Model systems for investigating mucin gene expression in airway diseases

The effects of metals and mixture exposure on lung function and the potential mediating effects of oxidative stress

Exposure to metals is associated with lung function decline. However, limited data are available about effects of co-exposure of metals on lung function. Additionally, the mechanism of the association between metals and lung function remains unclear. We conducted a longitudinal panel study in 2017-2018 among 45 healthy college students. Urinary 15 metals, lung function, biomarkers of oxidative stress and inflammation of participants were measured. Linear mixed effect (LME) and Bayesian kernel machine regression (BKMR) models were applied to explore the associations of urinary metals and mixture with lung function. Furthermore, we analyzed the mediating effect of biomarkers in the association between urinary metals and lung function. LME models showed the negative associations of aluminum (Al), vanadium (V), manganese (Mn), cobalt (Co), nickel (Ni), cadmium (Cd) or antimony (Sb) with Forced vital capacity (FVC), and V, Co, Ni, and Sb with Forced expiratory volume in one second (FEV1). BKMR models indicated the overall effect of metals mixture was negatively associated with FEV1 and FVC; urinary Sb was identified as the major contributor to decreased FVC and FEV1. Urinary 8-hydroxydeoxyguanosine mediated the association of Al, Mn, or Sb with FVC and the relationship of V with FEV1. The results revealed the longitudinal dose-response relationships of urinary metals with pulmonary function among healthy adults. Oxidative stress may be the underlying mechanisms of metals exposure associated with decreased lung function. Due to the small sample size, the interpretation of the results of this study should be cautious, and more studies are needed to verify the findings of this study.

Optimizations of In Vitro Mucus and Cell Culture Models to Better Predict In Vivo Gene Transfer in Pathological Lung Respiratory Airways: Cystic Fibrosis as an Example

The respiratory epithelium can be affected by many diseases that could be treated using aerosol gene therapy. Among these, cystic fibrosis (CF) is a lethal inherited disease characterized by airways complications, which determine the life expectancy and the effectiveness of aerosolized treatments. Beside evaluations performed under in vivo settings, cell culture models mimicking in vivo pathophysiological conditions can provide complementary insights into the potential of gene transfer strategies. Such models must consider multiple parameters, following the rationale that proper gene transfer evaluations depend on whether they are performed under experimental conditions close to pathophysiological settings. In addition, the mucus layer, which covers the epithelial cells, constitutes a physical barrier for gene delivery, especially in diseases such as CF. Artificial mucus models featuring physical and biological properties similar to CF mucus allow determining the ability of gene transfer systems to effectively reach the underlying epithelium. In this review, we describe mucus and cellular models relevant for CF aerosol gene therapy, with a particular emphasis on mucus rheology. We strongly believe that combining multiple pathophysiological features in single complex cell culture models could help bridge the gaps between in vitro and in vivo settings, as well as viral and non-viral gene delivery strategies.

Cross-sectional and longitudinal associations between urinary zinc and lung function among urban adults in China

Background

Exposure to zinc was suggested to be associated with pulmonary damage, but whether zinc exposure affects lung function remains unclear.

Objectives

To quantify the association between urinary zinc and lung function and explore the potential mechanisms.

Methods

Urinary zinc and lung function were measured in 3917 adults from the Wuhan-Zhuhai cohort and were repeated after 3 years of follow-up. Indicators of systemic inflammation (C reactive protein), lung epithelium integrity (club cell secretory protein-16) and oxidative damage (8-hydroxy-2′-deoxyguanosine and 8-isoprostane) were measured at baseline. Linear mixed models were used to estimate the exposure–response relationship between urinary zinc and lung function. Mediation analyses were conducted to assess mediating roles of inflammation and oxidative damage in above relationships.

Results

Each 1-unit increase in log-transformed urinary zinc values was associated with a 35.72 mL decrease in forced vital capacity (FVC) and a 24.89 mL decrease in forced expiratory volume in 1 s (FEV1) in the baseline analyses. In the follow-up analyses, there was a negative association between urinary zinc and FVC among participants with persistent high urinary zinc levels, with an estimated change of −93.31 mL (95% CI −178.47 to −8.14). Furthermore, urinary zinc was positively associated with restrictive ventilatory impairment. The mediation analyses suggested that C reactive protein mediated 8.62% and 8.71% of the associations of urinary zinc with FVC and FEV1, respectively.

Conclusion

Urinary zinc was negatively associated with lung function, and the systemic inflammation may be one of the underlying mechanisms.

Strategies for measuring airway mucus and mucins

Mucus secretion and mucociliary transport are essential defense mechanisms of the airways. Deviations in mucus composition and secretion can impede mucociliary transport and elicit airway obstruction. As such, mucus abnormalities are hallmark features of many respiratory diseases, including asthma, cystic fibrosis and chronic obstructive pulmonary disease (COPD). Studying mucus composition and its physical properties has therefore been of significant interest both clinically and scientifically. Yet, measuring mucus production, output, composition and transport presents several challenges. Here we summarize and discuss the advantages and limitations of several techniques from five broadly characterized strategies used to measure mucus secretion, composition and mucociliary transport, with an emphasis on the gel-forming mucins. Further, we summarize advances in the field, as well as suggest potential areas of improvement moving forward.

Whole Exome Sequencing Identifies New Host Genomic Susceptibility Factors in Empyema Caused by Streptococcus pneumoniae in Children: A Pilot Study

Pneumonia is the leading cause of death amongst infectious diseases. Streptococcus pneumoniae is responsible for about 25% of pneumonia cases worldwide, and it is a major cause of childhood mortality. We carried out a whole exome sequencing (WES) study in eight patients with complicated cases of pneumococcal pneumonia (empyema). An initial assessment of statistical association of WES variation with pneumonia was carried out using data from the 1000 Genomes Project (1000G) for the Iberian Peninsula (IBS) as reference controls. Pseudo-replication statistical analyses were carried out using different European control groups. Association tests pointed to single nucleotide polymorphism (SNP) rs201967957 (gene MEIS1; chromosome 2; p-value_IBS = 3.71 × 10^-13) and rs576099063 (gene TSPAN15; chromosome 10; p-value_IBS = 2.36 × 10^-8) as the best candidate variants associated to pneumococcal pneumonia. A burden gene test of pathogenicity signaled four genes, namely, OR9G9, MUC6, MUC3A and APOB, which carry significantly increased pathogenic variation when compared to controls. By analyzing various transcriptomic data repositories, we found strong supportive evidence for the role of MEIS1, TSPAN15 and APOBR (encoding the receptor of the APOB protein) in pneumonia in mouse and human models. Furthermore, the association of the olfactory receptor gene OR9G9 has recently been related to some viral infectious diseases, while the role of mucin genes (MUC6 and MUC3A), encoding mucin glycoproteins, are well-known factors related to chronic obstructive airway disease. WES emerges as a promising technique to disentangle the genetic basis of host genome susceptibility to infectious respiratory diseases.

Runx2, a novel regulator for goblet cell differentiation and asthma development

Airway goblet cell differentiation and related mucus overproduction are critical processes in the development of respiratory diseases, including asthma. The underlying mechanisms, however, are not fully understood. We identified Runt-related transcription factor 2 (Runx2) as a novel regulator for goblet cell differentiation. Runx2 was up-regulated by 6.4-fold during IL-13-induced goblet cell differentiation of human bronchial epithelial cells. Knockdown of Runx2 attenuated the IL-13-induced differentiation/mucus production by 67%. Mechanistically, Runx2 bound to the promoter of SAM-pointed domain-containing Ets-like factor (SPDEF), a known factor for goblet cell differentiation, resulting in an activation of SPDEF transcription. In vivo, Runx2 was induced by 6.2-fold in pulmonary epithelium of house dust mite-challenged mice. Blockade of Runx2 inhibited the house dust mite-induced goblet cell differentiation with a 75% reduction in mucus overproduction while improving airway responsiveness to methacholine by 41%. More importantly, a 12.3-fold increase in Runx2 expression was observed in human asthma lung epithelium, underlying the potential clinical importance of these findings.-Shi, N., Zhang, J., Chen, S.-Y. Runx2, a novel regulator for goblet cell differentiation and asthma development.

Dietary Enrichment with 20% Fish Oil Decreases Mucus Production and the Inflammatory Response in Mice with Ovalbumin-Induced Allergic Lung Inflammation

The prevalence of asthma has increased in recent decades, which may be related to higher dietary intake of (n-6) polyunsaturated fatty acids (PUFA) and lower intake of (n-3) PUFA, e.g., those contained in fish oil. The objective of this study was to determine if dietary PUFA enrichment decreases mucus production or the inflammatory response associated with ovalbumin (OVA)-induced allergic lung inflammation. Mice (n = 10/group) were fed control, 20% fish oil, or 20% corn oil enriched diets for a total of 12 weeks. At 8 and 10 weeks, mice were given an intraperitoneal injection of saline (10 control-fed mice) or OVA (30 remaining mice). Once at 10 weeks and on 3 consecutive days during week 12, mice were challenged by nebulizing with saline or OVA. Mice were euthanized 24 hours after the last challenge and blood was collected for plasma FA analysis. Bronchoalveolar lavage (BAL) fluid was collected to determine cell composition and Th2-type cytokine (IL-4, IL-13) concentrations. Periodic acid-Schiff (PAS) + mucus-producing cells and CD45+ inflammatory cell infiltrates in lung tissue were quantified using morphometric analysis. Relative abundance of mRNA for mucin (Muc4, Muc5ac, and Muc5b) and Th2-type cytokine (IL-4, IL-5, and IL-13) genes were compared with ß-actin by qPCR. Supplementation with either corn oil or fish oil effectively altered plasma FA profiles towards more (n-6) FA or (n-3) FA, respectively (P < 0.0001). Sensitization and challenge with OVA increased the proportion of neutrophils, lymphocytes, and eosinophils, and decreased the proportion of macrophages and concentrations of IL-13 in BAL fluid; increased the percentage of PAS+ mucus-producing cells and CD45+ inflammatory cell infiltrates in lung tissue; and increased gene expression of mucins (Muc4, Muc5ac, and Muc5b) and Th2-type cytokines (IL-5 and IL-13) in lung tissue of control-fed mice. Dietary PUFA reversed the increase in PAS+ mucus-producing cells (P = 0.003). In addition, dietary enrichment with fish oil attenuated the percentage of CD45+ inflammatory cell infiltrates in lung tissue, and increased Muc4 and Muc 5b gene expression compared with OVA-sensitized and challenged control mice. In conclusion, dietary enrichment with either (n-3) or (n-6) PUFA decreased mucus production in lung tissues of OVA-sensitized and challenged mice. More specifically, enrichment with dietary (n-3) PUFA decreased CD45+ inflammatory cell infiltrates, thus inducing potentially beneficial changes in lung tissue of OVA-sensitized and challenged mice.

Identification of PAM4 (clivatuzumab)-reactive epitope on MUC5AC: a promising biomarker and therapeutic target for pancreatic cancer

PAM4 is a monoclonal antibody showing high specificity for pancreatic ductal adenocarcinoma (PDAC). Humanized PAM4 labeled with ⁹⁰Y in combination with low-dose gemcitabine has shown promising therapeutic activity, and is being evaluated in a phase III clinical trial. Prior efforts have suggested that PAM4 potentially reacts with MUC5AC, a secretory mucin expressed de novo in early pancreatic neoplasia and retained throughout disease progression. In present study, we provide further evidence validating MUC5AC as the PAM4 antigen, and locate PAM4-reactive epitope within the N-terminal cysteine-rich subdomain 2 (Cys2), thus differentiating PAM4 from most anti-MUC5AC antibodies known to-date. Specifically, we show (i) PAM4-antigen and MUC5AC were co-localized in multiple human cancer cell lines, including Capan-1, BxPC-3, and CFPAC-1; (ii) MUC5AC-specific siRNA prominently reduced the expression of both MUC5AC and PAM4-antigen in CFPAC-1 cells; (iii) PAM4 preferentially binds to the void-volume fractions from Sepharose-CL2B chromatography of Capan-1 culture supernatants, which were revealed by Western blot to display the ladder pattern characteristic of oligomeric MUC5AC; and (iv) the N-terminal Cys2 within several recombinant MUC5AC fragments is essential for binding to PAM4. These findings shed light on the mechanism of PAM4-based diagnosis and treatment for pancreatic cancer, and guide further exploration of its clinical utility.

Lung adenocarcinomas: comparison between mice and men

A few human tumor types have been modeled in mice using genetic or chemical tools. The final goal of these efforts is to establish models that mimic not only the location and cellular origin of human cancers but also their genetic aberrations and morphologic appearances. The latter has been neglected by most investigators, and comparative histopathology of human versus mouse cancers is not readily available. This issue is exacerbated by the fact that some human malignancies comprise a whole spectrum of cancer subtypes that differ molecularly and morphologically. Lung cancer is a paradigm that appears not only as non-small cell and small-cell lung cancer but comprises a plethora of subtypes with distinct morphologic features. This review discusses species-specific and common morphological features of non-small cell lung cancer in mice and humans. Potential inconsistencies and the need for refined genetic tools are discussed in the context of a comparative analysis between commonly employed RAS-induced mouse tumors and human lung cancers.

β-Casein(94-123)-derived peptides differently modulate production of mucins in intestinal goblet cells

We recently reported the identification of a peptide from yoghurts with promising potential for intestinal health: the sequence (94-123) of bovine β-casein. This peptide, composed of 30 amino acid residues, maintains intestinal homoeostasis through production of the secreted mucin MUC2 and of the transmembrane-associated mucin MUC4. Our study aimed to search for the minimal sequence responsible for the biological activity of β-CN(94-123) by using several strategies based on (i) known bioactive peptides encrypted in β-CN(94-123), (ii) in silico prediction of peptides reactivity and (iii) digestion of β-CN(94-123) by enzymes of intestinal brush border membranes. The revealed sequences were tested in vitro on human intestinal mucus-producing HT29-MTX cells. We demonstrated that β-CN(108-113) (an ACE-inhibitory peptide) and β-CN(114-119) (an opioid peptide named neocasomorphin-6) up-regulated MUC4 expression whereas levels of the secreted mucins MUC2 and MUC5AC remained unchanged. The digestion of β-CN(94-123) by intestinal enzymes showed that the peptides β-CN(94-108) and β-CN(117-123) were present throughout 1·5 to 3 h of digestion, respectively. These two peptides raised MUC5AC expression while β-CN(117-123) also induced a decrease in the level of MUC2 mRNA and protein. In addition, this inhibitory effect was reproduced in airway epithelial cells. In conclusion, β-CN(94-123) is a multifunctional molecule but only the sequence of 30 amino acids has a stimulating effect on the production of MUC2, a crucial factor of intestinal protection.

Nicotine alters mucin rheological properties

Tobacco smoke exposure, the major cause of chronic obstructive pulmonary disease (COPD), instigates a dysfunctional clearance of thick obstructive mucus. However, the mechanism underlying the formation of abnormally viscous mucus remains elusive. We investigated whether nicotine can directly alter the rheological properties of mucin by examining its physicochemical interactions with human airway mucin gels secreted from A549 lung epithelial cells. Swelling kinetics and multiple particle tracking were utilized to assess mucin gel viscosity change when exposed to nicotine. Herein we show that nicotine (≤50 nM) significantly hindered postexocytotic swelling and hydration of released mucins, leading to higher viscosity, possibly by electrostatic and hydrophobic interactions. Moreover, the close association of nicotine and mucins allows airway mucus to function as a reservoir for prolonged nicotine release, leading to correlated pathogenic effects. Our results provide a novel explanation for the maltransport of poorly hydrated mucus in smokers. More importantly, this study further indicates that even low-concentration nicotine can profoundly increase mucus viscosity and thus highlights the health risks of secondhand smoke exposure.

Targeting EGFR signalling in chronic lung disease: therapeutic challenges and opportunities

Chronic respiratory diseases, including pulmonary fibrosis, chronic obstructive pulmonary disease (COPD) and lung cancer, are the second leading cause of death among Europeans. Despite this, there have been only a few therapeutic advances in these conditions over the past 20 years. In this review we provide evidence that targeting the epidermal growth factor receptor (EGFR) signalling pathway may represent a novel therapeutic panacea for treating chronic lung disease. Using evidence from human patient samples, transgenic animal models, and cell and molecular biology studies we highlight the roles of this signalling pathway in lung development, homeostasis, repair, and disease ontogeny. We identify mechanisms underlying lung EGFR pathway regulation and suggest how targeting these mechanisms using new and existing therapies has the potential to improve future lung cancer, COPD and pulmonary fibrosis patient outcomes.

An IL-4/IL-13 dual antagonist reduces lung inflammation, airway hyperresponsiveness, and IgE production in mice

IL-4 and IL-13 comprise promising targets for therapeutic interventions in asthma and other Th2-associated diseases, but agents targeting either IL-4 or IL-13 alone have shown limited efficacy in human clinical studies. Because these cytokines may involve redundant function, dual targeting holds promise for achieving greater efficacy. We describe a bifunctional therapeutic targeting IL-4 and IL-13, developed by a combination of specific binding domains. IL-4-targeted and IL-13-targeted single chain variable fragments were joined in an optimal configuration, using appropriate linker regions on a novel protein scaffold. The bifunctional IL-4/IL-13 antagonist displayed high affinity for both cytokines. It was a potent and efficient neutralizer of both murine IL-4 and murine IL-13 bioactivity in cytokine-responsive Ba/F3 cells, and exhibited a half-life of approximately 4.7 days in mice. In a murine model of ovalbumin-induced ear swelling, the bifunctional molecule blocked both the IL-4/IL-13-dependent early-phase response and the IL-4-dependent late-phase response. In the ovalbumin-induced lung inflammation model, the bifunctional IL-4/IL-13 antagonist reduced the IL-4-dependent rise in serum IgE titers, and reduced IL-13-dependent airway hyperresponsiveness, lung inflammation, mucin gene expression, and serum chitinase responses. Taken together, these findings demonstrate the effective dual blockade of IL-4 and IL-13 with a single agent, which resulted in the modulation of a more extensive range of endpoints than could be achieved by targeting either cytokine alone.

CD4(+) T-cell subsets and host defense in the lung

CD4(+) T-helper subsets are lineages of T cells that have effector function in the lung and control critical aspects of lung immunity. Depletion of these cells experimentally or by drugs or human immunodeficiency virus (HIV) infection in humans leads to the development of opportunistic infections as well as increased rates of bacteremia with certain bacterial pneumonias. Recently, it has been proposed that CD4(+) T-cell subsets may also be excellent targets for mucosal vaccination to prevent pulmonary infections in susceptible hosts. Here, we review recent findings that increase our understanding of T-cell subsets and their effector cytokines in the context of pulmonary infection.

Effects of normal saline and selenium-enriched hot spring water on experimentally induced rhinosinusitis in rats

OBJECTIVE

This prospective, randomized, and controlled study examined the effects of normal saline and selenium-enriched hot spring water on experimentally induced rhinosinusitis in rats.

METHODS

The study comprised two control groups (untreated and saline-treated) and three experimental groups of Sprague Dawley rats. The experimental groups received an instillation of lipopolysaccharide (LPS) only, LPS+normal saline (LPS/saline), or LPS+selenium-enriched hot spring water (LPS/selenium). Histopathological changes were identified using hematoxylin-eosin staining. Leakage of exudate was identified using fluorescence microscopy. Microvascular permeability was measured using the Evans blue dye technique. Expression of the Muc5ac gene was measured using reverse transcription-polymerase chain reaction.

RESULTS

Mucosal edema and expression of the Muc5ac gene were significantly lower in the LPS/saline group than in the LPS group. Microvascular permeability, mucosal edema, and expression of the Muc5ac gene were significantly lower in the LPS/selenium group than in the LPS group. Mucosal edema was similar in the LPS/selenium group and LPS/saline group, but capillary permeability and Muc5ac expression were lower in the LPS/selenium group.

CONCLUSIONS

This study shows that normal saline and selenium-enriched hot spring water reduce inflammatory activity and mucus hypersecretion in LPS-induced rhinosinusitis in rats.

Glucocorticoids inhibit MUC5AC production induced by transforming growth factor-α in human respiratory cells

BACKGROUND

Mucus hypersecretion from airway epithelium is a characteristic feature of severe asthma. Glucocorticoids (GCs) may suppress mucus production and diminish the harmful airway obstruction. We investigated the ability of GCs to suppress mRNA expression and protein synthesis of a gene encoding mucin, MUC5AC, induced by transforming growth factor (TGF)-α in human mucoepidermoid carcinoma (NCI-H292) cells and the molecular mechanisms underlying the suppression.

METHODS

We determined if GCs such as dexamethasone (DEX), budesonide (BUD), and fluticasone (FP) could suppress MUC5AC production induced by a combination of TGF-α and double-strand RNA, polyinosinic-polycytidylic acid (polyI:C). MUC5AC mRNA expression and MUC5AC protein production were evaluated. The signaling pathways activated by TGF-α and their inhibition by GCs were tested using a phosphoprotein assay and MUC5AC promoter assay.

RESULTS

DEX significantly suppressed the expression of MUC5AC mRNA and MUC5AC protein induced by TGF-α. The activation of the MUC5AC promoter by TGF-α was significantly inhibited by DEX. DEX did not affect activation of downstream pathways of the EGF receptor or mRNA stability of MUC5AC transcripts. DEX, BUD, and FP suppressed MUC5AC protein expression induced by a combination of TGF-α and polyI:C in a dose-dependent manner.

CONCLUSIONS

GCs inhibited MUC5AC production induced by TGF-α alone or a combination of TGF-α and polyI:C; the repression may be mediated at the transcriptional but not post-transcriptional level.

Acute inflammation induces insulin-like growth factor-1 to mediate Bcl-2 and Muc5ac expression in airway epithelial cells

Generally, exposure to LPS in human airways occurs in the form of aerosols and causes an acute inflammatory response or exacerbates existing chronic inflammatory conditions by enhancing airway remodeling and associated pathologies. The present study evaluated which inflammatory mediators may be responsible for the expression of Bcl-2 and mucus cell metaplasia when mice are exposed to aerosolized LPS. At 3 days after exposure, aerosolized LPS (for 20-40 min) with the estimated lung deposited dosage of 0, 0.02, 0.2, 1.4, and 20.2 μg showed a characteristic dose-dependent increase in polymorphonuclear neutrophils. Significant increases of proinflammatory mediators, including IL-1β, TNF-α, IL-6, growth-related oncogene or keratinocyte-derived cytokine, IFN-γ-induced protein-10, monocyte chemotactic protein-1, and macrophage inflammatory protein-1α, were detected at the highest doses. In addition to increased numbers of airway epithelial cells, mucus cell numbers and mucus production were increased in a dose-dependent manner. Hyperplastic epithelial cells expressed insulin-like growth factor (IGF)-1 and, similar to previous studies, increased expression of the prosurvival protein Bcl-2 and induced expression of Muc5ac. Suppression of IGF-1 expression using retroviral shRNA blocked Bcl-2 expression in human and murine airway epithelial cells and Muc5ac in primary murine airway epithelial cells. These findings show that acute inflammation induces IGF-1 to mediate Bcl-2 and Muc5ac expression in airway epithelial cells.

Docking protein Gab2 regulates mucin expression and goblet cell hyperplasia through TYK2/STAT6 pathway

Goblet cell hyperplasia (GCH) and mucous hypersecretion are common pathological features of chronic pulmonary diseases, including asthma, chronic obstructive pulmonary disease (COPD), lung cancer, and cystic fibrosis. Despite numerous studies, the molecular basis for this condition remains elusive. Gab2 is a member of the Dos/Gab subfamily scaffolding molecules and plays important roles in regulating growth, differentiation, and inflammation. We found that an elevated level of Gab2 correlates with up-regulated mucus in airway epithelia from patients with lung cancer or COPD, suggesting the potential involvement of Gab2 in pathological lesions in lungs. Knockdown of Gab2 in human airway epithelial cells in vitro decreases IL-13-induced expression of mucin genes. To address the in vivo role of Gab2 in lungs, Gab2-knockout (Gab2(-/-)) mice were sensitized and challenged with ovalbumin (OVA). Further analysis of lungs in an OVA-induced allergy model suggested that GCH and mucus production are remarkably reduced in Gab2(-/-) mice. Mechanistically, Gab2 positively regulates IL-13-induced activation of TYK2/STAT6 by decreasing SOCS3-mediated degradation of TYK2. Together, we define a novel role for Gab2 in mediating mucin gene expression and GCH; these findings have important implications for the pathogenesis and therapy of airway inflammatory diseases.

Chronic Aspergillus fumigatus exposure upregulates the expression of mucin 5AC in the airways of asthmatic rats

BACKGROUND

Airway mucus hypersecretion is associated with increased morbidity and mortality in patients with asthma. Chronic Aspergillus fumigatus (A. fumigatus) exposure leads to aggravation of airway inflammation and remodeling, including goblet cell hyperplasia (GCH) and mucus hypersecretion in a rat model of asthma. The effects of chronic A. fumigatus exposure on the expression of airway mucin 5AC (MUC5AC) are unknown.

METHODS

The rat model of chronic asthma was set up by systemic sensitization and repeated challenge to ovalbumin (OVA). The asthmatic rats were exposed to chronic intranasal inhalation of A. fumigatus spores. The changes of MUC5AC expression, the extent of GCH, and airway hyperreactivity (AHR) were measured after exposure to the fungus.

RESULTS AND CONCLUSIONS

Chronic exposure to A. fumigatus upregulates the expression of MUC5AC, and induces GCH in the airways of asthma rats, and the remodeling changes of the airway epithelium was positively correlated with AHR. Upregulation of MUC5AC and induction of GCH may be mechanisms by which chronic A. fumigatus exposure promotes the progression of asthma.

Immunohistochemical demonstration of airway epithelial cell markers of guinea pig

The guinea pig (Cavea porcellus) is a mammalian non-rodent species in the Caviidae family. The sensitivity of the respiratory system and the susceptibility to infectious diseases allows the guinea pig to be a useful model for both infectious and non-infectious lung diseases such as asthma and tuberculosis. In this report, we demonstrated for the first time, the major cell types and composition in the guinea pig airway epithelium, using cell type-specific markers by immunohistochemical staining using the commercial available immunological reagents that cross-react with guinea pig. Our results revealed the availability of antibodies cross-reacting with airway epithelial cell types of basal, non-ciliated columnar, ciliated, Clara, goblet and alveolar type II cells, as well as those cells expressing Mucin 5AC, Mucin 2, Aquaporin 4 and Calcitonin Gene Related Peptide. The distribution of these various cell types were quantified in the guinea pig airway by immunohistochemical staining and were comparable with morphometric studies using an electron microscopy assay. Moreover, this study also demonstrated that goblet cells are the main secretory cell type in the guinea pig's airway, distinguishing this species from rats and mice. These results provide useful information for the understanding of airway epithelial cell biology and mechanisms of epithelial-immune integration in guinea pig models.

Avian influenza viruses infect primary human bronchial epithelial cells unconstrained by sialic acid α2,3 residues

Avian influenza viruses (AIV) are an important emerging threat to public health. It is thought that sialic acid (sia) receptors are barriers in cross-species transmission where the binding preferences of AIV and human influenza viruses are sias α2,3 versus α2,6, respectively. In this study, we show that a normal fully differentiated, primary human bronchial epithelial cell model is readily infected by low pathogenic H5N1, H5N2 and H5N3 AIV, which primarily bind to sia α2,3 moieties, and replicate in these cells independent of specific sias on the cell surface. NHBE cells treated with neuraminidase prior to infection are infected by AIV despite removal of sia α2,3 moieties. Following AIV infection, higher levels of IP-10 and RANTES are secreted compared to human influenza virus infection, indicating differential chemokine expression patterns, a feature that may contribute to differences in disease pathogenesis between avian and human influenza virus infections in humans.

Effects of a tumor necrosis factor-α antagonist on experimentally induced rhinosinusitis

This prospective, randomized, and controlled study examined the effects of tumor necrosis factor soluble receptor type I (sTNFRI, a TNF-α antagonist) on experimentally induced rhinosinusitis in rats. The experimental groups received an instillation of lipopolysaccharide (LPS) plus an intramuscular injection of amoxicillin/clavulanate (antibiotic group), an instillation of sTNFRI (sTNFRI group), an instillation of sTNFRI and an injection of amoxicillin/clavulanate (sTNFRI/antibiotic group), or no additional treatment (LPS group). Histopathological changes were determined using hematoxylin-eosin and periodic acid-Schiff (PAS) staining. Leakage of exudate was determined using fluorescence microscopy. Vascular permeability was measured using the Evans blue dye technique. Expression of MUC5AC was measured using reverse transcriptase PCR. The sTNFRI, antibiotic, and sTNFRI/antibiotic groups had significantly less capillary permeability, mucosal edema, PAS staining, and expression of MUC5AC than the LPS group. There were no differences in capillary permeability, mucosal edema, PAS staining, and MUC5AC expression between the sTNFRI and sTNFRI/antibiotic groups. The antibiotic group had PAS staining similar to that of the sTNFRI and sTNFRI/antibiotic groups but had a greater increase in capillary permeability, mucosal edema, and MUC5AC expression. This study shows that sTNFRI reduces inflammatory activity and mucus hypersecretion in LPS-induced rhinosinusitis in rats.

Muc5ac: a critical component mediating the rejection of enteric nematodes

The mucin Muc5ac is essential for the expulsion of Trichuris muris and other gut-dwelling nematodes.

De novo expression of Muc5ac, a mucin not normally expressed in the intestinal tract, is induced in the cecum of mice resistant to Trichuris muris infection. In this study, we investigated the role of Muc5ac, which is detected shortly before worm expulsion and is associated with the production of interleukin-13 (IL-13), in resistance to this nematode. Muc5ac-deficient mice were incapable of expelling T. muris from the intestine and harbored long-term chronic infections, despite developing strong T_H2 responses. Muc5ac-deficient mice had elevated levels of IL-13 and, surprisingly, an increase in the T_H1 cytokine IFN-γ. Because T_H1 inflammation is thought to favor chronic nematode infection, IFN-γ was neutralized in vivo, resulting in an even stronger T_H2-type immune response. Nevertheless, despite a more robust T_H2 effector response, the Muc5ac-deficient mice remained highly susceptible to chronic T. muris infection. Importantly, human MUC5AC had a direct detrimental effect on nematode vitality. Moreover, the absence of Muc5ac caused a significant delay in the expulsion of two other gut-dwelling nematodes (Trichinella spiralis and Nippostrongylus brasiliensis). Thus, for the first time, we identify a single mucin, Muc5ac, as a direct and critical mediator of resistance during intestinal nematode infection.

Expression of leptin receptor in nasal polyps: leptin as a mucosecretagogue

OBJECTIVES/HYPOTHESIS

Leptin is a pleiotropic hormone that regulates food intake and metabolic and endocrine functions. Serum leptin levels have been reported to be increased in patients with allergic rhinitis and nasal polyposis; however, the explanation for this is unclear. We aimed to demonstrate the differential expression of leptin receptors in normal human nasal mucosa and nasal polyps, and to elucidate the effects of leptin on mucin gene expression in human nasal polyp epithelial cells.

STUDY DESIGN

Case-control and in vitro study.

METHODS

Normal ethmoid sinus mucosa was obtained from 10 subjects and used as a control; nasal polyps were obtained from 10 patients. Leptin receptor expression was analyzed using reverse transcriptase-polymerase chain reaction (RT-PCR) and Western blot analysis. Leptin-induced expression of major respiratory mucins (MUC5AC and MUC5B) in the human nasal polyp epithelial cells was determined using RT-PCR and enzyme-linked immunosorbent assay.

RESULTS

The leptin receptor expression was stronger in the nasal polyps than in the normal nasal mucosa. In human nasal polyp epithelial cells, leptin increased the expression of MUC5AC and MUC5B, in a dose- and time-dependent manner, at the gene and protein levels. Leptin-induced mucin expression was inhibited by the leptin receptor antagonist.

CONCLUSIONS

The increased expression of leptin receptors in nasal polyps implies leptin has a certain role in nasal polyposis. In addition, leptin appears to induce the expression of MUC5AC and MUC5B through leptin receptors in the human nasal polyp epithelial cells.

Pseudomonas aeruginosa exotoxin pyocyanin causes cystic fibrosis airway pathogenesis

The cystic fibrosis (CF) airway bacterial pathogen Pseudomonas aeruginosa secretes multiple virulence factors. Among these, the redox active exotoxin pyocyanin (PCN) is produced in concentrations up to 100 mumol/L during infection of CF and other bronchiectatic airways. However, the contributions of PCN during infection of bronchiectatic airways are not appreciated. In this study, we demonstrate that PCN is critical for chronic infection in mouse airways and orchestrates adaptive immune responses that mediate lung damage. Wild-type FVBN mice chronically exposed to PCN developed goblet cell hyperplasia and metaplasia, airway fibrosis, and alveolar airspace destruction. Furthermore, after 12 weeks of exposure to PCN, mouse lungs down-regulated the expression of T helper (Th) type 1 cytokines and polarized toward a Th2 response. Cellular analyses indicated that chronic exposure to PCN profoundly increased the lung population of recruited macrophages, CD4(+) T cells, and neutrophils responsible for the secretion of these cytokines. PCN-mediated goblet cell hyperplasia and metaplasia required Th2 cytokine signaling through the Stat6 pathway. In summary, this study establishes that PCN is an important P. aeruginosa virulence factor capable of directly inducing pulmonary pathophysiology in mice, consistent with changes observed in CF and other bronchiectasis lungs.

Regulation of airway mucin gene expression

Mucins are important components that exert a variety of functions in cell-cell interaction, epidermal growth factor receptor signaling, and airways protection. In the conducting airways of the lungs, mucins are the major contributor to the viscoelastic property of mucous secretion, which is the major barrier to trapping inhaled microbial organism, particulates, and oxidative pollutants. The homeostasis of mucin production is an important feature in conducting airways for the maintenance of mucociliary function. Aberrant mucin secretion and accumulation in airway lumen are clinical hallmarks associated with various lung diseases, such as asthma, chronic obstructive pulmonary disease, cystic fibrosis, emphysema, and lung cancer. Among 20 known mucin genes identified, 11 of them have been verified at either the mRNA and/or protein level in airways. The regulation of mucin genes is complicated, as are the mediators and signaling pathways. This review summarizes the current view on the mediators, the signaling pathways, and the transcriptional units that are involved in the regulation of airway mucin gene expression. In addition, we also point out essential features of epigenetic mechanisms for the regulation of these genes.

Effect of Dexamethasone and ACC on Bacteria-Induced Mucin Expression in Human Airway Mucosa

Gram-negative bacteria can stimulate mucin production, but excessive mucus supports bacterial infection and consequently leads to airway obstruction. Therefore, the effect of dexamethasone (DEX) and the antioxidant acetyl-cysteine (ACC) on bacteria-induced mucus expression was investigated. Explanted human airway mucosa and mucoepidermoid cells (Calu-3) were stimulated with lipopolysaccharide (LPS) or PAM3 (a synthetic lipoprotein). DEX or ACC were added to either LPS- or PAM3-stimulated airway mucosa or Calu-3 cells. Mucin mRNA expression (MUC5AC) and total mucus glycoconjugates (mucin protein) were quantified using real-time PCR and periodic acid Schiff staining. LPS and PAM3 significantly increased mucin expression in airway mucosa and Calu-3 cells (P < 0.05). DEX alone had no significant effect on mucin expression in airway mucosa or Calu-3 cells (P > 0.05). In contrast, DEX significantly reduced LPS- and PAM3-induced mucin expression in explanted mucosal tissue and mucin expression in Calu-3 cells (P < 0.05). In explanted human airway mucosa ACC alone significantly increased mucin expression (P < 0.05). In contrast, ACC significantly decreased LPS- and PAM3-induced mucin expression (P < 0.05). In Calu-3 cells ACC alone had no significant effect on mucin expression (P > 0.05). ACC decreased LPS- and PAM3-induced mucin expression, but this effect was not significant (P > 0.05). These data suggest that DEX can effectively reduce bacteria-induced mucin expression in the airways. ACC alone may increase mucin expression in noninfected mucosa, but it decreased bacteria-induced mucin expression. Further studies are warranted to evaluate whether the effect of DEX or ACC is clinically relevant.

Decreased expression of human aquaporin-5 correlated with mucus overproduction in airways of chronic obstructive pulmonary disease

AIM

To investigate the relationship between aquaporin-5 (AQP5) expression and mucus overproduction in the airways of Chinese patients with chronic obstructive pulmonary disease (COPD) and the correlation with pulmonary function change.

METHODS

Bronchial tissues were obtained from fiberoptic bronchoscopy and bronchial biopsy in West China Hospital from April to July 2004. Twenty-five patients were diagnosed as COPD patients, and another 20 were diagnosed as the control patients. The expressions of AQP5, mucin 5AC (MUC5AC), and mucin in bronchial tissues were detected by semiquantitative RT-PCR, in situ hybridization, and immunohistochemical and alcian blue-periodic acid-Schiff (AB-PAS) staining, respectively.

RESULTS

Compared with the control group, an attenuated expression of AQP5 was detected throughout the bronchial tissues from patients with COPD (P<0.01), but no difference existed in the lung tissues (P>0.05). Simultaneously, increased staining of MUC5AC and mucus in submucosal glands were noted (P<0.01, respectively). Smoking attenuated the expressions of AQP5 and increased the staining of MUC5AC and mucus in submucosal glands in the COPD groups (P<0.01), while there were no significant differences observed in the control group (P>0.05). The decreased expression of AQP5 mRNA was correlated with forced expiratory volume in 1 s (FEV1)/forced vital capacity (FVC) (r=0.60, P<0.01), FEV1% predicted value (r=0.60, P<0.01), maximal expiratory flow in 50% vital capacity (V50) % predicted value (r=0.55, P<0.01), and maximal expiratory flow in 25% vital capacity (V25) % predicted value (r=0.45, P<0.01). The decreased expression was negatively correlated with MUC5AC mRNA of the epithelium airways (r=-0.45, P<0.01) and the AB-PAS-stained area of submucosal glands (r=-0.61, P<0.01). The upregulation of MUC5AC mRNA correlated with the positively AB-PAS-stained area of submucosal glands and correlated negatively with FEV1/FVC (r=-0.53; P<0.01), FEV1% predicted value (r=-0.53; P<0.01), V50% predicted value (r=-0.48; P<0.01), and V25% predicted value (r=-0.43; P<0.01).

CONCLUSION

The attenuated gene expression of AQP5 existed in the airways of Chinese COPD patients, which was complicated by mucus hypersecretion. The decreased expression of AQP5 mRNA may be related to the severity of airflow obstruction.

Multifunctional transcription factor YY1: a therapeutic target in human cancer?

The multifunctional transcription factor Yin Yang 1 (YY1) is a complex protein that has been shown to play pivotal roles in development, differentiation, cellular proliferation and apoptosis. It can act as a transcriptional repressor, an activator, or an initiator element binding protein that directs and initiates transcription of numerous cellular and viral genes. Because the expression and function of YY1 are known to be intimately associated with cell-cycle progression, the physiological significance of YY1 activity has recently been applied to models of cancer biology. Several lines of evidence imply that YY1 expression and/or activation is associated with tumourigenesis, in addition to its regulatory roles in normal biological processes. However, controversial results also raised and indicated that further studies are still needed to piece all of the seemingly contradictory data into a complete picture. On the basis of YY1 regulations and functions, novel drugs and specific treatment strategies may be developed with new therapeutic applications for tumour patients in the future.

IL-9 modulated MUC4 gene and glycoprotein expression in airway epithelial cells

Compromised epithelial cell integrity is a common feature associated with chronic lung inflammatory states such as asthma. While epithelial cell damage is largely due to sustained effects of inflammatory mediators localized to airways, the subsequent process of epithelial cell differentiation is attributed to members of the transmembrane receptor tyrosine kinase family called the ErbB's. MUC4, a large molecular weight membrane-bound glycoprotein, has recently been identified as a potential ligand for the ErbB-2 receptor. In this study, we investigated the possible role of interleukin-9 (IL-9), a Th2 cytokine, on MUC4 expression using a lung cancer cell line, NCI-H650. We determined that IL-9 up-regulates MUC4 expression in a time and concentration-dependent fashion. Nuclear run-on assays indicated transcriptional regulation of MUC4 while no post-transcriptional mRNA stabilization was observed by actinomycin D chase experiments. IL-9 also increased MUC4 glycoprotein expression as determined by Western blots using a monoclonal antibody specific for a non-tandem repeat region on ASGP-2 region of MUC4. Furthermore, a JAK3-selective inhibitor 4-(4'-hydroxyphenyl) amino-6, 7-dimethoxyquinazoline (WHI-P131), substantially reduced IL-9-induced MUC4 mRNA expression in a dose-dependent fashion. These results implicate a potential role for IL-9 upon MUC4 expression in human airway epithelial cells.

IL-4 induced MUC4 enhancement in respiratory epithelial cells in vitro is mediated through JAK-3 selective signaling

BACKGROUND

Recent studies have identified MUC4 mucin as a ligand for activation of ErbB2, a receptor tyrosine kinase that modulates epithelial cell proliferation following epithelial damage in airways of asthmatics. In this study, we investigated the potential role of IL-4, one of the Th2 inflammatory cytokines persistent in asthmatic airways, in regulating MUC4 expression using a cell line NCI-H650.

METHODS

Real time PCR analysis was performed to determine concentration and time dependent effects of IL-4 upon MUC4 expression. Nuclear run on experiments were carried out to explore potential transcriptional modulation. Western blotting experiments using a monoclonal antibody specific to ASGP-2 domain of MUC4 were performed to analyze MUC4 glycoprotein levels in plasma membrane fractions. To analyze potential signal transduction cascades, IL-4 treated confluent cultures were co-incubated, separately with a pan-JAK inhibitor, a JAK-3 selective inhibitor or a MEK-1, 2 (MAPK) inhibitor at various concentrations before MUC4 transcript analysis. Corresponding transcription factor activation was tested by western blotting using a monoclonal p-STAT-6 antibody.

RESULTS

MUC4 levels increased in a concentration and time specific fashion reaching peak expression at 2.5 ng/ml and 8 h. Nuclear run on experiments revealed transcriptional enhancement. Corresponding increases in MUC4 glycoprotein levels were observed in plasma membrane fractions. Pan-JAK inhibitor revealed marked reduction in IL-4 stimulated MUC4 levels and JAK3 selective inhibitor down-regulated MUC4 mRNA expression in a concentration-dependent fashion. In accordance with the above observations, STAT-6 activation was detected within 5 minutes of IL-4 stimulus. No effect in MUC4 levels was observed on using a MAPK inhibitor.

CONCLUSION

These observations signify a potential role for IL-4 in MUC4 up-regulation in airway epithelia.

Differential Muc2 and Muc5ac secretion by stimulated guinea pig tracheal epithelial cells in vitro

BACKGROUND

Mucus overproduction is a characteristic of inflammatory pulmonary diseases including asthma, chronic bronchitis, and cystic fibrosis. Expression of two mucin genes, MUC2 and MUC5AC, and their protein products (mucins), is modulated in certain disease states. Understanding the signaling mechanisms that regulate the production and secretion of these major mucus components may contribute significantly to development of effective therapies to modify their expression in inflamed airways.

METHODS

To study the differential expression of Muc2 and Muc5ac, a novel monoclonal antibody recognizing guinea pig Muc2 and a commercially-available antibody against human MUC5AC were optimized for recognition of specific guinea pig mucins by enzyme-linked immunosorbent assay (ELISA), Western blot, and immunohistochemistry (IHC). These antibodies were then used to analyze expression of Muc2 and another mucin subtype (likely Muc5ac) in guinea pig tracheal epithelial (GPTE) cells stimulated with a mixture of pro-inflammatory cytokines [tumor necrosis factor-alpha (TNF-alpha), interleukin 1beta (IL-1beta), and interferon- gamma (IFN-gamma)].

RESULTS

The anti-Muc2 (C4) and anti-MUC5AC (45M1) monoclonal antibodies specifically recognized proteins located in Muc2-dominant small intestinal and Muc5ac-dominant stomach mucosae, respectively, in both Western and ELISA experimental protocols. IHC protocols confirmed that C4 recognizes murine small intestine mucosal proteins while 45M1 does not react. C4 and 45M1 also stained specific epithelial cells in guinea pig lung sections. In the resting state, Muc2 was recognized as a highly expressed intracellular mucin in GPTE cells in vitro. Following cytokine exposure, secretion of Muc2, but not the mucin recognized by the 45M1 antibody (likely Muc5ac), was increased from the GPTE cells, with a concomitant increase in intracellular expression of both mucins.

CONCLUSION

Given the tissue specificity in IHC and the differential hybridization to high molecular weight proteins by Western blot, we conclude that the antibodies used in this study can recognize specific mucin subtypes in guinea pig airway epithelium and in proteins from GPTE cells. In addition, Muc2 is highly expressed constitutively, modulated by inflammation, and secreted differentially (as compared to Muc5ac) in GPTE cells. This finding contrasts with expression patterns in the airway epithelium of a variety of mammalian species in which only Muc5ac predominates.

Respiratory tract mucin genes and mucin glycoproteins in health and disease

This review focuses on the role and regulation of mucin glycoproteins (mucins) in airway health and disease. Mucins are highly glycosylated macromolecules (> or =50% carbohydrate, wt/wt). MUC protein backbones are characterized by numerous tandem repeats that contain proline and are high in serine and/or threonine residues, the sites of O-glycosylation. Secretory and membrane-tethered mucins contribute to mucociliary defense, an innate immune defense system that protects the airways against pathogens and environmental toxins. Inflammatory/immune response mediators and the overproduction of mucus characterize chronic airway diseases: asthma, chronic obstructive pulmonary diseases (COPD), or cystic fibrosis (CF). Specific inflammatory/immune response mediators can activate mucin gene regulation and airway remodeling, including goblet cell hyperplasia (GCH). These processes sustain airway mucin overproduction and contribute to airway obstruction by mucus and therefore to the high morbidity and mortality associated with these diseases. Importantly, mucin overproduction and GCH, although linked, are not synonymous and may follow from different signaling and gene regulatory pathways. In section i, structure, expression, and localization of the 18 human MUC genes and MUC gene products having tandem repeat domains and the specificity and application of MUC-specific antibodies that identify mucin gene products in airway tissues, cells, and secretions are overviewed. Mucin overproduction in chronic airway diseases and secretory cell metaplasia in animal model systems are reviewed in section ii and addressed in disease-specific subsections on asthma, COPD, and CF. Information on regulation of mucin genes by inflammatory/immune response mediators is summarized in section iii. In section iv, deficiencies in understanding the functional roles of mucins at the molecular level are identified as areas for further investigations that will impact on airway health and disease. The underlying premise is that understanding the pathways and processes that lead to mucus overproduction in specific airway diseases will allow circumvention or amelioration of these processes.

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.

Regulation of mucin expression: mechanistic aspects and implications for cancer and inflammatory diseases

Mucins are large multifunctional glycoproteins whose primary functions are to protect and lubricate the surfaces of epithelial tissues lining ducts and lumens within the human body. Several lines of evidence also support the involvement of mucins in more complex biological processes such as epithelial cell renewal and differentiation, cell signaling, and cell adhesion. Recent studies have uncovered the role of select mucins in the pathogenesis of cancer, underscoring the importance of a detailed knowledge about mucin biology. Under normal physiological conditions, the production of mucins is optimally maintained by a host of elaborate and coordinated regulatory mechanisms, thereby affording a well-defined pattern of tissue-, time-, and developmental state-specific distribution. However, mucin homeostasis may be disrupted by the action of environmental and/or intrinsic factors that affect cellular integrity. This results in an altered cell behavior that often culminates into a variety of pathological conditions. Deregulated mucin production has indeed been associated with numerous types of cancers and inflammatory disorders. It is, therefore, crucial to comprehend the underlying basis of molecular mechanisms controlling mucin production in order to design and implement adequate therapeutic strategies for combating these diseases. Herein, we discuss some physiologically relevant regulatory aspects of mucin production, with a particular emphasis on aberrations that pertain to pathological situations. Our views of the achievements, the conceptual and technical limitations, as well as the future challenges associated with studies of mucin regulation are exposed.

IL-4 receptor signaling in Clara cells is required for allergen-induced mucus production

Excessive mucus production is an important pathological feature of asthma. The Th2 cytokines IL-4 and IL-13 have both been implicated in allergen-induced mucus production, inflammation, and airway hyperreactivity. Both of these cytokines use receptors that contain the IL-4Ralpha subunit, and these receptors are expressed on many cell types in the lung. It has been difficult to determine whether allergen-induced mucus production is strictly dependent on direct effects of IL-4 and IL-13 on epithelial cells or whether other independent mechanisms exist. To address this question, we used a cell type-specific inducible gene-targeting strategy to selectively disrupt the IL-4Ralpha gene in Clara cells, an airway epithelial cell population that gives rise to mucus-producing goblet cells. Clara cell-specific IL-4Ralpha-deficient mice and control mice developed similar elevations in serum IgE levels, airway inflammatory cell numbers, Th2 cytokine production, and airway reactivity following OVA sensitization and challenge. However, compared with control mice, Clara cell-specific IL-4Ralpha-deficient mice were nearly completely protected from allergen-induced mucus production. Because only IL-13 and IL-4 are thought to signal via IL-4Ralpha, we conclude that direct effects of IL-4 and/or IL-13 on Clara cells are required for allergen-induced mucus production in the airway epithelium.

Dexamethasone-mediated repression of MUC5AC gene expression in human lung epithelial cells

Glucocorticoids regulate gene expression via binding of the ligand-activated glucocorticoid receptor (GR) to glucocorticoid-responsive elements (GRE) in target gene promoters. The MUC5AC gene, which encodes the protein backbone of an abundant secreted airway mucin, has several putative GRE cis-elements in its 5' sequence. Mechanism(s) whereby glucocorticoids regulate mucin genes have not previously been described. In this study, the glucocorticoid dexamethasone (Dex) decreased MUC5AC mRNA abundance in A549 and NCI-H292 cell lines and primary differentiated normal bronchial epithelial cells by 50-80%, suggesting a common mechanism of MUC5AC gene repression in human lung epithelial cells. Kinetic analyses showed that MUC5AC mRNA was not significantly decreased until 6 h after Dex exposure, and that nuclear translocation of GR was biphasic, suggesting that Dex-mediated cis-repression of MUC5AC gene expression was a delayed response of GR translocation. Transfection analyses demonstrated that Dex transcriptionally repressed the MUC5AC promoter. Electrophoretic mobility shift assays with wild-type and mutant oligonucleotide probes showed that GR bound to two GRE cis-sites (nucleotides -930 to -912 and -369 to -351) in the MUC5AC promoter. Analyses of mutated MUC5AC promoter constructs demonstrated that NF-kappaB cis-sites were not involved in Dex-mediated repression of MUC5AC. Dex did not alter mRNA stability of MUC5AC transcripts. Taken together, the data indicate that Dex transcriptionally mediates repression of MUC5AC gene expression in human lung epithelial cells at quiescent states after binding of GR to one or more GRE cis-elements in the MUC5AC promoter.

Differential regulation of MUC5AC/Muc5ac and hCLCA-1/mGob-5 expression in airway epithelium

This study demonstrates that the two biomarkers, MUC5AC/ Muc5ac and hCLCA1/Gob5, which are frequently associated with surface mucous/goblet cells in asthmatic airways, are differentially regulated. Intratracheal instillation of IL-13 (0.5 mug/mouse lung) elicited 8- and 110-fold induction of Muc5ac and Gob5 messages, respectively, within 24 h in wild-type mouse lung, whereas these inductions were abrogated in Stat6 knockout mice. The induction of MUC5AC/Muc5ac message could not be duplicated in vitro with primary tracheobronchial epithelial (TBE) cells derived from wild-type mice or humans, despite significant inductions still seen for hCLCA1/Gob5. Further studies with JAK inhibitors and STAT6 signaling showed active signaling of the JAK/STAT6 pathway in these primary TBE cultures by IL-13 in the regulation of hCLCA1 expression. Dual immunofluorescent staining with antibodies specific to MUC5AC and hCLCA1 revealed a differential nature of the expression of these two biomarkers by distinct cell types of primary TBE cultures. Finally, MUC5AC expression could be elevated by a bacterial product, peptidoglycan, without any induction of hCLCA1. Thus, these results suggest that the two biomakers of the metaplastic airway mucous cell type are differentially regulated by JAK/STAT6-dependent and -independent pathways.

Altered O-glycosylation and sulfation of airway mucins associated with cystic fibrosis

Cystic fibrosis (CF) is the most lethal genetic disorder in Caucasians and is characterized by the production of excessive amounts of viscous mucus secretions in the airways of patients, leading to airway obstruction, chronic bacterial infections, and respiratory failure. Previous studies indicate that CF-derived airway mucins are glycosylated and sulfated differently compared with mucins from nondiseased (ND) individuals. To address unresolved questions about mucin glycosylation and sulfation, we examined O-glycan structures in mucins purified from mucus secretions of two CF donors versus two ND donors. All mucins contained galactose (Gal), N-acetylglucosamine (GlcNAc), N-acetylgalactosamine (GalNAc), fucose (Fuc), and sialic acid (Neu5Ac). However, CF mucins had higher sugar content and more O-glycans compared with ND mucins. Both ND and CF mucins contained GlcNAc-6-sulfate (GlcNAc-6-Sul), Gal-6-Sul, and Gal-3-Sul, but CF mucins had higher amounts of the 6-sulfated species. O-glycans were released from CF and ND mucins and derivatized with 2-aminobenzamide (2-AB), separated by ion exchange chromatography, and quantified by fluorescence. There was nearly a two-fold increase in sulfation and sialylation in CF compared with ND mucin. High performance liquid chromatography (HPLC) profiles of glycans showed differences between the two CF samples compared with the two ND samples. Glycan compositions were defined by matrix-assisted laser desorption/ionization time-of-flight mass spectrometry (MALDI-TOF-MS). Unexpectedly, 260 compositional types of O-glycans were identified, and CF mucins contained a higher proportion of sialylated and sulfated O-glycans compared with ND mucins. These profound structural differences in mucin glycosylation in CF patients may contribute to inflammatory responses and increased pathogenesis by Pseudomonas aeruginosa.

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.

Effects of carbocisteine on altered activities of glycosidase and glycosyltransferase and expression of Muc5ac in SO2-exposed rats

Carbocisteine is a mucoregulatory drug regulating fucose and sialic acid contents in mucus glycoprotein. To investigate the mechanism of carbocisteine action, we evaluated the effects of carbocisteine on the activity of fucosidase, sialidase, fucosyltransferase and sialyltransferase, and on the expression of Muc5ac mRNA in the airway epithelium of SO(2)-exposed rats. Wistar rats were repeatedly exposed to a 300-ppm SO(2) gas for 44 days. Carbocisteine (125 and 250 mg/kg x2/day) was administered for 25 days after 20 days of SO(2) gas exposure. These enzyme activities were measured by fluorogenic substrate or glycoproteinic exogenous acceptor method. The expression levels of Muc5ac mRNA and protein were determined with real-time reverse transcriptase-polymerase chain reaction (real-time RT-PCR) and enzyme-linked immunosorbent assay (ELISA), respectively. Carbocisteine (250 mg/kg x2/day) inhibited all the changes in these enzyme activities and the expressions of Muc5ac mRNA and protein in the lung after repeated SO(2) exposure. These findings suggest that carbocisteine may normalize fucose and sialic acid contents in mucin glycoprotein through regulation of these enzyme activities, and inhibition of both Muc5ac mRNA and protein expressions in SO(2)-exposed rats.

Neutrophil elastase induces mucus cell metaplasia in mouse lung

Goblet cell hyperplasia in the superficial airway epithelia is a signature pathological feature of chronic bronchitis and cystic fibrosis. In these chronic inflammatory airway diseases, neutrophil elastase (NE) is found in high concentrations in the epithelial lining fluid. NE has been reported to trigger mucin secretion and increase mucin gene expression in vitro. We hypothesized that chronic NE exposure to murine airways in vivo would induce goblet cell metaplasia. Human NE (50 microg) or PBS saline was aspirated intratracheally by male Balb/c (6 wk of age) mice on days 1, 4, and 7. On days 8, 11, and 14, lung tissues for histology and bronchoalveolar lavage (BAL) samples for cell counts and cytokine levels were obtained. NE induced Muc5ac mRNA and protein expression and goblet cell metaplasia on days 8, 11, and 14. These cellular changes were the result of proteolytic activity, since the addition of an elastase inhibitor, methoxysuccinyl Ala-Ala-Pro-Val chloromethylketone (AAPV-CMK), blocked NE-induced Muc5ac expression and goblet cell metaplasia. NE significantly increased keratinocyte-derived chemokine and IL-5 in BAL and increased lung tissue inflammation and BAL leukocyte counts. The addition of AAPV-CMK reduced these measures of inflammation to control levels. These experiments suggest that NE proteolytic activity initiates an inflammatory process leading to goblet cell metaplasia.

The CCT promoter directs high-level transgene expression in distal lung epithelial cell lines

Gene therapy requires the presence of a robust and yet small promoter to drive high-level expression of desired proteins. In comparative analysis, we investigated the promoter strength of the CTP:phosphocholine cytidylyltransferase promoter (CCT alpha) with other commonly used promoters, which were all cloned into a similar background vector (PGL3 basic). Transient promoter-reporter assays in murine lung epithelial (MLE-12) cells revealed that the core CCT alpha promoter (240 bp) was observed to exhibit a 40-fold, 8-fold, and 3-fold higher level of activity compared with the simian virus 40, human cytomegalovirus, and Rous sarcoma virus promoters, respectively. The CCT alpha promoter was significantly more active than the Clara cell 10, thymidine kinase, and phosphoglycerate kinase promoters. This pattern of high-level expression for CCT alpha was detected primarily in cell lines of distal lung epithelial origin (MLE-12, RLE, H441) and was reduced in other cell lines (A549, CHO, HepG 2). CCT alpha promoter-reporter activity, CCT alpha transcript levels, and immunoreactive protein levels increased significantly in the presence of all-trans retinoic acid. The CCT alpha promoter, in a retinoic acid-inducible manner, efficiently directed expression of murine erythropoietin in MLE-12 cells. Collectively, these observations suggest that the CCT alpha construct might be useful to drive high-level, regulatable expression of heterologous proteins in alveolar epithelia.

Human airway trypsin-like protease increases mucin gene expression in airway epithelial cells

Human airway trypsin-like protease (HAT) is a serine protease found in sputum of patients with chronic airway diseases and is an agonist of protease-activated receptor-2 (PAR-2). Results from this study show that HAT treatment also enhances mucus production by the airway epithelial cell line NCI-H292 in vitro. Histologic examination showed that HAT enhances mucous glycoconjugate synthesis, whereas the PAR-2 agonist peptide (PAR-2 AP) has no such effect. HAT, but not PAR-2 AP, enhances MUC2 and MUC5AC gene expression 23-fold and 32-fold, respectively. The proteolytic activity of HAT is required to enhance MUC5AC gene expression; the addition of the inhibitors of trypsin-like protease activity of HAT, aprotinin and leupeptin, abolishes its enhancing effect. AG1478, anti-epidermal growth factor receptor (anti-EGFR)-neutralizing antibody, and anti-amphiregulin (AR)-neutralizing antibody all inhibited the stimulatory effect of HAT. Furthermore, HAT increases AR gene expression and subsequent AR protein release, whereas PAR-2 AP shows no such effects. These results indicate that HAT enhances mucin gene expression through an AR-EGFR pathway, and PAR-2 is not sufficient for or does not directly cause HAT-induced mucin gene expression. Thus, HAT might be a possible therapeutic target to prevent excessive mucus production in patients with chronic airway diseases.

Stimulation of airway mucin gene expression by interleukin (IL)-17 through IL-6 paracrine/autocrine loop

Mucus hypersecretion and persistent airway inflammation are common features of various airway diseases, such as asthma, chronic obstructive pulmonary disease, and cystic fibrosis. One key question is: does the associated airway inflammation in these diseases affect mucus production? If so, what is the underlying mechanism? It appears that increased mucus secretion results from increased mucin gene expression and is also frequently accompanied by an increased number of mucous cells (goblet cell hyperplasia/metaplasia) in the airway epithelium. Many studies on mucin gene expression have been directed toward Th2 cytokines such as interleukin (IL)-4, IL-9, and IL-13 because of their known pathophysiological role in allergic airway diseases such as asthma. However, the effect of these cytokines has not been definitely linked to their direct interaction with airway epithelial cells. In our study, we treated highly differentiated cultures of primary human tracheobronchial epithelial (TBE) cells with a panel of cytokines (interleukin-1alpha, 1beta, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 15, 16, 17, 18, and tumor necrosis factor alpha). We found that IL-6 and IL-17 could stimulate the mucin genes, MUC5B and MUC5AC. The Th2 cytokines IL-4, IL-9, and IL-13 did not stimulate MUC5AC or MUC5B in our experiments. A similar stimulation of MUC5B/Muc5b expression by IL-6 and IL-17 was demonstrated in primary monkey and mouse TBE cells. Further investigation of MUC5B expression demonstrated that IL-17's effect is at least partly mediated through IL-6 by a JAK2-dependent autocrine/paracrine loop. Finally, evidence is presented to show that both IL-6 and IL-17 mediate MUC5B expression through the ERK signaling pathway.

Mucin genes in horse airways: MUC5AC, but not MUC2, may play a role in recurrent airway obstruction

REASONS FOR PERFORMING STUDY

Increased mucin gene expression may be an important cause of mucus accumulation observed in recurrent airway obstruction (RAO)-affected horses. To date, however, no mucin gene sequences are available for the horse.

OBJECTIVES

To identify equine homologues of gel-forming mucins and investigate their expression at different airway generations of healthy and RAO-affected horses.

METHODS

Two equine homologues were identified by cloning and sequencing fragments of equine (eq)MUC5AC and eqMUC2.

RESULTS

Semiquantitative RT-PCR on RNA from airways (generations 1, 5, 10, 15; small airways and parenchyma), stomach (glandular), and colon revealed that eqMUC5AC is expressed in equine stomach and in all of the airway samples. In contrast, eqMUC2 steady-state mRNA levels were detected in colon and very faintly in stomach, but not in airway tissue. EqMUC5AC expression was also compared to that of ZO-1, a tight junction protein, and eqMUC5AC/ZO-1 ratios were higher in RAO-affected compared to control horses at all airway generations.

CONCLUSIONS

That eqMUC5AC is expressed in horse airways, but any expression of MUC2 is undetectable and unlikely to be of physiological consequence.

POTENTIAL RELEVANCE

EqMUC5AC up-regulation may be a primary mechanism responsible for mucus hypersecretion and accumulation in RAO.

Expression of MUC2 and MUC4 proteins and cytokines: early markers of intestinal graft rejection

BACKGROUND

Histopathologic examination (HP) is the primary method of monitoring intestinal graft rejection. Alterations in mucin levels have been demonstrated in bowel diseases. The aim of this study was to detect early markers of intestinal graft rejection based on mucin and cytokine levels.

METHODS

Allogeneic and syngeneic orthotopic intestinal transplantations were performed in untreated Lewis strain recipient rats from Dark Agouti and Lewis strain donors, respectively (unmodified rejection and nonrejection groups). Similarly, allogeneic and syngeneic orthotopic intestinal transplantations were performed in tacrolimus (immunosuppression)-treated groups. HP was performed on hematoxylin-eosin and periodic acid Schiff-stained sections. Expression of MUC2 and MUC4 proteins and of mRNA was detected by immunohistochemistry and Northern analysis, respectively. Interferon (IFN)-gamma, tumor necrosis factor (TNF)-alpha, and transforming growth factor-beta(1) were measured by reverse transcription-polymerase chain reaction.

RESULTS

HP revealed early or mild rejection on day 3, moderate rejection on day 5, and severe rejection on day 7 posttransplantation (posttx) in the unmodified rejection group. A significant (P<0.01) increase in MUC2 and MUC4 expression was observed on day 3 posttx in the allogeneic rejection group compared with syngeneic controls; the levels decreased by day 7. Goblet cells were significantly more frequent on day 3 compared with days 5 and 7 posttx (P<0.01). IFN-gamma and TNF-alpha expression were also higher in the rejection group.

CONCLUSIONS

Early transplant rejection is associated with increased MUC2, MUC4, IFN-gamma, and TNF-alpha expression. These markers combined with HP may assist in the diagnosis of early intestinal graft rejection.

Transcriptional regulation of the hamster Muc1 gene: identification of a putative negative regulatory element

The mucin gene Muc1 is expressed in glandular epithelial cells and is involved in lubricative and protective functions. It is also overexpressed in many carcinomas including breast and lung cancer cells. To study the transcriptional regulation of Muc1, we cloned a 2.4-kb fragment containing the promoter region of the hamster Muc1 gene and analyzed it for its ability to mediate transcription. Transcriptional initiation was localized to 22 base pairs downstream of the TATA box. We performed functional analysis of the Muc1 promoter in hamster (HP-1 and Chinese hamster ovary) and human cells (MCF-7, A549, and BEAS-2B) using deletion/reporter constructs. A positive regulatory region between bases -555 and -252 and a putative negative regulatory element (P-NRE) between nucleotides -1,652 and -1,614 were found to be active in transfected cells. The P-NRE contains a yin yang 1 (YY1) transcription factor binding site, and electrophoretic mobility shift assays with HP-1 cell nuclear extract revealed the binding of YY1 to this site. Our data suggest that YY1 may play an inhibitory role in the transcription of the Muc1 gene.