135. AAV-Mediated Gene Delivery To Evaluate the Biology of an Inherited Macular Degeneration

Abstract

Malattia Leventinese (ML) is an autosomal dominant inherited macular degeneration with a middle-age onset. Phenotypically, the disease closely resembles Age-related Macular Degeneration (AMD), a condition affecting 20% of the population over age 65 and the leading cause of blindness in the elderly in the Western world. There is no cure for macular degeneration, and the supportive treatments are limited. Patients with ML suffer from decreased visual acuity and have a characteristic radial pattern of spots, called drusen, in their maculas. Clinical exam reveals geographic atrophy, pigmentary changes, and choroidal neovascularization. Histopathology reveals deposits between the retinal pigment epithelium (RPE) and Bruch's membrane, similar to what is found in AMD. A missense mutation, R345W, in the Epidermal Growth Factor Containing Fibrillin-like Extracellular Matrix Protein 1 (EFEMP1) gene is responsible for the disease, and leads to the misfolding and inefficient secretion of the protein. To gain insight into the role of EFEMP1 in the retina in health and disease, we studied the localization of the wild-type Efemp1 protein and mRNA in the developing mouse retina. Efemp1 protein localizes first to the inner retina and RPE of the mouse, with localization to photoreceptors detectable by postnatal day 14. We also found that Efemp1 protein colocalized with TIMP-3 in the inner retina throughout murine ocular development. Efemp1 mRNA was broadly distributed across the developing retina, and then was concentrated in photoreceptors and ganglion cells by adulthood. An AAV2/5 vector carrying FLAG-tagged mutant Efemp1 was delivered into the wild-type mouse retina, and this resulted in the targeting of the fusion protein to the photoreceptors and RPE. There, it was detected in cytoplasmic aggregates by EM immunohistochemistry. We also identified radial lesions resembling those seen in ML patients. Studies involving non-human primates are in progress. Our results demonstrate that EFEMP1 is a component of the inner and outer retina, but that the mutant form aggregates in the cytoplasm and induces lesions by a yet unknown mechanism. Generation of ML-like lesions in mice and non-human primates via gene delivery promises to be useful in generating animal models for macular degenerative disease in order to define the pathogenetics of the disease and to identify therapeutic targets.