Gene Replacement Therapy in a Mouse Model of AIPL1-Related LCA Results in Restoration of Beta-PDE Transport and Preservation of Photoreceptor Cells

Abstract

Purpose: : Defects in the gene encoding aryl hydrocarbon receptor-interacting protein-like 1 (AIPL1) result in Lebers Congenital Amaurosis (LCA) which is a severe form of early onset retinal dystrophy. The gene is expressed in rods and cones and encodes a specialised chaperone for the biosynthesis of cGMP phosphodiesterase (PDE), an enzyme involved in phototransduction. The aim of this study was to investigate the efficacy of gene replacement therapy in a hypomorphic AIPL1 transgenic mouse model.

Methods: : An AIPL1 expression cassette, driven by a CMV promoter, was packaged into a recombinant adeno-associated virus (rAAV) - serotype 2. The rAAV vector was delivered into the right eyes of AIPL1 knockdown transgenic mice by two subretinal injections into the superior and inferior hemispheres. The contralateral eyes were uninjected to serve as an internal control. Full field electroretinograms (ERGs) were recorded from both eyes simultaneously at monthly intervals up to 7 months. The retinas were analysed by immunostaining and histology after final follow-up.

Results: : . ERG b-wave amplitudes recorded from the treated eyes were 23% higher than untreated eyes (p<0.05) at 5 months after injection and this difference was maintained up to 7 months demonstrating sustained preservation of function. Treated eyes had thicker outer nuclear cell layer and better preservation of retinal architecture. Morphometric analysis showed that treated eyes had 30% more photoreceptor cells (p<0.003). Immunohistochemistry showed increased AIPL1 expression and correct localization of cGMP PDE to the outer segments in treated eyes, while in untreated eyes, cGMP PDE was mislocalised to inner segments.

Keywords: gene transfer/gene therapy • photoreceptors • retinal degenerations: cell biology