FoxO1, together with Notch1, promotes microglial activation to induce pathological changes in the retinal vasculature under hypoxia

Microglia, the resident immune cells in the retina, play important roles in the retinopathies. Although the role of the Notch signaling pathway in microglial activation and inflammation in neuroinflammatory diseases has been extensively studied, less is known about the effects of Notch signaling on retinal microglia in ischemic retinopathies. Here, we demonstrated that hypoxia triggers Notch1-FoxO1 nuclear translocation in retinal microglia, driving proinflammatory and proangiogenic phenotypes that disrupt vascular homeostasis. We first showed that hypoxia induced microglial activation and upregulated the levels of proinflammatory cytokines IL-1β, IL-6, and TNF-α and proangiogenic factors FGF2, VEGF, and PDGF-β, which promoted retinal vascular endothelial cell dysfunction, marked by increased cellular permeability, migration, and tube formation. We then identified the Jagged1-Notch1 pathway and FoxO1 nuclear translocation as a pivotal signaling axis driving this proinflammatory microglial response under hypoxia. Finally, we demonstrated the therapeutic potential of this axis by showing that inhibition of Notch1 or FoxO1 in hypoxia-activated microglia and in the eyes of oxygen-induced retinopathy mice ameliorated both inflammation and pathological neovascularization in the retina. These findings suggest that FoxO1, together with Notch1, promotes microglial activation to induce retinal vasculopathy under hypoxia, indicating that targeting the Notch1-FoxO1 axis may be a therapeutic strategy for ischemic retinopathies.