Abstract 3387: Hypoxia-induced Vascular Repair by Progenitor Cells Requires the Nadph Oxidase Nox2

Abstract

Endothelial progenitor cells (EPC) promote vascular repair but the impact of systemic hypoxia on EPC function is unclear. Hypoxia is a strong stimulus for angiogenesis and affects reactive-oxygen species (ROS) production and signalling. We studied the role of hypoxia for EPC mobilization and vascular repair and the contribution of the NADPH oxidase Nox2, the most important source of ROS in endothelial cells, in this process. Murine EPCs were defined as linage negative and sca-1/flk-1 positive and measured by FACS from whole blood. Vascular repair was induced by the carotid artery wire injury model. Hypoxia (10%, 96hours) induced mobilisation of EPC and improved vascular repair after wire injury in wild-type mice but not in NADPH oxidase knockout mice (Nox2y/−). Hypoxia induces the formation of erythropoietin (EPO), which might contribute to EPC mobilization. EPO production in response to hypoxia however was enhanced in Nox2y/− as compared to WT mice. Importantly, EPO, which induced pronounced EPC mobilization in WT mice, failed to do so in Nox2−/− mice. These data suggest that EPO signalling is defective in Nox2y/− mice. Indeed, in EPCs from WT-mice, EPO induced ROS production and proliferation and both responses were missing in EPCs from Nox2y/− mice. Transplantation of bone marrow from Nox2y/− mice into WT mice resulted in an attenuated mobilization in response to hypoxia and EPO, whereas the transplantation of WT bone marrow into Nox2y/− mice restored the normal phenotype . This demonstrates that a failure of bone marrow stem cells to generate ROS in response to EPO underly the mobilization defect. We conclude that Nox2-derived ROS are required for EPO-signalling in stem cells and that hypoxia-induced EPC mobilisation and vascular repair requires the NADPH oxidase Nox2.