Lung stem cells are instructed to produce lineage-specific progeny through unknown factors in their microenvironment. We used clonal 3D cocultures of endothelial cells and distal lung stem cells, ...bronchioalveolar stem cells (BASCs), to probe the instructive mechanisms. Single BASCs had bronchiolar and alveolar differentiation potential in lung endothelial cell cocultures. Gain- and loss-of-function experiments showed that BMP4-Bmpr1a signaling triggers calcineurin/NFATc1-dependent expression of thrombospondin-1 (Tsp1) in lung endothelial cells to drive alveolar lineage-specific BASC differentiation. Tsp1 null mice exhibited defective alveolar injury repair, confirming a crucial role for the BMP4-NFATc1-TSP1 axis in lung epithelial differentiation and regeneration in vivo. Discovery of this pathway points to methods to direct the derivation of specific lung epithelial lineages from multipotent cells. These findings elucidate a pathway that may be a critical target in lung diseases and provide tools to understand the mechanisms of respiratory diseases at the single-cell level.
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•Lung endothelial cells control lung stem cell differentiation•In vitro expansion and multilineage differentiation of single lung stem cells•Endothelial TSP1 is required for alveolar differentiation and lung regeneration•BMP4 induces lung-specific, calcineurin/NFATc1-dependent TSP1 expression
3D organoid lung cultures reveal a mechanism by which lung endothelial cells instruct lung stem cells to differentiate into a particular lineage, opening up potential avenues for stimulating these stem cells in response to respiratory-disease-associated injury.
The diversity of mesenchymal cell types in the lung that influence epithelial homeostasis and regeneration is poorly defined. We used genetic lineage tracing, single-cell RNA sequencing, and organoid ...culture approaches to show that Lgr5 and Lgr6, well-known markers of stem cells in epithelial tissues, are markers of mesenchymal cells in the adult lung. Lgr6+ cells comprise a subpopulation of smooth muscle cells surrounding airway epithelia and promote airway differentiation of epithelial progenitors via Wnt-Fgf10 cooperation. Genetic ablation of Lgr6+ cells impairs airway injury repair in vivo. Distinct Lgr5+ cells are located in alveolar compartments and are sufficient to promote alveolar differentiation of epithelial progenitors through Wnt activation. Modulating Wnt activity altered differentiation outcomes specified by mesenchymal cells. This identification of region- and lineage-specific crosstalk between epithelium and their neighboring mesenchymal partners provides new understanding of how different cell types are maintained in the adult lung.
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•Lgr5 and Lgr6 mark mesenchymal cells in adult lungs•Single-cell transcriptome analysis defines mesenchymal heterogeneity•Distinct mesenchymal niches drive airway and alveolar differentiation•Wnt activity affects epithelial differentiation specified by mesenchymal cells
Heterogeneous mesenchymal cell populations in the lung play a central role in epithelial maintenance and alveolar differentiation.
Non-small-cell lung cancers (NSCLCs), the most common lung cancers, are known to have diverse pathological features. During the past decade, in-depth analyses of lung cancer genomes and signalling ...pathways have further defined NSCLCs as a group of distinct diseases with genetic and cellular heterogeneity. Consequently, an impressive list of potential therapeutic targets was unveiled, drastically altering the clinical evaluation and treatment of patients. Many targeted therapies have been developed with compelling clinical proofs of concept; however, treatment responses are typically short-lived. Further studies of the tumour microenvironment have uncovered new possible avenues to control this deadly disease, including immunotherapy.
Lung epithelial cell damage and dysfunctional repair play a role in the development of lung disease. Effective repair likely requires the normal functioning of alveolar stem/progenitor cells. For ...example, we have shown in a mouse model of bronchopulmonary dysplasia (BPD) that mesenchymal stem cells (MSC) protect against hyperoxic lung injury at least in part by increasing the number of Epcam
Sca-1
distal lung epithelial cells. These cells are capable of differentiating into both small airway (CCSP
) and alveolar (SPC
) epithelial cells in three-dimensional (3D) organoid cultures. To further understand the interactions between MSC and distal lung epithelial cells, we added MSC to lung progenitor 3D cultures. MSC stimulated Epcam
Sca-1
derived organoid formation, increased alveolar differentiation and decreased self-renewal. MSC-conditioned media was sufficient to promote alveolar organoid formation, demonstrating that soluble factors secreted by MSC are likely responsible for the response. This work provides strong evidence of a direct effect of MSC-secreted factors on lung progenitor cell differentiation.
The population is aging at a rate never seen before in human history. As the number of elderly adults grows, it is imperative we expand our understanding of the underpinnings of aging biology. Human ...lungs are composed of a unique panoply of cell types that face ongoing chemical, mechanical, biological, immunological, and xenobiotic stress over a lifetime. Yet, we do not fully appreciate the mechanistic drivers of lung aging and why age increases the risk of parenchymal lung disease, fatal respiratory infection, and primary lung cancer. Here, we review the molecular and cellular aspects of lung aging, local stress response pathways, and how the aging process predisposes to the pathogenesis of pulmonary disease. We place these insights into context of the COVID-19 pandemic and discuss how innate and adaptive immunity within the lung is altered with age.
Recent cellular and molecular studies have given insight into why the incidence and/or severity of many lung diseases, from lung cancer to COVID-19, increase with age.
Polycomb repressive complexes (PRCs) play key roles in developmental epigenetic regulation. Yet the mechanisms that target PRCs to specific loci in mammalian cells remain incompletely understood. In ...this study we show that Bmi1, a core component of Polycomb Repressive Complex 1 (PRC1), binds directly to the Runx1/CBFβ transcription factor complex. Genome-wide studies in megakaryocytic cells demonstrate significant chromatin occupancy overlap between the PRC1 core component Ring1b and Runx1/CBFβ and functional regulation of a considerable fraction of commonly bound genes. Bmi1/Ring1b and Runx1/CBFβ deficiencies generate partial phenocopies of one another in vivo. We also show that Ring1b occupies key Runx1 binding sites in primary murine thymocytes and that this occurs via PRC2-independent mechanisms. Genetic depletion of Runx1 results in reduced Ring1b binding at these sites in vivo. These findings provide evidence for site-specific PRC1 chromatin recruitment by core binding transcription factors in mammalian cells.
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► PRC1 interacts with Runx1 and CBFβ ► PRC1 and Runx1/CBFβ colocalize on chromatin and coregulate a subset of genes ► PRC1 and Runx1/CBFβ deficiencies generate partial phenocopies of one another in vivo ► Runx1 directly recruits PRC1-independent of PRC2
Coronavirus disease 2019 (COVID-19) is the latest respiratory pandemic caused by severe acute respiratory syndrome-related coronavirus 2 (SARS-CoV-2). Although infection initiates in the proximal ...airways, severe and sometimes fatal symptoms of the disease are caused by infection of the alveolar type 2 (AT2) cells of the distal lung and associated inflammation. In this study, we develop primary human lung epithelial infection models to understand initial responses of proximal and distal lung epithelium to SARS-CoV-2 infection. Differentiated air-liquid interface (ALI) cultures of proximal airway epithelium and alveosphere cultures of distal lung AT2 cells are readily infected by SARS-CoV-2, leading to an epithelial cell-autonomous proinflammatory response with increased expression of interferon signaling genes. Studies to validate the efficacy of selected candidate COVID-19 drugs confirm that remdesivir strongly suppresses viral infection/replication. We provide a relevant platform for study of COVID-19 pathobiology and for rapid drug screening against SARS-CoV-2 and emergent respiratory pathogens.
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•Human alveospheres are composed of renewing AT2 cells and AT1-like cells•Alveolar epithelial cells are efficiently infected by SARS-CoV-2 in vitro•Interferon signaling is activated in SARS-CoV-2-infected alveolar epithelial cells•Lung organoid models provide a platform for drug discovery and disease modeling
In vitro models of human lung epithelium, including diverse cell types of the proximo-distal axis, are critical for modeling infection. Mulay et al. show that alveospheres, with epithelial type 2- and type 1-like cells, are infected by SARS-CoV-2, initiating an interferon response, and serve as a platform for screening antiviral drugs.
Injury models have suggested that the lung contains anatomically and functionally distinct epithelial stem cell populations. We have isolated such a regional pulmonary stem cell population, termed
...bronchio
alveolar
stem
cells (BASCs). Identified at the bronchioalveolar duct junction, BASCs were resistant to bronchiolar and alveolar damage and proliferated during epithelial cell renewal in vivo. BASCs exhibited self-renewal and were multipotent in clonal assays, highlighting their stem cell properties. Furthermore, BASCs expanded in response to oncogenic K-ras in culture and in precursors of lung tumors in vivo. These data support the hypothesis that BASCs are a stem cell population that maintains the bronchiolar Clara cells and alveolar cells of the distal lung and that their transformed counterparts give rise to adenocarcinoma. Although bronchiolar cells and alveolar cells are proposed to be the precursor cells of adenocarcinoma, this work points to BASCs as the putative cells of origin for this subtype of lung cancer.
An airway organoid is forever Paschini, Margherita; Kim, Carla F
The EMBO journal,
15 February 2019, Volume:
38, Issue:
4
Journal Article
Peer reviewed
Open access
In the last decade, the generation and maintenance of organotypic structures has been propelled to the center stage of biomedical research. In the lung, a variety of protocols has been devised to ...generate organoids mimicking lung structures, but most methods with human cells have complicated lengthy protocols or a progressive decline in differentiation potential and physiological function with increasing passaging. A new study from Sachs et al () seeks to solve these issues, providing a versatile methodology to efficiently isolate, indefinitely culture, and manipulate human airway organoids, potentially allowing the in vitro modeling of a plethora of lung diseases.
A new methods resource reports long‐term propagation of human lung epithelium as three dimensional organoids which can be exploited for disease modeling.
Mechanisms that regulate regional epithelial cell diversity and pathologic remodeling in airways are poorly understood. We hypothesized that regional differences in cell composition and ...injury‐related tissue remodeling result from the type and composition of local progenitors. We used surface markers and the spatial expression pattern of an SFTPC‐GFP transgene to subset epithelial progenitors by airway region. Green fluorescent protein (GFP) expression ranged from undetectable to high in a proximal‐to‐distal gradient. GFPhi cells were subdivided by CD24 staining into alveolar (CD24neg) and conducting airway (CD24low) populations. This allowed for the segregation of three types of progenitors displaying distinct clonal behavior in vitro. GFPneg and GFPlow progenitors both yielded lumen containing colonies but displayed transcriptomes reflective of pseudostratified and distal conducting airways, respectively. CD24lowGFPhi progenitors were present in an overlapping distribution with GFPlow progenitors in distal airways, yet expressed lower levels of Sox2 and expanded in culture to yield undifferentiated self‐renewing progeny. Colony‐forming ability was reduced for each progenitor cell type after in vivo bleomycin exposure, but only CD24lowGFPhi progenitors showed robust expansion during tissue remodeling. These data reveal intrinsic differences in the properties of regional progenitors and suggest that their unique responses to tissue damage drive local tissue remodeling. Stem Cells2012;30:1948–1960
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