Racial disparities of open angle glaucoma: A study of mitochondria and oxidative stress in human trabecular meshwork

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Project Abstract: Understanding the pathogenesis of glaucoma, a leading cause of blindness worldwide, is an important goal of vision research. As indicated in numerous population-based studies, individuals of African descent develop glaucoma at an earlier age with increased severity and risk of blindness. Many studies have identified oxidative damage to the trabecular meshwork (TM) cells, leading to decreased outflow facility and increased intraocular pressure. Although the evidence linking oxidative damage to glaucoma is strong, the causes of oxidative damage in glaucoma are not known. In the proposed studies, we will test the hypothesis that oxidative damage to the TM is associated with basic genetic and physiologic differences in oxygen metabolism leading to disparities in glaucoma based on racial background. Our hypothesis is based on intraocular measurements of oxygen partial pressure (pO2) made in the human eye during surgery. We identified strong correlations between pO2 and important risk factors for glaucoma, including central corneal thickness and African-American/Black (B) heritage. In addition, measurements of a cell marker for DNA oxidative damage were elevated in the aqueous humor of B patients with severe glaucoma compared to W patients. Cultured TM cells from B healthy donors compared to W cells had altered energy (ATP) and reactive oxygen species production, implicating the energy processing organelles, the mitochondria. Our specific aims will test these hypotheses: (Aim 1) will evaluate differences in TM gene expression between B and W donor controls and in patients at various glaucoma stages in order to identify the genetic basis of disparities in tissue function (controlling eye pressure) and susceptibility to damage. Genes of interest will be further studied (RT-qPCR, in situ hybridization) and delineate protein expression (Western blot) in the tissue and potential biological pathways involved, focusing on mitochondrial function, oxidative stress and antioxidant protection. (Aim 2A) will study mitochondrial functions in primary human TM cell cultures from specimens of B and W healthy donor controls and glaucoma patients at various severity stages. We will determine the effects of racial differences and exposure to varying levels of pO2 on detailed analyses of mitochondrial quantities and function, reactive oxygen species levels and antioxidant protection. (Aim 2B) will also assess the cellular effects of potential antioxidative therapies. The proposed research is innovative because understanding these physiological mechanisms potentially contributing to disease disparity based on racial ancestry, confirmed by blood and tissue ancestral genotyping and mitochondrial DNA haplogroup stratification, will provide important information about the pathophysiology of open angle glaucoma by identifying factors responsible for the TM dysfunction and loss of aqueous outflow facility. The knowledge gained in these studies may lead to new therapies and strategies to prevent this blinding disease.