Combined defects in epithelial and immunoregulatory factors exacerbate the pathogenesis of inflammation: Mucin 2-interleukin 10-deficient mice

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.

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