The Role of APOE Signaling in Microglia in Glaucoma

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This proposal describes a 3-year training program for the development of an academic career focused on understanding the role of retinal neuroinflammation in glaucoma. My research goal is to elucidate the role of microglia, resident immune cells in the retina and the brain, in the pathogenesis of glaucoma. Our preliminary data demonstrate that in the microbead glaucoma model, microglia suppress homeostatic genes and induce a disease-associated molecular signature (MGnD), which is shared with brain neurodegenerative diseases. In addition to the induction of proinflammatory cytokines and neurotoxic substances, MGnD microglia also significantly upregulate production of APOE, the major lipoprotein in the brain. APOE has recently been found to critically regulate MGnD molecular signature in brain microglia, and is genetically linked to Alzheimer’s disease, age-related macular degeneration, and glaucoma. Furthermore, we have found that mice in which APOE has been targeted only in myeloid cells (microglia and peripheral monocytes/macrophages) are protected from microbead-induced glaucoma. We hypothesize that APOE controls the switch of retinal microglia from homeostatic to a harmful neurodegenerative phenotype, and that in the absence of APOE, microglia remain in the homeostatic state, leading to a decreased retinal neuroinflammatory response and RGC degeneration following intraocular pressure (IOP) elevation. We will address this hypothesis in the following specific aims: 1) Determine the functional impact of microglia-specific APOE targeting in glaucoma. In this aim, we will address whether selective ablation of APOE in microglia utilizing tamoxifen-inducible Cx3cr1-CreERT2 APOEfl/fl mice leads to behavioral and functional neuroprotection after IOP induction, as assessed by optokinetic response, electroretinogram, and visual evoked potential testing. 2) Investigate the mechanism by which APOE signaling contributes to glaucoma pathogenesis. We will investigate the hypothesis that targeting APOE in microglia maintains these cells in the homeostatic state, resulting in decreased apoptotic neuron phagocytosis and cytokine production. 3) Characterize the role of human APOE isoforms in the mouse model of glaucoma. By using novel humanized-floxed APOE e2, e3 and e4 mice, we will investigate the hypothesis that mice with APOE e4 allele exhibit an altered microglial molecular signature and are less susceptible to RGC loss after microbead-induced IOP elevation. The research outlined in this proposal will serve to investigate the role of APOE signaling in microglia in glaucoma, with the ultimate goal of developing novel neuroprotective treatments for this common blinding disease. This research addresses an understudied area of neuroinflammation in glaucoma while also preparing me for a successful career as an independent clinician-scientist.