Normal GCAPs partly compensate for altered cGMP signaling in retinal dystrophies associated with mutations in GUCA1A

Daniele Dell’Orco,Giuditta Dal Cortivo

doi:10.1038/s41598-019-56606-5

Daniele Dell’Orco, Giuditta Dal Cortivo

Open Access

https://doi.org/10.1038/s41598-019-56606-5

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Journal: Scientific Reports	Publication Date: Dec 1, 2019
Citations: 18	License type: open-access

Affiliation: University of Verona

Abstract

Missense mutations in the GUCA1A gene encoding guanylate cyclase-activating protein 1 (GCAP1) are associated with autosomal dominant cone/cone-rod (CORD) dystrophies. The nature of the inheritance pattern implies that a pool of normal GCAP proteins is present in photoreceptors together with the mutated variant. To assess whether human GCAP1 and GCAP2 may similarly regulate the activity of the retinal membrane guanylate cyclase GC-1 (GC-E) in the presence of the recently discovered E111V-GCAP1 CORD-variant, we combined biochemical and in silico assays. Surprisingly, human GCAP2 does not activate GC1 over the physiological range of Ca2+ whereas wild-type GCAP1 significantly attenuates the dysregulation of GC1 induced by E111V-GCAP1. Simulation of the phototransduction cascade in a well-characterized murine system, where GCAP2 is able to activate the GC1, suggests that both GCAPs can act in a synergic manner to mitigate the effects of the CORD-mutation. We propose the existence of a species-dependent compensatory mechanism. In murine photoreceptors, slight increases of wild-type GCAPs levels may significantly attenuate the increase in intracellular Ca2+ and cGMP induced by E111V-GCAP1 in heterozygous conditions. In humans, however, the excess of wild-type GCAP1 may only partly attenuate the mutant-induced dysregulation of cGMP signaling due to the lack of GC1-regulation by GCAP2.

Highlights

Missense mutations in the GUCA1A gene encoding guanylate cyclase-activating protein 1 (GCAP1) are associated with autosomal dominant cone/cone-rod (CORD) dystrophies
It has been established that the GCAP1/2-mediated Ca2+ feedback on guanylate cyclase isoform 1 (GC1) activity is the only one that occurs at very dim light intensities, corresponding to the single photon response[39]
By integrating quantitative information arising from assays performed with recombinant systems and numerical simulations, we sought to clarify some mechanisms that are apparently perturbed in cases such as the severe CORD form recently associated with the E111V mutation in GCAP110

Summary

Introduction

Missense mutations in the GUCA1A gene encoding guanylate cyclase-activating protein 1 (GCAP1) are associated with autosomal dominant cone/cone-rod (CORD) dystrophies. The core of the Ca2+/cGMP signaling unit resides in the complex formed by the membrane retinal guanylate cyclase (GC1, called ROS-GC1 or GC-E being the main cyclase in photoreceptor outer segments5) and guanylate cyclase-activating proteins (GCAPs). This supramolecular machinery ensures a precise control of the cGMP synthesis by GC1 as a consequence of the level of intracellular free Ca2+, which drops from few hundred nanomolar in the dark to below 100 nM in the light[1,6]. The rate of photoreceptor cell loss increased with the level of Y99C-GCAP1 expression[26]

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Conclusion