Regulation of the secretory phenotype of human airway epithelium by retinoic acid, triiodothyronine, and extracellular matrix

Differential regulation of viral entry-associated genes modulated by inflammatory cytokines in the nasal epithelium

This study aimed to investigate the impact of different types of nasal inflammation on the regulation of entry-associated genes of respiratory viruses, including severe acute respiratory syndrome coronavirus 2 (SARS CoV-2), Middle East respiratory syndrome coronavirus (MERS-CoV), human coronavirus 229E (HCoV-229E), and influenza virus, in the nasal epithelium. Subjects were classified into three groups: control, eosinophilic chronic rhinosinusitis (ECRS), and noneosinophilic CRS (NECRS) groups. Angiotensin-converting enzyme 2 (ACE2) and transmembrane protease serine subtype 2 (TMPRSS2), alanyl aminopeptidase (ANPEP), dipeptidyl peptidase 4 (DPP4), and beta-galactoside alpha-2,6-sialyltransferase 1 (ST6GAL1), and beta-galactoside alpha-2,3-sialyltransferase 4 (ST3GAL4) were selected as key entry-associated genes for SARS-CoV-2, HCoV-229E, MERS-CoV, and influenza, respectively, and were evaluated. Brushing samples obtained from each group and human nasal epithelial cells cultured using an air-liquid interface system were treated for 7 days with typical inflammatory cytokines and analyzed using real-time polymerase chain reaction. Western blot analysis and confocal microscopy were performed. The entry-associated genes showed distinct regulation patterns in response to each interleukin-4 (IL-4), interleukin-13 (IL-13), tumor necrosis factor-α (TNF-α), and interferon-γ (IFN-γ). Specifically, ACE2 significantly decreased in type 2 cytokines (IL-4 and IL-13), while TMPRSS2 significantly decreased in type 1 cytokines (TNF-α and IFN-γ). ANPEP significantly decreased in both types of cytokines. Remarkably, DPP4 significantly increased in type 2 cytokines and decreased in type 1 cytokines. Moreover, ST6GAL1 and ST3GAL4 significantly increased in type 2 cytokines and decreased in type 1 cytokines, particularly IFN-γ. These findings were supported by western blot analysis and confocal imaging results, especially for ACE2 and DPP4. The findings regarding differential regulation suggest that patients with ECRS, primarily mediated by type 2 inflammation, may have lower susceptibility to SARS-CoV-2 and HCoV-229E infections but higher susceptibility to MERS-CoV and influenza infections.

IL-4 drastically decreases deuterosomal and multiciliated cells via alteration in progenitor cell differentiation

BACKGROUND

Allergic inflammation affects the epithelial cell populations resulting in goblet cell hyperplasia and decreased ciliated cells. Recent advances in single-cell RNA sequencing (scRNAseq) have enabled the identification of new cell subtypes and genomic features of single cells. In this study, we aimed to investigate the effect of allergic inflammation in nasal epithelial cell transcriptomes at the single-cell level.

METHODS

We performed scRNAseq in cultured primary human nasal epithelial (HNE) cells and in vivo nasal epithelium. The transcriptomic features and epithelial cell subtypes were determined under IL-4 stimulation, and cell-specific marker genes and proteins were identified.

RESULTS

We confirmed that cultured HNE cells were similar to in vivo epithelial cells through scRNAseq. Cell-specific marker genes were utilized to cluster the cell subtypes, and FOXJ1⁺ -ciliated cells were sub-classified into multiciliated and deuterosomal cells. PLK4 and CDC20B were specific for deuterosomal cells, and SNTN, CPASL, and GSTA2 were specific for multiciliated cells. IL-4 altered the proportions of cell subtypes, resulting in a decrease in multiciliated cells and loss of deuterosomal cells. The trajectory analysis revealed deuterosomal cells as precursor cells of multiciliated cells and deuterosomal cells function as a bridge between club and multiciliated cells. A decrease in deuterosomal cell marker genes was observed in nasal tissue samples with type 2 inflammation.

CONCLUSION

The effects of IL-4 appear to be mediated through the loss of the deuterosomal population, resulting in the reduction in multiciliated cells. This study also newly suggests cell-specific markers that might be pivotal for investigating respiratory inflammatory diseases.

Extracellular Microenvironmental Control for Organoid Assembly

Organoids, which are multicellular clusters with similar physiological functions to living organs, have gained increasing attention in bioengineering. As organoids become more advanced, methods to form complex structures continue to develop. There is evidence that the extracellular microenvironment can regulate organoid quality. The extracellular microenvironment consists of soluble bioactive molecules, extracellular matrix, and biofluid flow. However, few efforts have been made to discuss the microenvironment optimal to engineer specific organoids. Therefore, this review article examines the extent to which engineered extracellular microenvironments regulate organoid quality. First, we summarize the natural tissue and organ's unique chemical and mechanical properties, guiding researchers to design an extracellular microenvironment used for organoid engineering. Then, we summarize how the microenvironments contribute to the formation and growth of the brain, lung, intestine, liver, retinal, and kidney organoids. The approaches to forming and evaluating the resulting organoids are also discussed in detail. Impact statement Organoids, which are multicellular clusters with similar physiological function to living organs, have been gaining increasing attention in bioengineering. As organoids become more advanced, methods to form complex structures continue to develop. This review article focuses on recent efforts to engineer the extracellular microenvironment in organoid research. We summarized the natural organ's microenvironment, which informs researchers of key factors that can influence organoid formation. Then, we summarize how these microenvironmental controls significantly contribute to the formation and growth of the corresponding brain, lung, intestine, liver, retinal, and kidney organoids. The approaches to forming and evaluating the resulting organoids are discussed in detail, including extracellular matrix choice and properties, culture methods, and the evaluation of the morphology and functionality through imaging and biochemical analysis.

Mechanical compression enhances ciliary beating through cytoskeleton remodeling in human nasal epithelial cells

Nasal inflammatory diseases, including nasal polyps and acute/chronic sinusitis, are characterized by impaired mucociliary clearance and eventually inflammation and infection. Contact of nasal polyps with adjacent nasal mucosa or stagnated mucus within the maxillary sinus produces compressive mechanical stresses on the apical surface of epithelium which can induce cytoskeleton remodeling in epithelial cells. In this study, we hypothesized that compressive stress modulates ciliary beating by altering the mechanical properties of the cytoskeleton of ciliated cell basal bodies. For the primary human nasal epithelial cells, we found that the applied compressive stress higher than the critical value of 1.0 kPa increased the stroke speed of cilia leading to the enhancement of ciliary beating frequency and mucociliary transportability. Immunostained images of the cytoskeleton showed reorganization and compactness of the actin filaments in the presence of compressive stress. Analysis of beating trajectory with the computational modeling for ciliary beating revealed that the stroke speed of cilium increased as the relative elasticity to viscosity of the surrounding cytoskeleton increases. These results suggest that the compressive stress on epithelial cells increases the ciliary beating speed through cytoskeleton remodeling to prevent mucus stagnation at the early stage of airway obstruction. Our study provides an insight into the defensive mechanism of airway epithelium against pathological conditions. STATEMENT OF SIGNIFICANCE: Cilia dynamics of the nasal epithelium is critical for not only maintaining normal breathing but preventing inflammatory diseases. It has been shown that mechanical compressive stresses can alter the shape and phenotype of epithelial cells. However, the effect of compressive stress on cilia dynamics is unclear. In this study, we demonstrated that the oscillation speed of cilia in human nasal epithelial cells was increased by the applied compressive stress experimentally. The computational simulation revealed that the change of ciliary beating dynamics was attributed to the viscoelastic properties of the reorganized cytoskeleton in response to compressive stress. Our results will be beneficial in understanding the defensive mechanism of airway epithelium against pathological conditions.

Comparative Transcriptome Analyses Reveal a Transcriptional Landscape of Human Silicosis Lungs and Provide Potential Strategies for Silicosis Treatment

Silicosis is a fatal occupational lung disease which currently has no effective clinical cure. Recent studies examining the underlying mechanism of silicosis have primarily examined experimental models, which may not perfectly reflect the nature of human silicosis progression. A comprehensive profiling of the molecular changes in human silicosis lungs is urgently needed. Here, we conducted RNA sequencing (RNA-seq) on the lung tissues of 10 silicosis patients and 7 non-diseased donors. A total of 2,605 differentially expressed genes (DEGs) and critical pathway changes were identified in human silicosis lungs. Further, the DEGs in silicosis were compared with those in idiopathic pulmonary fibrosis (IPF) and chronic obstructive pulmonary diseases (COPD), to extend current knowledge about the disease mechanisms and develop potential drugs. This analysis revealed both common and specific regulations in silicosis, along with several critical genes (e.g., MUC5AC and FGF10), which are potential drug targets for silicosis treatment. Drugs including Plerixafor and Retinoic acid were predicted as potential candidates in treating silicosis. Overall, this study provides the first transcriptomic fingerprint of human silicosis lungs. The comparative transcriptome analyses comprehensively characterize pathological regulations resulting from silicosis, and provide valuable cues for silicosis treatment.

Th2 cytokines-DUOX2-ROS-HMGB1 translocation axis is important in the pathogenesis of allergic rhinitis

The function of high-mobility group box 1 (HMGB1) varies according to its location. However, the translocation mechanism behind HMGB1 remains unclear. We hypothesize that type 2 helper T cell (Th2) cytokines are involved in the translocation of HMGB1 in the upper airway epithelium. We investigated the mechanism behind HMGB1 translocation using Th2 cytokine stimulation and examined the clinical significance of HMGB1 translocation in allergic rhinitis (AR). Cytoplasmic and extracellular HMGB1 were increased in AR. Inhibiting HMGB1 translocation with glycyrrhizic acid (GA) decreased the level of antigen-specific immunoglobulin E (IgE), the degree of Periodic Acid-Schiff (PAS), and Sirius Red staining in the murine model. The in vivo reactive oxygen species (ROS) level in the nasal mucosa was higher in the mice with AR than in the controls. Th2 cytokine-induced up-regulation of the ROS and translocation of HMGB1 by Th2 cytokines was dependent on the generated ROS. The ROS level also increased in the murine model. We suggest that the Th2 cytokine-dual oxidase (DUOX)2-ROS-HMGB1 translocation axis is important in AR pathogenesis.

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

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

Temporal differentiation of bovine airway epithelial cells grown at an air-liquid interface

There is an urgent need to develop improved, physiologically-relevant in vitro models of airway epithelia with which to better understand the pathological processes associated with infection, allergies and toxicological insults of the respiratory tract of both humans and domesticated animals. In the present study, we have characterised the proliferation and differentiation of primary bovine bronchial epithelial cells (BBECs) grown at an air-liquid interface (ALI) at three-day intervals over a period of 42 days from the introduction of the ALI. The differentiated BBEC model was highly representative of the ex vivo epithelium from which the epithelial cells were derived; a columnar, pseudostratified epithelium that was highly reflective of native airway epithelium was formed which comprised ciliated, goblet and basal cells. The hallmark defences of the respiratory tract, namely barrier function and mucociliary clearance, were present, thus demonstrating that the model is an excellent mimic of bovine respiratory epithelium. The epithelium was fully differentiated by day 21 post-ALI and, crucially, remained healthy and stable for a further 21 days. Thus, the differentiated BBEC model has a three-week window which will allow wide-ranging and long-term experiments to be performed in the fields of infection, toxicology or general airway physiology.

Establishment and characterization of a telomerase-immortalized porcine bronchial epithelial cell line

Primary porcine bronchial epithelial cells (PBECs) are an ideal model to study the molecular and pathogenic mechanisms of various porcine respiratory pathogens. However, the short lifespan of primary PBECs greatly limit their application. Here, we isolated and cultured primary PBECs and established immortalized PBECs by transfecting primary PBECs with the pEGFP-hTERT recombinant plasmid containing human telomerase reverse transcriptase (hTERT). Immortalized PBECs (hTERT-PBECs) retained the morphological and functional features of primary PBECs as indicated by cytokeratin 18 expression, telomerase activity assay, proliferation assays, karyotype analysis, and quantitative reverse-transcriptase polymerase chain reaction. Compared to primary PBECs, hTERT-PBECs had higher telomerase activity, extended replicative lifespan, and displayed enhanced proliferative activity. Moreover, this cell line is not transformed in vitro and does not exhibit a malignant phenotype in vivo, suggesting that it can be safely used in further studies. Besides, hTERT-PBECs were susceptible to swine influenza virus of H3N2 subtype and porcine circovirus type 2. In conclusion, the immortalized hTERT-PBECs represent a valuable in vitro model, which can be widely used in the study of porcine respiratory pathogenic infections.

Optimisation of growth conditions for ovine airway epithelial cell differentiation at an air-liquid interface

Respiratory tract infections are of significant concern in the agriculture industry. There is a requirement for the development of well-characterised in vitro epithelial cell culture models in order to dissect the diverse molecular interactions occurring at the host-pathogen interface in airway epithelia. We have analysed key factors that influence growth and differentiation of ovine tracheal epithelial cells in an air-liquid interface (ALI) culture system. Cellular differentiation was assessed at 21 days post-ALI, a time-point which we have previously shown to be sufficient for differentiation in standard growth conditions. We identified a dose-dependent response to epidermal growth factor (EGF) in terms of both epithelial thickening and ciliation levels. Maximal ciliation levels were observed with 25 ng ml-1 EGF. We identified a strict requirement for retinoic acid (RA) in epithelial differentiation as RA exclusion resulted in the formation of a stratified squamous epithelium, devoid of cilia. The pore-density of the growth substrate also had an influence on differentiation as high pore-density inserts yielded higher levels of ciliation and more uniform cell layers than low pore-density inserts. Differentiation was also improved by culturing the cells in an atmosphere of sub-ambient oxygen concentration. We compared two submerged growth media and observed differences in the rate of proliferation/expansion, barrier formation and also in terminal differentiation. Taken together, these results indicate important differences between the response of ovine tracheal epithelial cells and other previously described airway epithelial models, to a variety of environmental conditions. These data also indicate that the phenotype of ovine tracheal epithelial cells can be tailored in vitro by precise modulation of growth conditions, thereby yielding a customisable, potential infection model.

Development and optimization of a differentiated airway epithelial cell model of the bovine respiratory tract

Cattle are subject to economically-important respiratory tract infections by various bacterial and viral pathogens and there is an urgent need for the development of more realistic in vitro models of the bovine respiratory tract to improve our knowledge of disease pathogenesis. In the present study, we have optimized the culture conditions in serum-free medium that allow bovine bronchial epithelial cells (BBECs) grown at an air-liquid interface to differentiate into a three-dimensional epithelium that is highly representative of the bovine airway. Epidermal growth factor was required to trigger both proliferation and differentiation of BBECs whilst retinoic acid was also essential for mucociliary differentiation. Triiodothyronine was demonstrated not to be important for the differentiation of BBECs. Oxygen concentration had a minimal effect although optimal ciliation was achieved when BBECs were cultured at 14% oxygen tension. Insert pore-density had a significant effect on the growth and differentiation of BBECs; a high-pore-density was required to trigger optimum differentiation. The established BBEC model will have wide-ranging applications for the study of bacterial and viral infections of the bovine respiratory tract; it will contribute to the development of improved vaccines and therapeutics and will reduce the use of cattle in in vivo experimentation.

Differentiation of respiratory epithelium in a 3-dimensional co-culture with fibroblasts embedded in fibrin gel

Background

Tracheal tissue engineering is a promising option for the treatment of tracheal defects. In a previous study we proved the suitability of fibrin gel as a scaffold for tracheal tissue engineering. This study investigates whether the differentiation of respiratory epithelium can be increased by culturing epithelial cells in a three dimensional system containing fibroblasts embedded into fibrin gel.

Methods

Respiratory epithelial cells were isolated from porcine trachea, seeded onto a fibrin gel and kept in air-liquid-interface culture for 33 days. Morphology as well as pan-cytokeratin, MUC5AC and claudin-1 expression of cells cultured on pure fibrin gel were compared to culture on gels containing fibroblasts.

Results

After two weeks, cells seeded on pure fibrin gel were multilayered, showed hyperproliferation and dedifferentiation. Co-cultured cells built up a pseudostratified epithelium. The differentiation and organization of epithelial structure improved with respect to time. After four weeks, morphology of the co-cultured respiratory epithelium resembled native tracheal epithelium. Immunohistochemistry showed that respiratory epithelium co-cultured with fibroblasts had an increasing similarity of pan-cytokeratin expression compared to native trachea. Cells cultured without fibroblasts differed in pan-cytokeratin expression from native trachea and did not show any improvement of differentiation. Immunohistochemical staining of MUC5AC and claudin-1 proved seeded cells being respiratory epithelial cells.

Conclusions

This study indicates that adding fibroblasts to fibrin gel positively influences the differentiation of respiratory epithelium.

The Induction of Pattern-Recognition Receptor Expression against Influenza A Virus through Duox2-Derived Reactive Oxygen Species in Nasal Mucosa

We studied the relative roles of Duox2-derived reactive oxygen species (ROS) in host defense against influenza A virus (IAV) infection in normal human nasal epithelial cells and mouse nasal mucosa. We found that Duox2 primarily generated ROS rapidly after IAV infection in normal human nasal epithelial cells and that knockdown of Duox2 aggravated IAV infection. In addition, Duox2-derived ROS enhancement significantly suppressed IAV infection in nasal epithelium. In particular, Duox2-derived ROS were required for the induction of retinoic acid-inducible gene (RIG)-I and melanoma differentiation-associated protein 5 (MDA5) transcription. After intranasal IAV inoculation into mice, viral infection was significantly aggravated from 3 days postinoculation (dpi) in the nasal mucosa, and the IAV viral titer was highest at 7 dpi. Both RIG-I and MDA5 messenger RNA levels increased dominantly in mouse nasal mucosa from 3 dpi; consistent with this, RIG-I and MDA5 proteins were also induced after IAV infection. RIG-I and MDA5 messenger RNA levels were induced to a lower extent in the nasal mucosa of the mice that were inoculated with Duox2 short hairpin RNA, and the IAV viral titer was significantly higher in nasal lavage. Taken together, Duox2-derived ROS are necessary for the innate immune response and trigger the induction of RIG-I and MDA5 to resist IAV infection in human nasal epithelium and mouse nasal mucosa.

A novel siderophore system is essential for the growth of Pseudomonas aeruginosa in airway mucus

Pseudomonas aeruginosa establishes airway infections in Cystic Fibrosis patients. Here, we investigate the molecular interactions between P. aeruginosa and airway mucus secretions (AMS) derived from the primary cultures of normal human tracheal epithelial (NHTE) cells. PAO1, a prototype strain of P. aeruginosa, was capable of proliferating during incubation with AMS, while all other tested bacterial species perished. A PAO1 mutant lacking PA4834 gene became susceptible to AMS treatment. The ΔPA4834 mutant was grown in AMS supplemented with 100 μM ferric iron, suggesting that the PA4834 gene product is involved in iron metabolism. Consistently, intracellular iron content was decreased in the mutant, but not in PAO1 after the AMS treatment. Importantly, a PAO1 mutant unable to produce both pyoverdine and pyochelin remained viable, suggesting that these two major siderophore molecules are dispensable for maintaining viability during incubation with AMS. The ΔPA4834 mutant was regrown in AMS amended with 100 μM nicotianamine, a phytosiderophore whose production is predicted to be mediated by the PA4836 gene. Infectivity of the ΔPA4834 mutant was also significantly compromised in vivo. Together, our results identify a genetic element encoding a novel iron acquisition system that plays a previously undiscovered role in P. aeruginosa airway infection.

Th2 cytokines differentially regulate psoriasin expression in human nasal epithelia

BACKGROUND

Psoriasin is known to be expressed in diverse organs, where it exerts antimicrobial activity. Psoriasin is also involved in the local host defense mechanism against pathogens. We hypothesized that allergy-related T-helper cell type 2 (Th2) cytokines may regulate the expression of psoriasin.

METHODS

We treated normal human nasal epithelial (NHNE) cells with IL-4 or IL-13. Using human nasal tissues, we compared the expression level of psoriasin. We performed real-time polymerase chain reaction and Western blot assays using NHNE cells. Immunohistochemical staining and Western blot assays were performed with human nasal tissues. Furthermore, we studied the antimicrobial activity of nasal secretions from normal and allergic rhinitis patients.

RESULTS

IL-13 markedly down-regulated psoriasin expression at the gene and protein levels in NHNE cells, and it also decreased the amount of psoriasin protein that was secreted into the extracellular compartment in NHNE cells. IL-4 had no statistically significant effect. Results from immunohistochemical staining and Western blot assays showed that psoriasin expression was decreased in allergic rhinitis patients compared with control subjects. Nasal secretions of allergic rhinitis patients exhibited decreased antimicrobial activity compared with control subjects.

CONCLUSION

We found that Th2 cytokines regulated psoriasin expression in NHNE cells, and psoriasin expression was decreased in allergic rhinitis patients compared with control subjects. The decreased expression of psoriasin may be related to the reduction in antimicrobial capacity of nasal secretions under allergic conditions, resulting in an increase in susceptibility to viruses or bacterial infections.

Alternative Method for Primary Nasal Epithelial Cell Culture Using Intranasal Brushing and Feasibility for the Study of Epithelial Functions in Allergic Rhinitis

Purpose

Although differentiated normal human nasal epithelial (NHNE) cells can be used to study the role of human nasal epithelium, there is a need for effective culture models of nasal epithelium in sinonasal disease status, including allergic rhinitis (AR). We aimed to examine the feasibility of intranasal brushing for culture of nasal epithelial cells in AR patients and to verify the hypothesis that allergic nasal epithelial (ARNE) cells differ in histologic and physiologic characteristics.

Methods

We established a system for isolating (via intranasal brushing) and culturing (with air-liquid interface, ALI) nasal epithelial cells from healthy volunteers (n=8) and AR patients (n=8). We used this system to compare the histologic findings and physiologic characteristics of NHNE and ARNE.

Results

The histology results showed that fully differentiated ALI culture was obtained at least 14 days after confluence and that both ciliated and secretory cells were well differentiated in ALI culture using nasal brushing. The histology results of ARNE culture were significantly different from NHNE. The number of ciliated cells was lower, and secretory cells were more dominant in ARNE cell culture compared to NHNE cells. We also observed, by electron microscopy, loose tight junctions and short cilia in cultured ARNE cells. In addition, the mRNA level of TSLP which was one of the epithelial-derived allergic cytokines was significantly higher, and the expressions of genes involved in ciliogenesis were lower in cultured ARNE cells without allergen stimulation.

Conclusions

Our findings suggest that ALI culture of ARNE cells using intranasal brushing may be an alternative method for epithelial cell culture in AR patients and that cultured ARNE cells will be useful for in vitro studies of the mechanisms at play during AR because they maintain unique allergic characteristics.

Hypoxia increases epithelial permeability in human nasal epithelia

PURPOSE

The nasal mucosa is the first site to encounter pathogens, and it forms continuous barriers to various stimuli. This barrier function is very important in the innate defense mechanism. Additionally, inflammation of the nasal sinus is known to be a hypoxic condition. Here, we studied the effect of hypoxia on barrier function in normal human nasal epithelial (NHNE) cells.

MATERIALS AND METHODS

The expression levels of various junction complex proteins were assessed in hypoxia-stimulated NHNE cells and human nasal mucosal tissues. We performed real-time polymerase chain reaction analysis, western blotting, and immunofluorescence assays to examine differences in the mRNA and protein expression of ZO-1, a tight junction protein, and E-cadherin in NHNE cells. Moreover, we evaluated the trans-epithelial resistance (TER) of NHNE cells under hypoxic conditions to check for changes in permeability. The expression of ZO-1 and E-cadherin was measured in human nasal mucosa samples by western blotting.

RESULTS

Hypoxia time-dependently decreased the expression of ZO-1 and E-cadherin at the gene and protein levels. In addition, hypoxia decreased the TER of NHNE cells, which indicates increased permeability. Human nasal mucosa samples, which are supposed to be hypoxic, showed significantly decreased levels of ZO-1 and E-cadherin expression compared with control.

CONCLUSION

Our results demonstrate that hypoxia altered the expression of junction complex molecules and increased epithelial permeability in human nasal epithelia. This suggests that hypoxia causes barrier dysfunction. Furthermore, it may be associated with innate immune dysfunction after encountering pathogens.

Reconstituted human upper airway epithelium as 3-d in vitro model for nasal polyposis

Background

Primary human airway epithelial cells cultured in an air-liquid interface (ALI) develop a well-differentiated epithelium. However, neither characterization of mucociliar differentiation overtime nor the inflammatory function of reconstituted nasal polyp (NP) epithelia have been described.

Objectives

1^st) To develop and characterize the mucociliar differentiation overtime of human epithelial cells of chronic rhinosinusitis with nasal polyps (CRSwNP) in ALI culture system; 2^nd) To corroborate that 3D in vitro model of NP reconstituted epithelium maintains, compared to control nasal mucosa (NM), an inflammatory function.

Methods

Epithelial cells were obtained from 9 NP and 7 control NM, and differentiated in ALI culture for 28 days. Mucociliary differentiation was characterized at different times (0, 7, 14, 21, and 28 days) using ultrastructure analysis by electron microscopy; ΔNp63 (basal stem/progenitor cell), β-tubulin IV (cilia), and MUC5AC (goblet cell) expression by immunocytochemistry; and mucous (MUC5AC, MUC5B) and serous (Lactoferrin) secretion by ELISA. Inflammatory function of ALI cultures (at days 0, 14, and 28) through cytokine (IL-8, IL-1β, IL-6, IL-10, TNF-α, and IL-12p70) and chemokine (RANTES, MIG, MCP-1, IP-10, eotaxin-1, and GM-CSF) production was analysed by CBA (Cytometric Bead Array).

Results

In both NP and control NM ALI cultures, pseudostratified epithelium with ciliated, mucus-secreting, and basal cells were observed by electron microscopy at days 14 and 28. Displaying epithelial cell re-differentation, β-tubulin IV and MUC5AC positive cells increased, while ΔNp63 positive cells decreased overtime. No significant differences were found overtime in MUC5AC, MUC5B, and lactoferrin secretions between both ALI cultures. IL-8 and GM-CSF were significantly increased in NP compared to control NM regenerated epithelia.

Conclusion

Reconstituted epithelia from human NP epithelial cells cultured in ALI system provides a 3D in vitro model that could be useful both for studying the role of epithelium in CRSwNP while developing new therapeutic strategies, including cell therapy, for CRSwNP.

Hypoxia-mediated mechanism of MUC5AC production in human nasal epithelia and its implication in rhinosinusitis

Background

Excessive mucus production is typical in various upper airway diseases. In sinusitis, the expression of MUC5AC, a major respiratory mucin gene, increases. However, the mechanisms leading to mucus hypersecretion in sinusitis have not been characterized. Hypoxia due to occlusion of the sinus ostium is one of the major pathologic mechanisms of sinusitis, but there have been no reports regarding the mechanism of hypoxia-induced mucus hypersecretion.

Methods and Findings

This study aims to identify whether hypoxia may induce mucus hypersecretion and elucidate its mechanism. Normal human nasal epithelial (NHNE) cells and human lung mucoepidermoid carcinoma cell line (NCI-H292) were used. Sinus mucosa from patients was also tested. Anoxic condition was in an anaerobic chamber with a 95% N₂/5% CO₂ atmosphere. The regulatory mechanism of MUC5AC by anoxia was investigated using RT-PCR, real-time PCR, western blot, ChIP, electrophoretic mobility shift, and luciferase assay. We show that levels of MUC5AC mRNA and the corresponding secreted protein increase in anoxic cultured NHNE cells. The major transcription factor for hypoxia-related signaling, HIF-1α, is induced during hypoxia, and transfection of a mammalian expression vector encoding HIF-1α results in increased MUC5AC mRNA levels under normoxic conditions. Moreover, hypoxia-induced expression of MUC5AC mRNA is down-regulated by transfected HIF-1α siRNA. We found increased MUC5AC promoter activity under anoxic conditions, as indicated by a luciferase reporter assay, and mutation of the putative hypoxia-response element in MUC5AC promoter attenuated this activity. Binding of over-expressed HIF-1α to the hypoxia-response element in the MUC5AC promoter was confirmed. In human sinusitis mucosa, which is supposed to be hypoxic, expression of MUC5AC and HIF-1α is higher than in control mucosa.

Conclusion

The results indicate that anoxia up-regulates MUC5AC by the HIF-1α signaling pathway in human nasal epithelia and suggest that hypoxia might be a pathogenic mechanism of mucus hypersecretion in sinusitis.

Reactive oxygen species induce antiviral innate immune response through IFN-λ regulation in human nasal epithelial cells

This study sought to explore the role of the IFN-related innate immune responses (IFN-β and IFN-λ) and of reactive oxygen species (ROS) after influenza A virus (IAV) infection for antiviral innate immune activity in normal human nasal epithelial (NHNE) cells that are highly exposed to IAV. Passage-2 NHNE cells were inoculated with the IAV WSN/33 for 1, 2, and 3 days to assess the capacity of IFN and the relationship between ROS generation and IFN-λ secretion for controlling IAV infection. Viral titers and IAV mRNA levels increased after infection. In concert with viral titers, we found that the generation of IFNs, such as IFN-β, IFN-λ1, and IFN-λ2/3, was induced after IAV infection until 3 days after infection. The induction of IFN-λ gene expression and protein secretion may be predominant after IAV infection. Similarly, we observed that intracellular ROS generation increased 60 minutes after IAV infection. Viral titers and mRNA levels of IAV were significantly higher in cases with scavenging ROS, in cases with an induced IFN-λ mRNA level, or where the secreted protein concentration of IFN-λ was attenuated after the suppression of ROS generation. Both mitochondrial and dual oxidase (Doux)2-generated ROS were correlated with IAV mRNA and viral titers. The inhibition of mitochondrial ROS generation and the knockdown of Duox2 gene expression highly increased IAV viral titers and decreased IFN-λ secretion. Our findings suggest that the production of ROS may be responsible for IFN-λ secretion to control IAV infection. Both mitochondria and Duox2 are possible sources of ROS generation, which is required to initiate an innate immune response in NHNE cells.

Bacterial-derived uracil as a modulator of mucosal immunity and gut-microbe homeostasis in Drosophila

All metazoan guts are subjected to immunologically unique conditions in which an efficient antimicrobial system operates to eliminate pathogens while tolerating symbiotic commensal microbiota. However, the molecular mechanisms controlling this process are only partially understood. Here, we show that bacterial-derived uracil acts as a ligand for dual oxidase (DUOX)-dependent reactive oxygen species generation in Drosophila gut and that the uracil production in bacteria causes inflammation in the gut. The acute and controlled uracil-induced immune response is required for efficient elimination of bacteria, intestinal cell repair, and host survival during infection of nonresident species. Among resident gut microbiota, uracil production is absent in symbionts, allowing harmonious colonization without DUOX activation, whereas uracil release from opportunistic pathobionts provokes chronic inflammation. These results reveal that bacteria with distinct abilities to activate uracil-induced gut inflammation, in terms of intensity and duration, act as critical factors that determine homeostasis or pathogenesis in gut-microbe interactions.

TGF-β₂ decreases baseline and IL-13-stimulated mucin production by primary human bronchial epithelial cells

INTRODUCTION

Mucus hypersecretion is a major contributor to asthma pathology and occurs as part of a spectrum of structural changes termed airway wall remodeling. Transforming growth factor (TGF)-β is proposed to play a key role in regulating airway matrix remodeling although less is known about the specific action of TGF-β isoforms in regulating mucus production.

METHODS

Primary human bronchial epithelial (HBE) cells cultured at air-liquid interface were treated with exogenous TGF-β(1), TGF-β(2), and/or a Th2 cytokine, interleukin (IL)-13. Expression and production of respiratory mucins, MUC5AC and MUC5B, were analyzed by real-time PCR, agarose gel electrophoresis, and western blotting. A murine-transformed Clara cell line (mtCC1-2) transfected with a luciferase reporter driven by the Muc5ac promoter containing Smad4 site-mutated cis sequences was used to determine whether exogenous TGF-β(2) affects Muc5ac promoter function.

RESULTS

Surprisingly, TGF-β(1) showed no measurable effect on MUC5AC or MUC5B production by HBE cells whereas TGF-β(2) caused a decrease in both MUC5AC and MUC5B mRNA and protein. Dual treatment with TGF-β(2) and IL-13 partially attenuated the increase in mucin production found with IL-13 alone. This effect was confirmed by using mtCC1-2 cells where addition of TGF-β(2) reduced the ability of IL-13/EGF to induce Muc5ac promoter expression in wild-type cells; however, this decrease was absent in mutant promoter-transfected cells.

DISCUSSION AND CONCLUSION

Findings suggest that normal regulation of MUC5AC and MUC5B production by HBE cells is TGF-β isoform-specific and that TGF-β(2) downregulates both MUC5AC and MUC5B. Furthermore, TGF-β(2) controls baseline and IL-13-driven Muc5ac promoter function in murine Clara cells via an endogenous Smad4 recognition motif.

Differentiated swine airway epithelial cell cultures for the investigation of influenza A virus infection and replication

Please cite this paper as: Bateman et al. (2013) Differentiated swine airway epithelial cell cultures for the investigation of influenza A virus infection and replication. Influenza and Other Respiratory Viruses 7(2) 139–150.

Background  Differentiated human airway epithelial cell cultures have been utilized to investigate cystic fibrosis, wound healing, and characteristics of viral infections. These cultures, grown at an air–liquid interface (ALI) in media with defined hormones and growth factors, recapitulate many aspects of the in vivo respiratory tract and allow for experimental studies at the cellular level.

Objectives  To optimize growth conditions for differentiated swine airway epithelial cultures and to use these cultures to examine influenza virus infection and replication.

Methods  Primary swine respiratory epithelial cells were grown at an air–liquid interface with varying amounts of retinoic acid and epidermal growth factor. Cells grown with optimized concentrations of these factors for 4 weeks differentiated into multilayer epithelial cell cultures resembling the lining of the swine respiratory tract. Influenza virus infection and replication were examined in these cultures.

Results/Conclusions  Retinoic acid promoted ciliogenesis, whereas epidermal growth factor controlled the thickness of the pseudoepithelium. The optimal concentrations for differentiated swine cell cultures were 1·5 ng/ml epidermal growth factor and 100 nm retinoic acid. Influenza A viruses infected and productively replicated in these cultures in the absence of exogenous trypsin, suggesting that the cultures express a protease capable of activating influenza virus hemagglutinin. Differences in virus infection and replication characteristics found previously in pigs in vivo were recapitulated in the swine cultures. This system could be a useful tool for a range of applications, including investigating influenza virus species specificity, defining cell tropism of influenza viruses in the swine respiratory epithelium, and studying other swine respiratory diseases.

Triiodothyronine represses MUC5AC expression by antagonizing Sp1 binding to its promoter in human bronchial epithelial HBE16 cells

Mucus hypersecretion is a distinguished feature of chronic inflammatory airway diseases. Interestingly, in this condition thyroid function is impaired with decreased level of triiodothyronine (T3), indicating potential link between low level of T3 and mucus hypersecretion. But the underlying mechanisms are poorly understood. In this study we aimed to elucidate the effect of T3 on MUC5AC secretion in human bronchial epithelial HBE16 cells and further investigate how T3 regulates MUC5AC gene expression at transcriptional level. By RT-PCR and ELISA we showed that T3 inhibited MUC5AC mRNA expression and protein secretion in HBE16 cells. Furthermore, luciferase assay and site-directed mutagenesis analysis demonstrated that T3 repressed MUC5AC expression at transcriptional level and the mechanism might partly lie in the specific inhibition of Sp1 binding to the promoter. Our results suggest that decreased T3 level leads to the release of repression of MUC5AC expression and thus contributes to mucus hypersecretion.

Dual oxidase 2 is essential for the toll-like receptor 5-mediated inflammatory response in airway mucosa

AIMS

Airway mucosa is constantly exposed to various airborne microbes, and epithelial host defense requires a robust innate immunity. Recently, it has been suggested that NADPH oxidase (NOX) isozymes serve functional roles in toll-like receptor (TLR)-mediated innate immune responses. However, the molecular mechanism between TLR and NOX-mediated reactive oxygen species (ROS) production in human airway mucosa has been poorly understood.

RESULTS

Here, we show that flagellin-induced ROS generation is dependent on dual oxidase 2 (DUOX2) activation, which is regulated by [Ca(2+)](i) mobilization in primary normal human nasal epithelial (NHNE) cells. Interestingly, we observed that silencing of DUOX2 expression in NHNE cells and nasal epithelium of Duox2 knockout mice failed to trigger mucin and MIP-2? production upon challenging flagellin.

INNOVATION

Our observation in this study reveals that flagellin-induced hydrogen peroxide (H(2)O(2)) generation is critical for TLR5-dependent innate immune responses, including IL-8 production and MUC5AC expression in the nasal epithelium. Furthermore, DUOX2-mediated H(2)O(2) generation activated by the flagellin-TLR5 axis might serve as a novel therapeutic target for infectious inflammation diseases in the airway tract.

CONCLUSION

Taken together, we propose that DUOX2 plays pivotal roles in TLR5-dependent inflammatory response of nasal airway epithelium.

Endoplasmic reticulum stress decreases intracellular thyroid hormone activation via an eIF2a-mediated decrease in type 2 deiodinase synthesis

Cells respond rapidly to endoplasmic reticulum (ER) stress by blocking protein translation, increasing protein folding capacity, and accelerating degradation of unfolded proteins via ubiquitination and ER-associated degradation pathways. The ER resident type 2 deiodinase (D2) is normally ubiquitinated and degraded in the proteasome, a pathway that is accelerated by enzyme catalysis of T(4) to T(3). To test whether D2 is normally processed through ER-associated degradation, ER stress was induced in cells that endogenously express D2 by exposure to thapsigargin or tunicamycin. In all cell models, D2 activity was rapidly lost, to as low as of 30% of control activity, without affecting D2 mRNA levels; loss of about 40% of D2 activity and protein was also seen in human embryonic kidney 293 cells transiently expressing D2. In primary human airway cells with ER stress resulting from cystic fibrosis, D2 activity was absent. The rapid ER stress-induced loss of D2 resulted in decreased intracellular D2-mediated T(3) production. ER stress-induced loss of D2 was prevented in the absence of T(4), by blocking the proteasome with MG-132 or by treatment with chemical chaperones. Notably, ER stress did not alter D2 activity half-life but rather decreased D2 synthesis as assessed by induction of D2 mRNA and by [(35)S]methionine labeling. Remarkably, ER-stress-induced loss in D2 activity is prevented in cells transiently expressing an inactive eukaryotic initiation factor 2, indicating that this pathway mediates the loss of D2 activity. In conclusion, D2 is selectively lost during ER stress due to an eukaryotic initiation factor 2-mediated decrease in D2 synthesis and sustained proteasomal degradation. This explains the lack of D2 activity in primary human airway cells with ER stress resulting from cystic fibrosis.

The extracellular signal-regulated kinase mitogen-activated protein kinase/ribosomal S6 protein kinase 1 cascade phosphorylates cAMP response element-binding protein to induce MUC5B gene expression via D-prostanoid receptor signaling

Mucus hypersecretion is a prominent feature of respiratory diseases, and MUC5B is a major airway mucin. Mucin gene expression can be affected by inflammatory mediators, including prostaglandin (PG) D(2,) an inflammatory mediator synthesized by hematopoietic PGD synthase (H-PGDS). PGD(2) binds to either D-prostanoid receptor (DP1) or chemoattractant receptor homologous molecule expressed on T-helper type 2 cells (CRTH2). We investigated the mechanisms by which PGD(2) induces MUC5B gene expression in airway epithelial cells. Western blot analysis showed that H-PGDS was highly expressed in nasal polyps. Similar results were obtained for PGD(2) expression. In addition, we could clearly detect the expressions of both H-PGDS and DP1 in nasal epithelial cells but not CRTH2. We demonstrated that PGD(2) increased MUC5B gene expression in normal human nasal epithelial cells as well as in NCI-H292 cells in vitro. S5751, a DP1 antagonist, inhibited PGD(2)-induced MUC5B expression, whereas a CRTH2 antagonist (OC0459) did not. These data suggest that PGD(2) induced MUC5B expression via DP1. Pretreatment with extracellular signal-regulated kinase (ERK) inhibitor (PD98059) blocked both PGD(2)-induced ERK mitogen-activated protein kinase (MAPK) activation and MUC5B expression. Proximity ligation assays showed direct interaction between RSK1 and cAMP response element-binding protein (CREB). Stimulation with PGD(2) caused an increase in intracellular cAMP levels, whereas intracellular Ca(2+) did not have such an effect. PGD(2)-induced MUC5B mRNA levels were regulated by CREB via direct interaction with two cAMP-response element sites (-921/-914 and -900/-893). Finally, we demonstrated that PGD(2) can induce MUC5B overproduction via ERK MAPK/RSK1/CREB signaling and that DP1 receptor may have suppressive effects in controlling MUC5B overproduction in the airway.

Crosstalk between platelet-derived growth factor-induced Nox4 activation and MUC8 gene overexpression in human airway epithelial cells

Reactive oxygen species (ROS) contribute to chronic airway inflammation, and NADPH oxidase (Nox) is an important source of ROS. However, little is known of the role that ROS play in chronic upper respiratory tract inflammation. We investigated the mechanism of ROS generation and its association with mucin gene overexpression in the nasal epithelium. The level of platelet-derived growth factor (PDGF) expression was increased in sinusitis mucosa, and high-level PDGF expression induced intracellular ROS, followed by MUC8 gene overexpression in normal human nasal epithelial cells. Knockdown of Nox4 expression with Nox4 siRNA decreased PDGF-induced intracellular ROS and MUC8 expression. Infection with an adenovirus containing Nox4 cDNA resulted in Nox4 overexpression and increased intracellular levels of ROS and MUC8 expression. PDGF and Nox4 overexpression are essential components of intracellular ROS generation and may contribute to chronic inflammation in the nasal epithelium through induction of MUC8 overexpression.

House dust mite extract activates apical Cl(-) channels through protease-activated receptor 2 in human airway epithelia

Adequate fluid secretion from airway mucosa is essential for maintaining mucociliary clearance, and fluid hypersecretion is a prominent feature of inflammatory airway diseases such as allergic rhinitis. House dust mite extract (HDM) has been reported to activate protease-activated receptors (PARs), which play various roles in airway epithelia. However, the role of HDM in regulating ion transporters and fluid secretion has not been investigated. We examined the effect of HDM on ion transport in human primary nasal epithelial cells. The Ca(2+)-sensitive dye Fura2-AM was used to determine intracellular Ca(2+) concentration ([Ca(2+)](i)) by means of spectrofluorometry in human normal nasal epithelial cells (NHNE). Short-circuit current (Isc) was measured using Ussing chambers. Fluid secretion from porcine airway mucosa was observed by optical measurement. HDM extract (10 microg/Ml) effectively cleaved the PAR-2 peptide and induced an increase of [Ca(2+)](i) that was abolished by desensitization with trypsin, but not with thrombin. Apical application of HDM-induced Isc sensitive to both a cystic fibrosis transmembrane conductance regulator (CFTR) inhibitor and a Ca(2+)-activated Cl(-) channel (CaCC) inhibitor. HDM extract also stimulated fluid secretion from porcine airway mucosa. HDM extract activated PAR-2 and apical Cl(-) secretion via CaCC and CFTR, and HDM-induced fluid secretion in porcine airway mucosa. Our results suggest a role for PAR-2 in mucociliary clearance and fluid hypersecretion of airway mucosa in response to air-borne allergens such as HDM.

All-trans retinoic acid mediates DUOX2 expression and function in respiratory tract epithelium

DUOX1 and DUOX2 are members of the NADPH oxidase family that are specifically regulated to produce hydrogen peroxide in epithelia of the thyroid, gastrointestinal tract, and respiratory tract. The determinants of DUOX1 or DUOX2 expression in various tissues have not been established. Using respiratory tract epithelial cells as a model, we investigated changes in DUOX mRNA and protein expression during the first 10 days of differentiation. By comparing a respiratory tract cell line, HBE1, with primary tracheobronchial epithelial (TBE) cells, we determined that DUOX2 was significantly expressed only in cell conditions that included all-trans retinoic acid (ATRA). In HBE1 cells, DUOX2 mRNA increased 6-fold after ATRA treatment. Similarly, ATRA induced a 19-fold increase in DUOX2 mRNA expression in primary TBE cells with parallel increases in DUOX protein and DUOX-mediated H(2)O(2) production as well. In addition, DUOX2 induction by rhinovirus required the presence of ATRA. ATRA had no effect on DUOX1 expression for all the conditions studied. Our data indicate that for respiratory epithelial cells, ATRA is important in the regulation of DUOX2 expression, function, and rhinovirus-mediated DUOX2 inducibility.

Human LPLUNC1 is a secreted product of goblet cells and minor glands of the respiratory and upper aerodigestive tracts

Long PLUNC1 (LPLUNC1, C20orf114) is a member of a family of poorly described proteins (PLUNCS) expressed in the upper respiratory tract and oral cavity, which may function in host defence. Although it is one of the most highly expressed genes in the upper airways and has been identified in sputum and nasal secretions by proteomic studies, localisation of LPLUNC1 protein has not yet been described. We developed affinity purified antibodies and localised the protein in tissues of the human respiratory tract, oro- and nasopharynx. We have complemented these studies with analysis of LPLUNC1 expression in primary human lung cell cultures and used Western blotting to study the protein in cell culture secretions and in BAL. LPLUNC1 is a product of a population of goblet cells in the airway epithelium and nasal passages and is also present in airway submucosal glands and minor glands of the oral and nasal cavities. The protein is not expressed in peripheral lung epithelial cells. LPLUNC1 is present in bronchoalveolar lavage fluid as two glycosylated isoforms and primary airway epithelial cells produce identical proteins as they undergo mucociliary differentiation. Our results suggest that LPLUNC1 is an abundant, secreted product of goblet cells and minor mucosal glands of the respiratory tract and oral cavity and suggest that the protein functions in the complex milieu that protects the mucosal surfaces in these locations.

A 3-D well-differentiated model of pediatric bronchial epithelium demonstrates unstimulated morphological differences between asthmatic and nonasthmatic cells

There is a need for reproducible and effective models of pediatric bronchial epithelium to study disease states such as asthma. We aimed to develop, characterize, and differentiate an effective, an efficient, and a reliable three-dimensional model of pediatric bronchial epithelium to test the hypothesis that children with asthma differ in their epithelial morphologic phenotype when compared with nonasthmatic children. Primary cell cultures from both asthmatic and nonasthmatic children were grown and differentiated at the air-liquid interface for 28 d. Tight junction formation, MUC5AC secretion, IL-8, IL-6, prostaglandin E2 production, and the percentage of goblet and ciliated cells in culture were assessed. Well-differentiated, multilayered, columnar epithelium containing both ciliated and goblet cells from asthmatic and nonasthmatic subjects were generated. All cultures demonstrated tight junction formation at the apical surface and exhibited mucus production and secretion. Asthmatic and nonasthmatic cultures secreted similar quantities of IL-8, IL-6, and prostaglandin E2. Cultures developed from asthmatic children contained considerably more goblet cells and fewer ciliated cells compared with those from nonasthmatic children. A well-differentiated model of pediatric epithelium has been developed that will be useful for more in vivo like study of the mechanisms at play during asthma.

Epicatechin gallate suppresses oxidative stress-induced MUC5AC overexpression by interaction with epidermal growth factor receptor

The goal of this study was to investigate the effect of epicatechin gallate (ECG), a component of green tea polyphenols, on the signal pathway for oxidative stress-induced intracellular reactive oxygen species (ROS) generation and MUC5AC overexpression in normal human nasal epithelial (NHNE) cells. Passage-2 NHNE cells were used, and ECG was administered before stimulation with exogenous hydrogen peroxide (H(2)O(2)). MUC5AC gene and protein levels were measured by real-time PCR and dot blot analysis. Western blot analysis and immunocytofluorescence study were performed for detecting the activity of epidermal growth factor receptor (EGFR). Exogenous H(2)O(2) increases intracellular ROS generation, leading to the overexpression of MUC5AC. The phosphorylation and internalization of EGFR were associated with this ROS generation. ECG decreased the phosphorylation and internalization of EGFR at the cell surface of NHNE cells, resulting in the attenuation of exogenous H(2)O(2)-induced intracellular ROS generation and MUC5AC overexpression. ECG may be a therapeutic material against oxidative stress-induced ROS generation and mucus hypersecretion in airways.

Ciliogenesis in cryopreserved mammalian tracheal epithelial cells cultured at the air-liquid interface

To determine air-liquid interface (ALI) culture derived from cryopreserved mammalian tracheal ciliated cells is a viable ciliated cell model for the investigations of regulatory mechanisms of ciliary beat frequency (CBF), two studies were performed using ovine and porcine tracheae obtained from local slaughterhouses. The protease-digested tracheal ciliated cells were harvested and cultured at the ALI using collagen-coated, porous membrane inserts. In study 1, the ALI culturing protocols were established using non-cryopreserved ovine tracheal ciliated cells. Ciliogenesis was documented with immuno-histology and electron micrographs. Vigorous beating cilia were video-recorded. CBF was measured by laser light scattering. The functional integrity of the autonomic receptors of the ciliated cells was confirmed with the stimulatory responses of CBF using luminal methacholine and basolateral terbutaline. In study 2, porcine tracheal ciliated cells stored in liquid nitrogen for a minimum of 4 weeks were used. The cryopreserved cells were thawed and cultured using the ALI protocol established in study 1. After two months, cilia outgrowths were confirmed using video microscopy and scanning electron micrograph (SEM). The trans-epithelial resistances were 28.5 kOmega (n=4). Luminal applications of 1 microM and 10 microM methacholine stimulated CBF from a baseline of 7.4+/-0.2 Hz to 8.4+/-0.8 Hz and 7.7+/-0.4 Hz, respectively (n=5). Basolateral applications of 1 microM and 10 microM terbutaline stimulated CBF from a baseline of 7.5+/-0.3 Hz to 8.2+/-0.4 Hz and 8.0+/-0.4 Hz, respectively (n=5). These data demonstrated that a ciliated cell bank can be established using cryopreserved ciliated cells for pulmonary drug discovery and toxicological screening.

Signal pathway of 17beta-estradiol-induced MUC5B expression in human airway epithelial cells

MUC5B is a major mucin of the human respiratory tract, and it is not clear how MUC5B expression is regulated in various airway diseases. The goal of this study was to determine the mechanisms by which 17beta-estradiol induces MUC5B gene expression in airway epithelial cells. It was found that E2, a sex hormone, stimulates MUC5B gene overexpression by interaction with estrogen receptor alpha (ERalpha) and by acting through extracellular signal-regulated kinase 1/2 (ERK1/2)-mitogen-activated protein kinase (MAPK). Pretreatment with ER antagonist ICI 182,780 blocked both E2-induced ERK1/2-MAPK activation and MUC5B gene expression. It was also found that the activation of p90 ribosomal S 6 protein kinase 1 (RSK1), cAMP-response element-binding protein (CREB), and cAMP-response element (CRE) (-956 region of the MUC5B promoter)-responsive signaling cascades via ERK1/2 MAPK are crucial aspects of the intracellular mechanisms that mediate MUC5B gene expression. Taken together, these studies give additional insights into the molecular mechanism of hormone-induced MUC5B gene expression and enhance our understanding of abnormal mucin secretion in response to hormonal imbalances.

The role of Nox4 in oxidative stress-induced MUC5AC overexpression in human airway epithelial cells

Mucus hypersecretion is a prominent manifestation in patients with chronic inflammatory airway diseases, and MUC5AC is a major airway mucin. It is well known that reactive oxygen species (ROS) may be involved in the pathogenesis of various inflammatory airway diseases. The purpose of this study was to identify which secreted mucin genes are induced by exogenous hydrogen peroxide and the mechanism by which these genes are up-regulated in normal human nasal epithelial (NHNE) cells. Exogenous H(2)O(2) induced the ligand-independent activation of epidermal growth factor receptors (EGFR) and the subsequent activation of ERK1 mitogen-activated protein kinase, resulting in the induction of intracellular ROS generation. Through this signal pathway, exogenous H(2)O(2) markedly induced overexpression of the MUC5AC gene alone. In addition, Nox4, a subtype of nonphagocytic NADPH oxidase, was found to play a key role in intracellular ROS generation and exogenous H(2)O(2)-induced MUC5AC gene expression in NHNE cells.

Epigallocatechin-3-gallate inhibits interleukin-1beta-induced MUC5AC gene expression and MUC5AC secretion in normal human nasal epithelial cells

It has been reported that the proinflammatory cytokine interleukin-1beta (IL-1beta) induces mucus hypersecretion in normal human nasal epithelial (NHNE) cells and that the MAP kinase pathway may be an important signal pathway in IL-1beta-induced MUC5AC gene expression. Green tea (Camellia sinensis) polyphenols are potent anti-inflammatory agents and have been shown to inhibit inflammation in tumor cell lines and cultured respiratory epithelial cells. In this study, we examined the effect of (-)-epigallocatechin-3-gallate (EGCG), a green tea polyphenol, on IL-1beta-induced MUC5AC gene expression and secretion in NHNE cells. After cells had been treated with IL-1beta (10 ng/ml) and pretreated with EGCG (10, 50 and 100 microM), mRNA expression of MUC5AC was determined by real-time polymerase chain reaction. The suppression of each signal pathway protein was determined by Western blot analysis after treatment with IL-1beta and EGCG, respectively. IL-1beta increased MUC5AC gene expression and MUC5AC secretion. EGCG markedly suppressed IL-1beta-induced MUC5AC gene expression and MUC5AC secretion via suppression of the phosphorylation of ERK MAP kinase, MSK1, and transcription factor, cAMP response element-binding protein. IL-1beta increased the number of cells staining positive with MUC5AC antibodies, and EGCG treatment decreased this number. Our data suggest that EGCG may be an effective inhibitor of IL-1beta-induced mucus hypersecretion.

Modulation of mucus production by interleukin-13 receptor alpha2 in the human airway epithelium

BACKGROUND

IL-13 induces goblet cell hyperplasia and mucus overproduction in airway epithelial cells. IL-13 receptor alpha2 (IL-13Ralpha(2)) has been suggested to act as a 'decoy receptor' in the airway epithelium by inhibiting the IL-13 signal. However, the regulatory mechanisms for mucus production by IL-13Ralpha(2) remain unclear.

OBJECTIVE

The aim of this study was to examine the role of IL-13Ralpha(2) in goblet cell hyperplasia and mucus overproduction by IL-13.

METHODS

Bronchi were obtained from patients who underwent a lung resection due to lung cancer or benign lung tumours. Normal human bronchial epithelial cells (NHBECs) were isolated and cultured using an air-liquid interface (ALI) method.

RESULTS

The number of periodic acid-Schiff's (PAS)-positive cells, goblet cells and MUC5AC-positive cells increased after adding IL-13 into NHBECs. The concentrations of MUC5AC protein in the supernatant and the mRNA expression of MUC5AC significantly increased after adding IL-13, and returned to control levels at 21 days. The mRNA expression of IL-13Ralpha(2) significantly increased at 7 days and then continuously increased up to 21 days. The protein of a soluble form of IL-13Ralpha(2) in the supernatants significantly increased at 14 and 21 days. Anti-IL-13Ralpha(1) antibody and recombinant IL-13Ralpha(2) reduced the number of PAS-positive cells, goblet cells and MUC5AC-positive cells, and MUC5AC mRNA, while the anti-IL-13Ralpha(2) antibody increased the number of these cells and MUC5AC mRNA. The concentration of MUC5AC protein in the supernatant induced by IL-13 was reduced by anti- IL-13Ralpha(1) antibody and recombinant IL-13Ralpha(2). IL-13-induced signal transducer and activator of transcription (STAT) activation was inhibited by anti-IL-13Ralpha(1) antibody and recombinant IL-13Ralpha(2). In contrast, the IL-4-induced mucus production, mucus secretion and STAT activation were not inhibited by recombinant IL-13Ralpha(2).

CONCLUSION

The soluble form of IL-13Ralpha(2) may therefore modulate mucus overproduction by IL-13 through the pathway including IL-13Ralpha(1) in NHBECs.

Acoustically detectable cellular-level lung injury induced by fluid mechanical stresses in microfluidic airway systems

We describe a microfabricated airway system integrated with computerized air-liquid two-phase microfluidics that enables on-chip engineering of human airway epithelia and precise reproduction of physiologic or pathologic liquid plug flows found in the respiratory system. Using this device, we demonstrate cellular-level lung injury under flow conditions that cause symptoms characteristic of a wide range of pulmonary diseases. Specifically, propagation and rupture of liquid plugs that simulate surfactant-deficient reopening of closed airways lead to significant injury of small airway epithelial cells by generating deleterious fluid mechanical stresses. We also show that the explosive pressure waves produced by plug rupture enable detection of the mechanical cellular injury as crackling sounds.

Molecular and functional expression of anion exchangers in cultured normal human nasal epithelial cells

Aims

Anions have an important role in the regulation of airway surface liquid (ASL) volume, viscosity and pH. However, functional localization and regulation of anion exchangers (AEs) have not been clearly described. The aim of this study was to investigate the regulation of AE mRNA expression level in accordance with mucociliary differentiation and the functional expression of AEs cultured normal human nasal epithelial (NHNE) cells.

Methods

Nasal mucosal specimens from three patients are obtained and serially cultured cells are subjected to morphological examinations, RT-PCR, Western blot analysis and immunocytochemistry. AE activity is assessed by pHi measurements.

Results

Expression of ciliated cells on the apical membrane and expression of MUC5AC, a marker of mucous differentiation, increased with time. AE2 and SLC26A4 mRNA expression decreased as mucociliary differentiation progressed, and AE4, SLC26A7 and SLC26A8 mRNA expression increased on the 14th and 28th day after confluence. Accordingly, AE4 protein expression also progressively increased. AE activity in 100 mm K⁺ buffer solutions was nearly twofold higher than that in 5 mm K⁺ buffer solutions. Moreover, only luminal AE activity increased about fourfold over the control in the presence of 5 μm forskolin. In the presence of 100 μm adenosine-5′-triphosphate (ATP) which evokes intracellular calcium signalling through activation of purinergic receptors, only luminal AE activity was again significantly increased. On the other hand, 500 μm 4,4′-diisothiocyanostilbene-2,2′-disulfonic acid (DIDS), an inhibitor of most SLC4 and SLC26AE isoforms, nearly abolished AE activity in both luminal and basolateral membranes. We found that AE activity was affected by intracellular cAMP and calcium signalling in the luminal membrane and was DIDS-sensitive in both membranes of cultured NHNE cells.

Conclusion

Our findings through molecular and functional studies using cultured NHNE cells suggest that AEs may have an important role in the regulation of ASL.

Hepatocyte growth factor and other fibroblast secretions modulate the phenotype of human bronchial epithelial cells

The luminal airway surface is lined with epithelial cells that provide a protective barrier from the external environment and clear inhaled pathogens from the lung. To accomplish this important function, human bronchial epithelial (HBE) cells must be able to rapidly regenerate a mucociliary layer of cells following epithelial injury. Whereas epithelial-fibroblast interactions are known to modulate the airway architecture during lung development and repair, little is known about how these two cells interact. Using a primary HBE and lung fibroblast coculture system, we demonstrate that 1) subepithelial fibroblasts provide a suitable environment for differentiation of HBE cells into a polarized ciliated phenotype despite being cultured in media that induces terminal squamous differentiation and growth arrest in the absence of fibroblasts, 2) HBE cells cocultured with subepithelial fibroblasts exhibit augmented ciliogenesis, accelerated wound repair, and diminished polarized ion transport compared with cells grown in control conditions, and 3) hepatocyte growth factor (HGF) is important for subepithelial fibroblast modulation of HBE cell differentiation. These results provide a model to study fibroblast modulation of epithelial phenotype and indicate that HGF secreted by subepithelial fibroblasts contributes to HBE cell differentiation.

The role of airway secretions in COPD: pathophysiology, epidemiology and pharmacotherapeutic options

Often considered an aggravating but otherwise benign component of chronic obstructive pulmonary disease (COPD), airway mucus hypersecretion is now recognised as a potential risk factor for an accelerated loss of lung function in COPD and is a key pathophysiological feature in many patients, particularly those prone to respiratory tract infection. Consequently, it is important to develop drugs that inhibit mucus hypersecretion in these susceptible patients. Conventional therapy including anticholinergics, beta2-adrenoceoptor agonists, alone or in combination with corticosteroids, mucolytics and macrolide antibiotics are not entirely or consistently effective in inhibiting airway mucus hypersecretion in COPD. Novel pharmacotherapeutic targets are being investigated, including inhibitors of nerve activity (e.g., BK(Ca) channel activators), tachykinin receptor antagonists, epoxygenase inducers (e.g., benzafibrate), inhibitors of mucin exocytosis (e.g., anti-MARCKS peptide and Munc-18B blockers), inhibitors of mucin synthesis and goblet cell hyperplasia (e.g., EGF receptor tyrosine kinase inhibitors, p38 MAP kinase inhibitors, MEK/ERK inhibitors, hCACL2 blockers and retinoic acid receptor-alpha antagonists), inducers of goblet cell apoptosis (e.g., Bax inducers or Bcl-2 inhibitors), and purinoceptor P(2Y2) antagonists to inhibit mucin secretion or P(2Y2) agonists to hydrate secretions. However, real and theoretical differences delineate the mucus hypersecretory phenotype in COPD from that in other hypersecretory diseases of the airways. More information is required on these differences to identify therapeutic targets pertinent to COPD which, in turn, should lead to rational design of anti-hypersecretory drugs for specific treatment of airway mucus hypersecretion in COPD.

Induction of the plasminogen activator system by mechanical stimulation of human bronchial epithelial cells

Mechanical stimulation of the airway epithelium, as would occur during bronchoconstriction, is a potent stimulus and can activate profibrotic pathways. We used DNA microarray technology to examine gene expression in compressed normal human bronchial epithelial cells (NHBE). Compressive stress applied continuously over an 8-h period to NHBE cells led to the upregulation of several families of genes, including a family of plasminogen-related genes that were previously not known to be regulated in this system. Real-time PCR demonstrated a peak increase in gene expression of 8.0-fold for urokinase plasminogen activator (uPA), 16.2-fold for urokinase plasminogen activator receptor (uPAR), 4.2-fold for plasminogen activator inhibitor-1 (PAI-1), and 3.9-fold for tissue plasminogen activator (tPA). Compressive stress also increased uPA protein levels in the cell lysates (112.0 versus 82.0 ng/ml, P = 0.0004), and increased uPA (4.7 versus 3.3 ng/ml, P = 0.02), uPAR (1.3 versus 0.86 ng/ml, P = 0.007), and PAI-1 (50 versus 36 ng/ml, P = 0.006) protein levels in cell culture media. Functional studies demonstrated increased urokinase-dependent plasmin generation in compression-stimulated cells (0.0090 versus 0.0033 OD/min, P = 0.03). In addition, compression led to increased activation of matrix metalloproteinase (MMP)-9 and MMP-2 in a urokinase-dependent manner. In postmortem human lung tissue, we observed an increase in epithelial uPA and uPAR immunostaining in the airways of two patients who died in status asthmaticus compared with minimal immunoreactivity noted in airways from seven lung donors without asthma. Together these observations suggest an integrated response of airway epithelial cells to mechanical stimulation, acting through the plasminogen-activating system to modify the airway microenvironment.

Relationship between calcium-activated chloride channel 1 and MUC5AC in goblet cell hyperplasia induced by interleukin-13 in human bronchial epithelial cells

BACKGROUND

Interleukin (IL)-13 has recently been reported as the major T-helper 2 cytokine involved in mucus overproduction and oversecretion in allergic airways. However, the relationship between human calcium-activated chloride channel-1 (hCLCA1) and MUC5AC induced by IL-13 in vitro has not been fully investigated.

OBJECTIVES

The present study examines whether IL-13 induces the expression of hCLCA1 in normal human bronchial epithelial (NHBE) cells. We also investigated the relationship between hCLCA1 and MUC5AC expression and the development of goblet cell hyperplasia (GCH).

METHODS

NHBE cells were isolated from human bronchi, and cultured with an air-liquid interface. hCLCA1 and MUC5AC gene and protein expression, as well as GCH were examined in the cells after exposure to IL-13.

RESULTS

Incubation with IL-13 for 14 and 21 days increased the total number of epithelial cells, the number of periodic acid-Schiff (PAS)-stained epithelial cells, the number of goblet cells, as well as expression of mRNA and protein of hCLCA1 and MUC5AC. The number of goblet cells with secretory granules also increased after 21 days of incubation with IL-13. Niflumic acid, a chloride channel inhibitor, reduced mRNA expression of hCLCA1 and MUC5AC, and reduced the number of PAS-positive cells after incubation with IL-13. NHBE cells exposed or not to IL-13 expressed IL-13 receptor alpha(1) (IL-13Ralpha(1)), and an antibody to IL-13 Ralpha(1) also reduced the number of PAS-positive cells after exposure to IL-13.

CONCLUSIONS

IL-13 might induce the expression of MUC5AC and hCLCA1 gene and protein in well-differentiated NHBE cells. These cells might also differentiate into goblet cells and become hyperplastic.

Effects of prostagladin E(2) on gel-forming mucin secretion in normal human nasal epithelial cells

CONCLUSION

The findings of this study indicate that prostaglandin E(2) (PGE(2)) induces MUC5AC gene expression and mucin secretion via the EP4 receptor in cultured normal human nasal epithelial cells.

OBJECTIVES

Recently, PGE(2) was found to induce MUC5AC production via an agonist of EP2/EP4, but not EP1/EP3, in normal human airway epithelium. However, the receptor that mediates MUC5AC has not been determined. This study aimed to investigate the MUC5AC mucin gene and mucin secretion by PGE(2) and its receptors in cultured normal human nasal epithelial cells.

METHODS

After treatment with PGE(2) and/or PGE(2) antagonist, gel-forming mucin mRNA expression was determined by reverse transcription-polymerase chain reaction. Total mucin and MUC5AC mucin levels were measured using an immuno-dot blotting assay.

RESULTS

PGE(2) increased only MUC5AC gene expression and MUC5AC mucin, but not expression of other gel-forming mucin genes. An EP2 receptor antagonist (AH 6809) did not suppress the PGE(2)-induced MUC5AC gene expression or MUC5AC mucin. However, an EP4 receptor antagonist (AH23848) significantly suppressed the level of PGE(2)-induced MUC5AC gene expression and MUC5AC mucin.

Treatment of airway mucus hypersecretion

Airway mucus hypersecretion is now recognized as a key pathophysiological feature in many patients with asthma, chronic obstructive pulmonary disease (COPD) and cystic fibrosis. Consequently, it is important to develop drugs that inhibit mucus hypersecretion in these susceptible patients. Conventional therapies, including anticholinergics, ss2-adrenoceptor agonists, corticosteroids, mucolytics and macrolide antibiotics, have variable efficacy in inhibiting airway mucus hypersecretion, and are less effective in COPD than in asthma. Novel pharmacotherapeutic targets are being investigated, including inhibitors of nerve activity (e.g. large conductance calcium-activated potassium, BKCa, channel activators), tachykinin receptor antagonists, epoxygenase inducers (e.g. benzafibrate), inhibitors of mucin exocytosis (e.g. anti-myristoylated alanine-rich C kinase substrate (MARCKS), peptide and Munc-18B blockers), inhibitors of mucin synthesis and goblet cell hyperplasia (e.g. epidermal growth factor (EGF), receptor tyrosine kinase inhibitors, p38 mitogen-activated protein (MAP), kinase inhibitors, MAP kinase kinase/extracellular signal-regulated kinase (MEK/ERK), inhibitors, human calcium-activated chloride (hCACL2), channel blockers and retinoic acid receptor-a antagonists), inducers of goblet cell apoptosis (e.g. Bax inducers or Bcl-2 inhibitors), and purinoceptor P(2Y2) antagonists to inhibit mucin secretion or P(2Y2) agonists to hydrate secretions. However, real and theoretical differences delineate the mucus hypersecretory phenotype in asthma from that in COPD. More information is required on these differences to identify specific therapeutic targets which, in turn, should lead to rational design of anti-hypersecretory drugs for treatment of airway mucus hypersecretion in asthma and COPD.

Effect of hypo-, iso- and hypertonic saline irrigation on secretory mucins and morphology of cultured human nasal epithelial cells

CONCLUSION

We speculate that isotonic saline is the most physiological irrigation solution in terms of mucus secretion and the cellular morphology of nasal epithelial cells.

OBJECTIVE

To determine the most physiologic and effective saline concentration for nasal irrigation in terms of mucus secretion and cellular morphology by using normal human nasal epithelial cells treated with hypo-, iso- and hypertonic saline.

MATERIAL AND METHODS

Fully differentiated passage-2 normal human nasal epithelial cells were treated with pure water and with 0.3% (hypotonic), 0.9% (isotonic) and 3% (hypertonic) saline solutions. mRNA expression levels of MUC5AC and MUC5B, which are known to be major airway mucins, were analyzed after 30 min using reverse transcriptase polymerase chain reaction. Total mucin and MUC5AC and MUC5B mucin secretions were analyzed using dot-blotting. Cellular morphology was observed with light microscopy after hematoxylin-eosin staining and with scanning electron microscopy.

RESULTS

MUC5AC and MUC5B mRNA levels did not change after treatment with pure water and various concentrations of saline. Total mucin and MUC5AC mucin secretions only increased following pure water treatment, while MUC5B mucin secretion increased with pure water, hypo- and hypertonic saline treatment. Morphologic analysis revealed that pure water severely damaged normal human nasal epithelial cells and that only isotonic saline did not affect their morphology.

Mucin biosynthesis: upregulation of core 2 beta 1,6 N-acetylglucosaminyltransferase by retinoic acid and Th2 cytokines in a human airway epithelial cell line

Vitamin A and the T helper 2 cytokines IL-4 and IL-13 play important roles in the induction of mucin gene expression and mucus hypersecretion. However, the effects of these agents on enzymes responsible for mucin glycosylation have received little attention. Here, we report the upregulation of core 2 beta1,6 N-acetylglucosaminyltransferase (C2GnT) activity both by all-trans retinoic acid (RA) and by IL-4 and IL-13 in the H292 airway epithelial cell line. Northern blotting analysis showed that the M isoform of C2GnT, which is expressed in mucus-secreting tissues and can form all mucin glycan beta1,6-branched structures, including core 2, core 4, and blood group I antigen, was upregulated by both RA and IL-4/13. The L isoform, which forms only the core 2 structure, was moderately upregulated by IL-4/13 but not by RA. Enhancement of the M isoform of C2GnT by RA was abolished by an inhibitor of RA receptor alpha, implicating RA receptor alpha in the effect of RA. Likewise, an inhibitor of the Janus kinase 3 pathway blocked the enhancing effects of IL-4/13 on the L and M isoforms of C2GnT, suggesting a role of this pathway in the upregulation of these two C2GnTs by these cytokines. Taken together, the results suggest that IL-4/13 T helper 2 cytokines and RA can alter the activity of enzymes that synthesize branching mucin carbohydrate structure in airway epithelial cells, potentially leading to altered mucin carbohydrate structure and properties.