Angiopoietin-1 and angiopoietin-2 activate trophoblast Tie-2 to promote growth and migration during placental development

Human placental development involves coordinated angiogenesis and trophobla st outgrowth that are compromised in intrauterine growth restriction (IUGR) . As Tie-2((-/-)) mice exhibit growth retardation and vascular network malf ormation, the expression of Tie-2 and its ligands, angiopoietin-1 (Ang-l) a nd angiopoietin-2 (Ang-a), were investigated in human placenta from normal pregnancies and those complicated by severe NGR, Ribonucleotide protection assays showed no significant change in the expression of Ang-2 mRNA between gestationally matched normal and IUGR placentas; however, immunoblots reve aled that Ang-2 protein was significantly decreased in IUGR, suggesting tha t this may contribute to the abnormal development of the villous vasculatur e, In situ hybridization studies showed that Ang-l and Tie-2 were detected in the cyto/syncytiotrophoblast bilayer in first-trimester placenta, wherea s Ang-2 mRNA was restricted to the cytotrophoblast, suggesting their role i n trophoblast function. At term, Ang-l mRNA and immunoreactive protein were restricted to the paravascular tissues of the primary stem villi, supporti ng its role in vessel maturation. In contrast, Ang-2 was expressed througho ut the term villous core, perhaps to permit the developing placental vascul ar network to remain in a state of fluidity, As these studies also revealed that trophoblast, in addition to endothelial cells, expressed Tie-2 recept ors,we Investigated the potential role of Ang-1/Ang-2 on trophoblast prolif eration, migration, and the release of NO. Using spontaneously transformed first-trimester trophoblast cell lines that exhibit cytotrophoblast-like (E D27) and extravillous trophoblast-like (ED77) properties, we show that the addition of Ang-2 (250 ng/ml) stimulated DNA synthesis in ED27 trophoblast cells and triggered the release of NO. Ang-l stimulated trophoblast (ED77) migration in a dose-dependent manner that was inhibited by recombinant Tie- 2-FC, These data thus imply, for the first time, a specific role for angiop oietins as regulators of trophoblast behavior in the development of the ute ro/fetoplacental circulation, an action independent of their well-establish ed roles in vascular endothelium.