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PubMed2000

The tight junction of pancreatic exocrine cells is a morphometrically dynamic structure altered by intraductal hypertension.

The tight junction of pancreatic exocrine cells is thought to regulate paracellular permeability, and is a possible reflux route of pancreatic juice into the blood flow. Morphological changes in the tight junction of canine pancreatic acinar cells following intraductal hypertension and secretin stimulation were morphometrically analyzed to obtain evidence of the control of the paracellular reflux. Pancreatic tissues obtained from 25 dogs after intraductal hypertension, 3 dogs after secretin stimulation, and 5 control dogs were studied. Intraductal pressure was either 20 cmH2O, 30 cmH2O, or 40 cmH2O. Freeze fracture replicas of these pancreatic tissues were observed by electron microscopy. Tight junctions were classified into six morphometric types. Reticular type, parallel type, and mixed type comprised the common types predominantly found in all groups, and three special types were found, infrequently, only after intraductal hypertension. The percentages of the common types were significantly different between the groups. The areas of the tight junctions, and other morphometric parameters, were significantly less after 20 cmH2O intraductal hypertension and secretin stimulation than in the controls. However, these findings after 30 cmH2O or 40 cmH2O intraductal hypertension did not differ from those in the controls. The areas of the three special types of tight junctions were larger than those of the common types. These results suggest that the tight junction of pancreatic exocrine cells is a morphologically dynamic structure that is altered by the extent of intraductal hypertension, and support the hypothesis that paracellular permeability is the mechanism of the reflux of pancreatic juice.

Animals↗
PubMed2004

The specific fates of tight junction proteins in apoptotic epithelial cells.

The polarized morphology of epithelial cells depends on the establishment and maintenance of characteristic intercellular junctions. The dramatic morphological changes observed in apoptotic epithelial cells were ascribed at least in part to the specific fragmentation of components of adherens junctions and desmosomes. Little, however, is known about tight junctions during apoptosis. We have found that after induction of apoptosis in epithelial cells, tight junction proteins undergo proteolytic cleavage in a distinctive manner correlated with a disruption of tight junctions. The transmembrane protein occludin and, likewise, the cytoplasmic adaptor proteins ZO-1 and ZO-2 are fragmented by caspase cleavage. In addition, occludin is cleaved at an extracellular site by a metalloproteinase. The caspase cleavage site in occludin was mapped C-terminally to Asp(320) within the C-terminal cytoplasmic domain. Mutagenesis of this site efficiently blocked fragmentation. In the presence of caspase and/or metalloproteinase inhibitors, fragmentation of occludin, ZO-1 and ZO-2 was blocked and cellular morphology was almost fully preserved. Interestingly, two members of the claudin family of transmembrane tight junction proteins exhibited a different behavior. While the amount of claudin-2 protein was reduced similarly to occludin, ZO-1 and ZO-2, claudin-1 was either fully preserved or was even increased in apoptotic cells.

Animals↗
PubMed2003

Polyunsaturated fatty acids induce tight junctions to form in brain capillary endothelial cells.

Tight junctions create a rate-limiting barrier to the diffusion of solutes between vertebrate epithelial cells and endothelial cells. They are also controlled within individual cells by a variety of physiologically relevant signals. We investigated the effects of polyunsaturated fatty acids on the formation of tight junctions in brain capillary endothelial cells, monitoring the transepithelial electrical resistance, and analyzed the expression of occludin messenger RNA. Brain-capillary endothelial cells were grown to confluence on filters and exposed to eicosapentaenoic acids, gamma linolenic acid and linoleic acid. Transepithelial electrical resistance was determined with voltage-measuring electrodes. The messenger RNA expression of occludin was quantitated by real-time quantitative reverse transcriptase-polymerase chain reaction. The basal resistance across monolayers of porcine brain capillary endothelial cells was 83+/-8.1 Omega cm(2). Cells cultured in eicosapentaenoic acids and gamma linolenic acid, but not linolenic acid, displayed a 2.7-fold increase in transepithelial electrical resistance at 10 microM in brain capillary endothelial cells. The expression level of occludin messenger RNA increased markedly immediately after the exposure to eicosapentaenoic acids or gamma linolenic acid. Following an 8 h exposure to exogenous eicosapentaenoic acids or gamma linolenic acid, occludin messenger RNA levels were significantly increased. In addition, the rise in transepithelial electrical resistance induced by eicosapentaenoic acids and gamma linolenic acid was markedly inhibited by the tyrosine kinase inhibitors genistein and PP2 and protein kinase C inhibitor, calphostin C. In contrast, the rise in transepithelial electrical resistance induced by eicosapentaenoic acids and gamma linolenic acid was not inhibited by the PI 3-kinase inhibitor, LY294002. We conclude that eicosapentaenoic acids and gamma linolenic acid increased the transepithelial electrical resistance and the expression of occludin messenger RNA in brain capillary endothelial cells. This gamma linolenic acid and eicosapentaenoic acid induced assembly of tight junction is likely to be regulated by protein kinase C and tyrosine kinase activity.

Animals↗
PubMedDate not supplied

Tight junctions of jejunal surface and crypt cells in celiac disease: a freeze-fracture study.

We studied mucosal biopsies of five children with celiac disease and five controls of similar age by freeze-fracture electron microscopy. Morphometric parameters of membrane structure (such as apical tight junctions, triple tight junctions, intramembrane particles) and of the brush border were obtained from a large number of micrographs. The quantitative comparison of celiac patients and control subjects showed similar values for the depth of tight junctions at the level of the crypts. At the surface level, the tight junctions of celiac patients showed reduced depth as well as a reduced number of strands. The number of intramembrane particles of microvillus membranes increases in control subjects and in celiac patients as the cells migrate from the crypts to the mucosal surface. The specimens from celiac disease patients possessed a reduced density of intramembrane particles. Differences in brush border morphology between celiac patients and control subjects were similar to earlier findings.

Celiac Disease↗
PubMed1994

A comparison between the epithelial tight junction morphology of human extrapulmonary bronchi and rat trachea.

Animal models have been used to investigate the involvement of epithelial tight junctions in the pathogenesis of human airway disease. However, no previous study has compared the tight junction morphologies of human and animal species in order to relate findings in animal models to human disease. In the present study, we therefore undertook a comprehensive quantitative evaluation of tight junction morphology, to determine what similarities or differences may exist in rat and human airways. Human tissue was obtained from grossly and histologically normal extrapulmonary bronchi from lungs resected for pulmonary tumour (n = 8); rat tracheal epithelium was acquired from Sprague-Dawley specific pathogen-free animals (n = 12). The tight junction morphologies of the two species were compared with respect to junctional depth, number of strands and junctional complexity. The basic architectural arrangement of the tight junctions in both species was found to be similar; however, tight junctions in rat tissues were less deep, comprised fewer strands, and had fewer strand interconnections compared with those in the human samples. The number of strands per interconnection was similar in the two species. We conclude that, in spite of a general similarity of rat and human airway epithelial tight junctions, there are specific quantitative details of morphology which need to be considered when attempting to extrapolate to the human the results of studies of airway epithelial permeability conducted in the rat. The precise biological significance of these differences, as yet, remains unclear.

Animals↗
PubMed1983

Structural integrity of hepatocyte tight junctions.

The significance of discontinuities frequently found in freeze-fracture replicas of the tight junction was evaluated using complementary replicas of hepatocyte junctions from control and bile duct-ligated rats. An extensive analysis of complementary replicas using rotary platinum shadowing indicates that discontinuities in the protoplasmic (P) fracture face do not represent structural breaks in the tight-junctional network. In no case did P-face discontinuities correspond with interruptions in the groove network on the complementary extracellular (E) face. Quantitative analysis of replicas shows that P-face discontinuities result in part from "transfer" of material to the complementary E face (approximately 7% of the junctional length). However, many P-face discontinuities (7-30% of the junctional length) are matched only by a groove on the complementary E face. This finding demonstrates that a significant amount of material can be lost during freeze-fracture. An analysis of junctions from bile duct-ligated rats, which are known to have an increased paracellular permeability, shows comparable transfer and loss of material. However, the number of junctional elements and the tight-junction network density was significantly reduced by bile duct ligation. These observations indicate that discontinuities in tight-junctional elements result during the preparation of freeze-fracture replicas and are not physiologically important features of the junctional barrier. Variation in the number of elements provides the best explanation for observed differences in tight-junction permeability.

Animals↗
PubMed1996

Catenins and zonula occludens-1 form a complex during early stages in the assembly of tight junctions.

We characterized the role of the E-cadherin adhesion system in the formation of epithelial tight junctions using the calcium switch model. In MDCK cells cultured in low (micromolar) calcium levels, the tight junctional protein Zonula Occludens-1 (ZO-1) is distributed intracellularly in granular clusters, the larger of which codistribute with E-cadherin. Two hours after activation of E-cadherin adhesion by transfer to normal (1.8 mM) calcium levels, ZO-1 dramatically redistributed to the cell surface, where it localized in regions rich in E-cadherin. Immunoprecipitation with ZO-1 antibodies of extracts from cells kept in low calcium and 2 h after shifting to 1.8 mM Ca2+ demonstrated the association of ZO-1 with alpha-, beta-, and gamma-catenins. E-cadherin was not detected in the ZO-1 immunoprecipitates but it was found in beta-catenin immunoprecipitates that excluded ZO-1, suggesting that the binding of ZO-1 to catenins may weaken the interaction of these proteins with E-cadherin. Immunofluorescence and immunoelectron microscopy confirmed a close association of beta-catenin and ZO-1 at 0 and 2 h after Ca2+ switch. 48 h after Ca2+ switch, upon complete polarization of the epithelium, most of the ZO-1 had segregated from lateral E-cadherin and formed a distinct, separate apical ring. The ZO-1-catenin complex was not detected in fully polarized monolayers. MDCK cells permanently transformed with Moloney sarcoma virus, which expresses low levels of E-cadherin, displayed clusters of cytoplasmic ZO-1 granules and very little of this protein at the cell surface. Upon transfection with E-cadherin into Moloney sarcoma virus-MDCK cells, ZO-1 redistributed to E-cadherin-rich lateral plasma membrane but later failed to segregate into mature tight junctions. Our experiments suggest that catenins participate in the mobilization of ZO-1 from the cytosol to the cell surface early in the development of tight junctions and that neoplastic transformation may block the formation of tight junctions, either by decreasing the levels of E-cadherin or by preventing a late event: the segregation of tight junction from the zonula adherens.

Animals↗
PubMed2004

[Tight junctions, a platform regulating cell proliferation and polarity].

Tight junctions (TJ) are specialized plasma membrane microdomains that encircle the apical pole of each epithelial and endothelial cell, separating apical from basolateral side. They form an intercellular diffusion barrier (or gate) regulating the passage of ions, water, and various macromolecules through the paracellular spaces, and a fence restricting the apical/basolateral diffusion of membrane proteins and lipids. This latter function is deeply involved in cancer cell biology, in terms of loss of cell polarity. Several TJ proteins are involved in organizing signal transduction at TJ. For example, the interaction of TJ protein ZO-1 (zonula occludens 1) with the transcription factor ZONAB (ZO-1 associated nucleic acid protein) is important in the regulation of expression of the proto-oncogene Erb-2 as well as epithelial proliferation/differentiation. Recent studies indicate that different proteins involved in membrane trafficking are associated with tight junctions. Among these proteins are the small G-proteins of the Rab family that regulate specific membrane transport events in both endocytic and exocytic pathways. Rab proteins may coordinate the recruitment of protein complexes necessary for the establishment-maintenance of cell polarity. Based on the studies reviewed here, tight junctions emerge as a platform used to coordinate and regulate cell polarity, and proliferation/differentiation.

Animals↗
PubMed1992

Influence of tight junctions on the interaction of salts with lingual epithelia: responses of chorda tympani and lingual nerves.

The role of tight junctions in modulating responses from chorda tympani (taste) and lingual (general sensory) nerves are clarified in regard to their responses to salts. Chorda tympani (CT) responses elicited by organic sodium salts require greater Na+ concentrations to elicit the same magnitude of response as NaCl. These data can be understood in terms of the organic anions (compared with Cl-) producing larger liquid-junction potentials across tight junctions between taste cells which, in turn, reduces Na+ influx into taste cells via amiloride-inhibitable channels. The anion contribution to the CT response to different Na+ salts can be eliminated (or enhanced) by voltage clamping the tongue with negative (with respect to the serosal solution) potentials. Whole nerve recordings from the lingual branch of the trigeminal nerve elicited by NaCl (and other salts) were reversibly inhibited by the tight junction blocker, LaCl3. These data suggest that small hydrophilic molecules elicit responses from trigeminal fibers by diffusing across tight junctions between epithelial cells and altering the composition of the extracellular space.

Amiloride↗
PubMed1987

Islet cells-tight junctions: changes in its number induced by glucose.

Cell-tight junctions were counted in rat isolated islets incubated for different periods of time in the presence of different extracellular glucose concentrations. The number of tight junctions increased as a function of the length of the incubation period and the concentration of glucose. These results would suggest the involvement of tight junctions in the regulatory process of glucose-induced insulin secretion. Key words: Tight junctions, islet cell ultrastructure, isolated islets, islet incubation, glucose-induced insulin secretion, islet cell secretory function.

Animals↗
PubMed2001

Junctional adhesion molecule (JAM) binds to PAR-3: a possible mechanism for the recruitment of PAR-3 to tight junctions.

At tight junctions (TJs), claudins with four transmembrane domains are incorporated into TJ strands. Junctional adhesion molecule (JAM), which belongs to the immunoglobulin superfamily, is also localized at TJs, but it remains unclear how JAM is integrated into TJs. Immunoreplica electron microscopy revealed that JAM showed an intimate spatial relationship with TJ strands in epithelial cells. In L fibroblasts expressing exogenous JAM, JAM was concentrated at cell-cell adhesion sites, where there were no strand-like structures, but rather characteristic membrane domains free of intramembranous particles were detected. These domains were specifically labeled with anti-JAM polyclonal antibody, suggesting that JAM forms planar aggregates through their lateral self-association. Immunofluorescence microscopy and in vitro binding assays revealed that ZO-1 directly binds to the COOH termini of claudins and JAM at its PDZ1 and PDZ3 domains, respectively. Furthermore, another PDZ-containing polarity-related protein, PAR-3, was directly bound to the COOH terminus of JAM, but not to that of claudins. These findings led to a molecular architectural model for TJs: small aggregates of JAM are tethered to claudin-based strands through ZO-1, and these JAM aggregates recruit PAR-3 to TJs. We also discuss the importance of this model from the perspective of the general molecular mechanisms behind the recruitment of PAR proteins to plasma membranes.

Animals↗
PubMed1997

Serum inhibits tight junction formation in cultured pigment epithelial cells.

PURPOSE: These experiments were designed to characterize tight junction formation by retinal pigment epithelial (RPE) cells in vitro and to compare the effects on this process of hormonally defined medium (HDM) and serum-containing medium. METHODS: Formation of RPE tight junctions was analyzed in freshly isolated rat RPE cells maintained either in HDM or serum-containing medium. Junctions were evaluated functionally by measuring transepithelial electrical resistance (TER) and permeability and structurally by immunolocalization of the junction-associated actin microfilaments. Calcium dependency of the junctions was determined by reducing media calcium concentration. RESULTS: RPE cells cultured in serum-free HDM developed calcium-dependent tight junctions, which exhibited TER levels > 150 omega cm2 and low paracellular permeability. Serum-containing media inhibited tight junction formation as indicated by significant reductions in TER and increases in permeability. Junction-associated actin microfilaments and cell density were unchanged. CONCLUSIONS: Tight junction formation by RPE cells is inhibited by serum. This activity may play an important role in responses of the RPE layer to injury, contributing to the pathologic progression of blood-retinal barrier dysfunction.

Animals↗
PubMed2006

Differences in expression of junctional adhesion molecule-A and beta-catenin in multiple sclerosis brain tissue: increasing evidence for the role of tight junction pathology.

Previously we have employed antibodies to the tight junction (TJ)-associated proteins ZO-1 and occludin to describe endothelial tight junction abnormalities, in lesional and normal appearing white matter, in primary and secondary progressive multiple sclerosis (MS). This work is extended here by use of antibodies to the independent TJ-specific proteins and junctional adhesion molecule A & B (JAM-A, JAM-B). We have also assessed the expression in MS of beta-catenin, a protein specific to the TJ-associated adherens junction. Immunocytochemistry and semiquantitative confocal microscopy for JAM-A and beta-catenin was performed on snap-frozen sections from MS cases (n=11) and controls (n=6). Data on 1,443 blood vessels was acquired from active lesions (n=13), inactive lesions (n=13), NAWM (n=20) and control white matter (n=13). In MS abnormal JAM-A expression was found in active (46%) and inactive lesions (21%), comparable to previous data using ZO-1. However, a lower level of TJ abnormality was found in MS NAWM using JAM-A (3%) compared to ZO-1 (13%). JAM-B was strongly expressed on a small number of large blood vessels in control and MS tissues but at too low a level for quantitative analysis. By comparison with the high levels of abnormality observed with the TJ proteins, the adherens junction protein beta-catenin was normally expressed in all MS and control tissue categories. These results confirm, by use of the independent marker JAM-A, that TJ abnormalities are most frequent in active white matter lesions. Altered expression of JAM-A, in addition to affecting junctional tightness may also both reflect and affect leukocyte trafficking, with implications for immune status within the diseased CNS. Conversely, the adherens junction component of the TJ, as indicated by beta-catenin expression is normally expressed in all MS and control tissue categories.

Brain↗
PubMed2002

The carboxyl terminus of zona occludens-3 binds and recruits a mammalian homologue of discs lost to tight junctions.

Mammalian homologues of the Drosophila polarity proteins Stardust, Discs Lost, and Crumbs have been identified as Pals1, Pals1-associated tight junction protein (PATJ), and human Crumbs homologue 1 (CRB1), respectively. We have previously demonstrated that PATJ, Pals1, and CRB1 can form a tripartite tight junction complex in epithelial cells and that PATJ recruits Pals1 to tight junctions. Here, we observed that the Pals1/PATJ interaction was not crucial for the ultimate targeting of PATJ itself to tight junctions. This prompted us to examine if any of the 10 post-synaptic density-95/Discs Large/zona occludens-1 (PDZ) domains of PATJ could bind to the carboxyl termini of known tight junction constituents. We found that the 6th and 8th PDZ domains of PATJ can interact with the carboxyl termini of zona occludens-3 (ZO-3) and claudin 1, respectively. PATJ missing the 6th PDZ domain was found to mislocalize away from cell contacts. Surprisingly, deleting the 8th PDZ domain had little effect on PATJ localization. Finally, reciprocal co-immunoprecipitation experiments revealed that full-length ZO-3 can associate with PATJ. Hence, the PATJ/ZO-3 interaction is likely important for recruiting PATJ and its associated proteins to tight junctions.

Amino Acid Sequence↗
PubMed1998

Epithelial tight junction structure in the jejunum of children with acute and treated celiac sprue.

Tight junction morphology was analyzed in freeze fracture electron micrographs from biopsies at two locations along the surface-crypt axis in the jejunum of children with treated and untreated sprue and in control subjects. In control jejunum, strand number, meshwork depth, and total depth of the tight junction decreased from surface to crypt, consistent with the concept of the crypt being more permeable than the surface epithelium. In acute sprue, strand number was reduced in all regions along the surface-crypt axis, from 5.5+/-0.2 to 3.4+/-0.3 (surface) and from 4.7+/-0.2 to 3.6+/-0.1 (crypt). Meshwork depth was also reduced at all regions along the surface-crypt axis. Strand discontinuities were more frequent in acute sprue. Aberrant strands appeared below the main meshwork of crypt tight junctions in acute sprue. In asymptomatic children treated with the gluten-free diet, jejunal tight junctional structure only partially recovered. Strand number was restored to normal at the surface, but was still decreased in the crypts, from 4.7+/-0.2 to 3.9+/-0.3. We conclude that the epithelial barrier function of the small intestine is seriously disturbed by structural modifications of the tight junction in acute symptomatic celiac disease, thereby accounting for increased ionic permeability noted in a parallel study on identical specimens. This epithelial barrier defect may contribute to diarrhea in celiac disease by a "leak flux mechanism." In children with sprue treated with a gluten-free diet, barrier dysfunction was only partly recovered, suggesting a level of "minimal damage."

Celiac Disease↗
PubMed1982

Structure and permeability of goblet cell tight junctions in rat small intestine.

Two major cell types, goblet and absorptive cells, dominate the epithelial lining of small intestinal villi. We used freeze-fracture replicas of rat ileal mucosa to examine the possibility that tight junction structure, known to relate to transepithelial resistance, might vary with cell type. Tight junctions between absorptive cells were uniform in structure while those associated with villus goblet cells displayed structural variability. In 23% of villus goblet cell tight junctions the strand count was less than 4 and in 30% the depth was less than 200 nm. In contrast, only 4% of absorptive cell tight junctions had less than 4 strands and only 9% had depth measurements less than 200 nm. Other structural features commonly associated with villus goblet cell tight junctions but less commonly with absorptive cell tight junctions were: deficient strand cross-linking, free-ending abluminal strands, and highly fragmented strands. Both in vivo ileal segments and everted loops were exposed to ionic lanthanum. Dense lanthanum precipitates in tight junctions and paracellular spaces were restricted to a subpopulation of villus goblet cells and were not found between villus absorptive cells. After exposure of prefixed ileal loops to lanthanum for 1 hour, faint precipitates of lanthanum were found in 14% of tight junctions and paracellular spaces between absorptive cells compared to 42% of tight junctions and paracellular spaces adjacent to villus goblet cells. When tested in Ussing chambers, the methods used for lanthanum exposure did not lower transepithelial resistance. Everted loops exposed to ionic barium and examined by light microscopy showed dense barium precipitates in the junctional zone and region of the paracellular space of villus goblet cells but not in these regions between absorptive cells. However, the macromolecular tracers, microperoxidase, cytochrome c and horseradish peroxidase, were excluded from both villus goblet cell and absorptive cell paracellular spaces in in vivo segments. These findings suggest that a subpopulation of villus goblet cells may serve as focal sites of high ionic permeability and contribute to the relatively low resistance to ionic flow which characterizes the small intestinal epithelium.

Animals↗
PubMed1982

Formation of tight junctions in differentiating and secretory ameloblasts of rat molar tooth germs.

Forty newborn rats were perfused with Karnovsky fixative and the tight junctions in differentiating and secretory ameloblasts were examined by conventional electron microscopy and freeze-fracture replications. Pre-ameloblasts were divided into types I, II and III based on morphology. Initial indications of tight-junction formation appeared as linear aggregations of particles in type II. The apparent tight junctional strands were observed in type III and in secretory ameloblasts. Though the junctional strands were numerous and long, no complete barrier between pre-ameloblasts at their distal ends was present. Complete zonular tight junctions were first observed at the distal ends of secretory ameloblasts; at this stage, proximal tight junctions incompletely sealed the paracellular spaces around the ameloblasts. Throughout their formative processes, the tight junctional strands were engaged in forming gap junctions. The structural features of tight junctions were considered to be closely associated with the cytodifferentiation of ameloblasts and permeability in the ameloblast layer.

Ameloblasts↗
PubMed2003

Regulation of tight junction permeability with switch-like speed.

PURPOSE OF REVIEW: The case is made that tight junctions can undergo large reversible conductance changes in a matter of seconds and yet preserve their permselectivity. The diuretic peptide leucokinin transforms (renal) Malpighian tubules of the yellow fever mosquito from a moderately tight epithelium to a leaky epithelium by increasing the chloride-conductance of the paracellular shunt pathway. The nine-fold increase in the paracellular chloride-conductance brings about a non-selective stimulation of transepithelial sodium chloride and potassium chloride secretion, as expected from a conductance increase in the pathway taken by the counterion of sodium and potassium. RECENT FINDINGS: The leucokinin signaling pathway consists in part of a receptor coupled G-protein, phospholipase C, inositol-1,4,5-trisphosphate, and increased intracellular calcium concentration that bring about the increase in the paracellular, tight junction chloride-conductance. As the conductance of the tight junction pathway increases it becomes more selective for the transepithelial passage of chloride. SUMMARY: Epithelial cells in Malpighian tubules taper to tight junctions at their lateral edges exposing them directly to apical and serosal solutions. Furthermore, evolutionary pressures to excrete salt and water at high rates without the aid of glomerular filtration have led to powerful mechanisms of tubular secretion, capable of diuresis when the mosquito is challenged with the volume expansion of a blood meal. The tubular diuresis is mediated in part by increasing the paracellular chloride conductance. Thus, anatomical and physiological specializations in Malpighian tubules combine to yield the evidence for the dynamic hormonal regulation of the tight junction pathway.

Animals↗