Reduced expression of aquaporin 5 water channel in nitrofen-induced hypoplastic lung with congenital diaphragmatic hernia rat model

Assessment of the nitrofen model of congenital diaphragmatic hernia and of the dysregulated factors involved in pulmonary hypoplasia

PURPOSE

To study pulmonary hypoplasia (PH) associated with congenital diaphragmatic hernia (CDH), investigators have been employing a fetal rat model based on nitrofen administration to dams. Herein, we aimed to: (1) investigate the validity of the model, and (2) synthesize the main biological pathways implicated in the development of PH associated with CDH.

METHODS

Using a defined strategy, we conducted a systematic review of the literature searching for studies reporting the incidence of CDH or factors involved in PH development. We also searched for PH factor interactions, relevance to lung development and to human PH.

RESULTS

Of 335 full-text articles, 116 reported the incidence of CDH after nitrofen exposure or dysregulated factors in the lungs of nitrofen-exposed rat fetuses. CDH incidence: 54% (27-85%) fetuses developed a diaphragmatic defect, whereas the whole litter had PH in varying degrees. Downregulated signaling pathways included FGF/FGFR, BMP/BMPR, Sonic Hedgehog and retinoid acid signaling pathway, resulting in a delay in early epithelial differentiation, immature distal epithelium and dysfunctional mesenchyme.

CONCLUSIONS

The nitrofen model effectively reproduces PH as it disrupts pathways that are critical for lung branching morphogenesis and alveolar differentiation. The low CDH rate confirms that PH is an associated phenomenon rather than the result of mechanical compression alone.

The role of alveolar epithelium in radiation-induced lung injury

Pneumonitis and fibrosis are major lung complications of irradiating thoracic malignancies. In the current study, we determined the effect of thoracic irradiation on the lungs of FVB/N mice. Survival data showed a dose-dependent increase in morbidity following thoracic irradiation with single (11–13 Gy) and fractionated doses (24–36 Gy) of ¹³⁷Cs γ-rays. Histological examination showed a thickening of vessel walls, accumulation of inflammatory cells, collagen deposition, and regional fibrosis in the lungs 14 weeks after a single 12 Gy dose and a fractionated 30 Gy dose; this damage was also seen 5 months after a fractionated 24 Gy dose. After both single and fractionated doses, i] aquaporin-5 was markedly decreased, ii] E-cadherin was reduced and iii] prosurfactant Protein C (pro-SP-c), the number of pro-SP-c⁺ cells and vimentin expression were increased in the lungs. Immunofluorescence analysis revealed co-localization of pro-SP-c and α-smooth muscle actin in the alveoli after a single dose of 12 Gy. These data suggest that, i] the FVB/N mouse strain is sensitive to thoracic radiation ii] aquaporin-5, E-cadherin, and pro-SP-c may serve as sensitive indicators of radiation-induced lung injury; and iii] the epithelial-to-mesenchymal transition may play an important role in the development of radiation-induced lung fibrosis.

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.

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.

Disturbance of parathyroid hormone-related protein signaling in the nitrofen-induced hypoplastic lung

PURPOSE

Despite remarkable progress in resuscitation and intensive care, the morbidity and mortality rates in congenital diaphragmatic hernia (CDH) remain high due to severe pulmonary hypoplasia. The pathogenesis of pulmonary hypoplasia associated with CDH is still not clearly understood. Pulmonary parathyroid hormone-related protein (PTHrP) is expressed in the type II epithelial cells and stimulates surfactant production by a paracrine feedback loop regulated by PTHrP receptor (PTHrP-R), which is expressed in the mesenchyme, during terminal airway differentiation. It has been reported that PTHrP knockout and PTHrP-R null mice both exhibit pulmonary hypoplasia, disrupting alveolar maturation before birth. We designed this study to test the hypothesis that gene expression of PTHrP and PTHrP-R is downregulated in the late stages of lung morphogenesis in the nitrofen-induced hypoplastic lung.

METHODS

Pregnant rats were exposed to either olive oil or nitrofen on day 9 of gestation (D9). Fetal lungs were harvested on D15, 18, and 21 and divided into three groups: control, nitrofen without CDH [CDH(-)], and nitrofen with CDH [CDH(+)] (n = 8 at each time point for each group, respectively). Total mRNA was extracted from fetal lungs and mRNA expression of PTHrP and PTHrP-R was analyzed by real-time RT-PCR and the significant differences between the groups were accepted at P < 0.05 by statistical analysis. Immunohistochemical studies were also performed to evaluate PTHrP and PTHrP-R protein expression at each time point.

RESULTS

Pulmonary mRNA expression of PTHrP-R was significantly decreased in both nitrofen groups [CDH(-) and CDH(+)] compared to controls at D18 and 21. The mRNA level of PTHrP was significantly decreased at D21 in both nitrofen groups compared to controls. Immunoreactivity of PTHrP and PTHrP-R at D18 and 21 was diminished in the distal epithelium and in the mesenchyme, respectively, in the nitrofen-induced hypoplastic lung compared to control lungs. There were no significant differences in both gene/protein expression of PTHrP and PTHrP-R on D15.

CONCLUSION

Downregulation of PTHrP and PTHrP-R gene expression during late lung morphogenesis may cause pulmonary hypoplasia in the nitrofen CDH model, disrupting alveolar maturation and surfactant production by interfering with mesenchymal-epithelial interactions.

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.

Management of congenital diaphragmatic hernia

PURPOSE OF REVIEW

To evaluate the impact of recent research on the management of congenital diaphragmatic hernia in the light of new theories on embryological development, earlier antenatal diagnosis, fetal and postnatal interventions together with advances in perinatal intensive care.

RECENT FINDINGS

The year 2007 provided in excess of 200 publications that address various aspects of congenital diaphragmatic hernia. The genetic basis and the causes of pulmonary hypoplasia at the molecular level are slowly being unravelled. Fetal MRI of lung volume, lung-head ratio, liver position and size of diaphragmatic defect have all been evaluated as early predictors of outcome and with a view to prenatal counselling. The impact of fetal interventions such as fetal endoluminal tracheal occlusion, the mode of delivery, the surgical techniques and agents for treating pulmonary hypertension were evaluated. The influence of associated anomalies and therapeutic interventions on the outcome and quality of life of survivors continue to be appraised.

SUMMARY

Deferred surgery after stabilization with gentle ventilation and reversal of pulmonary hypertension remain the cornerstones of management. Optimal presurgery and postsurgery ventilatory settings remain unproven. Continued improvement in neonatal intensive care raises the bar against which any intervention such as fetal endoluminal tracheal occlusion and extracorporeal membrane oxygenation will be judged.

NKCC-1 and ENaC are down-regulated in nitrofen-induced hypoplastic lungs with congenital diaphragmatic hernia

Congenital diaphragmatic hernia (CDH) is accompanied by pulmonary hypoplasia and pulmonary hypertension. Fetal lung growth is dependent on the secretion of lung liquid, which normally is absorbed at partus. The ion channel NKCC-1 is involved in this secretory process, but has recently also been reported to be implicated in absorption. CDH patients show a disturbed transition from secretion to absorption. alpha- and beta-ENaC are essential for lung liquid absorption. Common for all transcellular ion transport is the need for Na/K-ATPase as a primary driving force. The aim of the study was first to map the normal pulmonary expression of the above proteins during late gestation and secondly to see if the expression was affected in a CDH rat model. Pregnant Sprague-Dawley rat dams were given nitrofen on gestational day 9.5 to induce CDH. The fetuses were removed on gestational days E18 and E21. In addition, newborn rats were harvested postpartum on day P2. The fetuses were put into one of two groups: hypoplastic lungs without CDH (N-CDH) and hypoplastic lungs with CDH (N+CDH). The pulmonary expression of NKCC-1, alpha-/beta-ENaC and Na/K-ATPase was then analyzed using Western blot. We found that the protein levels of NKCC-1 on gestational days E18 and E21 were significantly lower among fetuses with N+CDH as well as N-CDH compared to controls. The expression of beta-ENaC was also significantly down-regulated in both the groups on E18 and E21. The protein levels of alpha-ENaC and Na/K-ATPase were not found to be significantly decreased, but both showed a tendency towards down-regulation. The marked down-regulation of NKCC-1 in fetal hypoplastic lungs with CDH indicates a possibly decreased lung liquid production. This may be one of the mechanisms behind the disturbed pulmonary development in CDH. We also show that beta-ENaC is down-regulated. Down-regulation of beta-ENaC may result in abnormal lung liquid absorption, which could be one of the mechanisms behind the respiratory distress seen in CDH patients postpartum.

Enhanced expression of 70-kilodalton heat shock protein limits cell division in a sepsis-induced model of acute respiratory distress syndrome

OBJECTIVE

Fibrotic changes are initiated early in acute respiratory distress syndrome. This may involve overproliferation of alveolar type II cells. In an animal model of acute respiratory distress syndrome, we have shown that the administration of an adenoviral vector overexpressing the 70-kd heat shock protein (AdHSP) limited pathophysiological changes. We hypothesized that this improvement may be modulated, in part, by an early AdHSP-induced attenuation of alveolar type II cell proliferation.

DESIGN

Laboratory investigation.

SETTING

Hadassah-Hebrew University and University of Pennsylvania animal laboratories.

SUBJECTS

Sprague-Dawley Rats (250 g).

INTERVENTIONS

Lung injury was induced in male Sprague-Dawley rats via cecal ligation and double puncture. At the time of cecal ligation and double puncture, we injected phosphate-buffered saline, AdHSP, or AdGFP (an adenoviral vector expressing the marker green fluorescent protein) into the trachea. Rats then received subcutaneous bromodeoxyuridine. In separate experiments, A549 cells were incubated with medium, AdHSP, or AdGFP. Some cells were also stimulated with tumor necrosis factor-alpha. After 48 hrs, cytosolic and nuclear proteins from rat lungs or cell cultures were isolated. These were subjected to immunoblotting, immunoprecipitation, electrophoretic mobility shift assay, fluorescent immunohistochemistry, and Northern blot analysis.

MEASUREMENTS AND MAIN RESULTS

Alveolar type I cells were lost within 48 hrs of inducing acute respiratory distress syndrome. This was accompanied by alveolar type II cell proliferation. Treatment with AdHSP preserved alveolar type I cells and limited alveolar type II cell proliferation. Heat shock protein 70 prevented overexuberant cell division, in part, by inhibiting hyperphosphorylation of the regulatory retinoblastoma protein. This prevented retinoblastoma protein ubiquitination and degradation and, thus, stabilized the interaction of retinoblastoma protein with E2F1, a key cell division transcription factor.

CONCLUSIONS

: Heat shock protein 70-induced attenuation of cell proliferation may be a useful strategy for limiting lung injury when treating acute respiratory distress syndrome if consistent in later time points.

Prenatal treatment with retinoic acid accelerates type 1 alveolar cell proliferation of the hypoplastic lung in the nitrofen model of congenital diaphragmatic hernia

PURPOSE

Retinoids play an important role in lung development. A recent study has demonstrated that prenatal treatment with retinoic acid (RA) stimulates alveologenesis in hypoplastic lungs in the nitrofen model of congenital diaphragmatic hernia (CDH). Furthermore, it has also been demonstrated that the differentiation from alveolar epithelial cells type II (AECs-II) into alveolar epithelial cells type I (AECs-I), which is the key process in lung development, is disturbed in this model. We hypothesized that retinoids promote alveologenesis by stimulating differentiation of AECs-II to AECs-I at the end of gestation; and therefore, we investigated the effect of RA on the pulmonary expression of intercellular adhesion molecule 1 (ICAM-1), a marker for AECs-I, and thyroid transcription factor 1 (Ttf-1), a marker for AECs-II, in nitrofen-induced hypoplastic lungs.

MATERIALS AND METHODS

Pregnant rats were exposed to either olive oil or 100 mg nitrofen on day of gestation (D) 9. Five milligrams per kilogram of RA was given intraperitoneally on D18, D19, and D20; and fetuses were recovered on D21. We had 4 study groups: control (n = 7), control + RA (n = 7), CDH (n = 6), and CDH + RA (n = 6). The expression of ICAM-1 and Ttf-1 was analysed in each lung by real-time reverse transcription polymerase chain reaction and immunohistochemistry. One-way analysis of variance test was used for statistical analysis.

RESULTS

Expression levels of ICAM-1 were significantly reduced in CDH lungs compared with normal controls, whereas levels increased significantly in CDH group after the addition of RA (P < .05). Expression levels of Ttf-1 were significantly decreased in lungs from RA-treated CDH animals compared with CDH without RA (P < .05). The ICAM-1 and Ttf-1 immunoreactivity demonstrated similar pattern of expression in various groups.

CONCLUSIONS

Our results demonstrate that prenatal treatment with RA accelerates AEC-I proliferation in the hypoplastic lung in CDH.

Lung tissue mechanics predict lung hypoplasia in a rabbit model for congenital diaphragmatic hernia

Several animal models have been proposed to study the pathophysiology of congenital diaphragmatic hernia (CDH). Surgical induction of CDH in fetal rabbits during the pseudoglandular phase has been shown to induce severe pulmonary hypoplasia, but functional studies in this model are scarce. We aimed to measure neonatal pulmonary impedance and related it to the severity of lung hypoplasia. CDH was surgically created in rabbits at 23 days of gestation. Following cesarean delivery at term (31 days) pups were subjected to measurement of total lung capacity (TLC), lung to body weight ratio (LBWR) and lung impedance by forced oscillation technique (FOT). Airway resistance (R(aw)), tissue elastance (H(L)), tissue damping (G(L)), and hysteresivity (eta) (G(L)/H(L)) were calculated from impedance data. Twelve CDH fetuses and 15 controls were available for final analysis. LBWR and TLC were significantly lower in the CDH group compared to gestational and age matched controls (P<0.001). R(aw), H(L), and G(L) were significantly increased in CCDH fetuses. eta and H(L) best reflected lung hypoplasia (LBWR) (r(2) = 0.42 and 0.43; P=0.001), indicating a dominant contribution of lung tissue mechanics to CDH-induced lung hypoplasia. We successfully introduced lung impedance measurement by FOT in neonatal rabbits. Following surgical induction of CDH in the pseudoglandular phase, they have, next to morphological evidence of pulmonary hypoplasia, changes in lung mechanics. Our results for lung tissue mechanics support the concept of delayed pulmonary tissue modeling. We propose to employ functional studies in future experiments when evaluating prenatal interventions aimed at reversing pulmonary hypoplasia.