Probiotic bacteria regulate intestinal epithelial permeability in experimental ileitis by a TNF-dependent mechanism

Background: We previously showed that the probiotic mixture, VSL#3, prevents the onset of ileitis in SAMP/YitFc (SAMP) mice, and this effect was associated with stimulation of epithelial-derived TNF. The aim of this study was to determine the mechanism(s) of VSL#3-mediated protection on epithelial barrier function and to further investigate the "paradoxical" effects of TNF in preventing SAMP ileitis. Methods: Permeability was evaluated in SAMP mice prior to the onset of inflammation and during established disease by measuring transepithelial electrical resistance (TEER) on ex vivo-cultured ilea following exposure to VSL#3 conditioned media (CM), TNF or VSL#3-CM + anti-TNF. Tight junction (TJ) proteins were assessed by qRT-PCR, Western blot, and confocal microscopy, and TNFRI/TNFRII expression measured in freshly isolated intestinal epithelial cells (IEC) from SAMP and control AKR mice. Results: Culture with either VSL#3-CM or TNF resulted in decreased ileal paracellular permeability in pre-inflamed SAMP, but not SAMP with established disease, while addition of anti-TNF abrogated these effects. Modulation of the TJ proteins, claudin-2 and occludin, occurred with a significant decrease in claudin-2 and increase in occludin following stimulation with VSL#3-CM or TNF. TNF protein levels increased in supernatants of SAMP ilea incubated with VSL#3-CM compared to vehicle, while IEC-derived TNFR mRNA expression decreased in young, and was elevated in inflamed, SAMP versus AKR mice. Conclusions: Our data demonstrate that the previously established efficacy of VSL#3 in preventing SAMP ileitis is due to direct innate and homeostatic effects of TNF on the gut epithelium, modulation of the TJ proteins, claudin-2 and occludin, and overall improvement of intestinal permeability

Cytokines and mucosal immunity

Purpose of review: Cytokines are integral mediators for maintaining intestinal mucosal homeostasis, as well as prominent effector molecules during chronic gut inflammatory diseases. This review focuses on recent studies of the role of specific cytokines in mucosal immunity. Recent findings: Dichotomous, or even opposing, functions have been described for several cytokines involved in intestinal innate immunity (most notably for members of the interleukin-1 family), which depend on the specific inflammatory conditions within the intestinal mucosa. For example, both interleukin-1a and interleukin-33 exhibit 'alarmin'-type properties that can signal tissue or cell damage, which further add to their well described proinflammatory roles. Costimulatory molecules of the tumor necrosis factor/tumor necrosis factor receptor superfamily, such as TNF-like cytokine 1A and LIGHT, are actively involved in mucosal proinflammatory pathways, but also may exert protection against infectious agents to facilitate recovery from acute inflammation. Finally, innate lymphoid cells are increasingly recognized as important cellular sources of pivotal mucosal cytokines, including the interleukin-23/T helper 17 cytokine, interleukin-22. Summary: Elucidating the complexity of cytokine signaling within the normal mucosa and during acute and chronic inflammation will be a pivotal step toward understanding the pathogenesis of immune-mediated gut diseases and developing effective therapies to treat them. © 2014 Wolters Kluwer Health | Lippincott Williams & Wilkins

Mouse models of inflammatory bowel disease for investigating mucosal immunity in the intestine

Purpose of review Currently several mouse models are considered representative of inflammatory bowel disease (IBD). This review presents recent developments regarding the role of animal models of intestinal inflammation as research tools in IBD. Recent findings Preclinical studies in animal models of intestinal inflammation have generated novel findings in several areas of IBD research. The combination of chemical and genetically engineered models have revealed protective or harmful roles for various components of the innate immune system in response to acute injury and repair mechanisms for the intestinal mucosa. Advances in the use of endoscopic and radiologic techniques have allowed identification of inflammatory biomarkers and in-vivo monitoring of cell trafficking towards inflammatory sites. Translational research has shed light on pathogenic mechanisms through which recent biological treatments may exert their beneficial effects in patients with IBD. Finally, novel therapies are continuously tested in animal models of IBD as part of preclinical drug development programs. Summary Animal models of intestinal inflammation continue to be important research tools with high significance for understanding the pathogenesis of IBD and exploring novel therapeutic options. Development of additional experimental models that address existing limitations, and more closely resemble the characteristics of Crohn's disease and ulcerative colitis are greatly needed. © 2017 Wolters Kluwer Health, Inc. All rights reserved

Intestinal-Specific TNFα Overexpression Induces Crohn's-Like Ileitis in Mice

Background and Aim:Human and animal studies have clearly established tumor necrosis factor (TNF)α as an important mediator of Crohn's disease pathogenesis. However, whether systemic or only local TNFα overproduction is required for the development of chronic intestinal inflammation and Crohn's disease remains unclear. The aim of this study was to assess the contribution of intestinal epithelial-derived TNFα to the development of murine Crohn's-like ileitis. Methods:We adapted the well-established TNFΔARE/+ mouse model of Crohn's disease (which systemically overexpresses TNFα) to generate a homozygous mutant strain that overexpress TNFα only within the intestinal epithelium. Intestinal-specific TNFiΔARE/iΔARE mice were examined for histopathological signs of gut inflammation and extraintestinal manifestations of Crohn's disease. The mucosal immune phenotype was characterized, and the contribution of specific lymphocyte populations to the pathogenesis of TNFiΔARE/iΔARE ileitis was assessed. Results:TNFiΔARE/iΔARE mice had increased mucosal and systemic TNFα levels compared to wild-type controls (P<0.001), as well as severe chronic ileitis with increased neutrophil infiltration and villous distortion, but no extraintestinal manifestations (P<0.001 vs. wild-type controls). The gut mucosal lymphocytic compartment was also expanded in TNFiΔARE/iΔARE mice (P<0.05), consisting of activated CD69+ and CD4+CD62L- lymphocytes (P<0.05). FasL expression was significantly elevated in the mesenteric lymph nodes of TNFiΔARE/iΔARE mice (P<0.05). Adoptive transfer of mucosal TNFiΔARE/iΔARE lymphocytes resulted in ileitis in immunologically naïve severe combined immunodeficiency recipients (P<0.05 vs. wild-type controls), indicating an effector phenotype that was associated with increased production of both Th1 (IFNγ) and Th2 (IL-5, IL-13) cytokines. Conclusion:Intestinal epithelial-derived TNFα is sufficient for the induction of Crohn's-like ileitis, but not for the occurrence of extraintestinal manifestations, in TNFiΔARE/iΔARE mice. These effects were associated with generation of effector lymphocytes within the intestinal mucosa and dysregulated apoptosis. Thus, targeted intestinal blockade of TNFα may provide an effective means to neutralize gut-derived TNFα with reduced side effects. © 2013 Bamias et al

A novel role for TL1A/DR3 in protection against intestinal injury and infection

TNF-like cytokine 1A (TL1A) is expressed on APCs and provides costimulatory signals to activated lymphocytes that bear its functional receptor, death receptor 3 (DR3). TL1A/DR3 signaling is involved in the pathogenesis of human and experimental inflammatory bowel disease. In the current study, we investigated the role of this cytokine/receptor pair in acute intestinal injury/repair pathways.We demonstrate that intact DR3 signaling protected mice from acute dextran sodium sulfate colitis because DR3-/- mice showed more severe mucosal inflammation and increased mortality. DR3-/- mice were compromised in their ability to maintain adequate numbers of CD4+CD25+Foxp3+ regulatory T cells in response to acute mucosal damage. This defect in immune regulation led to a nonspecific upregulation of effector proinflammatory pathways, which was most prominent for the Th17 immunophenotype. TL1A-/- mice were similarly more susceptible to dextran sodium sulfate colitis, although without mortality and with delayed kinetics compared with DR3-/- mice, and also displayed significantly reduced numbers of regulatory T cells. Infection of DR3-/- mice with Salmonella typhimurium was associated with defective microbial clearance and elevated bacterial load. Taken together, our findings indicate a novel protective role for the TL1A/DR3 axis in the regulation of mucosal homeostasis during acute intestinal injury/repair, which contrasts with its known pathogenic function during chronic intestinal inflammation. © Copyright 2016 by The American Association of Immunologists, Inc. All rights reserved

SAMP1/YitFc mouse strain : a spontaneous model of Crohn's disease-like ileitis

The SAMP1/YitFc mouse strain represents a model of Crohn's disease (CD)-like ileitis that is ideal for investigating the pathogenesis of chronic intestinal inflammation. Different from the vast majority of animal models of colitis, the ileal-specific phenotype characteristic of SAMP1/YitFc mice occurs spontaneously, without genetic, chemical, or immunological manipulation. In addition, SAMP1/YitFc mice possess remarkable similarities to the human condition with regard to disease location, histologic features, incidence of extraintestinal manifestations, and response to conventional therapies. SAMP1/YitFc mice also display a well-defined time course of a predisease state and phases of acute and chronic ileitis. As such, the SAMP1/YitFc model is particularly suitable for elucidating pathways that precede the clinical phenotype that may lead to preventive, and therefore more efficacious, intervention with the natural course of disease, or alternatively, for the development of therapeutic strategies directed against chronic, established ileitis. In this review we summarize important contributions made by our group and others that uncover potential mechanisms in the pathogenesis of CD using this unique murine model of chronic intestinal inflammation. Copyrigh

Death-domain-receptor 3 deletion normalizes inflammatory gene expression and prevents ileitis in experimental Crohn's disease

Background TNF-like cytokine 1A (TL1A) and its functional receptor, death-domain-receptor-3 (DR3), are multifunctional mediators of effector and regulatory immunity. We aimed to evaluate the functional role and therapeutic potential of TL1A/DR3 signaling in Crohn's disease-like ileitis. Methods Ileitis-prone SAMP1/YitFc (SAMP) and TNF ΔARE/+ mice were rendered deficient for DR3 or TL1A by microsatellite marker-assisted backcrossing. Pathological and immunological characteristics were compared between control and knockout mice, and mucosal immunophenotype was analyzed by Nanostring microarray assay. The therapeutic effect of pharmacological TL1A neutralization was also investigated. Results DR3 deficiency was associated with restoration of a homeostatic mucosal immunostat in SAMP mice through the regulation of several pro- A nd anti-inflammatory genes. This led to suppression of effector immunity, amelioration of ileitis severity, and compromised ability of either unfractionated CD4 + or CD4 + CD45RB hi mucosal lymphocytes to transfer ileitis to severe combined immunodeficient mice recipients. TNF-driven ileitis was also prevented in TNF ΔARE/+ xDR3 -/- mice, in association with decreased expression of the pro-inflammatory cytokines TNF and IFN-γ. In contrast to DR3, TL1A was dispensable for the development of ileitis although it affected the kinetics of inflammation, as TNF ΔARE/+ xTL1A-/-demonstrated delayed onset of inflammation, whereas administration of a neutralizing, anti-TL1A antibody ameliorated early but not late TNF ΔARE/+ ileitis. Conclusion We found a prominent pro-inflammatory role of DR3 in chronic ileitis, which is only partially mediated via interaction with TL1A, raising the possibility for additional DR3 ligands. Death-domain-receptor-3 appears to be a master regulator of mucosal homeostasis and inflammation and may represent a candidate therapeutic target for chronic inflammatory conditions of the bowel. © 2018 Crohn's and Colitis Foundation. Published by Oxford University Press. All rights reserved