Gene augmentation therapy restores cone function in PDE6c-acciocated achromatopsia

Abstract

Purpose : Achromatopsia is a rare autosomal recessive inherited retinal disease characterized by low visual acuity, photophobia, nystagmus, and color blindness. Our pervious study has reported a nonhuman primate (NHP) pedigree carrying a homozygous missense mutation in PDE6c impairing the cone photoreceptor response. In this study we evaluated the rescue effect of PDE6c augmentation therapy in PDE6c^-/- mice, as the preliminary study of PDE6c gene therapy in NHP.

Methods : Cone-specific promoter (PR1.7) delivering full length PDE6c cDNA was used for gene augmentation therapy, both AAV5 and AAV8 vectors were tested for comparing the higher rescue efficiency. AAVs were administered by subretinal (SR) injection on postnatal 14 days of PDE6c^-/- mice, on one eye of AAV5/AAV8-PR1.7-PDE6c, the other eye with AAV5/AAV8-PR1.7-EGFP as control (1x10¹³gc/ml, 1ul per eye). Rescue was assessed by restoration of the cone-mediated electroretinogram (ERG), optomotor responses (OKR). The protein expression in retina was detected by immunofluorescence and western blotting.

Results : The fundus photography showed positive GFP in the eye injected with AAV5/AAV8-PR1.7-EGFP one month after SR injection, and the immunofluorescence staining showed GFP signal was specifically expressed in photoreceptor cell layer. ERG showed marked improvement in cone function 3 month after treatment. AAV8-treated retinas showed greater preservation of light responses than AAV5-mediated treatments (LA 100: AAV8-PDE6c 72.8±12.4 uV; AAV8-GFP 4.9±0.8 uV; AAV5-PDE6c 31.4±6.3 uV; AAV5-GFP 6.9±1.8 uV; WT 94.6.8±1.8 uV. n=4). 9 months following treatment, ERG recording exhibited AAV8 mediation restored 80% of cone response by comparison of the WT mice, whereas AAV5 restored around 40%. Expression of PDE6c and GNAT2 were maintained in cone outer segments of the treated PDE6c-/-retina, with stronger signal than WT retinas. AAV8-PDE6c treated mice showed an significantly higher OKR score in visual acuity and contrast sensitivity than untreated PDE6c-/- group (n-5).

Conclusions : AAV-mediated PDE6c gene delivery effectively restore the cone function in PDE6c^-/- mice. Our results provided the foundation for AAV-based gene therapy for PDE6c achromatopsia.

This abstract was presented at the 2023 ARVO Annual Meeting, held in New Orleans, LA, April 23-27, 2023.