Testing Gene Therapy in Models of Geographic Atrophy

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Chronic inflammation is a characteristic, and possibly a cause, of the retinal damage associated with age related macular degeneration (AMD), a leading cause of blindness among the elderly. Inflammation may be a consequence of age related oxidative stress or accumulation of toxins within the RPE and retina. This is a project to develop gene therapy for AMD by preventing inflammatory processes signaled by potent cytokines such as IL-1β. It is our hypothesis that, by reducing inflammation associated with these signaling molecules, we can halt the progression of AMD in patients diagnosed with early stage disease. There are two forms of the advanced disease, wet (exudative) AMD and geographic atrophy, both of which lead to loss of central vision. While there are effective treatments for wet AMD, there is no treatment for geographic atrophy, which leads to death of the retinal pigment epithelium and photoreceptor cells in the macula. Furthermore, atrophic processes may persist in wet AMD, even when choroidal neovascularization is under control. This project is a collaboration between two groups that have generated distinct mouse models for geographic atrophy. One of the models increases oxidative stress in the retinal pigment epithelium (RPE) by deleting the gene for a protective enzyme, manganese superoxide dismutase. The second model deletes the gene for the aryl hydrocarbon receptor (AhR), causing ocular dysregulation of several pathways relevant to AMD including cholesterol homeostasis and clearance of oxidative stress-inducing toxins such as those found in cigarette smoke. Both models result in key features of dry AMD including accumulation of basal deposits in the RPE, damage to Bruch's membrane, RPE atrophy and dysfunction and death of photoreceptors. We propose to develop gene therapy in these models using adeno-associated virus (AAV) which has been demonstrated to be safe for gene transfer to the retina. Importantly, this virus does not provoke a severe inflammatory response. Our approach to therapy in the two models is to deliver genes for secreted, cell penetrating proteins that increase protection from oxidative stress or that reduce the production of inflammatory cytokines by stimulating synthesis of anti-oxidant enzymes or blocking the activity of the NLRP3 inflammasome and preventing the activation of caspase-1. We will validate that delivery of the secreted anti- inflammatory proteins to the vitreous produces peptides that permeate the retina and RPE. In the final component of the project, we will use cell-type specific viral vectors that produce non-secreted peptides in order to identify the cells that are major producers of inflammatory cytokines in our mouse models. Our goal is to develop gene therapy vectors that could be tested in patients, and we believe that one-time delivery of a therapeutic vector to the vitreous will be translatable to human gene therapy.