A role for hematopoietic stem cells in promoting angiogenesis

Angiogenesis is an important event for embryonic organogenesis as well as f or tissue repair in the adult. Here, we show that hematopoietic stem cells (HSCs) play important roles for angiogenesis during embryogenesis. To inves tigate the role of HSCs in endothelial cell (EC) development, we analyzed A ML1-deficient embryos, which lack definitive hematopoiesis. These embryos s howed defective angiogenesis in the head and pericardium. Pars-aortic splan chnopleural (P-Sp) explant cultures on stromal cells (P-Sp culture) did not generate definitive hematopoietic cells and showed defective angiogenesis in the AML1 null embryo. Disrupted angiogenesis in P-Sp cultures from AML1 null embryos was rescued by addition of HSCs or angiopoietin-1 (Ang1). HSCs , which express Ang1, directly promoted migration of ECs in vivo and in vit ro. These results indicate that HSCs are critical for angiogenesis.