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1.  Mucin Production during Prenatal and Postnatal Murine Lung Development 
Mucus is a protective gel that lines respiratory tract surfaces. To identify potential roles for secreted gel–forming mucins in lung development, we isolated murine lungs on embryonic days (E) 12.5–18.5, and postnatal days (PN) days 5, 14, and 28. We measured the mucin gene expression by quantitative RT-PCR, and localization by histochemical and immunohistochemical labeling. Alcian blue/periodic acid–Schiff–positive cells are present from E15.5 through PN28. Muc5b transcripts were abundant at all time points from E14.5 to PN28. By contrast, transcript levels of Muc5ac and Muc2 were approximately 300 and 85,000 times lower, respectively. These data are supported by immunohistochemical studies demonstrating the production and localization of Muc5ac and Muc5b protein. This study indicates that mucin production is prominent in developing murine lungs and that Muc5b is an early, abundant, and persistent marker of bronchial airway secretory cells, thereby implicating it as an intrinsic component of homeostatic mucosal defense in the lungs.
doi:10.1165/rcmb.2010-0020OC
PMCID: PMC3135838  PMID: 21653907
mouse; lung; mucin; Muc5ac; Muc5b
2.  Strain-Dependent Genomic Factors Affect Allergen-Induced Airway Hyperresponsiveness in Mice 
Asthma is etiologically and clinically heterogeneous, making the genomic basis of asthma difficult to identify. We exploited the strain-dependence of a murine model of allergic airway disease to identify different genomic responses in the lung. BALB/cJ and C57BL/6J mice were sensitized with the immunodominant allergen from the Dermatophagoides pteronyssinus species of house dust mite (Der p 1), without exogenous adjuvant, and the mice then underwent a single challenge with Der p 1. Allergic inflammation, serum antibody titers, mucous metaplasia, and airway hyperresponsiveness were evaluated 72 hours after airway challenge. Whole-lung gene expression analyses were conducted to identify genomic responses to allergen challenge. Der p 1–challenged BALB/cJ mice produced all the key features of allergic airway disease. In comparison, C57BL/6J mice produced exaggerated Th2-biased responses and inflammation, but exhibited an unexpected decrease in airway hyperresponsiveness compared with control mice. Lung gene expression analysis revealed genes that were shared by both strains and a set of down-regulated genes unique to C57BL/6J mice, including several G-protein–coupled receptors involved in airway smooth muscle contraction, most notably the M2 muscarinic receptor, which we show is expressed in airway smooth muscle and was decreased at the protein level after challenge with Der p 1. Murine strain–dependent genomic responses in the lung offer insights into the different biological pathways that develop after allergen challenge. This study of two different murine strains demonstrates that inflammation and airway hyperresponsiveness can be decoupled, and suggests that the down-modulation of expression of G-protein–coupled receptors involved in regulating airway smooth muscle contraction may contribute to this dissociation.
doi:10.1165/rcmb.2010-0315OC
PMCID: PMC3208613  PMID: 21378263
asthma; airway hyperresponsiveness; inflammation; house dust mite; Der p 1
3.  Haemophilus influenzae Lysate Induces Aspects of the Chronic Obstructive Pulmonary Disease Phenotype 
Nontypeable Haemophilus influenzae (NTHi) commonly colonizes the lower airways of patients with chronic obstructive pulmonary disease (COPD). Whether it contributes to COPD progression is unknown. Here, we determined which aspects of the COPD phenotype can be induced by repetitive exposure to NTHi products. Mice were exposed weekly to an aerosolized NTHi lysate, and inflammation was evaluated by measurement of cells and cytokines in bronchoalveolar lavage fluid (BALF) and immunohistochemical staining; structural changes were evaluated histochemically by periodic acid fluorescent Schiff's reagent, Masson's trichrome, and Picrosirius red staining; mucin gene expression was measured by quantitative RT-PCR; and the role of TNF-α was examined by transgenic airway overexpression and use of an inhibitory antibody. NTHi lysate induced rapid activation of NF-κB in airway cells and increases of inflammatory cytokines and neutrophils in BALF. Repetitive exposure induced infiltration of macrophages, CD8+ T cells, and B cells around airways and blood vessels, and collagen deposition in airway and alveolar walls, but airway mucin staining and gel-forming mucin transcripts were not increased. Transgenic overexpression of TNF-α caused BALF neutrophilia and inflammatory cell infiltration around airways, but not fibrosis, and TNF-α neutralization did not reduce BALF neutrophilia in response to NTHi lysate. In conclusion, NTHi products elicit airway inflammation in mice with a cellular and cytokine profile similar to that in COPD, and cause airway wall fibrosis but not mucous metaplasia. TNF-α is neither required for inflammatory cell recruitment nor sufficient for airway fibrosis. Colonization by NTHi may contribute to the pathogenesis of small airways disease in patients with COPD.
doi:10.1165/rcmb.2007-0366OC
PMCID: PMC2396243  PMID: 18096867
pulmonary disease, chronic obstructive; Haemophilus influenzae; bronchiolitis; inflammation; fibrosis
4.  Central Role of Muc5ac Expression in Mucous Metaplasia and Its Regulation by Conserved 5′ Elements 
Mucus hypersecretion contributes to morbidity and mortality in many obstructive lung diseases. Gel-forming mucins are the chief glycoprotein components of airway mucus, and elevated expression of these during mucous metaplasia precedes the hypersecretory phenotype. Five orthologous genes (MUC2, MUC5AC, MUC5B, MUC6, and MUC19) encode the mammalian gel-forming mucin family, and several have been implicated in asthma, cystic fibrosis, and chronic obstructive pulmonary disease pathologies. However, in the absence of a comprehensive analysis, their relative contributions remain unclear. Here, we assess the expression of the entire gel-forming mucin gene family in allergic mouse airways and show that Muc5ac is the predominant gel-forming mucin induced. We previously showed that the induction of mucous metaplasia in ovalbumin-sensitized and -challenged mouse lungs occurs within bronchial Clara cells. The temporal induction and localization of Muc5ac transcripts correlate with the induced expression and localization of mucin glycoproteins in bronchial airways. To better understand the tight regulation of Muc5ac expression, we analyzed all available 5′-flanking sequences of mammalian MUC5AC orthologs and identified evolutionarily conserved regions within domains proximal to the mRNA coding region. Analysis of luciferase reporter gene activity in a mouse transformed Clara cell line demonstrates that this region possesses strong promoter activity and harbors multiple conserved transcription factor–binding motifs. In particular, SMAD4 and HIF-1α bind to the promoter, and mutation of their recognition motifs abolishes promoter function. In conclusion, Muc5ac expression is the central event in antigen-induced mucous metaplasia, and phylogenetically conserved 5′ noncoding domains control its regulation.
doi:10.1165/rcmb.2005-0460OC
PMCID: PMC1994232  PMID: 17463395
mucin; metaplasia; airway; lung; epithelium
5.  A3 Adenosine Receptor Signaling Contributes to Airway Mucin Secretion after Allergen Challenge 
Mucin hypersecretion is a prominent feature of obstructive airway diseases such as asthma. Clara cells conditionally produce mucin in response to inflammatory signals in a process termed mucous metaplasia. This can be followed by mucin secretion stimulated by various signaling molecules. The cellular and molecular mechanisms that regulate mucin production and secretion are not well understood. Adenosine is a signaling nucleoside that has been implicated in airway diseases in which mucus obstruction is prominent. Furthermore, the A3 adenosine receptor (A3AR) is upregulated in mucin-producing goblet cells of the airway, thereby implicating it in processes involved in mucous cell biology. Here we use genetic approaches to investigate the contribution of A3AR signaling to mucus production and secretion in a mouse model of allergen-induced pulmonary disease. We found that the degree of mucin production in response to allergen is similar in wild-type and A3AR-deficient mice, and that overexpression of this receptor in Clara cells neither induces mucin production itself, nor enhances mucin production in response to allergen challenge. Collectively, these experiments demonstrate that the A3AR is neither necessary nor sufficient for mucous cell metaplasia. In contrast to the lack of effect on mucin production, agonist-induced mucin secretion was increased in goblet cells overexpressing the A3AR, and was absent in A3AR-deficient mice. Thus, the A3AR contributes to mucin secretion in allergen-induced metaplasia. Signaling through this receptor may contribute to mucus airway obstruction seen in pulmonary disorders in which adenosine levels are elevated.
doi:10.1165/rcmb.2006-0060OC
PMCID: PMC2643274  PMID: 16763221
mucin; mucous cell metaplasia; secretion; adenosine receptors; allergic lung disease
6.  Airway Mucus 
Mucus hypersecretion is a phenotype associated with multiple obstructive lung diseases. However, in spite of its nefarious reputation under pathologic conditions, there are significant benefits to having low levels of mucus present in the airways at baseline, such as the ability to trap and eliminate inhaled particles and to prevent desiccation of airway surfaces. Mucins are high–molecular-weight glycoproteins that are the chief components that render viscoelastic and gel-forming properties to mucus. Recent advances in animal models and in vitro systems have provided a wealth of information regarding the identification of the mucin genes that are expressed in the lungs, the signal transduction pathways that regulate the expression of these mucins, and the secretory pathways that mediate their release into the airways. In addition, the clinical and pathologic literature has corroborated many of the basic laboratory findings. As a result, mucin overproduction and hypersecretion are moving away from being markers of disease and toward being testable as functional components of lung disease processes.
doi:10.1165/rcmb.2005-0436SF
PMCID: PMC2644218  PMID: 16415249
epithelium; lung; metaplasia; mucin; secretion

Results 1-6 (6)