Congenital diaphragmatic hernia: a retinoid-signaling pathway disruption during lung development?

Global gene expression profiling in congenital diaphragmatic hernia (CDH) patients

Congenital diaphragmatic hernia (CDH) is an anomaly characterized by a defect in the diaphragm, leading to the passage of intra-abdominal organs into the thoracic cavity. Herein, the presented work analyzes the global gene expression profiles in nine CDH and one healthy newborn. All of the patients had left posterolateral (Bochdalek) diaphragmatic hernia, operated via an abdominal approach, and stomach and bowels in the thorax cavity. Some patients also had additional anomalies. A total of 560 differentially regulated genes were measured. Among them, 11 genes showed significant changes in expression associated with lung tissue, vascular structure development, and vitamin A metabolism, which are typical ontologies related to CDH etiology. Among them, SLC25A24 and RAB3IL1 are involved in angiogenesis, HIF1A and FOXC2-AS1 are related with the alveolus, MAGI2-AS3 is associated with the diaphragm, LHX4 and DHH are linked with the lung, and BRINP1, FZD9, WNT4, and BLOC1S1-RDH5 are involved in retinol. Besides, the expression levels of some previously claimed genes with CDH etiology also showed diverse expression patterns in different patients. All these indicated that CDH is a complex, multigenic anomaly, requiring holistic approaches for its elucidation.

Biallelic hypomorphic variants in ALDH1A2 cause a novel lethal human multiple congenital anomaly syndrome encompassing diaphragmatic, pulmonary, and cardiovascular defects

This study shows a causal association between ALDH1A2 variants and a novel, severe multiple congenital anomaly syndrome in humans that is neonatally lethal due to associated pulmonary hypoplasia and respiratory failure. In two families, exome sequencing identified compound heterozygous missense variants in ALDH1A2. ALDH1A2 is involved in the conversion of retinol (vitamin A) into retinoic acid (RA), which is an essential regulator of diaphragm and cardiovascular formation during embryogenesis. Reduced RA causes cardiovascular, diaphragmatic, and associated pulmonary defects in several animal models, matching the phenotype observed in our patients. In silico protein modeling showed probable impairment of ALDH1A2 for three of the four substitutions. In vitro studies show a reduction of RA. Few pathogenic variants in genes encoding components of the retinoic signaling pathway have been described to date, likely due to embryonic lethality. Thus, this study contributes significantly to knowledge of the role of this pathway in human diaphragm and cardiovascular development and disease. Some clinical features in our patients are also observed in Fryns syndrome (MIM# 229850), syndromic microphthalmia 9 (MIM# 601186), and DiGeorge syndrome (MIM# 188400). Patients with similar clinical features who are genetically undiagnosed should be tested for recessive ALDH1A2-deficient malformation syndrome.

Lung and liver growth and retinoic acid status in human fetuses with congenital diaphragmatic hernia

BACKGROUND

Abnormal retinoic acid (RA) signalling is considered a major cause of congenital diaphragmatic hernia (CDH). Pulmonary hypoplasia and pulmonary hypertension are the major causes of morbidity and mortality in infants born with CDH. Experimental studies in animals have found that RA signalling is involved in lung and liver development, but animal models of CDH do not directly correlate with CDH in human fetuses. This study investigated if RA status is also linked to lung and liver growth in human fetuses with CDH.

STUDY DESIGN AND PATIENTS

Hepatic stellate cells (HSC) in autopsy human fetal liver tissue were identified using cRBP-1 immunohistochemistry and the numbers of HSC manually counted. In mammals, RA is principally stored in HSC complexed to cRBP-1 and therefore cRBP-1⁺ HSC numbers were used as an indicator of fetal RA status. The number of HSCs was correlated with liver and lung weights, calculated relative to either normal biometric values or fetal body weight.

RESULTS

The number of cRBP-1⁺ HSCs correlated with lung weight contralateral to the side of the diaphragmatic hernia (r=0.82, p=0.025) and combined lung weight (r=0.78, p=0.039) but not with ipsilateral lung weight (r=0.43, p=0.33), in fetuses with right and left CDH and a case of giant omphalocoele. Liver growth was influenced by contact with diaphragm but not significantly correlated with cRBP-1 expression (r=0.52, p=0.056).

CONCLUSION

Fetal RA stores, reflected in the number of cRBP-1⁺ HSCs, influence lung growth as well as diaphragm development in human fetuses with CDH. Contact with diaphragm influenced liver growth.

Lung development, regeneration and plasticity: From disease physiopathology to drug design using induced pluripotent stem cells

Lungs have a complex structure composed of different cell types that form approximately 17 million airway branches of gas-delivering bronchioles connected to 500 million gas-exchanging alveoli. Airways and alveoli are lined by epithelial cells that display a low rate of turnover at steady-state, but can regenerate the epithelium in response to injuries. Here, we review the key points of lung development, homeostasis and epithelial cell plasticity in response to injury and disease, because this knowledge is required to develop new lung disease treatments. Of note, canonical signaling pathways that are essential for proper lung development during embryogenesis are also involved in the pathophysiology of most chronic airway diseases. Moreover, the perfect control of these interconnected pathways is needed for the successful differentiation of induced pluripotent stem cells (iPSC) into lung cells. Indeed, differentiation of iPSC into airway epithelium and alveoli is based on the use of biomimetics of normal embryonic and fetal lung development. In vitro iPSC-based models of lung diseases can help us to better understand the impaired lung repair capacity and to identify new therapeutic targets and new approaches, such as lung cell therapy.

Congenital diaphragmatic hernia after exposure to a triple retinoic acid antagonist during pregnancy

AIM

To establish a mouse model for the study of congenital defects, using exposure of pregnant females to the teratogen BMS-189453, a multiple retinoic acid competitive antagonist.We found not less than 60% of fetuses had transposition of the great arteries and l5% had other congenital heart defects such as double outlet right ventricle, tetralogy of Fallot, truncus and right aortic arch. Newborns exposed in utero to BMS-189453 were affected by thymus aplasia or hypoplasia, and severe congenital anomalies of the central nervous system due to neural tube defects. An anterior rotation of the right lung was also frequently present in our model. We also report a case of murine congenital diaphragmatic hernia associated with thymic aplasia and transposition of the great arteries.

CONCLUSION

These findings support the hypothesis that the combination of diaphragmatic hernia and congenital heart defects may be related to an alteration of the retinoic acid signaling pathways.

Congenital diaphragmatic hernias: from genes to mechanisms to therapies

Congenital diaphragmatic hernias (CDHs) and structural anomalies of the diaphragm are a common class of congenital birth defects that are associated with significant morbidity and mortality due to associated pulmonary hypoplasia, pulmonary hypertension and heart failure. In ∼30% of CDH patients, genomic analyses have identified a range of genetic defects, including chromosomal anomalies, copy number variants and sequence variants. The affected genes identified in CDH patients include transcription factors, such as GATA4, ZFPM2, NR2F2 and WT1, and signaling pathway components, including members of the retinoic acid pathway. Mutations in these genes affect diaphragm development and can have pleiotropic effects on pulmonary and cardiac development. New therapies, including fetal endoscopic tracheal occlusion and prenatal transplacental fetal treatments, aim to normalize lung development and pulmonary vascular tone to prevent and treat lung hypoplasia and pulmonary hypertension, respectively. Studies of the association between particular genetic mutations and clinical outcomes should allow us to better understand the origin of this birth defect and to improve our ability to predict and identify patients most likely to benefit from specialized treatment strategies.

Current Concepts in the Management of Congenital Diaphragmatic Hernia in Infants

The therapeutic approach to congenital diaphragmatic hernia (CDH) has shifted from one of immediate repair to management of pulmonary hypertension, physiologic stabilization, and delayed surgical repair. Lung hypoplasia, remodeled pulmonary vasculature, and ventricular dysfunction all contribute to the high morbidity and mortality associated with CDH. In addition, genetic syndromes associated with CDH can increase the incidence of serious anomalies and hence impact survival. Prenatal and postnatal management of infants with CDH is challenging in the best of circumstances and need multidisciplinary teams for optimal outcomes. However, advances using ultrasound and fetal MRI can predict prognosis and survival and plan for postnatal management. Survival rates for patients with CDH have increased for the past decade with better management at resuscitation; implementation of gentle ventilation strategies; and medical management of pulmonary hypertension, physiologic stabilization, and extracorporeal membrane oxygenation. However, follow-up of these infants for long-term morbidities is essential for optimal outcomes after discharge.

Nitrofen increases total retinol levels in placenta during lung morphogenesis in the nitrofen model of congenital diaphragmatic hernia

BACKGROUND

It has been shown that pulmonary retinol level is decreased during lung morphogenesis in the nitrofen-induced PH in congenital diaphragmatic hernia (CDH). Placenta has a major role in the retinol homeostasis in fetal life. Since there is no fetal retinol synthesis, maternal retinol has to cross the placenta. Placenta is the main fetal retinol store where retinol is stored in retinyl-ester formation. Trophoblasts have to produce its own retinol-binding protein (RBP) for retinol transport from placenta to fetus. Recently, we demonstrated that trophoblastic RBP expression is decreased in the nitrofen model of CDH. The aim of this study was to investigate the retinol transfer from mother to the placenta in nitrofen model of CDH.

METHODS

Pregnant rats were exposed to either olive oil or nitrofen on day 9 of gestation (D9). Fetal placenta harvested on D21 and divided into two groups: control (n = 11) and nitrofen with CDH (n = 11). Retinoid levels in placenta were measured using HPLC. Immunohistochemistry was performed to evaluate trophoblastic expression of main RSP genes.

RESULTS

Total retinol levels in the placenta were significantly increased in CDH placenta compared to control placenta. The retinyl-ester levels were significantly increased in CDH placenta compared to control placenta. Markedly, decreased immunoreactivity of retinoid signaling pathway was observed in trophoblast cells in CDH compared to control placenta.

CONCLUSIONS

Increased placental retinol levels show that retinol is transferred from mother to placenta and stored in the placenta in nitrofen model of CDH during lung morphogenesis. Nitrofen may disturb the mobilization of retinol from placenta to fetal circulation causing PH in CDH.

Increased trophoblastic apoptosis mediated by neutrophil gelatinase-associated lipocalin (NGAL) activation in the nitrofen model of congenital diaphragmatic hernia

BACKGROUND

Retinoids play a key role in fetal lung development. It has been suggested that the maternal-fetal retinol transport is disrupted by trophoblastic apoptosis. The mechanism underlying nitrofen-induced apoptosis in placenta is not fully understood. Neutrophil gelatinase-associated lipocalin (NGAL) is expressed in the fetal part of the maternal-fetal interface. NGAL is part of the immune barrier and serves primarily as a transport protein transferring biologically hazardous molecules in a safe and controlled way. It has been shown that over-activation of NGAL induces apoptosis. We hypothesized that increased placental NGAL expression induces trophoblastic apoptosis in the nitrofen model of CDH.

METHODS

Pregnant rats were exposed to either olive oil or nitrofen on day 9 of gestation (D9). Placenta harvested on D21 and divided into two groups: control and nitrofen with CDH. Immunohistochemistry was performed to evaluate trophoblasts (by cytokeratin expression), NGAL expression, and apoptotic trophoblastic cells (using TUNEL assay). Total RNA was extracted from each placenta and the relative mRNA expression levels of NGAL were analyzed using RT-PCR.

RESULTS

Immunohistochemistry showed NGAL immunoreactivity both in control and CDH in the fetal part of the fetal-maternal interface of placenta. Markedly increased NGAL expression was detected in CDH group compared to controls. Relative mRNA expression levels of NGAL gene were significantly increased in the CDH group compared to control in the placenta (5.924 ± 0.93 vs. 1.895 ± 0.54, p < 0.001). Markedly increased numbers of apoptotic trophoblastic cells were seen in the maternal-fetal interface in the CDH group compared to controls.

CONCLUSIONS

NGAL activation may lead to increased trophoblastic apoptosis in the maternal-fetal interface in the nitrofen model of CDH. These changes may therefore cause disturbance in maternal-fetal retinol transport affecting fetal lung morphogenesis.

Pulmonary vascular resistance in repaired congenital diaphragmatic hernia vs. age-matched controls

INTRODUCTION

Infants and children with repaired congenital diaphragmatic hernia (CDH) often continue to show delayed growth and development that may be, in part, secondary to unrecognized persistence of increased pulmonary vascular resistance (PVR).

METHODS

Data were reviewed from all patients ages 6-36 mo with repaired CDH who underwent cardiac catheterization from 2007 to 2010 and were compared to data from a control population of patients undergoing percutaneous closure of a patent ductus arteriosus (PDA). Indexed pulmonary blood flow (Qp), mean pulmonary artery pressure (mPAP), pulmonary capillary wedge pressure (PCWP), and PVR were examined.

RESULTS

Data from 8 CDH patients and 10 control patients were examined. The mPAP (22.5 ± 3.33 vs. 18.2 ± 4.13 mm Hg) and PVR (3.66 ± 0.79 vs. 1.22 ± 0.4 iwU (indexed Wood's units)) were both significantly elevated in the CDH population, whereas the Qp (4.08 ± 1.43 vs. 6.82 ± 1.46 l/min/m(2)) was significantly lower in this population. There was no significant difference in pulmonary capillary wedge pressure (PCWP). Less than half of the CDH patients had signs of pulmonary hypertension (PH) on echocardiogram.

DISCUSSION

Our data suggest that children who are ages 6-36 mo with repaired CDH have significantly increased PVR compared with controls and early consideration of cardiac catheterization may be warranted.

Local fetal lung renin-angiotensin system as a target to treat congenital diaphragmatic hernia

Antenatal stimulation of lung growth is a reasonable approach to treat congenital diaphragmatic hernia (CDH), a disease characterized by pulmonary hypoplasia and hypertension. Several evidences from the literature demonstrated a possible involvement of renin-angiotensin system (RAS) during fetal lung development. Thus, the expression pattern of renin, angiotensin-converting enzyme, angiotensinogen, type 1 (AT₁) and type 2 (AT₂) receptors of angiotensin II (ANGII) was assessed by immunohisto-chemistry throughout gestation, whereas the function of RAS in the fetal lung was evaluated using fetal rat lung explants. These were morphometrically analyzed and intracellular pathway alterations assessed by Western blot. In nitrofen-induced CDH model, pregnant rats were treated with saline or PD-123319. In pups, lung growth, protein/DNA ratio, radial saccular count, epithelial differentiation and lung maturation, vascular morphometry, right ventricular hypertrophy and overload molecular markers, gasometry and survival time were evaluated. Results demonstrated that all RAS components were constitutively expressed in the lung during gestation and that ANGII had a stimulatory effect on lung branching, mediated by AT₁ receptor, through p44/42 and Akt phosphorylation. This stimulatory effect on lung growth was mimicked by AT₂-antagonist (PD-123319) treatment. In vivo antenatal PD-123319 treatment increased lung growth, ameliorated indirect parameters of pulmonary hypertension, improved lung function and survival time in nonventilated CDH pups, without maternal or fetal deleterious effects. Therefore, this study demonstrated a local and physiologically active RAS during lung morphogenesis. Moreover, selective inhibition of AT₂ receptor is presented as a putative antenatal therapy for CDH.

Nitrofen interferes with trophoblastic expression of retinol-binding protein and transthyretin during lung morphogenesis in the nitrofen-induced congenital diaphragmatic hernia model

BACKGROUND

Retinoids play a key role in lung development. Retinoid signaling pathway has been shown to be disrupted in the nitrofen model of congenital diaphragmatic hernia (CDH) but the exact mechanism is not clearly understood. Retinol-binding protein (RBP) and transthyretin (TTR) are transport proteins for delivery of retinol to the tissues via circulation. Previous studies have shown that pulmonary retinol levels are decreased during lung morphogenesis in the nitrofen CDH model. In human newborns with CDH, both retinol and RBP levels are decreased. It has been reported that maternal RBP does not cross the placenta and the fetus produces its own RBP by trophoblast. RBP and TTR synthesized in the fetus are essential for retinol transport to the developing organs including lung morphogenesis. We hypothesized that nitrofen interferes with the trophoblastic expression of RBP and TTR during lung morphogenesis and designed this study to examine the trophoblastic expression of RBP and TTR, and the total level of RBP and TTR in the lung in the nitrofen model of CDH.

METHODS

Pregnant rats were exposed to either olive oil or nitrofen on day 9 of gestation (D9). Fetal lungs and placenta harvested on D21 and divided into two groups: control (n = 8) and nitrofen with CDH (n = 8). Total lung RBP and TTR levels using protein extraction were compared with enzyme linked immunoassay (ELISA). Immunohistochemistry was performed to evaluate trophoblastic RBP and TTR expression.

RESULTS

Total protein levels of lung RBP and TTR were significantly lower in CDH (0.26 ± 0.003 and 6.4 ± 0.5 μg/mL) compared with controls (0.4 ± 0.001 and 9.9 ± 1.6 μg/mL, p < 0.05). In the control group, immunohistochemical staining showed strong immunoreactivity of RBP and TTR in the trophoblast compared to CDH group.

CONCLUSIONS

Decreased trophoblast expression of retinol transport proteins suggest that nitrofen may interfere with the fetal retinol transport resulting in reduced pulmonary RBP and TTR levels and causing pulmonary hypoplasia in CDH.

Prenatal retinoic acid upregulates connexin 43 (Cx43) gene expression in pulmonary hypoplasia in the nitrofen-induced congenital diaphragmatic hernia rat model

PURPOSE

Connexin 43 (Cx43), a major gap junction protein, is necessary for alveologenesis and plays an important role in the differentiation of type II to type I alveolar epithelial cells. Knockout mice of Cx43 display severe pulmonary hypoplasia (PH). Prenatal administration of retinoic acid (RA) is known to stimulate alveologenesis in nitrofen-induced PH. Recent studies revealed that retinoids upregulate Cx43 expression. We hypothesized that gene expression of Cx43 is downregulated during alveologenesis and that administration of RA upregulates Cx43 expression in the nitrofen-induced PH.

METHODS

Pregnant rats were exposed to olive oil or nitrofen on day 9 (D9) of gestation. Retinoic acid was given intraperitoneally on D18, D19, and D20. Fetal lungs were harvested on D18 and D21 and divided into control, nitrofen, control+RA (D21), and nitrofen+RA (D21). The Cx43 expression levels were determined using reverse transcription polymerase chain reaction and immunohistochemistry.

RESULTS

On D18 and D21, Cx43 relative messenger RNA expression levels were significantly downregulated in nitrofen compared with those in the control group. On D21, expression levels of Cx43 were significantly upregulated in nitrofen+RA and control+RA compared with those in nitrofen group. Immunohistochemical studies confirmed these results.

CONCLUSION

Downregulation of Cx43 expression may interfere with normal alveologenesis. Upregulation of Cx43 pulmonary gene expression after RA treatment may promote lung growth by stimulating alveologenesis in nitrofen-induced PH.

Congenital diaphragmatic hernia

Congenital Diaphragmatic Hernia (CDH) is defined by the presence of an orifice in the diaphragm, more often left and posterolateral that permits the herniation of abdominal contents into the thorax. The lungs are hypoplastic and have abnormal vessels that cause respiratory insufficiency and persistent pulmonary hypertension with high mortality. About one third of cases have cardiovascular malformations and lesser proportions have skeletal, neural, genitourinary, gastrointestinal or other defects. CDH can be a component of Pallister-Killian, Fryns, Ghersoni-Baruch, WAGR, Denys-Drash, Brachman-De Lange, Donnai-Barrow or Wolf-Hirschhorn syndromes. Some chromosomal anomalies involve CDH as well. The incidence is < 5 in 10,000 live-births. The etiology is unknown although clinical, genetic and experimental evidence points to disturbances in the retinoid-signaling pathway during organogenesis. Antenatal diagnosis is often made and this allows prenatal management (open correction of the hernia in the past and reversible fetoscopic tracheal obstruction nowadays) that may be indicated in cases with severe lung hypoplasia and grim prognosis. Treatment after birth requires all the refinements of critical care including extracorporeal membrane oxygenation prior to surgical correction. The best hospital series report 80% survival but it remains around 50% in population-based studies. Chronic respiratory tract disease, neurodevelopmental problems, neurosensorial hearing loss and gastroesophageal reflux are common problems in survivors. Much more research on several aspects of this severe condition is warranted.

Prenatal administration of retinoic acid upregulates insulin-like growth factor receptors in the nitrofen-induced hypoplastic lung

BACKGROUND

Pulmonary hypoplasia (PH) is the main cause of mortality in newborns with congenital diaphragmatic hernia (CDH). Prenatal administration of retinoic acid (RA) stimulates alveologenesis in the nitrofen-induced pulmonary hypoplasia. Insulin-like growth factor receptors (IGFRs) play a crucial role in alveologenesis during lung development. We recently demonstrated that IGFRs were downregulated in later stages of lung development in the nitrofen CDH model. Several studies suggest the ability of RA to regulate insulin-like growth factor signaling. We hypothesized that IGFRs pulmonary gene expression is upregulated after the administration of RA in the nitrofen-induced CDH model.

METHODS

Pregnant rats were exposed to either olive oil or nitrofen on day 9 (D9) of gestation. RA was given intraperitoneally on days D18, D19, and D20. Fetal lungs were dissected on D21 and divided into control, control + RA, CDH, and CDH + RA group. IGFRs gene and protein expression were determined using RT-PCR and immunohistochemistry.

RESULTS

mRNA expression levels of IGFRs were significantly increased in control + RA and CDH + RA compared with CDH group. Immunoreactivity of IGFRs was markedly increased in control + RA and CDH + RA compared with CDH lungs.

CONCLUSIONS

Upregulation of pulmonary gene and protein expression of IGFRs after prenatal RA treatment in the nitrofen model suggests that RA may promote lung growth by stimulating IGFRs mediated alveologenesis.

[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.

Vitamin A metabolism: an update

Retinoids are required for maintaining many essential physiological processes in the body, including normal growth and development, normal vision, a healthy immune system, normal reproduction, and healthy skin and barrier functions. In excess of 500 genes are thought to be regulated by retinoic acid. 11-cis-retinal serves as the visual chromophore in vision. The body must acquire retinoid from the diet in order to maintain these essential physiological processes. Retinoid metabolism is complex and involves many different retinoid forms, including retinyl esters, retinol, retinal, retinoic acid and oxidized and conjugated metabolites of both retinol and retinoic acid. In addition, retinoid metabolism involves many carrier proteins and enzymes that are specific to retinoid metabolism, as well as other proteins which may be involved in mediating also triglyceride and/or cholesterol metabolism. This review will focus on recent advances for understanding retinoid metabolism that have taken place in the last ten to fifteen years.

Nitrofen induces apoptosis independently of retinaldehyde dehydrogenase (RALDH) inhibition

BACKGROUND

Nitrofen is a diphenyl ether that induces congenital diaphragmatic hernia (CDH) in rodents. Its mechanism of action has been hypothesized as inhibition of the retinaldehyde dehydrogenase (RALDH) enzymes with consequent reduced retinoic acid signaling.

METHODS

To determine if nitrofen inhibits RALDH enzymes, a reporter gene construct containing a retinoic acid response-element (RARE) was transfected into HEK-293 cells and treated with varying concentrations of nitrofen in the presence of retinaldehyde (retinal). Cell death was characterized by caspace-cleavage microplate assays and terminal deoxynucleotidyl transferase dUTP nick end-labeling (TUNEL) assays. Ex vivo analyses of cell viability were characterized in fetal rat lung explants using Live/Dead staining. Cell proliferation and apoptosis were assessed using fluorescent immunohistochemistry with phosphorylated histone and activated caspase antibodies on explant tissues. Nile red staining was used to identify intracellular lipid droplets.

RESULTS

Nitrofen-induced dose-dependent declines in RARE-reporter gene expression. However, similar reductions were observed in control-reporter constructs suggesting that nitrofen compromised cell viability. These observed declines in cell viability resulted from increased cell death and were confirmed using two independent assays. Ex vivo analyses showed that mesenchymal cells were particularly susceptible to nitrofen-induced apoptosis while epithelial cell proliferation was dramatically reduced in fetal rat lung explants. Nitrofen treatment of these explants also showed profound lipid redistribution, primarily to phagocytes.

CONCLUSIONS

The observed declines in nitrofen-associated retinoic acid signaling appear to be independent of RALDH inhibition and likely result from nitrofen induced cell death/apoptosis. These results support a cellular apoptotic mechanism of CDH development, independent of RALDH inhibition.

Impact of environmental chemicals on lung development

BACKGROUND

Disruption of fundamental biologic processes and associated signaling events may result in clinically significant alterations in lung development.

OBJECTIVES

We reviewed evidence on the impact of environmental chemicals on lung development and key signaling events in lung morphogenesis, and the relevance of potential outcomes to public health and regulatory science .

DATA SOURCES

We evaluated the peer-reviewed literature on developmental lung biology and toxicology, mechanistic studies, and supporting epidemiology.

DATA SYNTHESIS

Lung function in infancy predicts pulmonary function throughout life. In utero and early postnatal exposures influence both childhood and adult lung structure and function and may predispose individuals to chronic obstructive lung disease and other disorders. The nutritional and endogenous chemical environment affects development of the lung and can result in altered function in the adult. Studies now suggest that similar adverse impacts may occur in animals and humans after exposure to environmentally relevant doses of certain xenobiotics during critical windows in early life. Potential mechanisms include interference with highly conserved factors in developmental processes such as gene regulation, molecular signaling, and growth factors involved in branching morphogenesis and alveolarization.

CONCLUSIONS

Assessment of environmental chemical impacts on the lung requires studies that evaluate specific alterations in structure or function-end points not regularly assessed in standard toxicity tests. Identifying effects on important signaling events may inform protocols of developmental toxicology studies. Such knowledge may enable policies promoting true primary prevention of lung diseases. Evidence of relevant signaling disruption in the absence of adequate developmental toxicology data should influence the size of the uncertainty factors used in risk assessments.

Fetal skin fibroblasts: a cell model for studying the retinoid pathway in congenital diaphragmatic hernia

BACKGROUND

Although there is strong evidence that genetic factors play a pathogenic role in congenital diaphragmatic hernia (CDH), few causal genes have been identified in humans. A number of studies, essentially in animal models, have suggested that disruption of the retinoid signaling pathway plays a major role in the pathogenesis of CDH. Our hypothesis is that human fetal skin fibroblasts express some metabolic and molecular actors of the retinoid pathway and that they offer convenient cellular material for investigating the molecular retinoid pathway defects associated with CDH.

METHODS

We first established the expression of receptors, enzymes and binding proteins involved in the retinoic acid (RA) pathway in non-CDH fetal skin fibroblasts using RT-PCR and immunocytochemistry approaches. We then studied the expression of these genes in skin fibroblasts from seven fetuses with isolated and nonisolated CDH.

RESULTS

Fetal skin fibroblasts expressed enzymes involved in RA metabolism as well as nuclear receptors for signal transduction. Basal levels of retinoic acid receptor, retinaldehyde dehydrogenase 2, and CYP26 (cytochrome P450 RAI) expression were altered in two of seven fetuses. Interestingly, these genes were previously described as abnormally expressed in CDH physiopathology.

CONCLUSION

Our results suggest that human fetal skin fibroblasts could be useful for studying retinoid signaling pathway disruption in the context of CDH. Our proposal is strengthened by the fact that we identified CDH fetuses for which molecular and metabolic actors of the retinoid pathway were not detected.

Congenital diaphragmatic hernia: outcome review of 2,173 surgical repairs in US infants

Congenital diaphragmatic hernia (CDH) remains one of the most challenging conditions to treat within the pediatric surgical and medical communities. In spite of modern treatment modalities, including extracorporeal membrane oxygenation (ECMO) and improved ventilatory support, mortality remains high. The present study analyzes a US database containing information from nearly 93 million discharges in the US. Infants with congenital diaphragmatic hernia who underwent surgical repair were identified by ICD-9 procedure code and inclusion criteria including an age at admission of less than 1 year. Variables of gender, race, age, geographic region, co-existing diagnoses and procedures, hospital type, hospital charges adjusted to 2006 dollars, length of stay, and inpatient mortality were collected. A total of 89% of patients were either treated initially or rapidly transferred to urban teaching hospitals for definitive treatment of CDH. The inpatient mortality rate was 10.4% with a median length of stay of 20 days (interquartile range of 9-40 days). The median inflation-adjusted total hospital charge was $116,210. Respiratory distress was the most common co-existing condition (68.8%) followed by esophageal reflux (27.8%). The most common concomitant procedures performed were ECMO (17.8%) and fundoplication (17.6%). This study, which represents the largest characterization of US infants who have undergone CDH repair using data from a nationally representative non-voluntary database, demonstrates that surgical repair is associated with significant mortality and morbidity.

Prenatal retinoic acid up-regulates pulmonary gene expression of COUP-TFII, FOG2, and GATA4 in pulmonary hypoplasia

PURPOSE

Retinoids play an important role in lung development. Recently, prenatal treatment with retinoic acid (RA) has been reported to stimulate alveologenesis in hypoplastic lungs in the nitrofen model of congenital diaphragmatic hernia (CDH). Chicken ovalbumin upstream promoter-transcription factor II (COUP-TFII) is a transcription factor in the steroid/thyroid hormone receptor superfamily, and targeted ablation of COUP-TFII causes CDH and associated lung hypoplasia in mice. Friend of GATA 2 (FOG2) is a zinc finger-containing protein that modulates the transcriptional activity of GATA proteins. GATA4 is a member of a family of DNA-binding proteins, which is found in the promoter regions of many genes. The COUP-TFII, FOG2, and GATA4 genes, regulated by the retinoid signaling pathway, are located on chromosomes 15q26, 8q23, and 8p23.1 respectively, regions reported to be deleted in individuals with CDH. The aim of this study was to examine the pulmonary gene expression of COUP-TFII, FOG2, and GATA4 in the nitrofen model of CDH.

MATERIALS AND METHODS

Pregnant rats were exposed to either olive oil or 100 mg nitrofen on day 9 of gestation (D9). 5 mg/kg of RA was given intraperitoneally on days D18, D19, and D20. The fetuses were recovered by caesarean section on D21, and the diaphragm was carefully examined for the presence of a hernia under a microscope. Left lungs were obtained from CDH fetuses and controls and divided into four groups: control (n = 9), control + RA (n = 9), CDH (n = 9), and CDH + RA (n = 9). The relative mRNA expression levels of COUP-TFII, FOG2, and GATA4 were analyzed in each lung by real-time reverse transcriptase-polymerase chain reaction from cDNA generated by mRNA from pulmonary total RNA.

RESULTS

The relative mRNA expression levels of COUP-TFII, FOG2, and GATA4 were significantly increased in CDH + RA lungs compared to control, control + RA, and CDH (P < .05).

CONCLUSIONS

Up-regulation of pulmonary gene expression of COUP-TFII, FOG2, and GATA4 after prenatal treatment with retinoic acid in the nitrofen model of CDH suggests that RA may have a therapeutic potential in modulating lung growth. Furthermore, these results support the concept that these proteins work together to regulate downstream target genes that play an important role in the development of lung.

Phenotype and 244k array-CGH characterization of chromosome 13q deletions: an update of the phenotypic map of 13q21.1-qter

Partial deletions of the long arm of chromosome 13 lead to variable phenotypes dependant on the size and position of the deleted region. In order to update the phenotypic map of chromosome 13q21.1-qter deletions, we applied 244k Agilent oligonucleotide-based array-CGH to determine the exact breakpoints in 14 patients with partial deletions of this region. Subsequently, we linked the genotype to the patient's phenotype. Using this approach, we were able to refine the smallest deletion region linked to short stature (13q31.3: 89.5-91.6 Mb), microcephaly (13q33.3-q34), cortical development malformations (13q33.1-qter), Dandy-Walker malformation (DWM) (13q32.2-q33.1), corpus callosum agenesis (CCA) (13q32.3-q33.1), meningocele/encephalocele (13q31.3-qter), DWM, CCA, and neural tube defects (NTDs) taken together (13q32.3-q33.1), ano-/microphthalmia (13q31.3-13qter), cleft lip/palate (13q31.3-13q33.1), lung hypoplasia (13q31.3-13q33.1), and thumb a-/hypoplasia (13q31.3-q33.1 and 13q33.3-q34). Based on observations of this study and previous reports we suggest a new entity, "distal limb anomalies association," linked to 13q31.3q33.1 segment. Most of the individuals with deletion of any part of 13q21qter showed surprisingly similar facial dysmorphic features, and thus, a "13q deletion facial appearance" was suggested. Prominent nasal columella was mapped between 13q31.3 and 13q33.3, and micrognathia between 13q21.33 and 13q31.1. The degree of mental delay did not display a particular phenotype-genotype correlation on chromosome 13. In contrast to previous reports of carriers of 13q32 band deletions as the most seriously affected patients, we present two such individuals with long-term survival, 28 and 2.5 years.

Unique spatial and cellular expression patterns of Hoxa5, Hoxb4, and Hoxb6 proteins in normal developing murine lung are modified in pulmonary hypoplasia

BACKGROUND

Hox transcription factors modulate signaling pathways controlling organ morphogenesis and maintain cell fate and differentiation in adults. Retinoid signaling, key in regulating Hox expression, is altered in pulmonary hypoplasia. Information on pattern-specific expression of Hox proteins in normal lung development and in pulmonary hypoplasia is minimal. Our objective was to determine how pulmonary hypoplasia alters temporal, spatial, and cellular expression of Hoxa5, Hoxb4, and Hoxb6 proteins compared to normal lung development.

METHODS

Temporal, spatial, and cellular Hoxa5, Hoxb4, and Hoxb6 expression was studied in normal (untreated) and nitrofen-induced hypoplastic (NT-PH) lungs from gestational day 13.5, 16, and 19 fetuses and neonates using Western blot and immunohistochemistry.

RESULTS

Modification of protein levels and spatial and cellular Hox expression patterns in NT-PH lungs was consistent with delayed lung development. Distinct protein isoforms were detected for each Hox protein. Expression levels of the Hoxa5 and Hoxb6 protein isoforms changed with development and were altered further in NT-PH lungs. Compared to normal lungs, GD19 and neonatal NT-PH lungs had decreased Hoxb6 and increased Hoxa5 and Hoxb4. Hoxa5 cellular localization changed from mesenchyme to epithelia earlier in normal lungs. Hoxb4 was expressed in mesenchyme and epithelial cells throughout development. Hoxb6 remained mainly in mesenchymal cells around distal airways.

CONCLUSIONS

Unique spatial and cellular expression of Hoxa5, Hoxb4, and Hoxb6 participates in branching morphogenesis and terminal sac formation. Altered Hox protein temporal and cellular balance of expression either contributes to pulmonary hypoplasia or functions as a compensatory mechanism attempting to correct abnormal lung development and maturation in this condition.

Genetic aspects of human congenital diaphragmatic hernia

Congenital diaphragmatic hernia (CDH) is a common major malformation affecting 1/3000-1/4000 births, which continues to be associated with significant perinatal mortality. Much current research is focused on elucidating the genetics and pathophysiology contributing to CDH to develop more effective therapies. The latest data suggest that many cases of CDH are genetically determined and also indicate that CDH is etiologically heterogeneous. The present review will provide a brief summary of diaphragm development and model organism work most relevant to human CDH and will primarily describe important human phenotypes associated with CDH and also provide recommendations for diagnostic evaluation of a fetus or infant with CDH.

Effects of maternal retinoic acid administration in a congenital diaphragmatic hernia rabbit model

Maternal retinoid administration has beneficial effects on lung development in the nitrofen rodent toxic model of congenital diaphragmatic hernia (DH). We wanted to investigate the effects in a surgical model, where the retinoid signaling pathway is not primarily disrupted by the toxic agent. We created DH in fetal rabbits at day 23 of gestation, administrated to the does all trans-retinoic acid (ATRA) or vehicle (VHC) intramuscularly for 8 consecutive days and harvested normal and operated (DH) fetuses at 31 d (n = 7 in each group). Normal lungs exposed to ATRA had increased surfactant protein mRNA levels without change in type II pneumocyte density. There was no measurable effect on lung-to-body weight ratio and airway morphometry by ATRA. In DH lungs (DH/VHC) surfactant protein mRNA levels were increased, as well as the density of type II pneumocytes. When supplemented with ATRA (DH/ATRA) these parameters returned to normal (VHC). Cell proliferation or apoptosis were not influenced by ATRA supplementation. In conclusion, maternal ATRA supplementation does not affect gross anatomic, morphologic or proliferation indices in hypoplastic lungs related to surgically induced DH in rabbit. However, ATRA lowers surfactant protein expression and normalizes type I/II pneumocyte ratio to what is observed in normal lungs.

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.

Congenital diaphragmatic hernia (CDH) etiology as revealed by pathway genetics

Congenital diaphragmatic hernia (CDH) is a common birth defect with high mortality and morbidity. Two hundred seventy CDH patients were ascertained, carefully phenotyped, and classified as isolated (diaphragm defects alone) or complex (with additional anomalies) cases. We established different strategies to reveal CDH-critical chromosome loci and genes in humans. Candidate genes for sequencing analyses were selected from CDH animal models, genetic intervals of recurrent chromosomal aberration in humans, such as 15q26.1-q26.2 or 1q41-q42.12, as well as genes in the retinoic acid and related pathways and those known to be involved in embryonic lung development. For instance, FOG2, GATA4, and COUP-TFII are all needed for both normal diaphragm and lung development and are likely all in the same genetic and molecular pathway. Linkage analysis was applied first in a large inbred family and then in four multiplex families with Donnai-Barrow syndrome (DBS) associated with CDH. 10K SNP chip and microsatellite markers revealed a DBS locus on chromosome 2q23.3-q31.1. We applied array-based comparative genomic hybridization (aCGH) techniques to over 30, mostly complex, CDH patients and found a de novo microdeletion in a patient with Fryns syndrome related to CDH. Fluorescence in situ hybridization (FISH) and multiplex ligation-dependent probe amplification (MLPA) techniques allowed us to further define the deletion interval. Our aim is to identify genetic intervals and, in those, to prioritize genes that might reveal molecular pathways, mutations in any step of which, might contribute to the same phenotype. More important, the elucidation of pathways may ultimately provide clues to treatment strategies.

Altered regulation of retinoic acid synthesis in nitrofen-induced hypoplastic lung

Retinoids are a group of molecules derived from vitamin A, which play an important role in lung development. Within the cell, retinol can either be oxidized to retinal or esterified to retinyl esters by lecithin : retinol acyltransferase (LRAT) for storage. Retinal is then oxidized to an active metabolite of vitamin A, retinoic acid (RA) by retinal dehydrogenase (RALDH). RA is the active metabolite of vitamin A. Cyp26 (a1,b1, and c1), which is a member of the cytochrome P450 family, acts by reducing the activity of RA. Cyp26 type b1 is the predominant subtype expressed in the murine lung. Several studies have suggested that nitrofen may interfere with the retinoid pathway resulting in congenital diaphragmatic hernia (CDH) and pulmonary hypoplasia. Recently, it was reported that nitrofen may act by inhibiting RALDH2. The aim of this study was to examine the pulmonary expression of Cyp26b1, LRAT, and RALDH2, the key enzymes involved in the synthesis of RA, in order to understand the mechanisms underlying pulmonary hypoplasia in the nitrofen CDH model. Pregnant rats were exposed to either olive oil or 100 mg of nitrofen on day 9 of gestation (D9). Fetal lungs were harvested at D15, D17, D19, and D21. D17, D19, and D21 lungs were divided into three groups: control, nitrofen without CDH and nitrofen with CDH, whereas D15 lungs were divided into only two groups; control and nitrofen as the diaphragm is not fully formed yet at this stage. Real- time PCR was performed to evaluate the relative level of Cyp26b1, LRAT, and RALDH2 expression in the lung. Relative levels of Cyp26b1 mRNA were significantly decreased in the lungs of nitrofen with CDH (D17;0.19 +/- 0.09, D19;0.70 +/- 0.20, D21;0.40 +/- 0.36) and nitrofen without CDH (D17;0.14 +/- 0.06, D19;0.54 +/- 0.42, D21;0.51 +/- 0.56) compared to controls (D17;0.35 +/- 0.16, D19;1.15 +/- 0.48, D21;1.28 +/- 0.78) (P < 0.05). LRAT expression was also significantly decreased in nitrofen with CDH (D17; 19.3 +/- 7.8, D19; 4.3 +/- 1.1, D21; 3.3 +/- 1.6) and nitrofen without CDH (D17; 21.2 +/- 11.1, D19; 4.5 +/- 3.6, D21; 4.1 +/- 1.6) compared to controls (D17; 153.7 +/- 29.8, D19; 26.8 +/- 16.8 D21; 10.1 +/- 3.8) (P < 0.05). There was no significant difference in the relative levels of Cyp26b1 and LRAT between nitrofen with CDH and nitrofen without CDH. There were no significant differences in RALDH2 expression among the groups at any stages. Down-regulation of Cryp26b1 and LRAT demonstrates that RA content is decreased in nitrofen induced hypoplastic lungs compared to controls. The finding that RALDH2 expression in the hypoplastic lung is not altered suggests that nitrofen may act by interfering with the retinoid metabolism during the early stage of the retinoid signaling pathway.

Mutations in STRA6 cause a broad spectrum of malformations including anophthalmia, congenital heart defects, diaphragmatic hernia, alveolar capillary dysplasia, lung hypoplasia, and mental retardation

We observed two unrelated consanguineous families with malformation syndromes sharing anophthalmia and distinct eyebrows as common signs, but differing for alveolar capillary dysplasia or complex congenital heart defect in one and diaphragmatic hernia in the other family. Homozygosity mapping revealed linkage to a common locus on chromosome 15, and pathogenic homozygous mutations were identified in STRA6, a member of a large group of "stimulated by retinoic acid" genes encoding novel transmembrane proteins, transcription factors, and secreted signaling molecules or proteins of largely unknown function. Subsequently, homozygous STRA6 mutations were also demonstrated in 3 of 13 patients chosen on the basis of significant phenotypic overlap to the original cases. While a homozygous deletion generating a premature stop codon (p.G50AfsX22) led to absence of the immunoreactive protein in patient's fibroblast culture, structural analysis of three missense mutations (P90L, P293L, and T321P) suggested significant effects on the geometry of the loops connecting the transmembrane helices of STRA6. Two further variations in the C-terminus (T644M and R655C) alter specific functional sites, an SH2-binding motif and a phosphorylation site, respectively. STRA6 mutations thus define a pleiotropic malformation syndrome representing the first human phenotype associated with mutations in a gene from the "STRA" group.

Disturbance of retinol transportation causes nitrofen-induced hypoplastic lung

PURPOSE

Retinoids play a key role in lung development. Recent studies suggest that retinoid signalling pathway may be disrupted in the nitrofen model of congenital diaphragmatic hernia (CDH), but the exact mechanism is not clearly understood. We hypothesized that nitrofen interferes with cellular uptake of retinol during lung morphogenesis and therefore designed this study to examine total retinol levels in lung, liver, and serum, and the gene expression of main components of the retinoid pathway in the nitrofen model of CDH.

METHODS

Pregnant rats were exposed to vehicle or 100 mg of nitrofen on day 9 of gestation. Term fetuses were divided in control and nitrofen with CDH and without CDH groups. Retinol levels in serum, lungs, and liver were measured using high-performance liquid chromatography. Reverse transcriptase-polymerase chain reaction was performed to evaluate the relative amount of cellular retinol-biding protein I, retinal dehydrogenase 1a2 and 1a3 (Aldh1a2 and Aldh1a3), retinoic acid receptors alpha and beta (RARalpha, RARbeta), and retinoid X receptor alpha (RXRalpha) expression in the lung.

RESULTS

Total retinol levels in the lungs were significantly lower in both nitrofen with CDH (1.78 +/- 0.37 microg/g) and nitrofen without CDH (1.61 +/- 0.24 microg/g) groups compared with controls (2.43 +/- 0.31 microg/g) (P < .001), whereas serum retinol levels were significantly higher in nitrofen with and without CDH groups (0.77 +/- 0.13 and 0.75 +/- 0.11 microg/g, respectively) compared with controls (0.58 +/- 0.12 microg/g) (P < .001). There was no significant difference in liver retinol levels between the 3 groups. Relative expression of cellular retinol-biding protein I, Aldh1a3, RARalpha, RARbeta, and RXRalpha were significantly up-regulated in the lungs of the nitrofen with CDH group (0.70 +/- 0.15, 3.94 +/- 0.91, 2.15 +/- 0.47, 3.49 +/- 1.00, 1.88 +/- 0.42, respectively) and the nitrofen without CDH group (0.61 +/- 0.14, 3.72 +/- 0.31, 1.66 +/- 0.20, 3.28 +/- 1.02, 1.38 +/- 0.24, respectively) compared with controls (0.43 +/- 0.11, 2.71 +/- 0.47, 0.79 +/- 0.42, 1.85 +/- 0.69, 0.57 +/- 0.22, respectively) (P < .05).

CONCLUSION

Our data clearly show that lung retinol storage is decreased in the nitrofen model of CDH. The associated increase in gene expressions of most downstream components of the retinoid signalling pathway may be a feedback reaction to the deficiency of lung retinol. These results suggest that nitrofen acts by interfering with the cellular uptake of retinol during lung morphogenesis resulting in pulmonary hypoplasia in this model.

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.

Retinoic acid rescues lung hypoplasia in nitrofen-induced hypoplastic foetal rat lung explants

There is increasing evidence to suggest that the retinoid pathway is involved in the pathogenesis of congenital diaphragmatic hernia (CDH). We hypothesised that retinoids are involved in the pathogenesis of associated pulmonary hypoplasia in CDH and therefore designed this study to investigate the effects of retinoid acid on nitrofen-induced hypoplastic lungs. Pregnant rats were exposed to either olive oil or 100 mg nitrofen on day 9.5 of gestation. Foetal lungs were harvested on embryonic day 13.5 and were cultured for 96 h with or without exogenous retinoic acid (RA) (1 muM) added daily to the culture medium. Lungs were divided into four study groups: control (n=31); control + RA (n=19); nitrofen (n=19); and nitrofen + RA (n=12). Lung growth was assessed in each group by measuring branching morphogenesis, total DNA content and the proportion of proliferating cells stained by immunohistochemistry. One-way ANOVA test was used for statistical analysis. Retinoic acid significantly increased the growth of nitrofen-induced hypoplastic lungs, whilst growth of control lungs did not change. The number of lung buds and lung area of nitrofen-exposed hypoplastic lungs after 96 h of culture significantly increased after the addition of RA compared to the non-treated hypoplastic lungs (25.75+/-6.47 vs 15.11+/-3.29 and 0.98+/-0.18 mm(2) vs 0.65+/-0.13 mm(2), respectively; P<0.0001). Lung perimeter was also higher when RA was added to hypoplastic lungs compared to the non-treated ones, although it did not reach significance (12.51+/-2.53 mm vs 11.19+/-2.56 mm; P=0.17). Conversely, the addition of RA to control lungs did not affect the number of lung buds, lung area or lung perimeter after 96 h in culture compared to the non-treated ones (31.28+/-4.66 vs 31.81+/-6.67; 1.29+/-0.18(2) vs 1.29+/-0.23 mm(2) and 18.47+/-3.47 mm vs 17.89+/-2.94 mm, respectively; P=NS). Retinoic acid also increased the total DNA content and the proportion of proliferating cells in hypoplastic lungs compared to the non-treated ones (2.59+/-0.58 mug vs 1.96+/-0.31 mug and 57.89+/-9.46% vs 36.76+/-8.15%, respectively; P<0.001). The addition of RA did not affect either total DNA content or the proportion of proliferating cells in control lungs compared to the non-treated ones (4.04+/-0.64 mug vs 3.79+/-0.85 mug and 58.67+/-11.23% vs 56.03+/-10.36%, respectively; P=NS). This study demonstrates for the first time that RA rescues lung hypoplasia in nitrofen-induced hypoplastic lungs. These results suggest that retinoid pathway may be involved in the pathogenesis of associated pulmonary hypoplasia in CDH.