Loss of Guanylyl Cyclase C (GCC) Signaling Leads to Dysfunctional Intestinal Barrier

Division of Gastroenterology, Cincinnati Children's Hospital Medical Center, Cincinnati, Ohio, United States of America.
PLoS ONE (Impact Factor: 3.23). 01/2011; 6(1):e16139. DOI: 10.1371/journal.pone.0016139
Source: PubMed


Guanylyl Cyclase C (GCC) signaling via uroguanylin (UGN) and guanylin activation is a critical mediator of intestinal fluid homeostasis, intestinal cell proliferation/apoptosis, and tumorigenesis. As a mechanism for some of these effects, we hypothesized that GCC signaling mediates regulation of intestinal barrier function.
Paracellular permeability of intestinal segments was assessed in wild type (WT) and GCC deficient (GCC-/-) mice with and without lipopolysaccharide (LPS) challenge, as well as in UGN deficient (UGN-/-) mice. IFNγ and myosin light chain kinase (MLCK) levels were determined by real time PCR. Expression of tight junction proteins (TJPs), phosphorylation of myosin II regulatory light chain (MLC), and STAT1 activation were examined in intestinal epithelial cells (IECs) and intestinal mucosa. The permeability of Caco-2 and HT-29 IEC monolayers, grown on Transwell filters was determined in the absence and presence of GCC RNA interference (RNAi). We found that intestinal permeability was increased in GCC-/- and UGN-/- mice compared to WT, accompanied by increased IFNγ levels, MLCK and STAT1 activation in IECs. LPS challenge promotes greater IFNγ and STAT1 activation in IECs of GCC-/- mice compared to WT mice. Claudin-2 and JAM-A expression were reduced in GCC deficient intestine; the level of phosphorylated MLC in IECs was significantly increased in GCC-/- and UGN-/- mice compared to WT. GCC knockdown induced MLC phosphorylation, increased permeability in IEC monolayers under basal conditions, and enhanced TNFα and IFNγ-induced monolayer hyperpermeability.
GCC signaling plays a protective role in the integrity of the intestinal mucosal barrier by regulating MLCK activation and TJ disassembly. GCC signaling activation may therefore represent a novel mechanism in maintaining the small bowel barrier in response to injury.

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    • "The paracellular permeability of intestinal segments was examined in wild-type, GC-C-deficient, or uroguanylin-deficient mice (80). The GC-C- or uroguanylin-deficient mice showed increased intestinal permeability compared to wild-type mice. "
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    ABSTRACT: The isolation of heat-stable enterotoxin (STa) from Escherichia coli and cholera toxin from Vibrio cholerae has increased our knowledge of specific mechanisms of action that could be used as pharmacological tools to understand the guanylyl cyclase-C and the adenylyl cyclase enzymatic systems. These discoveries have also been instrumental in increasing our understanding of the basic mechanisms that control the electrolyte and water balance in the gut, kidney, and urinary tracts under normal conditions and in disease. Herein, we review the evolution of genes of the guanylin family and STa genes from bacteria to fish and mammals. We also describe new developments and perspectives regarding these novel bacterial compounds and peptide hormones that act in electrolyte and water balance. The available data point toward new therapeutic perspectives for pathological features such as functional gastrointestinal disorders associated with constipation, colorectal cancer, cystic fibrosis, asthma, hypertension, gastrointestinal barrier function damage associated with enteropathy, enteric infection, malnutrition, satiety, food preferences, obesity, metabolic syndrome, and effects on behavior and brain disorders such as attention deficit, hyperactivity disorder, and schizophrenia.
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    • "Diminished production of epithelial cGMP due to loss of GC-C activity results in barrier dysfunction and tight junction disassembly during experimental systemic LPS exposure. In addition, there is an increase in circulating cytokines such as IFNγ in GC-C−/− mice relative to control animals [12]. Accordingly, we speculated that the GC-C−/− intestine may be more sensitive to some forms of pro-inflammatory stimuli. "
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    Full-text · Article · Nov 2013 · PLoS ONE
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    • "Unlike GC-C+/+ mice, animals lacking GC-C had a substantial loss of barrier function following 4 days of C. rodentium infection as indicated by increased serum FITC fluorescence relative to infected GC-C+/+ mice (Figure  5A). Claudin proteins are essential for tight junction stability and loss of specific claudin isoforms is associated with barrier dysfunction during C. rodentium infection [16,36-38]. Therefore, we selected two relevant claudin proteins, claudins 2 and 3, and determined their localization and expression levels in C. rodentium-infected wildtype and GC-C−/− mice at day 4 p.i. Colonic sections (Figure  5B), counter-stained with E-cadherin and DAPI, showed no genotype-dependent differences in cell membrane localization of either claudin 2 or claudin 3. Furthermore, immunoblotting demonstrated that each was present in similar quantities within the colon of GC-C+/+ and GC-C−/− mice (Figure  5C). "
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    ABSTRACT: Guanylate Cyclase C (GC-C) is an apically-oriented transmembrane receptor that is expressed on epithelial cells of the intestine. Activation of GC-C by the endogenous ligands guanylin or uroguanylin elevates intracellular cGMP and is implicated in intestinal ion secretion, cell proliferation, apoptosis, intestinal barrier function, as well as the susceptibility of the intestine to inflammation. Our aim was to determine if GC-C is required for host defense during infection by the murine enteric pathogen Citrobacter rodentium of the family Enterobacteriacea. GC-C+/+ control mice or those having GC-C genetically ablated (GC-C-/-) were administered C. rodentium by orogastric gavage and analyzed at multiple time points up to post-infection day 20. Commensal bacteria were characterized in uninfected GC-C+/+ and GC-C-/- mice using 16S rRNA PCR analysis. GC-C-/- mice had an increase in C. rodentium bacterial load in stool relative to GC-C+/+. C. rodentium infection strongly decreased guanylin expression in GC-C+/+ mice and, to an even greater degree, in GC-C-/- animals. Fluorescent tracer studies indicated that mice lacking GC-C, unlike GC-C+/+ animals, had a substantial loss of intestinal barrier function early in the course of infection. Epithelial cell apoptosis was significantly increased in GC-C-/- mice following 10 days of infection and this was associated with increased frequency and numbers of C. rodentium translocation out of the intestine. Infection led to significant liver histopathology in GC-C-/- mice as well as lymphocyte infiltration and elevated cytokine and chemokine expression. Relative to naive GC-C+/+ mice, the commensal microflora load in uninfected GC-C-/- mice was decreased and bacterial composition was imbalanced and included outgrowth of the Enterobacteriacea family. This work demonstrates the novel finding that GC-C signaling is an essential component of host defense during murine enteric infection by reducing bacterial load and preventing systemic dissemination of attaching/effacing-lesion forming bacterial pathogens such as C. rodentium.
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