Gene therapy restores vision in rd1 mice after removal of a confounding mutation in

Abstract

Purpose: The rd1 mouse carries a naturally occurring non-sense mutation in the Pde6b gene and is a widely used animal model for studying mechanisms of retinal degeneration. Efforts to provide effective sustained rescue of visual function and to prevent degeneration through either local or systemic intervention, have resulted in limited success to date. Having demonstrated successful rescue in the fast retinal degeneration Aipl1^-/- mouse we sought to determine whether an optimized gene therapy could improve rescue of the rd1 mouse.

Methods: We administered AAV8 or AAV9 vectors containing an expression cassette of human rhodopsin promoter driving expression of the human PDE6B gene subretinally to rd1 C3H mice at postnatal day 9. We measured the impact on retinal structure and function using ERG, fundus and OCT imaging, immunohistochemistry, visual acuity and vision-guided fear conditioning.

Results: AAV-mediated gene supplementation of rd1 C3H mice resulted in preservation of photoreceptor cells and restoration of the photoreceptor-mediated a-wave, but did not restore the bipolar cell-mediated b-wave. Backcrossing the rd1 C3H line onto the C57Bl/6 background showed that rescue of the functional deficit in the rd1 mouse by PDE6B gene supplementation therapy was compromised by the presence of a confounding mutation in the Gpr179 gene, which encodes a G-protein coupled receptor localized to ON bipolar cells. PDE6B gene supplementation therapy in rd1 mice without the Gpr179 mutation was able to restore successfully the function of both photoreceptors and bipolar cells, with rescue of ONL thickness to 80% and recovery of ERG to 60%, of wild-type levels, maintained for up to 13 months.

Conclusions: Both AAV8 and AAV9 vectors can mediate robust, long-term structural, functional and behavioural rescue of blind rd1 mice. More importantly, the identification of a secondary mutation in the ON bipolar cells of the rd1 C3H line may explain failure of previous gene therapy attempts in this model. We propose that Grp179 mutation status should be taken into account in future studies involving rd1 mice.