Fetal tracheal occlusion for severe congenital diaphragmatic hernia in humans: a morphometric study of lung parenchyma and muscularization of pulmonary arterioles

Epithelial Dysfunction in Congenital Diaphragmatic Hernia: Mechanisms, Models and Emerging Therapies

Congenital diaphragmatic hernia (CDH) is a complex disorder whereby improper formation of the diaphragm allows herniation of the internal organs into the thoracic cavity, resulting in pulmonary hypoplasia among other complications. Although epithelial dysfunction is central to CDH pathology, relatively little attention has been paid to the underlying mechanisms orchestrating epithelial malfunction. Proinflammatory signaling downstream of impaired mechanotransduction due to in utero lung compression has been elucidated to drive epithelial cell phenotypes. This has been illustrated by a reduction in nuclear YAP and the upregulation of NF-kB in CDH models. In this review, we draw from recent findings using emerging technologies to examine epithelial cell mechanisms in CDH and discuss the role of compression as a central and, crucially, sufficient driver of CDH phenotypes. In recognition of the limitations of using genetic knockout models to recapitulate such a heterogenic and etiologically complicated disease, we discuss alternative models such as the established nitrofen rat model, air-liquid interface (ALI) cultures, organoids and ex vivo lung explants. Throughout, we acknowledge the importance of involving mechanical compression in the modeling of CDH in order to faithfully recapitulate the disease. Finally, we explore novel therapeutic strategies from stem cell and regenerative therapies to precision medicine and the importance of defining CDH endotypes in order to guide treatments.

Prenatal Diagnosis, In Utero Management, and Perinatal Outcomes of Congenital Diaphragmatic Hernia

Congenital diaphragmatic hernia (CDH) is a complex malformation complicating 0.02% to 0.03% of live births. The etiology of CDH is often multifactorial. Sonographic screening can aid in the detection of ~70% of CDH cases. Sonographic measures, that is, lung-to-head ratio, can also be utilized to predict the severity of fetal/neonatal disease and guide fetal eligibility for prenatal interventions, such as the FETO procedure. The FETO procedure has provided improved overall morbidity and mortality among fetuses with severe left-sided CDH, although limited data on its role in the treatment of right-sided CDH and long-term infant and childhood outcomes are limited.

Fetoscopic Endoluminal Tracheal Occlusion-Synergic Therapies in the Prenatal Treatment of Congenital Diaphragmatic Hernia

Congenital diaphragmatic hernia (CDH) is a relatively rare and severe developmental disease. Even with the most recent multidisciplinary therapies, the risk for neonatal mortality and morbidity remains high. Recent advancements in prenatal treatments, alongside experimental and clinical data, suggest that fetoscopic endoluminal tracheal occlusion (FETO) promotes lung development and offers a promising strategy against lung hypoplasia and pulmonary hypertension. It is the only existing direct mechanical therapy that intervenes in the regulation of pulmonary pressure. Its influence on lung development also interferes with tissue homeostasis and cell differentiation; it also enhances inflammation and apoptosis. Its physiopathology on cellular and molecular levels is still poorly understood. Unfortunately, the procedure also carries significant pregnancy-, maternal-, and fetus-related risks. Assessing a multifaceted intervention requires a collective view of all aspects. This scoping review uncovers potential materno-fetal procedure-related risks and highlights innovative solutions. Future research on lung development therapies in CDH may focus on the "dual hit" mechanism, combining molecular-targeting drugs and regenerative medicine with the mechanical nature of FETO for synergistic effects.

Congenital diaphragmatic hernia

Congenital diaphragmatic hernia (CDH) is a rare developmental defect of the diaphragm, characterized by the herniation of abdominal contents into the chest, resulting in varying degrees of pulmonary hypoplasia and pulmonary hypertension. Significant advances in the prenatal diagnosis and identification of prognostic factors have resulted in the continued refinement of the approach to fetal therapies for CDH. In the postnatal period, protocolized approaches to lung-protective ventilation, nutrition, prevention of infection, and early aggressive management of pulmonary hypertension have led to improved outcomes in infants with CDH. Surgical repair of CDH is not urgent in most circumstances and can be delayed until the pulmonary status of the patient has stabilized. This article provides a comprehensive review of CDH, focusing on the complex pathophysiology, advances in prenatal diagnosis, fetal interventions, and optimal postnatal management of CDH.

Characterization of Suboptimal Responses to Fetoscopic Endoluminal Tracheal Occlusion in Congenital Diaphragmatic Hernia

INTRODUCTION

The aim of the study was to characterize the changes in fetal lung volume following fetoscopic endoluminal tracheal occlusion (FETO) that are associated with infant survival and need for extracorporeal membrane oxygenation (ECMO) in congenital diaphragmatic hernia (CDH).

METHODS

Fetuses with CDH who underwent FETO at a single institution were included. CDH cases were reclassified by MRI metrics [observed-to-expected total lung volume (O/E TLV) and percent liver herniation]. The percent changes of MRI metrics after FETO were calculated. ROC-derived cutoffs of these changes were derived to predict infant survival to discharge. Regression analyses were done to determine the association between these cutoffs with infant survival and ECMO need, adjusted for site of CDH, gestational age at delivery, fetal sex, and CDH severity.

RESULTS

Thirty CDH cases were included. ROC analysis demonstrated that post-FETO increases in O/E TLV had an area under the curve of 0.74 (p = 0.035) for the prediction of survival to hospital discharge; a cutoff of less than 10% was selected. Fetuses with a <10% post-FETO increase in O/E TLV had lower survival to hospital discharge [44.8% vs. 91.7%; p = 0.018] and higher ECMO use [61.1% vs. 16.7%; p = 0.026] compared to those with an O/E TLV increase ≥10%. Similar results were observed when the analyses were restricted to left-sided CDH cases. A post-FETO <10% increase in O/E TLV was independently associated with lower survival at hospital discharge (aOR: 0.073, 95% CI: 0.008-0.689; p = 0.022) and at 12 months of age (aOR: 0.091, 95% CI: 0.01-0.825; p = 0.036) as well as with higher ECMO use (aOR: 7.88, 95% CI: 1.31-47.04; p = 0.024).

CONCLUSION

Fetuses with less than 10% increase in O/E TLV following the FETO procedure are at increased risk for requiring ECMO and for death in the postnatal period when adjusted for gestational age at delivery, CDH severity, and other confounders.

Prenatal management of congenital diaphragmatic hernia

Recently, two randomized controlled, prospective trials, the Tracheal Occlusion to Accelerate Lung Growth (TOTAL) trials, reported the outcomes on fetal endoluminal tracheal occlusion (FETO) for isolated left congenital diaphragmatic hernia (CDH). FETO significantly improved outcomes for severe hypoplasia. The effect in moderate cases, where the balloon was inserted later in pregnancy, did not reach significance. In a pooled analysis investigating the effect of the heterogeneity of the treatment effect by the time point of occlusion and severity, the difference may be explained by a difference in the duration of occlusion. Nevertheless, FETO carries a significant risk of preterm birth. The primary objective of this review is to provide an overview of the rationale for fetal intervention in CDH and the results of the randomized trials. The secondary objective is to discuss the technical aspects of FETO. Finally, recent developments of potential alternative fetal approaches will be highlighted.

The Cellular and Molecular Effects of Fetoscopic Endoluminal Tracheal Occlusion in Congenital Diaphragmatic Hernia

Congenital diaphragmatic hernia (CDH) is a complex disease associated with pulmonary hypoplasia and pulmonary hypertension. Great strides have been made in our ability to care for CDH patients, specifically in the prenatal improvement of lung volume and morphology with fetoscopic endoluminal tracheal occlusion (FETO). While the anatomic effects of FETO have been described in-depth, the changes it induces at the cellular and molecular level remain a budding area of CDH research. This review will delve into the cellular and molecular effects of FETO in the developing lung, emphasize areas in which further research may improve our understanding of CDH, and highlight opportunities to optimize the FETO procedure for improved postnatal outcomes.

When primary repair is not enough: a comparison of synthetic patch and muscle flap closure in congenital diaphragmatic hernia?

PURPOSE

Primary closure is often inadequate for large congenital diaphragmatic hernia (CDH) and necessitates repair by prosthetic patch or autologous muscle flap. Our aim was to evaluate outcomes of open patch versus flap repair, specifically diaphragmatic reherniation.

METHODS

A retrospective review (IRB #2017-6361) was performed on all CDH patients repaired from 2005 to 2016 at a single academic children's hospital. Patients were excluded from final analysis if they had primary or minimally invasive repair, expired, or were lost to follow-up.

RESULTS

Of 171 patients, 151 (88.3%) survived to discharge, 9 expired after discharge and 11 were lost to follow up, leaving 131 (86.8%) long-term survivors. Median follow-up was 5 years. Open repair was performed in 119 (90.8%) of which 28 (23.5%) underwent primary repair, 34 (28.6%) patch repair, and 57 (47.9%) flap repair. Overall, 6/119 (5%) patients reherniated, 1/28 (3.6%) in the primary group, 3/34 (8.8%) in the patch group, and 2/57 (3.5%) in the flap group. Comparing prosthetic patch to muscle flap repair, there was no significant difference in the number of patients who recurred nor time to reherniation (3 vs. 2, p = 0.295; 5.5 ± 0.00 months vs. 53.75 ± 71.06 months, p = 0.288). One patient in the patch group recurred twice.

CONCLUSIONS

Both muscle flap and patch repair of large CDH are feasible and durable with a relatively low risk of recurrence.

Heterogeneous Response in Rabbit Fetal Diaphragmatic Hernia Lungs After Tracheal Occlusion

BACKGROUND

Fetal tracheal occlusion (TO) is an experimental therapeutic approach to stimulate lung growth in the most severe congenital diaphragmatic hernia (CDH) cases. We have previously demonstrated a heterogeneous response of normal fetal rabbit lungs after TO with the appearance of at least two distinct zones. The aim of this study was to examine the fetal lung response after TO in a left CDH fetal rabbit model.

METHODS

Fetal rabbits at 25 d gestation underwent surgical creation of CDH followed by TO at 27 d and harvest on day 30. Morphometric analysis, global metabolomics, and fluorescence lifetime imaging microscopy (FLIM) were performed to evaluate structural and metabolic changes in control, CDH, and CDH + TO lungs.

RESULTS

Right and left lungs were different at the baseline and had a heterogeneous pulmonary growth response in CDH and after TO. The relative percent growth of the right lungs in CDH + TO was higher than the left lungs. Morphometric analyses revealed heterogeneous tissue-to-airspace ratios, in addition to size and number of airspaces within and between the lungs in the different groups. Global metabolomics demonstrated a slower rate of metabolism in the CDH group with the left lungs being less metabolically active. TO stimulated metabolic activity in both lungs to different degrees. FLIM analysis demonstrated local heterogeneity in glycolysis, oxidative phosphorylation (OXPHOS), and FLIM "lipid-surfactant" signal within and between the right and left lungs in all groups.

CONCLUSIONS

We demonstrate that TO leads to a heterogeneous morphologic and metabolic response within and between the right and left lungs in a left CDH rabbit model.

Fetal Surgery

Fetal surgery is an established but still rapidly evolving specialty, born from the rationale that destructive embryologic processes, recognized early in gestation, can be curtailed by prenatal correction. As more and more centers begin offering fetal interventions, quality of care must be verified through transparency about clinical capabilities and resources. Level designations should be assigned based on capability, as in trauma and neonatal ICU centers for excellence, and volume requirements must be set for fetal surgery certification. Regionalization of this specialty care may be required to optimize outcomes.

Lung function and pulmonary artery blood flow following prenatal maternal retinoic acid and imatinib in the nitrofen model of congenital diaphragmatic hernia

BACKGROUND

Lung and pulmonary vascular maldevelopment in congenital diaphragmatic hernia (CDH) results in significant morbidity and mortality. Retinoic acid (RA) and imatinib have been shown to improve pulmonary morphology following prenatal administration in the rat nitrofen-induced CDH model. It remains unclear if these changes translate into improved function. We evaluated the effect of prenatal RA and imatinib on postnatal lung function, structure, and pulmonary artery (PA) blood flow in the rat CDH model.

METHODS

Olive oil or nitrofen was administered alone or in combination with RA or imatinib to pregnant rats. Pups were assessed for PA blood flow by ultrasound and pulmonary function/morphology following delivery, intubation, and short-term ventilation.

RESULTS

Neither RA nor imatinib had a negative effect on lung and body growth. RA accelerated lung maturation indicated by increased alveoli number and thinner interalveolar septa and was associated with decreased PA resistance and improved oxygenation. With the exception of a decreased PA pulsatility index, no significant changes in morphology and pulmonary function were noted following imatinib.

CONCLUSION

Prenatal treatment with RA but not imatinib was associated with improved pulmonary morphology and function, and decreased pulmonary vascular resistance. This study highlights the potential of prenatal pharmacologic therapies, such as RA, for management of CDH.

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.

Combined antenatal therapy with retinoic acid and tracheal occlusion in a rat model of congenital diaphragmatic hernia

AIM

To investigate the effect of combined prenatal treatment with retinoic acid (RA) and tracheal occlusion (TO) on the pulmonary vascular morphology and expression of vascular endothelial growth factors (VEGF) and its receptors in a rat model of congenital diaphragmatic hernia (CDH).

MATERIAL AND METHODS

Rats were given nitrofen at 9 days of gestation followed by no treatment (CDH), RA (CDH + RA), TO (CDH + TO), or both (CDH + RA + TO) (n = 16). We measured the median wall thickness of the pulmonary arterioles (MWT) and analyzed the expression of VEGF and its receptors (VEGFR1 and VEGFR2).

RESULTS

Compared to control animals, CDH had increased MWT (44 ± 15 vs. 58 ± 7; p < 0.05) and decreased expression of VEGF, VEGFR1, and VEGFR2 (p < 0.05). Treatment with RA or TO alone, and RA + TO reduced the MWT (46 ± 9, 42 ± 11, 46 ± 8, respectively) and improved the expression of VEGF, VEGFR1, and VEGFR2 compared to CDH (p < 0.05). However, the combination of RA + TO did not confer additional benefit in the reduction of the MWT or in increasing the VEGF and its receptors compared to either treatment alone.

CONCLUSION

Antenatal treatment with either RA or TO improved the MWT and expression of VEGF and its receptors in a CDH rat model. However, combined treatment with RA + TO was not superior to either treatment alone.

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

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.

Controversies in the management of severe congenital diaphragmatic hernia

Despite years of progress in perinatal care, severe congenital diaphragmatic hernia (CDH) remains a clinical challenge. Controversies include almost every facet of clinical care: the definition of severe CDH by prenatal and postnatal criteria, fetal surgical intervention, ventilator management, pulmonary hypertension management, use of extracorporeal membrane oxygenation, surgical considerations, and long-term follow-up. Breakthroughs are likely only possible by sharing of experience, collaboration between institutions and innovative therapies within well-designed multicenter clinical trials.

Sildenafil stimulates and dexamethasone inhibits pulmonary vascular development in congenital diaphragmatic hernia rat lungs

BACKGROUND

A predictor of neonatal mortality in infants with congenital diaphragmatic hernia (CDH) is disrupted pulmonary vascular development, clinically expressed as pulmonary hypertension.

OBJECTIVE

To determine if prenatal corticosteroids and phosphodiesterase-5 (PDE-5) inhibitors have a beneficial effect on pulmonary vascular development in CDH lungs.

METHODS

We induced CDH in fetal rats by giving nitrofen. We then exposed them to dexamethasone or to sildenafil. We separated them into three groups: (1) DEX, 4 pregnant rats received dexamethasone at days E16, E18 and E20; (2) SILD, 4 pregnant rats received sildenafil and L-arginine between E14 and E22, and (3) placebo. We then analyzed the lung of each fetus with CDH at E22. We examined the number of arterioles and arteries, and their percent of medial wall thickness (%MWT).

RESULTS

We obtained 30 CDH-positive fetuses. We analyzed 3,560 arterioles and 211 arteries. SILD showed a significant increase in the number of arterioles, but no significant increase in the number of arteries. No change was noted in the arteriolar %MWT. In contrast, DEX showed significant decreases in the number of arterioles and arteries and a significant increase in %MWT.

CONCLUSIONS

PDE-5 inhibitors may improve pulmonary arteriolar development in fetuses with CDH. In contrast, prenatal corticosteroids could have deleterious effects on arteriolar and arterial development in CDH lungs.

Fetal production of growth factors and inflammatory mediators predicts pulmonary hypertension in congenital diaphragmatic hernia

BACKGROUND

Congenital diaphragmatic hernia (CDH) represents a spectrum of lung hypoplasia, and consequent pulmonary hypertension (PH) is an important cause of postnatal morbidity and mortality. We studied biomarkers at the maternal-fetal interface to understand factors associated with the persistence of PH.

METHODS

Maternal and cord blood samples from fetuses with CDH and unaffected controls were analyzed using a human 39plex immunoassay kit. Cellular trafficking between the mother and the fetus was quantified using quantitative real-time PCR for nonshared alleles. Biomarker profiles were then correlated with CDH severity on the basis of the degree of PH.

RESULTS

Cord blood levels of epidermal growth factor, platelet-derived growth factor, and several inflammatory mediators increased significantly as the severity of CDH increased, whereas maternal levels of growth factors and mediators decreased significantly with CDH severity. Maternal cells were increased in fetuses with severe CDH as compared with controls, with elevated levels of the CXC chemokine ligand-10 in patients with the highest trafficking.

CONCLUSION

Patients with CDH demonstrate proinflammatory and chemotactic signals in fetal blood at the time of birth. Because some of these molecules have been implicated in the development of PH, prenatal strategies targeting specific molecular pathways may be useful adjuncts to current fetal therapies.

Pulmonary alveolar and vascular morphometry after gel plug occlusion of the trachea in a fetal rabbit model of CDH

PURPOSE

Tracheal occlusion (TO) induces lung growth in congenital diaphragmatic hernia (CDH) but is also associated with drawbacks. We devised a temporary gel plug that induced lung growth when placed in the fetal trachea. This study evaluates the effects of temporary versus permanent TO on histologic radial alveolar count (RAC) and vascular morphometrics.

METHODS

Experimental CDH was created surgically in 64 New Zealand White rabbit fetuses on gestational day (GD) 24. On GD 27, these fetuses were randomized to intratracheal instillation of a fibrin gel plug (GP), tracheal suture ligation (SL), intratracheal instillation of normal saline (NS), or sham amniotomy (SH). Non-manipulated fetuses served as controls (NM). Histologic lung sections were assessed blindly for RAC and relative arterial adventitial thickness (%AT) as a variable for vascular remodelling. Results were statistically compared.

RESULTS

RAC was significantly lower in the ipsilateral lung of SH fetuses than in the contralateral lung (p = 0.011). Mean RAC was higher after SL (p < 0.001) and GP (p = 0.03) compared to SH. Furthermore, %AT was higher in GP (50 ± 28, p < 0.001) and SL (45 ±2 6, p = 0.003) fetuses than in controls (36 ± 19).

CONCLUSION

Temporary and permanent TO leads to increased RAC; this effect was more pronounced with permanent TO. Both interventions were associated with an increased %AT. These findings may explain the adverse clinical effects of TO, despite causing accelerated lung growth.

Use of ultrasound and MRI for evaluation of lung volumes in fetuses with isolated left congenital diaphragmatic hernia

Congenital diaphragmatic hernia (CDH) is an anomaly that results in lung hypoplasia and pulmonary hypertension. The lungs of the CDH fetus have an abnormal architecture, with fewer bronchial branches and decreased number of arteries and veins, factors which result in pulmonary compromise postnatally. The goal of this review is to evaluate prenatal prognostic factors in the fetus with isolated left CDH, with particular emphasis on fetal MRI. These imaging indicators may be used to provide health professionals and the parents with the most accurate information about fetal prognosis.

The Rho pathway mediates transition to an alveolar type I cell phenotype during static stretch of alveolar type II cells

Stretch is an essential mechanism for lung growth and development. Animal models in which fetal lungs have been chronically over or underdistended demonstrate a disrupted mix of type II and type I cells, with static overdistention typically promoting a type I cell phenotype. The Rho GTPase family, key regulators of cytoskeletal signaling, are known to mediate cellular differentiation in response to stretch in other organs. Using a well-described model of alveolar epithelial cell differentiation and a validated stretch device, we investigated the effects of supraphysiologic stretch on human fetal lung alveolar epithelial cell phenotype. Static stretch applied to epithelial cells suppressed type II cell markers (SP-B and Pepsinogen C, PGC), and induced type I cell markers (Caveolin-1, Claudin 7 and Plasminogen Activator Inhibitor-1, PAI-1) as predicted. Static stretch was also associated with Rho A activation. Furthermore, the Rho kinase inhibitor Y27632 decreased Rho A activation and blunted the stretch-induced changes in alveolar epithelial cell marker expression. Together these data provide further evidence that mechanical stimulation of the cytoskeleton and Rho activation are key upstream events in mechanotransduction-associated alveolar epithelial cell differentiation.

Prenatal factors in the development of chronic lung disease

Chronic lung disease (CLD), defined as chronic oxygen dependency, is a common outcome of neonatal intensive care. It occurs most frequently in infants born very prematurely, but also in infants born at term who had severe lung disease and those with abnormal antenatal lung growth due particularly to reduction in fetal breathing movements, amniotic fluid volume or intrathoracic space. There are, however, other causes and the importance of antenatal infection/inflammation regarding impairment of antenatal lung growth is increasingly recognised. Affected infants can suffer chronic respiratory morbidity including an excess of respiratory symptoms and lung function abnormalities even in adulthood. Antenatal interventions directed at improving lung growth are available, but require testing inappropriately designed trials with pulmonary function at follow-up as an outcome.

Expression of chloride channels in trachea-occluded hyperplastic lungs and nitrofen-induced hypoplastic lungs in rats

BACKGROUND

Congenital diaphragmatic hernia is accompanied by pulmonary hypoplasia. Fetal lung growth is dependent on the secretion of lung liquid, in which Cl(-) secretion by the pulmonary epithelium plays a crucial role. A decrease of lung liquid production during fetal development renders marked pulmonary hypoplasia, while accelerated fetal lung growth in the form of pulmonary hyperplasia can be achieved by in utero tracheal occlusion (TO). Cl(-) secretion presumably involves NKCC-1, the primary basolateral Cl(-) entry pathway in airway epithelia, coupled to an apical Cl(-) exit pathway. The chloride channels ClC-2, -3 and -5, members of the CLC gene family, are all localized to the apical membrane of fetal respiratory epithelia, which makes them possible candidates for being mediators of fetal apical Cl(-) secretion. The aim of the study was to examine the potential of ClC-2, -3 and -5 as alternative apical airway epithelial Cl(-) channels in normal lung development and their possible role in the development of hypoplastic lungs in CDH. We also wanted to examine ClC-2, -3 and -5 together with the NKCC-1 in hyperplastic lungs created by TO.

METHODS

Pregnant Sprague-Dawley rat dams were given nitrofen on gestational day 9.5 to induce pulmonary hypoplasia. Controls were given only olive oil. The rat fetuses were removed on days 17, 19 and 21. Hyperplastic lungs were created by intrauterine TO of rat fetuses on day 19 and the lungs were harvested on day 21. The pulmonary expression of ClC-2, -3, -5 and NKCC-1 was then analyzed using Western blot.

RESULTS

We found that the temporal expression of ClC-2 and -3 in normal fetal lungs points toward a developmental regulation. ClC-2 and -3 were also both down-regulated on day 21 in hypoplastic CDH lungs. In TO induced hyperplastic lungs, the levels of ClC-2 were found to be significantly up-regulated. NKCC-1 showed a tendency toward up-regulation in hyperplastic lungs, while ClC-3 showed a tendency to be down-regulated, but no statistically significant changes could be seen. There was no difference between controls and any of the groups for the expression of ClC-5.

CONCLUSION

We show that the developmental changes in ClC-2 and ClC-3 protein expression are negatively affected in hypoplastic CDH lungs. Lung hyperplasia created by TO up-regulates the expression of ClC-2. ClC-2 is therefore an interesting potential target in the development of novel, non-invasive, therapies for CDH treatment.