Inhibition of vascular and epithelial differentiation in murine nitrofen-induced diaphragmatic hernia

Endothelial-to-Mesenchymal Transition in Human and Murine Models of Congenital Diaphragmatic Hernia

INTRODUCTION

Congenital diaphragmatic hernia (CDH) is a complex congenital disorder, characterized by pulmonary hypertension (PH) and hypoplasia. PH secondary to CDH (CDH-PH) features devastating morbidity and mortality (25-30%) among neonates. An unmet need is determining mechanisms triggering CDH-PH to save infants. Prior data suggest abnormal remodeling of the pulmonary vascular extracellular matrix (ECM), presumed to be driven by endothelial-to-mesenchymal transition (EndoMT), hinders postnatal vasodilation and limits anti-PH therapy in CDH. There are limited data on the role of EndoMT in CDH-PH.

METHODS

The purpose of the study was to investigate how EndoMT contributes to CDH-PH by identifying cells undergoing EndoMT noted by alpha smooth muscle actin (α-SMA) expression in human umbilical vein endothelial cells (HUVECs) and lung tissue obtained from murine pups using the nitrofen model. N = 8 CDH, N = 8 control HUVECs were stained for α-SMA and CD31 after being exposed for 24 h to TGFB, a known EndoMT promoter. N = 8 nitrofen, N = 8 control murine pup lungs were also stained for α-SMA and CD31. α-SMA and CD31 expression was quantified in HUVECs and murine tissue using Fiji imaging software and normalized to the total number of cells per slide noted by DAPI staining.

RESULTS

CDH HUVECs demonstrated a 1.1-fold increase in α-SMA expression (p = 0.02). The murine model did not show statistical significance between nitrofen and control pup lungs; however, there was a 0.4-fold increase in α-SMA expression with a 0.8-fold decrease in CD31 expression in the nitrofen pup lungs when compared to controls.

CONCLUSION

These results suggest that EndoMT could potentially play a role in the ECM remodeling seen in CDH-PH.

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.

Intra-Amniotic Sildenafil Treatment Promotes Lung Growth and Attenuates Vascular Remodeling in an Experimental Model of Congenital Diaphragmatic Hernia

BACKGROUND

Defective lung development resulting in lung hypoplasia and an attenuated and hypermuscularized pulmonary vasculature contributes to significant postnatal mortality in congenital diaphragmatic hernia (CDH). We hypothesize that deficient embryonic pulmonary blood flow contributes to defective lung development in CDH, which may therefore be ameliorated via enhancement of embryonic pulmonary blood flow.

METHODS

The mouse nitrofen model of CDH was utilized to measure embryonic pulmonary blood flow by in utero intracardiac injection of FITC-labeled tomato lectin and color-flow Doppler ultrasound. The effect of prenatal intra-amniotic treatment with sildenafil on survival, lung growth, and vascular morphology in the nitrofen model was determined.

RESULTS

Nitrofen-treated embryos exhibited decreased blood flow in the lung periphery compared to controls, and intra-amniotic sildenafil significantly improved embryonic pulmonary blood flow. Similar to nitrofen alone, pups delivered after nitrofen treatment and intra-amniotic injection of dextrose control exhibited respiratory distress and never survived beyond 6 h. Intra-amniotic sildenafil ameliorated respiratory distress in nitrofen-treated pups and improved postnatal survival to 82%. Following intra-amniotic sildenafil treatment at embryonic day (E)10.5, nitrofen-treated P0 lungs were larger with increased left lobe weight, reduced small pulmonary arterial wall muscularization, and increased airway branching complexity compared to controls. Intra-amniotic sildenafil treatment later at E15.5 also resulted in improved survival, lung growth, and attenuation of vascular remodeling in nitrofen-treated embryos.

CONCLUSIONS

Defective embryonic pulmonary blood flow may contribute to lung maldevelopment in CDH. Enhancement of embryonic pulmonary blood flow via intra-amniotic sildenafil results in lung growth and attenuation of pulmonary vascular remodeling and may have therapeutic potential for CDH.

Defective parasympathetic innervation is associated with airway branching abnormalities in experimental CDH

Developmental mechanisms leading to lung hypoplasia in congenital diaphragmatic hernia (CDH) remain poorly defined. Pulmonary innervation is defective in the human disease and in the rodent models of CDH. We hypothesize that defective parasympathetic innervation may contribute to airway branching abnormalities and, therefore, lung hypoplasia, during lung development in CDH. The murine nitrofen model of CDH was utilized to study the effect of the cholinergic agonist carbachol on embryonic day 11.5 (E11.5) lung explant cultures. Airway branching and contractions were quantified. In a subset of experiments, verapamil was added to inhibit airway contractions. Sox9 immunostaining and 5-bromo-2-deoxyuridine incorporation were used to identify and quantify the number and proliferation of distal airway epithelial progenitor cells. Intra-amniotic injections were used to determine the in vivo effect of carbachol. Airway branching and airway contractions were significantly decreased in nitrofen-treated lungs compared with controls. Carbachol resulted in increased airway contractions and branching in nitrofen-treated lungs. Nitrofen-treated lungs exhibited an increased number of proliferating Sox9-positive distal epithelial progenitor cells, which were decreased and normalized by treatment with carbachol. Verapamil inhibited the carbachol-induced airway contractions in nitrofen-treated lungs but had no effect on the carbachol-induced increase in airway branching, suggesting a direct carbachol effect independent of airway contractions. In vivo treatment of nitrofen-treated embryos via amniotic injection of carbachol at E10.5 resulted in modest increases in lung size and branching at E17.5. These results suggest that defective parasympathetic innervation may contribute to airway branching abnormalities in CDH.

ANG-1 TIE-2 and BMPR signalling defects are not seen in the nitrofen model of pulmonary hypertension and congenital diaphragmatic hernia

BACKGROUND

Pulmonary hypertension (PH) is a lethal disease that is associated with characteristic histological abnormalities of the lung vasculature and defects of angiopoetin-1 (ANG-1), TIE-2 and bone morphogenetic protein receptor (BMPR)-related signalling. We hypothesized that if these signalling defects cause PH generically, they will be readily identifiable perinatally in congenital diaphragmatic hernia (CDH), where the typical pulmonary vascular changes are present before birth and are accompanied by PH after birth.

METHODS

CDH (predominantly left-sided, LCDH) was created in Sprague-Dawley rat pups by e9.5 maternal nitrofen administration. Left lungs from normal and LCDH pups were compared at fetal and postnatal time points for ANG-1, TIE-2, phosphorylated-TIE-2, phosphorylated-SMAD1/5/8 and phosphorylated-ERK1/2 by immunoprecipitation and Western blotting of lung protein extracts and by immunohistochemistry on lung sections.

RESULTS

In normal lung, pulmonary ANG-1 protein levels fall between fetal and postnatal life, while TIE-2 levels increase. Over the corresponding time period, LCDH lung retained normal expression of ANG-1, TIE-2, phosphorylated-TIE-2 and, downstream of BMPR, phosphorylated-SMAD1/5/8 and phosphorylated-p44/42.

CONCLUSION

In PH and CDH defects of ANG-1/TIE-2/BMPR-related signalling are not essential for the lethal vasculopathy.

Defective pulmonary innervation and autonomic imbalance in congenital diaphragmatic hernia

Congenital diaphragmatic hernia (CDH) is associated with significant mortality due to lung hypoplasia and pulmonary hypertension. The role of embryonic pulmonary innervation in normal lung development and lung maldevelopment in CDH has not been defined. We hypothesize that developmental defects of intrapulmonary innervation, in particular autonomic innervation, occur in CDH. This abnormal embryonic pulmonary innervation may contribute to lung developmental defects and postnatal physiological derangement in CDH. To define patterns of pulmonary innervation in CDH, human CDH and control lung autopsy specimens were stained with the pan-neural marker S-100. To further characterize patterns of overall and autonomic pulmonary innervation during lung development in CDH, the murine nitrofen model of CDH was utilized. Immunostaining for protein gene product 9.5 (a pan-neuronal marker), tyrosine hydroxylase (a sympathetic marker), vesicular acetylcholine transporter (a parasympathetic marker), or VIP (a parasympathetic marker) was performed on lung whole mounts and analyzed via confocal microscopy and three-dimensional reconstruction. Peribronchial and perivascular neuronal staining pattern is less complex in human CDH than control lung. In mice, protein gene product 9.5 staining reveals less complex neuronal branching and decreased neural tissue in nitrofen-treated lungs from embryonic day 12.5 to 16.5 compared with controls. Furthermore, nitrofen-treated embryonic lungs exhibited altered autonomic innervation, with a relative increase in sympathetic nerve staining and a decrease in parasympathetic nerve staining compared with controls. These results suggest a primary defect in pulmonary neural developmental in CDH, resulting in less complex neural innervation and autonomic imbalance. Defective embryonic pulmonary innervation may contribute to lung developmental defects and postnatal physiological derangement in CDH.

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 suppresses cell proliferation and promotes mitochondria-mediated apoptosis in type II pneumocytes

AIM

To characterize the molecular mechanisms of nitrofen-induced pulmonary hypoplasia.

METHODS

After administration of nitrofen to cultured type II A549 pneumocytes, cell proliferation and DNA synthesis were investigated by 3-(4,5- dimethylthiazol-2-yl)-2,5-diphenyl tetrazolium bromide colorimetry, colony formation assay, flow cytometry and [3H]-thymidine incorporation assay. Apoptosis was measured by terminal transferase-mediated dUTP nick-end-labeling, acridine orange-ethidium bromide staining and flow cytometry. Expression of proliferating cell nuclear antigen (PCNA) and apoptosis-related genes was assayed by immunofluorescence, RT-PCR and Western blot.

RESULTS

Nitrofen inhibited the cell proliferation of A549 cells in a dose- and time-dependent manner, accompanied by downregulation of PCNA. As a result, the DNA synthesis of nitrofentreated A549 cells decreased, while cell cycle was arrested at G0/G1 phase. Moreover, nitrofen induced apoptosis of A549 cells, which was not abolished by Z-Val-Ala- Asp(OCH3)- fluoromethylketone. In addition, nitrofen decreased the expression of Bcl-x( L), but not of Bcl-2, Bax, and Bak, resulting in a loss of mitochondrial membrane potential and the nuclear translocation of apoptosis-inducing factor (AIF). Meanwhile, nitrofen strongly activated the p38 mitogen-activated protein kinase (p38-MAPK). Pretreatment of cells with SB203580 (5 micromol/L) blocked nitrofen-induced phosphorylation of p38-MAPK and abolished nitrofen-induced AIF translocation and apoptosis in A549 cells.

CONCLUSION

Nitrofen suppresses the proliferation of cultured type II pneumocytes accompanied by the downregulation of PCNA, and induces mitochondria-mediated apoptosis involving the activation of p38-MAPK.

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.

Changes in fetal lung distension alter expression of vascular endothelial growth factor and its isoforms in developing rat lung

Vascular endothelial growth factor A (VEGF-A) is essential for normal pulmonary vascular and parenchymal development. Changes in fetal lung distension profoundly affect lung growth and maturation, including vascular development. To define developmental lung expression of VEGF-A and its receptors and investigate effects of changes in fetal lung distension, we studied fetal rats at embryonic day (ED) 16, 19, and 22, postnatal rats at postnatal day (PD) 5, 10, and 21, and adult rats. We used reverse transcriptase PCR to measure mRNA expression for VEGF-A isoforms (VEGF-A(120), (-144), (-164), and (-188)) and VEGF-A receptors, Flt-1 and Flk-1. With advancing development, mRNA content increased only for VEGF-A(188) (p < 0.05) and for Flt-1 (p < 0.02) and Flk-1 (p < 0.005). As a percentage of total VEGF-A mRNA, VEGF-A(188) (15% at ED 16) increased to become the dominant isoform at PD 21 (40%, p < 0.005) and adulthood; in contrast, there were decreases in both VEGF-A(144) (p < 0.05) and (-120) (p < 0.005). VEGF-A protein was expressed in alveolar epithelium (type I and II cells) and interstitium. Increasing fetal lung distension by tracheal occlusion (TO) accelerated the normal maturational pattern of VEGF-A isoforms and increased VEGF-A protein; decreasing fetal lung distension by congenital diaphragmatic hernia (CDH) retarded the normal developmental pattern and decreased VEGF-A protein. Neither TO nor CDH consistently affected Flt-1 or Flk-1 mRNA content. These results show that mechanical factors significantly affect lung VEGF-A expression and suggest that VEGF-A mediates previously described changes in lung vascular and parenchymal development caused by CDH and by TO.

Congenital diaphragmatic hernia, tracheal occlusion, thyroid transcription factor-1, and fetal pulmonary epithelial maturation

Congenital diaphragmatic hernia (CDH) occurs in ∼1:2,500 human births and has high morbidity and mortality rates, primarily due to pulmonary hypoplasia and pulmonary hypertension. Tracheal occlusion (TO), in experimental animals, distends lungs and increases lung growth and alveolar type I cell maturation but decreases surfactant components and reduces alveolar type II cell density. We examined effects of CDH and CDH+TO on lung growth and maturation in fetal rats. To induce CDH, we administered nitrofen (100 mg) to dams at 9.5 days of gestation. We compared lungs from fetuses with CDH, CDH+TO, and those exposed to nitrofen without CDH. CDH decreased lung wet weight bilaterally ( P < 0.0001) and DNA content in lung ipsilateral to CDH ( P < 0.05). CDH+TO significantly increased lung wet weights bilaterally; DNA content was intermediate between CDH and NC. To evaluate effects on the distal pulmonary epithelium, we examined surfactant mRNA and protein levels, type I and II cell-specific markers (RTI40 and RTII70, respectively), and transcriptional regulator thyroid transcription factor-1 (TTF-1). Decreased lung distension (due to CDH) increased SP-C mRNA and TTF-1 protein expression and reduced RTI40 ( P < 0.05 for all). Increased lung distension (due to CDH+TO) reduced expression of SP mRNAs and pro-SP-C and TTF-1 proteins and enhanced expression of RTI40 (mRNA and protein; P < 0.05 for all). We conclude that CDH+TO partially reverses effects of CDH; it corrects the pulmonary hypoplasia and restores type I cell differentiation but adversely affects SP expression in type II cells. These effects may be mediated through changes in TTF-1 expression.

Differential effects of vitamin A on fetal lung growth and diaphragmatic formation in nitrofen-induced rat model

Congenital diaphragmatic hernia (CDH) is associated with high neonatal mortality and morbidity due to pulmonary hypoplasia and pulmonary hypertension. Antenatal interventions have been developed in an attempt to reduce the unacceptable mortality rate of CDH. The pathogenesis of pulmonary hypoplasia is not fully understood. It is not clear whether the increase of lung growth would be necessary for diaphragmatic closure. Vitamin A is important for various aspects of lung development. Therefore, the aim of this study was to examine whether antenatal treatment with vitamin A can increase lung growth and reduce the incidence of CDH in a nitrofen-treated rat model. The animals were randomly assigned to four groups: control, vitamin A, nitrofen, and nitrofen/vitamin A (NIP/Vit A). The incidence of CDH in the NIP/Vit A group (54%) was markedly lower than that in the nitrofen-treated group (85%). Although lung weight was decreased in the nitrofen-treated and NIP/vitamin A groups, the fetal lung weight-to-body weight ratio was slightly increased in the NIP/vitamin A group, compared to the nitrofen-treated group. The mRNA levels of lung surfactant proteins were decreased in the NIP/vitamin A group. We conclude that antenatal treatment with vitamin A reduced the incidence of CDH without lung maturation in the nitrofen-induced rat model.

Role of oxygen and vascular development in epithelial branching morphogenesis of the developing mouse lung

Recent investigations have suggested an active role for endothelial cells in organ development, including the lung. Herein, we investigated some of the molecular mechanisms underlying normal pulmonary vascular development and their influence on epithelial branching morphogenesis. Because the lung in utero develops in a relative hypoxic environment, we first investigated the influence of low oxygen on epithelial and vascular branching morphogenesis. Two transgenic mouse models, the C101-LacZ (epithelial-LacZ marker) and the Tie2-LacZ (endothelial-LacZ marker), were used. At embryonic day 11.5, primitive lung buds were dissected and cultured at either 20 or 3% oxygen. At 24-h intervals, epithelial and endothelial LacZ gene expression was visualized by X-galactosidase staining. The rate of branching of both tissue elements was increased in explants cultured at 3% oxygen compared with 20% oxygen. Low oxygen increased expression of VEGF, but not that of the VEGF receptor (Flk-1). Expression of two crucial epithelial branching factors, fibroblast growth factor-10 and bone morphogenetic protein-4, were not affected by low oxygen. Epithelial differentiation was maintained at low oxygen as shown by surfactant protein C in situ hybridization. To explore epithelial-vascular interactions, we inhibited vascular development with antisense oligonucleotides targeted against either hypoxia inducible factor-1α or VEGF. Epithelial branching morphogenesis in vitro was dramatically abrogated when pulmonary vascular development was inhibited. Collectively, the in vitro data show that a low-oxygen environment enhances branching of both distal lung epithelium and vascular tissue and that pulmonary vascular development appears to be rate limiting for epithelial branching morphogenesis.

Increased levels of circulating adhesion molecules in neonates with congenital diaphragmatic hernia complicated by persistent pulmonary hypertension

The aim of this study was to determine circulating levels of adhesion molecules in serum from patients with congenital diaphragmatic hernia (CDH) to investigate the relationship between soluble ICAM-1, ELAM-1, and VCAM-1 liberated by activated vascular endothelium and the development of persistent pulmonary hypertension (PPH) in patients with CDH. We measured serum levels of ICAM-1, ELAM-1, and VCAM-1 in 20 high-risk neonates with CDH at the time of diagnosis (11 with PPH and 9 without PPH) and 7 age-matched controls using ELISA system. We further examined the lungs of 5 patients with CDH complicated by PPH who died during resuscitation and stabilization, and three control lung specimens for the expression of adhesion molecules using immunohistochemistry. The mean serum ICAM-1 levels in CDH patients with PPH (227.0+/-98.9 ng/ml) were increased compared with levels in CDH patients without PPH (140.29+/-37.4 ng/ml; p<0.05) and controls (130.0+/-23.8 ng/ml; p<0.05). Mean serum ELAM-1 levels in CDH patients with PPH (116.5+/-19.2 ng/ml) were significantly increased compared with levels in CDH patients without PPH (79.3+/-27.9 ng/ml; p<0.01) and controls (58.4+/-14.5 ng/ml; p<0.001). Mean serum VCAM-1 levels in CDH patients with PPH (1596.9+/-460.4 ng/ml) were significantly higher compared with levels in CDH patients without PPH (1069.3+/-444.6 ng/ml; p<0.01) and controls (838.0+/-171.2 ng/ml; p<0.001). But serum adhesion molecule levels in CDH patients without PPH were no different from controls statistically. Pulmonary vascular endothelial cells from CDH lung with PPH had strong expression of adhesion molecules compared with controls. Up-regulated expression of adhesion molecules on the endothelium of pulmonary vessels and high circulating levels of adhesion molecules in CDH patients with PPH suggest that adhesion molecules may play a role in the development of PPH in CDH.

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.

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

We evaluated the role of the key pulmonary morphogenetic gene fibroblast growth factor-10 (Fgf10) in murine nitrofen-induced primary lung hypoplasia, which is evident before the time of diaphragm closure. In situ hybridization and competitive RT-PCR revealed a profound disturbance in the temporospatial pattern as well as a 10-fold decrease in mRNA expression level of Fgf10 but not of the inducible inhibitor murine Sprouty2 (mSpry2) after nitrofen treatment. Exogenous FGF-10 increased branching not only of control lungs [13% (right) and 27% (left); P < 0.01] but also of nitrofen-exposed lungs [23% (right) and 77% (left); P < 0.01]. Expression of mSpry2 increased 10-fold with FGF-10 in both nitrofen-treated and control lungs, indicating intact downstream FGF signaling mechanisms after nitrofen treatment. We conclude that nitrofen inhibits Fgf10 expression, which is essential for lung growth and branching. Exogenous FGF-10 not only stimulates FGF signaling, marked by increased mSpry2 expression, in both nitrofen-treated and control lungs but also substantially rescues nitrofen-induced lung hypoplasia in culture.

Lung hypoplasia in the nitrofen model of congenital diaphragmatic hernia occurs early in development

The teratogen nitrofen produces a congenital diaphragmatic hernia (CDH) and pulmonary hypoplasia in rodent fetuses that closely parallel observations made in humans. We hypothesized that these changes may be due to primary pulmonary hypoplasia and not herniation of the abdominal contents. Timed-pregnant rats were given nitrofen on day 9, and fetuses were harvested on days 13 through 21. Initial evagination of lung buds on gestational day 11 was not delayed in nitrofen-treated fetuses. On gestational day 13, however, there was a significant decrease in the number of terminal end buds in the lungs of nitrofen-exposed fetuses vs. controls. Thymidine-labeled lung epithelial and mesenchymal cells were significantly decreased in nitrofen-treated lungs. Lungs from nitrofen-treated fetuses exhibited wide septae with disorganized, compacted tissue, particularly around the air spaces. Expression of surfactant protein B and C mRNAs was significantly decreased in the nitrofen litters. In situ hybridization of fetal lung tissue at all gestational ages showed no difference in the expression of vascular endothelial growth factor, Flk-1, or Flt-1 mRNAs. Because closure of the diaphragm is completed on gestational day 16 in the rat, our results suggest that lung hypoplasia in this model of CDH is due at least in part to a primary effect of nitrofen on the developing lung.

The latent transforming growth factor-beta-binding protein-1 promotes in vitro differentiation of embryonic stem cells into endothelium

The latent transforming growth factor-beta-binding protein-1 (LTBP-1) belongs to a family of extracellular glycoproteins that includes three additional isoforms (LTBP-2, -3, and -4) and the matrix proteins fibrillin-1 and -2. Originally described as a TGF-beta-masking protein, LTBP-1 is involved both in the sequestration of latent TGF-beta in the extracellular matrix and the regulation of its activation in the extracellular environment. Whereas the expression of LTBP-1 has been analyzed in normal and malignant cells and rodent and human tissues, little is known about LTBP-1 in embryonic development. To address this question, we used murine embryonic stem (ES) cells to analyze the appearance and role of LTBP-1 during ES cell differentiation. In vitro, ES cells aggregate to form embryoid bodies (EBs), which differentiate into multiple cell lineages. We analyzed LTBP-1 gene expression and LTBP-1 fiber appearance with respect to the emergence and distribution of cell types in differentiating EBs. LTBP-1 expression increased during the first 12 d in culture, appeared to remain constant between d 12 and 24, and declined thereafter. By immunostaining, fibrillar LTBP-1 was observed in those regions of the culture containing endothelial, smooth muscle, and epithelial cells. We found that inclusion of a polyclonal antibody to LTBP-1 during EB differentiation suppressed the expression of the endothelial specific genes ICAM-2 and von Willebrand factor and delayed the organization of differentiated endothelial cells into cord-like structures within the growing EBs. The same effect was observed when cultures were treated with either antibodies to TGF-beta or the latency associated peptide, which neutralize TGF-beta. Conversely, the organization of endothelial cells was enhanced by incubation with TGF-beta 1. These results suggest that during differentiation of ES cells LTBP-1 facilitates endothelial cell organization via a TGF-beta-dependent mechanism.