Variable phenotypes of enterocolitis in interleukin 10-deficient mice monoassociated with two different commensal bacteria

Altered enteric microbiota ecology in interleukin 10-deficient mice during development and progression of intestinal inflammation

Inflammatory bowel diseases (IBD) result from dysregulated immune responses toward microbial and perhaps other luminal antigens in a genetically susceptible host, and are associated with altered composition and diversity of the intestinal microbiota. The interleukin 10-deficient (IL-10 (-/-) ) mouse has been widely used to model human IBD; however the specific alterations that occur in the intestinal microbiota of this mouse model during the onset of colonic inflammation have not yet been defined. The aim of our study was to define the changes in diversity and composition that occur in the intestinal microbiota of IL-10 (-/-) mice during the onset and progression of colonic inflammation. We used high throughput sequencing of the 16S rRNA gene to characterize the diversity and composition of formerly germ-free, wild-type and IL-10 (-/-) mice associated with the same intestinal microbiota over time. Following two weeks of colonization with a specific pathogen-free (SPF) microbiota we observed a significant increase in the diversity and richness of the intestinal microbiota of wild-type mice. In contrast, a progressive decrease in diversity and richness was observed at three and four weeks in IL-10 (-/-) mice. This decrease in diversity and richness was mirrored by an increase in Proteobacteria and Escherichia coli in IL-10 (-/-) mice. An increase in E. coli was also observed in conventionally raised IL-10 (-/-) mice at the point of colonic inflammation. Our data reports the sequential changes in diversity and composition of the intestinal microbiota in an immune-mediated mouse model that may help provide insights into the primary vs. secondary role of dysbiosis in human IBD patients.

The complex interplay between inflammation, the microbiota and colorectal cancer

The microbiome has captured the attention of scientists from multiple research fields including ecology, immunology, microbiology and cancer biology. The microbial community living in the gastrointestinal tract is the most abundant and diverse niche of the human body and it is not surprising that microbiome research has predominantly focused upon this organ system. In this addendum, we summarize the latest developments in microbiome research on inflammatory bowel diseases and colorectal cancer. In addition, we highlight our recent findings that chronic intestinal inflammation modulates microbial community composition and the development of colorectal cancer. Our findings redefine the paradigm of inflammation-associated cancer by illuminating the key role of bacteria in development of colorectal cancer.

Environmental factors and inflammatory bowel disease: elusive or nonexistent?

Although abundant indirect evidence suggests that environmental factors contribute to the pathogenesis of inflammatory bowel disease (IBD), the search for specific etiological agents has been largely disappointing. Early life factors have been hypothesized to influence the risk of IBD; however, new data from the Nurses Health Study showed no associations between breastfeeding, gestational age, and birthweight and adult-onset IBD.

Diet, microbes, and host genetics: the perfect storm in inflammatory bowel diseases

The incidence of inflammatory bowel diseases (IBD), as well as other inflammatory conditions, has dramatically increased over the past half century. While many studies have shown that IBD exhibits a genetic component via genome-wide association studies, genetic drift alone cannot account for this increase, and other factors, such as those found in the environment must play a role, suggesting a "multiple hit" phenomenon that precipitates disease. One major environmental factor, dietary intake, has shifted to a high fat, high carbohydrate Western-type diet in developing nations, nearly in direct correlation with the increasing incidence of IBD. Recent evidence suggests that specific changes in dietary intake have led to a shift in the composite human gut microbiota, resulting in the emergence of pathobionts that can thrive under specific conditions. In the genetically susceptible host, the emerging pathobionts can lead to increasing incidence and severity of IBD and other inflammatory disorders. Since the gut microbiota is plastic and responds to dietary modulations, the use of probiotics, prebiotics, and/or dietary alterations are all intriguing complementary therapeutic approaches to alleviate IBD symptoms. However, the interactions are complex and it is unlikely that a one-size-fits all approach can be utilized across all populations affected by IBD. Exploration into and thoroughly understanding the interactions between host and microbes, primarily in the genetically susceptible host, will help define strategies that can be tailored to an individual as we move towards an era of personalized medicine to treat IBD.

Pro-angiogenic activity of TLRs and NLRs: a novel link between gut microbiota and intestinal angiogenesis

BACKGROUND & AIMS

In intestinal inflammation the gut microbiota induces an innate immune response by activating epithelial and immune cells that initiate or maintain inflammation. We investigated whether the microbiota also can activate local microvascular cells and induce angiogenesis.

METHODS

Human intestinal microvascular endothelial cells (HIMEC) and human intestinal fibroblasts (HIF) were exposed to bacterial ligands specific for Toll-like receptor (TLR)2/6 and 4, and NOD1 and NOD2, and cell proliferation, migration, transmigration, tube formation, and production of pro-angiogenic factors were measured. The ability of the ligands to induce ex vivo vessel sprouting in an aortic ring assay and in vivo angiogenesis using a collagen gel assay also were assessed.

RESULTS

Bacterial ligands induced proliferation, migration, transmigration, tube formation of HIMEC, vessel sprouting, and in vivo angiogenesis; they also stimulated production of angiogenic factors from HIMEC and HIF, and HIF-derived angiogenic factors promoted HIMEC proliferation. To various degrees, all ligands induced angiogenic responses, but these were ligand- and cell type-dependent. Responses were mediated through receptor interacting protein-2 (RIP2)- and tumor necrosis factor receptor-associated factor 6 (TRAF6)-dependent signaling, involved the mitogen-activated protein kinase (MAPK) and nuclear factor-κB (NF-κB) pathways and the up-regulation of vascular endothelial growth factor receptor 2 (VEGF-R2) and focal adhesion kinase (FAK). Knockdown of RIP2 and TRAF6 by RNA interference and neutralization of interleukin-8, basic fibroblast growth factor, and vascular endothelial growth factor inhibited TLR-/NOD-like receptor-induced HIMEC angiogenesis.

CONCLUSIONS

The gut microbiota can selectively activate mucosal endothelial and mesenchymal cells to promote specific angiogenic responses in a TLR- and NOD-like receptor-dependent fashion. This innate immunity-mediated response may expand the mucosal microvascular network, foster immune cell recruitment, and contribute to chronic intestinal inflammation.

Draft Genome Sequence of Enterococcus faecalis PC1.1, a Candidate Probiotic Strain Isolated from Human Feces

Enterococcus faecalis is commonly isolated from the gastrointestinal tract of healthy infants and adults, where it contributes to host health and well-being. We describe here the draft genome sequence of E. faecalis PC1.1, a candidate probiotic strain isolated from human feces.

Cyclooxygenase-2 generates the endogenous mutagen trans-4-hydroxy-2-nonenal in Enterococcus faecalis-infected macrophages

Infection of macrophages by the human intestinal commensal Enterococcus faecalis generates DNA damage and chromosomal instability in mammalian cells through bystander effects. These effects are characterized by clastogenesis and damage to mitotic spindles in target cells and are mediated, in part, by trans-4-hydroxy-2-nonenal (4-HNE). In this study, we investigated the role of COX and lipoxygenase (LOX) in producing this reactive aldehyde using E. faecalis-infected macrophages and interleukin (IL)-10-knockout mice colonized with this commensal. 4-HNE production by E. faecalis-infected macrophages was significantly reduced by COX and LOX inhibitors. The infection of macrophages led to decreased Cox1 and Alox5 expression whereas COX-2 and 4-HNE increased. Silencing Alox5 and Cox1 with gene-specific siRNAs had no effect on 4-HNE production. In contrast, silencing Cox2 significantly decreased 4-HNE production by E. faecalis-infected macrophages. Depleting intracellular glutathione increased 4-HNE production by these cells. Next, to confirm COX-2 as a source for 4-HNE, we assayed the products generated by recombinant human COX-2 and found 4-HNE in a concentration-dependent manner using arachidonic acid as a substrate. Finally, tissue macrophages in colon biopsies from IL-10-knockout mice colonized with E. faecalis were positive for COX-2 by immunohistochemical staining. This was associated with increased staining for 4-HNE protein adducts in surrounding stroma. These data show that E. faecalis, a human intestinal commensal, can trigger macrophages to produce 4-HNE through COX-2. Importantly, it reinforces the concept of COX-2 as a procarcinogenic enzyme capable of damaging DNA in target cells through bystander effects that contribute to colorectal carcinogenesis.

The Yin and Yang of host-commensal mutualism

The human body is populated by an extremely diverse group of microbes that live in a symbiotic relationship with their host. Among these, intestinal commensals are the most abundant, induce homeostatic mucosal immune responses, and fulfill physiologic functions that benefit the host. In some cases, gut symbionts, including Escherichia coli, may contribute to the pathogenesis of chronic intestinal inflammation by causing dysregulated immune activation in genetically susceptible hosts. Although immune responses to bacterial products are well-characterized, the impact of intestinal inflammation on the function of commensal luminal microbes is only beginning to be elucidated. We recently reported that chronic intestinal inflammation induces commensal E. coli to upregulate stress response genes that paradoxically limit their growth in vivo. Herein, we discuss our findings in the context of host-microbial interactions in health and disease and a developing paradigm that may distinguish pathogens from commensals.

The role of pattern recognition receptors in intestinal inflammation

Recognition of microorganisms by pattern-recognition receptors (PRRs) is the primary component of innate immunity that is responsible for the maintenance of host-microbial interactions in intestinal mucosa. Dysregulation in host-commensal interactions has been implicated as the central pathogenesis of inflammatory bowel disease (IBD), which predisposes to developing colorectal cancer. Recent animal studies have begun to outline some unique physiology and pathology involving each PRR signaling in the intestine. The major roles played by PRRs in the gut appear to be the regulation of the number and the composition of commensal bacteria, epithelial proliferation, and mucosal permeability in response to epithelial injury. In addition, PRR signaling in lamina propria immune cells may be involved in induction of inflammation in response to invasion of pathogens. Because some PRR-deficient mice have shown variable susceptibility to colitis, the outcome of intestinal inflammation may be modified depending on PRR signaling in epithelial cells, immune cells, and the composition of commensal flora. Through recent findings in animal models of IBD, this review will discuss how abnormal PRR signaling may contribute to the pathogenesis of inflammation and inflammation-associated tumorigenesis in the intestine.

Reduced diversity and imbalance of fecal microbiota in patients with ulcerative colitis

BACKGROUND

Clinical observations and experimental colitis models have indicated the importance of intestinal bacteria in the etiology of ulcerative colitis (UC), but a causative bacterial agent has not been identified.

AIM

To determine how intestinal bacteria are associated with UC, fecal microbiota and other components were compared for UC patients and healthy adults.

METHODS

Fresh feces were collected from 48 UC patients. Fecal microbiota were analyzed by use of terminal-restriction fragment length polymorphism (T-RFLP), real-time PCR, and culture. The concentrations of organic acids, indole, and ammonia, and pH and moisture, which are indicators of the intestinal environment, were measured and compared with healthy control data.

RESULTS

T-RFLP data divided the UC patients into four clusters; one cluster was obtained for healthy subjects. The diversity of fecal microbiota was significantly lower in UC patients. There were significantly fewer Bacteroides and Clostridium subcluster XIVab, and the amount of Enterococcus was higher in UC patients than in healthy subjects. The fecal concentration of organic acids was significantly lower in UC patients who were in remission.

CONCLUSION

UC patients have imbalances in the intestinal environment-less diversity of fecal microbiota, lower levels of major anaerobic bacteria (Bacteroides and Clostridium subcluster XIVab), and a lower concentration of organic acids.

Microbiota, disease, and back to health: a metastable journey

Alterations in the composition of the commensal microbiota have been observed in many complex diseases. Understanding the basis for these changes, how they relate to disease risk or activity, and the mechanisms by which the symbiotic state of colonization resistance and host homeostasis is restored is critical for future therapies aimed at manipulating the microbiota.

TNF-α mediates macrophage-induced bystander effects through Netrin-1

Macrophage-induced bystander effects have been implicated as an important mediator of chromosomal instability and colon cancer triggered by Enterococcus faecalis, a human intestinal commensal bacteria. There is little understanding about how inflammatory cytokines mediate bystander effects, but questions in this area are important because of the pivotal contributions made by inflammatory processes to cancer initiation and progression. Here, we report that the central proinflammatory cytokine TNF-α acts as a diffusible mediator of the bystander effects induced by macrophages, an effect caused by a proliferation of macrophages that trigger epithelial cell production of Netrin-1, a neuronal guidance molecule. TNF-α-mediated bystander assays used a murine coculture system of primary colonic epithelial cells and E. faecalis-infected macrophages (in vitro), with an interleukin 10 (IL-10)-deficient mouse model of colon cancer that involves long-term colonization with E. faecalis (in vivo). In cell cocultures, we observed increased expression of the TNF-α receptor Tnfrsf1b and Netrin-1. These effects were blocked by anti-TNF-α antibody or by pretreatment with an inhibitor of NF-κB signaling. RNAi-mediated attenuation of Tnfrsf1b decreased TNF-α-induced netrin-1 production and augmented epithelial cell apoptosis in culture. Extending these observations, colon biopsies from E. faecalis-colonized IL-10(-/-) mice exhibited crypt hyperplasia and increased staining for macrophages, TNF-α, netrin-1, NF-κB, Tnfrsf1b, and the proliferation marker proliferating cell nuclear antigen while also displaying a reduction in epithelial cell apoptosis. Together, our results define a pathway for macrophage-induced bystander effects in which TNF-α triggers TNFRSF1b receptor signaling leading to increased production of Netrin-1, crypt hyperplasia, and decreased epithelial cell apoptosis. In elucidating an important commensal-associated proinflammatory mechanism in the intestinal microenvironment, our work highlights the role of Netrin-1 and a specific TNF-α receptor as candidate targets to prevent or treat colorectal cancer.

Intestinal inflammation targets cancer-inducing activity of the microbiota

Inflammation alters host physiology to promote cancer, as seen in colitis-associated colorectal cancer (CRC). Here, we identify the intestinal microbiota as a target of inflammation that affects the progression of CRC. High-throughput sequencing revealed that inflammation modifies gut microbial composition in colitis-susceptible interleukin-10-deficient (Il10(-/-)) mice. Monocolonization with the commensal Escherichia coli NC101 promoted invasive carcinoma in azoxymethane (AOM)-treated Il10(-/-) mice. Deletion of the polyketide synthase (pks) genotoxic island from E. coli NC101 decreased tumor multiplicity and invasion in AOM/Il10(-/-) mice, without altering intestinal inflammation. Mucosa-associated pks(+) E. coli were found in a significantly high percentage of inflammatory bowel disease and CRC patients. This suggests that in mice, colitis can promote tumorigenesis by altering microbial composition and inducing the expansion of microorganisms with genotoxic capabilities.

The colitis-associated transcriptional profile of commensal Bacteroides thetaiotaomicron enhances adaptive immune responses to a bacterial antigen

Background

Inflammatory bowel diseases (IBD) may be caused in part by aberrant immune responses to commensal intestinal microbes including the well-characterized anaerobic gut commensal Bacteroides thetaiotaomicron (B. theta). Healthy, germ-free HLA-B27 transgenic (Tg) rats develop chronic colitis when colonized with complex gut commensal bacteria whereas non-transgenic (nTg) rats remain disease-free. However, the role of B. theta in causing disease in Tg rats is unknown nor is much known about how gut microbes respond to host inflammation.

Methods

Tg and nTg rats were monoassociated with a human isolate of B. theta. Colonic inflammation was assessed by histologic scoring and tissue pro-inflammatory cytokine measurement. Whole genome transcriptional profiling of B. theta recovered from ceca was performed using custom GeneChips and data analyzed using dChip, Significance Analysis of Microarrays, and Gene Set Enrichment Analysis (GSEA) software. Western Blots were used to determine adaptive immune responses to a differentially expressed B. theta gene.

Results

B. theta monoassociated Tg rats, but not nTg or germ-free controls, developed chronic colitis. Transcriptional profiles of cecal B. theta were significantly different in Tg vs. nTg rats. GSEA revealed that genes in KEGG canonical pathways involved in bacterial growth and metabolism were downregulated in B. theta from Tg rats with colitis though luminal bacterial concentrations were unaffected. Bacterial genes in the Gene Ontology molecular function “receptor activity”, most of which encode nutrient binding proteins, were significantly upregulated in B. theta from Tg rats and include a SusC homolog that induces adaptive immune responses in Tg rats.

Conclusions

B. theta induces colitis in HLA-B27 Tg rats, which is associated with regulation of bacterial genes in metabolic and nutrient binding pathways that may affect host immune responses. These studies of the host-microbial dialogue may lead to the identification of novel microbial targets for IBD therapies.

Cancer in inflammatory bowel disease: lessons from animal models

PURPOSE OF REVIEW

Human colitis-associated cancers (CAC) represent a heterogeneous group of conditions in which multiple oncogenic pathways are involved. In this article, we review the latest studies using genetic, chemical, bacterial and innate immune-mediated experimental models of CAC.

RECENT FINDINGS

Using the azoxymethane-dextran sodium sulfate model, wound healing pathways seem to be required in the development of CAC. There is also an emerging understanding that commensal and/or pathogenic bacteria can promote tumorigenesis, through T cell and TLR-mediated inflammation. Using specific transgenic mice (villin-CD98, T cell SMAD7, villin-TLR4) or specific knockout mice, investigators have determined that derangements in epithelial or innate and adaptive immune pathways can result in CAC. Subtle perturbations in epithelial repair - both too little or too exuberant - can render mice susceptible to tumorigenesis.

SUMMARY

With the aid of animal models, we have witnessed a rapid expansion of our knowledge of the molecular and immunologic mechanisms underlying inflammatory cancers. Though animal models have contributed a discrete amount of information to our understanding of tumorigenesis in the setting of intestinal inflammation, it is clear that no single animal model will be able to adequately recapitulate the pathogenesis of complex colorectal cancers, but each model gets us one step closer to comprehending the nature of CAC.

Type I interferons maintain Foxp3 expression and T-regulatory cell functions under inflammatory conditions in mice

BACKGROUND & AIMS

Foxp3(+) T-regulatory cells (Tregs) maintain intestinal homeostasis under conditions of continuous challenge with inflammatory microbes. However, plasticity of the Treg population under certain conditions has been reported; Foxp3(+) Tregs can be converted to Foxp3(-) CD4(+) T cells.

METHODS

We used mice with a T cell-induced colitis model to study the regulatory role of type I interferons (IFNs) in adaptive immunity. We transferred CD4(+)CD45RB(hi) (RB(hi)) T cells, with or without CD4(+)CD45RB(lo) CD25(+) T cells, from wild-type or IFN-αβR(-/-) mice into Rag1(-/-) recipients. We analyzed induction of colitis by flow cytometry, confocal microscopy, and enzyme-linked immunosorbent assay and reverse-transcription polymerase chain reaction analyses. IFN-αβR(-/-)Rag(-/-) mice were given injections of recombinant IFN-α following transfer of IFN-αβR(-/-) RB(hi) T cells and CD4(+)Foxp3(+) cells from Foxp3-eGFP mice.

RESULTS

Signaling by type I IFNs was required for maintenance of Foxp3 expression and the suppressive activity of Tregs in mice. Transfer of CD4(+)CD45RB(lo)CD25(+) Tregs from IFN-αβR(-/-) mice did not prevent T-cell induction of colitis in mice. Foxp3 expression by Tregs transferred from IFN-αβR(-/-) mice was significantly lower than that of Tregs from wild-type mice. Administration of recombinant IFN-α reduced T cell-mediated colitis by increasing the number of Foxp3(+) Tregs and their suppressive functions.

CONCLUSIONS

Type I IFNs regulate intestinal homeostasis by maintaining Foxp3 expression on Tregs in colons of mice under inflammatory conditions.

Host-microbiota interactions in inflammatory bowel disease

The interaction of the host with its abundant intestinal microbiota is complex and engages most of the cells in the intestinal mucosa. The inflammatory bowel diseases appear to be disorders of the host immune response to the microbiota. This is supported by data from induced gene mutations in mice and more recently by the identification of gene variants in humans that result in IBD or IBD susceptibility. These genetic studies have provided insights into the cells and molecular pathways involved in the host-microbiota dialog. This review discusses the innate, adaptive, and regulatory immune response to the microbiota in the context of the mouse and human genes that are involved in maintaining intestinal homeostasis and preventing inflammation. These data continue to support the hypothesis that inflammatory bowel disease results from a dysregulated adaptive immune response, particularly a CD4 T-cell response, to the microbiota. The microbiota itself is an active participant in these homeostatic processes. The microbiota composition is perturbed during inflammation, resulting in a dysbiosis that may induce or perpetuate inflammation. However, host genotype and the environment have a major impact on the shape of such dysbiosis, as well as upon which members of the microbiota stimulate pathogenic immune responses.

Non-invasive mapping of the gastrointestinal microbiota identifies children with inflammatory bowel disease

BACKGROUND

Pediatric inflammatory bowel disease (IBD) is challenging to diagnose because of the non-specificity of symptoms; an unequivocal diagnosis can only be made using colonoscopy, which clinicians are reluctant to recommend for children. Diagnosis of pediatric IBD is therefore frequently delayed, leading to inappropriate treatment plans and poor outcomes. We investigated the use of 16S rRNA sequencing of fecal samples and new analytical methods to assess differences in the microbiota of children with IBD and other gastrointestinal disorders.

METHODOLOGY/PRINCIPAL FINDINGS

We applied synthetic learning in microbial ecology (SLiME) analysis to 16S sequencing data obtained from i) published surveys of microbiota diversity in IBD and ii) fecal samples from 91 children and young adults who were treated in the gastroenterology program of Children's Hospital (Boston, USA). The developed method accurately distinguished control samples from those of patients with IBD; the area under the receiver-operating-characteristic curve (AUC) value was 0.83 (corresponding to 80.3% sensitivity and 69.7% specificity at a set threshold). The accuracy was maintained among data sets collected by different sampling and sequencing methods. The method identified taxa associated with disease states and distinguished patients with Crohn's disease from those with ulcerative colitis with reasonable accuracy. The findings were validated using samples from an additional group of 68 patients; the validation test identified patients with IBD with an AUC value of 0.84 (e.g. 92% sensitivity, 58.5% specificity).

CONCLUSIONS/SIGNIFICANCE

Microbiome-based diagnostics can distinguish pediatric patients with IBD from patients with similar symptoms. Although this test can not replace endoscopy and histological examination as diagnostic tools, classification based on microbial diversity is an effective complementary technique for IBD detection in pediatric patients.

Smokers with active Crohn's disease have a clinically relevant dysbiosis of the gastrointestinal microbiota

BACKGROUND

Patients with Crohn's disease (CD) have an intestinal dysbiosis with components of the microbiota exerting differential immune effects. Smoking is associated with an increased incidence of CD, more frequent relapse, and greater burden of surgery. This study aimed to investigate the association between smoking and the intestinal microbiota in patients with active CD.

METHODS

Patients with active CD (n = 103) and healthy controls (n = 66) were recruited and demographic and clinical data recorded including current smoking behavior. Fecal samples were collected and analyzed by fluorescent in situ hybridization using probes targeting 16S rRNA of bacteria previously shown to be altered in active CD (bifidobacteria, bacteroides, Clostridium coccoides-Eubacterium rectale, Escherichia coli, and Faecalibacterium prausnitzii).

RESULTS

In total, 29/101 (29%) patients with CD and 8/58 (14%) controls were current smokers (P = 0.032). Following multivariate analysis, smoking was found to have a significant and independent effect on the microbiota of patients with CD, with higher Bacteroides-Prevotella in smokers (38.4%) compared with nonsmokers (28.1%) (F((1,93)) = 12.6, P = 0.001). Healthy controls who smoked also had higher Bacteroides-Prevotella (34.8%) than nonsmokers (24.1%) (F((1,55)) = 4.5, P = 0.038). In the pooled multivariate analysis, patients with CD had higher bifidobacteria (F((1,156)) = 30.5, P < 0.001), higher Bacteroides-Prevotella (F((1,156)) = 6.5, P = 0.012), and lower F. prausnitzii (F((1,156)) = 3.8, P = 0.052) compared with healthy controls.

CONCLUSIONS

Smokers have luminal microbiota that consist of significantly higher bacteroides. Investigation of whether this is one mechanism through which the negative effects of smoking on CD are mediated is warranted.

The effects of commensal microbiota on immune cell subsets and inflammatory responses

Billions of years of coevolution shaped the mutually beneficial relationships between metazoans and symbiotic commensal microorganisms. Commensal microorganisms profoundly affect the physiology of the host and provide the host with survival advantages in several ways, while they could also trigger pathogenic immune responses and threaten the well-being of the host. Recent advances in DNA sequencing technology enabled the analysis of commensal microbiota, and improvements in the techniques of culturing gut-resident microorganisms and of rearing gnotobiotic rodents have made it possible to assess the effect of individual component of microbial communities on host physiology. In this review, we discuss the current understanding of the interactions of commensal microbiota with the host immune system.

4-hydroxy-2-nonenal mediates genotoxicity and bystander effects caused by Enterococcus faecalis-infected macrophages

BACKGROUND & AIMS

Enterococcus faecalis is a human intestinal commensal that produces extracellular superoxide and promotes chromosome instability via macrophage-induced bystander effects. We investigated the ability of 4-hydroxy-2-nonenal (4-HNE), a diffusible breakdown product of ω-6 polyunsaturated fatty acids, to mediate these effects.

METHODS

4-HNE was purified from E faecalis-infected macrophages; its genotoxicity was assessed in human colon cancer (HCT116) and primary murine colon epithelial (YAMC) cell lines.

RESULTS

4-HNE induced G(2)-M cell cycle arrest, led to formation γH2AX foci, and disrupted the mitotic spindle in both cell lines. Binucleate tetraploid cells that formed after incubation with 4-HNE were associated with the activation of stathmin and microtubule catastrophe. Silencing glutathione S-transferase α4, a scavenger of 4-HNE, increased the susceptibility of epithelial cells to 4-HNE-induced genotoxicity. Interleukin-10 knockout mice colonized with superoxide-producing E faecalis developed inflammation and colorectal cancer, whereas colonization with a superoxide-deficient strain resulted in inflammation but not cancer. 4-HNE-protein adducts were found in the lamina propria and macrophages in areas of colorectal inflammation.

CONCLUSIONS

4-HNE can act as an autochthonous mitotic spindle poison in normal colonic epithelial and colon cancer cells. This finding links the macrophage-induced bystander effects to colorectal carcinogenesis.

Host-microbe relationships in inflammatory bowel disease detected by bacterial and metaproteomic analysis of the mucosal-luminal interface

BACKGROUND

Host-microbe interactions at the intestinal mucosal-luminal interface (MLI) are critical factors in the biology of inflammatory bowel disease (IBD).

METHODS

To address this issue, we performed a series of investigations integrating analysis of the bacteria and metaproteome at the MLI of Crohn's disease, ulcerative colitis, and healthy human subjects. After quantifying these variables in mucosal specimens from a first sample set, we searched for bacteria exhibiting strong correlations with host proteins. This assessment identified a small subset of bacterial phylotypes possessing this host interaction property. Using a second and independent sample set, we tested the association of disease state with levels of these 14 "host interaction" bacterial phylotypes.

RESULTS

A high frequency of these bacteria (35%) significantly differentiated human subjects by disease type. Analysis of the MLI metaproteomes also yielded disease classification with exceptional confidence levels. Examination of the relationships between the bacteria and proteins, using regularized canonical correlation analysis (RCCA), sorted most subjects by disease type, supporting the concept that host-microbe interactions are involved in the biology underlying IBD. Moreover, this correlation analysis identified bacteria and proteins that were undetected by standard means-based methods such as analysis of variance, and identified associations of specific bacterial phylotypes with particular protein features of the innate immune response, some of which have been documented in model systems.

CONCLUSIONS

These findings suggest that computational mining of mucosa-associated bacteria for host interaction provides an unsupervised strategy to uncover networks of bacterial taxa and host processes relevant to normal and disease states. (Inflamm Bowel Dis 2012;).

Mouse background strain profoundly influences Paneth cell function and intestinal microbial composition

BACKGROUND

Increasing evidence supports the central role of Paneth cells in maintaining intestinal host-microbial homeostasis. However, the direct impact of host genotype on Paneth cell function remains unclear. Here, we characterize key differences in Paneth cell function and intestinal microbial composition in two widely utilized, genetically distinct mouse strains (C57BL/6 and 129/SvEv). In doing so, we demonstrate critical influences of host genotype on Paneth cell activity and the enteric microbiota.

METHODOLOGY AND PRINCIPAL FINDINGS

Paneth cell numbers were determined by flow cytometry. Antimicrobial peptide (AMP) expression was evaluated using quantitative reverse-transcriptase polymerase chain reaction (qRT-PCR), acid urea-polyacrylamide gel electrophoresis, and mass spectrometry. Effects of mouse background on microbial composition were assessed by reciprocal colonization of germ-free mice from both background strains, followed by compositional analysis of resultant gut bacterial communities using terminal restriction fragment length polymorphism analysis and 16 S qPCR. Our results revealed that 129/SvEv mice possessed fewer Paneth cells and a divergent AMP profile relative to C57BL/6 counterparts. Novel 129/SvEv á-defensin peptides were identified, including Defa2/18v, Defa11, Defa16, and Defa18. Host genotype profoundly affected the global profile of the intestinal microbiota, while both source and host factors were found to influence specific bacterial groups. Interestingly, ileal α-defensins from 129/SvEv mice displayed attenuated antimicrobial activity against pro-inflammatory E. coli strains, a bacterial species found to be expanded in these animals.

CONCLUSIONS AND SIGNIFICANCE

This work establishes the important impact of host genotype on Paneth cell function and the composition of the intestinal microbiota. It further identifies specific AMP and microbial alterations in two commonly used inbred mouse strains that have varying susceptibilities to a variety of disorders, ranging from obesity to intestinal inflammation. This will be critical for future studies utilizing these murine backgrounds to study the effects of Paneth cells and the intestinal microbiota on host health and disease.

Host genetics and environmental factors regulate ecological succession of the mouse colon tissue-associated microbiota

BACKGROUND

The integration of host genetics, environmental triggers and the microbiota is a recognised factor in the pathogenesis of barrier function diseases such as IBD. In order to determine how these factors interact to regulate the host immune response and ecological succession of the colon tissue-associated microbiota, we investigated the temporal interaction between the microbiota and the host following disruption of the colonic epithelial barrier.

METHODOLOGY/PRINCIPAL FINDINGS

Oral administration of DSS was applied as a mechanistic model of environmental damage of the colon and the resulting inflammation characterized for various parameters over time in WT and Nod2 KO mice.

RESULTS

In WT mice, DSS damage exposed the host to the commensal flora and led to a migration of the tissue-associated bacteria from the epithelium to mucosal and submucosal layers correlating with changes in proinflammatory cytokine profiles and a progressive transition from acute to chronic inflammation of the colon. Tissue-associated bacteria levels peaked at day 21 post-DSS and declined thereafter, correlating with recruitment of innate immune cells and development of the adaptive immune response. Histological parameters, immune cell infiltration and cytokine biomarkers of inflammation were indistinguishable between Nod2 and WT littermates following DSS, however, Nod2 KO mice demonstrated significantly higher tissue-associated bacterial levels in the colon. DSS damage and Nod2 genotype independently regulated the community structure of the colon microbiota.

CONCLUSIONS/SIGNIFICANCE

The results of these experiments demonstrate the integration of environmental and genetic factors in the ecological succession of the commensal flora in mammalian tissue. The association of Nod2 genotype (and other host polymorphisms) and environmental factors likely combine to influence the ecological succession of the tissue-associated microflora accounting in part for their association with the pathogenesis of inflammatory bowel diseases.

Time to include the gut microbiota in the hygienic standardisation of laboratory rodents

The gut microbiota (GM) composition and its impact on animal experiments has become currently dramatically relevant in our days: (1) recent progress in metagenomic technologies, (2) the availability of large scale quantitative analyses to characterize even subtle phenotypes, (3) the limited diversity of laboratory rodent GM due to strict barriers at laboratory animal vendors, and (4) the availability of up to 300.000 different transgenic mouse strains from different sources displaying a huge variety in their GM composition. In this review the GM is described as a variable in animal experiments which need to be reduced for scientific as well as ethical reasons, and strategies how to implement this in routine diagnostic procedures are proposed. We conclude that we have both enough information available to state that the GM has an essential impact on animal models, as well as the methods available to start dealing with these impacts.

Campylobacter jejuni induces colitis through activation of mammalian target of rapamycin signaling

BACKGROUND & AIMS

Campylobacter jejuni is the worldwide leading cause of bacterial-induced enteritis. The molecular and cellular events that lead to campylobacteriosis are poorly understood. We identify mammalian target of rapamycin (mTOR) as a signaling pathway that leads to C jejuni-induced intestinal inflammation.

METHODS

Germ-free (control) or conventionally derived Il10(-/-) mice that express enhanced green fluorescent protein (EGFP) under the control of nuclear factor κB (Il10(-/-); NF-κB(EGFP) mice) were infected with C jejuni (10(9) colony-forming units/mouse) for 12 days; their responses were determined using histologic, semiquantitative reverse-transcription polymerase chain reaction, fluorescence in situ hybridization, transmission electron microscopy, and tissue culture analyses. mTOR signaling was blocked by daily intraperitoneal injections of the pharmacologic inhibitor rapamycin (1.5 mg/kg). CD4(+) T cells were depleted by intraperitoneal injections of antibodies against CD4 (0.5 mg/mouse every 3 days). Bacterial survival in splenocytes was measured using a gentamycin killing assay.

RESULTS

C jejuni induced intestinal inflammation, which correlated with activation of mTOR signaling and neutrophil infiltration. The inflamed intestines of these mice had increased levels of interleukin-1β, Cxcl2, interleukin-17a, and EGFP; C jejuni localized to colons and extraintestinal tissues of infected Il10(-/-); NF-κB(EGFP) mice compared with controls. Rapamycin, administered before or after introduction of C jejuni, blocked C jejuni-induced intestinal inflammation and bacterial accumulation. LC3II processing and killing of C jejuni were increased in splenocytes incubated with rapamycin compared with controls.

CONCLUSIONS

mTOR signaling mediates C jejuni-induced colitis in Il10(-/-) mice, independently of T-cell activation. Factors involved in mTOR signaling might be therapeutic targets for campylobacteriosis.

Dextran sodium sulfate-induced inflammation alters the expression of proteins by intestinal Escherichia coli strains in a gnotobiotic mouse model

To identify Escherichia coli proteins involved in adaptation to intestinal inflammation, mice were monoassociated with the colitogenic E. coli strain UNC or with the probiotic E. coli strain Nissle. Intestinal inflammation was induced by treating the mice with 3.5% dextran sodium sulfate (DSS). Differentially expressed proteins in E. coli strains collected from cecal contents were identified by 2-dimensional difference gel electrophoresis. In both strains, acute inflammation led to the downregulation of pathways involved in carbohydrate breakdown and energy generation. Accordingly, DSS-treated mice had lower concentrations of bacterial fermentation products in their cecal contents than control mice. Differentially expressed proteins also included the Fe-S cluster repair protein NfuA, the tryptophanase TnaA, and the uncharacterized protein YggE. NfuA expression was 3-fold higher in E. coli strains from DSS-treated than from control mice. Reporter experiments confirmed the induction of nfuA in response to iron deprivation, mimicking Fe-S cluster destruction by inflammation. YggE expression, which has been reported to reduce the intracellular level of reactive oxygen species, was 4- to 8-fold higher in E. coli Nissle than in E. coli UNC. This was confirmed by in vitro reporter gene assays indicating that Nissle is better equipped to cope with oxidative stress than UNC. Nissle isolated from DSS-treated and control mice had TnaA levels 4- to 7-fold-higher than those of UNC. Levels of indole resulting from the TnaA reaction were higher in control animals associated with E. coli Nissle. Because of its anti-inflammatory effect, indole is hypothesized to be involved in the extension of the remission phase in ulcerative colitis described for E. coli Nissle.

Chronic intestinal inflammation induces stress-response genes in commensal Escherichia coli

BACKGROUND & AIMS

Intestinal microbes induce homeostatic mucosal immune responses, but can also cause inappropriate immune activation in genetically susceptible hosts. Although immune responses to bacterial products have been studied extensively, little is known about how intestinal inflammation affects functions of commensal luminal microbes.

METHODS

Microarrays and real-time polymerase chain reaction were used to profile transcriptional changes in luminal bacteria from wild-type and IL-10(-/-) mice monoassociated with a nonpathogenic, murine isolate of Escherichia coli (NC101, which causes colitis in gnotobiotic IL-10(-/-) mice). Colonic inflammation and innate and adaptive immune responses were measured in wild-type and IL-10(-/-) mice monoassociated with mutant NC101 that lack selected, up-regulated genes, and in IL-10(-/-) mice that were colonized with a combination of mutant and parental NC101. We measured intracellular survival of bacteria within primary macrophages from mice and resulting production of tumor necrosis factor.

RESULTS

Bacteria from IL-10(-/-) mice with colitis had significant up-regulation of the stress-response regulon, including the small heat shock proteins IbpA and IbpB that protect E coli from oxidative stress, compared to healthy, wild-type controls. In IL-10(-/-) mice, expression of ibpAB reduced histologic signs of colon inflammation, secretion of interleukin-12/23p40 in colonic explant cultures, serologic reactivity to NC101 antigens, and secretion of interferon-gamma by stimulated mesenteric lymph node cells. Infection of primary macrophages by bacteria that express ibpAB was associated with decreased intracellular survival and reduced secretion of tumor necrosis factor.

CONCLUSIONS

Chronic intestinal inflammation causes functional alterations in gene expression in commensal gut bacterium (E coli NC101). Further studies of these expression patterns might identify therapeutic targets for patients with inflammatory bowel diseases.

Pathogenesis of gastritis in ileitis-prone SAMP1/Yit mice

Inflammatory bowel disease is a chronic inflammatory disease of the gut which manifests as ulcerative colitis or Crohn's disease. One of the most studied animal models of spontaneous Crohn's disease is the senescence-accelerated mouse (SAMP1/Yit strain) model. In SAMP1/Yit mice, although many immunological responses are perturbed, some evidence suggests that the primary defect lies in the epithelial cell barrier. In the process of studying epithelial permeability, we observed that the stomach in SAMP1/Yit mice also had increased permeability. Upon further examination, these mice were shown to have marked, chronic gastritis with focal to diffuse aggregates of mononuclear cells of mixed lineages. These aggregates were located predominantly in the oxyntic mucosa, with occasional lesions in the forestomach but with relatively fewer cellular infiltrates in the antral mucosa. Real-time RT PCR showed an increase in several helper T cell (Th cell)-derived pro-inflammatory cytokines in the gastric mucosa of SAMP1/Yit mice. However, many of the cells in the aggregates of SAMP1/Yit mice were B cells. SAMP1/Yit B cells exacerbate ileitis when co-transferred into immunodeficient recipients. The gastritis also reflects a contribution by B cells. As SAMP1/Yit mice were derived from AKR mice, we examined AKR mice and determined that they too have an increased occurrence of gastritis, although they do not develop ileitis. B cells contributed to the gastric inflammation in these mice also. Thus, SAMP1/Yit mice display gastritis as well as ileitis, and B cells appear to play a role in the pathogenesis of inflammation at both sites. This review will discuss some of the mechanisms that may account for these different manifestations of gastrointestinal disease.

Prevalence of Campylobacter species in adult Crohn's disease and the preferential colonization sites of Campylobacter species in the human intestine

INTRODUCTION

Crohn's disease (CD) and ulcerative colitis (UC) are the two major forms of inflammatory bowel disease (IBD). A high prevalence of Campylobacter concisus was previously detected in paediatric CD and adult UC. Currently, the prevalence of C. concisus in adult CD and the preferential colonization sites of Campylobacter species in the human intestine are unknown. In this study, we examined the prevalence of Campylobacter species in biopsies collected from multiple anatomic sites of adult patients with IBD and controls.

METHODS

Three hundred and one biopsies collected from ileum, caecum, descending colon and rectum of 28 patients IBD (15 CD and 13 UC) and 33 controls were studied. Biopsies were used for DNA extraction and detection of Campylobacter species by PCR-sequencing and Campylobacter cultivation.

RESULTS

A significantly higher prevalence of C. concisus in colonic biopsies of patients with CD (53%) was detected as compared with the controls (18%). Campylobacter genus-PCR positivity and C. concisus positivity in patients with UC were 85% and 77% respectively, being significantly higher than that in the controls (48% and 36%). C. concisus was more often detected in descending colonic and rectal biopsies from patients with IBD in comparison to the controls. C. concisus was isolated from patients with IBD.

CONCLUSION

The high intestinal prevalence of C. concisus in patients with IBD, particularly in the proximal large intestine, suggests that future studies are needed to investigate the possible involvement of C. concisus in a subgroup of human IBD. To our knowledge, this is the first report of the association between adult CD and C. concisus as well as the first study of the preferential colonization sites of C. concisus in the human intestine.

Ectopic expression of blood type antigens in inflamed mucosa with higher incidence of FUT2 secretor status in colonic Crohn's disease

BACKGROUND

Host-intestinal microbial interaction plays an important role in the pathogenesis of inflammatory bowel diseases (IBDs). The surface molecules of the intestinal epithelium act as receptors for bacterial adhesion and regulate the intestinal bacteria. Some known receptors are the mucosal blood type antigens, which are regulated by the fucosyltransferase2 (FUT2) gene, and individuals who express these antigens in the gastrointestinal tract are called secretors. Recent research has revealed that the FUT2 gene is associated with Crohn's disease (CD) in western populations.

METHODS

To clarify the contribution of mucosal blood type antigens in IBD, we determined the incidence of five previously reported single-nucleotide polymorphisms of the FUT2 gene in Japanese patients. We also used immunohistochemistry to investigate the antigen expression in mucosal specimens from IBD patients and animal models.

RESULTS

Genetic analysis revealed that all of the patients with colonic CD were secretors, whereas the incidence of secretors was 80, 80, 67, and 80%, respectively, for the control, ileocolonic CD, ileal CD, and ulcerative colitis groups (P = 0.036). Abnormal expression of blood type antigens was observed only in colonic CD. Interleukin-10⁻/⁻ mice, but not dextran sulfate sodium colitis mice, had enhanced colonic expression of blood type antigens, and the expression of these antigens preceded the development of colitis in the interleukin-10⁻/⁻ mice.

CONCLUSIONS

FUT2 secretor status was associated with colonic-type CD. This finding, taken together with the immunohistochemistry data, suggests that the abnormal expression of blood type antigens in the colon may be a unique and essential factor for colonic CD.

Enterococcus faecalis metalloprotease compromises epithelial barrier and contributes to intestinal inflammation

BACKGROUND & AIMS

Matrix metalloproteases (MMPs) mediate pathogenesis of chronic intestinal inflammation. We characterized the role of the gelatinase (GelE), a metalloprotease from Enterococcus faecalis, in the development of colitis in mice.

METHODS

Germ-free, interleukin-10-deficient (IL-10(-/-)) mice were monoassociated with the colitogenic E faecalis strain OG1RF and isogenic, GelE-mutant strains. Barrier function was determined by measuring E-cadherin expression, transepithelial electrical resistance (TER), and translocation of permeability markers in colonic epithelial cells and colon segments from IL-10(-/-) and TNF(ΔARE/Wt) mice. GelE specificity was shown with the MMP inhibitor marimastat.

RESULTS

Histologic analysis (score 0-4) of E faecalis monoassociated IL-10(-/-) mice revealed a significant reduction in colonic tissue inflammation in the absence of bacteria-derived GelE. We identified cleavage sites for GelE in the sequence of recombinant mouse E-cadherin, indicating that it might be degraded by GelE. Experiments with Ussing chambers and purified GelE revealed the loss of barrier function and extracellular E-cadherin in mice susceptible to intestinal inflammation (IL-10(-/-) and TNF(ΔARE/Wt) mice) before inflammation developed. Colonic epithelial cells had reduced TER and increased translocation of permeability markers after stimulation with GelE from OG1RF or strains of E faecalis isolated from patients with Crohn's disease and ulcerative colitis.

CONCLUSIONS

The metalloprotease GelE, produced by commensal strains of E faecalis, contributes to development of chronic intestinal inflammation in mice that are susceptible to intestinal inflammation (IL-10(-/-) and TNF(ΔARE/Wt) mice) by impairing epithelial barrier integrity.

Investigating the biological and clinical significance of human dysbioses

Culture-independent microbiological technologies that interrogate complex microbial populations without prior axenic culture, coupled with high-throughput DNA sequencing, have revolutionized the scale, speed and economics of microbial ecological studies. Their application to the medical realm has led to a highly productive merger of clinical, experimental and environmental microbiology. The functional roles played by members of the human microbiota are being actively explored through experimental manipulation of animal model systems and studies of human populations. In concert, these studies have appreciably expanded our understanding of the composition and dynamics of human-associated microbial communities (microbiota). Of note, several human diseases have been linked to alterations in the composition of resident microbial communities, so-called dysbiosis. However, how changes in microbial communities contribute to disease etiology remains poorly defined. Correlation of microbial composition represents integration of only two datasets (phenotype and microbial composition). This article explores strategies for merging the human microbiome data with multiple additional datasets (e.g. host single nucleotide polymorphisms and host gene expression) and for integrating patient-based data with results from experimental animal models to gain deeper understanding of how host-microbe interactions impact disease.

Neonatal exposure to fecal antigens reduces intestinal inflammation

BACKGROUND

A role for bacterial antigens in the pathogenesis of inflammatory bowel disease (IBD) has been established in enhanced humoral and cellular immune response to ubiquitous antigens of the enteric flora. However, we have recently shown that bacterial antigens in the absence of live bacteria cannot initiate an intestinal inflammation in IBD-prone interleukin (IL)-10 gene-deficient mice. The objective was to investigate whether neonatal exposure to antigens of their own endogenous flora can tolerize mice to bacterial antigens.

METHODS

IL-10 gene-deficient neonates were injected intraperitoneally within 72 hours of birth with a sterile solution of bacterial lysates prepared from fecal material of either conventionally raised mice (contains bacterial antigens) or axenic mice (lacks bacterial antigens). The onset of intestinal inflammation was monitored as the appearance of occult blood in the stool in weekly hemoccult analysis. Mice were sacrificed between age 15 and 19 weeks and tested for histopathologic injury, intestinal inflammation, and systemic response to bacterial antigens.

RESULTS

In mice neonatally exposed to bacterial antigens the onset of intestinal inflammation was delayed and the incidence of histopathologic injury at age 18 weeks was reduced. In addition, mice injected with lysates from conventionally raised mice exhibited decreased release of proinflammatory cytokines (interferon gamma [IFN-γ] and IL-17) in intestinal tissue and demonstrated reduced bacteria-stimulated systemic responses when compared to mice injected with lysates derived from bacteria-free, axenic mice.

CONCLUSIONS

Neonatal intraperitoneal injection of antigens from the commensal flora causes long-lasting changes in systemic and mucosal immune responses resulting in delayed onset of intestinal inflammation and injury in IBD-prone IL-10 gene-deficient mice.

Key questions to guide a better understanding of host-commensal microbiota interactions in intestinal inflammation

Co-evolution with an extremely complex commensal enteric microbiota has helped shape mammalian mucosal immune responses. A yet incompletely defined subset of intestinal bacteria is required to stimulate chronic, immune-mediated intestinal inflammation, including human Crohn's disease, and intestinal microbiota composition is altered in a characteristic manner by the inflammatory response to create a dysbiotic relationship of protective vs. aggressive bacteria. We pose a number of questions regarding host interactions with the enteric microbiota, including influences of inflammation, host genetics, early environmental exposure, and diet on microbial composition and function, and conversely, the effect of bacterial metabolism, enteric fungi and viruses, and endogenous protective bacterial species on host immune and inflammatory responses. These questions are designed to stimulate research that will promote a better understanding of host-microbial interactions in the intestine and promote targeted novel therapeutic interventions.

[Gut microbiota and IBD]

Gut microbiota contains about 10(14) bacterial cells classified within 4 bacterial phyla, namely Firmicutes, Bacteroidetes, Actinobacteria, and Proteobacteria. Much of the information has been generated through the application of nucleic acid-based methodologies (16S rRNA) which provide a cornerstone of microbial taxonomy. Inflammatory bowel disease (IBD) involves a dysregulated immune response to the gut microbiota in genetically predisposed hosts. Experimental animal models of colitis provide the best evidence that bacteria present in the bowel of the animals have an essential role in the pathogenesis of colitis since in most models, germ-free animals do not develop disease. Moreover, in the immunodeficient mouse model of colitis called TRUC (T-bet-/- x RAG2-/-), a colitogenic gut microbiota is selected and can be transmitted to mice with intact immunity and induce colitis. Current interest therefore focuses on the bacterial community as the source of antigens that fuel the chronic inflammation seen in IBD. Dysbiosis, an imbalance between harmful and protective bacteria, has been evoked and investigated in IBD. Thus, besides the classical pathogens, gut microbiota can drive pathogenicity via two mechanisms: an expansion of 'pro-inflammatory' species or a restriction in the protective compounds of the microbiota. Complexity of the microbiota suggests that both mechanisms may contribute to chronic gut inflammation in IBD.

Effect of Lactobacillus plantarum LP-Onlly on gut flora and colitis in interleukin-10 knockout mice

BACKGROUND AND AIM

Probiotics are used in the therapy of inflammatory bowel disease. This study aimed to determine the effects of probiotic Lactobacillus plantarum LP-Onlly (LP) on gut flora and colitis in interleukin-10 knockout (IL-10(-/-) ) mice, a model of spontaneous colitis.

METHODS

IL-10(-/-) and wild-type mice were used at 8 weeks of age and LP by gavage was administered at a dose of 10(9) cells/day per mice for 4 weeks. Mice were maintained for another one week without LP treatment. The colonic tissues were collected for histological and ultrastructural analysis at death after 4 weeks treatment of LP, and the feces were collected at 1-week intervals throughout the experiment for the analysis of gut flora and LP using selective culture-based techniques.

RESULTS

Compared with control mice, IL-10(-/-) mice developed a severe intestinal inflammation and tissue damage, and had an abnormal composition of gut microflora. LP administration attenuated colitis with the decreased inflammatory scoring and histological injury in the colon of IL-10(-/-) mice. In addition, LP administration increased the numbers of beneficial total bifidobacteria and lactobacilli, and decreased the numbers of potential pathogenic enterococci and Clostridium perfringens, although the decrease of coliforms was not significant after LP treatment in IL-10(-/-) mice.

CONCLUSIONS

Oral administration of LP was effective in the treatment of colitis, with the direct modification of gut microflora in IL-10(-/-) mice. This probiotic strain could be used as a potential adjuvant in the therapy of inflammatory bowel disease, although further studies are required in human.

Distance burning: how gut microbes promote extraintestinal cancers

Gut microbes play a major role in carcinogenesis of the gastrointestinal tract. We and others have shown in mouse models that colonic bacteria also influence the development of extraintestinal cancers including hepatocellular and mammary carcinomas. Microbes such as Helicobacter hepaticus invoke a proinflammatory microenvironment in the lower bowel that may extend to distant organs, often in the absence of histologically evident inflammation. Innate immunity plays a crucial role in the promotion of liver cancer and other systemic diseases by gut microbes. Additional mechanisms include type 1 adaptive immunity, altered metabolism, and oxidative stress. Emerging links between host genetics, gut microbes, inflammatory bowel disease and colorectal cancer also may prove useful for the correlation of specific bacterial populations with extraintestinal neoplasms. Interruption of deleterious host-microbe networks through judicious use of antibiotics and targeted molecular therapies may help reduce the incidence of liver, breast, and other human cancers.

The struggle within: microbial influences on colorectal cancer

Recently, an unprecedented effort has been directed at understanding the interplay between chronic inflammation and development of cancer, with the case of inflammatory bowel disease (IBD)-associated colorectal cancer at the forefront of this research endeavor. The last decade has been particularly fertile, with the discovery of numerous innovative paradigms linking various inflammatory, proliferative, and innate and adaptive immune signaling pathways to the development of colorectal cancer. Because of the preponderant role of the intestinal microbiota in the initiation and progression of IBD, recent efforts have been directed at understanding the relationship between bacteria and colorectal cancer. The microbiota and its collective genome, the microbiome, form a diverse and complex ecological community that profoundly impacts intestinal homeostasis and disease states. This review will discuss the differential influence of the microbiota on the development of IBD-associated colorectal cancer and highlight the role of innate immune sensor-dependent as well as -independent mechanisms in this pathology.

Infectious causes of colorectal cancer

Colorectal cancer is a major cause of cancer-related morbidity and mortality in the United States and many other regions of the world. Our understanding of the pathogenesis of colorectal cancer, from the precursor adenomatous polyp to adenocarcinoma, has evolved rapidly. Colorectal carcinogenesis is a sequential process characterized by the accumulation of multiple genetic and molecular alterations in colonic epithelial cells. However, the development of colorectal cancer involves more then just a genetic predisposition. External or environmental factors presumably play a significant role, and inflammatory bowel diseases, obesity, alcohol consumption, and a diet high in fat and low in fiber have all been implicated as risk factors for the development of either colonic adenomas or carcinomas. We are becoming increasingly aware of microbes as causes of malignancies. This article reviews the various microbes that have been associated with the development of colorectal carcinomas.

Murine model of Clostridium difficile infection with aged gnotobiotic C57BL/6 mice and a BI/NAP1 strain

The increased incidence and severity of Clostridium difficile infection (CDI) in older adults (age, ≥65 years) corresponds with the emergence of the BI/NAP1 strain, making elucidation of the host immune response extremely important. We therefore infected germ-free C57BL/6 mice aged 7-14 months with a BI/NAP1 strain and monitored the mice for response. Infected mice were moribund 48-72 h after infection and developed gross and histological cecitis and colitis and elevated concentrations of keratinocyte chemoattractant, interleukin 1β, monocyte chemotactic protein 1, and granulocyte colony-stimulating factor and decreased levels of interferon γ, interleukin 12 p40, interleukin 12 p70, and interleukin 10 compared with controls. We conclude that aged, germ-free C57BL/6 mice are susceptible to fulminant CDI from a BI/NAP1 strain and represent a novel model to further elucidate the host immune response to acute CDI.

Altered macrophage function contributes to colitis in mice defective in the phosphoinositide-3 kinase subunit p110δ

BACKGROUND & AIMS

Innate immune responses are crucial for host defense against pathogens but need to be tightly regulated to prevent chronic inflammation. Initial characterization of mice with a targeted inactivating mutation in the p110δ subunit of phosphoinositide 3-kinase (PI3K p110δ(D910A/D910A)) revealed defects in B- and T-cell signaling and chronic colitis. Here, we further characterize features of inflammatory bowel diseases in these mice and investigate underlying innate immune defects.

METHODS

Colons and macrophages from PI3K p110δ(D910A/D910A) mice were evaluated for colonic inflammation and innate immune dysfunction. Colonic p110δ messenger RNA expression was examined in interleukin (IL)-10(-/-) and wild-type germ-free mice during transition to a conventional microbiota. To assess polygenic impact on development of colitis, p110δ(D910A/D910A) mice were backcrossed to IL-10(-/-) mice.

RESULTS

A mild spontaneous colitis was shown in PI3K p110δ(D910A/D910A) mice at 8 weeks, with inflammation increasing with age. An inflammatory mucosal and systemic cytokine profile was characterized by expression of IL-12/23. In PI3K p110δ(D910A/D910A) macrophages, augmented toll-like receptor signaling and defective bactericidal activity were observed. Consistent with an important homeostatic role for PI3K p110δ, wild-type mice raised in a germ-free environment markedly up-regulated colonic PI3K p110δ expression with the introduction of the enteric microbiota; however, colitis-prone IL-10(-/-) mice did not. Moreover, PI3K p110δ(D910A/D910A) mice crossed to IL-10(-/-) mice developed severe colitis at an early age.

CONCLUSIONS

This study describes a novel model of experimental colitis that highlights the importance of PI3K p110δ in maintaining mucosal homeostasis and could provide insight into the pathogenesis of human inflammatory bowel disease.

Significance of CEACAM6, Syndecan-1, PDGFA and HLA-DRB5 expression in patients with ulcerative colitis

AIM: To analyze the significance of the expression of carcinoembryonic antigen-related cell adhesion molecule 6 (CEACAM6), Syndecan-1, platelet-derived growth factor alpha (PDGFA) and HLA-DRB5 genes in the development and progression of ulcerative colitis.

METHODS: The mRNA expression of CEACAM6, Syndecan-1, PDGFA and HLA-DRB5 was detected by semiquantitative RT-PCR in peripheral blood mononuclear cells (PBMC) and colon specimens from 21 patients with ulcerative colitis.

RESULTS: The mRNA expression levels of CEACAM6, Syndecan-1 and PDGFA in patients with ulcerative colitis were significantly higher than those in normal controls (0.77 ± 0.23 vs 0.58 ± 0.14, 1.16 ± 0.39 vs 0.85 ± 0.16, 0.90 ± 0.18 vs 0.78 ± 0.13, all P < 0.01). The expression of HLA-DRB5 mRNA was also up-regulated in patients with ulcerative colitis compared with normal controls (0.58 ± 0.19 vs 0.42 ± 0.19, P < 0.01).

CONCLUSION: CEACAM6, Syndecan-1, PDGFA and HLA-DRB5 are highly expressed in ulcerative colitis and may therefore play an important role in the pathogenesis of ulcerative colitis.

Dietary oleic acid as a control fatty acid for polyunsaturated fatty acid intervention studies: a transcriptomics and proteomics investigation using interleukin-10 gene-deficient mice

Oleic acid (OA) has been used as a control fatty acid in dietary polyunsaturated fatty acid (PUFA) intervention studies due to its lack of effect on eiconasoid biosynthesis. Since the effect of OA as a control fatty acid has not yet been investigated for transcriptomics and proteomics studies, this study aimed to test whether colonic transcriptome and proteome profiles associated with colitis development in mice fed a linoleic acid-rich corn oil-AIN-76A diet (Il10(-/-) compared to C57 mice) where similar to those of OA-fed Il10(-/-) compared to C57 mice (genotype comparison). A close clustering of colonic gene and protein expression profiles between the mice fed the AIN-76A or OA diet was observed. Inflammation-induced regulatory processes associated with cellular and humoral immune responses, cellular stress response and metabolic processes related to energy utilization were identified in Il10(-/-) compared to C57 mice fed either diet. Thus OA was considered as a suitable control unsaturated fatty acid for use in multi-omics PUFA studies. The second aim of this study was to test the effect of an OA-enriched AIN-76A diet compared to a linoleic acid-rich corn oil-AIN-76A diet on colonic transcriptome and proteome changes within Il10(-/-) or C57 mice (diet comparison). Overall, there was a limited concordance observed between measureable transcriptomics and proteomics profiles for genotype and diet comparisons. This underlines the importance and validity of a systems biology approach to understand the effects of diet on gene expression as a function of the genotype.

Fucosyltransferase 2 (FUT2) non-secretor status is associated with Crohn's disease

Genetic variation in both innate and adaptive immune systems is associated with Crohn's disease (CD) susceptibility, but much of the heritability to CD remains unknown. We performed a genome-wide association study (GWAS) in 896 CD cases and 3204 healthy controls all of Caucasian origin as defined by multidimensional scaling. We found supportive evidence for 21 out of 40 CD loci identified in a recent CD GWAS meta-analysis, including two loci which had only nominally achieved replication (rs4807569, 19p13; rs991804, CCL2/CCL7). In addition, we identified associations with genes involved in tight junctions/epithelial integrity (ASHL, ARPC1A), innate immunity (EXOC2), dendritic cell biology [CADM1 (IGSF4)], macrophage development (MMD2), TGF-beta signaling (MAP3K7IP1) and FUT2 (a physiological trait that regulates gastrointestinal mucosal expression of blood group A and B antigens) (rs602662, P=3.4x10(-5)). Twenty percent of Caucasians are 'non-secretors' who do not express ABO antigens in saliva as a result of the FUT2 W134X allele. We demonstrated replication in an independent cohort of 1174 CD cases and 357 controls between the four primary FUT2 single nucleotide polymorphisms (SNPs) and CD (rs602662, combined P-value 4.90x10(-8)) and also association with FUT2 W143X (P=2.6x10(-5)). Further evidence of the relevance of this locus to CD pathogenesis was demonstrated by the association of the original four SNPs and CD in the recently published CD GWAS meta-analysis (rs602662, P=0.001). These findings strongly implicate this locus in CD susceptibility and highlight the role of the mucus layer in the development of CD.

Nutrigenomics and IBD: the intestinal microbiota at the cross-road between inflammation and metabolism

Nutrition-related factors together with components of the gut-associated microbial ecosystem (gut microbiota) emerge as prime environmental triggers for the development and modification of lifestyle-related chronic diseases including chronic inflammatory disorders of the gastro-intestinal tract such as Crohn's disease and ulcerative colitis. Although a variety of susceptibility genes were identified in genome-wide association studies, the impact of environmental factors in initiating or promoting the development of these complex diseases are unknown. Nutrigenomics is a transdisciplinary approach to understand the subtle but contentious impact of nutrition and/or microbes as prime environmental triggers in shaping the dynamic range between health and diseases. Profiling technologies such as transcriptomics, proteomics, and metabonomics at the interface of the host's genetic make-up and its metabolic phenotype are implemented to identify cellular and molecular targets to develop novel hypothesise with respect to the functional role of diet and gut bacteria in modulating chronic degenerative diseases including inflammatory bowel disease.