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Zuoming Zhang, Jijing Pang, Feng Xia, Qun Guo, Li Li, Jing An, Lei Zhang, William W. Hauswirth, Shaowei Yang, Zhenfeng Li; AAV-mediated Gene Therapy Restores Cone Function In A Rat With An M-cone Opsin Deficiency, A Model For Blue Cone Monochromacy. Invest. Ophthalmol. Vis. Sci. 2011;52(14):1403.
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© ARVO (1962-2015); The Authors (2016-present)
Using an AAV vector targeting human L-cone opsin or rat M-cone opsin expression to cones, we aimed to test gene therapy in a naturally occurring m-cone opsin mutant rat model.
Abnormal cone response phenotype male Sprague-Dawley (SD) rats (outbreed strain) were analyzed to identify the inherited trait and the causative mutation. To develop a gene therapy, two AAV vectors were constructed. The first was a serotype 5 AAV with the human red opsin promoter (PR2.1) driving expression of a human L-opsin cDNA (hROps). The second was a serotype 8 AAV containing a Y-F mutation at capsid position 733 (AAV8-733) with the same promoter driving a rat M-opsin cDNA. One microliter of each vector containing 1010 vector genomes was subretinally injected into one eye of a cohort of 30 mutant rats, respectively at postnatal day 14 (P14). At 2 months post-treatment the therapeutic effect of vector expression of the two opsin cDNAs was tested by full field photopic and flicker ERG analyses.
The rat with abnormal cone function has an X-linked recessive trait and the causative mutation is in the Opn1mw gene. There was no cone response or flicker ERG under standard intensity flashes in untreated rats, a phenotype that was stably maintained for 16 generations over 7 years. Histologically, there was no obvious change in retinal thickness, structure or the number of M-cones. After subretinal injection of the AAV5 vector expressing the human L-opsin in rat cones, there was no obviously change in cone single flash or flicker ERG at 2 months post-treatment. In contrast, the AAV8 (733) vector encoding the rat M-opsin yielded robust cone function rescue.
Since there is no L-cone opsin in the rat, this rat strain lacking M-cone function can be considered a model for combined L and M cone function loss in humans, a condition termed Blue Cone Monochromacy. Replacement gene therapy using a subretinally delivered AAV vector restores cone function in this model when using the homologous rat M-opsin cDNA but not when using the human L-opsin cDNA perhaps due to incompatibility of the human opsin with one or more components of the rat phototransduction complex.
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