Cystic fibrosis decreases the apical membrane chloride permeability of monolayers cultured from cells of tracheal epithelium.

302

342

Mucous cell hyperplasia and airway smooth muscle (ASM) hyperresponsiveness are hallmark features of inflammatory airway diseases, including asthma. Here, we show that the recently identified calciumactivated chloride channel (CaCC) TMEM16A is expressed in the adult airway surface epithelium and ASM. The epithelial expression is increased in asthmatics, particularly in secretory cells. Based on this and the proposed functions of CaCC, we hypothesized that TMEM16A inhibitors would negatively regulate both epithelial mucin secretion and ASM contraction. We used a high-throughput screen to identify small-molecule blockers of TMEM16A-CaCC channels. We show that inhibition of TMEM16A-CaCC significantly impairs mucus secretion in primary human airway surface epithelial cells. Furthermore, inhibition of TMEM16A-CaCC significantly reduces mouse and human ASM contraction in response to cholinergic agonists. TMEM16A-CaCC blockers, including those identified here, may positively impact multiple causes of asthma symptoms.A sthma is a significant cause of morbidity and mortality worldwide, and the prevalence of this disease is increasing among all age, sex, and racial groups. Characteristic features of asthma include inflammation, subepithelial fibrosis, hyperplasia of mucus-producing cells, accumulation of mucus within airway lumens, hyperplasia of airway smooth muscle (ASM), and ASM hyperresponsiveness. Together, these symptoms impair lung function by limiting the flow of gases to and from the alveoli in the distal lung.The current standard of care for asthma involves inhaled corticosteroids for the management of inflammation combined with long-acting agonists of β2-adrenergic receptors. Despite this treatment, lung function is not improved in 30-45% of asthmatic patients, and exacerbations continue to be a major problem (reviewed in ref. 1). Asthma can be divided into at least two distinct molecular phenotypes defined by the degree of Th2 inflammation (2, 3). Cytokines, including IL-4 and IL-13, promote airway epithelial mucous cell metaplasia, subepithelial fibrosis, and hyperplasia of smooth muscle in Th2-high asthmatics, and these patients generally show improved lung function with inhaled corticosteroid therapy. A greater understanding of this heterogeneity and the molecular and physiological events that lead to airway remodeling might lead to improved diagnosis and treatment.Calcium-activated chloride channels (CaCCs) have been ascribed numerous cellular functions (reviewed in refs. 4 and 5), among these are epithelial fluid secretion and smooth muscle contraction, both of which contribute to the progression and severity of asthma. Moreover, calcium-activated chloride currents in the airway epithelium are enhanced by the Th2 cytokines IL-4 and IL-13, as well as IFN-γ (6). For these reasons, CaCC is an attractive potential therapeutic target for asthma (7). However, the study of CaCC was impeded by lack of information about the gene(s) encoding this channel. It was only relatively recently that TMEM16A (transmembrane p...

Section: Increased Expression Of Tmem16a In Epithelial Cells From Astmentioning

confidence: 99%

Calcium-activated chloride channel TMEM16A modulates mucin secretion and airway smooth muscle contraction

Huang

Zhang

et al. 2012

302

342

“…Applying amiloride, an inhibitor of epithelial Na + channels (ENaC), caused a greater reduction in nasal Vt (ΔVt amil ) in CF epithelia. Subsequent studies revealed that CF epithelia were Cl − impermeable compared with non-CF epithelia (9,10). Studies of excised nasal epithelia in Ussing chambers yielded varying results that, as the authors noted, might be attributed to epithelial location (CF polyps vs. non-CF turbinates), tissue injury, medications, small sample sizes, chronic infection, inflammation, and exclusion bias (11).…”

mentioning

confidence: 99%

“…Loss of anion conductance has been apparent in nearly all studies of differentiated CF airway epithelial cultures (9,10,13,14). In addition, some studies showed an increased short-circuit current (Isc) and voltage under basal conditions (basal Isc and basal Vt, respectively) and increased reductions with amiloride application (ΔIsc amil and ΔVt amil , respectively) (7).…”

mentioning

confidence: 99%

Human cystic fibrosis airway epithelia have reduced Cl ⁻ conductance but not increased Na ⁺ conductance

Itani

Chen

Karp

et al. 2011

113

Loss of cystic fibrosis transmembrane conductance regulator (CFTR) anion channel function causes cystic fibrosis (CF) lung disease. CFTR is expressed in airway epithelia, but how CF alters electrolyte transport across airway epithelia has remained uncertain. Recent studies of a porcine model showed that in vivo, excised, and cultured CFTR −/− and CFTR ΔF508/ΔF508 airway epithelia lacked anion conductance, and they did not hyperabsorb Na + . Therefore, we asked whether Cl − and Na + conductances were altered in human CF airway epithelia. We studied differentiated primary cultures of tracheal/bronchial epithelia and found that transepithelial conductance (Gt) under basal conditions and the cAMP-stimulated increase in Gt were markedly attenuated in CF epithelia compared with non-CF epithelia. These data reflect loss of the CFTR anion conductance. In CF and non-CF epithelia, the Na + channel inhibitor amiloride produced similar reductions in Gt and Na + absorption, indicating that Na + conductance in CF epithelia did not exceed that in non-CF epithelia. Consistent with previous reports, adding amiloride caused greater reductions in transepithelial voltage and short-circuit current in CF epithelia than in non-CF epithelia; these changes are attributed to loss of a Cl − conductance. These results indicate that Na + conductance was not increased in these cultured CF tracheal/bronchial epithelia and point to loss of anion transport as key to airway epithelial dysfunction in CF.chloride secretion | epithelial Na + channels

“…Twenty-six years ago, epithelial cell membranes of CF patients were found to lack certain ion channels involved in transmembrane Cl Ϫ flux (7)(8)(9). Six years later, the gene defective in CF patients was identified (10)(11)(12).…”

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confidence: 99%

The antioxidant role of thiocyanate in the pathogenesis of cystic fibrosis and other inflammation-related diseases

Szép

Lü

2009

124

Cystic fibrosis (CF) is a pleiotropic disease, originating from mutations in the CF transmembrane conductance regulator (CFTR). Lung injuries inflicted by recurring infection and excessive inflammation cause Ϸ90% of the morbidity and mortality of CF patients. It remains unclear how CFTR mutations lead to lung illness. Although commonly known as a Cl ؊ channel, CFTR also conducts thiocyanate (SCN ؊ ) ions, important because, in several ways, they can limit potentially harmful accumulations of hydrogen peroxide (H 2O2) and hypochlorite (OCl ؊ ). First, lactoperoxidase (LPO) in the airways catalyzes oxidation of SCN ؊ to tissue-innocuous hypothiocyanite (OSCN ؊ ), while consuming H2O2. Second, SCN ؊ even at low concentrations competes effectively with Cl ؊ for myeloperoxidase (MPO) (which is released by white blood cells), thus limiting OCl ؊ production by the enzyme. Third, SCN ؊ can rapidly reduce OCl ؊ without catalysis. Here, we show that SCN ؊ and LPO protect a lung cell line from injuries caused by H 2O2; and that SCN ؊ protects from OCl ؊ made by MPO. Of relevance to inflammation in other diseases, we find that in three other tested cell types (arterial endothelial cells, a neuronal cell line, and a pancreatic ␤ cell line) SCN ؊ at concentrations of >100 M greatly attenuates the cytotoxicity of MPO. Humans naturally derive SCN ؊ from edible plants, and plasma SCN ؊ levels of the general population vary from 10 to 140 M. Our findings raise the possibility that insufficient levels of antioxidant SCN ؊ provide inadequate protection from OCl ؊ , thus worsening inflammatory diseases, and predisposing humans to diseases linked to MPO activity, including atherosclerosis, neurodegeneration, and certain cancers.hydrogen peroxide ͉ hypochlorite ͉ hypothiocyanite ͉ lactoperoxidase ͉ myeloperoxidase