Molecular basis of the core structure of tight junctions

Breaking the fortress: a mechanistic review of meningitis-causing bacteria breaching tactics in blood brain barrier

The blood-brain barrier is a physiological protective barrier around blood vessels in the brain. It prevents most bacteria and harmful substances from entering the brain through the blood. However, when bacterial meningitis occurs, bacteria enter the brain either from the circulation or by direct invasion from neighbouring structures, causing an inflammatory response that in severe cases may lead to death. High morbidity and mortality are prominent features of the disease. Many pathogenic bacteria can break through the blood-brain barrier and cause meningitis, such as Streptococcus pneumoniae, Group B Streptococcus, Streptococcus suis, Neisseria meningitidis, meningitis-associated Escherichia coli, etc. This article reviews the mechanisms by which these bacteria cross the blood-brain barrier when causing meningitis and the interactions between bacteria and host cells to help pathogens invade the brain. Clarifying the mechanism by which pathogens cross the blood-brain barrier can provide new ideas for developing effective treatments for bacterial meningitis.

The Blood-Brain Barrier: Composition, Properties, and Roles in Brain Health

Blood vessels are critical to deliver oxygen and nutrients to tissues and organs throughout the body. The blood vessels that vascularize the central nervous system (CNS) possess unique properties, termed the blood-brain barrier (BBB), which allow these vessels to tightly regulate the movement of ions, molecules, and cells between the blood and the brain. This precise control of CNS homeostasis allows for proper neuronal function and protects the neural tissue from toxins and pathogens, and alterations of this barrier are important components of the pathogenesis and progression of various neurological diseases. The physiological barrier is coordinated by a series of physical, transport, and metabolic properties possessed by the brain endothelial cells (ECs) that form the walls of the blood vessels. These properties are regulated by interactions between different vascular, perivascular, immune, and neural cells. Understanding how these cell populations interact to regulate barrier properties is essential for understanding how the brain functions in both health and disease contexts.

Caco2/HT-29 In Vitro Cell Co-Culture: Barrier Integrity, Permeability, and Tight Junctions' Composition During Progressive Passages of Parental Cells

Epithelial linings are crucial for the maintenance of physiological barriers. The intestinal epithelial barrier (IEB) consists of enterocytes through tight junctions and mucus-secreting cells and can undergo physiological modifications throughout life. To reproduce as closely as possible the IEB main features over time, in vitro co-cultures of Caco2/HT-29 70/30 formed by parental Caco2 and HT-29 cells sub-cultivated for more than 40 passages were set up. The measurements of the transepithelial electrical resistance (TEER) identified two populations: physiological TEER co-cultures (PC) with values > 50 Ωcm2 formed by parental cells with fewer than 40 passages, and leaky TEER co-cultures (LC) with values < 50 Ωcm2 formed by parental cells with more than 40 passages. In LC, paracellular permeability increased in parallel. By immunofluorescence and Western blot analysis, an increase in claudin 2 was observed in LC vs. PC, with no differences in occludin expression. MUC-2 immunoreactivity was stronger in PC than in LC. LC also showed an enhanced vulnerability to TNFα+IFN-γ. These results reproduce the main morpho-functional modifications reported in the human leaky/aged gut and support the usefulness of our in vitro cell model for studying the molecular processes underlying these modifications and testing drug/nutraceutical treatments to ameliorate leaky gut aging.

Advances in intestinal epithelium and gut microbiota interaction

The intestinal epithelium represents a critical interface between the host and external environment, serving as the second largest surface area in the human body after the lungs. This dynamic barrier is sustained by specialized epithelial cell types and their complex interactions with the gut microbiota. This review comprehensively examines the recent advances in understanding the bidirectional communication between intestinal epithelial cells and the microbiome. We briefly highlight the role of various intestinal epithelial cell types, such as Paneth cells, goblet cells, and enteroendocrine cells, in maintaining intestinal homeostasis and barrier function. Gut microbiota-derived metabolites, particularly short-chain fatty acids and bile acids, influence epithelial cell function and intestinal barrier integrity. Additionally, we highlight emerging evidence of the sophisticated cooperation between different epithelial cell types, with special emphasis on the interaction between tuft cells and Paneth cells in maintaining microbial balance. Understanding these complex interactions has important implications for developing targeted therapeutic strategies for various gastrointestinal disorders, including inflammatory bowel disease, metabolic disorders, and colorectal cancer.

Intestinal Permeability in Disorders of Gut-Brain Interaction: From Bench to Bedside

Intestinal barrier function lies at a critical interface of a range of peripheral and central processes that influence disorders of gut-brain interactions (DGBI). Although rigorously tested, the role of barrier dysfunction in driving clinical phenotype of DGBI remains to be fully elucidated. In vitro, in vivo, and ex vivo strategies can test various aspects of the broader permeability and barrier mechanisms in the gut. Luminal mediators of host, bacterial, and dietary origin can influence the barrier function and a disrupted barrier can also influence the luminal milieu. Critical to our understanding is how barrier dysfunction is influenced by stress and other comorbidities that associate with DGBI and the crosstalk between barrier and neural, hormonal, and immune responses. Additionally, the microbiome's significant role in the communication between the brain and gut has led to the integrative model of a microbiome gut-brain axis with reciprocal interactions between brain networks and networks composed of multiple cells in the gut, including immune cells, enterochromaffin cells, gut microbiota and the derived luminal mediators. This review highlights the techniques for assessment of barrier function, appraises evidence for barrier dysfunction in DGBI including mechanistic studies in humans, as well as provides an overview of therapeutic strategies that can be used to directly or indirectly restore barrier function in DGBI patients.

The impact of diabetes on tight junctions in cardiomyopathy dysfunction

Diabetic cardiomyopathy is a condition characterized by ventricular dysfunction in diabetic patients that is not caused by other cardiac ailments. It is associated with factors such as left ventricular hypertrophy, metabolic disturbances, and oxidative stress. Tight junctions, which form a barrier between cells, play a role in the vascular complications of diabetes. Proteins such as claudins and occludens are important for the structure and function of tight junctions. Zona occludens (ZO) proteins are also involved in tight junctions and their expression may be affected by diabetes. The review discusses the impact of diabetes on the tight junctions and the role of ZO proteins in diabetic cardiovascular dysfunction.

Single-nucleus RNA-seq dissection of choroid plexus tumor cell heterogeneity

The genomic, genetic and cellular events regulating the onset, growth and survival of rare, choroid plexus neoplasms remain poorly understood. Here, we examine the heterogeneity of human choroid plexus tumors by single-nucleus transcriptome analysis of 23,906 cells from four disease-free choroid plexus and eleven choroid plexus tumors. The resulting expression atlas profiles cellular and transcriptional diversity, copy number alterations, and cell-cell interaction networks in normal and cancerous choroid plexus. In choroid plexus tumor epithelial cells, we observe transcriptional changes that correlate with genome-wide methylation profiles. We further characterize tumor type-specific stromal microenvironments that include altered macrophage and mesenchymal cell states, as well as changes in extracellular matrix components. This first single-cell dataset resource from such scarce samples should be valuable for divising therapies against these little-studied neoplasms.

Feedback delivery of BMP 7 on the pathological oxidative stress via smart hyaluronic acid hydrogel potentiated the repairing of the gut epithelial integrity

The intestinal barrier integrity was substantially collapsed when colitis flaring up, accompanying by the hallmark of pathological oxidative stress. Bone morphogenetic protein 7 (BMP 7), an endogenous growth factor in gut had the potential to repair the damaged mucosa. Herein, a smart hydrogel (HDP) had been developed by the boronate-ester crosslinked hyaluronic acid to deliver BMP 7. Hydrogel loading BMP 7 (HDP-BMP 7) presented the comparable mechanical strength with that of the naïve gut mucus. HDP-BMP 7 as artificial mucus could specifically adhere to the inflamed colonic mucosa of colitis mice. Importantly, it could apperceive reactive oxygen species at diseased colon to adapt its intrinsic network, enabling the feedback release of BMP 7 on the pathological oxidative stress. Moreover, in vivo animal experiments showed that the disease symptoms of colitis mice were alleviated by HDP-BMP 7. Importantly, both the mucus barrier and the epithelial barriers were obviously recovered by HDP-BMP 7 treatment, which substantially attenuated the immune-inflammation response of colitis mice. Besides, HDP-BMP 7 enriched the diversity of gut flora, increasing the relative abundance of Lactobacillus and decreasing the ratio of Firmicutes/Bacteroidetes. Its therapeutic mechanism was associated with activating TGF-β/Smad signals. Conclusively, this smart hydrogel might potentiate the repairing effect of growth factors on the gut epithelial integrity.

Analysis of the Preventive Effect of Lonicera caerulea Pomace and Its Isolated Components on Colitis in Mice Based on Gut Microbiota and Serum Metabolomics

Inflammatory bowel disease (IBD), including relapsing-remitting ulcerative colitis and Crohn's disease, is a non-specific chronic intestinal inflammatory disease. Lonicera caerulea, which is rich in polyphenolic compounds, has been shown to exert antioxidative and anti-inflammatory effects. The research evaluates the dietary impacts of Lonicera caerulea pomace, its polyphenol-rich extract, and fiber-rich residue on colitis symptoms. Colitis was induced with 2.5% DSS (dextran sulfate sodium) aqueous solution after continuous feeding of customized Lonicera caerulea feed for 2.5 weeks. The results indicate that the intake of the polyphenol-rich extract has an effect in preventing colitis in mice, but the effect is less than that by the pomace itself, and the fiber residue alone does not prevent the condition when ingested. The pomace and polyphenol-rich extract have a positive regulatory effect on the gut microbiota of mice with colitis, and the intake of Lonicera caerulea pomace significantly restores 15 metabolites in mice with colitis, significantly improving five metabolic pathways, including steroid biosynthesis, with the regulation of metabolites and metabolic pathways being significantly correlated with the gut microbiota.

Role of the transcription factor NRF2 in maintaining the integrity of the Blood-Brain Barrier

BACKGROUND

The Blood-Brain Barrier (BBB) is a complex and dynamic interface that regulates the exchange of molecules and cells between the blood and the central nervous system. It undergoes structural and functional throughout oxidative stress and inflammation, which may compromise its integrity and contribute to the pathogenesis of neurodegenerative diseases.

MAIN BODY

Maintaining BBB integrity is of utmost importance in preventing a wide range of neurological disorders. NRF2 is the main transcription factor that regulates cellular redox balance and inflammation-related gene expression. It has also demonstrated a potential role in regulating tight junction integrity and contributing to the inhibition of ECM remodeling, by reducing the expression of several metalloprotease family members involved in maintaining BBB function. Overall, we review current insights on the role of NRF2 in addressing protection against the effects of BBB dysfunction, discuss its involvement in BBB maintenance in different neuropathological diseases, as well as, some of its potential activators that have been used in vitro and in vivo animal models for preventing barrier dysfunction.

CONCLUSIONS

Thus, emerging evidence suggests that upregulation of NRF2 and its target genes could suppress oxidative stress, and neuroinflammation, restore BBB integrity, and increase its protection.

Deciphering the mechanistic impact of acupuncture on the neurovascular unit in acute ischemic stroke: Insights from basic research in a narrative review

Ischemic stroke(IS), a severe acute cerebrovascular disease, not only imposes a heavy economic burden on society but also presents numerous challenges in treatment. During the acute phase, while thrombolysis and thrombectomy serve as primary treatments, these approaches are restricted by a narrow therapeutic window. During rehabilitation, commonly used neuroprotective agents struggle with their low drug delivery efficiency and inadequate preclinical testing, and the long-term pharmacological and toxicity effects of nanomedicines remain undefined. Meanwhile, acupuncture as a therapeutic approach is widely acknowledged for its effectiveness in treating IS and has been recommended by the World Health Organization (WHO) as an alternative and complementary therapy, even though its exact mechanisms remain unclear. This review aims to summarize the known mechanisms of acupuncture and electroacupuncture (EA) in the treatment of IS. Research shows that acupuncture treatment mainly protects the neurovascular unit through five mechanisms: 1) reducing neuronal apoptosis and promoting neuronal repair and proliferation; 2) maintaining the integrity of the blood-brain barrier (BBB); 3) inhibiting the overactivation and polarization imbalance of microglia; 4) regulating the movement of vascular smooth muscle (VSM) cells; 5) promoting the proliferation of oligodendrocyte precursors. Through an in-depth analysis, this review reveals the multi-level, multi-dimensional impact of acupuncture treatment on the neurovascular unit (NVU) following IS, providing stronger evidence and a theoretical basis for its clinical application.

Omega-3 Polyunsaturated Fatty Acids and Blood-Brain Barrier Integrity in Major Depressive Disorder: Restoring Balance for Neuroinflammation and Neuroprotection

Major depressive disorder (MDD), affecting over 264 million individuals globally, is associated with immune system dysregulation and chronic neuroinflammation, potentially linked to neurodegenerative processes. This review examines blood-brain barrier (BBB) dysfunction in MDD, focusing on key regulators like matrix metalloproteinase 9 (MMP9), aquaporin-4 (AQP4), and ATP-binding cassette subfamily B member 1 (ABCB1). We explore potential mechanisms by which compromised BBB integrity in MDD may contribute to neuroinflammation and discuss the therapeutic potential of omega-3 polyunsaturated fatty acids (n-3 PUFAs). n-3 PUFAs have demonstrated anti-inflammatory and neuroprotective effects, and potential ability to modulate MMP9, AQP4, and ABCB1, thereby restoring BBB integrity in MDD. This review aims to elucidate these potential mechanisms and evaluate the evidence for n-3 PUFAs as a strategy to mitigate BBB dysfunction and neuroinflammation in MDD.

The functional antagonist of sphingosine-1-phosphate, FTY720, impairs gut barrier function

FTY720 or fingolimod is a known functional antagonist of sphingosine-1-phosphate (S1P), and it is effective in treating multiple sclerosis and preventing inflammatory bowel disease (IBD). Evidence shows that its use in mice can increase the susceptibility to mucosal infections. Despite the significant contribution of S1P to barrier function, the effect of the administration of FTY720 on the mucosal barrier has never been investigated. In this study, we looked into how FTY720 therapy affected the function of the gut barrier susceptibility. Administration of FTY720 to C57BL/6 mice enhances the claudin-2 expression and reduces the expression of claudin-4 and occludin, as studied by qPCR, Western blot, and immunofluorescence. FTY720 inhibits the Akt-mTOR pathway to decrease occludin and claudin-4 expression and increase claudin-2 expression. FTY720 treatment induced increased colonic inflammation, with notably greater immune cell infiltration, colon histopathology, and increased production of TNF-α, IFN-γ, CXCL-1, and CXCL-2 than that in control mice. Taking into account the close association of "the leaky gut" and gut dysbiosis among the major diseases, we therefore can infer that the vigilance of gut pathology should be maintained, where FTY720 is used as a treatment option.

Oral alginate microspheres for the efficient site-specific delivery of epidermal growth factor attenuated murine ulcerative colitis via repairing the mucosal barrier

Ulcerative colitis (UC) is a chronic bowel inflammatory disease affecting the colorectum. Epidermal growth factor (EGF) has been demonstrated to be effective to counteract UC. However, there exists the gastrointestinal challenges such as stomach acid, enzyme and bile salts for oral delivery of EGF. Herein, calcium alginate microsphere was prepared by the microfluidic technique to encapsulate EGF. The morphology of EGF-loaded microsphere (MS-EGF) was spherical and its average particle size was 80 ± 23 μm. The encapsulation efficiency of EGF was reaching to 93.8 % ± 1.6 %. In vitro release experiments showed that MS-EGF presented the good pH-sensitive properties, that was, it could effectively resist the gastric acid and small intestinal fluids, and undergone the rapid dissolution in the artificial colon fluid. In vitro cellular experiments demonstrated that the bioactivity of EGF was well preserved by microsphere. Moreover, in vivo murine colitis model showed that MS-EGF presented the obvious colitis alleviation. Furthermore, the colonic morphology of colitis mice was effectively recovered and the tight junction between the gut epithelium was obviously repaired. In conclusion, calcium alginate microsphere might be a promising vehicle of EGF for UC treatment.

The microbiota: a crucial mediator in gut homeostasis and colonization resistance

The gut microbiota is a complex and diverse community of microorganisms that colonizes the human gastrointestinal tract and influences various aspects of human health. These microbes are closely related to enteric infections. As a foreign entity for the host, commensal microbiota is restricted and regulated by the barrier and immune system in the gut and contributes to gut homeostasis. Commensals also effectively resist the colonization of pathogens and the overgrowth of indigenous pathobionts by utilizing a variety of mechanisms, while pathogens have developed strategies to subvert colonization resistance. Dysbiosis of the microbial community can lead to enteric infections. The microbiota acts as a pivotal mediator in establishing a harmonious mutualistic symbiosis with the host and shielding the host against pathogens. This review aims to provide a comprehensive overview of the mechanisms underlying host-microbiome and microbiome-pathogen interactions, highlighting the multi-faceted roles of the gut microbiota in preventing enteric infections. We also discuss the applications of manipulating the microbiota to treat infectious diseases in the gut.

Membrane prewetting by condensates promotes tight-junction belt formation

Biomolecular condensates enable cell compartmentalization by acting as membraneless organelles1. How cells control the interactions of condensates with other cellular structures such as membranes to drive morphological transitions remains poorly understood. We discovered that formation of a tight-junction belt, which is essential for sealing epithelial tissues, is driven by a wetting phenomenon that promotes the growth of a condensed ZO-1 layer2 around the apical membrane interface. Using temporal proximity proteomics in combination with imaging and thermodynamic theory, we found that the polarity protein PATJ mediates a transition of ZO-1 into a condensed surface layer that elongates around the apical interface. In line with the experimental observations, our theory of condensate growth shows that the speed of elongation depends on the binding affinity of ZO-1 to the apical interface and is constant. Here, using PATJ mutations, we show that ZO-1 interface binding is necessary and sufficient for tight-junction belt formation. Our results demonstrate how cells exploit the collective biophysical properties of protein condensates at membrane interfaces to shape mesoscale structures.

Reversible opening of the blood-labyrinth barrier by low-pressure pulsed ultrasound and microbubbles for the treatment of inner ear diseases

Systemic drug administration provides convenience and non-invasive benefits for preventing and treating inner ear diseases. However, the blood-labyrinth barrier (BLB) restricts the transport of drugs to inner ear tissues. Ultrasound can stimulate specific areas and penetrate tissues, with the potential to overcome physiological barriers. We present a novel strategy based on low-pressure pulsed ultrasound assisted by microbubbles (USMB) to transiently open the BLB and deliver therapeutics into the inner ear. A pulsed ultrasound device with adjustable pressure was established; the generated ultrasound was transmitted through the external auditory canal into the guinea pig's inner ear. We observed that the application of microbubbles allowed the use of safe and efficient ultrasound conditions to penetrate the BLB. We found that USMB-mediated BLB opening seemed to be associated with a reduced expression of the tight junction proteins zonula occludens-1 and occludin. Following intravenous administration, hydrophilic dexamethasone sodium phosphate (DSP), hydrophobic curcumin (CUR), as well as drug-loaded nanoparticles (Fe3O4@CUR NPs) could be efficiently delivered into the inner ear. We observed better drug accumulation in the perilymph of the inner ear, resulting in less drug (cisplatin)-induced ototoxicity. Furthermore, physiological, hematological, and histological studies showed that the modulation of the BLB by low-pressure USMB was a safe process without significant adverse effects. We conclude that USMB could become a promising strategy for the systematic delivery of therapeutics in the treatment of inner ear diseases.

A novel histone deacetylase inhibitor W2A-16 improves the barrier integrity in brain vascular endothelial cells

The maturation of brain microvascular endothelial cells leads to the formation of a tightly sealed monolayer, known as the blood-brain barrier (BBB). The BBB damage is associated with the pathogenesis of age-related neurodegenerative diseases including vascular cognitive impairment and Alzheimer's disease. Growing knowledge in the field of epigenetics can enhance the understanding of molecular profile of the BBB and has great potential for the development of novel therapeutic strategies or targets to repair a disrupted BBB. Histone deacetylases (HDACs) inhibitors are epigenetic regulators that can induce acetylation of histones and induce open chromatin conformation, promoting gene expression by enhancing the binding of DNA with transcription factors. We investigated how HDAC inhibition influences the barrier integrity using immortalized human endothelial cells (HCMEC/D3) and the human induced pluripotent stem cell (iPSC)-derived brain vascular endothelial cells. The endothelial cells were treated with or without a novel compound named W2A-16. W2A-16 not only activates Wnt/β-catenin signaling but also functions as a class I HDAC inhibitor. We demonstrated that the administration with W2A-16 sustained barrier properties of the monolayer of endothelial cells, as evidenced by increased trans-endothelial electrical resistance (TEER). The BBB-related genes and protein expression were also increased compared with non-treated controls. Analysis of transcript profiles through RNA-sequencing in hCMEC/D3 cells indicated that W2A-16 potentially enhances BBB integrity by influencing genes associated with the regulation of the extracellular microenvironment. These findings collectively propose that the HDAC inhibition by W2A-16 plays a facilitating role in the formation of the BBB. Pharmacological approaches to inhibit HDAC may be a potential therapeutic strategy to boost and/or restore BBB integrity.

Microvascular destabilization and intricated network of the cytokines in diabetic retinopathy: from the perspective of cellular and molecular components

Microvascular destabilization is the primary cause of the inner blood-retinal barrier (iBRB) breakdown and increased vascular leakage in diabetic retinopathy (DR). Microvascular destabilization results from the combinational effects of increased levels of growth factors and cytokines, involvement of inflammation, and the changed cell-to-cell interactions, especially the loss of endothelial cells and pericytes, due to hyperglycemia and hypoxia. As the manifestation of microvascular destabilization, the fluid transports via paracellular and transcellular routes increase due to the disruption of endothelial intercellular junctional complexes and/or the altered caveolar transcellular transport across the retinal vascular endothelium. With diabetes progression, the functional and the structural changes of the iBRB components, including the cellular and noncellular components, further facilitate and aggravate microvascular destabilization, resulting in macular edema, the neuroretinal damage and the dysfunction of retinal inner neurovascular unit (iNVU). Although there have been considerable recent advances towards a better understanding of the complex cellular and molecular network underlying the microvascular destabilization, some still remain to be fully elucidated. Recent data indicate that targeting the intricate signaling pathways may allow to against the microvascular destabilization. Therefore, efforts have been made to better clarify the cellular and molecular mechanisms that are involved in the microvascular destabilization in DR. In this review, we discuss: (1) the brief introduction of DR and microvascular destabilization; (2) the cellular and molecular components of iBRB and iNVU, and the breakdown of iBRB; (3) the matrix and cell-to-cell contacts to maintain microvascular stabilization, including the endothelial glycocalyx, basement membrane, and various cell-cell interactions; (4) the molecular mechanisms mediated cell-cell contacts and vascular cell death; (5) the altered cytokines and signaling pathways as well as the intricate network of the cytokines involved in microvascular destabilization. This comprehensive review aimed to provide the insights for microvascular destabilization by targeting the key molecules or specific iBRB cells, thus restoring the function and structure of iBRB and iNVU, to treat DR.

Blood-brain barrier disruption in dementia: Nano-solutions as new treatment options

Candidate drugs targeting the central nervous system (CNS) demonstrate extremely low clinical success rates, with more than 98% of potential treatments being discontinued due to poor blood-brain barrier (BBB) permeability. Neurological conditions were shown to be the second leading cause of death globally in 2016, with the number of people currently affected by neurological disorders increasing rapidly. This increasing trend, along with an inability to develop BBB permeating drugs, is presenting a major hurdle in the treatment of CNS-related disorders, like dementia. To overcome this, it is necessary to understand the structure and function of the BBB, including the transport of molecules across its interface in both healthy and pathological conditions. The use of CNS drug carriers is rapidly gaining popularity in CNS research due to their ability to target BBB transport systems. Further research and development of drug delivery vehicles could provide essential information that can be used to develop novel treatments for neurological conditions. This review discusses the BBB and its transport systems and evaluates the potential of using nanoparticle-based delivery systems as drug carriers for CNS disease with a focus on dementia.

Regulation of Epithelial and Endothelial Barriers by Molecular Chaperones

The integrity and permeability of epithelial and endothelial barriers depend on the formation of tight junctions, adherens junctions, and a junction-associated cytoskeleton. The establishment of this junction-cytoskeletal module relies on the correct folding and oligomerization of its protein components. Molecular chaperones are known regulators of protein folding and complex formation in different cellular compartments. Mammalian cells possess an elaborate chaperone network consisting of several hundred chaperones and co-chaperones. Only a small part of this network has been linked, however, to the regulation of intercellular adhesions, and the systematic analysis of chaperone functions at epithelial and endothelial barriers is lacking. This review describes the functions and mechanisms of the chaperone-assisted regulation of intercellular junctions. The major focus of this review is on heat shock protein chaperones, their co-chaperones, and chaperonins since these molecules are the focus of the majority of the articles published on the chaperone-mediated control of tissue barriers. This review discusses the roles of chaperones in the regulation of the steady-state integrity of epithelial and vascular barriers as well as the disruption of these barriers by pathogenic factors and extracellular stressors. Since cytoskeletal coupling is essential for junctional integrity and remodeling, chaperone-assisted assembly of the actomyosin cytoskeleton is also discussed.

Fermentation enhances the amelioration effect of bee pollen on Caco-2 monolayer epithelial barrier dysfunction based on NF-κB-mediated MLCK-MLC signaling pathway

Intestinal barrier integrity is essential for normal nutrient digestion and absorption and disease resistance. This study aims to investigate how fermentation affects the ameliorative effect of bee pollen on the intestinal barrier dysfunction stimulated by interferon-γ and tumor necrosis factor (IFN-γ/TNF-α) cytokines. The results indicated that fermentation enhances the alleviating effect of bee pollen on intestinal barrier dysfunction (including elevated trans epithelial electrical resistance and decreased paracellular permeability). In addition, fermented bee pollen (FBP) significantly decreased (p < 0.05) the secretion levels of interleukin (IL)-6, IL-8, and IL-1β and expression of cyclooxygenase (COX)-2 protein in intestinal barrier cells. Furthermore, fermentation improved the ability of bee pollen to up-regulate the expression of tight junction proteins including zonula occludens (ZO)-1, occluding, and claudin-1. Notably, FBP showed stronger ability to inhibit the expression of nuclear factor kappa-B (NF-κB) mediated myosin light chain kinase (MLCK) and myosin light chain (MLC) signaling pathway associated with phosphorylated proteins. Overall, our results indicated that fermentation enhances the protective effect of bee pollen on the intestinal barrier, and FBP has promising potential to be used as a novel functional food to protect the intestinal barrier.

Myocardial Oedema as a Consequence of Viral Infection and Persistence-A Narrative Review with Focus on COVID-19 and Post COVID Sequelae

Microvascular integrity is a critical factor in myocardial fluid homeostasis. The subtle equilibrium between capillary filtration and lymphatic fluid removal is disturbed during pathological processes leading to inflammation, but also in hypoxia or due to alterations in vascular perfusion and coagulability. The degradation of the glycocalyx as the main component of the endothelial filtration barrier as well as pericyte disintegration results in the accumulation of interstitial and intracellular water. Moreover, lymphatic dysfunction evokes an increase in metabolic waste products, cytokines and inflammatory cells in the interstitial space contributing to myocardial oedema formation. This leads to myocardial stiffness and impaired contractility, eventually resulting in cardiomyocyte apoptosis, myocardial remodelling and fibrosis. The following article reviews pathophysiological inflammatory processes leading to myocardial oedema including myocarditis, ischaemia-reperfusion injury and viral infections with a special focus on the pathomechanisms evoked by severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) infection. In addition, clinical implications including potential long-term effects due to viral persistence (long COVID), as well as treatment options, are discussed.

A comprehensive review of advanced nasal delivery: Specially insulin and calcitonin

Peptide drugs through nasal mucous membrane, such as insulin and calcitonin have been widely used in the medical field. There are always two sides to a coin. One side, intranasal drug delivery can imitate the secretion pattern in human body, having advantages of physiological structure and convenient use. Another side, the low permeability of nasal mucosa, protease environment and clearance effect of nasal cilia hinder the intranasal absorption of peptide drugs. Researchers have taken multiple means to achieve faster therapeutic concentration, lower management dose, and fewer side effects for better nasal preparations. To improve the peptide drugs absorption, various strategies had been explored via the nasal mucosa route. In this paper, we reviewed the achievements of 18 peptide drugs in the past decade about the perspectives of the efficacy, mechanism of enhancing intranasal absorption and safety. The most studies were insulin and calcitonin. As a result, absorption enhancers, nanoparticles (NPs) and bio-adhesive system are the most widely used. Among them, chitosan (CS), cell penetrating peptides (CPPs), tight junction modulators (TJMs), soft NPs and gel/hydrogel are the most promising strategies. Moreover, two or three strategies can be combined to prepare drug vectors. In addition, spray freeze dried (SFD), self-emulsifying nano-system (SEN), and intelligent glucose reaction drug delivery system are new research directions in the future.

The role and mechanism of tight junctions in the regulation of salivary gland secretion

Tight junctions (TJs) are cell-cell interactions that localize at the most apical portion of epithelial/endothelial cells. One of the predominant functions of TJs is to regulate material transport through paracellular pathway, which serves as a selective barrier. In recent years, the expression and function of TJs in salivary glands has attracted great interest. The characteristics of multiple salivary gland TJ proteins have been identified. During salivation, the activation of muscarinic acetylcholine receptor and transient receptor potential vanilloid subtype 1, as well as other stimuli, promote the opening of acinar TJs by inducing internalization of TJs, thereby contributing to increased paracellular permeability. Besides, endothelial TJs are also redistributed with leakage of blood vessels in cholinergic-stimulated submandibular glands. Furthermore, under pathological conditions, such as Sjögren's syndrome, diabetes mellitus, immunoglobulin G4-related sialadenitis, and autotransplantation, the integrity and barrier function of TJ complex are impaired and may contribute to hyposalivation. Moreover, in submandibular glands of Sjögren's syndrome mouse model and patients, the endothelial barrier is disrupted and involved in hyposecretion and lymphocytic infiltration. These findings enrich our understanding of the secretory mechanisms that link the importance of epithelial and endothelial TJ functions to salivation under both physiological and pathophysiological conditions.

Pharmacological Modulation of β-Catenin Preserves Endothelial Barrier Integrity and Mitigates Retinal Vascular Permeability and Inflammation

Compromised blood-retinal barrier (BRB) integrity is a significant factor in ocular diseases like uveitis and retinopathies, leading to pathological vascular permeability and retinal edema. Adherens and tight junction (AJ and TJ) dysregulation due to retinal inflammation plays a pivotal role in BRB disruption. We investigated the potential of ICG001, which inhibits β-catenin-mediated transcription, in stabilizing cell junctions and preventing BRB leakage. In vitro studies using human retinal endothelial cells (HRECs) showed that ICG001 treatment improved β-Catenin distribution within AJs post lipopolysaccharide (LPS) treatment and enhanced monolayer barrier resistance. The in vivo experiments involved a mouse model of LPS-induced ocular inflammation. LPS treatment resulted in increased albumin leakage from retinal vessels, elevated vascular endothelial growth factor (VEGF) and Plasmalemmal Vesicle-Associated Protein (PLVAP) expression, as well as microglia and macroglia activation. ICG001 treatment (i.p.) effectively mitigated albumin leakage, reduced VEGF and PLVAP expression, and reduced the number of activated microglia/macrophages. Furthermore, ICG001 treatment suppressed the surge in inflammatory cytokine synthesis induced by LPS. These findings highlight the potential of interventions targeting β-Catenin to enhance cell junction stability and improve compromised barrier integrity in various ocular inflammatory diseases, offering hope for better management and treatment options.

Claudin-23 reshapes epithelial tight junction architecture to regulate barrier function

Claudin family tight junction proteins form charge- and size-selective paracellular channels that regulate epithelial barrier function. In the gastrointestinal tract, barrier heterogeneity is attributed to differential claudin expression. Here, we show that claudin-23 (CLDN23) is enriched in luminal intestinal epithelial cells where it strengthens the epithelial barrier. Complementary approaches reveal that CLDN23 regulates paracellular ion and macromolecule permeability by associating with CLDN3 and CLDN4 and regulating their distribution in tight junctions. Computational modeling suggests that CLDN23 forms heteromeric and heterotypic complexes with CLDN3 and CLDN4 that have unique pore architecture and overall net charge. These computational simulation analyses further suggest that pore properties are interaction-dependent, since differently organized complexes with the same claudin stoichiometry form pores with unique architecture. Our findings provide insight into tight junction organization and propose a model whereby different claudins combine to form multiple distinct complexes that modify epithelial barrier function by altering tight junction structure.

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.

Pathophysiology and probable etiology of cerebral small vessel disease in vascular dementia and Alzheimer's disease

Vascular cognitive impairment and dementia (VCID) is commonly caused by vascular injuries in cerebral large and small vessels and is a key driver of age-related cognitive decline. Severe VCID includes post-stroke dementia, subcortical ischemic vascular dementia, multi-infarct dementia, and mixed dementia. While VCID is acknowledged as the second most common form of dementia after Alzheimer's disease (AD) accounting for 20% of dementia cases, VCID and AD frequently coexist. In VCID, cerebral small vessel disease (cSVD) often affects arterioles, capillaries, and venules, where arteriolosclerosis and cerebral amyloid angiopathy (CAA) are major pathologies. White matter hyperintensities, recent small subcortical infarcts, lacunes of presumed vascular origin, enlarged perivascular space, microbleeds, and brain atrophy are neuroimaging hallmarks of cSVD. The current primary approach to cSVD treatment is to control vascular risk factors such as hypertension, dyslipidemia, diabetes, and smoking. However, causal therapeutic strategies have not been established partly due to the heterogeneous pathogenesis of cSVD. In this review, we summarize the pathophysiology of cSVD and discuss the probable etiological pathways by focusing on hypoperfusion/hypoxia, blood-brain barriers (BBB) dysregulation, brain fluid drainage disturbances, and vascular inflammation to define potential diagnostic and therapeutic targets for cSVD.

Non-Invasive and Label-Free On-Chip Impedance Monitoring of Heatstroke

Heatstroke (HS) is a life-threatening injury requiring neurocritical care which could lead to central nervous system dysfunction and severe multiple organ failure syndrome. The cell-cell adhesion and cell permeability are two key factors for characterizing HS. To investigate the process of HS, a biochip-based electrical model was proposed and applied to HS. During the process, the value of TEER is associated with cell permeability and C_I which represents cell-cell adhesion decreases that are consistent with the reduction in cell-cell adhesion and cell permeability characterized by proteins (occludin, VE-Cadherin and ZO-1) and RNA level. The results imply that the model can be used to monitor the biological process and other biomedical applications.

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.

The protective effects of electroacupuncture on intestinal barrier lesions in IBS and UC model

Irritable bowel syndrome (IBS) and ulcerative colitis (UC) are two intestinal diseases with different pathological changes. Electroacupuncture (EA) at Zusanli (ST36) on both IBS and UC is widely used in clinic practice. But it is unclear whether acupuncture at one acupoint can treat two different intestinal diseases at different layers of intestinal barrier. To address this question, we explored three intestinal barrier lesions in IBS and UC mice with the aid of transcriptome data analysis and studied the efficacy of EA at ST36 on them. The transcriptome data analysis showed that both UC and IBS had disrupted intestinal barrier in various layers. And both UC and IBS had epithelial barrier lesions with reduction of ZO-1, Occludin and Claudin-1, while UC rather than IBS had the destruction of the mucus barrier with less MUC2 expression. As to the vascular barrier, UC showed a higher CD31 level and mesenteric blood flow reduction, while IBS showed a lower PV-1 level. EA at ST36 can significantly improve the above lesions of intestinal barrier of IBS and UC. Our results gave more details about the comprehensive protective effect of EA for UC and IBS. We guess the effect of acupuncture may be a kind of homeostasis regulation.

Canine Intestinal Organoids as a Novel In Vitro Model of Intestinal Drug Permeability: A Proof-of-Concept Study

A key component of efforts to identify the biological and drug-specific aspects contributing to therapeutic failure or unexpected exposure-associated toxicity is the study of drug-intestinal barrier interactions. While methods supporting such assessments are widely described for human therapeutics, relatively little information is available for similar evaluations in support of veterinary pharmaceuticals. There is, therefore, a critical need to develop novel approaches for evaluating drug-gut interactions in veterinary medicine. Three-dimensional (3D) organoids can address these difficulties in a reasonably affordable system that circumvents the need for more invasive in vivo assays in live animals. However, a first step in developing such systems is understanding organoid interactions in a 2D monolayer. Given the importance of orally administered medications for meeting the therapeutic need of companion animals, we demonstrate growth conditions under which canine-colonoid-derived intestinal epithelial cells survive, mature, and differentiate into confluent cell systems with high monolayer integrity. We further examine the applicability of this canine-colonoid-derived 2D model to assess the permeability of three structurally diverse, passively absorbed β-blockers (e.g., propranolol, metoprolol, and atenolol). Both the absorptive and secretive apparent permeability (P_app) of these drugs at two different pH conditions were evaluated in canine-colonoid-derived monolayers and compared with that of Caco-2 cells. This proof-of-concept study provides promising preliminary results with regard to the utility of canine-derived organoid monolayers for species-specific assessments of therapeutic drug passive permeability.

The effect of claudin-15 deletion on cationic selectivity and transport in paracellular pathways of the cecum and large intestine

The large intestine plays a pivotal role in water and electrolyte balance. Paracellular transport may play a role in ion transport mechanisms in the cecum and large intestine; however, these molecular mechanisms and their physiological roles have not been fully studied. Claudin-15 forms a cation channel in tight junctions in the small intestine, but its role in the cecum and large intestine has not been investigated. This study aimed to explore the physiological role of claudin-15 in the cecum and large intestine using claudin-15 (Cldn15) KO mice. Electrical conductance, short-circuit current, Na⁺ flux, and dilution potential were assessed in isolated tissue preparations mounted in Ussing chambers. The induced short-circuit current of short-chain fatty acids, which are fermentative products in the intestinal tract, was also measured. Compared to wild type mice, the electrical conductance and paracellular Na⁺ flux was decreased in the cecum, but not the middle large intestine, while in both the cecum and the middle large intestine, paracellular Na⁺ permeability was decreased in Cldn15 KO mice. These results suggest that claudin-15 is responsible for Na⁺ permeability in the tight junctions of the cecum and large intestine and decreased Na⁺ permeability in the cecum may cause impaired absorption function.

Serum Cingulin levels are increased in children with autism spectrum disorder

Background

Autism spectrum disorder (ASD) is a group of neurodevelopmental disorders in which the underlying pathogenesis and etiologic factors are not fully understood. The blood brain barrier (BBB) ​​plays a critical role in central nervous system defense by limiting access to circulating solutes, macromolecules, and cells that can negatively affect neuronal activity. The loss of BBB integrity is likely to be seen as a common pathologic finding for many psychiatric disorders such as schizophrenia, ASD, and mood disorders. In this study, we aimed to investigate whether serum Cingulin levels are associated with ASD.

Subjects and Methods

A total of 40 treatment-naive children with ASD and 40 healthy controls were included in the present study. The Schedule for Affective Disorders and Schizophrenia for School-Aged Children, Present and Lifetime Version-DSM-5 (K-SADS-PL-DSM-5) has been used to screen healthy controls for psychiatric disorders by a psychiatrist after a physical examination by a paediatrician. The clinical severity of the ASD symptoms has been assessed by the Childhood Autism Rating Scale (CARS). Venous blood samples were collected and serum Cingulin levels were measured.

Results

When the ASD and control groups were compared, CARS and Cingulin values of the patient group were statistically higher than the healthy group. There is a statistically positive correlation between CARS and Cingulin values.

Discussion

To the best of our knowledge, this study is a first in the literature conducted about the serum Cingulin levels, which is a component of BBB, among patients with ASD. Our findings demonstrate that serum Cingulin levels are meaningfully higher in ASD group compared to the healthy control group. It has been also indicated that there has been a meaningful relationship between serum Cingulin levels and ASD symptom severity.

2'-Fucosyllactose and 3-Fucosyllactose Alleviates Interleukin-6-Induced Barrier Dysfunction and Dextran Sodium Sulfate-Induced Colitis by Improving Intestinal Barrier Function and Modulating the Intestinal Microbiome

Ulcerative colitis is an inflammatory bowel disease (IBD) with relapsing and remitting patterns, and it is caused by varied factors, such as the intestinal inflammation extent and duration. We examined the preventative effects of human milk oligosaccharides (HMOs) on epithelial barrier integrity and intestinal inflammation in an interleukin (IL)-6-induced cell model and dextran sodium sulfate (DSS)-induced acute mouse colitis model. HMOs including 2'-fucosyllactose (FL) and 3-FL and positive controls including fructooligosaccharide (FOS) and 5-acetylsalicylic acid (5-ASA) were orally administrated once per day to C57BL/6J mice with colitis induced by 5% DSS in the administered drinking water. 2'-FL and 3-FL did not affect the cell viability in Caco-2 cells. Meanwhile, these agents reversed IL-6-reduced intestinal barrier function in Caco-2 cells. Furthermore, 2'-FL and 3-FL reversed the body weight loss and the remarkably short colon lengths in DSS-induced acute colitis mice. Moreover, 2'-FL and 3-FL obviously protected the decreasing expression of zonula occluden-1 and occludin in colon tissue relative to the findings in the DSS-treated control group. 2'-FL and 3-FL significantly reduced IL-6 and tumor necrosis factor-α levels in serum relative to the control findings. The summary of these results shows that HMOs prevent colitis mainly by enhancing intestinal barrier function and advancing anti-inflammatory responses. Therefore, HMOs might suppress inflammatory responses and represent candidate treatments for IBD that protect intestinal integrity.

Identification of the genes encoding candidate septate junction components expressed during early development of the sea urchin, Strongylocentrotus purpuratus, and evidence of a role for Mesh in the formation of the gut barrier

Septate junctions (SJs) evolved as cell-cell junctions that regulate the paracellular barrier and integrity of epithelia in invertebrates. Multiple morphological variants of SJs exist specific to different epithelia and/or phyla but the biological significance of varied SJ morphology is unclear because the knowledge of the SJ associated proteins and their functions in non-insect invertebrates remains largely unknown. Here we report cell-specific expression of nine candidate SJ genes in the early life stages of the sea urchin Strongylocentrotus purpuratus. By use of in situ RNA hybridization and single cell RNA-seq we found that the expression of selected genes encoding putatively SJ associated transmembrane and cytoplasmic scaffold molecules was dynamically regulated during epithelial development in the embryos and larvae with different epithelia expressing different cohorts of SJ genes. We focused a functional analysis on SpMesh, a homolog of the Drosophila smooth SJ component Mesh, which was highly enriched in the endodermal epithelium of the mid- and hindgut. Functional perturbation of SpMesh by both CRISPR/Cas9 mutagenesis and vivo morpholino-mediated knockdown shows that loss of SpMesh does not disrupt the formation of the gut epithelium during gastrulation. However, loss of SpMesh resulted in a severely reduced gut-paracellular barrier as quantitated by increased permeability to 3-5 ​kDa FITC-dextran. Together, these studies provide a first look at the molecular SJ physiology during the development of a marine organism and suggest a shared role for Mesh-homologous proteins in forming an intestinal barrier in invertebrates. Results have implications for consideration of the traits underlying species-specific sensitivity of marine larvae to climate driven ocean change.

Precise alternating cellular pattern in the inner ear by coordinated hopping intercalations and delaminations

The mammalian hearing organ, the organ of Corti, is one of the most organized tissues in mammals. It contains a precisely positioned array of alternating sensory hair cells (HCs) and nonsensory supporting cells. How such precise alternating patterns emerge during embryonic development is not well understood. Here, we combine live imaging of mouse inner ear explants with hybrid mechano-regulatory models to identify the processes that underlie the formation of a single row of inner hair cells (IHCs). First, we identify a previously unobserved morphological transition, termed "hopping intercalation," that allows cells differentiating toward IHC fate to "hop" under the apical plane into their final position. Second, we show that out-of-row cells with low levels of the HC marker Atoh1 delaminate. Last, we show that differential adhesion between cell types contributes to straightening of the IHC row. Our results support a mechanism for precise patterning based on coordination between signaling and mechanical forces that is likely relevant for many developmental processes.

Insights of Endocytosis Signaling in Health and Disease

Endocytosis in mammalian cells is a fundamental cellular machinery that regulates vital physiological processes, such as the absorption of metabolites, release of neurotransmitters, uptake of hormone cellular defense, and delivery of biomolecules across the plasma membrane. A remarkable characteristic of the endocytic machinery is the sequential assembly of the complex proteins at the plasma membrane, followed by internalization and fusion of various biomolecules to different cellular compartments. In all eukaryotic cells, functional characterization of endocytic pathways is based on dynamics of the protein complex and signal transduction modules. To coordinate the assembly and functions of the numerous parts of the endocytic machinery, the endocytic proteins interact significantly within and between the modules. Clathrin-dependent and -independent endocytosis, caveolar pathway, and receptor mediated endocytosis have been attributed to a greater variety of physiological and pathophysiological roles such as, autophagy, metabolism, cell division, apoptosis, cellular defense, and intestinal permeabilization. Notably, any defect or alteration in the endocytic machinery results in the development of pathological consequences associated with human diseases such as cancer, cardiovascular diseases, neurological diseases, and inflammatory diseases. In this review, an in-depth endeavor has been made to illustrate the process of endocytosis, and associated mechanisms describing pathological manifestation associated with dysregulated endocytosis machinery.

Prenatal arsenic exposure stymies gut butyrate production and enhances gut permeability in post natal life even in absence of arsenic deftly through miR122-Occludin pathway

This discourse attempts to capture a few important dimensions of gut physiology like microbial homeostasis, short chain fatty acid (SCFA) production, occludin expression, and gut permeability in post-natal life of mice those received arsenic only during pre-natal life. Adult Balb/c mice were fed with 4 ppm arsenic trioxide in drinking water during breeding and gestation. After the birth of the pups, the arsenic water was withdrawn and replaced with clean drinking water. The pups were allowed to grow for 28 days (pAs-mice) and age matched Balb/c mice which were never exposed to arsenic served as control The pAs-mice showed a striking reduction in Firmicutes to Bacteroidetes (F/B) ratio coupled with a decrease in tight junction protein, occludin resulting in an increase in gut permeability, increased infiltration of inflammatory cells in the colon and decrease in common SCFAs in which butyrate reduction was quite prominent in fecal samples as compared to normal control. The above phenotypes of pAs-mice were mostly reversed by supplementing 5% sodium butyrate (w/w) with food from 21st to 28th day. The ability of butyrate in enhancing occludin expression, in particular, was dissected further. As miR122 causes degradation of Occludin mRNA, we transiently overexpressed miR122 by injecting appropriate plasmids and showed reversal of butyrate effects in pAs-mice. Thus, pre-natal arsenic exposure orchestrates variety of effects by decreasing butyrate in pAs-mice leading to increased permeability due to reduced occludin expression. Our research adds a new dimension to our understanding that pre-natal arsenic exposure imprints in post-natal life while there was no further arsenic exposure.

Fermented Glutinous Rice Extract Mitigates DSS-Induced Ulcerative Colitis by Alleviating Intestinal Barrier Function and Improving Gut Microbiota and Inflammation

Ulcerative colitis (UC) is an inflammatory bowel disease caused by various factors, including intestinal inflammation and barrier dysfunction. Herein, we determined the effects of fermented glutinous rice (FGR) on the expression of tight junction proteins and levels of inflammation and apoptosis in the dextran sodium sulfate (DSS)-induced acute colitis model. FGR was orally administered once per day to C57BL/6J mice with colitis induced by 5% DSS in drinking water. FGR administration recovered DSS-induced body weight loss and irregularly short colon lengths. FGR inhibited the DSS-induced decrease in FITC-dextran (FD)-4 permeability and myeloperoxidase activity. Moreover, FGR treatment repaired the reduction of zonula occluden-1 (ZO-1) and occludin expression and the increase in claudin-2 expression in colonic tissue relative to that following DSS administration. FGR treatment significantly recovered expression of cytokines, such as tumor necrosis factor (TNF)-α, interleukin (IL)-6, and IL-1β, in serum or respective mRNA expression in colonic tissue relative to that following DSS administration. FGR regulated levels of oxidative stress-related factors, such as malondialdehyde and glutathione, and the activity of catalase and superoxide dismutase in the colon tissue of the DSS-induced acute colitis mice model. Furthermore, FGR treatment inhibited apoptosis by reducing the activity of caspase-3 and the ratio of Bcl-2 associated X (Bax)/B-cell lymphoma 2 (Bcl-2). Collectively, FGR treatment protected the intestinal barrier from dysfunction and inhibited inflammation and apoptosis in DSS-induced colitis. Therefore, FGR may decrease the inflammatory response and be a candidate for treating and prevention inflammatory bowel disease by protecting the intestinal integrity.

Overview of junctional complexes during mammalian early embryonic development

Cell-cell junctions form strong intercellular connections and mediate communication between blastomeres during preimplantation embryonic development and thus are crucial for cell integrity, polarity, cell fate specification and morphogenesis. Together with cell adhesion molecules and cytoskeletal elements, intercellular junctions orchestrate mechanotransduction, morphokinetics and signaling networks during the development of early embryos. This review focuses on the structure, organization, function and expressional pattern of the cell-cell junction complexes during early embryonic development. Understanding the importance of dynamic junction formation and maturation processes will shed light on the molecular mechanism behind developmental abnormalities of early embryos during the preimplantation period.

RyhB in Avian Pathogenic Escherichia coli Regulates the Expression of Virulence-Related Genes and Contributes to Meningitis Development in a Mouse Model

Avian pathogenic Escherichia coli (APEC) is an important member of extraintestinal pathogenic Escherichia coli (ExPEC). It shares similar pathogenic strategies with neonatal meningitis E. coli (NMEC) and may threaten human health due to its potential zoonosis. RyhB is a small non-coding RNA that regulates iron homeostasis in E. coli. However, it is unclear whether RyhB regulates meningitis occurrence. To investigate the function of RyhB in the development of meningitis, we constructed the deletion mutant APEC XM∆ryhB and the complemented mutant APEC XM∆ryhB/pryhB, established a mouse meningitis model and evaluated the role of RyhB in virulence of APEC. The results showed that the deletion of ryhB decreased biofilm formation, adhesion to the brain microvascular endothelial cell line bEnd.3 and serum resistance. RNA-seq data showed that the expression of multiple virulence-related genes changed in the ryhB deletion mutant in the presence of duck serum. Deletion of ryhB reduced the clinical symptoms of mice, such as opisthotonus, diarrhea and neurological signs, when challenged with APEC. Compared with the mice infected with the wild-type APEC, fewer histopathological lesions were observed in the brain of mice infected with the ryhB deletion mutant APEC XM∆ryhB. The bacterial loads in the tissues and the relative expression of cytokines (IL-1β, IL-6, and TNF-α) in the brain significantly decreased when challenged with the APEC XM∆ryhB. The expressions of tight junction proteins (claudin-5, occludin and ZO-1) were not reduced in the brain of mice infected with APEC XM∆ryhB; that is, the blood-brain barrier permeability of mice was not significantly damaged. In conclusion, RyhB contributes to the pathogenicity of APEC XM in the meningitis-causing process by promoting biofilm formation, adhesion to endothelial cells, serum resistance and virulence-related genes expression.

The endothelium permeability after bioresorbable scaffolds implantation caused by the heterogeneous expression of tight junction proteins

As one of the main functions of vascular endothelial cells, Vascular permeability is determined by four tight junction proteins (TJPs): Zonula Occludens-1 (ZO-1), Claudin-5, Occludin and Tricellulin. The barrier function of blood vessels will be reconstructed after they are damaged by endothelial mechanical injuries caused by vascular interventions. In this study, the effects of balloon expansion (transient mechanical injury) on four TJPs and vascular permeability were compared with those of poly-l-lactic acid bioresorbable scaffolds (BRSs) implantation (continuous mechanical stimulation). We found that BRSs do not affect vascular permeability, while the recovery of vascular barrier function was found to be only related to the mechanical injuries and repair of endothelium. Mechanical stimulation affects and accelerates the recovery process of vascular permeability with the heterogeneous expression levels of TJPs induced after BRSs implantation. Different TJPs have different sensitivity to different loyal mechanical stimuli. ZO-1 is more sensitive to shear stress and tension than to static pressure. Occludin is sensitive to static pressure and shear stress. Tricellulin is more sensitive to tension stretching. Compared with the other three TJPs, Claudin-5 can respond to mechanical stimulation, with relatively low sensitivity, though. This difference in sensitivity determines the heterogeneous expression of TJPs. Mechanical stimulation of different kinds and strengths can also cause different cell morphological changes and inflammatory reactions. As an important element affecting endothelial function, the mechanical factors emerging after BRSs implantation are worthy of more attention.

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The repair of vascular permeability is directly related to the type of vascular injuries, while BRSs implantation has little effect on vascular permeability.

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Transient and persistent mechanical stimulation is the main reason to influence the expression of TJPs.

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Heterogeneous expression of TJPs caused by their different sensitivity to the form of mechanical stimuli.

Blood brain barrier and inflammation in depression

The blood brain barrier (BBB) is a vital structure to protect the brain, tightly filtering the passage of nutrients and molecules from the blood to the brain. This is critical for maintaining the proper functioning of the brain, and any disruption in the BBB has detrimental consequences often leading to diseases. It is not clear whether disruption of the BBB occurs first in depression or is the consequence of the disease, however disruption of the BBB has been observed in depressed patients and evidence points to the role of important culprits in depression, stress and inflammation in disrupting the integrity of the BBB. The mechanisms whereby stress, and inflammation affect the BBB remain to be fully understood. Yet, the role of cytokines in regulating tight junction protein expression seems crucial. Altogether, the findings in depression suggest that acting at the BBB level might provide therapeutic benefit in depression.

Junctional complexes in epithelial cells: sentinels for extracellular insults and intracellular homeostasis

The cell-cell and cell-ECM junctions within the epithelial tissues are crucial anchoring structures that provide architectural stability, mechanical resistance, and permeability control. Their indispensable role as signaling hubs orchestrating cell shape-related changes such as proliferation, differentiation, migration, and apoptosis has also been well recognized. However, growing amount of evidence now suggests that the multitasking nature of epithelial junctions extends well beyond anchorage-dependent or cell shape change-related biological processes. In this review, we discuss the emerging roles of junctional complexes in regulating innate immune defense, stress resistance, and intracellular proteostasis of the epithelial cells, with emphasis on the upstream regulation of epithelial junctions on various aspects of the epithelial barrier.

Molecular mechanism of claudin-15 strand flexibility: A computational study

Claudins are one of the major components of tight junctions that play a key role in the formation and maintenance of the epithelial barrier function. Tight junction strands are dynamic and capable of adapting their structure in response to large-scale tissue rearrangement and cellular movement. Here, we present molecular dynamics simulations of claudin-15 strands of up to 225 nm in length in two parallel lipid membranes and characterize their mechanical properties. The persistence length of claudin-15 strands is comparable with those obtained from analyses of freeze-fracture electron microscopy. Our results indicate that lateral flexibility of claudin strands is due to an interplay of three sets of interfacial interaction networks between two antiparallel double rows of claudins in the membranes. In this model, claudins are assembled into interlocking tetrameric ion channels along the strand that slide with respect to each other as the strands curve over submicrometer-length scales. These results suggest a novel molecular mechanism underlying claudin-15 strand flexibility. It also sheds light on intermolecular interactions and their role in maintaining epithelial barrier function.

In Vitro Assessment of Poly-N-Vinylpyrrolidone/Acrylic Acid Nanoparticles Biocompatibility in a Microvascular Endothelium Model

An amphiphilic copolymer of N-vinyl-2-pyrrolidone and acrylic acid-namely, p(VP-AA)-OD6000 (p(VP-AA))-was synthesized to prepare p(VP-AA) nanoparticles (NPs). Furthermore, the copolymer was linked with CFSE, and the so-prepared nanoparticles were loaded with the DiI dye to form D nanoparticles (DNPs). In this study, as demonstrated by immunofluorescence microscopy, immunofluorescence, and confocal microscopy, DNPs were readily taken up by human microvascular endothelial cells (HMEC-1) cells in a concentration-dependent manner. Upon uptake, both the CFSE dye (green stain) and the DiI dye (red stain) were localized to the cytoplasm of treated cells. Treatment with p(VP-AA) did not affect the viability of normal and challenged with LPS, HMEC-1 cells at 0.010 mg/mL and induced a dose-dependent decrease of these cells' viability at the higher concentrations of 0.033 and 0.066 mg/mL (p ≤ 0.01; p ≤ 0.001, respectively). Furthermore, we focused on the potential immunological activation of HMEC-1 endothelial cells upon p(VP-AA) NPs treatment by assessing the expression of adhesion molecules (E-Selectin, ICAM-1, and V-CAM). NPs treatments at concentrations utilized (p = NS) did not affect individual adhesion molecules' expression. p(VP-AA) NPs do not activate the endothelium and do not affect its viability at pharmacologically relevant concentrations.

Nanoscale segregation of channel and barrier claudins enables paracellular ion flux

The paracellular passage of ions and small molecules across epithelia is controlled by tight junctions, complex meshworks of claudin polymers that form tight seals between neighboring cells. How the nanoscale architecture of tight junction meshworks enables paracellular passage of specific ions or small molecules without compromising barrier function is unknown. Here we combine super-resolution stimulated emission depletion microscopy in live and fixed cells and tissues, multivariate classification of super-resolution images and fluorescence resonance energy transfer to reveal the nanoscale organization of tight junctions formed by mammalian claudins. We show that only a subset of claudins can assemble into characteristic homotypic meshworks, whereas tight junctions formed by multiple claudins display nanoscale organization principles of intermixing, integration, induction, segregation, and exclusion of strand assemblies. Interestingly, channel-forming claudins are spatially segregated from barrier-forming claudins via determinants mainly encoded in their extracellular domains also known to harbor mutations leading to human diseases. Electrophysiological analysis of claudins in epithelial cells suggests that nanoscale segregation of distinct channel-forming claudins enables barrier function combined with specific paracellular ion flux across tight junctions.

Meshworks of claudin polymers control the paracellular transport and barrier properties of epithelial tight junctions. Here, the authors show different claudin nanoscale organization principles, finding that claudin segregation enables barrier formation and paracellular ion flux across tight junctions.

Oxygen-dependent regulation of permeability in low resistance intestinal epithelial cells infected with Giardia lamblia

Intestinal epithelial cells (IECs) reside in a highly anaerobic environment that is subject to daily fluctuations in partial oxygen pressure (pO₂), depending on intestinal tissue perfusion. This condition, known as physiological hypoxia, has a major impact on the maintenance of gut homeostasis, such as effects on the integrity and function of the intestinal epithelial barrier. Giardia lamblia is a microaerophilic protozoan parasite that infects and colonizes the small intestine of its host, causing watery diarrhea. The disease, known as giardiasis, is associated with enhanced intestinal permeability and disruption or reorganization of tight junction (TJ) proteins between IECs. Given the central role of oxygen in gut homeostasis, in this study, we aimed to evaluate whether pO₂ affects intestinal permeability (flux of ions and macromolecules) and TJ protein expression in human IECs during G. lamblia infection. Using human cell lines HuTu-80 and Caco-2 as models of "loose" (low resistance) and "tight" (high resistance) intestines, respectively, we elucidated that low pO₂ drives intestinal barrier dysfunction in IECs infected with trophozoites through dephosphorylation of protein kinase C (PKC α/β II). Additionally, we demonstrated that IECs infected with trophozoites in the presence of a pharmacological PKC activator (phorbol 12-myristate 13-acetate) partially restored the barrier function, which was correlated with increased protein expression levels of zonula occludens (ZO)-2 and occludin. Collectively, these results support the emerging theory that molecular oxygen impacts gut homeostasis during Giardia infection via direct host signaling pathways. These findings further our knowledge regarding Giardia-host interactions and the pathophysiological mechanisms of human giardiasis.