Vascular endothelial cell (EC) or endothelial progenitor cells (EPC) derived from stem cells could potentially lead to a variety of clinically relevant therapeutic applications including building new blood vessels in both in damaged heart and skeletal muscle, lining small diameter vascular grafts for reduced thrombosis, or in the development of a variety of tissue-engineered materials that will need a vasculature for receiving an adequate blood supply. These cells are also valuable as target for screening for new anti-angiogenic and anti-thormobogenic molecules. However, EC exhibit a variety of functionally distinct subphenotypes. These include the arterial and venous EC, as well as sprouting “tip” and “stalk”, and the lesser understood “phalanx” EC in a sprouting blood vessel. The studies proposed in this grant application explore this potential (and limitations) for directing the fate of EC subphenotypes using biochemical and physical signaling, as well as, examine the molecular mechanisms underlying the specification of these EC subphenotypes. To date, we have been able to generate EC subphenotypes, called tip and stalk EC, consistent with highly angiogenic EC. These are the most relavant EC subphenotype for developing anti-angiogenic strategies associated with tumor progression, as well as, the best EC subphenotype to be used in repairing ischemia in the heart and/or limbs.