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PubMed2006

Role of epithelial cells in initiation and propagation of intestinal inflammation. Eliminating the static: tight junction dynamics exposed.

Like all mucosal surfaces, the intestine forms a barrier that separates the external environment, i.e., the gut lumen, from the protected internal milieu. The intestinal barrier is formed by the epithelial cells that line the luminal surface. Plasma membranes of these cells prevent free passage of hydrophilic molecules across this barrier but do not seal the space between cells. This function is provided by the tight junction. Each cell is encircled at the apicolateral boundary by the tight junction, which seals the paracellular space. The tight junction does not form a completely impermeant seal, however, because that would prevent paracellular absorption of essential nutrients and ions; intestinal tight junctions are "leaky" and allow solutes to be transported paracellularly according to size and charge. Abundant data are available to demonstrate that barrier properties of tight junctions can be modulated in response to physiological, pharmacological, and pathophysiological stimuli, but the structural modifications responsible for these responses are poorly defined. Recent advances in understanding the role of tight junction dynamics in response to such stimuli are the focus of this review.

Animals↗
PubMed1999

Protein interactions at the tight junction. Actin has multiple binding partners, and ZO-1 forms independent complexes with ZO-2 and ZO-3.

Defining how the molecular constituents of the tight junction interact is a prerequisite to understanding tight junction physiology. We utilized in vitro binding assays with purified recombinant proteins and immunoprecipitation analyses to define interactions between ZO-1, ZO-2, ZO-3, occludin, and the actin cytoskeleton. Actin cosedimentation studies showed that ZO-2, ZO-3, and occludin all interact directly with F-actin in vitro, indicating that actin is engaged in multiple interactions at the tight junction. Low speed sedimentation analyses demonstrated that neither ZO-2, ZO-3, nor occludin act as F-actin cross-linking proteins, and further evidence indicates that these proteins do not bind to actin filament ends. The binding interactions of ZO-2, ZO-3, and occludin were corroborated in vivo by immunofluorescence colocalization experiments which showed that all three proteins colocalized with actin aggregates at cell borders in cytochalasin D-treated Madin-Darby canine kidney cells. Exploration of other tight junction protein interactions demonstrated that ZO-2 binds directly to both ZO-1 and occludin. Contrary to previous beliefs, our immunoprecipitation results indicate that ZO-1, ZO-2, and ZO-3 exist in situ primarily as independent ZO-1.ZO-2 and ZO-1.ZO-3 complexes rather than a trimeric ZO-1.ZO-2.ZO-3 grouping. These studies elucidate direct binding interactions among tight junction-associated proteins, giving insight into their organization as a multimolecular structure.

Actins↗
PubMed2005

HLA-DR- and CD11c-positive dendritic cells penetrate beyond well-developed epithelial tight junctions in human nasal mucosa of allergic rhinitis.

The epithelial barrier of the upper respiratory tract plays a crucial role in host defense. In this study, to elucidate whether there is antigen monitoring by dendritic cells (DCs) beyond the epithelial tight-junction barrier in allergic rhinitis, we investigated the expression and function of tight junctions and characterized DCs in the epithelium of nasal mucosa from patients with allergic rhinitis. In reverse transcription-polymerase chain reaction, mRNAs of tight-junction proteins occludin, JAM-1, ZO-1, and claudin-1, -4, -7, -8, -12, -13, and -14 were detected in the nasal mucosa. Occludin, JAM-1, and ZO-1 were colocalized in the uppermost layer in the pseudostratified epithelium of the nasal mucosa, whereas claudin-1, -4, and -7 were found throughout the epithelium. In freeze-fracture replicas of the nasal mucosa, continuous tight-junction strands formed well-developed networks. Epithelial barrier function measured by a dye tracer was well maintained in occludin-positive tight junctions in the epithelium of the nasal mucosa. HLA-DR- and CD11c-positive DCs expressed claudin-1 and penetrated beyond occludin in the epithelium of the nasal mucosa with, but not without, allergic rhinitis. These results indicate that DCs may easily access antigens beyond epithelial tight junctions in the human nasal mucosa of allergic rhinitis.

Adult↗
PubMed2005

p38 MAP-kinase regulates function of gap and tight junctions during regeneration of rat hepatocytes.

BACKGROUND/AIMS: Hepatocyte regeneration is considered to be associated with adaptive changes in expression of gap and tight junctions through multiple signal transduction pathways including p38 MAP-kinase. The role of the stress responsitive MAP-kinase, p38 MAP-kinase, signaling pathway in function of gap and tight junctions was examined during regeneration of rat hepatocytes in vivo and in vitro. METHODS: We examined changes in formation, expression and function of gap and tight junctions in rat livers after 70% partial hepatectomy and in primary cultures of rat hepatocytes, by using a p38 MAP-kinase inhibitor, SB203580. RESULTS: When p38 MAP-kinase was activated during partial hepatectomy, down-regulation of Cx32 and up-regulation of claudin-1 were observed. By SB203580 treatment, the down-regulation of Cx32 was inhibited and the up-regulation of claudin-1 was enhanced, well maintaining the structures of gap and tight junctions. SB203580 treatment did not affect the increase of hepatocyte proliferation. In EGF induced proliferative rat hepatocytes treated with SB203580, the expression and function of Cx32 and claudin-1 were increased. CONCLUSIONS: Dynamic changes of formation of gap and tight junctions during regeneration of rat hepatocytes in vivo and in vitro are in part controlled via a p38 MAP-kinase signaling pathway, and are independent of cell growth.

Animals↗
PubMed1989

Structural alterations in vascular endothelial tight junctions in the course of their gradual degradation in vitro.

Rabbit aorta explants in organ culture maintained their endothelium as a confluent cell layer for 1-6 days. Depending on culture time, interendothelial tight junctions underwent gradual morphological changes in their substructure, as seen in freeze-fracture replicas. The formation of a P-face associated groove and concurrent confluence of tight junction particles on E-faces after 24 hr in vitro was followed by a rarefaction of particles and shortening of tight junctional strands. By day 6 in vitro, almost all tight junctions have disappeared. We interpret these findings as signs of a degradation of tight junctions in vitro, involving three different substructural components: a component facing the protoplasm, tight junction particles and a component facing the extracellular space. The degradation was inhibited by culturing under increased ambient pressure (910 mmHg).

Animals↗
PubMed2006

Tight junctions and compression therapy in chronic venous insufficiency.

Tight junctions (TJs) provide a barrier function, inhibiting solute and water flow through the paracellular space. There had been no analysis until now as to how tight junction molecules could be involved in the pathology of patients with chronic venous insufficiency. The aim of the study was to analyse the expression pattern of TJ-molecules occludin (OCLN), claudin-1 (CLDN-1), claudin-3 (CLDN-3) and claudin-5 (CLDN-5) on mRNA and protein level in patients with edema, venous leg ulcers and healthy controls. Biopsy specimens were taken in healthy individuals and in patients before, and four weeks after compression therapy. mRNA-expression was determined by using reverse-transcriptase and polymerase chain reaction (RT-PCR) and the protein-expression was determined by Western blotting from tissue specimens. Quantification performed determining the expression for TJ-molecules displayed diminished expression for CLDN-1 (p<0.01) and CLDN-5 (p<0.01) in patients with chronic venous insufficiency in comparison with healthy controls on mRNA as well as protein level. No statistical differences were detected for OCLN and CLDN-3 between the edema group and healthy controls. There was a significantly elevated expression (p<0.01) on mRNA and protein level between the leg ulcer group and healthy controls for OCLN and CLDN-3. Densitometric evaluation revealed a more significantly elevated expression (p<0.01) for CLDN-1 and CLDN-5 on mRNA and protein level after four weeks of compression therapy in comparison with prior to treatment for the edema as well as the leg ulcer group. Compression therapy tightens the paracellular barrier via elevated expression of specific TJs and prevents thereby the progression of chronic venous insufficiency due to inhibited permeability of fluid into the perivascular tissue.

Bandages↗
PubMed1993

Structural alterations of airway epithelial tight junctions in cystic fibrosis: comparison of transplant and postmortem tissue.

Previous descriptive freeze-fracture studies have suggested that the airway epithelium in cystic fibrosis (CF) is associated with proliferation and basal extension of tight junctional elements. The significance of these reports in CF has been difficult to evaluate because tight junctions are labile structures, capable of alteration, postmortem. The aim of the present study was to test the hypothesis that the abnormalities in tight junction structure reported previously are unique to CF airways, and to determine the confounding effects of postmortem autolysis. To this end, we analyzed human airway epithelial tight junctions in: (1) histologically normal tissue taken from lungs resected for pulmonary tumor (i.e., resection controls), (2) lungs from patients who died of nonrespiratory causes (i.e., postmortem controls), (3) lungs removed from CF patients undergoing transplantation, and (4) lungs from CF patients postmortem. Tight-junctional depth, strand number, and junctional complexity were analyzed. Basal extensions and isolated foci of tight-junctional elements were found in all groups except for the resection controls. The following two parameters were therefore assessed: (1) the number of times a junction extended below the maximal depth found in the resection controls and (2) the extent of junctional elements that were isolated and distant from the apico-lateral junctional belt. The mean frequencies of occurrence of junctional extension beyond the normal maximum were 4.8% for the CF transplant, 23.6% for the control postmortem, and 48.8% for the CF postmortem group.(ABSTRACT TRUNCATED AT 250 WORDS)

Adult↗
PubMed2006

Zonula occludens-1 function in the assembly of tight junctions in Madin-Darby canine kidney epithelial cells.

Zonula occludens (ZO)-1 was the first tight junction protein to be cloned and has been implicated as an important scaffold protein. It contains multiple domains that bind a diverse set of junction proteins. However, the molecular functions of ZO-1 and related proteins such as ZO-2 and ZO-3 have remained unclear. We now show that gene silencing of ZO-1 causes a delay of approximately 3 h in tight junction formation in Madin-Darby canine kidney (MDCK) epithelial cells, but mature junctions seem functionally normal even in the continuing absence of ZO-1. Depletion of ZO-2, cingulin, or occludin, proteins that can interact with ZO-1, had no discernible effects on tight junctions. Rescue of junction assembly using murine ZO-1 mutants demonstrated that the ZO-1 C terminus is neither necessary nor sufficient for normal assembly. Moreover, mutation of the PDZ1 domain did not block rescue. However, point mutations in the Src homology 3 (SH3) domain almost completely prevented rescue. Surprisingly, the isolated SH3 domain of ZO-1 could also rescue junction assembly. These data reveal an unexpected function for the SH3 domain of ZO-1 in regulating tight junction assembly in epithelial cells and show that cingulin, occludin, or ZO-2 are not limiting for junction assembly in MDCK monolayers.

Animals↗
PubMed1986

The function of tight junctions in maintaining differences in lipid composition between the apical and the basolateral cell surface domains of MDCK cells.

Tight junctions in epithelial cells have been postulated to act as barriers inhibiting lateral diffusion of lipids and proteins between the apical and basolateral plasma membrane domains. To study the fence function of the tight junction in more detail, we have fused liposomes containing the fluorescent phospholipid N-Rh-PE into the apical plasma membrane of MDCK cells. Liposome fusion was induced by low pH and mediated by the influenza virus hemagglutinin, which was expressed on the apical cell surface after viral infection. Redistribution of N-Rh-PE to the basolateral surface, monitored at 0 degree C by fluorescence microscopy, appeared to be dependent on the transbilayer orientation of the fluorescent lipids in the plasma membrane. Asymmetric liposomes containing over 85% of the N-Rh-PE in the external bilayer leaflet, as shown by a phospholipase A2 assay, were generated by octyl beta-D-glucoside dialysis. When these asymmetric liposomes were fused with the apical plasma membrane, fluorescent lipid did not move to the basolateral side. Symmetric liposomes which contained the marker in both leaflets were obtained by freeze-thawing asymmetric liposomes or by reverse-phase evaporation. Upon fusion of these with the apical membrane, redistribution to the basolateral membrane occurred immediately. Redistribution could be observed with asymmetric liposomes only when the tight junctions were opened by incubation in a Ca2+-free medium. During the normal experimental manipulations the tight junctions remained intact since a high trans-epithelial electrical resistance was maintained over the cell monolayer. We conclude that the tight junction acts as a diffusion barrier for the fluorescent phospholipid N-Rh-PE in the exoplasmic leaflet of the plasma membrane but not in the cytoplasmic leaflet.

Animals↗
PubMed1997

Expression of occludin, tight-junction-associated protein, in human digestive tract.

The tight junction seals cells together at a subapical location and functionally separates the plasma membrane into an apical and a basolateral domain. This junction is one of the most characteristic structural markers of the polarized epithelial cell. Recently, occludin has been identified as an integral transmembrane protein localizing at the tight junction and directly associated with ZO-1, an undercoat-constitutive cytoplasmic protein. We have investigated occludin expression in conjunction with ZO-1 in normal epithelia and cancers of human digestive tract by immunostaining with a new antibody raised against human occludin. In the normal simple columnar epithelium, occludin was expressed together with ZO-1 as a single line at the apical cell border. However, in the esophagus, which has a stratified squamous epithelium, no occludin expression could be detected, but ZO-1 was expressed in the spinous layer. As for cancers, both occludin and ZO-1 showed the same expression in differentiated adenocarcinoma cells as in normal epithelium, but in poorly differentiated adenocarcinomas, the expression of these two proteins was reduced. There was significant correlation between tumor differentiation and expression of these proteins. These results suggest that occludin, together with ZO-1, is involved in the formation of gland-like structures. In addition, occludin expression can serve as a histopathological indicator for differentiation in gastrointestinal adenocarcinomas.

Adenocarcinoma↗
PubMed2006

Increased blood-brain barrier permeability and altered tight junctions in experimental diabetes in the rat: contribution of hyperglycaemia and matrix metalloproteinases.

AIMS/HYPOTHESIS: Although diabetes mellitus is associated with peripheral microvascular complications and increased risk of neurological events, the mechanisms by which diabetes disrupts the blood-brain barrier (BBB) are not known. Matrix metalloproteinase (MMP) activity is increased in diabetic patients, is associated with degradation of tight junction proteins, and is a known mediator of BBB compromise. We hypothesise that diabetes leads to compromise of BBB tight junctions via stimulation of MMP activity. MATERIALS AND METHODS: Diabetes was induced in the rat with streptozotocin. At 14 days after injection, BBB function was assessed by in situ brain perfusion. Tight junction proteins were assessed by immunoblot and immunofluorescence. Plasma MMP activity was quantified by fluorometric gelatinase assay and gel zymography. RESULTS: In streptozotocin-treated animals, permeability to [(14)C]sucrose increased concurrently with decreased production of BBB tight junction proteins occludin (also known as OCLN) and zona occludens 1 (ZO-1, also known as tight junction protein 1 or TJP1). Insulin treatment, begun on day 7, normalised blood glucose levels and attenuated BBB hyperpermeability to [(14)C]sucrose. Neither acute hyperglycaemia in naive animals nor acute normalisation of blood glucose in streptozotocin-treated animals altered BBB permeability to [(14)C]sucrose. Plasma MMP activity was increased in streptozotocin-treated animals. CONCLUSIONS/INTERPRETATION: These data indicate that diabetes increases BBB permeability via a loss of tight junction proteins, and that increased BBB permeability in diabetes does not result from hyperglycaemia alone. Increased plasma MMP activity is implicated in degradation of BBB tight junction proteins and increased BBB permeability in diabetes. Peripheral MMP activity may present a novel target for protection of the BBB and prevention of neurological complications in diabetes.

Animals↗
PubMed2003

HIV-1 Tat protein alters tight junction protein expression and distribution in cultured brain endothelial cells.

Disruption of the blood-brain barrier (BBB) is widely believed to be the main route of human immunodeficiency virus (HIV) entry into the central nervous system (CNS). Although mechanisms of this process are not fully understood, alterations of tight junction protein expression can contribute, at least in part, to this phenomenon. Tight junctions are critical structural and functional elements of cerebral microvascular endothelial cells and the BBB. The aim of the present study was to examine the effects of HIV-1 Tat protein on expression of tight junction proteins. Primary cultures of brain microvascular endothelial cells (BMEC) were employed in these experiments. A 24-hr exposure of BMEC to Tat(1-72) resulted in a decrease of claudin-1, claudin-5, and zonula occludens (ZO)-2 expression, whereas total levels of occludin and ZO-1 remained unchanged. In addition, a short (3-hr) exposure of BMEC to Tat(1-72) induced cellular redistribution of claudin-5 immunoreactivity. Tat(1-72)-induced alterations of claudin-5 expression also were confirmed in vivo where Tat(1-72) was injected into the right hippocampus of mice. These findings indicate that HIV-1 Tat protein can markedly affect expression and distribution of specific tight junction proteins in brain endothelium. Alterations of only distinct tight junction proteins suggest a finely tuned effect of Tat(1-72) on the BBB. Because tight junction proteins are critical for the barrier function of the BBB, such alterations can lead to disturbances of the BBB integrity and contribute to HIV trafficking into the brain.

AIDS Dementia Complex↗
PubMed2001

Mutations in the gene encoding tight junction claudin-14 cause autosomal recessive deafness DFNB29.

Tight junctions in the cochlear duct are thought to compartmentalize endolymph and provide structural support for the auditory neuroepithelium. The claudin family of genes is known to express protein components of tight junctions in other tissues. The essential function of one of these claudins in the inner ear was established by identifying mutations in CLDN14 that cause nonsyndromic recessive deafness DFNB29 in two large consanguineous Pakistani families. In situ hybridization and immunofluorescence studies demonstrated mouse claudin-14 expression in the sensory epithelium of the organ of Corti.

Blotting, Northern↗
PubMed2004

Lactobacillus acidophilus protects tight junctions from aspirin damage in HT-29 cells.

BACKGROUND/AIMS: Non-steroidal anti-inflammatory drugs cause enterocyte damage inducing an increase of intestinal permeability. Tight junctions are the key structures in the permeability of the intestinal mucosa. ZO-1 is a tight junction associated protein considered a good marker of their integrity. It has been suggested that probiotics could play a protective role in the intestinal barrier function. We determined, in vitro, whether the heat-killed Lactobacillus acidophilus strain LB (LaLB) with its spent culture supernatant protects tight junctions of HT-29 cells from aspirin (ASA) damage. METHODS: HT-29 cells were treated with ASA alone or ASA and LaLB with its spent culture supernatant together. Morphological alterations of tight junctions were evaluated by immunofluorescence using an anti-ZO-1 antibody. Moreover, a semiquantitative assay for ZO-1 was performed by Western blot. RESULTS: Immunofluorescence analysis showed a fragmented and granulous ZO-1 staining, after ASA treatment. Using both ASA and LaLB with its spent culture supernatant together, we found a fine continuous linear web at cell-cell contacts similarly to control. Western blot revealed that ASA inhibited ZO-1 expression and LaLB with its spent culture supernatant counteracted this effect. CONCLUSIONS: This pilot study shows, for the first time, the protective effect of LaLB with its spent culture supernatant on tight junctions from ASA damage. These results suggest that probiotics could play a role in the prevention of ASA-induced alterations of intestinal permeability.

Adenocarcinoma↗
PubMed2002

Hypertonic saline increases tight junction permeability in airway epithelium.

Asthmatics are known to react to inhaled hyperosmolar solution. Therefore, the effect of hyperosmolar salt solutions on tight junctions of the airway epithelium was investigated by electron microscopy. Rat trachea was perfused with different concentrations of sodium chloride (NaCl) and then fixed from the luminal side with glutaraldehyde to which the electron dense tracer lanthanum chloride had been added. Lanthanum penetrated 3+/-1% of the tight junctions in trachea perfused with 295 mOsm Krebs-Ringer's buffer (KRB). Adding NaCl to the KRB (KRB-NaCl) increased osmolarity of the solution. After perfusion with 589 or 876 mOsm KRB-NaCl, lanthanum was observed in the lateral intercellular spaces in 50+/-11 and 57+/-6%, respectively. The effect of hyperosmolarity was reversible and only 6+/-1% of the tight junctions were penetrated after perfusion with 295 mOsm KRB solution following 589 mOsm KRB-NaCl perfusion. Adding mannitol to the KRB to an osmolarity of 589 mOsm only caused 5+/-1% of the tight junctions to open, even though osmotic effects were observed. Opening the tight junctions with hyperosmolar salt solutions may play a role in exercise-induced asthma. It may also open the prospect for increased penetration of inhaled drugs into the interstitium and the circulation.

Animals↗
PubMed1983

Tight junctions of human keratinocytes in primary culture: a freeze-fracture study.

Human skin explants obtained from 2- to 5-yr-old patients with harelips were cultured in NCTC 168 medium at 37 degrees C, in a humidified atmosphere containing 5% CO2 in air. After a 2-week incubation period, the newly grown cells were studied with special reference to tight junctions by freeze-fracture electron microscopy. Many completely formed tight junctions were observed between the uppermost living cells of migrating epithelium, and fragmented tight junctions were seen between the lower layer cells. The tight junctions in the uppermost cells developed so well that they formed a belt-like network consisting of two to six rows of strands. This observation may suggest that human keratinocytes have the ability to produce tight junctions perfectly enough to serve as a barrier, although no complete tight junctions were formed in situ.

Cells, Cultured↗
PubMed1996

Diffusion of nonelectrolytes in the canine trachea: effect of tight junction.

We recently demonstrated through theoretical modeling that the exhaled ethanol (EtOH) profile from humans is consistent with a molecular diffusion coefficient (cm2/s) in the bronchial mucosa (Dti) that is only 8% of the diffusion coefficient in water (Dw; J. Appl. Physiol. 75: 2439-2449, 1993). Because of the small oil-water partition coefficient (lambda o:w) of EtOH (lambda o:w = 0.074), the reduced diffusion coefficient may be due, in part, to the epithelial tight junction in the paracellular pathway. We hypothesized that opening the tight junction would open an aqueous pathway and increase the diffusion coefficient of small (mol wt < 100) hydrophilic compounds. We mounted the mucosa from the membranous canine trachea in an Ussing-type diffusion cell and measured the diffusion coefficient of 2-ethoxyethanol (2-Ethx; lambda o:w = 0.042), EtOH, and methyl ethyl ketone (MEK; lambda o:w = 1.04) in the presence and absence of the epithelial tight junction. The tight junction was opened using a phosphate-buffered saline free of Ca2+ and Mg2+ with 0.5 mM ethylene glycol-bis (beta-aminoethyl ether)-N,N,N',N'-tetraacetic acid, and its integrity was assessed by measuring the transepithelial electrical resistance. Dti/Dw in the presence of Ca2+ and Mg2+ was 0.39, 0.34, and 0.39 for 2-Ethx, EtOH, and MEK, respectively, and increased 24.6, 11.7, and 1.11% in the absence of Ca2+ and Mg2+. We conclude that the effect of the tight junction on Dti increases with increasing water solubility but can account for only a small portion of the reduced Dti of EtOH as predicted by exhaled profiles.

Animals↗
PubMed2003

Expression and function of tight junction associated molecules in human breast tumor cells is not affected by the Ras-MEK1 pathway.

Constitutive activation of Ras or Ras-mediated signaling pathways is one of the initial steps during tumorigenesis that promotes neoplastic transformation. Recently it was reported that in Ha-Ras overexpressing MDCK cells the tight junction proteins claudin-1, occludin and ZO-1 were absent at cell-cell contact sites but present in the cytoplasm. Inhibition of MEK1 activity recruited all three proteins to the cell membrane leading to a restoration of the tight junction barrier function in MDCK cells. In order to evaluate the relevance of the MEK1 pathway in tight junction regulation in breast cancer cells, we investigated the effect ofMEK1 inhibition on expression of claudin-1, occludin and ZO-1 in natively claudin-1 expressing T47-D cells (low Ras activity), claudin-1 negative MCF-7 cells (elevated Ras activity) as well as two retroviral claudin-1 transduced MCF-7 daughter cell lines with prominent membrane and cytoplasmic claudin-1 dominant homing, respectively. Although we effectively blocked phosphorylation of MAPKs ERK-1 and ERK-2 using the selective MEK1 inhibitor PD98059, no quantitative changes of mRNA or protein levels of claudin-1, occludin and ZO-1 could be detected in all cell lines investigated. Furthermore, immnfluorescence analysis of claudin-1 revealed that inhibition of the MAPK pathway did not alter th e subcellular cytoplasmic distribution of claudin-1 to be more membrane specific. Finally, the diffusion barrier properties of tight junctions as analyzed by transepithelial resistance (TER) or paracellular flux analysis of 3 and 40 kDa dextran of tight junctions were not altered in the claudin-1 positive T47-D and the MCF-7 cell lines. Our findings indicate that the proposed involvement of the Ras-MEK-ERK pathway is likely not involved in the dysregulated tight junction formation in breast tumor cells and indicates that elevated activity of Ras might not be of general importance for the disruption of tight junction structures in breast tumors.

Breast Neoplasms↗