Abstract
Purpose: :
Mutations in the gene encoding the beta-subunit of the cone cyclic nucleotide-gated channel (CNGB3) cause cone function loss in mammals including humans. We tested if AAV-mediated CNGB3 gene therapy can restore cone function in Cngb3 knockout mice, a model of human Achromatopsia 1.
Methods: :
A human CNGB3 cDNA with a cone-specific PR2.1 promoter was packaged into AAV serotype 8 capsids containing a point mutation in a surface-exposed tyrosine residue at position 733, AAV8 (Y733F)-PR2.1-hCNGB3 (1 x 1013 viral genome-containing particles /ml). At postnatal day 14, 1 µl of this vector was injected subretinally into one eye of 20 Cngb3 knockout mice. The untreated contralateral eye was used as a control. Dark- and light-adapted ERGs were recorded periodically from 4 weeks to 6 months after treatment. 6 months after injection, both treated and control eyes were harvested for histochemical studies.
Results: :
At 6 weeks post-treatment both treated and untreated eyes of Cngb3 knockout mice showed normal rod-derived ERGs. In untreated control eyes, cone-derived ERG signals were nearly unrecordable. In treated eyes, restored light-adapted cone-derived ERG waveforms were first recorded 6 weeks after treatment and remained stable for at least 6 months. These ERG amplitudes were about 2/3 of those of normal C57BL/6J mice. Immunohistochemistry showed human CNGB3 staining in the inner segment and outer nuclear layer of many cones in treated eyes but not in cones from partner untreated eyes. Anti-M-cone and S-cone opsin staining also showed that both M-and S-cone degeneration was rescued in treated eyes but not in untreated eyes of Cngb3 knockout mice.
Conclusions: :
AAV mediated human CNGB3 expression corrects a cone CNGB3 deficiency in a mouse model of human Achromatopsia 1. This genetic intervention restores cone function and prevents cone degeneration in Cngb3 knockout mice.
Keywords: color vision • gene transfer/gene therapy • retinal degenerations: hereditary