Impaired alveolar epithelial cell differentiation in the hypoplastic lung in nitrofen-induced congenital diaphragmatic hernia

Molecular insights using spatial transcriptomics of the distal lung in congenital diaphragmatic hernia

Abnormal pulmonary vascular development and function in congenital diaphragmatic hernia (CDH) is a significant factor leading to pulmonary hypertension. The lung is a very heterogenous organ and has marked cellular diversity that is differentially responsive to injury and therapeutic agents. Spatial transcriptomics provides the unmatched capability of discerning the differences in the transcriptional signature of these distinct cell subpopulations in the lung with regional specificity. We hypothesized that the distal lung parenchyma (selected as a region of interest) would show a distinct transcriptomic profile in the CDH lung compared with control (normal lung). We subjected lung sections obtained from male and female CDH and control neonates to spatial transcriptomics using the Nanostring GeoMx platform. Spatial transcriptomic analysis of the human CDH and control lung revealed key differences in the gene expression signature. Increased expression of alveolar epithelial-related genes (SFTPA1 and SFTPC) and angiogenesis-related genes (EPAS1 and FHL1) was seen in control lungs compared with CDH lungs. Response to vitamin A was enriched in the control lungs as opposed to abnormality of the coagulation cascade and TNF-alpha signaling via NF-kappa B in the CDH lung parenchyma. In male patients with CDH, higher expression of COL1A1 (ECM remodeling) and CD163 was seen. Increased type 2 alveolar epithelial cells (AT-2) and arterial and lung capillary endothelial cells were seen in control lung samples compared with CDH lung samples. To the best of our knowledge, this is the first use of spatial transcriptomics in patients with CDH that identifies the contribution of different lung cellular subpopulations in CDH pathophysiology and highlights sex-specific differences.NEW & NOTEWORTHY This is the first use of spatial transcriptomics in patients with congenital diaphragmatic hernia (CDH) that identifies the contribution of different lung cellular subpopulations in CDH pathophysiology and highlights sex-specific differences.

Distinct Epithelial Cell Profiles in Normal Versus Induced-Congenital Diaphragmatic Hernia Fetal Lungs

BACKGROUND

Recent studies identified a great diversity of cell types in precise number and position to create the architectural features of the lung that ventilation and respiration at birth depend on. With damaged respiratory function at birth, congenital diaphragmatic hernia (CDH) is one of the more severe causes of fetal lung hypoplasia with unspecified cellular dynamics.

OBJECTIVES

 To characterize the epithelial cell tissue in hypoplastic lungs, a careful analysis regarding pulmonary morphology and epithelial cell profile was conducted from pseudoglandular-to-saccular phases in normal versus nitrofen-induced CDH rat lungs.

DESIGN

Our analysis comprises three experimental groups, control, nitrofen (NF) and CDH, in which the relative expression levels (western blot) by group and developmental stage were analyzed in whole lung. Spatiotemporal distribution (immunohistochemistry) was revealed by pulmonary structure during normal and hypoplastic fetal lung development. Surfactant protein-C (SP-C), calcitonin gene-related peptide (CGRP), clara cell secretory protein (CCSP), and forkhead box J1 (FOXJ1) were the used molecular markers for alveolar epithelial cell type 2 (AEC2), pulmonary neuroendocrine, clara, and ciliated cell profiles, respectively.

RESULTS

Generally, we identified an aberrant expression of SP-C, CGRP, CCSP, and FOXJ1 in nitrofen-exposed lungs. For instance, the overexpression of FOXJ1 and CGRP in primordia of bronchiole defined the pseudoglandular stage in CDH lungs, whereas the increased expression of CGRP in bronchi; FOXJ1 and CGRP in terminal bronchiole; and SP-C in BADJ classified the canalicular and saccular stages in hypoplastic lungs. We also described higher expression levels in NF than CDH or control groups for both FOXJ1 in bronchi, terminal bronchiole and BADJ at canalicular stage, and SP-C in bronchi and terminal bronchiole at canalicular and saccular stages. Finally, we report an unexpected expression of FOXJ1 in BADJ at canalicular and saccular stages, whereas the multi cilia observed in bronchi were notably absent at embryonic day 21.5 in induced-CDH lungs.

CONCLUSION

The recognized alterations in the epithelial cell profile contribute to a better understanding of neonatal respiratory insufficiency in induced-CDH lungs and indicate a problem in the epithelial cell differentiation in hypoplastic lungs.

Cellular Origin(s) of Congenital Diaphragmatic Hernia

Congenital diaphragmatic hernia (CDH) is a structural birth defect characterized by a diaphragmatic defect, lung hypoplasia and structural vascular defects. In spite of recent developments, the pathogenesis of CDH is still poorly understood. CDH is a complex congenital disorder with multifactorial etiology consisting of genetic, cellular and mechanical factors. This review explores the cellular origin of CDH pathogenesis in the diaphragm and lungs and describes recent developments in basic and translational CDH research.

ROBO2 signaling in lung development regulates SOX2/SOX9 balance, branching morphogenesis and is dysregulated in nitrofen-induced congenital diaphragmatic hernia

Background

Characterized by abnormal lung growth or maturation, congenital diaphragmatic hernia (CDH) affects 1:3000 live births. Cellular studies report proximal (SOX2⁺) and distal (SOX9⁺) progenitor cells as key modulators of branching morphogenesis and epithelial differentiation, whereas transcriptome studies demonstrate ROBO/SLIT as potential therapeutic targets for diaphragm defect repair in CDH. In this study, we tested the hypothesis that (a) experimental-CDH could changes the expression profile of ROBO1, ROBO2, SOX2 and SOX9; and (b) ROBO1 or ROBO2 receptors are regulators of branching morphogenesis and SOX2/SOX9 balance.

Methods

The expression profile for receptors and epithelial progenitor markers were assessed by Western blot and immunohistochemistry in a nitrofen-induced CDH rat model. Immunohistochemistry signals by pulmonary structure were also quantified from embryonic-to-saccular stages in normal and hypoplastic lungs. Ex vivo lung explant cultures were harvested at E13.5, cultures during 4 days and treated with increasing doses of recombinant rat ROBO1 or human ROBO2 Fc Chimera proteins for ROBO1 and ROBO2 inhibition, respectively. The lung explants were analyzed morphometrically and ROBO1, ROBO2, SOX2, SOX9, BMP4, and β-Catenin were quantified by Western blot.

Results

Experimental-CDH induces distinct expression profiles by pulmonary structure and developmental stage for both receptors (ROBO1 and ROBO2) and epithelial progenitor markers (SOX2 and SOX9) that provide evidence of the impairment of proximodistal patterning in experimental-CDH. Ex vivo functional studies showed unchanged branching morphogenesis after ROBO1 inhibition; increased fetal lung growth after ROBO2 inhibition in a mechanism-dependent on SOX2 depletion and overexpression of SOX9, non-phospho β-Catenin, and BMP4.

Conclusions

These studies provided evidence of receptors and epithelial progenitor cells which are severely affected by CDH-induction from embryonic-to-saccular stages and established the ROBO2 inhibition as promoter of branching morphogenesis through SOX2/SOX9 balance.

Maldevelopment of intrapulmonary bronchial cartilage in congenital diaphragmatic hernia

BACKGROUND

Pulmonary hypoplasia is an important cause of morbidity and mortality in infants with congenital diaphragmatic hernia (CDH). This study aimed to verify our hypothesis that the abnormal development of bronchial cartilage as well as alveolar immaturity, might play a central role in hypoplasia of the lung in human CDH.

METHOD

We retrospectively analyzed autopsied lungs from 10 CDH cases and compared with nine age-matched controls to assess the bronchial cartilage and alveolar maturity using morphological techniques.

RESULT

Ki-67 and thyroid transcription factor-1 (TTF-1) expression in the alveoli significantly increased in bilateral lungs with CDH. The shortest distance from the bronchial cartilage to the pleura was significantly shorter in ipsilateral (left) lungs with CDH, showing a positive correlation with the radial alveolar count (RAC). Regarding the small bronchial cartilages less than 20 000 μm² , the average cartilage area significantly decreased in left lungs with CDH, and tended to decrease in right lungs with CDH. In addition, cartilage around the bronchi less than 200 μm in diameter tended to be smaller in left lungs with CDH. In contrast, regarding the cartilage around the bronchi 200 to 400 μm in diameter, the ratio of the total cartilage area relative to the bronchial diameter tended to be higher in left lungs with CDH, although there was a large variation.

CONCLUSIONS

These opposite directional cartilage abnormalities around the distal and more proximal bronchi support our hypothesis that abnormal development of bronchial cartilage might play an important role in the hypoplastic lung in CDH.

Basic and translational science advances in congenital diaphragmatic hernia

Congenital Diaphragmatic Hernia (CDH) is a birth defect that is characterized by lung hypoplasia, pulmonary hypertension and a diaphragmatic defect that allows herniation of abdominal organs into the thoracic cavity. Although widely unknown to the public, it occurs as frequently as cystic fibrosis (1:2500). There is no monogenetic cause, but different animal models revealed various biological processes and epigenetic factors involved in the pathogenesis. However, the pathobiology of CDH is not sufficiently understood and its mortality still ranges between 30 and 50%. Future collaborative initiatives are required to improve our basic knowledge and advance novel strategies to (prenatally) treat the abnormal lung development. This review focusses on the genetic, epigenetic and protein background and the latest advances in basic and translational aspects of CDH research.

Current strategies and opportunities to manufacture cells for modeling human lungs

Chronic lung diseases remain major healthcare burdens, for which the only curative treatment is lung transplantation. In vitro human models are promising platforms for identifying and testing novel compounds to potentially decrease this burden. Directed differentiation of pluripotent stem cells is an important strategy to generate lung cells to create such models. Current lung directed differentiation protocols are limited as they do not 1) recapitulate the diversity of respiratory epithelium, 2) generate consistent or sufficient cell numbers for drug discovery platforms, and 3) establish the histologic tissue-level organization critical for modeling lung function. In this review, we describe how lung development has formed the basis for directed differentiation protocols, and discuss the utility of available protocols for lung epithelial cell generation and drug development. We further highlight tissue engineering strategies for manipulating biophysical signals during directed differentiation such that future protocols can recapitulate both chemical and physical cues present during lung development.

An intra-amniotic injection of mesenchymal stem cells promotes lung maturity in a rat congenital diaphragmatic hernia model

PURPOSE

We aimed to evaluate the effect of human mesenchymal stem cells (hMSCs) on congenital diaphragmatic hernia (CDH) by intra-amniotic injection in a rat CDH model.

METHODS

Nitrofen (100 mg) was administered to pregnant rats at E9.5. hMSCs (1.0 × 10⁶) or PBS was injected into each amniotic cavity at E18, and fetuses were harvested at E21. The fetal lungs were classified into normal, CDH, and CDH-hMSCs groups. To determine the lung maturity, we assessed the alveolar histological structure by H&E and Weigert staining and the alveolar arteries by Elastica Van Gieson (EVG) staining. TTF-1, a marker of type II alveolar epithelial cells, was also evaluated by immunohistochemical staining and real-time reverse transcription polymerase chain reaction.

RESULTS

The survival rate after intra-amniotic injection was 72.1%. The CDH-hMSCs group had significantly more alveoli and secondary septa than the CDH group (p < 0.05). The CDH-hMSCs group had larger air spaces and thinner alveolar walls than the CDH group (p < 0.05). The medial and adventitial thickness of the pulmonary artery in the CDH-hMSCs group were significantly better (p < 0.001), and there were significantly fewer TTF-1-positive cells than in the CDH group (p < 0.001).

CONCLUSION

These results suggest that intra-amniotic injection of hMSCs has therapeutic potential for CDH.

Pulmonary hypertension secondary to congenital diaphragmatic hernia: factors and pathways involved in pulmonary vascular remodeling

Congenital diaphragmatic hernia (CDH) is a severe birth defect that is characterized by pulmonary hypoplasia and pulmonary hypertension (PHTN). PHTN secondary to CDH is a result of vascular remodeling, a structural alteration in the pulmonary vessel wall that occurs in the fetus. Factors involved in vascular remodeling have been reported in several studies, but their interactions remain unclear. To help understand PHTN pathophysiology and design novel preventative and treatment strategies, we have conducted a systematic review of the literature and comprehensively analyzed all factors and pathways involved in the pathogenesis of pulmonary vascular remodeling secondary to CDH in the nitrofen model. Moreover, we have linked the dysregulated factors with pathways involved in human CDH. Of the 358 full-text articles screened, 75 studies reported factors that play a critical role in vascular remodeling secondary to CDH. Overall, the impairment of epithelial homeostasis present in pulmonary hypoplasia results in altered signaling to endothelial cells, leading to endothelial dysfunction. This causes an impairment of the crosstalk between endothelial cells and pulmonary artery smooth muscle cells, resulting in increased smooth muscle cell proliferation, resistance to apoptosis, and vasoconstriction, which clinically translate into PHTN.

The proportion of alveolar type 1 cells decreases in murine hypoplastic congenital diaphragmatic hernia lungs

BACKGROUND

Pulmonary hypoplasia, characterized by incomplete alveolar development, remains a major cause of mortality and morbidity in congenital diaphragmatic hernia. Recently demonstrated to differentiate from a common bipotent progenitor during development, the two cell types that line the alveoli type 1 and type 2 alveolar cells have shown to alter their relative ratio in congenital diaphragmatic hernia lungs.

OBJECTIVE

We used the nitrofen/bisdiamine mouse model to induce congenital diaphragmatic hernia and accurately assess the status of alveolar epithelial cell differentiation in relation to the common bipotent progenitors.

STUDY DESIGN

Pregnant Swiss mice were gavage-fed with nitrofen/bisdiamine or vehicle at embryonic day 8.5. The administered dose was optimized by assessing the survival, congenital diaphragmatic hernia and facial abnormality rates of the exposed mouse pups. NanoCT was performed on embryonic day 11.5 and 16.5 to assess the embryonic and early canalicular stages of lung development. At embryonic day 17.5 corresponding to late canalicular stage, congenital diaphragmatic hernia lungs were characterized by measuring the lung weight/body weight ratio, morphometry, epithelial cell marker gene expression levels and alveolar cell type quantification.

RESULTS

Nitrofen/bisdiamine associated congenital diaphragmatic hernia lungs showed delayed development, hypoplasia with morphologic immaturity and thickened alveolar walls. Expression levels of distal epithelial progenitor marker Id2 increased, alveolar type 1 cell markers Pdpn and Hopx decreased, while type 2 cell markers pro-SPC and Muc1 remained constant during the canalicular stage. The number of Pdpn+ type 1 alveolar cells also decreased in congenital diaphragmatic hernia lungs.

CONCLUSION

The mouse nitrofen/bisdiamine model is a potential model allowing the study of congenital diaphragmatic hernia lung development from early stages using a wide array of methods. Based on this model, the alveolar epithelium showed a decrease in the number of alveolar type 1 cell in congenital diaphragmatic hernia lungs while type 2 cell population remains unchanged.

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.

Abnormal lung development in congenital diaphragmatic hernia

The outcomes of patients diagnosed with congenital diaphragmatic hernia (CDH) have recently improved. However, mortality and morbidity remain high, and this is primarily caused by the abnormal lung development resulting in pulmonary hypoplasia and persistent pulmonary hypertension. The pathogenesis of CDH is poorly understood, despite the identification of certain candidate genes disrupting normal diaphragm and lung morphogenesis in animal models of CDH. Defects within the lung mesenchyme and interstitium contribute to disturbed distal lung development. Frequently, a disturbance in the development of the pleuroperitoneal folds (PPFs) leads to the incomplete formation of the diaphragm and subsequent herniation. Most candidate genes identified in animal models have so far revealed relatively few strong associations in human CDH cases. CDH is likely a highly polygenic disease, and future studies will need to reconcile how disturbances in the expression of multiple genes cause the disease. Herein, we summarize the available literature on abnormal lung development associated with CDH.

Antenatal BAY 41-2272 reduces pulmonary hypertension in the rabbit model of congenital diaphragmatic hernia

Infants with congenital diaphragmatic hernia (CDH) fail to adapt at birth because of persistent pulmonary hypertension (PH), a condition characterized by excessive muscularization and abnormal vasoreactivity of pulmonary vessels. Activation of soluble guanylate cyclase by BAY 41-2272 prevents pulmonary vascular remodeling in neonatal rats with hypoxia-induced PH. By analogy, we hypothesized that prenatal administration of BAY 41-2272 would improve features of PH in the rabbit CDH model. Rabbit fetuses with surgically induced CDH at day 23 of gestation were randomized at day 28 for an intratracheal injection of BAY 41-2272 or vehicle. After term delivery (day 31), lung mechanics, right ventricular pressure, and serum NH2-terminal-pro-brain natriuretic peptide (NT-proBNP) levels were measured. After euthanasia, lungs were processed for biological or histological analyses. Compared with untouched fetuses, the surgical creation of CDH reduced the lung-to-body weight ratio, increased mean terminal bronchial density, and impaired lung mechanics. Typical characteristics of PH were found in the hypoplastic lungs, including increased right ventricular pressure, higher serum NT-proBNP levels, thickened adventitial and medial layers of pulmonary arteries, reduced capillary density, and lower levels of endothelial nitric oxide synthase. A single antenatal instillation of BAY 41-2272 reduced mean right ventricular pressure and medial thickness of small resistive arteries in CDH fetuses. Capillary density, endothelial cell proliferation, and transcripts of endothelial nitric oxide synthase increased, whereas airway morphometry, lung growth, and mechanics remained unchanged. These results suggest that pharmacological activation of soluble guanylate cyclase may provide a new approach to the prenatal treatment of PH associated with CDH.

Prenatal administration of neuropeptide bombesin promotes lung development in a rat model of nitrofen-induced congenital diaphragmatic hernia

BACKGROUND/PURPOSE

Fetal medical treatment to improve lung hypoplasia in congenital diaphragmatic hernia (CDH) has yet to be established. The neuropeptide bombesin (BBS) might play an important role in lung development. The present study aims to determine whether prenatally administered BBS could be useful to promote fetal lung development in a rat model of nitrofen-induced CDH.

METHODS

Pregnant rats were administered with nitrofen (100mg) on gestation day 9.5 (E9.5). BBS (50mg/kg/day) was then daily infused intraperitoneally from E14, and fetal lungs were harvested on E21. The expression of PCNA was assessed by both immunohistochemical staining and RT-PCR to determine the amount of cell proliferation. Lung maturity was assessed as the expression of TTF-1, a marker of alveolar epithelial cell type II.

RESULTS

The lung-body-weight ratio was significantly increased in CDH/BBS(+) compared with CDH/BBS(-) (p<0.05). The number of cells stained positive for PCNA and TTF-1 was significantly decreased in CDH/BBS(+) compared with CDH/BBS(-) (p<0.01). The TTF-1 mRNA expression levels were significantly decreased in CDH/BBS(+) compared with CDH/BBS(-) (p<0.05).

CONCLUSIONS

Prenatally administered BBS promotes lung development in a rat model of nitrofen-induced CDH. Neuropeptide BBS could help to rescue lung hypoplasia in fetal CDH.

Therapeutic potential of mesenchymal stem cell transplantation in a nitrofen-induced congenital diaphragmatic hernia rat model

PURPOSE

The aim of this study was to evaluate the efficacy of mesenchymal stem cells (MSCs) in a nitrofen-induced congenital diaphragmatic hernia (CDH) rat model.

METHODS

Pregnant rats were exposed to nitrofen on embryonic day 9.5 (E9.5). MSCs were isolated from the enhanced green fluorescent protein (eGFP) transgenic rat lungs. The MSCs were transplanted into the nitrofen-induced E12.5 rats via the uterine vein, and the E21 lung explants were harvested. The study animals were divided into three: the control group, the nitrofen-induced left CDH (CDH group), and the MSC-treated nitrofen-induced left CDH (MSC-treated CDH group). The specimens were morphologically analyzed using HE and immunohistochemical staining with proliferating cell nuclear antigen (PCNA), surfactant protein-C (SP-C), and α-smooth muscle actin.

RESULTS

The alveolar and medial walls of the pulmonary arteries were significantly thinner in the MSC-treated CDH group than in the CDH group. The alveolar air space areas were larger, while PCNA and the SP-C positive cells were significantly higher in the MSC-treated CDH group, than in the CDH group. MSC engraftment was identified on immunohistochemical staining of the GFP in the MSC-treated CDH group.

CONCLUSIONS

MSC transplantation potentially promotes alveolar and pulmonary artery development, thereby reducing the severity of pulmonary hypoplasia.

The expression of HoxB5 and its role in neonatal rats with chronic lung disease

The purpose of this investigation is to research the expression and effect of HoxB5 during pulmonary injury and to investigate the repairing ability of alveolar epithelial cells in such processes. Eighty neonatal rats were randomly divided into two groups: a group of high concentration of oxygen and the control group. The high oxygen group would inhale 85 to 90% oxygen and the control group would inhale air. The lung tissues on the 1(st), 3(rd), 7(th), 14(th), and 21(st) days would be obtained, in which immunohistochemical assay and Reverse Transcription Polymerase Chain Reaction (RT-PCR) would be performed to test the expressions of proteins and mRNAs of surfactant protein C (SPC) and AQP5. For expression of HoxB5 protein and its mRNA, immunohistochemical assay, western blot, in-situ hybridization, and RT-PCR would be run. The expression of SPC in the group of high concentration of oxygen was significantly reduced on day 3. Its expressions on day 14 and day 21 were significantly higher than those of the control group (p < 0.05). The expression of AQP5 in the group of high concentration of oxygen progressively decreased and such difference with the control group was significant (p < 0.05). The four experimental methods all showed the expression of HoxB5 in the group with high concentration of oxygen gradually decreased since day 7 (p < 0.05). High concentration of oxygen is damaging to alveolar epithelial cells. Although the number of type II alveolar epithelial cells (AECII) increases, its ability to differentiate and transform is significantly reduced and the reduced expression level of HoxB5 is possibly the reason for AECII to lose differentiation function to AECI.

Effect of insulin-like growth factors on lung development in a nitrofen-induced CDH rat model

PURPOSE

Both the mortality and morbidity associated with congenital diaphragmatic hernia (CDH) are mainly caused by pulmonary hypoplasia and persistent pulmonary hypertension. A previous study revealed that insulin-like growth factors (IGFs) play important roles in fetal lung development. The aim of this study was to investigate the effect of IGF-1 and IGF-2 on tissue cultures of fetal hypoplastic lungs obtained from nitrofen-induced CDH model rats.

METHODS

Pregnant rats were exposed to nitrofen on day 9 of gestation (D9). Fetuses were harvested on D18 by caesarian section. Lung specimens of the CDH (+) fetus were divided into three groups; control, IGF-1, and IGF-2. The specimens from the control group were cultured in culture medium without IGFs. The IGF-1 group specimens were cultured with IGF-1 (500 ng/ml), and those in the IGF-2 group were cultured with IGF-2 (500 ng/ml). The mRNA expression of TTF-1, T1α and α-SMA were analyzed in each group using real-time RT-PCR after 24 and 48 h of incubation. Immunohistochemical staining of these markers was also assessed for each of the cultured specimens.

RESULTS

There was a significant increase in the expression of both TTF-1 and T1α mRNA in the IGF-2 group, in comparison to the control group after 48 h of culture. Immunohistochemical staining revealed that the cell morphology was changed from cuboidal to squamous type in the IGF-2 group.

CONCLUSIONS

An increased mRNA expression of the markers related to type 1 and 2 alveolar epithelial cells, and morphological changes in the epithelial cells were observed in the IGF-2 group. The administration of IGF-2 to nitrofen-induced hypoplastic lungs might lead to alveolar maturation, which thus results in their improved development.

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.

Spatiotemporal alteration in phosphatidylinositide 3-kinase-serine/threonine protein kinase B signaling in the nitrofen-induced hypoplastic lung

PURPOSE

The pathogenesis of pulmonary hypoplasia in congenital diaphragmatic hernia (CDH) is not fully understood. The serine/threonine protein kinase B (AKT) plays important roles for lung morphogenesis through epithelial-mesenchymal interaction in phosphatidylinositide 3-kinase (PI3K)-dependent manner. It has been reported that the lung explant morphogenesis in mice is interfered by inhibitors of the PI3K-AKT pathway. We hypothesized that PI3K and AKT gene and protein expression/distribution are altered during epithelial 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, D18, and D21 and divided into 3 groups as follows: control, nitrofen with CDH (CDH[-]), and nitrofen without CDH (CDH[+]) (n = 8 at each time-point, respectively). Reverse transcription polymerase chain reaction and immunohistochemistry were performed.

RESULTS

Messenger RNA expression levels of PI3K at D21 was significantly decreased in CDH(-) and CDH(+) group (5.71 +/- 0.85 and 6.80 +/- 0.88, respectively) compared to controls (8.95 +/- 3.22; P < .05). Messenger RNA levels of AKT were also significantly decreased at D18 in CDH(-) and CDH(+) lungs (1.21 +/- 0.16 and 1.20 +/- 0.32, respectively) compared to controls (1.62 +/- 0.14; P < .01). The PI3K immunoreactivity was diminished in the distal epithelium at D18 and decreased in the overall intensity at D21 in hypoplastic lungs compared to controls. The AKT immunoreactivity was decreased in mesenchyme at D18 and decreased overall intensity at D21 in CDH lungs compared to controls.

CONCLUSION

Spatiotemporal alteration of pulmonary PI3K and AKT gene and protein expression during epithelial morphogenesis may interfere with epithelial-mesenchymal interaction, causing pulmonary hypoplasia in CDH by disrupting PI3K-AKT signaling pathway.

Thyroid transcription factor-1 (TTF-1/Nkx2.1/TITF1) gene regulation in the lung

TTF-1 [thyroid transcription factor-1; also known as Nkx2.1, T/EBP (thyroid-specific-enhancer-binding protein) or TITF1] is a homeodomain-containing transcription factor essential for the morphogenesis and differentiation of the thyroid, lung and ventral forebrain. TTF-1 controls the expression of select genes in the thyroid, lung and the central nervous system. In the lung, TTF-1 controls the expression of surfactant proteins that are essential for lung stability and lung host defence. Human TTF-1 is encoded by a single gene located on chromosome 14 and is organized into two/three exons and one/two introns. Multiple transcription start sites and alternative splicing produce mRNAs with heterogeneity at the 5' end. The 3' end of the TTF-1 mRNA is characterized by a rather long untranslated region. The amino acid sequences of TTF-1 from human, rat, mouse and other species are very similar, indicating a high degree of sequence conservation. TTF-1 promoter activity is maintained by the combinatorial or co-operative actions of HNF-3 [hepatocyte nuclear factor-3; also known as FOXA (forkhead box A)], Sp (specificity protein) 1, Sp3, GATA-6 and HOXB3 (homeobox B3) transcription factors. There is limited information on the regulation of TTF-1 gene expression by hormones, cytokines and other biological agents. Glucocorticoids, cAMP and TGF-beta (transforming growth factor-beta) have stimulatory effects on TTF-1 expression, whereas TNF-alpha (tumour necrosis factor-alpha) and ceramide have inhibitory effects on TTF-1 DNA-binding activity in lung cells. Haplo-insufficiency of TTF-1 in humans causes hypothyroidism, respiratory dysfunction and recurring pulmonary infections, underlining the importance of optimal TTF-1 levels for the maintenance of thyroid and lung function. Recent studies have implicated TTF-1 as a lineage-specific proto-oncogene for lung cancer.

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.

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.