Crohn's disease and ulcerative colitis, the two main types of chronic inflammatory bowel disease, are multifactorial conditions of unknown aetiology A susceptibility locus for Crohn's disease has been mapped to chromosome 16 Here we have used a positional-cloning strategy, based on linkage analysis followed by linkage disequilibrium mapping, to identify three independent associations for Crohn's disease: a frameshift variant and two missense variants of NOD2, encoding a member of the Apaf-1/Ced-4 superfamily of apoptosis regulators that is expressed in monocytes These NOD2 variants alter the structure of either the leucine-rich repeat domain of the protein or the adjacent region NOD2 activates nuclear factor NF-kB; this activating function is regulated by the carboxy-terminal leucine-rich repeat domain, which has an inhibitory role and also acts as an intracellular receptor for components of microbial pathogens These observations suggest that the NOD2 gene product confers susceptibility to Crohn's disease by altering the recognition of these components and/or by over-activating NF-kB in monocytes, thus documenting a molecular model for the pathogenic mechanism of Crohn's disease that can now be further investigated

Association of NOD2 leucine-rich repeat variants with susceptibility to Crohn's disease

Escherichia coli is the predominant nonpathogenic facultative flora of the human intestine. Some E. coli strains, however, have developed the ability to cause disease of the gastrointestinal, urinary, or central nervous system in even the most robust human hosts. Diarrheagenic strains of E. coli can be divided into at least six different categories with corresponding distinct pathogenic schemes. Taken together, these organisms probably represent the most common cause of pediatric diarrhea worldwide. Several distinct clinical syndromes accompany infection with diarrheagenic E. coli categories, including traveler’s diarrhea (enterotoxigenic E. coli), hemorrhagic colitis and hemolytic-uremic syndrome (enterohemorrhagic E. coli), persistent diarrhea (enteroaggregative E. coli), and watery diarrhea of infants (enteropathogenic E. coli). This review discusses the current level of understanding of the pathogenesis of the diarrheagenic E. coli strains and describes how their pathogenic schemes underlie the clinical manifestations, diagnostic approach, and epidemiologic investigation of these important pathogens.

Diarrheagenic Escherichia coli

Few microorganisms are as versatile as Escherichia coli. An important member of the normal intestinal microflora of humans and other mammals, E. coli has also been widely exploited as a cloning host in recombinant DNA technology. But E. coli is more than just a laboratory workhorse or harmless intestinal inhabitant; it can also be a highly versatile, and frequently deadly, pathogen. Several different E. coli strains cause diverse intestinal and extraintestinal diseases by means of virulence factors that affect a wide range of cellular processes.

Pathogenic Escherichia coli

Recent years have witnessed the rise of the gut microbiota as a major topic of research interest in biology. Studies are revealing how variations and changes in the composition of the gut microbiota influence normal physiology and contribute to diseases ranging from inflammation to obesity. Accumulating data now indicate that the gut microbiota also communicates with the CNS — possibly through neural, endocrine and immune pathways — and thereby influences brain function and behaviour. Studies in germ-free animals and in animals exposed to pathogenic bacterial infections, probiotic bacteria or antibiotic drugs suggest a role for the gut microbiota in the regulation of anxiety, mood, cognition and pain. Thus, the emerging concept of a microbiota-gut-brain axis suggests that modulation of the gut microbiota may be a tractable strategy for developing novel therapeutics for complex CNS disorders.

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Mind-altering microorganisms: the impact of the gut microbiota on brain and behaviour

Macrophages are innate immune cells with well-established roles in the primary response to pathogens, but also in tissue homeostasis, coordination of the adaptive immune response, inflammation, resolution, and repair. These cells recognize danger signals through receptors capable of inducing specialized activation programs. The classically known macrophage activation is induced by IFN-gamma, which triggers a harsh proinflammatory response that is required to kill intracellular pathogens. Macrophages also undergo alternative activation by IL-4 and IL-13, which trigger a different phenotype that is important for the immune response to parasites. Here we review the cellular sources of these cytokines, receptor signaling pathways, and induced markers and gene signatures. We draw attention to discrepancies found between mouse and human models of alternative activation. The evidence for in vivo alternative activation of macrophages is also analyzed, with nematode infection as prototypic disease. Finally, we revisit the concept of macrophage activation in the context of the immune response.

Alternative Activation of Macrophages: An Immunologic Functional Perspective

Background and aim: Chronic psychological stress, including water avoidance stress (WAS), induces intestinal mucosal barrier dysfunction and impairs mucosal defences against luminal bacteria. The a ...

/pdf/probiotics-prevent-bacterial-translocation-and-improve-4f1kownema.pdf

Probiotics prevent bacterial translocation and improve intestinal barrier function in rats following chronic psychological stress

BACKGROUND AND AIMS Glucagon-like peptide-2 (GLP-2) is a recently identified potent intestinotrophic factor. We have evaluated the effect of GLP-2 treatment on intestinal epithelial barrier function in mice. METHODS CD-1 mice were injected subcutaneously with GLP-2 or a protease resistant analogue, h[Gly 2 ]GLP-2, twice daily for up to 10 days. Saline injected mice served as controls. Jejunal segments were mounted in Ussing chambers. Tissue conductance was measured and unidirectional fluxes were determined for (i) Na + and the small inert probe Cr-EDTA (both transported via the paracellular pathway) and (ii) the macromolecule horseradish peroxidase (HRP, transported via the transcellular pathway). RESULTS Mice treated with GLP-2 or h[Gly 2 ]GLP-2 for 10 days demonstrated significantly reduced intestinal conductance and fluxes of Na + , Cr-EDTA, and HRP. Electron microscopy confirmed that GLP-2 reduced endocytic uptake of HRP into enterocytes. Functional changes (evident by four hours) preceded morphological changes (evident by 48 hours). CONCLUSIONS GLP-2 enhances intestinal epithelial barrier function by affecting both paracellular and transcellular pathways and thus may be of therapeutic value in a number of gastrointestinal conditions.

https://gut.bmj.com/content/gutjnl/47/1/112.full.pdf

Glucagon-like peptide-2 enhances intestinal epithelial barrier function of both transcellular and paracellular pathways in the mouse

Objective: Persistent stress and life events affect the course of ulcerativecolitis and irritable bowel syndrome by largely unknown mechanisms.Corticotropin-releasing hormone (CRH) has been implica ...

https://gut.bmj.com/content/gutjnl/57/1/50.full.pdf

Corticotropin releasing hormone (CRH) regulates macromolecular permeability via mast cells in normal human colonic biopsies in vitro

Wistar-Kyoto rats were subjected to 4 h restraint stress (RS) or cold restraint stress (CRS), and jejunal tissues were examined in Ussing chambers for alterations in transport functions compared with tissues from unstressed control rats. The baseline short-circuit current (Isc) was significantly elevated in tissues from RS (approximately 50%) and CRS (100%). Substitution of Cl- eliminated the abnormality, suggesting that stress stimulates Cl- secretion. Electrical transmural stimulation of enteric nerves caused a transient increase in Isc in all tissues. The magnitude of this response was significantly less in tissues from CRS than from control rats; however, the ability of the epithelium to secrete in response to exogenous stimulation with bethanechol or vasoactive intestinal polypeptide was unimpaired, implicating a neural change. Tissue conductance was higher in jejunum from RS and CRS rats than from controls. Increased intestinal epithelial permeability in stressed rats was confirmed by significantly greater fluxes of the inert radiolabeled probes, [3H]mannitol and 51Cr-labeled EDTA. No structural changes were observed. We conclude that acute stressors have profound effects on intestinal epithelial physiology, stimulating ion secretion and reducing barrier function.

Acute stressors stimulate ion secretion and increase epithelial permeability in rat intestine.

Enterohemorrhagic Escherichia coli O157:H7 (EHEC) is an enteric pathogen that causes potentially fatal symptoms after intimate adhesion, modulation of intestinal epithelial signal transduction, and alteration of epithelial function (eg, barrier disruption). Although the epithelial barrier is critical to gut homeostasis, only a few agents, such as transforming growth factor (TGF)-β, can enhance or protect epithelial barrier function. Our aims were to delineate the mechanism(s) behind TGF-β-induced barrier enhancement and to determine whether TGF-β could prevent EHEC-induced barrier disruption. Using monolayers of the human T84 colonic epithelial cell line, we found that TGF-β induced a significant increase in transepithelial electrical resistance (a measure of paracellular permeability) through activation of ERK MAPK and SMAD signaling pathways and up-regulation of the tight junction protein claudin-1. Additionally, TGF-β pretreatment of epithelia blocked the decrease in transepithelial electrical resistance and the increase in transepithelial passage of [3H]-mannitol caused by EHEC infection. EHEC infection was associated with reduced expression of zonula occludens-1, occludin, and claudin-2 (but not claudin-1 or claudin-4); TGF-β pretreatment prevented these changes. These studies provide insight into EHEC pathogenesis by illustrating the mechanisms underlying TGF-β-induced epithelial barrier enhancement and identifying TGF-β as an agent capable of blocking EHEC-induced increases in epithelial permeability via maintenance of claudin-2, occludin, and zonula occludens-1 levels.

Transforming Growth Factor-β Regulation of Epithelial Tight Junction Proteins Enhances Barrier Function and Blocks Enterohemorrhagic Escherichia coli O157:H7-Induced Increased Permeability

Derek M. McKay

Papers

Probiotics prevent bacterial translocation and improve intestinal barrier function in rats following chronic psychological stress

Glucagon-like peptide-2 enhances intestinal epithelial barrier function of both transcellular and paracellular pathways in the mouse

Corticotropin releasing hormone (CRH) regulates macromolecular permeability via mast cells in normal human colonic biopsies in vitro

Acute stressors stimulate ion secretion and increase epithelial permeability in rat intestine.

Transforming Growth Factor-β Regulation of Epithelial Tight Junction Proteins Enhances Barrier Function and Blocks Enterohemorrhagic Escherichia coli O157:H7-Induced Increased Permeability