Age-related macular degeneration (AMD) causes vision loss among many older individuals, and the retinal pigment epithelium (RPE) is thought to be a critical site of injury. Vision loss in AMD occurs due to photoreceptor degeneration and/or choroidal neovascularization. Geographic atrophy (GA), the advanced form of dry AMD, is characterized by the breakdown of RPE, choriocapillaris, and photoreceptors, especially in the macula. Lack of clear understanding of the molecular mechanisms of GA hinders the development of therapy. For lifelong maintenance of photoreceptors, RPE cells play an essential role in phagocytosis and degradation of tips shed from photoreceptor outer segments (POS). Photoreceptors and RPE cells are susceptible to injury from mitochondrial oxidative stress. The central goal of the project is to understand how photoreceptor degeneration occurs in GA. I hypothesize that oxidative stress impairs phagocytosis and lysosome function and ultimately activates inflammatory processes in RPE that stimulate geographic atrophy. I will test my hypothesis in RPE cell culture and in a new mouse model of age-dependent RPE atrophy that was recently developed in our lab. In this model we used the cre/lox system to generate an RPE-specific deletion of Sod2, the mitochondrial gene for manganese superoxide dismutase (MnSOD). These mice develop a normal RPE, but overtime the RPE has elevated oxidative stress resulting in phenotypic changes that are commonly observed in AMD, including RPE injury, loss of function and subsequent retinal degeneration. In the context of GA, I have following aims: (1) To characterize the impact of oxidative stress on phagocytosis, lysosomal function and inflammasome activation in RPE; (2) Identify molecular changes in RPE under oxidative stress. These studies will illuminate signaling pathways that drive photoreceptor and RPE loss and will provide a foundation to develop new therapeutic targets to prevent disease progression in AMD. Overall, this proposal will not only begin to unravel the novel molecular mechanisms of photoreceptor degeneration in GA but will also be instrumental in the training and career development of the candidate, Dr. Manas Biswal. The proposed training plan will allow him to branch into new areas of research including phagocytosis, lysosome biology, and ocular inflammation, and it will train him in new techniques: FACS, Immuno-EM, LC-MS, laser scanning single and multiphoton confocal microscopy, RNA-seq data analysis using bioinformatics tools, biotinylation and 2D-DIGE based quantitative proteomics. This proposal will also support courses, workshops and conferences relevant to his research and training, and will allow him to transition from a postdoctoral fellow to an independent researcher running his own lab.
Over 11 million people in the USA have AMD (Source: Bright Focus Foundation) and are at risk of vision loss due to advanced AMD. Although effective treatments are available for neovascular AMD, no treatments have been proven to prevent the onset or progression of geographic atrophy. Its prevention would be of paramount socioeconomic importance for both the patients and for the healthcare system. The proposed research is relevant to public health because it aims to understand to molecular mechanism of photoreceptor degeneration that occurs in advanced form of this disease. Understanding molecular mechanism will improve understanding of the pathogenesis of dry AMD and it would certainly provide a powerful avenue for development of novel therapeutic strategies.
|Biswal, Manas R; Han, Pingyang; Zhu, Ping et al. (2017) Timing of Antioxidant Gene Therapy: Implications for Treating Dry AMD. Invest Ophthalmol Vis Sci 58:1237-1245|