Human trophoblast stem cell-differentiated syncytiotrophoblasts as a model for hypoxia-enhanced secretion of the anti-angiogenic factor sFLT1

Preeclampsia (PE) is a major disease in the field of obstetrics. Onset and progression of PE are associated with abnormally high serum levels of soluble fms-like tyrosine kinase-1 (sFLT1), an anti-angiogenic factor primarily secreted by syncytiotrophoblasts (STBs) present in the placenta. Although a cell-based assay using primary human trophoblasts has been developed to identify compounds that inhibit sFLT1 secretion, routine application of this assay is limited owing to the complexity of isolating these cells from the placenta and their inability to be passaged. Recently, human trophoblast stem cell (hTSC) lines that can differentiate into STBs and extravillous trophoblasts have been established. Their high proliferative ability allows for obtaining sufficient STBs for drug screening. In the present study, we investigated whether hTSC-differentiated STBs (dSTBs) exhibit enhanced secretion of sFLT1 under hypoxic conditions, similar to primary trophoblasts. Hypoxic stimulation significantly increased sFLT1 secretion by the dSTBs. This response was markedly inhibited by small interfering RNAs targeting the hypoxia-inducible factor (HIF)-2α and HIF-1β, as well as by the HIF-2α inhibitor, belzutifan. These findings suggest that the dSTBs described above are a practical and scalable alternative to primary trophoblasts for drug screening in PE treatment.