Impact of microRNA in normal and pathological respiratory epithelia

Extensive sequencing efforts, combined with ad hoc bioinformatics developments, have now led to the identification of 1222 distinct miRNAs in human (derived from 1368 distinct genomic loci) and of many miRNAs in other multicellular organisms. The present chapter is aimed at describing a general experimental strategy to identify specific miRNA expression profiles and to highlight the functional networks operating between them and their mRNA targets, including several miRNAs deregulated in cystic fibrosis and during differentiation of airway epithelial cells.

Long acting beta2-agonist and corticosteroid restore airway glandular cell function altered by bacterial supernatant

BACKGROUND

Staphylococcus aureus releases virulence factors (VF) that may impair the innate protective functions of airway cells. The aim of this study was to determine whether a long-acting beta2 adrenergic receptor agonist (salmeterol hydroxynaphthoate, Sal) combined with a corticosteroid (fluticasone propionate, FP) was able to regulate ion content and cytokine expression by airway glandular cells after exposure to S. aureus supernatant.

METHODS

A human airway glandular cell line was incubated with S. aureus supernatant for 1 h and then treated with the combination Sal/FP for 4 h. The expression of actin and CFTR proteins was analyzed by immunofluorescence. Videomicroscopy was used to evaluate chloride secretion and X-ray microanalysis to measure the intracellular ion and water content. The pro-inflammatory cytokine expression was assessed by RT-PCR and ELISA.

RESULTS

When the cells were incubated with S. aureus supernatant and then with Sal/FP, the cellular localisation of CFTR was apical compared to the cytoplasmic localisation in cells incubated with S. aureus supernatant alone. The incubation of airway epithelial cells with S. aureus supernatant reduced by 66% the chloride efflux that was fully restored by Sal/FP treatment. We also observed that Sal/FP treatment induced the restoration of ion (Cl and S) and water content within the intracellular secretory granules of airway glandular cells and reduced the bacterial supernatant-dependent increase of pro-inflammatory cytokines IL8 and TNFalpha.

CONCLUSIONS

Our results demonstrate that treatment with the combination of a corticosteroid and a long-acting beta2 adrenergic receptor agonist after bacterial infection restores the airway glandular cell function. Abnormal mucus induced by defective ion transport during pulmonary infection could benefit from treatment with a combination of beta2 adrenergic receptor agonist and glucocorticoid.

{alpha}7 nicotinic acetylcholine receptor regulates airway epithelium differentiation by controlling basal cell proliferation

Airway epithelial basal cells are known to be critical for regenerating injured epithelium and maintaining tissue homeostasis. Recent evidence suggests that the alpha7 nicotinic acetylcholine receptor (nAChR), which is highly permeable to Ca(2+), is involved in lung morphogenesis. Here, we have investigated the potential role of the alpha7 nAChR in the regulation of airway epithelial basal cell proliferation and the differentiation of the human airway epithelium. In vivo during fetal development and in vitro during the regeneration of the human airway epithelium, alpha7 nAChR expression coincides with epithelium differentiation. Inactivating alpha7 nAChR function in vitro increases cell proliferation during the initial steps of the epithelium regeneration, leading to epithelial alterations such as basal cell hyperplasia and squamous metaplasia, remodeling observed in many bronchopulmonary diseases. The regeneration of the airway epithelium after injury in alpha7(-/-) mice is delayed and characterized by a transient hyperplasia of basal cells. Moreover, 1-year-old alpha7(-/-) mice more frequently present basal cells hyperplasia. Modulating nAChR function or expression shows that only alpha7 nAChR, as opposed to heteropentameric alpha(x)beta(y) nAChRs, controls the proliferation of human airway epithelial basal cells. These findings suggest that alpha7 nAChR is a key regulator of the plasticity of the human airway epithelium by controlling basal cell proliferation and differentiation pathway and is involved in airway remodeling during bronchopulmonary diseases.

Salmeterol restores secretory functions in cystic fibrosis airway submucosal gland serous cells

The activity of the cystic fibrosis (CF) transmembrane conductance regulator (CFTR) can be mediated by surface G protein-coupled receptors such as the beta(2)-adrenergic receptor. In this study, we explored the effect of a long-acting beta(2)-adrenergic agonist, salmeterol, on the CFTR-dependent secretory capacity of a human CF tracheal gland serous cell line (CF-KM4), homozygous for the delF508 mutation. We showed that, compared with the untreated CF serous cells, a 24-hour pre-incubation period with 200 nM salmeterol induced an 83% increase in delF508-CFTR-mediated chloride efflux. The restoration of the bioelectric properties is associated with increased apical surface pool of delF508-CFTR. Salmeterol induced a decrease in ion concentration and an increase in the level of hydration of the mucus packaged inside the CF secretory granules. The effects of salmeterol are not associated with a persistent production of cAMP. Western blotting on isolated secretory granules demonstrated immunoreactivity for CFTR and lysozyme. In parallel, we measured by atomic force microscopy an increased size of secretory granules isolated from CF serous cells compared with non-CF serous cells (MM39 cell line) and showed that salmeterol was able to restore a CF cell granule size similar to that of non-CF cells. To demonstrate that the salmeterol effect was a CFTR-dependent mechanism, we showed that the incubation of salmeterol-treated CF serous cells with CFTR-inh172 suppressed the restoration of normal secretory functions. The capacity of salmeterol to restore the secretory capacity of glandular serous cells suggests that it could also improve the airway mucociliary clearance in patients with CF.

Video-microscopic imaging of cell spatio-temporal dispersion and migration

Live-cell imaging has become a powerful analytical tool in most cell biology laboratories. The scope of this paper is to give an overview of the environmental considerations for maintaining living cells on the microscope stage and the technical advances permitting multi-parameter imaging. The paper will then focus on two-dimensional and three-dimensional analysis of cell dispersion and migration and finally give a brief insight on computational modeling of the cell behavior.

Feasibility of nasal epithelial brushing for the study of airway epithelial functions in CF infants

BACKGROUND

For a better understanding of the early stages of cystic fibrosis (CF), it is of major interest to study respiratory epithelial cells obtained as early as possible. Although bronchoalveolar lavage has been proposed for this purpose, nasal brushing, which is a much less invasive technique, has seldom been used in CF infants. The aim of the present study was to examine in a few infants the feasibility of a nasal brushing technique for studies of airway epithelial functions in very young CF infants.

METHODS

In 5 CF (median age 12, range 1-18 months) and 10 control infants (median age 5, range 1-17 months), a nasal brushing was performed by means of a soft sterile cytology brush, after premedication with oral paracetamol (15 mg/kg body weight) and rectal midazolam (0.2 mg/kg body weight). Samples were used for microbiological, cytological and functional studies.

RESULTS

The procedure was well tolerated. Number of cells collected was similar in CF and non-CF patients (CF: median 230x10(3), range 42x10(3)-900x10(3); non-CF: median 340x10(3), range 140x10(3)-900x10(3)). Median number of viable cells was 67% (range 31-84%). Freshly obtained samples were successfully used for studies of ciliary beating frequency and cAMP-dependent chloride efflux. In 7 out of 17 cell cultures, confluence was obtained (CF: 2 out of 7; non-CF: 5 out of 10). The feasibility of studying protein release and mRNA expression of IL-8, IL-6 and TNF-alpha, under basal conditions and after stimulation by Pseudomonas aeruginosa, was demonstrated.

CONCLUSIONS

By means of a simple nasal brushing technique easily performed and well tolerated, it is feasible, in infants, to harvest respiratory cells in sufficient amounts to study the airway epithelium using a broad range of techniques including cell culture.

Human airway surface epithelial regeneration is delayed and abnormal in cystic fibrosis

Cystic fibrosis (CF) at an advanced stage of the disease is characterized by airway epithelial injury and remodelling. Whether CF remodelling is related to infection and inflammation or due to an abnormal regenerative process is still undecided. We have recently established the expression and secretion profiles of interleukin (IL)-8, matrix metalloproteinase (MMP)-7, MMP-9, and tissue inhibitor of metalloproteinase (TIMP)-1 during non-CF airway epithelial regeneration in a humanized nude mouse xenograft model. To enhance our understanding of CF remodelling, we compared the regeneration process of non-infected human CF and non-CF nasal epithelia. In both CF and non-CF situations, epithelial regeneration was characterized by successive steps of cell adhesion and migration, proliferation, pseudostratification, and terminal differentiation. However, histological examination of the grafts showed a delay in differentiation of the CF airway epithelium. Cell proliferation was higher in the regenerating CF epithelium, and the differentiated CF epithelium exhibited a pronounced height increase and basal cell hyperplasia in comparison with non-CF epithelium. In addition, while the number of goblet cells expressing MUC5AC was similar in CF and non-CF regenerated epithelia, the number of MUC5B-immunopositive goblet cells was lower in CF grafts. The expression of human IL-8, MMP-7, MMP-9, and TIMP-1 was enhanced in CF epithelium, especially early in the regenerative process. Together, our data strongly suggest that the regeneration of human CF airway surface epithelium is characterized by remodelling, delayed differentiation, and altered pro-inflammatory and MMP responses.

Interleukin-13 interferes with CFTR and AQP5 expression and localization during human airway epithelial cell differentiation

Interleukin-13 (IL-13) is a central regulator of Th2-dominated respiratory disorders such as asthma. Lesions of the airway epithelial barrier frequently observed in chronic respiratory inflammatory diseases are repaired through proliferation, migration and differentiation of epithelial cells. Our work is focused on the effects of IL-13 in human cellular models of airway epithelial cell regeneration. We have previously shown that IL-13 altered epithelial cell polarity during mucociliary differentiation of human nasal epithelial cells. In particular, the cytokine inhibited ezrin expression and interfered with its apical localization during epithelial cell differentiation in vitro. Here we show that CFTR expression is enhanced in the presence of the cytokine, that two additional CFTR protein isoforms are expressed in IL-13-treated cells and that part of the protein is retained within the endoplasmic reticulum. We further show that aquaporin 5 expression, a water channel localized within the apical membrane of epithelial cells, is completely abolished in the presence of the cytokine. These results show that IL-13 interferes with ion and water channel expression and localization during epithelial regeneration and may thereby influence mucus composition and hydration.

Airway Epithelial Repair, Regeneration, and Remodeling after Injury in Chronic Obstructive Pulmonary Disease

In chronic obstructive pulmonary disease (COPD), exacerbations are generally associated with several causes, including pollutants, viruses, bacteria that are responsible for an excess of inflammatory mediators, and proinflammatory cytokines released by activated epithelial and inflammatory cells. The normal response of the airway surface epithelium to injury includes a succession of cellular events, varying from the loss of the surface epithelium integrity to partial shedding of the epithelium or even complete denudation of the basement membrane. The epithelium then has to repair and regenerate to restore its functions, through several mechanisms, including basal cell spreading and migration, followed by proliferation and differentiation of epithelial cells. In COPD, the remodeling of the airway epithelium, such as squamous metaplasia and mucous hyperplasia that occur during injury, may considerably disturb the innate immune functions of the airway epithelium. In vitro and in vivo models of airway epithelial wound repair and regeneration allow the study of the spatiotemporal modulation of cellular and molecular interaction factors-namely, the proinflammatory cytokines, the matrix metalloproteinases and their inhibitors, and the intercellular adhesion molecules. These factors may be markedly altered during exacerbation periods of COPD and their dysregulation may induce remodeling of the airway mucosa and a leakiness of the airway surface epithelium. More knowledge of the mechanisms involved in airway epithelium regeneration may pave the way to cytoprotective and regenerative therapeutics, allowing the reconstitution of a functional, well-differentiated airway epithelium in COPD.

Trefoil factor family 3 peptide promotes human airway epithelial ciliated cell differentiation

Human airway surface epithelium is frequently damaged by inhaled factors (viruses, bacteria, xenobiotic substances) as well as by inflammatory mediators that contribute to the shedding of surface epithelial cells. To regain its protective function, the epithelium must rapidly repair and redifferentiate. The Trefoil Factor Family (TFF) peptides are secretory products of many mucous cells. TFF3, the major TFF in the airways, is able to enhance airway epithelial cell migration, but the role of this protein in differentiation has not been defined. To identify the specific role of TFF3 in the differentiation of the human airway surface epithelium, we analyzed the temporal expression pattern of TFF3, MUC5AC, and MUC5B mucins (goblet cells) and ciliated cell markers beta-tubulin (cilia) and FOXJ1 (ciliogenesis) during human airway epithelial regeneration using in vivo humanized airway xenograft and in vitro air-liquid interface (ALI) culture models. We observed that TFF3, MUC5AC, MUC5B, and ciliated cell markers were expressed in well-differentiated airway epithelium. The addition of exogenous recombinant human TFF3 to epithelial cell cultures before the initiation of differentiation resulted in no change in MUC5AC or cytokeratin 13 (CK13, basal cell marker)-positive cells, but induced an increase in the number of FOXJ1-positive cells and in the number of beta-tubulin-positive ciliated cells (P < 0.05). Furthermore, this effect on ciliated cell differentiation could be reversed by specific epidermal growth factor (EGF) receptor (EGF-R) inhibition. These results indicate that TFF3 is able to induce ciliogenesis and to promote airway epithelial ciliated cell differentiation, in part through an EGF-R-dependent pathway.

Basal cells of the human adult airway surface epithelium retain transit-amplifying cell properties

In numerous airway diseases, such as cystic fibrosis, the epithelium is severely damaged and must regenerate to restore its defense functions. Although the human airway epithelial stem cells have not been identified yet, we have suggested recently that epithelial stem/progenitor cells exist among both human fetal basal and suprabasal cell subsets in the tracheal epithelium. In this study, we analyzed the capacity of human adult basal cells isolated from human adult airway tissues to restore a well-differentiated and functional airway epithelium. To this end, we used the human-specific basal cell markers tetraspanin CD151 and tissue factor (TF) to separate positive basal cells from negative columnar cells with a FACSAria cell sorter. Sorted epithelial cells were seeded into epithelium-denuded rat tracheae that were grafted subcutaneously in nude mice and on collagen-coated porous membranes, where they were grown at the air-liquid interface. Sorted basal and columnar populations were also analyzed for their telomerase activity, a specific transit-amplifying cell marker, by the telomeric repeat amplification protocol assay. After cell sorting, the pure and viable CD151/TF-positive basal cell population proliferated on plastic and adhered on epithelium-denuded rat tracheae, as well as on collagen-coated porous membranes, where it was able to restore a fully differentiated mucociliary and functional airway epithelium, whereas viable columnar negative cells did not. Telomerase activity was detected in the CD151/TF-positive basal cell population, but not in CD151/TF-negative columnar cells. These results demonstrate that human adult basal cells are at least airway surface transit-amplifying epithelial cells.

[Repair and regeneration of the airway epithelium]

Despite an efficient defence system, the airway surface epithelium, in permanent contact with the external milieu, is frequently injured by inhaled pollutants, microorganisms and viruses. The response of the airway surface epithelium to an acute injury includes a succession of cellular events varying from the loss of the surface epithelium integrity to partial shedding of the epithelium or even to complete denudation of the basement membrane. The epithelium has then to repair and regenerate to restore its functions, through several mechanisms including basal cell spreading and migration, followed by proliferation and differentiation of epithelial cells. The cellular and molecular factors involved in wound repair and epithelial regeneration are closely interacting and imply extracellular matrix proteins, matrix metalloproteinases (MMPs) and their inhibitors as well as cytokines and growth factors secreted by airway epithelial and mesenchymal cells. The development of in vitro and in vivo models of airway epithelium wound repair allowed the study of the spatio-temporal modulation of these factors during the different steps of epithelial repair and regeneration. In this context, several studies have demonstrated that the matrix and secretory environment are markedly involved in these mechanisms and that their dysregulation may induce remodelling of the airway mucosa. A better knowledge of the mechanisms involved in airway epithelium regeneration may pave the way to regenerative therapeutics allowing the reconstitution of a functional airway epithelium in numerous respiratory diseases such as asthma, chronic obstructive pulmonary diseases, cystic fibrosis and bronchiolitis.

alpha3alpha5beta2-Nicotinic acetylcholine receptor contributes to the wound repair of the respiratory epithelium by modulating intracellular calcium in migrating cells

Nicotinic acetylcholine receptors (nAChRs), present in human bronchial epithelial cells (HBECs), have been shown in vitro to modulate cell shape. Because cell spreading and migration are important mechanisms involved in the repair of the bronchial epithelium, we investigated the potential role of nAChRs in the wound repair of the bronchial epithelium. In vivo and in vitro, alpha3alpha5beta2-nAChRs accumulated in migrating HBECs involved in repairing a wound, whereas alpha7-nAChRs were predominantly observed in stationary confluent cells. Wound repair was improved in the presence of nAChR agonists, nicotine, and acetylcholine, and delayed in the presence of alpha3beta2 neuronal nAChR antagonists, mecamylamine, alpha-conotoxin MII, and kappa-bungarotoxin; alpha-bungarotoxin, an antagonist of alpha7-nAChR, had no effect. Addition of nicotine to a repairing wound resulted in a dose-dependent transient increase of intracellular calcium in migrating cells that line the wound edge. Mecamylamine and kappa-bungarotoxin inhibited both the cell-migration speed and the nicotine-induced intracellular calcium increase in wound-repairing migrating cells in vitro. On the contrary alpha-bungarotoxin had no significant effect on migrating cells. These results suggest that alpha3alpha5beta2-nAChRs actively contribute to the wound repair process of the respiratory epithelium by modulating intracellular calcium in wound-repairing migrating cells.