Role of angiopoietins in reproductive tract angiogenesis

Components of the female reproductive system undergo a number of programmed angiogenic processes coupled with cyclic evolution and decline of ovarian, endometrial, and placental structures. The development of a new vascular network requires a remarkable degree of coordination between different cell types undergoing complex changes. This implies that the expression of the inciting angiogenic factors are hormone dependent. Recently, a second family of vascular endothelial growth factors was identified, the angiopoietins. Angiopoietins are vascular endothelial cell-specific growth factors that play important roles principally during the later stages of angiogenesis, after the induction of new capillaries by vascular endothelial growth factor (VEGF), There are four known angiopoietins, and their specificity for the vascular endothelium results from the restricted expression pattern of their tyrosine kinase receptor, Tie2, In this review, we discuss the molecular characterization and mechanism of action of angiopoietin-1 and angiopoietin-2 in reproductive tract angiogenesis.