Abstract
BackgroundLung maturation is modulated by several factors, including glucocorticoids. Expression of hypothalamic-pituitary-adrenal (HPA) axis-related components, with proposed or described local regulatory systems analogous to the HPA axis, was reported in peripheral tissues. Here, HPA axis-related genes were studied in the mouse developing lung during a period overlapping the surge of surfactant production.MethodsExpression of genes encoding for corticotropin-releasing hormone (CRH), CRH receptors (CRHR) 1 and 2beta, CRH-binding protein, proopiomelanocortin (POMC), melanocortin receptor 2 (MC2R), and glucocorticoid receptor was quantified by real-time PCR and localized by in situ hydridization in fetal lungs at gestational days (GD) 15.5, 16.5, and 17.5, and was also quantified in primary mesenchymal- and epithelial cell-enriched cultures. In addition, the capability of CRH and adrenocorticotropic hormone (ACTH) to stimulate pulmonary expression of enzymes involved in the adrenal pathway of glucocorticoid synthesis was addressed, as well as the glucocorticoid production by fetal lung explants.ResultsWe report that all the studied genes are expressed in fetal lungs according to different patterns. On GD 15.5, Mc2r showed peaks in expression in samples that have previously presented high mRNA levels for glucocorticoid synthesizing enzymes, including 11beta-hydroxylase (Cyp11b1). Crhr1 mRNA co-localized with Pomc mRNA in cells surrounding the proximal epithelium on GD 15.5 and 16.5. A transition in expression sites toward distal epithelial cells was observed between GD 15.5 and 17.5 for all the studied genes. CRH or ACTH stimulation of genes involved in the adrenal pathway of glucocorticoid synthesis was not observed in lung explants on GD 15.5, whereas CRH significantly increased expression of 21-hydroxylase (Cyp21a1) on GD 17.5. A deoxycorticosterone production by fetal lung explants was observed.ConclusionsTemporal and spatial modulations of expression of HPA axis-related genes in late gestation are consistent with roles for these genes in lung development. Our data are likely to lead to valuable insights in relation to lung diseases originating from lung immaturity.
Highlights
Lung maturation is modulated by several factors, including glucocorticoids
Crh mRNA was localized in fetal mouse lungs around branching bronchioles [11], Corticotropin-releasing hormone (CRH) was detected in baboon fetal lungs [12], and POMC mRNA was detected in ovine fetal lungs [13]
Expression levels of HPA axis-related genes in male and female fetal mouse lungs The gene expression profiles of Crh, Crhbp, Crhr1, Crhr2b, Pomc, Mc2r, and Nr3c1 were determined in male and female fetal lung pools from several mouse litters collected on gestational days (GD) 15.5, 16.5, and 17.5 (Figure 1)
Summary
Lung maturation is modulated by several factors, including glucocorticoids. Expression of hypothalamic-pituitary-adrenal (HPA) axis-related components, with proposed or described local regulatory systems analogous to the HPA axis, was reported in peripheral tissues. HPA axis-related genes were studied in the mouse developing lung during a period overlapping the surge of surfactant production. Corticotropin-releasing hormone (CRH) and adrenocorticotropic hormone (ACTH) are classically involved in the modulation of the hypothalamic-pituitary-adrenal (HPA) axis, leading to secretion of glucocorticoids by the adrenal glands [1,2]. Limited information is available on expression of CRH, ACTH, and other HPA axis-related components in the fetal lung. CRH receptor type 1 (CRHR1), which is associated with pituitary ACTH secretion, was detected at the mRNA level in baboon fetal lungs [14]. The melanocortin 2 receptor (MC2R), which leads to glucocorticoid production in adrenal glands following binding to its only known ligand ACTH [5], was detected in developing mouse lungs [15]
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