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

Comparative Transcriptome Analysis of Human and Mouse Canalicular Lungs in Fetal Diaphragmatic Hernia

BACKGROUND

The nitrofen model of congenital diaphragmatic hernia (CDH) is widely used in translational research. However, the molecular pathways associated with pulmonary hypoplasia in this model compared to the human CDH phenotype have not been well described. The aim of this study was to investigate differentially expressed genes (DEG) and signaling pathways in early stage fetal lungs in mouse and human CDH.

METHODS

CDH lung tissue was obtained from human fetuses (21-23 weeks gestation) and nitrofen mouse pups (E15.5). NovaSeq Flowcell RNA-seq was performed to evaluate differentially expressed transcriptional and molecular pathways (DEGs) in fetal mice with CDH, compared with age-matched normal mouse lungs and human CDH samples.

RESULTS

There were thirteen overlapping DEGs in human and mouse CDH lung samples compared to controls. These genes were involved in extracellular matrix, myogenesis, cilia, and immune modulation pathways. Human CDH was associated with an upregulation of collagen formation and extracellular matrix reorganization whereas mouse CDH was associated with an increase in muscular contraction. The most common cell types upregulated in human and mouse CDH samples were ciliated airway cells.

CONCLUSIONS

This study highlights the unique gene transcriptional patterns in early fetal mouse and human lungs with CDH. These data have implications when determining the translational potential of novel therapies in CDH using nitrofen-based animal models.

LEVEL OF EVIDENCE

Level IV.

STUDY TYPE

Basic science/case series.

Congenital diaphragmatic hernia

Congenital diaphragmatic hernia (CDH) is a rare birth defect characterized by incomplete closure of the diaphragm and herniation of fetal abdominal organs into the chest that results in pulmonary hypoplasia, postnatal pulmonary hypertension owing to vascular remodelling and cardiac dysfunction. The high mortality and morbidity rates associated with CDH are directly related to the severity of cardiopulmonary pathophysiology. Although the aetiology remains unknown, CDH has a polygenic origin in approximately one-third of cases. CDH is typically diagnosed with antenatal ultrasonography, which also aids in risk stratification, alongside fetal MRI and echocardiography. At specialized centres, prenatal management includes fetal endoscopic tracheal occlusion, which is a surgical intervention aimed at promoting lung growth in utero. Postnatal management focuses on cardiopulmonary stabilization and, in severe cases, can involve extracorporeal life support. Clinical practice guidelines continue to evolve owing to the rapidly changing landscape of therapeutic options, which include pulmonary hypertension management, ventilation strategies and surgical approaches. Survivors often have long-term, multisystem morbidities, including pulmonary dysfunction, gastroesophageal reflux, musculoskeletal deformities and neurodevelopmental impairment. Emerging research focuses on small RNA species as biomarkers of severity and regenerative medicine approaches to improve fetal lung development.

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 mechanosensitive ion channel TRPV4 is a regulator of lung development and pulmonary vasculature stabilization

Introduction –

Clinical observations and animal models suggest a critical role for the dynamic regulation of transmural pressure and peristaltic airway smooth muscle contractions for proper lung development. However, it is currently unclear how such mechanical signals are transduced into molecular and transcriptional changes at the cell level. To connect these physical findings to a mechanotransduction mechanism, we identified a known mechanosensor, TRPV4, as a component of this pathway.

Methods –

Embryonic mouse lung explants were cultured on membranes and in submersion culture to modulate explant transmural pressure. Time-lapse imaging was used to capture active changes in lung biology, and whole-mount images were used to visualize the organization of the epithelial, smooth muscle, and vascular compartments. TRPV4 activity was modulated by pharmacological agonism and inhibition.

Results –

TRPV4 expression is present in the murine lung with strong localization to the epithelium and major pulmonary blood vessels. TRPV4 agonism and inhibition resulted in hyper- and hypoplastic airway branching, smooth muscle differentiation, and lung growth, respectively. Smooth muscle contractions also doubled in frequency with agonism and were reduced by 60% with inhibition demonstrating a functional role consistent with levels of smooth muscle differentiation. Activation of TRPV4 increased the vascular capillary density around the distal airways, and inhibition resulted in a near complete loss of the vasculature.

Conclusions –

These studies have identified TRPV4 as a potential mechanosensor involved in transducing mechanical forces on the airways to molecular and transcriptional events that regulate the morphogenesis of the three essential tissue compartments in the lung.

Congenital diaphragmatic disease: An unusual presentation in adulthood. Case report

INTRODUCTION

Congenital diaphragmatic disease is a quite common condition that usually occurs in the neonatal period, and the diagnosis of congenital diaphragmatic disease in adulthood is rare.

CASE PRESENTATION

A 64-years-old Caucasian woman was admitted in emergency at our Department, due to a bowel obstruction and dyspnea. A CT-scan showed a diaphragmatic herniation in the left area, with malposition of dilated transverse and descending colon in the chest. An emergency laparatomy was performed, showing a toxic megacolon, in the absence of a true diaphragmatic hernia, and a left diaphragm and left liver hypoplasia. An intraoperative bronchoscopy revealed concomitant hypoplasia of the left lung. A subtotal colectomy with ileo-rectal anastomosis was performed. The postoperative course was uneventful. Histological examination demonstrated hyperplasia of the muscularis mucosae of the colon and cytoplasmic vacuolization of the Auerbach plexus ganglia. The karyotype genetic analysis excluded concomitant microdeletion or duplication syndromes.

DISCUSSION

To our knowledge, this seems to be the first reported case of toxic megacolon in a patient with congenital hypoplasia of the left bronchial-lung system, of the left liver, and of the left diaphragm.

CONCLUSION

The correct development of the diaphragm is essential for the neighboring organs. The observed clinical pattern could be related to a partial modification of neural crest cell detachment or migration, which could be responsible for bowel and diaphragm defects, even though it was not included in typical neural crest cell syndromes. Further researches should be performed in order to define the sporadic or syndromic source of these multiorgan defects.

SERCA directs cell migration and branching across species and germ layers

Branching morphogenesis underlies organogenesis in vertebrates and invertebrates, yet is incompletely understood. Here, we show that the sarco-endoplasmic reticulum Ca2+ reuptake pump (SERCA) directs budding across germ layers and species. Clonal knockdown demonstrated a cell-autonomous role for SERCA in Drosophila air sac budding. Live imaging of Drosophila tracheogenesis revealed elevated Ca2+ levels in migratory tip cells as they form branches. SERCA blockade abolished this Ca2+ differential, aborting both cell migration and new branching. Activating protein kinase C (PKC) rescued Ca2+ in tip cells and restored cell migration and branching. Likewise, inhibiting SERCA abolished mammalian epithelial budding, PKC activation rescued budding, while morphogens did not. Mesoderm (zebrafish angiogenesis) and ectoderm (Drosophila nervous system) behaved similarly, suggesting a conserved requirement for cell-autonomous Ca2+ signaling, established by SERCA, in iterative budding.

The extracellular calcium-sensing receptor, CaSR, in fetal development

In fetal mammals, serum levels of both total and ionized calcium significantly exceed those in the adult. This relative fetal hypercalcemia is crucial for skeletal development and is maintained irrespectively of maternal serum calcium levels. Elegant studies by Kovacs and Kronenberg have previously addressed the role of the CaSR in creating and maintaining this relative fetal hypercalcemia, through the regulation of parathyroid hormone-related peptide secretion. More recently we have shown that the CaSR is widely distributed throughout the developing fetus, where the receptor plays major, unexpected roles in ensuring growth and maturation of several organs. In this article, we present evidence for a role of the CaSR in the control of skeletal development, and how fetal hypercalcemia, acting through the CaSR, regulates lung development.

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.

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.

[Congenital diaphragmatic hernia - mechanisms of pulmonary hypoplasia]

Congenital diaphragmatic hernia (CDH) is a common cause of severe neonatal respiratory distress. Mortality and morbidity are determined by the amount of pulmonary hypoplasia (PH) that occurs and by the development of therapy-resistant pulmonary hypertension. The pathogenesis and aetiology of CDH and its associated anomalies are still largely unknown despite all research efforts. The pathogenesis of CDH is based on an assumption linking herniation of abdominal viscera into the thorax with compression of the developing lung. PH, however, can also result from reduced distension of the developing lung secondary to impaired fetal breathing movements. Our understanding of CDH has also been aided by basic research with the use of dietary, teratogen-induced, and knockout models of CDH. These studies indicate that lung hypoplasia may involve disturbances of mitogenic signalling pathways fundamental to embryonic lung development. Recent data reveal the role of disruption of a retinoid-signalling pathway in the pathogenesis of CDH. Although multifactorial inheritance may best explain most cases of CDH in humans, much has been learned about the genetic factors that play a role in the development of CDH by studies of patients with CDH caused by specific genetic syndromes and chromosome anomalies. More research is warranted to improve our understanding of normal and abnormal lung development in relation to CDH. Such investigations will help in the design of new treatment strategies to improve the natural course or even to prevent this anomaly.

Transient in utero nicotine exposure stimulates mechanosensory-dependent lung development

Nicotine receptors are present in the developing lung yet their function is unknown. The transient role of nicotine receptors in lung development has not been addressed. In this study, nicotine's direct effect on smooth muscle contraction, necessary for mechanosensory-dependent fetal lung development, is examined after transient nicotine stimulation to determine the relationship between nicotine exposure, smooth muscle contraction, and fetal lung development. Rat fetuses at 16 days’ gestation were exposed in utero to 5 different concentrations of nicotine or control injected directly into the amniotic fluid. Specific concentrations of in utero nicotine increased the phosphorylated Western blot analysis and immunohistochemistry of muscle contraction proteins. Respiratory function tests on nicotine-exposed rat pups showed a statistically significant decrease in airway resistance earlier in life compared to control and an upward shift of the pressure-volume curve pointing towards a structural maturation of the in utero nicotine-exposed lung. These results are consistent with transient nicotine exposure during intrauterine life stimulating stretch-induced lung organogenesis by altering phosphorylation of muscle contraction proteins. The increase in smooth muscle phosphorylation may stimulate stretch-induced lung organogenesis, which affects lung development and accelerates lung maturation in rats.

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.

Embryonic lung growth is normal in a cftr-knockout mouse model

The role of the cystic fibrosis transmembrane conductance regulator (CFTR) chloride channel in embryonic lung growth remains uncertain. The authors used an established embryonic lung culture model to investigate the impact of cftr knockout on lung growth, airway peristalsis, and airway smooth muscle (ASM) distribution. Lung area, perimeter, lung bud count, and frequency of contraction were similar in wild-type (cftr +/+) and cftr knockout mice (cftr -/-). The percentage of mitotic cells was also consistent between genotypes in mesenchyme and epithelium. Smooth muscle distribution surrounding the airway appeared normally distributed in all genotypes. These data suggest that normal embryonic lung growth, ASM differentiation and airway peristalsis are CFTR independent.

CFTR and Wnt/beta-catenin signaling in lung development

BACKGROUND

Cystic fibrosis transmembrane conductance regulator (CFTR) was shown previously to modify stretch induced differentiation in the lung. The mechanism for CFTR modulation of lung development was examined by in utero gene transfer of either a sense or antisense construct to alter CFTR expression levels. The BAT-gal transgenic reporter mouse line, expressing beta-galactosidase under a canonical Wnt/beta-catenin-responsive promoter, was used to assess the relative roles of CFTR, Wnt, and parathyroid hormone-related peptide (PTHrP) in lung organogenesis. Adenoviruses containing full-length CFTR, a short anti-sense CFTR gene fragment, or a reporter gene as control were used in an intra-amniotic gene therapy procedure to transiently modify CFTR expression in the fetal lung.

RESULTS

A direct correlation between CFTR expression levels and PTHrP levels was found. An inverse correlation between CFTR and Wnt signaling activities was demonstrated.

CONCLUSION

These data are consistent with CFTR participating in the mechanicosensory process essential to regulate Wnt/beta-Catenin signaling required for lung organogenesis.

The Peter Pan paradigm

Genetic and environmental agents that disrupt organogenesis are numerous and well described. Less well established, however, is the role of delay in the developmental processes that yield functionally immature tissues at birth. Evidence is mounting that organs do not continue to develop postnatally in the context of these organogenesis insults, condemning the patient to utilize under-developed tissues for adult processes. These poorly differentiated organs may appear histologically normal at birth but with age may deteriorate revealing progressive or adult-onset pathology. The genetic and molecular underpinning of the proposed paradigm reveals the need for a comprehensive systems biology approach to evaluate the role of maternal-fetal environment on organogenesis."You may delay, but time will not" Benjamin Franklin, USA Founding Father.

Embryonic Essential Myosin Light Chain Regulates Fetal Lung Development in Rats

Congenital diaphragmatic hernia (CDH) is currently the most life-threatening congenital anomaly the major finding of which is lung hypoplasia. Lung hypoplasia pathophysiology involves early developmental molecular insult in branching morphogenesis and a late mechanical insult by abdominal herniation in maturation and differentiation processes. Since early determinants of lung hypoplasia might appear as promising targets for prenatal therapy, proteomics analysis of normal and nitrofen-induced hypoplastic lungs was performed at 17.5 days after conception. The major differentially expressed protein was identified by mass spectrometry as myosin light chain 1a (MLC1a). Embryonic essential MLC1a and regulatory myosin light chain 2 (MLC2) were characterized throughout normal and abnormal lung development by immunohistochemistry and Western blot. Disruption of MLC1a expression was assessed in normal lung explant cultures by antisense oligodeoxynucleotides. Since early stages of normal lung development, MLC1a was expressed in vascular smooth muscle (VSM) cells of pulmonary artery, and MLC2 was present in parabronchial smooth muscle and VSM cells of pulmonary vessels. In addition, early smooth muscle differentiation delay was observed by immunohistochemistry of alpha-smooth muscle actin and transforming growth factor-beta1. Disruption of MLC1a expression during normal pulmonary development led to significant growth and branching impairment, suggesting a role in branching morphogenesis. Both MLC1a and MLC2 were absent from hypoplastic fetal lungs during pseudoglandular stage of lung development, whereas their expression partially recovered by prenatal treatment with vitamin A. Thus, a deficiency in contractile proteins MLC1a and MLC2 might have a role among the early molecular determinants of lung hypoplasia in the rat model of nitrofen-induced CDH.

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.

Molecular genetics of congenital diaphragmatic defects

Congenital diaphragmatic hernia (CDH) is a severe birth defect that is accompanied by malformations of the lung, heart, testis, and other organs. Patients with CDH may have any combination of these extradiaphragmatic defects, suggesting that CDH is often a manifestation of a global embryopathy. This review highlights recent advances in human and mouse genetics that have led to the identification of genes involved in CDH. These include genes for transcription factors, molecules involved in cell migration, and extracellular matrix components. The expression patterns of these genes in the developing embryo suggest that mesenchymal cell function is compromised in the diaphragm and other affected organs in patients with CDH. We discuss potential mechanisms underlying the seemingly random combination of diaphragmatic, pulmonary, cardiovascular, and gonadal defects in these patients.