Evidence for the involvement of NOD2 in regulating colonic epithelial cell growth and survival

Ileocolonic Healing after Small Ileocecal Resection in Mice: NOD2 Deficiency Impairs Anastomotic Healing by Local Mechanisms

Ileocecal resection (ICR) is frequently performed in Crohn's disease (CD). NOD2 mutations are risk factors for CD. Nod2 knockout (ko) mice show impaired anastomotic healing after extended ICR. We further investigated the role of NOD2 after limited ICR. C57B16/J (wt) and Nod2 ko littermates underwent limited ICR including 1-2 cm terminal ileum and were randomly assigned to vehicle or MDP treatment. Bursting pressure was measured on POD 5, and the anastomosis was analyzed for matrix turn-over and granulation tissue. Wound fibroblasts from subcutaneously implanted sponges were used for comparison. The M1/M2 macrophage plasma cytokines were analyzed. Mortality was not different between groups. Bursting pressure was significantly decreased in ko mice. This was associated with less granulation tissue but was not affected by MDP. However, anastomotic leak (AL) rate tended to be lower in MDP-treated ko mice (29% vs. 11%, p = 0.07). mRNA expression of collagen-1α (col1 α), collagen-3α (col3 α), matrix metalloproteinase (mmp)2 and mmp9 was increased in ko mice, indicating increased matrix turn-over, specifically in the anastomosis. Systemic TNF-α expression was significantly lower in ko mice. Ileocolonic healing is impaired in Nod2 ko mice after limited ICR by local mechanisms maybe including local dysbiosis.

Postbiotic muramyl dipeptide alleviates colitis via activating autophagy in intestinal epithelial cells

The pathogenesis of IBD is complicated and still unclear. Nucleotide-binding oligomerization domain 2 (NOD2) plays a significant role in regulating gut inflammation under the activation of muramyl dipeptide (MDP), which is used as a postbiotic. The study aimed to investigate the effect of MDP on the intestinal barrier in colitis and the mechanism involved. In this study, C57BL/6 mice were challenged with dextran sodium sulfate (DSS) for establishing a colitis model with the pre-treatment of MDP in vivo. Intestinal permeability was reflected by detecting the serum concentration of 4 kDa Fluorescein Isothiocyanate-Dextran. The expression of inflammation, barrier-related proteins, and autophagy was tested by Western Blotting. Proliferation and apoptosis in intestinal epithelial cells were detected by immunohistochemistry. Caco-2 cells were exposed to lipopolysaccharide for imitating inflammation in vitro. The findings showed that administration of MDP ameliorated losses of body weight loss, gross injury, and histology score of the colon in the DSS-induced colitis mice. MDP significantly ameliorated the condition of gut permeability, and promoted intestinal barrier repair by increasing the expression of Zonula occludens-1 and E-cadherin. Meanwhile, MDP promoted proliferation and reduced apoptosis of intestinal epithelial cells. In the experiment group treated with MDP, LC3 was upregulated, and p62 was downregulated, respectively. These results suggested that MDP stimulation attenuates intestinal inflammation both in vivo and in vitro. Potentially, MDP reduced the intestinal barrier damage by regulating autophagy in intestinal epithelial cells. Future trials investigating the effects of MDP-based postbiotics on IBD may be promising.

Sending signals - The microbiota's contribution to intestinal epithelial homeostasis

The intestine is inhabited by a diverse range of microorganisms, which requires the host to employ numerous barrier measures to prevent bacterial invasion. However, the intestinal microbiota additionally acts symbiotically with host cells to maintain epithelial barrier function, and perturbation to this interaction plays a pivotal role in intestinal pathogenesis. In this review, we highlight current findings of how the intestinal microbiota influences host intestinal epithelial cells. In particular, we review the roles of numerous microbial-derived products as well as mechanisms by which these microbial products influence the regulation of intestinal epithelial population dynamics and barrier function.

A literature-based approach for curating gene signatures in multifaceted diseases

BACKGROUND AND AIMS

The task of identifying a representative and yet manageable target gene list for assessing the pathogenesis of complicated and multifaceted diseases is challenging. Using Inflammatory Bowel Disease (IBD) as an example, we conceived a bioinformatic approach to identify novel genes associated with the various disease subtypes, in combination with known clinical control genes.

METHODS

From the available literature, we used Acumenta Literature Lab^TM (LitLab), network analyses, and LitLab Gene Retriever to assemble a gene pool that has a high likelihood of representing immunity-related subtype-specific signatures of IBD.

RESULTS

We generated six relevant gene lists and 21 intersections that contain genes with unique literature associations to Crohn's Disease (n = 60), Ulcerative Colitis (n = 17), and unclassified (n = 45) subtypes of IBD. From this gene pool, we then filtered and constructed, using network analysis, a final list of 142 genes that are the most representative of the disease and its subtypes.

CONCLUSIONS

In this paper, we present the bioinformatic construction of a gene panel that putatively contains subtype signatures of IBD, a multifactorial disease. These gene signatures will be tested as biomarkers to classify patients with IBD, which has been a clinically challenging task. Such approach to diagnose and monitor complicated disease pathogenesis is a stepping-stone towards personalized care.

NOD Signaling and Cell Death

Innate immune signaling and programmed cell death are intimately linked, and many signaling pathways can regulate and induce both, transcription of inflammatory mediators or autonomous cell death. The best-characterized examples for these dual outcomes are members of the TNF superfamily, the inflammasome receptors, and the toll-like receptors. Signaling via the intracellular peptidoglycan receptors NOD1 and NOD2, however, does not appear to follow this trend, despite involving signaling proteins, or proteins with domains that are linked to programmed cell death, such as RIP kinases, inhibitors of apoptosis (IAP) proteins or the CARD domains on NOD1/2. To better understand the connections between NOD signaling and cell death induction, we here review the latest findings on the molecular regulation of signaling downstream of the NOD receptors and explore the links between this immune signaling pathway and the regulation of cell death.

NOD2 Expression in Intestinal Epithelial Cells Protects Toward the Development of Inflammation and Associated Carcinogenesis

Nucleotide-binding oligomerization domain 2 (NOD2) is an intracellular pattern recognition receptor that senses bacterial peptidoglycan-conserved motifs in cytosol and stimulates host immune response including epithelial and immune cells. The association of NOD2 mutations with a number of inflammatory pathologies including Crohn's disease (CD), graft-versus-host diseases, or Blau syndrome, highlights its pivotal role in inflammatory response and the associated-carcinogenesis development. Since its identification in 2001 and its association with CD, the role of NOD2 in epithelial cells and immune cells has been investigated extensively but the precise mechanism by which NOD2 mutations lead to CD and the associated carcinogenesis development is largely unknown. In this review, we present and discuss recent developments about the role of NOD2 inside epithelial cells on the control of the inflammatory process and its linked carcinogenesis development.

Microbial Host Interactions and Impaired Wound Healing in Mice and Humans: Defining a Role for BD14 and NOD2

Chronic wounds cause significant patient morbidity and mortality. A key factor in their etiology is microbial infection, yet skin host-microbiota interactions during wound repair remain poorly understood. Microbiome profiles of noninfected human chronic wounds are associated with subsequent healing outcome. Furthermore, poor clinical healing outcome was associated with increased local expression of the pattern recognition receptor NOD2. To investigate NOD2 function in the context of cutaneous healing, we treated mice with the NOD2 ligand muramyl dipeptide and analyzed wound repair parameters and expression of antimicrobial peptides. Muramyl dipeptide treatment of littermate controls significantly delayed wound repair associated with reduced re-epithelialization, heightened inflammation, and up-regulation of murine β-defensins 1, 3, and particularly 14. We postulated that although murine β-defensin 14 might affect local skin microbial communities, it may further affect other healing parameters. Indeed, exogenously administered murine β-defensin 14 directly delayed mouse primary keratinocyte scratch wound closure in vitro. To further explore the role of murine β-defensin 14 in wound repair, we used Defb14^-/- mice and showed they had a global delay in healing in vivo, associated with alterations in wound microbiota. Taken together, these studies suggest a key role for NOD2-mediated regulation of local skin microbiota, which in turn affects chronic wound etiology.

NOD1 and NOD2: Molecular targets in prevention and treatment of infectious diseases

Nucleotide-binding oligomerization domain (NOD) 1 and NOD2 are pattern-recognition receptors responsible for sensing fragments of bacterial peptidoglycan known as muropeptides. Stimulation of innate immunity by systemic or local administration of NOD1 and NOD2 agonists is an attractive means to prevent and treat infectious diseases. In this review, we discuss novel data concerning structural features of selective and non-selective (dual) NOD1 and NOD2 agonists, main signaling pathways and biological effects induced by NOD1 and NOD2 stimulation, including induction of pro-inflammatory cytokines, type I interferons and antimicrobial peptides, induction of autophagy, alterations of metabolism. We also discuss interactions between NOD1/NOD2 and Toll-like receptor agonists in terms of synergy and cross-tolerance. Finally, we review available animal data on the role of NOD1 and NOD2 in protection against infections, and discuss how these data could be applied in human infectious diseases.

From sensing to shaping microbiota: insights into the role of NOD2 in intestinal homeostasis and progression of Crohn's disease

NOD2 was the first susceptibility gene identified for Crohn's disease (CD), one of the major forms of inflammatory bowel disease (IBD). The field of NOD2 research has opened up many questions critical to understanding the complexities of microbiota-host interactions. In addition to sensing its specific bacterial components as a cytosolic pattern recognition receptor, NOD2 also appears to shape the colonization of intestinal microbiota. Activated NOD2 triggers downstream signaling cascades exampled by the NF-κB pathway to induce antimicrobial activities, however, defective or loss of NOD2 functions incur a similarly activated inflammatory response. Additional studies have identified the involvement of NOD2 in protection against non-microbiota-related intestinal damages as well as extraintestinal infections. We survey recent molecular and genetic studies of NOD2-mediated bacterial sensing and immunological modulation, and integrate evidence to suggest a highly reciprocal but still poorly understood cross talk between enteric microbiota and host cells.

Respective Roles of Hematopoietic and Nonhematopoietic Nod2 on the Gut Microbiota and Mucosal Homeostasis

BACKGROUND

NOD2 mutations are associated with Crohn's disease (CD). Both CD (in human) and Nod2 deficiency (in mice) are characterized by increased mucosal CD4 T-cells, an altered permeability and a microbial dysbiosis. However, the respective roles of the gut epithelial and immune compartments on the phenotype are not known.

METHODS

Microbial composition, epithelial peptide secretion, intestinal permeability, and immune cell composition of Peyer patches were studied in Nod2 knock-out mice transplanted with wild-type bone marrow cells and vice versa.

RESULTS

The nonhematopoietic cells control the microbiota composition and epithelial secretion of mucins and antimicrobial peptides. These parameters are correlated with recurrent associations between bacterial species and luminal products. In contrast, Nod2 in the hematopoietic compartment regulates the epithelial permeability and the gut-associated lymphoid tissue independently of the bacterial composition.

CONCLUSIONS

The immune system and the gut permeability in one hand and the microbial and epithelial peptide compositions in the other hand are separate couples of interdependent parameters, both controlled by Nod2 in either the hematopoietic or nonhematopoietic lineages.

A role for the pattern recognition receptor Nod2 in promoting recruitment of CD103+ dendritic cells to the colon in response to Trichuris muris infection

The ability of the colon to generate an immune response to pathogens, such as the model pathogen Trichuris muris, is a fundamental and critical defense mechanism. Resistance to T. muris infection is associated with the rapid recruitment of dendritic cells (DCs) to the colonic epithelium via epithelial chemokine production. However, the epithelial-pathogen interactions that drive chemokine production are not known. We addressed the role of the cytosolic pattern recognition receptor Nod2. In response to infection, there was a rapid influx of CD103(+)CD11c(+) DCs into the colonic epithelium in wild-type (WT) mice, whereas this was absent in Nod2(-/-) animals. In vitro chemotaxis assays and in vivo experiments using bone marrow chimeras of WT mice reconstituted with Nod2(-/-) bone marrow and infected with T. muris demonstrated that the migratory function of Nod2(-/-) DCs was normal. Investigation of colonic epithelial cell (CEC) innate responses revealed a significant reduction in epithelial production of the chemokines CCL2 and CCL5 but not CCL20 by Nod2-deficient CECs. Collectively, these data demonstrate the importance of Nod2 in CEC responses to infection and the requirement for functional Nod2 in initiating host epithelial chemokine-mediated responses and subsequent DC recruitment and T-cell responses following infection.

Hypoxia inducible NOD2 interacts with 3-O-sulfogalactoceramide and regulates vesicular homeostasis

BACKGROUND

Oxygen sensing in mammalian cells is a conserved signaling pathway regulated by hypoxia inducible factor type 1 (HIF-1). Inadequate oxygen supply (hypoxia) is common to many pathological disorders where autophagy plays an import role. The aim of this study was the identification and characterization of novel HIF-1 target genes that promote autophagy during hypoxia.

METHODS

Whole genome Chromatin Immune Precipitation from hypoxic HeLa cells was used to identify novel HIF-1 target genes. Hypoxia induced expression and transcription regulation was studied in wild type and HIF-deficient cells. siRNA silencing of candidate genes was used to establish their role during autophagy. Recombinant protein was used for screening immobilized glycosylated lipids to identify potential ligands.

RESULTS

We identified the Nucleotide Oligomerization Domain 2 (NOD2/CARD15) as a novel HIF-1 target and 3-O-sulfo-galactoceramide (sulfatide) and Mycobacterium sp. specific sulfolipid-1 as the first NOD2 ligands that both compete for binding to NOD2. Loss of NOD2 function impaired autophagy upstream of the autophagy inhibitor chloroquine by reducing the number of acidic vesicles. Inhibition of sulfatide synthesis elicited defects in autophagy similar to the NOD2 loss of function but did not influence NOD2-mediated NF-kB signaling.

CONCLUSIONS

Our findings suggest that the interaction of NOD2 with sulfatide may mediate the balance between autophagy and inflammation in hypoxic cells.

GENERAL SIGNIFICANCE

These findings may lead to a better understanding of complex inflammatory pathologies like Crohn's disease and tuberculosis where both NOD2 and hypoxia are implicated.

NOD1 and NOD2 stimulation triggers innate immune responses of human periodontal ligament cells

Nod-like receptors (NLRs) are cytosolic sensors for microbial molecules. Nucleotide-binding oligomerization domain (NOD)1 and NOD2 recognize the peptidoglycan derivatives, meso-diaminopimelic acid (meso-DAP) and muramyl dipeptide (MDP), respectively, and trigger host innate immune responses. In the present study, we examined the function of NOD1 and NOD2 on innate immune responses in human periodontal ligament (PDL) cells. The gene expression of NOD1 and NOD2 was examined by RT-PCR. IL-6 and IL-8 production in culture supernatants was measured by ELISA. Western blot analysis was performed to determine the activation of NF-κB and MAPK in response to Tri-DAP and MDP. The genes of NOD1 and NOD2 appeared to be expressed in PDL cells. Although the levels of NOD2 expression were weak in intact cells, MDP stimulation increased the gene expression of NOD2 in PDL cells. Tri-DAP and MDP led to the production of IL-6 and IL-8 and the activation of NF-κB and MAPK in PDL cells. Toll-like receptor (TLR) stimulation led to increased gene expression of NOD1 and NOD2 in PDL cells. Pam₃CSK₄ (a TLR2 agonist) and IFN-γ synergized with Tri-DAP and MDP to produce IL-8 and IL-6 in PDL cells. Our results indicate that NOD1 and NOD2 are functionally expressed in human PDL cells and can trigger innate immune responses.

Gut Nod2 calls the bone marrow for monocyte reinforcements

Nod2 is an intracellular sensor linked to Crohn's disease, an inflammatory malady of the intestinal tract. In this issue of Immunity, Kim et al. (2011) demonstrate that Nod2 is responsible for regulating monocyte-attracting chemokines to the inflamed gut.

The Nod2 sensor promotes intestinal pathogen eradication via the chemokine CCL2-dependent recruitment of inflammatory monocytes

The intracellular sensor Nod2 is activated in response to bacteria, and the impairment of this response is linked to Crohn's disease. However, the function of Nod2 in host defense remains poorly understood. We found that Nod2-/- mice exhibited impaired intestinal clearance of Citrobacter rodentium, an enteric bacterium that models human infection by pathogenic Escherichia coli. The increased bacterial burden was preceded by reduced CCL2 chemokine production, inflammatory monocyte recruitment, and Th1 cell responses in the intestine. Colonic stromal cells, but not epithelial cells or resident CD11b+ phagocytic cells, produced CCL2 in response to C. rodentium in a Nod2-dependent manner. Unlike resident phagocytic cells, inflammatory monocytes produced IL-12, a cytokine that induces adaptive immunity required for pathogen clearance. Adoptive transfer of Ly6C(hi) monocytes restored the clearance of the pathogen in infected Ccr2-/- mice. Thus, Nod2 mediates CCL2-CCR2-dependent recruitment of inflammatory monocytes, which is important in promoting bacterial eradication in the intestine.

The human gutome: nutrigenomics of the host-microbiome interactions

Demonstrating the importance of the gut microbiota in human health and well-being represents a major transformational task in both medical and nutritional research. Owing to the high-throughput -omics methodologies, the complexity, evolution with age, and individual nature of the gut microflora have been more thoroughly investigated. The balance between this complex community of gut bacteria, food nutrients, and intestinal genomic and physiological milieu is increasingly recognized as a major contributor to human health and disease. This article discusses the "gutome," that is, nutritional systems biology of gut microbiome and host-microbiome interactions. We examine the novel ways in which the study of the human gutome, and nutrigenomics more generally, can have translational and transformational impacts in 21st century practice of biomedicine. We describe the clinical context in which experimental methodologies, as well as data-driven and process-driven approaches are being utilized in nutrigenomics and microbiome research. We underscore the pivotal importance of the gutome as a common platform for sharing data in the emerging field of the integrated metagenomics of gut pathophysiology. This vision needs to be articulated in a manner that recognizes both the omics biotechnology nuances and the ways in which nutrigenomics science can effectively inform population health and public policy, and vice versa.

Rapid dendritic cell mobilization to the large intestinal epithelium is associated with resistance to Trichuris muris infection

The large intestine is a major site of infection and disease, yet little is known about how immunity is initiated within this site and the role of dendritic cells (DCs) in this process. We used the well-established model of Trichuris muris infection to investigate the innate response of colonic DCs in mice that are inherently resistant or susceptible to infection. One day postinfection, there was a significant increase in the number of immature colonic DCs in resistant but not susceptible mice. This increase was sustained at day 7 postinfection in resistant mice when the majority of the DCs were mature. There was no increase in DC numbers in susceptible mice until day 13 postinfection. In resistant mice, most colonic DCs were located in or adjacent to the epithelium postinfection. There were also marked differences in the expression of colonic epithelial chemokines in resistant mice and susceptible mice. Resistant mice had significantly increased levels of epithelium-derived CCL2, CCL3, CCL5, and CCL20 compared with susceptible mice. Furthermore, administering neutralizing CCL5 and CCL20 Abs to resistant mice prevented DC recruitment. This study provides clear evidence of differences in the kinetics of DC responses in hosts inherently resistant and susceptible to infection. DC responses in the colon correlate with resistance to infection. Differences in the production of DC chemotactic chemokines by colonic epithelial cells in response to infection in resistant vs susceptible mice may explain the different kinetics of the DC response.