PTD-A2 blocks retinal and Matrigel-induced angiogenesis. (A and B) TAT-A2 Matrigel-induced tube formation was assessed in HUVECs. Bars, 200 µm. Tube lengths are presented as the percentage of total tube length per field versus control cells. n = 5. (C) Visualization of blood vessels by iB4 staining of NGR-A2–injected retinas from P5.5 mice. Bars: (top) 500 µm; (bottom) 200 µm. Bottom images are enlargements of the boxed regions in the top panel. (D–F) Radial expansions (D), retinal vascular branch points (E), and sprouts per field (F) were quantified. n = 4–5. (G) Male C57BL/6 mice (n = 6 per group) received subcutaneous injections of Matrigel containing PBS, 200 ng VEGF, 25-µM Con with VEGF, or 25-µM TAT-A2 with VEGF. Matrigel plugs were removed 5 d after implantation, fixed, sectioned, and stained for immunohistochemistry with anti-CD31 antibody (red) for the identification of endothelial vessels. DAPI (blue) was used for nuclei labeling, and visualization was performed using confocal microscopy. Bars, 50 µm. (H) Quantification of neovessel formation by measuring hemoglobin in the Matrigel. (I) Quantitative assessment of CD31-positive ECs. *, P < 0.05; **, P < 0.005; ***, P < 0.0005; ns, not significant. Data are means ± SD.