TL1A/DR3 signaling regulates the generation of pathogenic Th9 cells in experimental inflammatory bowel disease.

OBJECTIVE: Death receptor 3 (DR3) and its ligand tumor necrosis factor like ligand 1A (TL1A), are involved in the regulation of the balance between effector and regulatory T cells in IBD. New evidence suggests a role of IL-9-secreting Th9 cells in the pathogenesis of ulcerative colitis (UC), although the molecular pathways through which IL-9 and Th9 cells may mediate intestinal inflammation in Crohn's disease (CD) are still unclear. DESIGN: We investigated the role of DR3 signaling in the differentiation of Th9 cells in mouse models of CD-like ileitis and colitis, including SAMP1/YitFc (SAMP) mice. RESULTS: Polarized-Th9 cells with functional DR3 from SAMP WT (Th9WT) harbor a pro-inflammatory signature compared to DR3-deficient Th9 cells that were obtained from DR3-/-xSAMP mice (Th9KO). Conversely, ablation of DR3 signaling generated anti-inflammatory responses, as reflected by higher numbers of IL-10 producing cells in DR3-/-xSAMP mice. Additionally, RNA-seq and phosphoproteomic analyses showed that inflammatory pathways are significantly more activated in Th9WT than in Th9KO cells. Finally, in the T-cell adoptive transfer model, Th9KO cells were less colitogenic than Th9WT, while IL-9 blockade diminished the severity of intestinal inflammation, indicating a crucial role of functional DR3 receptor in Th9 cells pathogenicity. CONCLUSION: We describe herein that a functional DR3 receptor is required for the pathogenicity of Th9 cells, thus, constituting a novel mechanism by which TL1A/DR3 signaling mediates experimental CD-like ileitis. The TL1A/DR3/Th9 pro-inflammatory pathway may offer a novel therapeutic target for patients with CD.

The Oral-Gut Axis: Periodontal Diseases and Gastrointestinal Disorders.

One of the prospective sequelae of periodontal disease (PD), chronic inflammation of the oral mucosa, is the development of inflammatory gastrointestinal (GI) disorders due to the amplification and expansion of the oral pathobionts. In addition, chronic inflammatory diseases related to the GI tract, which include inflammatory bowel disease (IBD), can lead to malignancy susceptibility in the colon of both animals and humans. Recent studies suggest that dysbiosis of the oral microbiota can alter the microbial composition in relative abundance or diversity of the distal gut, leading to the progression of digestive carcinogenesis. The link between PD and specific GI disorders is also closely associated with the migration and colonization of periodontal pathogens and the subsequent microbe-reactive T cell induction within the intestines. In this review, an in-depth examination of this relationship and the accessibility of different mouse models of IBD and PD may shed light on the current dogma. As such, oral microbiota dysbiosis involving specific bacteria, including Fusobacterium nucleatum and Porphyromonas gingivalis, can ultimately lead to gut malignancies. Further understanding the precise mechanism(s) of the oral-gut microbial axis in PD, IBD, and colorectal cancer pathogenesis will be pivotal in diagnosis, prognosis, and future treatment.

Chronic stress induces colonic tertiary lymphoid organ formation and protection against secondary injury through IL-23/IL-22 signaling.

Psychological stress has been previously reported to worsen symptoms of inflammatory bowel disease (IBD). Similarly, intestinal tertiary lymphoid organs (TLOs) are associated with more severe inflammation. While there is active debate about the role of TLOs and stress in IBD pathogenesis, there are no studies investigating TLO formation in the context of psychological stress. Our mouse model of Crohn's disease-like ileitis, the SAMP1/YitFc (SAMP) mouse, was subjected to 56 consecutive days of restraint stress (RS). Stressed mice had significantly increased colonic TLO formation. However, stress did not significantly increase small or large intestinal inflammation in the SAMP mice. Additionally, 16S analysis of the stressed SAMP microbiome revealed no genus-level changes. Fecal microbiome transplantation into germ-free SAMP mice using stool from unstressed and stressed mice replicated the behavioral phenotype seen in donor mice. However, there was no difference in TLO formation between recipient mice. Stress increased the TLO formation cytokines interleukin-23 (IL-23) and IL-22 followed by up-regulation of antimicrobial peptides. SAMP × IL-23r-/- (knockout [KO]) mice subjected to chronic RS did not have increased TLO formation. Furthermore, IL-23, but not IL-22, production was increased in KO mice, and administration of recombinant IL-22 rescued TLO formation. Following secondary colonic insult with dextran sodium sulfate, stressed mice had reduced colitis on both histology and colonoscopy. Our findings demonstrate that psychological stress induces colonic TLOs through intrinsic alterations in IL-23 signaling, not through extrinsic influence from the microbiome. Furthermore, chronic stress is protective against secondary insult from colitis, suggesting that TLOs may function to improve the mucosal barrier.

Parabacteroides distasonis induces depressive-like behavior in a mouse model of Crohn's disease.

Patients with inflammatory bowel disease (IBD) are particularly susceptible to behavioral diagnoses, and the microbiome has been repeatedly implicated in the pathogenesis of IBD. The intestinal microbiome's ability to affect behavior has become increasingly recognized and studied. The so-called 'psychobiome' has been linked to a plethora of neurological and psychological diagnoses, including autism and Parkinson's disease. Despite the ability of many bacterial species within the human intestinal microbiome to synthesize neurotransmitters, it has never been previously reported that a single bacterial species is sufficient to induce depression. Here, we demonstrate that our mouse model of Crohn's disease (CD)-like ileitis, the SAMP1/YitFc (SAMP1), does not exhibit baseline behavioral abnormalities. By comparison, SAMP6 mice develop depressive-like behavior that is associated with a rise in the GABA-producing bacterial genus Parabacteroides. We finally demonstrate that administration of Parabacteroides distasonis into our SAMP1 mice induces depressive-like behavior. Colonization with P. distasonis was not associated with increased intestinal inflammation or alterations in other measures of behavior. The intestinal environment of CD may be particularly conducive to colonization with P. distasonis and subsequent induction of depressive-like behavior. To our knowledge, this is the first report of a bacterial species specifically inducing depressive-like behavior.

Replacing Animal Protein with Soy-Pea Protein in an "American Diet" Controls Murine Crohn Disease-Like Ileitis Regardless of Firmicutes: Bacteroidetes Ratio.

BACKGROUND: The current nutritional composition of the "American diet" (AD; also known as Western diet) has been linked to the increasing incidence of chronic diseases, including inflammatory bowel disease (IBD), namely Crohn disease (CD). OBJECTIVES: This study investigated which of the 3 major macronutrients (protein, fat, carbohydrates) in the AD has the greatest impact on preventing chronic inflammation in experimental IBD mouse models. METHODS: We compared 5 rodent diets designed to mirror the 2011-2012 "What We Eat in America" NHANES. Each diet had 1 macronutrient dietary source replaced. The formulated diets were AD, AD-soy-pea (animal protein replaced by soy + pea protein), AD-CHO ("refined carbohydrate" by polysaccharides), AD-fat [redistribution of the ω-6:ω-3 (n-6:n-3) PUFA ratio; ∼10:1 to 1:1], and AD-mix (all 3 "healthier" macronutrients combined). In 3 separate experiments, 8-wk-old germ-free SAMP1/YitFC mice (SAMP) colonized with human gut microbiota ("hGF-SAMP") from CD or healthy donors were fed an AD, an AD-"modified," or laboratory rodent diet for 24 wk. Two subsequent dextran sodium sulfate-colitis experiments in hGF-SAMP (12-wk-old) and specific-pathogen-free (SPF) C57BL/6 (20-wk-old) mice, and a 6-wk feeding trial in 24-wk-old SPF SAMP were performed. Intestinal inflammation, gut metagenomics, and MS profiles were assessed. RESULTS: The AD-soy-pea diet resulted in lower histology scores [mean ± SD (56.1% ± 20.7% reduction)] in all feeding trials and IBD mouse models than did other diets (P < 0.05). Compared with the AD, the AD-soy-pea correlated with increased abundance in Lactobacillaceae and Leuconostraceae (1.5-4.7 log2 and 3.0-5.1 log2 difference, respectively), glutamine (6.5 ± 0.8 compared with 3.9 ± 0.3 ng/µg stool, P = 0.0005) and butyric acid (4:0; 3.3 ± 0.5 compared with 2.54 ± 0.4 ng/µg stool, P = 0.006) concentrations, and decreased linoleic acid (18:2n-6; 5.4 ± 0.4 compared with 8.6 ± 0.3 ng/µL plasma, P = 0.01). CONCLUSIONS: Replacement of animal protein in an AD by plant-based sources reduced the severity of experimental IBD in all mouse models studied, suggesting that similar, feasible adjustments to the daily human diet could help control/prevent IBD in humans.

Regulation of Intestinal Inflammation by Dietary Fats.

With the epidemic of human obesity, dietary fats have increasingly become a focal point of biomedical research. Epidemiological studies indicate that high-fat diets (HFDs), especially those rich in long-chain saturated fatty acids (e.g., Western Diet, National Health Examination survey; NHANES 'What We Eat in America' report) have multi-organ pro-inflammatory effects. Experimental studies have confirmed some of these disease associations, and have begun to elaborate mechanisms of disease induction. However, many of the observed effects from epidemiological studies appear to be an over-simplification of the mechanistic complexity that depends on dynamic interactions between the host, the particular fatty acid, and the rather personalized genetics and variability of the gut microbiota. Of interest, experimental studies have shown that certain saturated fats (e.g., lauric and myristic fatty acid-rich coconut oil) could exert the opposite effect; that is, desirable anti-inflammatory and protective mechanisms promoting gut health by unanticipated pathways. Owing to the experimental advantages of laboratory animals for the study of mechanisms under well-controlled dietary settings, we focus this review on the current understanding of how dietary fatty acids impact intestinal biology. We center this discussion on studies from mice and rats, with validation in cell culture systems or human studies. We provide a scoping overview of the most studied diseases mechanisms associated with the induction or prevention of Inflammatory Bowel Disease in rodent models relevant to Crohn's Disease and Ulcerative Colitis after feeding either high-fat diet (HFD) or feed containing specific fatty acid or other target dietary molecule. Finally, we provide a general outlook on areas that have been largely or scarcely studied, and assess the effects of HFDs on acute and chronic forms of intestinal inflammation.

Human Gut Microbiome Transplantation in Ileitis Prone Mice: A Tool for the Functional Characterization of the Microbiota in Inflammatory Bowel Disease Patients.

BACKGROUND: Inflammatory bowel disease (IBD) is a lifelong digestive disease characterized by periods of severe inflammation and remission. To our knowledge, this is the first study showing a variable effect on ileitis severity from human gut microbiota isolated from IBD donors in remission and that of healthy controls in a mouse model of IBD. METHODS: We conducted a series of single-donor intensive and nonintensive fecal microbiota transplantation (FMT) experiments using feces from IBD patients in remission and healthy non-IBD controls (N = 9 donors) in a mouse model of Crohn's disease (CD)-like ileitis that develops ileitis in germ-free (GF) conditions (SAMP1/YitFC; N = 96 mice). RESULTS: Engraftment studies demonstrated that the microbiome of IBD in remission could have variable effects on the ileum of CD-prone mice (pro-inflammatory, nonmodulatory, or anti-inflammatory), depending on the human donor. Fecal microbiota transplantation achieved a 95% ± 0.03 genus-level engraftment of human gut taxa in mice, as confirmed at the operational taxonomic unit level. In most donors, microbiome colonization abundance patterns remained consistent over 60 days. Microbiome-based metabolic predictions of GF mice with Crohn's or ileitic-mouse donor microbiota indicate that chronic amino/fatty acid (valine, leucine, isoleucine, histidine; linoleic; P < 1e-15) alterations (and not bacterial virulence markers; P > 0.37) precede severe ileitis in mice, supporting their potential use as predictors/biomarkers in human CD. CONCLUSION: The gut microbiome of IBD remission patients is not necessarily innocuous. Characterizing the inflammatory potential of each microbiota in IBD patients using mice may help identify the patients' best anti-inflammatory fecal sample for future use as an anti-inflammatory microbial autograft during disease flare-ups.