ZO-1 protein is required for hydrogen peroxide to increase MDCK cell paracellular permeability in an ERK 1/2-dependent manner

Wearable electrodriven switch actively delivers macromolecular drugs to fundus in non-invasive and controllable manners

Current treatments for fundus disorders, such as intravitreal injections, pose risks, including infection and retinal detachment, and are limited in their ability to deliver macromolecular drugs across the blood‒retinal barrier. Although non-invasive methods are safer, their delivery efficiency remains suboptimal (<5%). We have developed a wearable electrodriven switch (WES) that improves the non-invasive delivery of macromolecules to the fundus. The WES system, which integrates an electrodriven drug delivery lens with a square wave generator, leverages electrical stimulation to enhance drug penetration through the sclera-choroid-retina pathway. In our study, WES achieved a delivery efficiency of 14% for immunoglobulin G, comparable to that of intravitreal injection (16%). Moreover, WES-enhanced anti-VEGF administration resulted in an 86% inhibition of choroidal neovascularization, and anti-PDL1 delivery inhibited choroidal melanoma growth more effectively than intravenous injections, with no adverse effects on ocular health. These findings suggest that WES holds transformative potential for the non-invasive treatment of chronic fundus diseases.

Na-caprate-induced increase in MDCK II epithelial cell leak pathway permeability and opening number is associated with disruption of basal F-actin organization

Confluent populations of the epithelial cell line, MDCK II, develop circumferential tight junctions joining adjacent cells to create a barrier to the paracellular movement of solutes and water. Treatment of MDCK II cell populations from the apical surface with 1 mM Na-caprate increased permeability to macromolecules (Leak Pathway) without increasing monolayer disruption or cell death. Graphical analysis of the apparent permeability versus solute Stokes radius for a size range of fluorescein-dextran species indicates apical 1 mM Na-caprate enhances Leak Pathway permeability by increasing the number of Leak Pathway openings without significantly affecting opening size. Na-caprate treatment did not alter the content of any tight junction protein examined. Treatment of MDCK II cell populations with apical 1 mM Na-caprate disrupted basal F-actin stress fibers and decreased the tortuosity of the tight junctions. Treatment of MDCK II cell populations with blebbistatin, a myosin ATPase inhibitor, alone had little effect on Leak Pathway permeability but synergistically increased Leak Pathway permeability when added with 1 mM Na-caprate. Na-caprate exhibited a similar ability to increase Leak Pathway permeability in wild-type MDCK II cell monolayers and ZO-1 knockdown MDCK II cell monolayers but an enhanced ability to increase Leak Pathway permeability in monolayers of TOCA-1 knockout MDCK II cells. These results demonstrate that Na-caprate increases MDCK II cell population Leak Pathway permeability by increasing the number of Leak Pathway openings. This action is likely mediated by alterations in F-actin organization, primarily involving disruption of basal F-actin stress fibers.NEW & NOTEWORTHY This study determines the underlying change in the openings in the epithelial tight junction permeability barrier structure that leads to a change in the paracellular permeability to macromolecules (the Leak Pathway) and connects this to disruption of specific F-actin structures within the cells. It provides important and novel insights into how tight junction permeability to macromolecules is modulated by specific changes to cellular and tight junction composition/organization.

SHED-derived exosomes ameliorate hyposalivation caused by Sjögren's syndrome via Akt/GSK-3β/Slug-mediated ZO-1 expression

BACKGROUND

Sjögren's syndrome (SS) is an autoimmune disorder characterized by sicca syndrome and/or systemic manifestations. The treatment is still challenging. This study aimed to explore the therapeutic role and mechanism of exosomes obtained from the supernatant of stem cells derived from human exfoliated deciduous teeth (SHED-exos) in sialadenitis caused by SS.

METHODS

SHED-exos were administered to the submandibular glands (SMGs) of 14-week-old non-obese diabetic (NOD) mice, an animal model of the clinical phase of SS, by local injection or intraductal infusion. The saliva flow rate was measured after pilocarpine intraperitoneal injection in 21-week-old NOD mice. Protein expression was examined by western blot analysis. Exosomal microRNA (miRNAs) were identified by microarray analysis. Paracellular permeability was evaluated by transepithelial electrical resistance measurement.

RESULTS

SHED-exos were injected into the SMG of NOD mice and increased saliva secretion. The injected SHED-exos were taken up by glandular epithelial cells, and further increased paracellular permeability mediated by zonula occluden-1 (ZO-1). A total of 180 exosomal miRNAs were identified from SHED-exos, and Kyoto Encyclopedia of Genes and Genomes analysis suggested that the phosphatidylinositol 3 kinase (PI3K)/protein kinase B (Akt) pathway might play an important role. SHED-exos treatment down-regulated phospho-Akt (p-Akt)/Akt, phospho-glycogen synthase kinase 3β (p-GSK-3β)/GSK-3β, and Slug expressions and up-regulated ZO-1 expression in SMGs and SMG-C6 cells. Both the increased ZO-1 expression and paracellular permeability induced by SHED-exos were abolished by insulin-like growth factor 1, a PI3K agonist. Slug bound to the ZO-1 promoter and suppressed its expression. For safer and more effective clinical application, SHED-exos were intraductally infused into the SMGs of NOD mice, and saliva secretion was increased and accompanied by decreased levels of p-Akt/Akt, p-GSK-3β/GSK-3β, and Slug and increased ZO-1 expression.

CONCLUSION

Local application of SHED-exos in SMGs can ameliorate Sjögren syndrome-induced hyposalivation by increasing the paracellular permeability of glandular epithelial cells through Akt/GSK-3β/Slug pathway-mediated ZO-1 expression.

Irbesartan eases lipopolysaccharide-induced lung injury In Vitro and In Vivo

Acute lung injury (ALI) is classified as a devastating pulmonary disorder contributing to significant incidence and fatality rate. Irbesartan (IRB) is an angiotensin II receptor blocker that has been proposed to protect against oleic acid-induced ALI. To this end, the current study is concentrated on ascertaining the role of IRB in ALI and figuring out the probable action mechanism. First, cell counting kit-8 (CCK-8) appraised the viability of human pulmonary microvascular endothelial cells (HPMVECs) exposed to ascending concentrations of IRB. HPMVEC injury model and a mouse model of ALI induced by lipopolysaccharide (LPS) were pretreated by IRB. In vitro, cell viability was estimated by CCK-8 assay, and lactate dehydrogenase (LDH) release was tested by LDH assay kit. Enzyme-linked immunosorbent assay (ELISA) and Western blotting estimated the expression levels of inflammatory factors. Fluorescein isothiocyanate-dextran was used to assess HPMVEC permeability. Western blotting examined the expression of adherent and tight junction proteins. In vivo, hematoxylin and eosin staining evaluated lung tissue damage and lung wet/dry (W/D) weight was measured. ELISA analyzed the levels of inflammatory factors in the serum and bronchoalveolar lavage fluid (BALF), and Western blotting examined the expression of inflammatory factors. The total cell, neutrophil, and macrophage numbers in BALF were determined using a cell counter. Lung capillary permeability was assayed by Evans blue albumin and total protein concentration in BALF was measured using bicinchoninic acid method. Immunofluorescence assay and Western blotting examined the expression of adherent and tight junction proteins in lung tissues. It was observed that IRB dose-dependently enhanced the viability while reduced LDH release, inflammatory response as well as permeability in LPS-challenged HPMVECs in vitro. In addition, LPS-stimulated lung tissue damage, pulmonary edema, inflammatory response as well as lung capillary permeability in vivo were all reversed following IRB treatment. Collectively, IRB treatment might elicit protective behaviors against LPS-triggered ALI.

NMDARs antagonist MK801 suppresses LPS-induced apoptosis and mitochondrial dysfunction by regulating subunits of NMDARs via the CaM/CaMKII/ERK pathway

Lipopolysaccharide (LPS) displays a robust immunostimulatory ability upon Toll-like receptor 4 (TLR4) recognition. N-methyl-D-aspartate receptors (NMDARs) are highly compartmentalized in most cells and implicated in various inflammatory disorders. However, the relationship between TLR4 and NMDARs has not been explored deeply. This study aimed to examine the role of NMDARs and its specific inhibitor MK801 in LPS-treated endothelial cell dysfunction and the related mechanism in vivo and in vitro. The results showed that pre-treatment with MK801 significantly decreased LPS-induced cell death, cellular Ca²⁺, cellular reactive oxygen species, and glutamate efflux. Moreover, MK801 restrained LPS-induced mitochondrial dysfunction by regulating mitochondrial membrane potential and mitochondrial Ca²⁺ uptake. The oxygen consumption, basal and maximal respiration rate, and ATP production in LPS-treated HUVECs were reversed by MK801 via regulating ATP synthesis-related protein SDHB2, MTCO1, and ATP5A. The molecular pathway involved in MK801-regulated LPS injury was mediated by phosphorylation of CaMKII and ERK and the expression of MCU, MCUR1, and TLR4. LPS-decreased permeability in HUVECs was improved by MK801 via the Erk/ZO-1/occluding/Cx43 axis. Co-immunoprecipitation assay and western blotting showed three subtypes of NMDARs, NMDAζ1, NMDAε2, and NMDAε4 were bound explicitly to TLR4, suppressed by LPS, and promoted by MK801. Deficiency of NMDAζ1, NMDAε2, or NMDAε4 induced cell apoptosis, Ca²⁺ uptake, ROS production, and decreased basal and maximal respiration rate, and ATP production, suggesting that NMDARs integrity is vital for cell and mitochondrial function. In vivo investigation showed MK801 improved impairment of vascular permeability, especially in the lung and mesentery in LPS-injured mice. Our study displayed a novel mechanism and utilization of MK801 in LPS-induced ECs injury and permeability.

Simple graphical approach to investigate differences in transepithelial paracellular leak pathway permeability

Although many studies have reported differences in epithelial paracellular Leak Pathway permeability following genetic manipulations and treatment with various agents, the basis for these differences remains mostly unclear. Two primary mechanisms which could underlie differences in Leak Pathway permeability are differences in the density of Leak Pathway openings and differences in the opening size. Using a computational approach, we demonstrate that these two possibilities can be readily distinguished graphically by comparing the apparent paracellular permeabilities of a size panel of solutes measured across different cell layers. Using this approach, we demonstrated that depletion of ZO-1 protein in MDCK Type II renal epithelial cells decreased Leak Pathway opening size and increased opening density. Depletion of ZO-2 protein either had no effect or minimally decreased opening size and did not markedly change opening density. Comparison of MDCK Type II cells with MDCK Type I cells revealed that Type I cells exhibited a substantially smaller Leak Pathway permeability than did Type II cells. This lower permeability was due to a decrease in opening density with little or no change in opening size. These results demonstrate the utility of this approach to provide insights into the basis for observed differences in epithelial Leak Pathway permeability. This approach has wide applications including analysis of the molecular basis for Leak Pathway permeability, the effects of specific manipulations on Leak Pathway permeability properties, and the effects of permeation enhancers on Leak Pathway permeability properties.

Inactivation of the Wnt/β-catenin signaling contributes to the epithelial barrier dysfunction induced by sodium oxalate in canine renal epithelial cells

High oxalate consumption has been recognized as a risk factor for renal calcium oxalate stones in companion animals (dogs and cats). However, the cellular signaling involved in oxalate-induced dysfunction in renal tubular epithelial cells remains not fully elucidated. In this study, Mardin-Darby canine kidney (MDCK) cells, an epithelial cell line derived from canine kidney tubule, were tested for cell proliferation activity and barrier function after being exposed to sodium oxalate (NaOx). Further, the involvement of Wnt/β-catenin in NaOx-induced renal epithelial barrier dysfunction was evaluated. MDCK cells treated with NaOx exhibited reduction in cell proliferation and migration. Besides, NaOx exposure led to a decrease in transepithelial electrical resistance and an increase in paracellular permeability. The deleterious effects of NaOx on epithelial barrier function were related to the suppressed abundance of tight junction proteins including zonula occludens, occludin, and claudin-1. Of note, protein levels of β-catenin and phosphorylated (p)-β-catenin (Ser552) in MDCK cells were repressed by NaOx, indicating inhibitory effects on Wnt/β-catenin signaling. An inhibition of glycogen synthase kinase-3β (GSK-3β) by SB216763 enhanced the abundance of β-catenin and p-β-catenin (Ser552), and protected against epithelial barrier dysfunction in NaOx-treated MDCK cells. The results revealed a critical role of Wnt/β-catenin signaling in the epithelial barrier function of MDCK cells. Activation of Wnt/β-catenin signaling might be a potential therapeutic target for the treatment of oxalate-linked renal stones.

The Epithelial Cell Leak Pathway

The epithelial cell tight junction structure is the site of the transepithelial movement of solutes and water between epithelial cells (paracellular permeability). Paracellular permeability can be divided into two distinct pathways, the Pore Pathway mediating the movement of small ions and solutes and the Leak Pathway mediating the movement of large solutes. Claudin proteins form the basic paracellular permeability barrier and mediate the movement of small ions and solutes via the Pore Pathway. The Leak Pathway remains less understood. Several proteins have been implicated in mediating the Leak Pathway, including occludin, ZO proteins, tricellulin, and actin filaments, but the proteins comprising the Leak Pathway remain unresolved. Many aspects of the Leak Pathway, such as its molecular mechanism, its properties, and its regulation, remain controversial. In this review, we provide a historical background to the evolution of the Leak Pathway concept from the initial examinations of paracellular permeability. We then discuss current information about the properties of the Leak Pathway and present current theories for the Leak Pathway. Finally, we discuss some recent research suggesting a possible molecular basis for the Leak Pathway.

Mixtures of natural antimicrobials can reduce Campylobacter jejuni, Salmonella enterica and Clostridium perfringens infections and cellular inflammatory response in MDCK cells

Background

The classification of natural antimicrobials as potential antibiotic replacements is still hampered by the absence of clear biological mechanisms behind their mode of action. This study investigated the mechanisms underlying the anti-bacterial effect of a mixture of natural antimicrobials (maltodextrin, citric acid, sodium citrate, malic acid, citrus extract and olive extract) against Campylobacter jejuni RC039, Salmonella enterica SE 10/72 and Clostridium perfringens ATCC® 13124 invasion of Madin–Darby Canine Kidney cells (MDCK).

Results

Minimum sub-inhibitory concentrations were determined for Campylobacter jejuni (0.25%), Salmonella enterica (0.50%) and Clostridium perfringens (0.50%) required for the in vitro infection assays with MDCK cells. The antimicrobial mixture significantly reduced the virulence of all three pathogens towards MDCK cells and restored the integrity of cellular tight junctions through increased transepithelial resistance (TEER) and higher expression levels of ZO-1 (zonula occludens 1) and occludin. This study also identified the ERK (external regulated kinase) signalling pathway as a key mechanism in blocking the pro-inflammatory cytokine production (IL-1β, IL-6, IL-8, TNF-α) in infected cells. The reduction in hydrogen peroxide (H₂O₂) production and release by infected MDCK cells, in the presence of the antimicrobial mixture, was also associated with less tetrathionate formed by oxidation of thiosulphate (p < 0.0001).

Conclusion

The present study describes for the first time that mixtures of natural antimicrobials can prevent the formation of substrates used by bacterial pathogens to grow and survive in anaerobic environments (e.g. tetrathionate). Moreover, we provide further insights into pathogen invasion mechanisms through restoration of cellular structures and describe their ability to block the ERK–MAPK kinase pathway responsible for inflammatory cytokine release

Anthocyanins protect the gastrointestinal tract from high fat diet-induced alterations in redox signaling, barrier integrity and dysbiosis

The gastrointestinal (GI) tract can play a critical role in the development of pathologies associated with overeating, overweight and obesity. We previously observed that supplementation with anthocyanins (AC) (particularly glycosides of cyanidin and delphinidin) mitigated high fat diet (HFD)-induced development of obesity, dyslipidemia, insulin resistance and steatosis in C57BL/6J mice. This paper investigated whether these beneficial effects could be related to AC capacity to sustain intestinal monolayer integrity, prevent endotoxemia, and HFD-associated dysbiosis. The involvement of redox-related mechanisms were further investigated in Caco-2 cell monolayers. Consumption of a HFD for 14 weeks caused intestinal permeabilization and endotoxemia, which were associated with a decreased ileum expression of tight junction (TJ) proteins (occludin, ZO-1 and claudin-1), increased expression of NADPH oxidase (NOX1 and NOX4) and NOS2 and oxidative stress, and activation of redox sensitive signals (NF-κB and ERK1/2) that regulate TJ dynamics. AC supplementation mitigated all these events and increased GLP-2 levels, the intestinal hormone that upregulates TJ protein expression. AC also prevented, in vitro, tumor necrosis factor alpha-induced Caco-2 monolayer permeabilization, NOX1/4 upregulation, oxidative stress, and NF-κB and ERK activation. HFD-induced obesity in mice caused dysbiosis and affected the levels and secretion of MUC2, a mucin that participates in intestinal cell barrier protection and immune response. AC supplementation restored microbiota composition and MUC2 levels and distribution in HFD-fed mice. Thus, AC, particularly delphinidin and cyanidin, can preserve GI physiology in HFD-induced obesity in part through redox-regulated mechanisms. This can in part explain AC capacity to mitigate pathologies, i.e. insulin resistance and steatosis, associated with HFD-associated obesity.

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Anthocyanidins (AC) mitigate high fat diet (HFD)-induced intestinal permeabilization and endotoxemia.

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AC inhibit HFD-induced ileum NADPH oxidase upregulation and oxidative stress.

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AC inhibit the activation of redox sensitive signals that cause intestinal permeabilization.

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AC mitigate HFD-induced dysbiosis and improve ileum endocrine/immunological responses.

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AC's beneficial systemic effects in HFD-mice could begin at the GI tract.

Occludin knockdown is not sufficient to induce transepithelial macromolecule passage

Occludin, a tight junction protein, has been reported to regulate barrier function - particularly the leak pathway for larger solutes - in epithelia. Therefore, we aimed to precisely define its role in macromolecule passage at single cell-cell junctions. A combination of varying occludin expression by transient and stable knockdown including systematic seeding strategies was employed to achieve a broad and defined pattern of variance in occludin expression over epithelia. This variance model enabled us to examine occludin function in the leak pathway using global and local analysis, i.e. to analyze macromolecule flux across epithelia and macromolecule passage at single-cell level. Macromolecular flux was found not to correlate with occludin expression in intestinal epithelial cells. In fact, by spatially resolving macromolecular permeation sites using a recently developed method we uncovered leaky cell junctions at the edge of Transwells resulting in increased passage. This demonstrates that rare leaks can determine net flux of macromolecules across epithelia while the vast majority of cellular junctions do not contribute significantly. Hence, concomitant local analysis of macromolecule passage across epithelial barriers is indispensable for interpretation of global flux data. By combining this new approach with cell culture models of the leak pathway, we can present evidence that lack of occludin is not sufficient to stimulate the epithelial leak pathway.