http://repub.eur.nl/res/aut/32375/ List of Publications en http://repub.eur.nl/static-eur/img/logo.png http://repub.eur.nl http://repub.eur.nl/res/pub/24731/ 2009-07-01T00:00:00Z Objectives: Previous studies have shown that the intestine uses a major part of the dietary threonine intake for the synthesis of the structural component of the protective intestinal mucus layer, the secretory mucin Muc2. In this context, the high intestinal demand for dietary threonine probably results from its incorporation into secretory mucins rich in threonine residues. Therefore, we compared threonine utilization in the colon of Muc2 knockout (Muc2-/-) and wild-type (Muc2+/+) mice to investigate the intestinal dietary threonine metabolism in the absence of Muc2, which results in inflammation of the colon. Materials and Methods: Concentrations and isotopic enrichment of threonine were measured by gas chromatographyisotope ratio mass spectrometry in the serum, colon, and colonic content of mice given a bolus [U-13C]threonine enterally. Results: We retrieved 37.8% and 40.9% of dietary threonine in Muc2+/+and Muc2-/-mice, respectively, either as free or incorporated threonine. There were no major differences in the availability and concentration of free or incorporated threonine recovered in both serum and colon in both types of mice. However, the Muc2-/-mice did show overall significantly higher threonine oxidation rates compared with Muc2+/+mice. Conclusions: In the absence of Muc2, dietary threonine is mainly used for constitutive protein synthesis or becomes a substrate for metabolic oxidation. This indicates that inflammation also requires high threonine amounts. JPGN 49:99-107, 2009. http://repub.eur.nl/res/pub/28845/ 2008-06-24T00:00:00Z Expression of the mucin MUC2, the structural component of the colonic mucus layer, is lowered in ulcerative colitis. Furthermore, interleukin (IL)-10 knockout (IL-10-/-) mice develop colitis and have reduced Muc2 levels. Our aim was to obtain insight into the role of Muc2 and IL-10 in epithelial protection. Muc2-IL-10 double-knockout (Muc2/IL-10DKO) mice were characterized and compared to Muc2 knockout (Muc2-/-), IL-10-/-and wild-type (WT) mice. Clinical symptoms, intestinal morphology and differences in epithelial-specific protein levels were analyzed. In addition, levels of the pro-inflammatory cytokines in colonic tissue and serum were determined. IL-10-/-mice were indistinguishable from WT mice throughout this experiment and showed no clinical or histological signs of colitis. Muc2/IL-10DKOand Muc2-/-mice showed significant growth retardation and clinical signs of colitis at 4 and 5 weeks, respectively. Muc2/IL-10DKOmice had a high mortality rate (50% survival/5 weeks) compared to the other types of mice (100% survival). Microscopic analysis of the colon of Muc2/IL-10DKOmice showed mucosal thickening, increased proliferation, superficial erosions and a diminished Muc4 expression. Furthermore, pro-inflammatory cytokines were significantly upregulated, both in tissue (mRNA) and systemically in Muc2/IL-10DKOmice. In conclusion, Muc2/IL-10DKOmice develop colitis, which is more severe in every aspect compared to Muc2-/-and IL-10-/-mice. These data indicate that (i) in case of Muc2 deficiency, the anti-inflammatory cytokine IL-10 can control epithelial damage, though to a limited extent and (ii) the mucus layer is most likely a key factor determining colitis. http://repub.eur.nl/res/pub/35637/ 2007-01-01T00:00:00Z 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-α 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.