Restoration of the mucous phenotype by retinoic acid in retinoid-deficient human bronchial cell cultures: changes in mucin gene expression

Advances in regulation of homeostasis through chromatin modifications by airway commensals

Commensal bacteria are residents of the human airway where they interact with both colonizing pathogens and host respiratory epithelial cells of this mucosal surface. It is here that commensals exert their influence through host signaling cascades, host transcriptional responses and host immunity, all of which are rooted in chromatin remodeling and histone modifications. Recent studies show that airway commensals impact host chromatin, but compared the what is known for gut commensals, the field remains in its infancy. The mechanisms by which airway commensals regulate respiratory health and homeostasis through chromatin modifications is of increasing interest, specifically since their displacement precedes the increased potential for respiratory disease. Herein we will discuss recent advances and intriguing avenues of future work aimed at deciphering how airway commensals protect and influence respiratory health.

Bovine Airway Models: Approaches for Investigating Bovine Respiratory Disease

Bovine respiratory disease (BRD) is a multifactorial condition where different genera of bacteria, such as Mannheimia haemolytica, Histophilus somni, Pasteurella multocida, and Mycoplasma bovis, and viruses, like bovine respiratory syncytial virus, bovine viral diarrhea virus, and bovine herpes virus-1, infect the lower respiratory tract of cattle. These pathogens can co-infect cells in the respiratory system, thereby making specific treatment very difficult. Currently, the most common models for studying BRD include a submerged tissue culture (STC), where monolayers of epithelial cells are typically covered either in cellular or spent biofilm culture medium. Another model is an air-liquid interface (ALI), where epithelial cells are exposed on their apical side and allowed to differentiate. However, limited work has been reported on the study of three-dimensional (3D) bovine models that incorporate multiple cell types to represent the architecture of the respiratory tract. The roles of different defense mechanisms in an infected bovine respiratory system, such as mucin production, tight junction barriers, and the production of antimicrobial peptides in in vitro cultures require further investigation in order to provide a comprehensive understanding of the disease pathogenesis. In this report, we describe the different aspects of BRD, including the most implicated pathogens and the respiratory tract, which are important to incorporate in disease models assembled in vitro. Although current advancements of bovine respiratory cultures have led to knowledge of the disease, 3D multicellular organoids that better recapitulate the in vivo environment exhibit potential for future investigations.

Morphologically intact airways in lung fibrosis have an abnormal proteome

Honeycombing is a histological pattern consistent with Usual Interstitial Pneumonia (UIP). Honeycombing refers to cystic airways located at sites of dense fibrosis with marked mucus accumulation. Utilizing laser capture microdissection coupled mass spectrometry (LCM-MS), we interrogated the fibrotic honeycomb airway cells and fibrotic uninvolved airway cells (distant from honeycomb airways and morphologically intact) in specimens from 10 patients with UIP. Non-fibrotic airway cell specimens from 6 patients served as controls. Furthermore, we performed LCM-MS on the mucus plugs found in 6 patients with UIP and 6 patients with mucinous adenocarcinoma. The mass spectrometry data were subject to both qualitative and quantitative analysis and validated by immunohistochemistry. Surprisingly, fibrotic uninvolved airway cells share a similar protein profile to honeycomb airway cells, showing deregulation of the slit and roundabout receptor (Slit and Robo) pathway as the strongest category. We find that (BPI) fold-containing family B member 1 (BPIFB1) is the most significantly increased secretome-associated protein in UIP, whereas Mucin-5AC (MUC5AC) is the most significantly increased in mucinous adenocarcinoma. We conclude that fibrotic uninvolved airway cells share pathological features with fibrotic honeycomb airway cells. In addition, fibrotic honeycomb airway cells are enriched in mucin biogenesis proteins with a marked derangement in proteins essential for ciliogenesis. This unbiased spatial proteomic approach generates novel and testable hypotheses to decipher fibrosis progression.

LRAT coordinates the negative-feedback regulation of intestinal retinoid biosynthesis from β-carotene

There is increasing recognition that dietary lipids can affect the expression of genes encoding their metabolizing enzymes, transporters, and binding proteins. This mechanism plays a pivotal role in controlling tissue homeostasis of these compounds and avoiding diseases. The regulation of retinoid biosynthesis from β-carotene (BC) is a classic example for such an interaction. The intestine-specific homeodomain transcription factor (ISX) controls the activity of the vitamin A-forming enzyme β-carotene oxygenase-1 in intestinal enterocytes in response to increasing concentration of the vitamin A metabolite retinoic acid. However, it is unclear how cells control the concentration of the signaling molecule in this negative-feedback loop. We demonstrate in mice that the sequestration of retinyl esters by the enzyme lecithin:retinol acyltransferase (LRAT) is central for this process. Using genetic and pharmacological approaches in mice, we observed that in LRAT deficiency, the transcription factor ISX became hypersensitive to dietary vitamin A and suppressed retinoid biosynthesis. The dysregulation of the pathway resulted in BC accumulation and vitamin A deficiency of extrahepatic tissues. Pharmacological inhibition of retinoid signaling and genetic depletion of the Isx gene restored retinoid biosynthesis in enterocytes. We provide evidence that the catalytic activity of LRAT coordinates the negative-feedback regulation of intestinal retinoid biosynthesis and maintains optimal retinoid levels in the body.

Impact of vitamin A transport and storage on intestinal retinoid homeostasis and functions

Lecithin:retinol acyltransferase and retinol-binding protein enable vitamin A (VA) storage and transport, respectively, maintaining tissue homeostasis of retinoids (VA derivatives). The precarious VA status of the lecithin:retinol acyltransferase-deficient (Lrat-/-) retinol-binding protein-deficient (Rbp-/-) mice rapidly deteriorates upon dietary VA restriction, leading to signs of severe vitamin A deficiency (VAD). As retinoids impact gut morphology and functions, VAD is often linked to intestinal pathological conditions and microbial dysbiosis. Thus, we investigated the contribution of VA storage and transport to intestinal retinoid homeostasis and functionalities. We showed the occurrence of intestinal VAD in Lrat-/-Rbp-/- mice, demonstrating the critical role of both pathways in preserving gut retinoid homeostasis. Moreover, in the mutant colon, VAD resulted in a compromised intestinal barrier as manifested by reduced mucins and antimicrobial defense, leaky gut, increased inflammation and oxidative stress, and altered mucosal immunocytokine profiles. These perturbations were accompanied by fecal dysbiosis, revealing that the VA status (sufficient vs. deficient), rather than the amount of dietary VA per se, is likely a major initial discriminant of the intestinal microbiome. Our data also pointed to a specific fecal taxonomic profile and distinct microbial functionalities associated with VAD. Overall, our findings revealed the suitability of the Lrat-/-Rbp-/- mice as a model to study intestinal dysfunctions and dysbiosis promoted by changes in tissue retinoid homeostasis induced by the host VA status and/or intake.

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.

Fenretinide favorably affects mucins (MUC5AC/MUC5B) and fatty acid imbalance in a manner mimicking CFTR-induced correction

Cystic fibrosis (CF) is the most common genetic disease in Caucasians. CF is manifested by abnormal accumulation of mucus in the lungs, which serves as fertile ground for the growth of microorganisms leading to recurrent infections and ultimately, lung failure. Mucus in CF patients consists of DNA from dead neutrophils as well as mucins produced by goblet cells. MUC5AC mucin leads to pathological plugging of the airways whereas MUC5B has a protective role against bacterial infection. Therefore, decreasing the level of MUC5AC while maintaining MUC5B intact would in principle be a desirable mucoregulatory treatment outcome. Fenretinide prevented the lipopolysaccharide-induced increase of MUC5AC gene expression, without affecting the level of MUC5B, in a lung goblet cell line. Additionally, fenretinide treatment reversed the pro-inflammatory imbalance of fatty acids by increasing docosahexaenoic acid and decreasing the levels of arachidonic acid in a lung epithelial cell line and primary leukocytes derived from CF patients. Furthermore, for the first time we also demonstrate the effect of fenretinide on multiple unsaturated fatty acids, as well as differential effects on the levels of long- compared to very-long-chain saturated fatty acids which are important substrates of complex phospholipids. Finally, we demonstrate that pre-treating mice with fenretinide in a chronic model of P. aeruginosa lung infection efficiently decreases the accumulation of mucus. These findings suggest that fenretinide may offer a new approach to therapeutic modulation of pathological mucus production in CF.

Impact of Micronutrients on the Immune Response of Animals

Vitamins and minerals (micronutrients) play an important role in regulating and shaping an immune response. Deficiencies generally result in inadequate or dysregulated cellular activity and cytokine expression, thereby affecting the immune response. Decreased levels of natural killer, granulocyte, and phagocytic cell activity and T and B cell proliferation and trafficking are associated with inadequate levels of micronutrients, as well as increased susceptibility to various adverse health conditions, including inflammatory disorders, infection, and altered vaccine efficacy. In addition, most studies of micronutrient modulation of immune responses have been done in rodents and humans, thus limiting application to the health and well-being of livestock and companion animals. This exploratory review elucidates the role of vitamins and minerals on immune function and inflammatory responses in animals (pigs, dogs, cats, horses, goats, sheep, and cattle), with reference to rodents and humans.

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

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

Transcriptomic profiling revealed the signatures of intestinal barrier alteration and pathogen entry in turbot (Scophthalmus maximus) following Vibrio anguillarum challenge

The mucosal immune system serves as the frontline barriers of host defense against pathogen infection, especially for the fishes, which are living in the pathogen rich aquatic environment. The intestine constitutes the largest surface body area in constantly contact with the external pathogens, and plays a vital role in the immune defense against inflammation and pathogen infection. Previous studies have revealed that fish intestine might serves as the portal of entry for Vibrio anguillarum. To characterize the immune actors and their associated immune activities in turbot intestine barrier during bacterial infection, here we examined the gene expression profiles of turbot intestine at three time points following experimental infection with V. anguillarum utilizing RNA-seq technology. A total of 122 million reads were assembled into 183,101 contigs with an average length of 1151 bp and the N50 size of 2302 bp. Analysis of differential gene expression between control and infected samples at 1 h, 4 h, and 12 h revealed 2079 significantly expressed genes. Enrichment and pathway analysis of the differentially expressed genes showed the centrality of the pathogen attachment and recognition, antioxidant/apoptosis, mucus barrier modification and immune activation/inflammation in the pathogen entry and host immune responses. The present study reported the novel gene expression patterns in turbot mucosal immunity, which were overlooked in previous studies. Our results can help to understand the mechanisms of turbot host defense, and may also provide foundation to identify the biomarkers for future selection of disease-resistant broodstock and evaluation of disease prevention and treatment options.

Math1, retinoic acid, and TNF-α synergistically promote the differentiation of mucous cells in mouse middle ear epithelial cells in vitro

BACKGROUND

A key issue in otitis media (OM) is mucous cell metaplasia in the middle ear mucosa, a condition for hyperproduction of mucus in the middle ear mucosa and development of chronic OM. However, little is known about the driving force for the differentiation of mucous cells in OM.

METHODS

Mouse middle ear epithelial cells (mMEECs) were used in this study to test whether Math1, a critical transcription factor for the development of mucous cells in the intestine, synergizes with inflammatory cytokines (tumor necrosis factor-α (TNF-α)) and other epithelial differentiation factors (retinoid acid (RA)) to induce the differentiation of mMEECs into mucus-like cells in vitro. Simultaneously, Math1 was transduced into the middle ear mucosa in order to observe whether it induces mucous cell hyperplasia in vivo.

RESULTS

Math1 significantly increased the mucus cell numbers in the middle ear mucosa of mice. Math1, in the presence of TNF-α and epithelial differentiation factor RA, synergistically promoted the differentiation of mMEECs into mucus-like cells through upregulation of mucins and their chaperones: trefoil factors in vitro. RA treatment for 12 h activated Math1, although RA alone had very limited effects on mucus-like cell differentiation.

CONCLUSION

Math1 plays a critical role in the pathogenesis of OM by induction of mucous cell differentiation in the presence of TNF-α and RA.

Basal polarization of the mucosal compartment in Flavobacterium columnare susceptible and resistant channel catfish (Ictalurus punctatus)

The freshwater bacterial pathogen, Flavobacterium columnare, infects a variety of ornamental and farmed fish species worldwide through mucosal attachment points on the gill and skin. While previous studies have demonstrated a chemotactic response of F. columnare to fish mucus, little is known about how host gill mucosal molecular and cellular constituents may impact rates of adhesion, tissue invasion, and ultimately, mortality. Here, we describe the use of RNA-seq to profile gill expression differences between channel catfish (Ictalurus punctatus) differing in their susceptibility to F. columnare both basally (before infection) and at three early timepoints post-infection (1 h, 2 h, and 8 h). After sequencing and de novo assembly of over 350 million 100 base-pair transcript reads, between group comparisons revealed 1714 unique genes differentially expressed greater than 1.5-fold at one or more timepoints. In the large dataset, we focused our analysis on basal differential expression between resistant and susceptible catfish as these genes could potentially reveal genetic and/or environmental factors linked with differential rates of infection. A number of critical innate immune components including iNOS2b, lysozyme C, IL-8, and TNF-alpha were constitutively higher in resistant catfish gill, while susceptible fish showed high expression levels of secreted mucin forms, a rhamnose-binding lectin previously linked to susceptibility, and mucosal immune factors such as CD103 and IL-17. Taken together, the immune and mucin profiles obtained by RNA-seq suggest a basal polarization in the gill mucosa, with susceptible fish possessing a putative mucosecretory, toleragenic phenotype which may predispose them to F. columnare infection.

Increased mucociliary differentiation and aquaporins formation of respiratory epithelial cells on retinoic acid-loaded hyaluronan-derivative membranes

While playing a major role in maintaining the mucociliary phenotype of respiratory epithelial cells (RECs), retinoids are critical determinants of their normal function. However, despite being a powerful biological agent, retinoic acid (RA) is generally not used in regenerative medicine due to its scarce bioavailability via conventional administration. Therefore, the ability to incorporate RA into biomaterials allows for a combination of the biological effects of RA and biomaterials in influencing cellular behavior. This study attempts to develop RA-loaded hyaluronan-derivative membrane (RA-HAm) and investigates how this membrane affects the mucociliary differentiation and aquaporins (AQP) formation of RECs. In a simulated in vitro culture condition, the RA release from membranes is maintained for 7days. On the seventh day, the cumulative release rate of RA from supportive biomaterials is ~87% under detect limitation. RECs cultured on RA-HAm reveal numerous mature ciliated cells and microvilli compared to aggregated cilia-like structures on hyaluronan-derivative membrane (HAm). Moreover, the expression levels of MUC5AC and AQP on RA-HAm are higher than those on HAm. The proposed model elucidates the release of hydrophobic RA from hyaluronan-derivative biomaterials. We believe that RA-loaded hyaluronan biomaterials are highly promising biomaterials for use in sinonasal surgery and tissue engineering of the respiratory system.

Midkine is part of the antibacterial activity released at the surface of differentiated bronchial epithelial cells

To resist infections, robust defense mechanisms of the airways are essential. Retinoic acid promotes differentiation and maintains the phenotypic characteristics of bronchial epithelium. In addition, it induces the expression of the antibacterial growth factor midkine (MK). In the present study, we explored the expression and antibacterial activity of MK in an airway context. MK was detected in bronchial epithelial cells of large airways and type 2 pneumocytes of normal lungs by immunohistochemistry. Immunoelectron microscopy revealed a surface-associated distribution, both on the ciliated apical and basolateral sides, and MK was detected in sputum obtained from healthy individuals by ELISA. In vitro, MK killed the common respiratory pathogen Streptococcus pneumoniae at below micromolar concentrations, an activity retained in the presence of sodium chloride at physiological concentrations. The MK molecule consists of two domains with three anti-parallel β-sheets and a COOH-terminal tail. Although both the NH2- and COOH-terminal domains alone showed antibacterial activity, the COOH-terminal domain including the tail region possessed higher bactericidal activity, i.e. in the order of the holoprotein. Retinoic acid-induced differentiation of primary bronchial epithelial cells, using an air-liquid interface system, revealed bactericidal activity in the apical airway surface liquid, an activity that was reduced after immunoprecipitation of MK. This study shows that airway epithelial cells of large airways and alveoli have a constitutive production of MK that is part of the bactericidal activity present in the air surface liquid, at least in vitro, and may thus be an important part of this arm of airway host defense.

Macrophages are related to goblet cell hyperplasia and induce MUC5B but not MUC5AC in human bronchus epithelial cells

Airway goblet cell hyperplasia (GCH)--detectable by mucin staining--and abnormal macrophage infiltrate are pathological features present in many chronic respiratory disorders. However, it is unknown if both factors are associated. Using in-vivo and in-vitro models, we investigated whether macrophages are related with GCH and changes in mucin immunophenotypes. Lung sections from Sprague-Dawley rats treated for 48 h with one intra-tracheal dose of PBS or LPS (n=4-6 per group) were immunophenotyped for rat-goblet cells, immune, and proliferation markers. Human monocyte-derived macrophages (MDM) were pre-treated with or without LPS, immunophenotyped, and their supernatant, as well as cytokines at levels equivalent to supernatant were used to challenge primary culture of normal human bronchus epithelial cells (HBEC) in air-liquid interface, followed by MUC5B and MUC5AC mucin immunostaining. An association between increased bronchiolar goblet cells and terminal-bronchiolar proliferative epithelial cells confirmed the presence of GCH in our LPS rat model, which was related with augmented bronchiolar CD68 macrophage infiltration. The in-vitro experiments have shown that MUC5AC phenotype was inhibited when HBEC were challenged with supernatant from MDM pre-treated with or without LPS. In contrast, TNF-α and interleukin-1β at levels equivalent to supernatant from LPS-treated MDM increased MUC5AC. MUC5B was induced by LPS, supernatant from LPS-treated MDM, a mix of cytokines including TNF-α and TNF-α alone at levels present in supernatant from LPS-treated MDM. We demonstrated that macrophages are related with bronchiolar GCH, and that they induced MUC5B and inhibited MUC5AC in HBEC, suggesting a role for them in the pathogenesis of airway MUC5B-related GCH.

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

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

The human airway epithelial basal cell transcriptome

BACKGROUND

The human airway epithelium consists of 4 major cell types: ciliated, secretory, columnar and basal cells. During natural turnover and in response to injury, the airway basal cells function as stem/progenitor cells for the other airway cell types. The objective of this study is to better understand human airway epithelial basal cell biology by defining the gene expression signature of this cell population.

METHODOLOGY/PRINCIPAL FINDINGS

Bronchial brushing was used to obtain airway epithelium from healthy nonsmokers. Microarrays were used to assess the transcriptome of basal cells purified from the airway epithelium in comparison to the transcriptome of the differentiated airway epithelium. This analysis identified the "human airway basal cell signature" as 1,161 unique genes with >5-fold higher expression level in basal cells compared to differentiated epithelium. The basal cell signature was suppressed when the basal cells differentiated into a ciliated airway epithelium in vitro. The basal cell signature displayed overlap with genes expressed in basal-like cells from other human tissues and with that of murine airway basal cells. Consistent with self-modulation as well as signaling to other airway cell types, the human airway basal cell signature was characterized by genes encoding extracellular matrix components, growth factors and growth factor receptors, including genes related to the EGF and VEGF pathways. Interestingly, while the basal cell signature overlaps that of basal-like cells of other organs, the human airway basal cell signature has features not previously associated with this cell type, including a unique pattern of genes encoding extracellular matrix components, G protein-coupled receptors, neuroactive ligands and receptors, and ion channels.

CONCLUSION/SIGNIFICANCE

The human airway epithelial basal cell signature identified in the present study provides novel insights into the molecular phenotype and biology of the stem/progenitor cells of the human airway epithelium.

Prevention of bronchial hyperplasia by EGFR pathway inhibitors in an organotypic culture model

Lung cancer is the leading cause of cancer-related mortality worldwide. Early detection or prevention strategies are urgently needed to increase survival. Hyperplasia is the first morphologic change that occurs in the bronchial epithelium during lung cancer development, followed by squamous metaplasia, dysplasia, carcinoma in situ, and invasive tumor. This study was designed to determine the molecular mechanisms that control bronchial epithelium hyperplasia. Using primary normal human tracheobronchial epithelial (NHTBE) cells cultured by using the 3-dimensional (3D) organotypic method, we found that the epidermal growth factor receptor (EGFR) ligands, EGF, TGF-α, and amphiregulin induced hyperplasia, as determined by cell proliferation and multilayered epithelium formation. We also found that EGF induced increased cyclin D1 expression, which plays a critical role in bronchial hyperplasia; this overexpression was mediated by activating the mitogen-activated protein kinase pathway but not the phosphoinositide 3-kinase/Akt signaling pathway. Erlotinib, an EGFR tyrosine kinase inhibitor, and U0126, a MAP/ERK kinase (MEK) inhibitor, completely inhibited EGF-induced hyperplasia. Furthermore, a promoter analysis revealed that the activator protein-1 transcription factor regulates EGF-induced cyclin D1 overexpression. Activator protein-1 depletion by using siRNA targeting its c-Jun component completely abrogated EGF-induced cyclin D1 expression. In conclusion, we showed that bronchial hyperplasia can be modeled in vitro by using primary NHTBE cells maintained in a 3D organotypic culture. EGFR and MEK inhibitors completely blocked EGF-induced bronchial hyperplasia, suggesting that they have a chemopreventive role.

Quantitative real-time PCR for rhinovirus, and its use in determining the relationship between TCID50 and the number of viral particles

The development of a quantitative real-time PCR (qPCR) assay for human rhinovirus serotype 16 (HRV16) is described using the plasmid pR16.11, which contains the full-length genome of HRV16. A standard curve was generated by plotting the critical threshold (C(t)) against numbers of plasmid. The limit of sensitivity was less than10 cDNA copies, and the curve showed a high degree of linearity over a range of 10(1) to 10(6) cDNA copies with r(2)≥0.9989. Amplification efficiency of the qPCR was greater than 97.6 percent. The standard curve was highly reproducible with low intra- and inter-assay coefficients of variation. Standard curves were also generated from cDNA derived from two viral suspensions of known TCID(50), and were exactly parallel to those generated from the plasmid. Comparison of the curves generated from the plasmid or viral cDNA showed that for the two suspensions, TCID(50) corresponded to either 142 or 2088 viral particles. This new qPCR will permit quantitative assessments of interactions between virus and epithelium such as determinations of the affinity and number of viral binding sites or of the number of virus produced per infected cell.

Downregulation of Th17 cells in the small intestine by disruption of gut flora in the absence of retinoic acid

Retinoic acid (RA), a well-known vitamin A metabolite, mediates inhibition of the IL-6-driven induction of proinflammatory Th17 cells and promotes anti-inflammatory regulatory T cell generation in the presence of TGF-beta, which is mainly regulated by dendritic cells. To directly address the role of RA in Th17/regulatory T cell generation in vivo, we generated vitamin A-deficient (VAD) mice by continuous feeding of a VAD diet beginning in gestation. We found that a VAD diet resulted in significant inhibition of Th17 cell differentiation in the small intestine lamina propria by as early as age 5 wk. Furthermore, this diet resulted in low mRNA expression levels of IL-17, IFN regulatory factor 4, IL-21, IL-22, and IL-23 without alteration of other genes, such as RORgammat, TGF-beta, IL-6, IL-25, and IL-27 in the small intestine ileum. In vitro results of enhanced Th17 induction by VAD dendritic cells did not mirror in vivo results, suggesting the existence of other regulation factors. Interestingly, the VAD diet elicited high levels of mucin MUC2 by goblet cell hyperplasia and subsequently reduced gut microbiome, including segmented filamentous bacteria. Much like wild-type mice, the VAD diet-fed MyD88-/-TRIF-/- mice had significantly fewer IL-17-secreting CD4+ T cells than the control diet-fed MyD88-/-TRIF-/- mice. The results strongly suggest that RA deficiency altered gut microbiome, which in turn inhibited Th17 differentiation in the small intestine lamina propria.

Increased mucociliary differentiation of human respiratory epithelial cells on hyaluronan-derivative membranes

The selection of a scaffold to facilitate mucociliary differentiation of respiratory epithelial cells (RECs) is crucial in the development of tissue engineering of respiratory epithelium. However, how the differentiation of RECs is influenced by the biomaterials has never been thoroughly explored. Previously, hyaluronan derivatives were considered as unsuitable biomaterials for culture of respiratory epithelium. In contrast, this study demonstrates that the membranous scaffolds made from benzyl esters of hyaluronic acids are capable of providing a more preferential environment for human RECs than conventionally used collagen-based scaffolds. The proliferation and mucociliary differentiation of RECs were examined by MTT assays, scanning electron microscopy, immunofluorescence, immunoblotting and gene expression. The percentage of ciliated cells in cultured RECs increased from 12.4% on collagen to 20.4% on hyaluronan-derivative membranes with a pseudostratified polarized layer that closely resembled the composition of the native epithelium. The expression levels of MUC5AC and MUC5B mRNA were higher on hyaluronan-based scaffolds than those on collagen. The presence of a hyaluronan-binding domain, CD44 and the receptor for hyaluronan-mediated motility of RECs were also demonstrated. Accordingly, the mucociliary differentiation-promoting effect of hyaluronan-derivative membranes indicates that it may be applied to the tissue engineering of respiratory epithelium.

Culture of nasal epithelial cells using chitosan-based membranes

OBJECTIVES/HYPOTHESIS

The aim of this study was to evaluate whether chitosan-based membranes can be used as scaffolds for growth and differentiation of nasal epithelial cells (NECs). Our final goal was to establish a novel methodology for enhancing the regeneration of the respiratory system.

STUDY DESIGN

Prospective study.

METHODS

Human NECs were cultured on three various substrates, e.g., chitosan membranes, collagen, and chitosan-collagen membranes. Morphology of NECs was examined via light and electron microscopy, the area of ciliated cells was measured by confocal microscopy, and ciliary beat frequency was also evaluated. Expression of mucin genes was investigated with reverse-transcription polymerase chain reaction.

RESULTS

NECs were found to be successfully adhesive with collagen and chitosan-collagen membranes at day 3 after seeding, but not with chitosan membranes. The cilia area on collagen were 6.1% +/- 1.2%, 8.4% +/- 1.4%, and 12.5% +/- 1.9% at days 7, 14, and 21 after confluence, respectively, compared with 5.1% +/- 0.9%, 8.6% +/- 1.6%, and 12.3% +/- 2.1% in chitosan-collagen membranes, exhibited nonsignificant difference (P > .05). There were no significant differences in ciliary beat frequency between each group. The expression levels of mucin genes, namely, MUC5AC, MUC5B, and MUC2, in NECs on both collagen and chitosan-collagen membranes did not differ significantly (P > .05).

CONCLUSIONS

A small amount collagen mixed with chitosan substrate may improve the biocompatibility and promote the mucociliary differentiation in NECs. It appears that chitosan-collagen membrane is a promising scaffold for culture of the nasal epithelium, which sets the stage for studying tissue regeneration in the respiratory system.

Regulation of mucin expression in respiratory diseases

Respiratory diseases such as asthma and COPD (chronic obstructive pulmonary disease) are characterized by increased numbers of goblet cells and excessive mucus production, which contribute to the underlying disease pathology. Mucins form a major component of the mucus contributing to its viscoelastic properties, and in the airways the mucins MUC5AC and MUC5B are found at increased levels in both asthmatic and COPD subjects. A diverse range of stimuli have been shown to regulate MUC5AC expression and cause increases in the number of mucus-producing goblet cells. Perhaps the best characterized of these mediators is the cytokine IL (interleukin)-13, which causes increases in MUC5AC-expressing goblet cells in the airways. Several transcription factors have been linked with goblet cell formation and mucus production and include STAT6 (signal transducer and activator of transcription 6), FOXA2 (forkhead box A2) and the SPDEF [SAM (sterile alpha motif) domain-containing prostate-derived Ets factor]. In mouse airways, goblet cells are normally rare or absent, but increase rapidly in number in response to certain stimuli. The origins of these goblet cells are not well understood, although Clara cells and ciliated cells have been implicated as goblet cell progenitors. An understanding of the origin and processes regulating goblet cell formation in human airway epithelial cells has important implications for the identification of therapeutic targets to treat respiratory diseases.

Immunosensors for detection of Annexin II and MUC5AC for early diagnosis of lung cancer

Amperometric immunosensors were developed to diagnose lung cancer through the detection of Annexin II and MUC5AC. To fabricate the sensor probe, a conducting polymer (poly-terthiophene carboxylic acid; poly-TTCA) was electropolymerized onto a gold nanoparticle/glassy carbon electrode (AuNP/GCE) and a dendrimer (Den) was covalently bonded to the poly-TTCA through amide bond formation, where AuNPs were doped onto the dendrimer. To obtain the final sensor probe, an antibody (anti-Annexin II) and hydrazine (Hyd), which is a catalyst for the reduction of H(2)O(2) generated by glucose oxidase (GOx), were covalently attached onto the Den/AuNP-modified surface. Each surface was then characterized by SEM, impedance spectroscopy and XPS. The final sensor probe was examined before and after interaction with Annexin II and MUC5AC using impedance-spectroscopic, quartz crystal microbalance and amperometric methods. The performance of the immunosensor for the Annexin II was evaluated for the apical surface fluid labeled with GOx by the standard addition method. In this case, the detection limit of the proposed method was 0.051 ng/mL (k=3, n=5). The Annexin II concentration in the secretions collected from squamous metaplastic cells was determined to be 280+/-8.0 pg/mL (n=5).

Regulation of neuregulin 1beta1-induced MUC5AC and MUC5B expression in human airway epithelium

Excessive mucus production has been linked to many of the pathologic features of respiratory diseases, including obstruction of the airways, decline in lung function, increased rates of mortality, and increased infections. The mucins, MUC5AC and MUC5B, contribute to the viscoelastic properties of mucus, and are found at elevated levels in the airways of individuals with chronic respiratory diseases. The T helper type 2 cell cytokine, IL-13, is known to regulate MUC5AC expression in goblet cells of the airways, although much less is known about the regulation of MUC5B expression. In a study to further understand the mediators of MUC5AC and MUC5B expression, neuregulin (NRG) 1beta1 was identified as novel regulator of goblet cell formation in primary cultures of human bronchial epithelial cells (HBECs). NRG1beta1 increased expression of MUCAC and MUC5B proteins in a time- and dose-dependent fashion in HBEC cultures. NRG1beta1-induced expression of MU5AC and MUC5B was shown to involve v-erb-b2 erythroblastic leukemia viral oncogene homolog (ErbB) and ErbB3 receptors, but not ErbB4 receptors. Treatment of HBECs with inhibitors of p38 mitogen-activated protein kinase, extracellular signal-regulated kinase1/2, and phosphatidylinositol 3-kinase indicated that these kinases were involved in NRG1beta1-induced MUC5AC and MUC5B expression. Additionally, NRG1beta1 was shown to induce the phosphorylation of the ErbB2 receptor, AKT, and extracellular signal-regulated kinase 1/2. NRG1beta1 protein was found increased in the airways of antigen-challenged mice, together with increases in MUC5AC and MUC5B message. Together, these data indicate that NRG1beta1 is a novel mediator of MUC5AC and MUC5B expression in HBECs, and may represent a novel therapeutic target for mucus hypersecretion in respiratory diseases.

Cyclic AMP-responsive element binding protein- and nuclear factor-kappaB-regulated CXC chemokine gene expression in lung carcinogenesis

The recognition of the importance of angiogenesis in tumor progression has led to the development of antiangiogenesis as a new strategy for cancer treatment and prevention. By modulating tumor microenvironment and inducing angiogenesis, the proinflammatory cytokine interleukine (IL)-1beta has been reported to promote tumor development. However, the factors mediating IL-1beta-induced angiogenesis in non-small cell lung cancer (NSCLC) and the regulation of these angiogenic factors by IL-1beta are less clear. Here, we report that IL-1beta up-regulated an array of proangiogenic CXC chemokine genes in the NSCLC cell line A549 and in normal human tracheobronchial epithelium cells, as determined by microarray analysis. Further analysis revealed that IL-1beta induced much higher protein levels of CXC chemokines in NSCLC cells than in normal human tracheobronchial epithelium cells. Conditioned medium from IL-1beta-treated A549 cells markedly increased endothelial cell migration, which was suppressed by neutralizing antibodies against CXCL5 and CXCR2. We also found that IL-1beta-induced CXC chemokine gene overexpression in NSCLC cells was abrogated with the knockdown of cyclic AMP-responsive element binding protein (CREB) or nuclear factor kappaB (NF-kappaB). Moreover, the expression of the CXC chemokine genes as well as CREB and NF-kappaB activities was greatly increased in the tumorigenic NSCLC cell line compared with normal, premalignant immortalized or nontumorigenic cell lines. A disruptor of the interaction between CREB-binding protein and transcription factors such as CREB and NF-kappaB, 2-naphthol-AS-E-phosphate (KG-501), inhibited IL-1beta-induced CXC chemokine gene expression and angiogenic activity in NSCLC. We propose that targeting CREB or NF-kappaB using small-molecule inhibitors, such as KG-501, holds promise as a preventive and/or therapeutic approach for NSCLC.

Airway mucus: the good, the bad, the sticky

Mucus production is a primary defense mechanism for maintaining lung health. However, the overproduction of mucin (the chief glycoprotein component of mucus) is a common pathological feature in asthma, chronic obstructive pulmonary disease (COPD), cystic fibrosis (CF), and lung cancer. Although it is associated with disease progression, effective therapies that directly target mucin overproduction and hypersecretion are lacking. Recent advances in our understanding of the control of mucin gene expression in the lungs, the cells that produce airway mucins, and the mechanisms used for releasing them into the airways have provided new potentials for the development of efficacious interventions that will be discussed in this review.

Human basophils activated by mast cell–derived IL-3 express retinaldehyde dehydrogenase-II and produce the immunoregulatory mediator retinoic acid

The vitamin A metabolite retinoic acid (RA) plays a fundamental role in cellular functions by activating nuclear receptors. Retinaldehyde dehydrogenase-II (RALDH2) creates localized RA gradients needed for proper embryonic development, but very little is known regarding its regulated expression in adults. Using a human ex vivo model of aller-gic inflammation by coincubating IgE receptor–activated mast cells (MCs) with blood basophils, we observed prominent induction of a protein that was identified as RALDH2 by mass spectroscopy. RALDH2 was selectively induced in basophils by MC-derived interleukin-3 (IL-3) involving PI3-kinase and NF-κB pathways. Importantly, neither constitutive nor inducible RALDH2 expression was detectable in any other human myeloid or lymphoid leukocyte, including dendritic cells. RA generated by RALDH2 in basophils modulates IL-3–induced gene expression in an autocrine manner, providing positive (CD25) as well as negative (granzyme B) regulation. It also acts in a paracrine fashion on T-helper cells promoting the expression of CD38 and α4/β7 integrins. Furthermore, RA derived from IL-3–activated basophils provides a novel mechanism of Th2 polarization. Thus, RA must be viewed as a tightly controlled basophil-derived mediator with a high potential for regulating diverse functions of immune and resident cells in allergic diseases and other Th2-type immune responses.

Cyclic AMP response element-binding protein overexpression: a feature associated with negative prognosis in never smokers with non-small cell lung cancer

Lung cancer is the leading cause of cancer deaths worldwide. Recent advances in targeted therapies hold promise for the development of new treatments for certain subsets of cancer patients by targeting specific signaling molecule. Based on the identification of the transcription factor cyclic AMP response element-binding protein (CREB) as an important regulator of growth of several types of cancers and our recent findings of its importance in normal differentiation of bronchial epithelial cells, we hypothesized that CREB plays an important pathobiologic role in lung carcinogenesis. We conducted this initial study to determine whether the expression and activation status of CREB are altered in non-small cell lung cancer (NSCLC) and of any prognostic importance in NSCLC patients. We found that the expression levels of mRNA and protein of CREB and phosphorylated CREB (p-CREB) were significantly higher in most of the NSCLC cell lines and tumor specimens than in the normal human tracheobronchial epithelial cells and adjacent normal lung tissue, respectively. Analysis of CREB mRNA expression and the CREB gene copy number showed that CREB overexpression occurred mainly at the transcriptional level. Immunohistochemical analysis of tissue microarray slides containing sections of NSCLC specimens obtained from 310 patients showed that a decreased survival duration was significantly associated with overexpression of CREB or p-CREB in never smokers but not in current or former smokers with NSCLC. These are the first reported results illustrating the potential of CREB as a molecular target for the prevention and treatment of NSCLC, especially in never smokers.

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.

Sp1 up-regulates cAMP-response-element-binding protein expression during retinoic acid-induced mucous differentiation of normal human bronchial epithelial cells

CREB [CRE (cAMP-response element)-binding protein] is an important transcription factor that is differentially regulated in cells of various types. We recently reported that RA (retinoic acid) rapidly activates CREB without using RARs (RA receptors) or RXRs (retinoid X receptors) in NHTBE cells (normal human tracheobronchial epithelial cells). However, little is known about the role of RA in the physiological regulation of CREB expression in the early mucous differentiation of NHTBE cells. In the present study, we report that RA up-regulates CREB gene expression and that, using 5'-serial deletion promoter analysis and mutagenesis analyses, two Sp1 (specificity protein 1)-binding sites located at nt -217 and -150, which flank the transcription initiation site, are essential for RA induction of CREB gene transcription. Furthermore, we found that CREs located at nt -119 and -98 contributed to basal promoter activity. Interestingly, RA also up-regulated Sp1 in a time- and dose-dependent manner. Knockdown of endogenous Sp1 using siRNA (small interfering RNA) decreased RA-induced CREB gene expression. However, the converse was not true: knockdown of CREB using CREB siRNA did not affect RA-induced Sp1 gene expression. We conclude that RA up-regulates CREB gene expression during the early stage of NHTBE cell differentiation and that RA-inducible Sp1 plays a major role in up-regulating human CREB gene expression. This result implies that co-operation of these two transcription factors plays a crucial role in mediating early events of normal mucous cell differentiation of bronchial epithelial cells.

Growth suppression of lung cancer cells by targeting cyclic AMP response element-binding protein

Genes regulated by cyclic AMP-response element-binding protein (CREB) have been reported to suppress apoptosis, induce cell proliferation, and mediate inflammation and tumor metastasis. However, it is not clear whether CREB is critically involved in lung carcinogenesis. We found that non-small cell lung cancer (NSCLC) cell lines exhibited elevated constitutive activity in CREB, in its immediate upstream kinases (ribosomal s6 kinase and extracellular signal kinase), and in the CREB-regulated cell survival proteins Bcl-2 and Bcl-xL. We hypothesized that constitutively active CREB is important to lung cancer cell growth and survival and therefore could be a potential therapeutic target for NSCLC. Ectopic expression of dominant repressor CREB and transfection with small interfering RNA against CREB suppressed the growth and survival of NSCLC cells and induced apoptotic cell death. Furthermore, treating H1734 NSCLC cells with an inhibitor of the CREB signaling pathway Ro-31-8220 inhibited CREB activation by blocking the activity of extracellular signal kinase and ribosomal s6 kinase, arrested the cell cycle at the G(2)-M phase, and subsequently induced apoptosis with the suppression of Bcl-2 and Bcl-xL expression. Ro-31-8220 suppressed both the anchorage-dependent and independent growth of NSCLC cells, but its cytotoxic effect was much less prominent in normal bronchial epithelial cells. Our results indicate that active CREB plays an important role in NSCLC cell growth and survival. Thus, agents that suppress CREB activation could have potential therapeutic value for NSCLC treatment.

Rehabilitation of surgically traumatized paranasal sinus mucosa using retinoic acid

BACKGROUND

Paranasal sinus mucosa that regenerates after surgical stripping is characterized by sparse, dysmorphic cilia. Although such dysfunctional mucosal changes are thought to be irreversible, the potential rehabilitation of deciliated mucosa by topical therapies has not been explored. This study evaluated the effect of topical retinoic acid (RA) in rehabilitating deciliated sinus mucosa that has regenerated after surgical stripping.

METHODS

Twelve New Zealand rabbits underwent bilateral maxillary sinus mucosal stripping and were allowed to remucosalize for 10 days. In the first treatment arm (n = 6), 0.01% RA was applied to the regenerated mucosa of the left maxillary sinus and an aqueous control was placed contralaterally. In the second treatment arm, the regenerated mucosa was surgically restripped bilaterally before applying RA and control. After 14 additional days, mucosa was harvested and examined by scanning electron microscopy for ciliary density, orientation, and morphology.

RESULTS

In the first treatment arm, no significant differences in ciliary density, orientation, or morphology were noted between RA-treated sinuses and controls. In the second arm, RA-treated sinuses showed improved ciliary density, morphology, and orientation compared with controls.

CONCLUSION

RA does not appear to significantly enhance ciliogenesis when applied after mucosal regeneration has occurred. However, if deciliated mucosa is restripped and allowed to regenerate in the presence of RA, ciliary ultrastructural features may be enhanced. RA may have therapeutic value in rehabilitating deciliated sinus mucosa when applied before mucociliary differentiation of regenerating mucosa.

Proteomics-based identification of proteins secreted in apical surface fluid of squamous metaplastic human tracheobronchial epithelial cells cultured by three-dimensional organotypic air-liquid interface method

Squamous cell carcinoma in the lung originates from bronchial epithelial cells that acquire increasingly abnormal phenotypes. Currently, no known biomarkers are clinically efficient for the early detection of premalignant lesions and lung cancer. We sought to identify secreted molecules produced from squamous bronchial epithelial cells cultured with organotypic culture methods. We analyzed protein expression patterns in the apical surface fluid (ASF) from aberrantly differentiated squamous metaplastic normal human tracheobronchial epithelial (NHTBE) and mucous NHTBE cells. Comparative two-dimensional PAGE analysis revealed 174 unique proteins in the ASF of squamous NHTBE cells compared with normal mucociliary differentiated NHTBE cells. Among them, 64 well-separated protein spots were identified by liquid chromatography-tandem mass spectrometry, revealing 22 different proteins in the ASF from squamous NHTBE cells. Expression of six of these proteins [SCC antigen 1 (SCCA1), SCC antigen 2 (SCCA2), S100A8, S100A9, Annexin I, and Annexin II] in the squamous NHTBE cells was further confirmed with immunoblot analysis. Notably, SCCA1 and SCCA2 were verified as being expressed in squamous metaplastic NHTBE cells but not in normal mucous NHTBE or normal bronchial epithelium. Moreover, SCCA1 and SCCA2 expression increased in in vitro lung carcinogenesis model cell lines with increasing malignancy. In summary, we identified proteins that are uniquely secreted from squamous metaplastic primary human bronchial epithelial cells cultured by the organotypic air-liquid interface method. These ASF proteins may be used to detect abnormal lesions in the lung without collecting invasive biopsy specimens.

Regulation of mucin gene expression by CREB via a nonclassical retinoic acid signaling pathway

Vitamin A and its metabolite retinoic acid (RA) are essential elements for normal lung development and the differentiation of lung epithelial cells. We previously showed that RA rapidly activated cyclic AMP response element-binding protein (CREB) in a nonclassical manner in normal human tracheobronchial epithelial (NHTBE) cells. In the present study, we further demonstrated that this nonclassical signaling of RA on the activation of CREB plays a critical role in regulating the expression of airway epithelial cell differentiation markers, the MUC2, MUC5AC, and MUC5B genes. We found that RA rapidly activates the protein kinase Calpha isozyme and transmits the activation signal to CREB via the Raf/MEK/extracellular signal-regulated kinase/p90 ribosomal S6 kinase (RSK) pathway. Activated RSK translocated from the cytoplasm to the nucleus, where it phosphorylates CREB. Activated CREB then binds to a cis-acting replication element motif on the promoter (at nucleotides [nt] -878 to -871) of the MUC5AC gene. The depletion of CREB using small interfering RNA abolished not only the RA-induced MUC5AC but also RA-induced MUC2 and MUC5B. Taken together, our findings demonstrate that CREB activation via this nonclassical RA signaling pathway may play an important role in regulating the expression of mucin genes and mediating the early biological effects of RA during normal mucous differentiation in NHTBE cells.

Epigenetic regulation (DNA methylation, histone modifications) of the 11p15 mucin genes (MUC2, MUC5AC, MUC5B, MUC6) in epithelial cancer cells

The human genes MUC2, MUC5AC, MUC5B and MUC6 are clustered on chromosome 11 and encode large secreted gel-forming mucins. The frequent occurrence of their silencing in cancers and the GC-rich structure of their promoters led us to study the influence of epigenetics on their expression. Pre- and post-confluent cells were treated with demethylating agent 5-aza-2'-deoxycytidine and histone deacetylase (HDAC) inhibitor, trichostatin A. Mapping of methylated cytosines was performed by bisulfite-treated genomic DNA sequencing. Histone modification status at the promoters was assessed by chromatin immunoprecipitation assays. Our results indicate that MUC2 was regulated by site-specific DNA methylation associated with establishment of a repressive histone code, whereas hypermethylation of MUC5B promoter was the major mechanism responsible for its silencing. DNA methyltransferase 1 was identified by small interfering RNA approach as a regulator of MUC2 and MUC5B endogenous expression that was potentiated by HDAC2. MUC2 and MUC5B epigenetic regulation was cell-specific, depended on cell differentiation status and inhibited their activation by Sp1. The expression of MUC5AC was rarely influenced by epigenetic mechanisms and methylation of MUC6 promoter was not correlated to its silencing. In conclusion, this study demonstrates the important role for methylation and/or histone modifications in regulating the 11p15 mucin genes in epithelial cancer cells.

Transcriptional profiling of mucociliary differentiation in human airway epithelial cells

When cultured at an air-liquid interface (ALI) in the appropriate medium, primary human airway epithelial cells form a polarized, pseudostratified epithelium composed of ciliated and mucus-secreting cells. This culture system provides a useful tool for the in vitro study of airway epithelial biology and differentiation. We have performed microarray analysis on ALI cultures of human bronchial epithelial cells (HBECs) grown over a 28-d period to identify genes involved in mucociliary differentiation. We identified over 2,000 genes that displayed statistically significant 2-fold or greater changes in expression during the time course. Of the genes showing the largest increases, many are involved in processes associated with airway epithelial biology, such as cell adhesion, immunity, transport, and cilia formation; however, many novel genes were also identified. We compared our results with data from proteomic analyses of the ciliary axoneme and identified candidate genes that may have roles in cilia formation or function. Gene networks were generated using Ingenuity Pathways Analysis (Ingenuity Systems, Redwood City, CA) to identify signaling pathways involved in mucociliary cell differentiation or function. Networks containing genes involved in TGF-beta, WNT/beta-catenin, and epidermal growth factor receptor (EGFR) pathways were identified, suggesting potential roles for these families in airway epithelia. Microarray results were validated by real-time RT-PCR for a number of representative genes. This work has provided extensive information about gene expression changes during differentiation of airway epithelial cells, and will be a useful resource for researchers interested in respiratory function, pathology, and toxicology.

Expression and localization of surfactant proteins in human nasal epithelium

Surfactant proteins (SPs), designated SP-A, SP-B, SP-C, and SP-D, play an important role in surfactant metabolism and host defense mechanisms in the lung. This study investigates expression of the different SP types in human nasal mucosa and cultured normal human nasal epithelial (NHNE) cells and whether the expression of SP mRNA is influenced by the degree of mucociliary differentiation. RT-PCR was performed with mRNA from cultured NHNE cells and nasal mucosa. Immunohistochemical staining for SPs was performed on nasal mucosa specimens. Western blot analysis was performed on cell lysates from cultured NHNE cells. SP-A2, SP-B, and SP-D mRNAs were expressed in normal NHNE cells and human nasal mucosa. SPs were localized in ciliated cells of the surface epithelium and serous acini of the submucosal glands. SP-A, SP-B, and SP-D proteins were expressed in cultured NHNE cells. The degree of mucociliary differentiation influenced expression of the SP gene. We demonstrate that SP-A, SP-B, and SP-D are expressed in human nasal mucosa and cultured NHNE cells. Further study of the functional role of SPs in the upper airway is required.

β-Carotene and apocarotenals promote retinoid signaling in BEAS-2B human bronchioepithelial cells

High dose beta-carotene supplementation of smokers was associated with increased lung cancer risk in two intervention trials. It was proposed that generation of apocarotenals in smoke-exposed lungs impaired retinoic acid (RA) signaling, leading to squamous metaplasia and cell proliferation. To test this, we compared RA target gene regulation by retinoids, apocarotenals or beta-carotene by transcriptomics in BEAS-2B cells cultured to promote squamous differentiation. Retinoids, beta-carotene as well as apocarotenals induced known RA target genes. Retinoids upregulated involucrin, indicating that retinoids did not rescue BEAS-2B cells from squamous differentiation. Muc5AC, a marker for mucous differentiation, was transiently induced. beta-Carotene and apocarotenals less strongly induced involucrin and did not induce muc5AC. In summary, apocarotenals or beta-carotene upregulated RA target genes suggesting promotion, not inhibition, of RA signaling in BEAS-2B cells. Furthermore, apocarotenals and beta-carotene regulated gene expression independently of RA signaling. Squamous differentiation is not unequivocally linked to RA deficiency in BEAS-2B cells.

Effect of Fibroblasts on Tracheal Epithelial Regenerationin vitro

Several artificial grafts for covering deficient trachea have been produced through tissue engineering. Recently, our group clinically used an artificial trachea made from collagen sponge for patients with noncircumferential tracheal resection. However, the slowness of epithelial regeneration on the surface of the artificial trachea was confirmed as one particular problem. In this study, we co-cultured tracheal epithelial cells with fibroblasts and examined effects of fibroblasts on epithelial regeneration in vitro. Fibroblasts activated epithelial cell proliferation and migration. In co-culture with fibroblasts, epithelial cells reconstructed pseudostratified epithelium, which was composed of ciliated, goblet, and basal cells. Furthermore, a basement membrane was reconstructed between epithelial cells and fibroblasts, and integrin beta4 was also observed there. Fibroblasts rapidly increased mucin secretion by epithelial cells. These results indicate that stimulatory effects of fibroblasts on epithelial cell migration, proliferation, and differentiation would reduce the time required for covering of epithelial cells on the defect of luminal surface and hasten regeneration of morphologically and functionally normalized epithelium involving the reconstruction of basement membrane.

Retinoic acid improves ciliogenesis after surgery of the maxillary sinus in rabbits

OBJECTIVES/HYPOTHESIS

Retinoids have been shown to be important cofactors in regulating the differentiation and proliferation of ciliated epithelial cells of the respiratory tract. In particular, retinoic acid has been shown to enhance the regeneration of paranasal sinus mucosa. The objective of this study is to use scanning electron microscopy techniques to evaluate the effect of topical retinoic acid on mucosal wound healing in a rabbit model of maxillary sinus surgery. It is hypothesized that the application of topical retinoic acid will enhance ciliogenesis and improve the morphology of regenerated cilia compared with controls.

STUDY DESIGN

Prospective multi-arm controlled animal trial.

METHODS

Eighteen New Zealand white rabbits underwent surgical opening of the maxillary sinuses through a midline incision. The rabbits were divided among four experimental groups: 1) mucosal stripping alone (stripped control), 2) stripping followed by topical application of an inert aqueous gel, 3) stripping followed by application of 0.01% retinoic acid in aqueous gel, and 4) no mucosal stripping and no topical treatment (nonstripped control). After 14 days, the medial wall of the maxillary sinus was harvested and examined by scanning electron microscopy at x2,000 and x5,000 magnification. The micrographs were then rated by a blinded review panel for ciliary density, orientation, and morphology.

RESULTS

Mean scores for ciliary density, orientation, and morphology were all significantly higher for the retinoic acid treatment group compared with both the inert aqueous gel treatment group and the stripped control group (P=.004-.03 for all comparisons, Student's t test). Mean scores for the retinoic acid treatment group were numerically lower than the nonstripped control group but did not approach statistical significance for any parameter (P=.23-.31).

CONCLUSIONS

In a rabbit model of maxillary sinus surgery, topically delivered retinoic acid enhances ciliogenesis. Qualitative assessment of ciliary density, orientation, and morphology shows improved healing in retinoic acid treated sinuses compared with both untreated control sinuses and aqueous gel treated sinuses.

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.

Epidermal growth factor receptor activation by epidermal growth factor mediates oxidant-induced goblet cell metaplasia in human airway epithelium

Mucus overproduction in inflammatory and obstructive airway diseases is associated with goblet cell (GC) metaplasia in airways. Although the mechanisms involved in GC metaplasia and mucus hypersecretion are not completely understood, association with oxidative stress and epidermal growth factor receptor (EGFR) signaling has been reported. To explore the mechanisms involved in oxidative stress-induced GC metaplasia, cultures of differentiated normal human bronchial epithelial cells grown at the air-liquid interface were exposed to reactive oxygen species (ROS) generated by xanthine/xanthine oxidase. EGFR activation and signaling was assessed by measuring EGF and transforming growth factor-alpha release and EGFR and (44/42)MAPK phosphorylation. The GC population was evaluated by confocal microscopy. ROS-induced EGFR activation resulted in GC proliferation and increased MUC5AC gene and protein expression. Signaling was due to pro-EGF processing by tissue kallikrein (TK), which was activated by ROS-induced hyaluronan breakdown. It was inhibited by catalase, a TK inhibitor, and EGF-blocking antibodies. Exposure to recombinant TK mimicked the ROS effects, increasing the expression of MUC5AC and lactoperoxidase. In addition, ROS induced the antiapoptotic factor Bcl-2 in a TK-dependent fashion. In conclusion, ROS-induced GC metaplasia in normal human bronchial epithelial cells is associated with HA depolymerization and EGF processing by TK followed by EGFR signaling, suggesting that increases in TK activity could contribute to GC metaplasia and mucus hypersecretion in diseases such as asthma and chronic bronchitis. The data also suggest that increases in GC population could be sustained by the associated upregulation of Bcl-2 in airway epithelial cells.

Nonclassical action of retinoic acid on the activation of the cAMP response element-binding protein in normal human bronchial epithelial cells

Vitamin A (retinol) is essential for normal regulation of cell growth and differentiation. We have shown that the retinol metabolite retinoic acid (RA) induces mucous cell differentiation of normal human tracheobronchial epithelial (NHTBE) cells. However, early biological effects of RA in the differentiation of bronchial epithelia are largely unknown. Here, we showed that RA rapidly activated cAMP response element-binding protein (CREB). However, RA did not use the conventional retinoic acid receptor (RAR)/retinoid X receptor (RXR) to activate CREB. RA activated CREB in NHTBE and H1734 cells in which RARs/RXR were silenced with small interfering RNA (siRNA) targeting RAR/RXR expression or deactivated by antagonist. Inhibition of protein kinase C (PKC) or extracellular regulated kinase (ERK1/2) blocked the RA-mediated activation of CREB. In addition, depletion of p90 ribosomal S6 kinase (RSK) via siRSK1/2 completely abolished the activation, suggesting that PKC, ERK, and RSK are required for the activation. Altogether, this study provides the first evidence that RA rapidly activates CREB transcription factor via PKC, ERK, and RSK in a retinoid receptor-independent manner in normal bronchial epithelial cells. This noncanonical RA signaling pathway may play an important role in mediating early biological effects in the mucociliary differentiation of bronchial epithelia.

Global detection of molecular changes reveals concurrent alteration of several biological pathways in nonsmall cell lung cancer cells

To identify the molecular changes that occur in non-small cell lung carcinoma (NSCLC), we compared the gene expression profile of the NCI-H292 (H292) NSCLC cell line with that of normal human tracheobronchial epithelial (NHTBE) cells. The NHTBE cells were grown in a three-dimensional organotypic culture system that permits maintenance of the normal pseudostratified mucociliary phenotype characteristic of bronchial epithelium in vivo. Microarray analysis using the Affymetrix oligonucleotide chip U95Av2 revealed that 1,683 genes showed a >1.5-fold change in expression in the H292 cell line relative to the NHTBE cells. Specifically, 418 genes were downregulated and 1,265 were upregulated in the H292 cells. The expression data for selected genes were validated in several different NSCLC cell lines using quantitative real-time PCR and Western analysis. Further analysis of the differentially expressed genes indicated that WNT responses, apoptosis, cell cycle regulation and cell proliferation were significantly altered in the H292 cells. Functional analysis using fluorescence-activated cell sorting confirmed concurrent changes in the activity of these pathways in the H292 line. These findings show that (1) NSCLC cells display deregulation of the WNT, apoptosis, proliferation and cell cycle pathways, as has been found in many other types of cancer cells, and (2) that organotypically cultured NHTBE cells can be used as a reference to identify genes and pathways that are differentially expressed in tumor cells derived from bronchogenic epithelium.

Cell culture models of the respiratory tract relevant to pulmonary drug delivery

The respiratory tract holds promise as an alternative site of drug delivery due to fast absorption and rapid onset of drug action, with avoidance of hepatic and intestinal first-pass metabolism as an additional benefit compared to oral drug delivery. At present, the pharmaceutical industry increasingly relies on appropriate in vitro models for the faster evaluation of drug absorption and metabolism as an alternative to animal testing. This article reviews the various existing cell culture systems that may be applied as in vitro models of the human air-blood barrier, for instance, in order to enable the screening of large numbers of new drug candidates at low cost with high reliability and within a short time span. Apart from such screening, cell culture-based in vitro systems may also contribute to improve our understanding of the mechanisms of drug transport across such epithelial tissues, and the mechanisms of action how advanced drug carriers, such as nanoparticles or liposomes, can help to overcome these barriers. After all, the increasing use and acceptance of such in vitro models may lead to a significant acceleration of the drug development process by facilitating the progress into clinical studies and product registration.

β-Carotene interaction with NNK in the AJ-mouse model: Effects on cell proliferation, tumor formation and retinoic acid responsive genes

We studied the influence of beta-carotene on the tobacco smoke carcinogen 4-(N-Methyl-N-nitrosamino)-1-(3-pyridyl)-1-butanone (NNK)-induced lung tumor development in the A/J-mouse model. The normally low beta-carotene absorption was facilitated with a diet enriched in fat and bile salt, resulting in plasma and lung tissue levels similar to humans. beta-Carotene enhanced NNK-induced early bronchial cell proliferation, however, this effect was not predictive for later tumor development. Tumor multiplicity was not significantly affected by beta-carotene, neither in carcinogen-initiated nor in uninitiated mice, and regardless of dose and time point of supplementation during tumor development. RARbeta isoform and CYP26 gene expression levels analyzed by quantitative RT-PCR were weakly, but significantly, inversely correlated and showed evidence for altered retinoid signaling and catabolism in the lungs of NNK-initiated, beta-carotene supplemented mice. However, this interaction did not translate into enhanced tumor multiplicity. These results indicate that impaired retinoid signaling is not likely a key factor in lung tumorigenesis in this mouse model.