Placenta (2000), 21, Supplement A, Trophoblast Research, 14, S16–S24 doi:10.1053/plac.1999.0524, available online at http://www.idealibrary.com on CELL BIOLOGY Regulation of Placental Vascular Endothelial Growth Factor (VEGF) and Placenta Growth Factor (PlGF) and Soluble Flt-1 by Oxygen— A Review A. Ahmed a , C. Dunk, S. Ahmad and A. Khaliq Department of Reproductive and Vascular Biology, Division of Reproductive and Child Health, University of Birmingham, Birmingham Women’s Hospital, Edgbaston, Birmingham B15 2TG, UK Paper accepted 20 December 1999 Morphological studies show poor placental vascular development and an increase in the mitotic index of cytotrophoblast cells in intrauterine growth restriction (IUGR). We hypothesized that the reported relatively high oxygen level in the intervillous space in contact with IUGR placental villi will limit angiogenesis by changes in vascular endothelial growth factor (VEGF) and placenta growth factor (PlGF) expression and function. Western immunoblot analysis demonstrates a diametric expression of PlGF and VEGF proteins throughout pregnancy, with PlGF levels increasing and VEGF levels decreasing, consistent with placental oxygenation. PlGF mRNA and protein is increased in IUGR as compared to gestationally matched normal placentae. Increasing oxygen tension upregulates PlGF protein in term placental villous explants, whereas hypoxia downregulates PlGF and VEGFR-1 (Flt-1) autophosphorylation in term trophoblast choriocarcinoma cell line (BeWo). Levels of soluble Flt-1 (sFlt-1) protein in supernatant of term villous explants were upregulated by 1 per cent hypoxia, whereas hyperoxia (40 per cent) decreased sFlt-1 levels, indicating that under conditions of increasing oxygen tension, PlGF function may remain unopposed. The addition of PlGF-1 to a spontaneously transformed first trimester cytotrophoblast cell line (ED 27 ) stimulated cell proliferation while PlGF-2 had little effect. In contrast, the addition of PlGF-1 had little effect on endothelial cell proliferation while this was inhibited by PlGF-2. Taken together these changes provide a molecular explanation for the observed poor angiogenesis in the pathogenesis of IUGR.  2000 IFPA and Harcourt Publishers Ltd Placenta (2000), 21, Supplement A, Trophoblast Research, 14, S16–S24 PLACENTAL MORPHOLOGY Maternal blood flow into the intervillous space increases 20-fold during pregnancy due to vasomotor changes of the distal intramyometrial portions of the uteroplacental arteries, and to transformation and dilation of the decidual segments. The latter changes are due to invasion of the vessels by trophoblast cells that replace the maternal endothelium and media of the spiral arteries (Benirschke and Kaufmann, 1995). Maternal blood passes through the intervillous space over the villous trees and is collected and drained by the maternal uteroplacental veins. These are usually invaded to a lesser extent by the trophoblast and retain an intact endothelium. Therefore, in contrast with other placental exchange systems, the human placenta does not have an endothelium-lined maternal microvascular system connecting arteries and veins (for review see Benirschke and Kaufmann, 1995). However the core of the placental villi is supplied by an endothelium lined fetoplacental system, whose development is discussed below and is similar to that of the systemic vascular beds. The only major exception to this is the lack of innervation by the autonomic nervous system (Reilly and Russell, 1977). VASCULOGENESIS Vascularization of the placental villi starts at day 21 post- conception (Demir et al., 1989) and is the result of local de novo formation of capillaries rather than protrusion of embryonic vessels into the placenta. The villous trees at this stage are made up of solid trophoblastic or primary villi and secondary villi, which are characterized by a loose mesenchyme derived from the extra-embryonic coelomic cavity in the centre of the villi (Benirschke and Kaufmann, 1995). Prior to the a To whom correspondence should be addressed. Fax: +44 121 627 2705; E-mail: A.S.Ahmed@bham.ac.uk 0143–4004/00/0A00S16+09 $35.00/0  2000 IFPA and Harcourt Publishers Ltd