Preparing for the first breath: genetic and cellular mechanisms in lung development. Dev Cell. 2010;18:8-23. [PMID: 20152174 DOI: 10.1016/j.devcel.2009.12.010]

Branching morphogenesis

Over the past 5 years, several studies have begun to uncover the links between the classical signal transduction pathways and the physical mechanisms that are used to sculpt branched tissues. These advances have been made, in part, thanks to innovations in live imaging and reporter animals. With modern research tools, our conceptual models of branching morphogenesis are rapidly evolving, and the differences in branching mechanisms between each organ are becoming increasingly apparent. Here, we highlight four branched epithelia that develop at different spatial scales, within different surrounding tissues and via divergent physical mechanisms. Each of these organs has evolved to employ unique branching strategies to achieve a specialized final architecture.

Efficient Generation and Transcriptomic Profiling of Human iPSC-Derived Pulmonary Neuroendocrine Cells

Expansion of pulmonary neuroendocrine cells (PNECs) is a pathological feature of many human lung diseases. Human PNECs are inherently difficult to study due to their rarity (<1% of total lung cells) and a lack of established protocols for their isolation. We used induced pluripotent stem cells (iPSCs) to generate induced PNECs (iPNECs), which express core PNEC markers, including ROBO receptors, and secrete major neuropeptides, recapitulating known functions of primary PNECs. Furthermore, we demonstrate that differentiation efficiency is increased in the presence of an air-liquid interface and inhibition of Notch signaling. Single-cell RNA sequencing (scRNA-seq) revealed a PNEC-associated gene expression profile that is concordant between iPNECs and human fetal PNECs. In addition, pseudotime analysis of scRNA-seq results suggests a basal cell origin of human iPNECs. In conclusion, our model has the potential to provide an unlimited source of human iPNECs to explore PNEC pathophysiology associated with several lung diseases.

Evidence for Overlapping and Distinct Biological Activities and Transcriptional Targets Triggered by Fibroblast Growth Factor Receptor 2b Signaling between Mid- and Early Pseudoglandular Stages of Mouse Lung Development

Branching morphogenesis is the basic developmental mode common to organs such as the lungs that undergo a process of ramification from a rudimentary tree. However, the precise molecular and cellular bases underlying the formation of branching organs are still unclear. As inactivation of fibroblast growth factor receptor 2b (Fgfr2b) signaling during early development leads to lung agenesis, thereby preventing the analysis of this pathway at later developmental stages, we used transgenic mice to induce expression of a soluble form of Fgfr2b to inactivate Fgfr2b ligands at embryonic day (E) 14.5, corresponding to the mid-pseudoglandular stage of lung development. We identified an Fgfr2b signaling signature comprised of 46 genes enriched in the epithelium, some of which were common to, but most of them distinct from, the previously identified Fgfr2b signaling signature at E12.5. Our results indicate that Fgfr2b signaling at E14.5 controls mostly proliferation and alveolar type 2 cell (AT2) differentiation. In addition, inhibition of Fgfr2b signaling at E14.5 leads to morphological and cellular impairment at E18.5, with defective alveolar lineage formation. Further studies will have to be conducted to elucidate the role of Fgfr2b signaling at successive stages (canalicular/saccular/alveolar) of lung development as well as during homeostasis and regeneration and repair after injury.

Presence of N-acetylneuraminic acid in the lung during postnatal development

Sialic acids, particularly N-acetylneuraminic acid (Neu5Ac), are present as terminal components of rich and complex oligosaccharide chains, which are termed glycans, and are exhibited on the cell surfaces, especially on epithelial cells. Crucial in the 'social behavior' of the cell, sialic acids play vital roles in many physiological and pathological phenomena. The aim of the present study was to separate, identify, and quantify Neu5Ac in purified lung membranes from 4-, 14-, and 21-day-old animals, followed by the statistical analysis of these results with our previously reported data (0-day-old and adult results). Complementary, ultrastructural methodologies were used. The differences in the Neu5Ac values obtained across the examined postnatal-lung development relevant ages studied were found to be statistically significant. A substantial increase in the mean level of this compound was found during the period of 'bulk' alveolarization, which takes place from postnatal day 4 to 14 (P4-P14). The comparison of the mean levels of Neu5Ac, during microvascular maturation (mainly between P12 and P21), reveals that the difference, although statistically significant, is the least significant difference among all the pair-wise differences between the developmental stages. The presence of sub-terminal N-acetylgalactosamine (GalNAc)/Galactose (Gal) residues with terminal sialic acids on the bronchioloalveolar cell surfaces was confirmed using lung ultra-thin sections of adult and 0-day-old animals. These results showed that, although Neu5Ac levels increase throughout postnatal lung development, this sialic acid was substantially added to epithelial cell surfaces during the "bulk" alveolarization period, while its presence was less important during the microvascular maturation period. Bearing in mind that sialic acids are negatively charged and create charge repulsions between adjacent cells, we hypothesized that they can substantially contribute to postnatal alveolar formation and maturation.

[Lung organoids]

As burden of chronic respiratory diseases is constantly increasing, improving in vitro lung models is essential in order to reproduce as closely as possible the complex pulmonary architecture, responsible for oxygen uptake and carbon dioxide clearance. The study of diseases that affect the respiratory system has benefited from in vitro reconstructions of the respiratory epithelium with inserts in air/liquid interface (2D) or in organoids able to mimic up to the arborescence of the respiratory tree (3D). Recent development in the fields of pluripotent stem cells-derived organoids and genome editing technologies has provided new insights to better understand pulmonary diseases and to find new therapeutic perspectives.

Differentiation of human airway-organoids from induced pluripotent stem cells (iPSCs)

There was significant progress over the last decade in the ability to generate induced pluripotent stem cell (iPSC)-derived airway organoids. We and others have developed step-wise, directed differentiation protocols to recapitulate the key milestones in human airway development, generating iPSC-derived airway organoids that possess the major human airway cell types. These organoids have already shown feasibility for genetic disease modeling. They have great future potential for modeling a wider spectrum of lung diseases, interrogating disease mechanisms, predicting personalized drug responses, studying developmental lung biology, and ultimately may serve as candidates for future cell-based therapies for lung regeneration and repair. Herein we detail a step-by-step laboratory protocol to generate human airway organoids.

Nascent Lung Organoids Reveal Epithelium- and Bone Morphogenetic Protein-mediated Suppression of Fibroblast Activation

Reciprocal epithelial-mesenchymal interactions are pivotal in lung development, homeostasis, injury, and repair. Organoids have been used to investigate such interactions, but with a major focus on epithelial responses to mesenchyme and less attention to epithelial effects on mesenchyme. In the present study, we used nascent organoids composed of human and mouse lung epithelial and mesenchymal cells to demonstrate that healthy lung epithelium dramatically represses transcriptional, contractile, and matrix synthetic functions of lung fibroblasts. Repression of fibroblast activation requires signaling via the bone morphogenetic protein (BMP) pathway. BMP signaling is diminished after epithelial injury in vitro and in vivo, and exogenous BMP4 restores fibroblast repression in injured organoids. In contrast, inhibition of BMP signaling in healthy organoids is sufficient to derepress fibroblast matrix synthetic function. Our results reveal potent repression of fibroblast activation by healthy lung epithelium and a novel mechanism by which epithelial loss or injury is intrinsically coupled to mesenchymal activation via loss of repressive BMP signaling.

Targeting miR-34a/Pdgfra interactions partially corrects alveologenesis in experimental bronchopulmonary dysplasia

Bronchopulmonary dysplasia (BPD) is a common complication of preterm birth characterized by arrested lung alveolarization, which generates lungs that are incompetent for effective gas exchange. We report here deregulated expression of miR‐34a in a hyperoxia‐based mouse model of BPD, where miR‐34a expression was markedly increased in platelet‐derived growth factor receptor (PDGFR)α‐expressing myofibroblasts, a cell type critical for proper lung alveolarization. Global deletion of miR‐34a; and inducible, conditional deletion of miR‐34a in PDGFRα⁺ cells afforded partial protection to the developing lung against hyperoxia‐induced perturbations to lung architecture. Pdgfra mRNA was identified as the relevant miR‐34a target, and using a target site blocker in vivo, the miR‐34a/Pdgfra interaction was validated as a causal actor in arrested lung development. An antimiR directed against miR‐34a partially restored PDGFRα⁺ myofibroblast abundance and improved lung alveolarization in newborn mice in an experimental BPD model. We present here the first identification of a pathology‐relevant microRNA/mRNA target interaction in aberrant lung alveolarization and highlight the translational potential of targeting the miR‐34a/Pdgfra interaction to manage arrested lung development associated with preterm birth.

Smooth Muscle Differentiation Is Essential for Airway Size, Tracheal Cartilage Segmentation, but Dispensable for Epithelial Branching

Airway smooth muscle is best known for its role as an airway constrictor in diseases such as asthma. However, its function in lung development is debated. A prevalent model, supported by in vitro data, posits that airway smooth muscle promotes lung branching through peristalsis and pushing intraluminal fluid to branching tips. Here, we test this model in vivo by inactivating Myocardin, which prevented airway smooth muscle differentiation. We found that Myocardin mutants show normal branching, despite the absence of peristalsis. In contrast, tracheal cartilage, vasculature, and neural innervation patterns were all disrupted. Furthermore, airway diameter is reduced in the mutant, counter to the expectation that the absence of smooth muscle constriction would lead to a more relaxed and thereby wider airway. These findings together demonstrate that during development, while airway smooth muscle is dispensable for epithelial branching, it is integral for building the tracheal architecture and promoting airway growth.

Stromal Hedgehog pathway activation by IHH suppresses lung adenocarcinoma growth and metastasis by limiting reactive oxygen species

Activation of the Hedgehog (Hh) signaling pathway by mutations within its components drives the growth of several cancers. However, the role of Hh pathway activation in lung cancers has been controversial. Here, we demonstrate that the canonical Hh signaling pathway is activated in lung stroma by Hh ligands secreted from transformed lung epithelia. Genetic deletion of Shh, the primary Hh ligand expressed in the lung, in KrasG12D/+;Trp53fl/fl autochthonous murine lung adenocarcinoma had no effect on survival. Early abrogation of the pathway by an anti-SHH/IHH antibody 5E1 led to significantly worse survival with increased tumor and metastatic burden. Loss of IHH, another Hh ligand, by in vivo CRISPR led to more aggressive tumor growth suggesting that IHH, rather than SHH, activates the pathway in stroma to drive its tumor suppressive effects-a novel role for IHH in the lung. Tumors from mice treated with 5E1 had decreased blood vessel density and increased DNA damage suggestive of reactive oxygen species (ROS) activity. Treatment of KrasG12D/+;Trp53fl/fl mice with 5E1 and N-acetylcysteine, as a ROS scavenger, decreased tumor DNA damage, inhibited tumor growth and prolonged mouse survival. Thus, IHH induces stromal activation of the canonical Hh signaling pathway to suppress tumor growth and metastases, in part, by limiting ROS activity.

Molecular, cellular, and bioengineering approaches to stimulate lung regeneration after injury

The lung is susceptible to damage from a variety of sources throughout development and in adulthood. As a result, the lung has great capacities for repair and regeneration, directed by precisely controlled sequences of molecular and signaling pathways. Impairments or alterations in these signaling events can have deleterious effects on lung structure and function, ultimately leading to chronic lung disorders. When lung injury is too severe for the normal pathways to repair, or if those pathways do not function properly, lung regenerative medicine is needed to restore adequate structure and function. Great progress has been made in recent years in the number of regenerative techniques and their efficacy. This review will address recent progress in lung regenerative medicine focusing on pharmacotherapy including the expanding role of nanotechnology, stem cell-based therapies, and bioengineering techniques. The use of these techniques individually and collectively has the potential to significantly improve morbidity and mortality associated with congenital and acquired lung disorders.

SMAD Signaling Restricts Mucous Cell Differentiation in Human Airway Epithelium

Mucin-secreting goblet cell metaplasia and hyperplasia (GCMH) is a common pathological phenotype in many human respiratory diseases, including asthma, chronic obstructive pulmonary disease, cystic fibrosis, primary ciliary dyskinesia, and infections. A better understanding of how goblet cell quantities or proportions in the airway epithelium are regulated may provide novel therapeutic targets to mitigate GCMH in these devastating diseases. We identify canonical SMAD signaling as the principal pathway restricting goblet cell differentiation in human airway epithelium. Differentiated goblet cells express low levels of phosphorylated SMAD. Accordingly, inhibition of SMAD signaling markedly amplifies GCMH induced by mucous mediators. In contrast, SMAD signaling activation impedes goblet cell generation and accelerates the resolution of preexisting GCMH. SMAD signaling inhibition can override the suppressive effects imposed by a GABAergic receptor inhibitor, suggesting the GABAergic pathway likely operates through inhibition of SMAD signaling in regulating mucous differentiation. Collectively, our data demonstrate that SMAD signaling plays a determining role in mucous cell differentiation, and thus raise the possibility that dysregulation of this pathway contributes to respiratory pathophysiology during airway inflammation and pulmonary diseases. In addition, our study also highlights the potential for SMAD modulation as a therapeutic target in mitigating GCMH.

Tenascin-C inactivation impacts lung structure and function beyond lung development

Tenascin-C (TNC) is an extracellular matrix protein expressed at high levels during lung organogenesis. Later, TNC is only transiently de novo expressed to orchestrate tissue repair in pathological situations. We previously showed that TNC inactivation affects lung development and thus evaluated here the implications on lung function in newborn/adult mice. Respiratory function parameters were measured in anesthetized and mechanically ventilated wild-type (WT) and TNC-deficient mice at 5 (P5) and 90 (P90) days of age under basal conditions, as well as following high tidal volume (HTV) ventilation. At P5, TNC-deficient mice showed an increased static compliance (Cst) and inspiratory capacity (IC) relative to WT at baseline and throughout HTV. At P90, however, Cst and IC were only elevated at baseline. Control non-ventilated newborn and adult TNC-deficient mice showed similar lung morphology, but less alpha smooth muscle actin (α-SMA) around small airways. SMA + cells were decreased by 50% in adult TNC-deficient lungs and collagen layer thickened around small airways. Increased surfactant protein C (SP-C) and altered TGFβ and TLR4 signaling pathways were also detected. Thus, TNC inactivation-related defects during organogenesis led to persisting functional impairment in adulthood. This might be of interest in the context of pulmonary diseases with thickened airway smooth muscle layer or ventilation heterogeneity, like asthma and COPD.

Reduced Prenatal Pulmonary Lymphatic Function Is Observed in Clp1 K/K Embryos With Impaired Motor Functions Including Fetal Breathing Movements in Preparation of the Developing Lung for Inflation at Birth

Embryonic lungs must be inflated immediately after birth to establish respiration. In addition to pulmonary surfactant, recently, we have revealed lymphatic function as a previously unknown regulator of prenatal lung compliance that prepares the embryonic lung for inflation at birth. It is well-documented that the late gestation embryo performs episodic breathing-like movements called as fetal breathing movements (FBMs), but the physiological importance of these events is not clear. Here we aimed to study the physiological role of FBMs in preparation for air inflation at birth. Clp1^K/K late gestation embryos develop a progressive loss of spinal motor neurons associated with axonal degeneration and denervation of neuromuscular junctions serving as an ideal genetic model to test the possible role of FBMs. We demonstrated that Clp1^K/K newborns show impaired motor function resulting in fatal respiratory failure after birth. Next, we showed that the alveolar septa are thicker, and the alveolar area is reduced in Clp1^K/K late gestation embryos, while the expression of molecular markers of lung development are not affected. Importantly, pulmonary lymphatic vessels are dilated and the prenatal pulmonary lymphatic function is reduced in Clp1^K/K late gestation embryos. Our results have revealed that Clp1^K/K mice show impaired motor functions including FBMs, and late gestation Clp1^K/K embryos display reduced prenatal lymphatic function and impaired lung expansion represented as thickened alveolar septa and reduced alveolar area in preparation of the developing lung for inflation at birth. These findings suggest a possible mechanism that FBMs, similarly to breathing movements after birth, stimulate prenatal lymphatic function in pulmonary collecting lymphatics lacking smooth muscle coverage to prepare the developing lung for inflation and gas exchange at birth. Moreover, these results raise the possibility that stimulating FBMs during late gestation might be an effective way to reduce the risk of the development of neonatal respiratory failure.

FGF9 and FGF10 activate distinct signaling pathways to direct lung epithelial specification and branching

Fibroblast growth factors (FGFs) 9 and 10 are essential during the pseudoglandular stage of lung development. Mesothelium-produced FGF9 is principally responsible for mesenchymal growth, whereas epithelium-produced FGF9 and mesenchyme-produced FGF10 guide lung epithelial development, and loss of either of these ligands affects epithelial branching. Because FGF9 and FGF10 activate distinct FGF receptors (FGFRs), we hypothesized that they would control distinct developmental processes. Here, we found that FGF9 signaled through epithelial FGFR3 to directly promote distal epithelial fate specification and inhibit epithelial differentiation. By contrast, FGF10 signaled through epithelial FGFR2b to promote epithelial proliferation and differentiation. Furthermore, FGF9-FGFR3 signaling functionally opposed FGF10-FGFR2b signaling, and FGFR3 preferentially used downstream phosphoinositide 3-kinase (PI3K) pathways, whereas FGFR2b relied on downstream mitogen-activated protein kinase (MAPK) pathways. These data demonstrate that, within lung epithelial cells, different FGFRs function independently; they bind receptor-specific ligands and direct distinct developmental functions through the activation of distinct downstream signaling pathways.

Human lung organoids develop into adult airway-like structures directed by physico-chemical biomaterial properties

Tissues derived from human pluripotent stem cells (hPSCs) often represent early stages of fetal development, but mature at the molecular and structural level when transplanted into immunocompromised mice. hPSC-derived lung organoids (HLOs) transplantation has been further enhanced with biomaterial scaffolds, where HLOs had improved tissue structure and cellular differentiation. Here, our goal was to define the physico-chemical biomaterial properties that maximally enhanced transplant efficiency, including features such as the polymer type, degradation, and pore interconnectivity of the scaffolds. We found that transplantation of HLOs on microporous scaffolds formed from poly (ethylene glycol) (PEG) hydrogel scaffolds inhibit growth and maturation, and the transplanted HLOs possessed mostly immature lung progenitors. On the other hand, HLOs transplanted on poly (lactide-co-glycolide) (PLG) scaffolds or polycaprolactone (PCL) led to tube-like structures that resembled both the structure and cellular diversity of an adult airway. Our data suggests that scaffold pore interconnectivity and polymer degradation contributed to the maturation, and we found that the size of the airway structures and the total size of the transplanted tissue was influenced by the material degradation rate. Collectively, these biomaterial platforms provide a set of tools to promote maturation of the tissues and to control the size and structure of the organoids.

Cyp26b1 is an essential regulator of distal airway epithelial differentiation during lung development

Proper organ development depends on coordinated communication between multiple cell types. Retinoic acid (RA) is an autocrine and paracrine signaling molecule essential for the development of most organs, including the lung. Despite extensive work detailing effects of RA deficiency in early lung morphogenesis, little is known about how RA regulates late gestational lung maturation. Here, we investigate the role of the RA catabolizing protein Cyp26b1 in the lung. Cyp26b1 is highly enriched in lung endothelial cells (ECs) throughout development. We find that loss of Cyp26b1 leads to reduction of alveolar type 1 cells, failure of alveolar inflation and early postnatal lethality in mouse. Furthermore, we observe expansion of distal epithelial progenitors, but no appreciable changes in proximal airways, ECs or stromal populations. Exogenous administration of RA during late gestation partially mimics these defects; however, transcriptional analyses comparing Cyp26b1-/- with RA-treated lungs reveal overlapping, but distinct, responses. These data suggest that defects observed in Cyp26b1-/- lungs are caused by both RA-dependent and RA-independent mechanisms. This work reports crucial cellular crosstalk during lung development involving Cyp26b1-expressing endothelium and identifies a novel RA modulator in lung development.

Epithelial Vegfa Specifies a Distinct Endothelial Population in the Mouse Lung

The lung microvasculature is essential for gas exchange and commonly considered homogeneous. We show that VEGFA from the epithelium is required for a distinct endothelial cell (EC) population in the mouse lung. Vegfa is predominantly expressed by alveolar type 1 (AT1) cells and locally required to specify a subset of ECs. Single-cell RNA sequencing (scRNA-seq) reveals that ∼15% of lung ECs are transcriptionally distinct-marked by Carbonic anhydrase 4 (Car4)-and arise from bulk ECs, as suggested by trajectory analysis. Car4 ECs have extensive cellular projections and are separated from AT1 cells by a limited basement membrane without intervening pericytes. Car4 ECs are specifically lost upon epithelial Vegfa deletion; without Car4 ECs, the alveolar space is aberrantly enlarged despite the normal appearance of myofibroblasts. Lung Car4 ECs and retina tip ECs have common and distinct features. These findings support a signaling role of AT1 cells and shed light on alveologenesis.

Regenerative lineages and immune-mediated pruning in lung cancer metastasis

Developmental processes underlying normal tissue regeneration have been implicated in cancer, but the degree of their enactment during tumor progression and under the selective pressures of immune surveillance, remain unknown. Here, we show that human primary lung adenocarcinomas are characterized by the emergence of regenerative cell types typically seen in response to lung injury, and by striking infidelity amongst transcription factors specifying most alveolar and bronchial epithelial lineages. In contrast, metastases are enriched for key endoderm and lung-specifying transcription factors, SOX2 and SOX9, and recapitulate more primitive transcriptional programs spanning stem-like to regenerative pulmonary epithelial progenitor states. This developmental continuum mirrors the progressive stages of spontaneous outbreak from metastatic dormancy in a mouse model and exhibits SOX9-dependent resistance to Natural Killer (NK) cells. Loss of developmental stage-specific constraint in macrometastases triggered by NK cell depletion suggests a dynamic interplay between developmental plasticity and immune-mediated pruning during metastasis.

Congenital cystic adenomatoid malformations of the lung: an epithelial transcriptomic approach

Background

The pathophysiology of congenital cystic adenomatoid malformations (CCAM) of the lung remains poorly understood.

Aim

This study aimed to identify more precisely the molecular mechanisms limited to a compartment of lung tissue, through a transcriptomic analysis of the epithelium of macrocystic forms.

Methods

Tissue fragments displaying CCAM were obtained during planned surgical resections. Epithelial mRNA was obtained from cystic and normal areas after laser capture microdissection (LCM). Transcriptomic analyses were performed and the results were confirmed by RT-PCR and immunohistochemistry in independent samples.

Results

After controlling for RNA quality, we analysed the transcriptomes of six cystic areas and five control areas. In total, 393 transcripts were differentially expressed in the epithelium, between CCAM and control areas. The most highly redundant genes involved in biological functions and signalling pathways differentially expressed between CCAM and control epithelium included TGFB2, TGFBR1, and MAP 2 K1. These genes were considered particularly relevant as they have been implicated in branching morphogenesis. RT-qPCR analysis confirmed in independent samples that TGFBR1 was more strongly expressed in CCAM than in control tissues (p < 0.03). Immunohistochemistry analysis showed TGFBR1 (p = 0.0007) and TGFB2 (p < 0.02) levels to be significantly higher in the epithelium of CCAM than in that of control tissues.

Conclusions

This compartmentalised transcriptomic analysis of the epithelium of macrocystic lung malformations identified a dysregulation of TGFB signalling at the mRNA and protein levels, suggesting a possible role of this pathway in CCAM pathogenesis.

Trial registration

ClinicalTrials.gov Identifier: NCT01732185.

Retinoic Acid: A Key Regulator of Lung Development

Retinoic acid (RA) is a key molecular player in embryogenesis and adult tissue homeostasis. In embryo development, RA plays a crucial role in the formation of different organ systems, namely, the respiratory system. During lung development, there is a spatiotemporal regulation of RA levels that assures the formation of a fully functional organ. RA signaling influences lung specification, branching morphogenesis, and alveolarization by regulating the expression of particular target genes. Moreover, cooperation with other developmental pathways is essential to shape lung organogenesis. This review focuses on the events regulated by retinoic acid during lung developmental phases and pulmonary vascular development; also, it aims to provide a snapshot of RA interplay with other well-known regulators of lung development.

14-3-3β Is necessary in the regulation of polarization and directional migration of alveolar myofibroblasts by lipopolysaccharide

Aims:Bronchopulmonary dysplasia (BPD) is characterized by alveolarization arrest. During alveolarization, alveolar myofibroblasts are thought to migrate into the septal tips and elongate secondary septa. Lipopolysaccharide (LPS) exposure has been reported to disrupt directional migration and final location of alveolar myofibroblasts in a rat model of BPD induced by intra-amniotic injection of LPS. However, molecular mechanisms that control directional migration of alveolar myofibroblasts have not so far been investigated clearly. Materials and Methods: We assessed the polarization of myofibroblast using scrape wounding assays combined with Golgi tracking. Transwell migration assay was used to detect the directional migration of myofibroblasts. Pull-down assays were performed to isolate the active GTP-bound form using the RhoA activation assay kits. Western blotting analysis was performed to evaluate the changes in protein expression. Functional analysis was performed via siRNA interference. Results: Here, we showed that LPS might affect the directional migration of myofibroblasts by disturbing the polarization of myofibroblasts. In addition, as a main member of RhoGTPases family which plays a vital role in establishing and maintaining cell polarity, RhoA activity was significantly upregulated in myofibroblasts treated with LPS, while activity of epidermal growth factor receptor (EGFR) was upregulated and overexpression of its ligand, TGF-α, in myofibroblasts by LPS treatment. AG1478, an EGFR inhibitor, could abrogate the upregulated RhoA activity of myofibroblasts by LPS and rhTGF-α. Moreover, if we knock down 14-3-3β, LPS and rhTGF-α could not activate RhoA and disturb myofibroblasts polarization. Conclusions: Taken together, our findings suggest that LPS exposure may increase RhoA activity of myofibroblasts by TGF-α/EGFR/14-3-3β signaling pathway, and then disturb myofibroblasts polarization and directional migration.

Duplex kidney formation: developmental mechanisms and genetic predisposition

Congenital abnormalities of the kidney and urinary tract (CAKUT) are a highly diverse group of diseases that together belong to the most common abnormalities detected in the new-born child. Consistent with this diversity, CAKUT are caused by mutations in a large number of genes and present a wide spectrum of phenotypes. In this review, we will focus on duplex kidneys, a relatively frequent form of CAKUT that is often asymptomatic but predisposes to vesicoureteral reflux and hydronephrosis. We will summarise the molecular programs responsible for ureter induction, review the genes that have been identified as risk factors in duplex kidney formation and discuss molecular and cellular mechanisms that may lead to this malformation.

Effects of Exogenous Melatonin on MAM Induced Lung Injury and Lung Development in Mice Offspring

BACKGROUND

Melatonin as an antioxidant agent can have an effective role in lung development. In this study, the effect of melatonin administration on lung injury in the neonate mice was assessed.

MATERIALS AND METHODS

Lung injury was induced by two injections of 15 mg/kg methylazoxymethanol (MAM) on gestational day 15 (E15). Pregnant BALB/c mice were randomly divided into five groups: Control (CO), Melatonin (MEL), Luzindole (Luz), MAM, and MAM+MEL. Melatonin and luzindole were intra-peritoneally injected at a dose of 10 mg/kg (from E15 until delivery). Histopathological changes including: hemorrhage, neutrophils infiltration and fibrosis in the neonate lung were studied by hematoxylin and eosin (H&E) and Masson's Trichrome staining. Alveolarization and alveolar wall thickness were measured.

RESULTS

In histological examination, hemorrhage, neutrophils infiltration and fibrosis were seen in the MAM and Luz groups; however, these injuries were attenuated in the MAM plus melatonin group. Significant reduction of alveolarization was recorded in the MAM and Luz groups compared to the control group, while the alveolar wall thickness was significantly increased in these groups compared to control group.

CONCLUSION

Administration of exogenous melatonin in pregnant mice could have a protective effect on the pulmonary development of neonates and could decrease lung injury in neonate mice.

Current strategies and opportunities to manufacture cells for modeling human lungs

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

TBX2-positive cells represent a multi-potent mesenchymal progenitor pool in the developing lung

Background

In the embryonic mammalian lung, mesenchymal cells act both as a signaling center for epithelial proliferation, differentiation and morphogenesis as well as a source for a multitude of differentiated cell types that support the structure of the developing and mature organ. Whether the embryonic pulmonary mesenchyme is a homogenous precursor pool and how it diversifies into different cell lineages is poorly understood. We have previously shown that the T-box transcription factor gene Tbx2 is expressed in the pulmonary mesenchyme of the developing murine lung and is required therein to maintain branching morphogenesis.

Methods

We determined Tbx2/TBX2 expression in the developing murine lung by in situ hybridization and immunofluorescence analyses. We used a genetic lineage tracing approach with a Cre line under the control of endogenous Tbx2 control elements (Tbx2^cre), and the R26^mTmG reporter line to trace TBX2-positive cells in the murine lung. We determined the fate of the TBX2 lineage by co-immunofluorescence analysis of the GFP reporter and differentiation markers in normal murine lungs and in lungs lacking or overexpressing TBX2 in the pulmonary mesenchyme.

Results

We show that TBX2 is strongly expressed in mesenchymal progenitors in the developing murine lung. In differentiated smooth muscle cells and in fibroblasts, expression of TBX2 is still widespread but strongly reduced. In mesothelial and endothelial cells expression is more variable and scattered. All fetal smooth muscle cells, endothelial cells and fibroblasts derive from TBX2⁺ progenitors, whereas half of the mesothelial cells have a different descent. The fate of TBX2-expressing cells is not changed in Tbx2-deficient and in TBX2-constitutively overexpressing mice but the distribution and abundance of endothelial and smooth muscle cells is changed in the overexpression condition.

Conclusion

The fate of pulmonary mesenchymal progenitors is largely independent of TBX2. Nevertheless, a successive and precisely timed downregulation of TBX2 is necessary to allow proper differentiation and functionality of bronchial smooth muscle cells and to limit endothelial differentiation. Our work suggests expression of TBX2 in an early pulmonary mesenchymal progenitor and supports a role of TBX2 in maintaining the precursor state of these cells.

Dominant-negative antagonists of the Ras-ERK pathway: DA-Raf and its related proteins generated by alternative splicing of Raf

The Ras-ERK pathway regulates a variety of cellular and physiological responses, including cell proliferation, differentiation, morphogenesis during animal development, and homeostasis in adults. Deregulated activation of this pathway leads to cellular transformation and tumorigenesis as well as RASopathies. Several negative regulators of this pathway have been documented. Each of these proteins acts at particular points of the pathway, and they exert specific cellular and physiological functions. Among them, DA-Raf1 (DA-Raf), which is a splicing isoform of A-Raf and contains the Ras-binding domain but lacks the kinase domain, antagonizes the Ras-ERK pathway in a dominant-negative manner. DA-Raf induces apoptosis, skeletal myocyte differentiation, lung alveolarization, and fulfills tumor suppressor functions by interfering with the Ras-ERK pathway. After the findings of DA-Raf, several kinase-domain-truncated splicing variants of Raf proteins have also been reported. The family of these truncated proteins represents the concept that alternative splicing can generate antagonistic proteins to their full-length counterparts.

Mark1 regulates distal airspace expansion through type I pneumocyte flattening in lung development

During the later stages of lung development, two types of pneumocytes, cuboidal type II (AECII) and flattened type I (AECI) alveolar epithelial cells, form distal lung saccules. Here, we highlight how fibroblasts expressing MAP-microtubule affinity regulating kinase 1 (Mark1) are required for the terminal stages of pulmonary development, called lung sacculation. In Mark1-knockout (KO) mice, distal sacculation and AECI flattening are significantly impaired. Fetal epithelial cells generate alveolar organoids and differentiate into pneumocytes when co-cultured with fibroblasts. However, the size of organoids decreased and AECI flattening was impaired in the presence of Mark1 KO fibroblasts. In Mark1 KO fibroblasts themselves, cilia formation and the Hedgehog pathway were suppressed, resulting in the loss of type I collagen expression. The addition of type I collagen restored AECI flattening in organoids co-cultured with Mark1 KO fibroblasts and rescued the decreased size of organoids. Mathematical modeling of distal lung sacculation supports the view that AECI flattening is necessary for the proper formation of saccule-like structures. These results suggest that Mark1-mediated fibroblast activation induces AECI flattening and thereby regulates distal lung sacculation.

Isl1 Regulation of Nkx2.1 in the Early Foregut Epithelium Is Required for Trachea-Esophageal Separation and Lung Lobation

The esophagus and trachea arise from the dorsal and ventral aspects of the anterior foregut, respectively. Abnormal trachea-esophageal separation leads to the common birth defect esophageal atresia with or without trachea-esophageal fistula (EA/TEF). Yet the underlying cellular mechanisms remain unknown. Here, we combine Xenopus and mouse genetic models to identify that the transcription factor Isl1 orchestrates trachea-esophageal separation through modulating a specific epithelial progenitor cell population (midline epithelial cells [MECs], Isl1+ Nkx2.1+ Sox2+) located at the dorsal-ventral boundary of the foregut. Lineage tracing experiments show that MECs contribute to both tracheal and esophageal epithelium, and Isl1 is required for Nkx2.1 transcription in MECs. Deletion of the chromosomal region spanning the ISL1 gene has been found in patients with abnormal trachea-esophageal separation. Our studies thus provide definitive evidence that ISL1 is a critical player in the process of foregut morphogenesis, acting in a small progenitor population of boundary cells.

Triple-cell lineage tracing by a dual reporter on a single allele

Genetic lineage tracing is widely used to study organ development and tissue regeneration. Multicolor reporters are a powerful platform for simultaneously tracking discrete cell populations. Here, combining Dre-rox and Cre-loxP systems, we generated a new dual-recombinase reporter system, called Rosa26 traffic light reporter (R26-TLR), to monitor red, green, and yellow fluorescence. Using this new reporter system with the three distinct fluorescent reporters combined on one allele, we found that the readouts of the two recombinases Cre and Dre simultaneously reflect Cre⁺Dre^-, Cre^-Dre⁺, and Cre⁺Dre⁺ cell lineages. As proof of principle, we show specific labeling in three distinct progenitor/stem cell populations, including club cells, AT2 cells, and bronchoalveolar stem cells, in Sftpc-DreER;Scgb1a1-CreER;R26-TLR mice. By using this new dual-recombinase reporter system, we simultaneously traced the cell fate of these three distinct cell populations during lung repair and regeneration, providing a more comprehensive picture of stem cell function in distal airway repair and regeneration. We propose that this new reporter system will advance developmental and regenerative research by facilitating a more sophisticated genetic approach to studying in vivo cell fate plasticity.

Smooth muscle differentiation shapes domain branches during mouse lung development

During branching morphogenesis, a simple cluster of cells proliferates and branches to generate an arborized network that facilitates fluid flow. The overall architecture of the mouse lung is established by domain branching, wherein new branches form laterally off the side of an existing branch. The airway epithelium develops concomitantly with a layer of smooth muscle that is derived from the embryonic mesenchyme. Here, we examined the role of smooth muscle differentiation in shaping emerging domain branches. We found that the position and morphology of domain branches are highly stereotyped, as is the pattern of smooth muscle that differentiates around the base of each branch. Perturbing the pattern of smooth muscle differentiation genetically or pharmacologically causes abnormal domain branching. Loss of smooth muscle results in ectopic branching and decreases branch stereotypy. Increased smooth muscle suppresses branch initiation and extension. Computational modeling revealed that epithelial proliferation is insufficient to generate domain branches and that smooth muscle wrapping is required to shape the epithelium into a branch. Our work sheds light on the physical mechanisms of branching morphogenesis in the mouse lung.

Inositol 1,4,5-trisphosphate receptor 2 as a novel marker of vasculature to delineate processes of cardiopulmonary development

Congenital heart diseases (CHDs) involving the outflow tract (OFT), such as persistent truncus arteriosus (PTA), lead to mortality and morbidity with implications not only in the heart, but also in the pulmonary vasculature. The mechanisms of pulmonary artery (PA) development and the etiologies underlying PA disorders associated with CHD remain poorly understood partly because of a specific marker for PA development is nonexistent. The three subtypes of inositol 1,4,5-trisphosphate receptors (IP₃R1, 2, and 3) are intracellular Ca²⁺ channels that are essential for many tissues and organs. We discovered that IP₃R2 was expressed in the vasculature and heart during development using transgenic mice, in which a LacZ marker gene was knocked into the IP₃R2 locus. Whole-mount and section LacZ staining showed that IP₃R2-LacZ-positive cells were detectable exclusively in the smooth muscle cells, or tunica media, of PA, merging into αSMA-positive cells during development. Furthermore, our analyses suggested that IP₃R2-LacZ positive PA smooth muscle layers gradually elongate from the central PA to the peripheral PAs from E13.5 to E18.5, supporting the distal angiogenesis theory for the development of PA, whereas IP₃R2-LacZ was rarely expressed in smooth muscle cells in the pulmonary trunk. Crossing IP₃R-LacZ mice with mice hypomorphic for Tbx1 alleles revealed that PTA of Tbx1 mutants may result from agenesis or hypoplasia of the pulmonary trunk; thus, the left and right central to peripheral PAs connect directly to the dorsal side of the truncus arteriosus in these mutants. Additionally, we found hypercellular interstitial mesenchyme and delayed maturation of the lung endoderm in the Tbx1 mutant lungs. Our study identifies IP₃R2 as a novel marker for clear visualization of PA during development and can be utilized for studying cardiopulmonary development and disease.

Complete Tracheal Ring Deformity. A Translational Genomics Approach to Pathogenesis

Rationale: Complete tracheal ring deformity (CTRD) is a rare congenital abnormality of unknown etiology characterized by circumferentially continuous or nearly continuous cartilaginous tracheal rings, variable degrees of tracheal stenosis and/or shortening, and/or pulmonary arterial sling anomaly.Objectives: To test the hypothesis that CTRD is caused by inherited or de novo mutations in genes required for normal tracheal development.Methods: CTRD and normal tracheal tissues were examined microscopically to define the tracheal abnormalities present in CTRD. Whole-exome sequencing was performed in children with CTRD and their biological parents ("trio analysis") to identify gene variants in patients with CTRD. Mutations were confirmed by Sanger sequencing, and their potential impact on structure and/or function of encoded proteins was examined using human gene mutation databases. Relevance was further examined by comparison with the effects of targeted deletion of murine homologs important to tracheal development in mice.Measurements and Main Results: The trachealis muscle was absent in all of five patients with CTRD. Exome analysis identified six de novo, three recessive, and multiple compound-heterozygous or rare hemizygous variants in children with CTRD. De novo variants were identified in SHH (Sonic Hedgehog), and inherited variants were identified in HSPG2 (perlecan), ROR2 (receptor tyrosine kinase-like orphan receptor 2), and WLS (Wntless), genes involved in morphogenetic pathways known to mediate tracheoesophageal development in mice.Conclusions: The results of the present study demonstrate that absence of the trachealis muscle is associated with CTRD. Variants predicted to cause disease were identified in genes encoding Hedgehog and Wnt signaling pathway molecules, which are critical to cartilage formation and normal upper airway development in mice.

Concomitant deletion of HRAS and NRAS leads to pulmonary immaturity, respiratory failure and neonatal death in mice

We reported previously that adult (HRAS-/-; NRAS-/-) double knockout (DKO) mice showed no obvious external phenotype although lower-than-expected numbers of weaned DKO animals were consistently tallied after crossing NRAS-KO and HRAS-KO mice kept on mixed genetic backgrounds. Using mouse strains kept on pure C57Bl/6 background, here we performed an extensive analysis of the offspring from crosses between HRAS-KO and NRAS-KO mice and uncovered the occurrence of very high rates of perinatal mortality of the resulting DKO littermates due to respiratory failure during the first postnatal 24-48 h. The lungs of newborn DKO mice showed normal organ structure and branching but displayed marked defects of maturation including much-reduced alveolar space with thick separating septa and significant alterations of differentiation of alveolar (AT1, AT2 pneumocytes) and bronchiolar (ciliated, Clara cells) cell lineages. We also observed the retention of significantly increased numbers of undifferentiated progenitor precursor cells in distal lung epithelia and the presence of substantial accumulations of periodic acid-Schiff-positive (PAS+) material and ceramide in the lung airways of newborn DKO mice. Interestingly, antenatal dexamethasone treatment partially mitigated the defective lung maturation phenotypes and extended the lifespan of the DKO animals up to 6 days, but was not sufficient to abrogate lethality in these mice. RNA microarray hybridization analyses of the lungs of dexamethasone-treated and untreated mice uncovered transcriptional changes pointing to functional and metabolic alterations that may be mechanistically relevant for the defective lung phenotypes observed in DKO mice. Our data suggest that delayed alveolar differentiation, altered sphingolipid metabolism and ceramide accumulation are primary contributors to the respiratory stress and neonatal lethality shown by DKO mice and uncover specific, critical roles of HRAS and NRAS for correct lung differentiation that are essential for neonatal survival and cannot be substituted by the remaining KRAS function in this organ.

Postnatal Alveologenesis Depends on FOXF1 Signaling in c-KIT+ Endothelial Progenitor Cells

Rationale: Disruption of alveologenesis is associated with severe pediatric lung disorders, including bronchopulmonary dysplasia (BPD). Although c-KIT+ endothelial cell (EC) progenitors are abundant in embryonic and neonatal lungs, their role in alveolar septation and the therapeutic potential of these cells remain unknown.Objectives: To determine whether c-KIT+ EC progenitors stimulate alveologenesis in the neonatal lung.Methods: We used single-cell RNA sequencing of neonatal human and mouse lung tissues, immunostaining, and FACS analysis to identify transcriptional and signaling networks shared by human and mouse pulmonary c-KIT+ EC progenitors. A mouse model of perinatal hyperoxia-induced lung injury was used to identify molecular mechanisms that are critical for the survival, proliferation, and engraftment of c-KIT+ EC progenitors in the neonatal lung.Measurements and Main Results: Pulmonary c-KIT+ EC progenitors expressing PECAM-1, CD34, VE-Cadherin, FLK1, and TIE2 lacked mature arterial, venal, and lymphatic cell-surface markers. The transcriptomic signature of c-KIT+ ECs was conserved in mouse and human lungs and enriched in FOXF1-regulated transcriptional targets. Expression of FOXF1 and c-KIT was decreased in the lungs of infants with BPD. In the mouse, neonatal hyperoxia decreased the number of c-KIT+ EC progenitors. Haploinsufficiency or endothelial-specific deletion of Foxf1 in mice increased apoptosis and decreased proliferation of c-KIT+ ECs. Inactivation of either Foxf1 or c-Kit caused alveolar simplification. Adoptive transfer of c-KIT+ ECs into the neonatal circulation increased lung angiogenesis and prevented alveolar simplification in neonatal mice exposed to hyperoxia.Conclusions: Cell therapy involving c-KIT+ EC progenitors can be beneficial for the treatment of BPD.

Double knock-out of Hmga1 and Hipk2 genes causes perinatal death associated to respiratory distress and thyroid abnormalities in mice

The serine–threonine kinase homeodomain-interacting protein kinase 2 (HIPK2) modulates important cellular functions during development, acting as a signal integrator of a wide variety of stress signals, and as a regulator of transcription factors and cofactors. We have previously demonstrated that HIPK2 binds and phosphorylates High-Mobility Group A1 (HMGA1), an architectural chromatinic protein ubiquitously expressed in embryonic tissues, decreasing its binding affinity to DNA. To better define the functional role of HIPK2 and HMGA1 interaction in vivo, we generated mice in which both genes are disrupted. About 50% of these Hmga1/Hipk2 double knock-out (DKO) mice die within 12 h of life (P1) for respiratory failure. The DKO mice present an altered lung morphology, likely owing to a drastic reduction in the expression of surfactant proteins, that are required for lung development. Consistently, we report that both HMGA1 and HIPK2 proteins positively regulate the transcriptional activity of the genes encoding the surfactant proteins. Moreover, these mice display an altered expression of thyroid differentiation markers, reasonably because of a drastic reduction in the expression of the thyroid-specific transcription factors PAX8 and FOXE1, which we demonstrate here to be positively regulated by HMGA1 and HIPK2. Therefore, these data indicate a critical role of HIPK2/HMGA1 cooperation in lung and thyroid development and function, suggesting the potential involvement of their impairment in the pathogenesis of human lung and thyroid diseases.

Mouse models of preterm birth: suggested assessment and reporting guidelines

Preterm birth affects approximately 1 out of every 10 births in the United States, leading to high rates of mortality and long-term negative health consequences. To investigate the mechanisms leading to preterm birth so as to develop prevention strategies, researchers have developed numerous mouse models of preterm birth. However, the lack of standard definitions for preterm birth in mice limits our field's ability to compare models and make inferences about preterm birth in humans. In this review, we discuss numerous mouse preterm birth models, propose guidelines for experiments and reporting, and suggest markers that can be used to assess whether pups are premature or mature. We argue that adoption of these recommendations will enhance the utility of mice as models for preterm birth.

Transcriptional control of lung alveolar type 1 cell development and maintenance by NK homeobox 2-1

The extraordinarily thin alveolar type 1 (AT1) cell constitutes nearly the entire gas exchange surface and allows passive diffusion of oxygen into the blood stream. Despite such an essential role, the transcriptional network controlling AT1 cells remains unclear. Using cell-specific knockout mouse models, genomic profiling, and 3D imaging, we found that NK homeobox 2-1 (Nkx2-1) is expressed in AT1 cells and is required for the development and maintenance of AT1 cells. Without Nkx2-1, developing AT1 cells lose 3 defining features-molecular markers, expansive morphology, and cellular quiescence-leading to alveolar simplification and lethality. NKX2-1 is also cell-autonomously required for the same 3 defining features in mature AT1 cells. Intriguingly, Nkx2-1 mutant AT1 cells activate gastrointestinal (GI) genes and form dense microvilli-like structures apically. Single-cell RNA-seq supports a linear transformation of Nkx2-1 mutant AT1 cells toward a GI fate. Whole lung ChIP-seq shows NKX2-1 binding to 68% of genes that are down-regulated upon Nkx2-1 deletion, including 93% of known AT1 genes, but near-background binding to up-regulated genes. Our results place NKX2-1 at the top of the AT1 cell transcriptional hierarchy and demonstrate remarkable plasticity of an otherwise terminally differentiated cell type.

Mesenchyme-specific deletion of Tgf-β1 in the embryonic lung disrupts branching morphogenesis and induces lung hypoplasia

Proper lung development depends on the precise temporal and spatial expression of several morphogenic factors, including Fgf10, Fgf9, Shh, Bmp4, and Tgf-β. Over- or under-expression of these molecules often leads to aberrant embryonic or postnatal lung development. Herein, we deleted the Tgf-β1 gene specifically within the lung embryonic mesenchymal compartment at specific gestational stages to determine the contribution of this cytokine to lung development. Mutant embryos developed severe lung hypoplasia and died at birth due to the inability to breathe. Despite the markedly reduced lung size, proliferation and differentiation of the lung epithelium was not affected by the lack of mesenchymal expression of the Tgf-β1 gene, while apoptosis was significantly increased in the mutant lung parenchyma. Lack of mesenchymal expression of the Tgf-β1 gene was also associated with reduced lung branching morphogenesis, with accompanying inhibition of the local FGF10 signaling pathway as well as abnormal development of the vascular system. To shed light on the mechanism of lung hypoplasia, we quantified the phosphorylation of 226 proteins in the mutant E12.5 lung compared with control. We identified five proteins, Hrs, Vav2, c-Kit, the regulatory subunit of Pi3k (P85), and Fgfr1, that were over- or under-phosphorylated in the mutant lung, suggesting that they could be indispensable effectors of the TGF-β signaling program during embryonic lung development. In conclusion, we have uncovered novel roles of the mesenchyme-specific Tgf-β1 ligand in embryonic mouse lung development and generated a mouse model that may prove helpful to identify some of the key pathogenic mechanisms underlying lung hypoplasia in humans.

Characterization of an immortalized human small airway basal stem/progenitor cell line with airway region-specific differentiation capacity

Background

The pathology of chronic obstructive pulmonary disease (COPD), idiopathic pulmonary fibrosis (IPF) and most lung cancers involves the small airway epithelium (SAE), the single continuous layer of cells lining the airways ≥ 6th generations. The basal cells (BC) are the stem/progenitor cells of the SAE, responsible for the differentiation into intermediate cells and ciliated, club and mucous cells. To facilitate the study of the biology of the human SAE in health and disease, we immortalized and characterized a normal human SAE basal cell line.

Methods

Small airway basal cells were purified from brushed SAE of a healthy nonsmoker donor with a characteristic normal SAE transcriptome. The BC were immortalized by retrovirus-mediated telomerase reverse transcriptase (TERT) transduction and single cell drug selection. The resulting cell line (hSABCi-NS1.1) was characterized by RNAseq, TaqMan PCR, protein immunofluorescence, differentiation capacity on an air-liquid interface (ALI) culture, transepithelial electrical resistance (TEER), airway region-associated features and response to genetic modification with SPDEF.

Results

The hSABCi-NS1.1 single-clone-derived cell line continued to proliferate for > 200 doubling levels and > 70 passages, continuing to maintain basal cell features (TP63⁺, KRT5⁺). When cultured on ALI, hSABCi-NS1.1 cells consistently formed tight junctions and differentiated into ciliated, club (SCGB1A1⁺), mucous (MUC5AC⁺, MUC5B⁺), neuroendocrine (CHGA⁺), ionocyte (FOXI1⁺) and surfactant protein positive cells (SFTPA⁺, SFTPB⁺, SFTPD⁺), observations confirmed by RNAseq and TaqMan PCR. Annotation enrichment analysis showed that “cilium” and “immunity” were enriched in functions of the top-1500 up-regulated genes. RNAseq reads alignment corroborated expression of CD4, CD74 and MHC-II. Compared to the large airway cell line BCi-NS1.1, differentiated of hSABCi-NS1.1 cells on ALI were enriched with small airway epithelial genes, including surfactant protein genes, LTF and small airway development relevant transcription factors NKX2–1, GATA6, SOX9, HOPX, ID2 and ETV5. Lentivirus-mediated expression of SPDEF in hSABCi-NS1.1 cells induced secretory cell metaplasia, accompanied with characteristic COPD-associated SAE secretory cell changes, including up-regulation of MSMB, CEACAM5 and down-regulation of LTF.

Conclusions

The immortalized hSABCi-NS1.1 cell line has diverse differentiation capacities and retains SAE features, which will be useful for understanding the biology of SAE, the pathogenesis of SAE-related diseases, and testing new pharmacologic agents.

Electronic supplementary material

The online version of this article (10.1186/s12931-019-1140-9) contains supplementary material, which is available to authorized users.

Mesenchymal proteases and tissue fluidity remodel the extracellular matrix during airway epithelial branching in the embryonic avian lung

Reciprocal epithelial-mesenchymal signaling is essential for morphogenesis, including branching of the lung. In the mouse, mesenchymal cells differentiate into airway smooth muscle that wraps around epithelial branches, but this contractile tissue is absent from the early avian lung. Here, we have found that branching morphogenesis in the embryonic chicken lung requires extracellular matrix (ECM) remodeling driven by reciprocal interactions between the epithelium and mesenchyme. Before branching, the basement membrane wraps the airway epithelium as a spatially uniform sheath. After branch initiation, however, the basement membrane thins at branch tips; this remodeling requires mesenchymal expression of matrix metalloproteinase 2, which is necessary for branch extension but for not branch initiation. As branches extend, tenascin C (TNC) accumulates in the mesenchyme several cell diameters away from the epithelium. Despite its pattern of accumulation, TNC is expressed exclusively by epithelial cells. Branch extension coincides with deformation of adjacent mesenchymal cells, which correlates with an increase in mesenchymal fluidity at branch tips that may transport TNC away from the epithelium. These data reveal novel epithelial-mesenchymal interactions that direct ECM remodeling during airway branching morphogenesis.

Human Pluripotent Stem Cell-Derived Endoderm for Modeling Development and Clinical Applications

The liver, lung, pancreas, and digestive tract all originate from the endoderm germ layer, and these vital organs are subject to many life-threatening diseases affecting millions of patients. However, primary cells from endodermal organs are often difficult to grow in vitro. Human pluripotent stem cells thus hold great promise for generating endoderm cells and their derivatives as tools for the development of new therapeutics against a variety of global healthcare challenges. Here we describe recent advances in methods for generating endodermal cell types from human pluripotent stem cells and their use for disease modeling and cell-based therapy.

Role of KRAS in regulating normal human airway basal cell differentiation

BACKGROUND

KRAS is a GTPase that activates pathways involved in cell growth, differentiation and survival. In normal cells, KRAS-activity is tightly controlled, but with specific mutations, the KRAS protein is persistently activated, giving cells a growth advantage resulting in cancer. While a great deal of attention has been focused on the role of mutated KRAS as a common driver mutation for lung adenocarcinoma, little is known about the role of KRAS in regulating normal human airway differentiation.

METHODS

To assess the role of KRAS signaling in regulating differentiation of the human airway epithelium, primary human airway basal stem/progenitor cells (BC) from nonsmokers were cultured on air-liquid interface (ALI) cultures to mimic the airway epithelium in vitro. Modulation of KRAS signaling was achieved using siRNA-mediated knockdown of KRAS or lentivirus-mediated over-expression of wild-type KRAS or the constitutively active G12 V mutant. The impact on differentiation was quantified using TaqMan quantitative PCR, immunofluorescent and immunohistochemical staining analysis for cell type specific markers. Finally, the impact of cigarette smoke exposure on KRAS and RAS protein family activity in the airway epithelium was assessed in vitro and in vivo.

RESULTS

siRNA-mediated knockdown of KRAS decreased differentiation of BC into secretory and ciliated cells with a corresponding shift toward squamous cell differentiation. Conversely, activation of KRAS signaling via lentivirus mediated over-expression of the constitutively active G12 V KRAS mutant had the opposite effect, resulting in increased secretory and ciliated cell differentiation and decreased squamous cell differentiation. Exposure of BC to cigarette smoke extract increased KRAS and RAS protein family activation in vitro. Consistent with these observations, airway epithelium brushed from healthy smokers had elevated RAS activation compared to nonsmokers.

CONCLUSIONS

Together, these data suggest that KRAS-dependent signaling plays an important role in regulating the balance of secretory, ciliated and squamous cell differentiation of the human airway epithelium and that cigarette smoking-induced airway epithelial remodeling is mediated in part by abnormal activation of KRAS-dependent signaling mechanisms.

Heterochronic regulation of lung development via the Lin28-Let-7 pathway

The heterochronic gene Lin28 regulates diverse developmental processes. It was shown previously that global Lin28A overexpression during mouse embryogenesis results in perinatal lethality. However, the reason for this early lethality has not been elucidated. Here, we showed that Lin28A overexpression prevents normal lung development via the inhibition of the Let-7 micro RNAs, thus causing the perinatal lethality. We further found that Lin28A overexpression in lung mesenchymal cells, but not epithelial cells, is sufficient to recapitulate the lung phenotype. Moreover, we defined the specific time window wherein Lin28A expression exerts its effect. Deep characterization of the transgenic lungs suggests that the Lin28A-Let-7 pathway delays the transition from one developmental stage to another but does not completely abrogate the differentiation capacity of the lung progenitor cells. Finally, we suggested that the effect of Lin28A-Let-7 on embryonic lung development is mediated at least in part through the TGF-β1-signaling pathway. Altogether, these findings define for the first time the Lin28-Let-7 pathway as a critical heterochronic regulator of lung development.-Komarovsky Gulman, N., Armon, L., Shalit, T., Urbach, A. Heterochronic regulation of lung development via the Lin28-Let-7 pathway.

Pathogenesis and Cells of Origin of Barrett's Esophagus

In patients with Barrett's esophagus (BE), metaplastic columnar mucosa containing epithelial cells with gastric and intestinal features replaces esophageal squamous mucosa damaged by gastroesophageal reflux disease. This condition is estimated to affect 5.6% of adults in the United States, and is a major risk factor for esophageal adenocarcinoma. Despite the prevalence and importance of BE, its pathogenesis is incompletely understood and there are disagreements over the cells of origin. We review mechanisms of BE pathogenesis, including transdifferentiation and transcommitment, and discuss potential cells of origin, including basal cells of the squamous epithelium, cells of esophageal submucosal glands and their ducts, cells of the proximal stomach, and specialized populations of cells at the esophagogastric junction (residual embryonic cells and transitional basal cells). We discuss the concept of metaplasia as a wound-healing response, and how cardiac mucosa might be the precursor of the intestinal metaplasia of BE. Finally, we discuss shortcomings in current diagnostic criteria for BE that have important clinical implications.

STK11 is required for the normal program of ciliated cell differentiation in airways

The functional properties of mucosal surfaces are dependent on establishing the correct proportions of specialized epithelial cell types. Multiciliated cells (also known as ciliated cells) are evolutionarily conserved and functionally indispensable epithelial cells, as suggested by the link between ciliated cell dysfunction and chronic human disease. Ciliated cell differentiation is an ordered process that involves initial cell fate determination and multiciliogenesis. STK11, a serine/threonine kinase, has been reported to be downregulated in human diseases associated with ciliopathies and functions as a tumor suppressor. Here, we show that STK11 is a physiological factor for the normal program of ciliated cell differentiation by phosphorylating MARK3, which directly suppresses ERK1/2 mediated pRB inactivation. Loss of Stk11 in airway progenitors impairs the differentiation of ciliated cells in both embryonic and adult airways. Our study establishes that STK11/MARK3/ERK1/2 signaling cascade is a key regulator to integrate ciliated cell fate commitment and the subsequent process of multiciliogenesis.