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M. Mihelec, P. K. Buch, A. J. Smith, J. W. B. Bainbridge, D. M. Hunt, R. R. Ali; Gene Therapy in the RetGC Mouse Model of Dominant Cone-Rod Dystrophy. Invest. Ophthalmol. Vis. Sci. 2009;50(13):1739.
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© ARVO (1962-2015); The Authors (2016-present)
Mutations in phototransduction genes are commonly associated with severe retinal degeneration. One such gene is GUCY2D that codes for retinal guanylate cyclase (RetGC) protein. RetGC function is to replenish cGMP following its depletion by light-activated phosphodiesterase. Mutations in GUCY2D are a major cause of dominant cone-rod dystrophy in humans. Our aims are to characterise the retinal degeneration process and to rescue retinal function in RetGC knock-out mice using viral-vector mediated gene therapy.
Analysis of the retinal degeneration process in RetGC knock-out mice was performed using routine histology at various time points. Immunohistochemistry was used for detection of cone specific markers such as -transducin. Electroretinograms (ERGs) were performed to test for photoreceptor function. The human GUCY2D gene was cloned into a recombinant adeno-associated virus (rAAV2/8) vector and delivered using subretinal injections to RetGC knock-out mice.
We have tested knock-out animals at 6, 14, 20 weeks and 18 months of age. ERG analyses show no cone response and a reduced rod response from the earliest time point investigated. There is no change in ERG responses over time. Histological analysis and immunohistochemistry indicate that retinal degeneration in these animals begins with the cone cell loss from 14 weeks of age onwards. The GUCY2D gene was replaced in knock-out animals using rAAV2/8 vector. The rhodopsin kinase promoter was used to ensure the gene expression is driven exclusively in photoreceptors. The outcome of the gene replacement study is currently being investigated.
Our study of retinal degeneration in RetGC knock-out mouse model provides an insight into pathology of cone-rod dystrophies. Understanding the underlying basis of these debilitating diseases is an important step towards developing appropriate treatments for those affected. Our gene therapy study in a murine model of cone-rod dystrophy has direct implications for future treatments in the corresponding human condition.
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