 This growth factor is also a glycoprotein and functions as an agonist for the tyrosine receptor found in endothelial cells.Angiopoietin-1 and tyrosine kinase signaling are essential for regulating blood vessel development and the stability of mature vessels.The expression of Angiopoietin-2 in the absence of vascular endothelial growth factor (VEGF) leads to endothelial cell death and vascular regression.