Query: Tight junction

title: Tight junction proteins at the blood brain barrier: far more than claudin 5
abstract: At the blood brain barrier (BBB) claudin (Cldn) 5 is thought to be the dominant tight junction (TJ) protein, with minor contributions from Cldn3 and 12, and occludin. However, the BBB appears ultrastructurally normal in Cldn5 knock out mice, suggesting that further Cldns and/or TJ associated marvel proteins (TAMPs) are involved. Microdissected human and murine brain capillaries, quickly frozen to recapitulate the in vivo situation, showed high transcript expression of Cldn5, 11, 12, and 25, and occludin, but also abundant levels of Cldn1 and 27 in man. Protein levels were quantified by a novel epitope dilution assay and confirmed the respective mRNA data. In contrast to the in vivo situation, Cldn5 dominates BBB expression in vitro, since all other TJ proteins are at comparably low levels or are not expressed. Cldn11 was highly abundant in vivo and contributed to paracellular tightness by homophilic oligomerization, but almost disappeared in vitro. Cldn25, also found at high levels, neither tightened the paracellular barrier nor interconnected opposing cells, but contributed to proper TJ strand morphology. Pathological conditions (in vivo ischemia and in vitro hypoxia) down regulated Cldn1, 3, and 12, and occludin in cerebral capillaries, which was paralleled by up regulation of Cldn5 after middle cerebral artery occlusion in rats. Cldn1 expression increased after Cldn5 knock down. In conclusion, this complete Cldn/TAMP profile demonstrates the presence of up to a dozen TJ proteins in brain capillaries. Mouse and human share a similar and complex TJ profile in vivo, but this complexity is widely lost under in vitro conditions.

title: The Integral Role of Tight Junction Proteins in the Repair of Injured Intestinal Epithelium
abstract: The intestinal epithelial monolayer forms a transcellular and paracellular barrier that separates luminal contents from the interstitium. The paracellular barrier consists of a highly organized complex of intercellular junctions that is primarily regulated by apical tight junction proteins and tight junction associated proteins. This homeostatic barrier can be lost through a multitude of injurious events that cause the disruption of the tight junction complex. Acute repair after injury leading to the reestablishment of the tight junction barrier is crucial for the return of both barrier function as well as other cellular functions, including water regulation and nutrient absorption. This review provides an overview of the tight junction complex components and how they link to other plasmalemmal proteins, such as ion channels and transporters, to induce tight junction closure during repair of acute injury. Understanding the components of interepithelial tight junctions and the mechanisms of tight junction regulation after injury is crucial for developing future therapeutic targets for patients experiencing dysregulated intestinal permeability.

title: Tight Junction Proteins and Signaling Pathways in Cancer and Inflammation: A Functional Crosstalk
abstract: The ability of epithelial cells to organize through cell cell adhesion into a functioning epithelium serves the purpose of a tight epithelial protective barrier. Contacts between adjacent cells are made up of tight junctions (TJ) adherens junctions (AJ) and desmosomes with unique cellular functions and a complex molecular composition. These proteins mediate firm mechanical stability, serves as a gatekeeper for the paracellular pathway, and helps in preserving tissue homeostasis. TJ proteins are involved in maintaining cell polarity, in establishing organ specific apical domains and also in recruiting signaling proteins involved in the regulation of various important cellular functions including proliferation, differentiation, and migration. As a vital component of the epithelial barrier, TJs are under a constant threat from proinflammatory mediators, pathogenic viruses and bacteria, aiding inflammation and the development of disease. Inflammatory bowel disease (IBD) patients reveal loss of TJ barrier function, increased levels of proinflammatory cytokines, and immune dysregulation; yet, the relationship between these events is partly understood. Although TJ barrier defects are inadequate to cause experimental IBD, mucosal immune activation is changed in response to augmented epithelial permeability. Thus, the current studies suggest that altered barrier function may predispose or increase disease progression and therapies targeted to specifically restore the barrier function may provide a substitute or supplement to immunologic based therapies. This review provides a brief introduction about the TJs, AJs, structure and function of TJ proteins. The link between TJ proteins and key signaling pathways in cell proliferation, transformation, and metastasis is discussed thoroughly. We also discuss the compromised intestinal TJ integrity under inflammatory conditions, and the signaling mechanisms involved that bridge inflammation and cancer.

title: Antibiotics induced intestinal tight junction barrier dysfunction is associated with microbiota dysbiosis, activated NLRP3 inflammasome and autophagy
abstract: Tight junction barrier is critical to intestinal homeostasis. Applying antibiotics to treat infections is common in clinical practice, which may affect intestinal microbiota. Intestinal microbiota dysbiosis is involved in the occurrence of some gastrointestinal diseases. Therefore, this study was aimed to investigate the influence of antibiotics on intestinal tight junction barrier and the possible underlying mechanisms. Healthy adult female C57BL/6 mice were treated with a broad spectrum antibiotic cocktail for 14 days. 16S rDNA Illumina sequencing and headspace gas chromatography mass spectrometry (HS GC/MS) were respectively used to analyze microbial community and to detect short chain fatty acids (SCFAs) contents. In vivo intestinal paracellular permeability to fluorescein isothiocyanate dextran (FITC dextran) was measured. Protein expression was determined by immunoblotting. Immunofluoresence was applied to observe the distributions of ZO 1, LC3B and ASC. Antibiotics remarkably altered intestinal microbiota composition in healthy mice, accompanying reduced SCFAs' concentrations. In addition, the intestinal tight junction barrier was disrupted by antibiotic treatment, as evidenced by increased intestinal paracellular permeability to FITC dextran, decreased tight junction protein expressions, and disrupted ZO 1 morphology. Furthermore, NLRP3 inflammasome and autophagy were activated by antibiotic treatment. In conclusion, intestinal epithelial tight junction barrier dysfunction induced by antibiotics is associated with intestinal microbiota dysbiosis, activated NLRP3 inflammasome and autophagy in mice.

title: Selective loss of cortical endothelial tight junction proteins during Alzheimer's disease progression
abstract: While the accumulation and aggregation of amyloid b and tau are central events in the pathogenesis of Alzheimer's disease, there is increasing evidence that cerebrovascular pathology is also abundant in Alzheimer's disease brains. In brain capillaries, endothelial cells are connected closely with one another through transmembrane tight junction proteins forming the blood brain barrier. Because the blood brain barrier tightly regulates the exchange of molecules between brain and blood and maintains brain homeostasis, its impairment is increasingly recognized as a critical factor contributing to Alzheimer's disease pathogenesis. However, the pathological relationship between blood brain barrier properties and Alzheimer's disease progression in the human brain is not fully understood. In this study, we show that the loss of cortical tight junction proteins is a common event in Alzheimer's disease, and is correlated with synaptic degeneration. By quantifying the amounts of major tight junction proteins, claudin 5 and occludin, in 12 brain regions dissected from post mortem brains of normal ageing (n 10) pathological ageing (n 14) and Alzheimer's disease patients (n 19) we found that they were selectively decreased in cortical areas in Alzheimer's disease. Cortical tight junction proteins were decreased in association with the Braak neurofibrillary tangle stage. There was also a negative correlation between the amount of tight junction proteins and the amounts of insoluble Alzheimer's disease related proteins, in particular amyloid b40, in cortical areas. In addition, the amount of tight junction proteins in these areas correlated positively with those of synaptic markers. Thus, loss of cortical tight junction proteins in Alzheimer's disease is associated with insoluble amyloid b40 and loss of synaptic markers. Importantly, the positive correlation between claudin 5 and synaptic markers, in particular synaptophysin, was present independent of insoluble amyloid b40, amyloid b42 and tau values, suggesting that loss of cortical tight junction proteins and synaptic degeneration is present, at least in part, independent of insoluble Alzheimer's disease related proteins. Collectively, these results indicate that loss of tight junction proteins occurs predominantly in the neocortex during Alzheimer's disease progression. Further, our findings provide a neuropathological clue as to how endothelial tight junction pathology may contribute to Alzheimer's disease pathogenesis in both synergistic and additive manners to typical amyloid b and tau pathologies.

title: Claudins and JAM A coordinately regulate tight junction formation and epithelial polarity
abstract: Tight junctions (TJs) are a key component of barriers formed by polarized epithelial cells. Otani et al. found that the scaffolding proteins ZO 1/ZO 2 are essential for TJ formation and epithelial polarity. Claudins regulate the TJ strand and electrolyte permeability barrier, while JAM A regulates membrane apposition and the macromolecule permeability barrier. Claudins and JAM A act redundantly in regulating epithelial polarity.

title: Claudin 12 is not required for blood brain barrier tight junction function
abstract: The blood brain barrier (BBB) ensures central nervous system (CNS) homeostasis by strictly controlling the passage of molecules and solutes from the bloodstream into the CNS. Complex and continuous tight junctions (TJs) between brain endothelial cells block uncontrolled paracellular diffusion of molecules across the BBB, with claudin 5 being its dominant TJs protein. However, claudin 5 deficient mice still display ultrastructurally normal TJs, suggesting the contribution of other claudins or tight junction associated proteins in establishing BBB junctional complexes. Expression of claudin 12 at the BBB has been reported, however the exact function and subcellular localization of this atypical claudin remains unknown. We created claudin 12 lacZ knock in C57BL/6J mice to explore expression of claudin 12 and its role in establishing BBB TJs function during health and neuroinflammation. We furthermore performed a broad standardized phenotypic check up of the mouse mutant. Making use of the lacZ reporter allele, we found claudin 12 to be broadly expressed in numerous organs. In the CNS, expression of claudin 12 was detected in many cell types with very low expression in brain endothelium. Claudin 12lacZ/lacZ C57BL/6J mice lacking claudin 12 expression displayed an intact BBB and did not show any signs of BBB dysfunction or aggravated neuroinflammation in an animal model for multiple sclerosis. Determining the precise localization of claudin 12 at the BBB was prohibited by the fact that available anti claudin 12 antibodies showed comparable detection and staining patterns in tissues from wild type and claudin 12lacZ/lacZ C57BL/6J mice. Our present study thus shows that claudin 12 is not essential in establishing or maintaining BBB TJs integrity. Claudin 12 is rather expressed in cells that typically lack TJs suggesting that claudin 12 plays a role other than forming classical TJs. At the same time, in depth phenotypic screening of clinically relevant organ functions of claudin 12lacZ/lacZ C57BL/6J mice suggested the involvement of claudin 12 in some neurological but, more prominently, in cardiovascular functions.

title: Vitamin A inhibits the action of LPS on the intestinal epithelial barrier function and tight junction proteins.
abstract: Inflammation caused by either intrinsic or extrinsic toxins results in intestinal barrier dysfunction, contributing to inflammatory bowel disease (IBD) and other diseases. Vitamin A is a widely used food supplement although its mechanistic effect on intestinal structures is largely unknown. The goal of this study was to explore the mechanism by investigating the influence of vitamin A on the intestinal barrier function, represented by tight junctions. IPEC J2 cells were differentiated on transwell inserts and used as a model of intestinal barrier permeability. Transepithelial electrical resistance (TEER) was used as an indicator of monolayer integrity and paracellular permeability. Western blot and the reverse transcriptase polymerase chain reaction were used to assess the protein and mRNA expression of tight junction proteins. Immunofluorescence microscopy was used to evaluate the localization and expression of tight junctions. Differentiated cells were treated with a vehicle control (Ctrl) inflammatory stimulus (1 mg mL 1 LPS) LPS co treatment with 0.1 mmol L 1 Vitamin A (1 mg mL 1 LPS 0.1 mmol L 1 VA) and 0.1 mmol L 1 Vitamin A. LPS significantly decreased TEER by 24 hours, continuing this effect to 48 hours after application. Vitamin A alleviated the LPS induced decrease of TEER from 12 hours to 48 hours, while Vitamin A alone enhanced TEER, indicating that Vitamin A attenuated LPS induced intestinal epithelium permeability. Mechanistically, different concentrations of Vitamin A (0 20 mmol L 1) enhanced tight junction protein markers including Zo 1, Occludin and Claudin 1 both at protein and mRNA levels with an optimized dose of 0.1 mmol L 1. Immunofluorescence results demonstrated that majority of Zo 1 and Claudin 1 is located at the tight junctions, as we expected. LPS reduced the expression of these proteins and Vitamin A reversed LPS reduced expression of these proteins, consistent with the results of western blot. In conclusion, Vitamin A improves the intestinal barrier function and reverses LPS induced intestinal barrier damage via enhancing the expression of tight junction proteins.

title: Rho Flares Repair Local Tight Junction Leaks.
abstract: Tight junctions contribute to epithelial barrier function by selectively regulating the quantity and type of molecules that cross the paracellular barrier. Experimental approaches to evaluate the effectiveness of tight junctions are typically global, tissue scale measures. Here, we introduce Zinc based Ultrasensitive Microscopic Barrier Assay (ZnUMBA) which we used in Xenopus laevis embryos to visualize short lived, local breaches in epithelial barrier function. These breaches, or leaks, occur as cell boundaries elongate, correspond to visible breaks in the tight junction, and are followed by transient localized Rho activation, or Rho flares. We discovered that Rho flares restore barrier function by driving concentration of tight junction proteins through actin polymerization and ROCK mediated localized contraction of the cell boundary. We conclude that Rho flares constitute a damage control mechanism that reinstates barrier function when tight junctions become locally compromised because of normally occurring changes in cell shape and tissue tension.

title: Myosin IIA Regulated Tight Junction in Oxygen Glucose Deprived Brain Endothelial Cells Via Activation of TLR4/PI3K/Akt/JNK1/2/14 3 3e/NF kB/MMP9 Signal Transduction Pathway
abstract: Non muscle myosin heavy chain IIA (NMMHC IIA) a member of Myosin II family, plays a critical role in various cellular physiological processes. Our previous research had suggested that NMMHC IIA could participate in regulating tight junction morphological changes induced by ischemia stroke. Thus, in the current study, we attempted to uncover the regulation pattern of NMMHC IIA on tight junction dysfunction in oxygen glucose deprived (OGD) mouse brain bEND.3 endothelial cells. The regulation of NMMHC IIA on tight junction in OGD stimulated bEND.3 cells was evaluated by western blotting assay. Morphologic change of occludin, claudin 5, and ZO 1 tight junction proteins was compared with pretreatment with NMMHC II inhibitor blebbistatin via immunohistochemical staining. Detection of activation of NMMHC IIA on OGD mediated tight junction transduction pathway was investigated via Koch's postulate using corresponding protein inhibitor. Our results showed that NMMHC IIA was activated in OGD stimulated bEND.3 endothelial cells. The inhibition of NMMHC IIA could attenuate the morphologic change of occludin, claudin 5, and ZO 1 tight junction proteins. NMMHC IIA participated in regulating downstream transduction pathway TLR4, phosphatidylinositol 3 kinase (PI3K) Akt, JNK1/2, 14 3 3e, nuclear factor kappa B (NF kB) and matrix metalloprotein 9 (MMP9) Blocking of these pathways using indicated inhibitors demonstrated that NMMHC IIA destroyed the connection of tight junction via the activation of TLR4/PI3K/Akt/JNK1/2/14 3 3e/NF kB/MMP9 pathway. Our study described the key role of NMMHC IIA in OGD stimulated mouse brain bEND.3 endothelial cells, while also exhibited the molecule effect on tight junction dysfunction via TLR4/PI3K/Akt/JNK1/2/14 3 3e/NF kB/MMP9 signal transduction pathway.