Trophoblast survival signaling during human placentation requires HIF-induced transcription of HSP70

Abstract

Survival of trophoblast cells in the low oxygen environment of human placentation requires metalloproteinase-mediated shedding of HBEGF and downstream signaling. A matrix metalloproteinase (MMP) antibody array and quantitative RT-PCR revealed upregulation of MMP2 post-transcriptionally in human first trimester HTR-8/SVneo trophoblast cells and placental explants exposed to 2% O2. Specific MMP inhibitors established the requirement for MMP2 in HBEGF shedding and upregulation. Hypoxia inducible factors, HIF1A and EPAS1 (HIF2A), accumulated at 2% O2, and HIF target genes were identified by next-generation sequencing of RNA from trophoblast cells cultured at 2% O2 for 0, 1, 2 and 4 hrs. Of nine genes containing HIF-response elements upregulated at 1 hour, only HSPA6 (HSP70B) remained elevated after 4 hours. The HSP70 chaperone inhibitor VER155008 blocked upregulation of both MMP2 and HBEGF at 2% O2, and increased apoptosis. However, both HBEGF upregulation and apoptosis were rescued by exogenous MMP2. We propose that MMP2-mediated shedding of HBEGF, initiated by HSP70, contributes to trophoblast survival at the low O2 levels encountered during the first trimester, and is essential for successful pregnancy outcomes.\n\nSummary StatementTrophoblast survival during human placentation, when oxygenation is minimal, required HIF-induced transcription of HSP70, which mediated MMP2 accumulation and the transactivation of anti-apoptotic ERBB signaling by HBEGF shedding.