Characteristics and expression of a mucin-like glycoprotein produced by ocular surface epithelium

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Ocular surface epithelium produces a mucin-like glycoprotein recognized by R339 antibody. In normal, a mucin-like glycoprotein is found in the apical cell membrane adjacent to the tear film in the most apical cell, and is also found in the cytoplasm of the cells of the subapica cell layr. In keratinized corneal epithelium of vitamin A deficient rats, expression of the glycoprotein was absent or was remarkably reduced in the cell surface of the most apical cell. Electron microscopic study has shown that expression of the glycoprotein was not in the apical cell membrane in the most apical cell, but in the cytoplasm of the cells in the subapical 2 to 3 cell layrs. In contrast, a mucin-like glycoprotein was neither in the most apical cell, nor in the subapical cells in the central cornea showing high keratinization. With vitamin A treatment to vitamin A deficient rats, the corneal epithelium recovered expression of the glycoprotein correspondent to the the normalization of the cell morphol … More ogy. These observations suggest that expression and synthesis of a mucin-like glycoprotein was reduced in keratinized cells.In human study, a mucin-like glycoprotein by human ocular surface epithelium was also reduced in keratinized cells in superior limbic keratoconjunctivitis and ocular pemphigoid. The recovery of expression of the glycoprotein was found in the ocular surface epithelium.The induction of expression of the glycoprotein was investigated in the developing rats. The expression was not observed in the corneas of developing rats with the lids closed (at the age of less than 14 day), however, the expression was induced in the corneas of 50% of the rats with mucin secretagogue abdominally injection at the age of 12 day-old. The effect of the mucin secretagogue was reduced to 33% and 20% in the rats administrated at 11 day and 12 day old, respectively. Clinically, the expression of the glycoprotein was shown to be reduced in the ocular surface epithelium of dry eye patients. Therefore, these observation may lead to devolopment of the drug which induces expression of a mucin-like glycoprotein in the ocular surface epithelium. Less