes, photoreceptor survival, elevated p-mTOR and the eIF2α deactivation. This strategy may be useful as a therapy to treat retina degenerative diseases in future, however, all other safety parameters need to be accessed first for future implications.

This abstract was presented at the 2019 ARVO Annual Meeting, held in Vancouver, Canada, April 28 - May 2, 2019.