Expression and Oxygen Regulation of Endocrine Gland-Derived Vascular Endothelial Growth Factor/Prokineticin-1 and Its Receptors in Human Placenta during Early Pregnancy

Abstract

Angiogenesis is a key process of dynamic tissue remodeling occurring during placentation. Compelling evidence indicates that vascular endothelial growth factor (VEGF) is an important mediator of placental angiogenesis and appears to be deregulated in preeclampsia. Recently a new angiogenic factor, endocrine gland-derived VEGF (EG-VEGF), also known as prokineticin 1 (PK1), has been identified, and its expression was shown to be restricted to endocrine glands, including the placenta. In this study we investigated the pattern of expression of EG-VEGF, its related factor Bv8/PK2, and their common receptors, PKR1 and PKR2, in human placenta during the first trimester of pregnancy. We also examined EG-VEGF and PKR1 regulation by oxygen tension in isolated trophoblast cells (TCs). Our results show that EG-VEGF, but not Bv8/PK2, is expressed in human placenta. EG-VEGF is mainly localized to the syncytiotrophoblast layer with the highest expression detected between the 8th and 10th wk of gestation. EG-VEGF expression within placental villi is different from that of VEGF, which is mainly localized in the cytotrophoblast and extravillous trophoblast cells. In TCs, PKR1 mRNA is about 80 times more abundant than PKR2 mRNA. Both EG-VEGF and PKR1 mRNAs appear to be regulated by hypoxia. These findings suggest that EG-VEGF has a direct effect on TCs via its receptor PKR1 and is likely to play an important role in human placentation. The expression pattern of EG-VEGF, its regulation by oxygen tension, and its complementary localization to that of VEGF suggest that this new factor might also be deregulated in preeclampsia.