Lethal inflammasome activation by a multidrug-resistant pathobiont upon antibiotic disruption of the microbiota

The mammalian intestine harbors a complex microbial community that provides numerous benefits to its host. However, the microbiota can also include potentially virulent species, termed pathobiont, which can cause disease when intestinal homeostasis is disrupted. The molecular mechanisms by which pathobionts cause disease remain poorly understood. Here we describe a sepsis-like disease that occurs upon gut injury in antibiotic-treated mice. Sepsis was associated with the systemic spread of a specific multidrug-resistant Escherichia coli pathobiont that expanded markedly in the microbiota of antibiotic-treated mice. Rapid sepsis-like death required a component of the innate immune system, the Naip5-Nlrc4 inflammasome. In accordance with Koch's postulates, we found the E. coli pathobiont was sufficient to activate Naip5-Nlrc4 and cause disease when injected intravenously into unmanipulated mice. These findings reveal how sepsis-like disease can result from recognition of pathobionts by the innate immune system.     

T cell-associated CD18 but not CD62L, ICAM-1, or PSGL-1 is required for the induction of chronic colitis

The induction and perpetuation of chronic colitis are thought to involve a complex set of adhesive interactions between T cells and endothelial cells located on the vasculature within secondary lymphoid tissue and the intestine. The objective of this study was to assess the roles of T cell-associated CD18, CD62L (L-selectin), ICAM-1, and P-selectin glycoprotein ligand-1 (PSGL-1) in the induction of chronic colitis in mice. CD4(+)CD25(-) T cells derived from either wild-type (WT), CD18-deficient [CD18 knockout (KO)], CD62L KO, ICAM-1 KO, or PSGL-1 KO mice were adoptively transferred into recombinase activating gene-1 (RAG-1)-deficient mice (RAG KO mice) to assess the potential of these T cells to induce chronic colitis. At 8-10 wk following T cell transfer, we observed moderate to severe colitis as assessed by increases in colon weight-to-length ratios and by blinded histopathological analysis. In contrast, we found that transfer of CD18 KO T cells into RAG KO recipients resulted in the significant attenuation of colonic inflammation in these mice. Furthermore, we observed fewer infiltrating CD4(+) T cells in the colonic lamina propria in the CD18 KO-->RAG KO group compared with the WT-->RAG KO group. Finally, message levels of colonic TNF-alpha, IL-1beta, and IFN-gamma were significantly reduced in CD18 KO-->RAG KO mice compared with colitic control animals. We conclude that T cell-associated CD18, but not CD62L, ICAM-1, or PSGL-1, is required for the development of chronic colitis.     

对虾等甲壳类动物肠道与血淋巴菌群的组成、功能与动态平衡调控

对虾等甲壳类动物体内存在2个菌群:肠道菌群和血淋巴菌群。肠道菌群的种类和数量较多,而血淋巴菌群较少。两种菌群均包含益生菌和致病菌,在宿主体内代谢、营养和免疫反应中发挥重要功能。肠道菌群动态平衡的调控主要通过双氧化酶产生的活性氧来完成;血淋巴菌群通过C-型凝集素调控的抗菌肽表达及酚氧化酶原激活系统来维持其动态平衡。阐明对虾等甲壳类体内菌群的组成、功能和动态平衡调控的机理,可以为对虾等经济甲壳类健康养殖的微生态制剂开发和疾病控制提供指导。     

T cell-induced inflammation of the small and large intestine in immunodeficient mice

It is well known that transfer of CD4+CD45RBhigh (na?ve) T cells into syngeneic lymphocyte-deficient mice induces chronic colitis. However, no studies have reported the presence of small bowel inflammation in this T cell-dependent model. Therefore, the objective of this study was to evaluate and compare small and large bowel inflammation induced by transfer of na?ve T cells into two different immunodeficient recipient mice. T and B cell-deficient recombinase activating gene 1-deficient [RAG knockout (KO)] and T cell-deficient T cell receptor-beta x T cell receptor-delta double-deficient (TCR KO) mice were reconstituted with wild-type na?ve T cells and observed for signs of disease. We found that reconstituted RAG KO mice developed moderate to severe colitis and inflammation of the entire small intestine at 6-8 wk after T cell transfer. Adoptive transfer of na?ve T cells into TCR KO mice induced a milder form of chronic colitis and small bowel inflammation that was confined primarily to the duodenum at 10-12 wk after T cell transfer. T helper cell 1 and macrophage-derived proinflammatory cytokine mRNA levels correlated well with the localization and severity of the chronic large and small bowel inflammation. In addition, we observed comparable homing and expansion of donor lymphocytes in the gut and secondary lymphoid tissues of both recipients. Taken together, our data demonstrate that transfer of na?ve T cells into immunodeficient recipient mice induces both chronic small and large bowel inflammation and that the presence of B cells in the TCR KO recipients may play a role in regulating chronic intestinal inflammation.     

Deletion of the Toll-Like Receptor 5 Gene Per Se Does Not Determine the Gut Microbiome Profile That Induces Metabolic Syndrome: Environment Trumps Genotype

Over the past decade, emerging evidence has linked alterations in the gut microbial composition to a wide range of diseases including obesity, type 2 diabetes, and cardiovascular disease. Toll-like receptors (TLRs) are the major mediators for the interactions between gut microbiota and host innate immune system, which is involved in the localization and structuring of host gut microbiota. A previous study found that TLR5 deficient mice (TLR5KO1) had altered gut microbial composition which led to the development of metabolic syndrome including hyperlipidemia, hypertension, insulin resistance and increased adiposity. In the current study, a second TLR5-deficient mouse model was studied (TLR5KO2). TLR5 deficient mice did not manifest metabolic abnormalities related to the metabolic syndrome compared with littermate controls maintained on normal chow or after feeding a high fat diet. Analysis of the gut microbial composition of littermate TLR5KO2 and wild type mice revealed no significant difference in the overall microbiota structure between genotypes. However, the TLR5KO2 microbiota was distinctly different from that previously reported for TLR5KO1 mice with metabolic syndrome. We conclude that an altered composition of the microbiota in a given environment can result in metabolic syndrome, but it is not a consequence of TLR5 deficiency per se.     

Osteopontin Deficiency Accelerates Spontaneous Colitis in Mice with Disrupted Gut Microbiota and Macrophage Phagocytic Activity

Background

Osteopontin (OPN) is a multifunctional protein expressed in a variety of tissues and cells. Recent studies revealed increased OPN expression in the inflamed intestinal tissues of patients with inflammatory bowel disease (IBD). The role of OPN in the pathophysiology of IBD, however, remains unclear.

Aims

To investigate the role of OPN in the development of intestinal inflammation using a murine model of IBD, interleukin-10 knock out (IL-10 KO) mice.

Methods

We compared the development of colitis between IL-10 KO and OPN/IL-10 double KO (DKO) mice. OPN expression in the colonic tissues of IL-10 KO mice was examined by fluorescence in situ hybridization (FISH) analysis. Enteric microbiota were compared between IL-10 KO and OPN/IL-10 DKO mice by terminal restriction fragment length polymorphism analysis. The effect of OPN on macrophage phagocytic function was evaluated by phagocytosis assay.

Results

OPN/IL-10 DKO mice had an accelerated onset of colitis compared to IL-10 KO mice. FISH analysis revealed enhanced OPN synthesis in the colonic epithelial cells of IL-10 KO mice. OPN/IL-10 DKO mice had a distinctly different enteric bacterial profile with a significantly lower abundance of Clostridium subcluster XIVa and a greater abundance of Clostridium cluster XVIII compared to IL-10 KO mice. Intracellular OPN deletion in macrophages impaired phagocytosis of fluorescence particle-conjugated Escherichia coli in vitro. Exogenous OPN enhanced phagocytosis by OPN-deleted macrophages when administered at doses of 1 to 100 ng/ml, but not 1000 ng/ml.

Conclusions

OPN deficiency accelerated the spontaneous development of colitis in mice with disrupted gut microbiota and macrophage phagocytic activity.     

Intestinal inflammation responds to microbial tissue load independent of pathogen/non-pathogen discrimination

The intestinal immune system mounts inflammatory responses to pathogens but tolerates harmless commensal microbiota. Various mechanisms for pathogen/non-pathogen discrimination have been proposed but their general relevance for inflammation control is unclear. Here, we compared intestinal responses to pathogenic Salmonella and non-pathogenic E. coli. Both microbes entered intestinal Peyer's patches and, surprisingly, induced qualitatively and quantitatively similar initial inflammatory responses revealing a striking discrimination failure. Diverging inflammatory responses only occurred when Salmonella subsequently proliferated and induced escalating neutrophil infiltration, while harmless E. coli was rapidly cleared from the tissue and inflammation resolved. Transient intestinal inflammation induced by harmless E. coli tolerized against subsequent exposure thereby preventing chronic inflammation during repeated exposure. These data revealed a striking failure of the intestinal immune system to discriminate pathogens from harmless microbes based on distinct molecular signatures. Instead, appropriate intestinal responses to gut microbiota might be ensured by immediate inflammatory responses to any rise in microbial tissue loads, and desensitization after bacterial clearance.     

CD103+CD11b+ Dendritic Cells Induce Th17 T Cells in Muc2-Deficient Mice with Extensively Spread Colitis

Mucus alterations are a feature of ulcerative colitis (UC) and can drive inflammation by compromising the mucosal barrier to luminal bacteria. The exact pathogenesis of UC remains unclear, but CD4⁺ T cells reacting to commensal antigens appear to contribute to pathology. Given the unique capacity of dendritic cells (DCs) to activate naive T cells, colon DCs may activate pathogenic T cells and contribute to disease. Using Muc2^-/- mice, which lack a functional mucus barrier and develop spontaneous colitis, we show that colitic animals have reduced colon CD103⁺CD11b^- DCs and increased CD103^-CD11b⁺ phagocytes. Moreover, changes in colonic DC subsets and distinct cytokine patterns distinguish mice with distally localized colitis from mice with colitis spread proximally. Specifically, mice with proximally spread, but not distally contained, colitis have increased IL-1β, IL-6, IL-17, TNFα, and IFNγ combined with decreased IL-10 in the distal colon. These individuals also have increased numbers of CD103⁺CD11b⁺ DCs in the distal colon. CD103⁺CD11b⁺ DCs isolated from colitic but not noncolitic mice induced robust differentiation of Th17 cells but not Th1 cells ex vivo. In contrast, CD103^-CD11b⁺ DCs from colitic Muc2^-/- mice induced Th17 as well as Th1 differentiation. Thus, the local environment influences the capacity of intestinal DC subsets to induce T cell proliferation and differentiation, with CD103⁺CD11b⁺ DCs inducing IL-17-producing T cells being a key feature of extensively spread colitis.     

Systemic, but not intestinal, IL-7 is essential for the persistence of chronic colitis

We previously demonstrated that IL-7 is produced by intestinal goblet cells and is essential for the persistence of colitis. It is well known, however, that goblet cells are decreased or depleted in the chronically inflamed mucosa of animal colitis models or human inflammatory bowel diseases. Thus, in this study, we assess whether intestinal IL-7 is surely required for the persistence of colitis using a RAG-1/2-/- colitis model induced by the adoptive transfer of CD4+CD45RBhigh T cells in combination with parabiosis system. Surprisingly, both IL-7-/-xRAG-1-/- and IL-7+/+xRAG-1-/- host mice developed colitis 4 wk after parabiosis to a similar extent of colitic IL-7+/+xRAG-1-/- donor mice that were previously transferred with CD4+CD45RBhigh T cells. Of note, although the number of CD4+ T cells recovered from the spleen or the bone marrow of IL-7-/-xRAG-1-/- host mice was significantly decreased compared with that of IL-7+/+xRAG-1-/- host mice, an equivalent number of CD4+ T cells was recovered from the lamina propria of both mice, indicating that the expansion of CD4+ T cells in the spleen or in the bone marrow is dependent on IL-7, but not in the lamina propria. Development of colitis was never observed in parabionts between IL-7+/+xRAG-1-/- host and noncolitic IL-7-/-xRAG-1-/- donor mice that were transferred with CD4+CD45RBhigh T cells. Collectively, systemic, but not intestinal, IL-7 is essential for the persistence of colitis, suggesting that therapeutic approaches targeting the systemic IL-7/IL-7R signaling pathway may be feasible in the treatment of inflammatory bowel diseases.     

蜜蜂肠道菌群结构功能研究进展

在长期的共同进化中,肠道菌群与其宿主形成了紧密的联系,为宿主提供了许多有益的作用。作为一种社会性昆虫,蜜蜂的生活习性为其肠道菌群提供了良好而稳定的传播途径,因此,蜜蜂与其肠道菌群形成了一种紧密的互惠互利共生关系。近年来,随着对蜜蜂肠道菌群了解的不断加深,对蜜蜂肠道菌群功能的研究也不断深入,大量研究表明蜜蜂的肠道菌群在宿主食物的消化代谢、宿主免疫的激活和抵抗致病菌、调节宿主生理等方面都有着重要的作用,同时破坏肠道菌群的稳定对蜜蜂的健康有着明显的负面影响。本文对近年来西方蜜蜂肠道菌群功能研究进行了总结,旨在为进一步深入探索蜜蜂肠道菌群与其宿主的相互作用及在养蜂生产上应用肠道菌群防控疾病提供参考。     

Role of TNFR-related 2 mediated immune responses in dextran sulfate sodium-induced inflammatory bowel disease

Previous work has suggested that the LIGHT-TR2 costimulatory pathway plays a role in the acute and chronic stages of dextran sulfate sodium (DSS)-induced colitis [Steinberg et al. (2008); Wang et al. (2005)]. To clarify the role of TNFR-related 2 (TR2) signaling in the maintenance of intestinal homeostasis, we generated a TR2 knock-out (KO) mouse. Using DSS to induce colitis, we compared the colitic symptoms and pathological changes in wild type (WT) and TR2 KO mice, and the production of cytokines by the diseased colons. We also studied the role of TR2 in suppressing innate and adaptive immunity in the DSS model. TR2 deficient mice were characterized by reduced symptoms of intestinal inflammation compared with wild-type mice, and reduced production of cytokines. We therefore generated a monoclonal antibody against mouse TR2 which was specific to TR2 and capable of blocking TR2 signals. With this antibody, we demonstrated that antagonizing TR2 during the development of DSS-induced colitis reduced the symptoms of inflammation. Our findings suggest that TR2 is an important mediator in colitis, and may serve as a therapeutic target in inflammatory bowel disease.     

Bruton’s tyrosine kinase regulates gut immune homeostasis through attenuating Th1 response

Inflammatory bowel disease (IBD) is driven by multiple genetic and environmental risk factors. Patients with mutations in Bruton’s tyrosine kinase (BTK) is known to manifest high prevalence of intestinal disorders including IBD. Although BTK mediates the signaling of various immune receptors, little is known how BTK maintains the homeostasis of the gut immune system. Here, we show that BTK-deficiency promotes IBD progression in a mouse model of colitis. Interestingly, the increased colitis susceptibility of BTK-deficient mice is not caused by gut microbiota changes but rather arises from enhanced pro-inflammatory Th1 response. More importantly, we find the heightened Th1 response in BTK-deficient mice to result from both T cell-extrinsic and -intrinsic mechanisms. BTK-deficient dendritic cells secret elevated levels of the Th1-polarizing cytokine IL-12 and BTK-deficient T cells are inherently more prone to Th1 differentiation. Thus, BTK plays critical roles in maintaining gut immune homeostasis and preventing inflammation via regulating T-cell polarization.Subject terms: Inflammatory bowel disease, Inflammation, Mucosal immunology, Inflammation     

Gram-negative bacteria aggravate murine small intestinal Th1-type immunopathology following oral infection with Toxoplasma gondii

Oral infection of susceptible mice with Toxoplasma gondii results in Th1-type immunopathology in the ileum. We investigated gut flora changes during ileitis and determined contributions of gut bacteria to intestinal inflammation. Analysis of the intestinal microflora revealed that ileitis was accompanied by increasing bacterial load, decreasing species diversity, and bacterial translocation. Gram-negative bacteria identified as Escherichia coli and Bacteroides/Prevotella spp. accumulated in inflamed ileum at high concentrations. Prophylactic or therapeutic administration of ciprofloxacin and/or metronidazole ameliorated ileal immunopathology and reduced intestinal NO and IFN-gamma levels. Most strikingly, gnotobiotic mice in which cultivable gut bacteria were removed by quintuple antibiotic treatment did not develop ileitis after Toxoplasma gondii infection. A reduction in total numbers of lymphocytes was observed in the lamina propria of specific pathogen-free (SPF), but not gnotobiotic, mice upon development of ileitis. Relative numbers of CD4(+) T cells did not differ in naive vs infected gnotobiotic or SPF mice, but infected SPF mice showed a significant increase in the frequencies of activated CD4(+) T cells compared with gnotobiotic mice. Furthermore, recolonization with total gut flora, E. coli, or Bacteroides/Prevotella spp., but not Lactobacillus johnsonii, induced immunopathology in gnotobiotic mice. Animals recolonized with E. coli and/or total gut flora, but not L. johnsonii, showed elevated ileal NO and/or IFN-gamma levels. In conclusion, Gram-negative bacteria, i.e., E. coli, aggravate pathogen-induced intestinal Th1-type immunopathology. Thus, pathogen-induced acute ileitis may prove useful to study bacteria-host interactions in small intestinal inflammation and to test novel therapies based on modulation of gut flora.     

Treatment and mechanism of fecal microbiota transplantation in mice with experimentally induced ulcerative colitis

Restoring intestinal microbiota dysbiosis with fecal microbiota transplantation is considered as a promising treatment for ulcerative colitis. However, the mechanisms underlying its relieving effects remain unclear. Ulcerative colitis pathogenesis is associated with the involvement of immune cells and inflammatory cytokines. Here, we aimed to investigate the effect of fecal microbiota transplantation on T cell cytokines in a dextran sulfate sodium-induced ulcerative colitis mouse model. Five-aminosalicylic acid (5-ASA) was used as the positive control. Male C57BL/6 mice were randomly assigned to control, model (UC), UC + FMT, and UC + 5-ASA groups. Each group consisted of five mice. The establishment of the mouse model was verified by fecal occult-blood screening and hematoxylin–eosin staining. Results showed that fecal microbiota transplantation reduced colonic inflammation, significantly decreased T helper (Th)1 and Th17 cells, interferon-gamma, interleukin-2 and interleukin-17, as well as significantly increased Th2 and regulatory T (Treg) cells, interleukin-4, interleukin-10, and transforming growth factor-beta, and improved routine blood count. Furthermore, 16S rRNA gene-sequencing analysis showed a significant increase in the relative abundance of genus Akkermansia and a significant decrease in the relative abundance of genus Helicobacter in the ulcerative colitis group. Fecal microbiota transplantation restored the profile of the intestinal microbiota to that of the control group. These findings demonstrated the capability of fecal microbiota transplantation in controlling experimentally induced ulcerative colitis by improving Th1/Th2 and Th17/Treg imbalance through the regulation of intestinal microbiota.     

CD4CD8αα Lymphocytes,A Novel Human Regulatory T Cell Subset Induced by Colonic Bacteria and Deficient in Patients with Inflammatory Bowel Disease

How the microbiota affects health and disease is a crucial question. In mice, gut Clostridium bacteria are potent inducers of colonic interleukin (IL)-10-producing Foxp3 regulatory T cells (Treg), which play key roles in the prevention of colitis and in systemic immunity. In humans, although gut microbiota dysbiosis is associated with immune disorders, the underlying mechanism remains unknown. In contrast with mice, the contribution of Foxp3 Treg in colitis prevention has been questioned, suggesting that other compensatory regulatory cells or mechanisms may exist. Here we addressed the regulatory role of the CD4CD8 T cells whose presence had been reported in the intestinal mucosa and blood. Using colonic lamina propria lymphocytes (LPL) and peripheral blood lymphocytes (PBL) from healthy individuals, and those with colon cancer and irritable bowel disease (IBD), we demonstrated that CD4CD8αα (DP8α) T lymphocytes expressed most of the regulatory markers and functions of Foxp3 Treg and secreted IL-10. Strikingly, DP8α LPL and PBL exhibited a highly skewed repertoire toward the recognition of Faecalibacterium prausnitzii, a major Clostridium species of the human gut microbiota, which is decreased in patients with IBD. Furthermore, the frequencies of DP8α PBL and colonic LPL were lower in patients with IBD than in healthy donors and in the healthy mucosa of patients with colon cancer, respectively. Moreover, PBL and LPL from most patients with active IBD failed to respond to F. prausnitzii in contrast to PBL and LPL from patients in remission and/or healthy donors. These data (i) uncover a Clostridium-specific IL-10-secreting Treg subset present in the human colonic LP and blood, (ii) identify F. prausnitzii as a major inducer of these Treg, (iii) argue that these cells contribute to the control or prevention of colitis, opening new diagnostic and therapeutic strategies for IBD, and (iv) provide new tools to address the systemic impact of both these Treg and the intestinal microbiota on the human immune homeostasis.     

Analysis of the large bowel microbiota of colitic mice using PCR/DGGE

AIM: To test combined polymerase chain reaction amplification of 16S rRNA gene sequences and denaturing gradient gel electrophoresis (PCR/DGGE) as an analytical method to investigate the composition of the large bowel microbiota of mice during the development of colitis. METHODS AND RESULTS: The colonic microbiota of formerly germfree interleukin 10 (IL-10)-deficient mice that had been exposed to the faecal microbiota of specific pathogen-free animals was screened using PCR/DGGE. The composition of the large bowel microbiota of IL-10-deficient mice changed as colitis progressed. DNA fragments originating from four bacterial populations ('Bacteroides sp.', Bifidobacterium animalis, Clostridium cocleatum, enterococci) were more apparent in PCR/DGGE profiles of colitic mice relative to non-colitic animals, whereas two populations were less apparent (Eubacterium ventriosum, Acidophilus group lactobacilli). Specific DNA:RNA dot blot analysis showed that bifidobacterial ribosomal RNA (rRNA) abundance increased as colitis developed. CONCLUSIONS: PCR/DGGE was shown to be an effective method to demonstrate changes in the composition of the large bowel microbiota of mice in relation to progression of inflammatory disease. The intensity of staining of DNA fragments in DGGE profiles reflected increased abundance of bifidobacterial rRNA in the microbiota of colitic animals. As bifidobacterial fragments in PCR/DGGE profiles generated from microbiota DNA showed increased intensity of fragment staining, an increase in bifidobacterial numbers in colitic mice was indicated. SIGNIFICANCE AND IMPACT OF THE STUDY: PCR/DGGE analysis demonstrated an altered composition of the large bowel microbiota of colitic mice. This work will allow specific groups of bacteria to be targeted in future research concerning the pathogenesis of colitis.     

The intestinal microbiota plays a role in Salmonella-induced colitis independent of pathogen colonization

The intestinal microbiota is composed of hundreds of species of bacteria, fungi and protozoa and is critical for numerous biological processes, such as nutrient acquisition, vitamin production, and colonization resistance against bacterial pathogens. We studied the role of the intestinal microbiota on host resistance to Salmonella enterica serovar Typhimurium-induced colitis. Using multiple antibiotic treatments in 129S1/SvImJ mice, we showed that disruption of the intestinal microbiota alters host susceptibility to infection. Although all antibiotic treatments caused similar increases in pathogen colonization, the development of enterocolitis was seen only when streptomycin or vancomycin was used; no significant pathology was observed with the use of metronidazole. Interestingly, metronidazole-treated and infected C57BL/6 mice developed severe pathology. We hypothesized that the intestinal microbiota confers resistance to infectious colitis without affecting the ability of S. Typhimurium to colonize the intestine. Indeed, different antibiotic treatments caused distinct shifts in the intestinal microbiota prior to infection. Through fluorescence in situ hybridization, terminal restriction fragment length polymorphism, and real-time PCR, we showed that there is a strong correlation between the intestinal microbiota composition before infection and susceptibility to Salmonella-induced colitis. Members of the Bacteroidetes phylum were present at significantly higher levels in mice resistant to colitis. Further analysis revealed that Porphyromonadaceae levels were also increased in these mice. Conversely, there was a positive correlation between the abundance of Lactobacillus sp. and predisposition to colitis. Our data suggests that different members of the microbiota might be associated with S. Typhimurium colonization and colitis. Dissecting the mechanisms involved in resistance to infection and inflammation will be critical for the development of therapeutic and preventative measures against enteric pathogens.     

Intestinal anti-inflammatory effect of the probiotic Saccharomyces boulardii in DSS-induced colitis in mice: Impact on microRNAs expression and gut microbiota composition

The beneficial effects exerted by probiotics in inflammatory bowel disease (IBD) are well known, although their exact mechanisms have not been fully elucidated, and only few studies have focused on their impact on selected miRNAs and the gut microbiota composition. Therefore, our aim was to correlate the intestinal anti-inflammatory activity of the probiotic Saccharomyces boulardii in the dextran sodium sulphate (DSS) model of mouse colitis and the changes induced in miRNA expression and gut microbiota populations. Probiotic was given orally (5×10⁹ CFU) to C57BL/6 mice for 26 days. After 2 weeks, the colitis was induced adding DSS to the drinking water. Mice were scored daily using a Disease Activity Index (DAI). After sacrifice, the colonic specimens were evaluated by determining the expression of inflammatory markers and micro-RNAs by qRT-PCR. Moreover, changes in microbiota populations were evaluated by pyrosequencing. Probiotic ameliorated the colonic damage induced by DSS, as evidenced by lower DAI values and colonic weight/length compared with untreated mice. The treatment modified the colonic expression of different inflammatory markers and the epithelial integrity proteins, and induced changes in micro-RNAs expression. Moreover, microbiota characterization showed that probiotic treatment increased bacterial diversity, thus ameliorating the dysbiosis produced by DSS-colitis. Saccharomyces boulardii exerted intestinal anti-inflammatory effects in DSS-mouse colitis, through the modulation in the immune response, involving modification of altered miRNA expression, being associated to the improvement of the inflammation-associated dysbiosis in the intestinal lumen, which could be of great interest to control the complex pathogenesis of IBD.     

Initial gut microbiota structure affects sensitivity to DSS-induced colitis in a mouse model

The dextran sulfate sodium (DSS)-induced colitis model is a widely applied mouse model, but controversial results have been obtained from experiments using the same mouse strain under the same conditions. Because the gut microbiota play an important role in DSS-induced colitis, it is essential to evaluate the influence of the initial gut microbiota in this model. Here, we identified significant variations in the initial gut microbiota of different batches of mice and found that the initial intestinal microbiota had a profound influence on DSS-induced colitis. We performed three independent trials using the same C57BL/6J mouse model with DSS treatment and used high-throughput 16S rRNA gene sequencing to analyze the gut microbiota. We found that the structure and composition of the gut microbiota in mice with severe colitis, as compared with mice with milder colon damage, had unique features, such as an increase in Akkermansia bacteria and a decrease in Barnesiella spp. Moreover, these varied gut bacteria in the different trials also showed different responses to DSS treatment. Our work suggests that, in studies using mouse models, the gut microbiota must be considered when examining mechanisms of diseases, to ensure that comparable results are obtained.