Bacterial invasion by a paracellular route: divide and conquer

Campylobacter jejuni virulence factors: update on emerging issues and trends

Campylobacter jejuni is a very common cause of gastroenteritis, and is frequently transmitted to humans through contaminated food products or water. Importantly, C. jejuni infections have a range of short- and long-term sequelae such as irritable bowel syndrome and Guillain Barre syndrome. C. jejuni triggers disease by employing a range of molecular strategies which enable it to colonise the gut, invade the epithelium, persist intracellularly and avoid detection by the host immune response. The objective of this review is to explore and summarise recent advances in the understanding of the C. jejuni molecular factors involved in colonisation, invasion of cells, collective quorum sensing-mediated behaviours and persistence. Understanding the mechanisms that underpin the pathogenicity of C. jejuni will enable future development of effective preventative approaches and vaccines against this pathogen.

Differential Interaction between Invasive Thai Group B Streptococcus Sequence Type 283 and Caco-2 Cells

The emergence in Southeast Asia of invasive group B Streptococcus (GBS) infections in adults by sequence type (ST) 283 is suggested to be associated with fish consumption. Genotyping of 55 GBS clinical isolates revealed that 33/44 invasive isolates belonged to ST283/capsular polysaccharide type (CPS) III. This included 15/16 isolates recovered from younger adults aged 16–36 years. Seven ST283/CPSIII isolates from the blood, cerebrospinal fluid, or joint fluid were selected by the patient’s age at random to perform interaction studies with intestinal epithelial Caco-2 monolayers. The invasion efficiency profiles from this study classified these isolates into two groups; a higher invasion efficiency group 1 recovered from patients aged between 23 and 36 years, and a lower invasion efficiency group 2 recovered from the elderly and neonate. Intracellular survival tests revealed that only group 1 members could survive inside Caco-2 cells up to 32 h without replication. Additionally, all isolates tested were able to traverse across polarized Caco-2 monolayers. However, the timing of translocation varied among the isolates. These results indicated the potential of GBS invasion via the gastrointestinal tract and showed phenotypic variations in invasiveness, intracellular survival, and translocation efficiency between genetically closely related ST283 isolates infecting young adults and those infecting the elderly.

Cleavage of E-cadherin by porcine respiratory bacterial pathogens facilitates airway epithelial barrier disruption and bacterial paracellular transmigration

Airway epithelial cells are the first line of defense against respiratory pathogens. Porcine bacterial pathogens, such as Bordetella bronchiseptica, Actinobacillus pleuropneumoniae, Glaesserella (Haemophilus) parasuis, and Pasteurella multocida, breach this barrier to lead to local or systematic infections. Here, we demonstrated that respiratory bacterial pathogen infection disrupted the airway epithelial intercellular junction protein, E-cadherin, thus contributing to impaired epithelial cell integrity. E-cadherin knocking-out in newborn pig tracheal cells via CRISPR/Cas9 editing technology confirmed that E-cadherin was sufficient to suppress the paracellular transmigration of these porcine respiratory bacterial pathogens, including G. parasuis, A. pleuropneumoniae, P. multocida, and B. bronchiseptica. The E-cadherin ectodomain cleavage by these pathogens was probably attributed to bacterial HtrA/DegQ protease, but not host HtrA1, MMP7 and ADAM10, and the prominent proteolytic activity was further confirmed by a serine-to-alanine substitution mutation in the active center of HtrA/DegQ protein. Moreover, deletion of the htrA gene in G. parasuis led to severe defects in E-cadherin ectodomain cleavage, cell adherence and paracellular transmigration in vitro, as well as bacterial breaking through the tracheal epithelial cells, systemic invasion and dissemination in vivo. This common pathogenic mechanism shared by other porcine respiratory bacterial pathogens explains how these bacterial pathogens destroy the airway epithelial cell barriers and proliferate in respiratory mucosal surface or other systemic tissues.

Pathogenic Mannheimia haemolytica Invades Differentiated Bovine Airway Epithelial Cells

The Gram-negative bacterium Mannheimia haemolytica is the primary bacterial species associated with bovine respiratory disease (BRD) and is responsible for significant economic losses to livestock industries worldwide. Healthy cattle are frequently colonized by commensal serotype A2 strains, but disease is usually caused by pathogenic strains of serotype A1. For reasons that are poorly understood, a transition occurs within the respiratory tract and a sudden explosive proliferation of serotype A1 bacteria leads to the onset of pneumonic disease. Very little is known about the interactions of M. haemolytica with airway epithelial cells of the respiratory mucosa which might explain the different abilities of serotype A1 and A2 strains to cause disease. In the present study, host-pathogen interactions in the bovine respiratory tract were mimicked using a novel differentiated bovine bronchial epithelial cell (BBEC) infection model. In this model, differentiated BBECs were inoculated with serotype A1 or A2 strains of M. haemolytica and the course of infection followed over a 5-day period by microscopic assessment and measurement of key proinflammatory mediators. We have demonstrated that serotype A1, but not A2, M. haemolytica invades differentiated BBECs by transcytosis and subsequently undergoes rapid intracellular replication before spreading to adjacent cells and causing extensive cellular damage. Our findings suggest that the explosive proliferation of serotype A1 M. haemolytica that occurs within the bovine respiratory tract prior to the onset of pneumonic disease is potentially due to bacterial invasion of, and rapid proliferation within, the mucosal epithelium. The discovery of this previously unrecognized mechanism of pathogenesis is important because it will allow the serotype A1-specific virulence determinants responsible for invasion to be identified and thereby provide opportunities for the development of new strategies for combatting BRD aimed at preventing early colonization and infection of the bovine respiratory tract.

Cellular Tight Junctions Prevent Effective Campylobacter jejuni Invasion and Inflammatory Barrier Disruption Promoting Bacterial Invasion from Lateral Membrane in Polarized Intestinal Epithelial Cells

Campylobacter jejuni invasion is closely related to C. jejuni pathogenicity. The intestinal epithelium contains polarized epithelial cells that form tight junctions (TJs) to provide a physical barrier against bacterial invasion. Previous studies indicated that C. jejuni invasion of non-polarized cells involves several cellular features, including lipid rafts. However, the dynamics of C. jejuni invasion of polarized epithelial cells are not fully understood. Here we investigated the interaction between C. jejuni invasion and TJ formation to characterize the mechanism of C. jejuni invasion in polarized epithelial cells. In contrast to non-polarized epithelial cells, C. jejuni invasion was not affected by depletion of lipid rafts in polarized epithelial cells. However, depletion of lipid rafts significantly decreased C. jejuni invasion in TJ disrupted cells or basolateral infection and repair of cellular TJs suppressed lipid raft-mediated C. jejuni invasion in polarized epithelial cells. In addition, pro-inflammatory cytokine, TNF-α treatment that induce TJ disruption promote C. jejuni invasion and lipid rafts depletion significantly reduced C. jejuni invasion in TNF-α treated cells. These data demonstrated that TJs prevent C. jejuni invasion from the lateral side of epithelial cells, where they play a main part in bacterial invasion and suggest that C. jejuni invasion could be increased in inflammatory condition. Therefore, maintenance of TJs integrity should be considered important in the development of novel therapies for C. jejuni infection.

The impact of hypoxia on intestinal epithelial cell functions: consequences for invasion by bacterial pathogens

The maintenance of oxygen homeostasis in human tissues is mediated by several cellular adaptations in response to low-oxygen stress, called hypoxia. A decrease in tissue oxygen levels is initially counteracted by increasing local blood flow to overcome diminished oxygenation and avoid hypoxic stress. However, studies have shown that the physiological oxygen concentrations in several tissues are much lower than atmospheric (normoxic) conditions, and the oxygen supply is finely regulated in individual cell types. The gastrointestinal tract has been described to subsist in a state of physiologically low oxygen level and is thus depicted as a tissue in the state of constant low-grade inflammation. The intestinal epithelial cell layer plays a vital role in the immune response to inflammation and infections that occur within the intestinal tissue and is involved in many of the adaptation responses to hypoxic stress. This is especially relevant in the context of inflammatory disorders, such as inflammatory bowel disease (IBD). Therefore, this review aims to describe the intestinal epithelial cellular response to hypoxia and the consequences for host interactions with invading gastrointestinal bacterial pathogens.

Toll-Like Receptor Signalling and the Control of Intestinal Barrier Function

Epithelial barrier function and innate immunity are fundamental to the pathogenesis of inflammatory and infectious disease. Along with plasma membranes, epithelial cells are the primary cellular determinant of epithelial barrier function. The mechanism by which polarized epithelia form a permeability barrier is of fundamental importance to the prevention of many infectious and inflammatory diseases. Moreover, epithelial cells express Toll-like receptors (TLRs) which upon recognition of conserved microbial factors such as lipopolysaccharide (LPS) induce epithelial responses including epithelial cell proliferation, secretion of secretory IgA into the lumen and production mucins and antimicrobial peptides, thereby promoting intestinal barrier function. Understanding gut barrier integrity and regulation of permeability is crucial to increase our understanding of the pathogenesis of intestinal disease. A variety of tests have been developed to assess this barrier, including assessing intestinal epithelial cell proliferation or death, intestinal tight junction status and the consequence of intestinal barrier integrity loss such as increased intestinal permeability and susceptibility to bacterial infection. Using a mouse model, this chapter describes some of the methods to assess the functional integrity of this epithelial barrier and the part played by a TLR signalling pathway.

Methionine restriction fundamentally supports health by tightening epithelial barriers

Dietary methionine restriction (MR) has been found to affect one of the most primary tissue-level functions of an organism: the efficiency with which the epithelial linings of major organs separate the fluid compartments that they border. This process, epithelial barrier function, is basic for proper function of all organs, including the lung, liver, gastrointestinal tract, reproductive tract, blood-brain barrier, and kidney. Specifically, MR has been found to modify the protein composition of tight junctional complexes surrounding individual epithelial cells in a manner that renders the complexes less leaky. This has been observed in both a renal epithelial cell culture model and in gastrointestinal tissue. In both cases, MR increased the transepithelial electrical resistance across the epithelium, while decreasing passive leak of small nonelectrolytes. However, the specific target protein modifications involved were unique to each case. Overall, this provides an example of the primary level on which MR functions to modify, and improve, an organism.

Escherichia coli STb enterotoxin dislodges claudin-1 from epithelial tight junctions

Enterotoxigenic Escherichia coli produce various heat-labile and heat-stable enterotoxins. STb is a low molecular weight heat-resistant toxin responsible for diarrhea in farm animals, mainly young pigs. A previous study demonstrated that cells having internalized STb toxin induce epithelial barrier dysfunction through changes in tight junction (TJ) proteins. These modifications contribute probably to the diarrhea observed. To gain insight into the mechanism of increased intestinal permeability following STb exposure we treated human colon cells (T84) with purified STb toxin after which cells were harvested and proteins extracted. Using a 1% Nonidet P-40-containing solution we investigated the distribution of claudin-1, a major structural and functional TJ protein responsible for the epithelium impermeability, between membrane (NP40-insoluble) and the cytoplasmic (NP-40 soluble) location. Using immunoblot and confocal microscopy, we observed that treatment of T84 cell monolayers with STb induced redistribution of claudin-1. After 24 h, cells grown in Ca⁺⁺-free medium treated with STb showed about 40% more claudin-1 in the cytoplasm compare to the control. Switching from Ca⁺⁺-free to Ca⁺⁺-enriched medium (1.8 mM) increased the dislodgement rate of claudin-1 as comparable quantitative delocalization was observed after only 6 h. Medium supplemented with the same concentration of Mg⁺⁺ or Zn⁺⁺ did not affect the dislodgement rate compared to the Ca⁺⁺-free medium. Using anti-phosphoserine and anti-phosphothreonine antibodies, we observed that the loss of membrane claudin-1 was accompanied by dephosphorylation of this TJ protein. Overall, our findings showed an important redistribution of claudin-1 in cells treated with STb toxin. The loss of phosphorylated TJ membrane claudin-1 is likely to be involved in the increased permeability observed. The mechanisms by which these changes are brought about remain to be elucidated.

Destruction of the hepatocyte junction by intercellular invasion of Leptospira causes jaundice in a hamster model of Weil's disease

Weil's disease, the most severe form of leptospirosis, is characterized by jaundice, haemorrhage and renal failure. The mechanisms of jaundice caused by pathogenic Leptospira remain unclear. We therefore aimed to elucidate the mechanisms by integrating histopathological changes with serum biochemical abnormalities during the development of jaundice in a hamster model of Weil's disease. In this work, we obtained three-dimensional images of infected hamster livers using scanning electron microscope together with freeze-cracking and cross-cutting methods for sample preparation. The images displayed the corkscrew-shaped bacteria, which infiltrated the Disse's space, migrated between hepatocytes, detached the intercellular junctions and disrupted the bile canaliculi. Destruction of bile canaliculi coincided with the elevation of conjugated bilirubin, aspartate transaminase and alkaline phosphatase levels in serum, whereas serum alanine transaminase and γ-glutamyl transpeptidase levels increased slightly, but not significantly. We also found in ex vivo experiments that pathogenic, but not non-pathogenic leptospires, tend to adhere to the perijunctional region of hepatocyte couplets isolated from hamsters and initiate invasion of the intercellular junction within 1 h after co-incubation. Our results suggest that pathogenic leptospires invade the intercellular junctions of host hepatocytes, and this invasion contributes in the disruption of the junction. Subsequently, bile leaks from bile canaliculi and jaundice occurs immediately. Our findings revealed not only a novel pathogenicity of leptospires, but also a novel mechanism of jaundice induced by bacterial infection.

Dynamic monitoring of Salmonella typhimurium infection of polarized epithelia using organic transistors

Ion flow across polarized epithelia is a tightly regulated process. Measurement of the transepithelial resistance is a highly relevant parameter for assessing the function or health of the tissue. Dynamic, electrical measurements of transepithelial ion flow are preferred as they provide the most accurate snapshot of effects of external stimuli. Enteric pathogens such as Salmonella typhimurium are known to disrupt ion flow in gastrointestinal epithelia. Here, for the first time, the use of organic transistors as a powerful potential alternative for front-line, disposable, high-throughput diagnostics of enteric pathogens is demonstrated. The transistors' ability to detect early and subtle changes in transepithelial ion flow is capitalized upon to develop a highly sensitive detector of epithelial integrity. Stable operation of the organic devices under physiological conditions is shown, followed by dynamic, pathogen-specific diagnosis of infection of epithelia. Further, operation of the device is possible in complex matrices, showing particular promise for food and safety applications.

MyD88 adaptor-like (Mal) functions in the epithelial barrier and contributes to intestinal integrity via protein kinase C

MyD88 adapter-like (Mal)-deficient mice displayed increased susceptibility to oral but not intraperitoneal infection with Salmonella Typhimurium. Bone marrow chimeras demonstrated that mice with Mal-deficient non-hematopoietic cells were more susceptible to infection, indicating a role for Mal in non-myeloid cells. We observed perturbed barrier function in Mal(-/-) mice, as indicated by reduced electrical resistance and increased mucosa blood permeability following infection. Altered expression of occludin, Zonula occludens-1, and claudin-3 in intestinal epithelia from Mal(-/-) mice suggest that Mal regulates tight junction formation, which may in part contribute to intestinal integrity. Mal interacted with several protein kinase C (PKC) isoforms in a Caco-2 model of intestinal epithelia and inhibition of Mal or PKC increased permeability and bacterial invasion via a paracellular route, while a pan-PKC inhibitor increased susceptibility to oral infection in mice. Mal signaling is therefore beneficial to the integrity of the intestinal barrier during infection.

Transmigration route of Campylobacter jejuni across polarized intestinal epithelial cells: paracellular, transcellular or both?

Intact intercellular junctions and cellular matrix contacts are crucial structural components for the formation and maintenance of epithelial barrier functions in humans to control the commensal flora and protect against intruding microbes. Campylobacter jejuni is one of the most important zoonotic pathogens causing food-borne gastroenteritis and potentially more severe diseases such as reactive arthritis or Guillain–Barré syndrome. Crossing the intestinal epithelial barrier and host cell invasion by C. jejuni are considered to represent the primary reasons of gut tissue damage in humans and various animal model systems including monkeys, piglets, rabbits, hamsters and ferrets. C. jejuni is also able to invade underlying tissues such as the lamina propria, can enter the bloodstream, and possibly reach distinct organs such as spleen, liver or mesenteric lymph nodes. However, the molecular mechanisms as well as major bacterial and host cell factors involved in these activities are poorly understood. Various models exist by which the pathogen can trigger its own transmigration across polarized intestinal epithelial cells in vitro, the paracellular and/or transcellular mechanism. Recent studies suggest that bacterial factors such as flagellum, serine protease HtrA and lipooligosaccharide LOS may play an active role in bacterial transmigration. Here we review our knowledge on transmigration of C. jejuni as well as some other Campylobacter species, and discuss the pros and cons for the route(s) taken to travel across polarized epithelial cell monolayers. These studies provide fresh insights into the infection strategies employed by this important pathogen.

Escherichia coli heat-stable toxin b impairs intestinal epithelial barrier function by altering tight junction proteins

Escherichia coli heat-stable toxin b (STb) causes diarrhea in animals. STb binds to sulfatide, its receptor, and is then internalized. In the cytoplasm, through a cascade of events, STb triggers the opening of ion channels, allowing ion secretion and water loss and leading to diarrhea. Tight junctions (TJs) are well known for controlling paracellular traffic of ions and water by forming a physical intercellular barrier in epithelial cells, and some bacterial toxins are known to affect adversely TJs. The present study aimed at determining the effect of STb on TJs. T84 cells were treated for 24 h with purified STb and a nontoxic STb mutant (D30V). Transepithelial resistance (TER), paracellular flux marker, and confocal microscopy were used to analyze the effect of STb on TJs. Purified STb caused a significant reduction of TER parallel to an increase in paracellular permeability compared to the results seen in untreated cells or mutant D30V. The increased paracellular permeability was associated with a marked alteration of F-actin stress fibers. F-actin filament dissolution and condensation were accompanied by redistribution and/or fragmentation of ZO-1, claudin-1, and occludin. These changes were also observed following treatment of T84 cells with an 8-amino-acid peptide found in the STb sequence corresponding to a consensus sequence of Vibrio cholerae Zot toxin. These effects were not observed with a scrambled peptide or mutant D30V. Our findings indicate that STb induces epithelial barrier dysfunction through changes in TJ proteins that could contribute to diarrhea.

Group A streptococcal cysteine protease cleaves epithelial junctions and contributes to bacterial translocation

BACKGROUND

Group A Streptococcus (GAS) translocates across the host epithelial barrier.

RESULTS

Streptococcal pyrogenic exotoxin B (SpeB) directly cleaves junctional proteins.

CONCLUSION

The proteolytic efficacy of SpeB allows GAS to translocate across the epithelial barrier.

SIGNIFICANCE

SpeB-mediated dysfunction of the epithelial barrier may have important implications for not only bacterial invasion but also dissemination of other virulence factors throughout intercellular spaces. Group A Streptococcus (GAS) is an important human pathogen that possesses an ability to translocate across the epithelial barrier. In this study, culture supernatants of tested GAS strains showed proteolytic activity against human occludin and E-cadherin. Utilizing various types of protease inhibitors and amino acid sequence analysis, we identified SpeB (streptococcal pyrogenic exotoxin B) as the proteolytic factor that cleaves E-cadherin in the region neighboring the calcium-binding sites within the extracellular domain. The cleaving activities of culture supernatants from several GAS isolates were correlated with the amount of active SpeB, whereas culture supernatants from an speB mutant showed no such activities. Of note, the wild type strain efficiently translocated across the epithelial monolayer along with cleavage of occludin and E-cadherin, whereas deletion of the speB gene compromised those activities. Moreover, destabilization of the junctional proteins was apparently relieved in cells infected with the speB mutant, as compared with those infected with the wild type. Taken together, our findings indicate that the proteolytic efficacy of SpeB in junctional degradation allows GAS to invade deeper into tissues.

Validation of the organic electrochemical transistor for in vitro toxicology

BACKGROUND

The gastrointestinal epithelium provides a physical and biochemical barrier to the passage of ions and small molecules; however this barrier may be breached by pathogens and toxins. The effect of individual pathogens/toxins on the intestinal epithelium has been well characterized: they disrupt barrier tissue in a variety of ways, such as by targeting tight junction proteins, or other elements of the junctions between adjacent cells. A variety of methods have been used to characterize disruption in barrier tissue, such as immunofluorescence, permeability assays and electrical measurements of epithelia resistance, but these methods remain time consuming, costly and ill-suited to diagnostics or high throughput toxicology.

METHODS

The advent of organic electronics has created a unique opportunity to interface the worlds of electronics and biology, using devices such as the organic electrochemical transistor (OECT), whose low cost materials and potential for easy fabrication in high throughput formats represent a novel solution for assessing epithelial tissue integrity.

RESULTS

In this study, OECTs were integrated with gastro-intestinal cell monolayers to study the integrity of the gastrointestinal epithelium, providing a very sensitive way to detect minute changes in ion flow across the cell layer due to inherent amplification by the transistor.

MAJOR CONCLUSIONS

We validate the OECT against traditional methods by monitoring the effect of toxic compounds on epithelial tissue. We show a systematic characterization of this novel method, alongside existing methods used to assess barrier tissue function.

GENERAL SIGNIFICANCE

The toxic compounds induce a dramatic disruption of barrier tissue, and the OECT measures this disruption with increased temporal resolution and greater or equal sensitivity when compared with existing methods. This article is part of a Special Issue entitled Organic Bioelectronics - Novel Applications in Biomedicine.

Measurement of barrier tissue integrity with an organic electrochemical transistor

The integration of an organic electrochemical transistor with human barrier tissue cells provides a novel method for assessing toxicology of compounds in vitro. Minute variations in paracellular ionic flux induced by toxic compounds are measured in real time, with unprecedented temporal resolution and extreme sensitivity.

Rapid paracellular transmigration of Campylobacter jejuni across polarized epithelial cells without affecting TER: role of proteolytic-active HtrA cleaving E-cadherin but not fibronectin

Background

Campylobacter jejuni is one of the most important bacterial pathogens causing food-borne illness worldwide. Crossing the intestinal epithelial barrier and host cell entry by C. jejuni is considered the primary reason of damage to the intestinal tissue, but the molecular mechanisms as well as major bacterial and host cell factors involved in this process are still widely unclear.

Results

In the present study, we characterized the serine protease HtrA (high-temperature requirement A) of C. jejuni as a secreted virulence factor with important proteolytic functions. Infection studies and in vitro cleavage assays showed that C. jejuni’s HtrA triggers shedding of the extracellular E-cadherin NTF domain (90 kDa) of non-polarised INT-407 and polarized MKN-28 epithelial cells, but fibronectin was not cleaved as seen for H. pylori’s HtrA. Deletion of the htrA gene in C. jejuni or expression of a protease-deficient S197A point mutant did not lead to loss of flagella or reduced bacterial motility, but led to severe defects in E-cadherin cleavage and transmigration of the bacteria across polarized MKN-28 cell layers. Unlike other highly invasive pathogens, transmigration across polarized cells by wild-type C. jejuni is highly efficient and is achieved within a few minutes of infection. Interestingly, E-cadherin cleavage by C. jejuni occurs in a limited fashion and transmigration required the intact flagella as well as HtrA protease activity, but does not reduce transepithelial electrical resistance (TER) as seen with Salmonella, Shigella, Listeria or Neisseria.

Conclusion

These results suggest that HtrA-mediated E-cadherin cleavage is involved in rapid crossing of the epithelial barrier by C. jejuni via a very specific mechanism using the paracellular route to reach basolateral surfaces, but does not cleave the fibronectin receptor which is necessary for cell entry.

Distinct roles of secreted HtrA proteases from gram-negative pathogens in cleaving the junctional protein and tumor suppressor E-cadherin

The periplasmic chaperone and serine protease HtrA is important for bacterial stress responses and protein quality control. Recently, we discovered that HtrA from Helicobacter pylori is secreted and cleaves E-cadherin to disrupt the epithelial barrier, but it remained unknown whether this maybe a general virulence mechanism. Here, we show that important other pathogens including enteropathogenic Escherichia coli, Shigella flexneri, and Campylobacter jejuni, but not Neisseria gonorrhoeae, cleaved E-cadherin on host cells. HtrA deletion in C. jejuni led to severe defects in E-cadherin cleavage, loss of cell adherence, paracellular transmigration, and basolateral invasion. Computational modeling of HtrAs revealed a conserved pocket in the active center exhibiting pronounced proteolytic activity. Differential E-cadherin cleavage was determined by an alanine-to-glutamine exchange in the active center of neisserial HtrA. These data suggest that HtrA-mediated E-cadherin cleavage is a prevalent pathogenic mechanism of multiple gram-negative bacteria representing an attractive novel target for therapeutic intervention to combat bacterial infections.

Neisseria gonorrhoeae induced disruption of cell junction complexes in epithelial cells of the human genital tract

Pathogenic microorganisms, such as Neisseria gonorrhoeae, have developed mechanisms to alter epithelial barriers in order to reach subepithelial tissues for host colonization. The aim of this study was to examine the effects of gonococci on cell junction complexes of genital epithelial cells of women. Polarized Ishikawa cells, a cell line derived from endometrial epithelium, were used for experimental infection. Infected cells displayed a spindle-like shape with an irregular distribution, indicating potential alteration of cell-cell contacts. Accordingly, analysis by confocal microscopy and cellular fractionation revealed that gonococci induced redistribution of the adherens junction proteins E-cadherin and its adapter protein β-catenin from the membrane to a cytoplasmic pool, with no significant differences in protein levels. In contrast, gonococcal infection did not induce modification of either expression or distribution of the tight junction proteins Occludin and ZO-1. Similar results were observed for Fallopian tube epithelia. Interestingly, infected Ishikawa cells also showed an altered pattern of actin cytoskeleton, observed in the form of stress fibers across the cytoplasm, which in turn matched a strong alteration on the expression of fibronectin, an adhesive glycoprotein component of extracellular matrix. Interestingly, using western blotting, activation of the ERK pathway was detected after gonococcal infection while p38 pathway was not activated. All effects were pili and Opa independent. Altogether, results indicated that gonococcus, as a mechanism of pathogenesis, induced disruption of junction complexes with early detaching of E-cadherin and β-catenin from the adherens junction complex, followed by a redistribution and reorganization of actin cytoskeleton and fibronectin within the extracellular matrix.

Interaction of oral bacteria with gingival epithelial cell multilayers

Primary gingival epithelial cells were cultured in multilayers as a model for the study of interactions with oral bacteria associated with health and periodontal disease. Multilayers maintained at an air-liquid interface in low-calcium medium displayed differentiation and cytokeratin properties characteristic of junctional epithelium. Multilayers were infected with fluorescently labeled Porphyromonas gingivalis, Aggregatibacter actinomycetemcomitans, Fusobacterium nucleatum or Streptococcus gordonii, and bacterial association was determined by confocal microscopy and quantitative image analysis. Porphyromonas gingivalis invaded intracellularly and spread from cell to cell; A. actinomycetemcomitans and F. nucleatum remained extracellular and showed intercellular movement through the multilayer; whereas S. gordonii remained extracellular and predominantly associated with the superficial cell layer. None of the bacterial species disrupted barrier function as measured by transepithelial electrical resistance. P. gingivalis did not elicit secretion of proinflammatory cytokines. However, A. actinomycetemcomitans and S. gordonii induced interleukin-1β (IL-1β), tumor necrosis factor-α (TNF-α), IL-6 and IL-8 secretion; and F. nucleatum stimulated production of IL-1β and TNF-α. Aggregatibacter actinomycetemcomitans, F. nucleatum and S. gordonii, but not P. gingivalis, increased levels of apoptosis after 24 h infection. The results indicate that the organisms with pathogenic potential were able to traverse the epithelium, whereas the commensal bacteria did not. In addition, distinct host responses characterized the interaction between the junctional epithelium and oral bacteria.

Streptolysin S contributes to group A streptococcal translocation across an epithelial barrier

Group A Streptococcus pyogenes (GAS) is a human pathogen that causes local suppurative infections and severe invasive diseases. Systemic dissemination of GAS is initiated by bacterial penetration of the epithelial barrier of the pharynx or damaged skin. To gain insight into the mechanism by which GAS penetrates the epithelial barrier, we sought to identify both bacterial and host factors involved in the process. Screening of a transposon mutant library of a clinical GAS isolate recovered from an invasive episode allowed identification of streptolysin S (SLS) as a novel factor that facilitates the translocation of GAS. Of note, the wild type strain efficiently translocated across the epithelial monolayer, accompanied by a decrease in transepithelial electrical resistance and cleavage of transmembrane junctional proteins, including occludin and E-cadherin. Loss of integrity of intercellular junctions was inhibited after infection with a deletion mutant of the sagA gene encoding SLS, as compared with those infected with the wild type strain. Interestingly, following GAS infection, calpain was recruited to the plasma membrane along with E-cadherin. Moreover, bacterial translocation and destabilization of the junctions were partially inhibited by a pharmacological calpain inhibitor or genetic interference with calpain. Our data indicate a potential function of SLS that facilitates GAS invasion into deeper tissues via degradation of epithelial intercellular junctions in concert with the host cysteine protease calpain.

A role for syndecan-1 and claudin-2 in microbial translocation during HIV-1 infection

Microbial translocation from the gastrointestinal tract has been implicated in chronic activation of the immune system during progressive HIV-1 infection by ill-defined mechanisms. We recently identified a gene encoding syndecan-1 (SYN1) in microarray studies of HIV-1 infection in lymphatic tissues and show here that increased expression of SYN1 in the gut of HIV-1-infected individuals is associated with increased microbial translocation. We further show that: (1) microbial access to SYN1 in the intestinal epithelium could be mediated by compromised barrier function through the upregulation of claudin-2; (2) increases in SYN1 and microbial translocation are associated with systemic immune activation; and (3) SYN1 expression and microbial translocation are inversely correlated with peripheral blood CD4 T-cell counts. We thus propose a new mechanism in which claudin-2 and SYN1 work in concert to enhance microbial translocation across the intestinal epithelial barrier to contribute to chronic immune activation and CD4 T-cell depletion.

Dietary methionine restriction improves colon tight junction barrier function and alters claudin expression pattern

The beneficial effects of caloric restriction in increasing longevity and forestalling age-related diseases are well known. Dietary restriction of methionine also renders similar benefits. We recently showed in a renal epithelial cell culture system that reduction of culture medium methionine by 80% resulted in altered tight junctional (TJ) claudin composition and also improved epithelial barrier function (51). In the current study, we examined the effect of dietary restriction of methionine on TJ barrier function in rat gastrointestinal tissue to see whether this phenomenon also holds true in a tissue model and for a different epithelial cell type. After 28 days on methionine-restricted (MR) diet, rats showed small but significant reductions in the plasma and (intracellular) colonocyte levels of methionine. Colon mucosal sheets from rats on the MR diet showed increased transepithelial electrical resistance with concomitant decrease in paracellular diffusion of (14)C-D-mannitol, suggesting improved barrier function relative to rats on control diet. This improved barrier function could not be explained by changes in colon crypt length or frequency. Neither was the colonocyte mitotic index nor the apoptotic frequency altered significantly. However, TJ composition/structure was being altered by the MR diet. RT-PCR and Western blot analysis showed an increase in the abundance of claudin-3 and an apparent change in the posttranslational modification of occludin, data reinforcing a paracellular barrier alteration. Overall, our data suggest that reduction in dietary intake of methionine results in improved epithelial barrier function by inducing altered TJ protein composition.

Pseudomonas aeruginosa: host defence in lung diseases

Lung infections caused by the opportunistic pathogen Pseudomonas aeruginosa can present as a spectrum of clinical entities from a rapidly fatal pneumonia in a neutropenic patient to a multi-decade bronchitis in patients with cystic fibrosis. P. aeruginosa is ubiquitous in our environment, and one of the most versatile pathogens studied, capable of infecting a number of diverse life forms and surviving harsh environmental factors. It is also able to quickly adapt to new environments, including the lung, where it orchestrates virulence factors to acquire necessary nutrients, and if necessary, turn them off to prevent immune recognition. Despite these capabilities, P. aeruginosa rarely infects healthy human lungs. This is secondary to a highly evolved host defence mechanism that efficiently removes inhaled or aspirated pseudomonads. Many arms of the respiratory host defence have been elucidated using P. aeruginosa as a model pathogen. Human infections with P. aeruginosa have demonstrated the importance of the mechanical barrier functions including mucus clearance, and the innate immune system, including the critical role of the neutrophilic response. As more models of persistent or biofilm P. aeruginosa infections are developed, the role of the adaptive immune response will likely become more evident. Understanding the pathogenesis of P. aeruginosa, and the respiratory host defence response to it has, and will continue to, lead to novel therapeutic strategies to help patients.

Reciprocal interactions between commensal bacteria and gamma delta intraepithelial lymphocytes during mucosal injury

The intestinal mucosal surface is in direct contact with a vast beneficial microbiota. The symbiotic nature of this relationship is threatened when the surface epithelium is injured, yet little is known about how mucosal surfaces maintain homeostasis with commensal microbes following damage. Gammadelta intraepithelial lymphocytes (gammadelta IEL) reside at the gut epithelial surface, where they stimulate mucosal healing following acute injury. A genome-wide analysis of the gammadelta IEL response to dextran sulfate sodium-induced colonic damage revealed induction of a complex transcriptional program, including coordinate regulation of cytoprotective, immunomodulatory, and antibacterial factors. Studies in germfree mice demonstrated that commensal microbiota regulate key components of this transcriptional program, thus revealing a dialogue between commensal bacteria and gammadelta IEL in injured epithelia. Analysis of TCRdelta-deficient mice indicated that gammadelta T cells are essential for controlling mucosal penetration of commensal bacteria immediately following dextran sulfate sodium-induced damage, suggesting that a key function of gammadelta IEL is to maintain host-microbial homeostasis following acute mucosal injury. Taken together, these findings disclose a reciprocal relationship between gammadelta T cells and intestinal microbiota that promotes beneficial host-microbial relationships in the intestine.

Invasion of enteropathogenic Escherichia coli into host cells through epithelial tight junctions

Enteropathogenic Escherichia coli (EPEC) has been shown to disrupt the barrier function of host intestinal epithelial tissues through entering tight junctions. However, the mechanism by which this occurs remains poorly understood. In this study, we determined that EPEC invades host cells through tight junctions as it initiates infection. Immunofluorescence microscopy revealed redistribution of the tight-junction proteins occludin and ZO-1 from an intercellular to a cytoplasmic location after EPEC invasion. Flotillin-1 was recruited to sites of EPEC entry. EPEC entered host cells through tight-junction membrane microdomains. Tight-junction ultrastructure was disrupted following EPEC infection, accompanied by loss of barrier function. EPEC infection caused a time-dependent decrease in trans-epithelial electrical resistance. Subcellular fractionation using discontinuous sucrose density gradients demonstrated a decline in raft-associated occludin following exposure to EPEC. These results indicate the important role of host membrane tight-junction microdomains in EPEC invasion.

The interaction of Streptococcus pneumoniae with plasmin mediates transmigration across endothelial and epithelial monolayers by intercellular junction cleavage

The precise mechanisms by which Streptococcus pneumoniae overcomes epithelial and endothelial barriers to access underlying human tissues remain to be determined. The plasminogen system is highly important for the tissue barrier degradation which allows cell migration. Plasminogen is known to interact with pneumococci via enolase, glyceraldehyde-3-phosphate dehydrogenase, and choline-binding protein E. These observations prompted us to evaluate the role of this proteolytic system in the pneumococcal invasion process. We observed that coating of S. pneumoniae R6 strain with plasminogen or inactivated plasmin increased adherence to pulmonary epithelial A549 and vascular endothelial EaHy cells in vitro. This indicates that plasminogen-mediated adherence is independent of the protease activity and involves plasminogen binding to receptors on eukaryotic cell surfaces. Conversely, decreased adherence of bacterial cells coated with active plasmin was observed, indicating that the protease activity limits bacterial attachment on the cell surface. We were then interested in investigating the role of the proteolytic plasmin activity in the traversal of tissue barriers. We observed that adherence of plasmin-coated D39 (encapsulated) or R6 (unencapsulated) pneumococci induced sporadic disruptions of EaHy and A549 monolayer cell junctions. This was not observed when plasmin was inhibited by aprotinin. Endothelial junction disorganization may proceed by proteolysis of the cell junction components. This is supported by our observation of the in vitro cleavage by plasmin bound to pneumococci of recombinant vascular endothelial cadherin, the main component of endothelial adherens junctions. Finally, junction damage induced by plasmin may be related to tissue barrier traversal, as we measured an increase of S. pneumoniae transmigration across epithelial A549 and endothelial EaHy layers when active plasmin was present on the bacterial surface. Our results highlight a novel function for the plasminogen recruitment at the bacterial surface in facilitating adherence of pneumococci to endothelial and epithelial cells, while active plasmin degrades intercellular junctions. This process promotes migration of pneumococci through cell barriers by a pericellular route, a prerequisite for dissemination of S. pneumoniae in the host organism.

Tight junction claudins and the kidney in sickness and in health

The epithelial cell tight junction has several functions including the control of paracellular transport between epithelial cells. Renal paracellular transport has been long recognized to exhibit unique characteristics within different segments of the nephron, functions as an important component of normal renal physiology and has been speculated to contribute to renal related pathology if functioning abnormally. The discovery of a large family of tight junction associated 4-transmembrane spanning domain proteins named claudins has advanced our understanding on how the paracellular permeability properties of tight junctions are determined. In the kidney, claudins are expressed in a nephron-specific pattern and are major determinants of the paracellular permeability of tight junctions in different nephron segments. The combination of nephron segment claudin expression patterns, inherited renal diseases, and renal epithelial cell culture models is providing important clues about how tight junction claudin molecules function in different segments of the nephron under normal and pathological conditions. This review discusses early observations of renal tubule paracellular transport and more recent information on the discovery of the claudin family of tight junction associated membrane proteins and how they relate to normal renal function as well as diseases of the human kidney.

Role of the Clp system in stress tolerance, biofilm formation, and intracellular invasion in Porphyromonas gingivalis

Clp proteases and chaperones are ubiquitous among prokaryotes and eukaryotes, and in many pathogenic bacteria the Clp stress response system is also involved in regulation of virulence properties. In this study, the roles of ClpB, ClpC, and ClpXP in stress resistance, homotypic and heterotypic biofilm formation, and intracellular invasion in the oral opportunistic pathogen Porphyromonas gingivalis were investigated. Absence of ClpC and ClpXP, but not ClpB, resulted in diminished tolerance to high temperatures. Response to oxidative stress was not affected by the loss of any of the Clp proteins. The clpC and clpXP mutants demonstrated elevated monospecies biofilm formation, and the absence of ClpXP also enhanced heterotypic P. gingivalis-Streptococcus gordonii biofilm formation. All clp mutants adhered to gingival epithelial cells to the same level as the wild type; however, ClpC and ClpXP were found to be necessary for entry into host epithelial cells. ClpB did not play a role in entry but was required for intracellular replication and survival. ClpXP negatively regulated the surface exposure of the minor fimbrial (Mfa) protein subunit of P. gingivalis, which stimulates biofilm formation but interferes with epithelial cell entry. Collectively, these results show that the Clp protease complex and chaperones control several processes that are important for the colonization and survival of P. gingivalis in the oral cavity.

The novel porcine Lactobacillus sobrius strain protects intestinal cells from enterotoxigenic Escherichia coli K88 infection and prevents membrane barrier damage

Lactobacilli have a potential to overcome intestinal disorders; however, the exact mode of action is still largely unknown. In this study, we have used the intestinal porcine intestinal IPEC-1 epithelial cells as a model to investigate a possible protective activity of a new Lactobacillus species, the L. sobrius DSM 16698(T), against intestinal injury induced by enterotoxigenic Escherichia coli (ETEC) K88 infection and the underlying mechanisms. Treatment of infected cells with L. sobrius strongly reduced the pathogen adhesion. L. sobrius was also able to prevent the ETEC-induced membrane damage by inhibiting delocalization of zonula occludens (ZO)-1, reduction of occludin amount, rearrangement of F-actin, and dephosphorylation of occludin caused by ETEC. RT-PCR and ELISA experiments showed that L. sobrius counteracted the ETEC-induced increase of IL-8 and upregulated the IL-10 expression. The involvement of IL-8 in the deleterious effects of ETEC was proven by neutralization of IL-8 with a specific antibody. A crucial role of IL-10 was indicated by blockage of IL-10 production with neutralizing anti-IL-10 antibody that fully abrogated the L. sobrius protection. L. sobrius was also able to inhibit the internalization of ETEC, which was likely favored by the leaking barrier. The protective effects were not found with L. amylovorus DSM 20531(T) treatment, a strain derived from cattle waste but phylogenetically closely related to L. sobrius. Together, the data indicate that L. sobrius exerts protection against the harmful effects of ETEC by different mechanisms, including pathogen adhesion inhibition and maintenance of membrane barrier integrity through IL-10 regulation.

Claudins at the gate: determinants of renal epithelial tight junction paracellular permeability

The epithelial tight junction (TJ) is responsible for the control of paracellular transport between epithelial cells (gate function) and the maintenance of apical/basolateral polarity by preventing the diffusion of membrane lipids and/or proteins from one surface domain to another (fence function). Renal tubule epithelia in the mammalian nephron have TJs that determine paracellular transport characteristics. Paracellular transport across renal tubular epithelial TJs (gate function) varies in different segments of the nephron. A large family of recently identified TJ-associated transmembrane proteins named claudins appear to determine the paracellular permeability properties of the TJ. A combination of inherited human diseases, renal epithelial cell culture models, and nephron expression patterns of claudins is providing important clues about how claudin molecules determine the TJ gate function of renal epithelia in different segments of the nephron.

Attaching and effacing pathogen-induced tight junction disruption in vivo

Diarrhoea is a hallmark of infections by the human attaching and effacing (A/E) pathogens, enterohaemorrhagic Escherichia coli (EHEC) and enteropathogenic E. coli (EPEC). Although the mechanisms underlying diarrhoea induced by these pathogens remain unknown, cell culture results have suggested that these pathogens may target tight junctions. Tight junctions in the colon function as physical intercellular barriers that separate and prevent mixing of the luminal contents with adlumenal regions of the epithelium. Consequently, it is thought that the disruption of intestinal epithelial tight junctions by A/E pathogens could result in a loss of barrier function in the alimentary tract; however, this remains unexamined. Here we demonstrate for the first time that A/E pathogen infection results in the morphological alteration of tight junctions during natural disease. Tight junction alteration, characterized by relocalization of the transmembrane tight junction proteins claudin 1, 3 and 5, is a functional disruption; molecular tracers, which do not normally penetrate uninfected epithelia, pass across pathogen-infected epithelia. Functional junction disruption occurs with a concomitant increase in colon luminal water content. The effects on tissue are dependent upon the bacterial type III effector EspF (E. coli secreted protein F), because bacteria lacking EspF, while able to colonize, are defective for junction disruption and result in decreased proportions of water in the colon compared with wild-type infection. These results suggest that the diarrhoea induced by A/E pathogens occurs as part of functional tight junction disruption.

Intercellular spreading of Porphyromonas gingivalis infection in primary gingival epithelial cells

Porphyromonas gingivalis, an important periodontal pathogen, is an effective colonizer of oral tissues. The organism successfully invades, multiplies in, and survives for extended periods in primary gingival epithelial cells (GECs). It is unknown whether P. gingivalis resides in the cytoplasm of infected cells throughout the infection or can spread to adjacent cells over time. We developed a technique based on flow cytofluorometry and fluorescence microscopy to study propagation of the organism at different stages of infection of GECs. Results showed that P. gingivalis spreads cell to cell and that the amount of spreading increases gradually over time. There was a very low level of propagation of bacteria to uninfected cells early in the infection (3 h postinfection), but there were 20-fold and 45-fold increases in the propagation rate after 24 h and 48 h, respectively, of infection. Immunofluorescence microscopy of infected cells suggested that intercellular translocation of P. gingivalis may be mediated through actin-based membrane protrusions, bypassing the need for release of bacteria into extracellular medium. Consistent with these observations, cytochalasin D treatment of infected cells resulted in significant inhibition of bacterial spreading. This study shows for the first time that P. gingivalis disseminates from cell to cell without passing through the extracellular space. This mechanism of spreading may allow P. gingivalis to colonize oral tissues without exposure to the humoral immune response.

Novel effects of the prototype translocating Escherichia coli, strain C25 on intestinal epithelial structure and barrier function

Intestinal bacteria play an etiologic role in triggering and perpetuating chronic inflammatory bowel disorders. However, the precise mechanisms whereby the gut microflora influences intestinal cell function remain undefined. Therefore, the effects of the non-pathogenic prototype translocating Escherichia coli, strain C25 on the barrier properties of human T84 and Madine-Darby canine kidney type 1 epithelial cells were examined. T-84 cells were also infected with commensal E. coil, strains F18 and HB101, and enterohaemorrhagic E. coli, serotype O157:H7. Strains F18 and HB101 had no effect on transepithelial electrical resistance (TER) of T84 monolayers. By contrast, epithelial cells infected with strain C25 displayed a time-dependent decrease in TER, preceded by an altered distribution of the cytoskeletal protein alpha-actinin, comparable to infection with E. coli O157:H7. E. coli C25 infection also led to activation of nuclear factor kappaB (NF-kappaB), interleukin-8 secretion and alterations in localization of claudin-1, but not zona occludens-1 or claudin-4, in T84 cells. There were adherent C25 bacteria on the intact apical surface of infected T84 cells, while mitochondria appeared swollen and vacuolated. These novel findings demonstrate the ability of a translocating commensal bacterium to adhere to and modulate intestinal epithelial barrier function and to induce morphological changes in a manner distinct from the known enteric pathogen, E. coli O157:H7.

Disruption of tight junctions during traversal of the respiratory epithelium by Burkholderia cenocepacia

Burkholderia cenocepacia is an opportunistic bacterial species capable of causing life-threatening respiratory tract infection in persons with cystic fibrosis (CF). Unlike most other pathogens in CF, which typically remain confined to the endobronchial spaces, B. cenocepacia can traverse airway epithelium to cause bacteremia and sepsis. The mechanisms by which this occurs, however, are unknown. We examined the transmigration of B. cenocepacia through polarized respiratory epithelium. Representatives of three "epidemic" lineages common among CF patients in North America were able to traverse polarized 16HBE14o- cells in vitro. Transmigration of bacteria was associated with significant perturbations in epithelial permeability, as measured by a loss of transepithelial electrical resistance and increased flux of bovine serum albumin across the cell layer. Terminal deoxynucleotidyltransferase-mediated dUTP-biotin nick end labeling and trypan blue exclusion assays, as well as lactate dehydrogenase levels, did not indicate excessive cytotoxicity or cell death in infected cell layers. Rather, confocal fluorescence microscopy demonstrated the loss of occludin from tight junctions. In contrast, zonula occludens 1 was well preserved along intercellular borders. Western blot analysis showed a shift in the major occludin isoforms from high- to low-phosphorylation states during infection. These observations suggest that B. cenocepacia traverses polarized respiratory epithelium by the dephosphorylation and dissociation of occludin from the tight-junction complex.

Barriers built on claudins

The fundamental functions of epithelia and endothelia in multicellular organisms are to separate compositionally distinct compartments and regulate the exchange of small solutes and other substances between them. Tight junctions (TJs) between adjacent cells constitute the barrier to the passage of ions and molecules through the paracellular pathway and function as a 'fence' within the plasma membrane to create and maintain apical and basolateral membrane domains. How TJs achieve this is only beginning to be understood. Recently identified components of TJs include the claudins, a family of four-transmembrane-span proteins that are prime candidates for molecules that function in TJ permeability. Their identification and characterization have provided new insight into the diversity of different TJs and heterogeneity of barrier functions in different epithelia and endothelia.

Intestinal barrier dysfunction by enteropathogenic Escherichia coli is mediated by two effector molecules and a bacterial surface protein

The human intestinal pathogen, enteropathogenic Escherichia coli (EPEC), causes diarrhoeal disease by a mechanism that is dependent on the injection of effector proteins into the host cell. One effector, EspF, is reported to be required for EPEC to disrupt tight junction integrity of intestinal cells and increase the paracellular movement of molecules, which is likely to contribute to diarrhoea. Here, we show that not one but three EPEC-encoded factors play important roles in this process. Thus, the Map (Mitochondria-associated protein) effector is shown to: (i) be as essential as EspF for disrupting intestinal barrier function, (ii) be able to function independently of EspF, (iii) alter tight junction structure and (iv) mediate these effects in the absence of mitochondrial targeting. Additionally, the outer membrane protein Intimin is shown to be crucial for EspF and Map to disrupt the intestinal barrier function. This function of Intimin is completely independent of its interaction with its known receptor Tir, revealing a physiologically relevant requirement for Intimin interaction with alternative receptor(s). This work demonstrates that EPEC uses multiple multifunctional proteins to elicit specific responses in intestinal cells and that EPEC can control the activity of its injected effector molecules from its extracellular location.

Improvement of barrier function and stimulation of colonic epithelial anion secretion by Menoease Pills

AIM: Menoease Pills (MP), a Chinese medicine-based new formula for postmenopausal women, has been shown to modulate the endocrine and immune systems^[1]. The present study investigated the effects of MP and one of its active ingredients, ligustrazine, on epithelial barrier and ion transport function in a human colonic cell line, T₈₄.

METHODS: Colonic transepithelial electrophysiological characteristics and colonic anion secretion were studied using the short circuit current (I_SC) technique. RT-PCR was used to examine the expression of cytoplasmic proteins associated with the tight junctions, ZO-1 (zonula occludens-1) and ZO-2 (zonula occludens-2).

RESULTS: Pretreatment of T₈₄ cells with MP (15 μg/mL) for 72 h significantly increased basal potential difference, transepithelial resistance and basal I_SC. RT-PCR results showed that the expressions of ZO-1 and ZO-2 were significantly increased after MP treatment, consistent with improved epithelial barrier function. Results of acute stimulation showed that apical addition of MP produced a concentration-dependent (10-5000 μg/mL, EC₅₀ = 293.9 μg/mL) increase in I_SC. MP-induced I_SC was inhibited by basolateral treatment with bumetanide (100 μmol/L), an inhibitor of the Na ⁺ -K ⁺ -2Cl^- cotransporter, apical addition of Cl^- channel blockers, diphenylamine-2, 2’-dicarboxylic acid (1 mmol/L) or glibenclamide (1 mmol/L), but not 4, 4’-diisothiocyanostilbene-2, 2’-disulfonic acid or epithelial Na ⁺ channel blocker, amiloride. The effect of MP on ZO-1 and ZO-2 was mimicked by Ligustrazine and the ligustrazine-induced I_SC was also blocked by basolateral application of bumetanide and apical addition of diphenylamine-2, 2'-dicarboxylic acid or glibenclamide, and reduced by a removal of extracellular Cl^-.

CONCLUSION: The results of the present study suggest that MP and ligustrazine may improve epithelial barrier function and exert a stimulatory effect on colonic anion secretion, indicating the potential use of MP and its active ingredients for improvement of GI tract host defense and alleviation of constipation often seen in the elderly.