Redistribution of tight junction proteins during EPEC infection in vivo

Study on the mechanism of mitigating radiation damage by improving the hematopoietic system and intestinal barrier with Tenebrio molitor peptides

Research on plant and animal peptides has garnered significant attention, but there is a lack of studies on the functional properties of Tenebrio molitor peptides, particularly in relation to their potential mitigating effect on radiation damage and the underlying mechanisms. This study aims to explore the protective effects of Tenebrio molitor peptides against radiation-induced damage. Mice were divided into five groups: normal, radiation model, and low-, medium-, and high-dose Tenebrio molitor peptide (TMP) groups (0.15 g per kg BW, 0.30 g per kg BW, and 0.60 g per kg BW). Various parameters such as blood cell counts, bone marrow DNA content, immune organ indices, serum levels of D-lactic acid, diamine oxidase (DAO), endotoxin (LPS), and inflammatory factors were assessed at 3 and 15 days post gamma irradiation. Additionally, the intestinal tissue morphology was examined through H&E staining, RT-qPCR experiments were conducted to analyze the expression of inflammatory factors in the intestine, and immunohistochemistry was utilized to evaluate the expression of tight junction proteins ZO-1 and Occludin in the intestine. The findings revealed that high-dose TMP significantly enhanced the hematopoietic system function in mice post radiation exposure, leading to increased spleen index, thymus index, blood cell counts, and bone marrow DNA production (p < 0.05). Moreover, TMP improved the intestinal barrier integrity and reduced the intestinal permeability. Mechanistic insights suggested that these peptides may safeguard intestinal barrier function by downregulating the gene expression of inflammatory factors TNF-α, IL-1β, and IL-6, while upregulating the expression of tight junction proteins ZO-1 and Occludin (p < 0.05). Overall, supplementation with TMP mitigates radiation-induced intestinal damage by enhancing the hematopoietic system and the intestinal barrier, offering valuable insights for further investigations into the mechanisms underlying the protective effects of these peptides against ionizing radiation.

The metabolic impact of bacterial infection in the gut

Bacterial infections of the gut are one of the major causes of morbidity and mortality worldwide. The interplay between the pathogen and the host is finely balanced, with the bacteria evolving to proliferate and establish infection. In contrast, the host mounts a response to first restrict and then eliminate the infection. The intestine is a rapidly proliferating tissue, and metabolism is tuned to cater to the demands of proliferation and differentiation along the crypt-villus axis (CVA) in the gut. As bacterial pathogens encounter the intestinal epithelium, they elicit changes in the host cell, and core metabolic pathways such as the tricarboxylic acid (TCA) cycle, lipid metabolism and glycolysis are affected. This review highlights the mechanisms utilized by diverse gut bacterial pathogens to subvert host metabolism and describes host responses to the infection.

Effect of rifaximin on gut-lung axis in mice infected with influenza A virus

Gut-lung axis injury is a common finding in patients with respiratory diseases as well as in animal model of influenza virus infection. Influenza virus damages the intestinal microecology while affecting the lungs. Rifaximin, a non-absorbable derivative of rifamycin, is an effective antibiotic that acts by inhibiting bacterial RNA synthesis. This study aimed to determine whether rifaximin-perturbation of the intestinal microbiome leads to protective effects against influenza infection, via the gut-lung axis. Our results showed that influenza virus infection caused inflammation of and damage to the lungs. The expression of tight junction proteins in the lung and colon of H1N1 infected mice decreased significantly, attesting that the barrier structure of the lung and colon was damaged. Due to this perturbation in the gut-lung axis, the intestinal microbiota became imbalanced as Escherichia coli bacteria replicated opportunistically, causing intestinal injury. When influenza infection was treated with rifamixin, qPCR results from the gut showed significant increases in Lactobacillus and Bifidobacterium populations, while Escherichia coli populations markedly decreased. Furthermore, pathology sections and western blotting results illustrated that rifaximin treatment strengthened the physical barriers of the lung-gut axis through increased expression of tight junction protein in the colon and lungs. These results indicated that rifaximin ameliorated lung and intestine injury induced by influenza virus infection. The mechanisms identified were the regulation of gut flora balance and intestinal and lung permeability, which might be related to the regulation of the gut-lung axis. Rifaximin might be useful as a co-treatment drug for the prevention of influenza virus infection.

Enteropathogenic Escherichia coli Infection Induces Diarrhea, Intestinal Damage, Metabolic Alterations, and Increased Intestinal Permeability in a Murine Model

Enteropathogenic E. coli (EPEC) are recognized as one of the leading bacterial causes of infantile diarrhea worldwide. Weaned C57BL/6 mice pretreated with antibiotics were challenged orally with wild-type EPEC or escN mutant (lacking type 3 secretion system) to determine colonization, inflammatory responses and clinical outcomes during infection. Antibiotic disruption of intestinal microbiota enabled efficient colonization by wild-type EPEC resulting in growth impairment and diarrhea. Increase in inflammatory biomarkers, chemokines, cellular recruitment and pro-inflammatory cytokines were observed in intestinal tissues. Metabolomic changes were also observed in EPEC infected mice with changes in tricarboxylic acid (TCA) cycle intermediates, increased creatine excretion and shifts in gut microbial metabolite levels. In addition, by 7 days after infection, although weights were recovering, EPEC-infected mice had increased intestinal permeability and decreased colonic claudin-1 levels. The escN mutant colonized the mice with no weight loss or increased inflammatory biomarkers, showing the importance of the T3SS in EPEC virulence in this model. In conclusion, a murine infection model treated with antibiotics has been developed to mimic clinical outcomes seen in children with EPEC infection and to examine potential roles of selected virulence traits. This model can help in further understanding mechanisms involved in the pathogenesis of EPEC infections and potential outcomes and thus assist in the development of potential preventive or therapeutic interventions.

Dietary genistein supplementation improves intestinal mucosal barrier function in Escherichia coli O78-challenged broilers

Genistein has multiple biological activities in both humans and animals. However, a protective effect of genistein on Escherichia coli (E. coli)-induced intestinal mucosal barrier dysfunction remains unknown. In the present study, a total of 288 1-day-old male Arbor Acre broilers fed a corn-soybean basal diet unsupplemented or supplemented with 20 mg genistein/kg diet were subjected to E. coli serotype O78 (10⁸ cfu per bird) infection or equal volume of sodium chloride at 19 days of age. Sera and tissue samples were collected 2 days after E. coli infection. Growth performance, index of immune-related organs, intestinal barrier permeability, protein level of inflammatory cytokines, sIgA, tight junction protein, and mRNA level of apoptotic genes in jejunum were determined. Mortality rate at 7 days post infection was recorded. The results showed that E. coli challenge led to a reduced average daily gain, a decreased thymus index, and bursal index in broilers, an increase of fluorescein isothiocyanate (FITC)-dextran in serum, and a decreased sIgA in jejunum. These effects were abrogated by genistein administration. Western blot results showed that E. coli infection led to increased protein level of claudin-1 and zonula occludens (ZO)-1, which was largely abolished by genistein. Moreover, E. coli infection resulted increased protein level of TNF-α and IL-6, enhanced mRNA level of Bax and caspase-3, as well as decreased mRNA level of Bcl-2 were abrogated by genistein in jujunum of broilers. In conclusion, the results indicate that genistein supplementation improves intestinal mucosal barrier function which is associated with a regulatory effect on tight junction proteins, sIgA, apoptosis, and secretion of inflammatory cytokines in jejunum of E. coli-challenged broilers.

Intestinal barrier dysfunction in severe burn injury

Severe burn injury is often accompanied by intestinal barrier dysfunction, which is closely associated with post-burn shock, bacterial translocation, systemic inflammatory response syndrome, hypercatabolism, sepsis, multiple organ dysfunction syndrome, and other complications. The intestinal epithelium forms a physical barrier that separates the intestinal lumen from the internal milieu, in which the tight junction plays a principal role. It has been well documented that after severe burn injury, many factors such as stress, ischemia/hypoxia, proinflammatory cytokines, and endotoxins can induce intestinal barrier dysfunction via multiple signaling pathways. Recent advances have provided new insights into the mechanisms and the therapeutic strategies of intestinal epithelial barrier dysfunction associated with severe burn injury. In this review, we will describe the current knowledge of the mechanisms involved in intestinal barrier dysfunction in response to severe burn injury and the emerging therapies for treating intestinal barrier dysfunction following severe burn injury.

Extracellular vesicles and soluble factors secreted by Escherichia coli Nissle 1917 and ECOR63 protect against enteropathogenic E. coli-induced intestinal epithelial barrier dysfunction

Background

Enteric pathogens have developed mechanisms to disrupt tight junctions and increase gut permeability. Many studies have analysed the ability of live probiotics to protect intestinal epithelial cells against tight junction damage caused by bacterial pathogens. Escherichia coli Nissle 1917 (EcN) is among the probiotics that positively modulates the intestinal epithelial barrier by regulating expression and distribution of tight junction proteins. We previously reported that regulation of ZO-1, claudin-14 and claudin-2 is mediated by EcN secreted factors, either free-released or associated with outer membrane vesicles (OMVs). Factors secreted by commensal ECOR63 elicited comparable effects in intact epithelial T-84 and Caco-2 cell monolayers.

Results

Here we analyse the ability of OMVs and soluble secreted factors to protect epithelial barrier function in polarized T-84 and Caco-2 cells infected with enteropathogenic Escherichia coli (EPEC). Transepithelial electrical resistance, paracellular permeability, mRNA levels and subcellular distribution of tight junction proteins were monitored in the absence or presence of EcN and ECOR63 extracellular fractions. EPEC downregulated expression of ZO-1 ZO-2, occludin and claudin-14 and altered the subcellular localization of ZO-1, occludin and F-actin cytoskeleton. OMVs and soluble factors secreted by EcN and ECOR63 counteracted EPEC-altered transepithelial resistance and paracellular permeability, preserved occludin and claudin-14 mRNA levels, retained ZO-1 and occludin at tight junctions in the cell boundaries and ameliorated F-actin disorganization. Redistribution of ZO-1 was not accompanied by changes at mRNA level.

Conclusion

This study provides new insights on the role of microbiota secreted factors on the modulation of intestinal tight junctions, expanding their barrier-protective effects against pathogen-induced disruption.

Intestinal cell migration damage induced by enteropathogenic Escherichia coli strains

Epithelial cell migration is an essential response to enteric pathogens such as enteropathogenic Escherichia coli (EPEC). This study aimed to investigate the effects of EPEC infection on intestinal epithelial cell migration in vitro, as well as the involvement of type III secretion system (T3SS) and Rho GTPases. Crypt intestinal epithelial cells (IEC-6) were infected with EPEC strains (E2348/69, ΔescF, and the LDI001 strain isolated from a malnourished Brazilian child) and commensal E. coli HS. Wound migration and cell death assays were performed at different time-points. Transcription and expression of Rho GTPases were evaluated using real-time PCR and western blotting. Overall, EPEC E2348/69 reduced migration and increased apoptosis and necrosis levels compared to EPEC LDI001 and E. coli HS strains. Moreover, EPEC LDI001 impaired cell migration at a higher level than E. coli HS and increased necrosis after 24 hours compared to the control group. The different profiles of virulence genes between the two wild-type EPEC strains, characterized by the absence of espL and nleE genes in the LDI001, might explain the phenotypic results, playing significant roles on cell migration impairment and cell death-related events. Moreover, the type III secretion system is determinant for the inhibition of intestinal epithelial cell migration by EPEC 2348/69, as its deletion prevented the effect. Active Rac1 concentrations were increased in E2348/69 and LDI001-infected cells, while the T3SS-deficient strain did not demonstrate this activation. This study contributes with valuable insight to characterize the mechanisms involved in the impairment of intestinal cell migration induced by EPEC.

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.

From clinical uncertainties to precision medicine: the emerging role of the gut barrier and microbiome in small bowel functional diseases

Over the last decade, remarkable progress has been made in the understanding of disease pathophysiology. Many new theories expound on the importance of emerging factors such as microbiome influences, genomics/omics, stem cells, innate intestinal immunity or mucosal barrier complexities. This has introduced a further dimension of uncertainty into clinical decision-making, but equally, may shed some light on less well-understood and difficult to manage conditions. Areas covered: Comprehensive review of the literature on gut barrier and microbiome relevant to small bowel pathology. A PubMed/Medline search from 1990 to April 2017 was undertaken and papers from this range were included. Expert commentary: The scenario of clinical uncertainty is well-illustrated by functional gastrointestinal disorders (FGIDs). The movement towards achieving a better understanding of FGIDs is expressed in the Rome IV guidelines. Novel diagnostic and therapeutic protocols focused on the GB and SB microbiome can facilitate diagnosis, management and improve our understanding of the underlying pathological mechanisms in FGIDs.

EPEC effector EspF promotes Crumbs3 endocytosis and disrupts epithelial cell polarity

Enteropathogenic Escherichia coli (EPEC) uses a type III secretion system to inject effector proteins into host intestinal epithelial cells causing diarrhoea. EPEC infection redistributes basolateral proteins β1-integrin and Na⁺ /K⁺ ATPase to the apical membrane of host cells. The Crumbs (Crb) polarity complex (Crb3/Pals1/Patj) is essential for epithelial cell polarisation and tight junction (TJ) assembly. Here, we demonstrate that EPEC displaces Crb3 and Pals1 from the apical membrane to the cytoplasm of cultured intestinal epithelial cells and colonocytes of infected mice. In vitro studies show that EspF, but not Map, alters Crb3, whereas both effectors modulate Pals1. EspF perturbs polarity formation in cyst morphogenesis assays and induces endocytosis and apical redistribution of Na⁺ /K⁺ ATPase. EspF binds to sorting nexin 9 (SNX9) causing membrane remodelling in host cells. Infection with ΔespF/pespFD3, a mutant strain that ablates EspF binding to SNX9, or inhibition of dynamin, attenuates Crb3 endocytosis caused by EPEC. In addition, infection with ΔespF/pespFD3 has no impact on Na⁺ /K⁺ ATPase endocytosis. These data support the hypothesis that EPEC perturbs apical-basal polarity in an EspF-dependent manner, which would contribute to EPEC-associated diarrhoea by disruption of TJ and altering the crucial positioning of membrane transporters involved in the absorption of ions and solutes.

Review on the effects of potential prebiotics on controlling intestinal enteropathogens Salmonella and Escherichia coli in pig production

Salmonella enterica serotypes (Salmonella sp.) are the second cause of bacterial foodborne zoonoses in humans after campylobacteriosis. Pork is the third most important cause for outbreak-associated salmonellosis, and colibacillosis is the most important disease in piglets and swine. Attachment to host cells, translocation of effector proteins into host cells, invasion and replication in tissues are the vital virulence steps of these pathogens that help them to thrive in the intestinal environment and invade tissues. Feed contamination is an important source for Salmonella infection in pig production. Many on-farm feeding strategies intervene to avoid the introduction of pathogens onto the farm by contaminated feeds or to reduce infection pressure when pathogens are present. Among the latter, prebiotics could be effective at protecting against these enteric bacterial pathogens. Nowadays, a wide range of molecules can potentially serve as prebiotics. Here, we summarize the prevalence of Salmonella sp. and Escherichia coli in pigs, understanding of the mechanisms by which pathogens can cause disease, the feed related to pathogen contamination in pigs and detail the mechanisms on which prebiotics are likely to act in order to fulfil their protective action against these pathogens in pig production. Many different mechanisms involve the inhibition of Salmonella and E. coli by prebiotics such as coating the host surface, modulation of intestinal ecology, downregulating the expression of adhesin factors or virulence genes, reinforcing the host immune system.

Tight Junction Disruption Induced by Type 3 Secretion System Effectors Injected by Enteropathogenic and Enterohemorrhagic Escherichia coli

The intestinal epithelium consists of a single cell layer, which is a critical selectively permeable barrier to both absorb nutrients and avoid the entry of potentially harmful entities, including microorganisms. Epithelial cells are held together by the apical junctional complexes, consisting of adherens junctions, and tight junctions (TJs), and by underlying desmosomes. TJs lay in the apical domain of epithelial cells and are mainly composed by transmembrane proteins such as occludin, claudins, JAMs, and tricellulin, that are associated with the cytoplasmic plaque formed by proteins from the MAGUK family, such as ZO-1/2/3, connecting TJ to the actin cytoskeleton, and cingulin and paracingulin connecting TJ to the microtubule network. Extracellular bacteria such as EPEC and EHEC living in the intestinal lumen inject effectors proteins directly from the bacterial cytoplasm to the host cell cytoplasm, where they play a relevant role in the manipulation of the eukaryotic cell functions by modifying or blocking cell signaling pathways. TJ integrity depends on various cell functions such as actin cytoskeleton, microtubule network for vesicular trafficking, membrane integrity, inflammation, and cell survival. EPEC and EHEC effectors target most of these functions. Effectors encoded inside or outside of locus of enterocyte effacement (LEE) disrupt the TJ strands. EPEC and EHEC exploit the TJ dynamics to open this structure, for causing diarrhea. EPEC and EHEC secrete effectors that mimic host proteins to manipulate the signaling pathways, including those related to TJ dynamics. In this review, we focus on the known mechanisms exploited by EPEC and EHEC effectors for causing TJ disruption.

Signalling at tight junctions during epithelial differentiation and microbial pathogenesis

Tight junctions are a component of the epithelial junctional complex, and they form the paracellular diffusion barrier that enables epithelial cells to create cellular sheets that separate compartments with different compositions. The assembly and function of tight junctions are intimately linked to the actomyosin cytoskeleton and, hence, are under the control of signalling mechanisms that regulate cytoskeletal dynamics. Tight junctions not only receive signals that guide their assembly and function, but transmit information to the cell interior to regulate cell proliferation, migration and survival. As a crucial component of the epithelial barrier, they are often targeted by pathogenic viruses and bacteria, aiding infection and the development of disease. In this Commentary, we review recent progress in the understanding of the molecular signalling mechanisms that drive junction assembly and function, and the signalling processes by which tight junctions regulate cell behaviour and survival. We also discuss the way in which junctional components are exploited by pathogenic viruses and bacteria, and how this might affect junctional signalling mechanisms.

The impact of heat stress on intestinal function and productivity in grow-finish pigs

Heat stress is a physiological condition when animals can no longer regulate their internal euthermic temperature. When livestock such as pigs are subjected to this environmental stress, it can be detrimental to performance, health and well-being, and if severe enough even death. Growing pigs are particularly susceptible to heat stress and one of the major organs first affected by heat stress is the gastrointestinal tract. As a result, reductions in appetite, intestinal function and integrity and increased risk of endotoxemia can modify post-absorptive metabolism and tissue accretion. These changes in intestinal integrity may be a result of altered expression of tight junction proteins, increased circulating endotoxin concentrations and markers of cellular stress (heat shock and hypoxia response), which is evident as early on as 2 h after heat-stress onset. Due to restricted blood flow, the ileum is more severely affected compared with the colon. Interestingly, many of the negative effects of heat stress on intestinal integrity appear to be similar to those observed with pigs reared under reduced nutrient and caloric intakes. Altogether, these depress pig performance and health, and extend days to market. Despite this impact on the gastrointestinal tract, under heat-stress conditions, intestinal glucose transport pathways are upregulated. This review discussed how heat stress (directly and indirectly via reduced feed intake) affects intestinal integrity and how heat stress contributes to decreased growth performance in growing pigs.

Enteropathogenic E. coli effectors EspG1/G2 disrupt microtubules, contribute to tight junction perturbation and inhibit restoration

Enteropathogenic Escherichia coli (EPEC) uses a type 3 secretion system to transfer effector proteins into the host intestinal epithelial cell. Several effector molecules contribute to tight junction disruption including EspG1 and its homologue EspG2 via a mechanism thought to involve microtubule destruction. The aim of this study was to investigate the contribution of EspG-mediated microtubule disruption to TJ perturbation. We demonstrate that wild type EPEC infection disassembles microtubules and induces the progressive movement of occludin away from the membrane and into the cytosol. Deletion of espG1/G2 attenuates both of these phenotypes. In addition, EPEC infection impedes barrier recovery from calcium switch, suggesting that inhibition of TJ restoration, not merely disruption, prolongs barrier loss. TJs recover more rapidly following infection with ΔespG1/G2 than with wild type EPEC, demonstrating that EspG1/G2 perpetuate barrier loss. Although EspG regulates ADP-ribosylation factor (ARF) and p21-activated kinase (PAK), these activities are not necessary for microtubule destruction or perturbation of TJ structure and function. These data strongly support a role for EspG1/G2 and its associated effects on microtubules in delaying the recovery of damaged tight junctions caused by EPEC infection.

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.

Enteropathogenic Escherichia coli inhibits type I interferon- and RNase L-mediated host defense to disrupt intestinal epithelial cell barrier function

Enteropathogenic Escherichia coli (EPEC) primarily infects children in developing countries and causes diarrhea that can be deadly. EPEC pathogenesis occurs through type III secretion system (T3SS)-mediated injection of effectors into intestinal epithelial cells (IECs); these effectors alter actin dynamics, modulate the immune response, and disrupt tight junction (TJ) integrity. The resulting compromised barrier function and increased gastrointestinal (GI) permeability may be responsible for the clinical symptoms of infection. Type I interferon (IFN) mediates anti-inflammatory activities and serves essential functions in intestinal immunity and homeostasis; however, its role in the immune response to enteric pathogens, such as EPEC, and its impact on IEC barrier function have not been examined. Here, we report that IFN-β is induced following EPEC infection and regulates IEC TJ proteins to maintain barrier function. The EPEC T3SS effector NleD counteracts this protective activity by inhibiting IFN-β induction and enhancing tumor necrosis factor alpha to promote barrier disruption. The endoribonuclease RNase L is a key mediator of IFN induction and action that promotes TJ protein expression and IEC barrier integrity. EPEC infection inhibits RNase L in a T3SS-dependent manner, providing a mechanism by which EPEC evades IFN-induced antibacterial activities. This work identifies novel roles for IFN-β and RNase L in IEC barrier functions that are targeted by EPEC effectors to escape host defense mechanisms and promote virulence. The IFN-RNase L axis thus represents a potential therapeutic target for enteric infections and GI diseases involving compromised barrier function.

Heat stress reduces intestinal barrier integrity and favors intestinal glucose transport in growing pigs

Excessive heat exposure reduces intestinal integrity and post-absorptive energetics that can inhibit wellbeing and be fatal. Therefore, our objectives were to examine how acute heat stress (HS) alters intestinal integrity and metabolism in growing pigs. Animals were exposed to either thermal neutral (TN, 21°C; 35–50% humidity; n = 8) or HS conditions (35°C; 24–43% humidity; n = 8) for 24 h. Compared to TN, rectal temperatures in HS pigs increased by 1.6°C and respiration rates by 2-fold (P<0.05). As expected, HS decreased feed intake by 53% (P<0.05) and body weight (P<0.05) compared to TN pigs. Ileum heat shock protein 70 expression increased (P<0.05), while intestinal integrity was compromised in the HS pigs (ileum and colon TER decreased; P<0.05). Furthermore, HS increased serum endotoxin concentrations (P = 0.05). Intestinal permeability was accompanied by an increase in protein expression of myosin light chain kinase (P<0.05) and casein kinase II-α (P = 0.06). Protein expression of tight junction (TJ) proteins in the ileum revealed claudin 3 and occludin expression to be increased overall due to HS (P<0.05), while there were no differences in claudin 1 expression. Intestinal glucose transport and blood glucose were elevated due to HS (P<0.05). This was supported by increased ileum Na⁺/K⁺ ATPase activity in HS pigs. SGLT-1 protein expression was unaltered; however, HS increased ileal GLUT-2 protein expression (P = 0.06). Altogether, these data indicate that HS reduce intestinal integrity and increase intestinal stress and glucose transport.

Claudins in intestines: Distribution and functional significance in health and diseases

Intestines are organs that not only digest food and absorb nutrients, but also provide a defense barrier against pathogens and noxious agents ingested. Tight junctions (TJs) are the most apical component of the junctional complex, providing one form of cell-cell adhesion in enterocytes and playing a critical role in regulating paracellular barrier permeability. Alteration of TJs leads to a number of pathophysiological diseases causing malabsorption of nutrition and intestinal structure disruption, which may even contribute to systemic organ failure. Claudins are the major structural and functional components of TJs with at least 24 members in mammals. Claudins have distinct charge-selectivity, either by tightening the paracellular pathway or functioning as paracellular channels, regulating ions and small molecules passing through the paracellular pathway. In this review, we have discussed the functions of claudin family members, their distribution and localization in the intestinal tract of mammals, their alterations in intestine-related diseases and chemicals/agents that regulate the expression and localization of claudins as well as the intestinal permeability, which provide a therapeutic view for treating intestinal diseases.

In vitro and in vivo model systems for studying enteropathogenic Escherichia coli infections

Enteropathogenic Escherichia coli (EPEC) and enterohemorrhagic E. coli (EHEC) belong to a group of bacteria known as attaching and effacing (A/E) pathogens that cause disease by adhering to the lumenal surfaces of their host's intestinal epithelium. EPEC and EHEC are major causes of infectious diarrhea that result in significant childhood morbidity and mortality worldwide. Recent advances in in vitro and in vivo modeling of these pathogens have contributed to our knowledge of how EPEC and EHEC attach to host cells and subvert host-cell signaling pathways to promote infection and cause disease. A more detailed understanding of how these pathogenic microbes infect their hosts and how the host responds to infection could ultimately lead to new therapeutic strategies to help control these significant enteric pathogens.

Enteropathogenic E. coli effectors EspG1/G2 disrupt tight junctions: new roles and mechanisms

Enteropathogenic E. coli (EPEC) infection is a major cause of infantile diarrhea in the developing world. Using a type-three secretion system, bacterial effector proteins are transferred to the host cell cytosol where they affect multiple physiological functions, ultimately leading to diarrheal disease. Disruption of intestinal epithelial cell tight junctions is a major consequence of EPEC infection and is mediated by multiple effector proteins, among them EspG1 and its homologue EspG2. EspG1/G2 contribute to loss of barrier function via an undefined mechanism that may be linked to their disruption of microtubule networks. Recently new investigations have identified additional roles for EspG. Sequestration of active ADP-ribosylating factor (ARF) proteins and promotion of p21-activated kinase (PAK) activity as well as inhibition of Golgi-mediated protein secretion have all been linked to EspG. In this review, we examine the functions of EspG1/G2 and discuss potential mechanisms of EspG-mediated tight junction disruption.