Wnt7b stimulates embryonic lung growth by coordinately increasing the replication of epithelium and mesenchyme

A founder variant expands the phenotype of WNT7B-related PDAC syndrome

Pulmonary hypoplasia, Diaphragmatic anomalies, Anophthalmia/microphthalmia, and Cardiac defects (PDAC) syndrome is a genetically heterogeneous multiple congenital malformation syndrome. Although pathogenic variants in RARB and STRA6 are established causes of PDAC, many PDAC cases remain unsolved at the molecular level. Recently, we proposed biallelic WNT7B variants as a novel etiology based on several families with typical features of PDAC syndrome albeit with variable expressivity. Here, we report three patients from two families that share a novel founder variant in WNT7B (c.739C > T; Arg247Trp). The phenotypic expression of this variant ranges from typical PDAC features to isolated genitourinary anomalies. Similar to previously reported PDAC-associated WNT7B variants, this variant was found to significantly impair WNT7B signaling activity further corroborating its proposed pathogenicity. This report adds further evidence to WNT7B-related PDAC and expands its variable expressivity.

The molecular and cellular choreography of early mammalian lung development

Mammalian lung development starts from a specific cluster of endodermal cells situated within the ventral foregut region. With the orchestrating of delicate choreography of transcription factors, signaling pathways, and cell-cell communications, the endodermal diverticulum extends into the surrounding mesenchyme, and builds the cellular and structural basis of the complex respiratory system. This review provides a comprehensive overview of the current molecular insights of mammalian lung development, with a particular focus on the early stage of lung cell fate differentiation and spatial patterning. Furthermore, we explore the implications of several congenital respiratory diseases and the relevance to early organogenesis. Finally, we summarize the unprecedented knowledge concerning lung cell compositions, regulatory networks as well as the promising prospect for gaining an unbiased understanding of lung development and lung malformations through state-of-the-art single-cell omics.

The Fgf9-Nolz1-Wnt2 axis regulates morphogenesis of the lung

Morphological development of the lung requires complex signal crosstalk between the mesenchymal and epithelial progenitors. Elucidating the genetic cascades underlying signal crosstalk is essential to understanding lung morphogenesis. Here, we identified Nolz1 as a mesenchymal lineage-specific transcriptional regulator that plays a key role in lung morphogenesis. Nolz1 null mutation resulted in a severe hypoplasia phenotype, including a decreased proliferation of mesenchymal cells, aberrant differentiation of epithelial cells and defective growth of epithelial branches. Nolz1 deletion also downregulated Wnt2, Lef1, Fgf10, Gli3 and Bmp4 mRNAs. Mechanistically, Nolz1 regulates lung morphogenesis primarily through Wnt2 signaling. Loss-of-function and overexpression studies demonstrated that Nolz1 transcriptionally activated Wnt2 and downstream β-catenin signaling to control mesenchymal cell proliferation and epithelial branching. Exogenous Wnt2 could rescue defective proliferation and epithelial branching in Nolz1 knockout lungs. Finally, we identified Fgf9 as an upstream regulator of Nolz1. Collectively, Fgf9-Nolz1-Wnt2 signaling represents a novel axis in the control of lung morphogenesis. These findings are relevant to lung tumorigenesis, in which a pathological function of Nolz1 is implicated.

α7nAChR activation in AT2 cells promotes alveolar regeneration through WNT7B signaling in acute lung injury

Reducing inflammatory damage and improving alveolar epithelium regeneration are two key approaches to promoting lung repair in acute lung injury/acute respiratory distress syndrome (ALI/ARDS). Stimulation of cholinergic α7 nicotinic acetylcholine receptor (α7nAChR, coded by Chrna7) signaling could dampen lung inflammatory injury. However, whether activation of α7nAChR in alveolar type II (AT2) cells promotes alveolar epithelial injury repair and underlying mechanisms is elusive. Here, we found that α7nAChR was expressed on AT2 cells and was upregulated in response to LPS-induced ALI. Meanwhile, deletion of Chrna7 in AT2 cells impeded lung repair process and worsened lung inflammation in ALI. Using in vivo AT2 lineage-labeled mice and ex vivo AT2 cell-derived alveolar organoids, we demonstrated that activation of α7nAChR expressed on AT2 cells improved alveolar regeneration by promoting AT2 cells to proliferate and subsequently differentiate toward alveolar type I cells. Then, we screened out the WNT7B signaling pathway by the RNA-Seq analysis of in vivo AT2 lineage-labeled cells and further confirmed its indispensability for α7nAChR activation-mediated alveolar epithelial proliferation and differentiation. Thus, we have identified a potentially unrecognized pathway in which cholinergic α7nAChR signaling determines alveolar regeneration and repair, which might provide us a novel therapeutic target for combating ALI.

Targeted alveolar regeneration with Frizzled-specific agonists

Wnt ligands oligomerize Frizzled (Fzd) and Lrp5/6 receptors to control the specification and activity of stem cells in many species. How Wnt signaling is selectively activated in different stem cell populations, often within the same organ, is not understood. In lung alveoli, we show that distinct Wnt receptors are expressed by epithelial (Fzd5/6), endothelial (Fzd4), and stromal (Fzd1) cells. Fzd5 is uniquely required for alveolar epithelial stem cell activity, whereas fibroblasts utilize distinct Fzd receptors. Using an expanded repertoire of Fzd-Lrp agonists, we could activate canonical Wnt signaling in alveolar epithelial stem cells via either Fzd5 or, unexpectedly, non-canonical Fzd6. A Fzd5 agonist (Fzd5ag) or Fzd6ag stimulated alveolar epithelial stem cell activity and promoted survival in mice after lung injury, but only Fzd6ag promoted an alveolar fate in airway-derived progenitors. Therefore, we identify a potential strategy for promoting regeneration without exacerbating fibrosis during lung injury.

Bi-allelic variants in WNT7B disrupt the development of multiple organs in humans

BACKGROUND

Pulmonary hypoplasia, Diaphragmatic anomalies, Anophthalmia/microphthalmia and Cardiac defects delineate the PDAC syndrome. We aim to identify the cause of PDAC syndrome in patients who do not carry pathogenic variants in RARB and STRA6, which have been previously associated with this disorder.

METHODS

We sequenced the exome of patients with unexplained PDAC syndrome and performed functional validation of candidate variants.

RESULTS

We identified bi-allelic variants in WNT7B in fetuses with PDAC syndrome from two unrelated families. In one family, the fetus was homozygous for the c.292C>T (p.(Arg98*)) variant whereas the fetuses from the other family were compound heterozygous for the variants c.225C>G (p.(Tyr75*)) and c.562G>A (p.(Gly188Ser)). Finally, a molecular autopsy by proxy in a consanguineous couple that lost two babies due to lung hypoplasia revealed that both parents carry the p.(Arg98*) variant. Using a WNT signalling canonical luciferase assay, we demonstrated that the identified variants are deleterious. In addition, we found that wnt7bb mutant zebrafish display a defect of the swimbladder, an air-filled organ that is a structural homolog of the mammalian lung, suggesting that the function of WNT7B has been conserved during evolution for the development of these structures.

CONCLUSION

Our findings indicate that defective WNT7B function underlies a form of lung hypoplasia that is associated with the PDAC syndrome, and provide evidence for involvement of the WNT-β-catenin pathway in human lung, tracheal, ocular, cardiac, and renal development.

Lung epithelium development and airway regeneration

The lung is composed of a highly branched airway structure, which humidifies and warms the inhaled air before entering the alveolar compartment. In the alveoli, a thin layer of epithelium is in close proximity with the capillary endothelium, allowing for an efficient exchange of oxygen and carbon dioxide. During development proliferation and differentiation of progenitor cells generates the lung architecture, and in the adult lung a proper function of progenitor cells is needed to regenerate after injury. Malfunctioning of progenitors during development results in various congenital lung disorders, such as Congenital Diaphragmatic Hernia (CDH) and Congenital Pulmonary Adenomatoid Malformation (CPAM). In addition, many premature neonates experience continuous insults on the lung caused by artificial ventilation and supplemental oxygen, which requires a highly controlled mechanism of airway repair. Malfunctioning of airway progenitors during regeneration can result in reduction of respiratory function or (chronic) airway diseases. Pathways that are active during development are frequently re-activated upon damage. Understanding the basic mechanisms of lung development and the behavior of progenitor cell in the ontogeny and regeneration of the lung may help to better understand the underlying cause of lung diseases, especially those occurring in prenatal development or in the immediate postnatal period of life. This review provides an overview of lung development and the cell types involved in repair of lung damage with a focus on the airway.

Loading-induced bone formation is mediated by Wnt1 induction in osteoblast-lineage cells

Mechanical loading on the skeleton stimulates bone formation. Although the exact mechanism underlying this process remains unknown, a growing body of evidence indicates that the Wnt signaling pathway is necessary for the skeletal response to loading. Recently, we showed that Wnts produced by osteoblast lineage cells mediate the osteo-anabolic response to tibial loading in adult mice. Here, we report that Wnt1 specifically plays a crucial role in mediating the mechano-adaptive response to loading. Independent of loading, short-term loss of Wnt1 in the Osx-lineage resulted in a decreased cortical bone area in the tibias of 5-month-old mice. In females, strain-matched loading enhanced periosteal bone formation in Wnt1F/F controls, but not in Wnt1F/F; OsxCreERT2 knockouts. In males, strain-matched loading increased periosteal bone formation in both control and knockout mice; however, the periosteal relative bone formation rate was 65% lower in Wnt1 knockouts versus controls. Together, these findings show that Wnt1 supports adult bone homeostasis and mediates the bone anabolic response to mechanical loading.

R-SPONDIN2+ mesenchymal cells form the bud tip progenitor niche during human lung development

The human respiratory epithelium is derived from a progenitor cell in the distal buds of the developing lung. These "bud tip progenitors" are regulated by reciprocal signaling with surrounding mesenchyme; however, mesenchymal heterogeneity and function in the developing human lung are poorly understood. We interrogated single-cell RNA sequencing data from multiple human lung specimens and identified a mesenchymal cell population present during development that is highly enriched for expression of the WNT agonist RSPO2, and we found that the adjacent bud tip progenitors are enriched for the RSPO2 receptor LGR5. Functional experiments using organoid models, explant cultures, and FACS-isolated RSPO2+ mesenchyme show that RSPO2 is a critical niche cue that potentiates WNT signaling in bud tip progenitors to support their maintenance and multipotency.

The WNT7A/WNT7B/GPR124/RECK signaling module plays an essential role in mammalian limb development

In central nervous system vascular endothelial cells, signaling via the partially redundant ligands WNT7A and WNT7B requires two co-activator proteins, GPR124 and RECK. WNT7A and RECK have been shown previously to play a role in limb development, but the mechanism of RECK action in this context is unknown. The roles of WNT7B and GPR124 in limb development have not been investigated. Using combinations of conventional and/or conditional loss-of-function alleles for mouse Wnt7a, Wnt7b, Gpr124 and Reck, including a Reck allele that codes for a protein that is specifically defective in WNT7A/WNT7B signaling, we show that reductions in ligand and/or co-activator function synergize to cause reduced and dysmorphic limb bone growth. Two additional limb phenotypes – loss of distal Lmx1b expression and ectopic growth of nail-like structures – occur with reduced Wnt7a/Wnt7b gene copy number and, respectively, with Reck mutations and with combined Reck and Gpr124 mutations. A third limb phenotype – bleeding into a digit – occurs with the most severe combinations of Wnt7a/Wnt7b, Reck and Gpr124 mutations. These data imply that the WNT7A/WNT7B-FRIZZLED-LRP5/LRP6-GPR124-RECK signaling system functions as an integral unit in limb development.

Summary: Genetic analyses in mice show that the WNT7A/WNT7B-FRIZZLED-LRP5/LRP6-GPR124-RECK signaling system, first defined in the context of CNS angiogenesis and barrier development, also functions as an integral unit in limb development.

Tracheal Ring Formation

The trachea is a long tube that enables air passage between the larynx and the bronchi. C-shaped cartilage rings on the ventral side stabilise the structure. On its esophagus-facing dorsal side, deformable smooth muscle facilitates the passage of food in the esophagus. While the symmetry break along the dorsal-ventral axis is well understood, the molecular mechanism that results in the periodic Sox9 expression pattern that translates into the cartilage rings has remained elusive. Here, we review the molecular regulatory interactions that have been elucidated, and discuss possible patterning mechanisms. Understanding the principles of self-organisation is important, both to define biomedical interventions and to enable tissue engineering.

Epithelial Wntless regulates postnatal alveologenesis

Alveologenesis requires the coordinated modulation of the epithelial and mesenchymal compartments to generate mature alveolar saccules for efficient gas exchange. However, the molecular mechanisms underlying the epithelial-mesenchymal interaction during alveologenesis are poorly understood. Here, we report that Wnts produced by epithelial cells are crucial for neonatal alveologenesis. Deletion of the Wnt chaperone protein Wntless homolog (Wls) disrupts alveolar formation, resulting in enlarged saccules in Sftpc-Cre/Nkx2.1-Cre; Wlsloxp/loxp mutants. Although commitment of the alveolar epithelium is unaffected, α-SMA+ mesenchymal cells persist in the alveoli, accompanied by increased collagen deposition, and mutants exhibit exacerbated fibrosis following bleomycin challenge. Notably, α-SMA+ cells include a significant number of endothelial cells resembling endothelial to mesenchymal transition (EndMT), which is also present in Ager-CreER; Wlsloxp/loxp mutants following early postnatal Wls deletion. These findings provide initial evidence that epithelial-derived Wnts are crucial for the differentiation of the surrounding mesenchyme during early postnatal alveologenesis.

Developmental Pathways Underlying Lung Development and Congenital Lung Disorders

Lung organogenesis is a highly coordinated process governed by a network of conserved signaling pathways that ultimately control patterning, growth, and differentiation. This rigorously regulated developmental process culminates with the formation of a fully functional organ. Conversely, failure to correctly regulate this intricate series of events results in severe abnormalities that may compromise postnatal survival or affect/disrupt lung function through early life and adulthood. Conditions like congenital pulmonary airway malformation, bronchopulmonary sequestration, bronchogenic cysts, and congenital diaphragmatic hernia display unique forms of lung abnormalities. The etiology of these disorders is not yet completely understood; however, specific developmental pathways have already been reported as deregulated. In this sense, this review focuses on the molecular mechanisms that contribute to normal/abnormal lung growth and development and their impact on postnatal survival.

Organoid models: assessing lung cell fate decisions and disease responses

Organoids can be derived from various cell types in the lung, and they provide a reproducible and tractable model for understanding the complex signals driving cell fate decisions in a regenerative context. In this review, we provide a retrospective account of organoid methodologies and outline new opportunities for optimizing these methods to further explore emerging concepts in lung biology. Moreover, we examine the benefits of integrating organoid assays with in vivo modeling to explore how the various niches and compartments in the respiratory system respond to both acute and chronic lung disease. The strategic implementation and improvement of organoid techniques will provide exciting new opportunities to understand and identify new therapeutic approaches to ameliorate lung disease states.

Mammalian tracheal development and reconstruction: insights from in vivo and in vitro studies

The trachea delivers inhaled air into the lungs for gas exchange. Anomalies in tracheal development can result in life-threatening malformations, such as tracheoesophageal fistula and tracheomalacia. Given the limitations of current therapeutic approaches, development of technologies for the reconstitution of a three-dimensional trachea from stem cells is urgently required. Recently, single-cell sequencing technologies and quantitative analyses from cell to tissue scale have been employed to decipher the cellular basis of tracheal morphogenesis. In this Review, recent advances in mammalian tracheal development and the generation of tracheal tissues from pluripotent stem cells are summarized.

Uncoupling of macrophage inflammation from self-renewal modulates host recovery from respiratory viral infection

Tissue macrophages self-renew during homeostasis and produce inflammatory mediators upon microbial infection. We examined the relationship between proliferative and inflammatory properties of tissue macrophages by defining the impact of the Wnt/β-catenin pathway, a central regulator of self-renewal, in alveolar macrophages (AMs). Activation of β-catenin by Wnt ligand inhibited AM proliferation and stemness, but promoted inflammatory activity. In a murine influenza viral pneumonia model, β-catenin-mediated AM inflammatory activity promoted acute host morbidity; in contrast, AM proliferation enabled repopulation of reparative AMs and tissue recovery following viral clearance. Mechanistically, Wnt treatment promoted β-catenin-HIF-1α interaction and glycolysis-dependent inflammation while suppressing mitochondrial metabolism and thereby, AM proliferation. Differential HIF-1α activities distinguished proliferative and inflammatory AMs in vivo. This β-catenin-HIF-1α axis was conserved in human AMs and enhanced HIF-1α expression associated with macrophage inflammation in COVID-19 patients. Thus, inflammatory and reparative activities of lung macrophages are regulated by β-catenin-HIF-1α signaling, with implications for the treatment of severe respiratory diseases.

Wnt signaling in lung development, regeneration, and disease progression

The respiratory tract is a vital, intricate system for several important biological processes including mucociliary clearance, airway conductance, and gas exchange. The Wnt signaling pathway plays several crucial and indispensable roles across lung biology in multiple contexts. This review highlights the progress made in characterizing the role of Wnt signaling across several disciplines in lung biology, including development, homeostasis, regeneration following injury, in vitro directed differentiation efforts, and disease progression. We further note uncharted directions in the field that may illuminate important biology. The discoveries made collectively advance our understanding of Wnt signaling in lung biology and have the potential to inform therapeutic advancements for lung diseases.

Cody Aros, Carla Pantoja, and Brigitte Gomperts review the key role of Wnt signaling in all aspects of lung development, repair, and disease progression. They provide an overview of recent research findings and highlight where research is needed to further elucidate mechanisms of action, with the aim of improving disease treatments.

Combined genomic and proteomic approaches reveal DNA binding sites and interaction partners of TBX2 in the developing lung

BACKGROUND

Tbx2 encodes a transcriptional repressor implicated in the development of numerous organs in mouse. During lung development TBX2 maintains the proliferation of mesenchymal progenitors, and hence, epithelial proliferation and branching morphogenesis. The pro-proliferative function was traced to direct repression of the cell-cycle inhibitor genes Cdkn1a and Cdkn1b, as well as of genes encoding WNT antagonists, Frzb and Shisa3, to increase pro-proliferative WNT signaling. Despite these important molecular insights, we still lack knowledge of the DNA occupancy of TBX2 in the genome, and of the protein interaction partners involved in transcriptional repression of target genes.

METHODS

We used chromatin immunoprecipitation (ChIP)-sequencing and expression analyses to identify genomic DNA-binding sites and transcription units directly regulated by TBX2 in the developing lung. Moreover, we purified TBX2 containing protein complexes from embryonic lung tissue and identified potential interaction partners by subsequent liquid chromatography/mass spectrometry. The interaction with candidate proteins was validated by immunofluorescence, proximity ligation and individual co-immunoprecipitation analyses.

RESULTS

We identified Il33 and Ccn4 as additional direct target genes of TBX2 in the pulmonary mesenchyme. Analyzing TBX2 occupancy data unveiled the enrichment of five consensus sequences, three of which match T-box binding elements. The remaining two correspond to a high mobility group (HMG)-box and a homeobox consensus sequence motif. We found and validated binding of TBX2 to the HMG-box transcription factor HMGB2 and the homeobox transcription factor PBX1, to the heterochromatin protein CBX3, and to various members of the nucleosome remodeling and deacetylase (NuRD) chromatin remodeling complex including HDAC1, HDAC2 and CHD4.

CONCLUSION

Our data suggest that TBX2 interacts with homeobox and HMG-box transcription factors as well as with the NuRD chromatin remodeling complex to repress transcription of anti-proliferative genes in the pulmonary mesenchyme.

WNT Signalling in Lung Physiology and Pathology

The main physiological function of the lung is gas exchange, mediated at the interface between the alveoli and the pulmonary microcapillary network and facilitated by conducting airway structures that regulate the transport of these gases from and to the alveoli. Exposure to microbial and environmental factors such as allergens, viruses, air pollution, and smoke contributes to the development of chronic lung diseases such as asthma, chronic obstructive pulmonary disease (COPD), idiopathic pulmonary fibrosis (IPF), and lung cancer. Respiratory diseases as a cluster are the commonest cause of chronic disease and of hospitalization in children and are among the three most common causes of morbidity and mortality in the adult population worldwide. Many of these chronic respiratory diseases are associated with inflammation and structural remodelling of the airways and/or alveolar tissues. They can often only be treated symptomatically with no disease-modifying therapies that normalize the pathological tissue destruction driven by inflammation and remodelling. In search for novel therapeutic strategies for these diseases, several lines of evidence revealed the WNT pathway as an emerging target for regenerative strategies in the lung. WNT proteins, their receptors, and signalling effectors have central regulatory roles under (patho)physiological conditions underpinning lung function and (chronic) lung diseases and we summarize these roles and discuss how pharmacological targeting of the WNT pathway may be utilized for the treatment of chronic lung diseases.

Disruption of a hedgehog-foxf1-rspo2 signaling axis leads to tracheomalacia and a loss of sox9+ tracheal chondrocytes

Congenital tracheomalacia, resulting from incomplete tracheal cartilage development, is a relatively common birth defect that severely impairs breathing in neonates. Mutations in the Hedgehog (HH) pathway and downstream Gli transcription factors are associated with tracheomalacia in patients and mouse models; however, the underlying molecular mechanisms are unclear. Using multiple HH/Gli mouse mutants including one that mimics Pallister-Hall Syndrome, we show that excessive Gli repressor activity prevents specification of tracheal chondrocytes. Lineage tracing experiments show that Sox9+ chondrocytes arise from HH-responsive splanchnic mesoderm in the fetal foregut that expresses the transcription factor Foxf1. Disrupted HH/Gli signaling results in 1) loss of Foxf1 which in turn is required to support Sox9+ chondrocyte progenitors and 2) a dramatic reduction in Rspo2, a secreted ligand that potentiates Wnt signaling known to be required for chondrogenesis. These results reveal a HH-Foxf1-Rspo2 signaling axis that governs tracheal cartilage development and informs the etiology of tracheomalacia.

How to Use Online Tools to Generate New Hypotheses for Mammary Gland Biology Research: A Case Study for Wnt7b

An increasing number of '-omics' datasets, generated by labs all across the world, are becoming available. They contain a wealth of data that are largely unexplored. Not every scientist, however, will have access to the required resources and expertise to analyze such data from scratch. Fortunately, a growing number of investigators is dedicating their time and effort to the development of user friendly, online applications that allow researchers to use and investigate these datasets. Here, we will illustrate the usefulness of such an approach. Using regulation of Wnt7b expression as an example, we will highlight a selection of accessible tools and resources that are available to researchers in the area of mammary gland biology. We show how they can be used for in silico analyses of gene regulatory mechanisms, resulting in new hypotheses and providing leads for experimental follow up. We also call out to the mammary gland community to join forces in a coordinated effort to generate and share additional tissue-specific '-omics' datasets and thereby expand the in silico toolbox.

Combined Omics Approaches Reveal the Roles of Non-canonical WNT7B Signaling and YY1 in the Proliferation of Human Pancreatic Progenitor Cells

The proliferation of human pancreatic progenitor cells (PPCs) is critical for developing cell therapies for diabetes. Here, using transcriptome analysis combined with small interfering RNA (siRNA) screening, we revealed that WNT7B is a downstream growth factor of AT7867, a compound known to promote the proliferation of PPCs generated from human pluripotent stem cells. Feeder cell lines stably expressing mouse Wnt7a or Wnt7b, but not other Wnts, enhanced PPC proliferation in the absence of AT7867. Importantly, Wnt7a/b ligands did not activate the canonical Wnt pathway, and PPC proliferation depended on the non-canonical Wnt/PKC pathway. A comparison of the phosphoproteome in response to AT7867 or a newly synthesized AT7867 derivative uncovered the function of YY1 as a transcriptional regulator of WNT7B. Overall, our data highlight unknown roles of non-canonical WNT7B/PKC signaling and YY1 in human PPC proliferation and will contribute to the stable supply of a cell source for pancreatic disease modeling and therapeutic applications.

The mechanisms in the altered ontogenetic development and lung-related pathology in microcystin-leucine arginine (MC-LR)-paternal-exposed offspring mice

A father's lifetime experience is a major risk factor for a range of diseases in an individual, and the consequences of the exposure can also be transmitted to his offspring. Our previous work has demonstrated that damage to testicular structures and decline in sperm quality in male mice can be caused by microcystin-leucine arginine (MC-LR), but the overall effects of the scope and extent of paternal exposure on health and disease in the offspring remain underexplored. Here, we report that MC-LR-paternal-exposed offspring mice showed reduced litter size and body weight accompanied by increased abnormalities in the lung. Analyses of the small noncoding RNAs (sncRNAs) in the sperm from MC-LR-exposed males demonstrated the downregulation of a wide range of piRNAs enriched for those target genes involved in the regulation of the embryo implantation pathways. Gene and protein expression analyses, as well as biochemical and functional studies, revealed suppressed expression of Hsp90α in testicular tissues from MC-LR-exposed males. Decreased Hsp90α in testicular tissues impaired the development of the offspring. In this study, we revealed that MC-LR alters the expression of Hsp90α in testicular tissues to cause changes in the expression profiles of sperm piRNAs produced by paternal mice. These changes lead to aberrant activation of the Wnt/β-catenin signaling pathway in pulmonary tissues of offspring mice, causing lung tissue damage and abnormal development. We hereby confirmed that MC-LR-induced alterations in epigenetic inheritance are capable of contributing to intergenerational developmental defects in paternal-exposed offspring mice.

Delineating the early transcriptional specification of the mammalian trachea and esophagus

The genome-scale transcriptional programs that specify the mammalian trachea and esophagus are unknown. Though NKX2-1 and SOX2 are hypothesized to be co-repressive master regulators of tracheoesophageal fates, this is untested at a whole transcriptomic scale and their downstream networks remain unidentified. By combining single-cell RNA-sequencing with bulk RNA-sequencing of Nkx2-1 mutants and NKX2-1 ChIP-sequencing in mouse embryos, we delineate the NKX2-1 transcriptional program in tracheoesophageal specification, and discover that the majority of the tracheal and esophageal transcriptome is NKX2-1 independent. To decouple the NKX2-1 transcriptional program from regulation by SOX2, we interrogate the expression of newly-identified tracheal and esophageal markers in Sox2/Nkx2-1 compound mutants. Finally, we discover that NKX2-1 binds directly to Shh and Wnt7b and regulates their expression to control mesenchymal specification to cartilage and smooth muscle, coupling epithelial identity with mesenchymal specification. These findings create a new framework for understanding early tracheoesophageal fate specification at the genome-wide level.

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.

Analysis of Wnt7B and BMP4 expression patterns in congenital pulmonary airway malformation

BACKGROUND

Congenital pulmonary airway malformation (CPAM) is a rare disorder characterized by aberrant overgrowth of terminal bronchioles. The objective of this study was to describe wingless-type MMTV integration site family 7B (Wnt7B) and bone morphogenetic protein 4 (BMP4) expression patterns in human CPAM lesions and to explore the possible roles of Wnt7B and BMP4 in the pathogenesis of CPAM.

METHODS

Fifteen tissue samples from patients with CPAM were obtained from the Pathology Department of Shengjing Hospital of China Medical University. Samples representing CPAM lesions and adjacent normal lung tissues were collected and Wnt7B and BMP4 expression was detected through immunohistochemical (IHC) staining, quantitative real-time polymerase chain reaction (qRT-PCR), and Western blotting.

RESULTS

IHC revealed that Wnt7B immunopositive cells were only detected in epithelial cells, whereas BMP4 immunopositive cells were detected in epithelial and mesenchymal cells. Expression of Wnt7B and BMP4 immunopositive cells was higher in CPAM lesions than that in adjacent normal lung tissue. qRT-PCR and Western blotting showed that Wnt7B and BMP4 mRNA and protein expression were significantly higher in CPAM lesions than in adjacent normal lung tissue (P < .05). Overall, the level of BMP4 was higher than that of Wnt7B.

CONCLUSIONS

Increased expression of Wnt7B and BMP4 appear to be related to the pathogenesis of CPAM and abnormal pulmonary development. Upregulation of Wnt7B and BMP4 could play an important role in the development of the bronchial-alveolar structures that characterize CPAM.

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.

Macrophages as an Emerging Source of Wnt Ligands: Relevance in Mucosal Integrity

The Wnt signaling pathway is a conserved pathway involved in important cellular processes such as the control of embryonic development, cellular polarity, cellular migration, and cell proliferation. In addition to playing a central role during embryogenesis, this pathway is also an essential part of adult homeostasis. Indeed, it controls the proliferation of epithelial cells in different organs such as intestine, lung, and kidney, and guarantees the maintenance of the mucosa in physiological conditions. The origin of this molecular pathway is the binding between Wnt ligands (belonging to a family of 19 different homologous secreted glycoproteins) and their specific membrane receptors, from the Frizzled receptor family. This specific interaction triggers the activation of the signaling cascade, which in turn activates or suppresses the expression of different genes in order to change the behavior of the cell. On the other hand, alterations of this pathway have been described in pathological conditions such as inflammation, fibrosis, and cancer. In recent years, macrophages-among other cell types-have emerged as a potential source of Wnt ligands. Due to their high plasticity, macrophages, which are central to the innate immune response, are capable of adopting different phenotypes depending on their microenvironment. In the past, two different phenotypes were described: a proinflammatory phenotype-M1 macrophages-and an anti-inflammatory phenotype-M2 macrophages-and a selective expression of Wnt ligands has been associated with said phenotypes. However, nowadays it is assumed that macrophages in vivo move through a continual spectrum of functional phenotypes. In both physiological and pathological (inflammation, fibrosis and cancer) conditions, the accumulation and polarization of macrophages conditions the future of the tissue, facilitating various scenarios, such as resolution of inflammation, activation of fibrosis, and cancer development due to the modulation of the Wnt signaling pathway, in autocrine and paracrine manner. In this work, we provide an overview of studies that have explored the role of macrophages and how they act as a source of Wnt ligands and as mediators of mucosal integrity.

The role of Wnt7B in the mediation of dentinogenesis via the ERK1/2 pathway

OBJECTIVES

This study investigates the role of Wnt7b in mouse dentin formation.

DESIGN

C57BL/6 mouse tooth germs at different developmental stages were collected to measure the expression of Wnt7b by immunohistochemical staining. The morphology of mandibles of Dmp1-cre;ROSA26-Wnt7b transgenic mice and ROSA26-Wnt7b littermates was analyzed by Micro-CT and HE staining. The ultramicrostructure of dentin was scanned with an electron microscope. Primary mouse dental papillae cells (MDPCs) and odontoblastic cell line (A11) were cultured and infected with adenovirus to overexpress Wnt7b. Cell proliferation and cell apoptosis were evaluated using CCK-8 and flow cytometry. Osteogenic differentiation of MDPCs and A11 was assessed by Alizarin red staining, and qPCR detection of osteogenic gene expression. The activation of signaling pathways was measured by the use of western blot analysis. The ERK1/2 inhibitor was used to test the effect of Wnt7b regulated cell differentiation.

RESULTS

Wnt7b was expressed principally in the mouse odontoblast layer after the early bell stage. In transgenic mice, Wnt7b was over-expressed in tooth mesenchyme, with a thinner predentin layer and thicker intertubular dentin. Both the micro-hardness value and the Ca/Pi ratio of dentin of transgenic mice were higher. Wnt7b promoted proliferation and mineralization of MDPCs and A11. The protein level of p-ERK1/2 was found to be higher in A11 infected with Ad-Wnt7b. The ERK signaling pathway inhibitor partly rescued the Wnt7b-induced differentiation of A11.

CONCLUSIONS

Wnt7b enhances dentinogenesis by increasing the proliferation and differentiation of dental mesenchymal cells partly through ERK1/2 pathway.

TGF-β activation impairs fibroblast ability to support adult lung epithelial progenitor cell organoid formation

Transforming growth factor-β (TGF-β)-induced fibroblast-to-myofibroblast differentiation contributes to remodeling in chronic obstructive pulmonary disease and idiopathic pulmonary fibrosis, but whether this impacts the ability of fibroblasts to support lung epithelial repair remains little explored. We pretreated human lung fibroblasts [primary (phFB) or MRC5 cells] with recombinant human TGF-β to induce myofibroblast differentiation, then cocultured them with adult mouse lung epithelial cell adhesion molecule-positive cells (EpCAM⁺) to investigate their capacity to support epithelial organoid formation in vitro. While control phFB and MRC5 lung fibroblasts supported organoid formation of mouse EpCAM⁺ cells, TGF-β pretreatment of both phFB and MRC5 impaired organoid-supporting ability. We performed RNA sequencing of TGF-β-treated phFB, which revealed altered expression of key Wnt signaling pathway components and Wnt/β-catenin target genes, and modulated expression of secreted factors involved in mesenchymal-epithelial signaling. TGF-β profoundly skewed the transcriptional program induced by the Wnt/β-catenin activator CHIR99021. Supplementing organoid culture media recombinant hepatocyte growth factor or fibroblast growth factor 7 promoted organoid formation when using TGF-β pretreated fibroblasts. In conclusion, TGF-β-induced myofibroblast differentiation results in Wnt/β-catenin pathway skewing and impairs fibroblast ability to support epithelial repair likely through multiple mechanisms, including modulation of secreted growth factors.

A natural WNT signaling variant potently synergizes with Cdkn2ab loss in skin carcinogenesis

Cdkn2ab knockout mice, generated from 129P2 ES cells develop skin carcinomas. Here we show that the incidence of these carcinomas drops gradually in the course of backcrossing to the FVB/N background. Microsatellite analyses indicate that this cancer phenotype is linked to a 20 Mb region of 129P2 chromosome 15 harboring the Wnt7b gene, which is preferentially expressed from the 129P2 allele in skin carcinomas and derived cell lines. ChIPseq analysis shows enrichment of H3K27-Ac, a mark for active enhancers, in the 5' region of the Wnt7b 129P2 gene. The Wnt7b 129P2 allele appears sufficient to cause in vitro transformation of Cdkn2ab-deficient cell lines primarily through CDK6 activation. These results point to a critical role of the Cdkn2ab locus in keeping the oncogenic potential of physiological levels of WNT signaling in check and illustrate that GWAS-based searches for cancer predisposing allelic variants can be enhanced by including defined somatically acquired lesions as an additional input.

Hippo signaling promotes lung epithelial lineage commitment by curbing Fgf10 and β-catenin signaling

Organ growth and tissue homeostasis rely on the proliferation and differentiation of progenitor cell populations. In the developing lung, localized Fgf10 expression maintains distal Sox9-expressing epithelial progenitors and promotes basal cell differentiation in the cartilaginous airways. Mesenchymal Fgf10 expression is induced by Wnt signaling but inhibited by Shh signaling, and epithelial Fgf10 signaling activates β-catenin signaling. The Hippo pathway is a well-conserved signaling cascade that regulates organ size and stem/progenitor cell behavior. Here, we show that Hippo signaling promotes lineage commitment of lung epithelial progenitors by curbing Fgf10 and β-catenin signaling. Our findings show that both inactivation of the Hippo pathway (nuclear Yap) or ablation of Yap result in increased β-catenin and Fgf10 signaling, suggesting a cytoplasmic role for Yap in epithelial lineage commitment. We further demonstrate redundant and non-redundant functions for the two nuclear effectors of the Hippo pathway, Yap and Taz, during lung development.

LRP5 in age-related changes in vascular and alveolar morphogenesis in the lung

Aging is associated with impaired angiogenesis and lung alveolar regeneration, which contributes to the increased susceptibility to chronic lung diseases (CLD). We have reported that the Wnt ligand co-receptor, low-density lipoprotein receptor-related protein 5 (LRP5), stimulates angiogenesis and lung alveolar regeneration. However, the role of LRP5 in age-related decline in vascular and alveolar morphogenesis remains unclear. In this report, we have demonstrated that vascular and alveolar structures are disrupted in the 24-month (24M) old mouse lungs. The expression of LRP5 and the major angiogenic factors, VEGFR2 and Tie2, is lower in endothelial cells (ECs) isolated from 24M old mouse lungs compared to those from 2M old mouse lungs. Vascular and alveolar formation is attenuated in the hydrogel implanted on the 24M old mouse lungs, while overexpression of LRP5, which restores angiogenic factor expression, reverses vascular and alveolar morphogenesis in the gel. Compensatory lung growth after unilateral pneumonectomy is inhibited in 24M old mice, which is reversed by overexpression of LRP5. These results suggest that LRP5 mediates age-related inhibition of angiogenesis and alveolar morphogenesis. Modulation of LRP5 may be a novel intervention to rejuvenate regenerative ability in aged lung and will lead to the development of efficient strategies for aging-associated CLD.

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.

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.

Notum attenuates Wnt/β-catenin signaling to promote tracheal cartilage patterning

Tracheobronchomalacia (TBM) is a common congenital disorder in which the cartilaginous rings of the trachea are weakened or missing. Despite the high prevalence and clinical issues associated with TBM, the etiology is largely unknown. Our previous studies demonstrated that Wntless (Wls) and its associated Wnt pathways are critical for patterning of the upper airways. Deletion of Wls in respiratory endoderm caused TBM and ectopic trachealis muscle. To understand mechanisms by which Wls mediates tracheal patterning, we performed RNA sequencing in prechondrogenic tracheal tissue of Wls^f/f;Shh^Cre/wt embryos. Chondrogenic Bmp4, and Sox9 were decreased, while expression of myogenic genes was increased. We identified Notum, a deacylase that inactivates Wnt ligands, as a target of Wls induced Wnt signaling. Notum's mesenchymal ventral expression in prechondrogenic trachea overlaps with expression of Axin2, a Wnt/β-catenin target and inhibitor. Notum is induced by Wnt/β-catenin in developing trachea. Deletion of Notum activated mesenchymal Wnt/β-catenin and caused tracheal mispatterning of trachealis muscle and cartilage as well as tracheal stenosis. Notum is required for tracheal morphogenesis, influencing mesenchymal condensations critical for patterning of tracheal cartilage and muscle. We propose that Notum influences mesenchymal cell differentiation by generating a barrier for Wnt ligands produced and secreted by airway epithelial cells to attenuate Wnt signaling.

Single-cell Wnt signaling niches maintain stemness of alveolar type 2 cells

Alveoli, the lung's respiratory units, are tiny sacs where oxygen enters the bloodstream. They are lined by flat alveolar type 1 (AT1) cells, which mediate gas exchange, and AT2 cells, which secrete surfactant. Rare AT2s also function as alveolar stem cells. We show that AT2 lung stem cells display active Wnt signaling, and many of them are near single, Wnt-expressing fibroblasts. Blocking Wnt secretion depletes these stem cells. Daughter cells leaving the Wnt niche transdifferentiate into AT1s: Maintaining Wnt signaling prevents transdifferentiation, whereas abrogating Wnt signaling promotes it. Injury induces AT2 autocrine Wnts, recruiting "bulk" AT2s as progenitors. Thus, individual AT2 stem cells reside in single-cell fibroblast niches providing juxtacrine Wnts that maintain them, whereas injury induces autocrine Wnts that transiently expand the progenitor pool. This simple niche maintains the gas exchange surface and is coopted in cancer.

Regeneration of functional alveoli by adult human SOX9+ airway basal cell transplantation

Irreversible destruction of bronchi and alveoli can lead to multiple incurable lung diseases. Identifying lung stem/progenitor cells with regenerative capacity and utilizing them to reconstruct functional tissue is one of the biggest hopes to reverse the damage and cure such diseases. Here we showed that a rare population of SOX9⁺ basal cells (BCs) located at airway epithelium rugae can regenerate adult human lung. Human SOX9⁺ BCs can be readily isolated by bronchoscopic brushing and indefinitely expanded in feeder-free condition. Expanded human SOX9⁺ BCs can give rise to alveolar and bronchiolar epithelium after being transplanted into injured mouse lung, with air-blood exchange system reconstructed and recipient’s lung function improved. Manipulation of lung microenvironment with Pirfenidone to suppress TGF-β signaling could further boost the transplantation efficiency. Moreover, we conducted the first autologous SOX9⁺ BCs transplantation clinical trial in two bronchiectasis patients. Lung tissue repair and pulmonary function enhancement was observed in patients 3–12 months after cell transplantation. Altogether our current work indicated that functional adult human lung structure can be reconstituted by orthotopic transplantation of tissue-specific stem/progenitor cells, which could be translated into a mature regenerative therapeutic strategy in near future.

Emergence of a Wave of Wnt Signaling that Regulates Lung Alveologenesis by Controlling Epithelial Self-Renewal and Differentiation

Alveologenesis is the culmination of lung development and involves the correct temporal and spatial signals to generate the delicate gas exchange interface required for respiration. Using a Wnt-signaling reporter system, we demonstrate the emergence of a Wnt-responsive alveolar epithelial cell sublineage, which arises during alveologenesis, called the axin2+ alveolar type 2 cell, or AT2^Axin2. The number of AT2^Axin2 cells increases substantially during late lung development, correlating with a wave of Wnt signaling during alveologenesis. Transcriptome analysis, in vivo clonal analysis, and ex vivo lung organoid assays reveal that AT2s^Axin2 promote enhanced AT2 cell growth during generation of the alveolus. Activating Wnt signaling results in the expansion of AT2s, whereas inhibition of Wnt signaling inhibits AT2 cell development and shunts alveolar epithelial development toward the alveolar type 1 cell lineage. These findings reveal a wave of Wnt-dependent AT2 expansion required for lung alveologenesis and maturation.

Fgf10-Hippo Epithelial-Mesenchymal Crosstalk Maintains and Recruits Lung Basal Stem Cells

The lung harbors its basal stem/progenitor cells (BSCs) in the protected environment of the cartilaginous airways. After major lung injuries, BSCs are activated and recruited to sites of injury. Here, we show that during homeostasis, BSCs in cartilaginous airways maintain their stem cell state by downregulating the Hippo pathway (resulting in increased nuclear Yap), which generates a localized Fgf10-expressing stromal niche; in contrast, differentiated epithelial cells in non-cartilaginous airways maintain quiescence by activating the Hippo pathway and inhibiting Fgf10 expression in airway smooth muscle cells (ASMCs). However, upon injury, surviving differentiated epithelial cells spread to maintain barrier function and recruit integrin-linked kinase to adhesion sites, which leads to Merlin degradation, downregulation of the Hippo pathway, nuclear Yap translocation, and expression and secretion of Wnt7b. Epithelial-derived Wnt7b, then in turn, induces Fgf10 expression in ASMCs, which extends the BSC niche to promote regeneration.

Reck and Gpr124 Are Essential Receptor Cofactors for Wnt7a/Wnt7b-Specific Signaling in Mammalian CNS Angiogenesis and Blood-Brain Barrier Regulation

Reck, a GPI-anchored membrane protein, and Gpr124, an orphan GPCR, have been implicated in Wnt7a/Wnt7b signaling in the CNS vasculature. We show here that vascular endothelial cell (EC)-specific reduction in Reck impairs CNS angiogenesis and that EC-specific postnatal loss of Reck, combined with loss of Norrin, impairs blood-brain barrier (BBB) maintenance. The most N-terminal domain of Reck binds to the leucine-rich repeat (LRR) and immunoglobulin (Ig) domains of Gpr124, and weakening this interaction by targeted mutagenesis reduces Reck/Gpr124 stimulation of Wnt7a signaling in cell culture and impairs CNS angiogenesis. Finally, a soluble Gpr124(LRR-Ig) probe binds to cells expressing Frizzled, Wnt7a or Wnt7b, and Reck, and a soluble Reck(CC1-5) probe binds to cells expressing Frizzled, Wnt7a or Wnt7b, and Gpr124. These experiments indicate that Reck and Gpr124 are part of the cell surface protein complex that transduces Wnt7a- and Wnt7b-specific signals in mammalian CNS ECs to promote angiogenesis and regulate the BBB.

Modeling coexistence of oscillation and Delta/Notch-mediated lateral inhibition in pancreas development and neurogenesis

During pancreas development, Neurog3 positive endocrine progenitors are specified by Delta/Notch (D/N) mediated lateral inhibition in the growing ducts. During neurogenesis, genes that determine the transition from the proneural state to neuronal or glial lineages are oscillating before their expression is sustained. Although the basic gene regulatory network is very similar, cycling gene expression in pancreatic development was not investigated yet, and previous simulations of lateral inhibition in pancreas development excluded by design the possibility of oscillations. To explore this possibility, we developed a dynamic model of a growing duct that results in an oscillatory phase before the determination of endocrine progenitors by lateral inhibition. The basic network (D/N + Hes1 + Neurog3) shows scattered, stable Neurog3 expression after displaying transient expression. Furthermore, we included the Hes1 negative feedback as previously discussed in neurogenesis and show the consequences for Neurog3 expression in pancreatic duct development. Interestingly, a weakened HES1 action on the Hes1 promoter allows the coexistence of stable patterning and oscillations. In conclusion, cycling gene expression and lateral inhibition are not mutually exclusive. In this way, we argue for a unified mode of D/N mediated lateral inhibition in neurogenic and pancreatic progenitor specification.

Wnt proteins synergize to activate β-catenin signaling

Wnt ligands are involved in diverse signaling pathways that are active during development, maintenance of tissue homeostasis and in various disease states. While signaling regulated by individual Wnts has been extensively studied, Wnts are rarely expressed alone, and the consequences of Wnt gene co-expression are not well understood. Here, we studied the effect of co-expression of Wnts on the β-catenin signaling pathway. While some Wnts are deemed 'non-canonical' due to their limited ability to activate β-catenin when expressed alone, unexpectedly, we find that multiple Wnt combinations can synergistically activate β-catenin signaling in multiple cell types. WNT1- and WNT7B-mediated synergistic Wnt signaling requires FZD5, FZD8 and LRP6, as well as the WNT7B co-receptors GPR124 (also known as ADGRA2) and RECK. Unexpectedly, this synergistic signaling occurs downstream of β-catenin stabilization, and is correlated with increased lysine acetylation of β-catenin. Wnt synergy provides a general mechanism to confer increased combinatorial control over this important regulatory pathway.

Maternal smoke exposure decreases mesenchymal proliferation and modulates Rho-GTPase-dependent actin cytoskeletal signaling in fetal lungs

The present study tested the hypothesis that maternal smoke exposure results in fetal lung growth retardation due to dysregulation in various signaling pathways, including the Wnt (wingless-related integration site)/β-catenin pathway. Pregnant female C57BL/6J mice were exposed to cigarette smoke (100-150 mg/m³) or room air, and offspring were humanely killed on 12.5, 14.5, 16.5, and 18.5 d post coitum (dpc). We assessed lung stereology with Cavalieri estimation; apoptosis with proliferating cell nuclear antigen, TUNEL, and caspase assays; and gene expression with quantitative PCR (qPCR) and RNA sequencing on lung epithelium and mesenchyme retrieved by laser capture microdissection. Results demonstrated a significant decrease in body weight and lung volume of smoke-exposed embryos. At 16.5 dpc, the reduction in lung volume was due to loss of lung mesenchymal tissue correlating with a decrease in cell proliferation (n = 10; air: 61.65% vs. smoke: 44.21%, P < 0.05). RNA sequence analysis demonstrated an alteration in the Wnt pathway, and qPCR confirmed an increased expression of secreted frizzled-related protein 1 (sFRP-1) [n = 12; relative quantification (RQ) 1 vs. 2.33, P < 0.05] and down-regulation of Cyclin D1 (n = 7; RQ 1 vs. 0.61, P < 0.05) in mesenchymal tissue. Furthermore, genome expression studies revealed a smoke-induced up-regulation of Rho-GTPase-dependent actin cytoskeletal signaling that can lead to loss of tissue integrity.-Unachukwu, U., Trischler, J., Goldklang, M., Xiao, R., D'Armiento, J. Maternal smoke exposure decreases mesenchymal proliferation and modulates Rho-GTPase-dependent actin cytoskeletal signaling in fetal lungs.

Arl4c is a key regulator of tubulogenesis and tumourigenesis as a target gene of Wnt-β-catenin and growth factor-Ras signalling

Epithelial tubular morphogenesis (tubulogenesis) is a fundamental morphogenetic process of many epithelial organs. In this developmental process, epithelial cells migrate, proliferate, polarize and differentiate towards surrounding mesenchymal tissue to form tubule structures. Although epithelial tissue structures are basically stable in the postnatal period, epithelial cells regain highly proliferative and invasive potentials within mesenchymal tissue during tumour formation (tumourigenesis). Therefore, there must be a common molecular basis orchestrating the cellular behaviours involved in both tubulogenesis and tumourigenesis. ADP-ribosylation factor (Arf)-like protein 4c (Arl4c), which belongs to the small GTP-binding protein family, is expressed by the simultaneous activation of Wnt-β-catenin and growth factor-Ras-mitogen-activated protein kinase signalling, was identified as an essential regulator of tubulogenesis. Arl4c expression was also involved in the tumour formation of colorectal and lung cancers. In this review, we focus on Arl4c as a novel Wnt signal target molecule that links epithelial tubulogenesis to tumourigenesis.

Linking bronchopulmonary dysplasia to adult chronic lung diseases: role of WNT signaling

Bronchopulmonary dysplasia (BPD) is one of the most common chronic lung diseases in infants caused by pre- and/or postnatal lung injury. BPD is characterized by arrested alveolarization and vascularization due to extracellular matrix remodeling, inflammation, and impaired growth factor signaling. WNT signaling is a critical pathway for normal lung development, and its altered signaling has been shown to be involved in the onset and progression of incurable chronic lung diseases in adulthood, such as chronic obstructive pulmonary disease (COPD) or idiopathic pulmonary fibrosis (IPF). In this review, we summarize the impact of WNT signaling on different stages of lung development and its potential contribution to developmental lung diseases, especially BPD, and chronic lung diseases in adulthood.

Tbx2 and Tbx3 Act Downstream of Shh to Maintain Canonical Wnt Signaling during Branching Morphogenesis of the Murine Lung

Numerous signals drive the proliferative expansion of the distal endoderm and the underlying mesenchyme during lung branching morphogenesis, but little is known about how these signals are integrated. Here, we show by analysis of conditional double mutants that the two T-box transcription factor genes Tbx2 and Tbx3 act together in the lung mesenchyme to maintain branching morphogenesis. Expression of both genes depends on epithelially derived Shh signaling, with additional modulation by Bmp, Wnt, and Tgfβ signaling. Genetic rescue experiments reveal that Tbx2 and Tbx3 function downstream of Shh to maintain pro-proliferative mesenchymal Wnt signaling, in part by direct repression of the Wnt antagonists Frzb and Shisa3. In combination with our previous finding that Tbx2 and Tbx3 repress the cell-cycle inhibitors Cdkn1a and Cdkn1b, we conclude that Tbx2 and Tbx3 maintain proliferation of the lung mesenchyme by way of at least two molecular mechanisms: regulating cell-cycle regulation and integrating the activity of multiple signaling pathways.

Molecular developmental mechanism in polypterid fish provides insight into the origin of vertebrate lungs

The lung is an important organ for air breathing in tetrapods and originated well before the terrestrialization of vertebrates. Therefore, to better understand lung evolution, we investigated lung development in the extant basal actinopterygian fish Senegal bichir (Polypterus senegalus). First, we histologically confirmed that lung development in this species is very similar to that of tetrapods. We also found that the mesenchymal expression patterns of three genes that are known to play important roles in early lung development in tetrapods (Fgf10, Tbx4, and Tbx5) were quite similar to those of tetrapods. Moreover, we found a Tbx4 core lung mesenchyme-specific enhancer (C-LME) in the genomes of bichir and coelacanth (Latimeria chalumnae) and experimentally confirmed that these were functional in tetrapods. These findings provide the first molecular evidence that the developmental program for lung was already established in the common ancestor of actinopterygians and sarcopterygians.

Wnt7b Signaling from the Ureteric Bud Epithelium Regulates Medullary Capillary Development

The renal vasculature is integral to the physiologic function of the kidneys in regulating hemodynamics of the body and maintaining organ health. The close inter-relationship of capillaries and the renal epithelium is key to renal physiology, but how renal tubules regulate capillary development remains unclear. Our previous work showed that Wnt7b is expressed in the ureteric trunk epithelium and activates canonical Wnt signaling in the surrounding medullary interstitium, where the capillaries reside. In this study, we showed by immunofluorescence that the target interstitial cells of Wnt7b/canonical Wnt signaling are mural cells of periureteric bud capillaries in the nascent renal medulla of embryonic mice. Genetic ablation of Wnt7b enhanced the proliferation of Wnt7b target mural cells, an effect that associated with decreased expression of PDGFRβ and p57kip2, a cyclin-dependent kinase inhibitor, in these cells. Furthermore, Wnt7b regulated lumen formation of the capillary endothelium in the renal medulla. In the absence of Wnt7b signaling, the periureteric bud medullary capillaries displayed narrower lumens lined with less flattened endothelial cells and a significantly increased presence of luminal endothelial cell-cell junctions, a transient configuration in the forming blood vessels in the controls. Moreover, the absence of Wnt7b led to greatly diminished levels of vascular endothelial (VE)-cadherin at the cell surface in these blood vessels. VE-cadherin is essential for blood vessel lumen formation; thus, Wnt7b may regulate lumen formation through modulation of VE-cadherin localization. Overall, these results indicate a novel role of Wnt7b signaling and the ureteric bud epithelium in renal medullary capillary development.

How to Grow a Lung: Applying Principles of Developmental Biology to Generate Lung Lineages from Human Pluripotent Stem Cells

The number and severity of diseases affecting human lung development and adult respiratory function has stimulated great interest in new in vitro models to study the human lung. This review summarizes the most recent breakthroughs deriving lung lineages in a dish by directing the differentiation of human pluripotent stem cells. A variety of culturing platforms have been developed, including two-dimensional and three-dimensional (organoid) culture platforms, to derive specific cell types and structures of the lung. These stem cell-derived lung models will further our understanding of human lung development, disease, and regeneration.