Interleukin-1 receptor phosphorylation activates Rho kinase to disrupt human gastric tight junctional claudin-4 during Helicobacter pylori infection

Gastric Epithelial Barrier Disruption, Inflammation and Oncogenic Signal Transduction by Helicobacter pylori

Helicobacter pylori exemplifies one of the most favourable bacterial pathogens worldwide. The bacterium colonizes the gastric mucosa in about half of the human population and constitutes a major risk factor for triggering gastric diseases such as stomach cancer. H. pylori infection represents a prime example of chronic inflammation and cancer-inducing bacterial pathogens. The microbe utilizes a remarkable set of virulence factors and strategies to control cellular checkpoints of inflammation and oncogenic signal transduction. This chapter emphasizes on the pathogenicity determinants of H. pylori such as the cytotoxin-associated genes pathogenicity island (cagPAI)-encoded type-IV secretion system (T4SS), effector protein CagA, lipopolysaccharide (LPS) metabolite ADP-glycero-β-D-manno-heptose (ADP-heptose), cytotoxin VacA, serine protease HtrA, and urease, and how they manipulate various key host cell signaling networks in the gastric epithelium. In particular, we highlight the H. pylori-induced disruption of cell-to-cell junctions, pro-inflammatory activities, as well as proliferative, pro-apoptotic and anti-apoptotic responses. Here we review these hijacked signal transduction events and their impact on gastric disease development.

Lactic Acid Bacteria Strains Used as Starters for Kimchi Fermentation Protect the Disruption of Tight Junctions in the Caco-2 Cell Monolayer Model

In this study, we investigated the effect of lactic acid bacteria (LAB) strains used as starters for kimchi fermentation, namely Lactococcus lactis WiKim0124, Companilactobacillus allii WiKim39, Leuconostoc mesenteroides WiKim0121 Leuconostoc mesenteroides WiKim33, and Leuconostoc mesenteroides WiKim32, on the intestinal epithelial tight junctions (TJs). These LAB strains were not cytotoxic to Caco-2 cells at 500 μg/ml concentration. In addition, hydrogen peroxide (H₂O₂) decreased Caco-2 viability, but the LAB strains protected the cells against H₂O₂-induced cytotoxicity. We also found that lipopolysaccharide (LPS) promoted Caco-2 proliferation; however, no specific changes were observed upon treatment with LAB strains and LPS. Our evaluation of the permeability in the Caco-2 monolayer model confirmed its increase by both LPS and H₂O₂. The LAB strains inhibited the increase in permeability by protecting TJs, which we evaluated by measuring TJ proteins such as zonula occludens-1 and occludin, and analyzing them by western blotting and immunofluorescence staining. Our findings show that LAB strains used for kimchi fermentation can suppress the increase in intestinal permeability due to LPS and H₂O₂ by protecting TJs. Therefore, these results suggest the possibility of enhancing the functionality of kimchi through its fermentation using functional LAB strains.

Under the Radar: Strategies Used by Helicobacter pylori to Evade Host Responses

The body depends on its physical barriers and innate and adaptive immune responses to defend against the constant assault of potentially harmful microbes. In turn, successful pathogens have evolved unique mechanisms to adapt to the host environment and manipulate host defenses. Helicobacter pylori (Hp), a human gastric pathogen that is acquired in childhood and persists throughout life, is an example of a bacterium that is very successful at remodeling the host-pathogen interface to promote a long-term persistent infection. Using a combination of secreted virulence factors, immune subversion, and manipulation of cellular mechanisms, Hp can colonize and persist in the hostile environment of the human stomach. Here, we review the most recent and relevant information regarding how this successful pathogen overcomes gastric epithelial host defense responses to facilitate its own survival and establish a chronic infection. Expected final online publication date for the Annual Review of Physiology, Volume 84 is February 2022. Please see http://www.annualreviews.org/page/journal/pubdates for revised estimates.

The neuromicrobiology of Parkinson's disease: A unifying theory

Recent evidence confirms that PD is indeed a multifactorial disease with different aetiologies and prodromal symptomatology that likely depend on the initial trigger. New players with important roles as triggers, facilitators and aggravators of the PD neurodegenerative process have re-emerged in the last few years, the microbes. Having evolved in association with humans for ages, microbes and their products are now seen as fundamental regulators of human physiology with disturbances in their balance being increasingly accepted to have a relevant impact on the progression of disease in general and on PD in particular. In this review, we comprehensively address early studies that have directly or indirectly linked bacteria or other infectious agents to the onset and progression of PD, from the earliest suspects to the most recent culprits, the gut microbiota. The quest for effective treatments to arrest PD progression must inevitably address the different interactions between microbiota and human cells, and naturally consider the gut-brain axis. The comprehensive characterization of such mechanisms will help design innovative bacteriotherapeutic approaches to selectively shape the gut microbiota profile ultimately to halt PD progression. The present review describes our current understanding of the role of microorganisms and their endosymbiotic relatives, the mitochondria, in inducing, facilitating, or aggravating PD pathogenesis.

Gut Microbiota: Influence on Carcinogenesis and Modulation Strategies by Drug Delivery Systems to Improve Cancer Therapy

Gut microbiota have close interactions with the host. It can affect cancer progression and the outcomes of cancer therapy, including chemotherapy, immunotherapy, and radiotherapy. Therefore, approaches toward the modulation of gut microbiota will enhance cancer prevention and treatment. Modern drug delivery systems (DDS) are emerging as rational and promising tools for microbiota intervention. These delivery systems have compensated for the obstacles associated with traditional treatments. In this review, the essential roles of gut microbiota in carcinogenesis, cancer progression, and various cancer therapies are first introduced. Next, advances in DDS that are aimed at enhancing the efficacy of cancer therapy by modulating or engineering gut microbiota are highlighted. Finally, the challenges and opportunities associated with the application of DDS targeting gut microbiota for cancer prevention and treatment are briefly discussed.

Tight Junctions as a Key for Pathogens Invasion in Intestinal Epithelial Cells

Tight junctions play a major role in maintaining the integrity and impermeability of the intestinal barrier. As such, they act as an ideal target for pathogens to promote their translocation through the intestinal mucosa and invade their host. Different strategies are used by pathogens, aimed at directly destabilizing the junctional network or modulating the different signaling pathways involved in the modulation of these junctions. After a brief presentation of the organization and modulation of tight junctions, we provide the state of the art of the molecular mechanisms leading to permeability breakdown of the gut barrier as a consequence of tight junctions’ attack by pathogens, including bacteria, viruses, fungi, and parasites.

Expression of Tight Junction Proteins According to Functional Dyspepsia Subtype and Sex

Background/Aims

To determine whether the expression of tight junction proteins (TJPs) differs depending on the subtype of functional dyspepsia (FD) and sex.

Methods

Control (n = 95) and FD (n = 165) groups based on Rome III criteria were prospectively enrolled. Gastric mucosal mRNA expression levels of various TJPs (claudins [CLDN] 1, 2, and 4; zonula occludens-1; occludin [OCLN]) were assessed by reverse transcription polymerase chain reaction. Western blot was performed to determine the levels of various TJPs. Helicobacter pylori infection status was evaluated by histology, rapid urease test, and culture. Questionnaires were analyzed.

Results

In all groups irrespective of H. pylori, FD group showed significantly higher CLDN2 mRNA levels than control group (P = 0.048). The level of CLDN4 mRNA expression was significantly lower in female FD group than in male FD group (P = 0.018). In H. pylori uninfected subjects, the level of CLDN1 mRNA expression in female FD group was significantly lower than that of male FD group (P = 0.014). The level of CLDN2 mRNA expression was significantly higher in the male postprandial distress syndrome (P = 0.001) and male epigastric pain syndrome (P = 0.023) groups than in the male control group. In Western blot analysis, the expression of OCLN was significantly elevated 48 hour after the culture with H. pylori strain 43504.

Conclusions

H. pylori can affect a variety of TJPs, particularly claudin-4 and occludin. Claudin-2 is thought to be involved in FD irrespective of H. pylori status, especially in the pathophysiology of male FD.

Targeting claudin-4 enhances CDDP-chemosensitivity in gastric cancer

Claudins are major tight-junction proteins that mediate cellular polarity and differentiation. The present study investigated whether the 4D3 antibody to the human CLDN4 extracellular domain (that we previously established) is capable of modulating chemotherapeutic sensitivity in gastric cancer (GC). The results of the present study showed that CLDN4 was overexpressed in 137 of the 192 analyzed GC cases, and that CLDN4 expression was retained in tumors of a lower histological grade (more differentiated), and/or those that were caudal-type homeobox protein 2 (CDX2)-positive, but was reduced in more highly undifferentiated, and CDX2-negative GC cases. The study also compared the synergic effects of combining 4D3 with CDDP treatment and knocking down CLDN4 expression in MKN74 and TMK-1 human GC cells. Co-treatment with 4D3 increased anti-tumor effects of CDDP, whereas CLDN4 knockdown did not. In the TMK-1 cells, non-tight junction CLDN4 associated with integrin β1, increasing stem cell-associated proteins via FAK-c-SRC signals. The anti-tumoral effect of CDDP and 4D3 was examined in a nude mouse subcutaneous tumor model. In the two GC cell lines, concurrent treatment with 4D3 and CDDP synergistically inhibited cell proliferation and increased tumor necrosis and apoptosis to a greater degree than CDDP treatment alone. These findings suggest that 4D3 might increase chemotherapeutic sensitivity by evoking structural disintegration of tight-junction CLDN4 expressed in gastric cancer.

EGF receptor plays a role in the mechanism of glutamine-mediated prevention of alcohol-induced gut barrier dysfunction and liver injury

Recent study indicated that glutamine prevents alcoholic tissue injury in mouse gut and liver. Here we investigated the potential role of Epidermal Growth Factor Receptor (EGFR) in glutamine-mediated prevention of ethanol-induced colonic barrier dysfunction, endotoxemia and liver damage. Wild-type and EGFR*Tg transgenic (expressing dominant negative EGFR) mice were fed 1-6% ethanol in Lieber-DeCarli diet. Gut permeability was measured by vascular-to-luminal flux of FITC-inulin, and junctional integrity assessed by confocal microscopy. Liver injury was evaluated by plasma transaminases, histopathology and triglyceride analyses. Glutamine effect on acetaldehyde-induced tight junction disruption was investigated in Caco-2 cell monolayers. Doxycycline-induced expression of EGFR* blocked glutamine-mediated prevention of ethanol-induced disruption of colonic epithelial tight junction, mucosal permeability and endotoxemia. Ethanol activated cofilin and disrupted actin cytoskeleton, which was blocked by glutamine in an EGFR-dependent mechanism. Ethanol down-regulated antioxidant gene expression and up-regulated cytokine and chemokine gene expression, which were blocked by glutamine in wild-type mice in the presence or absence of doxycycline, but not in EGFR*Tg mice in the presence of doxycycline. Histopathology, plasma transaminases, triglyceride and expression of chemokine and antioxidant genes indicated ethanol-induced liver damage, which were blocked by glutamine in an EGFR-dependent mechanism. Src kinase activity and extracellular ligand binding domain of EGFR are required for glutamine-mediated protection of barrier function in Caco-2 cell monolayers. Glutamine released metalloproteinases into the medium, and metalloproteinase inhibitors blocked glutamine-mediated protection of barrier function. Results demonstrate that EGFR plays an important role in glutamine-mediated prevention of alcoholic gut permeability, endotoxemia and liver damage.

Leaky brain in neurological and psychiatric disorders: Drivers and consequences

BACKGROUND

The blood-brain barrier acts as a highly regulated interface; its dysfunction may exacerbate, and perhaps initiate, neurological and neuropsychiatric disorders.

METHODS

In this narrative review, focussing on redox, inflammatory and mitochondrial pathways and their effects on the blood-brain barrier, a model is proposed detailing mechanisms which might explain how increases in blood-brain barrier permeability occur and can be maintained with increasing inflammatory and oxidative and nitrosative stress being the initial drivers.

RESULTS

Peripheral inflammation, which is causatively implicated in the pathogenesis of major psychiatric disorders, is associated with elevated peripheral pro-inflammatory cytokines, which in turn cause increased blood-brain barrier permeability. Reactive oxygen species, such as superoxide radicals and hydrogen peroxide, and reactive nitrogen species, such as nitric oxide and peroxynitrite, play essential roles in normal brain capillary endothelial cell functioning; however, chronically elevated oxidative and nitrosative stress can lead to mitochondrial dysfunction and damage to the blood-brain barrier. Activated microglia, redox control of which is mediated by nitric oxide synthases and nicotinamide adenine dinucleotide phosphate (NADPH) oxidases, secrete neurotoxic molecules such as reactive oxygen species, nitric oxide, prostaglandin, cyclooxygenase-2, quinolinic acid, several chemokines (including monocyte chemoattractant protein-1 [MCP-1], C-X-C motif chemokine ligand 1 [CXCL-1] and macrophage inflammatory protein 1α [MIP-1α]) and the pro-inflammatory cytokines interleukin-6, tumour necrosis factor-α and interleukin-1β, which can exert a detrimental effect on blood-brain barrier integrity and function. Similarly, reactive astrocytes produce neurotoxic molecules such as prostaglandin E2 and pro-inflammatory cytokines, which can cause a 'leaky brain'.

CONCLUSION

Chronic inflammatory and oxidative and nitrosative stress is associated with the development of a 'leaky gut'. The following evidence-based approaches, which address the leaky gut and blood-brain barrier dysfunction, are suggested as potential therapeutic interventions for neurological and neuropsychiatric disorders: melatonin, statins, probiotics containing Bifidobacteria and Lactobacilli, N-acetylcysteine, and prebiotics containing fructo-oligosaccharides and galacto-oligosaccharides.

Invasive non-typhoidal Salmonella in sickle cell disease in Africa: is increased gut permeability the missing link?

Non-typhoidal Salmonella usually induces self-limiting gastroenteritis. However, in many parts of Africa, especially in individuals who are malnourished, infected with malaria, or have sickle cell disease, the organism causes serious and potentially fatal systemic infections. Since the portal of entry of non-typhoidal Salmonella into the systemic circulation is by way of the intestine, we argue that an increased gut permeability plays a vital role in the initiation of invasive non-typhoidal Salmonella in these patients. Here, we will appraise the evidence supporting a breach in the intestinal barrier and propose the mechanisms for the increased risks for invasive non-typhoidal Salmonella infections in these individuals.

Impact of microbiota in colorectal carcinogenesis: lessons from experimental models

A role of gut microbiota in colorectal cancer (CRC) growth was first suggested in germ-free rats almost 50 years ago, and the existence of disease-associated bacteria (termed pathobionts) had becoming increasingly evident from experimental data of fecal transplantation, and microbial gavage or monoassociation. Altered bacterial compositions in fecal and mucosal specimens were observed in CRC patients compared to healthy subjects. Microbial fluctuations were found at various cancer stages; an increase of bacterial diversity was noted in the adenoma specimens, while a reduction of bacterial richness was documented in CRC samples. The bacterial species enriched in the human cancerous tissues included Escherichia coli, Fusobacterium nucleatum, and enterotoxigenic Bacteroides fragilis. The causal relationship of gut bacteria in tumorigenesis was established by introducing particular bacterial strains in in situ mouse CRC models. Detailed experimental protocols of bacterial gavage and the advantages and caveats of different experimental models are summarized in this review. The microbial genotoxins, enterotoxins, and virulence factors implicated in the mechanisms of bacteria-driven tumorigenesis are described. In conclusion, intestinal microbiota is involved in colon tumorigenesis. Bacteria-targeting intervention would be the next challenge for CRC.

The Role of Macrophage Migration Inhibitory Factor in the Function of Intestinal Barrier

Macrophage migration inhibitory factor (MIF) is a multifunctional protein that is involved in the development of gut-related inflammation. To investigate the role of MIF in the function of the intestinal barrier, we have explored intestinal permeability and gut-associated immune response in MIF-deficient (MIF-KO) mice. The absence of MIF provoked impairment of tight and adherens epithelial junctions in the colon through the disturbance of E-cadherin, zonula occludens-1, occludin and claudin-2 expression, which lead to the increase of intestinal barrier permeability. In these circumstances the diversity and content of gut microbiota in MIF-KO mice was considerably different compared to wild type mice. This change in microbiota was accompanied by an increased intestinal IgA concentration and a higher production of pro-inflammatory cytokines TNF and IFN-γ in mesenteric lymph nodes of MIF-KO mice. The forced changes of microbiota executed by antibiotics prevented the "leakage" of the barrier in MIF-KO mice, probably through up-regulation of occludin expression and normalization of cellular pore diameters. In addition, cytokine secretion was normalized after the treatment with antibiotics. These results suggest that MIF participates in the maintenance of physiological microbiota diversity and immunosurveillance, which in turn enables the proper intestinal barrier function.

Modulation of Intestinal Paracellular Transport by Bacterial Pathogens

The passive and regulated movement of ions, solutes, and water via spaces between cells of the epithelial monolayer plays a critical role in the normal intestinal functioning. This paracellular pathway displays a high level of structural and functional specialization, with the membrane-spanning complexes of the tight junctions, adherens junctions, and desmosomes ensuring its integrity. Tight junction proteins, like occludin, tricellulin, and the claudin family isoforms, play prominent roles as barriers to unrestricted paracellular transport. The past decade has witnessed major advances in our understanding of the architecture and function of epithelial tight junctions. While it has been long appreciated that microbes, notably bacterial and viral pathogens, target and disrupt junctional complexes and alter paracellular permeability, the precise mechanisms remain to be defined. Notably, renewed efforts will be required to interpret the available data on pathogen-mediated barrier disruption in the context of the most recent findings on tight junction structure and function. While much of the focus has been on pathogen-induced dysregulation of junctional complexes, commensal microbiota and their products may influence paracellular permeability and contribute to the normal physiology of the gut. Finally, microbes and their products have become important tools in exploring host systems, including the junctional properties of epithelial cells. © 2018 American Physiological Society. Compr Physiol 8:823-842, 2018.

Sensing the enemy, containing the threat: cell-autonomous immunity to Chlamydia trachomatis

The bacterium Chlamydia trachomatis is the etiological agent of the most common sexually transmitted infection in North America and Europe. Medical complications resulting from genital C. trachomatis infections arise predominantly in women where the initial infections often remain asymptomatic and thus unrecognized. Untreated asymptomatic infections in women can ascend into the upper genital tract and establish persistence, ultimately resulting in extensive scarring of the reproductive organs, pelvic inflammatory disease, infertility and ectopic pregnancies. Previously resolved C. trachomatis infections fail to provide protective immune memory, and no effective vaccine against C. trachomatis is currently available. Critical determinants of the pathogenesis and immunogenicity of genital C. trachomatis infections are cell-autonomous immune responses. Cell-autonomous immunity describes the ability of an individual host cell to launch intrinsic immune circuits that execute the detection, containment and elimination of cell-invading pathogens. As an obligate intracellular pathogen C. trachomatis is constantly under attack by cell-intrinsic host defenses. Accordingly, C. trachomatis evolved to subvert and co-opt cell-autonomous immune pathways. This review will provide a critical summary of our current understanding of cell-autonomous immunity to C. trachomatis and its role in shaping host resistance, inflammation and adaptive immunity to genital C. trachomatis infections.

Tight junction disruption: Helicobacter pylori and dysregulation of the gastric mucosal barrier

Long-term chronic infection with Helicobacter pylori (H. pylori) is a risk factor for gastric cancer development. In the multi-step process that leads to gastric cancer, tight junction dysfunction is thought to occur and serve as a risk factor by permitting the permeation of luminal contents across an otherwise tight mucosa. Mechanisms that regulate tight junction function and structure in the normal stomach, or dysfunction in the infected stomach, however, are largely unknown. Although conventional tight junction components are expressed in gastric epithelial cells, claudins regulate paracellular permeability and are likely the target of inflammation or H. pylori itself. There are 27 different claudin molecules, each with unique properties that render the mucosa an intact barrier that is permselective in a way that is consistent with cell physiology. Understanding the architecture of tight junctions in the normal stomach and then changes that occur during infection is important but challenging, because most of the reports that catalog claudin expression in gastric cancer pathogenesis are contradictory. Furthermore, the role of H. pylori virulence factors, such as cytotoxin-associated gene A and vacoulating cytotoxin, in regulating tight junction dysfunction during infection is inconsistent in different gastric cell lines and in vivo, likely because non-gastric epithelial cell cultures were initially used to unravel the details of their effects on the stomach. Hampering further study, as well, is the relative lack of cultured cell models that have tight junction claudins that are consistent with native tissues. This summary will review the current state of knowledge about gastric tight junctions, normally and in H. pylori infection, and make predictions about the consequences of claudin reorganization during H. pylori infection.

New NCI-N87-derived human gastric epithelial line after human telomerase catalytic subunit over-expression

AIM: To establish a cellular model correctly mimicking the gastric epithelium to overcome the limitation in the study of Helicobacter pylori (H. pylori) infection.

METHODS: Aiming to overcome this limitation, clones of the heterogenic cancer-derived NCI-N87 cell line were isolated, by stably-transducing it with the human telomerase reverse-transcriptase (hTERT) catalytic subunit gene. The clones were first characterized regarding their cell growth pattern and phenotype. For that we measured the clones’ adherence properties, expression of cell-cell junctions’ markers (ZO-1 and E-cadherin) and ability to generate a sustained transepithelial electrical resistance. The gastric properties of the clones, concerning expression of mucins, zymogens and glycan contents, were then evaluated by haematoxylin and eosin staining, Periodic acid Schiff (PAS) and PAS/Alcian Blue-staining, immunocytochemistry and Western blot. In addition, we assessed the usefulness of the hTERT-expressing gastric cell line for H. pylori research, by performing co-culture assays and measuring the IL-8 secretion, by ELISA, upon infection with two H. pylori strains differing in virulence.

RESULTS: Compared with the parental cell line, the most promising NCI-hTERT-derived clones (CL5 and CL6) were composed of cells with homogenous phenotype, presented higher relative telomerase activities, better adhesion properties, ability to be maintained in culture for longer periods after confluency, and were more efficient in PAS-reactive mucins secretion. Both clones were shown to produce high amounts of MUC1, MUC2 and MUC13. NCI-hTERT-CL5 mucins were shown to be decorated with blood group H type 2 (BG-H), Lewis-x (Le^x), Le^y and Le^a and, in a less extent, with BG-A antigens, but the former two antigens were not detected in the NCI-hTERT-CL6. None of the clones exhibited detectable levels of MUC6 nor sialylated Le^x and Le^a glycans. Entailing good gastric properties, both NCI-hTERT-clones were found to produce pepsinogen-5 and human gastric lipase. The progenitor-like phenotype of NCI-hTERT-CL6 cells was highlighted by large nuclei and by the apical vesicular-like distribution of mucin 5AC and Pg5, supporting the accumulation of mucus-secreting and zymogens-chief mature cells functions.

CONCLUSION: These traits, in addition to resistance to microaerobic conditions and good responsiveness to H. pylori co-culture, in a strain virulence-dependent manner, make the NCI-hTERT-CL6 a promising model for future in vitro studies.

Intestinal permeability--a new target for disease prevention and therapy

Data are accumulating that emphasize the important role of the intestinal barrier and intestinal permeability for health and disease. However, these terms are poorly defined, their assessment is a matter of debate, and their clinical significance is not clearly established. In the present review, current knowledge on mucosal barrier and its role in disease prevention and therapy is summarized. First, the relevant terms 'intestinal barrier' and 'intestinal permeability' are defined. Secondly, the key element of the intestinal barrier affecting permeability are described. This barrier represents a huge mucosal surface, where billions of bacteria face the largest immune system of our body. On the one hand, an intact intestinal barrier protects the human organism against invasion of microorganisms and toxins, on the other hand, this barrier must be open to absorb essential fluids and nutrients. Such opposing goals are achieved by a complex anatomical and functional structure the intestinal barrier consists of, the functional status of which is described by 'intestinal permeability'. Third, the regulation of intestinal permeability by diet and bacteria is depicted. In particular, potential barrier disruptors such as hypoperfusion of the gut, infections and toxins, but also selected over-dosed nutrients, drugs, and other lifestyle factors have to be considered. In the fourth part, the means to assess intestinal permeability are presented and critically discussed. The means vary enormously and probably assess different functional components of the barrier. The barrier assessments are further hindered by the natural variability of this functional entity depending on species and genes as well as on diet and other environmental factors. In the final part, we discuss selected diseases associated with increased intestinal permeability such as critically illness, inflammatory bowel diseases, celiac disease, food allergy, irritable bowel syndrome, and--more recently recognized--obesity and metabolic diseases. All these diseases are characterized by inflammation that might be triggered by the translocation of luminal components into the host. In summary, intestinal permeability, which is a feature of intestinal barrier function, is increasingly recognized as being of relevance for health and disease, and therefore, this topic warrants more attention.

The role of epithelial tight junctions involved in pathogen infections

Tight junctions (TJs) are sealing complexes between adjacent epithelial cells, functioning by controlling paracellular passage and maintaining cell polarity. These functions of TJs are primarily based on structural integrity as well as dynamic regulatory balance, indicating plasticity of TJ in response to external stimuli. An indispensable role of TJs involved in pathogen infection has been widely demonstrated since disruption of TJs leads to a distinct increase in paracellular permeability and polarity defects which facilitate viral or bacterial entry and spread. In addition to pathological changes in TJ integrity, TJ proteins such as occludin and claudins can either function as receptors for pathogen entry or interact with viral/bacterial effector molecules as an essential step for characterizing an infective stage. This suggests a more complicated role for TJ itself and especially specific TJ components. Thus, this review surveys the role of the epithelial TJs involved in various pathogen infections, and extends TJ targeted therapeutic and pharmacological application prospects.

The P2Y6 receptor mediates Clostridium difficile toxin-induced CXCL8/IL-8 production and intestinal epithelial barrier dysfunction

C. difficile is a Gram-positive spore-forming anaerobic bacterium that is the leading cause of nosocomial diarrhea in the developed world. The pathogenesis of C. difficile infections (CDI) is driven by toxin A (TcdA) and toxin B (TcdB), secreted factors that trigger the release of inflammatory mediators and contribute to disruption of the intestinal epithelial barrier. Neutrophils play a key role in the inflammatory response and the induction of pseudomembranous colitis in CDI. TcdA and TcdB alter cytoskeletal signaling and trigger the release of CXCL8/IL-8, a potent neutrophil chemoattractant, from intestinal epithelial cells; however, little is known about the surface receptor(s) that mediate these events. In the current study, we sought to assess whether toxin-induced CXCL8/IL-8 release and barrier dysfunction are driven by the activation of the P2Y₆ receptor following the release of UDP, a danger signal, from intoxicated Caco-2 cells. Caco-2 cells express a functional P2Y₆ receptor and release measurable amounts of UDP upon exposure to TcdA/B. Toxin-induced CXCL8/IL-8 production and release were attenuated in the presence of a selective P2Y₆ inhibitor (MRS2578). This was associated with inhibition of TcdA/B-induced activation of NFκB. Blockade of the P2Y₆ receptor also attenuated toxin-induced barrier dysfunction in polarized Caco-2 cells. Lastly, pretreating mice with the P2Y₆ receptor antagonists (MSR2578) attenuated TcdA/B-induced inflammation and intestinal permeability in an intrarectal toxin exposure model. Taken together these data outline a novel role for the P2Y₆ receptor in the induction of CXCL8/IL-8 production and barrier dysfunction in response to C. difficile toxin exposure and may provide a new therapeutic target for the treatment of CDI.

Mechanisms underlying role of probiotics in recovering Helicobacter pylori-associated intestinal mucosal barrier damage

Helicobacter pylori (H. pylori) is closely associated with many gastrointestinal diseases, including peptic ulcers, chronic gastritis, gastric cancer and gastric mucosa-associated lymphoid tumors. In recent year, traditional triple therapy for H. pylori eradication has become less effective than the past, which is related to the resistance of bacteria. The addition of probiotics into the regimen has been proved to be able to significantly enhance the eradication rate and reduce side effects. Probiotics increase the eradication of H. pylori by recovering the damage of the chemical barrier, biological barrier, mechanical barrier and immune barrier.

Claudin-20 promotes an aggressive phenotype in human breast cancer cells

Claudin-20 is a member of the Claudin family of transmembrane proteins located in the tight junction (TJ) of cells of epithelial origin. Due to the increasing evidence supporting the role of TJ proteins in preventing tumor cell metastatic behavior, this study sought to evaluate the distribution of Claudin-20 in human breast cancer and the effect of Claudin-20 overexpression in human breast cancer cells. Q-PCR data from breast cancer primary tumors (n = 114) and matched background tissue (n = 30) showed that high claudin-20 expression was correlated with poor survival of patients with breast cancer (p = 0.022). Following transformation of the breast cancer cell lines MDA-MB-231 and MCF7 with a Claudin-20 expression construct functional assays were performed to ascertain changes in cell behavior. Claudin-20 transformed cells showed significantly increased invasion (p < 0.005) and were significantly less adhesive than wild type cells (p < 0.05). There was no effect on growth (either in vitro or in vivo) for either cell line. Overexpression of Claudin-20 resulted in reduced transepithelial resistance (induced by the motogen HGF at 25 ng/ml, p = 0.0007). Interestingly, this was not mirrored by paracellular permeability, as overexpression of Claudin-20 caused a decrease in permeability. The introduction of Claudin-20 into human breast cancer cells resulted in breast cancer cells with an aggressive phenotype and reduced trans-epithelial resistance. There was no corresponding decrease in paracellular permeability, indicating that this Claudin has a differential function in epithelial TJ. This provides further insight into the importance of correctly functioning TJ in preventing the progression of human breast cancer.

TGF-β1 induces the dissolution of tight junctions in human renal proximal tubular cells: role of the RhoA/ROCK signaling pathway

The RhoA/ROCK signaling pathway plays a significant role in transforming growth factor (TGF)-β1-mediated epithelial-mesenchymal transition (EMT). It remains unclear, however, whether the RhoA/ROCK signaling pathway mediates TGF-β1-induced EMT by promoting the dissolution of tight junctions (TJs) in renal proximal tubular epithelial cells. In this study, we aimed to investigate the association between TGF-β1-mediated Rho/ROCK signaling and TJs in a cell line derived from human renal proximal tubular cells (HK-2 cells). HK-2 cells were treated with 5 ng/ml TGF-β1 for 0, 12, 24 and 48 h. Zona occludens protein 1 (also known as tight junction protein 1; ZO-1) and occludin mRNA and protein levels were determined by real-time PCR and western blot analysis, respectively. The HK-2 cells were then divided into three groups: a control group (serum-free culture medium for 24 h); a TGF-β1 group (treated with 5 ng/ml TGF-β1 for 24 h); and a TGF-β1 + Y-27632 (a specific ROCK inhibitor) group (pre-treated with 10 µM Y-27632 for 2 h and subsequently treated with 5 ng/ml TGF-β1 for 24 h). The levels of ZO-1 and occludin were detected by real-time PCR, western blot analysis and immunofluorescence. As shown by our results, the mRNA and protein levels of ZO-1 and occludin were decreased in the HK-2 cells following treatment with TGF-β1 in a time-dependent manner; in addition, ZO-1 and occludin levels in the TGF-β1 + Y-27632 group were significantly increased compared with those of the TGF-β1 group (P<0.05), with no significant changes compared with the control group. Our results indicate that the Rho/ROCK signaling pathway mediated by TGF-β1 plays a role in the dissolution of TJs during EMT.

Urease from Helicobacter pylori is inactivated by sulforaphane and other isothiocyanates

Infections by Helicobacter pylori are very common, causing gastroduodenal inflammation including peptic ulcers, and increasing the risk of gastric neoplasia. The isothiocyanate (ITC) sulforaphane [SF; 1-isothiocyanato-4-(methylsulfinyl)butane] derived from edible crucifers such as broccoli is potently bactericidal against Helicobacter, including antibiotic-resistant strains, suggesting a possible dietary therapy. Gastric H. pylori infections express high urease activity which generates ammonia, neutralizes gastric acidity, and promotes inflammation. The finding that SF inhibits (inactivates) urease (jack bean and Helicobacter) raised the issue of whether these properties might be functionally related. The rates of inactivation of urease activity depend on enzyme and SF concentrations and show first order kinetics. Treatment with SF results in time-dependent increases in the ultraviolet absorption of partially purified Helicobacter urease in the 260-320 nm region. This provides direct spectroscopic evidence for the formation of dithiocarbamates between the ITC group of SF and cysteine thiols of urease. The potencies of inactivation of Helicobacter urease by isothiocyanates structurally related to SF were surprisingly variable. Natural isothiocyanates closely related to SF, previously shown to be bactericidal (berteroin, hirsutin, phenethyl isothiocyanate, alyssin, and erucin), did not inactivate urease activity. Furthermore, SF is bactericidal against both urease positive and negative H. pylori strains. In contrast, some isothiocyanates such as benzoyl-ITC, are very potent urease inactivators, but are not bactericidal. The bactericidal effects of SF and other ITC against Helicobacter are therefore not obligatorily linked to urease inactivation, but may reduce the inflammatory component of Helicobacter infections.

Helicobacter pylori-induced disruption of monolayer permeability and proinflammatory cytokine secretion in polarized human gastric epithelial cells

Helicobacter pylori infection of the stomach is related to the development of diverse gastric pathologies. The ability of H. pylori to compromise epithelial junctional complexes and to induce proinflammatory cytokines is believed to contribute to pathogenesis. The purpose of this study was to use an in vitro human gastric epithelial model to investigate the ability of H. pylori to affect permeability and the extent and polarity of the host inflammatory response. NCI-N87 monolayers were cocultured with live or heat-killed H. pylori or culture supernatants. Epithelial barrier function was measured by transepithelial electric resistance (TEER) analysis, diffusion of fluorescein isothiocyanate (FITC)-labeled markers, and immunostaining for tight junction proteins. Supernatants from both apical and basolateral chambers were tested for cytokine production by multiplex analysis. H. pylori caused a significant decrease in TEER, an increased passage of markers through the infected monolayer, and severe disruption and mislocalization of ZO-1 and claudin-1 proteins. Cell viability was not altered by H. pylori, indicating that loss of barrier function could be attributed to a breakdown of tight junction integrity. Significantly high levels of cytokine secretion were induced by either viable or heat-killed H. pylori. H. pylori affects monolayer permeability of polarized human gastric epithelial cells. Proinflammatory cytokines were secreted in a polarized manner, mostly basolaterally. Live bacteria are required for disruption of tight junctions but not for the induction of cytokine secretion. The NCI-N87 cell line provides an excellent model for the in vitro study of H. pylori pathogenesis and the epithelial cell host response to infection.

Adherens junctions as targets of microorganisms: a focus on Helicobacter pylori

Mucosal epithelia are targeted by several microorganisms as a way of adhesion, internalization, and/or exploitation of the host properties to induce disease. Helicobacter pylori are worldwide prevalent bacteria that colonize the human stomach. Persistent infection of the gastric mucosa with H. pylori and concurrent chronic gastritis are risk factors for ulcer disease and gastric carcinoma. Therefore, interactions at the H. pylori-epithelial interface are important to understand the pathogenesis of these bacteria and the host responses that contribute to disease development. Here, we provide an overview of the interactions between microorganisms and the adherens junctions with an emphasis on H. pylori.

Statin pleiotropy prevents rho kinase-mediated intestinal epithelial barrier compromise induced by Blastocystis cysteine proteases

Blastocystis is an enteric parasite that causes acute and chronic intestinal infections, often non-responsive to conventional antibiotics. The effects of Blastocystis infections on human epithelial permeability are not known, and molecular mechanisms of Blastocystis-induced intestinal pathology remain unclear. This study was conducted to determine whether Blastocystis species alters human intestinal epithelial permeability, to assess whether these abnormalities are rho kinase (ROCK)-dependent, and to investigate the therapeutic potential of the HMG-CoA reductase inhibitor Simvastatin in altered intestinal epithelial barrier function. The effect of metronidazole resistant (Mz(r)) Blastocystis isolated from a symptomatic patient on human colonic epithelial monolayers (Caco-2) was assessed. Modulation of enterocyte myosin light chain phosphorylation, transepithelial fluorescein isothiocyanate-dextran fluxes, transepithelial resistance, cytoskeletal F-actin and tight junctional zonula occludens-1 (ZO-1) by parasite cysteine proteases were measured in the presence or absence of HMG-CoA reductase and ROCK inhibition. Blastocystis significantly decreased transepithelial resistance, increased epithelial permeability, phosphorylated myosin light chain and reorganized epithelial actin cytoskeleton and ZO-1. These alterations were abolished by inhibition of enterocyte ROCK, HMG-CoA reductase and parasite cysteine protease. Our findings suggest that cysteine proteases of Mz(r) Blastocystis induce ROCK-dependent disruption of intestinal epithelial barrier function and correlates with reorganization of cytoskeletal F-actin and tight junctional ZO-1. Simvastatin prevented parasite-induced barrier-compromise, suggesting a therapeutic potential of statins in intestinal infections.

Occludin is required for apoptosis when claudin-claudin interactions are disrupted

Disruption of tight junctions is often seen during pathogen infection, inflammation, and tumor progression. Mislocalization of the tight junction proteins occludin and claudin in mammary epithelial monolayers leads to apoptosis through the extrinsic pathway. To further investigate the mechanism of this response, a normal mammary epithelial cell line (EpH4) as well as primary mammary epithelial cells were treated with a claudin-disrupting mimic peptide, DFYNP (aspartic acid–phenylalanine–tyrosine–asparagine–proline). Using fluorescent indicators, we found that caspase-3 activation, resulting from treatment with DFYNP, was restricted to EpH4 and primary mammary epithelial cells with mislocalized claudin-4. Mislocalized claudin-4 and occludin were colocalized in non-junctional puncta, and both molecules were found in the death-inducing signaling complex (DISC) where they colocalized with Fas, fas-associated protein with death domain (FADD), active caspase-8 and caspase-3 at distinct apical domains. Importantly, caspase-3 activation was totally repressed in primary mammary epithelial cells from occludin null mice. Thus, the apoptotic response appears to be initiated by the movement of occludin to the DISC suggesting that this molecule has signaling properties that initiate cell death when its tight junction location is disrupted.

Significant role of IL-1 signaling, but limited role of inflammasome activation, in oviduct pathology during Chlamydia muridarum genital infection

IL-1β has been implicated in the development of oviduct pathology during Chlamydia muridarum genital infection in the mouse model. The goal of this study was to characterize the role of IL-1 signaling and the inflammasome-activation pathways during genital chlamydial infection. Compared with control mice, IL-1R-deficient mice displayed delayed clearance and increased chlamydial colonization. Consistent with the role for IL-1 signaling in infection clearance, mice deficient for the IL-1R antagonist cleared infection at a faster rate. Despite increased infection, IL-1R-deficient mice had significantly reduced oviduct pathology, which was associated with decreased numbers of neutrophils, but more macrophages, in the genital tract. IL-1β secretion is dependent on caspase-1 and apoptosis-associated speck-like protein containing caspase recruitment domain (ASC) inflammasome during in vitro infection of primed macrophages with C. muridarum. To investigate the role of inflammasome components during in vivo genital infection, mice lacking NLRP3, NLRC4, and ASC were tested and found to display no reduction in oviduct pathology compared with control mice. Mice deficient for ASC displayed a prolonged course of infection, which was associated with reduced T cell recruitment and proliferation. Further, ASC-deficient mice displayed normal levels of IL-1β in genital secretions. However, a significant decrease in caspase-1-dependent IL-18 was observed in both ASC- and NLRP3-deficient mice. These data demonstrate a major role for IL-1 signaling, but a limited role for the inflammasome pathway, in IL-1β secretion and development of oviduct pathology during genital chlamydial infection. The data also suggest an IL-1-independent role for ASC in adaptive immunity during genital chlamydial infection.

Interleukin-18 facilitates neutrophil transmigration via myosin light chain kinase-dependent disruption of occludin, without altering epithelial permeability

Compromised epithelial barrier function and tight junction alterations are hallmarks of a number of gastrointestinal disorders, including inflammatory bowel disease (IBD). Increased levels of IL-18 have been observed in mucosal samples from Crohn's disease and ulcerative colitis patients. Remarkably, several reports have demonstrated that immunological or genetic blockage of IL-18 ameliorates the severity of colitis in multiple in vivo models of IBD. Nevertheless, the effects of IL-18 on intestinal epithelial barrier function remain unclear. We hypothesized that IL-18 could disrupt intestinal epithelial barrier structure and function, thus contributing to tissue damage in the context of IBD. The aims of the present study were to determine the effects of IL-18 on epithelial barrier structure and function and to characterize the mechanisms involved in these modulatory properties. Human colonic epithelial Caco-2 monolayers were coincubated with IL-18 for 24 h and processed for immunocytochemistry, immunoblotting, quantitative PCR, and permeability measurements (transepithelial resistance, FITC-dextran fluxes, and bacterial translocation). Our findings indicate that IL-18 selectively disrupts tight junctional occludin, without affecting the distribution pattern of claudin-4, claudin-5, zonula occludens-1, or E-cadherin. This effect coincided with a significant increase in myosin light chain kinase (MLCK) protein levels and activity. Pharmacological inhibition of MLCK and NF-κB prevented IL-18-induced loss of occludin. Although too subtle to alter paracellular permeability, these fine changes correlated with an MLCK-dependent increase in neutrophil transepithelial migration. In conclusion, our data suggest that IL-18 may potentiate inflammation in the context of IBD by facilitating neutrophil transepithelial migration via MLCK-dependent disruption of tight junctional occludin.

Bacteria and host interactions in the gut epithelial barrier

The gut mucosa acts as a barrier against microbial invaders, whereas resident commensal and foreign invading bacteria interact intimately with the gut epithelium and influence the host cellular and immune systems. The epithelial barrier serves as an infectious foothold for many bacterial pathogens and as an entry port for pathogens to disseminate into deeper tissues. Enteric bacterial pathogens can efficiently infect the gut mucosa using highly sophisticated virulence mechanisms that allow bacteria to circumvent the defense barriers in the gut. We provide an overview of the components of the mucosal barrier and discuss the bacterial stratagems that circumvent these barriers with particular emphasis on the roles of bacterial effector proteins.

"Targeted disruption of the epithelial-barrier by Helicobacter pylori"

Helicobacter pylori colonizes the human gastric epithelium and induces chronic gastritis, which can lead to gastric cancer. Through cell-cell contacts the gastric epithelium forms a barrier to protect underlying tissue from pathogenic bacteria; however, H. pylori have evolved numerous strategies to perturb the integrity of the gastric barrier. In this review, we summarize recent research into the mechanisms through which H. pylori disrupts intercellular junctions and disrupts the gastric epithelial barrier.

Pathogenesis of Helicobacter pylori infection

Helicobacter pylori infections and clinical outcome are dependent on sophisticated interactions between the bacteria and its host. Crucial bacterial factors associated with pathogenicity comprise a type IV secretion system encoded by the cag pathogenicity island, the effector protein CagA, the vacuolating cytotoxin (VacA), peptidoglycan, lipopolysaccharide (LPS), γ-glutamyl transpeptidase (GGT), protease HtrA, and the adhesins BabA, SabA, and others. The high number of these factors and allelic variation of the involved genes generates a highly complex scenario and reveals the difficulties in testing the contribution of each individual factor. Much effort has been put into identifying the molecular mechanisms associated with H. pylori-associated pathogenesis using human primary tissues, Mongolian gerbils, transgenic, knockout, and other mice as well as in vitro cell model systems. Interactions between bacterial factors and host signal transduction pathways seem to be critical for mediating the induction of pathogenic downstream processes and disease development. In this review article, we discuss the most recent progress in this research field.

Claudins in lung diseases

Tight junctions are the most apically localized part of the epithelial junctional complex. They regulate the permeability and polarity of cell layers and create compartments in cell membranes. Claudins are structural molecules of tight junctions. There are 27 claudins known, and expression of different claudins is responsible for changes in the electrolyte and solute permeability in cells layers. Studies have shown that claudins and tight junctions also protect multicellular organisms from infections and that some infectious agents may use claudins as targets to invade and weaken the host's defense. In neoplastic diseases, claudin expression may be up- or downregulated. Since their expression is associated with specific tumor types or with specific locations of tumors to a certain degree, they can, in a restricted sense, also be used as tumor markers. However, the regulation of claudin expression is complex involving growth factors and integrins, protein kinases, proto-oncogens and transcription factors. In this review, the significance of claudins is discussed in lung disease and development.

Helicobacter pylori CagA disrupts epithelial patterning by activating myosin light chain

Helicobacter pylori infection is a leading cause of ulcers and gastric cancer. We show that expression of the H. pylori virulence factor CagA in a model Drosophila melanogaster epithelium induces morphological disruptions including ectopic furrowing. We find that CagA alters the distribution and increases the levels of activated myosin regulatory light chain (MLC), a key regulator of epithelial integrity. Reducing MLC activity suppresses CagA-induced disruptions. A CagA mutant lacking EPIYA motifs (CagA^EPISA) induces less epithelial disruption and is not targeted to apical foci like wild-type CagA. In a cell culture model in which CagA^EPISA and CagA have equivalent subcellular localization, CagA^EPISA is equally potent in activating MLC. Therefore, in our transgenic system, CagA is targeted by EPIYA motifs to a specific apical region of the epithelium where it efficiently activates MLC to disrupt epithelial integrity.

Inflammation, immunity, and vaccines for Helicobacter

Helicobacter pylori represents the major etiologic agent of gastritis, gastric, and duodenal ulcer disease and can cause gastric cancer and mucosa-associated lymphoid tissue B-cell lymphoma. It is clear that the consequences of infection reflect diverse outcomes of the interaction of bacteria and host immune system. The hope is that by deciphering the deterministic rules--if any--of this interplay, we will eventually be able to predict, treat, and ultimately prevent disease. Over the past year, research on the immunology of this infection started to probe the role of small noncoding RNAs, a novel class of immune response regulators. Furthermore, we learned new details on how infection is detected by innate pattern recognition receptors. Induction of effective cell-mediated immunity will be key for the development of a vaccine, and new work published analyzed the relevance and contribution of CD4 T helper cell subsets to the immune reaction. Th17 cells, which are also induced during natural infection, were shown to be particularly important for vaccination. Cost-efficiency of vaccination was re-assessed and confirmed. Thus, induction and shaping of the effector roles of such protective Th populations will be a target of the newly described vaccine antigens, formulations, and modes of application that we also review here.