FAB-MS characterization of sialyl Lewis x determinants on polylactosamine chains of human airway mucins secreted by patients suffering from cystic fibrosis or chronic bronchitis

Respiratory mucus as a virus-host range determinant

Efficient penetration of the mucus layer is needed for respiratory viruses to avoid mucociliary clearance prior to infection. Many respiratory viruses bind to glycans on the heavily glycosylated mucins that give mucus its gel-like characteristics. Influenza viruses, some paramyxoviruses, and coronaviruses avoid becoming trapped in the mucus by releasing themselves by means of their envelope-embedded enzymes that destroy glycan receptors. For efficient infection, receptor binding and destruction need to be in balance with the host receptor repertoire. Establishment in a novel host species requires resetting of the balance to adapt to the different glycan repertoire encountered. Growing understanding of species-specific mucosal glycosylation patterns and the dynamic interaction with respiratory viruses identifies the mucus layer as a major host-range determinant and barrier for zoonotic transfer.

Pseudomonas aeruginosa pyocyanin modulates mucin glycosylation with sialyl-Lewis(x) to increase binding to airway epithelial cells

Cystic fibrosis (CF) patients battle life-long pulmonary infections with the respiratory pathogen Pseudomonas aeruginosa (PA). An overabundance of mucus in CF airways provides a favorable niche for PA growth. When compared with that of non-CF individuals, mucus of CF airways is enriched in sialyl-Lewis(x), a preferred binding receptor for PA. Notably, the levels of sialyl-Lewis(x) directly correlate with infection severity in CF patients. However, the mechanism by which PA causes increased sialylation remains uncharacterized. In this study, we examined the ability of PA virulence factors to modulate sialyl-Lewis(x) modification in airway mucins. We found pyocyanin (PCN) to be a potent inducer of sialyl-Lewis(x) in both mouse airways and in primary and immortalized CF and non-CF human airway epithelial cells. PCN increased the expression of C2/4GnT and ST3Gal-IV, two of the glycosyltransferases responsible for the stepwise biosynthesis of sialyl-Lewis(x), through a tumor necrosis factor (TNF)-α-mediated phosphoinositol-specific phospholipase C (PI-PLC)-dependent pathway. Furthermore, PA bound more efficiently to airway epithelial cells pre-exposed to PCN in a flagellar cap-dependent manner. Importantly, antibodies against sialyl-Lewis(x) and anti-TNF-α attenuated PA binding. These results indicate that PA secretes PCN to induce a favorable environment for chronic colonization of CF lungs by increasing the glycosylation of airway mucins with sialyl-Lewis(x).

Glycomic analysis of human respiratory tract tissues and correlation with influenza virus infection

The first step in influenza infection of the human respiratory tract is binding of the virus to sialic (Sia) acid terminated receptors. The binding of different strains of virus for the receptor is determined by the α linkage of the sialic acid to galactose and the adjacent glycan structure. In this study the N- and O-glycan composition of the human lung, bronchus and nasopharynx was characterized by mass spectrometry. Analysis showed that there was a wide spectrum of both Sia α2-3 and α2-6 glycans in the lung and bronchus. This glycan structural data was then utilized in combination with binding data from 4 of the published glycan arrays to assess whether these current glycan arrays were able to predict replication of human, avian and swine viruses in human ex vivo respiratory tract tissues. The most comprehensive array from the Consortium for Functional Glycomics contained the greatest diversity of sialylated glycans, but was not predictive of productive replication in the bronchus and lung. Our findings indicate that more comprehensive but focused arrays need to be developed to investigate influenza virus binding in an assessment of newly emerging influenza viruses.

This study was performed to determine what possible glycan receptors for influenza were present in the human respiratory tract. We compared the glycans present on existing published glycan arrays with the actual glycans identified in the human respiratory tract by mass spectrometric analysis to determine how representative these arrays would be for potential binding. The most comprehensive array to date only contained approximately half the range of the actual glycans present. Over the past 5 years we have performed ex-vivo infection of 113 bronchial and 185 lung samples with seasonal, avian and swine influenza viruses, and have demonstrated that the lung is able to be infected by all types of influenza viruses but that the bronchus can also be infected by a limited range of avian, swine and seasonal viruses. The key findings are that there is wide spectrum of glycans present in the respiratory tract which can be used by influenza viruses for infection, and the currently available arrays are not predictive of successful infection. Our findings will be of use for researchers in developing more comprehensive and focused arrays for the screening of emerging influenza viruses and bacteria in order to determine their potential threat to humans.

Pseudomonas aeruginosa mucoid strain 8830 binds glycans containing the sialyl-Lewis x epitope

Pseudomonas aeruginosa infection of patients with cystic fibrosis (CF) is a leading cause of their morbidity and mortality. Pathogenesis is initiated in part by molecular interactions of P. aeruginosa with carbohydrate residues in airway mucins that accumulate in the lungs of patients with this disease. To explore the nature of the glycans recognized by a stable, mucoid, alginate-producing strain P. aeruginosa 8830 we generated a genetically modified Pa8830 expressing green fluorescent protein (Pa3380-GFP). We tested its binding to a panel of glycolipids and neoglycolipids in which selected glycans were covalently attached to dipalmitoyl phosphatidylethanolamine and analyzed on silica gel surfaces. Among all glycans tested, Pa8830-GFP bound best to sialyl-Le(x)-containing glycan NeuAc(alpha2-3)Gal(beta1-4)[Fuc(alpha1-3)]GlcNAc-R and bound weakly to H-type blood group Fucalpha1-2Galbeta1-4GlcNAc-R, sialyl-lactose, and Le(x), and exhibited little binding toward non-fucosylated derivatives. Interestingly, while Pa8830-GFP bound to the glycosphingolipid asialoGM1, it did not appear to bind to a wide variety of other glycosphingolipids including GM1, GM2, asialoGM2, and sulfatide. These results indicate that P. aeruginosa 8830 has preferential binding to sialyl-Le(x)-containing glycans and has weak recognition of related fucose- and sialic acid-containing glycans. The finding that Pa8830 binds sialyl-Le(x)-containing glycans, which occur at increased levels in mucins from CF patients, is consistent with studies of other strains of P. aeruginosa and further suggests that such glycans on CF mucins contribute to disease pathogenesis.

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.

Mucins and their O-Glycans from human bronchial epithelial cell cultures

A longstanding question in obstructive airway disease is whether observed changes in mucin composition and/or posttranslational glycosylation are due to genetic or to environmental factors. We tested whether the mucins secreted by second-passage primary human bronchial epithelial cell cultures derived from noncystic fibrosis (CF) or CF patients have intrinsically different specific mucin compositions, and whether these mucins are glycosylated differently. Both CF and non-CF cultures produced MUC5B, predominantly, as judged by quantitative agarose gel Western blots with mucin-specific antibodies: MUC5B was present at approximately 10-fold higher levels than MUC5AC, consistent with our previous mRNA studies (Bernacki SH, Nelson AL, Abdullah L, Sheehan JK, Harris A, William DC, and Randell SH. Am J Respir Cell Mol Biol 20: 595-604, 1999). O-linked oligosaccharides released from purified non-CF and CF mucins and studied by HPLC mass spectrometry had highly variable glycan structures, and there were no observable differences between the two groups. Hence, there were no differences in either the specific mucins or their O-glycans that correlated with the CF phenotype under the noninfected/noninflammatory conditions of cell culture. We conclude that the differences observed in the mucins sampled directly from patients are most likely due to environmental factors relating to infection and/or inflammation.

Sulfated oligosaccharides isolated from the respiratory mucins of a secretor patient suffering from chronic bronchitis

The most acidic carbohydrate chains released by alkaline borohydride treatment of the bulk of airway mucins secreted by a patient (blood group O, secretor) suffering from a mildly infected chronic bronchitis have been fractionated using high-performance anion-exchange chromatography (HPAEC) according to a protocol already described [Lo-Guidice et al., J. Biol. Chem. 269 (1994) 18794] and were analyzed using 1H-NMR spectroscopy and matrix-assisted laser-adsorption-time-of-flight (MALDI-TOF) spectrometry. Many fractions corresponded to mixtures of oligosaccharides. This confirmed the wide diversity of the post-translational processes involved in the biosynthesis of airway mucins, which had already been observed in bronchial diseases, such as chronic bronchitis and cystic fibrosis (CF). Seven fractions were directly purified by HPAEC, allowing their structural determination. Six of them corresponded to 3-O-sulfated oligosaccharide chains terminated by a sulfated N-acetyllactosamine, a sulfated Lewis X or a sulfated Lewis A determinant, and the last one corresponded to a 6-O-sulfated chain terminated by a sulfated H-2 determinant. Three oligosaccharides had core type 2 and the other four had core type 4: IIIc2-9: Gal(beta1-3)[HSO(3)-3-Gal(beta1-4)GlcNAc(beta1-6)]GalNAc-ol, IIIc2-10: Gal(beta1-3)[Fuc(alpha1-2)Gal(beta1-4)[HSO(3)-6-]GlcNAc(beta1-6)]GalNAc-ol, IIIc2-4: Fuc(alpha1-2)Gal(beta1-3)[HSO(3)-3-Gal(beta1-4)[Fuc(alpha1-3)]GlcNAc(beta1-6)]GalNAc-ol, IIIc2-8: Fuc(alpha1-2)Gal(beta1-3)GlcNAc(beta1-3)[HSO(3)-3-Gal(beta1-4)GlcNAc(beta1-6)]GalNAc-ol, IIIc2-7: Fuc(alpha1-2)Gal(beta1-3)GlcNAc(beta1-3)[Gal(beta1-4)[HSO(3)-6-]GlcNAc(beta1-6)]GalNAc-ol, IIIc2-3: Fuc(alpha1-2)Gal(beta1-3)GlcNAc(beta1-3)[HSO(3)-3-Gal(beta1-4)[Fuc(alpha1-3)]GlcNAc(beta1-6)]GalNAc-ol, IIIc1-4: Fuc(alpha1-2)Gal(beta1-3)GlcNAc(beta1-3)[HSO(3) -3-Gal(beta1-3)[Fuc(alpha1-4)]GlcNAc(beta1-3)Gal(beta1-4)GlcNAc(beta1-6)]GalNAc-ol. Like previous data concerning the airway mucins from another patient (blood group O and non-secretor) suffering from chronic bronchitis [Lo-Guidice et al., Glycoconj. J. 14 (1997) 113], no disialylated oligosaccharide and no sialylated and sulfated oligosaccharide bearing sialyl Lewis X epitope could be isolated. This is in contrast with the data obtained with the airway mucins secreted by the patient severely infected by Pseudomonas aeruginosa and suffering from CF, suggesting that important differences occur in the biosynthesis of airway mucins secreted by patients suffering from different bronchial diseases with or without severe infection.