Pathogenic Role of DNA-Damage Response Pathway in the Diabetic Retina

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Diabetic retinopathy has been associated with oxidative stress, mitochondrial dysfunction, and chronic activation of inflammatory and degenerative pathways. Substantial evidence implicates the retinal mitochondrial ‒ oxidative stress axis as a major unifying pathogenic factor for virtually all diabetes-induced cellular changes implicated in the development of retinal complications. Therapies directed against these individual pathways have provided disappointing results in human clinical trials. Likewise, clinical trials utilizing antioxidants have produced equally ambiguous results. Taken together, these trials suggest a significant knowledge gap regarding underlying mechanism(s) linking oxidative stress to activation of pro-inflammatory and pro-degenerative pathways in diabetic retinas. Based on our previous work in Spinocerebellar ataxia type 3 patients, together with new data provided in this revised application using relevant retinal cells, we propose the novel hypothesis that ROS-mediated DNA damage in diabetes chronically activates the DNA damage response (DDR) ATM (ataxia-telangiectasia mutated) pathway. There is a strong link between increased DNA damage accumulation and development of diabetic complications including retinopathy. Also, there is a growing consensus that ATM not only acts as a DNA damage sensor to coordinate repair of damaged sites to maintain genome integrity but also plays a critical role in modulating the activities of cellular metabolic sensors to interfere with mitochondrial function, cellular energy homeostasis, inflammation, and apoptosis. How the DDR-ATM pathway interconnects various signaling components to disrupt cellular energy metabolism and enhance pro-degenerative signaling is the subject of intense investigation but remains unexplored in the retina. Our recent studies have shown that chronic activation of the DDR pathway interferes with mitochondrial function by suppressing PGC-1α activity, a key transcription co-activator that regulates mitochondrial biogenesis, oxidative phosphorylation, and cellular energy homeostasis. Our new preliminary data demonstrating increased DNA damage and ATM activation in diabetic retina supports our hypothesis. The experiments proposed in this application will test the central hypothesis that diabetes-induced oxidative stress causes double stranded DNA damage resulting in ATM activation, leading to downregulation of PGC1α that impacts multiple pathogenic pathways observed in diabetic retinas. We hypothesize that ATM activation induces a significant amplification of diabetes-induced oxidative stress via mitochondrial disruption by multiple mechanisms (aim 1), vascular and neuronal degeneration (aim 2), and chronic inflammation (aim 3). These aims have the potential to establish a unifying molecular mechanism that links enhanced DNA damage to chronic oxidative, degenerative, and inflammatory abnormalities observed in diabetes. The greatest impact of our work is to provide a regulatory mechanism offering a novel explanation for how hyperglycemia impacts mitochondrial dysfunction to amplify oxidative, inflammatory and degenerative changes in the retina. PHS 398/2590 (Rev. 06/09) Page Continuation Format Page