Small lungs and suspect smooth muscle: congenital diaphragmatic hernia and the smooth muscle hypothesis

Comparative Transcriptome Analysis of Human and Mouse Canalicular Lungs in Fetal Diaphragmatic Hernia

BACKGROUND

The nitrofen model of congenital diaphragmatic hernia (CDH) is widely used in translational research. However, the molecular pathways associated with pulmonary hypoplasia in this model compared to the human CDH phenotype have not been well described. The aim of this study was to investigate differentially expressed genes (DEG) and signaling pathways in early stage fetal lungs in mouse and human CDH.

METHODS

CDH lung tissue was obtained from human fetuses (21-23 weeks gestation) and nitrofen mouse pups (E15.5). NovaSeq Flowcell RNA-seq was performed to evaluate differentially expressed transcriptional and molecular pathways (DEGs) in fetal mice with CDH, compared with age-matched normal mouse lungs and human CDH samples.

RESULTS

There were thirteen overlapping DEGs in human and mouse CDH lung samples compared to controls. These genes were involved in extracellular matrix, myogenesis, cilia, and immune modulation pathways. Human CDH was associated with an upregulation of collagen formation and extracellular matrix reorganization whereas mouse CDH was associated with an increase in muscular contraction. The most common cell types upregulated in human and mouse CDH samples were ciliated airway cells.

CONCLUSIONS

This study highlights the unique gene transcriptional patterns in early fetal mouse and human lungs with CDH. These data have implications when determining the translational potential of novel therapies in CDH using nitrofen-based animal models.

LEVEL OF EVIDENCE

Level IV.

STUDY TYPE

Basic science/case series.

Role of genetics and the environment in the etiology of congenital diaphragmatic hernia

Congenital diaphragmatic hernia (CDH) is a congenital malformation characterized by failure of diaphragm closure during embryonic development, leading to pulmonary hypoplasia and pulmonary hypertension, which contribute significantly to morbidity and mortality. The occurrence of CDH and pulmonary hypoplasia is theorized to result from both abnormalities in signaling pathways of smooth muscle cells in pleuroperitoneal folds and mechanical compression by abdominal organs within the chest cavity on the developing lungs. Although, the precise etiology of diaphragm maldevelopment in CDH is not fully understood, it is believed that interplay between genes and the environment contributes to its onset. Approximately 30% of patients with CDH possess chromosomal or single gene defects and these patients tend to have inferior outcomes compared with those without genetic associations. At present, approximately 150 gene variants have been linked to the occurrence of CDH. The variable expression of the CDH phenotype in the presence of a recognized genetic predisposition can be explained by an environmental effect on gene penetrance and expression. The retinoic acid pathway is thought to play an essential role in the interactions of genes and environment in CDH. However, apart from the gradually maturing retinol hypothesis, there is limited evidence implicating other environmental factors in CDH occurrence. This review aims to describe the pathogenesis of CDH by summarizing the genetic defects and potential environmental influences on CDH development.

Beyond the diaphragm and the lung: a multisystem approach to understanding congenital diaphragmatic hernia

Congenital diaphragmatic hernia (CDH) is a birth defect characterized by the incomplete closure of the diaphragm and herniation of abdominal organs into the chest during gestation. This invariably leads to an impairment in fetal lung development (pulmonary hypoplasia) that involves the pulmonary vessels (vascular remodeling) leading to postnatal pulmonary hypertension. Moreover, approximately 60% of CDH survivors have long-term comorbidities, including critical cardiac anomalies, neurodevelopmental impairment, gastroesophageal reflux, and musculoskeletal malformations. While the pathophysiology of the diaphragmatic defect and pulmonary hypoplasia have been studied in detail over the decades, less is known about the other organs affected in CDH. In this review, we searched the literature for reports on other organs beyond the lung and diaphragm in human and experimental models of CDH. We found studies reporting gross morphometric changes and alterations to biological pathways in the heart, brain, liver, kidney, gastrointestinal tract, and musculoskeletal system. Given the paucity of literature and the importance that these comorbidities play in the life of patients with CDH, further studies are needed to comprehensively uncover the pathophysiology of the changes observed in these other organs.

Congenital diaphragmatic hernia

Congenital diaphragmatic hernia (CDH) is a rare birth defect characterized by incomplete closure of the diaphragm and herniation of fetal abdominal organs into the chest that results in pulmonary hypoplasia, postnatal pulmonary hypertension owing to vascular remodelling and cardiac dysfunction. The high mortality and morbidity rates associated with CDH are directly related to the severity of cardiopulmonary pathophysiology. Although the aetiology remains unknown, CDH has a polygenic origin in approximately one-third of cases. CDH is typically diagnosed with antenatal ultrasonography, which also aids in risk stratification, alongside fetal MRI and echocardiography. At specialized centres, prenatal management includes fetal endoscopic tracheal occlusion, which is a surgical intervention aimed at promoting lung growth in utero. Postnatal management focuses on cardiopulmonary stabilization and, in severe cases, can involve extracorporeal life support. Clinical practice guidelines continue to evolve owing to the rapidly changing landscape of therapeutic options, which include pulmonary hypertension management, ventilation strategies and surgical approaches. Survivors often have long-term, multisystem morbidities, including pulmonary dysfunction, gastroesophageal reflux, musculoskeletal deformities and neurodevelopmental impairment. Emerging research focuses on small RNA species as biomarkers of severity and regenerative medicine approaches to improve fetal lung development.

Fetal lung regeneration using stem cell-derived extracellular vesicles: A new frontier for pulmonary hypoplasia secondary to congenital diaphragmatic hernia

The poor outcomes of babies with congenital diaphragmatic hernia (CDH) are directly related to pulmonary hypoplasia, a cosndition characterized by impaired lung development. Although the pathogenesis of pulmonary hypoplasia is not fully elucidated, there is now evidence that CDH patients have missing or dysregulated microRNAs (miRNAs) that regulate lung development. A prenatal therapy that supplements these missing/dysregulated miRNAs could be a strategy to rescue normal lung development. Extracellular vesicles (EVs), also known as exosomes when of small dimensions, are lipid-bound nanoparticles that can transfer their heterogeneous cargo (proteins, lipids, small RNAs) to target cells to induce biological responses. Herein, we review all studies that show evidence for stem cell-derived EVs as a regenerative therapy to rescue normal development in CDH fetal lungs. Particularly, we report studies showing that administration of EVs derived from amniotic fluid stem cells (AFSC-EVs) to models of pulmonary hypoplasia promotes fetal lung growth and maturation via transfer of miRNAs that are known to regulate lung developmental processes. We also describe that stem cell-derived EVs exert effects on vascular remodeling, thus possibly preventing postnatal pulmonary hypertension. Finally, we discuss future perspectives and challenges to translate this promising stem cell EV-based therapy to clinical practice. This article is protected by copyright. All rights reserved.

Human induced pluripotent stem cell-derived lung organoids in an ex vivo model of the congenital diaphragmatic hernia fetal lung

Three‐dimensional lung organoids (LOs) derived from pluripotent stem cells have the potential to enhance our understanding of disease mechanisms and to enable novel therapeutic approaches in neonates with pulmonary disorders. We established a reproducible ex vivo model of lung development using transgene‐free human induced pluripotent stem cells generated from fetuses and infants with Bochdalek congenital diaphragmatic hernia (CDH), a polygenic disorder associated with fetal lung compression and pulmonary hypoplasia at birth. Molecular and cellular comparisons of CDH LOs revealed impaired generation of NKX2.1⁺ progenitors, type II alveolar epithelial cells, and PDGFRα⁺ myofibroblasts. We then subjected these LOs to disease relevant mechanical cues through ex vivo compression and observed significant changes in genes associated with pulmonary progenitors, alveolar epithelial cells, and mesenchymal fibroblasts. Collectively, these data suggest both primary cell‐intrinsic and secondary mechanical causes of CDH lung hypoplasia and support the use of this stem cell‐based approach for disease modeling in CDH.

Pulmonary Hypertension in Patients with Congenital Diaphragmatic Hernia: Does Lung Size Matter?

PURPOSE

 The relationship between pulmonary hypoplasia and pulmonary arterial hypertension (PHTN) in patients with congenital diaphragmatic hernia (CDH) remains ill-defined. We hypothesized that prenatal estimates of lung size would directly correlate with PHTN severity.

METHODS

 Infants with isolated CDH (born 2004-2015) at a single institution were included. Estimates of lung size included observed-to-expected LHR (o:eLHR) and %-predicted lung volumes (PPLV = observed/predicted volumes). The primary outcome was severity of PHTN (grade 0-3) on echocardiography performed between day of life 3 and 30.

RESULTS

 Among 62 patients included, there was 32% mortality and 65% ECMO utilization. PPLV (odds ratio [OR] = 0.94 per 1 grade in PHTN severity, 95% confidence interval [CI] = 0.89-0.98, p < 0.01) and o:eLHR (OR = 0.97, 95% CI = 0.94-0.99, p < 0.01) were significantly associated with PHTN grade. Among patients on ECMO, PPLV (OR = 0.92, 95% CI = 0.84-0.99, p = 0.03) and o:eLHR (OR = 0.95, 95% CI = 0.92-0.99, p = 0.01) were more strongly associated with PHTN grade. PPLV and o:eLHR were significantly associated with the use of inhaled nitric oxide (iNO) (OR = 0.90, 95% CI = 0.83-0.98, p = 0.01 and OR = 0.94, 95% CI = 0.91-0.98, p < 0.01, respectively) and epoprostenol (OR = 0.91, 95% CI = 0.84-0.99, p = 0.02 and OR = 0.93, 95% CI = 0.89-0.98, p < 0.01, respectively).

CONCLUSION

 Among infants with isolated CDH, PPLV, and o:eLHR were significantly associated with PHTN severity, especially among patients requiring ECMO. Prenatal lung size may help predict postnatal PHTN and associated therapies.

The mechanosensitive ion channel TRPV4 is a regulator of lung development and pulmonary vasculature stabilization

Introduction –

Clinical observations and animal models suggest a critical role for the dynamic regulation of transmural pressure and peristaltic airway smooth muscle contractions for proper lung development. However, it is currently unclear how such mechanical signals are transduced into molecular and transcriptional changes at the cell level. To connect these physical findings to a mechanotransduction mechanism, we identified a known mechanosensor, TRPV4, as a component of this pathway.

Methods –

Embryonic mouse lung explants were cultured on membranes and in submersion culture to modulate explant transmural pressure. Time-lapse imaging was used to capture active changes in lung biology, and whole-mount images were used to visualize the organization of the epithelial, smooth muscle, and vascular compartments. TRPV4 activity was modulated by pharmacological agonism and inhibition.

Results –

TRPV4 expression is present in the murine lung with strong localization to the epithelium and major pulmonary blood vessels. TRPV4 agonism and inhibition resulted in hyper- and hypoplastic airway branching, smooth muscle differentiation, and lung growth, respectively. Smooth muscle contractions also doubled in frequency with agonism and were reduced by 60% with inhibition demonstrating a functional role consistent with levels of smooth muscle differentiation. Activation of TRPV4 increased the vascular capillary density around the distal airways, and inhibition resulted in a near complete loss of the vasculature.

Conclusions –

These studies have identified TRPV4 as a potential mechanosensor involved in transducing mechanical forces on the airways to molecular and transcriptional events that regulate the morphogenesis of the three essential tissue compartments in the lung.

Fetal lung transcriptome patterns in an ex vivo compression model of diaphragmatic hernia

BACKGROUND

The purpose of this study was to employ a novel ex vivo lung model of congenital diaphragmatic hernia (CDH) to determine how a mechanical compression affects early pulmonary development.

METHODS

Day-15 whole fetal rat lungs (n = 6-12/group) from nitrofen-exposed and normal (vehicle only) dams were explanted and cultured ex vivo in compression microdevices (0.2 or 0.4 kPa) for 16 h to mimic physiologic compression forces that occur in CDH in vivo. Lungs were evaluated with significance set at P < 0.05.

RESULTS

Nitrofen-exposed lungs were hypoplastic and expressed lower levels of surfactant protein C at baseline. Although compression alone did not alter the α-smooth muscle actin (ACTA2) expression in normal lungs, nitrofen-exposed lungs had significantly increased ACTA2 transcripts (0.2 kPa: 2.04 ± 0.15; 0.4 kPa: 2.22 ± 0.11; both P < 0.001). Nitrofen-exposed lungs also showed further reductions in surfactant protein C expression at 0.2 and 0.4 kPa (0.53 ± 0.04, P < 0.01; 0.69 ± 0.23, P < 0.001; respectively). Whereas normal lungs exposed to 0.2 and 0.4 kPa showed significant increases in periostin (POSTN), a mechanical stress-response molecule (1.79 ± 0.10 and 2.12 ± 0.39, respectively; both P < 0.001), nitrofen-exposed lungs had a significant decrease in POSTN expression (0.4 kPa: 0.67 ± 0.15, P < 0.001), which was confirmed by immunohistochemistry.

CONCLUSIONS

Collectively, these pilot data in a model of CDH lung hypoplasia suggest a primary aberration in response to mechanical stress within the nitrofen lung, characterized by an upregulation of ACTA2 and a downregulation in SPFTC and POSTN. This ex vivo compression system may serve as a novel research platform to better understand the mechanobiology and complex regulation of matricellular dynamics during CDH fetal lung development.

Quantifying cellular and subcellular stretches in embryonic lung epithelia under peristalsis: where to look for mechanosensing

Peristalsis begins in the lung as soon as the smooth muscle (SM) forms, and persists until birth. As the prenatal lung is filled with liquid, SM action can, through lumen pressure, deform tissues far from the immediately adjacent tissues. Stretching of embryonic tissues has been shown to have potent morphogenetic effects. We hypothesize that these effects are at work in lung morphogenesis. In order to refine that broad hypothesis in a quantitative framework, we geometrically analyse cell shapes in an epithelial tissue, and individual cell deformations resulting from peristaltic waves that completely occlude the airway. Typical distortions can be very large, with opposite orientations in the stalk and tip regions. Apical distortions are always greater than basal distortions. We give a quantitative estimate of the relationship between length of occluded airway and the resulting tissue stretch in the distal tip. We refine our analysis of cell stresses and strains from peristalsis with a simple mechanical model of deformation of cells within an epithelium, which accounts for basic subcellular geometry and material properties. The model identifies likely stress concentrations near the nucleus and at the apical cell-cell junction. The surprisingly large strains of airway peristalsis may serve to rearrange cells and stimulate other mechanosensitive processes by repeatedly aligning cytoskeletal components and/or breaking and reforming lateral cell-cell adhesions. Stress concentrations between nuclei of adjacent cells may serve as a mechanical control mechanism guiding the alignment of nuclei as an epithelium matures.

Morphogenetic implications of peristaltic fluid-tissue dynamics in the embryonic lung

Peristalsis begins in the lung as soon as the smooth muscle forms, and persists until birth. Since the prenatal lung is liquid-filled, smooth muscle action can deform tissues and transport fluid far from the immediately adjacent tissues. Stretching of embryonic tissues and sensation of internal fluid flows have been shown to have potent morphogenetic effects. We hypothesize that these effects are at work in lung morphogenesis. To place that hypothesis in a quantitative framework, we analyze a model of the fluid-structure interactions between embryonic tissues and lumen fluid resulting from peristaltic waves that partially occlude the airway. We find that if the airway is closed, deformations are synchronized; by contrast, if the trachea is open, maximal occlusion precedes maximal pressure. We perform a parametric analysis of how occlusion, stretch, and flow depend on tissue stiffnesses, smooth muscle force, tissue shape and size, and fluid viscosity. We find that most of these relationships are governed by simple ratios.

Identification of dosage-sensitive genes in fetuses referred with severe isolated congenital diaphragmatic hernia

OBJECTIVE

Congenital diaphragmatic hernia (CDH) is a fetal abnormality affecting diaphragm and lung development with a high mortality rate despite advances in fetal and neonatal therapy. CDH may occur either as an isolated defect or in syndromic form for which the prognosis is worse. Although conventional karyotyping and, more recently, chromosomal microarrays support a substantial role for genetic factors, causal genes responsible for isolated CDH remain elusive. We propose that chromosomal microarray analysis will identify copy number variations (CNVs) associated with isolated CDH.

METHODS

We perform a prospective genome-wide screen for CNVs using chromosomal microarrays on 75 fetuses referred with apparently isolated CDH, six of which were later reclassified as non-isolated CDH.

RESULTS

The results pinpoint haploinsufficiency of NR2F2 as a cause of CDH and cardiovascular malformations. In addition, the 15q25.2 and 16p11.2 recurrent microdeletions are associated with isolated CDH. By using gene prioritisation and network analysis, we provide strong evidence for several novel dosage-sensitive candidate genes associated with CDH.

CONCLUSIONS

Chromosomal microarray analysis detects submicroscopic CNVs associated with isolated CDH or CDH with cardiovascular malformations.

Congenital diaphragmatic hernia and protective ventilation strategies in pediatric surgery

Infants affected with congenital diaphragmatic hernias (CDH) suffer from some degree of respiratory insufficiency arising from a combination of pulmonary hypoplasia and pulmonary hypertension. Respiratory care strategies to optimize blood gasses lead to significant barotrauma, increased morbidity, and overuse of extracorporeal membrane oxygenation (ECMO). Newer permissive hypercapnia/spontaneous ventilation protocols geared to accept moderate hypercapnia at lower peak airway pressures have led to improved outcomes. High-frequency oscillatory ventilation can be used in infants who continue to have persistent respiratory distress despite conventional ventilation. ECMO can be used successfully as a resuscitative strategy to minimize further barotrauma in carefully selected patients.

[Congenital diaphragmatic hernia - mechanisms of pulmonary hypoplasia]

Congenital diaphragmatic hernia (CDH) is a common cause of severe neonatal respiratory distress. Mortality and morbidity are determined by the amount of pulmonary hypoplasia (PH) that occurs and by the development of therapy-resistant pulmonary hypertension. The pathogenesis and aetiology of CDH and its associated anomalies are still largely unknown despite all research efforts. The pathogenesis of CDH is based on an assumption linking herniation of abdominal viscera into the thorax with compression of the developing lung. PH, however, can also result from reduced distension of the developing lung secondary to impaired fetal breathing movements. Our understanding of CDH has also been aided by basic research with the use of dietary, teratogen-induced, and knockout models of CDH. These studies indicate that lung hypoplasia may involve disturbances of mitogenic signalling pathways fundamental to embryonic lung development. Recent data reveal the role of disruption of a retinoid-signalling pathway in the pathogenesis of CDH. Although multifactorial inheritance may best explain most cases of CDH in humans, much has been learned about the genetic factors that play a role in the development of CDH by studies of patients with CDH caused by specific genetic syndromes and chromosome anomalies. More research is warranted to improve our understanding of normal and abnormal lung development in relation to CDH. Such investigations will help in the design of new treatment strategies to improve the natural course or even to prevent this anomaly.

Gene expression analysis in hypoplastic lungs in the nitrofen model of congenital diaphragmatic hernia

BACKGROUND

Pulmonary hypoplasia and persistent pulmonary hypertension are the main causes of mortality and morbidity in newborns with congenital diaphragmatic hernia (CDH). Nitrofen is well known to induce CDH and lung hypoplasia in a rat model, but the mechanism remains unknown. To increase the understanding of the underlying pathogenesis of CDH, we performed a global gene expression analysis using microarray technology.

METHODS

Pregnant rats were given 100 mg nitrofen on gestational day 9.5 to create CDH. On day 21, fetuses after nitrofen administration and control fetuses were removed; and lungs were harvested. Global gene expression analysis was performed using Affymetrix Platform and the RAE 230 set arrays. For validation of microarray data, we performed real-time polymerase chain reaction and Western blot analysis.

RESULTS

Significantly decreased genes after nitrofen administration included several growth factors and growth factors receptors involved in lung development, transcription factors, water and ion channels, and genes involved in angiogenesis and extracellular matrix. These results could be confirmed with real-time polymerase chain reaction and protein expression studies.

CONCLUSIONS

The pathogenesis of lung hypoplasia and CDH in the nitrofen model includes alteration at a molecular level of several pathways involved in lung development. The complexity of the nitrofen mechanism of action reminds of human CDH; and the picture is consistent with lung hypoplasia and vascular disease, both important contributors to the high mortality and morbidity in CDH. Increased understanding of the molecular mechanisms that control lung growth may be the key to develop novel therapeutic techniques to stimulate pre- and postnatal lung growth.

Lung organogenesis

Developmental lung biology is a field that has the potential for significant human impact: lung disease at the extremes of age continues to cause major morbidity and mortality worldwide. Understanding how the lung develops holds the promise that investigators can use this knowledge to aid lung repair and regeneration. In the decade since the "molecular embryology" of the lung was first comprehensively reviewed, new challenges have emerged-and it is on these that we focus the current review. Firstly, there is a critical need to understand the progenitor cell biology of the lung in order to exploit the potential of stem cells for the treatment of lung disease. Secondly, the current familiar descriptions of lung morphogenesis governed by growth and transcription factors need to be elaborated upon with the reinclusion and reconsideration of other factors, such as mechanics, in lung growth. Thirdly, efforts to parse the finer detail of lung bud signaling may need to be combined with broader consideration of overarching mechanisms that may be therapeutically easier to target: in this arena, we advance the proposal that looking at the lung in general (and branching in particular) in terms of clocks may yield unexpected benefits.

Tracheal innervation is abnormal in rats with experimental congenital diaphragmatic hernia

BACKGROUND

Tracheobronchial motility influences lung development. Lung hypoplasia and lung sequelae accompany congenital diaphragmatic hernia (CDH) in which the vagus nerves and esophageal innervation are abnormal. As the vagus supplies tracheal innervation, this study tested the hypothesis that it might also be abnormal in rats with CDH.

MATERIAL AND METHODS

Intrinsic ganglia were counted and measured in whole mount acetylcholinesterase-stained tracheas from CDH and control E21 fetal rats. The relative surfaces occupied by neural structures were measured in tracheal sections immunostained for p75(NTR) and PGP 9.5. PGP 9.5 protein and mRNA expression were determined. Mann-Whitney tests were used for comparisons between groups using P < .05 as significant.

RESULTS

p75(NTR) staining showed the neural crest origin of tracheal innervation. Scarce neural structures and smaller ganglia were found in CDH fetuses. PGP 9.5 protein expression was decreased in CDH fetuses, whereas PGP 9.5 mRNA levels were increased in comparison with controls.

CONCLUSIONS

Decreased density of neural structures and size of intramural ganglia, reduced expression of neural tissue and PGP 9.5 protein, and increased levels of PGP 9.5 mRNA reveal deficient tracheal innervation in rats with CDH. If similar anomalies exist in the human condition, they could contribute to explaining the pathogenesis of lung hypoplasia and bronchopulmonary sequelae.

Timing of delivery and survival rates for infants with prenatal diagnoses of congenital diaphragmatic hernia

OBJECTIVES

The goal of the study was to test the hypothesis that infants with known congenital diaphragmatic hernias born at early term gestation (37-38 weeks) rather than later (39-41 weeks) had greater survival rates and less extracorporeal membrane oxygenation use. Primary outcomes were survival to hospital discharge or transfer and extracorporeal membrane oxygenation use. METHODS; A retrospective cohort study of term infants with prenatal diagnoses of congenital diaphragmatic hernia was performed with the Congenital Diaphragmatic Hernia Study Group Registry of patients with congenital diaphragmatic hernias who were treated between January 1995 and December 2006.

RESULTS

Among 628 term infants at 37 to 41 weeks of gestation who had prenatal diagnoses of congenital diaphragmatic hernia and were free of major associated anomalies, early term birth (37 vs 39-41 weeks) and greater birth weight were associated independently with survival, whereas black race was related inversely to survival. Infants born at early term with birth weights at or above the group mean (3.1 kg) had the greatest survival rate (80%). Among infants born through elective cesarean delivery, infants born at 37 to 38 weeks of gestation, compared with 39 to 41 weeks, had less use of extracorporeal membrane oxygenation (22.0% vs 35.5%) and a trend toward a greater survival rate (75.0% vs 65.8%).

CONCLUSIONS

The timing of delivery is an independent, potentially important factor in the consideration of elective delivery for infants diagnosed prenatally as having congenital diaphragmatic hernias. Among fetuses with prenatally diagnosed congenital diaphragmatic hernias and without major associated anomalies, early term delivery may confer advantage.

Abnormal development of tracheal innervation in rats with experimental diaphragmatic hernia

BACKGROUND

We previously demonstrated that tracheobronchial innervation, originated from the vagus nerve and hence of neural crest origin, is deficient in rats with experimental congenital diaphragmatic hernia (CDH). The present study examines the development of this innervation during fetal life in an attempt to understand the nature of these deficiencies.

MATERIALS AND METHODS

Pregnant rats were given either 100 mg nitrofen or vehicle on E 9.5. Embryos were recovered on E15 and E18. Control and nitrofen/CDH pups (n = 10 each) were studied on each of these days and compared with our previous results on E21. Whole mount preparations of tracheas stained for anti-protein gene product 9.5 (PGP 9.5) and smooth muscle contractile alpha-actin were examined under confocal microscopy for the morphology of intrinsic neural network. Sections of tracheas were immunostained with anti-low-affinity neurotrophin receptor (p75(NTR)), neural cell marker PGP 9.5, and anti-glial cell marker S100 antibodies. The proportions of sectional areas occupied by neural and glial structures were measured in the proximal and distal trachea. PGP 9.5 protein, and mRNA expressions were determined. Mann-Whitney tests with a threshold of significance of P < 0.05 were used for comparison.

RESULTS

Positive staining for p75(NTR) confirmed the neural crest origin of tracheal neural cells. The neural network appeared less organized on E15, and it was less dense on E18 in nitrofen-exposed embryos than in controls. The proportions of section surface occupied by neural elements were similar in both groups on E15, but that of glial tissue was significantly increased in nitrofen-exposed embryos. On E18, the relative neural surface was significantly reduced in CDH embryos in contrast with increased glial tissue surface. On E21 the proportion of neural tissue was reduced only in the distal trachea. The expression of PGP 9.5 protein was decreased in CDH fetuses on E18 and E21. In contrast, PGP 9.5 mRNA levels were increased in CDH fetuses on E18 and E21.

CONCLUSIONS

The development of intrinsic innervation of the trachea in rats with CDH is abnormal with reduction of neural tissue accompanied by increase of glial tissue that could represent a response to neural damage. The significance of increased PGP 9.5 mRNA levels is unclear.

Congenital diaphragmatic hernia

The incidence of congenital diaphragmatic hernia (CDH) may be as high as 1 in 2000. Over the past two decades, antenatal diagnosis rates have increased, the pathophysiology of CDH has become better understood, and advances in clinical care, including foetal surgery, have occurred. However, there remains a paucity of randomised controlled trials to provide evidence-based management guidelines. Reports of improved survival rates appear to be confined to a select subset of CDH infants, surviving to surgical repair, while the overall mortality, at over 60%, appears to be unchanged, largely due to the often forgotten 'hidden mortality' of CDH. The significant long-term morbidity in surviving infants has become apparent, and the need for long-term multidisciplinary follow up established. A total of 10% of cases may present later in life, and misdiagnosis on initial chest X-ray may lead to significant morbidity.

Exploiting mechanical stimuli to rescue growth of the hypoplastic lung

Impaired lung development afflicts a range of newborns cared for by paediatric surgeons. As a result the speciality has led in the development of surgical models that illustrate the biomechanical regulation of lung growth. Using transgenic mutants, biologists have similarly discovered much about the biochemical regulation of prenatal lung growth. Airway smooth muscle (ASM) and its prenatal contractility airway peristalsis (AP) represent a novel link between these areas: ASM progenitors produce an essential biochemical factor for lung morphogenesis, whilst calcium-driven biomechanical ASM activity appears to regulate the same. In this invited paper, I take the opportunity both to review our recent findings on lung growth and prenatal ASM, and also to discuss mechanisms by which ASM contractility can regulate growth. Finally, I will introduce some novel ideas for exploration: ASM contractility could help to schedule parturition (pulmonary parturition clock) and could even be a generic model for smooth muscle regulation of morphogenesis in similar organs.

Vitamin A deficiency (VAD), teratogenic, and surgical models of congenital diaphragmatic hernia (CDH)

Congenital diaphragmatic hernia (CDH) is a congenital malformation that occurs with a frequency of 0.08 to 0.45 per 1,000 births. Children with CDH are born with the abdominal contents herniated through the diaphragm and exhibit an associated pulmonary hypoplasia which is frequently accompanied by severe morbidity and mortality. Although the etiology of CDH is largely unknown, considerable progress has been made in understanding its molecular mechanisms through the usage of genetic, teratogenic, and surgical models. The following review focuses on the teratogenic and surgical models of CDH and the possible molecular mechanisms of nitrofen (a diphenyl ether, formerly used as an herbicide) in both induction of CDH and pulmonary hypoplasia. In addition, the mechanisms of other compounds including several anti-inflammatory agents that have been linked to CDH will be discussed. Furthermore, this review will also explore the importance of vitamin A in lung and diaphragm development and the possible mechanisms of teratogen interference in vitamin A homeostasis. Continued exploration of these models will bring forth a clearer understanding of CDH and its molecular underpinnings, which will ultimately facilitate development of therapeutic strategies.

Impaired mesenchymal cell function in Gata4 mutant mice leads to diaphragmatic hernias and primary lung defects

Congenital diaphragmatic hernia (CDH) is an often fatal birth defect that is commonly associated with pulmonary hypoplasia and cardiac malformations. Some investigators hypothesize that this constellation of defects results from genetic or environmental triggers that disrupt mesenchymal cell function in not only the primordial diaphragm but also the thoracic organs. The alternative hypothesis is that the displacement of the abdominal viscera in the chest secondarily perturbs the development of the heart and lungs. Recently, loss-of-function mutations in the gene encoding FOG-2, a transcriptional co-regulator, have been linked to CDH and pulmonary hypoplasia in humans and mice. Here we show that mutagenesis of the gene for GATA-4, a transcription factor known to functionally interact with FOG-2, predisposes inbred mice to a similar set of birth defects. Analysis of wild-type mouse embryos demonstrated co-expression of Gata4 and Fog2 in mesenchymal cells of the developing diaphragm, lungs, and heart. A significant fraction of C57Bl/6 mice heterozygous for a Gata4 deletion mutation died within 1 day of birth. Developmental defects in the heterozygotes included midline diaphragmatic hernias, dilated distal airways, and cardiac malformations. Heterozygotes had any combination of these defects or none. In chimeric mice, Gata4(-/-) cells retained the capacity to contribute to cells in the diaphragmatic central tendon and lung mesenchyme, indicating that GATA-4 is not required for differentiation of these lineages. We conclude that GATA-4, like its co-regulator FOG-2, is required for proper mesenchymal cell function in the developing diaphragm, lungs, and heart.

Molecular genetics of congenital diaphragmatic defects

Congenital diaphragmatic hernia (CDH) is a severe birth defect that is accompanied by malformations of the lung, heart, testis, and other organs. Patients with CDH may have any combination of these extradiaphragmatic defects, suggesting that CDH is often a manifestation of a global embryopathy. This review highlights recent advances in human and mouse genetics that have led to the identification of genes involved in CDH. These include genes for transcription factors, molecules involved in cell migration, and extracellular matrix components. The expression patterns of these genes in the developing embryo suggest that mesenchymal cell function is compromised in the diaphragm and other affected organs in patients with CDH. We discuss potential mechanisms underlying the seemingly random combination of diaphragmatic, pulmonary, cardiovascular, and gonadal defects in these patients.

Airway smooth muscle dysfunction precedes teratogenic congenital diaphragmatic hernia and may contribute to hypoplastic lung morphogenesis

Fetal intervention aims to improve lung growth and survival in congenital diaphragmatic hernia (CDH). Airway smooth muscle (ASM) is important in lung development: ASM progenitors produce a key growth factor for lung morphogenesis (fibroblast growth factor 10); ASM contractility is also coupled to growth. ASM hyperreactivity occurs in postnatal CDH and may exacerbate barotrauma via impaired lung compliance. We hypothesize that ASM hyperreactivity and its sequelae are based on an early developmental lesion of ASM activity in hypoplastic lung. Sprague-Dawley rats were fed 100 mg nitrofen on Day 9.5 of pregnancy to induce lung hypoplasia in offspring (controls had vehicle alone). Normal and hypoplastic lung primordia were cultured from Day 13.5 of gestation at 37 degrees C in 5% CO(2) and loaded at 54 or 78 h with Ca(2+)-sensitive indicators: Fluo-4 for confocal imaging and Indo-1 or Fura-2 for photometric measurements of [Ca(2+)](i). Hypoplastic lung features spontaneous propagating ASM Ca(2+) transients with reduced frequency, increased amplitude, and significantly prolonged plateau duration, relative to control lung. Nonetheless, hypoplastic lung exhibits normal requirement for extracellular calcium entry and intracellular calcium release in initiation and regulation of ASM Ca(2+) waves. Early ASM dysfunction in lung hypoplasia is apparent as specific anomalies of Ca(2+) transients that indicate a problem with plasmalemmal ion channels/action potential generation. Elucidation of such an ASM lesion may allow pharmacologic amelioration not only of ASM hyperreactivity and its sequelae, but also of hypoplastic lung growth itself.

Peristalsis of airway smooth muscle is developmentally regulated and uncoupled from hypoplastic lung growth

Prenatal airway smooth muscle (ASM) peristalsis appears coupled to lung growth. Moreover, ASM progenitors produce fibroblast growth factor-10 (FGF-10) for lung morphogenesis. Congenital diaphragmatic hernia (CDH) is associated with lung hypoplasia, FGF-10 deficiency, and postnatal ASM dysfunction. We hypothesized ASM dysfunction emerges in tandem with, and may contribute toward, the primordial lung hypoplasia that precedes experimental CDH. Spatial origin and frequency of ASM peristaltic waves were measured in normal and hypoplastic rat lungs cultured from day 13.5 of gestation (lung hypoplasia was generated by nitrofen dosing of pregnant dams). Longitudinal lung growth was assayed by bud counts and tracing photomicrographs of cultures. Coupling of lung growth and peristalsis was tested by stimulation studies using serum, FGF-10, or nicotine and inhibition studies with nifedipine or U0126 (MEK1/2 inhibitor). In normal lung, ASM peristalsis is developmentally regulated: proximal ASM becomes quiescent (while retaining capacity for cholinergic-stimulated peristalsis). However, in hypoplastic lung, spontaneous proximal ASM activity persists. FGF-10 corrects this aberrant ASM activity in tandem with improved growth. Stimulation and inhibition studies showed that, unlike normal lung, changes in growth or peristalsis are not consistently accompanied by parallel modulation of the other. ASM peristalsis undergoes FGF-10-regulated spatiotemporal development coupled to lung growth: this process is disrupted early in lung hypoplasia. ASM dysfunction emerges in tandem with and may therefore contribute toward lung hypoplasia in CDH.