The goblet cell-derived mediator RELM-ß drives spontaneous colitis in Muc2-deficient mice by promoting commensal microbial dysbiosis.

Intestinal goblet cells are potentially key players in controlling susceptibility to ulcerative colitis (UC). Although impaired mucin (Muc2) production by goblet cells increases microbial stimulation of the colonic mucosa, goblet cells secrete other mediators that may influence or promote UC development. Correspondingly, Muc2-deficient ((-/-)) mice develop spontaneous colitis, concurrent with the dramatic upregulation of the goblet cell mediator, resistin-like molecule-beta (RELM-ß). Testing RELM-ß's role, we generated Muc2(-/-)/Retnlb(-/-) mice, finding that RELM-ß deficiency significantly attenuated colitis development and symptoms compared with Muc2(-/-) mice. RELM-ß expression in Muc2(-/-) mice strongly induced the production/secretion of the antimicrobial lectin RegIIIß, that exerted its microbicidal effect predominantly on Gram-positive Lactobacillus species. Compared with Muc2(-/-)/Retnlb(-/-) mice, this worsened intestinal microbial dysbiosis with a selective loss of colonic Lactobacilli spp. in Muc2(-/-) mice. Orally replenishing Muc2(-/-) mice with murine Lactobacillus spp., but not with a probiotic formulation containing several human Lactobacillus spp. (VSL#3), ameliorated their spontaneous colitis in concert with increased production of short-chain fatty acids. These studies demonstrate that the goblet cell mediator RELM-ß drives colitis in Muc2(-/-) mice by depleting protective commensal microbes. The ability of selective commensal microbial replacement to ameliorate colitis suggests that personalized bacterial therapy may prove beneficial for treatment of UC.

Saccharomyces boulardii ameliorates Citrobacter rodentium-induced colitis through actions on bacterial virulence factors.

Saccharomyces boulardii has received increasing attention as a probiotic effective in the prevention and treatment of infectious and inflammatory bowel diseases. The aim of this study was to examine the ameliorating effects of S. boulardii on Citrobacter rodentium colitis in vivo and identify potential mechanisms of action. C57BL/6 mice received 2.5 x 10(8) C. rodentium by gavage on day 0, followed by S. boulardii (25 mg; 5 x 10(8) live cells) gavaged twice daily from day 2 to day 9. Animal weights were monitored until death on day 10. Colons were removed and assessed for epithelial barrier function, histology, and myeloperoxidase activity. Bacterial epithelial attachment and type III secreted proteins translocated intimin receptor Tir (the receptor for bacterial intimin) and EspB (a translocation apparatus protein) required for bacterial virulence were assayed. In infected mice, S. boulardii treatment significantly attenuated weight loss, ameliorated crypt hyperplasia (234.7 +/- 7.2 vs. 297.8 +/- 17.6 microm) and histological damage score (0.67 +/- 0.67 vs. 4.75 +/- 0.75), reduced myeloperoxidase activity (2.1 +/- 0.4 vs. 4.7 +/- 0.9 U/mg), and attenuated increased mannitol flux (17.2 +/- 5.0 vs. 31.2 +/- 8.2 nm.cm(-2).h(-1)). The ameliorating effects of S. boulardii were associated with significantly reduced numbers of mucosal adherent C. rodentium, a marked reduction in Tir protein secretion and translocation into mouse colonocytes, and a striking reduction in EspB expression and secretion. We conclude that S. boulardii maintained colonic epithelial barrier integrity and ameliorated inflammatory sequelae associated with C. rodentium infection by attenuating C. rodentium adherence to host epithelial cells through putative actions on the type III secretion system.

MyD88 signalling plays a critical role in host defence by controlling pathogen burden and promoting epithelial cell homeostasis during Citrobacter rodentium-induced colitis.

Myeloid differentiation factor (MyD)88, an adaptor protein shared by the Toll-interleukin 1 receptor superfamily, plays a critical role in host defence during many systemic bacterial infections by inducing protective inflammatory responses that limit bacterial growth. However, the role of innate responses during gastrointestinal (GI) infections is less clear, in part because the GI tract is tolerant to commensal antigens. The current study investigated the role of MyD88 following infection by the murine bacterial pathogen, Citrobacter rodentium. MyD88-deficient mice suffered a lethal colitis coincident with colonic mucosal ulcerations and bleeding. Their susceptibility was associated with an overwhelming bacterial burden and selectively impaired immune responses in colonic tissues, which included delayed inflammatory cell recruitment, reduced iNOS and abrogated production of TNF-alpha and IL-6 from MyD88-deficient macrophages and colons cultured ex vivo. Immunostaining for Ki67 and BrDU revealed that MyD88 signalling mediated epithelial hyper-proliferation in response to C. rodentium infection. Thus, MyD88-deficient mice could not promote epithelial cell turnover and repair, leading to deep bacterial invasion of colonic crypts, intestinal barrier dysfunction and, ultimately, widespread mucosal ulcerations. In conclusion, MyD88 signalling within the GI tract plays a critical role in mediating host defence against an enteric bacterial pathogen, by controlling bacterial numbers and promoting intestinal epithelial homeostasis.