Developmental Expression and Glucocorticoid Control of the Leptin Receptor in Fetal Ovine Lung

Abstract

The effects of endogenous and synthetic glucocorticoids on fetal lung maturation are well-established, although the role of leptin in lung development before birth is unclear. This study examined mRNA and protein levels of the signalling long-form leptin receptor (Ob-Rb) in fetal ovine lungs towards term, and after experimental manipulation of glucocorticoid levels in utero by fetal cortisol infusion or maternal dexamethasone treatment. In fetal ovine lungs, Ob-Rb protein was localised to bronchiolar epithelium, bronchial cartilage, vascular endothelium, alveolar macrophages and type II pneumocytes. Pulmonary Ob-Rb mRNA abundance increased between 100 (0.69 fractional gestational age) and 144 days (0.99) of gestation, and by 2–4-fold in response to fetal cortisol infusion and maternal dexamethasone treatment. In contrast, pulmonary Ob-Rb protein levels decreased near term and were halved by glucocorticoid treatment, without any significant change in phosphorylated signal transducer and activator of transcription-3 (pSTAT3) at Ser727, total STAT3 or the pulmonary pSTAT3:STAT3 ratio. Leptin mRNA was undetectable in fetal ovine lungs at the gestational ages studied. These findings demonstrate differential control of pulmonary Ob-Rb transcript abundance and protein translation, and/or post-translational processing, by glucocorticoids in utero. Localisation of Ob-Rb in the fetal ovine lungs, including alveolar type II pneumocytes, suggests a role for leptin signalling in the control of lung growth and maturation before birth.

Leptin Matures Aspects of Lung Structure and Function in the Ovine Fetus

“…Tissue RNA was isolated from 15-mg samples of fetal lung (saline n = 6; 0.5 LEP n = 10; 1.0 LEP n = 7), and reverse transcription was carried out as described previously ( 29 ). TaqMan quantitative real-time-PCR was performed to measure mRNA abundance of target genes.…”

“…TaqMan quantitative real-time-PCR was performed to measure mRNA abundance of target genes. Samples were analyzed using a TaqMan 7900HT, and data were acquired and processed with Sequence Detector v.2.3 software (Applied Biosystems) ( 29 ). The ovine mRNA probes and primers for leptin, the active long form of the leptin receptor (Ob-Rb), and all forms of the leptin receptor (Ob-R), elastin, VEGF-A and VEGFR2, ACE, PPARγ, bovine PTHrP, and SP-A, SP-B, and SP-C, and bovine SP-D are shown in Table 1 .…”

“…The pulmonary protein contents of Ob-Rb and the total and phosphorylated forms of one of its signaling molecules, the signal transducers and activators of transcription-3 (STAT3), were determined by Western blotting. Frozen samples of fetal lung (100 mg) were homogenized, and the protein concentration of the lysates were measured as described previously ( 29 ). Equal amounts of sample protein were separated using 7.5% Mini-PROTEAN precast gels followed by incubation overnight at 4°C with rabbit polyclonal primary antibodies ( Table 2 ) to 1) the ovine long-form leptin receptor (Ob-Rb) (2-μg/mL orb6312; Biorbyt); 2) the mouse phosphorylated STAT3 containing Ser727 (0.5-μg/mL sc-8001-R; Insight Biotechnology Ltd); or 3) the human STAT3 (1:500, 07-2173; Millipore) ( 29 ).…”

Obesity Affects the Microbiota–Gut–Brain Axis and the Regulation Thereof by Endocannabinoids and Related Mediators

“…In mammals, leptin plays a two-fold role as a hormone and a cytokine. As a hormone, it modulates energy homeostasis by affecting energy expenditure, satiety and appetite [116][117][118]. As a pro-inflammatory adipokine, leptin is implicated, among others, in the modulation of gut microbiota composition through its receptors (LepRb) expressed in the submucosal intestinal zone, with increasing density of LepRb cells from the proximal tract to the colon [119].…”

What is the identity of fibroblast-pneumocyte factor?

“…This is consistent with Slieker et al (94), who demonstrated that glucocorticoids increased both leptin mRNA and secretion in mouse adipocytes. Furthermore, Ob-Rb localisation in fetal ovine lungs, including alveolar type II pneumocytes, and an elevation in Ob-Rb mRNA levels in response to glucocorticoid treatment suggest a role for glucocorticoid control of leptin signaling in prenatal lung maturation (95). …”