Identification of 9-O-acetyl-N-acetylneuraminic acid in normal canine pre-ocular tear film secreted mucins and its depletion in Keratoconjunctivitis sicca |
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Authors: | A P Corfield S R Donapaty S D Carrington S J Hicks R Schauer G Kohla |
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Institution: | Mucin Research Group, Clinical Sciences at South Bristol, Level 7, Bristol Royal Infirmary, Bristol, BS2 8HW, UK. |
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Abstract: | O-Acetylated sialic acids have been reported in many sialoglycoproteins where they mediate a variety of immune and other biological
events. We have previously demonstrated that the protective mucus barrier on the surface of the canine eye contains sialoglycoproteins.
We have also investigated the occurrence of O-Acetylated sialic acids in these ocular mucins. Mucus aspirated from the surface of normal dog eyes and those with keratoconjunctivitis
sicca (KCS) was fractionated into three pools by density gradient centrifugation. Sialic acids comprised 0.6–0.9% of the dry
weight of the mucins isolated. The sialic acid profile in these pools was examined using HPLC. O-Acetylated sialic acids, mainly Neu5,9Ac2, were detected in normal animals and made up 10–30% of the total sialic acids detected. A doubling of the sialic acid content
was found in KCS mucins, but the level of 9-O-Acetylated sialic acid was reduced below 4% of total.
Histological analysis of conjunctival tissue from normal and KCS dogs showed the presence of sialic acids, detected with the
α(2–6) sialic acid-specific lectin Sambucus nigra, in the goblet cells and corresponding to the staining pattern for MUC5AC, the major ocular-secreted mucin gene product.
In KCS animals a disruption of the normal pattern of conjunctival goblet cells was seen with preservation of the pattern of
lectin binding observed in normal animals.
Thus the data demonstrate the presence of mono-O-Acetylated sialic acids in normal canine ocular mucins and a loss of this population of sialic acids in dry eye disease in
spite of a significant increase in total sialic acids in KCS mucin. |
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Keywords: | mucins sialic acids pre-ocular tear film 9-O-acetylation Keratoconjunctivitis Sicca |
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