A.W.C. Einerhand

Gastric‐type mucin and TFF‐peptide expression in Barrett's oesophagus is disturbed during increased expression of MUC2

Aims:  Barretts oesophagus constitutes metaplastic epithelium, often diagnosed by mucin histochemistry. We determined the mucins and trefoil factor family (TFF)‐peptides that were expressed in Barretts oesophagus, in order to study changes in protein expression in early stages of Barretts oesophagus development.

Spontaneous development of colitis in mice deficient for Mucin 2

Inflammatory bowel disease (IBD) is influenced by genetic, immunoregulatory and environmental factors. Mucin 2 (MUC2) is the major mucin of the mucus layer covering the colonic epithelium. Previous studies have shown that the expression of MUC2 is altered in IBD, and therefore might play a role in the onset or perpetuation of IBD. Our aim was to obtain insight in the role of MUC2 in epithelial barrier function, and its role in the pathogenesis of IBD. In this study we used Muc2 knockout mice. These mice were back-crossed onto a 129SV genetic background. Wild type (WT), heterozygous (HZ) and knock out (KO) littermates were scored weekly for weight, softness of the stool and appearance of occult faecal blood, to obtain a disease activity score (DAI). At age 5, 8, 12 and 16 weeks, groups of each four mice were sacrificed. Intestinal segments were collected for histological and biochemical analysis. The Muc2 knockout mice all showed clinical signs of colitis (KO DAI1⁄4471 vs. WT/ HZ DAI1⁄40 at 5 weeks) aggravating in time (KODAI1⁄4872 vs. WT/HZ1⁄40 at 16 weeks) and incidentally rectal prolapses. Microscopic analysis of the distal colon showed mucosal thickening, increased proliferation, superficial erosions and distinct changes in goblet cell morphology. RT-PCR was used to monitor the RNA expression of other secretory mucins present in the gastrointestinal tract: Muc5AC, Muc5B and Muc6. Muc5AC, and -5B mRNAs were not detectable in the distal colon of both WT and KO mice. Muc6 was not expressed in WT colon. In the KO mice, however, Muc6 mRNA expression was present at 5 weeks of age, but expression declined as the mice matured.

Methotrexate-induced mucositis in mucin 2 deficient mice

The mucin Muc2 or Mycin2 (Muc2), which is the main structural component of the protective mucus layer, has shown to be upregulated during chemotherapy-induced mucositis. As Muc2 has shown to have protective capacities, upregulation of Muc2 may be a counter reaction of the intestine protecting against mucositis. Therefore, increasing Muc2 protein levels could be a therapeutic target in mucositis prevention or reduction. Our aim was to determine the role of Muc2 in chemotherapy-induced mucositis. Mucositis was induced in Muc2 knockout (Muc2(-/-)) and wild type (Muc2(+/+)) mice by injecting methotrexate (MTX). Animals were weighed and sacrificed on Days 2-6 after MTX treatment and jejunal segments were analyzed. Before MTX treatment, the small intestine of Muc2(+/+) and Muc2(-/-) mice were similar with respect to epithelial morphology and proliferation. Moreover, sucrase-isomaltase and trefoil factor-3 protein expression levels were comparable between Muc2(+/+) and Muc2(-/-) mice. Up to Day 3 after MTX treatment, percentages of weight-loss did not differ. Thereafter, Muc2(+/+) mice showed a trend towards regaining weight, whereas Muc2(-/-) mice continued to lose weight. Surprisingly, MTX-induced intestinal damage of Muc2(-/-) and Muc2(+/+) mice was comparable. Prior to MTX-injection, tumor necrosis factor-alpha and interleukin-10 mRNAs were upregulated in Muc2(-/-) mice, probably due to continuous exposure of the intestine to luminal antigens. Muc2 deficiency does not lead to an increase in chemotherapy-induced mucositis. A possible explanation is the mechanism by which Muc2 deficiency may trigger the immune system to release interleukin-10, an anti-inflammatory cytokine before MTX-treatment.