Neutrophil transmigration in inflammatory bowel disease is associated with differential expression of epithelial intercellular junction proteins

Expression of tight and adherens junction proteins in ulcerative colitis associated colorectal carcinoma: upregulation of claudin-1, claudin-3, claudin-4, and beta-catenin

BACKGROUND

Tight junction (TJ) proteins play a critical role in cellular adhesion, glandular differentiation, and cellular proliferation. The function of these proteins is compromised in a number of intestinal diseases, including ulcerative colitis that has an increased incidence for colorectal carcinoma (CAC). The aim of this study was to determine the expression of TJ proteins, claudin-1-4, occludin, ZO-1, and the adherens junction (AJ) protein beta-catenin in CAC.

METHODS

Sixteen colectomy specimens with CAC, adjoining intraepithelial neoplasia, and normal mucosa were studied by immunofluorescence. A semiquantitative evaluation of all investigated proteins was performed by scoring the staining intensity, and the TJ and AJ protein expression in neoplastic cells was compared to normal and intraepithelial neoplastic colonic mucosa.

RESULTS

Using an intensity scoring system, mucosa of crypts and surfaces of CAC exhibited significantly elevated expression levels of claudin-1, claudin-3, claudin-4, and beta-catenin compared to intraepithelial neoplasia and normal mucosa (p<0.05). These data were confirmed by a comparative score. The expression of claudin-2, occludin, and ZO-1 showed no differences between the groups.

CONCLUSION

TJ proteins claudin-1, claudin-3, claudin-4, and the AJ protein beta-catenin are overexpressed in CAC. This suggests that these proteins may become potential markers and targets in CAC.

Supplemental zinc reduced intestinal permeability by enhancing occludin and zonula occludens protein-1 (ZO-1) expression in weaning piglets

The present study was carried out to evaluate the pharmacological effect of Zn in diarrhoea in relation to intestinal permeability. Seventy-two weaning piglets, aged 24 d, were allocated to three dietary treatments: (1) control diet without supplemental Zn; (2) control diet supplemented with 2000 mg Zn/kg from ZnO; (3) control diet supplemented with 2000 mg Zn/kg from tetrabasic zinc chloride (TBZC). At the end of a 14 d experiment period, piglets were weighed, feed consumption was measured, and mucosal barrier function was determined using the lactulose/mannitol test. Expression of mucosal tight junction protein was measured at RNA and protein level. Inclusion of TBZC or ZnO in the diet significantly increased average daily gain (P < 0.01) and average daily feed intake (P < 0.05), while leading to reduced feed conversion ratio (P < 0.05) and faecal scores (P < 0.01). TBZC reduced urinary lactulose:mannitol ratios of weaning piglets (P < 0.05), while dietary supplementation with ZnO tended to reduce urinary lactulose:mannitol ratios (P = 0.061). ZnO or TBZC significantly enhanced the mRNA and protein expression of occludin (P < 0.05) and zonula occludens protein-1 (ZO-1) (P < 0.05) in the ileal mucosa. Piglets fed the TBZC-supplemented diet had a higher level of occludin than pigs fed the ZnO-supplemented diet (P < 0.05). The results indicate that Zn supplementation decreased faecal scores and the reduction was accompanied by reduced intestinal permeability, which was evident from the reduced urinary lactulose:mannitol ratios and increased expression of occludin and ZO-1. Therefore, the protective effect of pharmacological levels of dietary Zn in reducing diarrhoea might, at least partly, be associated with reduced intestinal permeability.

Neutrophil-related immunoinflammatory disturbance in steroid-overdosed ulcerative colitis patients

BACKGROUND

There is some evidence that large preoperative doses of steroids are a causative factor for postoperative higher morbidity in ulcerative colitis (UC) patients. This study aimed to assess steroid-related changes in functional profiles of neutrophils in UC patients to estimate the immunological changes under surgical stress.

METHODS

Neutrophils were extracted from peripheral blood of 30 UC patients and 30 healthy controls. UC patients whose neutrophils were isolated were divided into two subgroups according to their total preoperative dosage of prednisolone: group H, > or =10,000 mg; group L, <10,000 mg. Expression of neutrophil surface antigens was analyzed and neutrophil phagocytosis was evaluated. Patterns of cell death of neutrophils were evaluated by co-culturing with Escherichia coli. Production of inflammatory mediators in cultured neutrophils was assessed.

RESULTS

There were no significant differences in the expression rates of TLR4, CD11b, and CD16b on neutrophils (CD15(+) cells) between the two patient groups and controls. There was also no significant difference in neutrophil phagocytosis between the two patient groups and controls. The neutrophil necrosis rate in group H was higher than that in group L and the controls 3 h after exposure to E. coli. Neutrophils from group H released the highest levels of proinflammatory cytokines following interleukin-1beta or lipopolysaccharide stimulation. Neutrophils from group H also released the highest levels of proteolytic enzymes.

CONCLUSIONS

Steroid-overdosed UC patients may have a functional deficit in neutrophils, which may cause a postsurgical systemic "storm" of inflammatory mediators.

Differential effect of ethanol and hydrogen peroxide on barrier function and prostaglandin E2 release in differentiated Caco-2 cells: selective prevention by growth factors

The present study investigates the effects of ethanol and hydrogen peroxide (H(2)O(2)) on the barrier function and prostaglandin E(2) (PGE(2)) release in differentiated Caco-2 cells. Epithelial barrier integrity was estimated by measuring transepithelial electrical resistance (TEER), the transport of reference compounds and lactate dehydrogenase leakage, the PGE(2) release by enzyme immunoassay. Ethanol and H(2)O(2) decreased TEER and increased the transport of lucifer yellow without affecting that of propranolol and phenylalanine. Only the effects of ethanol were accompanied by PGE(2) production and were reversible without causing long-term cytotoxicity. The cyclooxygenase-2 inhibitor, NS-398, prevented the effect of ethanol on both PGE(2) release and TEER, while inhibition of both cyclooxygenase-2 and tyrosine kinase drastically compromised cell viability and TEER recovery. Hepatocyte growth factor, keratinocyte growth factor or insulin prevented the effect of ethanol on cell permeability, but not on PGE(2) release. Their combination prevented the effect of H(2)O(2). In conclusion, ethanol and H(2)O(2) increased paracellular permeability in differentiated Caco-2 cells without affecting transcellular and active transport. Cyclooxygenase-2 stimulated PGE(2) release mediated the reversible effect of ethanol on tight junctions and, meanwhile, contributed to cell survival. Growth factors, normally present in the intestine, exerted a selective protective effect toward paracellular permeability increase induced by irritants.

3,4-Diamino-1,2,5-thiadiazole as potent and selective CXCR2 antagonists

A series of potent and selective 3,4-diamino-1,2,5-thiadiazoles were prepared and found to show excellent binding affinities towards CXCR2 receptor.

Changes in the expression of claudins in active ulcerative colitis

BACKGROUND AND AIM

Epithelial barrier function is impaired in ulcerative colitis (UC), but the pathophysiological mechanisms leading to this barrier defect are still far from clear. Because epithelial barrier function is primarily regulated by the most apical intercellular junction, referred to as the tight junction (TJ), we investigated the expression of TJ proteins on rectal epithelial mucosa in UC.

METHODS

Biopsies from the rectum of patients with active UC and of controls were studied. Tight-junction proteins were dual stained using specific antibodies (claudin-1, -2, -3, -4, and -7) as primary antibodies, and Cy-3 conjugated anti-rabbit IgG and Alexa488-conjugated anti-mouse IgG as secondary antibodies. Samples were analyzed by immunofluorescence microscopy. Immunoblotting and real-time polymerase chain reaction were performed to quantify TJ proteins and mRNA, respectively.

RESULTS

At TJ, claudin-4 and -7 staining was down-regulated in active UC, whereas claudin-2 staining was up-regulated. Claudin-4 and -7 proteins were down-regulated on immunoblotting, whereas claudin-2 protein was up-regulated in active UC. Claudin-1 and -3 expression levels were unchanged in controls and active UC. In active UC claudin-2 mRNA was increased, whereas claudin-4 and -7 mRNA were decreased.

CONCLUSIONS

Down-regulation of claudin-4 and claudin-7, and up-regulation of claudin-2, might lead to altered TJ structure and be related to the impaired epithelial function in active UC.

Increased expression of the tight junction molecule claudin-18 A1 in both experimental colitis and ulcerative colitis

BACKGROUND

We previously identified a major quantitative trait locus (qtl) on mouse chromosome 9 (Tnbs1) that confers resistance/susceptibility to trinitrobenzene sulfonic acid (TNBS) induced colitis. Here we wanted to identify possible candidate genes in this locus.

METHODS

We applied micro-array technology and identified claudin-18 as a plausible candidate gene in the Tnbs1 region. Subsequently we studied the expression profile of this gene by means of RT-PCR in resistant and susceptible mice as well as in human inflammatory bowel disease.

RESULTS

Expression of this gene was markedly upregulated during colitis in mice. Also in humans relative expression of claudin-18 in patients with ulcerative colitis was significantly upregulated as compared to healthy individuals undergoing surveillance endoscopy (n = 13, P < 0.0005). Expression was not related to the histological severity of the disease.

CONCLUSIONS

Claudins belong to the integral membrane proteins of the tight junction, a structure that seals off the intercellular space between adjacent epithelial cells and regulates passive diffusion of solutes and macromolecules. This study demonstrates for the first time that claudin-18 is expressed in human and mouse colon. Expression is upregulated during experimental colitis and in patients with ulcerative colitis. The observation that this is unrelated to the severity of inflammation might point to a primary defect in regulation in patients with ulcerative colitis and warrants further genetic examination.

Molecular pathogenesis of inflammatory bowel disease: relevance for novel therapies

The immense load of microorganisms within the gastrointestinal tract is a great challenge for the mucosal immune system. Whereas the vast majority of commensal bacteria should be tolerated, pathogenic organisms have to be attacked. During inflammatory bowel disease, the balanced interaction between the mucosal flora and the intestinal immune system is disturbed. Various defective components of this complex interaction have been described, such as different susceptibility genes, impaired innate immune responses and environmental factors, suggesting that inflammatory bowel diseases are multifactorial diseases. Based on new insights into the pathogenesis of inflammatory bowel disease, various targets for future drugs have been identified and new substances are emerging. The following article will review the current understanding of inflammatory bowel disease pathogenesis in context with genetic risk factors, imbalanced innate and acquired immune responses, and altered barrier function. Clinical treatment of the diseases will be summarized and emerging therapies as well as individual management based on recent insights into pathogenesis will be discussed.

Pathophysiology of nasal polyposis: the role of desmosomal junctions

BACKGROUND

Many mucosal inflammatory conditions are associated with alterations in epithelial intercellular junctions and barrier function; however, little is known about the role of intercellular junctions in inflammatory diseases of the upper airways. In this study, we examined nasal polyps for altered intercellular junctions and protein expression.

METHODS

Biopsy specimens of nasal polyps and normal tissue were obtained intraoperatively from 11 patients and 6 controls. Tissue was analyzed for expression of intercellular junctional proteins by immunofluorescence. In parallel, cultured human bronchial epithelial (HBE) cells were treated with tumor necrosis factor (TNF) alpha, interferon (IFN) gamma, and IL-13 to simulate inflammatory conditions followed by assessment for changes in junctional proteins by immunofluorescence and Western blot.

RESULTS

Of the intercellular junctional proteins analyzed, including proteins comprising tight and adherens junctions, the only alterations observed were in desmosomal proteins in nasal polyp epithelium compared with normal controls. Specifically, expression of desmosomal proteins DSG2 and DSG3 were significantly decreased in polyps versus controls (0.53 pixel/microm2 versus 1.09 pixel/microm2 [p = 0.009], and 0.29 pixel/microm2 versus 1.11 pixel/microm2 [p = 0.0078], respectively). In vitro experiments involving exposure of cultured HBE cells with inflammatory cytokines revealed that TNF-alpha treatment resulted in internalization and decreased expression of DSG2 by immunofluorescence and Western blotting. Treatment with IFN-gamma resulted in increased expression of DSG2 and evidence of protein cleavage by Western blot. IL-13 exposure resulted in down-regulation of DSG2 expression and evidence of protein cleavage.

CONCLUSION

These results indicate that nasal polyps express decreased levels of DSG2 and DSG3 components of desmosomal junctions. This is likely linked to the mucosal inflammatory response. Exposure of a respiratory cell line to Th1/Th2 cytokines results in similar expressional alterations in DSG2, suggesting protein internalization and cleavage. We speculate that weakened desmosomal junctions in nasal mucosa secondary to inflammatory cytokines may contribute to the formation of nasal polyposis.

Effects of cardiopulmonary bypass on tight junction protein expressions in intestinal mucosa of rats

AIM: To investigate the tight junction protein expressions of intestinal mucosa in an experimental model of cardiopulmonary bypass (CPB) in rats.

METHODS: Thirty anesthetized rats were randomly divided into two groups: Group S (n = 10) served as sham operation and group C (n = 20) served as CPB which underwent CPB for 1 h. Expression of occludin and zonula occludens-1 (ZO-1) were determined by Western blotting and immunocytochemistry, respectively. Plasma levels of diamine oxidase (DAO) and d-lactate were determined using an enzymatic spectrophotometry.

RESULTS: Immunohistochemical localization of occludin and ZO-1 showed disruption of the tight junctions in enterocytes lining villi at the end of CPB and 2 h after CPB. The intensities of the occludin and ZO-1 at the end of CPB were lower than those of control group (76.4% ± 22.5% vs 96.5% ± 28.5% and 62.4% ± 10.1% vs 85.5% ± 25.6%, P < 0.05) and were further lower at 2 h after CPB (50.5% ± 10.5% and 45.3% ± 9.5%, P < 0.05). Plasma d-lactate and DAO levels increased significantly (8.688 ± 0.704 vs 5.745 ± 0.364 and 0.898 ± 0.062 vs 0.562 ± 0.035, P < 0.05) at the end of CPB compared with control group and were significantly higher at 2 h after CPB than those at the end of CPB (9.377 ± 0.769 and 1.038 ± 0.252, P < 0.05). There were significant negative correlations between occludin or ZO-1 expression and DAO (r² = 0.5629, r² = 0.5424, P < 0.05) or d-lactate levels (r² = 0.6512, r² = 0.7073, P < 0.05) both at the end of CPB and 2 h after CPB.

CONCLUSION: CPB markedly down-regulates the expression of occludin and ZO-1 proteins in intestinal mucosa of rats. The close correlation between expression of tight junctions (TJs) and plasma levels of DAO or d-lactate supports the hypothesis that intestinal permeability increases during and after CPB because of decreases in the expressions of TJs.

Zinc deficiency induces membrane barrier damage and increases neutrophil transmigration in Caco-2 cells

Zinc may contribute to the host defense by maintaining the membrane barrier. In this study, we questioned whether zinc deficiency affects the membrane function and junctional structure of intestinal epithelial cells, causing increased neutrophil migration. We used the Caco-2 cell line grown in control (C), zinc-deficient, or zinc-replete medium until differentiation. Zinc deprivation induced a decrease of transepithelial electrical resistance and alterations to tight and adherens junctions, with delocalization of zonula occludens (ZO-1), occludin, beta-catenin, and E-cadherin. Disorganization of F-actin and beta-tubulin was also found in zinc deficiency. These changes were associated with a loss of the amounts of ZO-1, occluding, and beta-tubulin. In addition, zinc deficiency caused a dephosphorylation of occludin and hyperphosphorylation of beta-catenin and ZO-1. Disruption of membrane barrier integrity led to increased migration of neutrophils. In addition, zinc deficiency induced an increase in the secretion of interleukin-8, epithelial neutrophil activating peptide-78, and growth-regulated oncogene-alpha, alterations that were not found when culture medium was replete with zinc. These results provide new information on the critical role played by dietary zinc in the maintenance of membrane barrier integrity and in controlling inflammatory cell infiltration.

Advanced oxidation protein products: a novel marker of oxidative stress in ulcerative colitis

BACKGROUND/GOALS

The etiology and pathogenesis of chronic inflammatory bowel diseases are still poorly understood. Oxidative stress takes place in the pathogenesis of ulcerative colitis (UC) and advanced oxidation protein products (AOPP) are accepted as a novel marker of oxidative stress. There are no data concerning whether AOPP may be used as a simple serum marker to assess the disease activity, predict severity of the disease course in UC.

STUDY

In this study, we determine the importance of neutrophil activation and the role of oxidative stress in the pathogenesis of UC, by quantification of AOPP and total thiol levels as markers of oxidative protein damage, malondialdehyde levels as a marker of lipid peroxidation, and myeloperoxidase activity as a marker of neutrophil activation in patients with UC.

RESULTS

Serum levels of AOPP, thiol, myeloperoxidase activity, and malondialdehyde were found as increased in UC group compared with controls (P=0.004, 0.047, 0.001, and 0.001 respectively).

CONCLUSIONS

Our finding of increased levels of plasma AOPP levels supports the presence of oxidative stress and protein oxidation in UC and this marker may be used as a simple serum marker to assess disease activity, predict the severity of disease course, and perhaps response to therapy.

Innate and adaptive immune responses related to IBD pathogenesis

Although the adaptive immune system traditionally has been the primary focus of investigations into the pathogenesis of inflammatory bowel disease (IBD), it is now clear that innate immune responses play an equally important, or perhaps even primary, role in disease initiation. Intestinal barrier function defects and genetic associations with the nucleotide-binding oligomerization domain and Toll-like receptor pathways suggest that the innate immune system has failed to protect the host against the vast array of commensal bacteria in the gut. This hypothesis is supported further by the observation that probiotic agents exert anti-inflammatory effects in the intestine through stimulation, rather than suppression, of the mucosal innate immune system. Moreover, it is now clear that adaptive immune responses involved in IBD pathogenesis are more complex than the traditionally dichotomous Th1/Th2 paradigm. Finally, mounting evidence suggests that the Th17 effector pathway may contribute to Crohn's disease pathogenesis.

Cis-dimerization mediates function of junctional adhesion molecule A

Junctional adhesion molecule-A (JAM-A) is a transmembrane component of tight junctions that has been proposed to play a role in regulating epithelial cell adhesion and migration, yet mechanistic structure-function studies are lacking. Although biochemical and structural studies indicate that JAM-A forms cis-homodimers, the functional significance of dimerization is unclear. Here, we report the effects of cis-dimerization-defective JAM-A mutants on epithelial cell migration and adhesion. Overexpression of dimerization-defective JAM-A mutants in 293T cells inhibited cell spreading and migration across permeable filters. Similar inhibition was observed with using dimerization-blocking antibodies. Analyses of cells expressing the JAM-A dimerization-defective mutant proteins revealed diminished beta1 integrin protein but not mRNA levels. Further analyses of beta1 protein localization and expression after disruption of JAM-A dimerization suggested that internalization of beta1 integrin precedes degradation. A functional link between JAM-A and beta1 integrin was confirmed by restoration of cell migration to control levels after overexpression of beta1 integrin in JAM-A dimerization-defective cells. Last, we show that the functional effects of JAM dimerization require its carboxy-terminal postsynaptic density 95/disc-large/zonula occludins-1 binding motif. These results suggest that dimerization of JAM-A regulates cell migration and adhesion through indirect mechanisms involving posttranscriptional control of beta1 integrin levels.

Hepatitis C virus receptor expression in normal and diseased liver tissue

The principal site of hepatitis C virus (HCV) replication is the liver. HCV pseudoparticles infect human liver derived cell lines and this suggests that liver-specific receptors contribute to defining HCV hepatotropism. At least three host cell molecules have been reported to be important for HCV entry: the tetraspanin CD81, scavenger receptor class B member I (SR-BI), and the tight junction (TJ) protein Claudin 1 (CLDN1). Hepatocytes in liver tissue coexpress CD81, SR-BI, and CLDN1, consistent with their ability to support HCV entry. CLDN1 localized at the apical-canalicular TJ region and at basolateral-sinusoidal hepatocyte surfaces in normal tissue and colocalized with CD81 at both sites. In contrast, CLDN1 appeared to colocalize with SR-BI at the basolateral-sinusoidal surface. CLDN1 expression was increased on basolateral hepatocyte membranes in HCV-infected and other chronically inflamed liver tissue compared with normal liver. In contrast, CLDN4 hepatocellular staining was comparable in normal and diseased liver tissue.

CONCLUSION

HCV infection of Huh-7.5 hepatoma cells in vitro significantly increased CLDN1 expression levels, consistent with a direct modulation of CLDN1 by virus infection. In HCV infected livers, immunohistochemical studies revealed focal patterns of CLDN1 staining, suggesting localized areas of increased CLDN1 expression in vivo which may potentiate local viral spread within the liver.

Novel role of the vitamin D receptor in maintaining the integrity of the intestinal mucosal barrier

Emerging evidence supports a pathological link between vitamin D deficiency and the risk of inflammatory bowel disease (IBD). To explore the mechanism we used the dextran sulfate sodium (DSS)-induced colitis model to investigate the role of the vitamin D receptor (VDR) in mucosal barrier homeostasis. While VDR(+/+) mice were mostly resistant to 2.5% DSS, VDR(-/-) mice developed severe diarrhea, rectal bleeding, and marked body weight loss, leading to death in 2 wk. Histological examination revealed extensive ulceration and impaired wound healing in the colonic epithelium of DSS-treated VDR(-/-) mice. Severe ulceration in VDR(-/-) mice was preceded by a greater loss of intestinal transepithelial electric resistance (TER) compared with VDR(+/+) mice. Confocal and electron microscopy (EM) revealed severe disruption in epithelial junctions in VDR(-/-) mice after 3-day DSS treatment. Therefore, VDR(-/-) mice were much more susceptible to DSS-induced mucosal injury than VDR(+/+) mice. In cell cultures, 1,25-dihydroxy-vitamin D(3) [1,25(OH)(2)D(3)] markedly enhanced tight junctions formed by Caco-2 monolayers by increasing junction protein expression and TER and preserved the structural integrity of tight junctions in the presence of DSS. VDR knockdown with small interfering (si)RNA reduced the junction proteins and TER in Caco-2 monolayers. 1,25(OH)(2)D(3) can also stimulate epithelial cell migration in vitro. These observations suggest that VDR plays a critical role in mucosal barrier homeostasis by preserving the integrity of junction complexes and the healing capacity of the colonic epithelium. Therefore, vitamin D deficiency may compromise the mucosal barrier, leading to increased susceptibility to mucosal damage and increased risk of IBD.

Effect of n-3 polyunsaturated fatty acids on membrane microdomain localization of tight junction proteins in experimental colitis

Ulcerative colitis (UC) is a gastrointestinal disorder characterized by an inflammatory process associated with mucosal damage. Many studies have shown that n-3 polyunsaturated fatty acids (PUFAs) possess anti-inflammatory effects in inflammatory bowel disease. The aim of this study was to investigate whether n-3 PUFAs could alleviate intestinal damage in experimental UC. In the present study, we found that in 2,4,6-trinitrobenzenesulfonic acid-induced colitic rats, the damage to the intestinal mucosa was accompanied by a disrupted tight junction (TJ) structure. In accordance with these changes, the distribution and expression of TJ proteins, including occludin, claudin-1, claudin-3, claudin-5, claudin-8 and ZO-1, in membrane microdomains was altered. The distribution of flotillin-1, a lipid raft marker protein, was also changed. Moreover, we found for the first time that n-3 PUFAs prevented redistribution of TJ proteins from Triton X-100-insoluble raft-like membrane microdomains to Triton X-100-soluble fractions. The expression of ZO-1, claudin-1, claudin-5 and claudin-8 was significantly elevated by n-3 PUFAs. n-3 PUFAs also attenuated the disruption of TJ structure and improved the histological score. Our results demonstrate that the expression and distribution of TJ proteins in TJ membrane microdomains might be affected in UC, and that such altered expression of TJ proteins in membrane microdomains in experimental UC is affected by n-3 PUFAs. These findings may have therapeutic potential in intestinal inflammation.

Aggravation of different types of experimental colitis by depletion or adhesion blockade of neutrophils

BACKGROUND & AIMS

Neutrophils are generally thought to play an important proinflammatory role in the pathogenesis of inflammatory bowel disease. The objective of this study was to evaluate whether blocking the invasion of neutrophils by anti-L-selectin monoclonal antibodies modulates chemically induced colitis and how this modulation is accomplished.

METHODS

Trinitrobenzene sulfonic acid/dinitrobenzene sulfonic acid (TNBS/DNBS)-induced colitis was studied in rats on treatment with anti-L-selectin monoclonal antibodies (mAb) or antineutrophil antiserum. Different anti-L-selectin mAb, either blocking or nonblocking, as well as F(ab)(2) fragments were evaluated. Additionally, leukocyte migration was examined using intravital microscopy. Furthermore, the effect of neutrophil depletion in rat TNBS-induced colitis was studied either prior to or after colitis induction as well as murine CD4(+)CD45RB(high) transfer colitis. Finally, bacterial translocation during DNBS-induced colitis was studied in neutrophil-depleted and control rats.

RESULTS

Anti-L-selectin mAb treatment resulted in increased mortality and bowel inflammation as well as hemorrhagic eye secretion. No clear difference was found between blocking and nonblocking mAb or F(ab)(2) fragments. For all investigated antibodies/fragments, either complete blockade of leukocyte invasion or marked neutrophil depletion was found. Accordingly, neutrophil depletion by antiserum resulted in aggravation of rat DNBS-induced colitis as well as murine transfer colitis.

CONCLUSIONS

Adhesion blockade or neutrophil depletion aggravates rat TNBS/DNBS-induced colitis together with extraintestinal manifestations of the eyes. Therefore, neutrophils appear to have an important role in mucosal repair processes. Importantly, adhesion blockade as a therapeutic concept can be detrimental in inflammatory bowel disease.

3,4-Diamino-2,5-thiadiazole-1-oxides as potent CXCR2/CXCR1 antagonists

A series of novel and potent 3,4-diamino-2,5-thiadiazole-1-oxides were prepared and found to show excellent binding affinities for CXCR2 and CXCR1 receptors and excellent inhibitory activity of Gro-alpha and IL-8 mediated in vitro hPMN MPO release of CXCR2 and CXCR1 expressing cell lines. On the other hand, a closely related 3,4-diamino-2,5-thiadiazole-dioxide did not show functional activity despite its excellent binding affinities for CXCR2 and CXCR1 in membrane binding assays. A detailed SAR has been discussed in these two closely related structures.

Interferon-gamma and tumor necrosis factor-alpha disrupt epithelial barrier function by altering lipid composition in membrane microdomains of tight junction

Tight junctions (TJs) are specialized membrane microdomains of plasma membrane and play an important role in barrier function. IFN-gamma and TNF-alpha have been implicated in intestinal barrier dysfunction. In the present study, we analyzed the effect of IFN-gamma and TNF-alpha on epithelial barrier function and determined the contribution of apoptosis to this process using T84 cells, a model intestinal epithelial cell line. We found that TNF-alpha and IFN-gamma synergistically affected the epithelial barrier and disrupted the structure of TJs. We demonstrated for the first time that treatment with TNF-alpha and IFN-gamma changed lipid composition and fatty acyl substitutions of phospholipids in membrane microdomains of TJs. Alterations of lipid environment affected TJs barrier function and partly removed flotillin-1 and displaced occludin from membrane microdomains of TJs to detergent-soluble fractions. The distribution of claudin isoforms was unaffected by TNF-alpha and IFN-gamma treatment. These findings indicated the interaction between inflammatory cytokines and alterations of lipid composition in membrane microdomains of TJs in the inflammatory processes. The apoptosis inhibitor did not prevent cytokine-induced decrease in TER and increase in permeability to FITC-dextran. Our results suggest that the cytokines directly influence TJ function and modulate both the membrane microdomain localization of TJ proteins and lipid composition of TJs. The effects of proinflammatory cytokines on TJ structure and function provide a mechanism in the pathophysiology of Crohn's disease (CD). Understanding the intracellular mechanisms involved could be important in devising future therapeutic strategies to induce retightening of the leaky TJ barrier.

Invasive Escherichia coli are a feature of Crohn's disease

Crohn's disease (CD) and ulcerative colitis (UC) are idiopathic inflammatory conditions of the gut. Our goal was to investigate if invasive Escherichia coli strains were present in patients with inflammatory bowel disease (IBD). Bacterial strains were isolated from biopsy material obtained from normal controls, and patients with a clinical diagnosis of CD and UC. Invasive bacteria were characterized by gentamicin protection assay and biochemical profiling (Api-20E). Strains were characterized by induction of cytokine expression in epithelial and macrophage cell cultures, measurement of epithelial barrier function, and confocal microscopy. Of all invasive bacterial strains in CD 98.9% were identified as E. coli as opposed to 42.1% in UC and 2.1% in normal controls. Epithelial invasion in vitro was significantly higher for CD-associated E. coli (8.4%, +/-5.5 of initial inoculum (I/O)) in comparison to UC (2.5%, +/-0.4 I/O), but highest for strains from inflamed CD tissue (11.3%, +/-4.3 I/O). Both, CD and UC E. coli strains induced high mean TNF-alpha expression in macrophage cell lines (2604.8 pg/10(5) cells, +/-447.4; 2,402.6 pg/10(5) cells, +/-476.3, respectively), but concentrations were significantly higher for isolates from inflamed CD tissue (3071.3 pg/10(5) cells, +/-226.0). Invasive E. coli from IBD tissue induced similar concentrations of interleukin (IL)-8 in epithelial cell cultures, but strains from inflamed CD tissue induced significantly less epithelial IL-8 (674.1 pg/10(5) cells, +/-58.0 vs 920.5 pg/10(5) cells, +/-94.6). IBD-associated E. coli strains significantly decreased transepithelial resistance, induced disorganization of F-actin and displacement of ZO-1, and E-cadherin from the apical junctional complex (AJC). In comparison to normal controls and UC, E. coli are more prevalent in CD, are highly invasive, and do not encode for known effector proteins. E. coli strains from IBD patients regulate cytokine expression and epithelial barrier function, two pathological features of IBD.

Escherichia coli isolated from a Crohn's disease patient adheres, invades, and induces inflammatory responses in polarized intestinal epithelial cells

Inflammatory diseases of the intestinal tract are a major health concern both in the United States and around the world. Evidence now suggests that a new category of Escherichia coli, designated Adherent Invasive E. coli (AIEC) is highly prevalent in Crohn's Disease (CD) patients. AIEC strains have been shown to colonize and adhere to intestinal epithelial cells (IEC). However, the role AIEC strains play in the induction of an inflammatory response is not known. Therefore, we examined several E. coli strains (designated LF82, O83:H1, 6604 and 6655) that were isolated from CD patients for their ability to induce inflammation in two IEC, Caco-2BBe and T-84 cells. Results showed that each strain had varying abilities to adhere to and invade IEC as well as induced cytokine secretion from polarized IEC. However, E. coli O83:H1 displayed the best characteristics of AIEC strains as compared to the prototype AIEC strain LF82, inducing cytokine secretion from IEC and promoting immune cell migration through IEC. Upon further analysis, E. coli O83:H1 did not harbor virulence genes present in known pathogenic intestinal organisms. Further characterization of E. coli O83:H1 virulence determinants showed that a non-flagellated O83:H1 strain significantly decreased the organism's ability to adhere to and invade both IEC and elicit IEC cytokine secretion compared to the wild type and complemented strains. These findings demonstrate that E. coli O83:H1 possesses the characteristics of the AIEC LF82 strain that may contribute to the low-grade, chronic inflammation observed in Crohn's disease.

Altered claudin expression is a feature of chronic plaque psoriasis

Epithelial tight junctions play a central role in cell-cell adhesion and are necessary for the selective paracellular movement of ions. Claudins are key components of tight junctions and their expression is altered in gut epithelia in a variety of inflammatory enteropathies, including ulcerative colitis and Crohn's disease. Psoriasis is a chronic inflammatory skin disease affecting approximately 2% of the western population, with significantly increased occurrence in individuals with Crohn's disease. Initial studies investigated the expression of claudins in skin of healthy volunteers and patients with chronic plaque psoriasis. We report here that claudins-1 and -3 are the major protein species present in the epidermis of healthy skin; they are expressed on the surface of epidermal keratinocytes, consistent with their localization to tight junctions. In plaques of psoriasis, claudin-1 was not identifiable in the epidermis, although typical staining patterns were observed in clinically normal, uninvolved skin of patients with psoriasis. Claudin-3 was present in the epidermal granular cell layer in normal skin, but was only identified within the cytosol of epidermal keratinocytes in both involved and uninvolved skin of psoriasis patients. We examined further whether exposure of keratinocytes in vitro to pro-inflammatory cytokines mimicked the observed changes in claudin expression seen in chronic plaque psoriasis; lipopolysaccharide, interferon-gamma and tumour necrosis factor-alpha had no effect on claudin protein expression or distribution. Addition of interleukin-1beta, however, resulted in down-regulation of claudins-1 and -3. Tumour necrosis factor-alpha and interleukin-1beta were further used in an in vivo model of skin inflammation; interleukin-1beta alone modulated claudin protein expression in this system. These data demonstrate that epidermal claudin expression is altered in chronic plaque psoriasis and that expression is in part modulated by interleukin-1beta.

Evolution of collagenous colitis into severe and extensive ulcerative colitis

Collagenous colitis is an inflammatory mucosal disorder of the colon with distinctive histopathological features, including a thickened subepithelial collagen layer. The clinical course is usually benign, but serious complications, including death, may occur. In the present report, a 69-year-old woman with watery diarrhea and collagenous colitis developed bloody diarrhea that was refractory to treatment medications, including corticosteroids and azathioprine. Endoscopic and histopathological studies showed a focal neutrophilic inflammatory process that progressed to a diffuse and extensive form of colitis, eventually requiring total proctocolectomy. Careful histological review of the resected colon showed no evidence of persistent collagenous colitis. These findings suggest an important need for continued long-term follow-up of patients with collagenous colitis because superimposed and serious colonic complications may occur, including a severe and extensive pancolitis refractory to medications and necessitating total proctocolectomy.

Apical junction complex protein expression in the canine colon: differential expression of claudin-2 in the colonic mucosa in dogs with idiopathic colitis

Canine idiopathic lymphocytic-plasmacytic colitis (LPC) is a well-recognized clinical and pathological entity in the dog, associated with altered immune cell populations and cytokine expression profiles. Clinical and experimental data indicate that alterations in the permeability of the intestinal epithelium contribute to the pathogenesis of a range of related conditions. The apical junction complex plays a significant role in regulating epithelial paracellular permeability, and we have characterized the distribution of a number of its component tight junction (ZO-1, occludin, claudin-2) and adherens junction (E-cadherin and beta-catenin) proteins in normal colon and colon from dogs with idiopathic LPC. ZO-1, occludin, E-cadherin, and beta-catenin exhibited a distribution in normal canine colon similar to that described previously in humans and rodents. In contrast to the situation in humans, claudin-2-specific labeling was observed in the normal canine colonic crypt epithelium, decreasing in intensity from the distal to the proximal crypt and becoming barely detectable at the luminal surface of the colon. There was little evidence for significant changes in ZO-1, occludin, E-cadherin, or beta-catenin expression in dogs affected by idiopathic LPC. However, claudin-2 expression markedly increased in the proximal crypt and luminal colonic epithelium in affected dogs, suggesting a role in the pathogenesis of canine LPC.

Dextran sulfate sodium enhances interleukin-1 beta release via activation of p38 MAPK and ERK1/2 pathways in murine peritoneal macrophages

Interleukin (IL)-1 beta is a pro-inflammatory cytokine that has been shown to play a pivotal role in the onset of inflammatory bowel disease (IBD), however, the molecular mechanisms underlying the production of IL-1 beta in IBD are not fully understood. We investigated dextran sulfate sodium (DSS)-induced IL-1 beta production and caspase-1 activities in murine peritoneal macrophages (pM phi). Further, the activation status of p38 mitogen-activated protein kinase (MAPK), extracellular signal-regulated kinase 1/2 (ERK1/2), and c-Jun NH(2)-terminal kinase (JNK1/2), as well as their upstream target kinases, were examined by Western blotting. In addition, mRNA expression was assessed by RT-PCR and CXC chemokine ligand 16 (CXCL16) protein was detected by immunocytochemistry. DSS-treated pM phi released IL-1 beta protein in a time-dependent manner without affecting mRNA levels during 3-24 h, and caspase-1 activity peaked at 5 min (29-fold). IL-1 beta release and caspase-1 activity induced by DSS were significantly inhibited by a MAPK kinase 1/2 inhibitor, a p38 MAPK inhibitor, and NAC, however, not by JNK1/2 or a protein kinase C inhibitor. In addition, DSS strikingly induced the phosphorylation of p38 MAPK and ERK1/2 within 2 and 10 min, respectively. DSS also induced intracellular generation of reactive oxygen species (ROS). Pre-treatment with anti-CXCL16 for 24 h, but not anti-scavenger receptor-A, anti-CD36, or anti-CD68 antibodies, significantly suppressed DSS-induced IL-1 beta production. Our results suggest that DSS triggers the release of IL-1 beta protein from murine pM phi at a post-translational level through binding with CXCL16, ROS generation, and resultant activation of both p38 MAPK and ERK1/2 pathways, and finally caspase-1 activation.

Neutrophil recruitment and barrier impairment in celiac disease: a genomic study

BACKGROUND & AIMS

Celiac disease is an enteropathy featuring villous atrophy, crypt hyperplasia, and lymphocytosis. Tissue remodeling is driven by an inflammatory reaction to gluten in genetically susceptible individuals. The adaptive pathway is considered the major immune response but recent evidence has indicated the involvement of innate immunity as well. To assess the contribution of either immune response we performed global gene expression profiling of the regenerating mucosa.

METHODS

Microarray hybridizations were performed with biopsy samples from 13 untreated patients, 31 patients on a gluten-free diet in various stages of remission, and 21 controls. Additional data were generated using low-density array and conventional quantitative reverse-transcription polymerase chain reaction, and immunohistochemistry.

RESULTS

A total of 108 differentially expressed immune-related genes were identified (50 innate, 43 adaptive, 9 both innate/adaptive, and 6 immunoregulatory). Expression levels showed a gradual change as opposed to the discrete histological transitions. In addition to details provided on the adaptive and innate immune pathways used, we observed a chronic recruitment of activated neutrophils. Neutrophil involvement was unabated in otherwise completely normalized remission patients.

CONCLUSIONS

We observed a contribution of both the innate and adaptive immune response in celiac disease pathogenesis. The discrepancy between the histological classification and the observed incremental change in immune-gene expression may have consequences for current diagnostic inclusion criteria. Enhanced neutrophil infiltration in both active and remission patients points to a genetic impairment of the intestinal barrier that may contribute to the cause rather than the consequence of celiac disease.

Loss of the tight junction protein ZO-1 in dextran sulfate sodium induced colitis

BACKGROUND

Inflammatory bowel disease (IBD) is associated with increased intestinal permeability and decreased expression of tight junction (TJ) proteins in the inflamed mucosa. Whether this alteration in TJ expression is a prerequisite for the development of intestinal inflammation or a secondary result of that inflammation is unknown. This study looked at the expression of the TJ protein ZO-1 and the corresponding permeability changes in dextran sulfate sodium (DSS) induced colitis in a mouse model.

MATERIALS AND METHODS

BALB/c mice were fed 3% DSS or water for 1, 3, 5, or 7 days. The animals were weighed, stool was checked for blood, and the colon length measured. Segments of the colon were used for histology, immunohistochemistry for ZO-1, or Western blot for TJ proteins. Colonic permeability was measured using Evan's Blue dye.

RESULTS

DSS treated animals had heme positive stools, colitis by histology, significant weight loss, and colon shortening. There was an absence of ZO-1 by Western blot in the 7-day DSS treated animals, double the amount of claudin-1 and normal cytokeratin. The loss of ZO-1 started after 1 d of DSS treatment and was followed by a significant increase in permeability to Evan's blue by day 3.

CONCLUSIONS

The loss of ZO-1 and increased permeability preceded the development of significant intestinal inflammation suggesting that in DSS colitis alterations in the TJ complex occur before the intestinal inflammation and not as a consequence of it. These changes in the TJ complex may facilitate the development of the inflammatory infiltrate seen in colitis.

Differentiation restricted endocytosis of cell penetrating peptides in MDCK cells corresponds with activities of Rho-GTPases

PURPOSE

Cellular entry of biomacromolecules is restricted by the barrier function of cell membranes. Tethering such molecules to cell penetrating peptides (CPPs) that can translocate cell membranes has opened new horizons in biomedical research. Here, we investigate the cellular internalization of hCT(9-32)-br, a human calcitonin derived branched CPP, and SAP, a gamma-zein related sequence.

METHODS

Internalization of fluorescence labelled CPPs was performed with both proliferating and confluent MDCK cells by means of confocal laser scanning microscopy (CLSM) and fluorescence activated cell sorting (FACS) using appropriate controls. Internalization was further elaborated in an inflammatory, IFN-gamma/TNF-alphaa induced confluent MDCK model mimicking inflammatory epithelial pathologies. Activities of active form Rho-GTPases (Rho-A and Rac-1) in proliferating and confluent MDCK cells were monitored by pull-down assay and Western blot analysis.

RESULTS

We observed marked endocytic uptake of the peptides into proliferating MDCK by a process suggesting both lipid rafts and clathrin-coated pits. In confluent MDCK, however, we noted a massive but compound-unspecific slow-down of endocytosis. This corresponded with a down-regulation of endocytosis by Rho-GTPases, previously identified to be intimately involved in endocytic traffic. In fact, we found endocytic internalization to relate with active Rho-A; vice versa, MDCK cell density, degree of cellular differentiation and endocytic slow-down were found to relate with active Rac-1. To our knowledge, this is the first study to cast light on the previously observed differentiation restricted internalization of CPPs into epithelial cell models. In the inflammatory IFN-gamma/TNF-alphaa induced confluent MDCK model mimicking inflammatory epithelial pathologies, CPP internalization was enhanced in a cytokine concentration-dependent way resulting in maximum enhancement rates of up to 90%. We suggest a cytokine induced redistribution of lipid rafts in confluent MDCK to cause this enhancement.

CONCLUSION

Our findings emphasize the significance of differentiated cell models in the study of CPP internalization and point towards inflammatory epithelial pathologies as potential niche for the application of CPPs for cellular delivery.

Deoxycholate-induced colitis is markedly attenuated in Nos2 knockout mice in association with modulation of gene expression profiles

Nos2 knockout mice were compared to wild-type mice for susceptibility to colitis in response to a diet supplemented with deoxycholate, a bile acid increased in the colon of individuals on a high-fat diet. Wild-type mice fed a fat-related diet, supplemented with 0.2% DOC, develop colonic inflammation associated with increases in nitrosative stress, proliferation, oxidative DNA/RNA damage, and angiogenesis, as well as altered expression of numerous genes. However, Nos2 knockout mice fed a diet supplemented with deoxycholate were resistant to these alterations. In particular, 35 genes were identified whose expression was significantly altered at the mRNA level in deoxycholate-fed Nos2(+/+) mice but not in deoxycholate-fed Nos2(-/-) mice. Some of these alterations in NOS2-dependent gene expression correspond to those reported in human inflammatory bowel disease. Overall, our results indicate that NOS2 expression is necessary for the development of deoxycholate-induced colitis in mice, a unique dietary-related model of colitis.

Tight junction proteins in gallbladder epithelium: different expression in acute acalculous and calculous cholecystitis

There is a paucity of information of tight junction (TJ) proteins in gallbladder epithelium, and disturbances in the structure of these proteins may play a role in the pathogenesis of acute acalculous cholecystitis (AAC) and acute calculous cholecystitis (ACC). Using immunohistochemistry, we investigated the expression of TJ proteins claudin-1, -2, -3, and -4, occludin, zonula occludens (ZO-1), and E-cadherin in 9 normal gallbladders, 30 gallbladders with AAC, and 21 gallbladders with ACC. The number of positive epithelial and endothelial cells and the intensity of the immunoreaction were determined. Membrane-bound and cytoplasmic immunoreactivities were separately assessed. We found that TJ proteins were uniformly expressed in normal gallbladder epithelium, with the exception of claudin-2, which was present in less than half of the cells. In AAC, expression of cytoplasmic occludin and claudin-1 were decreased, as compared with normal gallbladder. In ACC, expression of claudin-2 was increased, and expression of claudin-1, -3, and -4, occludin, and ZO-1 were decreased, as compared with normal gallbladder or AAC. We conclude that there are significant differences in expression of TJ proteins in AAC and ACC, supporting the idea that AAC represents a manifestation of systemic inflammatory disease, whereas ACC is a local inflammatory and often infectious disease.

Molecular basis of epithelial barrier regulation: from basic mechanisms to clinical application

The intestinal epithelium is faced with the complex task of providing a barrier while also allowing nutrient and water absorption. The frequency with which these processes are disrupted in disease can be taken as evidence of their importance. It is therefore of interest to define the mechanisms of altered intestinal barrier and transport function and develop means to correct disease-associated defects. Over the past 10 years, some of the molecular events underlying physiological epithelial barrier regulation have been described. Remarkably, recent advances have shown that activation of the same mechanisms is central to barrier dysfunction in both in vitro and in vivo models of disease. Although the contribution of barrier dysfunction to pathogenesis of chronic disease remains incompletely understood, it is now clear that cytoskeletal regulation of barrier function is both an important pathogenic process and that targeted inhibition of myosin light chain kinase, which affects this cytoskeleton-dependent tight junction dysfunction, is an attractive candidate for therapeutic intervention.

Changes in expression and distribution of claudin 2, 5 and 8 lead to discontinuous tight junctions and barrier dysfunction in active Crohn's disease

BACKGROUND

Epithelial barrier function is impaired in Crohn's disease.

AIM

To define the underlying cellular mechanisms with special attention to tight junctions.

METHODS

Biopsy specimens from the sigmoid colon of patients with mild to moderately active or inactive Crohn's disease were studied in Ussing chambers, and barrier function was determined by impedance analysis and conductance scanning. Tight junction structure was analysed by freeze fracture electron microscopy, and tight junction proteins were investigated immunohistochemically by confocal laser scanning microscopy and quantified in immunoblots. Epithelial apoptosis was analysed in terminal deoxynucleotidyl transferase-mediated deoxyuridine triphosphate nick-end labelling and 4',6-diamidino-2-phenylindole staining.

RESULTS

Patients with active Crohn's disease showed an impaired intestinal barrier function as indicated by a distinct reduction in epithelial resistance. As distribution of conductivity was even, focal epithelial lesions (eg, microerosions) did not contribute to barrier dysfunction. Instead, freeze fracture electron microscopy analysis showed reduced and discontinuous tight junction strands. Occludin and the sealing tight junction proteins claudin 5 and claudin 8 were downregulated and redistributed off the tight junction, whereas the pore-forming tight junctions protein claudin 2 was strongly upregulated, which constitute the molecular basis of tight junction changes. Other claudins were unchanged (claudins 1, 4 and 7) or not detectable in sigmoid colon (claudins 11, 12, 14, 15 and 16). Claudin 2 upregulation was less pronounced in active Crohn's disease compared with active ulcerative colitis and was inducible by tumour necrosis factor alpha. As a second source of impaired barrier function, epithelial apoptosis was distinctly increased in active Crohn's disease (mean (SD) 5.2 (0.5)% v 1.9 (0.2)% in control). By contrast, barrier function, tight junction proteins and apoptosis were unaffected in Crohn's disease in remission.

CONCLUSION

Upregulation of pore-forming claudin 2 and downregulation and redistribution of sealing claudins 5 and 8 lead to altered tight junction structure and pronounced barrier dysfunction already in mild to moderately active Crohn's disease.

Inflammatory bowel disease and the apical junctional complex

A critical function of the intestinal mucosa is to form a barrier that separates luminal contents from the underlying interstitium. This intestinal barrier is primarily regulated by the apical junctional complex (AJC) consisting of tight junctions (TJs) and adherens junctions (AJs) and is compromised in a number of intestinal diseases, including inflammatory bowel disease (IBD). In vitro studies have demonstrated that proinflammatory cytokines, such as interferon-gamma (IFN-gamma) and tumor necrosis factor-alpha (TNF-alpha), that are increased in the intestinal mucosa of patients with IBD can induce a leaky mucosal barrier. There is a growing evidence that the increased permeability and altered AJC structure observed in IBD are mediated by internalization of junctional proteins. This review summarizes barrier defects observed in IBD and addresses mechanisms by which proinflammatory cytokines, such as IFN-gamma and TNF-alpha, modulate AJC structure and epithelial barrier function.

Intestinal barrier failure during experimental necrotizing enterocolitis: protective effect of EGF treatment

Necrotizing enterocolitis (NEC) is the most common intestinal disease of premature infants. Although increased mucosal permeability and altered epithelial structure have been associated with many intestinal disorders, the role of intestinal barrier function in NEC pathogenesis is currently unknown. We investigated the structural and functional changes of the intestinal barrier in a rat model of NEC. In addition, the effect of EGF treatment on intestinal barrier function was evaluated. Premature rats were divided into three groups: dam fed (DF), formula fed (NEC), or fed with formula supplemented with 500 ng/ml EGF (NEC + EGF); all groups were exposed to asphyxia/cold stress to develop NEC. Intestinal permeability, goblet cell density, mucin production, and composition of tight junction (TJ) proteins were evaluated in the terminal ileum, the site of NEC injury, and compared with the proximal jejunum, which was unaffected by NEC. Animals with NEC had significantly increased intestinal paracellular permeability compared with DF pups. Ileal goblet cell morphology, mucin production, and TJ composition were altered in animals with NEC. EGF treatment significantly decreased intestinal paracellular permeability, increased goblet cell density and mucin production, and normalized expression of two major TJ proteins, occludin and claudin-3, in the ileum. In conclusion, experimental NEC is associated with disruption of the intestinal barrier. EGF treatment maintains intestinal integrity at the site of injury by accelerating goblet cell maturation and mucin production and normalizing expression of TJ proteins, leading to improved intestinal barrier function.

ADAM15 upregulation and interaction with multiple binding partners in inflammatory bowel disease

A disintegrin and metalloproteinase (ADAM)15 is upregulated in some tissues undergoing remodeling. This glycoprotein is characterized by adhesive function through its interaction with members of the integrin family and protease properties. The goal of this work was to describe the tissue distribution of ADAM15 and its spatial relationship with its known binding partners in inflammatory bowel disease. ADAM15 expression was examined using frozen tissues from eight patients with ulcerative colitis or Crohn's disease and four normal colons by immunohistochemistry, immunoblotting and quantitative reverse transcription-polymerase chain reaction. In addition expression of alpha5beta1- and alphavbeta3-integrins, VE-cadherin, alpha-smooth muscle actin (alpha-SMA) and collagen IV was examined using immunohistochemistry and confocal microscopy. In the normal colon, ADAM15 was expressed by all epithelial cells throughout the crypt and by pericryptic myofibroblasts coexpressing alpha-SMA and collagen IV. ADAM15 was also expressed by endothelial cells and vascular myocytes in all layers of the intestinal wall as well as by nonvascular myocytes of the muscularis mucosae and muscularis propria. In inflammatory bowel diseases, ADAM15 was strongly upregulated at the mRNA level and expressed only as an active form as shown by immunoblotting analysis. Parallel to its upregulation, ADAM15 expression was found both at the plasma membrane and in the cytoplasm of epithelial cells in acute attacks of the disease. In the crypt abcesses, ADAM15-positive epithelial cells were in close contact with alpha5beta1-integrin-positive leukocytes localized between these cells and in the crypt lumen. In the regenerative areas, ADAM15-positive epithelial cells were in close contact with alpha5beta1- and alphavbeta3-positive pericryptic myofibroblasts. In endothelial cells, VE-cadherin was decreased. In contrast, ADAM15 was strongly expressed by endothelial cells and was in close contact with alpha5beta1-positive leukocytes. There is a differential expression of ADAM15 in epithelial cells during inflammatory bowel disease compared with the normal colon. In addition, the spatial relationships with its binding partners suggest a role for ADAM15 in the differentiation of regenerative colonic mucosa as well as in leukocyte transmigration across epithelial and endothelial barriers.

Claudins--key pieces in the tight junction puzzle

Tight junctions restrict the flow of ions and aqueous molecules between cells by forming a selective barrier to the paracellular pathway. Permeability of the tight junction barrier is determined by a class of transmembrane proteins known as claudins. The relationship between claudins and paracellular permeability is complex and determined not only by the profile of claudin expression but also by the arrangement of claudins and other proteins into tight junction strands. This review summarizes progress in understanding how claudins are assembled into tight junctions and how they interact with other tight junction proteins.

Breakdown of intestinal mucosa via accelerated apoptosis increases intestinal permeability in experimental severe acute pancreatitis

BACKGROUND

Bacterial translocation plays an important role for infectious complications in severe acute pancreatitis (SAP). Breakdown of intestinal mucosal integrity may increase intestinal permeability and may be implicated in bacterial translocation. It is suggested that increase in intestinal permeability is correlated with the changes of tight junction and/or apoptosis in intestinal epithelial cells. The aim of this study was to investigate the changes of intestinal mucosa and its permeability in SAP.

METHODS

SAP was induced by injection of 3% sodium deoxycholate into the biliopancreatic ducts in rats. Permeability of intestinal wall was assayed ex vivo by measuring the leaked amount of FITC-dextran from the ileum pouch. Alteration of tight junction proteins such as zonula occludens (ZO)-1 and Occludin was evaluated by Western blotting and immunofluorescence staining. Apoptotic change of intestinal mucosa was detected by TUNEL staining and DNA fragmentation ELISA. In vitro, apoptosis-inducing effect of pancreatitis-associated ascitic fluid (PAAF) was examined using T84 cells. Integrity of monolayer cells was assessed by transepithelial electric resistance (TEER).

RESULTS

Permeability of ileum was significantly increased 6 h after induction of SAP. Blood endotoxin level was significantly elevated and bacterial translocation occurred 18 h after induction of SAP. Six hours after induction of SAP, expressions of ZO-1 and Occludin were not altered, but apoptosis of ileum mucosa was significantly accelerated. Addition of PAAF to T84 cells did not affect expressions of ZO-1 or Occludin, but significantly increased the apoptosis and significantly decreased TEER.

CONCLUSIONS

These results suggest that breakdown of intestinal mucosa via accelerated apoptosis may increase in intestinal permeability in SAP and that PAAF contains factor(s) that accelerates the apoptosis of intestinal epithelial cells.

Lipopolysaccharide induces CXCL2/macrophage inflammatory protein-2 gene expression in enterocytes via NF-kappaB activation: independence from endogenous TNF-alpha and platelet-activating factor

CXCL2 (macrophage inflammatory protein-2 (MIP-2)), a critical chemokine for neutrophils, has been shown to be produced in the rat intestine in response to platelet-activating factor (PAF) and to mediate intestinal inflammation and injury. The intestinal epithelium, constantly exposed to bacterial products, is the first line of defence against micro-organisms. It has been reported that enterocytes produce proinflammatory mediators, including tumour necrosis factor (TNF) and PAF, and we showed that lipopolysaccharide (LPS) and TNF activate nuclear factor (NF)-kappaB in enterocytes. However, it remains elusive whether enterocytes release CXCL2 in response to LPS and TNF via a NF-kappaB-dependent pathway and whether this involves the endogenous production of TNF and PAF. In this study, we found that TNF and LPS markedly induced CXCL2 gene expression in IEC-6 cells, TNF within 30 min, peaking at 45 min, while LPS more slowly, peaking after 2 hr. TNF- and LPS- induced CXCL2 gene expression and protein release were completely blocked by pyrrolidine dithiocarbamate (PDTC) and helenalin, two potent NF-kappaB inhibitors. NEMO-binding domain peptide, a specific inhibitor of inhibitor protein kappaB kinase (IKK) activation, a major upstream kinase mediating NF-kappaB activation, significantly blocked CXCL2 gene expression and protein release induced by LPS. WEB2170 (PAF antagonist) and anti-TNF antibodies had no effect on LPS-induced CXCL2 expression. In conclusion, CXCL2 gene is expressed in enterocytes in response to both TNF and LPS. LPS-induced CXCL2 expression is dependent on NF-kappaB activation via the IKK pathway. The effect of LPS is independent of endogenous TNF and PAF.

Cellular Networks of Human Thymic Medullary Stromas Coordinated by p53-Related Transcription Factors

The final elimination step of self-reactive T cells occurs in the medulla of the thymus where a complex framework provided by stromal cells supports an optimal milieu for their selection. Here we present evidence that tight junctions (TJs) widely join medullary stromal cells of the human thymus. Occludin (OCLN) and claudin-1 (CLDN-1) of TJ-associated molecules were dominantly expressed in medullary thymic epithelial cells (mTECs), and CLDN-4 and CLDN-7 were also localized in some mTECs near Hassall's corpuscles. Interestingly, p53-like transcription factors were found to upregulate OCLN and CLDN-1 in human TEC lines, as recently suggested in the regulation of mTEC function. Furthermore, dendritic cells (DCs) of the medulla, with a major role for selection of thymocytes, expressed CLDN-1 and OCLN as well, implying that the interposition of DCs within the mTEC scaffold is also helped by TJs. Analysis of freeze-fracture replicas of the thymus revealed TJ strand structures in the vicinity of gap junction plaques through which small molecules might move, as implied by dye-transfer analysis of a medullary cell line. Thus, it is thought that p53-like molecules regulate TJ-associated interactions of medullary stromal cells and that this mechanism might be associated with an intercellular communication network, probably for preserving the medullary niches.

Transgenic mice rich in endogenous omega-3 fatty acids are protected from colitis

Omega-6 (n-6) and omega-3 (n-3) polyunsaturated fatty acids (PUFA) are the precursors of potent lipid mediators and play an important role in regulation of inflammation. Generally, n-6 PUFA promote inflammation whereas n-3 PUFA have antiinflammatory properties, traditionally attributed to their ability to inhibit the formation of n-6 PUFA-derived proinflammatory eicosanoids. Newly discovered resolvins and protectins are potent antiinflammatory lipid mediators derived directly from n-3 PUFA with distinct pathways of action. However, the role of the n-3 PUFA tissue status in the formation of these antiinflammatory mediators has not been addressed. Here we show that an increased n-3 PUFA tissue status in transgenic mice that endogenously biosynthesize n-3 PUFA from n-6 PUFA leads to significant formation of antiinflammatory resolvins and effective reduction in inflammation and tissue injury in colitis. The endogenous increase in n-3 PUFA and related products did not decrease n-6 PUFA-derived lipid mediators such as leukotriene B4 and prostaglandin E2. The observed inflammation protection might result from decreased NF-kappaB activity and expression of TNFalpha, inducible NO synthase, and IL-1beta, with enhanced mucoprotection probably because of the higher expression of trefoil factor 3, Toll-interacting protein, and zonula occludens-1. These results thus establish the fat-1 transgenic mouse as a new experimental model for the study of n-3 PUFA-derived lipid mediators. They add insight into the molecular mechanisms of inflammation protection afforded by n-3 PUFA through formation of resolvins and protectins other than inhibition of n-6 PUFA-derived eicosanoid formation.

Fecal S100A12: a novel noninvasive marker in children with Crohn's disease

BACKGROUND

The calcium-binding protein S100A12 is related to calprotectin, a protein shown to be a useful marker of gut inflammation. S100A12 levels are elevated in serum and mucosa of children with inflammatory bowel disease (IBD) and may be implicated in the pathogenesis of IBD. The aims of this study were to validate an immunoassay for the detection of fecal S100A12, to assess its value as a new noninvasive marker of gut inflammation, and to investigate S100A12 levels in feces of children with IBD at diagnosis and during treatment.

MATERIALS AND METHODS

Feces were collected from children with active IBD at diagnosis and during treatment for IBD and from normal healthy control subjects. Fecal and serum levels of S100A12 were measured by immunoassay.

RESULTS

A sensitivity of 96% and a specificity of 92% were observed when 10 mg/kg fecal S100A12 was used as a cutoff. S100A12 levels were evenly distributed throughout fecal samples and were stable for 7 days when stored at room temperature. Fecal S100A12 was elevated in children with IBD compared with healthy control subjects, with levels closely correlated to disease activity and other serum inflammatory markers, particularly lower gut involvement. Fecal S100A12 levels fell during therapy in children entering remission with normal C-reactive protein levels.

CONCLUSIONS

Fecal S100A12 is a novel noninvasive marker that distinguishes children with active IBD from healthy control subjects with high sensitivity and specificity. Fecal S100A12 possesses characteristics that are desirable for a noninvasive disease marker and therefore is a suitable candidate marker for IBD. Further evaluation is required to examine this marker in additional contexts.

Microscopic colitis demonstrates a T helper cell type 1 mucosal cytokine profile

BACKGROUND

Microscopic colitis (MC) is an inflammatory disorder of unknown aetiology.

AIM

To characterise the mucosal cytokine profile of MC, with a view to understanding its potential pathogenic mechanisms.

METHODS

Cytokine profiles of mucosal biopse specimens taken at flexible sigmoidoscopy from 18 patients (8 with lymphocytic colitis and 10 with collagenous colitis) were analysed using real-time reverse transcriptase-PCR, in comparison with those from 13 aged-matched controls with diarrhoea-predominant irritable bowel syndrome. Biopsy specimens from six patients with histologically documented remission were available for comparative analysis. Biopsy specimens were also taken to determine the cellular expression of cytokine and cytokine-related proteins using immunohistochemistry.

RESULTS

Mucosal mRNA levels were 100 times greater for interferon (IFN)gamma and interleukin (IL) 15, 60 times greater for tumour necrosis factor alpha, and 35 times greater for inducible nitric oxide synthase in MC compared with controls. Apart from a trend for increased levels of IL10, levels of other T helper cell type 2 (T(H)2) cytokines including IL2 and IL4 were too low to be accurately quantified. Mucosal IFNgamma mRNA levels correlated with the degree of diarrhoea, and returned to normal in remission. The immunohistochemical expression of cell junction proteins E-cadherin and ZO-1 was reduced in active disease. No differences were noted between lymphocytic and collagenous colitis for any of the above parameters.

CONCLUSIONS

MC demonstrates a T(H)1 mucosal cytokine profile with IFNgamma as the predominantly upregulated cytokine, with concurrent induction of nitric oxide synthase and down regulation of IFNgamma-related cell junction proteins. This pattern is similar to that in coeliac disease and suggests that it might represent a response to a luminal antigen.

Casein kinase I epsilon associates with and phosphorylates the tight junction protein occludin

Occludin is an integral-membrane protein that contributes to tight junction function. We have identified casein kinase I epsilon (CKI epsilon) as a binding partner for the C-terminal cytoplasmic domain of occludin by yeast two-hybrid screening. CKI epsilon phosphorylated occludin and co-localised and co-immunoprecipitated with occludin from human endothelial cells. Amino acids 265-318 of occludin were sufficient for CKI epsilon binding and phosphorylation. Deletion of the C-terminal 48 amino acids of occludin increased CKI epsilon binding and phosphorylation, suggesting that this region inhibits CKI epsilon binding. These data identify CKI epsilon as a novel occludin kinase that may be important for the regulation of occludin.