Sex‐specific effects of betamethasone on glucocorticoid and apoptotic signalling pathways in the sheep placenta

Antenatal corticosteroid therapy (ACS, e.g. betamethasone) is standard clinical care for pregnancies at risk of preterm delivery to reduce the incidence of neonatal lung disease and death. Variable and sex-specific impacts of ACS on the placenta have been reported and may reflect differing expression profiles of glucocorticoid receptor (GR) isoforms. We therefore examined placental GR isoforms and molecular and structural responses to betamethasone in the clinically relevant sheep pregnancy. Pregnant Merino ewes at 138 days of gestation (term = 150 days) received i.m. injections of saline or 11.6 mg of betamethasone 48 and 24 h prior to Caesarean section delivery of lambs and tissue collection. Placental glucocorticoid concentrations were measured using liquid chromatography-tandem mass spectrometry. Markers of GR signalling and placental development and function were measured using histology, western blotting and quantitative real-time PCR. Betamethasone increased diffusion barrier thickness in female placentae only and reduced placental cortisol concentrations in both sexes. Betamethasone increased cytoplasmic GRαC, GR-P and GRαD isoforms in female placentae only; neither treatment nor sex impacted nuclear GR isoform expression. Expression of angiogenic genes was higher, whereas that of growth-promoting genes was lower, in betamethasone-exposed placentae, independent of sex. Similarly, expression of endoplasmic reticulum stress genes was lower in betamethasone-exposed than control placentae, whereas those involved in oxidative stress and apoptosis were higher, particularly in females. Betamethasone induced molecular changes in the placenta within 48 h of exposure. The apoptotic response was heightened in female placentae, possibly driven by higher expression of specific GR isoforms, which contributes to a greater risk of ACS-induced placental insufficiency. KEY POINTS: Betamethasone treatment for pregnancies at risk of preterm delivery not only reduces the risk of neonatal death, but also acts on glucocorticoid receptors (GR) in the placenta, inducing sex-specific changes that may impact function and fetal growth. In this study, we explored sex-specific placental molecular responses to betamethasone in the clinically relevant sheep pregnancy. Betamethasone increased markers of angiogenesis and decreased markers of growth and proliferation in placentae of both sexes. In females only, betamethasone increased expression of the pro-apoptotic GR isoform, GRαC, which coincided with an enriched pro-apoptotic response and an increased placental diffusion barrier thickness, indicative of placental insufficiency. Our findings highlight that betamethasone induces several molecular changes in the sheep placenta within 48 h of exposure and supports previous sex-specific findings in other species, indicative of a conserved female response.