The goal of this project is to develop a genetic therapy for autosomal dominant retinitis pigmentosa (ADRP). Retinitis pigmentosa is a type of inherited retinal degeneration caused by the death of rod photoreceptor cells. It affects about 1 person in 3500 and leads to a progressive loss of vision and ultimately blindness, usually over a period of decades. Mutations in over 30 genes lead to retinitis pigmentosa, but defects in the gene for rhodopsin, the major light-harvesting pigment of the rod cell, are the predominant cause of ADRP. These dominant mutations lead to a malfunctioning, mis-sorted, or poorly folded molecule that eventually kills the rod cell that makes it. Our underlying hypothesis is that reducing the expression of these mutated forms of rhodopsin can rescue rod photoreceptors and preserve vision. The genetic tool we will employ for this purpose is a catalytic RNA molecule or ribozyme. Small ribozymes can be engineered to sever almost any RNA in a sequence-specific manner. The instrument we use to introduce the ribozymes into retinal cells is recombinant Adeno-Associated Virus or AAV. During the current funding period, we have designed ribozymes specific for mutant rhodopsin mRNA present in transgenic rat models of ADRP. When delivered to animals bearing the P23H rhodopsin mutation, these hammerhead and hairpin ribozymes protected photoreceptors structurally and functionally for up to 8 months. In this proposal, we describe plans to extend these promising results by improving the ribozymes and the AAV vectors that deliver them; by testing the therapy in a large animal model of ADRP (transgenic pigs); by developing allele-independent ribozymes to treat a variety of rhodopsin mutations; by employing novel RNA catalysts to increase the number of potential target sites in rhodopsin mRNA; and by evaluating gene therapy in outbred mice carrying the P23H mutation. This work will be aided by non-invasive analytical techniques that permit us to monitor retinal degeneration and the efficacy of therapy in living animals. We hope that the successful completion of this project will bring us close to employing AAV-vectored ribozymes as therapy for autosomal dominant retinitis pigmentosa in human patients.
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