Globally, ~10% of babies are born preterm, prior to the late gestation surge in circulating glucocorticoids that is critical for fetal lung maturation. To elucidate the independent impacts of cortisol on fetal lung maturation before birth, we suppressed cortisol synthesis in fetal sheep for 15 days in late gestation.
Fetal sheep were infused with vehicle (tartaric acid, 0.6 M, 0.4 ml/h, n = 11) or metyrapone (competitive inhibitor of cortisol biosynthesis, 4.8 mmol/d in 0.6 M tartaric acid, 0.4 ml/h, n = 13) via the jugular vein from 125 gestational days (gD) until 140 gD (term=150 gD), then delivered and humanely killed for collection of lung tissue. Expression of glucocorticoid receptor (GR) isoforms in cytosolic and nuclear fractions of fetal lung were assessed by western blotting. Lung tissue hormone concentrations will be analysed with LC-MS/MS. Effects of treatment and sex were analysed by two-way ANOVA in Prism. P<0.05 was considered significant.
The proportion of cytosolic GRα-A to nuclear GRα-A was higher in metyrapone compared to control fetuses (P=0.0216). In females, there was lower expression of cytosolic GR-P (P=0.209), nuclear GRα-D1/2, and cytosolic (P=0.0110) and nuclear GRα-D3 (P=0.0023) in metyrapone compared to control fetuses.
Given that nuclear translocation is required for GR activation of gene expression, the lower GRα-A ratio may imply that metyrapone infusion leads to lower GR activation in the fetal lung. The difference in cytosolic and nuclear expression of specific GR isoforms in female control and metyrapone fetuses suggests that cortisol regulates GR isoforms in a sex-dependent manner. Ongoing analyses of hormone concentrations and maturational markers in lung tissue will determine the extent of and determine the functional significance of the changes in GR expression