Gastrointestinal mucins of Fut2-null mice lack terminal fucosylation without affecting colonization by Candida albicans

Abstract

Posttranslational modification of apomucins by the sequential action of glycosyltransferases is required to produce mature mucins. The Secretor gene (FUT2) encodes an alpha(1,2)fucosyltransferase (EC 2.4.1.69) that catalyzes addition of terminal alpha(1,2)fucose residues on mucins and other molecules in mucosal epithelium. Mutant mice containing targeted replacement of Fut2 with the bacterial reporter gene lacZ were studied to determine the affect of the loss of Fut2 on glycosylation of mucins in the gastrointestinal tract. By whole organ X-gal staining, lacZ activity is prominently expressed in the foveolar pit and chief cells of the glandular stomach, Brunner's glands of the duodenum, and goblet cells in the large intestine of Fut2-LacZ-null mice. Staining with Aleuria aurantia agglutinin demonstrates loss of L-fucosylated epithelial glycans throughout the gastrointestinal tract of Fut2-LacZ-null mice, however, histologic appearance of the tissues appears normal. Analysis of oligosaccharides released from insoluble colonic mucins, largely Muc2, by mass spectrometry shows complete lack of terminal fucosylation of O-linked oligosaccharides in Fut2-LacZ-null mice. Precursor glycans accumulate with no evidence of compensation by other fucosyltransferases or sialyltransferases on mucin glycosylation. Because Candida albicans has been reported to adhere to intestinal mucins creating a potential reservoir associated with vaginitis, Fut2-LacZ-null and wild-type mice were inoculated by gastric lavage with C. albicans. We observe no difference in colonization between genotypes suggesting mucin terminal fucosylation does not significantly influence C. albicans-host interaction in the intestine, highlighting that infections caused by the same organism at different mucosal surfaces are not equal.

Fig. 1.

Whole organ and tissue-specific examination of X-gal staining within the gastrointestinal tract of Fut2-LacZ null mice. Specific X-gal staining was observed within antral-duodenal junction (A), cecum (C), proximal (E) and distal colon (G) from Fut2-LacZ null mice and photographed at 10-fold magnification. Histological analysis of these tissues showed specific X-gal staining was most intense in Brunners glands of the duodenum (B), and goblet cells of the cecum (D), proximal (F), and distal (H) colon.

Fig. 2.

Microscopic view of Fut2-LacZ null and C57BL/6J tissues isolated from the gastrointestinal tract stained with Aleuria aurantia agglutinin. Intense brown lectin staining was associated with foveolar pit and chief cells of the antrum (A) and goblet cells of the proximal (C) and distal (E) colon of wild type mice which was absent, respectively, in antrum (B), proximal (D) and distal (F) colon of Fut2-LacZ null mice.

Fig. 3.

Total mass chromatograms of neutral and sulfated O-linked oligosaccharides released from colonic insoluble mucins of C57BL/6J wild type (A) and Fut2-LacZ null mice (B). The B chromatogram did not show any additional peaks when analysis was performed for longer times (not shown). Peaks marked by * indicate impurities within the peak in addition to trace amounts of the oligosaccharide, precluding calculation of relative abundances.