Placental Hypoxia-Induced Ferroptosis Drives Vascular Damage in Preeclampsia

BACKGROUND: Iron is an essential micronutrient for cell survival and growth; however, excess of this metal drives ferroptosis. Although maternal iron imbalance and placental hypoxia are independent contributors to the pathogenesis of preeclampsia, a hypertensive disorder of pregnancy, the mechanisms by which their interaction impinge on maternal and placental health remain elusive. METHODS: We used placentae from normotensive and preeclampsia pregnancy cohorts, human H9 embryonic stem cells differentiated into cytotrophoblast-like cells, and placenta-specific Phd2 −/− preeclamptic mice. Lipid peroxidation and iron cargo of placenta-derived small extracellular vesicles (sEVs) isolated from the maternal circulation of control and preeclampsia individuals were examined by mass spectrometry, flow cytometry, and colorimetry. Human microvascular endothelial cells’ angiogenic capacity and function were examined after exposure to control and pathological sEVs. RESULTS: Placentae from preeclampsia pregnancies contain increased ferrous iron and lipid peroxidation byproduct, malondialdehyde. Antioxidant capacity is significantly lower in preeclampsia placentae, with decreased glutathione content, and GPx4 (glutathione peroxidase 4) expression and activity. Hypoxia triggers the occurrence of ferroptosis in human trophoblast cells and mouse Phd2 − /− placentae. Disrupted placental iron homeostasis in preeclampsia is accompanied by improper extrusion of iron through sEVs mediated by the pentaspan protein prominin-2. Heightened lipid peroxidation content was found in villous explants and maternal circulating sEVs of preeclampsia individuals. Exposure of human microvascular endothelial cells to preeclampsia-derived placental sEVs results in endothelial activation and impaired angiogenesis, which is rescued by treatment with hinokitiol, a compound known to restore tissue iron balance. CONCLUSIONS: In pregnancy, iron and oxygen work synergistically to conserve an operative antioxidant system to maintain iron homeostasis and protect the placenta from ferroptotic death. Hindrance to this system due to hypoxia results in heightened ferroptosis rates and sEV-mediated extrusion of harmful lipid peroxides from trophoblast cells into the circulation thereby contributing to maternal endothelial dysfunction characterizing preeclampsia.