Resolution Of Intestinal Inflammation Research Articles

POSTСOLITIS ALTERATIONS IN NOCICEPTIVE PROPERTIES OF NEURONS IN THE RAT RAPHE MAGNUS AND DORSAL RAPHE NUCLEI

Dysfunction of the brain serotonergic system is thought to play a leading role in the pathogenesis of chronic abdominal pain and comorbid somatic hyperalgesia, which disturb a significant proportion of patients with digestive tract diseases, even in remission. However, the specific changes in the serotonergic structures nociceptive properties that can be initiated by organic pathology and persist after its resolution remain unclear. The aim of our neurophysiological study on anesthetized rats – healthy and recovered from colitis – was to identify the alterations in the raphe magnus (RMg) and dorsal raphe (DR) nuclei neuronal responses to visceral (colorectal distension) and somatic (squeezing of the tail) noxious stimulations that persist after resolution of intestinal inflammation. It has been shown that both nuclei contain different groups of nociceptive neurons: 1) responding with activation only to colorectal distension (visceral); 2) excited only by tail squeezing (somatic); 3) reacting with excitation to the both irritations (general); 4) responding with discharge inhibition to any of the stimulations (inhibited). Compared with healthy animals, in RMg of colitis-exposed rats the number of the inhibited cells was increased and the total proportion of excited nociceptive neurons was reduced. Distension of the inflammation-undergone intestine caused enhanced RMg neuronal inhibition, whereas squeezing of the pathology-unaffected tail led to increased excitation of the RMg selective somatic and general nociceptive cells. In turn, in the DR of postcolitis rats the inhibited neuron proportion was reduced, while the increased population of excited neurons included fewer visceral and more somatic selective cells. This was accompanied by an increase in the selective reactions of the latter to somatic pain stimuli and by an increase in non-selective DR neuron excitation by visceral and somatic pain signals. The identified neuronal alterations can contribute to the postcolitis impairment of the studied raphe nuclei functions in the endogenous control of visceral and somatic pain sensitivity.

A179 MECHANISMS OF ACTION INVOLVED IN THE WOUND HEALING EFFECT OF THE DIETARY FIBRE RHAMNOGALACTURONAN

Abstract Background Inflammatory bowel diseases (IBD) are chronic and relapsing inflammatory conditions associated with impaired intestinal epithelial barrier. Mucosal healing is the primary goal for IBD treatment since it is a good predictor of clinical remission. We previously showed the direct beneficial effects of rhamnogalacturonan (RGal), a polysaccharide isolated from the plant Acmella oleracea, on intestinal epithelial barrier function with participation of TLR4 and PKC activation. RNAseq data and pathway analysis have indicated the involvement of the canonical nuclear factor kB (NF-kB) signaling pathway. Purpose We hypothesize that RGal increases intestinal epithelial wound healing through FAK-Src/PI3K/NF-kB signaling pathways. Method Caco-2 and T84 cells, and human primary cell monolayers grown from ulcerative colitis patient-derived organoids, were wounded and treated with vehicle (media or 0.5% DMSO in media) or RGal (1000 μg/ml) for 48 h. Wound healing was assessed using either the IncuCyte or ImageXpress Pico live cell imaging systems. Proliferation and apoptosis of cells were evaluated using EdU and TUNEL assays, respectively. Inhibitors were added at the same time (transcription inhibitor Actinomycin D, 5 μg/ml) or 1 h (FAK inhibitor FAK-14, 10 μM, Src inhibitor PP2, 5 μM, PI3K inhibitor LY294002, 20 μM, NF-kB inhibitors Bay 11-7082 and JSH-23, 10 and 20 μM, respectively, or COX-2 inhibitor NS-398, 20 μM) before RGal treatment. Unwounded Caco-2 monolayers treated with RGal (1000 μg/ml) were collected for Western blotting for COX-2 protein. Result(s) In the wound healing assay, RGal (1000 μg/ml) enhanced wound healing by 12.5% at 48 h in Caco-2 cells and by 14.7% at 24 h in T84 cells, compared to control group. RGal (1000 μg/ml) also accelerated the wound closure in colonoid monolayers obtained from ulcerative colitis patient biopsies by 81.3% at 48 h. Neither proliferation nor apoptosis were involved in the RGal effect on wound healing. Treatment of cells with FAK14 (10 μM), PP2 (5 μM), and PI3K (20 μM) significantly prevented the RGal-induced wound healing. Actinomycin D (5 μg/ml), Bay 11-7082 (10 μM) or JSH-23 (20 μM) treatment significantly reversed the effect of RGal on wound healing, showing that the response was transcriptionally dependent and involved NF-kB signaling. Treatment of cells with NS-398 (20 μM) also reversed the effect of RGal on wound healing. COX-2 protein expression was significantly increased at 6 and 12 h after RGal addition to Caco-2 monolayers. Conclusion(s) These data suggest that the plant-based polysaccharide RGal increases intestinal epithelial cell wound healing by increasing cell migration. The RGal effect is dependent on the activation of the FAK-Src/PI3K signaling pathways and subsequently the transcription factor NF-kB and downstream COX-2 protein expression and activity. Our findings show a novel mechanism of action of RGal in wound healing that could help in the resolution of intestinal inflammation and mucosal healing. Please acknowledge all funding agencies by checking the applicable boxes below Other Please indicate your source of funding; NSERC Disclosure of Interest None Declared

PET/CT imaging detects intestinal inflammation in a mouse model of doxorubicin-induced mucositis.

A severe side effect of cancer chemotherapy is the development of gastrointestinal mucositis, characterised by mucosal inflammation. We investigated if 2-deoxy-2-[18F] fluoro-D-glucose positron emission tomography combined with computed tomography (2-[18F]FDG-PET/CT) could visualise gastrointestinal mucositis in mice treated with the chemotherapeutic agent doxorubicin. In this study, gastrointestinal inflammation was longitudinally evaluated by 2-[18F]FDG-PET/CT scans before and 1, 3, 6, and 10 days after treatment with doxorubicin. Doxorubicin-treated mice were compared to saline-treated littermates using the abdominal standard uptake value of 2-[18F]FDG corrected for body weight (SUVBW). Abdominal SUVBW was significantly increased on day 1 (p < 0.0001), day 3 (p < 0.0001), and day 6 (p < 0.05) in the doxorubicin-treated group compared to controls. Abdominal SUVBW returned to baseline levels on day 10. In the doxorubicin group, the largest weight loss was observed on day 3 (control vs doxorubicin, mean percent of baseline weight: (98.5 ± 3.2% vs 87.9 ± 4.6%, p < 0.0001). Moreover, in the doxorubicin-treated group, villus lengths were decreased by 23-28% on days 1 and 3 in the small intestine (p < 0.05), and jejunal levels of tumour necrosis factor and interleukin-1β were significantly increased on day 3 (p < 0.05). Together, these findings indicate that sequential 2-[18F]FDG-PET/CT scans can objectively quantify and evaluate the development and resolution of intestinal inflammation over time in a mouse model of doxorubicin-induced mucositis.

A64 THE DIETARY FIBRE RHAMNOGALACTURONAN PROMOTES INTESTINAL EPITHELIAL CELL MIGRATION THROUGH THE NF-κB SIGNALING PATHWAY

BackgroundDamaged intestinal epithelial barrier is characteristic of inflammatory bowel diseases (IBD) and mucosal healing is the primary goal for IBD treatment. We previously showed the direct beneficial effects of rhamnogalacturonan (RGal), a polysaccharide isolated from the plant Acmella oleracea, on intestinal epithelial barrier function with participation of TLR4 and PKC activation. We also observed that RGal accelerates wound healing in human colonic epithelial Caco-2 cells. RNAseq data and pathway analysis have indicated the involvement of the canonical nuclear factor kB (NF-kB) signaling pathway.AimsWe hypothesize that RGal increases intestinal epithelial wound healing through NF-kB signaling pathway.MethodsCaco-2 cells monolayers were scratched and treated with vehicle (media or 0.5% DMSO in media) or RGal (1000 mg/ml) for 48 h. Wound healing was assessed using the IncuCyte live cell imaging system. Proliferation and apoptosis of cells were evaluated using EdU and TUNEL assays, respectively. Inhibitors were added at the same time (transcription inhibitor Actinomycin D, 5 mg/ml) or 1 h (NF-kB inhibitors Bay 11–7082 and JSH-23, 10 and 20 mM, respectively, or COX-2 inhibitor NS-398, 20 mM) before RGal treatment. Unwounded Caco-2 monolayers treated with RGal (1000 mg/ml) were collected for Western blotting for COX-2 protein.ResultsIn the wound healing assay, RGal at a concentration of 1000 µg/ml enhanced wound healing by 12.5% at 48 h compared to control group, under 10% serum conditions. Neither proliferation nor apoptosis were involved in the RGal effect on wound healing, suggesting the response was due solely to cell migration. Actinomycin D (5 mg/ml), Bay 11–7082 (10 mM) or JSH-23 (20 mM) treatment significantly reversed the effect of RGal on wound healing, showing that the response was transcriptionally dependent and involved NF-kB signaling. Treatment of cells with NS-398 (20 mM) also reversed the effect of RGal on wound healing. COX-2 protein expression was significantly increased at 6 and 12 h after RGal addition to Caco-2 monolayers.ConclusionsThese data suggest that the plant-based polysaccharide RGal increases intestinal epithelial cell wound healing by increasing cell migration. The RGal effect is dependent on the activation of the transcription factor NF-kB and downstream COX-2 protein expression and activity. Our findings show a novel mechanism of action of RGal in wound healing that could help in the resolution of intestinal inflammation and mucosal healing.Funding AgenciesNSERC

P540 Longitudinal Dynamics of Gut Microbiome and Metabolome After Biological Therapy in Inflammatory Bowel Diseases

Abstract Background Inflammatory bowel diseases (IBD), including Crohn’s disease (CD) and ulcerative colitis (UC) are chronic inflammatory conditions that affect the gastrointestinal tract. Biological therapy with monoclonal antibodies has provided significant benefit for patients with IBD, resulting in clinical and endoscopic remission. Gut microbiome alterations were shown to serve as a marker of response to treatment in IBD. The aim of the study is to characterize gut microbiome and metabolome in patients with CD and UC after initiation of biological therapy. Methods We studied a prospective cohort of 41 CD and 39 UC patients initiating biological therapy. Biological therapy included anti-TNF (Adalimumab, Infliximab and Golimumab), anti-α4β7 integrin (Vedolizumab) or anti-IL-12/23 p40 antibody (Ustekinumab). One-year follow up showed that up to 60% of the patients achieved clinical and endoscopic remission. Fecal samples and mucosal biopsies were collected both at baseline and 14 or 52 weeks after initiation of therapy. Microbiota and metabolite changes were analyzed using 16S rRNA gene sequencing and targeted/untargeted metabolomics. Results Longitudinal profiling of luminal and mucosal bacteria reflected the individual patient-related variations over the study duration. CD and UC patients showed distinct luminal and mucosal bacterial communities. Bacterial dysbiosis was significantly higher in patients with CD than with UC, as shown by community richness and diversity. While fecal microbiota of patients with CD was enriched in Escherichia coli and Bacteroides, both Faecalibacterium and Bifidobacterium were enriched in UC. In contrast to fecal bacterial communities, mucosal bacteria from patients with ileal and colonic CD showed a clear separation of microbial profiles based on disease location. Members belonging to Haemophiles, Fusobacterium, and Escherichia coli were significantly more abundant in IBD patients with active disease. Machine-learning based analysis showed that fecal and biopsy profiles equally classified patients based on their disease subtype, with an area under the curve (AUC)=0.86. Metabolite profiling revealed enrichment of platelet-activating factor and the glycosphingolipid lactosylceramide in inflamed phenotypes. Conversely, enrichment of bile acids, such as deoxy cholic acid, chenodeoxycholic acid and Lithocholic acid was observed in responders or patients during remission. Conclusion Gut microbial and metabolomic profiling revealed associations between gut microbial taxonomic or functional profiles and IBD subtypes. The association between enrichment of fatty acids and bile acids and disease activity suggests an important role of these pathways in the development or the resolution of intestinal inflammation.

E-type prostanoid receptor 4 drives resolution of intestinal inflammation by blocking epithelial necroptosis.

Inflammatory bowel diseases present with elevated levels of intestinal epithelial cell (IEC) death, which compromises the gut barrier, activating immune cells and triggering more IEC death. The endogenous signals that prevent IEC death and break this vicious cycle, allowing resolution of intestinal inflammation, remain largely unknown. Here we show that prostaglandin E2 signalling via the E-type prostanoid receptor 4 (EP4) on IECs represses epithelial necroptosis and induces resolution of colitis. We found that EP4 expression correlates with an improved IBD outcome and that EP4 activation induces a transcriptional signature consistent with resolution of intestinal inflammation. We further show that dysregulated necroptosis prevents resolution, and EP4 agonism suppresses necroptosis in human and mouse IECs. Mechanistically, EP4 signalling on IECs converges on receptor-interacting protein kinase 1 to suppress tumour necrosis factor-induced activation and membrane translocation of the necroptosis effector mixed-lineage kinase domain-like pseudokinase. In summary, our study indicates that EP4 promotes the resolution of colitis by suppressing IEC necroptosis.

Features of Intestinal Disease Associated With COVID-Related Multisystem Inflammatory Syndrome in Children.

ABSTRACTMultisystem inflammatory syndrome in children (MIS-C) is a recently identified syndrome that appears to be temporally associated with novel coronavirus 2019 infection. MIS-C presents with fever and evidence of systemic inflammation, which can manifest as cardiovascular, pulmonary, neurologic, and gastrointestinal (GI) system dysfunction. Presenting GI symptoms are seen in the majority, including abdominal pain, diarrhea, and vomiting. Any segment of the GI tract may be affected; however, inflammation in the ileum and colon predominates. Progressive bowel wall thickening can lead to luminal narrowing and obstruction. Most will have resolution of intestinal inflammation with medical therapies; however, in rare instances, surgical resection may be required.

Resolvin E1 is a pro-repair molecule that promotes intestinal epithelial wound healing

Resolution of intestinal inflammation and wound repair are active processes that mediate epithelial healing at mucosal surfaces. Lipid molecules referred to as specialized proresolving mediators (SPMs) play an important role in the restorative response. Resolvin E1 (RvE1), a SPM derived from omega-3 fatty acids, has been reported to dampen intestinal inflammation by promoting anti-inflammatory responses including increased neutrophil spherocytosis and macrophage production of IL-10. Despite these observations, a role for RvE1 in regulating intestinal epithelial cell migration and proliferation during mucosal wound repair has not been explored. Using an endoscopic biopsy-based wound healing model, we report that RvE1 is locally produced in response to intestinal mucosal injury. Exposure of intestinal epithelial cells to RvE1 promoted wound repair by increasing cellular proliferation and migration through activation of signaling pathways including CREB, mTOR, and Src-FAK. Additionally, RvE1-triggered activation of the small GTPase Rac1 led to increased intracellular reactive oxygen species (ROS) production, cell-matrix adhesion, and cellular protrusions at the leading edge of migrating cells. Furthermore, in situ administration of RvE1-encapsulated synthetic targeted polymeric nanoparticles into intestinal wounds promoted mucosal repair. Together, these findings demonstrate that RvE1 functions as a prorepair lipid mediator by increasing intestinal epithelial cell migration and proliferation, and highlight potential therapeutic applications for this SPM to promote mucosal healing in the intestine.

Immunological mechanisms underpinning faecal microbiota transplantation for the treatment of inflammatory bowel disease.

Inflammatory bowel disease (IBD) is a chronic gastrointestinal disease that results from a dysregulated immune response against specific environmental triggers in a genetically predisposed individual. Increasing evidence has indicated a causal role for changes in gut microbiota (dysbiosis) contributing to this immune-mediated intestinal inflammation. These mechanisms involve dysregulation of multiple facets of the host immune pathways that are potentially reversible. Faecal microbiota transplantation (FMT) is the transfer of processed stool from a healthy donor into an individual with an illness. FMT has shown promising results in both animal model experiments and clinical studies in IBD in the resolution of intestinal inflammation. The underlying mechanisms, however, are unclear. Insights from these studies have shown interactions between modulation of dysbiosis via changes in abundances of specific members of the gut microbial community and changes in host immunological pathways. Unravelling these causal relationships has promising potential for a translational therapy role to develop targeted microbial therapies and understand the mechanisms that underpin IBD aetiopathogenesis. In this review, we discuss current evidence for the contribution of gut microbiota in the disruption of intestinal immune homeostasis and immunoregulatory mechanisms that are associated with the resolution of inflammation through FMT in IBD.

Macrophages in intestinal inflammation and resolution: a potential therapeutic target in IBD

Macrophages are the gatekeepers of intestinal immune homeostasis as they discriminate between innocuous antigens and potential pathogens to maintain oral tolerance. However, in individuals with a genetic and environmental predisposition, regulation of intestinal immunity is impaired, leading to chronic relapsing immune activation and pathologies of the gastrointestinal tract, such as IBD. As evidence suggests a causal link between defects in the resolution of intestinal inflammation and altered monocyte-macrophage differentiation in patients with IBD, macrophages have been considered as a novel potential target to develop new treatment approaches. This Review discusses the molecular and cellular mechanisms involved in the differentiation and function of intestinal macrophages in homeostasis and inflammation, and their role in resolving the inflammatory process. Understanding the molecular pathways involved in the specification of intestinal macrophages might lead to a new class of targets that promote remission in patients with IBD.

The Rac1 splice form Rac1b favors mouse colonic mucosa regeneration and contributes to intestinal cancer progression.

We previously have identified the ectopic expression of Rac1b, an activated and novel splice variant of Rac1, in a subset of human colorectal adenocarcinomas, as well as in inflammatory bowel diseases and in colitis mouse model. Rac1b overexpression has been further evidenced in breast, pancreatic, thyroid, ovarian, and lung cancers. In this context, the aim of our study was to investigate the physiopathological implications of Rac1b in intestinal inflammation and carcinogenesis in vivo. The ectopic expression of Rac1b was induced in mouse intestinal epithelial cells after crossing Rosa26-LSL-Rac1b and villin-Cre mice. These animals were let to age or were challenged with dextran sulfate sodium (DSS) to induce experimental colitis, or either received azoxymethane (AOM)/DSS treatment, or were bred with ApcMin/+ or Il10-/- mice to trigger intestinal tumors. Rac1b ectopic expression increased the intestinal epithelial cell proliferation and migration, enhanced the production of reactive oxygen species, and promoted the Paneth cell lineage. Although Rac1b overexpression alone was not sufficient to drive intestinal neoplasia, it enhanced Apc-dependent intestinal tumorigenesis. In the context of Il10 knockout, the Rac1b transgene strengthened colonic inflammation due to induced intestinal mucosa permeability and promoted cecum and proximal colon carcinogenesis. In contrast, Rac1b alleviated carcinogen/acute inflammation-associated colon carcinogenesis (AOM/DSS). This resulted at least partly from the early mucosal repair after resolution of inflammation. Our data highlight the critical role of Rac1b in driving wound-healing after resolution of intestinal inflammation, and in cooperating with Wnt pathway dysregulation and chronic inflammation to promote intestinal carcinogenesis.

Actors and Factors in the Resolution of Intestinal Inflammation: Lipid Mediators As a New Approach to Therapy in Inflammatory Bowel Diseases.

In the last few decades, the pathogenesis of inflammatory bowel disease (IBD) in genetically predisposed subjects susceptible to specific environmental factors has been attributed to disturbance of both the immune and non-immune system and/or to the imbalanced interactions with microbes. However, increasing evidences support the idea that defects in pro-resolving pathways might strongly contribute to IBD onset. The resolution of inflammation is now recognized as a dynamic event coordinated by specialized pro-resolving lipid mediators (LMs), which dampen inflammation-sustaining events, such as angiogenesis, release of pro-inflammatory cytokines, clearance of apoptotic cells, and microorganisms. Among these pro-resolving molecules, those derived from essential polyunsaturated fatty acids (PUFAs) have been shown to induce favorable effects on a plethora of human inflammatory disorders, including IBD. Here, we offer a summary of mechanisms involving both cellular and molecular components of the immune response and underlying the anti-inflammatory and pro-resolving properties of PUFAs and their derivatives in the gut, focusing on both ω-3 and ω-6 LMs. These fatty acids may influence IBD progression by: reducing neutrophil transmigration across the intestinal vasculature and the epithelium, preventing the release of pro-inflammatory cytokines and the up-regulation of adhesion molecules, and finally by promoting the production of other pro-resolving molecules. We also discuss the numerous attempts in using pro-resolving PUFAs to ameliorate intestinal inflammation, both in patients with IBD and mouse models. Although their effects in reducing inflammation is incontestable, results from previous works describing the effects of PUFA administration to prevent or treat IBD are controversial. Therefore, more efforts are needed not only to identify and explain the physiological functions of PUFAs in the gut, but also to unveil novel biosynthetic pathways of these pro-resolving LMs that may be dysregulated in these gut-related disorders. We suppose that either PUFAs or new medications specifically promoting resolution-regulating mediators and pathways will be much better tolerated by patients with IBD, with the advantage of avoiding immune suppression.

Purinergic Signaling as a Regulator of Th17 Cell Plasticity.

T helper type 17 (Th17) lymphocytes, characterized by the production of interleukin-17 and other pro-inflammatory cytokines, are present in intestinal lamina propria and have been described as important players driving intestinal inflammation. Recent evidence, supporting the notion of a functional and phenotypic instability of Th17 cells, has shown that Th17 differentiate into type 1 regulatory (Tr1) T cells during the resolution of intestinal inflammation. Moreover, it has been suggested that the expression of CD39 ectonucleotidase endows Th17 cells with immunosuppressive properties. However, the exact role of CD39 ectonucleotidase in Th17 cells has not been studied in the context of intestinal inflammation. Here we show that Th17 cells expressing CD39 ectonucleotidase can hydrolyze ATP and survive to ATP-induced cell death. Moreover, in vitro-generated Th17 cells expressing the CD39 ectonucleotidase produce IL-10 and are less pathogenic than CD39 negative Th17 cells in a model of experimental colitis in Rag-/- mice. Remarkably, we show that CD39 activity regulates the conversion of Th17 cells to IL-10-producing cells in vitro, which is abrogated in the presence of ATP and the CD39-specific inhibitor ARL67156. All these data suggest that CD39 expression by Th17 cells allows the depletion of ATP and is crucial for IL-10 production and survival during the resolution of intestinal inflammation.

Fc Receptor-mediated Effector Function Contributes to the Therapeutic Response of Anti-TNF Monoclonal Antibodies in a Mouse Model of Inflammatory Bowel Disease.

Anti-tumour necrosis factor [TNF] monoclonal antibodies [infliximab, adalimumab] induce complete mucosal healing in a proportion of patients with Crohn's disease whereas a TNF receptor fusion protein [etanercept] is not effective and the anti-TNF F[ab']2 fragment [certolizumab] shows a very low rate of complete mucosal healing. In contrast, all four TNF-neutralising drugs have demonstrated efficacy in the treatment of rheumatoid arthritis. These observations suggest that factors other than neutralisation of TNF may contribute to clinical outcomes in Crohn's disease. Here we tested the hypothesis that Fc receptor [FcR]-mediated effects may contribute to the therapeutic response of anti-TNF antibodies in inflammatory bowel disease. We modified an IgG2c mouse anti-TNF antibody that binds the high-affinity FcRs to generate an IgG1 isotype with strongly diminished binding. We examined the therapeutic effects of both antibodies in the T cell transfer model of inflammatory bowel disease and the collagen-induced arthritis model. The IgG2c anti-TNF antibody prevented colonic inflammation in the T cell transfer model of colitis, whereas the IgG1 anti-TNF did not. Conversely, both the IgG2c and IgG1 anti-TNFs were similarly effective in reducing the severity of articular inflammation in mouse collagen-induced arthritis. These data support the concept that the mechanism of action for TNF-neutralising drugs may differ across immune-mediated diseases and, potentially, between therapeutics within a particular disease. Our data suggest a specific role of Fc-mediated immune regulation in the resolution of intestinal inflammation by anti-TNF monoclonal antibodies.

Dynamic changes in macrophage activation and proliferation during the development and resolution of intestinal inflammation.

Macrophages (Mφs) accumulate at sites of inflammation, and, because they can assume several functionally distinct states of activation, they can either drive or restrain inflammatory responses. Once believed to depend on the recruitment of blood monocytes, it is now clear that the accumulation of Mφs in some tissues can result from the proliferation of resident Mφs in situ. However, little is known about the proliferation and activation state of Mφ subsets in the gut during the development and resolution of intestinal inflammation. We show that inflammatory Mφs accumulate in the large intestine of mice during the local inflammatory response to infection with the gastrointestinal nematode parasite Trichuris muris. Classically activated Mφs predominate initially (as the inflammation develops) and then, following worm expulsion (as the inflammation resolves), both the resident and inflammatory populations of Mφs become alternatively activated. A small but significant increase in the proliferation of inflammatory Mφs is seen but only during the resolution phase of the inflammatory response following both worm expulsion and the peak in Mφ accumulation. In contrast to recent studies in the pleural and peritoneal cavities, the proliferation of resident and alternatively activated Mφs does not increase during the inflammatory response. Furthermore, in CCR2−/− mice, monocyte recruitment to the gut is impeded, and the accumulation of alternatively activated Mφs is greatly reduced. In conclusion, the recruitment of blood monocytes is the principle mechanism of Mφ accumulation in the large intestine. This study provides a novel insight into the phenotype and behavior of intestinal Mφ during infection-driven inflammation.

Tyro3, Axl, and Mertk receptor signaling in inflammatory bowel disease and colitis-associated cancer.

Three receptor tyrosine kinases, Tyro3, Axl, and Mertk (TAM) and their ligands Gas6 and Protein S, have emerged as potent negative regulators of innate immune responses. A number of studies using genetic ablation of TAM loci in mice have elucidated the mechanism of TAM engagement and function during the immune response and removal of apoptotic cells. Following phagocytosis of apoptotic cells or the induction of T-cell dependent adaptive immune responses, ligand-induced TAM signaling dampens proinflammatory cytokine production and thus prevents exaggerated or prolonged inflammation. It is believed that the TAM pathway may play an important role in the pathogenesis of inflammatory bowel disease. Suppression of inflammation and removal of apoptotic cells followed by tissue repair are essential processes for disease remission and the successful management of inflammatory bowel disease. In light of the key role of TAMs in controlling inflammatory responses, here, we review the recent advances on TAM research vis-à-vis the resolution of intestinal inflammation. Targeted activation of TAM receptor tyrosine kinases may represent a potent therapeutic opportunity in inflammatory bowel disease.

The precipitation of behavioral defects due to inflammation in the DSS mouse model of colitis (LB748)

Background: Anxiety, depression, and altered memory have been previously associated with intestinal diseases, including inflammatory bowel disease (IBD). Understanding the association between these behavioral changes and IBD may provide clinical significance seeing as concomitant mood disorders often increase a patient’s risk of developing secondary functional gastrointestinal diseases (FGIDs).Aims: The aim of this study was to determine whether active intestinal inflammation precipitates behavioral defects in memory and anxiety and to determine if these changes persist through the resolution of inflammation.Methods: Dextran Sodium Sulfate (DSS) was administered for 5 days via drinking water followed by either 3 days for active inflammation studies or 8 days for resolution of inflammation studies. Mice were weighed daily and colon lengths were measure at the time of sacrifice in order to assess the degree of sickness. Anxiety‐like behavior (light/dark box) and memory (novel object test) were assessed in the DSS mice vs. controls (WT;C57BL/6).Results: DSS mice at the peak of inflammation demonstrated impairments in non‐spatial memory with an exploration ratio of 54.06 +/‐ 1.84 while controls had a mean exploration ratio of 57.91 +/‐ 1.29 (p&lt;.01; n=13). Anxiety‐like behavior was also evident in the DSS mice, which spent 133.91 +/‐10.17 seconds in the light area of the light/dark box while the controls spent 174 +/‐ 14.51 seconds in the light area (p&lt;.04; n=11). These behavioral defects did not persist at the resolution of intestinal inflammation. However, physiological changes, such as a shortening of the colon, were equally evident at the peak of inflammation as well as at the resolution phase.Conclusions: At the peak of inflammation, the DSS mouse model of colitis displays altered baseline behaviors in regards to memory and anxiety. Although physiological changes persist at the resolution of colitis as seen with persistent shortening of the colon, behavioral defects are not evident post inflammation. Taken together, these findings indicate and underlying connection between the brain and the gut relevant to the context of Inflammatory Bowel Disease.

CD137 Facilitates the Resolution of Acute DSS-Induced Colonic Inflammation in Mice

BackgroundCD137 and its ligand (CD137L) are potent immunoregulatory molecules that influence activation, proliferation, differentiation and cell death of leukocytes. Expression of CD137 is upregulated in the lamina propria cells of Crohn’s disease patients. Here, the role of CD137 in acute Dextran-Sodium-Sulfate (DSS)-induced colitis in mice was examined.MethodsWe induced acute large bowel inflammation (colitis) via DSS administration in CD137−/− and wild-type (WT) mice. Colitis severity was evaluated by clinical parameters (weight loss), cytokine secretion in colon segment cultures, and scoring of histological inflammatory parameters. Additionally, populations of lamina propria mononuclear cells (LPMNC) and intraepithelial lymphocytes (IEL) were characterized by flow cytometry. In a subset of mice, resolution of intestinal inflammation was evaluated 3 and 7 days after withdrawal of DSS.ResultsWe found that both CD137−/− and WT mice demonstrated a similar degree of inflammation after 5 days of DSS exposure. However, the resolution of colonic inflammation was impaired in the absence of CD137. This was accompanied by a higher histological score of inflammation, and increased release of the pro-inflammatory mediators granulocyte macrophage colony-stimulating factor (GM-CSF), CXCL1, IL-17 and IFN-γ. Further, there were significantly more neutrophils among the LPMNC of CD137−/− mice, and reduced numbers of macrophages among the IEL.ConclusionWe conclude that CD137 plays an essential role in the resolution of acute DSS-induced intestinal inflammation in mice.

Postinflammatory visceral sensitivity and pain mechanisms

The inflammatory reaction is normally tightly regulated, and as soon as the original insult has been cleared, a resolution phase starts that aims at leading the tissues back to a normal physiological state. However, after intestinal inflammation, a number of patients develop postinflammatory hypersensitivity symptoms, which can be defined as an excessive sensitivity to gut nociceptive stimulation. The pain experienced by those patients has been largely studied in the context of postinfectious intestinal diseases. The mechanisms of postinflammatory persistent visceral pain involve peripheral and central neuroplastic changes, low-grade chronic inflammation that sensitizes visceral afferent pathways and sensitization of non-neuronal resident cells of the gut. Several molecular determinants such as neurokinins, serotonin, proteases and voltage-gated ion channels seem to play a significant role in the control of postinflammatory visceral sensation. This review tries to give insights into the mechanisms of persistent visceral pain following the resolution of intestinal inflammation and tries to identify what needs to be done to further advance the field of postinflammatory hypersensitivity clinical management.

Persistent epithelial dysfunction and bacterial translocation after resolution of intestinal inflammation.

Epithelial secretion may play an important role in reducing bacterial colonization and translocation in intestine. If so, secretory dysfunction could result in increased susceptibility to infection and inflammation. We investigated whether long-term colonic secretory dysfunction occurs after a bout of colitis and if this is accompanied by an increase in bacterial colonization and translocation. Rats were studied 6 wk after induction of colitis with trinitrobenzene sulfonic acid when inflammation had completely resolved, and epithelial permeability was normal. Intestinal loops were stimulated with either Clostridium difficile toxin A or a phosphodiesterase inhibitor. In vitro, colonic tissue from previously sensitized rats was exposed to antigen (ovalbumin). Secretory responses to all three stimuli were suppressed in rats that had previously had colitis. These rats exhibited increased (16-fold) numbers of colonic aerobic bacteria and increased (>3-fold) bacterial translocation, similar to results in rats studied after resolution of enteritis. Postcolitis bacterial translocation was prevented by daily treatment with an inhibitor of inducible nitric oxide synthase. This study demonstrates that intestinal inflammation results in prolonged impairment of colonic epithelial secretion, which may contribute to increases in bacterial load and bacterial translocation. Epithelial dysfunction of this type could underlie an increased propensity for further bouts of inflammation, a hallmark of diseases such as inflammatory bowel disease.