Introduction: We posit that preeclampsia (PE) results from a hypoxia/ reperfusion injury at the maternal-fetal interface in early pregnancy leading to excessive ferroptosis, a process of programmed cell death due to ironmediated lipid peroxidation. Glutathione peroxidase 4 (GPX4) is the key intracellular enzyme that protects cells from ferroptosis. The current study investigates the potential involvement of GPX4 and ferroptosis in the pathogenesis of PE. Methods: Immunohistochemistry for GPX4 and the major lipid peroxidation products, 4-hydroxynonenal (4-HNE) and malondialdehyde (MDA), was performed in placenta/fetal membranes from 12 PE and 10 uncomplicated term births. Small molecule erastin was used to inhibit GPX4 activity (by depleting intracellular glutathione) and induce ferroptosis in immortalized human endometrial stromal cells (HESCs) and extravillous trophoblast cell line Sw.71. In vitro decidualization of HESCs was induced by incubation with 1μM medroxyprogesterone acetate and 0.5mM dibutyryl-cAMP for 9 days. The effect of iron overload was tested by adding ferric ammonium citrate (FAC) and knockdown of ferroportin (Fpn), the only known iron exporter in human cells. The effect on cell survival was measured by MTT assay. Results: GPX4 was expressed in both trophoblasts and decidual cells in normal term tissues. Staining was significantly reduced in trophoblast cells in PE tissues (P=0.008, Mann-Whitney). Both lipid peroxidation products MDA and 4-HNE were detectable in term and PE fetal membranes, whereas placental tissues showed only MDA staining. Intense MDA staining was found in fetal blood vessels and secretions in the intervillous spaces. Compared with HESCs, Sw.71 trophoblast cells were significantly more sensitive to induction of ferroptosis by erastin (IC50=1μM). Interestingly, decidualized HESCs were more resistant to erastin than uninduced HESCs (IC50=3.3μM vs IC50=1.8μM), whereas FAC supplementation or Fpn knockdown significantly increased erastin sensitivity. Western blot analysis of erastin-treated HESCs and Sw.71 cells showed increased MDA production as early as 3h. Concomitantly, GPX4 expression was reduced over time. Conclusion: In vitro cell line studies show that trophoblast cells are highly vulnerable to erastin-induced ferroptosis. Iron overload or reduced iron export sensitized cells to erastin cytotoxicity. Cellular GPX4 expression was inversely correlated with MDA levels. Reduced GPX4 expression in trophoblasts may play a critical role in the pathogenesis of PE.