Secreted canine ocular mucins have truncated oligosaccharides

Purpose. Clinical observations in both human and dog indicate differences in ocular mucus between normal and dry eye patients. These may be caused by ocular mucin glycosylation changes. This investigation surveys the structure of oligosaccharide side chains in normal canine secreted ocular mucins as a basis for future comparisons with mucins from dry eye patients. Methods. Ocular mucus was collected by suction from the ocular surface of 28 female dogs; dispersed in a cocktail of proteinase inhibitors; and three secreted mucin fractions purified by CsCl density gradient centrifugation and gel filtration as previously reported [1]. Oligosaccharides were released from mucins by β-elimination with sodium boro[³H]hydride; size-fractionated on Biogel P4; and subjected to thin layer chromatography (TLC) with and without sialidase digestion. Bands were visualised by autoradiography. Results. The majority of oligosaccharides in normal canine secreted ocular mucins were eluted in the mono- and di-saccharide range, with no evidence of larger or partially degraded oligosaccharides. The profile of oligosaccharides released was similar for the different mucins, but the proportions of each carbohydrate structure varied between the three. TLC showed bands migrating similarly to GalNAc-ol and sialylα2-6GalNAc-ol; sialidase digestion reverted the latter to material migrating similarly to GalNAc-ol. Conclusions. Canine ocular mucins show a remarkably simple pattern of short oligosaccharides, probably comprising sialylα2-6GalNAc-ol and GalNAc-ol. These structures have previously been found in bovine and ovine salivary mucins.