Hyperconcentrated Mucus Unifies Submucosal Gland and Superficial Airway Dysfunction in Cystic Fibrosis

Cystic fibrosis (CF) is characterized by abnormal transepithelial ion transport. However, a description of CF lung disease pathophysiology unifying superficial epithelial and submucosal gland (SMG) dysfunctions has remained elusive. We hypothesized that biophysical abnormalities associated with CF mucus hyperconcentration provide a unifying mechanism. Studies of the anion secretion-inhibited pig airway CF model revealed elevated SMG mucus concentrations, osmotic pressures, and SMG mucus accumulation. Human airway studies revealed hyperconcentrated CF SMG mucus with raised osmotic pressures and cohesive forces predicted to limit SMG mucus secretion/release. Utilizing proline-rich protein 4 (PRR4) as a biomarker of SMG secretion, proteomics analyses of CF sputum revealed markedly lower PRR4 levels compared to healthy and bronchiectasis controls, consistent with a failure of CF SMGs to secrete mucus onto airway surfaces. Raised mucus osmotic/cohesive forces, reflecting mucus hyperconcentration, provide a unifying mechanism that describes disease-initiating mucus accumulation on airway surfaces and within SMGs of the CF lung.

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Effect of anion transport inhibition on mucus secretion by airway submucosal glands

AJP Lung Cellular and Molecular Physiology ◽

10.1152/ajplung.1997.272.2.l372 ◽

1997 ◽

Vol 272 (2) ◽

pp. L372-L377 ◽

Cited By ~ 16

Author(s):

S. K. Inglis ◽

M. R. Corboz ◽

A. E. Taylor ◽

S. T. Ballard

Keyword(s):

Cystic Fibrosis ◽

Anion Transport ◽

Mucus Secretion ◽

Disulfonic Acid ◽

Pathological Changes ◽

Submucosal Gland ◽

Anion Secretion ◽

Submucosal Glands ◽

Gland Duct

To model the airway glandular defect in cystic fibrosis (CF), the effect of anion secretion blockers on submucosal gland mucus secretion was investigated. Porcine distal bronchi were isolated, pretreated with a Cl- secretion blocker (bumetanide) and/or a combination of blockers to inhibit HCO3- secretion (dimethylamiloride, acetazolamide, and 4,4'-diisothiocyanostilbene-2,2'-disulfonic acid), and then treated with acetylcholine (ACh), a glandular liquid and mucus secretagogue. Bronchi were then fixed, sectioned, and stained for mucins. Each gland duct was ranked for mucin content from zero (no mucin) to five (duct completely occluded with mucin). Untreated bronchi, bronchi treated only with ACh, and ACh-treated bronchi that received either bumetanide or the HCO3- secretion blockers all exhibited low gland duct mucin content (1.18 +/- 0.34, 0.59 +/- 0.07, 0.65 +/- 0.03, and 0.83 +/- 0.11, respectively). However, pretreatment with both Cl- and HCO3- secretion blockers before ACh addition resulted in substantial and significant ductal mucus accumulation (3.57 +/- 0.22). In situ videomicroscopy studies of intact airways confirmed these results. Thus inhibition of the anion (and presumably liquid) secretion response to ACh leads to mucus obstruction of submucosal gland ducts that resembles the early pathological changes observed in CF.

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Defective Ion Channel in Cystic Fibrosis: Current Development in Treatment of Cystic Fibrosis

Asian Journal of Biochemistry, Genetics and Molecular Biology ◽

10.9734/ajbgmb/2020/v4i130099 ◽

2020 ◽

pp. 28-34

Author(s):

Ngoga Godfrey ◽

M. M. Ganyam ◽

G.O. Ibiang ◽

C. A. Difa ◽

Nelson Christian

Keyword(s):

Cystic Fibrosis ◽

Ion Transport ◽

Ion Channel ◽

Lung Disease ◽

Defense Mechanisms ◽

Respiratory Infections ◽

The Body ◽

Transmembrane Conductance Regulator ◽

Transmembrane Conductance ◽

Airway Defense

Cystic fibrosis is an inherited disorder that causes severe damage to the lungs, digestive system and other organs in the body. Cystic fibrosis transmembrane conductance regulator (CFTR) is involved in the production of mucus, sweat and digestive juices. These secreted fluids are normally thin and slippery. But in people with cystic fibrosis, a defective gene in CFTR causes the secretions to become sticky and thick. Instead of acting as a lubricant, the secretions plug up tubes, ducts and passage ways, especially in the lungs and pancreas. This mucus leads to the formation of bacterial microenvironments known as biofilms (a niche that harbors bacteria; Staphylococcus aureus, Haemophilus influenzae, and Pseudomonas aeruginosa ) that are difficult for immune cells and antibiotics to penetrate. Viscous secretions and persistent respiratory infections repeatedly damage the lung by gradually remodeling the airways, which makes infection even more difficult to eradicate. CFTR, a Cl– selective ion channel, is a prototypic member of the ATP-binding cassette transporter super family that is expressed in several organs. Understanding how these complexes regulate the intracellular trafficking and activity of CFTR provides a unique insight into the aetiology of cystic fibrosis and other diseases associated to it. Cystic fibrosis patients exhibit lung disease consistent with a failure of innate airway defense mechanisms. The link between abnormal ion transport, disease initiation and progression is not fully understood, but airway mucus dehydration seems paramount in the initiation of CF lung disease. New therapies are currently in development that target the ion transport defects in CF with the intention of rehydrating airway surfaces.

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Molecular and cell biology of cystic fibrosis

Journal of Applied Physiology ◽

10.1152/jappl.1991.70.5.2331 ◽

1991 ◽

Vol 70 (5) ◽

pp. 2331-2333 ◽

Cited By ~ 6

Author(s):

P. B. Davis

Keyword(s):

Cystic Fibrosis ◽

Gene Therapy ◽

Life Expectancy ◽

Ion Transport ◽

Lung Disease ◽

Cell Biology ◽

Know How ◽

Therapeutic Alternatives

The questions emerged in better focus: we need to know, definitively, what CFTR is and what it does. We need to know how mutant CFTR expression leads to the relentless lung disease that takes the lives of the patients. We need to know how the different mutations in CFTR behave functionally. Much more information is needed on the pathways for ion transport in the airways in order for us to consider therapeutic alternatives. Better information on CFTR expression, particularly in the lung, would greatly facilitate consideration of pathophysiology as well as gene therapy. Many of these questions can be attacked by imaginative use of the tools already in hand. The need is urgent. The wondrous scientific advancements of the last five years and the additional money being spent on CF research have bought no dramatic increase in life expectancy for the patients. Every day, three more succumb.

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Mucin glycosylation changes in cystic fibrosis lung disease are not manifest in submucosal gland secretions

Biochemical Journal ◽

10.1042/bj20041641 ◽

2005 ◽

Vol 387 (3) ◽

pp. 911-919 ◽

Cited By ~ 38

Author(s):

Benjamin L. SCHULZ ◽

Andrew J. SLOANE ◽

Leanne J. ROBINSON ◽

Lucille T. SEBASTIAN ◽

Allan R. GLANVILLE ◽

...

Keyword(s):

Cystic Fibrosis ◽

Lung Disease ◽

Blood Type ◽

Submucosal Gland ◽

Bacterial Binding ◽

Cystic Fibrosis Lung Disease ◽

A Minor ◽

End Stage ◽

Severe Lung Disease ◽

Severe Lung

SMG (submucosal gland) secretions are a major component of the airway surface liquid, are associated with innate immunity in the lung, and have been reported to be altered in lung disease. Changes in lung mucosal glycosylation have been reported in CF (cystic fibrosis), which may be responsible for differential bacterial binding to glycosylated components in the lung mucosa and hence increased pre-disposition to pulmonary infection. Glycoproteomic analysis was performed on SMG secretions collected from explanted bronchial tissue of subjects with severe lung disease, with and without CF, and controls without lung disease. Mucins MUC5B and MUC5AC were shown to be the dominant high-molecular-mass glycoprotein components, with a minor non-mucin glycoprotein component, gp-340, also present. Oligosaccharides containing blood-group determinants corresponding to subjects' blood type were abundant on MUC5B/MUC5AC, as were Lewis-type epitopes and their sialylated analogues, which are ligands for pathogens and leucocytes. No significant differences were found in the glycosylation of MUC5B/MUC5AC or gp-340 between CF and non-CF subjects with severe lung disease, implying that CF does not influence SMG secretion mucin glycosylation in end-stage lung disease. There were also no significant differences found in the glycosylation of these components in severe lung disease compared with non-diseased lungs. This suggests that previously reported changes in the glycosylation of respiratory glycoconjugates in CF, and other pulmonary conditions, are not due to the glycosylation of components in SMG secretions, but may involve other secretions, responses or extracellular factors.

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Progenitor cells of the adult human airway involved in submucosal gland development

Development ◽

10.1242/dev.121.7.2031 ◽

1995 ◽

Vol 121 (7) ◽

pp. 2031-2046 ◽

Cited By ~ 2

Author(s):

J.F. Engelhardt ◽

H. Schlossberg ◽

J.R. Yankaskas ◽

L. Dudus

Keyword(s):

Cystic Fibrosis ◽

Progenitor Cells ◽

Airway Epithelium ◽

Progenitor Cell ◽

Xenograft Model ◽

Submucosal Gland ◽

Adult Human ◽

Human Airway ◽

Submucosal Glands ◽

Gland Development

A bronchial xenograft model of the human airway was used to identify submucosal gland progenitor cells within the surface airway epithelium. Lineage analysis using recombinant retroviruses has demonstrated considerable diversity in the cellular composition of expanded clones within reconstituted xenograft airway epithelium. These findings provide evidence for the existence of multiple progenitors in the airway with either limited or pluripotent capacity for differentiation. Furthermore, the development of transgene-expressing submucosal glands was associated with a single subset of surface airway epithelial clones. This gland progenitor cell demonstrated two discernible characteristics consistent with the identification of an airway stem cell including: (1) pluripotent capacity for airway differentiation and (2) a two-fold higher proliferative rate than other observed clone types. The number of progenitor cells involved in gland development was also assessed by clonal analysis using alkaline phosphatase and beta-galactosidase transgenes. These studies demonstrated that more than one airway progenitor cell is involved in the initial stages of gland development. A second explanation for the high prevalence of non-clonality in developing glands was suggested from three-dimensional reconstruction of transgene marked glands. These reconstruction experiments demonstrated that 27% of glands contained more than one duct to the surface airway epithelium. This observation suggests a novel mechanism of gland morphogenesis by which independently formed glands interact to join glandular lumens. Such a mechanism of glandular development and morphogenesis may play an important role in normal submucosal gland development and/or the progression of hypersecretory diseases of the adult human airway as seen in cystic fibrosis, chronic bronchitis and asthma. The identification of progenitor cells with the capacity to form submucosal glands has implications on the targets for gene therapy in cystic fibrosis.

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Bicarbonate and Chloride Secretion in Calu-3 Human Airway Epithelial Cells

The Journal of General Physiology ◽

10.1085/jgp.113.5.743 ◽

1999 ◽

Vol 113 (5) ◽

pp. 743-760 ◽

Cited By ~ 202

Author(s):

Daniel C. Devor ◽

Ashvani K. Singh ◽

Linda C. Lambert ◽

Arthur DeLuca ◽

Raymond A. Frizzell ◽

...

Keyword(s):

Cystic Fibrosis ◽

Basolateral Membrane ◽

Disulfonic Acid ◽

Transmembrane Conductance Regulator ◽

Submucosal Gland ◽

Transmembrane Conductance ◽

Cl Secretion ◽

Human Airway ◽

Serous Cell ◽

Cystic Fibrosis Transmembrane

Serous cells are the predominant site of cystic fibrosis transmembrane conductance regulator expression in the airways, and they make a significant contribution to the volume, composition, and consistency of the submucosal gland secretions. We have employed the human airway serous cell line Calu-3 as a model system to investigate the mechanisms of serous cell anion secretion. Forskolin-stimulated Calu-3 cells secrete HCO−3 by a Cl −-independent, serosal Na+-dependent, serosal bumetanide-insensitive, and serosal 4,4′-dinitrostilben-2,2′-disulfonic acid (DNDS)–sensitive, electrogenic mechanism as judged by transepithelial currents, isotopic fluxes, and the results of ion substitution, pharmacology, and pH studies. Similar studies revealed that stimulation of Calu-3 cells with 1-ethyl-2-benzimidazolinone (1-EBIO), an activator of basolateral membrane Ca2+-activated K+ channels, reduced HCO−3 secretion and caused the secretion of Cl − by a bumetanide-sensitive, electrogenic mechanism. Nystatin permeabilization of Calu-3 monolayers demonstrated 1-EBIO activated a charybdotoxin- and clotrimazole- inhibited basolateral membrane K+ current. Patch-clamp studies confirmed the presence of an intermediate conductance inwardly rectified K+ channel with this pharmacological profile. We propose that hyperpolarization of the basolateral membrane voltage elicits a switch from HCO−3 secretion to Cl − secretion because the uptake of HCO−3 across the basolateral membrane is mediated by a 4,4 ′-dinitrostilben-2,2′-disulfonic acid (DNDS)–sensitive Na+:HCO−3 cotransporter. Since the stoichiometry reported for Na +:HCO−3 cotransport is 1:2 or 1:3, hyperpolarization of the basolateral membrane potential by 1-EBIO would inhibit HCO−3 entry and favor the secretion of Cl −. Therefore, differential regulation of the basolateral membrane K+ conductance by secretory agonists could provide a means of stimulating HCO−3 and Cl − secretion. In this context, cystic fibrosis transmembrane conductance regulator could serve as both a HCO−3 and a Cl − channel, mediating the apical membrane exit of either anion depending on basolateral membrane anion entry mechanisms and the driving forces that prevail. If these results with Calu-3 cells accurately reflect the transport properties of native submucosal gland serous cells, then HCO−3 secretion in the human airways warrants greater attention.

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