Molecular organization of tricellular tight junctions

Nanostructure-Mediated Transport of Therapeutics through Epithelial Barriers

The ability to precisely treat human disease is facilitated by the sophisticated design of pharmacologic agents. Nanotechnology has emerged as a valuable approach to creating vehicles that can specifically target organ systems, effectively traverse epithelial barriers, and protect agents from premature degradation. In this review, we discuss the molecular basis for epithelial barrier function, focusing on tight junctions, and describe different pathways that drugs can use to cross barrier-forming tissue, including the paracellular route and transcytosis. Unique features of drug delivery applied to different organ systems are addressed: transdermal, ocular, pulmonary, and oral delivery. We also discuss how design elements of different nanoscale systems, such as composition and nanostructured architecture, can be used to specifically enhance transepithelial delivery. The ability to tailor nanoscale drug delivery vehicles to leverage epithelial barrier biology is an emerging theme in the pursuit of facilitating the efficacious delivery of pharmacologic agents.

The Basic Requirement of Tight Junction Proteins in Blood-Brain Barrier Function and Their Role in Pathologies

This review addresses the role of tight junction proteins at the blood-brain barrier (BBB). Their expression is described, and their role in physiological and pathological processes at the BBB is discussed. Based on this, new approaches are depicted for paracellular drug delivery and diagnostics in the treatment of cerebral diseases. Recent data provide convincing evidence that, in addition to its impairment in the course of diseases, the BBB could be involved in the aetiology of CNS disorders. Further progress will be expected based on new insights in tight junction protein structure and in their involvement in signalling pathways.

Tight junction proteins and biliary diseases

PURPOSE OF REVIEW

In the pathophysiological context of cholangiopathies and more broadly of hepatopathies, while it is conceptually clear that the maintenance of inter-cholangiocyte and inter-hepatocyte tight junction integrity would be crucial for liver protection, only scarce studies have been devoted to this topic. Indeed, in the liver, alteration of tight junctions, the intercellular adhesion complexes that control paracellular permeability would result in leaky bile ducts and bile canaliculi, allowing bile reflux towards hepatic parenchyma, contributing to injury during the disease process.

RECENT FINDINGS

Last decades have provided a great deal of information regarding both tight junction structural organization and signaling pathways related to tight junctions, providing clues about potential intervention to modulate paracellular permeability during cholangiopathies pathogenesis. Interestingly, several liver diseases have been reported to be associated with abnormal expression of one or several tight junction proteins. However, the question remains unanswered if these alterations would be primarily involved in the disease pathogenesis or if they would occur secondarily in the pathological course.

SUMMARY

In this review, we provide an overview of tight junction disruptions described in various biliary diseases that should pave the way for defining new therapeutic targets in this field.

Benvitimod Inhibits IL-4- and IL-13-Induced Tight Junction Impairment by Activating AHR/ARNT Pathway and Inhibiting STAT6 Phosphorylation in Human Keratinocytes

Tight junctions are involved in skin barrier functions. In this study, the expression of CLDN1, CLDN4, and OCLN was found to decrease in skin lesions of atopic dermatitis by bioinformatics analysis. Immunohistochemistry staining in skin specimens from 12 patients with atopic dermatitis and 12 healthy controls also showed decreased CLDN1, CLDN4, and OCLN expression in atopic dermatitis lesions. In vitro studies showed that IL-4 and IL-13 downregulated CLDN1, CLDN4, and OCLN expression in HaCaT cells as well as CLDN4 and OCLN expression in human primary keratinocytes. This effect, which was mediated through the Jak-signal transducer and activator of transcription 6 signaling pathway, increased paracellular flux of 4-kDa dextran. Benvitimod, a new drug for atopic dermatitis, upregulated CLDN4 and OCLN through the aryl hydrocarbon receptor/aryl hydrocarbon receptor nuclear translocator pathway. Benvitimod induced nuclear translocation of NRF2 and reduced production of ROS in keratinocytes, thus inhibiting IL-4-/IL-13-induced CLDN1 downregulation and signal transducer and activator of transcription 6 phosphorylation. These results indicate that T helper 2 cytokines are involved in tight junction impairment, and benvitimod can inhibit these effects.

Cellular Uptake and Cytotoxicity of Clostridium perfringens Iota-Toxin

Clostridium perfringens iota-toxin is composed of two separate proteins: a binding protein (Ib) that recognizes a host cell receptor and promotes the cellular uptake of a catalytic protein and (Ia) possessing ADP-ribosyltransferase activity that induces actin cytoskeleton disorganization. Ib exhibits the overall structure of bacterial pore-forming toxins (PFTs). Lipolysis-stimulated lipoprotein receptor (LSR) is defined as a host cell receptor for Ib. The binding of Ib to LSR causes an oligomer formation of Ib in lipid rafts of plasma membranes, mediating the entry of Ia into the cytoplasm. Ia induces actin cytoskeleton disruption via the ADP-ribosylation of G-actin and causes cell rounding and death. The binding protein alone disrupts the cell membrane and induces cytotoxicity in sensitive cells. Host cells permeabilized by the pore formation of Ib are repaired by a Ca2+-dependent plasma repair pathway. This review shows that the cellular uptake of iota-toxin utilizes a pathway of plasma membrane repair and that Ib alone induces cytotoxicity.

Cell Adhesion at the Tight Junctions: New Aspects and New Functions

Tight junctions (TJ) are cell-cell adhesive structures that define the permeability of barrier-forming epithelia and endothelia. In contrast to this seemingly static function, TJs display a surprisingly high molecular complexity and unexpected dynamic regulation, which allows the TJs to maintain a barrier in the presence of physiological forces and in response to perturbations. Cell-cell adhesion receptors play key roles during the dynamic regulation of TJs. They connect individual cells within cellular sheets and link sites of cell-cell contacts to the underlying actin cytoskeleton. Recent findings support the roles of adhesion receptors in transmitting mechanical forces and promoting phase separation. In this review, we discuss the newly discovered functions of cell adhesion receptors localized at the TJs and their role in the regulation of the barrier function.

Storming the gate: New approaches for targeting the dynamic tight junction for improved drug delivery

As biologics used in the clinic outpace the number of new small molecule drugs, an important challenge for their efficacy and widespread use has emerged, namely tissue penetrance. Macromolecular drugs - bulky, high-molecular weight, hydrophilic agents - exhibit low permeability across biological barriers. Epithelial and endothelial layers, for example within the gastrointestinal tract or at the blood-brain barrier, present the most significant obstacle to drug transport. Within epithelium, two subcellular structures are responsible for limiting absorption: cell membranes and intercellular tight junctions. Previously considered impenetrable to macromolecular drugs, tight junctions control paracellular flux and dictate drug transport between cells. Recent work, however, has shown tight junctions to be dynamic, anisotropic structures that can be targeted for delivery. This review aims to summarize new approaches for targeting tight junctions, both directly and indirectly, and to highlight how manipulation of tight junction interactions may help usher in a new era of precision drug delivery.

Matrix stiffness regulates the tight junction phenotypes and local barrier properties in tricellular regions in an iPSC-derived BBB model

The blood-brain barrier (BBB) can respond to various mechanical cues such as shear stress and substrate stiffness. In the human brain, the compromised barrier function of the BBB is closely associated with a series of neurological disorders that are often also accompanied by the alteration of brain stiffness. In many types of peripheral vasculature, higher matrix stiffness decreases barrier function of endothelial cells through mechanotransduction pathways that alter cell-cell junction integrity. However, human brain endothelial cells are specialized endothelial cells that largely resist changes in cell morphology and key BBB markers. Therefore, it has remained an open question how matrix stiffness affects barrier integrity in the human BBB. To gain insight into the effects of matrix stiffness on BBB permeability, we differentiated brain microvascular endothelial-like cells from human induced pluripotent stem cells (iBMEC-like cells) and cultured the cells on extracellular matrix-coated hydrogels of varying stiffness. We first detected and quantified the junction presentation of key tight junction (TJ) proteins. Our results show matrix-dependent junction phenotypes in iBMEC-like cells, where cells on softer gels (1 kPa) have significantly lower continuous and total TJ coverages. We also determined that these softer gels also lead to decreased barrier function in a local permeability assay. Furthermore, we found that matrix stiffness regulates the local permeability of iBMEC-like cells through the balance of continuous ZO-1 TJs and no junction regions ZO-1 in tricellular regions. Together, these findings provide valuable insights into the effects of matrix stiffness on TJ phenotypes and local permeability of iBMEC-like cells. STATEMENT OF SIGNIFICANCE: Brain mechanical properties, including stiffness, are particularly sensitive indicators for pathophysiological changes in neural tissue. The compromised function of the blood-brain barrier is closely associated with a series of neurological disorders often accompanied by altered brain stiffness. In this study, we use polymeric biomaterials and provide new evidence that biomaterial stiffness regulates the local permeability in iPSC-derived brain endothelial cells in tricellular regions through the tight junction protein ZO-1. Our findings provide valuable insights into the changes in junction architecture and barrier permeability in response to different substrate stiffnesses. Since BBB dysfunction has been linked to many diseases, understanding the influence of substrate stiffness on junction presentations and barrier permeability could lead to the development of new treatments for diseases associated with BBB dysfunction or drug delivery across BBB systems.

Intranasal administration of sodium nitroprusside augments antigen-specific mucosal and systemic antibody production in mice

The coronavirus disease 2019, i.e., the COVID-19 pandemic, caused by a highly virulent and transmissible pathogen, has profoundly impacted global society. One approach to combat infectious diseases caused by pathogenic microbes is using mucosal vaccines, which can induce antigen-specific immune responses at both the mucosal and systemic sites. Despite its potential, the clinical implementation of mucosal vaccination is hampered by the lack of safe and effective mucosal adjuvants. Therefore, developing safe and effective mucosal adjuvants is essential for the fight against infectious diseases and the widespread clinical use of mucosal vaccines. In this study, we demonstrated the potent mucosal adjuvant effects of intranasal administration of sodium nitroprusside (SNP), a known nitric oxide (NO) donor, in mice. The results showed that intranasal administration of ovalbumin (OVA) in combination with SNP induced the production of OVA-specific immunoglobulin A in the mucosa and increased serum immunoglobulin G1 levels, indicating a T helper-2 (Th2)-type immune response. However, an analog of SNP, sodium ferrocyanide, which does not generate NO, failed to show any adjuvant effects, suggesting the critical role of NO generation in activating an immune response. In addition, SNPs facilitated the delivery of antigens to the lamina propria, where antigen-presenting cells are located, when co-administered with antigens, and also transiently elicited the expression of interleukin-6, interleukin-1β, granulocyte colony-stimulating factor, C-X-C motif chemokine ligand 1, and C-X-C motif chemokine ligand 2 in nasal tissue. These result suggest that SNP is a dual-functional formulation with antigen delivery capabilities to the lamina propria and the capacity to activate innate immunity. In summary, these results demonstrate the ability of SNP to induce immune responses via an antigen-specific Th2-type response, making it a promising candidate for further development as a mucosal vaccine formulation against infectious diseases.

Downregulation of angulin-1/LSR induces malignancy via upregulation of EGF-dependent claudin-2 and TGF-β-dependent cell metabolism in human lung adenocarcinoma A549 cells

Abnormal expression of bicellular tight junction claudins, including claudin-2 are observed during carcinogenesis in human lung adenocarcinoma. However, little is known about the role of tricellular tight junction molecule angulin-1/lipolysis-stimulated lipoprotein receptor (LSR). In the lung adenocarcinoma tissues examined in the present study, expression of claudin-2 was higher than in normal lung tissues, while angulin-1/LSR was poorly or faintly expressed. We investigated how loss of angulin-1/LSR affects the malignancy of lung adenocarcinoma cell line A549 and normal human lung epithelial (HLE) cells. The EGF receptor tyrosine kinase inhibitor AG1478 prevented the increase of claudin-2 expression induced by EGF in A549 cells. Knockdown of LSR induced expression of claudin-2 at the protein and mRNA levels and AG1478 prevented the upregulation of claudin-2 in A549 cells. Knockdown of LSR induced cell proliferation, cell migration and cell metabolism in A549 cells. Knockdown of claudin-2 inhibited the cell proliferation but did not affect the cell migration or cell metabolism of A549 cells. The TGF-β type I receptor inhibitor EW-7197 prevented the decrease of LSR and claudin-2 induced by TGF-β1 in A549 cells and 2D culture of normal HLE cells. EW-7197 prevented the increase of cell migration and cell metabolism induced by TGF-β1 in A549 cells. EW-7197 prevented the increase of epithelial permeability of FITC-4kD dextran induced by TGF-β1 in 2.5D culture of normal HLE cells. In conclusion, downregulation of angulin-1/LSR induces malignancy via EGF-dependent claudin-2 and TGF-β-dependent cell metabolism in human lung adenocarcinoma.

Small noncoding vault RNA2-1 disrupts gut epithelial barrier function via interaction with HuR

Vault RNAs (vtRNAs) are small noncoding RNAs and highly expressed in many eukaryotes. Here, we identified vtRNA2-1 as a novel regulator of the intestinal barrier via interaction with RNA-binding protein HuR. Intestinal mucosal tissues from patients with inflammatory bowel diseases and from mice with colitis or sepsis express increased levels of vtRNAs relative to controls. Ectopically expressed vtRNA2-1 decreases the levels of intercellular junction (IJ) proteins claudin 1, occludin, and E-cadherin and causes intestinal epithelial barrier dysfunction in vitro, whereas vtRNA2-1 silencing promotes barrier function. Increased vtRNA2-1 also decreases IJs in intestinal organoid, inhibits epithelial renewal, and causes Paneth cell defects ex vivo. Elevating the levels of tissue vtRNA2-1 in the intestinal mucosa increases the vulnerability of the gut barrier to septic stress in mice. vtRNA2-1 interacts with HuR and prevents HuR binding to claudin 1 and occludin mRNAs, thus decreasing their translation. These results indicate that vtRNA2-1 impairs intestinal barrier function by repressing HuR-facilitated translation of claudin 1 and occludin.

Porcine Epidemic Diarrhea Virus: An Updated Overview of Virus Epidemiology, Virulence Variation Patterns and Virus-Host Interactions

The porcine epidemic diarrhea virus (PEDV) is a member of the coronavirus family, causing deadly watery diarrhea in newborn piglets. The global pandemic of PEDV, with significant morbidity and mortality, poses a huge threat to the swine industry. The currently developed vaccines and drugs are only effective against the classic GI strains that were prevalent before 2010, while there is no effective control against the GII variant strains that are currently a global pandemic. In this review, we summarize the latest progress in the biology of PEDV, including its transmission and origin, structure and function, evolution, and virus-host interaction, in an attempt to find the potential virulence factors influencing PEDV pathogenesis. We conclude with the mechanism by which PEDV components antagonize the immune responses of the virus, and the role of host factors in virus infection. Essentially, this review serves as a valuable reference for the development of attenuated virus vaccines and the potential of host factors as antiviral targets for the prevention and control of PEDV infection.

LSR antibody promotes apoptosis and disrupts epithelial barriers via signal pathways in endometrial cancer

Lipolysis-stimulated lipoprotein receptor (LSR), a lipid metabolism-related factor localized in tricellular tight junctions (tTJs), plays an important role in maintaining the epithelial barrier. LSR is highly expressed in well-differentiated endometrial endometrioid carcinoma (EEC), and its expression decreases during malignancy. Angubindin-1, a novel LSR ligand peptide, regulates tTJs without cytotoxicity, enhances paracellular permeability, and regulates epithelial barrier via c-Jun N-terminal kinase (JNK)/cofilin. In this study, we investigated the immune-modulatory roles of an anti-LSR antibody in the treatment of EEC in vitro compared to those of angubindin-1. We prepared an antibody against the extracellular N-terminal domain of human LSR (LSR-N-ab) and angubindin-1. EEC cell-line Sawano cells in 2D and 2.5D cultures were treated with 100 μg/ml LSR-N-ab or 2.5 μg/ml angubindin-1 with or without protein tyrosine kinase 2β inhibitor PF431396 (PF43) and JNK inhibitor SP600125 (SP60) at 10 μM. Treatment with LSR-N-ab and angubindin-1 decreased LSR at the membranes of tTJs and the activity of phosphorylated LSR and phosphorylated cofilin in 2D culture. Treatment with LSR-N-ab and angubindin-1 decreased the epithelial barrier measured as TEER values in 2D culture and enhanced the epithelial permeability of FD-4 in 2.5D culture. Treatment with LSR-N-ab, but not angubindin-1, induced apoptosis in 2D culture. Pretreatment with PF43 and SP60 prevented all the changes induced by treatment with LSR-N-ab and angubindin-1. Treatment with LSR-N-ab and angubindin-1 enhanced the cell metabolism measured as the mitochondrial respiration levels in 2D culture. LSR-N-ab and angubindin-1 may be useful for therapy of human EEC via enhanced apoptosis or drug absorption.

Modelling the Human Blood-Brain Barrier in Huntington Disease

While blood–brain barrier (BBB) dysfunction has been described in neurological disorders, including Huntington’s disease (HD), it is not known if endothelial cells themselves are functionally compromised when promoting BBB dysfunction. Furthermore, the underlying mechanisms of BBB dysfunction remain elusive given the limitations with mouse models and post mortem tissue to identify primary deficits. We established models of BBB and undertook a transcriptome and functional analysis of human induced pluripotent stem cell (iPSC)-derived brain-like microvascular endothelial cells (iBMEC) from HD patients or unaffected controls. We demonstrated that HD-iBMECs have abnormalities in barrier properties, as well as in specific BBB functions such as receptor-mediated transcytosis.

Modifying the blood-brain barrier by targeting claudin-5: Safety and risks

The blood-brain barrier is a major obstacle to the delivery of drugs to the central nervous system. In the blood-brain barrier, the spaces between adjacent brain microvascular endothelial cells are sealed by multiprotein complexes known as tight junctions. Among the many components of the tight junction, claudin-5 has received the most attention as a target for loosening the tight-junction seal and allowing drugs to be delivered to the brain. In mice, transient knockdown of claudin-5 and the use of claudin-5 binders have been shown to enhance the permeation of small molecules from the blood into the brain without apparent adverse effects. However, sustained knockdown of claudin-5 in mice is lethal within 40 days, and administration of an anti-claudin-5 antibody induced convulsions in a nonhuman primate. Here, we review the safety concerns of claudin-5-targeted technologies with respect to their clinical application.

The Roles of Tricellular Tight Junction Protein Angulin-1/Lipolysis-Stimulated Lipoprotein Receptor (LSR) in Endometriosis and Endometrioid-Endometrial Carcinoma

Tight junction proteins play roles beyond permeability barriers functions and control cell proliferation and differentiation. The relation between tight junctions and the signal transduction pathways affects cell growth, invasion and migration. Abnormality of tight junction proteins closely contributes to epithelial mesenchymal transition (EMT) and malignancy of various cancers. Angulin-1/lipolysis-stimulated lipoprotein receptor (LSR) forms tricellular contacts that has a barrier function. Downregulation of angulin-1/LSR correlates with the malignancy in various cancers, including endometrioid-endometrial carcinoma (EEC). These alterations have been shown to link to not only multiple signaling pathways such as Hippo/YAP, HDAC, AMPK, but also cell metabolism in ECC cell line Sawano. Moreover, loss of angulin-1/LSR upregulates claudin-1, and loss of apoptosis stimulating p53 protein 2 (ASPP2) downregulates angulin-1/LSR. Angulin-1/LSR and ASPP2 concentrate at both midbody and centrosome in cytokinesis. In EEC tissues, angulin-1/LSR and ASPP2 are reduced and claudin-2 is overexpressed during malignancy, while in the tissues of endometriosis changes in localization of angulin-1/LSR and claudin-2 are seen. This review highlights how downregulation of angulin-1/LSR promotes development of endometriosis and EEC and discusses about the roles of angulin-1/LSR and its related proteins, including claudins and ASPP2.

Surface-Displayed Amuc_1100 From Akkermansia muciniphila on Lactococcus lactis ZHY1 Improves Hepatic Steatosis and Intestinal Health in High-Fat-Fed Zebrafish

Fatty liver and intestinal barrier damage were widespread in most farmed fish, which severely restrict the development of aquaculture. Therefore, there was an urgent need to develop green feed additives to maintain host liver and intestinal health. In this study, a probiotic pili-like protein, Amuc_1100 (AM protein), was anchored to the surface of Lactococcus lactis ZHY1, and the effects of the recombinant bacteria AM-ZHY1 on liver fat accumulation and intestinal health were evaluated. Zebrafish were fed a basal diet, high-fat diet, and high-fat diet with AM-ZHY1 (10⁸ cfu/g) or control bacteria ZHY1 for 4 weeks. Treatment with AM-ZHY1 significantly reduced hepatic steatosis in zebrafish. Quantitative PCR (qPCR) detection showed that the expression of the lipogenesis [peroxisome-proliferator-activated receptors (PPARγ), sterol regulatory element-binding proteins-1c (SREBP-1c), fatty acid synthase (FAS), and acetyl-CoA carboxylase 1 (ACC1)] and lipid transport genes (CD36 and FABP6) in the liver were significantly downregulated (p < 0.05), indicating that AM-ZHY1 could reduce liver fat accumulation by inhibiting lipid synthesis and absorption. Moreover, supplementing AM-ZHY1 to a high-fat diet could significantly reduce serum aspartate aminotransferase (AST) and alanine aminotransferase (ALT) levels, indicating that liver injury caused by high-fat diets was improved. The expression of tumor necrosis factor (TNF)-a and interleukin (IL)-6 in the liver decreased significantly (p < 0.05), while IL-1β and IL-10 did not change significantly in the AM-ZHY1 group. Compared to the high-fat diet-fed group, the AM-ZHY1 group, but not the ZHY1 group, significantly increased the expression of intestinal tight junction (TJ) proteins (TJP1a, claudina, claudin7, claudin7b, claudin11a, claudin12, and claudin15a; p < 0.05). Compared to the high-fat diet group, the Proteobacteria and Fusobacteria were significantly reduced and increased in the AM-ZHY1 group, respectively. In conclusion, the recombinant bacteria AM-ZHY1 has the capacity to maintain intestinal health by protecting intestinal integrity and improving intestinal flora structure and improving fatty liver disease by inhibiting lipid synthesis and absorption. This study will lay a foundation for the application of AM protein in improving abnormal fat deposition and restoring the intestinal barrier in fish.

Dysfunction of epithelial permeability barrier induced by HMGB1 in 2.5D cultures of human epithelial cells

Airway and intestinal epithelial permeability barriers are crucial in epithelial homeostasis. High mobility group box 1 (HMGB1), increased by various stimuli, is involved in the induction of airway inflammation, as well as the pathogenesis of inflammatory bowel disease. HMGB1 enhances epithelial hyperpermeability. Two-and-a-half dimensional (2.5D) culture assays are experimentally convenient and induce cells to form a more physiological tissue architecture than 2D culture assays for molecular transfer mechanism analysis. In 2.5D culture, treatment with HMGB1 induced permeability of FITC-dextran into the lumen formed by human lung, nasal and intestinal epithelial cells. The tricellular tight junction molecule angulin-1/LSR is responsible for the epithelial permeability barrier at tricellular contacts and contributes to various human airway and intestinal inflammatory diseases. In this review, we indicate the mechanisms including angulin-1/LSR and multiple signaling in dysfunction of the epithelial permeability barrier induced by HMGB1 in 2.5D culture of human airway and intestinal epithelial cells.

Angulin-1 seals tricellular contacts independently of tricellulin and claudins

Tricellular tight junctions (tTJs) are specialized tight junctions (TJs) that seal the intercellular space at tricellular contacts (TCs), where the vertices of three epithelial cells meet. Tricellulin and angulin family membrane proteins are known constituents of tTJs, but the molecular mechanism of tTJ formation remains elusive. Here, we investigated the roles of angulin-1 and tricellulin in tTJ formation in MDCK II cells by genome editing. Angulin-1-deficient cells lost the plasma membrane contact at TCs with impaired epithelial barrier function. The C terminus of angulin-1 bound to the TJ scaffold protein ZO-1, and disruption of their interaction influenced the localization of claudins at TCs, but not the tricellular sealing. Strikingly, the plasma membrane contact at TCs was formed in tricellulin- or claudin-deficient cells. These findings demonstrate that angulin-1 is responsible for the plasma membrane seal at TCs independently of tricellulin and claudins.

Angulin-1 (LSR) Affects Paracellular Water Transport, However Only in Tight Epithelial Cells

Water transport in epithelia occurs transcellularly (aquaporins) and paracellularly (claudin-2, claudin-15). Recently, we showed that downregulated tricellulin, a protein of the tricellular tight junction (tTJ, the site where three epithelial cells meet), increased transepithelial water flux. We now check the hypothesis that another tTJ-associated protein, angulin-1 (alias lipolysis-stimulated lipoprotein receptor, LSR) is a direct negative actuator of tTJ water permeability depending on the tightness of the epithelium. For this, a tight and an intermediate-tight epithelial cell line, MDCK C7 and HT-29/B6, were stably transfected with CRISPR/Cas9 and single-guide RNA targeting angulin-1 and morphologically and functionally characterized. Water flux induced by an osmotic gradient using 4-kDa dextran caused water flux to increase in angulin-1 KO clones in MDCK C7 cells, but not in HT-29/B6 cells. In addition, we found that water permeability in HT-29/B6 cells was not modified after either angulin-1 knockout or tricellulin knockdown, which may be related to the presence of other pathways, which reduce the impact of the tTJ pathway. In conclusion, modulation of the tTJ by knockout or knockdown of tTJ proteins affects ion and macromolecule permeability in tight and intermediate-tight epithelial cell lines, while the transepithelial water permeability was affected only in tight cell lines.

Spatio-temporal expression pattern and role of the tight junction protein MarvelD3 in pancreas development and function

Tight junction complexes are involved in the establishment and maintenance of cell polarity and the regulation of signalling pathways, controlling biological processes such as cell differentiation and cell proliferation. MarvelD3 is a tight junction protein expressed in adult epithelial and endothelial cells. In Xenopus laevis, MarvelD3 morphants present differentiation defects of several ectodermal derivatives. In vitro experiments further revealed that MarvelD3 couples tight junctions to the MEKK1-JNK pathway to regulate cell behaviour and survival. In this work, we found that MarvelD3 is expressed from early developmental stages in the exocrine and endocrine compartments of the pancreas, as well as in endothelial cells of this organ. We thoroughly characterized MarvelD3 expression pattern in developing pancreas and evaluated its function by genetic ablation. Surprisingly, inactivation of MarvelD3 in mice did not alter development and differentiation of the pancreatic tissue. Moreover, tight junction formation and organization, cell polarization, and activity of the JNK-pathway were not impacted by the deletion of MarvelD3.

Brain endothelial tricellular junctions as novel sites for T cell diapedesis across the blood-brain barrier

The migration of activated T cells across the blood–brain barrier (BBB) is a critical step in central nervous system (CNS) immune surveillance and inflammation. Whereas T cell diapedesis across the intact BBB seems to occur preferentially through the BBB cellular junctions, impaired BBB integrity during neuroinflammation is accompanied by increased transcellular T cell diapedesis. The underlying mechanisms directing T cells to paracellular versus transcellular sites of diapedesis across the BBB remain to be explored. By combining in vitro live-cell imaging of T cell migration across primary mouse brain microvascular endothelial cells (pMBMECs) under physiological flow with serial block-face scanning electron microscopy (SBF-SEM), we have identified BBB tricellular junctions as novel sites for T cell diapedesis across the BBB. Downregulated expression of tricellular junctional proteins or protein-based targeting of their interactions in pMBMEC monolayers correlated with enhanced transcellular T cell diapedesis, and abluminal presence of chemokines increased T cell diapedesis through tricellular junctions. Our observations assign an entirely novel role to BBB tricellular junctions in regulating T cell entry into the CNS.

This article has an associated First Person interview with the first author of the paper.

Highlighted Article: Ultrastructural analysis of T cell migration across the blood–brain barrier (BBB) under physiological flow identifies BBB tricellular junctions as sites of T cell diapedesis.

E-cigarettes compromise the gut barrier and trigger inflammation

E-cigarette usage continues to rise, yet the safety of e-cigarette aerosols is questioned. Using murine models of acute and chronic e-cigarette aerosol inhalation, murine colon transcriptomics, and murine and human gut-derived organoids in co-culture models, we assessed the effects of e-cigarette use on the gut barrier. Histologic and transcriptome analyses revealed that chronic, but not acute, nicotine-free e-cigarette use increased inflammation and reduced expression of tight junction (TJ) markers. Exposure of murine and human enteroid-derived monolayers (EDMs) to nicotine-free e-cigarette aerosols alone or in co-culture with bacteria also causes barrier disruption, downregulation of TJ protein, and enhanced inflammation in response to infection. These data highlight the harmful effects of "non-nicotine" component of e-cigarettes on the gut barrier. Considering the importance of an intact gut barrier for host fitness and the impact of gut mucosal inflammation on a multitude of chronic diseases, these findings are broadly relevant to both medicine and public health.

E-cigarettes compromise the gut barrier and trigger inflammation

E-cigarette usage continues to rise, yet the safety of e-cigarette aerosols is questioned. Using murine models of acute and chronic e-cigarette aerosol inhalation, murine colon transcriptomics, and murine and human gut-derived organoids in co-culture models, we assessed the effects of e-cigarette use on the gut barrier. Histologic and transcriptome analyses revealed that chronic, but not acute, nicotine-free e-cigarette use increased inflammation and reduced expression of tight junction (TJ) markers. Exposure of murine and human enteroid-derived monolayers (EDMs) to nicotine-free e-cigarette aerosols alone or in co-culture with bacteria also causes barrier disruption, downregulation of TJ protein, and enhanced inflammation in response to infection. These data highlight the harmful effects of "non-nicotine" component of e-cigarettes on the gut barrier. Considering the importance of an intact gut barrier for host fitness and the impact of gut mucosal inflammation on a multitude of chronic diseases, these findings are broadly relevant to both medicine and public health.

Tight Junction Modulating Bioprobes for Drug Delivery System to the Brain: A Review

The blood-brain barrier (BBB), which is composed of endothelial cells, pericytes, astrocytes, and neurons, separates the brain extracellular fluid from the circulating blood, and maintains the homeostasis of the central nervous system (CNS). The BBB endothelial cells have well-developed tight junctions (TJs) and express specific polarized transport systems to tightly control the paracellular movements of solutes, ions, and water. There are two types of TJs: bicellular TJs (bTJs), which is a structure at the contact of two cells, and tricellular TJs (tTJs), which is a structure at the contact of three cells. Claudin-5 and angulin-1 are important components of bTJs and tTJs in the brain, respectively. Here, we review TJ-modulating bioprobes that enable drug delivery to the brain across the BBB, focusing on claudin-5 and angulin-1.

Increase in Epithelial Permeability and Cell Metabolism by High Mobility Group Box 1, Inflammatory Cytokines and TPEN in Caco-2 Cells as a Novel Model of Inflammatory Bowel Disease

High mobility group box 1 protein (HMGB1) is involved in the pathogenesis of inflammatory bowel disease (IBD). Patients with IBD develop zinc deficiency. However, the detailed roles of HMGB1 and zinc deficiency in the intestinal epithelial barrier and cellular metabolism of IBD remain unknown. In the present study, Caco-2 cells in 2D culture and 2.5D Matrigel culture were pretreated with transforming growth factor-β (TGF-β) type 1 receptor kinase inhibitor EW-7197, epidermal growth factor receptor (EGFR) kinase inhibitor AG-1478 and a TNFα antibody before treatment with HMGB1 and inflammatory cytokines (TNFα and IFNγ). EW-7197, AG-1478 and the TNFα antibody prevented hyperpermeability induced by HMGB1 and inflammatory cytokines in 2.5D culture. HMGB1 affected cilia formation in 2.5D culture. EW-7197, AG-1478 and the TNFα antibody prevented the increase in cell metabolism induced by HMGB1 and inflammatory cytokines in 2D culture. Furthermore, ZnSO₄ prevented the hyperpermeability induced by zinc chelator TPEN in 2.5D culture. ZnSO₄ and TPEN induced cellular metabolism in 2D culture. The disruption of the epithelial barrier induced by HMGB1 and inflammatory cytokines contributed to TGF-β/EGF signaling in Caco-2 cells. The TNFα antibody and ZnSO₄ as well as EW-7197 and AG-1478 may have potential for use in therapy for IBD.

Intestinal permeation enhancers to improve oral bioavailability of macromolecules: reasons for low efficacy in humans

INTRODUCTION

Intestinal permeation enhancers (PEs) are substances that transiently alter the intestinal epithelial barrier to facilitate permeation of macromolecules with low oral bioavailability (BA). While a number of PEs have progressed to clinical testing in conventional formulations with macromolecules, there has been only low single digit increases in oral BA, irrespective of whether the drug met primary or secondary clinical endpoints.

AREAS COVERED

This article considers the causes of sub-optimal BA of macromolecules from PE dosage forms and suggests approaches that may improve performance in humans.

EXPERT OPINION

Permeation enhancement is most effective when the PE is co-localized with the macromolecule at the epithelial surface. Conditions in the GI tract impede optimal co-localization. Novel delivery systems that limit dilution and spreading of the PE and macromolecule in the small intestine have attempted to replicate promising enhancement efficacy observed in static drug delivery models.

Interplay between Anakonda, Gliotactin, and M6 for Tricellular Junction Assembly and Anchoring of Septate Junctions in Drosophila Epithelium

In epithelia, tricellular junctions (TCJs) serve as pivotal sites for barrier function and integration of both biochemical and mechanical signals [1-3]. In Drosophila, TCJs are composed of the transmembrane protein Sidekick at the adherens junction (AJ) level, which plays a role in cell-cell contact rearrangement [4-6]. At the septate junction (SJ) level, TCJs are formed by Gliotactin (Gli) [7], Anakonda (Aka) [8, 9], and the Myelin proteolipid protein (PLP) M6 [10, 11]. Despite previous data on TCJ organization [12-14], TCJ assembly, composition, and links to adjacent bicellular junctions (BCJs) remain poorly understood. Here, we have characterized the making of TCJs within the plane of adherens junctions (tricellular adherens junction [tAJ]) and the plane of septate junctions (tricellular septate junction [tSJ]) and report that their assembly is independent of each other. Aka and M6, whose localizations are interdependent, act upstream to localize Gli. In turn, Gli stabilizes Aka at tSJ. Moreover, tSJ components are not only essential at vertex, as we found that loss of tSJ integrity induces micron-length bicellular SJ (bSJ) deformations. This phenotype is associated with the disappearance of SJ components at tricellular contacts, indicating that bSJs are no longer connected to tSJs. Reciprocally, SJ components are required to restrict the localization of Aka and Gli at vertex. We propose that tSJs function as pillars to anchor bSJs to ensure the maintenance of tissue integrity in Drosophila proliferative epithelia.

The Role of Tricellulin in Epithelial Jamming and Unjamming via Segmentation of Tricellular Junctions

Collective cellular behavior in confluent monolayers supports physiological and pathological processes of epithelial development, regeneration, and carcinogenesis. Here, the attainment of a mature and static tissue configuration or the local reactivation of cell motility involve a dynamic regulation of the junctions established between neighboring cells. Tricellular junctions (tTJs), established at vertexes where three cells meet, are ideally located to control cellular shape and coordinate multicellular movements. However, their function in epithelial tissue dynamic remains poorly defined. To investigate the role of tTJs establishment and maturation in the jamming and unjamming transitions of epithelial monolayers, a semi-automatic image-processing pipeline is developed and validated enabling the unbiased and spatially resolved determination of the tTJ maturity state based on the localization of fluorescent reporters. The software resolves the variation of tTJ maturity accompanying collective transitions during tissue maturation, wound healing, and upon the adaptation to osmolarity changes. Altogether, this work establishes junctional maturity at tricellular contacts as a novel biological descriptor of collective responses in epithelial monolayers.

Angulin-2/ILDR1, a tricellular tight junction protein, does not affect water transport in the mouse large intestine

Angulin-2/ILDR1 is a member of the angulin protein family, which is exclusively expressed at tricellular tight junctions in epithelia. Tricellular tight junctions are found where three cells meet and where three bicellular tight junction strands converge. Tricellular tight junctions are thought to be important for paracellular permeability of ions and water in epithelial tissues. It was recently reported that angulin-2/ILDR1 knockout mice have water transport abnormalities in the kidney. Since angulin-2/ILDR1 is the main tricellular tight junction protein in the large intestine, the goal of this research was to examine the effect of angulin-2/ILDR1 knockout on large intestinal paracellular water transport. We found that Ildr1 knockout mice showed no detectable phenotype other than deafness. In addition, paracellular transport as assessed by Ussing chamber was unchanged in Ildr1 knockout mice. However, we found that in the colon and the kidney of Ildr1 knockout mice, another tricellular tight junction protein, angulin-1/LSR, changes its expression pattern. We propose that with this replacement in tissue localization, angulin-1/LSR compensates for the loss of angulin-2/ILDR1 and maintains the barrier and function of the epithelia in the large intestine as well as the kidney.

ASPP2 suppression promotes malignancy via LSR and YAP in human endometrial cancer

Apoptosis-stimulating p53 protein 2 (ASPP2) is an apoptosis inducer that acts via binding with p53 and epithelial polarity molecule PAR3. Lipolysis-stimulated lipoprotein receptor (LSR) is an important molecule at tricellular contacts, and loss of LSR promotes cell migration and invasion via Yes-associated protein (YAP) in human endometrial cancer cells. In the present study, to find how ASPP2 suppression promotes malignancy in human endometrial cancer, we investigated its mechanisms including the relationship with LSR. In endometriosis and endometrial cancers (G1 and G2), ASPP2 was observed as well as PAR3 and LSR in the subapical region. ASPP2 decreased in G3 endometrial cancer compared to G1. In human endometrial cancer cell line Sawano, ASPP2 was colocalized with LSR and tricellulin at tricellular contacts and binding to PAR3, LSR, and tricellulin in the confluent state. ASPP2 suppression promoted cell migration and invasion, decreased LSR expression, and induced expression of phosphorylated YAP, claudin-1, -4, and -7 as effectively as the loss of LSR. Knockdown of YAP prevented the upregulation of pYAP, cell migration and invasion induced by the ASPP2 suppression. Treatment with a specific antibody against ASPP2 downregulated ASPP2 and LSR, affected F-actin at tricellular contacts, upregulated expression of pYAP and claudin-1, and induced cell migration and invasion via YAP. In normal human endometrial epithelial cells, ASPP2 was in part colocalized with LSR at tricellular contacts and knockdown of ASPP2 or LSR induced expression of claudin-1 and claudin-4. ASPP2 suppression promoted cell invasion and migration via LSR and YAP in human endometrial cancer cells.

Relationship between apical junction proteins, gene expression and cancer

The apical junctional complex (AJC) is a cell-cell adhesion system present at the upper portion of the lateral membrane of epithelial cells integrated by the tight junction (TJ) and the adherens junction (AJ). This complex is crucial to initiate and stabilize cell-cell adhesion, to regulate the paracellular transit of ions and molecules and to maintain cell polarity. Moreover, we now consider the AJC as a hub of signal transduction that regulates cell-cell adhesion, gene transcription and cell proliferation and differentiation. The molecular components of the AJC are multiple and diverse and depending on the cellular context some of the proteins in this complex act as tumor suppressors or as promoters of cell transformation, migration and metastasis outgrowth. Here, we describe these new roles played by TJ and AJ proteins and their potential use in cancer diagnostics and as targets for therapeutic intervention.

The stress polarity signaling (SPS) pathway serves as a marker and a target in the leaky gut barrier: implications in aging and cancer

The gut barrier separates trillions of microbes from the largest immune system in the body; when compromised, a "leaky" gut barrier fuels systemic inflammation, which hastens the progression of chronic diseases. Strategies to detect and repair the leaky gut barrier remain urgent and unmet needs. Recently, a stress-polarity signaling (SPS) pathway has been described in which the metabolic sensor, AMP-kinase acts via its effector, GIV (also known as Girdin) to augment epithelial polarity exclusively under energetic stress and suppresses tumor formation. Using murine and human colon-derived organoids, and enteroid-derived monolayers (EDMs) that are exposed to stressors, we reveal that the SPS-pathway is active in the intestinal epithelium and requires a catalytically active AMP-kinase. Its pharmacologic augmentation resists stress-induced collapse of the epithelium when challenged with microbes or microbial products. In addition, the SPS-pathway is suppressed in the aging gut, and its reactivation in enteroid-derived monolayers reverses aging-associated inflammation and loss of barrier function. It is also silenced during progression of colorectal cancers. These findings reveal the importance of the SPS-pathway in the gut and highlights its therapeutic potential for treating gut barrier dysfunction in aging, cancer, and dysbiosis.

A Method to Prepare a Bioprobe for Regulatory Science of the Drug Delivery System to the Brain: An Angulin Binder to Modulate Tricellular Tight Junction-Seal

Epithelium acts as a barrier separating the interior and exterior of the body, and the epithelial and endothelial cells form tight junctions (TJs) by sealing the paracellular space. The blood-brain barrier (BBB) endothelial cells have well-developed TJs and express specific polarized transport systems to tightly control paracellular movements of solutes, ions, and water. Thus, more than 98% of small-molecular-weight drugs cannot pass the BBB. The tricellular TJ (tTJ) is a structure at contacts of three cells. Angulin-1, also known as lipolysis-stimulated lipoprotein receptor (LSR), is one of angulin family and is abundantly expressed in brain endothelial cells, which plays an important role in barrier function of the BBB. The C-terminal domain of a receptor-binding component of Clostridium perfringens iota-toxin (Ib421-664), also named as angubindin-1, binds to its receptors angulin-1 and angulin-3. This angubindin-1 modulates the tTJ barrier and is able to deliver a 16-mer gapmer antisense oligonucleotide (5.3 kDa) without adverse effects. Thus, angulin binders, such as angubindin-1, are useful tools for studying the safety assessment of tTJ-targeted drug delivery and BBB permeability modulation. Here, we provide a protocol for the expression and purification of recombinant angubindin-1 protein as angulin binders, an analysis method for angubindin-1 binding affinity, and a procedure for assessing the effect of modulating tight junction integrity.

Tricellulin Modulates Transport of Macromolecules in the Salivary Gland

Volume and composition of saliva are crucial for oral and systemic health. How substances, particularly macromolecules, are transported across the salivary gland epithelium has not been established in detail. Tricellulin is a component of tricellular tight junctions that form a central tube to serve as an important route for macromolecule transport. Whether tricellulin is expressed in the submandibular gland (SMG) and involved in salivation has been unknown. Here, by using Western blotting and immunofluorescence, tricellulin was found to be characteristically localized at tricellular contacts of human, rat, and mouse SMGs. Knockdown of tricellulin significantly increased, whereas overexpression of tricellulin decreased, paracellular permeability for 40-kDa but not for 4-kDa fluorescein isothiocyanate–dextran, while transepithelial electrical resistance was unaffected. Conversely, claudin-4 knockdown and overexpression affected transepithelial electrical resistance but not 40-kDa fluorescein isothiocyanate–dextran transport, suggesting that tricellulin regulated transport of macromolecules but not ions, which were mainly regulated by bicellular tight junctions (bTJs). Moreover, tricellulin was dynamically redistributed from tri- to bicellular membranes in cholinergically stimulated SMG tissues and cells. Immunoglobulin-like domain-containing receptor 1 (ILDR1) recruits tricellulin to tricellular contacts. The proportion of macromolecules in the saliva was increased, whereas the amount of stimulated saliva was unchanged in Ildr1-/- mice, which displayed abnormal tricellulin distribution in SMGs. Furthermore, tricellulin interacted with bTJ proteins, such as occludin, claudin-1, claudin-3, claudin-4, and ZO-1, in rat SMG epithelial polarized cell line SMG-C6. Knockdown of tricellulin decreased occludin levels. Thus, we revealed a specific expression pattern of tricellulin in SMG epithelium. Tricellulin not only functioned as a barrier for macromolecules but also modulated the connection of bTJs to the tight junction complex. Alterations in tricellulin expression and distribution could thereby change salivary composition. Our study provided novel insights on salivary gland tight junction organization and function.

Epithelial barrier dysfunction and cell migration induction via JNK/cofilin/actin by angubindin-1

Angulin-1/LSR is a tricellular tight junction molecule, that plays an important role in maintaining the epithelial and endothelial barriers. The actin cytoskeleton at tricellular contacts also contributes to the maintenance of the epithelial barrier. Loss of angulin-1/LSR enhances the migration of various cancer cells. Angubindin-1 is a novel binder to angulin-1/LSR and angulin-3. It is a peptide generated from the angulin-1 binding site of Clostridium perfringens iota toxin, which affects the actin cytoskeleton and decreases the epithelial and endothelial barrier functions. However, its regulatory mechanisms are not well understood. To investigate the regulatory mechanisms of the epithelial barrier dysfunction and cell migration induction by angubindin-1, we used human endometrial cancer cell line Sawano, which has high LSR expression and the epithelial barrier function. Angubindin-1 decreased LSR expression and the epithelial barrier function and increased cell migration. It inhibited the recovery of the epithelial barrier function in a Ca-switch model. At tricellular contacts, sinking of the membrane and an increase of actin fibers near the junctions were caused by angubindin-1. It dynamically changed F-actin from lines to dot-like structures at tricellular contacts. Angubindin-1 transiently increased the phosphorylation of cofilin and JNK, which are involved in the regulation of the intracellular actin cytoskeleton. Furthermore, knockdown of JNK and the JNK inhibitor SP600125 prevented the decrease of the epithelial barrier function and the increase of cell migration induced by angubindin-1. These findings suggest that angubindin-1 might reversibly regulate the epithelial barrier and cell migration at tricellular contacts via JNK/cofilin/actin cytoskeleton dynamics.

Localization of Tricellular Tight Junction Molecule LSR at Midbody and Centrosome During Cytokinesis in Human Epithelial Cells

Epithelial integrity and barrier function are maintained during cytokinesis in vertebrate epithelial tissues. The changes in localization and the roles of tricellular tight junction molecule lipolysis-stimulated lipoprotein receptor (LSR) during cytokinesis are not well known, although new tricellular tight junctions form at the flank of the midbody during cytokinesis. In this study, we investigated the changes in localization and the role of LSR at the midbody and centrosome during cytokinesis using human endometrial carcinoma cell line Sawano, comparing the tricellular tight junction molecule tricellulin; bicellular tight junction molecules occludin, claudin-7, zonula occludens-1, and cingulin; and the epithelial polarized related molecules apoptosis-stimulating of p53 protein 2, PAR3, and yes-associated protein. During cytokinesis induced by treatment with taxol, the epithelial barrier was maintained and the tricellular tight junction molecules LSR and tricellulin were concentrated at the flank of the acetylated tubulin-positive midbody and in γ-tubulin-positive centrosomes with the dynein adaptor Hook2, whereas the other molecules were localized there as well. All the molecules disappeared by knockdown using small interfering RNAs. Furthermore, by the knockdown of Hook2, the epithelial barrier was maintained and most of the molecules disappeared from the centrosome. These findings suggest that LSR may play crucial roles not only in barrier function but also in cytokinesis.

Tricellulin Expression and its Deletion Effects in the Endolymphatic Sac

OBJECTIVES

Tricellulin is a tight junction (TJ)-forming protein that participates in the sealing function of tricellular TJs. Tricellulin-knockout (Tric-/-) mice show progressive hearing loss with degeneration of hair cells in the cochlea without physiological or physical disorders. In the present study, we investigated the tricellulin expression and its deletion effects in the endolymphatic sac (ES) using Tric-/- mice.

MATERIALS AND METHODS

The ES epithelia from wild-type (WT) mice were laser-microdissected, and RT-PCR was performed. The ES sections from Tric-/- and WT mice were immunostained with an anti-tricellulin antibody. Hematoxylin and eosin staining was performed for morphological examination. The inner ear of Tric-/- mice was perfused with biotinylation reagents, and the ES sections were observed for tracer permeability assay after applying streptavidin-Alexa Fluor 488 conjugate.

RESULTS

The tricellulin expression was confirmed by RT-PCR and by immunohistochemistry in the WT ES. The ES in Tric-/- mice showed normal morphology and revealed no biotin leakage from the lumen.

CONCLUSION

The ES in Tric-/- mice showed no changes in morphology or disruption in macromolecular barrier function. The effects of solute leakages in the ES of Tric-/- mice may be very limited and compensatable, or that the ES epithelia may have other sealing system covering the lack of tricellulin.

The mechanobiology of tight junctions

Tight junctions (TJ) play a central role in the homeostasis of epithelial and endothelial tissues, by providing a semipermeable barrier to ions and solutes, by contributing to the maintenance of cell polarity, and by functioning as signaling platforms. TJ are associated with the actomyosin and microtubule cytoskeletons, and the crosstalk with the cytoskeleton is fundamental for junction biogenesis and physiology. TJ are spatially and functionally connected to adherens junctions (AJ), which are essential for the maintenance of tissue integrity. Mechano-sensing and mechano-transduction properties of several AJ proteins have been characterized during the last decade. However, little is known about how mechanical forces act on TJ and their proteins, how TJ control the mechanical properties of cells and tissues, and what are the underlying molecular mechanisms. Here I review recent studies that have advanced our understanding of the relationships between mechanical force and TJ biology.

Role of Tricellular Tight Junction Protein Lipolysis-Stimulated Lipoprotein Receptor (LSR) in Cancer Cells

Maintaining a robust epithelial barrier requires the accumulation of tight junction proteins, LSR/angulin-1 and tricellulin, at the tricellular contacts. Alterations in the localization of these proteins temporarily cause epithelial barrier dysfunction, which is closely associated with not only physiological differentiation but also cancer progression and metastasis. In normal human endometrial tissues, the endometrial cells undergo repeated proliferation and differentiation under physiological conditions. Recent observations have revealed that the localization and expression of LSR/angulin-1 and tricellulin are altered in a menstrual cycle-dependent manner. Moreover, it has been shown that endometrial cancer progression affects these alterations. This review highlights the differences in the localization and expression of tight junction proteins in normal endometrial cells and endometrial cancers and how they cause functional changes in cells.

Oral Mucosal Epithelial Cells

Cellular Phenotype and Apoptosis: The function of epithelial tissues is the protection of the organism from chemical, microbial, and physical challenges which is indispensable for viability. To fulfill this task, oral epithelial cells follow a strongly regulated scheme of differentiation that results in the formation of structural proteins that manage the integrity of epithelial tissues and operate as a barrier. Oral epithelial cells are connected by various transmembrane proteins with specialized structures and functions. Keratin filaments adhere to the plasma membrane by desmosomes building a three-dimensional matrix.

Cell-Cell Contacts and Bacterial Influence: It is known that pathogenic oral bacteria are able to affect the expression and configuration of cell-cell junctions. Human keratinocytes up-regulate immune-modulatory receptors upon stimulation with bacterial components. Periodontal pathogens including P. gingivalis are able to inhibit oral epithelial innate immune responses through various mechanisms and to escape from host immune reaction, which supports the persistence of periodontitis and furthermore is able to affect the epithelial barrier function by altering expression and distribution of cell-cell interactions including tight junctions (TJs) and adherens junctions (AJs).

In the pathogenesis of periodontitis a highly organized biofilm community shifts from symbiosis to dysbiosis which results in destructive local inflammatory reactions.

Cellular Receptors: Cell-surface located toll like receptors (TLRs) and cytoplasmatic nucleotide-binding oligomerization domain (NOD)-like receptors (NLRs) belong to the pattern recognition receptors (PRRs). PRRs recognize microbial parts that represent pathogen-associated molecular patterns (PAMPs).

A multimeric complex of proteins known as inflammasome, which is a subset of NLRs, assembles after activation and proceeds to pro-inflammatory cytokine release.

Cytokine Production and Release: Cytokines and bacterial products may lead to host cell mediated tissue destruction. Keratinocytes are able to produce diverse pro-inflammatory cytokines and chemokines, including interleukin (IL)-1, IL-6, IL-8 and tumor necrosis factor (TNF)-α. Infection by pathogenic bacteria such as Porphyromonas gingivalis (P. gingivalis) and Aggregatibacter actinomycetemcomitans (A. actinomycetemcomitans) can induce a differentiated production of these cytokines.

Immuno-modulation, Bacterial Infection, and Cancer Cells: There is a known association between bacterial infection and cancer. Bacterial components are able to up-regulate immune-modulatory receptors on cancer cells. Interactions of bacteria with tumor cells could support malignant transformation an environment with deficient immune regulation.

The aim of this review is to present a set of molecular mechanisms of oral epithelial cells and their reactions to a number of toxic influences.

LncRNAs regulating stemness in aging

One of the most outstanding observations from next-generation sequencing approaches was that only 1.5% of our genes code for proteins. The biggest part is transcribed but give rise to different families of RNAs without coding potential. The functional relevance of these abundant transcripts remains far from elucidated. Among them are the long non-coding RNAs (lncRNAs), a relatively large and heterogeneous group of RNAs shown to be highly tissue-specific, indicating a prominent role in processes controlling cellular identity. In particular, lncRNAs have been linked to both stemness properties and detrimental pathways regulating the aging process, being novel players in the intricate network guiding tissue homeostasis. Here, we summarize the up-to-date information on the role of lncRNAs that affect stemness and hence impact upon aging, highlighting the likelihood that lncRNAs may represent an unexploited reservoir of potential therapeutic targets for reprogramming applications and aging-related diseases.

Interaction of Clostridium perfringens Iota Toxin and Lipolysis-Stimulated Lipoprotein Receptor (LSR)

Iota toxin produced by Clostridium perfringens is a binary, actin ADP-ribosylating toxin that is organized into the enzymatically active component Ia and the binding component Ib. Lipolysis-stimulated lipoprotein receptor (LSR) has been identified as a cellular receptor of Ib. Here, we investigated the functional interaction between Ib and LSR, where siRNA for LSR blocked the toxin-mediated cytotoxicity and the binding of Ib. The addition of Ib to LSR-green fluorescence protein (GFP)-transfected cells at 4 °C resulted in colocalization with LSR and Ib on the cell surface. Upon transfer of the cells from 4 °C to 37 °C, LSR and Ib were internalized and observed in cytoplasmic vesicles. When the cells were incubated with Ib at 37 °C and fractionated using the Triton-insoluble membrane, Ib oligomer was localized in insoluble factions that fulfilled the criteria of lipid rafts, and LSR was clustered in lipid rafts. To examine the interaction between N-terminal extracellular region of LSR and Ib, we constructed a series of LSR N-terminal deletions. Ten amino acids residues can be deleted from this end without any reduction of Ib binding. However, deletion of 15 N-terminal residues drastically reduces its ability to bind Ib. These results demonstrate that Ib binds to the LSR N-terminal 10 to 15 residues and endocytoses into trafficking endosomes together with LSR.