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Freya M. Mowat, Joshua T. Bartoe, Ashlee Bruewer, Astra Dinculescu, Sanford L. Boye, William W. Hauswirth, Simon M. Petersen-Jones; Evaluation Of Rod Photoreceptor Function And Preservation Following Retinal Gene Therapy In The PDE6A Mutant Dog. Invest. Ophthalmol. Vis. Sci. 2012;53(14):1928.
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The PDE6A mutant dog has a null mutation in the phosphodiesterase 6A gene (PDE6A) that results in absence of rod function and rapid rod degeneration. The affected dogs lack both gamma and beta subunits of PDE6 as well as the alpha subunit. Our attempts to rescue this severe phenotype with an adeno-associated viral vector serotype 5 (AAV5) vector proved unsuccessful. Our hypothesis was that a next-generation AAV serotype 8 vector-type containing an engineered capsid mutation would be successful in rescuing this phenotype.
30-day old PDE6A mutant dogs received a unilateral subretinal injection of AAV8 mut733 smCBA-cPDE6A. Approximately 100µl of 4.19 x1011 vector genomes/ml were delivered. Dark- and light-adapted ERGs were recorded and rod-mediated vision was assessed via dim-light maze testing at 2-week intervals following treatment. Animals were sacrificed 3-4 months after injection and immunohistochemistry for retinal antigens including PDE, rod, cone and inner retinal markers was performed on retinal cryosections from treated and untreated eyes.
There was evidence of rod function in the treated eyes. ERGs showed improved threshold with a scotopic threshold response and small rod-shaped ERG responses. Improvement in rod-mediated vision was detected in treated eyes using maze testing. In treated eyes, rod photoreceptors were preserved in the injected area, and PDE expression correlated with both photoreceptor preservation and improved localization of rhodopsin to the rod outer-segments.
We have shown for the first time that AAV gene therapy can provide partial rescue of rapid retinal degeneration in the PDE6A mutant dog, an important model for a form of human retinitis pigmentosa.
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