Interleukin 13-Induced Inflammation Increases DPP4 Abundance but Does Not Enhance Middle East Respiratory Syndrome Coronavirus Replication in Airway Epithelia

BACKGROUND

Chronic pulmonary conditions such as asthma and chronic obstructive pulmonary disease increase the risk of morbidity and mortality during infection with the Middle East respiratory syndrome coronavirus (MERS-CoV). We hypothesized that individuals with such comorbidities are more susceptible to MERS-CoV infection due to increased expression of its receptor, dipeptidyl peptidase 4 (DPP4).

METHODS

We modeled chronic airway disease by treating primary human airway epithelia with the Th2 cytokine interleukin 13 (IL-13), examining how this affected DPP4 protein levels with MERS-CoV entry and replication.

RESULTS

IL-13 exposure for 3 days led to greater DPP4 protein abundance, while a 21-day treatment raised DPP4 levels and caused goblet cell metaplasia. Surprisingly, despite this increase in receptor availability, MERS-CoV entry and replication were not significantly affected by IL-13 treatment.

CONCLUSIONS

Our results suggest that greater DPP4 abundance is likely not the primary mechanism leading to increased MERS severity in the setting of Th2 inflammation. Transcriptional profiling analysis highlighted the complexity of IL-13-induced changes in airway epithelia, including altered expression of genes involved in innate immunity, antiviral responses, and maintenance of the extracellular mucus barrier. These data suggest that additional factors likely interact with DPP4 abundance to determine MERS-CoV infection outcomes.

CFTR dysfunction leads to defective bacterial eradication on cystic fibrosis airways

Dysfunction of the cystic fibrosis transmembrane conductance regulator (CFTR) anion channel by genetic mutations causes the inherited disease cystic fibrosis (CF). CF lung disease that involves multiple disorders of epithelial function likely results from loss of CFTR function as an anion channel conducting chloride and bicarbonate ions and its function as a cellular regulator modulating the activity of membrane and cytosol proteins. In the absence of CFTR activity, abundant mucus accumulation, bacterial infection and inflammation characterize CF airways, in which inflammation-associated tissue remodeling and damage gradually destroys the lung. Deciphering the link between CFTR dysfunction and bacterial infection in CF airways may reveal the pathogenesis of CF lung disease and guide the development of new treatments. Research efforts towards this goal, including high salt, low volume, airway surface liquid acidosis and abnormal mucus hypotheses are critically reviewed.

Changes in the Proportion of Each Cell Type After hiPSC-Derived Airway Epithelia Transplantation

No radical treatment is available for the regeneration of dysfunction and defects in airway epithelia. Artificial tracheae made of polypropylene and collagen sponge were used in clinical studies to reconstitute tracheae after resection. For early epithelialization of the luminal surface of the artificial trachea, a model was established, that is, an artificial trachea covered with human-induced pluripotent stem cell-derived airway epithelial cells (hiPSC-AECs) was transplanted into a tracheal defect in an immunodeficient rat. Unlike the cell types of hiPSC-derived cells that are currently used in clinical studies, AECs maintain tissues by proliferation and differentiation of basal cells into various cell types that constitute AECs constantly. Therefore, post-transplantation, the proportion of each cell type, such as ciliated and goblet cells, may change; however, no studies have examined this possibility. In this study, using our hiPSC-AEC-transplanted rat model, we investigated changes in the proportion of each cell type in hiPSC-AECs pre-transplantation and post-transplantation. As a result, the proportion of each cell type changed post-transplantation. The proportion of ciliated, basal, and club cells increased, and the proportion of goblet cells decreased post-transplantation. In addition, the proportion of each cell type in engrafted hiPSC-AECs is more similar to the proportion of each cell type in normal proximal airway tissue than the proportion of each cell type pre-transplantation. The results of this study are useful for the development of therapeutic techniques using hiPSC-AEC transplantation.

Reciprocal mutations of lung-tropic AAV capsids lead to improved transduction properties

Considerable effort has been devoted to developing adeno-associated virus (AAV)-based vectors for gene therapy in cystic fibrosis (CF). As a result of directed evolution and capsid shuffling technology, AAV capsids are available with widespread tropism for airway epithelial cells. For example, AAV2.5T and AAV6.2 are two evolved capsids with improved airway epithelial cell transduction properties over their parental serotypes. However, limited research has been focused on identifying their specific cellular tropism. Restoring cystic fibrosis transmembrane conductance regulator (CFTR) expression in surface columnar epithelial cells is necessary for the correction of the CF airway phenotype. Basal cells are a progenitor population of the conducting airways responsible for replenishing surface epithelial cells (including secretory cells and ionocytes), making correction of this cell population vital for a long-lived gene therapy strategy. In this study, we investigate the tropism of AAV capsids for three cell types in primary cultures of well-differentiated human airway epithelial (HAE) cells and primary human airway basal cells. We observed that AAV2.5T transduced surface epithelial cells better than AAV6.2, while AAV6.2 transduced airway basal cells better than AAV2.5T. We also investigated a recently developed capsid, AAV6.2FF, which has two surface tyrosines converted to phenylalanines. Next, we incorporated reciprocal mutations to create AAV capsids with further improved surface and basal cell transduction characteristics. Lastly, we successfully employed a split-intein approach using AAV to deliver an adenine base editor (ABE) to repair the CFTR R553X mutation. Our results suggest that rational incorporation of AAV capsid mutations improves AAV transduction of the airway surface and progenitor cells and may ultimately lead to improved pulmonary function in people with CF.

CC16 drives VLA-2-dependent SPLUNC1 expression

Rationale

CC16 (Club Cell Secretory Protein) is a protein produced by club cells and other non-ciliated epithelial cells within the lungs. CC16 has been shown to protect against the development of obstructive lung diseases and attenuate pulmonary pathogen burden. Despite recent advances in understanding CC16 effects in circulation, the biological mechanisms of CC16 in pulmonary epithelial responses have not been elucidated.

Objectives

We sought to determine if CC16 deficiency impairs epithelial-driven host responses and identify novel receptors expressed within the pulmonary epithelium through which CC16 imparts activity.

Methods

We utilized mass spectrometry and quantitative proteomics to investigate how CC16 deficiency impacts apically secreted pulmonary epithelial proteins. Mouse tracheal epithelial cells (MTECS), human nasal epithelial cells (HNECs) and mice were studied in naïve conditions and after Mp challenge.

Measurements and main results

We identified 8 antimicrobial proteins significantly decreased by CC16-/- MTECS, 6 of which were validated by mRNA expression in Severe Asthma Research Program (SARP) cohorts. Short Palate Lung and Nasal Epithelial Clone 1 (SPLUNC1) was the most differentially expressed protein (66-fold) and was the focus of this study. Using a combination of MTECs and HNECs, we found that CC16 enhances pulmonary epithelial-driven SPLUNC1 expression via signaling through the receptor complex Very Late Antigen-2 (VLA-2) and that rCC16 given to mice enhances pulmonary SPLUNC1 production and decreases Mycoplasma pneumoniae (Mp) burden. Likewise, rSPLUNC1 results in decreased Mp burden in mice lacking CC16 mice. The VLA-2 integrin binding site within rCC16 is necessary for induction of SPLUNC1 and the reduction in Mp burden.

Conclusion

Our findings demonstrate a novel role for CC16 in epithelial-driven host defense by up-regulating antimicrobials and define a novel epithelial receptor for CC16, VLA-2, through which signaling is necessary for enhanced SPLUNC1 production.

A Novel Co-Culture Model Reveals Enhanced CFTR Rescue in Primary Cystic Fibrosis Airway Epithelial Cultures with Persistent Pseudomonas aeruginosa Infection

People with cystic fibrosis (pwCF) suffer from chronic and recurring bacterial lung infections that begin very early in life and contribute to progressive lung failure. CF is caused by mutations in the CF transmembrane conductance regulator (CFTR) gene, which encodes an ion channel important for maintaining the proper hydration of pulmonary surfaces. When CFTR function is ablated or impaired, airways develop thickened, adherent mucus that contributes to a vicious cycle of infection and inflammation. Therapeutics for pwCF, called CFTR modulators, target the CFTR defect directly, restoring airway surface hydration and mucociliary clearance. However, even with CFTR modulator therapy, bacterial infections persist. To develop a relevant model of diseased airway epithelium, we established a primary human airway epithelium culture system with persistent Pseudomonas aeruginosa infection. We used this model to examine the effects of CFTR modulators on CFTR maturation, CFTR function, and bacterial persistence. We found that the presence of P. aeruginosa increased CFTR mRNA, protein, and function. We also found that CFTR modulators caused a decrease in P. aeruginosa burden. These results demonstrate the importance of including live bacteria to accurately model the CF lung, and that understanding the effects of infection on CFTR rescue by CFTR modulators is critical to evaluating and optimizing drug therapies for all pwCF.

Transplantation of Induced Pluripotent Stem Cell-Derived Airway Epithelia with a Collagen Scaffold into the Nasal Cavity

The nasal cavity is covered with respiratory epithelia, including ciliated cells that eliminate foreign substances trapped in the mucus. In hereditary diseases such as primary ciliary dyskinesia and cystic fibrosis, respiratory epithelial functions are irreversibly impaired; however, no radical treatment has been established yet. Thus, we considered that the transplantation of normal airway epithelia (AE) into the nasal epithelia is one of the strategies that could lead to radical treatment in the future. In our previous study, human induced pluripotent stem cell-derived AE (hiPSC-AE) on the vitrigel membrane were transplanted into the scraped area of the nasal septal mucosa of nude rats. Although human-derived ciliated cells, club cells, and basal cells were observed, they were located in the cysts within the submucosal granulation tissue but not in the nasal mucosal epithelia and the transplanted cells may not contribute to the function of the nasal mucosa with this condition. Therefore, to achieve more functional transplantation, we prepared the graft differently in this study by wrapping the collagen sponge in hiPSC-AE on the vitrigel membrane. As a result, we found the transplanted cells surviving in the nasal mucosal epithelia. These results suggest that hiPSC-AE transplanted into the nasal cavity could be viable in the nasal mucosa. In addition, our method leads to the establishment of nasal mucosa-humanized rats that are used for the development of the drugs and therapeutic methods for hereditary diseases of nasal respiratory epithelia.

Chronic alcohol use primes bronchial cells for altered inflammatory response and barrier dysfunction during SARS-CoV-2 infection

Alcohol use disorder (AUD) is a significant public health concern and people with AUD are more likely to develop severe acute respiratory distress syndrome (ARDS) in response to respiratory infections. To examine whether AUD was a risk factor for more severe outcome in response to severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) infection, we examined early responses to infection using cultured differentiated bronchial epithelial cells derived from brushings obtained from people with AUD or without AUD. RNA-seq analysis of uninfected cells determined that AUD cells were enriched for expression of epidermal genes as compared with non-AUD cells. Bronchial epithelial cells from patients with AUD showed a significant decrease in barrier function 72 h postinfection, as determined by transepithelial electrical resistance. In contrast, barrier function of non-AUD cells was enhanced 72 h after SARS-CoV-2 infection. AUD cells showed claudin-7 that did not colocalize with zonula occludens-1 (ZO-1), indicative of disorganized tight junctions. However, both AUD and non-AUD cells showed decreased β-catenin expression following SARS-CoV-2 infection. To determine the impact of AUD on the inflammatory response to SARS-CoV-2 infection, cytokine secretion was measured by multiplex analysis. SARS-CoV-2-infected AUD bronchial cells had enhanced secretion of multiple proinflammatory cytokines including TNFα, IL-1β, and IFNγ as opposed to non-AUD cells. In contrast, secretion of the barrier-protective cytokines epidermal growth factor (EGF) and granulocyte macrophage-colony stimulating factor (GM-CSF) was enhanced for non-AUD bronchial cells. Taken together, these data support the hypothesis that AUD is a risk factor for COVID-19, where alcohol primes airway epithelial cells for increased inflammation and increased barrier dysfunction and increased inflammation in response to infection by SARS-CoV-2.NEW & NOTEWORTHY Alcohol use disorder (AUD) is a significant risk factor for severe acute respiratory distress syndrome. We found that AUD causes a phenotypic shift in gene expression in human bronchial epithelial cells, enhancing expression of epidermal genes. AUD cells infected with severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) had higher levels of proinflammatory cytokine secretion and barrier dysfunction not present in infected non-AUD cells, consistent with increased early COVID-19 severity due to AUD.

Genome Editing in Ferret Airway Epithelia Mediated by CRISPR/Nucleases Delivered with Amphiphilic Shuttle Peptides

Gene editing strategies are attractive for treating genetic pulmonary diseases such as cystic fibrosis (CF). However, challenges have included the development of safe and effective vector systems for gene editing of airway epithelia and model systems to report their efficiency and durability. The domestic ferret (Mustela putorius furo) has a high degree of conservation in lung cellular anatomy with humans, and has served as an excellent model for many types of lung diseases, including CF. In this study, we evaluated the efficiency of amphiphilic shuttle peptide S10 for protein delivery and gene editing using SpCas9, and AsCas12a (Cpf1) ribonucleoproteins (RNPs). These approaches were evaluated in proliferating ferret airway basal cells, polarized airway epithelia in vitro, and lungs in vivo, by accessing the editing efficiency using reporter ferrets and measuring indels at the ferret CFTR locus. Our results demonstrate that shuttle peptides efficiently enable delivery of reporter proteins/peptides and gene editing SpCas9 or Cpf1 RNP complexes to ferret airway epithelial cells in vitro and in vivo. We measured S10 delivery efficiency of green fluorescent protein (GFP)-nuclear localization signal (NLS) protein or SpCas9 RNP into ferret airway basal cells and fully differentiated ciliated and nonciliated epithelial cells in vitro. In vitro and in vivo gene editing efficiencies were determined by Cas/LoxP-gRNA RNP-mediated conversion of a ROSA-TG Cre recombinase reporter using transgenic primary cells and ferrets. S10/Cas9 RNP was more effective, relative to S10/Cpf1 RNP at gene editing of the ROSA-TG locus. Intratracheal lung delivery of the S10 shuttle combined with GFP-NLS protein or D-Retro-Inverso (DRI)-NLS peptide demonstrated efficiencies of protein delivery that were ∼3-fold or 14-fold greater, respectively, than the efficiency of gene editing at the ROSA-TG locus using S10/Cas9/LoxP-gRNA. Cpf1 RNPs was less effective than SpCas9 at gene editing of LoxP locus. These data demonstrate the feasibility of shuttle peptide delivery of Cas RNPs to the ferret airways and the potential utility for developing ex vivo stem cell-based and in vivo gene editing therapies for genetic pulmonary diseases such as CF.

Autofluorescence imaging permits label-free cell type assignment and reveals the dynamic formation of airway secretory cell associated antigen passages (SAPs)

The specific functional properties of a tissue are distributed amongst its component cell types. The various cells act coherently, as an ensemble, in order to execute a physiologic response. Modern approaches for identifying and dissecting novel physiologic mechanisms would benefit from an ability to identify specific cell types in live tissues that could then be imaged in real time. Current techniques require the use of fluorescent genetic reporters that are not only cumbersome, but which only allow the study of three or four cell types at a time. We report a non-invasive imaging modality that capitalizes on the endogenous autofluorescence signatures of the metabolic cofactors NAD(P)H and FAD. By marrying morphological characteristics with autofluorescence signatures, all seven of the airway epithelial cell types can be distinguished simultaneously in mouse tracheal explants in real time. Furthermore, we find that this methodology for direct cell type-specific identification avoids pitfalls associated with the use of ostensibly cell type-specific markers that are, in fact, altered by clinically relevant physiologic stimuli. Finally, we utilize this methodology to interrogate real-time physiology and identify dynamic secretory cell associated antigen passages (SAPs) that form in response to cholinergic stimulus. The identical process has been well documented in the intestine where the dynamic formation of SAPs and goblet cell associated antigen passages (GAPs) enable luminal antigen sampling. Airway secretory cells with SAPs are frequently juxtaposed to antigen presenting cells, suggesting that airway SAPs, like their intestinal counterparts, not only sample antigen but convey their cargo for immune cell processing.

Revisiting Host-Pathogen Interactions in Cystic Fibrosis Lungs in the Era of CFTR Modulators

Cystic fibrosis transmembrane conductance regulator (CFTR) modulators, a new series of therapeutics that correct and potentiate some classes of mutations of the CFTR, have provided a great therapeutic advantage to people with cystic fibrosis (pwCF). The main hindrances of the present CFTR modulators are related to their limitations in reducing chronic lung bacterial infection and inflammation, the main causes of pulmonary tissue damage and progressive respiratory insufficiency, particularly in adults with CF. Here, the most debated issues of the pulmonary bacterial infection and inflammatory processes in pwCF are revisited. Special attention is given to the mechanisms favoring the bacterial infection of pwCF, the progressive adaptation of Pseudomonas aeruginosa and its interplay with Staphylococcus aureus, the cross-talk among bacteria, the bronchial epithelial cells and the phagocytes of the host immune defenses. The most recent findings of the effect of CFTR modulators on bacterial infection and the inflammatory process are also presented to provide critical hints towards the identification of relevant therapeutic targets to overcome the respiratory pathology of pwCF.

Regulatory roles of external cholesterol in human airway epithelial mitochondrial function through STARD3 signalling

BACKGROUND

Hypercholesterolemia is found in patients with chronic lung inflammation, during which airway epithelial cells play important roles in maintenance of inflammatory responses to pathogens. The present study aims at molecular mechanisms by which cholesterol changes airway epithelial sensitivity in response to smoking.

METHODS

Human bronchial epithelial cells (HBEs) were stimulated with cigarette smoke extract (CSE) and mice were exposed to CS/lipopolysaccharide (LPS) as models in vitro and in vivo. Severe COPD patients and healthy volunteers were also enrolled and the level of cholesterol in plasma was detected by metabolomics. Filipin III and elisa kits were used to stain free cholesterol. Mitochondrial function was detected by mitotracker green, mitotracker green, and Seahorse. Mitochondrial morphology was detected by high content screening and electron microscopy. The mRNA and protein levels of mitochondrial dynamics-related proteins were detected by RT-qPCR and Western blot,respectively. BODIPY 493/503 was used to stain lipid droplets. Lipidomics was used to detect intracellular lipid components. The mRNA level of interleukin (IL)-6 and IL-8 were detected by RT-qPCR.

RESULTS

We found that the cholesterol overload was associated with chronic obstructive pulmonary disease (COPD) and airway epithelia-driven inflammation, evidenced by hypercholesterolemia in patients with COPD and preclinical models, alteration of lipid metabolism-associated genes in CSE-induced airway epithelia and production of ILs. External cholesterol altered airway epithelial sensitivity of inflammation in response to CSE, through the regulation of STARD3-MFN2 pathway, cholesterol re-distribution, altered transport and accumulation of cholesterol, activities of lipid transport regulators and disorder of mitochondrial function and dynamics. MFN2 down-regulation increased airway epithelial sensitivity and production of ILs after smoking, at least partially by injuring fatty acid oxidation and activating mTOR phosphorylation.

CONCLUSIONS

Our data provide new insights for understanding molecular mechanisms of cholesterol-altered airway epithelial inflammation and for developing diagnostic biomarkers and therapeutic targets to improve patient outcomes.

A Single-Cell Atlas of Large and Small Airways at Birth in a Porcine Model of Cystic Fibrosis

Lack of CFTR (cystic fibrosis transmembrane conductance regulator) affects the transcriptome, composition, and function of large and small airway epithelia in people with advanced cystic fibrosis (CF); however, whether lack of CFTR causes cell-intrinsic abnormalities present at birth versus inflammation-dependent abnormalities is unclear. We performed a single-cell RNA-sequencing census of microdissected small airways from newborn CF pigs, which recapitulate CF host defense defects and pathology over time. Lack of CFTR minimally affected the transcriptome of large and small airways at birth, suggesting that infection and inflammation drive transcriptomic abnormalities in advanced CF. Importantly, common small airway epithelial cell types expressed a markedly different transcriptome than corresponding large airway cell types. Quantitative immunohistochemistry and electrophysiology of small airway epithelia demonstrated basal cells that reach the apical surface and a water and ion transport advantage. This single cell atlas highlights the archetypal nature of airway epithelial cells with location-dependent gene expression and function.

Inter-individual Variation in Receptor Expression Influences MERS-CoV Infection and Immune Responses in Airway Epithelia

Middle East respiratory syndrome coronavirus (MERS-CoV) causes respiratory infection in humans, with symptom severity that ranges from asymptomatic to severe pneumonia. Known risk factors for severe MERS include male sex, older age, and the presence of various comorbidities. MERS-CoV gains entry into cells by binding its receptor, dipeptidyl peptidase 4 (DPP4), on the surface of airway epithelia. We hypothesized that expression of this receptor might be an additional determinant of outcomes in different individuals during MERS-CoV infection. To learn more about the role of DPP4 in facilitating MERS-CoV infection and spread, we used ELISA and immunofluorescent staining to characterize DPP4 expression in well-differentiated primary human airway epithelia (HAE). We noted wide inter-individual variation in DPP4 abundance, varying by as much as 1000-fold between HAE donors. This variability appears to influence multiple aspects of MERS-CoV infection and pathogenesis, with greater DPP4 abundance correlating with early, robust virus replication and increased cell sloughing. We also observed increased induction of interferon and some interferon-stimulated genes in response to MERS-CoV infection in epithelia with the greatest DPP4 abundance. Overall, our results indicate that inter-individual differences in DPP4 abundance are one host factor contributing to MERS-CoV replication and host defense responses, and highlight how HAE may serve as a useful model for identifying risk factors associated with heightened susceptibility to serious respiratory pathogens.

Intersubject Variation in ACE2 Protein Expression in Human Airway Epithelia and Its Relationship to Severe Acute Respiratory Syndrome Coronavirus 2

BACKGROUND

Severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2 ) initiates entry into airway epithelia by binding its receptor, angiotensin-converting enzyme 2 (ACE2).

METHODS

To explore whether interindividual variation in ACE2 abundance contributes to variability in coronavirus disease 2019 (COVID-19) outcomes, we measured ACE2 protein abundance in primary airway epithelial cultures derived from 58 human donor lungs.

RESULTS

We found no evidence for sex- or age-dependent differences in ACE2 protein expression. Furthermore, we found that variations in ACE2 abundance had minimal effects on viral replication and induction of the interferon response in airway epithelia infected with SARS-CoV-2.

CONCLUSIONS

Our results highlight the relative importance of additional host factors, beyond viral receptor expression, in determining COVID-19 lung disease outcomes.

The TMPRSS2 Inhibitor Nafamostat Reduces SARS-CoV-2 Pulmonary Infection in Mouse Models of COVID-19

The coronavirus disease 2019 (COVID-19) pandemic has caused significant morbidity and mortality on a global scale. The etiologic agent, severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2), initiates host cell entry when its spike protein (S) binds to its receptor, angiotensin-converting enzyme 2 (ACE2). In airway epithelia, the spike protein is cleaved by the cell surface protease TMPRSS2, facilitating membrane fusion and entry at the cell surface. This dependence on TMPRSS2 and related proteases suggests that protease inhibitors might limit SARS-CoV-2 infection in the respiratory tract. Here, we tested two serine protease inhibitors, camostat mesylate and nafamostat mesylate, for their ability to inhibit entry of SARS-CoV-2 and that of a second pathogenic coronavirus, Middle East respiratory syndrome coronavirus (MERS-CoV). Both camostat and nafamostat reduced infection in primary human airway epithelia and in the Calu-3 2B4 cell line, with nafamostat exhibiting greater potency. We then assessed whether nafamostat was protective against SARS-CoV-2 in vivo using two mouse models. In mice sensitized to SARS-CoV-2 infection by transduction with human ACE2, intranasal nafamostat treatment prior to or shortly after SARS-CoV-2 infection significantly reduced weight loss and lung tissue titers. Similarly, prophylactic intranasal treatment with nafamostat reduced weight loss, viral burden, and mortality in K18-hACE2 transgenic mice. These findings establish nafamostat as a candidate for the prevention or treatment of SARS-CoV-2 infection and disease pathogenesis.

Airway Epithelial Nucleotide Release Contributes to Mucociliary Clearance

Mucociliary clearance (MCC) is a dominant component of pulmonary host defense. In health, the periciliary layer (PCL) is optimally hydrated, thus acting as an efficient lubricant layer over which the mucus layer moves by ciliary force. Airway surface dehydration and production of hyperconcentrated mucus is a common feature of chronic obstructive lung diseases such as cystic fibrosis (CF) and chronic bronchitis (CB). Mucus hydration is driven by electrolyte transport activities, which in turn are regulated by airway epithelial purinergic receptors. The activity of these receptors is controlled by the extracellular concentrations of ATP and its metabolite adenosine. Vesicular and conducted pathways contribute to ATP release from airway epithelial cells. In this study, we review the evidence leading to the identification of major components of these pathways: (a) the vesicular nucleotide transporter VNUT (the product of the SLC17A9 gene), the ATP transporter mediating ATP storage in (and release from) mucin granules and secretory vesicles; and (b) the ATP conduit pannexin 1 expressed in non-mucous airway epithelial cells. We further illustrate that ablation of pannexin 1 reduces, at least in part, airway surface liquid (ASL) volume production, ciliary beating, and MCC rates.

ColdZyme Maintains Integrity in SARS-CoV-2-Infected Airway Epithelia

SARS-CoV-2 infection causing the COVID-19 pandemic calls for immediate interventions to avoid viral transmission, disease progression, and subsequent excessive inflammation and tissue destruction. Primary normal human bronchial epithelial cells are among the first targets of SARS-CoV-2 infection. Here, we show that ColdZyme medical device mouth spray efficiently protected against virus entry, excessive inflammation, and tissue damage. Applying ColdZyme to fully differentiated, polarized human epithelium cultured at an air-liquid interphase (ALI) completely blocked binding of SARS-CoV-2 and increased local complement activation mediated by the virus as well as productive infection of the tissue model. While SARS-CoV-2 infection resulted in exaggerated intracellular complement activation immediately following infection and a drop in transepithelial resistance, these parameters were bypassed by single pretreatment of the tissues with ColdZyme mouth spray. Crucially, our study highlights the importance of testing already evaluated and safe drugs such as ColdZyme mouth spray for maintaining epithelial integrity and hindering SARS-CoV-2 entry within standardized three-dimensional (3D) in vitro models mimicking the in vivo human airway epithelium.IMPORTANCE Although our understanding of COVID-19 continuously progresses, essential questions regarding prophylaxis and treatment remain open. A hallmark of severe SARS-CoV-2 infection is a hitherto-undescribed mechanism leading to excessive inflammation and tissue destruction associated with enhanced pathogenicity and mortality. To tackle the problem at the source, transfer of SARS-CoV-2, subsequent binding, infection, and inflammatory responses have to be avoided. In this study, we used fully differentiated, mucus-producing, and ciliated human airway epithelial cultures to test the efficacy of ColdZyme medical device mouth spray in terms of protection from SARS-CoV-2 infection. Importantly, we found that pretreatment of the in vitro airway cultures using ColdZyme mouth spray resulted in significantly shielding the epithelial integrity, hindering virus binding and infection, and blocking excessive intrinsic complement activation within the airway cultures. Our in vitro data suggest that ColdZyme mouth spray may have an impact in prevention of COVID-19.

IRE1α Is a Therapeutic Target for Cystic Fibrosis Airway Inflammation

New anti-inflammatory treatments are needed for CF airway disease. Studies have implicated the endoplasmic reticulum stress transducer inositol requiring enzyme 1α (IRE1α) in CF airway inflammation. The activation of IRE1α promotes activation of its cytoplasmic kinase and RNase, resulting in mRNA splicing of X-box binding protein-1 (XBP-1s), a transcription factor required for cytokine production. We tested whether IRE1α kinase and RNase inhibition decreases cytokine production induced by the exposure of primary cultures of homozygous F508del CF human bronchial epithelia (HBE) to supernatant of mucopurulent material (SMM) from CF airways. We evaluated whether IRE1α expression is increased in freshly isolated and native CF HBE, and couples with increased XBP-1s levels. A FRET assay confirmed binding of the IRE1α kinase and RNase inhibitor, KIRA6, to the IRE1α kinase. F508del HBE cultures were exposed to SMM with or without KIRA6, and we evaluated the mRNA levels of XBP-1s, IL-6, and IL-8, and the secretion of IL-6 and IL-8. IRE1α mRNA levels were up-regulated in freshly isolated CF vs. normal HBE and coupled to increased XBP-1s mRNA levels. SMM increased XBP-1s, IL-6, and IL-8 mRNA levels and up-regulated IL-6 and IL-8 secretion, and KIRA6 blunted these responses in a dose-dependent manner. Moreover, a triple combination of CFTR modulators currently used in the clinic had no effect on SMM-increased XBP-1s levels coupled with increased cytokine production in presence or absence of KIRA6. These findings indicate that IRE1α mediates cytokine production in CF airways. Small molecule IRE1α kinase inhibitors that allosterically reduce RNase-dependent XBP-1s may represent a new therapeutic strategy for CF airway inflammation.

Activity of Tracheal Cytotoxin of Bordetella pertussis in a Human Tracheobronchial 3D Tissue Model

Bordetella pertussis is a highly contagious pathogen which causes whooping cough in humans. A major pathophysiology of infection is the extrusion of ciliated cells and subsequent disruption of the respiratory mucosa. Tracheal cytotoxin (TCT) is the only virulence factor produced by B. pertussis that has been able to recapitulate this pathology in animal models. This pathophysiology is well characterized in a hamster tracheal model, but human data are lacking due to scarcity of donor material. We assessed the impact of TCT and lipopolysaccharide (LPS) on the functional integrity of the human airway mucosa by using in vitro airway mucosa models developed by co-culturing human tracheobronchial epithelial cells and human tracheobronchial fibroblasts on porcine small intestinal submucosa scaffold under airlift conditions. TCT and LPS either alone and in combination induced blebbing and necrosis of the ciliated epithelia. TCT and LPS induced loss of ciliated epithelial cells and hyper-mucus production which interfered with mucociliary clearance. In addition, the toxins had a disruptive effect on the tight junction organization, significantly reduced transepithelial electrical resistance and increased FITC-Dextran permeability after toxin incubation. In summary, the results indicate that TCT collaborates with LPS to induce the disruption of the human airway mucosa as reported for the hamster tracheal model.

RSV and HMPV Infections in 3D Tissue Cultures: Mechanisms Involved in Virus-Host and Virus-Virus Interactions

Respiratory viral infections constitute a global public health concern. Among prevalent respiratory viruses, two pneumoviruses can be life-threatening in high-risk populations. In young children, they constitute the first cause of hospitalization due to severe lower respiratory tract diseases. A better understanding of their pathogenesis is still needed as there are no approved efficient anti-viral nor vaccine against pneumoviruses. We studied Respiratory Syncytial virus (RSV) and human Metapneumovirus (HMPV) in single and dual infections in three-dimensional cultures, a highly relevant model to study viral respiratory infections of the airway epithelium. Our investigation showed that HMPV is less pathogenic than RSV in this model. Compared to RSV, HMPV replicated less efficiently, induced a lower immune response, did not block cilia beating, and was more sensitive to IFNs. In dual infections, RSV-infected epithelia were less permissive to HMPV. By neutralizing IFNs in co-infection assays, we partially prevented HMPV inhibition by RSV and significantly increased the number of co-infected cells in the tissue. This suggests that interference in dual infection would be at least partly mediated by the host immune response. In summary, this work provides new insight regarding virus-host and virus-virus interactions of pneumoviruses in the airway epithelium. This could be helpful for the proper handling of at-risk patients.

ΔN-Tp63 Mediates Wnt/β-Catenin-Induced Inhibition of Differentiation in Basal Stem Cells of Mucociliary Epithelia

Mucociliary epithelia provide a first line of defense against pathogens. Impaired regeneration and remodeling of mucociliary epithelia are associated with dysregulated Wnt/β-catenin signaling in chronic airway diseases, but underlying mechanisms remain elusive, and studies yield seemingly contradicting results. Employing the Xenopus mucociliary epidermis, the mouse airway, and human airway Basal cells, we characterize the evolutionarily conserved roles of Wnt/β-catenin signaling in vertebrates. In multiciliated cells, Wnt is required for cilia formation during differentiation. In Basal cells, Wnt prevents specification of epithelial cell types by activating ΔN-TP63, a master transcription factor, which is necessary and sufficient to mediate the Wnt-induced inhibition of specification and is required to retain Basal cells during development. Chronic Wnt activation leads to remodeling and Basal cell hyperplasia, which are reversible in vivo and in vitro, suggesting Wnt inhibition as a treatment option in chronic lung diseases. Our work provides important insights into mucociliary signaling, development, and disease.

Impaired (re-)generation of lung epithelia is associated with Wnt signaling changes in animals and human lung disease patients. Haas et al. demonstrate that ΔN-TP63 is a Wnt-regulated master transcription factor inhibiting (re-) generation of new epithelial cells from stem cells. These findings are equally important for understanding animal development and disease mechanisms.

Pellino-1 Regulates the Responses of the Airway to Viral Infection

Exposure to respiratory pathogens is a leading cause of exacerbations of airway diseases such as asthma and chronic obstructive pulmonary disease (COPD). Pellino-1 is an E3 ubiquitin ligase known to regulate virally-induced inflammation. We wished to determine the role of Pellino-1 in the host response to respiratory viruses in health and disease. Pellino-1 expression was examined in bronchial sections from patients with GOLD stage two COPD and healthy controls. Primary bronchial epithelial cells (PBECs) in which Pellino-1 expression had been knocked down were extracellularly challenged with the TLR3 agonist poly(I:C). C57BL/6 Peli1^-/- mice and wild type littermates were subjected to intranasal infection with clinically-relevant respiratory viruses: rhinovirus (RV1B) and influenza A. We found that Pellino-1 is expressed in the airways of normal subjects and those with COPD, and that Pellino-1 regulates TLR3 signaling and responses to airways viruses. In particular we observed that knockout of Pellino-1 in the murine lung resulted in increased production of proinflammatory cytokines IL-6 and TNFα upon viral infection, accompanied by enhanced recruitment of immune cells to the airways, without any change in viral replication. Pellino-1 therefore regulates inflammatory airway responses without altering replication of respiratory viruses.

E-cigarettes, nicotine, the lung and the brain: multi-level cascading pathophysiology

Tobacco smoking is highly addictive and causes respiratory disease, cardiovascular disease and multiple types of cancer. Electronic-cigarettes (e-cigarettes) are non-combustible tobacco alternatives that aerosolize nicotine and flavouring agents in a propylene glycol-vegetable glycerine vehicle. They were originally envisaged as a tobacco cessation aid, but whether or not they help people to quit tobacco use is controversial. In this review, we have compared and contrasted what is known regarding the effects of nicotine on the lungs vs. the effects of nicotine in the brain in the context of addiction. Critically, both combustible tobacco products and e-cigarettes contain nicotine, a highly addictive, plant-derived alkaloid that binds to nicotinic acetylcholine receptors (nAChRs). Nicotine's reinforcing properties are primarily mediated by activation of the brain's mesolimbic reward circuitry and release of the neurotransmitter dopamine that contribute to the development of addiction. Moreover, nicotine addiction drives repeated intake that results in chronic pulmonary exposure to either tobacco smoke or e-cigarettes despite negative respiratory symptoms. Beyond the brain, nAChRs are also highly expressed in peripheral neurons, epithelia and immune cells, where their activation may cause harmful effects. Thus, nicotine, a key ingredient of both conventional and electronic cigarettes, produces neurological effects that drive addiction and may damage the lungs in the process, producing a complex, multilevel pathological state. We conclude that vaping needs to be studied by multi-disciplinary teams that include pulmonary and neurophysiologists as well as behaviourists and addiction specialists to fully understand their impact on human physiology.

TNFα and IL-17 alkalinize airway surface liquid through CFTR and pendrin

The pH of airway surface liquid (ASL) is a key factor that determines respiratory host defense; ASL acidification impairs and alkalinization enhances key defense mechanisms. Under healthy conditions, airway epithelia secrete base ([Formula: see text]) and acid (H⁺) to control ASL pH (pH_ASL). Neutrophil-predominant inflammation is a hallmark of several airway diseases, and TNFα and IL-17 are key drivers. However, how these cytokines perturb pH_ASL regulation is uncertain. In primary cultures of differentiated human airway epithelia, TNFα decreased and IL-17 did not change pH_ASL. However, the combination (TNFα+IL-17) markedly increased pH_ASL by increasing [Formula: see text] secretion. TNFα+IL-17 increased expression and function of two apical [Formula: see text] transporters, CFTR anion channels and pendrin Cl^-/[Formula: see text] exchangers. Both were required for maximal alkalinization. TNFα+IL-17 induced pendrin expression primarily in secretory cells where it was coexpressed with CFTR. Interestingly, significant pendrin expression was not detected in CFTR-rich ionocytes. These results indicate that TNFα+IL-17 stimulate [Formula: see text] secretion via CFTR and pendrin to alkalinize ASL, which may represent an important defense mechanism in inflamed airways.

β2 adrenoceptor signaling regulates ion transport in 16HBE14o- human airway epithelial cells

We investigated the regulation of Cl^- secretion by adrenoceptors in polarized 16HBE14o- human bronchial epithelial cells. Treatment with the nonselective β adrenoceptor agonist isoprenaline stimulated an increase in short-circuit current (I_SC ), which was inhibited by the β adrenoceptor blocker propranolol. Treatment with procaterol, an agonist specific for the β₂ adrenoceptor subtype, stimulated a similar increase in I_SC , which was inhibited by the β₂ adrenoceptor antagonist ICI 118551. Inhibitors of cystic fibrosis transmembrane conductance regulator (CFTR) and calcium-activated Cl^- channel (CaCC), but not K⁺ channel blockers, were able to inhibit the increase in I_SC . "Trimultaneous" recording of I_SC and intracellular cyclic adenosine monophosphate (cAMP) and Ca²⁺ levels in 16HBE14o- epithelia confirmed that the I_SC induced by isoprenaline or procaterol involved both cAMP and Ca²⁺ signaling. Our results demonstrate that β₂ adrenoceptors regulate Cl^- secretion in the human airway epithelium by activating apical CFTRs and CaCCs via cAMP-dependent and intracellular Ca²⁺ -dependent mechanisms, respectively.

XBP1S Regulates MUC5B in a Promoter Variant-Dependent Pathway in Idiopathic Pulmonary Fibrosis Airway Epithelia

Rationale: The goal was to connect elements of idiopathic pulmonary fibrosis (IPF) pathogenesis, including chronic endoplasmic reticulum stress in respiratory epithelia associated with injury/inflammation and remodeling, distal airway mucus obstruction and honeycomb cyst formation with accumulation of MUC5B (mucin 5B), and associations between IPF risk and polymorphisms in the MUC5B promoter. Objectives: To test whether the endoplasmic reticulum (ER) stress sensor protein ERN2 (ER-to-nucleus signaling 2) and its downstream effector, the spliced form of XBP1S (X-box-binding protein 1), regulate MUC5B expression and differentially activate the MUC5B promoter variant in respiratory epithelia. Methods: Primary human airway epithelial (HAE) cells, transgenic mouse models, human IPF lung tissues, and cell lines expressing XBP1S and MUC5B promoters were used to explore relationships between the ERN2/XBP1S pathway and MUC5B. An inhibitor of the pathway, KIRA6, and XBP1 CRISPR-Cas9 were used in HAE cells to explore therapeutic potential. Measurements and Main Results: ERN2 regulated MUC5B and MUC5AC mRNAs. Downstream XBP1S selectively promoted MUC5B expression in vitro and in distal murine airway epithelia in vivo. XBP1S bound to the proximal region of the MUC5B promoter and differentially upregulated MUC5B expression in the context of the MUC5B promoter rs35705950 variant. High levels of ERN2 and XBP1S were associated with excessive MUC5B mRNAs in distal airways of human IPF lungs. Cytokine-induced MUC5B expression in HAE cells was inhibited by KIRA6 and XBP1 CRISPR-Cas9. Conclusions: A positive feedback bistable ERN2-XBP1S pathway regulates MUC5B-dominated mucus obstruction in IPF, providing an unfolded protein response-dependent mechanism linking the MUC5B promoter rs35705950 polymorphism with IPF pathogenesis. Inhibiting ERN2-dependent pathways/elements may provide a therapeutic option for IPF.

Newborn Cystic Fibrosis Pigs Have a Blunted Early Response to an Inflammatory Stimulus

RATIONALE

Studies suggest that inappropriate responses to proinflammatory stimuli might contribute to inflammation in cystic fibrosis (CF) lungs. However, technical challenges have made it difficult to distinguish whether altered responses in CF airways are an intrinsic defect or a secondary effect of chronic disease in their tissue of origin. The CF pig model provides an opportunity to study the inflammatory responses of CF airways at birth, before the onset of infection and inflammation.

OBJECTIVES

To test the hypothesis that acute inflammatory responses are perturbed in porcine CF airways.

METHODS

We investigated the inflammatory responses of newborn CF and non-CF pig airways following a 4-hour exposure to heat-killed Staphylococcus aureus, in vivo and in vitro.

MEASUREMENTS AND MAIN RESULTS

Following an in vivo S. aureus challenge, markers of inflammation were similar between CF and littermate control animals through evaluation of bronchoalveolar lavage and tissues. However, transcriptome analysis revealed genotype-dependent differences as CF pigs showed a diminished host defense response compared with their non-CF counterparts. Furthermore, CF pig airways exhibited an increase in apoptotic pathways and a suppression of ciliary and flagellar biosynthetic pathways. Similar differences were observed in cultured airway epithelia from CF and non-CF pigs exposed to the stimulus.

CONCLUSIONS

Transcriptome profiling suggests that acute inflammatory responses are dysregulated in the airways of newborn CF pigs.

Bordetella pertussis Adenylate Cyclase Toxin Disrupts Functional Integrity of Bronchial Epithelial Layers

The airway epithelium restricts the penetration of inhaled pathogens into the underlying tissue and plays a crucial role in the innate immune defense against respiratory infections. The whooping cough agent, Bordetella pertussis, adheres to ciliated cells of the human airway epithelium and subverts its defense functions through the action of secreted toxins and other virulence factors. We examined the impact of B. pertussis infection and of adenylate cyclase toxin-hemolysin (CyaA) action on the functional integrity of human bronchial epithelial cells cultured at the air-liquid interface (ALI). B. pertussis adhesion to the apical surface of polarized pseudostratified VA10 cell layers provoked a disruption of tight junctions and caused a drop in transepithelial electrical resistance (TEER). The reduction of TEER depended on the capacity of the secreted CyaA toxin to elicit cAMP signaling in epithelial cells through its adenylyl cyclase enzyme activity. Both purified CyaA and cAMP-signaling drugs triggered a decrease in the TEER of VA10 cell layers. Toxin-produced cAMP signaling caused actin cytoskeleton rearrangement and induced mucin 5AC production and interleukin-6 (IL-6) secretion, while it inhibited the IL-17A-induced secretion of the IL-8 chemokine and of the antimicrobial peptide beta-defensin 2. These results indicate that CyaA toxin activity compromises the barrier and innate immune functions of Bordetella-infected airway epithelia.

SLC6A14 Is a Genetic Modifier of Cystic Fibrosis That Regulates Pseudomonas aeruginosa Attachment to Human Bronchial Epithelial Cells

Cystic fibrosis (CF) is caused by mutations in the CFTR gene and is associated with progressive and ultimately fatal infectious lung disease. There can be considerable variability in disease severity among individuals with the same CFTR mutations, and recent genome-wide association studies have identified secondary genetic factors that contribute to this. One of these modifier genes is SLC6A14, which encodes an amino acid transporter. Importantly, variants of this gene have been associated with age at first acquisition of Pseudomonas aeruginosa In this study, we aimed to determine the function of SLC6A14 in airway epithelia and how it might affect colonization by P. aeruginosa We show that SLC6A14 is expressed in respiratory epithelial cells and transports l-arginine out of the airway surface liquid (ASL). Exposure of airway epithelia to flagellin from P. aeruginosa led to upregulation of SLC6A14 expression and increased SLC6A14-dependent uptake of l-arginine from the ASL. In support of the hypothesis that l-arginine affects P. aeruginosa attachment, we showed that l-arginine supplementation promoted P. aeruginosa attachment to an abiotic surface in a dose-dependent manner. In a coculture model, we found that inhibition of SLC6A14-dependent l-arginine transport enhanced P. aeruginosa attachment. In Slc6a14^-/y (knockout) mice, P. aeruginosa attachment to lung tissue was also significantly enhanced. Together, these findings suggest that SLC6A14 activity plays a role in the modification of the initial stages of airway infection by altering the level of l-arginine in the ASL, which in turn affects the attachment of P. aeruginosaIMPORTANCE CF patients with shared CFTR gene mutations show significant variability in their clinical presentation of infectious lung disease. Genome-wide association studies have been used to identify secondary genetic factors that may explain the variable susceptibility to infection by opportunistic pathogens, including P. aeruginosa, the leading cause of pathogen-induced lung damage in nonpediatric CF patients. Once identified and characterized, these secondary genetic modifiers may allow for the development of personalized medicine for patients and ultimately the extension of life. In this study, we interrogated the biological role of one of these modifiers, SLC6A14, and showed that it contributes to host defense by depleting extracellular arginine (an attachment-promoting metabolite for P. aeruginosa) from the airway surface liquid.

Human Parvovirus Infection of Human Airway Epithelia Induces Pyroptotic Cell Death by Inhibiting Apoptosis

Human bocavirus 1 (HBoV1) is a human parvovirus that causes acute respiratory tract infections in young children. In this study, we confirmed that, when polarized/well-differentiated human airway epithelia are infected with HBoV1 in vitro, they develop damage characterized by barrier function disruption and cell hypotrophy. Cell death mechanism analyses indicated that the infection induced pyroptotic cell death characterized by caspase-1 activation. Unlike infections with other parvoviruses, HBoV1 infection did not activate the apoptotic or necroptotic cell death pathway. When the NLRP3-ASC-caspase-1 inflammasome-induced pathway was inhibited by short hairpin RNA (shRNA), HBoV1-induced cell death dropped significantly; thus, NLRP3 mediated by ASC appears to be the pattern recognition receptor driving HBoV1 infection-induced pyroptosis. HBoV1 infection induced steady increases in the expression of interleukin 1α (IL-1α) and IL-18. HBoV1 infection was also associated with the marked expression of the antiapoptotic genes BIRC5 and IFI6 When the expression of BIRC5 and/or IFI6 was inhibited by shRNA, the infected cells underwent apoptosis rather than pyroptosis, as indicated by increased cleaved caspase-3 levels and the absence of caspase-1. BIRC5 and/or IFI6 gene inhibition also significantly reduced HBoV1 replication. Thus, HBoV1 infection of human airway epithelial cells activates antiapoptotic proteins that suppress apoptosis and promote pyroptosis. This response may have evolved to confer a replicative advantage, thus allowing HBoV1 to establish a persistent airway epithelial infection. This is the first report of pyroptosis in airway epithelia infected by a respiratory virus.IMPORTANCE Microbial infection of immune cells often induces pyroptosis, which is mediated by a cytosolic protein complex called the inflammasome that senses microbial pathogens and then activates the proinflammatory cytokines IL-1 and IL-18. While virus-infected airway epithelia often activate NLRP3 inflammasomes, studies to date suggest that these viruses kill the airway epithelial cells via the apoptotic or necrotic pathway; involvement of the pyroptosis pathway has not been reported previously. Here, we show for the first time that virus infection of human airway epithelia can also induce pyroptosis. Human bocavirus 1 (HBoV1), a human parvovirus, causes lower respiratory tract infections in young children. This study indicates that HBoV1 kills airway epithelial cells by activating genes that suppress apoptosis and thereby promote pyroptosis. This strategy appears to promote HBoV1 replication and may have evolved to allow HBoV1 to establish persistent infection of human airway epithelia.

Store-operated Ca2+ channels in airway epithelial cell function and implications for asthma

The epithelial cells of the lung are at the interface of a host and its environment and are therefore directly exposed to the inhaled air-borne particles. Rather than serving as a simple physical barrier, airway epithelia detect allergens and other irritants and then help organize the subsequent immune response through release of a plethora of secreted signals. Many of these signals are generated in response to opening of store-operated Ca²⁺ channels in the plasma membrane. In this review, we describe the properties of airway store-operated channels and their role in regulating airway epithelial cell function.

This article is part of the themed issue ‘Evolution brings Ca²⁺ and ATP together to control life and death’.

Airway ciliary dysfunction: Association with adverse postoperative outcomes in nonheterotaxy congenital heart disease patients

OBJECTIVE

Heterotaxy (HTX) congenital heart disease (CHD) patients with ciliary dysfunction (CD) have been shown to have increased postoperative respiratory morbidity. We hypothesized that non-HTX CHD infants with CD also will have increased postoperative morbidity, particularly respiratory complications.

METHODS

Sixty-three infants with non-HTX CHD undergoing cardiac surgery were enrolled. Tests commonly used to assess for CD, nasal nitric oxide (nNO) measurements and nasal epithelial ciliary motion (CM) assessment, were obtained. Baseline characteristics and postoperative outcomes were collected and analyzed.

RESULTS

Non-HTX CHD infants exhibited a high prevalence of abnormal CM (32%) and low nNO (39%). This finding was not correlated with demographics or surgical complexity. Infants with abnormal CM had increased odds of requiring noninvasive positive pressure ventilation (odds ratio [OR], 6.5; 95% confidence interval [CI], 1.5-29.4; P = .016) and respiratory medication use (OR, 4.4; 95% CI, 1.5-13.3; P = .01). In contrast, infants with low nNO showed evidence of abnormal pre- and postoperative systolic function (40% vs 4%; P = .004, and 34% vs 13%; P = .056, respectively) and had greater odds of acquiring infections (OR, 4.9; 95% CI, 1.4-17; P = .014).

CONCLUSIONS

Non-HTX CHD infants with abnormal CM showed increased postoperative morbidity associated with poor respiratory outcomes. In contrast, low nNO correlated with reduced hemodynamic function. These findings suggest screening for abnormal CM may allow perioperative interventions to reduce pulmonary morbidities. Whether low nNO may prognosticate poor hemodynamic function warrants further investigation.

[Role of epidermal growth factor receptor in house dust mite-induced airway epithelial barrier dysfunction]

OBJECTIVE

To investigate the role of epidermal growth factor receptor (EGFR) signaling pathway in bronchial epithelial actin stress fiber (F-actin) rearrangement induced by house dust mite (HDM).

METHODS

Normal human bronchial epithelial cells (16HBE) were stimulated with HDM with or without pretreatment with AG-1478, an EGFR inhibitor. The levels of phospho(p)-EGFR, F-actin, E-cadherin and β-catenin in the cell cultures were detected with Western blotting. The localizations of F-actin, E-cadherin and β-catenin in the bronchial epithelial cells were determined with immunofluorescence assay, and the transmembrane electrical resistance (TER) and FITC-dextran flux (FITC-DX) in the cells were measured to assess the barrier function of the bronchial epithelia.

RESULTS

HDM stimulation of the cells for 10 min resulted in significantly increased p-EGFR expression (P<0.05) without causing obvious changes in the expression of E-cadherin (P>0.05) or β-catenin (P>0.05). Immunofluorescence assay revealed delocalization of E-cadherin and β-catenin in HDM-treated 16HBE cells, shown by their diffusion from the cell membrane to the cytoplasm. In HDM-treated cells, the TER was significantly decreased to (70.00∓4.33)% and the FITC-DX was significantly increased to (115.98∓4.34)%; Inhibition of EGFR reversed the delocalization of E-cadherin and β-catenin, improved the TER to (90.00∓3.75)% and lowered the FITC-DX to (101.10∓2.10)%. HDM induced increased expression and rearrangement of F-actin, which was obviously inhibited by pretreatment of the cells with AG-1478 (P<0.05).

CONCLUSION

EGFR signaling pathway mediates HDM-induced F-actin rearrangement in human bronchial epithelial cells to contribute to epithelial barrier dysfunction.

Insulin signaling via the PI3-kinase/Akt pathway regulates airway glucose uptake and barrier function in a CFTR-dependent manner

Cystic fibrosis-related diabetes is the most common comorbidity associated with cystic fibrosis (CF) and correlates with increased rates of lung function decline. Because glucose is a nutrient present in the airways of patients with bacterial airway infections and because insulin controls glucose metabolism, the effect of insulin on CF airway epithelia was investigated to determine the role of insulin receptors and glucose transport in regulating glucose availability in the airway. The response to insulin by human airway epithelial cells was characterized by quantitative PCR, immunoblot, immunofluorescence, and glucose uptake assays. Phosphatidylinositol 3-kinase/protein kinase B (Akt) signaling and cystic fibrosis transmembrane conductance regulator (CFTR) activity were analyzed by pharmacological and immunoblot assays. We found that normal human primary airway epithelial cells expressed glucose transporter 4 and that application of insulin stimulated cytochalasin B-inhibitable glucose uptake, consistent with a requirement for glucose transporter translocation. Application of insulin to normal primary human airway epithelial cells promoted airway barrier function as demonstrated by increased transepithelial electrical resistance and decreased paracellular flux of small molecules. This provides the first demonstration that airway cells express insulin-regulated glucose transporters that act in concert with tight junctions to form an airway glucose barrier. However, insulin failed to increase glucose uptake or decrease paracellular flux of small molecules in human airway epithelia expressing F508del-CFTR. Insulin stimulation of Akt1 and Akt2 signaling in CF airway cells was diminished compared with that observed in airway cells expressing wild-type CFTR. These results indicate that the airway glucose barrier is regulated by insulin and is dysfunctional in CF.

Evaluating Adverse Effects of Inhaled Nanoparticles by Realistic In Vitro Technology

The number of daily products containing nanoparticles (NP) is rapidly increasing. NP in powders, dispersions, or sprays are a yet unknown risk for incidental exposure, especially at workplaces during NP production and processing, and for consumers of any health status and age using NP containing sprays. We developed the nano aerosol chamber for in vitro toxicity (NACIVT), a portable instrument for realistic safety testing of inhaled NP in vitro and evaluated effects of silver (Ag) and carbon (C) NP—which belong to the most widely used nanomaterials—on normal and compromised airway epithelia. We review the development, physical performance, and suitability of NACIVT for short and long-term exposures with air-liquid interface (ALI) cell cultures in regard to the prerequisites of a realistic in vitro test system for inhalation toxicology and in comparison to other commercially available, well characterized systems. We also review doses applied to cell cultures in vitro and acknowledge that a single exposure to realistic doses of spark generated 20-nm Ag- or CNP results in small, similar cellular responses to both NP types and that cytokine release generally increased with increasing NP dose.

Role of IRE1α/XBP-1 in Cystic Fibrosis Airway Inflammation

Cystic fibrosis (CF) pulmonary disease is characterized by chronic airway infection and inflammation. The infectious and inflamed CF airway environment impacts on the innate defense of airway epithelia and airway macrophages. The CF airway milieu induces an adaptation in these cells characterized by increased basal inflammation and a robust inflammatory response to inflammatory mediators. Recent studies have indicated that these responses depend on activation of the unfolded protein response (UPR). This review discusses the contribution of airway epithelia and airway macrophages to CF airway inflammatory responses and specifically highlights the functional importance of the UPR pathway mediated by IRE1/XBP-1 in these processes. These findings suggest that targeting the IRE1/XBP-1 UPR pathway may be a therapeutic strategy for CF airway disease.

SYVN1, NEDD8, and FBXO2 Proteins Regulate ΔF508 Cystic Fibrosis Transmembrane Conductance Regulator (CFTR) Ubiquitin-mediated Proteasomal Degradation

We previously reported that delivery of a microRNA-138 mimic or siRNA against SIN3A to cultured cystic fibrosis (ΔF508/ΔF508) airway epithelia partially restored ΔF508-cystic fibrosis transmembrane conductance regulator (CFTR)-mediated cAMP-stimulated Cl^- conductance. We hypothesized that dissecting this microRNA-138/SIN3A-regulated gene network would identify individual proteins contributing to the rescue of ΔF508-CFTR function. Among the genes in the network, we rigorously validated candidates using functional CFTR maturation and electrolyte transport assays in polarized airway epithelia. We found that depletion of the ubiquitin ligase SYVN1, the ubiquitin/proteasome system regulator NEDD8, or the F-box protein FBXO2 partially restored ΔF508-CFTR-mediated Cl^- transport in primary cultures of human cystic fibrosis airway epithelia. Moreover, knockdown of SYVN1, NEDD8, or FBXO2 in combination with corrector compound 18 further potentiated rescue of ΔF508-CFTR-mediated Cl^- conductance. This study provides new knowledge of the CFTR biosynthetic pathway. It suggests that SYVN1 and FBXO2 represent two distinct multiprotein complexes that may degrade ΔF508-CFTR in airway epithelia and identifies a new role for NEDD8 in regulating ΔF508-CFTR ubiquitination.

A genomic signature approach to rescue ΔF508-cystic fibrosis transmembrane conductance regulator biosynthesis and function

The most common cystic fibrosis (CF) mutation, ΔF508, causes protein misfolding, leading to proteosomal degradation. We recently showed that expression of miR-138 enhances CF transmembrane conductance regulator (CFTR) biogenesis and partially rescues ΔF508-CFTR function in CF airway epithelia. We hypothesized that a genomic signature approach can be used to identify new bioactive small molecules affecting ΔF508-CFTR rescue. The Connectivity Map was used to identify 27 small molecules with potential to restore ΔF508-CFTR function in airway epithelia. The molecules were screened in vitro for efficacy in improving ΔF508-CFTR trafficking, maturation, and chloride current. We identified four small molecules that partially restore ΔF508-CFTR function in primary CF airway epithelia. Of these, pyridostigmine showed cooperativity with corrector compound 18 in improving ΔF508-CFTR function. There are few CF therapies based on new molecular insights. Querying the Connectivity Map with relevant genomic signatures offers a method to identify new candidates for rescuing ΔF508-CFTR function.

Epinephrine stimulation of anion secretion in the Calu-3 serous cell model

Calu-3 is a well-differentiated human bronchial cell line with the characteristics of the serous cells of airway submucosal glands. The submucosal glands play a major role in mucociliary clearance because they secrete electrolytes that facilitate airway hydration. Given the significance of both long- and short-term β-adrenergic receptor agonists in the treatment of respiratory diseases, it is important to determine the role of these receptors and their ligands in normal physiological function. The present studies were designed to characterize the effect of epinephrine, the naturally occurring β-adrenergic receptor agonist, on electrolyte transport of the airway serous cells. Interestingly, epinephrine stimulated two anion secretory channels, the cystic fibrosis transmembrane conductance regulator and a Ca(2+)-activated Cl(-) channel, with the characteristics of transmembrane protein 16A, thereby potentially altering mucociliary clearance via multiple channels. Consistent with the dual channel activation, epinephrine treatment resulted in increases in both intracellular cAMP and Ca(2+). Furthermore, the present results extend previous reports indicating that the two anion channels are functionally linked.

Bioinformatic Analysis of Differential Protein Expression in Calu-3 Cells Exposed to Carbon Nanotubes

Carbon nanomaterials are widely produced and used in industry, medicine and scientific research. To examine the impact of exposure to nanoparticles on human health, the human airway epithelial cell line, Calu-3, was used to evaluate changes in the cellular proteome that could account for alterations in cellular function of airway epithelia after 24 hexposure to 10 μg/mL and 100 ng/mLof two common carbon nanoparticles, single- and multi-wall carbon nanotubes (SWCNT, MWCNT). After exposure to the nanoparticles, label-free quantitative mass spectrometry (LFQMS) was used to study the differential protein expression. Ingenuity Pathway Analysis (IPA) was used to conduct a bioinformaticanalysis of proteins identified in LFQMS. Interestingly, after exposure to ahigh concentration (10 μg/mL; 0.4 μg/cm²) of MWCNT or SWCNT, only 8 and 13 proteins, respectively, exhibited changes in abundance. In contrast, the abundance of hundreds of proteins was altered in response to a low concentration (100 ng/mL; 4 ng/cm²) of either CNT. Of the 281 and 282 proteins that were significantly altered in response to MWCNT or SWCNT respectively, 231 proteins were the same. Bioinformatic analyses found that the proteins in common to both nanotubes occurred within the cellular functions of cell death and survival, cell-to-cell signaling and interaction, cellular assembly and organization, cellular growth and proliferation, infectious disease, molecular transport and protein synthesis. The majority of the protein changes represent a decrease in amount suggesting a general stress response to protect cells. The STRING database was used to analyze the various functional protein networks. Interestingly, some proteins like cadherin 1 (CDH1), signal transducer and activator of transcription 1 (STAT1), junction plakoglobin (JUP), and apoptosis-associated speck-like protein containing a CARD (PYCARD), appear in several functional categories and tend to be in the center of the networks. This central positioning suggests they may play important roles in multiple cellular functions and activities that are altered in response to carbon nanotube exposure.

Activation of the cystic fibrosis transmembrane conductance regulator by the flavonoid quercetin: potential use as a biomarker of ΔF508 cystic fibrosis transmembrane conductance regulator rescue

Therapies to correct the ΔF508 cystic fibrosis transmembrane conductance regulator (CFTR) folding defect require sensitive methods to detect channel activity in vivo. The β₂ adrenergic receptor agonists, which provide the CFTR stimuli commonly used in nasal potential difference assays, may not overcome the channel gating defects seen in ΔF508 CFTR after plasma membrane localization. In this study, we identify an agent, quercetin, that enhances the detection of surface ΔF508 CFTR, and is suitable for nasal perfusion. A screen of flavonoids in CFBE41o⁻ cells stably transduced with ΔF508 CFTR, corrected to the cell surface with low temperature growth, revealed that quercetin stimulated an increase in the short-circuit current. This increase was dose-dependent in both Fisher rat thyroid and CFBE41o⁻ cells. High concentrations inhibited Cl⁻ conductance. In CFBE41o⁻ airway cells, quercetin (20 μg/ml) activated ΔF508 CFTR, whereas the β₂ adrenergic receptor agonist isoproterenol did not. Quercetin had limited effects on cAMP levels, but did not produce detectable phosphorylation of the isolated CFTR R-domain, suggesting an activation independent of channel phosphorylation. When perfused in the nares of Cftr(+) mice, quercetin (20 μg/ml) produced a hyperpolarization of the potential difference that was absent in Cftr(-/-) mice. Finally, quercetin-induced, dose-dependent hyperpolarization of the nasal potential difference was also seen in normal human subjects. Quercetin activates CFTR-mediated anion transport in respiratory epithelia in vitro and in vivo, and may be useful in studies intended to detect the rescue of ΔF508 CFTR by nasal potential difference.

Regulation of murine airway surface liquid volume by CFTR and Ca2+-activated Cl- conductances

Two Cl(-) conductances have been described in the apical membrane of both human and murine proximal airway epithelia that are thought to play predominant roles in airway hydration: (1) CFTR, which is cAMP regulated and (2) the Ca(2+)-activated Cl(-) conductance (CaCC) whose molecular identity is uncertain. In addition to second messenger regulation, cross talk between these two channels may also exist and, whereas CFTR is absent or defective in cystic fibrosis (CF) airways, CaCC is preserved, and may even be up-regulated. Increased CaCC activity in CF airways is controversial. Hence, we have investigated the effects of CFTR on CaCC activity and have also assessed the relative contributions of these two conductances to airway surface liquid (ASL) height (volume) in murine tracheal epithelia. We find that CaCC is up-regulated in intact murine CF tracheal epithelia, which leads to an increase in UTP-mediated Cl(-)/volume secretion. This up-regulation is dependent on cell polarity and is lost in nonpolarized epithelia. We find no role for an increased electrical driving force in CaCC up-regulation but do find an increased Ca(2+) signal in response to mucosal nucleotides that may contribute to the increased Cl(-)/volume secretion seen in intact epithelia. CFTR plays a critical role in maintaining ASL height under basal conditions and accordingly, ASL height is reduced in CF epithelia. In contrast, CaCC does not appear to significantly affect basal ASL height, but does appear to be important in regulating ASL height in response to released agonists (e.g., mucosal nucleotides). We conclude that both CaCC and the Ca(2+) signal are increased in CF airway epithelia, and that they contribute to acute but not basal regulation of ASL height.