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-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.