A Non-Human Primate Model of Achromatopsia

Abstract

Purpose : Inherited retinal diseases cause a significant proportion of untreatable blindness worldwide. The absence of animal models that recapitulate human retinal anatomy is a major limitation to the development of effective therapies. The cone-rich macula of non-human primates (NHPs) closely mirrors that of the human retina. Therefore, NHP models of inherited retinal diseases, particularly cone disorders and macular diseases, are necessary to advance new therapies for patients. The purpose of this study is to determine the molecular mechanism of disease in a cohort of NHPs identified with visual impairment.

Methods : Originally, four rhesus macaques (Macaca mulatta) identified with behaviors consistent with visual impairment were identified. An ophthalmic examination under sedation was performed that included assessment of pupillary light reflexes, slit lamp biomicroscopy, indirect ophthalmoscopy, spectral domain optical coherence tomography, fundus autofluorescence, fluorescein angiography, and electroretinography. DNA was extracted from blood samples of the original four animals and their relatives. Whole genome sequencing was performed. For protein studies, biochemical analyses were done in transfected HEK293T cells, and enzyme activity was measured on cell extracts.

Results : We have identified NHPs at the California National Primate Research Center with visual impairment and findings from clinical ophthalmic examination, advanced retinal imaging, and electrophysiology consistent with achromatopsia. Genetic sequencing confirmed a homozygous R565Q missense mutation in the catalytic domain of PDE6C, a cone-specific phototransduction enzyme associated with achromatopsia in humans. Biochemical studies demonstrate the mutant mRNA is translated into a relatively stable protein that displays normal cellular localization but is unable to hydrolyze cGMP. Five living homozygous affected individuals have been confirmed as well as 40 heterozygote living relatives. The now deceased carrier of the de novo mutation has been identified.

Conclusions : This NHP model of a cone disorder will not only serve as a therapeutic testing ground for achromatopsia gene replacement, but also for optimization of gene editing in the macula and of cone cell replacement in general.

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

 

Figure 1: Visually impaired macaques have electroretinography tracings characteristic of achromatopsia. Affected subjects have absent cone-mediated recordings with normal rod function.