The adhesion of Pseudomonas aeruginosa to high molecular weight human tear film species corresponds to glycoproteins reactive with Sambucus nigra lectin

Tear film, contact lenses and tear biomarkers

This article summarises research undertaken since 1993 in the Willcox laboratory at the University of New South Wales, Sydney on the tear film, its interactions with contact lenses, and the use of tears as a source of biomarkers for ocular and non-ocular diseases. The proteome, lipidome and glycome of tears all contribute to important aspects of the tear film, including its structure, its ability to defend the ocular surface against microbes and to help heal ocular surface injuries. The tear film interacts with contact lenses in vivo and interactions between tears and lenses can affect the biocompatibility of lenses, and may be important in mediating discomfort responses during lens wear. Suggestions are made for follow-up research.

TNF induces the expression of the sialyltransferase ST3Gal IV in human bronchial mucosa via MSK1/2 protein kinases and increases FliD/sialyl-Lewis(x)-mediated adhesion of Pseudomonas aeruginosa

We have shown previously that the pro-inflammatory cytokine TNF (tumour necrosis factor) could drive sLe(x) (sialyl-Lewis(x)) biosynthesis through the up-regulation of the BX transcript isoform of the ST3GAL4 (ST3 β-galactoside α-2,3-sialyltransferase 4) sialyltransferase gene in lung epithelial cells and human bronchial mucosa. In the present study, we show that the TNF-induced up-regulation of the ST3GAL4 BX transcript is mediated by MSK1/2 (mitogen- and stress-activated kinase 1/2) through the ERK (extracellular-signal-regulated kinase) and p38 MAPK (mitogen-activated protein kinase) pathways, and increases sLe(x) expression on high-molecular-mass glycoproteins in inflamed airway epithelium. We also show that the TNF-induced sLe(x) expression increases the adhesion of the Pseudomonas aeruginosa PAO1 and PAK strains to lung epithelial cells in a FliD-dependent manner. These results suggest that ERK and p38 MAPK, and the downstream kinase MSK1/2, should be considered as potential targets to hamper inflammation, bronchial mucin glycosylation changes and P. aeruginosa binding in the lung of patients suffering from lung diseases such as chronic bronchitis or cystic fibrosis.

Glycobiology of the ocular surface: mucins and lectins

Glycosylation is an important and common form of posttranscriptional modification of proteins in cells. During the last decade, a vast array of biological functions has been ascribed to glycans because of a rapid evolution in glycomic technologies. Glycogenes that are highly expressed at the human ocular surface include families of glycosyltransferases, proteoglycans, and glycan degradation proteins, as well as mucins and carbohydrate-binding proteins, such as the galectins. On the apical glycocalyx, mucin O-glycans promote boundary lubrication, prevent bacterial adhesion and endocytic activity, and maintain epithelial barrier function through interactions with galectins. The emerging roles attributed to glycans are contributing to the appreciation of their biological capabilities at the ocular surface.

Sialylated glycans and mucins in the lacrimal gland and eyelid of man and pig. Potential receptors for pathogenic microorganisms

The conjunctiva of the eyelid is coated by secretion products from the lacrimal and eyelid glands, and by mucins produced by conjunctival goblet cells, which together form a glycoprotein-rich layer that lubricates and protects the surface of the eye. However, these ocular carbohydrates may also act as adhesives for viruses and bacteria and thereby facilitate their colonization. This paper provides histochemical demonstration of the in situ localization of such carbohydrate receptors in the form of sialylated glycans and mucins in the lacrimal and eyelid glands and conjunctiva from both humans and pigs. The pig is included in this study because viruses of swine origin may be capable of transmission to humans. We found that the human and pig ocular surfaces contain receptors for bacteria and viruses in the form of mucins (both membrane bound and secreted) and carbohydrates terminating in Sialylα2-6Gal epitopes and to a lesser degree in Sialylα2-3Gal. The glycosylation of the human soft palate could indicate a mucinous route for the spread of microorganisms from the eye via the nasolacrimal duct to the nasopharynx and thus to the upper part of the respiratory tract.

Assessment of Streptococcus pneumoniae capsule in conjunctivitis and keratitis in vivo neuraminidase activity increases in nonencapsulated pneumococci following conjunctival infection

PURPOSE

The pneumococcal capsule is required for pathogenesis in systemic infections, yet reports show most conjunctivitis outbreaks are caused by nonencapsulated pneumococci, while keratitis infections are caused by encapsulated strains. This study aims to determine the effect of capsule in pneumococcal keratitis and conjunctivitis in rabbit models of infection.

METHODS

A capsule-deficient isogenic mutant was created using homologous transformation. Parent and mutant strains were injected within the upper bulbar conjunctiva (conjunctivitis) or into the corneal stroma (keratitis) of New Zealand white rabbits. Clinical examinations were performed 24 and 48 hr post-infection at which time corneas or conjunctivae were removed, homogenized, and plated to determine the recovered bacterial load. Whole eyes were removed for histological examination. The neuraminidase activity was determined following in vitro and in vivo growth.

RESULTS

There were no significant differences in clinical scores between the eyes infected with the parent or mutant for either infection, nor was there a difference in the amount of bacteria recovered from the cornea. In the conjunctivae, however, the mutant strain was cleared by the host faster than the parent strain. Histological examination showed slightly more infiltrating polymorphonuclear leukocytes (PMN) and macrophages in the conjunctivae infected with the parent strain. The neuraminidase activity of both strains was not significantly different when the strains were grown in vitro. However, the neuraminidase activity of the parent was significantly less than that of the mutant at 3 and 12 hr post conjunctival infection.

CONCLUSIONS

Although more outbreaks of pneumococcal conjunctivitis are tied to nonencapsulated S. pneumoniae strains, this study showed that an encapsulated strain was capable of establishing conjunctivitis in a rabbit injection model and survive attack by the host immune system longer than its nonencapsulated isogenic mutant. Nonetheless, the nonencapsulated pneumococci had an increased neuraminidase activity level in vivo when compared to the parent strain.

Mucin-type O-glycans in tears of normal subjects and patients with non-Sjögren's dry eye

PURPOSE

O-linked carbohydrates (O-glycans) contribute to the hydrophilic character of mucins in mucosal tissues. This study was conducted to identify the repertoire of O-glycans in the tear film and the glycosyltransferases associated with their biosynthesis, in normal subjects and patients with non-Sjögren's dry eye.

METHODS

Human tear fluid was collected from the inferior conjunctival fornix. O-glycans were released by hydrazinolysis, labeled with 2-aminobenzamide, and analyzed by fluorometric, high-performance liquid chromatography (HPLC) coupled with exoglycosidase digestions. O-glycan structures identified in tears were related to potential biosynthetic pathways in human conjunctival epithelium by using a glycogene microarray database. Lectin-binding analyses were performed with agglutinins from Arachis hypogaea, Maackia amurensis, and Sambucus nigra.

RESULTS

The O-glycan profile of human tears consisted primarily of core 1 (Gal beta 1-3GalNAc alpha 1-Ser/Thr)-based structures. Mono-sialyl O-glycans represented approximately 66% of the glycan pool, with alpha2-6-sialyl core 1 being the predominant O-glycan structure in human tears (48%). Four families of glycosyltransferases potentially related to the biosynthesis of these structures were identified in human conjunctiva. These included 13 polypeptide-GalNAc-transferases (GALNT), the core 1 beta-3-galactosyltransferase (T-synthase), three alpha2-6-sialyltransferases (ST6GalNAc), and two alpha2-3-sialyltransferases (ST3Gal). No significant differences in total amount of O-glycans were detected between tears of normal subjects and patients with dry eye, by HPLC and lectin blot. Likewise, no differences in glycosyltransferase expression were found by glycogene microarray.

CONCLUSIONS

This study identified the most common mucin-type O-glycans in human tears and their expected biosynthetic pathways in ocular surface epithelia. Patients with non-Sjögren's dry eye showed no alterations in composition and amount of O-glycans in the tear fluid.

Larvicidal activity of lectins from Myracrodruon urundeuva on Aedes aegypti

Aedes aegypti transmits etiologic agents of yellow fever and dengue. Vaccine for dengue virus is not available and vector control is essential to minimize dengue incidence. This report deals with the larvicidal activity of lectins isolated from Myracrodruon urundeuva bark (MuBL) and heartwood (MuHL). The lectins were isolated by ammonium sulphate treatment of crude extracts followed by chromatography on chitin. MuBL and MuHL were evaluated by electrophoresis under native (PAGE) and denaturing conditions (SDS-PAGE). Carbohydrate specificity of lectins was evaluated by hemagglutinating activity (HA) inhibition assay using N-acetyl-d-glucosamine and by affinity chromatography on N-acetyl-D-glucosamine immobilized in agarose gel. Larvicidal activity against A. aegypti was investigated with the extracts, salt fractions and isolated lectins. MuBL and MuHL were characterized by PAGE as basic proteins of molecular masses of 14.0 and 14.4 kDa, respectively. The interaction of lectins with N-acetylglucosamine was detected by inhibition of HA by monosaccharide and lectin adsorptions on N-acetyl-D-glucosamine matrix. All M. urundeuva preparations promoted larvae mortality. LC16, LC50 and LC84 values of 0.077, 0.125, 0.173 for MuBL and 0.03, 0.04 and 0.05 mg/mL for MuHL were obtained. To our knowledge this is the first report of larvicidal activity of lectins against A. aegypti.