Restoration of cone vision in a mouse model of achromatopsia

Abstract

Loss of cone function in the central retina is a pivotal event in the development of severe vision impairment for many prevalent blinding diseases. Complete achromatopsia is a genetic defect resulting in cone vision loss in 1 in 30,000 individuals. Using adeno-associated virus (AAV) gene therapy, we show that it is possible to target cones and rescue both the cone-mediated electroretinogram response and visual acuity in the Gnat2 ( cpfl3 ) mouse model of achromatopsia.

Figure 1

Cone targeting and rescue of the light-adapted ERG response in Gnat2^cpfl3 mice. (a) Confocal fluorescence microscopy depicting antibody staining for mouse cone arrestin (mCAR) colocalizing with GFP expressed from an AAV5-PR2.1-GFP vector in a Gnat2^cpfl3 retinal section. Scale bar, 47 µm. POS, photoreceptor outer segment; IS, photoreceptor inner segment; ONL, outer nuclear layer; P, cone pedicle. (b) Representative dark-adapted ERG traces from an untreated 2-month-old Gnat2^cpfl3 mouse (cpfl3) and a 1.5-month-old wild-type (WT) mouse. (c) As in b but for light-adapted ERG response. Dark-adapted ERG traces in response to 0.1 cd·s/m² flashes, light-adapted ERG traces in response to 10 cd·s/m² flashes, in the presence of a 100 cd/m² background light. (d) Representative light-adapted ERG traces recorded from the AAV5-PR2.1-Gnat2–treated (Tx) and untreated (no Tx) eyes of a 2-month-old Gnat2^cpfl3 mouse; rescue seen only in the treated eye. (e) ERG b-wave maximum values recorded from individual Gnat2^cpfl3 eyes, measured at 2 or 3 months of age and then measured again at 6 or 7 months of age. The normal ERG range is the span between the dashed green lines. Values above the dashed red lines were considered to be indicative of a response to therapy. (f) Representative paired-flash ERG traces recorded from the treated and untreated eyes of a 3-month-old Gnat2^cpfl3 mouse in response to a rod-saturating test flash (T) and a cone-isolating probe flash (P). Paired-flash ERG traces in response to 0.55 cd·s/m² flashes. (g) Light-adapted ERG traces recorded from the treated and untreated eyes of a 10-month-old Gnat2^cpfl3 mouse treated at 9 months of age. OD, right eye; OS, left eye. The animal studies were approved by the Institutional Animal Care and Use Committees at the University of Florida and SUNY Upstate Medical University.

Figure 2

Rescue of visual acuity in Gnat2^cpfl3 mice. (a) Light-adapted ERGs from untreated (no Tx), AAV5-PR2.1-GFP–treated (GFP) and AAV5-PR2.1-Gnat2–treated (Tx) Gnat2^cpfl3 eyes, measured at 2 months of age, after vector treatment at 1 month of age (M1–M6, mouse identifiers). OS, left eye; OD, right eye. (b) Corresponding visual acuity measurements for the left and right eyes of the six Gnat2^cpfl3 mice (M1–M6) analyzed in a, and the average of three wild-type (WT) left and right eyes. Acuities are expressed as the mean (± s.e.m.) for each eye. (c) Comparison of the mean (± s.e.m.) visual acuity measurements for all wild-type, treated and untreated (including one GFP control) eyes shown in b.