Regulation of human airway mucins by acrolein and inflammatory mediators

Association Study between Mucin 4 (MUC4) Polymorphisms and Idiopathic Recurrent Pregnancy Loss in a Korean Population

Recurrent pregnancy loss (RPL) is the loss of two or more consecutive pregnancies before 20 weeks of gestational age. Our study investigated whether mucin 4 (MUC4) polymorphisms are associated with RPL. MUC polymorphisms (rs882605 C>A, rs1104760 A>G, rs2688513 A>G, rs2258447 C>T, and rs2291652 A>G) were genotyped in 374 women with RPL and 239 controls of Korean ethnicity using polymerase chain reaction-restriction fragment length polymorphism analysis and the TaqMan probe SNP genotyping assay. Differences in genotype frequencies between cases of RPL and the controls were compared. MUC4 rs882605 C>A and rs1104760 A>G polymorphisms were associated with increased incidence of RPL in three and four or more pregnancy loss patients. The haplotype analyses showed a tendency for the allelic effect including the association of MUC4 rs882605 A and rs1104760 G alleles with increased incidence of RPL. In addition, the MUC4 rs882605 CA/MUC4 rs2258447 CC genotype combination was associated with increased RPL prevalence. The two exonic polymorphisms lead to amino acid changes of protein and may act as pathogenic variants for RPL. In conclusion, the MUC4 rs882605 C>A and MUC4 rs1104760 A>G polymorphisms were associated with the susceptibility of RPL and we considered them as potential biomarkers for RPL.

Apiaceous vegetables protect against acrolein-induced pulmonary injuries through modulating hepatic detoxification and inflammation in C57BL/6 male mice

Acrolein (Acr) is a reactive aldehyde in the environment. Acr causes oxidative stress and a cascade of catalytic events and has, thereby, been associated with increased risk of pulmonary diseases. Whether apiaceous vegetables (API) consumption can prevent Acr-induced pulmonary toxicity has not yet been explored hence, we investigated the effects of API on Acr-induced pulmonary damages in C57BL/6J mice. The mice were assigned into either negative control [NEG group; American Institute of Nutrition (AIN)-93G diet only], positive control (POS group; AIN-93G+Acr) or API intervention group (API group; AIN-93G+21% API+Acr). After 1 week of dietary intervention, the POS and API mice were exposed to Acr (10 µmol/kg body weight/day) for 5 days. During the exposure period, assigned diets remained the same. Prominent indicators lung of toxicity of POS mice were found, including mucus accumulation, macrophage infiltration, and hemorrhage, all of which were ameliorated by the API. Serum and lung inflammation markers, such as a tumor necrosis factor alpha were also increased by Acr while reduced by API. In the liver, API upregulated expression of glutathione S-transferases, which enhanced the metabolism of Acr into water-soluble 3-hydroxypropyl mercapturic acid for excretion. This is consistent with observed reductions in serum Acr-protein adducts. Taken together, our results suggest that API may provide protection against Acr-induced pulmonary damages and inflammation via enhancement of the hepatic detoxification of Acr.

Differential responses to e-cig generated aerosols from humectants and different forms of nicotine in epithelial cells from nonsmokers and smokers

In the United States, millions of adults use electronic cigarettes (e-cigs), and a majority of these users are former or current cigarette smokers. It is unclear, whether prior smoking status affects biological responses induced by e-cigs. In this study, differentiated human nasal epithelial cells (hNECs) from nonsmokers and smokers at air-liquid interface were acutely exposed to the e-cig generated aerosols of humectants, propylene glycol (PG), and glycerol (GLY). Mucin levels were examined in the apical washes, and cytokine levels were assessed in the basolateral supernatants 24 h postexposure. The aerosol from the GLY exposure increased mucin 5, subtype AC (MUC5AC) levels in the apical wash of hNECs from nonsmokers, but not smokers. However, the aerosol from GLY induced pro-inflammatory responses in hNECs from smokers. We also exposed hNECs from nonsmokers and smokers to e-cig generated aerosol from PG:GLY with freebase nicotine or nicotine salt. The PG:GLY with freebase nicotine exposure increased MUC5AC and mucin 5, subtype B (MUC5B) levels in hNECs from nonsmokers, but the nicotine salt exposure did not. The PG:GLY with nicotine salt exposure increased pro-inflammatory cytokines in hNECs from smokers, which was not seen with the freebase nicotine exposure. Taken together, these data indicate that the e-cig generated aerosols from the humectants, mostly GLY, and the type of nicotine used cause differential effects in airway epithelial cells from nonsmokers and smokers. As e-cig use is increasing, it is important to understand that the biological effects of e-cig use are likely dependent on prior cigarette smoke exposure.

Postoperative Complications Are Associated with Long-Term Changes in the Gut Microbiota Following Colorectal Cancer Surgery

Changes in the gut microbiome have already been associated with postoperative complications in major abdominal surgery. However, it is still unclear whether these changes are transient or a long-lasting effect. Therefore, the aim of this prospective clinical pilot study was to examine long-term changes in the gut microbiota and to correlate these changes with the clinical course of the patient. Methods: In total, stool samples of 62 newly diagnosed colorectal cancer patients undergoing primary tumor resection were analyzed by 16S-rDNA next-generation sequencing. Stool samples were collected preoperatively in order to determine the gut microbiome at baseline as well as at 6, 12, and 24 months thereafter to observe longitudinal changes. Postoperatively, the study patients were separated into two groups-patients who suffered from postoperative complications (n = 30) and those without complication (n = 32). Patients with postoperative complications showed a significantly stronger reduction in the alpha diversity starting 6 months after operation, which does not resolve, even after 24 months. The structure of the microbiome was also significantly altered from baseline at six-month follow-up in patients with complications (p = 0.006). This was associated with a long-lasting decrease of a large number of species in the gut microbiota indicating an impact in the commensal microbiota and a long-lasting increase of Fusobacterium ulcerans. The microbial composition of the gut microbiome shows significant changes in patients with postoperative complications up to 24 months after surgery.

Mucociliary Respiratory Epithelium Integrity in Molecular Defense and Susceptibility to Pulmonary Viral Infections

Mucociliary defense, mediated by the ciliated and goblet cells, is fundamental to respiratory fitness. The concerted action of ciliary movement on the respiratory epithelial surface and the pathogen entrapment function of mucus help to maintain healthy airways. Consequently, genetic or acquired defects in lung defense elicit respiratory diseases and secondary microbial infections that inflict damage on pulmonary function and may even be fatal. Individuals living with chronic and acute respiratory diseases are more susceptible to develop severe coronavirus disease-19 (COVID-19) illness and hence should be proficiently managed. In light of the prevailing pandemic, we review the current understanding of the respiratory system and its molecular components with a major focus on the pathophysiology arising due to collapsed respiratory epithelium integrity such as abnormal ciliary movement, cilia loss and dysfunction, ciliated cell destruction, and changes in mucus rheology. The review includes protein interaction networks of coronavirus infection-manifested implications on the molecular machinery that regulates mucociliary clearance. We also provide an insight into the alteration of the transcriptional networks of genes in the nasopharynx associated with the mucociliary clearance apparatus in humans upon infection by severe acute respiratory syndrome coronavirus-2.

Analysis of Acrolein Exposure Induced Pulmonary Response in Seven Inbred Mouse Strains and Human Primary Bronchial Epithelial Cells Cultured at Air-Liquid Interface

Background

Acrolein is a major component of environmental pollutants, cigarette smoke, and is also formed by heating cooking oil. We evaluated the interstrain variability of response to subchronic inhalation exposure to acrolein among inbred mouse strains for inflammation, oxidative stress, and tissue injury responses. Furthermore, we studied the response to acrolein vapor in the lung mucosa model using human primary bronchial epithelial cells (PBEC) cultured at an air-liquid interface (ALI) to evaluate the findings of mouse studies.

Methods

Female 129S1/SvlmJ, A/J, BALB/cByJ, C3H/HeJ, C57BL/6J, DBA/2J, and FVB/NJ mice were exposed to 1 part per million (ppm) acrolein or filtered air for 11 weeks. Total cell counts and protein concentrations were measured in bronchoalveolar lavage (BAL) fluid to assess airway inflammation and membrane integrity. PBEC-ALI models were exposed to acrolein vapor (0.1 and 0.2 ppm) for 30 minutes. Gene expression of proinflammatory, oxidative stress, and tissue injury-repair markers was assessed (cut off: ≥2 folds; p < 0.05) in the lung models.

Results

Total BAL cell numbers and protein concentrations remained unchanged following acrolein exposure in all mouse strains. BALB/cByJ, C57BL/6J, and 129S1/SvlmJ strains were the most affected with an increased expression of proinflammatory, oxidative stress, and/or tissue injury markers. DBA/2J, C3H/HeJ, A/J, and FVB/NJ were affected to a lesser extent. Both matrix metalloproteinase 9 (Mmp9) and tissue inhibitor of metalloproteinase 1 (Timp1) were upregulated in the strains DBA/2J, C3H/HeJ, and FVB/NJ indicating altered protease/antiprotease balance. Upregulation of lung interleukin- (IL-) 17b transcript in the susceptible strains led us to investigate the IL-17 pathway genes in the PBEC-ALI model. Acrolein exposure resulted in an increased expression of IL-17A, C, and D; IL-1B; IL-22; and RAR-related orphan receptor A in the PBEC-ALI model.

Conclusion

The interstrain differences in response to subchronic acrolein exposure in mouse suggest a genetic predisposition. Altered expression of IL-17 pathway genes following acrolein exposure in the PBEC-ALI models indicates that it has a central role in chemical irritant toxicity. The findings also indicate that genetically determined differences in IL-17 signaling pathway genes in the different mouse strains may explain their susceptibility to different chemical irritants.

Mucin gene polymorphisms are associated with endometriosis in Korean women

OBJECTIVE

Mucin family members mucin 1 (MUC1) and mucin 4 (MUC4) play an important role in transformation and adhesion, and are known markers for the detection of cancer. However, the pathophysiology of endometriosis associated with the mucin gene is unclear. In this study, we analyzed the relationship between MUC1 and MUC4 single-nucleotide polymorphisms (SNPs) and the risk for endometriosis.

METHODS

We performed a case-controlled study of 29 endometriosis clinical samples and 27 functional cysts as control. Sixteen SNPs (rs145224844, rs139620330, rs144273480, rs1611770, rs146141676, rs201798179, rs201815857, rs199840128, rs200788986, rs141460657, rs183700327, rs199768496, rs191544901, rs200639498, rs148332231, and rs11465209) of MUC1 gene and eight SNPs (rs1104760, rs1106502, rs882605, rs2291651, rs2291652, rs2291653, rs2291654, and rs375068067) of the MUC4 gene were identified. We amplified SNP sites by polymerase chain reaction (PCR) using specific primer sets followed by DNA sequencing.

RESULTS

The single mutation analysis of MUC4 showed that MUC4 mutations had no effect on the risk for endometriosis, but the frequencies of haplotypes [T/T + T/T + C/C] (rs2291653, 2291654 and rs375068067) were associated with endometriosis.

CONCLUSION

The MUC1 genotype may not be correlated with endometriosis susceptibility. However, MUC4 polymorphisms are associated with the risk for endometriosis in Korean women.

Gut microbiome patterns correlate with higher postoperative complication rates after pancreatic surgery

Background

Postoperative complications are of great relevance in daily clinical practice, and the gut microbiome might play an important role by preventing pathogens from crossing the intestinal barrier. The two aims of this prospective clinical pilot study were: (1) to examine changes in the gut microbiome following pancreatic surgery, and (2) to correlate these changes with the postoperative course of the patient.

Results

In total, 116 stool samples of 32 patients undergoing pancreatic surgery were analysed by 16S-rRNA gene next-generation sequencing. One sample per patient was collected preoperatively in order to determine the baseline gut microbiome without exposure to surgical stress and/or antibiotic use. At least two further samples were obtained within the first 10 days following the surgical procedure to observe longitudinal changes in the gut microbiome. Whenever complications occurred, further samples were examined.

Based on the structure of the gut microbiome, the samples could be allocated into three different microbial communities (A, B and C). Community B showed an increase in Akkermansia, Enterobacteriaceae and Bacteroidales as well as a decrease in Lachnospiraceae, Prevotella and Bacteroides. Patients showing a microbial composition resembling community B at least once during the observation period were found to have a significantly higher risk for developing postoperative complications (B vs. A, odds ratio = 4.96, p < 0.01**; B vs. C, odds ratio = 2.89, p = 0.019*).

Conclusions

The structure of the gut microbiome is associated with the development of postoperative complications.

Electronic supplementary material

The online version of this article (10.1186/s12866-019-1399-5) contains supplementary material, which is available to authorized users.

Posttranscriptional control of airway inflammation

Acute inflammation in the lungs is a vital protective response, efficiently and swiftly eliminating inciters of tissue injury. However, in respiratory diseases characterized by chronic inflammation, such as chronic obstructive pulmonary disease and asthma, enhanced expression of inflammatory mediators leads to tissue damage and impaired lung function. Although transcription is an essential first step in the induction of proinflammatory genes, tight regulation of inflammation requires more rapid, flexible responses. Increasing evidence shows that such responses are achieved by posttranscriptional mechanisms directly affecting mRNA stability and translation initiation. RNA-binding proteins, microRNAs, and long noncoding RNAs interact with messenger RNA and each other to impact the stability and/or translation of mRNAs implicated in lung inflammation. Recent research has shown that these biological processes play a central role in the pathogenesis of several important pulmonary conditions. This review will highlight several posttranscriptional control mechanisms that influence lung inflammation and the known associations of derangements in these mechanisms with common respiratory diseases. WIREs RNA 2018, 9:e1455. doi: 10.1002/wrna.1455 This article is categorized under: RNA in Disease and Development > RNA in Disease RNA Structure and Dynamics > Influence of RNA Structure in Biological Systems RNA Interactions with Proteins and Other Molecules > Protein-RNA Interactions: Functional Implications RNA Turnover and Surveillance > Regulation of RNA Stability.

Chemical and pathogen-induced inflammation disrupt the murine intestinal microbiome

BACKGROUND

Salmonella is one of the most significant food-borne pathogens to affect humans and agriculture. While it is well documented that Salmonella infection triggers host inflammation, the impacts on the gut environment are largely unknown. A CBA/J mouse model was used to evaluate intestinal responses to Salmonella-induced inflammation. In parallel, we evaluated chemically induced inflammation by dextran sodium sulfate (DSS) and a non-inflammation control. We profiled gut microbial diversity by sequencing 16S ribosomal ribonucleic acid (rRNA) genes from fecal and cecal samples. These data were correlated to the inflammation marker lipocalin-2 and short-chain fatty acid concentrations.

RESULTS

We demonstrated that inflammation, chemically or biologically induced, restructures the chemical and microbial environment of the gut over a 16-day period. We observed that the ten mice within the Salmonella treatment group had a variable Salmonella relative abundance, with three high responding mice dominated by >46% Salmonella at later time points and the remaining seven mice denoted as low responders. These low- and high-responding Salmonella groups, along with the chemical DSS treatment, established an inflammation gradient with chemical and low levels of Salmonella having at least 3 log-fold lower lipocalin-2 concentration than the high-responding Salmonella mice. Total short-chain fatty acid and individual butyrate concentrations each negatively correlated with inflammation levels. Microbial communities were also structured along this inflammation gradient. Low levels of inflammation, regardless of chemical or biological induction, enriched for Akkermansia spp. in the Verrucomicrobiaceae and members of the Bacteroidetes family S24-7. Relative to the control or low inflammation groups, high levels of Salmonella drastically decreased the overall microbial diversity, specifically driven by the reduction of Alistipes and Lachnospiraceae in the Bacteroidetes and Firmicutes phyla, respectively. Conversely, members of the Enterobacteriaceae and Lactobacillus were positively correlated to high levels of Salmonella-induced inflammation.

CONCLUSIONS

Our results show that enteropathogenic infection and intestinal inflammation are interrelated factors modulating gut homeostasis. These findings may prove informative with regard to prophylactic or therapeutic strategies to prevent disruption of microbial communities, or promote their restoration.

Indoor Air Quality and Asthma: Has Unrecognized Exposure to Acrolein Confounded Results of Previous Studies?

Numerous contaminants in indoor air and their potential to cause or exacerbate asthma continue to be a subject of public health concern. Many agents are causally associated with or can exacerbate asthma, particularly in children. For formaldehyde, an established respiratory irritant based on numerous studies, the evidence for an association with asthma is still considered only limited or suggestive. However, there is no evidence that indicates increased sensitivity to sensory irritation to formaldehyde in people often regarded as susceptible such as asthmatics. Acrolein, but not formaldehyde, was significantly associated with asthma in a large cohort of children. This prompted an evaluation of this highly irritating chemical that had never previously been considered in the context of the indoor air/childhood asthma issue. Because acrolein is more potent than formaldehyde as a respiratory irritant and ubiquitous in indoor air, it is plausible that previous studies on potential risk factors and childhood asthma may be confounded by formaldehyde acting as an unrecognized proxy for acrolein.

A Potential Role for Acrolein in Neutrophil-Mediated Chronic Inflammation

Neutrophils (PMNs) are key mediators of inflammatory processes throughout the body. In this study, we investigated the role of acrolein, a highly reactive aldehyde that is ubiquitously present in the environment and produced endogenously at sites of inflammation, in mediating PMN-mediated degradation of collagen facilitating proline-glycine-proline (PGP) production. We treated peripheral blood neutrophils with acrolein and analyzed cell supernatants and lysates for matrix metalloproteinase-9 (MMP-9) and prolyl endopeptidase (PE), assessed their ability to break down collagen and release PGP, and assayed for the presence of leukotriene A4 hydrolase (LTA4H) and its ability to degrade PGP. Acrolein treatment induced elevated production and functionality of collagen-degrading enzymes and generation of PGP fragments. Meanwhile, LTA4H levels and triaminopeptidase activity declined with increasing concentrations of acrolein thereby sparing PGP from enzymatic destruction. These findings suggest that acrolein exacerbates the acute inflammatory response mediated by neutrophils and sets the stage for chronic pulmonary and systemic inflammation.

Airway hydration and COPD

Chronic obstructive pulmonary disease (COPD) is one of the prevalent causes of worldwide mortality and encompasses two major clinical phenotypes, i.e., chronic bronchitis (CB) and emphysema. The most common cause of COPD is chronic tobacco inhalation. Research focused on the chronic bronchitic phenotype of COPD has identified several pathological processes that drive disease initiation and progression. For example, the lung's mucociliary clearance (MCC) system performs the critical task of clearing inhaled pathogens and toxic materials from the lung. MCC efficiency is dependent on: (1) the ability of apical plasma membrane ion channels such as the cystic fibrosis transmembrane conductance regulator (CFTR) and the epithelial Na(+) channel (ENaC) to maintain airway hydration; (2) ciliary beating; and (3) appropriate rates of mucin secretion. Each of these components is impaired in CB and likely contributes to the mucus stasis/accumulation seen in CB patients. This review highlights the cellular components responsible for maintaining MCC and how this process is disrupted following tobacco exposure and with CB. We shall also discuss existing therapeutic strategies for the treatment of chronic bronchitis and how components of the MCC can be used as biomarkers for the evaluation of tobacco or tobacco-like-product exposure.

Integrity of airway epithelium in pediatric burn autopsies: Association with age and extent of burn injury

This study examines the structural integrity of the airway epithelium in autopsy tissues from pediatric burn subjects.

METHODS

A semi-quantitative score for the degree of airway epithelial integrity was made for seventy- two pediatric burn autopsies. Multivariate ordinal logistic regression was performed to identify relationships between epithelial integrity and conditions related to tissue fixation, time of death after injury, age, total body surface area burn (TBSA), extent of 3rd degree burn, presence of inhalation injury, ventilator days and pneumonia.

RESULTS

No significant difference in epithelial integrity scores was identified between burn only cases and those with inhalation injury. Significant correlations with bronchiolar epithelial integrity scores were identified for age, p=0.02, and percent 3rd degree burn, p=0.02. There was no significant relationship between epithelial integrity and time between death and autopsy, p>0.44.

CONCLUSIONS

Airway epithelial loss seen in autopsy tissue is not simply an artifact of tissue fixation. The degree of compromise correlates most strongly with age and degree of burn. Further studies are needed to identify physiological or critical care factors following burn injury that contribute to compromise in the structural and functional properties of the airway epithelium.

NCOA3-mediated upregulation of mucin expression via transcriptional and post-translational changes during the development of pancreatic cancer

Pancreatic cancer (PC) is characterized by aberrant overexpression of mucins that contribute to its pathogenesis. Although the inflammatory cytokines contribute to mucin overexpression, the mucin profile of PC is markedly distinct from that of normal or inflamed pancreas. We postulated that de novo expression of various mucins in PC involves chromatin modifications. Analysis of chromatin modifying enzymes by PCR array identified differential expression of NCOA3 in MUC4-expressing PC cell lines. Immunohistochemistry analysis in tumor tissues from patients and spontaneous mouse models, and microarray analysis following the knockdown of NCOA3 were performed to elucidate its role in mucin regulation and overall impact on PC. Silencing of NCOA3 in PC cell lines resulted in significant downregulation of two most differentially expressed mucins in PC, MUC4 and MUC1 (P<0.01). Immunohistochemistry analysis in PC tissues and metastatic lesions established an association between NCOA3 and mucin (MUC1 and MUC4) expression. Spontaneous mouse model of PC (K-ras(G12D); Pdx-1cre) showed early expression of Ncoa3 during pre-neoplastic lesions. Mechanistically, NCOA3 knockdown abrogated retinoic acid-mediated MUC4 upregulation by restricting MUC4 promoter accessibility as demonstrated by micrococcus nuclease digestion (P<0.05) and chromatin immuno-precipitation analysis. NCOA3 also created pro-inflammatory conditions by upregulating chemokines like CXCL1, 2, 5 and CCL20 (P<0.001). AKT, ubiquitin C, ERK1/2 and NF-κB occupied dominant nodes in the networks significantly modulated after NCOA3 silencing. In addition, NCOA3 stabilized mucins post translationally through fucosylation by FUT8, as the knockdown of FUT8 resulted in the downregulation of MUC4 and MUC1 at protein levels.

Mechanisms of cilia-driven transport in the airways in the absence of mucus

Airway mucus is thought to be required for the clearance of inhaled particles by mucociliary transport, but this view has recently been challenged. To test if mucus is necessary for cilia-driven particle transport, we removed mucus from murine and human ex vivo airway preparations by thorough rinsing with buffer with or without additional dithiothreitol washing. The transport of particles with diameters of 4.5 μm, 200 nm, and 40 nm and of bacteria was analyzed by video microscopy. Complete removal of mucus was verified by wheat germ agglutinin staining and by scanning electron microscopy. In the absence of mucus, we observed efficient transport of particles and bacteria by direct cilia-mediated propulsion or via fluid flow generated by ciliary beating. Virus-sized particles had the tendency to attach to cilia. Because direct contact of particles with ciliated cells occurs in the absence of mucus, we examined if this direct interaction changes epithelial function. Neither bacteria- nor LPS-induced nuclear translocation of NF-κB p65 in ciliated cells occurred, indicating that mere contact between ciliated cells and bacteria during transport does not activate the epithelium. Attachment of virus-sized particles to cilia could induce mucus release and/or increase the ciliary beat frequency. Our results indicate that cilia-driven transport of particles with various sizes is possible in murine and human airways without the presence of mucus. If mucus-free transport fails, the epithelium can react by releasing mucus or increasing the ciliary beat frequency to maintain particle transport.

Early-life exposure to combustion-derived particulate matter causes pulmonary immunosuppression

Elevated levels of combustion-derived particulate matter (CDPM) are a risk factor for the development of lung diseases such as asthma. Studies have shown that CDPM exacerbates asthma, inducing acute lung dysfunction and inflammation; however, the impact of CDPM exposure on early immunological responses to allergens remains unclear. To determine the effects of early-life CDPM exposure on allergic asthma development in infants, we exposed infant mice to CDPM and then induced a mouse model of asthma using house dust mite (HDM) allergen. Mice exposed to CDPM+HDM failed to develop a typical asthma phenotype including airway hyper-responsiveness, T-helper type 2 (Th2) inflammation, Muc5ac expression, eosinophilia, and HDM-specific immunoglobulin (Ig) compared with HDM-exposed mice. Although HDM-specific IgE was attenuated, total IgE was twofold higher in CDPM+HDM mice compared with HDM mice. We further demonstrate that CDPM exposure during early life induced an immunosuppressive environment in the lung, concurrent with increases in tolerogenic dendritic cells and regulatory T cells, resulting in the suppression of Th2 responses. Despite having early immunosuppression, these mice develop severe allergic inflammation when challenged with allergen as adults. These findings demonstrate a mechanism whereby CDPM exposure modulates adaptive immunity, inducing specific antigen tolerance while amplifying total IgE, and leading to a predisposition to develop asthma upon rechallenge later in life.

Vocal fold ion transport and mucin expression following acrolein exposure

The vocal fold epithelium is exposed to inhaled particulates including pollutants during breathing in everyday environments. Yet, our understanding of the effects of pollutants on vocal fold epithelial function is extremely limited. The objective of this study was to investigate the effect of the pollutant acrolein on two vocal fold epithelial mechanisms: ion transport and mucin (MUC) synthesis. These mechanisms were chosen as each plays a critical role in vocal defense and in maintaining surface hydration which is necessary for optimal voice production. Healthy, native porcine vocal folds (N = 85) were excised and exposed to an acrolein or sham challenge. A 60-min acrolein, but not sham challenge significantly reduced ion transport and inhibited cyclic adenosine monophosphate-dependent, increases in ion transport. Decreases in ion transport were associated with reduced sodium absorption. Within the same timeline, no significant acrolein-induced changes in MUC gene or protein expression were observed. These results improve our understanding of the effects of acrolein on key vocal fold epithelial functions and inform the development of future investigations that seek to elucidate the impact of a wide range of pollutant exposures on vocal fold health.

A modular cell-type focused inflammatory process network model for non-diseased pulmonary tissue

Exposure to environmental stressors such as cigarette smoke (CS) elicits a variety of biological responses in humans, including the induction of inflammatory responses. These responses are especially pronounced in the lung, where pulmonary cells sit at the interface between the body’s internal and external environments. We combined a literature survey with a computational analysis of multiple transcriptomic data sets to construct a computable causal network model (the Inflammatory Process Network (IPN)) of the main pulmonary inflammatory processes. The IPN model predicted decreased epithelial cell barrier defenses and increased mucus hypersecretion in human bronchial epithelial cells, and an attenuated pro-inflammatory (M1) profile in alveolar macrophages following exposure to CS, consistent with prior results. The IPN provides a comprehensive framework of experimentally supported pathways related to CS-induced pulmonary inflammation. The IPN is freely available to the scientific community as a resource with broad applicability to study the pathogenesis of pulmonary disease.

Barrier function of airway tract epithelium

Airway epithelium contributes significantly to the barrier function of airway tract. Mucociliary escalator, intercellular apical junctional complexes which regulate paracellular permeability and antimicrobial peptides secreted by the airway epithelial cells are the three primary components of barrier function of airway tract. These three components act cooperatively to clear inhaled pathogens, allergens and particulate matter without inducing inflammation and maintain tissue homeostasis. Therefore impairment of one or more of these essential components of barrier function may increase susceptibility to infection and promote exaggerated and prolonged innate immune responses to environmental factors including allergens and pathogens resulting in chronic inflammation. Here we review the regulation of components of barrier function with respect to chronic airways diseases.

Magnolol protects against oxidative stress-mediated neural cell damage by modulating mitochondrial dysfunction and PI3K/Akt signaling

Magnolol, an orally available compound from Magnolia officinalis used widely in traditional herbal medicine against a variety of neuronal diseases, possesses potent antioxidant properties and protects the brain against oxidative damage. The aim of the work is to examine the protective mechanisms of magnolol on human neuroblastoma SH-SY5Y cells against apoptosis induced by the neurotoxin acrolein, which can cause neurodegenerative disorders by inducing oxidative stress. By investigating the effect of magnolol on neural cell damage induced by the neurotoxin acrolein, we found that magnolol pretreatment significantly attenuated acrolein-induced oxidative stress through inhibiting reactive oxygen species accumulation caused by intracellular glutathione depletion and nicotinamide adenine dinucleotide phosphate oxidase activation. We next examined the signaling cascade(s) involved in magnolol-mediated antiapoptotic effects. The results showed that acrolein induced SH-SY5Y cell apoptosis by activating mitochondria/caspase and MEK/ERK signaling pathways. Our findings provide the first evidence that magnolol protects SH-SY5Y cells against acrolein-induced oxidative stress and prolongs SH-SY5Y cell survival through regulating JNK/mitochondria/caspase, PI3K/MEK/ERK, and PI3K/Akt/FoxO1 signaling pathways.

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.

The effects of acrolein on the thioredoxin system: implications for redox-sensitive signaling

The reactive aldehyde acrolein is a ubiquitous environmental pollutant and is also generated endogenously. It is a strong electrophile and reacts rapidly with nucleophiles including thiolates. This review focuses on the effects of acrolein on thioredoxin reductase (TrxR) and thioredoxin (Trx), which are major regulators of intracellular protein thiol redox balance. Acrolein causes irreversible effects on TrxR and Trx, which are consistent with the formation of covalent adducts to selenocysteine and cysteine residues that are key to their activity. TrxR and Trx are more sensitive than some other redox-sensitive proteins, and their prolonged inhibition could disrupt a number of redox-sensitive functions in cells. Among these effects are the oxidation of peroxiredoxins and the activation of apoptosis signal regulating kinase (ASK1). ASK1 promotes MAP kinase activation, and p38 activation contributes to apoptosis and a number of other acrolein-induced stress responses. Overall, the disruption of the TrxR/Trx system by acrolein could be significant early and prolonged events that affect many aspects of redox-sensitive signaling and oxidant stress.

A common MUC5B promoter polymorphism and pulmonary fibrosis

BACKGROUND

The mutations that have been implicated in pulmonary fibrosis account for only a small proportion of the population risk.

METHODS

Using a genomewide linkage scan, we detected linkage between idiopathic interstitial pneumonia and a 3.4-Mb region of chromosome 11p15 in 82 families. We then evaluated genetic variation in this region in gel-forming mucin genes expressed in the lung among 83 subjects with familial interstitial pneumonia, 492 subjects with idiopathic pulmonary fibrosis, and 322 controls. MUC5B expression was assessed in lung tissue.

RESULTS

Linkage and fine mapping were used to identify a region of interest on the p-terminus of chromosome 11 that included gel-forming mucin genes. The minor-allele of the single-nucleotide polymorphism (SNP) rs35705950, located 3 kb upstream of the MUC5B transcription start site, was present at a frequency of 34% among subjects with familial interstitial pneumonia, 38% among subjects with idiopathic pulmonary fibrosis, and 9% among controls (allelic association with familial interstitial pneumonia, P=1.2×10(-15); allelic association with idiopathic pulmonary fibrosis, P=2.5×10(-37)). The odds ratios for disease among subjects who were heterozygous and those who were homozygous for the minor allele of this SNP were 6.8 (95% confidence interval [CI], 3.9 to 12.0) and 20.8 (95% CI, 3.8 to 113.7), respectively, for familial interstitial pneumonia and 9.0 (95% CI, 6.2 to 13.1) and 21.8 (95% CI, 5.1 to 93.5), respectively, for idiopathic pulmonary fibrosis. MUC5B expression in the lung was 14.1 times as high in subjects who had idiopathic pulmonary fibrosis as in those who did not (P<0.001). The variant allele of rs35705950 was associated with up-regulation in MUC5B expression in the lung in unaffected subjects (expression was 37.4 times as high as in unaffected subjects homozygous for the wild-type allele, P<0.001). MUC5B protein was expressed in lesions of idiopathic pulmonary fibrosis.

CONCLUSIONS

A common polymorphism in the promoter of MUC5B is associated with familial interstitial pneumonia and idiopathic pulmonary fibrosis. Our findings suggest that dysregulated MUC5B expression in the lung may be involved in the pathogenesis of pulmonary fibrosis. (Funded by the National Heart, Lung, and Blood Institute and others.).

Induction of MUC5AC mucin by conjugated bile acids in the esophagus involves the phosphatidylinositol 3-kinase/protein kinase C/activator protein-1 pathway

BACKGROUND

Bile reflux contributes to the development of esophageal injury and neoplasia. The mucin 5AC (MUC5AC) is absent in the normal squamous epithelium of the esophagus but is strongly expressed in Barrett esophagus (BE). The objective of this study was to determine whether and how bile acids influence the expression of MUC5AC in the esophagus.

METHODS

MUC5AC expression was studied by immunohistochemistry and immunoblotting in human tissues, in tissues from a rat model of BE, and in SKGT-4 cultured esophageal epithelial cells. MUC5AC transcription was studied by real-time polymerase chain reaction and transient transfection assays.

RESULTS

MUC5AC was absent from normal squamous epithelium but was present in 100% of Barrett specimens and in 61.5% of human esophageal adenocarcinoma tissues that were examined. MUC5AC protein expression was induced to a greater degree by conjugated bile acids than by unconjugated bile acids, and this occurred at the transcriptional level. In the rat reflux model, MUC5AC mucin was expressed abundantly in tissues of BE stimulated by duodenoesophageal reflux. Conjugated bile acids induced AKT phosphorylation in SKGT-4 cells but had no effect on extracellular signal-regulated protein kinases 1 and 2, c-Jun N-terminal kinase, or protein-38 kinase phosphorylation. The phosphatidylinositol 3-kinase (PI3K) inhibitor LY294002 and a dominant-negative protein kinase C (AKT) construct prevented the induction of MUC5AC by conjugated bile acids. Transactivation of AP-1 by conjugated bile acids coincided with MUC5AC induction, and cotransfection with a dominant-negative activator protein-1 (AP-1) vector decreased MUC5AC transcription and its induction.

CONCLUSIONS

Conjugated bile acids in the bile refluxate contribute to MUC5AC induction in the esophagus. This occurs at the level of transcription and involves activation of the PI3K/AKT/AP-1 pathway.

Nicotine suppresses inflammatory factors in HBE16 airway epithelial cells after exposure to cigarette smoke extract and lipopolysaccharide

Cigarette smoke is a major cause of chronic inflammatory pulmonary disease, leading to inflammation, mucin (MUC) production, tissue damage, and remodeling. It is also well known that the major addictive component of cigarette smoke is nicotine. This study focused on the role of nicotine in the development of inflammatory pulmonary disease induced by cigarette smoke. HBE16 human airway epithelial cells were treated with serial dilutions of cigarette smoke chloroform extract (CE), lipopolysaccharide (LPS), and nicotine. The release of MUC5AC, tumor necrosis factor (TNF)-α, interleukin (IL)-8, and IL-6 protein were assayed by enzyme-linked immunosorbent assay. The MUC5AC protein also was observed by immunofluorescence. The expression of MUC5AC, TNF-α, IL-8, and IL-6 mRNA were detected by real-time polymerase chain reaction. We found that the mRNA of the proinflammatory mediators TNF-α, IL-8, and IL-6, as well as MUC5AC was highly expressed after CE and LPS stimulation. Nicotine did not cause an excessive expression of TNF-α, IL-8, and IL-6, nor did it affect protein production from the MUC5AC gene. Nicotine not only failed to stimulate production of TNF-α, IL-8, and IL-6, but its presence was shown to suppress the activation resulting from exposure to CE and LPS (P < 0.05). Preincubation with nicotine also would reduce the level of MUC5AC protein in culture supernatants of CE- and LPS-treated cells. However, mRNA expression of MUC5AC showed no significant change in nicotine-treated cells when compared with normal control cells. This distinctive pattern implies that nicotine may have potential to suppress airway inflammation and maintain the mucus over retention in airway secretory cells to some extent, thus forming a balance between mucus hyperproduction and hypersecretion in airways exposed to smoking and LPS.

Matrix metalloproteinase-14 mediates a phenotypic shift in the airways to increase mucin production

RATIONALE

Induced mainly by cigarette smoking, chronic obstructive pulmonary disease (COPD) is a global public health problem characterized by progressive difficulty in breathing and increased mucin production. Previously, we reported that acrolein levels found in COPD sputum could activate matrix metalloproteinase-9 (MMP9).

OBJECTIVES

To determine whether acrolein increases expression and activity of MMP14, a critical membrane-bound endopeptidase that can initial a MMP-activation cascade.

METHODS

MMP14 activity and adduct formation were measured following direct acrolein treatment. MMP14 expression and activity was measured in human airway epithelial cells. MMP14 immunohistochemistry was performed with COPD tissue, and in acrolein- or tobacco-exposed mice.

MEASUREMENTS AND MAIN RESULTS

In a cell-free system, acrolein, in concentrations equal to those found in COPD sputum, directly adducted cysteine 319 in the MMP14 hemopexin-like domain and activated MMP14. In cells, acrolein increased MMP14 activity, which was inhibited by a proprotein convertase inhibitor, hexa-d-arginine. In the airway epithelium of COPD subjects, immunoreactive MMP14 protein increased. In mouse lung, acrolein or tobacco smoke increased lung MMP14 activity and protein. In cells, acrolein-induced MMP14 transcripts were inhibited by an epidermal growth factor receptor (EGFR) neutralizing antibody, EGFR kinase inhibitor, metalloproteinase inhibitor, or mitogen-activated protein kinase (MAPK) 3/2 or MAPK8 inhibitors, but not a MAPK14 inhibitor. Decreasing the MMP14 protein and activity in vitro by small interfering (si)RNA to MMP14 diminished the acrolein-induced MUC5AC transcripts. In acrolein-exposed mice or transgenic mice with lung-specific transforming growth factor-alpha (an EGFR ligand) expression, lung MMP14 and MUC5AC levels increased and these effects were inhibited by a EGFR inhibitor, erlotinib.

CONCLUSIONS

Taken together, these findings implicate acrolein-induced MMP14 expression and activity in mucin production in COPD.

MKP1 regulates the induction of MUC5AC mucin by Streptococcus pneumoniae pneumolysin by inhibiting the PAK4-JNK signaling pathway

Mucosal epithelial cells in the respiratory tract act as the first line of host innate defense against inhaled microbes by producing a range of molecules for clearance. In particular, epithelial mucins facilitate the mucociliary clearance by physically trapping the inhaled microbes. Up-regulation of mucin production thus represents an important host innate defense response against invading microbes. Excess mucin production, however, overwhelms the mucociliary clearance, resulting in defective mucosal defenses. Thus, tight regulation of mucin production is critical for maintaining an appropriate balance between beneficial and detrimental outcomes. Among various mechanisms, negative regulation plays an important role in tightly regulating mucin production. Here we show that the PAK4-JNK signaling pathway acted as a negative regulator for Streptococcus pneumoniae pneumolysin-induced MUC5AC mucin transcription. Moreover pneumolysin also selectively induced expression of MKP1 via a TLR4-dependent MyD88-TRAF6-ERK signaling pathway, which inhibited the PAK4-JNK signaling pathway, thereby leading to up-regulation of MUC5AC mucin production to maintain effective mucosal protection against S. pneumoniae infection. These studies provide novel insights into the molecular mechanisms underlying the tight regulation of mucin overproduction in the pathogenesis of airway infectious diseases and may lead to development of new therapeutic strategies.

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.

Emerging role of MAP kinase pathways as therapeutic targets in COPD

Studies examining the cellular mechanisms of inflammation and protease production in the lung tissue and airways of COPD patients have shed light on the important role of kinase-based signaling cascades. These pathways can be activated by environmental stimuli such as tobacco smoke, and by endogenous signals such as cytokines, growth factors, and inflammation-derived oxidants. The three most widely characterized cascades are those directed by the classical mitogen activated protein (MAP) kinase (ERK1/2), stress activated protein kinase/c-Jun N-terminal protein kinase, and p38 enzymes. These phosphorylation cascades transmit and amplify extracellular, receptor-mediated signals through the cytoplasm of the cell to activate nuclear transcription factors which bind and induce expression of target genes. The result is tight control of diverse cellular events, and rapid responses to external stimuli. However, recent research suggests that constitutive or aberrant activation of MAP kinases contributes to several COPD-associated phenotypes, including mucus overproduction and secretion, inflammation, cytokine expression, apoptosis, T cell activation, matrix metalloproteinase production, and fibrosis. This review explores the biological functions of the MAP kinase pathways in the pathogenesis of COPD, their activation by cigarette smoke, and discusses the potential role of MAP kinase inhibitors in COPD therapy.

The expression of MUC5AC and MUC5B mucin genes in the mucosa of chronic rhinosinusitis and nasal polyposis

BACKGROUND

The aim of this study was to investigate the expression of MUC5AC and MUC5B messenger RNAs (mRNAs) and localization of these proteins in human sinus mucosa of chronic rhinosinusitis (CRS) and CRS with nasal polyposis (CRS/NP).

METHODS

Maxillary sinus ostia mucosa was harvested from patients undergoing endoscopic sinus surgery for CRS, CRS/NP, and non-CRS pathologies (control). Then, sinus mucosa was analyzed using reverse-transcription polymerase chain reaction to detect mRNA of MUC5AC and MUC5B. Hematoxylin and eosin staining and immunofluorescent staining were used to localize MUC5AC and MUC5B proteins in the sinus mucosa.

RESULTS

mRNAs of MUC5AC and MUC5B in the sinus mucosa of CRS and CRS/NP were significantly increased compared with that in normal sinus mucosa (p < 0.01), and no significant difference was found between the mucosa of CRS and that of CRS/NP (p > 0.05). MUC5AC protein was expressed mainly in the goblet cells, and MUC5B expression was located in the submucosal glands cells and the epithelia of sinus mucosa. ARPC in staining of MUC5AC and MUC5B were found no different between the CRS group and the CRS/NP group (p > 0.05), whereas they were significantly lower in the normal group compared with the other two groups, respectively (p < 0.05).

CONCLUSION

This study showed that MUC5AC and MUC5B mucin genes were up-regulated in sinus mucosa of CRS and CRS/NP. MUC5AC and MUC5B may play an important role in the pathogenesis of CRS and NP.

Mucin overproduction in chronic inflammatory lung disease

Mucus overproduction and hypersecretion are commonly observed in chronic inflammatory lung disease. Mucins are gel-forming glycoproteins that can be stimulated by a variety of mediators. The present review addresses the mechanisms involved in the upregulation of secreted mucins. Mucin induction by neutrophil elastase, bacteria, cytokines, growth factors, smoke and cystic fibrosis transmembrane conductance regulator malfunction are also discussed.

Functional analysis of human MUC7 mucin gene 5'-flanking region in lung epithelial cells

The human MUC7 gene encodes a low-molecular-mass mucin glycoprotein that functions in modulation of microbial flora in the oral cavity and respiratory tracts. MUC7 gene expression is tissue- and cell-specific, with dominant expression in salivary gland acinar cells. To begin to understand the molecular mechanisms responsible for controlling MUC7 gene expression, we analyzed the promoter activity of MUC7 5'-flanking region in a human lung epithelial cell line A549. We demonstrated that MUC7 gene is expressed constitutively in this cell line and is upregulated by TNF-alpha stimulation. The promoter activities of a 2,762-bp fragment of the human genomic DNA (-2,732/+30 bp) and its deletion series, subcloned into a luciferase reporter vector, were characterized at the basal level and under stimulation by TNF-alpha. The results indicated that the minimal functional MUC7 promoter is in the region of -138/+30 bp. This region also revealed the greatest increase in the promoter activity upon TNF-alpha stimulation. Two putative AP1-binding elements and one NF-kappaB-binding element were identified within the proximal promoter. Further analyses demonstrated that mutations of these elements dramatically reduced specific DNA-protein binding ability and reporter gene expression. AP1 elements played an essential role in the constitutive expression, while the NF-kappaB element was crucially important in the response to TNF-alpha stimulation, demonstrating that TNF-alpha activates MUC7 transcription via NF-kappaB signaling pathway.

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.

Regulation of mucin genes in chronic inflammatory airway diseases

In this review, we summarize work over the past 15 years on mucin gene expression and regulation in the lung, as well as how mucin gene expression is altered in chronic lung diseases. This field owes a great debt to Carol Basbaum for her pioneering work in dissecting signaling pathways regulating mucin gene expression and for her tremendous energy in promoting the importance of understanding the basic pathogenic mechanisms that drive mucus overproduction in cystic fibrosis, chronic obstructive pulmonary disease, and asthma.

Metalloproteinases mediate mucin 5AC expression by epidermal growth factor receptor activation

Chronic obstructive pulmonary disease is marked by alveolar enlargement and excess production of airway mucus. Acrolein, a component of cigarette smoke, increases mucin 5AC (MUC5AC), a prevalent airway mucin in NCI-H292 cells by transcriptional activation, but the signal transduction pathways involved in acrolein-induced MUC5AC expression are unknown. Acrolein depleted cellular glutathione at doses of 10 muM or greater, higher than those sufficient (0.03 muM) to increase MUC5AC mRNA, suggesting that MUC5AC expression was independent of oxidative stress. In contrast, acrolein increased MUC5AC mRNA levels by phosphorylating epidermal growth factor receptor (EGFR) and mitogen-activated protein kinase 3/2, or MAPK 3/2(ERK1/2). Pretreating the cells with an EGFR-neutralizing antibody, or a metalloproteinase inhibitor, decreased the acrolein-induced MUC5AC mRNA increase. Small, interfering RNA directed against ADAM17 or MMP9 inhibited the acrolein-induced MUC5AC mRNA increase. Acrolein increased the release and subsequent activation of pro-MMP9. Acrolein increased MMP9 and decreased tissue inhibitor of metalloproteinase 3 (TIMP3), an endogenous inhibitor of ADAM17, transcripts. Together, these data suggest that acrolein induces MUC5AC expression via an initial ligand-dependent activation of EGFR mediated by ADAM17 and MMP9. In addition, a prolonged effect of acrolein may be mediated by altering MMP9 and TIMP3 transcription.

Regulation of MUC5AC mucin secretion and airway surface liquid metabolism by IL-1beta in human bronchial epithelia

Mucociliary transport in the airways significantly depends on the liquid and mucin components of the airway surface liquid (ASL). The regulation of ASL water and mucin content during pathological conditions is not well understood. We hypothesized that airway epithelial mucin production and liquid transport are regulated in response to inflammatory stimuli and tested this hypothesis by investigating the effects of the pleiotropic, early-response cytokine, IL-1beta, on cultured primary human bronchial epithelial and second-passage, normal human tracheo-bronchial epithelial (NHTBE) cell cultures. Fully differentiated NHTBE cultures secreted two major airway mucins, MUC5AC and MUC5B. IL-1beta, in a dose- and time-dependent manner, increased the secretion of MUC5AC, but not MUC5B. MUC5AC mRNA levels were only transiently increased at 1 and 4 h after the start of IL-1beta treatment and returned to control levels thereafter, even though MUC5AC mucin production remained elevated for at least 72 h. Synchronous with elevated MUC5AC secretion, ASL volume increased, its percentage of solid was reduced, and the pH/[HCO(3)(-)] of the ASL was elevated. ASL volume changes reflected altered ion transport, including an upregulation of Cl(-) secretory currents (via CFTR and Ca(2+)-activated Cl(-) conductance) and an inhibition of epithelial sodium channel (ENaC)-mediated absorptive Na(+) currents. IL-1beta increased CFTR mRNA levels without affecting those for ENaC subunits. The synchronous regulation of ASL mucin and liquid metabolism triggered by IL-1beta may be an important defense mechanism of the airway epithelium to enhance mucociliary clearance during airway inflammation.

Clarithromycin inhibits overproduction of muc5ac core protein in murine model of diffuse panbronchiolitis

Long-term treatment of macrolide antibiotics is considered an effective treatment for diffuse panbronchiolitis (DPB). Although hypersecretion is a common feature of this disease, and it is known that macrolides inhibit mucin production, the mechanism of the effect on mucin production is unclear. The aim of our study was to determine the production of muc5ac core protein, a major core protein of mucin in airway secretion, and the effect of clarithromycin treatment on such production in a mouse model mimicking DPB. Alcian blue-periodic acid-Schiff-positive cells were detected in the lungs of Pseudomonas aeruginosa-infected mice. Western blots of these mice showed muc5ac glycoprotein at day 1 and increased progressively from day 4 to day 14 after inoculation of bacteria. Clarithromycin (10 mg. kg-1. day-1 for 7 days) significantly reduced the muc5ac expression at both the mRNA and protein levels. To investigate the role of molecules upstream in muc5ac regulation, we examined the role of mitogen-activated protein kinase. Extracellular signal-regulated kinase 1/2 phosphorylation increased in the infected lung and decreased after treatment. Our results suggest that overproduction of muc5ac plays an important role in the pathogenesis of DPB and that clinical improvement following macrolide therapy seems to involve, at least in part, its inhibition of mucin overproduction, through modulation of intracellular signal transduction.

Neutrophil elastase increases MUC4 expression in normal human bronchial epithelial cells

In chronic obstructive pulmonary diseases, the airway epithelium is chronically exposed to neutrophil elastase, an inflammatory protease. The cellular response to neutrophil elastase dictates the balance between epithelial injury and repair. Key regulators of epithelial migration and proliferation are the ErbB receptor tyrosine kinases, including the epidermal growth factor receptor. In this context, we investigated whether neutrophil elastase may regulate expression of MUC4, a membrane-tethered mucin that has recently been identified as a ligand for ErbB2, the major heterodimerization partner of the epidermal growth factor receptor. In normal human bronchial epithelial cells, neutrophil elastase increased MUC4 mRNA levels in both a concentration- and time-dependent manner. RNA stability assays revealed that neutrophil elastase increased MUC4 mRNA levels by prolonging the mRNA half-life from 5 to 21 h. Neutrophil elastase also increased MUC4 glycoprotein levels as determined by Western analysis, using a monoclonal antibody specific for a nontandem repeat MUC4 sequence. Therefore, airway epithelial cells respond to neutrophil elastase exposure by increasing expression of MUC4, a potential activator of epithelial repair mechanisms.

Human airway mucin glycosylation: a combinatory of carbohydrate determinants which vary in cystic fibrosis

Human airway mucins represent a very broad family of polydisperse high molecular mass glycoproteins, which are part of the airway innate immunity. Apomucins, which correspond to their peptide part, are encoded by at least 6 different mucin genes (MUC1, MUC2, MUC4, MUC5B, MUC5AC and MUC7). The expression of some of these genes (at least MUC2 and MUC5AC) is induced by bacterial products, tobacco smoke and different cytokines. Human airway mucins are highly glycosylated (70-80% per weight). They contain from one single to several hundred carbohydrate chains. The carbohydrate chains that cover the apomucins are extremely diverse, adding to the complexity of these molecules. Structural information is available for more than 150 different O-glycan chains corresponding to the shortest chains (less than 12 sugars). The biosynthesis of these carbohydrate chains is a stepwise process involving many glycosyl- or sulfo-transferases. The only structural element shared by all mucin O-glycan chains is a GalNAc residue linked to a serine or threonine residue of the apomucin. There is growing evidence that the apomucin sequences influence the first glycosylation reactions. The elongation of the chains leads to various linear or branched extensions. Their non-reducing end, which corresponds to the termination of the chains, may bear different carbohydrate structures, such as histo-blood groups A or B determinants, H and sulfated H determinants, Lewis a, Lewis b, Lewis x or Lewis y epitopes, as well as sialyl- or sulfo- (sometimes sialyl- and sulfo-) Lewis a or Lewis x determinants. The synthesis of these different terminal determinants involves three different pathways with a whole set of glycosyl- and sulfo-transferases. Due to their wide structural diversity forming a combinatory of carbohydrate determinants as well as their location at the surface of the airways, mucins are involved in multiple interactions with microorganisms and are very important in the protection of the underlying airway mucosa. Airway mucins are oversulfated in cystic fibrosis and this feature has been considered as being linked to a primary defect of the disease. However, a similar pattern is observed in mucins from patients suffering from chronic bronchitis when they are severely infected. Airway mucins from severely infected patients suffering either from cystic fibrosis or from chronic bronchitis are also highly sialylated, and highly express sialylated and sulfated Lewis x determinants, a feature which may reflect severe mucosal inflammation or infection. These determinants are potential sites of attachment for Pseudomonas aeruginosa, the pathogen responsible for most of the morbidity and mortality in cystic fibrosis, and the expression of the sulfo- and glycosyl-transferases involved in their biosynthesis is increased by TNFalpha. In summary, airway inflammation may simultaneously induce the expression of mucin genes (MUC2 and MUC5AC) and the expression of several glycosyl- and sulfo-transferases, therefore modifying the combinatory glycosylation of these molecules.

Mechanisms of allergic rhinitis

The pathogenesis of allergic rhinitis can be better appreciated by understanding the numerous protective mechanisms available for mucosal defense. The system of TH2 lymphocytes, IgE production, mast cell degranulation, eosinophil infiltration, and resident cell responses are central to our understanding and treatment of allergic rhinitis. Histamine remains preeminent in causing the cardinal symptoms of the immediate allergic reaction: itching, watery discharge, and nasal swelling. Recruitment and activation mechanisms responsible for the late-phase allergic response are also reviewed.

Expression of mucin genes in chronic ethmoiditis

We have investigated the profiles of MUC genes expressed in chronic ethmoiditis mucosa and normal ethmoid mucosa using RT-PCR, and the morphology of chronic ethmoiditis by a combination of light and electron microscope was observed. In the light- and electron-microscopic studies, chronic ethmoiditis mucosa revealed increased numbers of goblet cells with higher production of mucus in comparison to normal ethmoid mucosa. RT-PCR of cDNAs from three normal ethmoid mucosa revealed the same pattern of mucin gene expression, such as MUC5AC and MUC8. However, RT-PCR of cDNAs from eight chronic ethmoiditis mucosa showed the expression of two MUC1, six MUC4, eight MUC5AC, five MUC5B, seven MUC7, and eight MUC8. MUC2 and MUC6 were not detected. These results suggest that MUC4, MUC5AC, MUC5B, MUC7, and MUC8 are major mucins in the ethmoid mucosa and are up-regulated by chronic inflammation.