Respiratory mucous secretions in patients with cystic fibrosis: relationship between levels of highly sulfated mucin component and severity of the disease

Mucins Inhibit Coronavirus Infection in a Glycan-Dependent Manner

Mucins are a diverse and heterogeneous family of glycoproteins that comprise the bulk of mucus and the epithelial glycocalyx. Mucins are intimately involved in viral transmission. Mucin and virus laden particles can be expelled from the mouth and nose to later infect others. Viruses must also penetrate the mucus layer before cell entry and replication. The role of mucins and their molecular structure have not been well-characterized in coronavirus transmission studies. Laboratory studies predicting high rates of fomite transmission have not translated to real-world infections, and mucins may be one culprit. Here, we probed both surface and direct contact transmission scenarios for their dependence on mucins and their structure. We utilized disease-causing, bovine-derived, human coronavirus OC43. We found that bovine mucins could inhibit the infection of live cells in a concentration- and glycan-dependent manner. The effects were observed in both mock fomite and direct contact transmission experiments and were not dependent upon surface material or time-on-surface. However, the effects were abrogated by removal of the glycans or in a cross-species infection scenario where bovine mucin could not inhibit the infection of a murine coronavirus. Together, our data indicate that the mucin molecular structure plays a complex and important role in host defense.

Molecular Dynamics Simulations to Explore the Structure and Rheological Properties of Normal and Hyperconcentrated Airway Mucus

We develop the first molecular dynamics model of airway mucus based on the detailed physical properties and chemical structure of the predominant gel-forming mucin MUC5B. Our airway mucus model leverages the LAMMPS open-source code [https://lammps.sandia.gov], based on the statistical physics of polymers, from single molecules to networks. On top of the LAMMPS platform, the chemical structure of MUC5B is used to superimpose proximity-based, non-covalent, transient interactions within and between the specific domains of MUC5B polymers. We explore feasible ranges of hydrophobic and electrostatic interaction strengths between MUC5B domains with 9 nanometer spatial and 1 nanosecond temporal resolution. Our goal here is to propose and test a mechanistic hypothesis for a striking clinical observation with respect to airway mucus: a 10-fold increase in non-swellable, dense structures called flakes during progression of cystic fibrosis disease. Among the myriad possible effects that might promote self-organization of MUC5B networks into flake structures, we hypothesize and confirm that the clinically confirmed increase in mucin concentration, from 1.5 to 5 mg/mL, alone is sufficient to drive the structure changes observed with scanning electron microscopy images from experimental samples. We post-process the LAMMPS simulated datasets at 1.5 and 5 mg/mL, both to image the structure transition and compare with scanning electron micrographs and to show that the 3.33-fold increase in concentration induces closer proximity of interacting electrostatic and hydrophobic domains, thereby amplifying the proximity-based strength of the interactions.

Evidence of early increased sialylation of airway mucins and defective mucociliary clearance in CFTR-deficient piglets

BACKGROUND

Bacterial colonization in cystic fibrosis (CF) lungs has been directly associated to the loss of CFTR function, and/or secondarily linked to repetitive cycles of chronic inflammation/infection. We hypothesized that altered molecular properties of mucins could contribute to this process.

METHODS

Newborn CFTR^+/+ and CFTR^-/- were sacrificed before and 6 h after inoculation with luminescent Pseudomonas aeruginosa into the tracheal carina. Tracheal mucosa and the bronchoalveolar lavage (BAL) fluid were collected to determine the level of mucin O-glycosylation, bacteria binding to mucins and the airways transcriptome. Disturbances in mucociliary transport were determined by ex-vivo imaging of luminescent Pseudomonas aeruginosa.

RESULTS

We provide evidence of an increased sialylation of CF airway mucins and impaired mucociliary transport that occur before the onset of inflammation. Hypersialylation of mucins was reproduced on tracheal explants from non CF animals treated with GlyH101, an inhibitor of CFTR channel activity, indicating a causal relationship between the absence of CFTR expression and the sialylation of mucins. This increased sialylation was correlated to an increased adherence of P. aeruginosa to mucins. In vivo infection of newborn CF piglets by live luminescent P. aeruginosa demonstrated an impairment of mucociliary transport of this bacterium, with no evidence of pre-existing inflammation.

CONCLUSIONS

Our results document for the first time in a well-defined CF animal model modifications that affect the O-glycan chains of mucins. These alterations precede infection and inflammation of airway tissues, and provide a favorable context for microbial development in CF lung that hallmarks this disease.

Comparative Membrane N-Glycomics of Different Breast Cancer Cell Lines To Understand Breast Cancer Brain Metastasis

The mechanism of brain metastatic breast cancer has gained attention because of its increased incidence rate and its low survival rate. Aberrant protein glycosylation is thought to be a contributing factor in this metastatic mechanism, in which metastatic cancer cells can pass through the blood-brain barrier (BBB). The cell membrane is the outermost layer of a cell and in direct contact with the environment and with other cells, making membrane glycans especially important in many biological processes that include mediating cell-cell adhesion, cell signaling, and interactions. Thus, membrane glycomics has attracted more interest for a variety of disease studies in recent years. To reveal the role that membrane N-glycans play in breast cancer brain metastasis, in this study, membrane enrichment was achieved by ultracentrifugation. Liquid chromatography-tandem mass spectrometry was employed to analyze enriched membrane N-glycomes from five breast cancer cell lines and one brain cancer cell line. Relative quantitative glycomic data from each cell line were compared to MDA-MB-231BR, which is the brain-seeking cell line. The higher sialylation level observed in MDA-MB-231BR suggested the importance of sialylation as it might assist with cell invasion and the penetration of the BBB. Some highly sialylated N-glycans, such as HexNAc₅Hex₆DeoxyHex₁NeuAc₃ and HexNAc₆Hex₇DeoxyHex₁NeuAc₃, exhibited higher abundances in 231BR, indicating their possible contributions to breast cancer brain metastasis as well as their potential to be indicators for the breast cancer brain metastasis.

Sialic acid-to-urea ratio as a measure of airway surface hydration

Although airway mucus dehydration is key to pathophysiology of cystic fibrosis (CF) and other airways diseases, measuring mucus hydration is challenging. We explored a robust method to estimate mucus hydration using sialic acid as a marker for mucin content. Terminal sialic acid residues from mucins were cleaved by acid hydrolysis from airway samples, and concentrations of sialic acid, urea, and other biomarkers were analyzed by mass spectrometry. In mucins purified from human airway epithelial (HAE), sialic acid concentrations after acid hydrolysis correlated with mucin concentrations (r² = 0.92). Sialic acid-to-urea ratios measured from filters applied to the apical surface of cultured HAE correlated to percent solids and were elevated in samples from CF HAEs relative to controls (2.2 ± 1.1 vs. 0.93 ± 1.8, P < 0.01). Sialic acid-to-urea ratios were elevated in bronchoalveolar lavage fluid (BALF) from β-epithelial sodium channel (ENaC) transgenic mice, known to have reduced mucus hydration, and mice sensitized to house dust mite allergen. In a translational application, elevated sialic acid-to-urea ratios were measured in BALF from young children with CF who had airway infection relative to those who did not (5.5 ± 3.7 vs. 1.9 ± 1.4, P < 0.02) and could be assessed simultaneously with established biomarkers of inflammation. The sialic acid-to-urea ratio performed similarly to percent solids, the gold standard measure of mucus hydration. The method proved robust and has potential to serve as flexible techniques to assess mucin hydration, particularly in samples like BALF in which established methods such as percent solids cannot be utilized.

PSEA-Quant: a protein set enrichment analysis on label-free and label-based protein quantification data

The majority of large-scale proteomics quantification methods yield long lists of quantified proteins that are often difficult to interpret and poorly reproduced. Computational approaches are required to analyze such intricate quantitative proteomics data sets. We propose a statistical approach to computationally identify protein sets (e.g., Gene Ontology (GO) terms) that are significantly enriched with abundant proteins with reproducible quantification measurements across a set of replicates. To this end, we developed PSEA-Quant, a protein set enrichment analysis algorithm for label-free and label-based protein quantification data sets. It offers an alternative approach to classic GO analyses, models protein annotation biases, and allows the analysis of samples originating from a single condition, unlike analogous approaches such as GSEA and PSEA. We demonstrate that PSEA-Quant produces results complementary to GO analyses. We also show that PSEA-Quant provides valuable information about the biological processes involved in cystic fibrosis using label-free protein quantification of a cell line expressing a CFTR mutant. Finally, PSEA-Quant highlights the differences in the mechanisms taking place in the human, rat, and mouse brain frontal cortices based on tandem mass tag quantification. Our approach, which is available online, will thus improve the analysis of proteomics quantification data sets by providing meaningful biological insights.

CFTR, mucins, and mucus obstruction in cystic fibrosis

Mucus pathology in cystic fibrosis (CF) has been known for as long as the disease has been recognized and is sometimes called mucoviscidosis. The disease is marked by mucus hyperproduction and plugging in many organs, which are usually most fatal in the airways of CF patients, once the problem of meconium ileus at birth is resolved. After the CF gene, CFTR, was cloned and its protein product identified as a cAMP-regulated Cl(-) channel, causal mechanisms underlying the strong mucus phenotype of the disease became obscure. Here we focus on mucin genes and polymeric mucin glycoproteins, examining their regulation and potential relationships to a dysfunctional cystic fibrosis transmembrane conductance regulator (CFTR). Detailed examination of CFTR expression in organs and different cell types indicates that changes in CFTR expression do not always correlate with the severity of CF disease or mucus accumulation. Thus, the mucus hyperproduction that typifies CF does not appear to be a direct cause of a defective CFTR but, rather, to be a downstream consequence. In organs like the lung, up-regulation of mucin gene expression by inflammation results from chronic infection; however, in other instances and organs, the inflammation may have a non-infectious origin. The mucus plugging phenotype of the β-subunit of the epithelial Na(+) channel (βENaC)-overexpressing mouse is proving to be an archetypal example of this kind of inflammation, with a dehydrated airway surface/concentrated mucus gel apparently providing the inflammatory stimulus. Data indicate that the luminal HCO(3)(-) deficiency recently described for CF epithelia may also provide such a stimulus, perhaps by causing a mal-maturation of mucins as they are released onto luminal surfaces. In any event, the path between CFTR dysfunction and mucus hyperproduction has proven tortuous, and its unraveling continues to offer its own twists and turns, along with fascinating glimpses into biology.

Comparative transcriptome analyses of Pseudomonas aeruginosa

One of the hallmarks of bacterial survival is their ability to adapt rapidly to changing environmental conditions. Niche adaptation is a response to the signals received that are relayed, often to regulators that modulate gene expression. In the post-genomic era, DNA microarrays are used to study the dynamics of gene expression on a global scale. Numerous studies have used Pseudomonas aeruginosa--a Gram-negative environmental and opportunistic human pathogenic bacterium--as the model organism in whole-genome transcriptome analysis. This paper reviews the transcriptome studies that have led to immense advances in our understanding of the biology of this intractable human pathogen. Comparative analysis of 23 P. aeruginosa transcriptome studies has led to the identification of a unique set of genes that are signal specific and a core set that is differentially regulated. The 303 genes in the core set are involved in bacterial homeostasis, making them attractive therapeutic targets.

Transcriptomic analysis of the sulfate starvation response of Pseudomonas aeruginosa

Pseudomonas aeruginosa is an opportunistic pathogen that causes a number of infections in humans, but is best known for its association with cystic fibrosis. It is able to use a wide range of sulfur compounds as sources of sulfur for growth. Gene expression in response to changes in sulfur supply was studied in P. aeruginosa E601, a cystic fibrosis isolate that displays mucin sulfatase activity, and in P. aeruginosa PAO1. A large family of genes was found to be upregulated by sulfate limitation in both isolates, encoding sulfatases and sulfonatases, transport systems, oxidative stress proteins, and a sulfate-regulated TonB/ExbBD complex. These genes were localized in five distinct islands on the genome and encoded proteins with a significantly reduced content of cysteine and methionine. Growth of P. aeruginosa E601 with mucin as the sulfur source led not only to a sulfate starvation response but also to induction of genes involved with type III secretion systems.

Glycosylation of sputum mucins is altered in cystic fibrosis patients

Cystic fibrosis (CF) is characterized by chronic lung infection and inflammation, with periods of acute exacerbation causing severe and irreversible lung tissue damage. We used protein and glycosylation analysis of high-molecular mass proteins in saline-induced sputum from CF adults with and without an acute exacerbation, CF children with stable disease and preserved lung function, and healthy non-CF adult and child controls to identify potential biomarkers of lung condition. While the main high-molecular mass proteins in the sputum from all subjects were the mucins MUC5B and MUC5AC, these appeared degraded in CF adults with an exacerbation. The glycosylation of these mucins also showed reduced sulfation, increased sialylation, and reduced fucosylation in CF adults compared with controls. Despite improvements in pulmonary function after hospitalization, these differences remained. Two CF children showed glycoprotein profiles similar to those of CF adults with exacerbations and also presented with pulmonary flares shortly after sampling, while the remaining CF children had profiles indistinguishable from those of healthy non-CF controls. Sputum mucin glycosylation and degradation are therefore not inherently different in CF, and may also be useful predictive biomarkers of lung condition.

Characterization of a bifunctional catalase-peroxidase of Burkholderia cenocepacia

Isolates of Burkholderia cenocepacia express a putative haem-binding protein (molecular mass 97 kDa) that displays intrinsic peroxidase activity. Its role has been re-evaluated, and we now show that it is a bifunctional catalase-peroxidase, with activity against tetramethylbenzidine (TMB), o-dianisidine, pyrogallol, and 2,2'-azino-bis(3-ethylbenzthiazoline-6-sulphonic) acid (ABTS). Both peroxidase and catalase activities are optimal at pH 5.5-6.0. The gene encoding this enzyme was cloned and expressed in Escherichia coli. We have named it katG because of its similarity to other katGs, including that from Burkholderia pseudomallei. It is substantially similar to a previously described catalase-peroxidase of B. cenocepacia (katA). MS analysis indicated that the initial katG translation product may be post-translationally modified in B. cenocepacia to give rise to the mature 97-kDa catalase-peroxidase.

Altered O-glycosylation and sulfation of airway mucins associated with cystic fibrosis

Cystic fibrosis (CF) is the most lethal genetic disorder in Caucasians and is characterized by the production of excessive amounts of viscous mucus secretions in the airways of patients, leading to airway obstruction, chronic bacterial infections, and respiratory failure. Previous studies indicate that CF-derived airway mucins are glycosylated and sulfated differently compared with mucins from nondiseased (ND) individuals. To address unresolved questions about mucin glycosylation and sulfation, we examined O-glycan structures in mucins purified from mucus secretions of two CF donors versus two ND donors. All mucins contained galactose (Gal), N-acetylglucosamine (GlcNAc), N-acetylgalactosamine (GalNAc), fucose (Fuc), and sialic acid (Neu5Ac). However, CF mucins had higher sugar content and more O-glycans compared with ND mucins. Both ND and CF mucins contained GlcNAc-6-sulfate (GlcNAc-6-Sul), Gal-6-Sul, and Gal-3-Sul, but CF mucins had higher amounts of the 6-sulfated species. O-glycans were released from CF and ND mucins and derivatized with 2-aminobenzamide (2-AB), separated by ion exchange chromatography, and quantified by fluorescence. There was nearly a two-fold increase in sulfation and sialylation in CF compared with ND mucin. High performance liquid chromatography (HPLC) profiles of glycans showed differences between the two CF samples compared with the two ND samples. Glycan compositions were defined by matrix-assisted laser desorption/ionization time-of-flight mass spectrometry (MALDI-TOF-MS). Unexpectedly, 260 compositional types of O-glycans were identified, and CF mucins contained a higher proportion of sialylated and sulfated O-glycans compared with ND mucins. These profound structural differences in mucin glycosylation in CF patients may contribute to inflammatory responses and increased pathogenesis by Pseudomonas aeruginosa.

Does deficiency of arylsulfatase B have a role in cystic fibrosis?

Cystic fibrosis (CF) is associated with mutation and abnormal function of the cystic fibrosis transmembrane conductance regulator (CFTR) that affects cellular chloride transport. Clinically, CF of the lung is associated with excessive accumulation of secretions, including the sulfated glycosaminoglycans, chondroitin sulfate and dermatan sulfate (DS), both of which contain sulfated N-acetylgalactosamine residues. The sulfatase enzymes, which are a highly conserved group of enzymes with high specificity for designated sulfate groups, include arylsulfatase B, a lysosomal enzyme. Arylsulfatase B, also known as N-acetyl galactosamine 4-sulfatase, can degrade DS and chondroitin-4 sulfate. Previously reported data demonstrated diminished activity of arylsulfatase B in lymphoid cell lines of patients with CF compared to normal control subjects. Frequent infections with Pseudomonas, a sulfatase-producing organism, occur in patients with CF, whereas infections with Mycobacterium tuberculosis, which lacks sulfatase activity, are infrequent. Additional investigation to determine if diminished function of arylsulfatase B is a consistent finding in cells of patients with CF may be informative, and may help to correlate the molecular, biochemical, and clinical characteristics of CF.

Effect of chondroitinase ABC on purulent sputum from cystic fibrosis and other patients

Cystic fibrosis (CF) patients develop chronic lung infections associated with airway obstruction by viscous and insoluble mucus secretions. Although mucus glycoproteins (mucins) are thought to be responsible for mucus plugs, other glycoconjugate components of airway secretions have not been systematically evaluated. The aim of the present study was to determine whether chondroitin sulfate proteoglycans (CSPG) contribute to the insolubility of CF sputum. Sputa obtained from 18 CF patients were incubated with chondroitinase ABC (ChABC) or buffer (control) for 18 h at 37 degrees C, and after centrifugation at 12,000 g, the volume of the insoluble pellet and turbidity of the supernatant were determined as measures of solubility. ChABC caused a 70-90% reduction in supernatant turbidity and a 60-70% decrease in pellet volume of the 13 purulent CF sputa, but had much less effect on the five nonpurulent CF sputa tested. Similar results were obtained with two non-CF purulent and two non-CF, nonpurulent sputa. Gel electrophoresis, Western blot, and slot blot immunoassays with antichondroitin sulfate and antimucin antibodies revealed that purulent sputa (CF and non-CF) contained more CSPG and less mucin than nonpurulent sputa. In vitro mixing experiments showed that mucin in nonpurulent sputa was reduced upon incubation with purulent sputa, presumably because of degradation or a loss of immunoreactive mucin epitopes from leukocyte and/or bacterial enzymes present in purulent sputa. Our results suggest that CSPG contribute more significantly than mucins to the insolubility of purulent tracheobronchial secretions from CF patients. Because purulent sputa from non-CF patients showed a similar pattern, our observations with CF sputa may have wider applicability.

Pharmacological approaches to discovery and development of new mucolytic agents

Airway mucus is the secretory product of the mucous cells; it is a variable mixture of water, mucous glycoproteins, low molecular weight ions, proteins, and lipids, whose physical properties are important for airway defense. The factors that contribute to the physical properties of mucus are complex, and there are a number of pharmacological strategies that can potentially serve to improve the clearability of airway mucus. Novel mucoactive approaches include strategies for mucoregulation--decreasing the abnormal volume of mucus secretion--and medications designed to improve the cough clearability of airway secretions. In vitro results suggest potential benefits from the additive effects of selected combinations of mucoactive medications. Further studies are required to confirm these findings, to perform direct assessments of mucus clearability, and to extend the observations to patients with various types of pulmonary diseases where mucoactive treatments are required.

Early airway infection, inflammation, and lung function in cystic fibrosis

AIMS

To determine the relation between lower airway infection and inflammation, respiratory symptoms, and lung function in infants and young children with cystic fibrosis (CF).

METHODS

A prospective study of children with CF aged younger than 3 years, diagnosed by a newborn screening programme. All were clinically stable and had testing as outpatients. Subjects underwent bronchial lavage (BL) and lung function testing by the raised volume rapid thoracoabdominal compression technique under general anaesthesia. BL fluid was cultured and analysed for neutrophil count, interleukin 8, and neutrophil elastase. Lung function was assessed by forced expiratory volume in 0.5, 0.75, and 1 second.

RESULTS

Thirty six children with CF were tested on 54 occasions. Lower airway infection shown by BL was associated with a 10% reduction in FEV(0.5) compared with subjects without infection. No relation was identified between airway inflammation and lung function. Daily moist cough within the week before testing was reported on 20/54 occasions, but in only seven (35%) was infection detected. Independent of either infection status or airway inflammation, those with daily cough had lower lung function than those without respiratory symptoms at the time of BL (mean adjusted FEV(0.5) 195 ml and 236 ml respectively).

CONCLUSIONS

In young children with CF, both respiratory symptoms and airway infection have independent, additive effects on lung function, unrelated to airway inflammation. Further studies are needed to understand the mechanisms of airway obstruction in these young patients.

Mucociliary clearance in cystic fibrosis

Abnormal mucociliary clearance (MCC) is one of the central hypotheses for the development of lung disease in patients with cystic fibrosis (CF). However, attempts to demonstrate this decrease of MCC in vivo have proved to be somewhat less definitive, with the evidence barely favoring impaired clearance. Any apparent disparities are most likely due to the variety of methodologies used by different laboratories to measure MCC. The limitations of the various methodologies are examined in this review, in an attempt to better facilitate comparison of results. A number of physical and pharmacological therapies have been developed to promote mucus clearance from the CF airway. A summary of the results of interventional studies utilizing the measurement of MCC as an outcome measure is presented.

Biosynthesis of mucin type O-glycans: lack of correlation between glycosyltransferase and sulfotransferase activities and CFTR expression

Structural differences have been reported in the glycosylation patterns of cystic fibrosis glycoproteins. Although the gene mutated in cystic fibrosis (CFTR) has been cloned and characterized as a chloride channel, its relationship to the highly viscous mucus and structural glycoprotein and mucin abnormalities in cystic fibrosis still remains to be defined. We have evaluated O-glycan biosynthesis in CHO and BHK cells that express CFTR and DeltaF508 CFTR as in vitro models, and utilized the cftr knockout mouse as an in vivo model of CFTR dysfunction. Activities of glycosyltransferases and sulfotransferases synthesizing mucin type O-glycan chains were determined in these models. Differences in transferase activity levels were found between tissues and cell types and during mouse development. No specific patterns of activities were associated with the lack of CFTR or with DeltaF508CFTR expression. This suggests that it is not the presence or absence of normal CFTR, or the presence of mutant CFTR alone, but rather cell specific additional factors or pathophysiological consequences that determine the changes in mucin glycosylation in cystic fibrosis.

Carbohydrate sulfation effects on growth of Pseudomonas aeruginosa

Pseudomonas aeruginosa is a key player in the pathology and morbidity of cystic fibrosis. Chronic obstructive pulmonary disease, which results from the most common and severe mutations in this genetic disorder, typically includes chronic infection with P. aeruginosa which, even with rugged antibiotic and physical therapy regimens, is rarely eradicated. It is not known whether the increased oligosaccharide sulfation characteristic of cystic fibrosis tracheobronchial mucins plays a role in the survival of P. aeruginosa in the airway. In this study, sulfated monosaccharides were synthesized and tested for their effects on the growth of clinical isolates and laboratory strains of this organism when supplied as the sole carbon source in vitro. Carbohydrate sulfation was observed to reduce, but not prohibit, growth of P. aeruginosa on carbohydrates normally utilized in their nonsulfated form. The various sulfated sugars employed as the sole carbon source gave characteristic and consistent growth profiles and maximum growth values across the strains tested. P. aeruginosa isolates from patients with cystic fibrosis often express a mucoid phenotype, which is thought to contribute to their ability to survive in harsh conditions. Carbohydrate sulfation effects on growth did not differ significantly between mucoid and nonmucoid strains. These results suggest that the additional sulfation of tracheobronchial mucin documented in cystic fibrosis may in fact contribute to the mucin's resistance to utilization by P. aeruginosa and potentially other pathogens, providing an additional level of host protection, and limiting the available nutrient pool and thereby bacterial growth.

Terminal glycosylation in cystic fibrosis

Cystic fibrosis (CF) is a common genetic disease for which the gene was identified within the last decade. Pulmonary disease predominates in this ultimately fatal disease and current therapy only slows the progression. CF transmembrane regulator (CFTR), the gene product, is an integral membrane glycoprotein that normally functions as a chloride channel in epithelial cells. The most common mutation, deltaF508, results in mislocalization and altered glycosylation of CFTR. Altered fucosylation and sialylation are hallmarks of both membrane and secreted glycoproteins in CF and the focus here is on these investigations. Oligosaccharides from CF membrane glycoproteins have the Lewis x, selectin ligand in terminal positions. In addition, two major bacterial pathogens in CF, Pseudomonas aeruginosa and Haemophilus influenzae, have binding proteins, which recognize fucose in alpha1,3 linkage and asialoglycoconjugates. We speculate that the altered terminal glycosylation of airway epithelial glycoproteins in CF contributes to the chronic infection and robust inflammatory response in the CF lung. Understanding the effects of mutant CFTR on glycosylation may provide further insight into the regulation of glycoconjugate processing as well as therapy for CF.

Surface hydrophobicity is increased in the ileum and proximal colon of cystic fibrosis mice

Patients with cystic fibrosis (CF) have abnormal concentrations and composition of electrolytes and macromolecules in gastrointestinal secretions. Such alterations could change intestinal surface properties, such as surface hydrophobicity, and may influence the adhesion of macromolecules, bacteria, or microbial toxins to the intestinal surface. The objective of this study was to compare the surface hydrophobicity of the gastrointestinal tract in wild type and CF mice. We used axisymmetric drop shape analysis-contact diameter to determine surface hydrophobicity by measuring contact angles of sessile water droplets placed onto epithelial surfaces. In wild type mice, there were no differences in contact angles between the duodenum, upper jejunum, lower jejunum, and ileum. The contact angle of the gastric mucosa was lower than the rest of the gastrointestinal tract. Contact angles of the proximal colon and distal colon were both higher than that of the gastric mucosa and those of the small intestinal sections. In CF mice, contact angles along the gastrointestinal tract followed the same pattern as in wild type mice. However, contact angles in the ileum and proximal colon of CF mice were greater than those from wild type mice. This study of the murine intestine showed regional differences in surface hydrophobicity comparable to those observed in other mammalian species. In addition, we showed that the ileum and proximal colon of CF mice were more hydrophobic than the corresponding segments in wild type mice. These observations are of potential clinical relevance because patients with CF exhibit clinical manifestations of gastrointestinal disease primarily in the ileum and proximal colon.

Organ-specific over-sulfation of glycosaminoglycans and altered extracellular matrix in a mouse model of cystic fibrosis

Cystic fibrosis (CF) is a fatal inherited disease caused by the loss of function of a plasma membrane chloride channel-the cystic fibrosis transmembrane conductance regulator (CFTR). It is characterized by viscous mucous secretions which have abnormal glycosylation and sulfation. The development of a CFTR knockout mouse has allowed in vivo experiments aimed at investigating the over-sulfation phenomenon reported for CF glycoconjugates. Four CF and five control mice injected with [35S]sulfate were examined for differences in the sulfation of glycosaminoglycans (GAGs) synthesized by 12 tissues after 48 h. The liver and pancreas of CF mice incorporated significantly higher amounts of [35S]sulfate into GAGs (dpm/microg) than the controls, while the ileum, jejunum, colon, cecum, spleen, trachea, and gall bladder of CF mice exhibited higher incorporation levels that were not significant. The lung and nasal septum were not different, and the nasal mucosa of CF mice was significantly lower (P < 0.05). Structural analysis of the chondroitin/dermatan sulfate component by strong anion-exchange HPLC revealed that the liver and ileum of CF mice incorporated significantly more total sulfate than controls. However, for other organs, the explanation for higher isotope incorporation was a 40-50% higher specific activity of [35S]sulfate within GAGs. This finding implied different uptake kinetics of sulfate from the circulation or that CF mice have altered sulfate pools. CF mice also had altered proportions of chondroitin/dermatan sulfate to heparan sulfate in the ileum and gall bladder (P < 0.05). We conclude that extracellular matrix architecture in some CF organs may be abnormal and that sulfation of glycoconjugates by some organs and sulfate utilization in others have been affected by the loss of CFTR. This study provides the first in vivo evidence for an influence of CFTR on glycoconjugate sulfation and suggests other secondary manifestations of CFTR dysfunction associated with abnormalities of the extracellular matrix.

Lung surfactant in a cystic fibrosis animal model: increased alveolar phospholipid pool size without altered composition and surface tension function in cftrm1HGU/m1HGU mice

BACKGROUND

Progressive pulmonary dysfunction is a characteristic symptom of cystic fibrosis (CF) and is associated with functional impairment and biochemical alterations of surfactant phospholipids in the airways. However, the fundamental question of whether surfactant alterations in the CF lung are secondary to the pulmonary damage or are present before initiation of chronic infection and inflammation has yet to be resolved in patients with cystic fibrosis but can now be addressed in CF mice that exhibit the basic defect in the airways. A study was therefore undertaken to investigate the pool sizes, composition, and function of lung surfactant in the non-infected cftrm1HGU/m1HGU mouse.

METHODS

The amount and composition of phospholipid classes and phosphatidylcholine molecular species were determined in bronchoalveolar lavage (BAL) fluid and lavaged lungs by high performance liquid chromatography (HPLC). Surfactant protein A (SP-A) levels in BAL fluid were determined by ELISA and surfactant for functional measurements was isolated from BAL fluid by differential ultracentrifugation. Equilibrium and minimal surface tension of surfactant was assessed by the pulsating bubble surfactometer technique. MF1, BALB/c, C57/BL6, and C3H/He mice served as controls.

RESULTS

BAL fluid of cftrm1HGU/m1HGU mice contained 1.02 (95% confidence interval (CI) 0.89 to 1.16) mumol phospholipid and 259 (239 to 279) ng SP-A. BAL fluid of MF1, BALB/c, C57BL/6, and C3H/He mice contained 0.69 (0.63 to 0.75), 0.50 (0.42 to 0.57), 0.52 (0.40 to 0.64), and 0.45 (0.27 to 0.63) mumol phospholipid, respectively. After correction for the different body weights of mouse strains, phospholipid levels in BAL fluid of cftrm1HGU/m1HGU mice were increased by 64 (52 to 76)%, 60 (39 to 89)%, 72 (45 to 113)%, and 92 (49 to 163)%, respectively, compared with controls. The amount of SP-A in BAL fluid and the composition of phospholipid as well as phosphatidylcholine molecular species in BAL fluid and lung tissue was unchanged in cftrm1HGU/m1HGU mice compared with controls. The increase in phospholipids in BAL fluid of cftrm1HGU/m1HGU mice resulted from an increased fraction of large aggregates which exhibited normal surface tension function.

CONCLUSION

In cftrm1HGU/m1HGU mice surfactant homeostasis is perturbed by an increased phospholipid pool in the alveolar compartment.

Cystic fibrosis transmembrane conductance regulator-associated ATP and adenosine 3'-phosphate 5'-phosphosulfate channels in endoplasmic reticulum and plasma membranes

Cystic fibrosis (CF) is characterized by abnormal regulation of epithelial ion and fluid transport due to mutations in the CF transmembrane conductance regulator (CFTR), an apical membrane-localized Cl- channel, that usually prevent it from exiting the endoplasmic reticulum. Defective or absent CFTR in the epithelium is believed to disrupt fluid balance in human airways and thereby contribute to chronic respiratory inflammation. Patch-clamp of the plasma membrane and outer membrane of the nuclear envelope of nuclei isolated from CFTR-expressing Chinese hamster ovary cells revealed that CFTR is associated with a regulated ATP channel in both membrane compartments. CFTR expression was also shown to be associated with permeability to another adenine nucleotide, adenosine 3'-phosphate 5'-phosphosulfate, the universal sulfate donor in cells. These results may provide a link between the ion channel function of CFTR and abnormal glycoprotein processing observed in CF.

Heterologous expression of delta F508 CFTR results in decreased sialylation of membrane glycoconjugates

The cystic fibrosis transmembrane conductance regulator (CFTR) is commonly mutated in cystic fibrosis to the delta F508 CFTR. CFTR has been shown to function as a adenosine 3',5'-cyclic monophosphate-dependent Cl- channel at the cell surface, and there is evidence to suggest that CFTR may also have a role in transmembrane Cl- conductance in intracellular membrane compartments. Studies using cells from cystic fibrosis patients or heterologous expression systems have demonstrated that defective Cl- conductance at the cell surface and defective acidification of the Golgi compartment are associated with the presence of mutant forms of CFTR. It is possible that mutation of CFTR could also result in altered Golgi function, consistent with reports of changes in the glycosylation of cell surface and secreted glycoproteins in cystic fibrosis. Glycosylation of cell surface glycoproteins, particularly levels of sialylation, may also be related to the increased binding of Pseudomonas to cystic fibrosis cells. The current study was undertaken to compare the sialylation of cell surface glycoconjugates in heterologous cells overexpressing normal CFTR or delta F508 CFTR. The presence of sialylated residues on cells was assessed by the surface binding of the specific lectins, wheat germ agglutinin and elderberry bark lectin. A fluorescent cholera toxin B subunit probe was used to measure surface binding to sialylated gangliosides in transfected cells. Our studies show that cells lacking CFTR and cells expressing normal CFTR have unaltered levels of sialylation. In contrast, cells expressing the delta F508 CFTR have significantly decreased amounts of sialylated glycoproteins and gangliosides on the cell surface.(ABSTRACT TRUNCATED AT 250 WORDS)

Clinical aspects of glycoprotein biosynthesis

Glycoproteins are widely distributed among species in soluble and membrane-bound forms, associated with many different functions. The heterogenous sugar moieties of glycoproteins are assembled in the endoplasmic reticulum and in the Golgi and are implicated in many roles that require further elucidation. Glycoprotein-bound oligosaccharides show significant changes in their structures and relative occurrences during growth, development, and differentiation. Diverse alterations of these carbohydrate chains occur in diseases such as cancer, metastasis, leukemia, inflammatory, and other diseases. Structural alterations may correlate with activities of glycosyltransferases that assemble glycans, but often the biochemical origin of these changes remains unclear. This suggests a multitude of biosynthetic control mechanisms that are functional in vivo but have not yet been unraveled by in vitro studies. The multitude of carbohydrate alterations observed in disease states may not be the primary cause but may reflect the growth and biochemical activity of the affected cell. However, knowledge of the control mechanisms in the biosynthesis of glycoprotein glycans may be helpful in understanding, diagnosing, and treating disease.

Altered sulfate transport via anion exchange in CFPAC is corrected by retrovirus-mediated CFTR gene transfer

PANC-1 (a permanent epithelioid cell line initiated from a pancreatic carcinoma of ductal origin) and CFPAC (a ductal epithelioid cell line established from a cystic fibrosis patient with pancreatic adenocarcinoma) display sulfate transport via carrier-mediated anion exchange as supported by the following lines of evidence: 1) saturation kinetics, 2) inhibition by the anion exchange inhibitor 4,4'-diisothiocyanostilbene-2,2'-disulfonic acid (DIDS), and 3) substrate specificity. The DIDS-sensitive component of sulfate uptake is markedly inhibited by S2O3(2-) and MoO4(2-) but not by HAsO4(2-), H2PO4-, or gluconate-. Competitive inhibition of SO4(2-) uptake by extracellular Cl- (Cl-o) and stimulation of SO4(2-) efflux by Cl-o support the possibility that SO4(2-) transport occurs via a SO4(2-)-Cl- exchange mechanism. Inhibition of sulfate uptake and stimulation of sulfate efflux by extracellular HCO3- indicate that SO4(2-)-HCO3- exchange is an alternative mechanism for sulfate transport in these cells. Further support for SO4(2-) being transported via a typical anion exchanger is the stimulation of its uptake at low extracellular pH and high intracellular pH. Amphotropic viruses have been used by others (M. L. Drumm, H. A. Pope, W. H. Cliff, J. M. Rommens, S. A. Marvin, L.-C. Tsui, F. S. Collins, R. A. Frizzell, and J. M. Wilson. Cell 62: 1227-1233, 1990) to transduce a functional cystic fibrosis transmembrane regulator (CFTR) cDNA into CFPAC, resulting in the PLJ-CFTR clones. Control clones (PLJ) were obtained by exposing CFPAC cells to control virus. In the present study, we report a striking 10-fold increase in the capacity of the DIDS-sensitive component of the sulfate transporter in two PLJ-CFTR clones (which had been shown by others to express corrected Cl- channel activity) compared with CFPAC and two PLJ clones. Our findings indicate that expression of the CFTR gene from a retroviral vector, which confers normal Cl- channel activity in the PLJ-CFTR pancreas epithelial clones, is capable of correcting a second aspect of the cystic fibrosis phenotype, altered sulfate transport via an anion exchange mechanism.

Phospholipid composition and surface-active properties of tracheobronchial secretions from patients with cystic fibrosis and chronic obstructive pulmonary diseases

Among the various components of tracheobronchial secretions, lipids and particularly phospholipids have been shown to influence rheological properties of airway secretions in patients with cystic fibrosis. We studied the phospholipid composition of tracheobronchial secretions, collected from patients suffering from cystic fibrosis (CF) and other chronic obstructive pulmonary diseases (COPD), and we analyzed the possible relationship between the phospholipid profile and the wettability of tracheobronchial secretions evaluated by the measurement of contact angle. Although total phospholipid content and contact angle of tracheobronchial secretions were significantly increased (P less than 0.01) in CF compared to COPD, no significant relationship existed between these two parameters. The concentrations of the different phospholipid subclasses were not homogeneously modified according to the origin of the secretions. Compared to COPD secretions, the CF secretions were characterized by a significant (P less than 0.001) increase in rigidifying fractions such as sphingomyelin and phosphatidylserine/phosphatidylinositol and a significant (P less than 0.001) decrease in surface-active fractions, such as phosphatidylcholine and phosphatidylglycerol (PG) (P less than 0.001). In the two groups, the surface-active phospholipid fraction, PG, was negatively correlated to the contact angle of tracheobronchial secretions. These results suggest that a decrease in PG content in CF secretions may be one factor responsible for an increase in their adhesivity to the respiratory mucosa, and, consequently, for mucus stasis and severity of bronchial obstruction in cystic fibrosis.

Carrier-mediated sulfate transport in human ureteral epithelial cells cultured in serum-free medium

Sulfate transport studies were carried out in secondary cultures of epithelial cells isolated from the human ureter. Results demonstrate the presence of carrier-mediated SO4(2-) transport as supported by three lines of evidence: 1) saturation kinetics, 2) substrate specificity, and 3) inhibition by the anion transport inhibitor 4,4'-diisothiocyanostilbene-2,2'-disulfonic acid (DIDS). The DIDS-insensitive component of SO4(2-) transport was markedly lower than the DIDS-sensitive component and was not affected by changes in extracellular pH (pHo) or Cl- concentration. The mechanism of this DIDS-insensitive component is not clear. The DIDS-sensitive component of SO4(2-) uptake was a saturable function of the extracellular sulfate concentration ([SO4(2-)]o). Increasing the extracellular chloride concentration ([Cl-]o) inhibited DIDS-sensitive SO4(2-) uptake competitively. Taken together with the fact that increasing [Cl-]o stimulated SO4(2-) efflux, these results suggest that SO4(2-) uptake in uroepithelial cells occurs via SO4(2-)-Cl- anion exchange. Cis-inhibition studies with a variety of anions indicate that this anion-exchange system may be shared by S2O3(2-) and MoO4(2-) but not by NO3- and H2PO4-. SO4(2-) uptake was stimulated at decreasing pHo with a pK approximately 7.4. Decreasing pHo from 7 to 6 lowered the apparent Michaelis constant significantly but had no significant effect on kcat, suggesting that protons may increase the affinity of the SO4(2-) transporter for SO4(2-). SO4(2-) efflux was inhibited at low pHo and was stimulated by increasing [Cl-]o. This study is the first to demonstrate an ion transport process in epithelial cell cultures isolated from the human ureter. In contrast to epithelial cells from the upper urinary tract, no Na(+)-dependent SO4(2-) transport could be demonstrated in these lower urinary tract epithelial cells. In conclusion, the major mechanism for SO4(2-) transport in ureteral epithelial cells is a carrier-mediated, DIDS-sensitive, pHo-sensitive SO4(2-)/Cl- anion-exchange mechanism. These studies suggest that varying [SO4(2-)]o and [Cl-]o or pHo in the ureteral lumen will affect SO4(2-) influx and efflux and may influence the size of the intracellular pool of SO4(2-) available for macromolecular sulfation in these cells.

Chondroitin sulfate in sputum from patients with cystic fibrosis and chronic bronchitis

In order to ascertain whether or not the presence of glycosaminoglycans in sputa of patients suffering from chronic bronchial disorders was related to tracheobronchial infection, an electrophoretic procedure was set up. The different acidic macromolecular components of sputum, namely nucleic acids, glycosaminoglycans, and bronchial glycopeptides could be identified in proteolyzed sputum using agarose electrophoresis before and after the action of different enzymes: nucleases, chondroitinases, hyaluronidase and heparinase. This procedure was used to analyze 13 sputum samples from patients suffering from cystic fibrosis (CF) and 12 sputum samples from patients suffering from chronic bronchitis. Chondroitin sulfate was identified in 11 infected sputum samples from patients with CF and also in the noninfected sputum from a patient with chronic bronchitis. These data suggest a relationship between the presence of chondroitin sulfate proteoglycans in sputum and severe tracheobronchial infection in CF.

Heterogeneity of mucus glycoproteins from cystic fibrotic sputum. Are there different families of mucins?

High-Mr mucin glycopeptides prepared from sputum of an individual with cystic fibrosis (CF) were studied by ion-exchange h.p.l.c. The glycopeptides were heterogeneous and a number of partially resolved populations were identified. Whole mucins from the gel phase were separated into four fractions by isopycnic density-gradient centrifugation in CsCl, and high-Mr glycopeptides from these fractions were examined by ion-exchange h.p.l.c. The acidic nature of the high-Mr glycopeptides increased with increasing buoyant density of the intact mucins, and a periodate-Schiff (PAS)-rich and an extremely high-iron diamine (HID)-reactive component were present in the lowest and highest density fractions respectively. The various glycopeptide populations were identified in different proportions in mucins from four other individuals with CF. CF sputum thus seems to contain distinct mucin populations containing different oligosaccharide clusters corresponding to these high-Mr glycopeptides.

Effect of reserpine on the histochemical and biochemical properties of rat intestinal mucin

Biochemical and histochemical parameters of intestinal mucins were examined in control and reserpine-treated rats. An assay for intestinal mucin sulfotransferase was developed and the activity shown to increase 3.4 times over control levels in rats given intraperitonal reserpine (0.5 mg/kg body wt) daily for 7 days. Histochemical staining of intestinal sections revealed an increase in sulfomucins in goblet cells of reserpine-treated rats. The effects were prominent as early as 1 day following injection, particularly in the distal third of the small intestine, and during the next 6 days these changes spread progressively to the middle and proximal thirds. After 3 days of treatment mucins were purified from each intestinal segment and compared to control mucins with respect to composition and [35S]NaSO4 incorporation. Although individual amino acid and carbohydrate molar ratios were unchanged, the total carbohydrate and sulfate content of mucins in treated animals was elevated (two to three times above control) in the middle and distal thirds of the intestine. In vivo [35S]SO4 incorporation into these mucins was also proportionaltely elevated, and was targetted to O-linked oligosaccharide side chains. These findings are consistent with an action of reserpine causing an increased production of mucin which is enriched in glycoprotein components bearing sulfated oligosaccharide chains. The relevance of these findings to the production of hypersulfated and hyperglycosylated mucins in cystic fibrosis is discussed.

Sulfated O-glycoproteins secreted by guinea pig trachea in organ culture

Organ culture of guinea pig trachea was performed in the presence of [35S]sulfate in order to characterize the sulfated glycoproteins released from the respiratory epithelium and mucosa. The sulfated macromolecules that were synthesized during a 6-h incorporation were separated by CsBr density-gradient centrifugation and gel-filtration chromatography successively. Most of the sulfated secreted macromolecules corresponded to a population of glycoproteins sensitive to reductive beta-elimination but resistant to both chondroitinase ABC and heparinase. These glycoproteins had different buoyant densities (ranging from 1.48 g/ml to 1.16 g/ml) and could be subfractionated according to molecular mass. A major part of the radioactivity was incorporated into high-molecular-mass mucins that were excluded from a Sepharose CL-2B column and did not penetrate into polyacrylamide gel in PAGE. However, a mixture of sulfated O-glycoproteins of much lower molecular mass was also characterized in addition to low amounts of chondroitin sulfate. Epithelial goblet cells are the predominant mucin-containing cells of the respiratory guinea pig trachea. Our results suggest that a wide range of sulfated O-glycoproteins are secreted by the guinea pig tracheal mucosa.

Abnormal fucosylation of ileal mucus in cystic fibrosis: I. A histochemical study using peroxidase labelled lectins

Peroxidase conjugated lectins were used to analyse the glycoproteins of small intestinal mucins in normal infants and those with cystic fibrosis to ascertain whether there are any detectable histochemical differences in saccharide composition. A significant decrease in Lotus tetragonolobus (LTG) binding fucose was shown in normal small intestinal mucin starting around 36 weeks' gestation with total absence of staining at term and beyond. In contrast, the age matched patients with cystic fibrosis showed persistent and intense LTG binding of fucose. These results provide the first clear histochemical evidence that cystic fibrosis mucin is abnormal and confirm the findings of previous biochemical studies.

Physical properties of purified human respiratory mucus glycoproteins: effects of sodium chloride concentration on the aggregation properties and shape

The biophysical properties of purified native (nonreduced) mucus glycoproteins (mucins) isolated from lung mucus secretions of cystic fibrosis (CF) patients and subjects with normal lungs were studied using the technique of light scattering. The effects of different NaCl concentrations and 6 M guanidine hydrochloride on the molecular size of mucins, their ability to form aggregates, and their shape were investigated. Under the concentration range studied (0.05-3.5 mg/ml), in buffered 0.03 and 0.01 M NaCl, the CF mucins had higher molecular weights (12.2 x 10(6) to 17.1 x 10(6) and 9.5 x 10(6) to 10.4 x 10(6), respectively) than those observed in buffered 0.15 M NaCl (4.3 x 10(6) to 6.6 x 10(6]. These results were interpreted in terms of CF mucins self-aggregating in buffered 0.03 and 0.01 M NaCl. In contrast, in the both buffered 0.3 and 0.15 M NaCl, the normal respiratory mucins had molecular weights of 6.3 x 10(6) to 8.6 x 10(6), thus suggesting the absence of normal mucin aggregation in buffered 0.03 M NaCl. In the presence of 6 M guanidine HCl both CF and normal mucins had molecular weights of about 5 x 10(6) and showed more extended structure (i.e., larger radius of gyration) than in the presence of 0.03 or 0.15 M NaCl. Studies of the relationship of the light scattering intensity with scattering angle showed that, under the above experimental conditions studied, both CF and normal respiratory mucins were polydisperse flexible coil-shaped molecules. The increased aggregation of CF mucins observed at lower salt concentrations may alter the viscoelastic properties of CF lung mucus secretions.

Increased sulfation of glycoconjugates by cultured nasal epithelial cells from patients with cystic fibrosis

Cystic fibrosis (CF) respiratory epithelia exhibit abnormal anion transport that may be linked to abnormal lung defense. In these studies, we investigated whether primary cultures of CF respiratory epithelial cells regulate abnormally the sulfate content of high molecular weight glycoconjugates (HMG) participating in airways' mucosal defense. HMG, including glycosaminoglycans and mucin-type glycoproteins released spontaneously into medium and HMG released from cell surfaces by trypsin, were metabolically labeled with 35SO4- and [6-3H]-glucosamine (GlcN) or 35SO4- and [3H]serine. All three classes of HMG from CF cells exhibited 35S/3H labeling ratios 1.5-4-fold greater than HMG from normal or disease control cells. Differences for labeling ratios of HMG from CF cells were shown to be the consequence of increased 35SO4- incorporation rather than decreased peptide synthesis and release or HMG glycosylation. The buoyant density of CF mucin-type HMG also was increased, consistent with increased sulfation. These observations suggest that oversulfation of a spectrum of HMG is a genetically determined characteristic of CF epithelial cells and may play an important pathophysiological role by altering the properties of mucous secretions and/or the interactions between selected bacteria and HMG at the airways' surface.

Alterations in specific activity of lysosomal alpha-glucosidase in cystic fibrosis

Cultured skin fibroblasts derived from patients with cystic fibrosis contain 2.1-fold more acid alpha-glucosidase (EC 3.2.1.3) than normal fibroblasts. This difference is amplified to 2.3-fold when the cells are extracted in Triton X-100. In a study of 14 fibroblast cell lines derived from CF homozygotes and heterozygotes, normal individuals and patients with other recessively inherited disorders, normal individuals could be distinguished from either CF homozygotes or heterozygotes based on the ratio of acid alpha-glucosidase to beta-hexosaminidase when fibroblasts were extracted in either water or Triton X-100. However, the best distinction could be made with water extracts as there was no overlap among individual data points in the three categories. The acid to neural alpha-glucosidase ratio only distinguished CF homozygotes from normal individuals when cells were extracted in Triton X-100. The use of a ratio relationship of acid alpha-glucosidase with beta-hexosaminidase allows the comparison of data from multiple experiments on different days of assay and on cells at different passage numbers. These results suggest that alpha glucosidase may have a role in the primary defect in cystic fibrosis.

Increased sulfate uptake in skin fibroblasts isolated from cystic fibrosis patients

Sulfate uptake into skin fibroblasts from patients with cystic fibrosis is increased. Sulfate transport studies were carried out in skin fibroblasts isolated from age/sex matched cystic fibrosis and normal subjects. Sulfate transport occurred mainly via a carrier-mediated proton-stimulated S04(2)-/Cl-exchange. The capacity (Vmax) of the uptake system operating at physiological concentrations of sulfate was stimulated in cystic fibrosis, but the affinity of the carrier for sulfate was not altered.

Sulfate transport in apical membrane vesicles isolated from tracheal epithelium

Sulfate uptake in apical membrane vesicles isolated from bovine tracheal epithelium is shown to occur into an osmotically sensitive intravesicular space, via a carrier-mediated system. This conclusion is based on three lines of evidence: 1) saturation kinetics; 2) substrate specificity; and 3) inhibition by the anion transport inhibitors SITS and DIDS. The affinity of the transport system is highest in low ionic strength media (apparent Km = 0.13 mM) and decreases in the presence of gluconate (apparent Km = 0.68 mM). Chloride appears to cis-inhibit sulfate uptake and to trans-stimulate sulfate efflux. Cis-inhibition and trans-stimulation studies with a variety of anions indicate that this exchange system may be shared by HCO3-, S2O3(2-), SeO4(2-), and MoO4(2-) but not by H2PO4- or HAsO4(2-). Studies indicate that protons may play two distinct roles in sulfate transport in this system. 1) Their possible modifier role is suggested by the fact that protons affect SO2-4 transport in an uncompetitive manner. 2) The possibility that the proton gradient may act as an energy source for a secondary active transport is indicated by the fact that the imposition of a proton gradient stimulates a transient movement of sulfate in to the tracheal apical membrane vesicle, against its concentration gradient, causing an "overshoot" phenomenon. Our studies show that the carrier-mediated system can function in the absence of chloride. The overshoot observed in the presence of a proton gradient (OH- gradient) indicates that under those conditions the mechanism of transport may be a SO4(2-)-OH- exchange. The fact that chloride cis-inhibits and trans-stimulates SO4(2-) transport indicates that SO2-4 uptake may also occur via a SO4(2-)-Cl- exchange. Studies carried out so far do not enable us to conclude unequivocally whether the tracheal apical membrane system displays two distinct carrier activities (SO4(2-)-Cl-; SO4(2-)-OH-) or one anion exchanger, which like the erythrocyte anion exchanger, may interact with SO4(2-), Cl-, and H+. The fact that the anion transport inhibitors DIDS and SITS inhibit SO4(2-) transport in the presence or absence of chloride suggests that the latter possibility may be the case.

Relationships between the lipid content and the rheological properties of airway secretions in cystic fibrosis

The lipid composition and rheological properties of expectorated airway secretions have been analyzed in 16 patients with cystic fibrosis (CF), separated into two groups according to whether their secretions were superinfected or not. The total lipid content was higher in the superinfected CF secretions. The content in cholesterol and GL1, GL3 and GL4 glycosphingolipid fractions were significantly higher in the superinfected in comparison to the non-superinfected group. The viscosity was two-fold higher in the CF superinfected group. A significant correlation (r = 0.72, p less than 0.01) was observed between the apparent viscosity and the total lipid content of CF secretions. Cholesterol, glycosphingolipids and sphingomyelin were the lipid components which were the most closely and positively correlated to the viscosity. On the opposite, phosphoglycerol was negatively correlated (r = -0.72, p less than 0.05) to the viscoelastic properties of CF airway secretions.

Rheological and transport properties of airway secretions in cystic fibrosis--relationships with the degree of infection and severity of the disease

It has recently been suggested that in cystic fibrosis (CF), there is no rheological abnormality of airway secretions other than that associated with purulence, and that the apparent inhibition in the mucociliary transport rate might be partly due to a ciliary inhibitor present in these secretions. In order to ascertain this assumption, expectorated airway secretions were collected without salivary contamination in twenty-four CF patients and the rheological properties were measured. Using a photometric method, the effects of CF sputum samples were analysed on the ciliary beat frequency (Fm) of the frog palate, and we measured their mucociliary transport rate (TR). In all but one CF sputum, TR and Fm were lower than that of the control frog mucus (median TR: 18.7 and 11.6 mm min-1; median Fm: 12.3 and 11.3 Hz, respectively). In the eighteen patients in whom the rheological properties were outside the range for optimal mucociliary transport, the clinical Shwachman score was significantly (P less than 0.05) lower (median score: 66.2 points) than in the six patients with optimal rheologic properties (median score: 73 points). In the eleven CF patients with superinfection, the apparent viscosity (eta o) was significantly higher (P less than 0.01; median eta o: 24.4 Pa. s) and TR, expressed as a percentage of the reference value, was significantly lower (P less than 0.05; median Tr: 54.5%) in comparison with the values obtained for the thirteen non-superinfected CF patients (median eta o: 15 Pa. s and median TR: 66% respectively). The CF patients with markedly hyperviscous sputum (eta o higher than 30 Pa. s) exhibited a low Shwachman score.