Hypoxia-inducible factor-1β is essential for upregulation of the hypoxia-induced FLT1 gene in placental trophoblasts

Placental hypoxia and increased levels of maternal blood anti-angiogenic protein, soluble fms-like tyrosine kinase-1 (sFLT1), are associated with the pathogenesis of pre-eclampsia. We have demonstrated that hypoxia-inducible factor (HIF)-2 alpha mediates the upregulation of the hypoxia-induced FLT1 gene in trophoblasts and their cell lines. Here, we investigated the involvement of HIF-1 beta, which acts as a dimerization partner for HIF-alpha, in the upregulation of the FLT1 gene via hypoxia. We confirmed the interactions between HIF-1 beta and HIF-2a in the nuclei of BeWo, JAR and JEG-3 cells under hypoxia via co-immunoprecipitation. We found that hypoxia-induced upregulation of the FLT1 gene in BeWo cells and secretion of sFLT1 in human primary trophoblasts were significantly reduced by siRNAs targeting HIF-1b. Moreover, the upregulation of the FLT1 gene in BeWo cells induced by dimethyloxaloylglycine (DMOG) was also inhibited by silencing either HIF-2 alpha or HIF-1 beta mRNA. It was recently shown that DNA demethylation increases both basal and hypoxia-induced expression levels of the FLT1 gene in three trophoblast-derived cell lines. In the demethylated BeWo cells, siRNAs targeting HIF-2 alpha and HIF-1 beta suppressed the further increase in the expression levels of the FLT1 gene due to hypoxia or treatment with DMOG. However, luciferase reporter assays and bisulfite sequencing revealed that a hypoxia response element (-966 to -962) of the FLT1 gene is not involved in hypoxia or DMOG-induced upregulation of the FLT1 gene. These findings suggest that HIF-1b is essential for the elevated production of sFLT1 in the hypoxic trophoblasts and that the HIF-2 alpha/HIF-1 beta complex may be a crucial therapeutic target for pre-eclampsia.

Automated summary

The study suggests that HIF-1β is essential for the elevated production of sFLT1 in hypoxic trophoblasts, and the HIF-2α/HIF-1β complex may be a crucial therapeutic target for pre-eclampsia.