Prenatal non-infectious mild stressor modulates early-life lung development in a time-specific manner

BACKGROUND: Maternal exposure to various insults during pregnancy can influence early-life organ development. Whether this applies to seemingly mild stressors remains unclearly defined. Better understanding of the nature and strength of prenatal exposure factor to trigger fetal programming effect in the lung may help to optimize perinatal-neonatal health care. METHODS: Pregnant wild type C57BL/6J mice were randomized at 15.5 day post coitum (dpc) or 18.5 dpc to intraperitoneal (i.p.) injection of sterile physiological saline. Mice undergoing a natural process of pregnancy without any intervention served as blank controls. Newborn mice were euthanized at postnatal day 1 for lung harvests. Lung tissues were subjected to Weigert staining to visualize elastic fiber distribution and quantify total parenchymal cells. Additionally, qPCR, immunofluorescence staining and western blot were performed to assess the expression of signature markers of the lung epithelium and other compartments. RESULTS: No adverse perinatal outcomes occurred except a non-significant reduction in maternal weight gain after i.p. injection of sterile physiological saline. Pups demonstrated similar birth weights across groups. The total number of lung parenchymal cells increased in exposed pups compared with blank controls, with no significant difference in elastin fiber distribution. Enhanced macrophage infiltration with predominant type 2 cytokine responses was observed in newborn mice lungs following maternal i.p. injection of saline. There was an elevated surfactant protein C (Sftpc) expression in alveolar type 2 (AT2) cells in the 15.5 dpc exposure group compared to blank controls. No sex-dependent difference was demonstrated in Sftpc expression. Correlational analysis of signature gene expression indicated crosstalk between AT2 cells and other lung cellular compartments. The expression of stem cell antigen (Sca1) in lung mesenchymal progenitor cells demonstrated a time-related response without sex differentiation upon prenatal exposure to maternal i.p. injection of sterile physiological saline. CONCLUSIONS: Results of this preclinical study in newborn mice contribute to current understanding of fetal programming by showing that maternal exposure to even non-infectious mild stressors before birth is able to modulate early-life lung development. This underscores an intensified sensibility of unborn fetus to seemingly harmless low-magnitude maternal stressors.