Vitamin A and glycoproteins of rat corneal epithelium

Abstract

Previous work from this laboratory has shown that the uptake of labeled precursors into a single specific glycopeptide in the rat intestinal mucosa was depressed significantly in vitamin A deficiency (De Luca et al ., 1970). A very similar pattern to the intestinal glycopeptide pattern was obtained from the rat corneal epithelium; namely, the glycopeptide affected by vitamin A was eluted with 0.4 N LiCl solution by a stepwise column chromatography on DEAE-Sephadex A-50. A specific "peak S" glycopeptide eluted between 0.35 N and 0.42 N LiCl solution was found to be the most decreased (approximately by 50%) glycopeptide component by vitamin A deficiency when a new continuous gradient column chromatography of the same anion exchanger was employed. "Peak S" glycopeptide was further characterized by polyacrylamide (7.5%) gel electrophoresis and gas-liquid chromatography. The affected "peak S" glycopeptide was found to be rich in sialic acid, possibly as an end-sugar. Topical application for one hour in vivo of water-dispersible vitamin A palmitate to corneas of deficient rats resulted in a stimulation of glycoprotein/glycopeptide synthesis upon subsequent incubation in vitro. Upon fractionation of glycopeptide prepared from vitamin A-deficient control and deficient, vitamin A-treated rat corneal epithelium by DEAE-Sephadex A-50 column chromatography, the fraction eluted in 0.2 N LiCl solution showed a marked increase in labeling of 14c-glucosamine into glycopeptides. This stimulated fraction appears to consist of small molecules probably lacking sialic acid. The in vitro stimulation of glycopeptide synthesis in vitamin A-deficient corneal epithelium seems to be confined also to the 0.2 N LiCl fraction. Histologically, corneal epithelium, and particularly the mucus-secreting conjunctival gland showed a strong fluorescent response to fluorescent antibody made against the intestinal glycopeptide affected by vitamin A.