Cell type-specific mechanisms coupling protease-activated receptor-1 to infectious colitis pathogenesis

BACKGROUND

Protease-activated receptor-1 (PAR-1) plays a major role in multiple disease processes, including colitis. Understanding the mechanisms coupling PAR-1 to disease pathogenesis is complicated by the fact that PAR-1 is broadly expressed across multiple cell types.

OBJECTIVE

Determine the specific contributions of PAR-1 expressed by macrophages and colonic enterocytes to infectious colitis.

METHODS

Mice carrying a conditional PAR-1 allele were generated and bred to mice expressing Cre recombinase in a myeloid- (PAR-1ΔM ) or enterocyte-specific (PAR-1ΔEPI ) fashion. Citrobacter rodentium colitis pathogenesis was analyzed in mice with global PAR-1 deletion (PAR-1-/- ) and cell type-specific deletions.

RESULTS

Constitutive deletion of PAR-1 had no significant impact on weight loss, crypt hypertrophy, crypt abscess formation, or leukocyte infiltration in Citrobacter colitis. However, colonic shortening was significantly blunted in infected PAR-1-/- mice, and these animals exhibited decreased local levels of IL-1β, IL-22, IL-6, and IL-17A. In contrast, infected PAR-1ΔM mice lost less weight and had fewer crypt abscesses relative to controls. PAR-1ΔM mice had diminished CD3+ T cell infiltration into colonic tissue, but macrophage and CD4+ T cell infiltration were similar to controls. Also contrasting results in global knockouts, PAR-1ΔM mice exhibited lower levels of IL-1β, but not Th17-related cytokines (ie, IL-22, IL-6, IL-17A). Infected PAR-1ΔEPI mice exhibited increased crypt hypertrophy and crypt abscess formation, but local cytokine elaboration was similar to controls.

CONCLUSIONS

These studies reveal complex, cell type-specific roles for PAR-1 in modulating the immune response to Citrobacter colitis that are not readily apparent in analyses limited to mice with global PAR-1 deficiency.

Protease-activated receptor-1 impedes prostate and intestinal tumor progression in mice

Essentials Protease activated receptor-1 (PAR-1) has been proposed to drive cancer progression. Surprisingly, PAR-1 deletion accelerated tumor progression in two distinct experimental settings. PAR-1 deletion was shown to limit the apoptosis of transformed epithelial cells. Thrombin- and activated protein C-mediated PAR-1 activation have unique effects on tumor cell biology. SUMMARY: Background Multiple studies have implicated protease-activated receptor-1 (PAR-1), a G-protein-coupled receptor activated by proteolytic cleavage of its N-terminus, as one target coupling thrombin-mediated proteolysis to tumor progression. Objective To analyze the role of PAR-1 in the setting of two distinct spontaneously developing tumor models in mice. Methods We interbred PAR-1-deficient mice with Transgenic Adenocarcinoma of the Mouse Prostate (TRAMP) mice, which spontaneously develop prostate tumors, and adenomatous polyposis coli Min (APCMin/+ ) mice, which spontaneously develop intestinal adenomas. Results Analyses of TRAMP mice with advanced disease (30 weeks) revealed that PAR-1 deficiency resulted in significantly larger and more aggressive prostate tumors. Prostates collected at an earlier time point (12 weeks of age) revealed that PAR-1 promotes apoptosis in transformed epithelia. In vitro analyses of TRAMP-derived cells revealed that activated protein C-mediated PAR-1 cleavage can induce tumor cell apoptosis, suggesting that tumor cell-intrinsic PAR-1 functions can limit tumor progression. Paralleling results in TRAMP mice, PAR-1-deficient APCMin/+ mice developed three-fold more adenomas than PAR-1-expressing mice, and the adenomas that formed were significantly larger. Moreover, loss of PAR-1 expression was shown to limit apoptosis in transformed intestinal epithelial cells. Conclusions Together, these results demonstrate a previously unrecognized role for PAR-1 in impeding tumor progression in vivo. These results also offer a cautionary note suggesting that long-term PAR-1 inhibition could increase malignancy risk in some contexts.

Enhanced survival following oral and systemic Salmonella enterica serovar Typhimurium infection in polymeric immunoglobulin receptor knockout mice

Background

Polymeric immunoglobulin receptor (pIgR) transport of secretory immunoglobulin A (SIgA) to mucosal surfaces is thought to promote gut integrity and immunity to Salmonella enterica serovar Typhimurium (S. Typhimurium), an invasive pathogen in mice. To elucidate potential mechanisms, we assessed intestinal barrier function and both oral and systemic S. Typhimurium virulence in pIgR knockout (KO) and wildtype (WT) mice.

Methods

In uninfected animals, we harvested jejunal segments for Ussing chamber analyses of transepithelial resistance (TER); mesenteric lymph nodes (mLN) for bacterial culture; and serum and stool for IgA. Separately, we infected mice either orally or intravenously (IV) with S. Typhimurium to compare colonization, tissue dynamics, and inflammation between KOs and WTs.

Results

Uninfected KOs displayed decreased TER and dramatically increased serum IgA and decreased fecal IgA vs. WT; however, KO mLNs yielded fewer bacterial counts. Remarkably, WTs challenged orally with S. Typhimurium exhibited increased splenomegaly, tissue colonization, and pro-inflammatory cytokines vs. pIgR KOs, which showed increased survival following either oral or IV infection.

Conclusions

Absence of pIgR compromises gut integrity but does not exacerbate bacterial translocation nor S. Typhimurium infection. These findings raise the possibility that immune adaptation to increased gut permeability and elevated serum IgA in the setting of SIgA deficiency provides compensatory protection against invasive gut pathogens.

NF-κB RelA renders tumor-associated macrophages resistant to and capable of directly suppressing CD8+ T cells for tumor promotion

Activation of the inflammatory transcription factor NF-κB in tumor-associated macrophages (TAMs) is assumed to contribute to tumor promotion. However, whether and how NF-κB drives the antitumor macrophages to become pro-tumorigenic have not been determined in any cancer type yet. Similarly, how TAMs repress CD8⁺ cytotoxic T lymphocytes (CTLs) remains largely unknown, although their importance in regulatory T (Treg) cell regulation and tumor promotion has been well appreciated. Here, using an endogenous lung cancer model we uncover a direct crosstalk between TAMs and CTLs. TAMs suppress CTLs through the T-cell inhibitory molecule B7x (B7-H4/B7S1) in a cell-cell contact manner, whereas CTLs kill TAMs in a tumor antigen-specific manner. Remarkably, TAMs secrete the known T-cell suppressive cytokine interleukin-10 (IL-10) to activate, but not to repress, CTLs. Notably, one major role of cell-intrinsic NF-κB RelA is to drive TAMs to suppress CTLs for tumor promotion. It induces B7x expression in TAMs directly, and restricts IL-10 expression indirectly by repressing expression of the NF-κB cofactor Bcl3 and subsequent Bcl3/NF-κB1-mediated transcription of IL-10. It also renders TAMs resistant to CTLs by up-regulating anti-apoptotic genes. These studies help understand how immunity is shaped in lung tumorigenesis, and suggest a RelA-targeted immunotherapy for this deadliest cancer.

Guanylate cyclase C reduces invasion of intestinal epithelial cells by bacterial pathogens

The guanylate cyclase C (GC-C) receptor regulates electrolyte and water secretion into the gut following activation by the E. coli enterotoxin STa, or by weaker endogenous agonists guanylin and uroguanylin. Our previous work has demonstrated that GC-C plays an important role in controlling initial infection as well as carrying load of non-invasive bacterial pathogens in the gut. Here, we use Salmonella enterica serovar Typhimurium to determine whether GC-C signaling is important in host defense against pathogens that actively invade enterocytes. In vitro studies indicated that GC-C signaling significantly reduces Salmonella invasion into Caco2-BBE monolayers. Relative to controls, GC-C knockout mice develop severe systemic illness following oral Salmonella infection, characterized by disrupted intestinal mucus layer, elevated cytokines and organ CFUs, and reduced animal survival. In Salmonella-infected wildtype mice, oral gavage of GC-C agonist peptide reduced host/pathogen physical interaction and diminished bacterial translocation to mesenteric lymph nodes. These studies suggest that early life susceptibility to STa-secreting enterotoxigenic E. coli may be counter-balanced by a critical role of GC-C in protecting the mucosa from non-STa producing, invasive bacterial pathogens.

Activation of TGF-β activated kinase 1 promotes colon mucosal pathogenesis in inflammatory bowel disease

The etiology and mechanisms for inflammatory bowel disease (IBD) are incompletely known. Determination of new, clinically important mechanisms for intestinal inflammation is imperative for developing effective therapies to treat IBD. We sought to define a widespread mechanism for colon mucosal inflammation via the activation of TGF‐β activated Kinase 1 (TAK1), a central regulator of cellular inflammatory actions. Activation of TAK1 and the downstream inflammatory signaling mediators was determined in pediatric patients with ulcerative colitis (UC) or Crohn's disease (CD) as well as in DSS‐induced and spontaneous IBD in mice. The role of TAK1 in facilitating intestinal inflammation in murine models of IBD was investigated by using (5Z)‐7‐Oxozeaenol, a highly selective pharmacological inhibitor of TAK1. We found hyper‐activation of TAK1 in patients with UC or CD and in murine models of IBD. Pharmacological inhibition of TAK1 prevented loss in body weight, disease activity, microscopic histopathology, infiltration of inflammatory cells in the colon mucosa, and elevated proinflammatory cytokine production in two murine models of IBD. We demonstrated that at the early phase of the disease activation of TAK1 is restricted in the epithelial cells. However, at a more advanced stage of the disease, TAK1 activation predominantly occurs in nonepithelial cells, especially in macrophages. These findings elucidate the activation of TAK1 as crucial in promoting intestinal inflammation. Thus, the TAK1 activation pathway may represent a suitable target to design new therapies for treating IBD in humans.

Guanylate cyclase 2C agonism corrects CFTR mutants

Cystic fibrosis (CF) is a genetic disorder in which epithelium-generated fluid flow from the lung, intestine, and pancreas is impaired due to mutations disrupting CF transmembrane conductance regulator (CFTR) channel function. CF manifestations of the pancreas and lung are present in the vast majority of CF patients, and 15% of CF infants are born with obstructed gut or meconium ileus. However, constipation is a significantly underreported outcome of CF disease, affecting 47% of the CF patients, and management becomes critical in the wake of increasing life span of CF patients. In this study, we unraveled a potentially novel molecular role of a membrane-bound cyclic guanosine monophosphate-synthesizing (cGMP-synthesizing) intestinal enzyme, guanylate cyclase 2C (GCC) that could be targeted to ameliorate CF-associated intestinal fluid deficit. We demonstrated that GCC agonism results in functional rescue of murine F508del/F508del and R117H/R117H Cftr and CFTR mutants in CF patient-derived intestinal spheres. GCC coexpression and activation facilitated processing and ER exit of F508del CFTR and presented a potentially novel rescue modality in the intestine, similar to the CF corrector VX-809. Our findings identify GCC as a biological CFTR corrector and potentiator in the intestine.

Thermoneutral housing exacerbates nonalcoholic fatty liver disease in mice and allows for sex-independent disease modeling

Nonalcoholic fatty liver disease (NAFLD), a common prelude to cirrhosis and hepatocellular carcinoma, is the most common chronic liver disease worldwide. Defining the molecular mechanisms underlying the pathogenesis of NAFLD has been hampered by a lack of animal models that closely recapitulate the severe end of the disease spectrum in humans, including bridging hepatic fibrosis. Here we demonstrate that a novel experimental model employing thermoneutral housing, as opposed to standard housing, resulted in lower stress-driven production of corticosterone, augmented mouse proinflammatory immune responses and markedly exacerbated high-fat diet (HFD)-induced NAFLD pathogenesis. Disease exacerbation at thermoneutrality was conserved across multiple mouse strains and was associated with augmented intestinal permeability, an altered microbiome and activation of inflammatory pathways that are associated with the disease in humans. Depletion of Gram-negative microbiota, hematopoietic cell deletion of Toll-like receptor 4 (TLR4) and inactivation of the IL-17 axis resulted in altered immune responsiveness and protection from thermoneutral-housing-driven NAFLD amplification. Finally, female mice, typically resistant to HFD-induced obesity and NAFLD, develop full disease characteristics at thermoneutrality. Thus, thermoneutral housing provides a sex-independent model of exacerbated NAFLD in mice and represents a novel approach for interrogation of the cellular and molecular mechanisms underlying disease pathogenesis.

Myeloid-derived NF-κB negative regulation of PU.1 and c/EBP-β-driven pro-inflammatory cytokine production restrains LPS-induced shock

Sepsis is a life-threatening event predominantly caused by Gram-negative bacteria. Bacterial infection causes a pronounced macrophage (MΦ) and dendritic cell activation that leads to excessive pro-inflammatory cytokine IL-1β, IL-6 and TNF-α production (cytokine storm), resulting in endotoxic shock. Previous experimental studies have revealed that inhibiting NF-κB signaling ameliorates disease symptoms; however, the contribution of myeloid p65 in endotoxic shock remains elusive. In this study, we demonstrate increased mortality in mice lacking p65 in the myeloid lineage (p65Δmye) compared with wild type mice upon ultra-pure LPS challenge. We show that increased susceptibility to LPS-induced shock was associated with elevated serum level of IL-1β and IL-6. Mechanistic analyses revealed that LPS-induced pro-inflammatory cytokine production was ameliorated in p65-deficient bone marrow-derived MΦs; however, p65-deficient 'activated' peritoneal MΦs exhibited elevated IL-1β and IL-6. We show that the elevated pro-inflammatory cytokine secretion was due, in part, to increased accumulation of IL-1β mRNA and protein in activated inflammatory MΦs. The increased IL-1β was linked with heightened binding of PU.1 and CCAAT/enhancer binding protein-β to Il1b and Il6 promoters in activated inflammatory MΦs. Our data provide insight into a role for NF-κB in the negative regulation of pro-inflammatory cytokines in myeloid cells.

Guanylin and uroguanylin are produced by mouse intestinal epithelial cells of columnar and secretory lineage

Guanylin (GN) and uroguanylin (UGN), through activation of guanylyl cyclase C (GCC), serve to control intestinal fluid homeostasis. Both peptides are produced in the intestinal epithelium, but their cellular origin has not been fully charted. Using quantitative PCR and an improved in situ hybridization technique (RNAscope), we have assessed the expression of GN (Guca2a), UGN (Guca2b), and GCC (Gucy2c) in mouse intestine. In the crypts of Lieberkühn, expression of Guca2a and Guca2b was restricted to cells of secretory lineage, at the crypt's base, and to a region above, previously identified as a common origin of cellular differentiation. In this compartment, comparatively uniform levels of Guca2a and Guca2b expression were observed throughout the length of the gut. In contrast, Guca2a and Guca2b expression in the villus-surface region was more variable, and reflected the distinct, but overlapping expression pattern observed previously. Accordingly, in jejunum and ileum, Guca2a and Guca2b were abundantly expressed by enterocytes, whereas in colon only Guca2a transcript was found in the surface region. In duodenum, only low levels of Guca2b transcript were observed in columnar cells, and Guca2a expression was restricted entirely to cells of the secretory lineage. Gucy2c was shown to be expressed relatively uniformly along the rostrocaudal and crypt-villus axes and was also found in the duodenal glands. Our study reveals novel aspects of the cellular localization of the GCC signaling axis that, apart from its role in the regulation of fluid balance, link it to pH regulation, cell cycle control, and host defense.

Effect of guanylate cyclase-C activity on energy and glucose homeostasis

Uroguanylin is a gastrointestinal hormone primarily involved in fluid and electrolyte handling. It has recently been reported that prouroguanylin, secreted postprandially, is converted to uroguanylin in the brain and activates the receptor guanylate cyclase-C (GC-C) to reduce food intake and prevent obesity. We tested central nervous system administration of two GC-C agonists and found no significant reduction of food intake. We also carefully phenotyped mice lacking the GC-C receptor and found them to have normal body weight, adiposity, and glucose tolerance. Interestingly, uroguanylin knockout mice had a small but significant increase in body weight and adiposity that was accompanied by glucose intolerance. Our data indicate that the modest effects of uroguanylin on energy and glucose homeostasis are not mediated by central GC-C receptors.

IL-17 signaling accelerates the progression of nonalcoholic fatty liver disease in mice

Inflammation plays a central pathogenic role in the pernicious metabolic and end-organ sequelae of obesity. Among these sequelae, nonalcoholic fatty liver disease (NAFLD) has become the most common chronic liver disease in the developed world. The twinned observations that obesity is associated with increased activation of the interleukin (IL)-17 axis and that this axis can regulate liver damage in diverse contexts prompted us to address the role of IL-17RA signaling in the progression of NAFLD. We further examined whether microbe-driven IL-17A regulated NAFLD development and progression. We show here that IL-17RA(-/-) mice respond to high-fat diet stress with significantly greater weight gain, visceral adiposity, and hepatic steatosis than wild-type controls. However, obesity-driven lipid accumulation was uncoupled from its end-organ consequences in IL-17RA(-/-) mice, which exhibited decreased steatohepatitis, nicotinamide adenine dinucleotide phosphate (NADPH)-oxidase enzyme expression, and hepatocellular damage. Neutralization of IL-17A significantly reduced obesity-driven hepatocellular damage in wild-type mice. Further, colonization of mice with segmented filamentous bacteria (SFB), a commensal that induces IL-17A production, exacerbated obesity-induced hepatocellular damage. In contrast, SFB depletion protected from obesity-induced hepatocellular damage.

CONCLUSION

These data indicate that obesity-driven activation of the IL-17 axis is central to the development and progression of NAFLD to steatohepatitis and identify the IL-17 pathway as a novel therapeutic target in this condition.

Thrombin drives tumorigenesis in colitis-associated colon cancer

The established association between inflammatory bowel disease and colorectal cancer underscores the importance of inflammation in colon cancer development. On the basis of evidence that hemostatic proteases are powerful modifiers of both inflammatory pathologies and tumor biology, gene-targeted mice carrying low levels of prothrombin were used to directly test the hypothesis that prothrombin contributes to tumor development in colitis-associated colon cancer (CAC). Remarkably, imposing a modest 50% reduction in circulating prothrombin in fII+/- mice, a level that carries no significant bleeding risk, dramatically decreased adenoma formation following an azoxymethane/dextran sodium sulfate challenge. Similar results were obtained with pharmacologic inhibition of prothrombin expression or inhibition of thrombin proteolytic activity. Detailed longitudinal analyses showed that the role of thrombin in tumor development in CAC was temporally associated with the antecedent inflammatory colitis. However, direct studies of the antecedent colitis showed that mice carrying half-normal prothrombin levels were comparable to control mice in mucosal damage, inflammatory cell infiltration, and associated local cytokine levels. These results suggest that thrombin supports early events coupled to inflammation-mediated tumorigenesis in CAC that are distinct from overall inflammation-induced tissue damage and inflammatory cell trafficking. That prothrombin is linked to early events in CAC was strongly inferred by the observation that prothrombin deficiency dramatically reduced the formation of very early, precancerous aberrant crypt foci. Given the importance of inflammation in the development of colon cancer, these studies suggest that therapeutic interventions at the level of hemostatic factors may be an effective means to prevent and/or impede colitis-associated colon cancer progression.

Guanylate cyclase C deficiency causes severe inflammation in a murine model of spontaneous colitis

Background

Guanylate Cyclase C (GC-C; Gucy2c) is a transmembrane receptor expressed in intestinal epithelial cells. Activation of GC-C by its secreted ligand guanylin stimulates intestinal fluid secretion. Familial mutations in GC-C cause chronic diarrheal disease or constipation and are associated with intestinal inflammation and infection. Here, we investigated the impact of GC-C activity on mucosal immune responses.

Methods

We utilized intraperitoneal injection of lipopolysaccharide to elicit a systemic cytokine challenge and then measured pro-inflammatory gene expression in colonic mucosa. GC-C^+/+ and GC-C^−/− mice were bred with interleukin (IL)-10 deficient animals and colonic inflammation were assessed. Immune cell influx and cytokine/chemokine expression was measured in the colon of wildtype, IL-10^−/−, GC-C^+/+IL-10^−/− and GC-C^−/−IL-10^−/− mice. GC-C and guanylin production were examined in the colon of these animals and in a cytokine-treated colon epithelial cell line.

Results

Relative to GC-C^+/+ animals, intraperitoneal lipopolysaccharide injection into GC-C^−/− mice increased proinflammatory gene expression in both whole colon tissue and in partially purified colonocyte isolations. Spontaneous colitis in GC-C^−/−IL-10^−/− animals was significantly more severe relative to GC-C^+/+IL-10^−/− mice. Unlike GC-C^+/+IL-10^−/− controls, colon pathology in GC-C^−/−IL-10^−/− animals was apparent at an early age and was characterized by severely altered mucosal architecture, crypt abscesses, and hyperplastic subepithelial lesions. F4/80 and myeloperoxidase positive cells as well as proinflammatory gene expression were elevated in GC-C^−/−IL-10^−/− mucosa relative to control animals. Guanylin was diminished early in colitis in vivo and tumor necrosis factor α suppressed guanylin mRNA and protein in intestinal goblet cell-like HT29-18-N2 cells.

Conclusions

The GC-C signaling pathway blunts colonic mucosal inflammation that is initiated by systemic cytokine burst or loss of mucosal immune cell immunosuppression. These data as well as the apparent intestinal inflammation in human GC-C mutant kindred underscore the importance of GC-C in regulating the response to injury and inflammation within the gut.

Immunosuppressive CD71+ erythroid cells compromise neonatal host defence against infection

Newborn infants are highly susceptible to infection. This defect in host defence has generally been ascribed to the immaturity of neonatal immune cells; however, the degree of hyporesponsiveness is highly variable and depends on the stimulation conditions. These discordant responses illustrate the need for a more unified explanation for why immunity is compromised in neonates. Here we show that physiologically enriched CD71(+) erythroid cells in neonatal mice and human cord blood have distinctive immunosuppressive properties. The production of innate immune protective cytokines by adult cells is diminished after transfer to neonatal mice or after co-culture with neonatal splenocytes. Neonatal CD71(+) cells express the enzyme arginase-2, and arginase activity is essential for the immunosuppressive properties of these cells because molecular inhibition of this enzyme or supplementation with L-arginine overrides immunosuppression. In addition, the ablation of CD71(+) cells in neonatal mice, or the decline in number of these cells as postnatal development progresses parallels the loss of suppression, and restored resistance to the perinatal pathogens Listeria monocytogenes and Escherichia coli. However, CD71(+) cell-mediated susceptibility to infection is counterbalanced by CD71(+) cell-mediated protection against aberrant immune cell activation in the intestine, where colonization with commensal microorganisms occurs swiftly after parturition. Conversely, circumventing such colonization by using antimicrobials or gnotobiotic germ-free mice overrides these protective benefits. Thus, CD71(+) cells quench the excessive inflammation induced by abrupt colonization with commensal microorganisms after parturition. This finding challenges the idea that the susceptibility of neonates to infection reflects immune-cell-intrinsic defects and instead highlights processes that are developmentally more essential and inadvertently mitigate innate immune protection. We anticipate that these results will spark renewed investigation into the need for immunosuppression in neonates, as well as improved strategies for augmenting host defence in this vulnerable population.

Guanylate cyclase C limits systemic dissemination of a murine enteric pathogen

Background

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.

Methods

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.

Results

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 naïve 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.

Conclusions

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.

Intestinal CCL11 and eosinophilic inflammation is regulated by myeloid cell-specific RelA/p65 in mice

In inflammatory bowel diseases (IBDs), particularly ulcerative colitis, intestinal macrophages (MΦs), eosinophils, and the eosinophil-selective chemokine CCL11, have been associated with disease pathogenesis. MΦs, a source of CCL11, have been reported to be of a mixed classical (NF-κB-mediated) and alternatively activated (STAT-6-mediated) phenotype. The importance of NF-κB and STAT-6 pathways to the intestinal MΦ/CCL11 response and eosinophilic inflammation in the histopathology of experimental colitis is not yet understood. Our gene array analyses demonstrated elevated STAT-6- and NF-κB-dependent genes in pediatric ulcerative colitis colonic biopsies. Dextran sodium sulfate (DSS) exposure induced STAT-6 and NF-κB activation in mouse intestinal F4/80(+)CD11b(+)Ly6C(hi) (inflammatory) MΦs. DSS-induced CCL11 expression, eosinophilic inflammation, and histopathology were attenuated in RelA/p65(Δmye) mice, but not in the absence of STAT-6. Deletion of p65 in myeloid cells did not affect inflammatory MΦ recruitment or alter apoptosis, but did attenuate LPS-induced cytokine production (IL-6) and Ccl11 expression in purified F4/80(+)CD11b(+)Ly6C(hi) inflammatory MΦs. Molecular and cellular analyses revealed a link between expression of calprotectin (S100a8/S100a9), Ccl11 expression, and eosinophil numbers in the DSS-treated colon. In vitro studies of bone marrow-derived MΦs showed calprotectin-induced CCL11 production via a p65-dependent mechanism. Our results indicate that myeloid cell-specific NF-κB-dependent pathways play an unexpected role in CCL11 expression and maintenance of eosinophilic inflammation in experimental colitis. These data indicate that targeting myeloid cells and NF-κB-dependent pathways may be of therapeutic benefit for the treatment of eosinophilic inflammation and histopathology in IBD.

Murine guanylate cyclase C regulates colonic injury and inflammation

Guanylate cyclase C (GUCY2C or GC-C) and its ligands, guanylin (GUCA2A or Gn) and uroguanylin (GUCA2B or Ugn), are expressed in intestinal epithelial cells and regulate ion secretion, intestinal barrier function, and epithelial monolayer homeostasis via cGMP-dependent signaling pathways. The aim of this study was to determine whether GC-C and its ligands direct the course of intestinal inflammation. In this article, we show that dextran sodium sulfate (DSS)-induced clinical disease and histological damage to the colonic mucosa were significantly less severe in GC-C(-/-) mice and moderately reduced in Gn(-/-) animals. Relative to wild-type controls, GC-C(-/-) and Gn(-/-) mice had reduced apoptosis and increased proliferation of intestinal epithelial cells during DSS colitis. Basal and DSS-induced production of resistin-like molecule β (RELMβ) was substantially diminished in GC-C(-/-) mice. RELMβ is thought to stimulate cytokine production in macrophages in this disease model and, consistent with this, TNF-α and IFN-γ production was minimal in GC-C(-/-) animals. RELMβ and cytokine levels were similar to wild-type in Gn(-/-) mice, however. Colonic instillation of recombinant RELMβ by enema into GC-C(-/-) mice restores sensitivity to DSS-mediated mucosal injury. These findings demonstrate a novel role for GC-C signaling in facilitating mucosal wounding and inflammation, and further suggest that this may be mediated, in part, through control of RELMβ production.

Interleukin-13 (IL-13)/IL-13 receptor alpha1 (IL-13Ralpha1) signaling regulates intestinal epithelial cystic fibrosis transmembrane conductance regulator channel-dependent Cl- secretion

Interleukin-13 (IL-13) has been linked to the pathogenesis of inflammatory diseases of the gastrointestinal tract. It is postulated that IL-13 drives inflammatory lesions through the modulation of both hematopoietic and nonhematopoietic cell function in the intestine. To delineate the relevant contribution of elevated levels of intestinal IL-13 to intestinal structure and function, we generated an intestinal IL-13 transgenic mouse (iIL-13Tg). We show that constitutive overexpression of IL-13 in the small bowel induces modification of intestinal epithelial architecture (villus blunting, goblet cell hyperplasia, and increased epithelial proliferation) and epithelial function (altered basolateral → apical Cl(-) ion conductance). Pharmacological analyses in vitro and in vivo determined that elevated Cl(-) conductance is mediated by altered cystic fibrosis transmembrane conductance regulator expression and activity. Generation of iIL-13Tg/Il13rα1(-/-), iIL-13Tg/Il13rα2(-/-), and iIL-13Tg/Stat6(-/-) mice revealed that IL-13-mediated dysregulation of epithelial architecture and Cl(-) conductance is dependent on IL-13Rα1 and STAT-6. These observations demonstrate a central role for the IL-13/IL-13Rα1 pathway in the regulation of intestinal epithelial cell Cl(-) secretion via up-regulation of cystic fibrosis transmembrane conductance regulator, suggesting an important role for this pathway in secretory diarrhea.

Loss of guanylyl cyclase C (GCC) signaling leads to dysfunctional intestinal barrier

Background

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.

Methodology/Principal Findings

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.

Conclusions/Significance

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.

Colitis-associated cancer is dependent on the interplay between the hemostatic and inflammatory systems and supported by integrin alpha(M)beta(2) engagement of fibrinogen

A link between colitis and colon cancer is well established, but the mechanisms regulating inflammation in this context are not fully defined. Given substantial evidence that hemostatic system components are powerful modulators of both inflammation and tumor progression, we used gene-targeted mice to directly test the hypothesis that the coagulation factor fibrinogen contributes to colitis-associated colon cancer in mice. This fundamental provisional matrix protein was found to be an important determinant of colon cancer. Fibrinogen deficiency resulted in a dramatic diminution in the number of colonic adenomas formed following azoxymethane/dextran sodium sulfate challenge. More detailed analyses in mice expressing a mutant form of fibrinogen that retains clotting function, but lacks the leukocyte integrin receptor alpha(M)beta(2) binding motif (Fibgamma(390-396A)), revealed that alpha(M)beta(2)-mediated engagement of fibrin(ogen) is mechanistically coupled to local inflammatory processes (e.g., interleukin-6 elaboration) and epithelial alterations that contribute to adenoma formation. Consistent with these findings, the majority of Fibgamma(390-396A) mice developed no discernable adenomas, whereas penetrance was 100% in controls. Furthermore, the adenomas harvested from Fibgamma(390-396A) mice were significantly smaller than those from control mice and less proliferative based on quantitative analyses of mitotic indices, suggesting an additional role for fibrin(ogen) in the growth of established adenomas. These studies show, for the first time, a unique link between fibrin(ogen) and the development of inflammation-driven malignancy. Given the importance of antecedent inflammation in the progression of numerous cancers, these studies suggest that therapies targeting fibrin(ogen)-alpha(M)beta(2) interactions may be useful in preventing and/or treating this important subset of malignancies.

Loss of epithelial RelA results in deregulated intestinal proliferative/apoptotic homeostasis and susceptibility to inflammation

NF-kappaB plays a central, proinflammatory role in chronic intestinal inflammation, yet recent work suggests a predominantly protective function for this transcription factor group in some cell types of the intestine. We herein describe the conditional deletion of the NF-kappaB RelA gene in murine intestinal epithelia and determine its function in homeostatic control of enterocyte proliferation/apoptosis and susceptibility to colonic inflammation. Mice lacking RelA in ileal and colonic enterocytes were born in expected Mendelian ratios, and RelA-null epithelia differentiated normally. Spontaneous intestinal disease and death occurred with low penetrance in neonates lacking epithelial RelA. IkappaBalpha and IkappaBbeta were significantly diminished in RelA-null epithelia, and endotoxin challenge revealed elevated p50 and c-Rel DNA binding activity as compared with controls. Deletion of RelA resulted in diminished expression of antimicrobial (defensin-related cryptdin 4, defensin-related cryptdin 5, RegIIIgamma) and antiapoptotic, prorestitution genes (Bcl-x(L), RegIV, IL-11, IL-18), and basal rates of epithelial apoptosis and proliferation were elevated. Mice lacking colonic RelA were sensitive to dextran sodium sulfate-induced colitis. Although experimental colitis enhanced proliferation in cells lacking RelA, sustained epithelial cell apoptosis precluded mucosal healing and decreased animal survival. We conclude that activation of RelA is required for homeostatic regulation of cell death and division in intestinal epithelia, as well as for protection from development of severe, acute inflammation of the intestine.

Molecular cloning and promoter analysis of downregulated in adenoma (DRA)

Downregulated in adenoma (DRA), also referred to as SLC26A3, is an intestinal anion transporter essential for intestinal chloride absorption. Mutations in DRA result in congenital chloride diarrhea. DRA expression has been shown to be induced by differentiation and to be modulated by cytokines. However, mechanisms of DRA gene transcription and its tissue-specific targeting have not yet been investigated. In this study, we cloned a 3,765-bp promoter fragment of human DRA gene and characterized its activity in human colonic LS174T and Caco-2 human colon cell lines. Primer extension identified a single transcriptional initiation site that was identical in both colon cancer cell lines and normal colon. Although hepatic nuclear factor HNF-4 is involved in the basal activity of DRA promoter, sodium butyrate induces its activity in LS174T cells via the binding of Yin Yang 1 (YY1) and GATA transcription factors to their respective cis-elements in promoter region. We also demonstrated a reduction in DRA promoter activity in Caco-2 cells by IFN-gamma, suggesting that regulation of DRA promoter by IFN-gamma may contribute to the pathophysiology of intestinal inflammation. Furthermore, we showed that the DRA promoter fragment is sufficient to drive human growth hormone transgene expression specifically in villus epithelial cells of the small intestine and in differentiated upper crypt and surface epithelial cells of the colon. Our studies provide evidence for the involvement of HNF-4, YY1, and GATA transcription factors in DRA expression in intestinal differentiated epithelial cells.

Novel mechanism of cyclic AMP mediated extracellular signal regulated kinase activation in an intestinal cell line

The extracellular signal regulated kinase (ERK1/2) signaling cascade has been implicated as both a pro-apoptotic and anti-apoptotic pathway depending on cell type and context. In the T84 intestinal epithelial cell line, cAMP activates ERK1/2 resulting in the inhibition of apoptosis. Cyclic-AMP signaling relies on the binding and activation of a cAMP binding protein. In most cell types, the majority of this signaling occurs through an isoform of protein kinase A (PKAI or PKAII). Despite evidence to the contrary, we hypothesized that ERK1/2 activation is through a PKA isoform. Pharmacological activators and inhibitors of PKA as well as siRNA were used to further interrogate this potential signaling pathway. Our results demonstrate that at doses sufficient to increase PKA activity, PKAII specific cAMP analogs activate ERK1/2 while PKAI analogs do not. Pharmacological inhibition of the PKAII regulatory subunit and catalytic subunit as well as siRNA knockdown of the catalytic subunit blocks ERK1/2 activation. We conclude that in the T84 cell line, cAMP binding to the PKAII regulatory subunit leads to the subsequent phosphorylation of ERK1/2 and provides insight into the mechanism of cAMP mediated survival signaling in the intestinal epithelium. These results directly implicate PKAII as a mediator of cell survival in T84 cells and provide evidence for an additional means by which cAMP can influence intestinal cell turnover.

Wound-induced p38MAPK-dependent histone H3 phosphorylation correlates with increased COX-2 expression in enterocytes

Gastrointestinal epithelial cell damage triggers an important biological response called restitution, a process aimed at re-epithelializing the wounded areas. Unfortunately, little is known about the intrinsic molecular signaling events implicated in this host response. We hypothesized that wounding intestinal epithelial cells activates signaling pathways leading to chromatin modification and COX-2 upregulation during restitution. Confluent rat IEC18 cells were mechanically wounded by multiple parallel scratches using a pipet tip. NF-kappaB(Ser536), p38, and histone H3(Ser10) (H3S10) phosphorylation were determined by Western blot using specific phospho-antibodies. COX-2 gene expression was evaluated by RT-PCR, Western Blot, and ELISA. Association of phosphorylated H3, RelA (NF-kappaB), and RNA polymerase II to the COX-2 gene promoter was evaluated by chromatin immunoprecipitation (ChIP). The specific inhibitors Bay11-7082 and SB239063 as well as Ad5IkappaB-superrepressor (Ad5IkappaBAA) and Ad5dnp38 were used to block NF-kappaB- and p38-signaling pathways, respectively. Wounding induced a rapid and sustained (24 h) phosphorylation of RelAS536, H3S10, and p38MAPK in enterocytes. ChIP analysis of the COX-2 gene promoter demonstrated the presence of phospho-H3S10 and recruitment of RelA and RNA polymerase II, a process blocked by SB239063. Finally, molecular blockade of NF-kappaB (Ad5IkappaBAA) or p38MAPK (Ad5dnp38) signaling strongly inhibited enterocyte restitution. p38MAPK-dependent histone 3 phosphorylation is an important component of the intestinal wound-healing response. Targeting-signaling pathways selectively involved in healing/restitution may provide a novel means to maintain or re-establish host intestinal barrier integrity.

Glycogen synthase kinase 3beta functions to specify gene-specific, NF-kappaB-dependent transcription

Loss of glycogen synthase kinase 3beta (GSK-3beta) in mice results in embryonic lethality via hepatocyte apoptosis. Consistent with this result, cells from these mice have diminished nuclear factor kappaB (NF-kappaB) activity, implying a functional role for GSK-3beta in regulating NF-kappaB. Here, we have explored mechanisms by which GSK-3beta may control NF-kappaB function. We show that cytokine-induced IkappaB kinase activity and subsequent phosphorylation of IkappaBalpha, p105, and p65 are not affected by the absence of GSK-3beta activity. Furthermore, nuclear accumulation of p65 following tumor necrosis factor treatment is unaffected by the loss of GSK-3beta. However, NF-kappaB DNA binding activity is reduced in GSK-3beta null cells and in cells treated with a pharmacological inhibitor of GSK-3. Expression of certain NF-kappaB-regulated genes, such as IkappaBalpha and macrophage inflammatory protein 2, is minimally affected by the absence of GSK-3beta. Conversely, we have identified a subset of NF-kappaB-regulated genes, including those for interleukin-6 and monocyte chemoattractant protein 1, that require GSK-3beta for efficient expression. We show that efficient localization of p65 to the promoter regions of the interleukin-6 and monocyte chemoattractant protein 1 genes following tumor necrosis factor alpha treatment requires GSK-3beta. Therefore, GSK-3beta has profound effects on transcription in a gene-specific manner through a mechanism involving control of promoter-specific recruitment of NF-kappaB.

Lack of guanylyl cyclase C, the receptor for Escherichia coli heat-stable enterotoxin, results in reduced polyp formation and increased apoptosis in the multiple intestinal neoplasia (Min) mouse model

Guanylyl cyclase C (GC-C), a transmembrane receptor for bacterial heat-stable enterotoxin and the mammalian peptides guanylin and uroguanylin, mediates intestinal ion secretion and affects intestinal cell growth via cyclic GMP signaling. In intestinal tumors, GC-C expression is maintained while guanylin and uroguanylin expression is lost, suggesting a role for GC-C activation in tumor formation or growth. We show by in situ hybridization that GC-C expression is retained in adenomas from multiple intestinal neoplasia (Apc(Min/+)) mice. In order to determine the in vivo role of GC-C in intestinal tumorigenesis, we generated Apc(Min/+) mice homozygous for a targeted deletion of the gene encoding GC-C and hypothesized that these mice would have increased tumor multiplicity and size compared to wild-type Apc(Min/+) mice on the same genetic background. In contrast, the absence of GC-C resulted in a reduction of median polyp number by 55%. There was no change in the median diameter of polyps, suggesting no effect on tumor growth. Somatic loss of the wild-type Apc allele, an initiating event in intestinal tumorigenesis, also occurred in polyps from GC-C-deficient Apc(Min/+) mice. We have found increased levels of apoptosis as well as increased caspase-3 and caspase-7 gene expression in the intestines of GC-C-deficient Apc(Min/+) mice compared with Apc(Min/+) mice. We propose that these alterations are a possible compensatory mechanism by which loss of GC-C signaling also affects tumorigenesis.

Effect of secretagogues and pH on intestinal transport in guanylin-deficient mice

The small and large intestine secrete guanylin, a peptide homologous to heat stable enterotoxin (STa) elaborated by enterotoxigenic Escherichia coli. Guanylin's role in intestinal electrolyte transport was investigated in guanylin-deficient knockout mice and heterozygous littermate controls. Segments of mid-jejunum, distal ileum, and proximal and distal colon were studied in Ussing chambers in HCO3- Ringer under short circuit conditions. We found that (1) under basal conditions, all segments in control and knockout mice absorb Na+, and the knockout mouse proximal colon secretes Cl-; (2) all segments except the jejunum of knockout mice respond by increasing absorption in response to reductions in pH from 7.6 to 7.1; (3) all segments exhibit decreased absorption in response to 1 mM cAMP; (4) the jejunum and ileum of knockout and control mice, and the proximal colon of control mice (but not knockout mice) respond to the mucosal addition of 50 nM STa with decreases in absorption; and (5) mucosal guanylin caused similar decreases in proximal colon absorption in control and guanylin-deficient mice. These findings suggest that guanylin deficiency causes basal Cl- secretion and reduced responsiveness to STa in mouse proximal colon. The effectiveness of guanylin in this segment suggests a difference in the intestinal secretory actions of STa and guanylin.

A nucleosomal function for IkappaB kinase-alpha in NF-kappaB-dependent gene expression

NF-kappaB is a principal transcriptional regulator of diverse cytokine-mediated processes and is tightly controlled by the IkappaB kinase complex (IKK-alpha/beta/gamma). IKK-beta and IKK-gamma are critical for cytokine-induced NF-kappaB function, whereas IKK-alpha is thought to be involved in other regulatory pathways. However, recent data suggest a role for IKK-alpha in NF-kappaB-dependent gene expression in response to cytokine treatment. Here we demonstrate nuclear accumulation of IKK-alpha after cytokine exposure, suggesting a nuclear function for this protein. Consistent with this, chromatin immunoprecipitation (ChIP) assays reveal that IKK-alpha was recruited to the promoter regions of NF-kappaB-regulated genes on stimulation with tumour-necrosis factor-alpha. Notably, NF-kappaB-regulated gene expression is suppressed by the loss of IKK-alpha and this correlates with a complete loss of gene-specific phosphorylation of histone H3 on serine 10, a modification previously associated with positive gene expression. Furthermore, we show that IKK-alpha can directly phosphorylate histone H3 in vitro, suggesting a new substrate for this kinase. We propose that IKK-alpha is an essential regulator of NF-kappaB-dependent gene expression through control of promoter-associated histone phosphorylation after cytokine exposure. These findings provide additional insight into the role of the IKK complex in NF-kappaB-regulated gene expression.

Coordinate upregulation of guanylin and uroguanylin expression by hypertonicity in HT29-18-N2 cells

Guanylin and uroguanylin are particulate guanylate cyclase-activating peptides that are secreted from the epithelia of the intestine, kidney, pancreas, and salivary gland. These peptides elicit chloride and bicarbonate secretion via the cystic fibrosis transmembrane conductance regulator. To test the hypothesis that hypertonicity mediates an increase in guanylin and uroguanylin mRNA, we subjected HT29-18-N2 to osmotic stress. Guanylin and uroguanylin RNA were increased substantially in the presence of hypertonicity but only with solutes that were relatively impermeable to the cell membrane. This hypertonicity-mediated increase was transcriptional and did not require protein synthesis. Herbimycin A and mitogen-activated protein kinase inhibitors SB-203580 and PD-98059 had no effect on basal or induced levels of guanylin or uroguanylin. Both staurosporine and prolonged exposure to phorbol ester reduced basal levels and completely blocked hypertonicity-related increases in guanylin or uroguanylin RNA. These data suggest that serine/theonine protein kinases, possibly protein kinase C (PKC), mediate the hypertonicity-associated increase in guanylin and uroguanylin RNA. We conclude that guanylin and uroguanylin are released in response to hypertonic stress and that regulation of these genes may be mediated by PKC isoforms.

Targeted inactivation of the mouse guanylin gene results in altered dynamics of colonic epithelial proliferation

Heat-stable enterotoxin (STa), elaborated by enterotoxigenic Echerichia coli, is a worldwide cause of secretory diarrhea in infants and travelers. Both STa and guanylin, a peptide structurally similar to STa, increase intracellular cGMP levels after binding to the same intestinal receptor, guanylate cyclase C (GC-C). Distinct from its role as an intestinal secretagogue, guanylin may also have a role in intestinal proliferation, as guanylin expression is lost in intestinal adenomas. To determine the function of guanylin in intestinal epithelia, guanylin null mice were generated using a Cre/loxP-based targeting vector. Guanylin null mice grew normally, were fertile and showed no signs of malabsorption. However, the levels of cGMP in colonic mucosa of guanylin null mice were significantly reduced. The colonic epithelial cell migration rate was increased and increased numbers of colonocytes expressing proliferating cell nuclear antigen (PCNA) were present in crypts of guanylin null mice as well. The apoptotic index was similar in guanylin null mice and littermate controls. We conclude from these studies that loss of guanylin results in increased proliferation of colonic epithelia. We speculate that the increase in colonocyte number is related to decreased levels of cGMP and that this increase in proliferation plays a role in susceptibility to intestinal adenoma formation and/or progression.

Novel genes and functional relationships in the adult mouse gastrointestinal tract identified by microarray analysis

BACKGROUND & AIMS

A genome-level understanding of the molecular basis of segmental gene expression along the anterior-posterior (A-P) axis of the mammalian gastrointestinal (GI) tract is lacking. We hypothesized that functional patterning along the A-P axis of the GI tract could be defined at the molecular level by analyzing expression profiles of large numbers of genes.

METHODS

Incyte GEM1 microarrays containing 8638 complementary DNAs (cDNAs) were used to define expression profiles in adult mouse stomach, duodenum, jejunum, ileum, cecum, proximal colon, and distal colon. Highly expressed cDNAs were classified based on segmental expression patterns and protein function.

RESULTS

571 cDNAs were expressed 2-fold higher than reference in at least 1 GI tissue. Most of these genes displayed sharp segmental expression boundaries, the majority of which were at anatomically defined locations. Boundaries were particularly striking for genes encoding proteins that function in intermediary metabolism, transport, and cell-cell communication. Genes with distinctive expression profiles were compared with mouse and human genomic sequence for promoter analysis and gene discovery.

CONCLUSIONS

The anatomically defined organs of the GI tract (stomach, small intestine, colon) can be distinguished based on a genome-level analysis of gene expression profiles. However, distinctions between various regions of the small intestine and colon are much less striking. We have identified novel genes not previously known to be expressed in the adult GI tract. Identification of genes coordinately regulated along the A-P axis provides a basis for new insights and gene discovery relevant to GI development, differentiation, function, and disease.

Increases in guanylin and uroguanylin in a mouse model of osmotic diarrhea are guanylate cyclase C-independent

BACKGROUND & AIMS

Guanylin and uroguanylin are peptide hormones that are homologous to the diarrhea-causing Escherichia coli enterotoxins. These secretagogues are released from the intestinal epithelia into the intestinal lumen and systemic circulation and bind to the receptor guanylate cyclase C (GC-C). We hypothesized that a hypertonic diet would result in osmotic diarrhea and cause a compensatory down-regulation of guanylin/uroguanylin.

METHODS

Gut-to-carcass weights were used to measure fluid accumulation in the intestine. Northern and/or Western analysis was used to determine the levels of guanylin, uroguanylin, and GC-C in mice with osmotic diarrhea.

RESULTS

Wild-type mice fed a polyethylene glycol or lactose-based diet developed weight loss, diarrhea, and an increased gut-to-carcass ratio. Unexpectedly, 2 days on either diet resulted in increased guanylin/uroguanylin RNA and prohormone throughout the intestine, elevated uroguanylin RNA, and prohormone levels in the kidney and increased levels of circulating prouroguanylin. GC-C-deficient mice given the lactose diet reacted with higher gut-to-carcass ratios. Although they did not develop diarrhea, GC-C-sufficient and -deficient mice on the lactose diet responded with elevated levels of guanylin and uroguanylin RNA and protein. A polyethylene glycol drinking water solution resulted in diarrhea, higher gut-to-carcass ratios, and induction of guanylin and uroguanylin in both GC-C heterozygous and null animals.

CONCLUSIONS

We conclude that this model of osmotic diarrhea results in a GC-C-independent increase in intestinal fluid accumulation, in levels of these peptide ligands in the epithelia of the intestine, and in prouroguanylin in the kidney and blood.

Expression of guanylin is downregulated in mouse and human intestinal adenomas

Guanylin is a pro-secretory hormone that is expressed in intestinal epithelia. Previously, we mapped the guanylin gene to mouse and human chromosomal regions containing multiple intestinal tumor-modifying loci. Here, we investigate whether guanylin expression is downregulated in precancerous human and mouse intestinal adenomas and whether diminished guanylin expression increases adenoma susceptibility in an animal model of intestinal cancer, the multiple intestinal neoplasia (Min) mouse. In situ hybridization analysis indicated diminished guanylin expression in both mouse and human adenomas. Northern analysis of mouse intestinal tissues showed strain-specific levels of guanylin expression but no correlation with the resistance or susceptibility of each strain to adenoma formation. Similarly, cDNA sequence analysis indicated no inactivating mutations or polymorphisms common to either the high or low adenoma-risk groups. Nonetheless, we have shown that significant loss of guanylin RNA in adenomas of mouse and human is a marker of intestinal epithelial cell transformation.

The uroguanylin gene (Guca1b) is linked to guanylin (Guca2) on mouse chromosome 4

Uroguanylin is an endogenous ligand of the intestinal receptor guanylate cyclase-C (GC-C). Both uroguanylin and the related peptide ligand guanylin bind to GC-C and stimulate an increase in cyclic GMP, inducing chloride secretion via the cystic fibrosis transmembrane conductance regulator. We describe the cloning of the complete mouse uroguanylin gene (Guca1b) and show that Guca1b is tightly linked to the mouse guanylin gene on chromosome 4. The two genes are structurally similar, being composed of three short exons; the uroguanylin gene spans 2.4 kb and the guanylin gene spans 1.7 kb. Uroguanylin mRNA is most prominent in proximal small intestine, whereas guanylin mRNA is predominantly expressed in distal small intestine and colon. The upstream promoter sequence of the mouse uroguanylin gene contains a canonical TATA element at the site of transcription initiation and consensus binding sites for several known transcription factors, including HNF-1 and Sp1 within the first 1 kb. Although the gene structure and coding sequences of uroguanylin and guanylin are similar, the 5' flanking sequences and patterns of expression of these two genes in the intestine are different. It is likely that uroguanylin and guanylin represent gene duplications that have evolved to allow overlapping and complementary patterns of expression in the intestine.