Heat shock protein 90 alpha (Hsp90 alpha) is a ubiquitously expressed molecular chaperone, which is essential for the maintenance of eukaryote homeostasis. Hsp90 alpha can also be secreted extracellularly and is associated with several physiological and pathological processes including wound healing, cancer, infectious diseases and diabetes. Angiogenesis, defined as the sprouting of new blood vessels from pre-existing capillaries via endothelial cell proliferation and migration, commonly occurs in and contributes to the above mentioned processes. However, the secretion of Hsp90 alpha from endothelial cells and also its function in angiogenesis are still unclear. Here we investigated the role of extracellular Hsp90 alpha in angiogenesis using dermal endothelial cells in vitro and a wound healing model in vivo. We find that the secretion of Hsp90 alpha but not Hsp90 beta is increased in activated endothelial cells with the induction of angiogenic factors and matrix proteins. Secreted Hsp90 alpha localizes on the leading edge of endothelial cells and promotes their angiogenic activities, whereas Hsp90 alpha neutralizing antibodies reverse the effect. Furthermore, using a mouse skin wound healing model in vivo, we demonstrate that extracellular Hsp90 alpha localizes on blood vessels in granulation tissues of wounded skin and promotes angiogenesis during wound healing. Taken together, our study reveals that Hsp90 alpha can be secreted by activated endothelial cells and is a positive regulator of angiogenesis, suggesting the potential application of Hsp90 alpha as a stimulator for wound repair. (C) 2010 Elsevier Inc. All rights reserved.