PCDH15-associated retinopathy in an orthologous Usher mouse and evaluation of potential therapies for progressive vision loss

Abstract

Purpose : Usher syndrome type I (USH1) is characterized by congenital deafness, vestibular areflexia, and progressive retinal degeneration. The protein-truncating p.Arg245* founder variant of PCDH15 has ~2% carrier frequency among Ashkenazi Jews, accounting for nearly 60% of their USH1 cases. Here we will investigate the precise role of protocadherin-15 in light transduction and mechanism of visual deficits and rescue of vision in the Pcdh15^KI/KI mouse model (Pcdh15^R250X; equivalent to human p.Arg245*) by two different modalities.

Methods : Pcdh15^KI mice were generated using CRISPR/Cas9. Retinal function was assessed by electroretinography (ERG),structural integrity by optical coherence tomography (OCT). Light-dependent translocation of phototransduction cascade proteins was determined using immunostaining. RPE65 and CRALBP levels by immunoblot. Rescue strategies included exogenous retinoids delivery via intraperitoneal injections, and AAV mediated gene delivery via subretinal injections.

Results : Our results showed Pcdh15^KI mutants recapitulates human p.Arg245* visual deficit phenotype. ERG showed attenuated a- and b-wave amplitudes and OCT showed no gross retinal degeneration. We found light-dependent translocation of arrestin and transducin was perturbed in mutant mice, indicating protocadherin-15 has an important role in rapid shuttling of proteins from outer segments to inner segments and vice versa, under light adapted conditions. We found lower levels of visual retinal cycle proteins RPE65 and CRALBP. For the rescue of retinal phenotype, administration of exogenous 9-cis retinal, improved ERG amplitudes in these mutant mice. We evaluated dual AAV PCDH15 mediated expression of full length PCDH15 in Pcdh15^KI/KI MSC’s (Mesenchymal stem cells). Currently, we are evaluating the impact of subretinal injections of dual AAV vector containing full length PCDH15 gene in Pcdh15^KI mutant mice. Results of these studies will be presented in the meeting.

Conclusions : Our current findings support a role for visual retinoid cycle dysfunction in Pcdh15^R250X mutant mice suggesting a basis for a clinical trial of exogenous FDA approved retinoids to preserve vision in USH1F patients. Finally, dual AAV PCDH15 vectors mediated gene replacement therapy is one of the treatment modalities to rescue vision function in USHIF patients at the early stage.

This is a 2021 ARVO Annual Meeting abstract.