Up-regulation of COUP-TFII gene expression in the nitrofen-induced hypoplastic lung

A successful centre for translational paediatric surgical research

The National Children's Research Centre (NCRC), the single largest paediatric research centre in Ireland, has been in existence for over 50 years and is located on the grounds of the largest children's hospital in Ireland; Children's Health Ireland at Crumlin. Professor Puri was appointed as the Director of the Research in 1989 and became President of the NCRC in 2009, a position he held until 2016. Professor Puri is one of the most cited paediatric surgical researchers in the world. His research work has been cited over 23,500 times in peer-reviewed articles with an h-index of 76 and i10-index of 494. The aim of this review is to analyse the most relevant areas of academic research at the NCRC, Dublin, during the years when Prof. Puri was Director/President of the NCRC. In addition, the relevant factors essential to create a successful paediatric surgical research centre will be discussed. A literature search using PubMed/Medline was carried out using the search terms "Prem Puri" over a 40-year period (1980-2020). Articles were analysed to identify the most significant research areas in the field of paediatric surgical research and the relevant laboratory and clinical findings. In addition, a separate analysis of successful funding and human factors, such as research fellows working at the NCRC, was also carried out. During the period under review, Professor Puri's team published 750 articles in peer-reviewed journals. Three main areas of research were reviewed with a total number of 391 articles: congenital diaphragmatic hernia (CDH) was the topic with the largest number of publications (153), followed by Hirschsprung's disease (HSCR) (144) and Vesicoureteral reflux (VUR) (94). Eighty research fellows, all paediatric surgeons, from 18 different countries were trained in basic science under the supervision of Professor Puri at the NCRC. Over the last three decades, the NCRC has been one of the most successful centres for paediatric surgical research in the world. The three areas of research with the largest number of publications were identified as CDH, HSCR and VUR. Various factors can explain the success of the NCRC: (a) the constant presence, for over 30 years, of a very successful paediatric surgeon leading the centre, (b) a multicultural laboratory with research fellows from all over the world and (c) grants of more than 15 million raised over the years, which guaranteed a constant flow of resources for laboratory research.

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.

Prenatal administration of all-trans retinoic acid upregulates leptin signaling in hypoplastic rat lungs with experimental congenital diaphragmatic hernia

PURPOSE

Pulmonary hypoplasia (PH), characterized by alveolar immaturity, is one of the leading causes of respiratory insufficiency in newborns with congenital diaphragmatic hernia (CDH). Leptin (Lep) and its receptor (Lep-R) play an important role in fetal lung growth by stimulating alveolar differentiation and maturation. Lep and Lep-R are strongly expressed by alveolar cells during the saccular stage of fetal lung development. Lep-deficient mice exhibit decreased alveolarization with reduced pulmonary surfactant phospholipid synthesis, similar to human and nitrofen-induced PH. Prenatal administration of all-trans retinoic acid (ATRA) has been shown to stimulate alveolarization in nitrofen-induced PH. Recent studies have demonstrated that Lep and Lep-R expression in developing lungs is regulated by ATRA. We hypothesized that prenatal treatment with ATRA increases pulmonary Lep and Lep-R expression in the nitrofen model of CDH-associated PH.

METHODS

Time-mated rats received either 100 mg nitrofen or vehicle via oral-gastric lavage on embryonic day 9.5 (E9.5). Control and nitrofen-exposed dams were randomly assigned to either intraperitoneal ATRA (5 mg/kg/d) or placebo administration on E18.5, E19.5 and E20.5. Fetal lungs were harvested on E21.5, and divided into Control+Placebo, Control+ATRA, Nitrofen+Placebo and Nitrofen+ATRA. Alveolarization was assessed using stereo- and morphometric analysis techniques. Surfactant phospholipid synthesis was analyzed by labeling for surfactant protein B (SP-B). Pulmonary gene expression levels of Lep and Lep-R were determined using quantitative real-time polymerase chain reaction. Immunohistochemical staining for Lep and Lep-R was performed to evaluate alveolar protein expression and localization.

RESULTS

In vivo administration of ATRA resulted in significantly increased lung-to-body weight ratio with enhanced radial alveolar count and decreased mean linear intercept compared to placebo treatment. Immunofluorescence analysis demonstrated markedly increased pulmonary SP-B expression in Nitrofen+ATRA compared to Nitrofen+Placebo. Relative mRNA expression of Lep and Lep-R was significantly increased in Nitrofen+ATRA compared to Nitrofen+Placebo. Lep and Lep-R immunoreactivity was markedly increased in interstitial and alveolar epithelial cells of Nitrofen+ATRA compared to Nitrofen+Placebo.

CONCLUSION

Increased Lep and Lep-R expression after prenatal administration of ATRA in nitrofen-induced PH suggests that ATRA may have therapeutic potential in attenuating CDH-associated PH by stimulating alveolarization and de novo surfactant production.

Alterations of peroxisome proliferator-activated receptor γ and monocyte chemoattractant protein 1 gene expression in the nitrofen-induced hypoplastic lung

BACKGROUND/PURPOSE

Peroxisome proliferator-activated receptor γ (PPARγ) plays a key role in normal lung development. Peroxisome proliferator-activated receptor γ messenger RNA (mRNA) is detectable at 18 days of gestation in fetal rat lungs, and levels peak just before birth. Peroxisome proliferator-activated receptor γ agonists are reported to stimulate lung development, whereas inhibition of PPARγ disrupts postnatal lung maturation. Monocyte chemoattractant protein 1 (MCP-1), which is inhibited by PPARγ, is reported to disrupt late lung morphogenesis. This study was designed to investigate the hypothesis that PPARγ expression is downregulated and that MCP-1 expression is upregulated during the late stages of lung development in nitrofen-induced hypoplastic lungs.

METHODS

Pregnant rats were treated with nitrofen or vehicle on D9. RNA was extracted from fetal lungs (D18 and D21), and relative mRNA expression levels of PPARγ and MCP-1 were determined by reverse transcriptase-polymerase chain reaction. Immunohistochemistry was performed to evaluate protein expression/distribution of PPARγ and MCP-1.

RESULTS

Relative mRNA expression levels of PPARγ were significantly downregulated in the nitrofen group compared with controls on D21, whereas MCP-1 levels were upregulated. Immunohistochemical study showed markedly decreased PPARγ and increased MCP-1 immunoreactivity in the nitrofen-induced hypoplastic lungs compared with controls on gestational day 21.

CONCLUSION

Altered pulmonary gene expression of PPARγ and MCP-1 during late gestation may impair lung development and maturation, contributing to pulmonary hypoplasia in the nitrofen-induced congenital diaphragmatic hernia model.

Abnormal platelet-derived growth factor signaling accounting for lung hypoplasia in experimental congenital diaphragmatic hernia

PURPOSE

The pathogenesis of pulmonary hypoplasia in congenital diaphragmatic hernia (CDH) is not fully understood. Platelet-derived growth factor A (PDGFA) and platelet-derived growth factor receptor α (PDGFRα) play a crucial role in lung development. It has been reported that PDGF induces H(2)O(2)-production and that oxidative stress may be an important mechanism for the impaired lung development in the nitrofen rat model. We hypothesized that pulmonary expression of PDGFA and PDGFRα is altered in the nitrofen induced CDH model.

MATERIALS AND METHODS

Pregnant rats received 100 mg nitrofen or vehicle on gestational day 9 (D9) and were sacrificed on D15, D18 or D21. RNA was extracted from fetal left lungs and mRNA levels of PDGFA and PDGFRα were determined using real-time polymerase chain reaction. Immunohistochemistry for protein expression of PDGFA and PDGFRα was performed. Pulmonary H(2)O(2) was measured colorimetrically.

RESULTS

mRNA levels of PDGFRα at D15 (4.50 ± 0.87) and PDGFA at D18 (2.90 ± 1.38) were increased in the nitrofen group (P < .05). Immunohistochemistry revealed increased pulmonary expression of PDGFRα and PDGFA. H(2)O(2) content was significantly higher in the nitrofen group.

CONCLUSIONS

Increased expression of PDGFA and PDGFRα suggests that pulmonary hypoplasia in the nitrofen CDH model may be owing to PDGF-induced oxidative stress during lung development.

Prenatal retinoic acid upregulates pulmonary gene expression of PI3K and AKT in nitrofen-induced pulmonary hypoplasia

BACKGROUND

The precise mechanism of pulmonary hypoplasia associated with congenital diaphragmatic hernia (CDH) still remains unclear. Recently, prenatal treatment with retinoic acid (RA) has been reported to stimulate alveologenesis in hypoplastic lungs in the nitrofen model of CDH. The serine/threonine protein kinase B (AKT) plays a key role in lung morphogenesis through epithelial-mesenchymal interaction in phosphatidylinositide 3-kinase (PI3K)-dependent manner. It has been reported that the lung morphogenesis in explants in mice is interfered by inhibitors of PI3K-AKT signaling pathway. Furthermore, we have recently shown that nitrofen inhibits PI3K-AKT signaling during mid-to-late lung morphogenesis in the nitrofen-induced hypoplastic lung. We hypothesized that prenatal administration of RA upregulates pulmonary gene expression of PI3K and AKT in the nitrofen-induced hypoplastic lung.

METHODS

Pregnant rats were exposed to either olive oil or nitrofen on day 9 of gestation (D9). 5 mg/kg of RA was given on D18, D19 and D20. The fetuses were harvested on D21, and fetal lungs were obtained and divided into four groups: control, control + RA, nitrofen, nitrofen + RA. The mRNA expression levels of PI3K and AKT were analyzed in each lung by real-time RT-PCR and statistically analyzed. Immunohistochemistry was also performed to evaluate protein expression of PI3K and AKT in the fetal lungs at D21.

RESULTS

The pulmonary gene expression levels of PI3K and AKT were significantly upregulated in nitrofen + RA group compared to nitrofen group and control + RA group (p < 0.05), whereas there were no significant differences between controls and control + RA group. Immunoreactivity of PI3K and AKT was markedly increased in nitrofen + RA lungs compared to nitrofen-induced hypoplastic lungs.

CONCLUSIONS

Upregulation of PI3K and AKT genes after prenatal treatment with RA in the nitrofen-induced hypoplastic lung suggests that RA may have a therapeutic potential in modulating lung alveologenesis by stimulating epithelial-mesenchymal interaction via PI3K-AKT signaling.

Congenital diaphragmatic hernia

Congenital diaphragmatic hernia (CDH) is a congenital anomaly consisting of a posterolateral defect in the diaphragm also known as a Bochdalek hernia. It occurs in 1 in 2000 to 3000 newborns and is associated with a variable degree of pulmonary hypoplasia (PH) and persistent pulmonary hypertension (PPH). Despite remarkable advances in neonatal resuscitation and intensive care and the new postnatal treatment strategies, many newborns with CDH continue to have high rates of mortality and morbidity as the result of severe respiratory failure secondary to PH and PPH. The pathogenesis of CDH and associated PH and PPH is poorly understood. Herein, we aim to review diaphragm and pulmonary development and correlate this to the abnormalities found in CDH.

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.

Congenital diaphragmatic hernia: review of the literature in reflection of unresolved dilemmas

BACKGROUND

Congenital diaphragmatic hernia (CDH) is a rare but clinically and scientifically challenging condition. The introduction of ultrasound has enabled early prenatal detection and consequently, hope of early therapeutic intervention.

AIM

We undertook the task to review the recent developments in understanding the pathology of CDH as well as the history and current management strategies to aid perinatologists in consultations with parents of CDH-affected foetuses.

STUDY DESIGN

A Medline search was undertaken of all reports and reviews published between 1980 and 2008 using MeSH search terms 'diaphragmatic hernia', 'congenital' and 'newborn'.

RESULTS

The true incidence of CDH is still difficult to estimate because of the high incidence of hidden mortality of CDH. Complete case ascertainment also poses difficulties in assessment of the impact of new therapeutic modalities on overall survival. Recent improvements in prenatal detection are a milestone in affording time for re-assessments and parental counselling. The true benefit of antenatal therapy is circumscribed and should be offered only in selected cases of isolated severe CDH as defined by existing guidelines. Postnatal intensive respiratory supportive therapy and innovative surgical techniques within specialized tertiary centres has had a major impact on survival of babies with CDH.

CONCLUSION

The high survival of 'selected cases' that are live births and benefit from optimal care will be difficult to improve by antenatal interventions. The multidisciplinary approach to basic research and randomized clinical trials will further define the best approach to the foetus and neonate with CDH.