Maternal estradiol impacts fetal HPA axis and pulmonary transcriptomes in sheep

Precise coordination of parturition and fetal organ maturation is critical for neonatal survival. In sheep, a fetal cortisol surge, triggered by hypothalamic-pituitary-adrenal (HPA) axis activation, drives organ maturation and placental estradiol (E2) synthesis to promote labor, but the upstream signals initiating this cascade remain unclear. We tested whether maternal E2 administration at physiological levels alters fetal endocrine and pulmonary maturation through transcriptional regulation. Pregnant ewes (139-142 days gestation) received Silastic implants containing E2 (200 mg; n = 6) or empty controls (n = 6). Fetal hypothalamus, pituitary, adrenal, and lung tissues were collected 26 h post treatment for RNA sequencing; lung samples also underwent immunohistochemistry, and maternal, fetal, and umbilical plasma were analyzed for hormones. Maternal E2 increased approximately fourfold (P < 0.01), whereas fetal and umbilical E2 remained unchanged. Transcriptomic responses were strongest in the pituitary (914 differentially expressed genes, DEGs), followed by lung (150), adrenal (16), and hypothalamus (6) (FDR ≤ 0.1, |log₂FC| ≥ 1). Pituitary responses included pro-opiomelanocortin (POMC) downregulation and enrichment of neurogenesis, axon guidance, and cell adhesion pathways. The hypothalamus showed enrichment for hormone secretion, neuroendocrine regulation, and estrogen signaling. In the lungs, ERα-positive nuclei increased (P = 0.04), whereas surfactant proteins A and C were unchanged. These findings demonstrate that maternal E2, without altering fetal circulating E2, induces tissue-specific fetal transcriptomic changes consistent with endocrine and pulmonary maturation. Maternal E2 may therefore contribute to fetal readiness for birth through indirect mechanisms acting independently of, or in concert with, fetal cortisol.NEW & NOTEWORTHY Successful birth requires precise coordination between fetal organ maturation and the hormonal signals that trigger labor. Using a sheep model, we show that maternal estradiol (E2) administered at physiological levels induces broad transcriptomic changes in fetal endocrine and pulmonary tissues without altering fetal circulating E2 levels. These findings highlight a previously unrecognized role for maternal estrogen in modulating fetal development, suggesting alternative or complementary pathways to cortisol in preparing the fetus for birth.