Increased lung prolyl hydroxylase and decreased glucocorticoid receptor are related to decreased surfactant protein in the growth-restricted sheep fetus

Abstract

Experimental placental restriction (PR) by carunclectomy in fetal sheep results in intrauterine growth restriction (IUGR), chronic hypoxemia, increased plasma cortisol, and decreased lung surfactant protein (SP) expression. The mechanisms responsible for decreased SP expression are unknown but may involve decreased glucocorticoid (GC) action or changes in hypoxia signaling. Endometrial caruncles were removed from nonpregnant ewes to induce PR. Lungs were collected from control and PR fetuses at 130-135 (n = 19) and 139-145 (n = 28) days of gestation. qRT-PCR and Western blotting were used to quantify lung mRNA and protein expression, respectively, of molecular regulators and downstream targets of the GC and hypoxia-signaling pathways. We confirmed a decrease in SP-A, -B, and -C, but not SP-D, mRNA expression in PR fetuses at both ages. There was a net downregulation of GC signaling with a reduction in GC receptor (GR)-α and -β protein expression and a decrease in the cofactor, GATA-6. GC-responsive genes including transforming growth factor-β1, IL-1β, and β2-adrenergic receptor were not stimulated. Prolyl hydroxylase domain (PHD)2 mRNA and protein and PHD3 mRNA expression increased with a concomitant increase in hypoxia-inducible factor-1α (HIF-1α) and HIF-1β mRNA expression. There was an increase in mRNA expression of several, but not all, hypoxia-responsive genes. Hence, both GC and hypoxia signaling may contribute to reduced SP expression. Although acute hypoxia normally inactivates PHDs, chronic hypoxemia in the PR fetus increased PHD abundance, which normally prevents HIF signaling. This may represent a mechanism by which chronic hypoxemia contributes to the decrease in SP production in the IUGR fetal lung.

Ventilation-induced lung injury is not exacerbated by growth restriction in preterm lambs

“…This is in contrast to previous studies showing significantly reduced PC content and lower lung volume in growth-restricted rats (13). In sheep, growth restriction resulted in decreased surfactant protein (41), which was speculated to result from glucocorticoid and hypoxic signaling pathways (42). Importantly, none of these studies have looked at levels of PC in the airway lumen (e.g., in BALF).…”

Structural and molecular regulation of lung maturation by intratracheal vascular endothelial growth factor administration in the normally grown and placentally restricted fetus

“…); antigen KI‐67, MKI67 , XM_004020367.1; proliferating cell nuclear antigen, PCNA , XM_004014340.1 (Orgeig et al . )] were determined. Furthermore, the expression of chemokines [chemokine (C‐C motif) ligand 2, CCL2 , NM_174006; chemokine (C‐C motif) ligand 4, CCL4 , NM_001075147], pro‐inflammatory markers [interleukin‐1β, IL1B , NM_001009465.2 (Orgeig et al .…”

“…; Orgeig et al . ). The PHDs normally function to limit hypoxia signalling by degradation of the HIF‐α subunit during periods of normoxaemia, although their expression has been shown to increase during periods of chronic hypoxaemia (Epstein et al .…”

“…; Orgeig et al . ). Thus, altered regulation of hypoxia signalling by increased PHDs, despite the chronically hypoxaemic conditions experienced by the PR fetus, presents a potential mechanism leading to delayed surfactant maturation and an increased risk of RDS (Avery & Mead, ; Orgeig et al .…”

“…; Orgeig et al . ). In the present study, we have examined the effect of recombinant human VEGF administration, a key hypoxia signalling factor, with respect to bypassing the endogenous regulation of hypoxia signalling (e.g.…”