CD151 Maintains Endolysosomal Protein Quality to Inhibit Vascular Inflammation.

BACKGROUND: Tetraspanin CD151 is highly expressed in endothelia and reinforces cell adhesion, but its role in vascular inflammation remains largely unknown. METHODS: In vitro molecular and cellular biological analyses on genetically modified endothelial cells, in vivo vascular biological analyses on genetically engineered mouse models, and in silico systems biology and bioinformatics analyses on CD151-related events. RESULTS: Endothelial ablation of Cd151 leads to pulmonary and cardiac inflammation, severe sepsis, and perilous COVID-19, and endothelial CD151 becomes downregulated in inflammation. Mechanistically, CD151 restrains endothelial release of proinflammatory molecules for less leukocyte infiltration. At the subcellular level, CD151 determines the integrity of multivesicular bodies/lysosomes and confines the production of exosomes that carry cytokines such as ANGPT2 (angiopoietin-2) and proteases such as cathepsin-D. At the molecular level, CD151 docks VCP (valosin-containing protein)/p97, which controls protein quality via mediating deubiquitination for proteolytic degradation, onto endolysosomes to facilitate VCP/p97 function. At the endolysosome membrane, CD151 links VCP/p97 to (1) IFITM3 (interferon-induced transmembrane protein 3), which regulates multivesicular body functions, to restrain IFITM3-mediated exosomal sorting, and (2) V-ATPase, which dictates endolysosome pH, to support functional assembly of V-ATPase. CONCLUSIONS: Distinct from its canonical function in strengthening cell adhesion at cell surface, CD151 maintains endolysosome function by sustaining VCP/p97-mediated protein unfolding and turnover. By supporting protein quality control and protein degradation, CD151 prevents proteins from (1) buildup in endolysosomes and (2) discharge through exosomes, to limit vascular inflammation. Also, our study conceptualizes that balance between degradation and discharge of proteins in endothelial cells determines vascular information. Thus, the IFITM3/V-ATPase-tetraspanin-VCP/p97 complexes on endolysosome, as a protein quality control and inflammation-inhibitory machinery, could be beneficial for therapeutic intervention against vascular inflammation.

The emerging role of NOTCH3 receptor signalling in human lung diseases.

The mammalian respiratory system or lung is a tree-like branching structure, and the main site of gas exchange with the external environment. Structurally, the lung is broadly classified into the proximal (or conducting) airways and the distal alveolar region, where the gas exchange occurs. In parallel with the respiratory tree, the pulmonary vasculature starts with large pulmonary arteries that subdivide rapidly ending in capillaries adjacent to alveolar structures to enable gas exchange. The NOTCH signalling pathway plays an important role in lung development, differentiation and regeneration post-injury. Signalling via the NOTCH pathway is mediated through activation of four NOTCH receptors (NOTCH1-4), with each receptor capable of regulating unique biological processes. Dysregulation of the NOTCH pathway has been associated with development and pathophysiology of multiple adult acute and chronic lung diseases. This includes accumulating evidence that alteration of NOTCH3 signalling plays an important role in the development and pathogenesis of chronic obstructive pulmonary disease, lung cancer, asthma, idiopathic pulmonary fibrosis and pulmonary arterial hypertension. Herein, we provide a comprehensive summary of the role of NOTCH3 signalling in regulating repair/regeneration of the adult lung, its association with development of lung disease and potential therapeutic strategies to target its signalling activity.

Cigarette Smoke Activates NOTCH3 to Promote Goblet Cell Differentiation in Human Airway Epithelial Cells.

Chronic obstructive pulmonary disease (COPD) is the third leading cause of death in the United States and is primarily caused by cigarette smoking. Increased numbers of mucus-producing secretory ("goblet") cells, defined as goblet cell metaplasia or hyperplasia (GCMH), contributes significantly to COPD pathophysiology. The objective of this study was to determine whether NOTCH signaling regulates goblet cell differentiation in response to cigarette smoke. Primary human bronchial epithelial cells (HBECs) from nonsmokers and smokers with COPD were differentiated in vitro on air-liquid interface and exposed to cigarette smoke extract (CSE) for 7 days. NOTCH signaling activity was modulated using 1) the NOTCH/γ-secretase inhibitor dibenzazepine (DBZ), 2) lentiviral overexpression of the NICD3 (NOTCH3-intracellular domain), or 3) NOTCH3-specific siRNA. Cell differentiation and response to CSE were evaluated by quantitative PCR, Western blotting, immunostaining, and RNA sequencing. We found that CSE exposure of nonsmoker airway epithelium induced goblet cell differentiation characteristic of GCMH. Treatment with DBZ suppressed CSE-dependent induction of goblet cell differentiation. Furthermore, CSE induced NOTCH3 activation, as revealed by increased NOTCH3 nuclear localization and elevated NICD3 protein levels. Overexpression of NICD3 increased the expression of goblet cell-associated genes SPDEF and MUC5AC, whereas NOTCH3 knockdown suppressed CSE-mediated induction of SPDEF and MUC5AC. Finally, CSE exposure of COPD airway epithelium induced goblet cell differentiation in a NOTCH3-dependent manner. These results identify NOTCH3 activation as one of the important mechanisms by which cigarette smoke induces goblet cell differentiation, thus providing a novel potential strategy to control GCMH-related pathologies in smokers and patients with COPD.

Role of KRAS in regulating normal human airway basal cell differentiation.

BACKGROUND: KRAS is a GTPase that activates pathways involved in cell growth, differentiation and survival. In normal cells, KRAS-activity is tightly controlled, but with specific mutations, the KRAS protein is persistently activated, giving cells a growth advantage resulting in cancer. While a great deal of attention has been focused on the role of mutated KRAS as a common driver mutation for lung adenocarcinoma, little is known about the role of KRAS in regulating normal human airway differentiation. METHODS: To assess the role of KRAS signaling in regulating differentiation of the human airway epithelium, primary human airway basal stem/progenitor cells (BC) from nonsmokers were cultured on air-liquid interface (ALI) cultures to mimic the airway epithelium in vitro. Modulation of KRAS signaling was achieved using siRNA-mediated knockdown of KRAS or lentivirus-mediated over-expression of wild-type KRAS or the constitutively active G12 V mutant. The impact on differentiation was quantified using TaqMan quantitative PCR, immunofluorescent and immunohistochemical staining analysis for cell type specific markers. Finally, the impact of cigarette smoke exposure on KRAS and RAS protein family activity in the airway epithelium was assessed in vitro and in vivo. RESULTS: siRNA-mediated knockdown of KRAS decreased differentiation of BC into secretory and ciliated cells with a corresponding shift toward squamous cell differentiation. Conversely, activation of KRAS signaling via lentivirus mediated over-expression of the constitutively active G12 V KRAS mutant had the opposite effect, resulting in increased secretory and ciliated cell differentiation and decreased squamous cell differentiation. Exposure of BC to cigarette smoke extract increased KRAS and RAS protein family activation in vitro. Consistent with these observations, airway epithelium brushed from healthy smokers had elevated RAS activation compared to nonsmokers. CONCLUSIONS: Together, these data suggest that KRAS-dependent signaling plays an important role in regulating the balance of secretory, ciliated and squamous cell differentiation of the human airway epithelium and that cigarette smoking-induced airway epithelial remodeling is mediated in part by abnormal activation of KRAS-dependent signaling mechanisms.

Ontogeny and Biology of Human Small Airway Epithelial Club Cells.

RATIONALE: Little is known about human club cells, dome-shaped cells with dense cytoplasmic granules and microvilli that represent the major secretory cells of the human small airways (at least sixth-generation bronchi). OBJECTIVES: To define the ontogeny and biology of the human small airway epithelium club cell. METHODS: The small airway epithelium was sampled from the normal human lung by bronchoscopy and brushing. Single-cell transcriptome analysis and air-liquid interface culture were used to assess club cell ontogeny and biology. MEASUREMENTS AND MAIN RESULTS: We identified the club cell population by unbiased clustering using single-cell transcriptome sequencing. Principal component gradient analysis uncovered an ontologic link between KRT5 (keratin 5)+ basal cells and SCGB1A1 (secretoglobin family 1A member 1)+ club cells, a hypothesis verified by demonstrating in vitro that a pure population of human KRT5+ SCGB1A1- small airway epithelial basal cells differentiate into SCGB1A1+KRT5- club cells on air-liquid interface culture. Using SCGB1A1 as the marker of club cells, the single-cell analysis identified novel roles for these cells in host defense, xenobiotic metabolism, antiprotease, physical barrier function, monogenic lung disorders, and receptors for human viruses. CONCLUSIONS: These observations provide novel insights into the molecular phenotype and biologic functions of the human club cell population and identify basal cells as the human progenitor cells for club cells.

Cilia dysfunction in lung disease.

A characteristic feature of the human airway epithelium is the presence of ciliated cells bearing motile cilia, specialized cell surface projections containing axonemes composed of microtubules and dynein arms, which provide ATP-driven motility. In the airways, cilia function in concert with airway mucus to mediate the critical function of mucociliary clearance, cleansing the airways of inhaled particles and pathogens. The prototypical disorder of respiratory cilia is primary ciliary dyskinesia, an inherited disorder that leads to impaired mucociliary clearance, to repeated chest infections, and to the progressive destruction of lung architecture. Numerous acquired lung diseases are also marked by abnormalities in both cilia structure and function. In this review we summarize current knowledge regarding airway ciliated cells and cilia, how they function to maintain a healthy epithelium, and how disorders of cilia structure and function contribute to inherited and acquired lung disease.

POU2AF1 Functions in the Human Airway Epithelium To Regulate Expression of Host Defense Genes.

In the process of seeking novel lung host defense regulators by analyzing genome-wide RNA sequence data from normal human airway epithelium, we detected expression of POU domain class 2-associating factor 1 (POU2AF1), a known transcription cofactor previously thought to be expressed only in lymphocytes. Lymphocyte contamination of human airway epithelial samples obtained by bronchoscopy and brushing was excluded by immunohistochemistry staining, the observation of upregulation of POU2AF1 in purified airway basal stem/progenitor cells undergoing differentiation, and analysis of differentiating single basal cell clones. Lentivirus-mediated upregulation of POU2AF1 in airway basal cells induced upregulation of host defense genes, including MX1, IFIT3, IFITM, and known POU2AF1 downstream genes HLA-DRA, ID2, ID3, IL6, and BCL6. Interestingly, expression of these genes paralleled changes of POU2AF1 expression during airway epithelium differentiation in vitro, suggesting POU2AF1 helps to maintain a host defense tone even in pathogen-free condition. Cigarette smoke, a known risk factor for airway infection, suppressed POU2AF1 expression both in vivo in humans and in vitro in human airway epithelial cultures, accompanied by deregulation of POU2AF1 downstream genes. Finally, enhancing POU2AF1 expression in human airway epithelium attenuated the suppression of host defense genes by smoking. Together, these findings suggest a novel function of POU2AF1 as a potential regulator of host defense genes in the human airway epithelium.

Endothelial MMP14 is required for endothelial-dependent growth support of human airway basal cells.

Human airway basal cells are the stem (or progenitor) population of the airway epithelium, and play a central role in anchoring the epithelium to the basement membrane. The anatomic position of basal cells allows for potential paracrine signaling between them and the underlying non-epithelial stromal cells. In support of this, we have previously demonstrated that endothelial cells support growth of basal cells during co-culture through vascular endothelial growth factor A (VEGFA)-mediated signaling. Building on these findings, we found, by RNA sequencing analysis, that basal cells expressed multiple fibroblast growth factor (FGF) ligands (FGF2, FGF5, FGF11 and FGF13) and that only FGF2 and FGF5 were capable of functioning in a paracrine manner to activate classical FGF receptor (FGFR) signaling. Antibody-mediated blocking of FGFR1 during basal-cell-endothelial-cell co-culture significantly reduced the endothelial-cell-dependent basal cell growth. Stimulation of endothelial cells with basal-cell-derived growth factors induced endothelial cell expression of matrix metallopeptidase 14 (MMP14), and short hairpin RNA (shRNA)-mediated knockdown of endothelial cell MMP14 significantly reduced the endothelial-cell-dependent growth of basal cells. Overall, these data characterize a new growth-factor-mediated reciprocal 'crosstalk' between human airway basal cells and endothelial cells that regulates proliferation of basal cells.

SOS1 and Ras regulate epithelial tight junction formation in the human airway through EMP1.

The human airway is lined with respiratory epithelial cells, which create a critical barrier through the formation of apical tight junctions. To investigate the molecular mechanisms underlying this process, an RNAi screen for guanine nucleotide exchange factors (GEFs) was performed in human bronchial epithelial cells (16HBE). We report that SOS1, acting through the Ras/MEK/ERK pathway, is essential for tight junction formation. Global microarray analysis identifies epithelial membrane protein 1 (EMP1), an integral tetraspan membrane protein, as a major transcriptional target. EMP1 is indispensable for tight junction formation and function in 16HBE cells and in a human airway basal progenitor-like cell line (BCi-NS1.1). Furthermore, EMP1 is significantly downregulated in human lung cancers. Together, these data identify important roles for SOS1/Ras and EMP1 in tight junction assembly during airway morphogenesis.

Pulmonary Abnormalities in Young, Light-Use Waterpipe (Hookah) Smokers.

RATIONALE: Waterpipes, also called hookahs, are currently used by millions of people worldwide. Despite the increasing use of waterpipe smoking, there is limited data on the health effects of waterpipe smoking and there are no federal regulations regarding its use. OBJECTIVES: To assess the effects of waterpipe smoking on the human lung using clinical and biological parameters in young, light-use waterpipe smokers. METHODS: We assessed young, light-use, waterpipe-only smokers in comparison with lifelong nonsmokers using clinical parameters of cough and sputum scores, lung function, and chest high-resolution computed tomography as well as biological parameters of lung epithelial lining fluid metabolome, small airway epithelial (SAE) cell differential and transcriptome, alveolar macrophage transcriptome, and plasma apoptotic endothelial cell microparticles. MEASUREMENTS AND MAIN RESULTS: Compared with nonsmokers, waterpipe smokers had more cough and sputum as well as a lower lung diffusing capacity, abnormal epithelial lining fluid metabolome profile, increased proportions of SAE secretory and intermediate cells, reduced proportions of SAE ciliated and basal cells, markedly abnormal SAE and alveolar macrophage transcriptomes, and elevated levels of apoptotic endothelial cell microparticles. CONCLUSIONS: Young, light-use, waterpipe-only smokers have a variety of abnormalities in multiple lung-related biological and clinical parameters, suggesting that even limited waterpipe use has broad consequences on human lung biology and health. We suggest that large epidemiological studies should be initiated to investigate the harmful effects of waterpipe smoking.

Smoking-Associated Disordering of the Airway Basal Stem/Progenitor Cell Metabotype.

The airway epithelium is a complex pseudostratified multicellular layer lining the tracheobronchial tree, functioning as the primary defense against inhaled environmental contaminants. The major cell types of the airway epithelium include basal, intermediate columnar, ciliated, and secretory. Basal cells (BCs) are the proliferating stem/progenitor population that differentiate into the other specialized cell types of the airway epithelium during normal turnover and repair. Given that cigarette smoke delivers thousands of xenobiotics and high levels of reactive molecules to the lung epithelial surface, we hypothesized that cigarette smoke broadly perturbs BC metabolism. To test this hypothesis, primary airway BCs were isolated from healthy nonsmokers (n = 11) and healthy smokers (n = 7) and assessed by global metabolic profiling by liquid chromatography-mass spectrometry. The analysis identified 52 significant metabolites in BCs differentially expressed between smokers and nonsmokers (P < 0.05). These changes included metabolites associated with redox pathways, energy production, and inflammatory processes. Notably, BCs from smokers exhibited altered levels of the key enzyme cofactors/substrates nicotinamide adenine dinucleotide, flavin adenine dinucleotide, acetyl coenzyme A, and membrane phospholipid levels. Consistent with the high burden of oxidants in cigarette smoke, glutathione levels were diminished, whereas 3-nitrotyrosine levels were increased, suggesting that protection of airway epithelial cells against oxidative and nitrosative stress is significantly compromised in smoker BCs. It is likely that this altered metabotype is a reflection of, and likely contributes to, the disordered biology of airway BCs consequent to the stress cigarette smoking puts on the airway epithelium.

Cigarette smoking induces small airway epithelial epigenetic changes with corresponding modulation of gene expression.

The small airway epithelium (SAE), the first site of smoking-induced lung pathology, exhibits genome-wide changes in gene expression in response to cigarette smoking. Based on the increasing evidence that the epigenome can respond to external stimuli in a rapid manner, we assessed the SAE of smokers for genome-wide DNA methylation changes compared with nonsmokers, and whether changes in SAE DNA methylation were linked to the transcriptional output of these cells. Using genome-wide methylation analysis of SAE DNA of nonsmokers and smokers, the data identified 204 unique genes differentially methylated in SAE DNA of smokers compared with nonsmokers, with 67% of the regions with differential methylation occurring within 2 kb of the transcriptional start site. Among the genes with differential methylation were those related to metabolism, transcription, signal transduction and transport. For the differentially methylated genes, 35 exhibited a correlation with gene expression, 54% with an inverse correlation of DNA methylation with gene expression and 46% a direct correlation. These observations provide evidence that cigarette smoking alters the DNA methylation patterning of the SAE and that, for some genes, these changes are associated with the smoking-related changes in gene expression.

FOXJ1 prevents cilia growth inhibition by cigarette smoke in human airway epithelium in vitro.

Airway epithelium ciliated cells play a central role in clearing the lung of inhaled pathogens and xenobiotics, and cilia length and coordinated beating are important for airway clearance. Based on in vivo studies showing that the airway epithelium of healthy smokers has shorter cilia than that of healthy nonsmokers, we investigated the mechanisms involved in cigarette smoke-mediated inhibition of ciliogenesis by assessing normal human airway basal cell differentiation in air-liquid interface (ALI) cultures in the presence of nontoxic concentrations of cigarette smoke extract (CSE). Measurements of cilia length from Day 28 ALI cultures demonstrated that CSE exposure was associated with shorter cilia (P < 0.05), reproducing the effect of cigarette smoking on cilia length observed in vivo. This phenotype correlated with a broad CSE-mediated suppression of genes involved in cilia-related transcriptional regulation, intraflagellar transport, cilia motility, structural integrity, and basal body development but not of control genes or epithelial barrier integrity. The CSE-mediated inhibition of cilia growth could be prevented by lentivirus-mediated overexpression of FOXJ1, the major cilia-related transcription factor, which led to partial reversal of expression of cilia-related genes suppressed by CSE. Together, the data suggest that components of cigarette smoke are responsible for a broad suppression of genes involved in cilia growth, but, by stimulating ciliogenesis with the transcription factor FOXJ1, it may be possible to maintain close to normal cilia length despite the stress of cigarette smoking.

Smoking accelerates aging of the small airway epithelium.

BACKGROUND: Aging involves multiple biologically complex processes characterized by a decline in cellular homeostasis over time leading to a loss and impairment of physiological integrity and function. Specific cellular hallmarks of aging include abnormal gene expression patterns, shortened telomeres and associated biological dysfunction. Like all organs, the lung demonstrates both physiological and structural changes with age that result in a progressive decrease in lung function in healthy individuals. Cigarette smoking accelerates lung function decline over time, suggesting smoking accelerates aging of the lung. Based on this data, we hypothesized that cigarette smoking accelerates the aging of the small airway epithelium, the cells that take the initial brunt of inhaled toxins from the cigarette smoke and one of the primary sites of pathology associated with cigarette smoking. METHODS: Using the sensitive molecular parameters of aging-related gene expression and telomere length, the aging process of the small airway epithelium was assessed in age matched healthy nonsmokers and healthy smokers with no physical manifestation of lung disease or abnormalities in lung function. RESULTS: Analysis of a 73 gene aging signature demonstrated that smoking significantly dysregulates 18 aging-related genes in the small airway epithelium. In an independent cohort of male subjects, smoking significantly reduced telomere length in the small airway epithelium of smokers by 14% compared to nonsmokers. CONCLUSION: These data provide biologic evidence that smoking accelerates aging of the small airway epithelium.

Translational 3D-Cell Culture Model to Assess Hyperoxia Effects on Human Neonatal Airway Epithelial Cells.

The preterm neonatal airway epithelium is constantly exposed to environmental stressors. One of these stressors in neonates with lung disease includes oxygen (O2) tension higher than the ambient atmosphere - termed hyperoxia (>21% O2). The effect of hyperoxia on the airway depends on various factors, including the developmental stage of the airway, the degree of hyperoxia, and the duration of exposure, with variable exposures potentially leading to unique phenotypes. While there has been extensive research on the effect of hyperoxia on neonatal lung alveolarization and airway hyperreactivity, little is known about the short and long-term underlying effect of hyperoxia on human neonatal airway epithelial cells. A major reason for this is the scarcity of an effective in vitro model to study human neonatal airway epithelial development and function. Here, we describe a method for isolating and expanding human neonatal tracheal airway epithelial cells (nTAECs) utilizing human neonatal tracheal aspirates and culturing these cells in air-liquid interface (ALI) culture. We demonstrate that nTAECs form a mature polarized cell-monolayer in ALI culture and undergo mucociliary differentiation. We also present a method for moderate hyperoxia exposure of the cell monolayer in ALI culture using a specialized incubator. Additionally, we describe an assay to measure cellular oxidative stress following hyperoxia exposure in ALI culture using fluorescent quantification, which confirms that moderate hyperoxia exposure induces cellular oxidative stress but does not cause significant cell membrane damage or apoptosis. This model can potentially be used to simulate clinically relevant hyperoxia exposure encountered by neonatal airways in the Neonatal Intensive Care Unit (NICU) and used to study the short and long-lasting effects of O2 on neonatal airway epithelial programming. Studies using this model could be utilized to explore ways to mitigate early-life oxidative injury to developing airways, which is implicated in the development of long-term airway diseases in former premature infants.

RFX3 modulation of FOXJ1 regulation of cilia genes in the human airway epithelium.

BACKGROUND: Ciliated cells play a central role in cleansing the airways of inhaled contaminants. They are derived from basal cells that include the airway stem/progenitor cells. In animal models, the transcription factor FOXJ1 has been shown to induce differentiation to the ciliated cell lineage, and the RFX transcription factor-family has been shown to be necessary for, but not sufficient to induce, correct cilia development. METHODS: To test the hypothesis that FOXJ1 and RFX3 cooperatively induce expression of ciliated genes in the differentiation process of basal progenitor cells toward a ciliated cell linage in the human airway epithelium, primary human airway basal cells were assessed under conditions of in vitro differentiation induced by plasmid-mediated gene transfer of FOXJ1 and/or RFX3. TaqMan PCR was used to quantify mRNA levels of basal, secretory, and cilia-associated genes. RESULTS: Basal cells, when cultured in air-liquid interface, differentiated into a ciliated epithelium, expressing FOXJ1 and RFX3. Transfection of FOXJ1 into resting basal cells activated promoters and induced expression of ciliated cell genes as well as both FOXJ1 and RFX3, but not basal cell genes. Transfection of RFX3 induced expression of RFX3 but not FOXJ1, nor the expression of cilia-related genes. The combination of FOXJ1 + RFX3 enhanced ciliated gene promoter activity and mRNA expression beyond that due to FOXJ1 alone. Corroborating immunoprecipitation studies demonstrated an interaction between FOXJ1 and RFX3. CONCLUSION: FOXJ1 is an important regulator of cilia gene expression during ciliated cell differentiation, with RFX3 as a transcriptional co-activator to FOXJ1, helping to induce the expression of cilia genes in the process of ciliated cell differentiation of basal/progenitor cells.

Generation of a human airway epithelium derived basal cell line with multipotent differentiation capacity.

BACKGROUND: As the multipotent progenitor population of the airway epithelium, human airway basal cells (BC) replenish the specialized differentiated cell populations of the mucociliated airway epithelium during physiological turnover and repair. Cultured primary BC divide a limited number of times before entering a state of replicative senescence, preventing the establishment of long-term replicating cultures of airway BC that maintain their original phenotype. METHODS: To generate an immortalized human airway BC cell line, primary human airway BC obtained by brushing the airway epithelium of healthy nonsmokers were infected with a retrovirus expressing human telomerase (hTERT). The resulting immortalized cell line was then characterized under non-differentiating and differentiating air-liquid interface (ALI) culture conditions using ELISA, TaqMan quantitative PCR, Western analysis, and immunofluorescent and immunohistochemical staining analysis for cell type specific markers. In addition, the ability of the cell line to respond to environmental stimuli under differentiating ALI culture was assessed. RESULTS: We successfully generated an immortalized human airway BC cell line termed BCi-NS1 via expression of hTERT. A single cell derived clone from the parental BCi-NS1 cells, BCi-NS1.1, retains characteristics of the original primary cells for over 40 passages and demonstrates a multipotent differentiation capacity into secretory (MUC5AC, MUC5B), goblet (TFF3), Clara (CC10) and ciliated (DNAI1, FOXJ1) cells on ALI culture. The cells can respond to external stimuli such as IL-13, resulting in alteration of the normal differentiation process. CONCLUSION: Development of immortalized human airway BC that retain multipotent differentiation capacity over long-term culture should be useful in understanding the biology of BC, the response of BC to environmental stress, and as a target for assessment of pharmacologic agents.

Airway basal cell vascular endothelial growth factor-mediated cross-talk regulates endothelial cell-dependent growth support of human airway basal cells.

The human airway epithelium is a pseudostratified heterogenous layer comprised of ciliated, secretory, intermediate, and basal cells. As the stem/progenitor population of the airway epithelium, airway basal cells differentiate into ciliated and secretory cells to replenish the airway epithelium during physiological turnover and repair. Transcriptome analysis of airway basal cells revealed high expression of vascular endothelial growth factor A (VEGFA), a gene not typically associated with the function of this cell type. Using cultures of primary human airway basal cells, we demonstrate that basal cells express all of the three major isoforms of VEGFA (121, 165 and 189) but lack functional expression of the classical VEGFA receptors VEGFR1 and VEGFR2. The VEGFA is actively secreted by basal cells and while it appears to have no direct autocrine function on basal cell growth and proliferation, it functions in a paracrine manner to activate MAPK signaling cascades in endothelium via VEGFR2-dependent signaling pathways. Using a cytokine- and serum-free co-culture system of primary human airway basal cells and human endothelial cells revealed that basal cell-secreted VEGFA activated endothelium to express mediators that, in turn, stimulate and support basal cell proliferation and growth. These data demonstrate novel VEGFA-mediated cross-talk between airway basal cells and endothelium, the purpose of which is to modulate endothelial activation and in turn stimulate and sustain basal cell growth.

The Isolation and In Vitro Differentiation of Primary Fetal Baboon Tracheal Epithelial Cells for the Study of SARS-CoV-2 Host-Virus Interactions.

The mucociliary airway epithelium lines the human airways and is the primary site of host-environmental interactions in the lung. Following virus infection, airway epithelial cells initiate an innate immune response to suppress virus replication. Therefore, defining the virus-host interactions of the mucociliary airway epithelium is critical for understanding the mechanisms that regulate virus infection, including Severe Acute Respiratory Syndrome Coronavirus 2 (SARS-CoV-2). Non-human primates (NHP) are closely related to humans and provide a model to study human disease. However, ethical considerations and high costs can restrict the use of in vivo NHP models. Therefore, there is a need to develop in vitro NHP models of human respiratory virus infection that would allow for rapidly characterizing virus tropism and the suitability of specific NHP species to model human infection. Using the olive baboon (Papio anubis), we have developed methodologies for the isolation, in vitro expansion, cryopreservation, and mucociliary differentiation of primary fetal baboon tracheal epithelial cells (FBTECs). Furthermore, we demonstrate that in vitro differentiated FBTECs are permissive to SARS-CoV-2 infection and produce a potent host innate-immune response. In summary, we have developed an in vitro NHP model that provides a platform for the study of SARS-CoV-2 infection and other human respiratory viruses.