Increased TGF-β: a drawback of tracheal occlusion in human and experimental congenital diaphragmatic hernia?

Abstract

Survivors of severe congenital diaphragmatic hernia (CDH) present significant respiratory morbidity despite lung growth induced by fetal tracheal occlusion (TO). We hypothesized that the underlying mechanisms would involve changes in lung extracellular matrix and dysregulated transforming growth factor (TGF)-β pathway, a key player in lung development and repair. Pulmonary expression of TGF-β signaling components, downstream effectors, and extracellular matrix targets were evaluated in CDH neonates who died between birth and the first few weeks of life after prenatal conservative management or TO, and in rabbit pups that were prenatally randomized for surgical CDH and TO vs. sham operation. Before tissue harvesting, lung tissue mechanics in rabbits was measured using the constant-phase model during the first 30 min of life. Human CDH and control fetal lungs were also collected from midterm onwards. Human and experimental CDH did not affect TGF-β/Smad2/3 expression and activity. In human and rabbit CDH lungs, TO upregulated TGF-β transcripts. Analysis of downstream pathways indicated increased Rho-associated kinases to the detriment of Smad2/3 activation. After TO, subtle accumulation of collagen and α-smooth muscle actin within alveolar walls was detected in rabbit pups and human CDH lungs with short-term mechanical ventilation. Despite TO-induced lung growth, mediocre lung tissue mechanics in the rabbit model was associated with increased transcription of extracellular matrix components. These results suggest that prenatal TO increases TGF-β/Rho kinase pathway, myofibroblast differentiation, and matrix deposition in neonatal rabbit and human CDH lungs. Whether this might influence postnatal development of sustainably ventilated lungs remains to be determined.

Excessive Reversal of Epidermal Growth Factor Receptor and Ephrin Signaling Following Tracheal Occlusion in Rabbit Model of congenital Diaphragmatic Hernia

“…Vukovich, et al reported both elastogenesis and transforming growth factor-β signaling were increased in DHTO to levels beyond those of DH or control (6,7). Again, our findings regarding these processes did not reach statistical significance; however their findings are consistent with the observed pattern that processes impacted by DH are excessively reversed in DHTO.…”

“…While TO for CDH may gain more widespread acceptance in the coming years, there remains an urgent need to understand the cellular responses to CDH and TO so that targeted therapies may be developed to improve fetal lung development and to limit any undesirable effects of TO. There have been reports of how CDH and TO impact lung matrix synthesis (6)(7)(8)(9), lung epithelial function and surfactant (10)(11)(12)(13) and microvascular development (14)(15)(16), and that tracheal occlusion reverses some of resulting in severe pulmonary hypoplasia (2). Despite optimal medical and surgical care, mortality remains high with survivors experiencing severe restrictive lung disease and significant pulmonary hypertension (1).…”

MicroRNA 200b is upregulated in the lungs of fetal rabbits with surgically induced diaphragmatic hernia

“…In the lamb model of CDH (GD80; term = 145; late pseudoglandular), there was upregulation of TGF‐β2 following TO (GD110; canalicular), both at the protein and RNA levels, with no concomitant increase in TGF‐β1. In the rabbit model, Vuckovic et al found an upregulation of mRNA expression of TGF‐β2 yet TGF‐β2 peptide levels could not be quantified . Likewise, we found no differences in protein expression of TGF‐β2 in hypoplastic lungs in either the late canalicular or alveolar stages of lung development.…”

“…We previously demonstrated that hypoplastic human lungs have decreased TGF‐β2 expression in the alveolar stage of lung development . A larger series of human lungs between 21 and 39 weeks of gestation failed to show major differences in protein expression between any of the isoforms of TGF‐β in control and DH lungs . In the lamb model of CDH (GD80; term = 145; late pseudoglandular), there was upregulation of TGF‐β2 following TO (GD110; canalicular), both at the protein and RNA levels, with no concomitant increase in TGF‐β1.…”

“…13 A larger series of human lungs between 21 and 39 weeks of gestation failed to show major differences in protein expression between any of the isoforms of TGF-β in control and DH lungs. 27 In the lamb model of CDH (GD80; term = 145; late pseudoglandular), there was upregulation of TGF-β2 following TO (GD110; canalicular), both at the protein and RNA levels, with no concomitant increase 18 in TGF-β1. In the rabbit model, Vuckovic et al found an upregulation of mRNA expression of TGF-β2 yet TGF-β2 peptide levels could not be quantified.…”