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

Abstract

SummaryMyeloid 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-a 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.

Irinotecan-Induced Gastrointestinal Dysfunction and Pain Are Mediated by Common TLR4-Dependent Mechanisms

“…For example, significant improvements in acute inflammation have been shown in the absence of TLR4 and MyD88, a downstream signaling molecule of TLR, following acute infection with Citrobacter rodentium (35). Similar results have also been demonstrated in methotrexate-induced gut toxicity, with MD-2 (TLR4 accessory protein) deletion improving clinical and histological parameters of toxicity (36).…”

“…Extensive literature exists showing the protective effect of TLR4 deletion in an inflammatory setting, however this appears to be limited to only acute insults, with TLR4 deficiency exacerbating chronic inflammatory diseases (35). For example, significant improvements in acute inflammation have been shown in the absence of TLR4 and MyD88, a downstream signaling molecule of TLR, following acute infection with Citrobacter rodentium (35).…”

Gut barrier disruption by an enteric bacterial pathogen accelerates insulitis in NOD mice

“…Mice were fed with LabDiet 5053 Irradiated Picolab Rodent Diet 20 (PMI Nutrition International, Jamieson's Pet Foods International, Vancouver, BC, Canada). Infection of mice and culturing of WT and ΔespF C. rodentium was performed as previously described [22,24]. In brief, mice were infected by oral gavage with 0.1 ml of an overnight bacterial culture in Luria broth containing approximately 2.5×10 8 colony-forming units (CFUs) of WT or ΔespF C. rodentium.…”

“…In brief, mice were infected by oral gavage with 0.1 ml of an overnight bacterial culture in Luria broth containing approximately 2.5×10 8 colony-forming units (CFUs) of WT or ΔespF C. rodentium. To enumerate C. rodentium, whole gut tissues (including stools) or LNs were collected from infected mice, homogenised, plated on MacConkey plates, incubated at 37°C, and colonies counted the following day [22,24]. Experiments were conducted as approved by the institutional animal ethics committee.…”

“…The FITC-dextran assay was performed as described [24]. Briefly, for assessment of barrier function in the upper GI tract, 0.15 ml of 80 g/l of FITCdextran (FD4; Sigma-Aldrich, Oakville, ON, Canada) in PBS was introduced to mice by oral gavage, whereas 0.1 ml was introduced by enema for studies assessing colonic barrier function following C. rodentium infection.…”