Abstract
Vascular development consists of two processes termed vasculogenesis and angiogenesis. The system of TIE 2-Angiopoietin (Ang) is involved in the later, angiogenesis. It has been demonstrated that the function of TIE 2 is associated with adhesion and dissociation between endothelial cells and mural cells, and survival, apoptosis, and chemotaxis of endothelial cells Ang 2, which is produced from endothelial cells under tissue hypoxia, has been suggested to be a key regulator for the initiation of endothelial cell sprouting from pre-existing vessels. Although Ang 2 binds to TIE 2, Ang 2 does not promote activation of TIE 2. Ang 2 produced from endothelial cells under hypoxia inhibits the binding of Ang 1 to TIE 2. Ang 1 promotes activation of TIE 2 and adhesion between endothelial cells and mural cells. Therefore, endothelial cells detouched from mural cells by Ang 2 are permitted to move to avascular area in which oxygen or nutrient is desired. We recently found that hematopoietic stem cells promote chemotaxis and nextwork formation of TIE 2 positive endothelial cells by producing angiopoietin-1. This novel function may be utilized for regeneration therapy of neovascularization in the patient by transplanting the hematopoietic stem cell into the location.
