Previous studies suggest that inflammatory cell adhesion molecules may modulate endothelial cell migration and angiogenesis through unknown mechanisms. Using a combination of in vitro and in vivo approaches, herein we reveal a novel redox-sensitive mechanism by which ICAM-1 modulates endothelial GSH that controls VEGF-A-induced eNOS activity, endothelial chemotaxis, and angiogenesis. In vivo disk angiogenesis assays showed attenuated VEGF-A-mediated angiogenesis in ICAM-1-/- mice. Moreover, VEGF-A-dependent chemotaxis, eNOS phosphorylation, and nitric oxide production were impaired in ICAM-1-/- mouse aortic endothelial cells (MAEC) compared to WT MAEC. Decreasing intracellular GSH in ICAM-1-/- MAEC to levels observed in WT MAEC with 150 μM buthionine sulfoximine restored VEGF-A responses. Conversely, GSH supplementation of WT MAEC with 5 mM glutathione ethyl ester mimicked defects observed in ICAM-1-/- cells. Deficient angiogenic responses in ICAM-1-/- cells were associated with increased expression of the lipid phosphatase PTEN, consistent with antagonism of signaling pathways leading to eNOS activation. PTEN expression was also sensitive to GSH status, decreasing or increasing in proportion to intracellular GSH concentrations. These data suggest a novel role for ICAM-1 in modulating VEGF-A-induced angiogenesis and eNOS activity through regulation of PTEN expression via modulation of intracellular GSH status. © 2006 Elsevier Inc. All rights reserved.