Hum. Reprod. Advance Access originally published online on April 14, 2008
Human Reproduction 2008 23(6):1407-1415; doi:10.1093/humrep/den114
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Hypoxia is responsible for soluble vascular endothelial growth factor receptor-1 (VEGFR-1) but not for soluble endoglin induction in villous trophoblast
1 Laboratory of Tumor and Development Biology, CRCE, CHU, GIGA, University of Liège, Tour de Pathologie (B23), Sart Tilman B-4000, Liège, Belgium 2 Department of Obstetrics and Gynecology, Hôpital of la Citadelle, Liège, Belgium
3 Correspondance address. Tel: +32-4-366-2453; Fax: +32-4-366-2936; E-mail: c.munaut{at}ulg.ac.be
BACKGROUND: Pre-eclampsia is a pregnancy disorder characterized by a maternal endothelial cell dysfunction associated with low levels of circulating placental growth factor (PlGF) and increased levels of total vascular endothelial growth factor (VEGF), soluble VEGF receptor-1 (sVEGFR-1), and soluble endoglin, a transforming growth factor β1 and 3 coreceptor. Here, we tested the hypothesis that these altered levels of angiogenic cytokines and of the anti-angiogenic soluble forms of cytokine receptors could be the consequence of hypoxia.
METHODS: Normal human umbilical vein endothelial cells, immortalized first trimester extravillous trophoblast cells (HTR8/SVneo) and first trimester placental villi explants (8–14 weeks) were used for culture under normoxia (20% O2) or hypoxia (1% O2). Culture media were collected for the measurement of cytokines by enzyme-linked immunosorbent assay. Total RNA was extracted for RT-PCR analysis.
RESULTS: Under hypoxia, villous trophoblast expressed higher levels of VEGF, VEGFR-1, sVEGFR-1 and VEGFR-2 mRNAs (P < 0.001), and secreted more VEGF and sVEGFR-1 proteins (P < 0.05). In contrast, PlGF mRNA and protein were decreased in 1% O2 (P < 0.001), whereas endoglin (Eng) was not modulated. Additionally, sVEGFR-1 directly abolished VEGF/PlGF-induced angiogenesis in the rat aortic ring assay.
CONCLUSIONS: Our results support the hypotheses that, in pre-eclampsia, (i) overproduction of VEGF family factors by pre-eclamptic placenta is a consequence of induced hypoxia; (ii) overproduction of sVEGFR-1 by hypoxic villous trophoblast accounts for maternal free VEGF depletion; (iii) low circulating level of free PlGF is not only related to sVEGFR-1 overproduction, but also to hypoxia-induced mRNA down-regulation; (iv) Eng is not modulated by hypoxia.
Key words: hypoxic trophoblast/vascular endothelial growth factor receptor-1/soluble endoglin/pre-eclampsia/pregnancy
Submitted on November 22, 2007; resubmitted on February 25, 2008; accepted on March 10, 2008.