Hypoxia induced HIF-1/HIF-2 activity alters trophoblast transcriptional regulation and promotes invasion

Reduced or absent cytotrophoblast invasion of the maternal uterine spiral arteries is a common clinical finding in studies of pregnancies complicated by preeclampsia, suggesting that the mechanisms behind invasion of these cells is perturbed. The placenta initially develops in a low oxygen environment of 1-2% oxygen until after the 10th week of pregnancy. During this time oxygen concentration exerts a major influence over trophoblast activity and, in vitro, hypoxia inducible factors are proposed to be one of many key regulators of first trimester trophoblast behaviour. We used a global gene expression microarray approach to identify signalling pathways involved in invasion of the first trimester trophoblast cell line HTR8/SVneo under hypoxic conditions where HIF-1 was active. Additionally, first trimester placental samples from different gestational age groups were labelled with anti HIF-1 and HIF-2 to evaluate whether HIFs are differentially expressed and localised across the period of development characterised by hypoxia (6-8 weeks) and maternal blood perfusion (10-12 weeks). Eighty-eight genes were differentially expressed between cells cultured in 1% oxygen (where HIF-1 was localised to the nucleus) and 5% oxygen (where HIF-1 was cytoplasmic). 65% of the genes were predicted to contain HIF-1:ARNT transcription factor binding sites. Increased nuclear localisation of HIF-1 was seen in extravillous cytotrophoblasts in early first trimester compared with late, while cellular expression of HIF-2 in the villous stroma was higher in late first trimester. While HIFs and their downstream targets are clearly induced in trophoblasts during early placental development, and in vitro hypoxic conditions, the mechanism and pathways by which invasion is increased under hypoxic conditions is not clear from the gene expression profile. Further insight beyond the transcription level is required to fully understand this complex phenomenon.

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Highet AR, Khoda SM, Buckberry S, Leemaqz S, Bianco-Miotto T, Harrington E, Ricciardelli C, Roberts CT