Abstract
Background
Patients with inflammatory bowel disease (IBD) often display a dysbiotic microbiome as well as a defective intestinal mucus layer, which appears thinner and more penetrable than the mucus layer of healthy subjects. Tributyrin (TB), a prodrug of butyric acid, has shown beneficial effects in models of IBD due to its anti-inflammatory effects. We previously showed that mice lacking the major intestinal mucin Muc2 (Muc2-/-) or lacking the “Core1” enzyme responsible for glycosylating Muc2 (C1galt1-/-) were highly susceptible to infection by Citrobacter rodentium, a murine model of intestinal inflammation.
Aims
The study explored the role of gut mucus in providing host defense against C. rodentium, as well as the effects of TB supplementation in the prevention of mucosal damage in this model.
Methods
Six to ten week old wildtype (WT), Muc2-/-, flox control (C1galt1f/f) and C1galt1-/- mice were infected with C. rodentium (∼2.5 × 108 CFU) by oral gavage. For TB supplementation experiments, mice received 100µL of TB or glycerol as a control by oral gavage every other day starting on day 1 post infection. Mice were monitored daily throughout the experiment and were euthanized at day 6 of infection. Several tissues of interest were collected to verify bacterial colonization in the gut and at systemic sites as well as histological tissue damage. Cecal contents were collected for the analysis of short chain fatty acids, while blood was collected by cardiac puncture after oral gavage with FITC-dextran to measure intestinal permeability.
Results
While WT and C1galt1f/f mice were only modestly susceptible to C. rodentium infection, Muc2-/- and C1galt1-/- mice displayed dramatically (100 fold) increased pathogen burdens, significantly greater intestinal macroscopic and histopathology scores, and heightened barrier disruption as compared to controls. Moreover, Muc2-/- and C1galt1-/- mice showed significantly lower levels of butyric acid as compared to control mice under baseline conditions. Interestingly, when supplemented with TB, Muc2-/- and C1galt1-/- proved less susceptible to C. rodentium infection, as indicated by reduced weight loss and clinical signs of colitis, while pathogen burdens were greatly reduced as was histological tissue damage, and epithelial barrier dysfunction. The same protection was conferred when TB was administered as a dietary supplementation, thus confirming its beneficial effect in protecting mice against C. rodentium infection.
Conclusions
These findings demonstrate that intestinal mucus controls host susceptibility to C. rodentium infection via control over butyrate levels, and highlight the need to explore the mechanisms by which gut mucus modulates the resident microbiota and its metabolites.
Funding Agencies
CCC, CIHR
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