Myeloid glycolysis in pathological ocular angiogenesis

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PROJECT SUMMARY This proposal seeks to develop a new molecular strategy to limit pathological retinal angiogenesis in blinding eye disease. An emerging consensus is that macrophages/microglia drive aberrant neovascularization. However, the mechanisms involved remain poorly defined. Glycolysis is a major metabolic process in macrophages. PFKFB3 (6-phosphofructo-2-kinase/fructose-2, 6-bisphosphatase isoform 3, Pfkfb3 for mice) is a critical enzyme for activation of glycolysis in vascular cells and leukocytes. It catalyzes the synthesis of fructose-2, 6- bisphosphate, which is the most potent allosteric activator of 6-phosphofructo-1-kinase, a rate-limiting enzyme for glycolysis. PFKFB3 is critical for the inflammatory phenotype of macrophages, and glycolysis has been shown to promote activation of hypoxia-inducible factor (HIF) or histone acetylation signaling in some cell types. However the role of PFKFB3 in regulating angiogenesis and the underlying signaling pathways are completely unknown. Our preliminary data show that myeloid cells in the retinas of the mouse model of oxygen-induced retinopathy are hyper-glycolytic, as evidenced by high levels of glycolytic molecules and regulators/activators of glycolysis including Pfkfb3. The majority of these retinal macrophages exhibit a mixed phenotype characterized by increased levels of cell surface markers for both classical and alternative activation and increased expression of both pro-inflammatory and pro-angiogenic factors. This macrophage phenotype is recapitulated in mouse bone marrow derived macrophages treated with conditioned medium from hypoxic mouse retinal endothelial cells or the glycolytic metabolite lactate. We term these unique macrophages as Pathological Angiogenesis- associated Glycolytic Macrophages (PAGMs). Pfkfb3 knockdown in macrophages reduces their expression of pro-inflammatory and pro-angiogenic factors and suppresses neovascularization in hypoxic retinas. These data inform the hypothesis that Pfkfb3-mediated glycolysis in myeloid cells induces vascular growth by activating Hifs and histone acetylation leading to increased production of pro-inflammatory and pro-angiogenic factors. To test our hypothesis, we have generated myeloid cell specific Pfkfb3-deficient mice. We have also established methods for generating BMDMs that are Pfkfb3 deficient (hypo-glycolytic), Pfkfb3 overexpressing (hyper- glycolytic) or Pfkfb3 wild type and for knockdown of Hif1a and Hif2a. We will investigate the effect of modulating glycolysis in PAGMs on pathological angiogenesis using these genetic tools and in vivo, ex vivo, and in vitro models. We propose three specific aims. 1) Hyper-glycolytic PAGMs regulate the sprouting and proliferation of retinal or choroidal endothelial cells by production and release of pro-inflammatory and pro-angiogenic factors. 2) Hifs and histone acetylation pathways are critically involved in PAGM polarization and activation induced by endogenous glycolysis or endothelial derived glycolytic metabolites. 3) Pfkfb3-mediated glycolysis in macrophages/microglia plays an important role in the development of pathological choroidal and intraretinal neovascularization. 1