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P. Argueso, A. Guzman, F. Mantelli; Mucin-Type O-Glycans in Tears of Normal Subjects and Patients With Non-Sjögren’s Dry Eye. Invest. Ophthalmol. Vis. Sci. 2009;50(13):2543.
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O-linked carbohydrates are known to confer a hydrophilic character to mucins. Alteration in the distribution of cell surface O-glycans correlates with epithelial damage in dry eye patients. By contrast, the character of secreted O-glycans in the tear film remains poorly characterized. The purpose of this study was to identify the repertoire of mucin-type O-glycans present in human tears, and the glycosyltransferases associated with their biosynthesis, in normal subjects and patients with non-Sjögren’s dry eye.
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 sequential exoglycosidase digestions. O-glycan structures identified in tears were related to potential biosynthetic pathways in human conjunctival epithelium using a glycogene microarray database. Lectin binding analyses of tear fluid samples were performed using agglutinins from Arachis hypogaea, Maackia amurensis and Sambucus nigra.
The O-glycosylation profile of the human tear fluid consisted mostly of core 1-based (Galß1-3GalNAc1-Ser/Thr) structures. Mono-sialyl core 1 glycans represented approximately 74% of the glycan pool, being 2-6-sialyl core 1 the predominant O-glycan structure in human tears (54%). Four families of glycosyltranferases potentially related to the biosynthesis of these structures were identified in human conjunctiva. These included thirteen polypeptide GalNAc transferases (GalNAcT), the core 1 ß-3-galactosyltransferase (T-synthase), three 2-6-sialyltransferases (ST6GalNAc) and two 2-3-sialyltransferases (ST3Gal). No significant differences in the total amount of O-glycans were detected in tears of normal subjects and dry eye patients by HPLC and lectin blot. Likewise, no differences in glycosyltransferase expression were found by glycogene microarray analysis.
The most common mucin-type O-glycans in human tears and their biosynthetic pathways in the ocular surface epithelia have been identified. As compared to cell surface O-glycans, no changes in secreted O-glycans were detected in patients with dry eye.
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