Hypoxia-Inducible Factor 2 (EPAS1) Decreases Syncytialization in Primary Villous Cytotrophoblasts

Colson, Arthur [UCL] Depoix, Christophe [UCL] Hubinont, Corinne [UCL] Debiève, Frédéric [UCL] et al.

INTRODUCTION It is now well accepted that the placenta develops under low oxygen tension during the first trimester of pregnancy. This hypoxia reduces cell fusion and promotes invasion and remodeling of the uterine arteries by extravillous cytotrophoblasts. Even if the low pO2 during the first trimester can be considered as physiological, it is currently recognized that pregnancy-related diseases such as preeclampsia, Hemolysis Elevated Liver enzymes Low Platelets (HELPP) and FGR are linked to a persistent oxidative stress related to chronic hypoxia. Interestingly, these pathological placentas have shown decreased syncytialization levels with lower expression of GCM1, syncytin-1 and PlGF than control. It is currently well known that the nuclear hypoxia-inducible factors 1 (HIF1), 2 (EPAS1) and their common beta subunit aryl hydrocarbon receptor nuclear translocator (ARNT) are widely implicated in cellular processes occurring under hypoxia.5 Here, we hypothesize that HIF1 and/or EPAS1 production alters the development of the syncytium by reducing fusion and differentiation of the villous cytotrophoblasts. OBJECTIVE To study the anti-fusion effects of hypoxia on cytotrophoblasts via HIF1 and EPAS1. METHODS Villous cytotrophoblasts were extracted from normal term placentae after elective cesarean section. The cells were cultured under normoxic (21% O2) or hypoxic (2.5% O2) conditions. The production of HIF1, EPAS1 and ARNT in cytotrophoblasts was reduced using small interfering RNAs (siRNA), and the expression of several genes respectively involved in syncytialization (Syncytin-1, E-cadherin), differentiation (bHCG, Inhibin A) and placental angiogenesis (PlGF, sFLT-1) was quantified by real-time qPCR. RESULTS Our results showed that a reduced production of EPAS1 or ARNT under low oxygen tension increased by 50% the expression of syncytin-1 gene (p=0.03) and doubled HCGB (p=0.007) gene expression. Furthermore, decreasing the quantity of EPAS1-ARNT complex in the cytotrophoblast enhanced the syncytialization process. Conversely, altering HIF1 expression had no significant impact on these genes. On the other hand, we observed an increase in PlGF gene expression and a decrease in sFLT1 gene expression (p=0.02) when EPAS1 expression was reduced. At last, transfected cytotrophoblasts cultured under normoxia showed no difference in gene expression compared to control. This fact is coherent with the recognized operating mode of HIFs consisting in its rapid degradation under 21% O2. CONCLUSION We can conclude that EPAS1 decreases the fusion of the villous cytotrophoblasts and alters the normal angiogenic balance under low oxygen condition. A better understanding of the genomic regulation of syncytialization, and of PlGF/sFLT1 balance under hypoxia remain crucial since therapeutic targets for IUFGR or PE are still lacking in clinical practice.