Transcriptional Control by FOXO4 Regulates Trophoblast Differentiation and Safeguards Placental Development Through MITD1- and PCBP2-Mediated Redox Homeostasis.

Forkhead box O4 (FOXO4) is highly expressed in the placenta, but its molecular role in trophoblast biology remains unclear. Transcriptomic analysis of human placenta revealed FOXO4 abundance, prompting investigation of its function in trophoblast differentiation and placental development. We found that FOXO4 expression is induced during mouse trophoblast stem (TS) cell differentiation. Gain- and loss-of-function studies demonstrated that FOXO4 promotes differentiation of TS cells towards the trophoblast giant cell (TGC) lineage. Chromatin immunoprecipitation sequencing (ChIP-seq) identified FOXO4 binding to promoters of genes involved in cell cycle regulation, epigenetic modification, metabolism, and ferroptosis. Among these, MITD1 and PCBP2 emerged as key downstream effectors mediating ferroptosis resistance. FOXO4 knockdown enhanced lipid peroxidation and ferroptotic cell death, whereas FOXO4 overexpression upregulated MITD1 and PCBP2 and restored cell viability. Similar protective effects were observed in human JEG-3 trophoblast cells, indicating conservation of FOXO4's function across species. In vivo, FOXO4 expression was elevated in invasive trophoblast cells of E14.5 mouse placenta, whereas FOXO4, MITD1, PCBP2, and GPX4 were reduced in human intrauterine growth restriction (IUGR) placentae, consistent with enhanced ferroptosis. Collectively, these findings define FOXO4 as a transcriptional regulator that protects trophoblast cells from ferroptosis via MITD1 and PCBP2, thereby supporting placental development and function.