Gene Therapy Restores Vision and Delays Degeneration in the CNGB1-/- Mouse Model of Retinitis Pigmentosa
Hum. Mol. Genet., 2012, doi: 10.1093/hmg/dds290, published on 16.07.2012
Retinitis pigmentosa (RP) is a group of genetically heterogeneous severe retinal diseases commonly leading to legal blindness. Mutations in the CNGB1a subunit of the rod cyclic nucleotide-gated (CNG) channel have been found to cause RP in patients. Here, we demonstrate the efficacy of gene therapy as a potential treatment for RP by means of recombinant adeno-associated viral (AAV) vectors in the CNGB1 knockout (CNGB1-/-) mouse model. To enable efficient packaging and rod-specific expression of the relatively large CNGB1a cDNA (approx. 4 kb), we used an AAV expression cassette with a short rod-specific promoter and short regulatory elements. After injection of therapeutic AAVs into the subretinal space of two-week-old CNGB1-/- mice, we assessed the restoration of the visual system by analyzing i) CNG channel expression and localization, ii) retinal function and morphology and iii) vision-guided behavior. We found that the treatment not only led to expression of full-length CNGB1a, but also restored normal levels of the previously degraded CNGA1 subunit of the rod CNG channel. Both proteins co-localized in rod outer segments and formed regular CNG channel complexes within the treated area of the CNGB1-/- retina, leading to significant morphological preservation and a delay of retinal degeneration. In the electroretinographic analysis (ERG), we also observed restoration of rod-driven light responses. Finally, treated CNGB1-/- mice performed significantly better than untreated mice in a rod-dependent vision-guided behavior test. In summary, this work provides a proof-of-concept for the treatment of rod channelopathy-associated retinitis pigmentosa by AAV-mediated gene replacement.