Dominant GUCA1A and GUCY2D photoreceptor degenerations can be decelerated in mouse models using transgenic expression of a recombinant non-photoreceptor phosphodiesterase.

Abstract

Purpose : Various dominant mutations in human GUCY2D (retinal guanylyl cyclase RetGC1) and GUCA1A (guanylyl cyclase activating protein GCAP1) trigger cone and rod degenerations by reducing sensitivity of RetGC1:GCAP1 complex to inhibition by Ca²⁺– thus elevating cGMP production and increasing Ca²⁺ influx via cGMP-gated channels in the dark. We explored a possibility that such degenerations can be suppressed by accelerating the decay of cGMP in the dark, achieved by a non-photoreceptor recombinant cGMP-specific phosphodiesterase (PDEr) introduced in photoreceptor outer segment.

Methods : We engineered two types of recombinant non-photoreceptor PDE (PDEr) targeted to the outer segment using a prenylation signal at the C-terminus. The PDEr expressing mice (PDEr^Tg) have been bred into two mouse models harboring R838S RetGC1 (a GUCY2D mutation causing autosomal dominant progressive cone-rod dystrophy) or Y99C GCAP1 (one of multiple GUCA1A mutations causing dominant cone- and cone-rod degenerations). The progression of retinal degeneration in the PDEr-expressing hybrids in comparison with the respective R838S RetGC1^Tg and Y99C GCAP1^Tg models was analyzed using optical coherence tomography (OCT) and histological sectioning. The retinal function was assessed using dark-adapted electroretinography (ERG).

Results : One chimeric PDEr variant was expressed in mouse retinas under the control of rod opsin promoter. The non-photoreceptor PDEr harboring prenylation signal accumulated in PDEr^Tg rod outer segments. Expression of PDEr strongly suppressed the reduction of the outer nuclear layer in PDEr^Tg R838S RetGC1^Tg and PDEr^Tg Y99C GCAP1^Tg retinas as compared to R838S RetGC1^Tg and Y99C GCAP1^Tg aged ~ 4 months and offset the loss of dark-adapted ERG.

Conclusions : The results indicate that in mouse models expression of PDEr can counteract both GUCY2D- and GUCA1A-linked mutations that cause photoreceptor degenerations by elevating of cGMP production in the dark.

This abstract was presented at the 2024 ARVO Annual Meeting, held in Seattle, WA, May 5-9, 2024.