Mutation of the type IV collagen alpha 1 gene (Col4a1) gene cause retinal phenotypes in mice that resemble age-related macular degeneration (AMD). Understanding the cellular mechanism(s) that lead from mutation to retinopathy will identify pathways that underlie AMD and/or other retinal diseases. Mutant COL4A1 is misfolded, and secretion is impaired, leading to intracellular accumulation. COL4A1 is the most abundant basement membrane protein and is secreted both from retinal pigment epithelial cells (RPE) and choroidal vascular endothelial cells to contribute to Bruch's membrane. The RPE/Bruch's membrane/choroid complex is an important site of pathogenesis in several retinal diseases. Our preliminary data couple the basic cellular processes of endoplasmic reticulum (ER) homeostasis and detoxification of reactive oxygen species to retinal disease. Physiological insults, including misfolded proteins, can lead to stress in the ER. ER stress activates signaling cascades that seek to restore a homeostasis between the demands of protein production and the protein folding capacity of the ER. Chronic ER stress generates reactive oxygen species that lead to oxidative damage. The ability to detoxify reactive oxygen species decreases with age and oxidative damage is a key mechanism in several diseases of aging. Oxidative damage contributes to chronic inflammation and de-regulation of the alternate complement pathway of innate immunity. Here, we test our hypothesis that misfolded mutant COL4A1 leads to retinopathy via a mechanism of ER and oxidative stress in the RPE and/or choroidal vascular endothelial cells.
In Aim 1 we will conduct a thorough and detailed examination of Col4a1-induced retinopathy via clinical, functional, histological, ultrastructural and molecular analyses.
In Aim 2 we will test the involvement of ER and oxidative stress by molecular interrogation of the pathogenic pathways. RPE and choroidal endothelial cells will be compared for potential molecular differences that could identify the site of primary disease processes.
In Aim 3 we will use mice with impaired ability to alleviate ER stress and mice with impaired ability to detoxify reactive oxygen species to genetically test the relationship and relative importance of each of these pathways. The experiments outlined in this proposal will reveal tangible cellular processes important in pathophysiology of the retina and with potential for broader application. Knowledge of the relative roles of ER and oxidative stress can be exploited in development of targeted therapeutics that could prevent or reduce vision loss in millions of people worldwide.
This application will study two key cellular pathways that lead to a retinal disease in mice that resembles human age-related macular degeneration. Understanding when, where and how these pathways interact could expose them as novel pharmaceutical targets for prevention or treatment of blindness in millions of people worldwide.