Glaucoma is a common disease of the optic nerve that affects over 60 million people worldwide and is a leading cause of blindness and visual disability in the United States. However, the biological pathways that lead to glaucoma are not well understood, and this has hindered efforts for early detection and treatment of this condition. Consequently, there is great need to clarify the causes of glaucoma at the molecular level. We discovered that duplication of the TANK binding kinase 1 (TBK1) gene is associated with glaucoma that occurs without elevation of eye pressure - termed normal tension glaucoma (NTG). TBK1 function hasn't been studied in the eye although TBK1 has been shown to have a role in autophagy in non-ocular tissue. Autophagy is a cellular process that delivers cytosolic proteins, organelles, and even intracellular pathogens to lysosomes for clearance. Remarkably, three known NTG genes (TBK1, OPTN, TLR4) all interact with each other and have important roles in activating autophagy, which suggests that autophagy may be an important common pathway in NTG pathogenesis. Moreover, autophagy has also been implicated in the retinal ganglion cell death and optic nerve damage in animal models of glaucoma. Based on these data, we hypothesize that TBK1 gene duplication alters autophagy and leads to the retinal ganglion cell death and vision loss of NTG. We have created a unique set of resources to study TBK1, autophagy, and glaucoma: cultured retinal ganglion cells (using induced stem cell technology) that have an extra dose of the TBK1 gene - the same defect as our patients with TBK1-associated glaucoma. Preliminary studies of these cells have provided more evidence that duplication of TBK1 gene activates autophagy and causes glaucoma. To test our hypothesis and investigate the role of autophagy in glaucoma we propose this two-part aim: DETERMINE THE ROLE OF TBK1 GENE DUPLICATION AND AUTOPHAGY IN THE PATHOGENESIS OF NTG USING IPSC-DERIVED RGC-LIKE NEURONS ? Aim 1A: Test cells cultured from patients with NTG due to a TBK1 gene duplication (skin fibroblasts, iPSCs and iPSC-derived RGC-like neurons) for altered autophagy molecules with microscopic, biochemical, and autophagic flux assays. ? Aim 1B: Determine the effect of TBK1 gene duplication on the phosphorylation of its substrate OPTN at key residues necessary for its function in autophagy with immunoprecipitation and western blot analysis with anti-phospho-OPTN antibodies. With these experiments, we will begin to characterize the biological pathway by which defects in the TBK1 gene alter autophagy and lead to glaucoma. These studies will also provide the basis for development of novel glaucoma therapies that are targeted to autophagy and glaucoma that occurs without elevation of eye pressure.

Public Health Relevance

We discovered that defects in the gene TANK binding kinase 1 (TBK1) are a cause of glaucoma, a common optic nerve disease that is a leading cause of blindness and visual disability in the United States. We have proposed a series of experiments that use the unique and powerful resources we have created and collected (adult stem cell-derived optic nerve cells) to elucidate the biological pathway by which defects in TBK1 lead to glaucoma. These experiments will facilitate improved diagnosis of glaucoma; facilitate more accurate prognosis; and provide key insights into the development of novel sight-saving interventions for glaucoma.

National Institute of Health (NIH)
National Eye Institute (NEI)
Exploratory/Developmental Grants (R21)
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Diseases and Pathophysiology of the Visual System Study Section (DPVS)
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Liberman, Ellen S
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University of Iowa
Schools of Medicine
Iowa City
United States
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DeLuca, Adam P; Alward, Wallace L M; Liebmann, Jeffrey et al. (2017) Genomic Organization of TBK1 Copy Number Variations in Glaucoma Patients. J Glaucoma 26:1063-1067