Figure 3.

Process of angiogenesis involving hematopoietic cells (HC). When hypoxia occurs in a location, sprouting angiogenesis is initiated by budding of endothelial cells (EC) from pre‐existing vessels. Ischemic tissue provides chemoattractive factors for hematopoietic cells (HC). We found several functions for EC in the process of sprouting angiogenesis. (1) Hematopoietic stem cells (HSC) migrate into the avascular area before movement of EC, produce angiopoietin‐1 (Ang‐1), which stimulates tyrosine kinase with Ig and EGF homology domain 2 (TIE2) on EC, and induces migration of EC by acting as a chemoattractant. (2) Neuropilin‐1 (NP‐1) on HC binds vascular endothelial growth factor (VEGF) in serum or tissue. The NP‐1–VEGF complex stimulates VEGF receptor/Flk‐1 exogenously and induces brisk proliferation of EC.