The role of activin in regulating human trophoblast invasion and vascular mimicry

During implantation, extravillous cytotrophoblast (EVT) differentiation follows invasive interstitial and endovascular routes. Aberrant placentation due to restricted trophoblast invasion and spiral artery remodeling is responsible for the pathogenesis of common complications during pregnancy, including miscarriage, preeclampsia and IUGR. Activin A, which is abundantly produced at the maternal-fetal interface, exerts its stimulatory effect in trophoblast invasion. Whether two additional activin isoforms, activin B and AB exert similar effects as activin A in trophoblast invasion remains unknown. We hypothesized that mesenchymal adhesion molecule neural cadherin (N-cadherin) and matrix metalloproteinase 2 (MMP2) play essential roles in activin-induced trophoblast invasion. In addition, the effect of activin A on trophoblast endovascular differentiation has never been studied. Vascular endothelial growth factor-A (VEGF-A) is well recognized as a key regulator in trophoblast endovascular differentiation and activin A has been shown to stimulate VEGF-A expression in human hepatocellular carcinoma cells. Whether and how activin A might regulate VEGF-A production in human trophoblasts and its relationship to endovascular differentiation has yet to be determined. An established immortalized EVT cell line HTR8/SVneo and primary cultures of human EVT cells were used as study models. Trophoblast invasiveness and endovascular differentiation were assessed by matrigel-coated transwell assays and endothelial-like tube formation assays following exposure to recombinant human activin. Small interfering RNA (siRNA)-mediated knockdown approaches were used to investigate the molecular determinants of activin-mediated functions. In summary, our results demonstrate that activin A, B and AB produce comparable increases in human trophoblast cell invasion by up-regulating N-cadherin expression. Activin A induces human trophoblast cell invasion by up-regulating SNAIL-mediated MMP2 expression through ALK4 in a SMAD2/3-SMAD4-dependent manner. In addition, activin A induces human trophoblast cells endothelial-like tube formation by up-regulating VEGF-A expression in a SMAD2/3-SMAD4-dependent manner. Our findings provide important insights into the molecular mechanisms underlying the dual effects of activin on human EVTs, and enhance our understanding of the establishment of pregnancy under normal or pathological conditions.Medicine, Faculty ofObstetrics and Gynaecology, Department ofGraduat