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

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% O 2 . Specific MMP inhibitors established the requirement for MMP2 in HBEGF shedding and upregulation. Hypoxia inducible factors, HIF1A and EPAS1 (HIF2A), accumulated at 2% O 2 , and HIF target genes were identified by next-generation sequencing of RNA from trophoblast cells cultured at 2% O 2 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% O 2 , 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 O 2 levels encountered during the first trimester, and is essential for successful pregnancy outcomes. Summary Statement Trophoblast 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.