Novel mechanisms in murine nitrofen-induced pulmonary hypoplasia: FGF-10 rescue in culture

Effectiveness of extracellular vesicles derived from hiPSCs in repairing hyperoxia-induced injury in a fetal murine lung explant model

BACKGROUND

Despite advances in neonatal care, the incidence of Bronchopulmonary Dysplasia (BPD) remains high among preterm infants. Human induced pluripotent stem cells (hiPSCs) have shown promise in repairing injury in animal BPD models. Evidence suggests they exert their effects via paracrine mechanisms. We aim herein to assess the effectiveness of extracellular vesicles (EVs) derived from hiPSCs and their alveolar progenies (diPSCs) in attenuating hyperoxic injury in a preterm lung explant model.

METHODS

Murine lung lobes were harvested on embryonic day 17.5 and maintained in air-liquid interface. Following exposure to 95% O2 for 24 h, media was supplemented with 5 × 106 particles/mL of EVs isolated from hiPSCs or diPSCs by size-exclusion chromatography. On day 3, explants were assessed using Hematoxylin-Eosin staining with mean linear intercept (MLI) measurements, immunohistochemistry, VEGFa and antioxidant gene expression. Statistical analysis was conducted using one-way ANOVA and Multiple Comparison Test. EV proteomic profiling was performed, and annotations focused on alveolarization and angiogenesis signaling pathways, as well as anti-inflammatory, anti-oxidant, and regenerative pathways.

RESULTS

Exposure of fetal lung explants to hyperoxia induced airspace enlargement, increased MLI, upregulation of anti-oxidants Prdx5 and Nfe2l2 with decreased VEGFa expression. Treatment with hiPSC-EVs improved parenchymal histologic changes. No overt changes in vasculature structure were observed on immunohistochemistry in our in vitro model. However, VEGFa and anti-oxidant genes were upregulated with diPSC-EVs, suggesting a pro-angiogenic and cytoprotective potential. EV proteomic analysis provided new insights in regard to potential pathways influencing lung regeneration.

CONCLUSION

This proof-of-concept in vitro study reveals a potential role for hiPSC- and diPSC-EVs in attenuating lung changes associated with prematurity and oxygen exposure. Our findings pave the way for a novel cell free approach to prevent and/or treat BPD, and ultimately reduce the global burden of the disease.

Treatment with Amniotic Fluid Stem Cell Extracellular Vesicles Promotes Fetal Lung Branching and Cell Differentiation at Canalicular and Saccular Stages in Experimental Pulmonary Hypoplasia Secondary to Congenital Diaphragmatic Hernia

Pulmonary hypoplasia secondary to congenital diaphragmatic hernia (CDH) is characterized by impaired branching morphogenesis and differentiation. We have previously demonstrated that administration of extracellular vesicles derived from rat amniotic fluid stem cells (AFSC-EVs) rescues development of hypoplastic lungs at the pseudoglandular and alveolar stages in rodent models of CDH. Herein, we tested whether AFSC-EVs exert their regenerative effects at the canalicular and saccular stages, as these are translationally relevant for clinical intervention. To induce fetal pulmonary hypoplasia, we gavaged rat dams with nitrofen at embryonic day 9.5 and demonstrated that nitrofen-exposed lungs had impaired branching morphogenesis, dysregulated signaling pathways relevant to lung development (FGF10/FGFR2, ROBO/SLIT, Ephrin, Neuropilin 1, β-catenin) and impaired epithelial and mesenchymal cell marker expression at both stages. AFSC-EVs administered to nitrofen-exposed lung explants rescued airspace density and increased the expression levels of key factors responsible for branching morphogenesis. Moreover, AFSC-EVs rescued the expression of alveolar type 1 and 2 cell markers at both canalicular and saccular stages and restored markers of club, ciliated epithelial, and pulmonary neuroendocrine cells at the saccular stage. AFSC-EV-treated lungs also had restored markers of lipofibroblasts and PDGFRA+ cells to control levels at both stages. EV tracking showed uptake of AFSC-EV RNA cargo throughout the fetal lung and an mRNA-miRNA network analysis identified that several miRNAs responsible for regulating lung development processes were contained in the AFSC-EV cargo. These findings suggest that AFSC-EV-based therapies hold potential for restoring fetal lung growth and maturation in babies with pulmonary hypoplasia secondary to CDH.

Extractive removal of micro and trace nitrofen, 2, 4-dichlorophenol and p-nitrotrophenol from water/soil by humic acid ester ether

The amphiphilic humic acid ester ether (HAEE), as a kind of solid-phase extractant with characteristics of easy separation and hydrophilic-hydrophobic amphiphilic property, was prepared and used to extract micro or trace nitrofen, 2,4-dichlorophenol and p-nitrotrophenol (NIPs) from water and soil. Degradation of NIPs and extractant regeneration were carried out by simple photocatalysis. The adsorption equilibrium of the mono- or three mixed NIPs by HAEE in aqueous could be quickly reached within 20 min. The adsorption process was fit to quasi-second-order kinetics model and Friendlich thermodynamics model. The possible adsorption interaction was discussed. Results suggested that the adsorption of NIPs onto HAEE predominated by hydrogen bonding, hydrophobic interaction and π-π interaction. The extraction capacity of mixed NIPs (80 μg/L each component) by HAEE was up to 0.38 mg/g and tended to be multi-layer adsorption, in which p-nitrotrophenol had higher adsorption competitiveness because of lower resistance to HAEE. When HAEE-NIPs were degraded by photo-catalyst Fe⁰/F-TiO₂ for 8 h, not only the adsorbed NIPs could be totally degraded and mineralized, but also the HAEE could be effectively regenerated. When the NIPs were continuously extracted from 40-year aging soil for three times (regenerative twice) by combined extractant (48 mL H₂O + 2 mL n-hexane + 0.1 g HAEE), the total extraction efficiency of NIPs could reach to 84.66%. This research could supplement the theory and technique for harmless treatment of NIPs contaminated water and soil.

Negative Transpulmonary Pressure Disrupts Airway Morphogenesis by Suppressing Fgf10

Mechanical forces are increasingly recognized as important determinants of cell and tissue phenotype and also appear to play a critical role in organ development. During the fetal stages of lung morphogenesis, the pressure of the fluid within the lumen of the airways is higher than that within the chest cavity, resulting in a positive transpulmonary pressure. Several congenital defects decrease or reverse transpulmonary pressure across the developing airways and are associated with a reduced number of branches and a correspondingly underdeveloped lung that is insufficient for gas exchange after birth. The small size of the early pseudoglandular stage lung and its relative inaccessibility in utero have precluded experimental investigation of the effects of transpulmonary pressure on early branching morphogenesis. Here, we present a simple culture model to explore the effects of negative transpulmonary pressure on development of the embryonic airways. We found that negative transpulmonary pressure decreases branching, and that it does so in part by altering the expression of fibroblast growth factor 10 (Fgf10). The morphogenesis of lungs maintained under negative transpulmonary pressure can be rescued by supplementing the culture medium with exogenous FGF10. These data suggest that Fgf10 expression is regulated by mechanical stress in the developing airways. Understanding the mechanical signaling pathways that connect transpulmonary pressure to FGF10 can lead to the establishment of novel non-surgical approaches for ameliorating congenital lung defects.

Human induced pluripotent stem cell-derived lung organoids in an ex vivo model of the congenital diaphragmatic hernia fetal lung

Three‐dimensional lung organoids (LOs) derived from pluripotent stem cells have the potential to enhance our understanding of disease mechanisms and to enable novel therapeutic approaches in neonates with pulmonary disorders. We established a reproducible ex vivo model of lung development using transgene‐free human induced pluripotent stem cells generated from fetuses and infants with Bochdalek congenital diaphragmatic hernia (CDH), a polygenic disorder associated with fetal lung compression and pulmonary hypoplasia at birth. Molecular and cellular comparisons of CDH LOs revealed impaired generation of NKX2.1⁺ progenitors, type II alveolar epithelial cells, and PDGFRα⁺ myofibroblasts. We then subjected these LOs to disease relevant mechanical cues through ex vivo compression and observed significant changes in genes associated with pulmonary progenitors, alveolar epithelial cells, and mesenchymal fibroblasts. Collectively, these data suggest both primary cell‐intrinsic and secondary mechanical causes of CDH lung hypoplasia and support the use of this stem cell‐based approach for disease modeling in CDH.

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.

Impaired Angiogenic Supportive Capacity and Altered Gene Expression Profile of Resident CD146+ Mesenchymal Stromal Cells Isolated from Hyperoxia-Injured Neonatal Rat Lungs

Bronchopulmonary dysplasia (BPD), the most common complication of extreme preterm birth, can be caused by oxygen-related lung injury and is characterized by impaired alveolar and vascular development. Mesenchymal stromal cells (MSCs) have lung protective effects. Conversely, BPD is associated with increased MSCs in tracheal aspirates. We hypothesized that endogenous lung (L-)MSCs are perturbed in a well-established oxygen-induced rat model mimicking BPD features. Rat pups were exposed to 21% or 95% oxygen from birth to postnatal day 10. On day 12, CD146⁺ L-MSCs were isolated and characterized according to the International Society for Cellular Therapy criteria. Epithelial and vascular repair potential were tested by scratch assay and endothelial network formation, respectively, immune function by mixed lymphocyte reaction assay. Microarray analysis was performed using the Affymetrix GeneChip and gene set enrichment analysis software. CD146⁺ L-MSCs isolated from rat pups exposed to hyperoxia had decreased CD73 expression and inhibited lung endothelial network formation. CD146⁺ L-MSCs indiscriminately promoted epithelial wound healing and limited T cell proliferation. Expression of potent antiangiogenic genes of the axonal guidance cue and CDC42 pathways was increased after in vivo hyperoxia, whereas genes of the anti-inflammatory Janus kinase (JAK)/signal transducer and activator of transcription (STAT) and lung/vascular growth-promoting fibroblast growth factor (FGF) pathways were decreased. In conclusion, in vivo hyperoxia exposure alters the proangiogenic effects and FGF expression of L-MSCs. In addition, decreased CD73 and JAK/STAT expression suggests decreased immune function. L-MSC function may be perturbed and contribute to BPD pathogenesis. These findings may lead to improvements in manufacturing exogenous MSCs with superior repair capabilities.

Impaired FGF10 Signaling and Epithelial Development in Experimental Lung Hypoplasia With Esophageal Atresia

Patients with esophageal atresia (EA) and tracheoesophageal fistula (TEF) often experience persistent respiratory tract disease. In experimental models, doxorubicin-induced developmental lung abnormalities may result from downregulation of branching morphogenesis factor fibroblast growth factor (Fgf10). This study investigated the temporospatial expression of Fgf10 pathway components and lung epithelial factors in an doxorubicin-induced EA-TEF model by quantitative polymerase chain reaction, immunohistochemistry, and immunoblotting. Epigenetic regulation of gene expression by histone deacetylation was also investigated. Bone morphogenetic protein (Bmp) 4 and Cathepsin H (Ctsh), downstream targets of Fgf10, were significantly downregulated in the EA-TEF model during the saccular stage, consistent with Fgf10 expression. The developmental expression pattern of P2x7 receptor (ATI-cell marker), Sftpa, and Sftpb in lung epithelial cells was not affected. Sftpc (ATII-cell Marker) and Scgb1a1 (Clara cell marker) were significantly downregulated at the canalicular stage. Meanwhile, histone deacetylase (Hdac) 1 was upregulated and subsequently decreased acetylation of histone H3 Lys56 in the EA-TEF model, which returned to a normal level at the saccular stage. In conclusion, disturbed molecular signaling involving Fgf10/Ctsh was associated with impaired airway branching and epithelial cell development in lung morphogenesis, as evidenced by downregulated Sftpc and Scgb1a1 protein expression. The influence of Hdac1 activity on gene and protein expression in lung epithelial cells deserves further study.

Amniotic fluid derived mesenchymal stromal cells augment fetal lung growth in a nitrofen explant model

PURPOSE

Recent experimental work suggests the therapeutic role of mesenchymal stromal cells (MSCs) during lung morphogenesis. The purpose of this study was to investigate the potential paracrine effects of amniotic fluid-derived MSCs (AF-MSCs) on fetal lung growth in a nitrofen explant model.

METHODS

Pregnant Sprague-Dawley dams were gavage fed nitrofen on gestational day 9.5 (E9.5). E14.5 lung explants were subsequently harvested and cultured ex vivo for three days on filter membranes in conditioned media from rat AF-MSCs isolated from control (AF-Ctr) or nitrofen-exposed (AF-Nitro) dams. The lungs were analyzed morphometrically and by quantitative gene expression.

RESULTS

Although there were no significant differences in total lung surface area among hypoplastic lungs, there were significant increases in terminal budding among E14.5+3 nitrofen explants exposed to AF-Ctr compared to explants exposed to medium alone (58.8±8.4 vs. 39.0±10.0 terminal buds, respectively; p<0.05). In contrast, lungs cultured in AF-Nitro medium failed to augment terminal budding. Nitrofen explants exposed to AF-Ctr showed significant upregulation of surfactant protein C to levels observed in normal fetal lungs.

CONCLUSIONS

AF-MSCs can augment branching morphogenesis and lung epithelial maturation in a fetal explant model of pulmonary hypoplasia. Cell therapy using donor-derived AF-MSCs may represent a novel strategy for the treatment of fetal congenital diaphragmatic hernia.

Abnormal control of lung branching in experimental esophageal atresia

PURPOSE

Esophageal atresia and tracheo-esophageal fistula (EA-TEF) result from abnormal division of the foregut into esophagus and trachea thus, it may influence airway branching and lung development. The present study examined lung morphogenesis in fetuses with EA-TEF focusing in the expression of FGF10 and its receptor FGFR2 IIIb.

METHODS

Pregnant rats received either 1.75 mg/kg i.p. adriamycin or vehicle on E7, E8 and E9. Embryos were recovered at E15, E18 and E21 and lungs processed for immunohistochemistry and RT-PCR. Three groups were studied: control, adriamycin-exposed with EA-TEF, and adriamycin-exposed without EA-TEF. Comparisons were performed with Mann-Whitney or t tests (significance level, 5 %).

RESULTS

Lung weight at E15 and E18 were significantly lower in adriaEA fetuses in which the relative mRNA levels of FGF10 were significantly higher. These differences disappeared near term. The receptor FGFR2 IIIb messenger was only significantly increased in adria noEA fetuses at E15. Immunohistochemical study was consistent with these findings.

CONCLUSIONS

Abnormal expression of FGF10 during earlier stages of development, when the lungs are smaller than controls, suggests a compensatory response aimed at "catching up" delayed tracheobronchial branching. Whether similar changes take place in the human condition and influence respiratory physiology remain to be determined.

Amniotic fluid stem cells rescue both in vitro and in vivo growth, innervation, and motility in nitrofen-exposed hypoplastic rat lungs through paracrine effects

Lung hypoplasia can be prevented in vitro by retinoic acid (RA). Recent evidence suggests that amniotic fluid stem (AFS) cells may integrate injured lungs and influence their recovery. We tested the hypothesis that AFS cells might improve lung growth and motility by paracrine mechanisms. Pregnant rats received either nitrofen or vehicle on E9.5. In vitro E13 embryonic lungs were cultured in the presence of culture medium alone or with RA, basophils, or AFS cells. In vivo green fluorescent protein-expressing (GFP(+)) rat AFS cells were transplanted in nitrofen-exposed rats on E10.5. E13 lung explants were cultured before analysis. The surface, the number of terminal buds, and the frequency of bronchial contractions were assessed. Protein gene product 9.5 (PGP 9.5) and α-actin protein levels were measured. The lung explants transplanted with AFS cells were stained for α-actin, PGP 9.5, and TTF-1. The levels of FGF-10, VEGFα, and TGF-β1 secreted by the AFS cells in the culture medium were measured. Comparison between groups was made by ANOVA. In vitro, the surface, the number of terminal buds, and the bronchial peristalsis were increased in nitrofen+AFS cell explants in comparison with nitrofen-exposed lungs. While nitrofen+RA lungs were similar to nitrofen+AFS ones, basophils did not normalize these measurements. PGP 9.5 protein was decreased in nitrofen lungs, but after adding AFS cells, the value was similar to controls. No differences were found in the expression of α-actin. In vivo, the surface, number of terminal buds, and peristalsis were similar to control after injection of AFS cells in nitrofen-exposed rats. Colocalization with TTF-1-positive cells was found. The levels of FGF-10 and VEGFα were increased in nitrofen+AFS cell explants, while the levels of TGF-β1 were similar to controls. Lung growth, bronchial motility, and innervation were decreased in nitrofen explants and rescued by AFS cells both in vitro and in vivo, similarly to that observed before with RA. The AFS cell beneficial effect was probably related to paracrine action of growth factor secretion.

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.

Leukemia inhibitory factor in rat fetal lung development: expression and functional studies

Background

Leukemia inhibitory factor (LIF) and interleukin-6 (IL-6) are members of the family of the glycoprotein 130 (gp130)-type cytokines. These cytokines share gp130 as a common signal transducer, which explains why they show some functional redundancy. Recently, it was demonstrated that IL-6 promotes fetal lung branching. Additionally, LIF has been implicated in developmental processes of some branching organs. Thus, in this study LIF expression pattern and its effects on fetal rat lung morphogenesis were assessed.

Methodology/Principal Findings

LIF and its subunit receptor LIFRα expression levels were evaluated by immunohistochemistry and western blot in fetal rat lungs of different gestational ages, ranging from 13.5 to 21.5 days post-conception. Throughout all gestational ages studied, LIF was constitutively expressed in pulmonary epithelium, whereas LIFRα was first mainly expressed in the mesenchyme, but after pseudoglandular stage it was also observed in epithelial cells. These results point to a LIF epithelium-mesenchyme cross-talk, which is known to be important for lung branching process. Regarding functional studies, fetal lung explants were cultured with increasing doses of LIF or LIF neutralizing antibodies during 4 days. MAPK, AKT, and STAT3 phosphorylation in the treated lung explants was analyzed. LIF supplementation significantly inhibited lung growth in spite of an increase in p44/42 phosphorylation. On the other hand, LIF inhibition significantly stimulated lung growth via p38 and Akt pathways.

Conclusions/Significance

The present study describes that LIF and its subunit receptor LIFRα are constitutively expressed during fetal lung development and that they have an inhibitory physiological role on fetal lung branching.

Structure and epitope distribution of heparan sulfate is disrupted in experimental lung hypoplasia: a glycobiological epigenetic cause for malformation?

BACKGROUND

Heparan sulfate (HS) is present on the surface of virtually all mammalian cells and is a major component of the extracellular matrix (ECM), where it plays a pivotal role in cell-cell and cell-matrix cross-talk through its large interactome. Disruption of HS biosynthesis in mice results in neonatal death as a consequence of malformed lungs, indicating that HS is crucial for airway morphogenesis. Neonatal mortality (~50%) in newborns with congenital diaphragmatic hernia (CDH) is principally associated with lung hypoplasia and pulmonary hypertension. Given the importance of HS for lung morphogenesis, we investigated developmental changes in HS structure in normal and hypoplastic lungs using the nitrofen rat model of CDH and semi-synthetic bacteriophage ('phage) display antibodies, which identify distinct HS structures.

RESULTS

The pulmonary pattern of elaborated HS structures is developmentally regulated. For example, the HS4E4V epitope is highly expressed in sub-epithelial mesenchyme of E15.5 - E17.5 lungs and at a lower level in more distal mesenchyme. However, by E19.5, this epitope is expressed similarly throughout the lung mesenchyme.We also reveal abnormalities in HS fine structure and spatiotemporal distribution of HS epitopes in hypoplastic CDH lungs. These changes involve structures recognised by key growth factors, FGF2 and FGF9. For example, the EV3C3V epitope, which was abnormally distributed in the mesenchyme of hypoplastic lungs, is recognised by FGF2.

CONCLUSIONS

The observed spatiotemporal changes in HS structure during normal lung development will likely reflect altered activities of many HS-binding proteins regulating lung morphogenesis. Abnormalities in HS structure and distribution in hypoplastic lungs can be expected to perturb HS:protein interactions, ECM microenvironments and crucial epithelial-mesenchyme communication, which may contribute to lung dysmorphogenesis. Indeed, a number of epitopes correlate with structures recognised by FGFs, suggesting a functional consequence of the observed changes in HS in these lungs. These results identify a novel, significant molecular defect in hypoplastic lungs and reveals HS as a potential contributor to hypoplastic lung development in CDH. Finally, these results afford the prospect that HS-mimetic therapeutics could repair defective signalling in hypoplastic lungs, improve lung growth, and reduce CDH mortality.

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.

Heparan sulfate in lung morphogenesis: The elephant in the room

Heparan sulfate (HS) is a structurally complex polysaccharide located on the cell surface and in the extracellular matrix, where it participates in numerous biological processes through interactions with a vast number of regulatory proteins such as growth factors and morphogens. HS is crucial for lung development; disruption of HS synthesis in flies and mice results in a major aberration of airway branching, and in mice, it results in neonatal death as a consequence of malformed lungs and respiratory distress. Epithelial-mesenchymal interactions governing lung morphogenesis are directed by various diffusible proteins, many of which bind to, and are regulated by HS, including fibroblast growth factors, sonic hedgehog, and bone morphogenetic proteins. The majority of research into the molecular mechanisms underlying defective lung morphogenesis and pulmonary pathologies, such as bronchopulmonary dysplasia and pulmonary hypoplasia associated with congenital diaphragmatic hernia (CDH), has focused on abnormal protein expression. The potential contribution of HS to abnormalities of lung development has yet to be explored to any significant extent, which is somewhat surprising given the abnormal lung phenotype exhibited by mutant mice synthesizing abnormal HS. This review summarizes our current understanding of the role of HS and HS-binding proteins in lung morphogenesis and will present in vitro and in vivo evidence for the fundamental importance of HS in airway development. Finally, we will discuss the future possibility of HS-based therapeutics for ameliorating insufficient lung growth associated with lung diseases such as CDH.

Lung organogenesis

Developmental lung biology is a field that has the potential for significant human impact: lung disease at the extremes of age continues to cause major morbidity and mortality worldwide. Understanding how the lung develops holds the promise that investigators can use this knowledge to aid lung repair and regeneration. In the decade since the "molecular embryology" of the lung was first comprehensively reviewed, new challenges have emerged-and it is on these that we focus the current review. Firstly, there is a critical need to understand the progenitor cell biology of the lung in order to exploit the potential of stem cells for the treatment of lung disease. Secondly, the current familiar descriptions of lung morphogenesis governed by growth and transcription factors need to be elaborated upon with the reinclusion and reconsideration of other factors, such as mechanics, in lung growth. Thirdly, efforts to parse the finer detail of lung bud signaling may need to be combined with broader consideration of overarching mechanisms that may be therapeutically easier to target: in this arena, we advance the proposal that looking at the lung in general (and branching in particular) in terms of clocks may yield unexpected benefits.

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.

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.

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.

Exploiting mechanical stimuli to rescue growth of the hypoplastic lung

Impaired lung development afflicts a range of newborns cared for by paediatric surgeons. As a result the speciality has led in the development of surgical models that illustrate the biomechanical regulation of lung growth. Using transgenic mutants, biologists have similarly discovered much about the biochemical regulation of prenatal lung growth. Airway smooth muscle (ASM) and its prenatal contractility airway peristalsis (AP) represent a novel link between these areas: ASM progenitors produce an essential biochemical factor for lung morphogenesis, whilst calcium-driven biomechanical ASM activity appears to regulate the same. In this invited paper, I take the opportunity both to review our recent findings on lung growth and prenatal ASM, and also to discuss mechanisms by which ASM contractility can regulate growth. Finally, I will introduce some novel ideas for exploration: ASM contractility could help to schedule parturition (pulmonary parturition clock) and could even be a generic model for smooth muscle regulation of morphogenesis in similar organs.

Syndrome de Fryns. Présentation de 3 nouvelles observations

BACKGROUND

Fryns syndrome is a lethal autosomal recessive syndrome which includes congenital diaphragmatic hernia (CDH), pulmonary hypoplasia, cranio-facial manifestations including a coarse face, a cleft palate / lip and cloudy corneae, distal limb hypoplasia and internal malformations including central nervous system, cardiovascular, gastrointestinal, urogenital and skeletal anomalies.

CASES REPORT

We report on 3 patients with Fryns syndrome in the french Indian Ocean islands (La Réunion and Mayotte islands). Pregnancies were complicated by polyhydramnios. All patients had coarse face, cloudy corneae, cleft lip / palate or high-arched palate, hypoplastic nails and brachytelephalangy. They died in the neonatal period. Two had CDH and 1 did not have a diaphragmatic involvement but a severe respiratory distress syndrome with refractory hypoxemia. Cytogenetic studies of blood lymphocytes and skin fibroblasts were normal.

CONCLUSIONS

Fryns syndrome is the most common multiple congenital anomaly associated with CDH. The diagnosis is strongly suggested when CHD and brachytelephalangy are associated. Phenotypes with CDH similar to Fryns syndrome have been described with cytogenetic aberrations with G-banded chromosome analysis and submicroscopic chromosome deletions detected by high resolution karyotyping or array comparative genomic hybridization (CGH). Exclusion of chromosome aberrations (including isochromosome 12p in skin fibroblasts) is needed prior to making the diagnosis of Fryns syndrome. In sporadic cases, high resolution karyotyping or array CGH should be performed for correct diagnosis and genetic counselling.

A tissue-engineered model of fetal distal lung tissue

In extending our previous studies toward development of an engineered distal lung tissue construct (M. J. Mondrinos, S. Koutzaki, E. Jiwanmall, M. Li, J. P. Dechadarevian, P. I. Lelkes, and C. M. Finck. Tissue Eng 12: 717-728, 2006), we studied the effects of exogenous fibroblast growth factors FGF10, FGF7, and FGF2 on mixed populations of embryonic day 17.5 murine fetal pulmonary cells cultured in three-dimensional collagen gels. The morphogenic effects of the FGFs alone and in various combinations were assessed by whole mount immunohistochemistry and confocal microscopy. FGF10/7 significantly increased epithelial budding and proliferation; however, only FGF10 alone induced widespread budding. FGF7 alone induced dilation of epithelial structures but not widespread budding. FGF2 alone had a similar dilation, but not budding, effect in epithelial structures, and, in addition, significantly enhanced endothelial tubular morphogenesis and network formation, as well as mesenchymal proliferation. The combination of FGF10/7/2 induced robust budding of epithelial structures and the formation of uniform endothelial networks in parallel. These data suggest that appropriate combinations of exogenous FGFs chosen to target specific FGF receptor isoforms will allow for control of lung epithelial and mesenchymal cell behavior in the context of an engineered system. We propose that tissue-engineered fetal distal lung constructs could provide a potential source of tissue or cells for lung augmentation in pediatric pulmonary pathologies, such as pulmonary hypoplasia and bronchopulmonary dysplasia. In addition, engineered systems will provide alternative in vitro venues for the study of lung developmental biology and pathobiology.

Airway smooth muscle dysfunction precedes teratogenic congenital diaphragmatic hernia and may contribute to hypoplastic lung morphogenesis

Fetal intervention aims to improve lung growth and survival in congenital diaphragmatic hernia (CDH). Airway smooth muscle (ASM) is important in lung development: ASM progenitors produce a key growth factor for lung morphogenesis (fibroblast growth factor 10); ASM contractility is also coupled to growth. ASM hyperreactivity occurs in postnatal CDH and may exacerbate barotrauma via impaired lung compliance. We hypothesize that ASM hyperreactivity and its sequelae are based on an early developmental lesion of ASM activity in hypoplastic lung. Sprague-Dawley rats were fed 100 mg nitrofen on Day 9.5 of pregnancy to induce lung hypoplasia in offspring (controls had vehicle alone). Normal and hypoplastic lung primordia were cultured from Day 13.5 of gestation at 37 degrees C in 5% CO(2) and loaded at 54 or 78 h with Ca(2+)-sensitive indicators: Fluo-4 for confocal imaging and Indo-1 or Fura-2 for photometric measurements of [Ca(2+)](i). Hypoplastic lung features spontaneous propagating ASM Ca(2+) transients with reduced frequency, increased amplitude, and significantly prolonged plateau duration, relative to control lung. Nonetheless, hypoplastic lung exhibits normal requirement for extracellular calcium entry and intracellular calcium release in initiation and regulation of ASM Ca(2+) waves. Early ASM dysfunction in lung hypoplasia is apparent as specific anomalies of Ca(2+) transients that indicate a problem with plasmalemmal ion channels/action potential generation. Elucidation of such an ASM lesion may allow pharmacologic amelioration not only of ASM hyperreactivity and its sequelae, but also of hypoplastic lung growth itself.

Peristalsis of airway smooth muscle is developmentally regulated and uncoupled from hypoplastic lung growth

Prenatal airway smooth muscle (ASM) peristalsis appears coupled to lung growth. Moreover, ASM progenitors produce fibroblast growth factor-10 (FGF-10) for lung morphogenesis. Congenital diaphragmatic hernia (CDH) is associated with lung hypoplasia, FGF-10 deficiency, and postnatal ASM dysfunction. We hypothesized ASM dysfunction emerges in tandem with, and may contribute toward, the primordial lung hypoplasia that precedes experimental CDH. Spatial origin and frequency of ASM peristaltic waves were measured in normal and hypoplastic rat lungs cultured from day 13.5 of gestation (lung hypoplasia was generated by nitrofen dosing of pregnant dams). Longitudinal lung growth was assayed by bud counts and tracing photomicrographs of cultures. Coupling of lung growth and peristalsis was tested by stimulation studies using serum, FGF-10, or nicotine and inhibition studies with nifedipine or U0126 (MEK1/2 inhibitor). In normal lung, ASM peristalsis is developmentally regulated: proximal ASM becomes quiescent (while retaining capacity for cholinergic-stimulated peristalsis). However, in hypoplastic lung, spontaneous proximal ASM activity persists. FGF-10 corrects this aberrant ASM activity in tandem with improved growth. Stimulation and inhibition studies showed that, unlike normal lung, changes in growth or peristalsis are not consistently accompanied by parallel modulation of the other. ASM peristalsis undergoes FGF-10-regulated spatiotemporal development coupled to lung growth: this process is disrupted early in lung hypoplasia. ASM dysfunction emerges in tandem with and may therefore contribute toward lung hypoplasia in CDH.

Small lungs and suspect smooth muscle: congenital diaphragmatic hernia and the smooth muscle hypothesis

Lung hypoplasia and congenital diaphragmatic hernia (CDH) represent an unsolved clinical and scientific problem. Early lung morphogenesis is coupled to development and function of pulmonary smooth muscle. Activity of the latter is abnormal from the earliest stages of hypoplastic lung development and before supervening CDH. A "smooth muscle hypothesis" is advanced to help explain embryonic lung malformations, fetal failure of lung growth, and postnatal susceptibility to barotrauma, airway hyperreactivity, and pulmonary hypertension in CDH. Exploring the interaction of smooth muscle function and airway pressures may help optimise tracheal occlusion and provide support for both an adequately powered trial of glucocorticoids and also for experimental "preventilation" strategies in fetal CDH.

Sonic hedgehog-patched Gli signaling in the developing rat prostate gland: lobe-specific suppression by neonatal estrogens reduces ductal growth and branching

While prostate gland development is dependent on androgens, other hormones including retinoids and estrogens can influence this process. Brief exposure to high-dose estrogen during the neonatal period in rats leads to permanent, lobe-specific aberrations in the prostate gland, a phenomenon referred to as developmental estrogenization. We have previously shown that this response is mediated through alterations in steroid receptor expression; however, further downstream mechanisms remain unclear. Herein, we examined Sonic hedgehog (Shh)-patched (ptc)-gli in the developing rat prostate gland, its role in branching morphogenesis, and the effects of neonatal estrogens on its expression and localization to determine whether a disturbance in this signaling pathway is involved in mediating the estrogenized phenotype. Shh was expressed in epithelial cells at the distal tips of elongating ducts in discreet, heterogeneous foci, while ptc and gli1-3 were expressed in the adjacent mesenchymal cells in the developing gland. The addition of Shh protein to cultured neonatal prostates reduced ductal growth and branching, decreased Fgf10 transcript, and increased Bmp4 expression in the adjacent mesenchyme. Shh-induced growth suppression was reversed by exogenous Fgf10, but not noggin, indicating that Fgf10 suppression is the proximate cause of the growth inhibition. A model is proposed to show how highly localized Shh expression along with regulation of downstream morphogens participates in dichotomous branching during prostate morphogenesis. Neonatal exposure to high-dose estradiol suppressed Shh, ptc, gli1, and gli3 expressions and concomitantly blocked ductal branching in the dorsal and lateral prostate lobes specifically. In contrast, ventral lobe branching and Shh-ptc-gli expression were minimally affected by estrogen exposure. Organ culture studies with lateral prostates confirmed that estradiol suppressed Shh-ptc-gli expression directly at the prostatic level. Taken together, the present findings indicate that lobe-specific decreases in Shh-ptc-gli expression are involved in mediating estradiol-induced suppression of dorsal and lateral lobe ductal growth and branching during prostate morphogenesis.

The impact of advances in developmental biology on the management of neonatal surgical anomalies

While advances in the clinical management of various congenital anomalies in pediatric surgery have led to new and exciting therapeutic modalities, our understanding of the mechanisms responsible for these defects lags far behind. In a new era of developmental biology, the prospect of unlocking some of these mysteries has become a real possibility. Advances in gene sequencing has allowed us to create new phenotypes that closely mimic those seen in patients, and has created a setting where we are now better able to understand and develop new therapeutic interventions. Here we discuss the implications of some of the molecular mechanisms underlying various congenital anomalies encountered in pediatric surgery, and how continued research will impact the future of these disease processes.

Fetal heart development in the nitrofen-induced CDH rat model: the role of mechanical and nonmechanical factors

BACKGROUND/PURPOSE

In congenital diaphragmatic hernia (CDH), it was recently shown that early and late gestational lung underdevelopment is caused by nonmechanical and mechanical factors, respectively. Heart underdevelopment, which might predict lung hypoplasia, is commonly attributed to mechanical factors. The authors analyzed whether nonmechanical and mechanical factors affect cardiac growth and correlations between lung and heart weights during gestation.

METHODS

Left-sided CDH was induced in pregnant Wistar rats by administration of nitrofen on E9.5. At selected gestational ages (E18, E20, and E22), the lungs and heart were harvested, weighed, and analyzed for DNA and protein contents. Left lung and heart weights were correlated at those gestational ages. Two experimental groups: nitrofen without CDH (nitrofen), and nitrofen with CDH (CDH), were compared with normal controls.

RESULTS

At E18, both nitrofen-exposed groups presented similar and significant left lung (LL) hypoplasia. As gestation progressed (E20 and E22), in the nitrofen group left lung (LL) hypoplasia decreased, whereas in the CDH group LL hypoplasia was exacerbated relative to normal controls. In contrast, at E18 and E20, heart-to-body weight ratios as well as cardiac DNA and protein contents were reduced significantly in all animals exposed to nitrofen, with no significant differences observed between nitrofen and CDH groups. As gestation progressed, the difference between cardiac parameters in nitrofen-exposed and normal control rats diminished, and at E22 no significant differences were documented. In the CDH group, significant correlations were seen between lung and heart weights at E18 (r = 0.65; P <.05) and E20 (r = 0.4; P <.05), whereas at term gestation (E22) no significant correlation was observed (r = 0.21, not significant).

CONCLUSIONS

Nonmechanical factors, which might be directed by nitrofen, play a role in the pathogenesis of lung and heart hypoplasia manifested precociously in fetal life, whereas mechanical compression might influence only lung growth during late gestation. Heart weight predicts lung weight only in early gestational ages.

Gene expression of fibroblast growth factors 10 and 7 is downregulated in the lung of nitrofen-induced diaphragmatic hernia in rats

BACKGROUND/PURPOSE

Newborns with congenital diaphragmatic hernia (CDH) still have a high mortality rate, which has been attributed to pulmonary hypoplasia and pulmonary hypertension. Fibroblast growth factors (FGFs) are essential components of the gene network that regulates lung development. Recent studies suggest that the new member of FGF family, FGF-10, plays a fundamental role in branching morphogenesis and is essential for lung formation. FGF-10-deficient mice exhibit complete absence of lungs. FGF-7 promotes epithelial proliferation and expansion leading to the formation of cystlike structures. The aim of this study was to determine the gene level expression of FGF-10 and FGF-7 in the lung of nitrofen-induced CDH.

METHODS

Congenital diaphragmatic hernia (CDH) was induced in pregnant rats after administration of 100 mg of nitrofen on day 9.5 of gestation (term, 22 days). In control animals, the same dose of olive oil was given without nitrofen. Cesarean section was performed on day 21 of gestation. The fetuses were divided into 3 groups: normal controls (n = 16), nitrofen induced without CDH (n = 16), and nitrofen-induced CDH (n = 16). Total RNA and DNA were extracted from the lung in each group and measured. mRNA was extracted from total RNA. Reverse transcription polymerase chain reaction (RT-PCR) was performed to evaluate mRNA expressions of FGF-10 and FGF-7. Levels of mRNA were expressed as a ratio of the band density divided by that of beta-actin, a house-keeping gene.

RESULTS

FGF-10 mRNA expression was decreased significantly in CDH lung (2.914 +/- 0.320) compared with controls (4.062 +/- 0.307; P <.05) and nitrofen induced without CDH lung (3.923 +/- 0.250; P <.01). FGF-7 mRNA expression was decreased significantly in CDH lung (0.777 +/- 0.097) compared with controls (1.028 +/- 0.093; P <.01).

CONCLUSIONS

Decreased gene expression of FGF-10 and FGF-7 in the hypoplastic lung suggests that pulmonary hypoplasia in nitrofen-induced CDH rat may be caused by reduced synthesis of FGF-10 and FGF-7 during lung morphogenesis.

Etiology of congenital diaphragmatic hernia: the retinoid hypothesis

Congenital diaphragmatic hernia (CDH) is a major life-threatening cause of respiratory failure in the newborn. Although significant efforts have been undertaken to unravel the pathophysiology of CDH, our current understanding of the etiology remains spare. Here we outline recent evidence suggesting that abnormalities linked with the retinoid signaling pathway early in gestation may contribute to the etiology of CDH. These studies include 1) the effect of altering the retinoid system in vitamin A deficient and transgenic animals; 2) disruption of the retinoid system in teratogen-induced CDH in rodents, 3) the effect of co-administration of retinoids in nitrofen-induced CDH on lung and diaphragm development, and 4) clinical evidence suggesting decreased markers of vitamin A status in human CDH. Given the substantial mortality and morbidity associated with this serious developmental anomaly, advancements in this area will be critical. We feel that there is now sufficient circumstantial and direct experimental evidence to warrant further testing of the retinoid-CDH etiology hypothesis, including examination of retinoid-regulated target genes that could be candidates for involvement in CDH.