The annexin A2 system promotes retinal neoangiogenesis in OIR. (A) Schematic diagram showing areas occupied by total retina (green), regions of vaso-obliteration (yellow), and regions of neovascularization (red) in mice maintained in room air (RA) or treated with oxygen from P7 to P12 (OIR). (B) Representative retinal images showing total retinal area and regions of vaso-obliteration and neovascularization in P17 oxygen-treated Anxa2^+/+ and Anxa2^−/− mice. Pixel number corresponding to each compartment is indicated below each image. (C) Ratios of vaso-obliterative (VO) to total retinal area (25.6% ± 1.0% vs 27.5% ± 1.1%) and neovascular (NV) to total retinal area (12.1% ± 0.5% vs 4.7% ± 0.4%) in oxygen-treated P17 Anxa2^+/+ (n = 7) and Anxa2^−/− (n = 9) mice (NS indicates no significant difference; ***P < .001). (D) Representative retinal cross-sections (magnification ×40), with close-up views of peripheral region (magnification ×200) of retinas from oxygen-treated P17 Anxa2^+/+ and Anxa2^−/− mice stained with DAPI (blue) and isolectin B4 (green). Neovascular tufts penetrating the inner limiting membrane (highlighted with a white dashed line) are indicated by arrowheads. (E) Enumeration of neovascular nuclei in retinal sections from P17 oxygen-treated Anxa2^+/+ versus Anxa2^−/− (194.5 ± 5.2; n = 8 vs 87.4 ± 4.6; n = 10; ***P < .001) mice. Scale bars, 200 μm (B; magnification ×50), 500 μm (D; magnification ×40), 100 μm (D; magnification ×200).