Angiopoietin-1 protects endothelial cells from hypoxia-induced apoptosis via inhibition of phosphatase and tensin homologue deleted from chromosome ten

Background and Objectives: Angiopoietin-1 (Ang1) is a regulator of blood vessel growth and maturation, and prevents radiation-induced or serum deprivation-induced apoptosis. Phosphatase and tensin homologue deleted from chromosome ten (PTEN), a well-known tumor suppressor, regulates cell cycle arrest and apoptosis. Hypoxia induces apoptosis by increasing the expression of PTEN. We hypothesized that Angl may regulate PTEN expression and, thus, reduce endothelial apoptosis under hypoxia in vitro and in vivo. Materials and Methods: In vitro, human umbilical vein endothelial cells (HUVECs) were treated with Ang1, and signaling pathways were investigated. In vivo, eight-week-old C57BL/6 mice were used for a hind limb ischemia model. Ang1 or normal saline was intramusculary injected. Blood flow was evaluated by a laser Doppler perfusion analyzer and tissue histology. Results: The expression of PTEN was markedly upregulated in HUVECs after hypoxic stimulation, whereas Ang1 suppressed PTEN expression. Tie2-Fc, a soluble form of Tie2 (sTie2) that blocks Ang1, reversed the Ang1 effect on PTEN reduction under hypoxia. Ang1 inhibited the nuclear translocation of nuclear transcription factor-kB (NFkB), a binding factor for the PTEN promoter and Foxo1. Hypoxia-induced p27 expression and apoptosis were also suppressed by Ang1. In the mouse hind limb ischemia model, we observed a high capillary density, numerous proliferating cells and diminished cell death in skeletal muscle tissue in the Ang1 injected group. Conclusion: Ang1 enhanced endothelial cell survival by reducing apoptosis via PTEN down-regulation in HUVECs under hypoxia. Local injection of Ang1 significantly reduced apoptotic cells in vivo, and prevented limb loss for ischemic hind limb mice. Thus, Ang1 may be an effective therapeutic for protection from ischemic-endothelial cell injury.