The straw that stirs the drink: insight into the pathogenesis of inflammatory bowel disease revealed through the study of microflora-induced inflammation in genetically modified mice

Carrageenan Gum and Adherent Invasive Escherichia coli in a Piglet Model of Inflammatory Bowel Disease: Impact on Intestinal Mucosa-associated Microbiota

Inflammatory bowel diseases (IBD) including Crohn's disease (CD), and ulcerative colitis (UC), are chronic conditions characterized by chronic intestinal inflammation. Adherent invasive Escherichia coli (AIEC) pathotype has been increasingly implicated in the etiopathogenesis of IBD. In a 21-day study, we investigated the effects of AIEC strain UM146 inoculation on microbiota profile of the ileal, cecal, ascending and descending colon in a pig model of experimental colitis. Carrageenan gum (CG) was used to induce colitis in weaner piglets whereas AIEC strain UM146 previously isolated from a CD patient was included to investigate a cause or consequence effect in IBD. Treatments were: (1) control; (2) CG; (3) AIEC strain UM146; and (4) CG+UM146. Pigs in groups 2 and 4 received 1% CG in drinking water from day 1 of the study while pigs in groups 3 and 4 were inoculated with UM146 on day 8. Following euthanization on day 21, tissue mucosal scrapings were collected and used for DNA extraction. The V4 region of bacterial 16S rRNA gene was then subjected to Illumina sequencing. Microbial diversity, composition, and the predicted functional metagenome were determined in addition to short chain fatty acids profiles in the digesta and inflammatory cytokines in the intestinal tissue. CG-induced colitis decreased bacterial species richness and shifted community composition. At the phylum level, an increase in Proteobacteria and Deferribacteres and a decrease in Firmicutes, Actinobacteria, and Bacteroidetes were observed in CG and CGUM146 compared to control and UM146. The metabolic capacity of the microbiome was also altered in CG and CGUM146 compared to UM146 and control in the colon. We demonstrated that CG resulted in bacterial dysbiosis and shifted community composition similar to what has been previously observed in IBD patients. However, AIEC strain UM146 alone did not cause any clear changes compared to CG or control in our experimental IBD pig model.

Disease severity and mortality can be independently regulated in a mouse model of experimental graft versus host disease

Graft versus host disease (GVHD) is the major limitation of allogeneic hematopoietic stem cell transplantation (HSCT) presenting high mortality and morbidity rates. However, the exact cause of death is not completely understood and does not correlate with specific clinical and histological parameters of disease. Here we show, by using a semi-allogeneic mouse model of GVHD, that mortality and morbidity can be experimentally separated. We injected bone marrow-derived dendritic cells (BMDC) from NOD2/CARD15-deficient donors into semi-allogeneic irradiated chimaeras and observed that recipients were protected from death. However, no protection was observed regarding clinical or pathological scores up to 20 days after transplantation. Protection from death was associated with decreased bacterial translocation, faster hematologic recovery and epithelial integrity maintenance despite mononuclear infiltration at day 20 post-GVHD induction with no skew towards different T helper phenotypes. The protected mice recovered from aGVHD and progressively reached scores compatible with healthy animals. Altogether, our data indicate that severity and mortality can be separate events providing a model to study transplant-related mortality.

Systemic macrophage depletion inhibits Helicobacter bilis-induced proinflammatory cytokine-mediated typhlocolitis and impairs bacterial colonization dynamics in a BALB/c Rag2-/- mouse model of inflammatory bowel disease

Helicobacter bilis, an enterohepatic helicobacter, is associated with chronic hepatitis in aged immunocompetent inbred mice and inflammatory bowel disease (IBD) in immunodeficient mice. To evaluate the role of macrophages in H. bilis-induced IBD, Rag2(-/-) BALB/c or wild-type (WT) BALB/c mice were either sham dosed or infected with H. bilis Missouri strain under specific-pathogen-free conditions, followed by an intravenous injection of a 0.2-ml suspension of liposomes coated with either phosphate-buffered saline (control) or clodronate (a macrophage depleting drug) at 15 weeks postinfection (wpi). At 16 wpi, the ceca of H. bilis-infected Rag2(-/-) mice treated with control liposomes had significantly higher histopathological lesional scores (for cumulative typhlitis index, inflammation, edema, epithelial defects, and hyperplasia) and higher counts of F4/80(+) macrophages and MPO(+) neutrophils compared to H. bilis-infected Rag2(-/-) mice treated with clodronate liposomes. In addition, cecal quantitative PCR analyses revealed a significant suppression in the expression of macrophage-related cytokine genes, namely, Tnfa, Il-1β, Il-10, Cxcl1, and iNos, in the clodronate-treated H. bilis-infected Rag2(-/-) mice compared to the H. bilis-infected Rag2(-/-) control mice. Finally, cecal quantitative PCR analyses also revealed a significant reduction in bacterial colonization in the clodronate-treated Rag2(-/-) mice. Taken together, our results suggest that macrophages are critical inflammatory cellular mediators for promoting H. bilis-induced typhlocolitis in mice.

Microbial and histopathologic considerations in the use of mouse models of inflammatory bowel diseases

Mouse models provide powerful tools to investigate disease mechanisms and are widely used in inflammatory bowel disease research. However, it is common for reports of mouse model studies to lack potentially important information about the microbial status of the mice and the method used to evaluate disease expression for statistical analysis. For example, it is common practice to state that the mice were housed under specific pathogen-free conditions but provide no further information regarding the presence or absence of organisms such as Helicobacter spp. that are known or likely to affect disease expression, thus omitting information potentially important to the expected phenotype of the mice and their responses to experimental manipulation. We therefore encourage authors to use such terms as "conventional" and "specific pathogen-free" precisely, to state the agents from which the mice are represented to be free, and to provide a brief description of the health monitoring protocol. Descriptions of histopathologic methods used to evaluate colitis in mouse models also often do not include sufficient detail to allow readers to understand and evaluate the methods; in addition, the lesions commonly are shown in photomicrographs that are too small and of too low resolution to be interpreted. Inasmuch as such methods are often the major or only source of data upon which conclusions regarding genotype or experimental treatment effects are based, the method employed should be fully described, and photomicrographs should be of adequate size and resolution to allow independent assessment.

Inflamed gut mucosa: downstream of interleukin-10

BACKGROUND

Interleukin-10 is a pleiotropic cytokine, whose main function is limitation and ultimately termination of immune responses. This is especially true for environmental interfaces such as the gastrointestinal tract. IL-10 acts as a key mediator for maintaining gut homeostasis. IL-10 knockout mice are well established as a genetic model for inflammatory bowel disease (IBD), and sequence variants in the IL-10 locus contribute to ulcerative colitis (UC).

DESIGN

This review covers the significance of IL-10 signalling in the intestinal immune response both in health and disease. It explains the biological role of IL-10, its deregulation in IBD and its contribution to intestinal inflammation via endoplasmic reticulum stress response.

RESULTS

Many IBD susceptibility genes have been discovered in the past years, linking fundamental biological systems, like innate and adaptive immunity, stress responses, autophagy and mucosal barrier to the pathogenesis of Crohn's disease (CD) and UC. IL-10 has long been known for its substantial role in regulating gut immunity, but its contribution to IBD was somewhat elusive. A recent study identified mutations in either IL-10 receptor subunits that are associated with early-onset enterocolitis, a severe phenotype of IBD. Other than genetic variants of IL-10 receptors, IL-10 and STAT3 genes are also associated with IBD, emphasizing the involvement of the IL-10 signalling cascade in the pathogenesis of CD and UC.

CONCLUSIONS

  The discovery of inherited deregulations in the IL-10 signalling cascade is not only considered the missing link between IL-10 and intestinal homeostasis, but also demonstrates how findings made in animal models help explaining human disease.

Prebiotic treatment in experimental colitis reduces the risk of colitic cancer

BACKGROUND AND AIM

  Germinated barley foodstuff (GBF) is a prebiotic product that reduces colonic mucosal inflammation and the clinical symptoms observed in ulcerative colitis (UC). The risk of contracting colorectal cancer is higher in patients with UC than in that of the general population. The aim of this study is to apply this prebiotic approach to control chronic colitis and to reduce the incidence of colitic cancer.

METHODS

  Repeated and intermitted dextran sulfate sodium administration to male Sprague-Dawley rats was used for the chronic and subacute colitis models. GBF was added as the diet (10% w/v). The incidence of adenomatous high-grade dysplasia, and pathophysiological observations, including the proliferative cell nuclear antigen (PCNA) labeling index, and clinical score, cecal organic acid profile, and the accompanying β-glucosidase activity were determined.

RESULTS

  In the chronic phase, the incidence of adenomatous dysplasia was only confirmed in the control group, and the GBF group had no dysplasia in the entire colon; the stratified squamous epithelium area of GBF was significantly lower than that of the controls. GBF treatment significantly lowered the cecal succinate content and significantly increased β-glucosidase activity compared to the controls. In addition, colonic mucosal inflammatory damage was comparable between the two groups, while the PCNA labeling index of the colonic mucosa in the GBF group was significantly lower than that of the control group. However, in the subacute phase, the mucosal damage score of GBF was significantly attenuated, and the PCNA labeling index of the colonic mucosa in the GBF group was significantly higher than that of the control group.

CONCLUSION

  This preliminary study demonstrated that GBF effectively prevents colitis-related dysplasia and inflammatory change in chronic and subacute colitis models by modulating the intestinal environment as a prebiotic. This prebiotic might contribute to the prevention of mucosal damage, to show different proliferative effects on the epithelium in the regeneration and steady states.

Abnormal glucose, lipid and protein metabolism in patients with Crohn's disease

Inflammatory bowel disease (IBD), consisting of Crohn's disease (CD) and ulcerative colitis (UC), poses a great threat to human health. It results from an inappropriate immune response, in genetically susceptible individuals, to microbial antigens of commensal microorganisms. This paper reviews abnormal glucose, lipid and protein metabolism in patients with CD and highlights the application of metabonomics in biomarker revelation for CD.

Differential mechanisms in the pathogenesis of autoimmune cholangitis versus inflammatory bowel disease in interleukin-2Ralpha(-/-) mice

Interleukin-2 (IL-2) receptor alpha knockout (IL-2Ralpha(-/-)) mice have a deficiency of CD25 and a corresponding functional defect in T regulatory cells (Tregs). These mice spontaneously develop portal inflammation with biliary ductular damage and colitis with features similar to human inflammatory bowel disease with T cell infiltrates in both the liver and colon. In humans, inflammatory bowel disease may be accompanied by primary sclerosing cholangitis (PSC), but seldom primary biliary cirrhosis (PBC). We hypothesized that the effector mechanism responsible for T cell infiltrates would differ for colon versus liver. To address this thesis, we developed three colonies of double-knockout mice including IL-2Ralpha(-/-) CD4(-/-), IL-2Ralpha(-/-) CD8(-/-), and IL-2Ralpha(-/-) T cell receptor (TCR)-beta(-/-). Tissue immunopathology, body weight, and serum levels of cytokines, immunoglobulins, and anti-mitochondrial antibodies (AMA) were assayed at 3 months of age. Relative to IL-2Ralpha(-/-) mice, IL-2Ralpha(-/-) CD4(-/-) mice had increased biliary ductular damage but reduced inflammation in the colon. In contrast, IL-2Ralpha(-/-) CD8(-/-) mice had increased colon inflammation but markedly attenuated biliary ductular damage. Both IL-2Ralpha(-/-) CD4(-/-) and IL-2Ralpha(-/-) CD8(-/-) mice demonstrated elevated serum levels of tumor necrosis factor alpha (TNF-alpha), interferon gamma (IFN-gamma), interleukin-12p40 (IL-12p40), and interleukin-2 (IL-2) compared with C57BL/6J controls, but only IL-2Ralpha(-/-) CD8(-/-) mice had increased serum levels of immunoglobulin A (IgA), AMA and interleukin-17 (IL-17). Finally, and of importance, IL-2Ralpha(-/-) TCR-beta(-/-) mice had abrogation of liver and colon pathological conditions and lacked AMA. In conclusion, on loss of Treg function in mice, CD8 T cells mediate biliary ductular damage whereas CD4 T cells mediate induction of colon-specific autoimmunity.

An antibiotic-responsive mouse model of fulminant ulcerative colitis

BACKGROUND

The constellation of human inflammatory bowel disease (IBD) includes ulcerative colitis and Crohn's disease, which both display a wide spectrum in the severity of pathology. One theory is that multiple genetic hits to the host immune system may contribute to the susceptibility and severity of IBD. However, experimental proof of this concept is still lacking. Several genetic mouse models that each recapitulate some aspects of human IBD have utilized a single gene defect to induce colitis. However, none have produced pathology clearly distinguishable as either ulcerative colitis or Crohn's disease, in part because none of them reproduce the most severe forms of disease that are observed in human patients. This lack of severe IBD models has posed a challenge for research into pathogenic mechanisms and development of new treatments. We hypothesized that multiple genetic hits to the regulatory machinery that normally inhibits immune activation in the intestine would generate more severe, reproducible pathology that would mimic either ulcerative colitis or Crohn's disease.

METHODS AND FINDINGS

We generated a novel mouse line (dnKO) that possessed defects in both TGFbetaRII and IL-10R2 signaling. These mice rapidly and reproducibly developed a disease resembling fulminant human ulcerative colitis that was quite distinct from the much longer and more variable course of pathology observed previously in mice possessing only single defects. Pathogenesis was driven by uncontrolled production of proinflammatory cytokines resulting in large part from T cell activation. The disease process could be significantly ameliorated by administration of antibodies against IFNgamma and TNFalpha and was completely inhibited by a combination of broad-spectrum antibiotics.

CONCLUSIONS

Here, we develop to our knowledge the first mouse model of fulminant ulcerative colitis by combining multiple genetic hits in immune regulation and demonstrate that the resulting disease is sensitive to both anticytokine therapy and broad-spectrum antibiotics. These findings indicated the IL-10 and TGFbeta pathways synergize to inhibit microbially induced production of proinflammatory cytokines, including IFNgamma and TNFalpha, which are known to play a role in the pathogenesis of human ulcerative colitis. Our findings also provide evidence that broad-spectrum antibiotics may have an application in the treatment of patients with ulcerative colitis. This model system will be useful in the future to explore the microbial factors that induce immune activation and characterize how these interactions produce disease.