Transfer: Molecular Mechanisms of Glaucoma

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SUMMARY Glaucoma is a group of optic neuropathies characterized by slow, progressive loss of retinal ganglion cells (RGCs), optic nerve degeneration and as a consequence, vision loss. It has been estimated that more than 70 million people are currently affected by glaucoma with approximately 10% being bilaterally blind, making it the leading cause of irreversible blindness in the world. Several glaucoma categories exist, but in United States, most of the cases are primary open-angle glaucoma (POAG), a variant particularly prevalent amongst African Americans. POAG is recognized as a complex disease in which multiple genetic and environmental factors interact. The two leading risk factors, increase intraocular pressure (IOP) and age are related to the extent and rate of RGC loss. Recent advances in genomics have allowed researchers to describe genetic association between the risk of glaucoma and specific genomic loci. Nevertheless, despite years of research, the molecular basis of glaucoma is poorly understood and the factors contributing to its progression have not been fully characterized. In our recent work, we have used a mouse model to study the molecular impact of Six6 risk variant in development of glaucoma and in RGC death. We observed that upon increased IOP, expression of Six6 increases and directly regulates the expression of p16Ink4a, leading to enhanced senescence in RGCs and most likely directly causing RGC death. The gene encoding p16INK4a, CDKN2A, lies within the tumor suppressor locus on human chromosome 9p21. This locus has been independently identified by several groups to have the highest association with POAG in different population samples. Gene regulation within the 9p21 locus has been extensively studied in many laboratories; however, a molecular analysis has never been performed specifically in relation to glaucoma. Mouse Six6 harbors His at position 141 and therefore is ideal to investigate the molecular role of this variant in glaucoma. However, due to the lack of non-risk variant in mouse strains, it is not possible to study the contribution of both variants on RGC development and degeneration in a mouse model. Here, we propose to use CRISPR/Cas9 technology to engineer mice harboring human non-risk variant of SIX6 to study the impact of each variant in pathogenesis of glaucoma. We will use state-of-the art molecular and cellular technologies to study retinal development and RGC degeneration upon elevated intraocular pressure as a function of the particular variant of SIX6. In addition, we will investigate the molecular mechanisms of p16Ink4a upregulation in the etiology of the disease using transcriptomic and epigenomic approaches, and we will propose the methodology to downregulate its expression in the eye. The proposed combination of approaches will move forward the general understanding of the etiology of glaucoma and provide the molecular basis for development of novel, personalized, therapeutic strategies to improve the quality of life for glaucoma patients.