Development of Neuroprotective and Gene Replacement Therapies for Models of Retinitis Pigmentosa and Neuronal Ceroid Lipofuscinosis

Inherited retinal degenerations affect millions of people worldwide, with few or no treatment options. The most prevalent form of progressive retinal degeneration is retinitis pigmentosa, a heterogenous disease affecting over one million people around the world. Over 70 genes have been shown to cause retinitis pigmentosa, mainly affecting rod photoreceptors. As genetic mechanisms are identified, gene therapy becomes a promising potential treatment through gene replacement./nHowever, gene replacement therapy is not a viable option for several of these diseases, where autosomal dominant forms such as the P23H mutation of rhodopsin require gene silencing instead of replacement. Since retinitis pigmentosa patients mostly present mutations in genes necessary for correct function of rod photoreceptors, leading to subsequent loss of cones, it is possible to target cone survival and provide a wide-ranging solution. Rod-derived cone viability factor (RdCVF) has been shown to be essential for cone survival, as it is produced and secreted by rods and promotes glucose uptake by cones. Chapter 2 of this dissertation examines the delivery of RdCVF through an AAV viral vector to a transgenic pig model of autosomal dominant P23H retinitis pigmentosa. Previous studies have shown cone rescue through delivery of RdCVF in mice, and here we explore therapeutic delivery to a large animal model that more closely resembles humans. In this study we report that RdCVF rescue is dose-dependent, as well as dependent on retinal regions reached by AAV. While electroretinogram results are not conclusive, immunohistochemistry indicates improvements in cone morphology and even rod retention in the retinal tissue./nFor more common recessive retinal diseases, such as the wide variety involving neuronal ceroid lipofuscinoses (NCL), gene replacement therapy is desirable. Of the 14 genes responsible for NCL, all but one are recessive, causing lysosomal dysfunction that leads to cerebellar atrophy, seizures, and in most cases retinopathies and vision loss. As gene therapies are developed targeting the brain, it is also advantageous to target the retina, as patients would require both forms of treatment. In chapter 3 of this dissertation, a gene therapy for CLN11, caused by mutations to the progranulin gene, is developed. Progranulin is a protein secreted mainly by microglia in the brain and retina, and is then endocytosed by neurons, thus regulating their lysosomal function. Absence of progranulin causes cerebellar atrophy, seizures, ataxia, dementia and vision loss. In this study we characterize the retinal degeneration in a progranulin knockout mouse model of CLN11 and study the effects of gene replacement at different time points. While mice that receive AAV vectors carrying the progranulin gene at post-natal day 3 or 4 show reduction in retina thinning, mice intravitreously injected at months 1 and 6 show no improvement, and mice injected at 12 months of age show increased retinal thinning in comparison to their controls. Thus, delivery of progranulin proves to be time sensitive, requiring early delivery. This is potentially due to its secretion, although further studies are required to elucidate this phenomenon.

Advisor: Flannery, John G