Proangiogenic M2-type macrophages and choroidal neovascularization

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SUMMARY Macrophages infiltrate the site of inflammation and polarize to either antiangiogenic M1-type macrophages or proangiogenic M2-type macrophages, depending on the presence of various cytokines and other external factors. Proangiogenic M2-type macrophages are major contributors to inflammatory angiogenesis in many common diseases, in part by secreting proangiogenic factors, such as VEGF-A or IL-1b. Notably, M2-type macrophages accumulate in areas of choroidal neovascularization (CNV) in patients with neovascular AMD. The increase in M2-type macrophage-derived cytokines in eyes of patients with neovascular AMD has implicated this cell population as a major driver of CNV pathogenesis. This hypothesis is further supported by the observation of an accumulation of M2-type macrophages in laser-induced CNV or in a genetic VEGF-A-induced mouse model of neovascular AMD. Ablation of macrophages in laser-induced CNV, which are predominantly M2-type macrophages, blocked CNV, whereas administration of M2-type macrophages in the eye promoted CNV. Based on these findings we propose that pharmacologic therapies that prevent M2-type polarization of macrophages can serve as a novel approach to potently inhibit CNV progression in patients with neovascular AMD. The limited understanding of the signaling mechanisms that are regulating M1- versus M2-type polarization of macrophages has hindered the identification of molecular targets and pharmacologic inhibitors to selectively block M2-type macrophage polarization. To address this unmet need, we have performed global quantitative time-course proteomics and phosphoproteomics and identified kinase activation events that are associated with M1- versus M2-type macrophage polarization. Furthermore, we identified in chemical screens pharmacologic inhibitors of M2-type polarization that selectively block M2- but not M1-type polarization. Thus, the combination of these two approaches provides us now with a unique resource to establish novel therapies that selectively block proangiogenic M2- but not antiangiogenic M1-type macrophages in CNV. In proof-of-principle experiments we can show that two of the identified inhibitors, the MEK inhibitor trametinib and the HDAC inhibitor panobinostat, blocked M2-type macrophage polarization in CNV lesions and potently inhibited CNV lesion formation in laser- induced CNV experiments. Our proposed experiments will test identified kinase and non-kinase inhibitors in a systematic manner for their ability to selectively block M2-type polarization in detailed in vitro experiments as well as in three well-established mouse models of neovascular AMD. Our proposal is based on extensive preliminary data that provide a strong scientific premise. The proposed experiments have high rigor and important clinical relevance and will likely lead to novel therapeutic approaches for neovascular AMD.