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Suddhasil Mookherjee, Peter Colosi, Suja Hiriyanna, Kayleigh Kaneshiro, Linjing Li, Haohua Qian, Tiansen Li, Hemant Khanna, Anand Swaroop, Zhijian Wu; A Low Dose AAV Vector Administration Preserves Cone Function in an Rp2 Knockout Mouse Model for Retinitis Pigmentosa. Invest. Ophthalmol. Vis. Sci. 2014;55(13):3310.
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© ARVO (1962-2015); The Authors (2016-present)
Retinitis pigmentosa (RP) is a retinal degenerative disease inherited as autosomal dominant, recessive or X-linked pattern. Mutations in RP2 gene account for approximately 10-20% of X-linked RP cases. To develop gene replacement therapy for the disease, we generated an adeno-associated virus (AAV) vector carrying a human RP2 expression cassette, and tested its ability to complement the Rp2 knockout mouse model.
A self-complementary AAV8 vector composed of a human rhodopsin kinase promoter, CMV/beta-globin intron, the human RP2 cDNA, and the human beta-globin polyadenylation site was generated. Rp2 knockout mice received unilateral subretinal injections of vector at 4-6 weeks of age at doses of 1e8, 3e8 or 1e9 vector genomes (vg) per eye. The fellow eyes were injected with vehicle as a control. The expression of the transgene was analyzed by immunohistochemistry and Western blot. Retinal function and structure of the treated mice were assessed by electroretinography (ERG) and optical coherence tomography (OCT). The mice were sacrificed at 18 months of age for histological and immunohistochemical analysis.
Expression of human RP2 protein was detected in the photoreceptor layer of vector-treated retina. Western blot demonstrated the expected weight of the expressed RP2 protein. A significantly higher photopic ERG response was revealed in vector-treated eyes compared to the control eyes between 4 and 18 months of age for all vector doses. Consistent with this observation, immunohistochemical analysis indicated higher cone density in vector-treated eyes, compared to control eyes, at the final 18 month time point. The progression of rod degeneration is much slower than cone degeneration in this mouse model. At 18 months of age, no significant difference was observed between the vector-treated and the control eyes in either the scotopic ERG amplitude or outer nuclear layer thickness, at a dose of 1e8 vg/eye. However, a decline in the scotopic ERG was observed in 1e9 and 3e8 vg/eye groups at 4 and 12 months of age, respectively. It is likely that the vector is toxic at these higher doses.
Our study demonstrates that an AAV8 RP2 vector preserves cone function and promotes cone survival in an Rp2 knockout mouse model of retinitis pigmentosa. As a potential clinical candidate for the disease, a detailed dose-efficacy profile is being investigated.
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