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]

The Role of Hedgehog Signaling in Adult Lung Regeneration and Maintenance

As a secreted morphogen, Sonic Hedgehog (SHH) determines differential cell fates, behaviors, and functions by forming a gradient of Hedgehog (Hh) activation along an axis of Hh-receptive cells during development. Despite clearly delineated roles for Hh during organ morphogenesis, whether Hh continues to regulate cell fate and behavior in the same fashion in adult organs is less understood. Adult organs, particularly barrier organs interfacing with the ambient environment, are exposed to insults that require renewal of cellular populations to maintain structural integrity. Understanding key aspects of Hh’s ability to generate an organ could translate into conceptual understanding of Hh’s ability to maintain organ homeostasis and stimulate regeneration. In this review, we will summarize the current knowledge about Hh signaling in regulating adult lung regeneration and maintenance, and discuss how alteration of Hh signaling contributes to adult lung diseases.

Morphogenesis of the kidney and lung requires branch-tip directed activity of the Adamts18 metalloprotease

Adamts18 encodes a secreted metalloprotease restricted to branch-tip progenitor pools directing the morphogenesis of multiple mammalian organs. Adamts18 was targeted to explore a potential role in branching morphogenesis. In the kidney, an arborized collecting system develops through extensive branching morphogenesis of an initial epithelial outgrowth of the mesonephric duct, the ureteric bud. Adamts18 mutants displayed a weakly penetrant phenotype: duplicated ureteric outgrowths forming enlarged, bi-lobed kidneys with an increased nephron endowment. In contrast, Adamts18 mutants showed a fully penetrant lung phenotype: epithelial growth was markedly reduced and early secondary branching scaled to the reduced length of the primary airways. Furthermore, there was a pronounced delay in the appearance of differentiated cell types in both proximal and distally positions of the developing airways. Adamts18 is closely related to Adamts16. In the kidney but not the lung, broad epithelial Adamts16 expression overlaps Adamts18 in branch tips. However, compound Adamts16/18 mutants displayed a comparable low penetrance duplicated ureteric phenotype, ruling out a possible role for Adamts16 as a functional modifier of the Adamts18 kidney phenotype. Given the predicted action of secreted Adamts18 metalloprotease, and broad expression of Adamts18 in branching organ systems, these findings suggest distinct requirements for matrix modelling in the morphogenesis of epithelial networks.

Cellular crosstalk in the development and regeneration of the respiratory system

The respiratory system, including the peripheral lungs, large airways and trachea, is one of the most recently evolved adaptations to terrestrial life. To support the exchange of respiratory gases, the respiratory system is interconnected with the cardiovascular system, and this interconnective nature requires a complex interplay between a myriad of cell types. Until recently, this complexity has hampered our understanding of how the respiratory system develops and responds to postnatal injury to maintain homeostasis. The advent of new single-cell sequencing technologies, developments in cellular and tissue imaging and advances in cell lineage tracing have begun to fill this gap. The view that emerges from these studies is that cellular and functional heterogeneity of the respiratory system is even greater than expected and also highly adaptive. In this Review, we explore the cellular crosstalk that coordinates the development and regeneration of the respiratory system. We discuss both the classic cell and developmental biology studies and recent single-cell analysis to provide an integrated understanding of the cellular niches that control how the respiratory system develops, interacts with the external environment and responds to injury.

The Other Side of the Fascia: The Smooth Muscle Part 1

According to current scientific standards, the fascia is a connective tissue derived from two separate germ layers, the mesoderm (trunk and limbs, part of the neck) and the ectoderm (cervical tract and skull). The fascia has the property of maintaining the shape and function of its anatomical district, but it also can adapt to mechanical-metabolic stimuli. Smooth muscle and non-voluntary striated musculature originated from the mesoderm have never been properly considered as a type of fascia. They are some of the viscera present in the mediastinum, in the abdomen and in the pelvic floor. This text represents the first article in the international scientific field that discusses the inclusion of some viscera in the context of what is considered fascia, thanks to the efforts of our committee for the definition and nomenclature of the fascial tissue of the Foundation of Osteopathic Research and Clinical Endorsement (FORCE).

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

BACKGROUND

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

OBJECTIVE

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

STUDY DESIGN

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

RESULTS

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

CONCLUSION

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

Repairing the lungs one breath at a time: How dedicated or facultative are you?

In this review, Leach and Morrisey focus on lung regeneration to explore the importance of facultative regeneration controlled by functional and differentiated cell lineages as well as how they are positioned and regulated by distinct tissue niches.

Tissue regeneration involves various types of cellular and molecular responses depending on the type of tissue and the injury or disease that is inflicted. While many tissues contain dedicated stem/progenitor cell lineages, many others contain cells that, during homeostasis, are considered physiologically functional and fully differentiated but, after injury or in disease states, exhibit stem/progenitor-like activity. Recent identification of subsets of defined cell types as facultative stem/progenitor cells has led to a re-examination of how certain tissues respond to injury to mount a regenerative response. In this review, we focus on lung regeneration to explore the importance of facultative regeneration controlled by functional and differentiated cell lineages as well as how they are positioned and regulated by distinct tissue niches. Additionally, we discuss the molecular signals to which cells respond in their differentiated state during homeostasis and those signals that promote effective regeneration of damaged or lost cells and structures after injury.

Lung tissue engineering: An update

Pulmonary disease is a worldwide public health problem that reduces the life quality and increases the need for hospital admissions as well as the risk of premature death. A common problem is the significant shortage of lungs for transplantation as well as patients must also take immunosuppressive drugs for the rest of their lives to keep the immune system from attacking transplanted organs. Recently, a new strategy has been proposed in the cellular engineering of lung tissue as decellularization approaches. The main components for the lung tissue engineering are: (1) A suitable biological or synthetic three-dimensional (3D) scaffold, (2) source of stem cells or cells, (3) growth factors required to drive cell differentiation and proliferation, and (4) bioreactor, a system that supports a 3D composite biologically active. Although a number of synthetic as well biological 3D scaffold suggested for lung tissue engineering, the current favorite scaffold is decellularized extracellular matrix scaffold. There are a large number of commercial and academic made bioreactors, the favor has been, the one easy to sterilize, physiologically stimuli and support active cell growth as well as clinically translational. The challenges would be to develop a functional lung will depend on the endothelialized microvascular network and alveolar-capillary surface area to exchange gas. A critical review of the each components of lung tissue engineering is presented, following an appraisal of the literature in the last 5 years. This is a multibillion dollar industry and consider unmet clinical need.

Alteration of cystic airway mesenchyme in congenital pulmonary airway malformation

Congenital pulmonary airway malformation (CPAM) is the most common congenital lesion detected in the neonatal lung, which may lead to respiratory distress, infection, and pneumothorax. CPAM is thought to result from abnormal branching morphogenesis during fetal lung development, arising from different locations within the developing respiratory tract. However, the pathogenic mechanisms are unknown, and previous studies have focused on abnormalities in airway epithelial cells. We have analyzed 13 excised lung specimens from infants (age < 1 year) with a confirmed diagnosis of type 2 CPAM, which is supposed to be derived from abnormal growth of intrapulmonary distal airways. By examining the mesenchymal components including smooth muscle cells, laminin, and elastin in airway and cystic walls using immunofluorescence staining, we found that the thickness and area of the smooth muscle layer underlining the airway cysts in these CPAM tissue sections were significantly decreased compared with those in bronchiolar walls of normal controls. Extracellular elastin fibers were also visually reduced or absent in airway cystic walls. In particular, a layer of elastin fibers seen in normal lung between airway epithelia and underlying smooth muscle cells was missing in type 2 CPAM samples. Thus, our data demonstrate for the first time that airway cystic lesions in type 2 CPAM occur not only in airway epithelial cells, but also in adjacent mesenchymal tissues, including airway smooth muscle cells and their extracellular protein products. This provides a new direction to study the molecular and cellular mechanisms of CPAM pathogenesis in human.

Live imaging of alveologenesis in precision-cut lung slices reveals dynamic epithelial cell behaviour

Damage to alveoli, the gas-exchanging region of the lungs, is a component of many chronic and acute lung diseases. In addition, insufficient generation of alveoli results in bronchopulmonary dysplasia, a disease of prematurity. Therefore visualising the process of alveolar development (alveologenesis) is critical for our understanding of lung homeostasis and for the development of treatments to repair and regenerate lung tissue. Here we show live alveologenesis, using long-term, time-lapse imaging of precision-cut lung slices. We reveal that during this process, epithelial cells are highly mobile and we identify specific cell behaviours that contribute to alveologenesis: cell clustering, hollowing and cell extension. Using the cytoskeleton inhibitors blebbistatin and cytochalasin D, we show that cell migration is a key driver of alveologenesis. This study reveals important novel information about lung biology and provides a new system in which to manipulate alveologenesis genetically and pharmacologically.

The process of alveologenesis is incompletely understood, partly due to the lack of applicable real-time imaging methods. Here the authors describe the process of alveologenesis and the behaviour of epithelial cells in real-time, using widefield microscopy and image deconvolution in precision-cut lung slices, revealing the dominant role of epithelial cell migration.

Engraftment and proliferation potential of embryonic lung tissue cells in irradiated mice with emphysema

Recently, there has been increasing interest in stem cell transplantation therapy, to treat chronic respiratory diseases, using lung epithelial cells or alveolospheres derived from endogenous lung progenitor cells. However, optimal transplantation strategy of these cells has not been addressed. To gain insight into the optimization of stem cell transplantation therapy, we investigated whether lung cell engraftment potential differ among different developmental stages. After preconditioning with irradiation and elastase to induce lung damage, we infused embryonic day 15.5 (E15.5) CAG-EGFP whole lung cells, and confirmed the engraftment of epithelial cells, endothelial cells, and mesenchymal cells. The number of EGFP-positive epithelial cells increased from day 7 to 28 after infusion. Among epithelial cells derived from E13.5, E15.5, E18.5, P7, P14, and P56 mice, E15.5 cells demonstrated the most efficient engraftment. In vitro, E15.5 epithelial cells showed high proliferation potential. Transcriptome analyses of sorted epithelial cells from E13.5, E15.5, E18.5, P14, and P56 mice revealed that cell cycle and cell-cell adhesion genes were highly enriched in E15.5 epithelial cells. Our findings suggest that cell therapy for lung diseases might be most effective when epithelial cells with transcriptional traits similar to those of E15.5 epithelial cells are used.

Recent Developments in mRNA-Based Protein Supplementation Therapy to Target Lung Diseases

Protein supplementation therapy using in vitro-transcribed (IVT) mRNA for genetic diseases contains huge potential as a new class of therapy. From the early ages of synthetic mRNA discovery, a great number of studies showed the versatile use of IVT mRNA as a novel approach to supplement faulty or absent protein and also as a vaccine. Many modifications have been made to produce high expressions of mRNA causing less immunogenicity and more stability. Recent advancements in the in vivo lung delivery of mRNA complexed with various carriers encouraged the whole mRNA community to tackle various genetic lung diseases. This review gives a comprehensive overview of cells associated with various lung diseases and recent advancements in mRNA-based protein replacement therapy. This review also covers a brief summary of developments in mRNA modifications and nanocarriers toward clinical translation.

Challenges Facing Airway Epithelial Cell-Based Therapy for Cystic Fibrosis

Mutations in the cystic fibrosis transmembrane conductance regulator (CFTR) gene cause the life-limiting hereditary disease, cystic fibrosis (CF). Decreased or absent functional CFTR protein in airway epithelial cells leads to abnormally viscous mucus and impaired mucociliary transport, resulting in bacterial infections and inflammation causing progressive lung damage. There are more than 2000 known variants in the CFTR gene. A subset of CF individuals with specific CFTR mutations qualify for pharmacotherapies of variable efficacy. These drugs, termed CFTR modulators, address key defects in protein folding, trafficking, abundance, and function at the apical cell membrane resulting from specific CFTR mutations. However, some CFTR mutations result in little or no CFTR mRNA or protein expression for which a pharmaceutical strategy is more challenging and remote. One approach to rescue CFTR function in the airway epithelium is to replace cells that carry a mutant CFTR sequence with cells that express a normal copy of the gene. Cell-based therapy theoretically has the potential to serve as a one-time cure for CF lung disease regardless of the causative CFTR mutation. In this review, we explore major challenges and recent progress toward this ambitious goal. The ideal therapeutic cell would: (1) be autologous to avoid the complications of rejection and immune-suppression; (2) be safely modified to express functional CFTR; (3) be expandable ex vivo to generate sufficient cell quantities to restore CFTR function; and (4) have the capacity to engraft, proliferate and persist long-term in recipient airways without complications. Herein, we explore human bronchial epithelial cells (HBECs) and induced pluripotent stem cells (iPSCs) as candidate cell therapies for CF and explore the challenges facing their delivery to the human airway.

Alveolar type 2 progenitor cells for lung injury repair

Alveolar type 2 progenitor cells (AT2) seem closest to clinical translation, specifying the evidence that AT2 may satisfactorily control the immune response to decrease lung injury by stabilizing host immune-competence and a classic and crucial resource for lung regeneration and repair. AT2 establish potential in benefiting injured lungs. However, significant discrepancies linger in our understanding vis-à-vis the mechanisms for AT2 as a regime for stem cell therapy as well as essential guiding information for clinical trials, including effectiveness in appropriate pre-clinical models, safety, mostly specifications for divergent lung injury patients. These important gaps shall be systematically investigated prior to the vast therapeutic perspective of AT2 cells for pulmonary diseases can be considered. This review focused on AT2 cells homeostasis, pathophysiological changes in the pathogenesis of lung injury, physiological function of AT2 cells, apoptosis of AT2 cells in lung diseases, the role of AT2 cells in repairing processes after lung injury, mechanism of AT2 cells activation promote repairing processes after lung injury, and potential therapy of lung disease by utilizing the AT2 progenitor cells. The advancement remains to causally connect the molecular and cellular alteration of AT2 cells to lung injury and repair. Conclusively, it is identified that AT2 cells can convert into AT1 cells; but, the comprehensive cellular mechanisms involved in this transition are unrevealed. Further investigation is mandatory to determine new strategies to prevent lung injury.

Building and Regenerating the Lung Cell by Cell

The unique architecture of the mammalian lung is required for adaptation to air breathing at birth and thereafter. Understanding the cellular and molecular mechanisms controlling its morphogenesis provides the framework for understanding the pathogenesis of acute and chronic lung diseases. Recent single-cell RNA sequencing data and high-resolution imaging identify the remarkable heterogeneity of pulmonary cell types and provides cell selective gene expression underlying lung development. We will address fundamental issues related to the diversity of pulmonary cells, to the formation and function of the mammalian lung, and will review recent advances regarding the cellular and molecular pathways involved in lung organogenesis. What cells form the lung in the early embryo? How are cell proliferation, migration, and differentiation regulated during lung morphogenesis? How do cells interact during lung formation and repair? How do signaling and transcriptional programs determine cell-cell interactions necessary for lung morphogenesis and function?

Presence of N-acetylglucosamine residues on the surface coating of bronchioloalveolar cells during rat postnatal development: What is their purpose?

Mammalian lung development is a complex process that is partially accomplished during the postnatal period. Surface carbohydrates are crucial in many biological and pathological phenomena and are key partners during development. The outer surface of lung epithelial cells, which is rich in carbohydrate components, plays a pivotal role throughout the developmental process. However, systematic studies on the sugar residue content of the cell surface coating during postnatal rat lung development are scarce. The aim of the present study was to identify and determine the localization of N-acetylglucosamine residues on the bronchioloalveolar cell surface during rat lung development using light and pre-embedding transmission electron microscopy methodologies, and to associate these data with the components underlying postnatal lung growth. Strong binding sites for the lectin Triticum vulgare (common name Wheat Germ, WGA) are present on the luminal surface of adult rat bronchioloalveolar cells throughout the entire postnatal period and have been identified as N-acetylglucosamine residues. The consistent positive reaction observed on the surface coating of bronchioloalveolar lining cells before and after neuraminidase treatment suggests that aside from possible terminal sialic acids, the lectin specificity for N-acetylglucosamine residues is still evident. Our results also suggest a stronger positive reaction on the bronchioloalveolar cell surface when compared with endothelial cell surface. N-acetylglucosamine residues for lectin binding can be present in glycoproteins in the membrane and also within heparin sulfate chains of glycosaminoglycans, which are crucial for lung development. The work described here has sought to highlight the presence and possible importance of N-acetylglucosamine residues on the glycocalyx of bronchioloalveolar cells, during postnatal lung development.

Stem cell-based Lung-on-Chips: The best of both worlds?

Pathologies of the respiratory system such as lung infections, chronic inflammatory lung diseases, and lung cancer are among the leading causes of morbidity and mortality, killing one in six people worldwide. Development of more effective treatments is hindered by the lack of preclinical models of the human lung that can capture the disease complexity, highly heterogeneous disease phenotypes, and pharmacokinetics and pharmacodynamics observed in patients. The merger of two novel technologies, Organs-on-Chips and human stem cell engineering, has the potential to deliver such urgently needed models. Organs-on-Chips, which are microengineered bioinspired tissue systems, recapitulate the mechanochemical environment and physiological functions of human organs while concurrent advances in generating and differentiating human stem cells promise a renewable supply of patient-specific cells for personalized and precision medicine. Here, we discuss the challenges of modeling human lung pathophysiology in vitro, evaluate past and current models including Organs-on-Chips, review the current status of lung tissue modeling using human pluripotent stem cells, explore in depth how stem-cell based Lung-on-Chips may advance disease modeling and drug testing, and summarize practical consideration for the design of Lung-on-Chips for academic and industry applications.

Mesothelial mobilization in the developing lung and heart differs in timing, quantity, and pathway dependency

The mesothelial lining of the lung, the visceral pleura, and of the heart, the epicardium, derive from a common multipotent precursor tissue, the mesothelium of the embryonic thoracic cavity that also contributes to organ-specific mesenchymal cell types. Insight into mesothelial mobilization and differentiation has prevailedin the developing heart while the mesenchymal transition and fate of the visceral pleura are poorly understood. Here, we use the fact that the early mesothelium of both the lung and the heart expresses the transcription factor gene Wt1, to comparatively analyze mesothelial mobilization in the two organs by a genetic cre-loxP-based conditional approach. We show that epicardial cells are mobilized in a large number between E12.5 and E14.5, whereas pleural mobilization occurs only sporadically and variably in few regions of the lung in a temporally highly confined manner shortly after E12.5. Mesothelium-specific inactivation of unique pathway components using a Wt1^creERT2 line excluded a requirement for canonical WNT, NOTCH, HH, TGFB, PDGFRA, and FGFR1/FGFR2 signaling in the mesenchymal transition of the visceral pleura but indicated a deleterious effect of activated WNT, NOTCH, and HH signaling on lung development. Epicardial mobilization was negatively impacted on by loss of HH, PDGFRA, FGFR1/2 signaling. Epicardial overactivation of WNT, NOTCH, and HH disturbed epicardial and myocardial integrity. We conclude that mesothelial mobilization in the developing lung and heart differs in timing, quantity and pathway dependency, indicating the organ specificity of the program.

Branching pattern and morphogenesis of medusa tentacles in the jellyfish Cladonema pacificum (Hydrozoa, Cnidaria)

BACKGROUND

Branched structures are found in many natural settings, and the molecular and cellular mechanisms underlying their formation in animal development have extensively studied in recent years. Despite their importance and the accumulated knowledge from studies on several organs of Drosophila and mammals, much remains unknown about branching mechanisms in other animal species. We chose to study the jellyfish species Cladonema pacificum. Unlike many other jellyfish, this species has branched medusa tentacles, and its basal phylogenetic position in animal evolution makes it an ideal organism for studying and understanding branching morphogenesis more broadly. Branched tentacles are unique compared to other well-studied branched structures in that they have two functionally distinct identities: one with adhesive organs for attaching to a substratum, and another with nematocyst clusters for capturing prey.

RESULTS

We began our analyses on C. pacificum tentacles by observing their branching during growth. We found that tentacle branches form through repeated addition of new branches to the proximal region of the main tentacle while it is elongating. At the site of branch bud formation, we observed apical thickening of the epidermal epithelial layer, possibly caused by extension of the epithelial cells along the apico-basal axis. Interestingly, tentacle branch formation required receptor tyrosine kinase signaling, which is an essential factor for branching morphogenesis in Drosophila and mammals. We also found that new branches form adhesive organs first, and then are transformed into branches with nematocyst clusters as they develop.

CONCLUSIONS

These results highlight unique features in branch generation in C. pacificum medusa tentacles and illuminate conserved and fundamental mechanisms by which branched structures are created across a variety of animal species.

Rat lung decellularization using chemical detergents for lung tissue engineering

Although pulmonary diseases account for a large number of deaths in the world, most have no treatment other than transplantation. New therapeutic methods for lung treatment include lung tissue engineering and regenerative medicine. Lung decellularization has been used to produce an appropriate scaffold for recellularization and implantation. We investigated 3-[(3-cholamidopropyl) dimethylammonio]-1-propanesulfonate (CHAPS) with sodium dodecyl sulfate (SDS) and Triton X-100 detergents for effecting rat lung decellularization. We evaluated using conventional histology, immunofluorescence staining and SEM methods for removing nuclear material while leaving intact extracellular matrix proteins and three-dimensional architecture. We investigated different concentrations of CHAPS, SDS and Triton X-100 for different periods. We found that 2 mM CHAPS + 0/1% SDS for 48 h was the best among the treatments investigated. Our method can be used to produce an appropriate scaffold for recellularization by stem cells and for investigations ex vivo and in vivo.

Use of three-dimensional organoids and lung-on-a-chip methods to study lung development, regeneration and disease

Differences in lung anatomy between mice and humans, as well as frequently disappointing results when using animal models for drug discovery, emphasise the unmet need for in vitro models that can complement animal studies and improve our understanding of human lung physiology, regeneration and disease. Recent papers have highlighted the use of three-dimensional organoids and organs-on-a-chip to mimic tissue morphogenesis and function in vitro Here, we focus on the respiratory system and provide an overview of these in vitro models, which can be derived from primary lung cells and pluripotent stem cells, as well as healthy or diseased lungs. We emphasise their potential application in studies of respiratory development, regeneration and disease modelling.

Cancer-associated fibroblasts suppress SOX2-induced dysplasia in a lung squamous cancer coculture

Tumor−stroma interactions play a critical role in regulating tumorigenesis. However, how these interactions contribute to changes in tissue architecture and cell polarity observed during tumor development is unclear. Here we report a 3D coculture system that recapitulates key phenotypic changes during the progression of lung squamous carcinoma (LUSC) as well as the dynamic interactions between LUSC cells and components of the tumor microenvironment (TME). Our data suggest that two major components of TME, including the extracellular matrix and cancer-associated fibroblasts, could override cell intrinsic oncogenic changes in determining the disease phenotype in the context of LUSC. These findings may have broad implications for LUSC biology as well as the design of future therapies.

Tumorigenesis depends on intricate interactions between genetically altered tumor cells and their surrounding microenvironment. While oncogenic drivers in lung squamous carcinoma (LUSC) have been described, the role of stroma in modulating tissue architecture, particularly cell polarity, remains unclear. Here, we report the establishment of a 3D coculture system of LUSC epithelial cells with cancer-associated fibroblasts (CAFs) and extracellular matrix that together capture key components of the tumor microenvironment (TME). Single LUSC epithelial cells develop into acinar-like structures with 0.02% efficiency, and addition of CAFs provides proper tumor−stromal interactions within an appropriate 3D architectural context. Using this model, we recapitulate key pathological changes during tumorigenesis, from hyperplasia to dysplasia and eventually invasion, in malignant LUSC spheroids that undergo phenotypic switching in response to cell intrinsic and extrinsic changes. Overexpression of SOX2 is sufficient to mediate the transition from hyperplasia to dysplasia in LUSC spheroids, while the presence of CAFs makes them invasive. Unexpectedly, CAFs suppress the activity of high SOX2 levels, restore hyperplasia, and enhance the formation of acinar-like structures. Taken together, these observations suggest that stromal factors can override cell intrinsic oncogenic changes in determining the disease phenotype, thus providing fundamental evidence for the existence of dynamic reciprocity between the nucleus and the TME of LUSC.

Impact of Maternal Air Pollution Exposure on Children's Lung Health: An Indian Perspective

Air pollution has become an emerging invisible killer in recent years and is a major cause of morbidity and mortality globally. More than 90% of the world’s children breathe toxic air every day. India is among the top ten most highly polluted countries with an average PM₁₀ level of 134 μg/m³ per year. It is reported that 99% of India’s population encounters air pollution levels that exceed the World Health Organization Air Quality Guideline, advising a PM_2.5 permissible level of 10 μg/m³. Maternal exposure to air pollution has serious health outcomes in offspring because it can affect embryonic phases of development during the gestation period. A fetus is more prone to effects from air pollution during embryonic developmental phases due to resulting oxidative stress as antioxidant mechanisms are lacking at that stage. Any injury during this vulnerable period (embryonic phase) will have a long-term impact on offspring health, both early and later in life. Epidemiological studies have revealed that maternal exposure to air pollution increases the risk of development of airway disease in the offspring due to impaired lung development in utero. In this review, we discuss cellular mechanisms involved in maternal exposure to air pollution and how it can impact airway disease development in offspring. A better understanding of these mechanisms in the context of maternal exposure to air pollution can offer a new avenue to prevent the development of airway disease in offspring.

Expression of Lung Surfactant Proteins SP-B and SP-C and Their Regulatory Factors in Fetal Lung of GDM Rats

This study investigated the expression of lung surfactant proteins (SP-B and SP-C), and regulatory factors [forkhead box A2 (FOXA2) and nitrolyogenic FOXA2 (N-FOXA2)] in the fetal lung of rats with gestational diabetes mellitus (GDM) in order to study the mechanism of pulmonary dysplasia. The rat GDM model was established by using streptozotocin intraperitoneally in the first stage of pregnancy. There were 10 rats in the GDM group, and 10 healthy rats in normal control group without any treatment. Fetal lungs of two groups were taken at day 21 of pregnancy. Blood glucose levels of maternal rats and fetal rats were measured by Roche blood glucose meter. The histological changes in the fetal lung were observed under the light microscope in both groups. The SP-B, SP-C and FOXA2 were determined in the fetal lung of two groups immunohistochemically. The expression levels of SP-B, SP-C, total FOXA2, FOXA2 in nucleus (n-FOXA2), N-FOXA2 proteins were detected by Western blotting, and the relative expression levels of SP-B, SP-C, FOXA2 mRNA in the fetal lung of two groups were detected by RTPCR. The results showed that blood glucose levels of maternal rats and fetal rats in GDM group were higher than those in control group. The light microscope revealed fetal lung development retardation in GDM group. The expression of SP-B and SP-C in GDM group was significantly reduced as compared with control group (P<0.05). As compared with control group, the n-FOXA2 expression was significantly decreased in the fetal lung tissue, and N-FOXA2 was significantly increased in control group (P<0.05), but there was no significant changes in the total FOXA2 (P>0.05). It was concluded that GDM can cause fetal lung development and maturation disorders, and FOXA2 in fetal lung tissue decreases while nitrocellulose FOXA2 increases.

The Lineage-Defining Transcription Factors SOX2 and NKX2-1 Determine Lung Cancer Cell Fate and Shape the Tumor Immune Microenvironment

The major types of non-small-cell lung cancer (NSCLC)-squamous cell carcinoma and adenocarcinoma-have distinct immune microenvironments. We developed a genetic model of squamous NSCLC on the basis of overexpression of the transcription factor Sox2, which specifies lung basal cell fate, and loss of the tumor suppressor Lkb1 (SL mice). SL tumors recapitulated gene-expression and immune-infiltrate features of human squamous NSCLC; such features included enrichment of tumor-associated neutrophils (TANs) and decreased expression of NKX2-1, a transcriptional regulator that specifies alveolar cell fate. In Kras-driven adenocarcinomas, mis-expression of Sox2 or loss of Nkx2-1 led to TAN recruitment. TAN recruitment involved SOX2-mediated production of the chemokine CXCL5. Deletion of Nkx2-1 in SL mice (SNL) revealed that NKX2-1 suppresses SOX2-driven squamous tumorigenesis by repressing adeno-to-squamous transdifferentiation. Depletion of TANs in SNL mice reduced squamous tumors, suggesting that TANs foster squamous cell fate. Thus, lineage-defining transcription factors determine the tumor immune microenvironment, which in turn might impact the nature of the tumor.

Proteomic profiling of tracheal fluid in an ovine model of congenital diaphragmatic hernia and fetal tracheal occlusion

Congenital diaphragmatic hernia (CDH) occurs in ~1:2,000 pregnancies and is associated with substantial morbidity and mortality. Fetal tracheal occlusion (TO) is an emerging therapy that improves lung growth and reduces mortality, although substantial respiratory compromise persists in survivors. In this study, we used tracheal fluid in a fetal sheep model of CDH with TO for proteomic analysis with subsequent validation of findings in sheep lung tissue. We found that the proteomic profiles of CDH tracheal fluid was most similar to control lung and CDH/TO lung most similar to TO lung. Among 118 proteins altered in CDH, only 11 were reciprocally regulated in CDH/TO. The most significantly altered pathways and processes were cell proliferation, phosphatidylinositol 3-kinase/AKT/mammalian target of rapamycin signaling, inflammation, and microtubule dynamics. CDH suppressed and TO promoted cell proliferation and AKT-related signaling cascades. By Western blot analysis and immunohistochemistry, epithelial PCNA and phosphorylated AKT were decreased in CDH and increased in TO and CDH/TO lungs. The Wnt target Axin2 was decreased threefold in CDH lung compared with control without a significant increase in CDH/TO lung. Cilia-related pathways were among the most dysregulated with CDH lung having a nearly twofold increase in acetylated α-tubulin and a relative increase in the number of ciliated cells. While TO improves lung growth and patient survival in CDH, the procedure substantially alters many processes important in lung development and cell differentiation. Further elucidation of these changes will be critical to improving lung health in infants with CDH treated with TO.

Anxa4 mediated airway progenitor cell migration promotes distal epithelial cell fate specification

Genetic studies have shown that FGF10/FGFR2 signaling is required for airway branching morphogenesis and FGF10 functions as a chemoattractant factor for distal epithelial cells during lung development. However, the detail downstream cellular and molecular mechanisms have not been fully characterized. Using live imaging of ex vivo cultured lungs, we found that tip airway epithelial progenitor cells migrate faster than cleft cells during airway bud formation and this migration process is controlled by FGFR2-mediated ERK1/2 signaling. Additionally, we found that airway progenitor cells that migrate faster tend to become distal airway progenitor cells. We identified that Anxa4 is a downstream target of ERK1/2 signaling. Anxa4^-/- airway epithelial cells exhibit a "lag-behind" behavior and tend to stay at the stalk airways. Moreover, we found that Anxa4-overexpressing cells tend to migrate to the bud tips. Finally, we demonstrated that Anxa4 functions redundantly with Anxa1 and Anxa6 in regulating endoderm budding process. Our study demonstrates that ERK1/2/Anxa4 signaling plays a role in promoting the migration of airway epithelial progenitor cells to distal airway tips and ensuring their distal cell fate.

The reduction in FOXA2 activity during lung development in fetuses from diabetic rat mothers is reversed by Akt inhibition

Hyperglycemia during pregnancy is associated with fetal lung development disorders and surfactant protein (SP) deficiency. Here, we examined the role of FOXA2 and Akt signaling in fetal lung development during diabetic pregnancy. Sprague‐Dawley rats were injected with streptozocin (STZ) during pregnancy to induce diabetes (DM). DM‐exposed fetal lungs exhibited reduced numbers of alveoli, irregularities in the appearance and thickness of the alveolar septum, increased levels of glycogen and lipids in type II alveolar epithelial cells, fewer microvilli and mature lamellar bodies, and swollen mitochondria. SP‐B and SP‐C in DM amniotic fluid and DM lungs were lower than in the control group (P < 0.05). DM lung nuclear FOXA2 was lower compared with the control group (P < 0.05), but p‐FOXA2 was higher (P < 0.05). In murine lung epithelial (MLE) 12 cells, p‐AKT levels were increased by high glucose/insulin, but decreased by the Akt inhibitor MK2206 (P < 0.05). Expression of nuclear FOXA2 was increased by MK2206 compared with the high glucose/insulin group (P < 0.05). These results suggest that maternal diabetes induces fetal lung FOXA2 phosphorylation through the Akt pathway, and also affects the maturation of alveolar epithelial cells and reduces levels of SP‐B and SP‐C in the fetal lungs. An Akt inhibitor reversed the changes in SP expression in vitro.

Transcriptional regulation of cell shape during organ morphogenesis

The emerging field of transcriptional regulation of cell shape changes aims to address the critical question of how gene expression programs produce a change in cell shape. Together with cell growth, division, and death, changes in cell shape are essential for organ morphogenesis. Whereas most studies of cell shape focus on posttranslational events involved in protein organization and distribution, cell shape changes can be genetically programmed. This review highlights the essential role of transcriptional regulation of cell shape during morphogenesis of the heart, lungs, gastrointestinal tract, and kidneys. We emphasize the evolutionary conservation of these processes across different model organisms and discuss perspectives on open questions and research avenues that may provide mechanistic insights toward understanding birth defects.

Pulmonary adenocarcinoma with high-grade fetal adenocarcinoma component has a poor prognosis, comparable to that of micropapillary adenocarcinoma

Fetal adenocarcinoma is a rare variant of lung adenocarcinoma, which is subcategorized into low-grade and high-grade forms. High-grade fetal adenocarcinoma confers worse prognosis than low-grade fetal adenocarcinoma, but the prognostic differences between high-grade fetal adenocarcinoma and conventional lung adenocarcinoma are unknown. We reviewed tissue sections of 3719 cases of surgically resected primary lung cancers and found 53 lung cancers with a high-grade fetal adenocarcinoma component. We analyzed their clinicopathological and immunohistochemical features, and performed a prognostic analysis of adenocarcinomas with the fetal-type component. We further analyzed the prognostic differences between adenocarcinomas with the fetal-type component and conventional adenocarcinomas without the fetal-type component. Lung cancers with the fetal-type component predominantly occurred in elderly men with a smoking history. Twenty-nine patients had stage I disease, 13 patients had stage II, and 11 patients had stage III. The fetal-type histology was combined with conventional-type adenocarcinoma (41 cases), squamous cell carcinoma (5 cases), large cell neuroendocrine carcinoma (5 cases), enteric adenocarcinoma (2 cases), and small cell carcinoma (1 case). The fetal-type component showed immunopositivity for α-fetoprotein (39%), glypican-3 (37%), and SALL4 (17%). The 5-year overall survivals of fetal-type-predominant and fetal-type-nonpredominant patients were 44 and 56%, respectively (P = 0.962). The 5-year overall survivals of lepidic-, acinar-, papillary-, solid-, and micropapillary-predominant adenocarcinomas, invasive mucinous adenocarcinomas, and adenocarcinomas with the fetal-type component were 94, 82, 77, 69, 57, 83, and 41%, respectively (P < 0.001). Univariate and multivariate analyses showed that adenocarcinomas with the fetal-type component had a significantly lower overall survival rate than the other histological subtypes, except for the micropapillary-predominant subtype. Our study demonstrated that adenocarcinomas with the fetal-type component had a poor prognosis that was comparable to that of micropapillary adenocarcinoma. The presence of the high-grade fetal adenocarcinoma component in lung adenocarcinomas is an important prognostic marker.

Lessons learned from lung and liver in-vivo gene therapy: implications for the future

INTRODUCTION

Ex-vivo gene therapy has had significant clinical impact over the last couple of years and in-vivo gene therapy products are being approved for clinical use. Gene therapy and gene editing approaches have huge potential to treat genetic disease and chronic illness.

AREAS COVERED

This article provides a review of in-vivo approaches for gene therapy in the lung and liver, exploiting non-viral and viral vectors with varying serotypes and pseudotypes to target-specific cells. Antibody responses inhibiting viral vectors continue to constrain effective repeat administration. Lessons learned from ex-vivo gene therapy and genome editing are also discussed.

EXPERT OPINION

The fields of lung and liver in-vivo gene therapy are thriving and a comparison highlights obstacles and opportunities for both. Overcoming immunological issues associated with repeated administration of viral vectors remains a key challenge. The addition of targeted small molecules in combination with viral vectors may offer one solution. A substantial bottleneck to the widespread adoption of in-vivo gene therapy is how to ensure sufficient capacity for clinical-grade vector production. In the future, the exploitation of gene editing approaches for in-vivo disease treatment may facilitate the resurgence of non-viral gene transfer approaches, which tend to be eclipsed by more efficient viral vectors.

FOXF1 transcription factor promotes lung morphogenesis by inducing cellular proliferation in fetal lung mesenchyme

Organogenesis is regulated by mesenchymal-epithelial signaling events that induce expression of cell-type specific transcription factors critical for cellular proliferation, differentiation and appropriate tissue patterning. While mesenchymal transcription factors play a key role in mesenchymal-epithelial interactions, transcriptional networks in septum transversum and splanchnic mesenchyme remain poorly characterized. Forkhead Box F1 (FOXF1) transcription factor is expressed in mesenchymal cell lineages; however, its role in organogenesis remains uncharacterized due to early embryonic lethality of Foxf1^-/- mice. In the present study, we generated mesenchyme-specific Foxf1 knockout mice (Dermo1-Cre Foxf1^-/-) and demonstrated that FOXF1 is required for development of respiratory, cardiovascular and gastrointestinal organ systems. Deletion of Foxf1 from mesenchyme caused embryonic lethality in the middle of gestation due to multiple developmental defects in the heart, lung, liver and esophagus. Deletion of Foxf1 inhibited mesenchyme proliferation and delayed branching lung morphogenesis. Gene expression profiling of micro-dissected distal lung mesenchyme and ChIP sequencing of fetal lung tissue identified multiple target genes activated by FOXF1, including Wnt2, Wnt11, Wnt5A and Hoxb7. FOXF1 decreased expression of the Wnt inhibitor Wif1 through direct transcriptional repression. Furthermore, using a global Foxf1 knockout mouse line (Foxf1^-/-) we demonstrated that FOXF1-deficiency disrupts the formation of the lung bud in foregut tissue explants. Finally, deletion of Foxf1 from smooth muscle cell lineage (smMHC-Cre Foxf1^-/-) caused hyper-extension of esophagus and trachea, loss of tracheal and esophageal muscle, mispatterning of esophageal epithelium and decreased proliferation of smooth muscle cells. Altogether, FOXF1 promotes lung morphogenesis by regulating mesenchymal-epithelial signaling and stimulating cellular proliferation in fetal lung mesenchyme.

Developmental pathways in the pathogenesis of lung fibrosis

Idiopathic pulmonary fibrosis (IPF) is a progressive and terminal lung disease with no known cure. IPF is a disease of aging, with median age of diagnosis over 65 years. Median survival is between 3 and 5 years after diagnosis. IPF is characterized primarily by excessive deposition of extracellular matrix (ECM) proteins by activated lung fibroblasts and myofibroblasts, resulting in reduced gas exchange and impaired pulmonary function. Growing evidence supports the concept of a pro-fibrotic environment orchestrated by underlying factors such as genetic predisposition, chronic injury and aging, oxidative stress, and impaired regenerative responses may account for disease development and persistence. Currently, two FDA approved drugs have limited efficacy in the treatment of IPF. Many of the genes and gene networks associated with lung development are induced or activated in IPF. In this review, we analyze current knowledge in the field, gained from both basic and clinical research, to provide new insights into the disease process, and potential approaches to treatment of pulmonary fibrosis.

Human lung development: recent progress and new challenges

Recent studies have revealed biologically significant differences between human and mouse lung development, and have reported new in vitro systems that allow experimental manipulation of human lung models. At the same time, emerging clinical data suggest that the origins of some adult lung diseases are found in embryonic development and childhood. The convergence of these research themes has fuelled a resurgence of interest in human lung developmental biology. In this Review, we discuss our current understanding of human lung development, which has been profoundly influenced by studies in mice and, more recently, by experiments using in vitro human lung developmental models and RNA sequencing of human foetal lung tissue. Together, these approaches are helping to shed light on the mechanisms underlying human lung development and disease, and may help pave the way for new therapies.

Summary: This Review describes how recent technological advances have shed light on the mechanisms underlying human lung development and disease, and outlines the future challenges in this field.

Understanding alveolarization to induce lung regeneration

Background

Gas exchange represents the key physiological function of the lung, and is dependent upon proper formation of the delicate alveolar structure. Malformation or destruction of the alveolar gas-exchange regions are key histopathological hallmarks of diseases such as bronchopulmonary dysplasia (BPD), chronic obstructive pulmonary disease (COPD), and pulmonary fibrosis; all of which are characterized by perturbations to the alveolo-capillary barrier structure. Impaired gas-exchange is the primary initial consequence of these perturbations, resulting in severe clinical symptoms, reduced quality of life, and death. The pronounced morbidity and mortality associated with malformation or destruction of alveoli underscores a pressing need for new therapeutic concepts. The re-induction of alveolarization in diseased lungs is a new and exciting concept in a regenerative medicine approach to manage pulmonary diseases that are characterized by an absence of alveoli.

Main text

Mechanisms of alveolarization first need to be understood, to identify pathways and mediators that may be exploited to drive the induction of alveolarization in the diseased lung. With this in mind, a variety of candidate cell-types, pathways, and molecular mediators have recently been identified. Using lineage tracing approaches and lung injury models, new progenitor cells for epithelial and mesenchymal cell types – as well as cell lineages which are able to acquire stem cell properties – have been discovered. However, the underlying mechanisms that orchestrate the complex process of lung alveolar septation remain largely unknown.

Conclusion

While important progress has been made, further characterization of the contributing cell-types, the cell type-specific molecular signatures, and the time-dependent chemical and mechanical processes in the developing, adult and diseased lung is needed in order to implement a regenerative therapeutic approach for pulmonary diseases.

Branching morphogenesis in the developing kidney is not impacted by nephron formation or integration

Branching morphogenesis of the ureteric bud is integral to kidney development; establishing the collecting ducts of the adult organ and driving organ expansion via peripheral interactions with nephron progenitor cells. A recent study suggested that termination of tip branching within the developing kidney involved stochastic exhaustion in response to nephron formation, with such a termination event representing a unifying developmental process evident in many organs. To examine this possibility, we have profiled the impact of nephron formation and maturation on elaboration of the ureteric bud during mouse kidney development. We find a distinct absence of random branch termination events within the kidney or evidence that nephrogenesis impacts the branching program or cell proliferation in either tip or progenitor cell niches. Instead, organogenesis proceeds in a manner indifferent to the development of these structures. Hence, stochastic cessation of branching is not a unifying developmental feature in all branching organs.

During development and before birth, many organs develop from branched tubes. Whether forming the airways of the lungs, the collecting ducts of the kidneys or the milk ducts of the breast, there are many similarities between these structures. Given their shared tree-like structures, one possibility is that these tissues all form through the same general process.

A key challenge is understanding why branched networks develop and pattern in such a way as to assume their functional roles in the adult organ. A unifying theory, which proposes that certain tips stop growing in a random manner, has been proposed to solve this problem. In this theory, the branched mammary gland structures stop growing when the tips of the structure impinge on neighbouring branches. In the kidney, this cessation has been proposed to occur when nephrons – the structures that filter urine from blood – form near the end of the collecting ducts.

By growing kidneys in the laboratory and studying developing kidneys in mice, Short et al. investigated whether nephrons do affect collecting duct growth and branch development. The results of these experiments instead suggest that nephron formation has no effect on duct growth or branching. The nephrons also do not appear to affect how quickly the duct cells grow and divide. Moreover, there is no evidence that the cell proliferation in individual branch tips ceases randomly by any other mechanism.

Overall, the experiments Short et al. performed suggest that a unifying theory of branching in developing organs may not hold true, at least not in the way that has been envisioned previously.

Histone arginine methylation by Prmt5 is required for lung branching morphogenesis through repression of BMP signaling

Branching morphogenesis is essential for the successful development of a functional lung to accomplish its gas exchange function. Although many studies have highlighted requirements for the bone morphogenetic protein (BMP) signaling pathway during branching morphogenesis, little is known about how BMP signaling is regulated. Here, we report that the protein arginine methyltransferase 5 (Prmt5) and symmetric dimethylation at histone H4 arginine 3 (H4R3sme2) directly associate with chromatin of Bmp4 to suppress its transcription. Inactivation of Prmt5 in the lung epithelium results in halted branching morphogenesis, altered epithelial cell differentiation and neonatal lethality. These defects are accompanied by increased apoptosis and reduced proliferation of lung epithelium, as a consequence of elevated canonical BMP-Smad1/5/9 signaling. Inhibition of BMP signaling by Noggin rescues the lung branching defects of Prmt5 mutant in vitro Taken together, our results identify a novel mechanism through which Prmt5-mediated histone arginine methylation represses canonical BMP signaling to regulate lung branching morphogenesis.

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.

Chronic lung disease, lung regeneration and future therapeutic strategies

Chronic lung diseases have been recognized as one of the world's leading causes of death in recent decades. Lacking effective treatments brings the patients not only bad quality of life but also higher risk for lung cancer development. By increasing the understanding of deeper mechanism of how lung develops and regenerates, researchers now focus on studying lung regenerative medicine, aiming to apply different and more efficient therapies to treat chronic lung diseases. This review will provide a wide picture of both basic lung developmental, regeneration mechanism and different designed strategies for treating chronic lung diseases in the future decades.

Expression Analysis of ACSL5 and Wnt2B in Human Congenital Pulmonary Airway Malformations

BACKGROUND

The objective of this study was to determine acyl-CoA synthetase 5 (ACSL5) and Wnt2B expression patterns in human congenital pulmonary airway malformations (CPAMs) and to identify the possible roles of ACSL5 and Wnt2B in the pathogenesis of CPAM.

METHODS

Expression of ACSL5 and Wnt2B was evaluated by immunohistochemical staining, Western blotting, and quantitative real-time polymerase chain reaction, which were performed on surgical specimens of CPAM and adjacent normal lung tissues as controls.

RESULTS

Immunohistochemistry revealed that ACSL5 and Wnt2B immunopositive cells were predominantly detected in the mesenchymal cell nucleus, and there were lower expressions of ACSL5 and Wnt2B immunopositive cells in CPAM tissues than those in adjacent normal lung tissues. Western blotting and quantitative real-time polymerase chain reaction showed that ACSL5 and Wnt2B protein and mRNA expressions were significantly decreased in CPAM tissues as compared to the adjacent normal lung tissues (P < 0.05). In addition, there was a reduced level of ACSL5 relative to that of Wnt2B.

CONCLUSIONS

The decreased ACSL5 and Wnt2B expressions correlated with aberrations in pulmonary development and in the pathogenesis of CPAM, so downregulation of ACSL5 and Wnt2B could play an important role in the development of bronchial-alveolar structures in CPAM.

Pulmonary pericytes regulate lung morphogenesis

Blood vessels are essential for blood circulation but also control organ growth, homeostasis, and regeneration, which has been attributed to the release of paracrine signals by endothelial cells. Endothelial tubules are associated with specialised mesenchymal cells, termed pericytes, which help to maintain vessel wall integrity. Here we identify pericytes as regulators of epithelial and endothelial morphogenesis in postnatal lung. Mice lacking expression of the Hippo pathway components YAP and TAZ in pericytes show defective alveologenesis. Mutant pericytes are present in normal numbers but display strongly reduced expression of hepatocyte growth factor leading to impaired activation of the c-Met receptor, which is expressed by alveolar epithelial cells. YAP and TAZ are also required for expression of angiopoietin-1 by pulmonary pericytes, which also controls hepatocyte growth factor expression and thereby alveologenesis in an autocrine fashion. These findings establish that pericytes have important, organ-specific signalling properties and coordinate the behavior of epithelial and vascular cells during lung morphogenesis.

Pericytes surround endothelial tubules and help maintain the integrity of blood vessels. Here the authors show that pericytes regulate lung morphogenesis via paracrine signalling controlled by components of the Hippo pathway.

Cell type specific expression of Follistatin-like 1 (Fstl1) in mouse embryonic lung development

Follistatin like-1 (Fstl1) is a secreted glycoprotein and can be up-regulated by TGF-β1. To better study the function of Fstl1 in lung development, we examined Fstl1 expression in the developing lung, in a cell type specific manner, using a tamoxifen inducible Fstl1-reporter mouse strain. Our results show that Fstl1 is ubiquitously expressed at saccular stage in the developing lung. At E18.5, Fstl1 expression is robust in most type of mesenchymal cells, including airway smooth muscle cells surrounding airways, vascular smooth muscle cells, endothelial cells, and vascular pericytes from blood vessel, but not PDGFRα⁺ fibroblasts in the distal alveolar sacs. Meanwhile, relative weak and sporadic signals of Fstl1 expression are observed in epithelium, including a subgroup of club cells in proximal airways and a few type II alveolar epithelial cells in distal airways. Our data help to understand the critical role of Fstl1 in lung development and lung disease pathogenesis.

The Lung and Esophagus: Developmental and Regenerative Overlap

Lung and esophageal development and organogenesis involve a complex interplay of signaling pathways and transcriptional factors. Once the lung and esophagus do separate, their epithelial proliferation and differentiation programs share certain common properties that may fuel adaptive responses to injury and subsequent regeneration. Lung and esophageal tissue organogenesis and regeneration provide perspectives on squamous cell cancers and adenocarcinomas in each tissue.

Spatial-Temporal Lineage Restrictions of Embryonic p63+ Progenitors Establish Distinct Stem Cell Pools in Adult Airways

Basal cells (BCs) are p63-expressing multipotent progenitors of skin, tracheoesophageal and urinary tracts. p63 is abundant in developing airways; however, it remains largely unclear how embryonic p63⁺ cells contribute to the developing and postnatal respiratory tract epithelium, and ultimately how they relate to adult BCs. Using lineage-tracing and functional approaches in vivo, we show that p63⁺ cells arising from the lung primordium are initially multipotent progenitors of airway and alveolar lineages but later become restricted proximally to generate the tracheal adult stem cell pool. In intrapulmonary airways, these cells are maintained immature to adulthood in bronchi, establishing a rare p63⁺Krt5^- progenitor cell population that responds to H1N1 virus-induced severe injury. Intriguingly, this pool includes a CC10 lineage-labeled p63⁺Krt5^- cell subpopulation required for a full H1N1-response. These data elucidate key aspects in the establishment of regionally distinct adult stem cell pools in the respiratory system, potentially with relevance to other organs.

Spatial and temporal changes in extracellular elastin and laminin distribution during lung alveolar development

Lung alveolarization requires precise coordination of cell growth with extracellular matrix (ECM) synthesis and deposition. The role of extracellular matrices in alveogenesis is not fully understood, because prior knowledge is largely extrapolated from two-dimensional structural analysis. Herein, we studied temporospatial changes of two important ECM proteins, laminin and elastin that are tightly associated with alveolar capillary growth and lung elastic recoil respectively, during both mouse and human lung alveolarization. By combining protein immunofluorescence staining with two- and three-dimensional imaging, we found that the laminin network was simplified along with the thinning of septal walls during alveogenesis, and more tightly associated with alveolar endothelial cells in matured lung. In contrast, elastin fibers were initially localized to the saccular openings of nascent alveoli, forming a ring-like structure. Then, throughout alveolar growth, the number of such alveolar mouth ring-like structures increased, while the relative ring size decreased. These rings were interconnected via additional elastin fibers. The apparent patches and dots of elastin at the tips of alveolar septae found in two-dimensional images were cross sections of elastin ring fibers in the three-dimension. Thus, the previous concept that deposition of elastin at alveolar tips drives septal inward growth may potentially be conceptually challenged by our data.

Basal Cells in Lung Development and Repair

Basal cells are an important stem cell lineage in many tissues, including the lung. In this issue of Developmental Cell, Yang et. al. (2018) find that basal cells emerge very early in lung development and that a subset of these contributes to the expansive epithelial wound response observed after influenza injury.

Loss of Hox5 function results in myofibroblast mislocalization and distal lung matrix defects during postnatal development

Alveologenesis is the final stage of lung development and is responsible for the formation of the principle gas exchange units called alveoli. The lung mesenchyme, in particular the alveolar myofibroblasts, are drivers of alveolar development, however, few key regulators that govern the proper distribution and behavior of these cells in the distal lung during alveologenesis have been identified. While Hox5 triple mutants (Hox5 aabbcc) exhibit neonatal lethality, four-allele, compound mutant mice (Hox5 AabbCc) are born in Mendelian ratios and are phenotypically normal at birth. However, they exhibit defects in alveologenesis characterized by a BPD-like phenotype by early postnatal stages that becomes more pronounced at adult stages. Invasive pulmonary functional analyses demonstrate significant increases in total lung volume and compliance and a decrease in elastance in Hox5 compound mutants. SMA+ myofibroblasts in the distal lung are distributed abnormally during peak stages of alveologenesis and aggregate, resulting in the formation of a disrupted elastin network. Examination of other key components of the distal lung ECM, as well as other epithelial cells and lipofibroblasts reveal no differences in distribution. Collectively, these data indicate that Hox5 genes play a critical role in alveolar development by governing the proper cellular behavior of myofibroblasts during alveologenesis.