Crosstalk of tight junction components with signaling pathways. Biochim Biophys Acta. 2008;1778:729-756. [PMID: 17950242 DOI: 10.1016/j.bbamem.2007.08.018]

Effects of Natural Polysaccharides on the Gut Microbiota Related to Human Metabolic Health

Natural polysaccharides (NPs) are sugar chains bound by glycosidic bonds that are composed of at least 10 monosaccharides and have broad biological activity. The human body microbiome is a complex ecosystem that plays a role in host metabolism, immunity, and other important life activities. Numerous studies have demonstrated an obvious relationship between the gut flora and the occurrence of many human diseases. Many studies have reviewed and investigated the effects of polysaccharides on the microbiome, but the underlying mechanisms remain unclear. Most of these studies have focused on the effects of NPs on microbes, as they are important "foods" for the intestinal flora. However, polysaccharides can also affect microbes by improving gut homeostasis. Therefore, the purpose of this review is to introduce recent research that looks at how NPs affect microbiomes by directly acting as fermentation substrates and enhancing gut homeostasis. In addition, this study provides a succinct summary of NP extraction, purification, and structural characteristics, as well as a discussion of their structure‒activity correlations. This study also sheds light on future directions and obstacles in the use of NPs with protective properties, with the aim of providing insights into their potential applications in disease treatment.

Exploring therapeutic potential of claudin in Flavivirus infection: A review on current advances and future perspectives

Flavivirus such as Dengue, Zika, West Nile, Japanese encephalitis, and yellow fever virus, composed of single-stranded positive-sense RNA, predominantly contaminated through arthropods. Flavivirus infection characterises from asymptomatic signs to severe hemorrhagic fever and encephalitis. The host's immune system detects these viruses and provides a defence mechanism to sustain their life and growth. However, flaviviruses through different mechanisms compromise the host's immune defence. The current pharmacotherapeutic strategies against Flavivirus infection target different stages of the Flavivirus life cycle and its proteins. On the contrary, the host's immune defence mechanism is equally important to restrict their growth. It has been suggested that flaviviruses compromise claudins to sustain their life and growth inside the mammalian cells. This review primarily focuses on the effect of Flavivirus on claudins (CLDNs), transmembrane proteins that form tight junctions in mammalian cells. CLDNs are crucial in viral entry and pathogenesis by regulating paracellular permeability, particularly in tissues and the blood-brain barrier. Recent studies indicate that the Dengue and Zika viruses can potentially be treated by targeting specific CLDNs-specifically CLDN 1, CLDN 5, and CLDN 7 to inhibit viral entry and fusion. Additionally, it highlights the current challenges and future prospects in developing claudin-based antiviral agents against Flavivirus infections.

Prognostic role of claudin-18.2 in intrahepatic cholangiocarcinoma

Claudins are key components of tight junctions, essential for maintaining cellular adhesion, regulating intercellular molecule transport, and preserving cell polarity. Altered claudin expression can lead to tight junction dysfunction, potentially disrupting signaling pathways and contributing to the development of epithelial cancers. This study aims to explore the understudied role of CLDN18.2 in intrahepatic cholangiocarcinoma and its relationship with clinical outcomes. We analyzed tissue samples from 182 patients who underwent curative surgery for intrahepatic cholangiocarcinoma. Our research examined the relationship between CLDN18.2 expression and various clinical factors, including patient characteristics, pathological findings, and survival metrics such as overall survival (OS), disease-free survival (DFS), metastasis-free survival (MeFS), and local recurrence-free survival (LRFS). Overexpression of CLDN18.2 showed significant associations with R1 resection (p = 0.032) and advanced T stage (p = 0.043). Univariate analysis revealed that high CLDN18.2 expression was correlated with poorer OS (p = 0.0002), DFS (p < 0.0001), LRFS (p < 0.0001), and MeFS (p < 0.0001). Multivariate analysis further confirmed that high CLDN18.2 expression was independently associated with worse OS (p = 0.015), DFS (p < 0.001), LRFS (p < 0.001), and MeFS (p < 0.001). Overexpression of CLDN18.2 was associated with unfavorable clinical prognosis and adverse pathological features in intrahepatic cholangiocarcinoma. These findings suggest that CLDN18.2 could serve as a potential prognostic biomarker for intrahepatic cholangiocarcinoma.

The Minute Virus of Canines (MVC) Activates the RhoA/ROCK1/MLC2 Signal Transduction Pathway Resulting in the Dissociation of Tight Junctions and Facilitating Occludin-Mediated Viral Infection

The Minute Virus of Canines (MVC), belonging to the genus Bocaparvovirus within the family Parvoviridae, is associated with enteritis and embryonic infection in neonatal canines. Viral attachment to host cells is a critical step in infection, and viral protein 2 (VP2) as an important structural protein of MVC influences host selection and infection severity. Nevertheless, little is known about the interaction between VP2 protein and host cells. In this study, we identified that VP2 directly interacts with the kinase domain of RhoA-associated protein kinase 1 (ROCK1) by using mass spectrometry and immunoprecipitation approach and demonstrated that the RhoA/ROCK1/myosin light chain 2 (MLC2) signaling pathway was activated during the early stage of MVC infection in Walter Reed canine cell/3873D (WRD) cells. Further studies indicated that RhoA/ROCK1-mediated phosphorylation of MLC2 triggers the contraction of the actomyosin ring, disrupts tight junctions, and exposes the tight junction protein Occludin, which facilitates the interaction between VP2 and Occludin. Specific inhibitors of RhoA and ROCK1 restored the MVC-induced intracellular translocation of Occludin and the increase in cell membrane permeability. Moreover, the two inhibitors significantly reduced viral protein expression and genomic copy number. Collectively, our study provides the first evidence that there is a direct interaction between the structural protein VP2 of MVC and ROCK1, and that the tight junction protein Occludin can serve as a potential co-receptor for MVC infection, which may offer new targets for anti-MVC strategies.

Involvement of RhoA/ROCK Signaling Pathway in Methamphetamine-Induced Blood-Brain Barrier Disruption

Methamphetamine (METH) is a powerful addictive psychostimulant that gives rise to severe abusers worldwide. While many studies have reported on the neurotoxicity of METH, blood-brain barrier (BBB) dysfunction has recently attracted attention as an essential target in METH-induced pathological changes in the brain. However, its mechanism has not been fully understood. We found that METH increased paracellular permeability and decreased vascular integrity through FITC-dextran and trans-endothelial electrical resistance (TEER) assay in primary human brain endothelial cells (HBMECs). Also, redistribution of tight junction proteins (zonula occluden-1 and claudin-5) and reorganization of F-actin cytoskeleton were observed in METH-exposed HBMECs. To determine the mechanism of METH-induced BBB disruption, the RhoA/ROCK signaling pathway was examined in METH-treated HBMECs. METH-activated RhoA, followed by an increase in the phosphorylation of downstream effectors, myosin light chain (MLC) and cofilin, occurs in HBMECs. Pretreatment with ROCK inhibitors Y-27632 and fasudil reduced the METH-induced increase in phosphorylation of MLC and cofilin, preventing METH-induced redistribution of junction proteins and F-actin cytoskeletal reorganization. Moreover, METH-induced BBB leakage was alleviated by ROCK inhibitors in vitro and in vivo. Taken together, these results suggest that METH induces BBB dysfunction by activating the RhoA/ROCK signaling pathway, which results in the redistribution of junction proteins via F-actin cytoskeletal reorganization.

Sleep deprivation-induced shifts in gut microbiota: Implications for neurological disorders

Sleep deprivation is a prevalent issue in contemporary society, with significant ramifications for both physical and mental well-being. Emerging scientific evidence illuminates its intricate interplay with the gut-brain axis, a vital determinant of neurological function. Disruptions in sleep patterns disturb the delicate equilibrium of the gut microbiota, resulting in dysbiosis characterized by alterations in microbial composition and function. This dysbiosis contributes to the exacerbation of neurological disorders such as depression, anxiety, and cognitive decline through multifaceted mechanisms, including heightened neuroinflammation, disturbances in neurotransmitter signalling, and compromised integrity of the gut barrier. In response to these challenges, there is a burgeoning interest in therapeutic interventions aimed at restoring gut microbial balance and alleviating neurological symptoms precipitated by sleep deprivation. Probiotics, dietary modifications, and behavioural strategies represent promising avenues for modulating the gut microbiota and mitigating the adverse effects of sleep disturbances on neurological health. Moreover, the advent of personalized interventions guided by advanced omics technologies holds considerable potential for tailoring treatments to individualized needs and optimizing therapeutic outcomes. Interdisciplinary collaboration and concerted research efforts are imperative for elucidating the underlying mechanisms linking sleep, gut microbiota, and neurological function. Longitudinal studies, translational research endeavours, and advancements in technology are pivotal for unravelling the complex interplay between these intricate systems.

Polymerase delta-interacting protein 2 mediates brain vascular permeability by regulating ROS-mediated ZO-1 phosphorylation and localization at the interendothelial border

BACKGROUND

Polymerase delta-interacting protein 2 (Poldip2) is a novel regulator of vascular permeability that has been shown to be involved in aggravating blood-brain barrier (BBB) disruption following stroke; however, the underlying mechanisms are unknown. While endothelial tight junctions (TJ) are critical mediators of BBB permeability, the effect of Poldip2 on TJ function has not been elucidated yet. Here, we aim to define the mechanism by which Poldip2 mediates BBB disruption, specifically focusing on phosphorylation and stabilization of the TJ integral protein ZO-1.

METHODS AND RESULTS

Cerebral ischemia was induced in endothelial-specific Poldip2 knockout mice and controls. Cerebral vascular permeability was assessed by Evans blue dye extravasation. Endothelial-specific Poldip2 deletion abolished Evans blue dye extravasation after ischemia induction. In vitro permeability assays demonstrated that Poldip2 knockdown suppressed TNF-α-induced endothelial cell (EC) permeability. Immunofluorescence staining showed that Poldip2 depletion prevented TNF-α-induced ZO-1 disruption at interendothelial junctions. Conversely, Poldip2 overexpression increased endothelial permeability, loss of ZO-1 localization at cell-cell junctions and enhanced reactive oxygen species (ROS) production. Treatment with the antioxidant N-acetyl cysteine (NAC) reduced Poldip2-induced ZO-1 disruption at inter interendothelial junctions. Immunoprecipitation studies demonstrated Poldip2 overexpression induced tyrosine phosphorylation of ZO-1, which was prevented by treatment with NAC or MitoTEMPO, a mitochondrial ROS scavenger.

CONCLUSIONS

These data reveal a novel mitochondrial ROS-driven mechanism by which Poldip2 induces ZO-1 tyrosine phosphorylation and promotes EC permeability following cerebral ischemia.

The role of the neurovascular unit in vascular cognitive impairment: Current evidence and future perspectives

Vascular cognitive impairment (VCI) is a progressive cognitive impairment caused by cerebrovascular disease or vascular risk factors. It is the second most common type of cognitive impairment after Alzheimer's disease. The pathogenesis of VCI is complex, and neurovascular unit destruction is one of its important mechanisms. The neurovascular unit (NVU) is responsible for combining blood flow with brain activity and includes endothelial cells, pericytes, astrocytes and many regulatory nerve terminals. The concept of an NVU emphasizes that interactions between different types of cells are essential for maintaining brain homeostasis. A stable NVU is the basis of normal brain function. Therefore, understanding the structure and function of the neurovascular unit and its role in VCI development is crucial for gaining insights into its pathogenesis. This article reviews the structure and function of the neurovascular unit and its contribution to VCI, providing valuable information for early diagnosis and prevention.

An Adverse Outcome Pathway for food nanomaterial-induced intestinal barrier disruption

Introduction

The ingestion of nanomaterials (NMs) may impair the intestinal barrier, but the underlying mechanisms remain evasive, and evidence has not been systematically gathered or produced. A mechanistic-based approach would be instrumental in assessing whether relevant NMs disrupt the intestinal barrier, thereby supporting the NM risk assessment in the food sector.

Methods

In this study, we developed an adverse outcome pathway (AOP) based on biological plausibility and by leveraging information from an existing NM-relevant AOP that leads to hepatic outcomes. We then extracted the current evidence from the literature for a targeted selection of NMs with high relevance to the food sector, namely, ZnO, CuO, FeO, SiO2, and Ag NMs and nanocellulose.

Results

We propose a new AOP (AOP 530) that starts with endocytic lysosomal uptake, leading to lysosomal disruption inducing mitochondrial dysfunction. Mitochondrial impairments can lead to cell injury/death and disrupt the intestinal barrier. The evidence collected supports that these food-related NMs can be taken up by intestinal cells and indicates that intestinal barrier disruption may occur due to Ag, CuO, and SiO2 NMs, while only few studies support this outcome for FeO and ZnO. Lysosomal disruption and mitochondrial dysfunction are rarely evaluated. For nanocellulose, none of the studies report toxicity-related events.

Conclusion

The collection of existing scientific evidence supporting our AOP linking NM uptake to intestinal barrier impairments allowed us to highlight current evidence gaps and data inconsistencies. These inconsistencies could be associated with the variety of stressors, biological systems, and key event (KE)-related assays used in different studies. This underscores the need for further harmonized methodologies and the production of mechanistic evidence for the safety regulatory assessment of NMs in the food sector.

Gut-microbiota-brain Axis and post-traumatic epilepsy

There has been growing evidence that perturbations in gut-microbiota-brain axis (GMBA) are involved in mechanisms of chronic sequelae of traumatic brain injury (TBI). This review discusses the connection between GMBA and post-traumatic epilepsy (PTE), the latter being a common outcome of TBI. The focus is on two aspects of post-TBI GMBA dysfunction that are relevant to epilepsy. First are impairments in intestinal permeability with subsequent translocation of gut bacteria into the bloodstream. Specifically, endotoxemia following TBI may have a serendipitous protective effect against PTE through lipopolysaccharide conditioning, which may be leveraged for the development of therapeutic interventions. Second are changes in microbial composition (i.e., dysbiosis). Here, the GMBA-PTE connection is explored from predictive biomarker perspective, whereby the risk of PTE can be stratified based on specific microbial profiles. Finally, microbiota transplantation is discussed both as a tool to examine the role of gut microbiota in PTE and as a prelude to novel approaches for PTE therapy and prevention.

Neuropeptides regulate embryonic salivary gland branching through the FGF/FGFR pathway in aging klotho-deficient mice

Salivary gland branching morphogenesis is regulated by the functional integration of neuronal signaling, but the underlying mechanisms are not fully understood in aging accelerated klotho-deficient (Kl-/-) mice. Here, we investigated whether the neuropeptides substance P (SP) and neuropeptide Y (NPY) affect the branching morphogenesis of embryonic salivary glands in aging Kl-/- mice. In the salivary glands of embryonic Kl-/- mice, morphological analysis and immunostaining revealed that epithelial bud formation, neuronal cell proliferation/differentiation, and the expression of the salivary gland functional marker ZO-1 were decreased in embryonic ductal cells. Incubation with SP/NPY at E12-E13d promoted branching morphogenesis, parasympathetic innervation, and epithelial proliferation in salivary glands of embryonic Kl-/- mice. The ERK inhibitor U0126 specifically inhibited neuronal substance-induced epithelial bud formation in the embryonic salivary gland. RNA-seq profiling analysis revealed that the expression of fibroblast growth factors/fibroblast growth factors (FGFs/FGFRs) and their receptors was significantly regulated by SP/NPY treatment in the embryonic salivary gland (E15). The FGFR inhibitor BGJ389 inhibited new branching formation induced by SP and NPY treatment and ERK1/2 expression. These results showed that aging may affect virtually the development of salivary gland by neuronal dysfunction. The neuropeptides SP/NPY induced embryonic salivary gland development through FGF/FGFR/ERK1/2-mediated signaling.

Absorption of food-derived peptides: Mechanisms, influencing factors, and enhancement strategies

Food-derived peptides (FPs) are bioactive molecules produced from dietary proteins through enzymatic hydrolysis or fermentation. These peptides exhibit various biological activities. However, their efficacy largely depends on bioavailability, the ability to cross absorption barriers, and reach target sites within the body. This review addresses key issues in FP absorption, including barriers, pathways, influencing factors, and strategies to enhance absorption. The biochemical and physical barriers to FP absorption include pH variations, enzymes, unstirred water layer, mucus layer, and intestinal epithelial cells. FPs enter the bloodstream via four main pathways: carrier-mediated transport, endocytosis, paracellular, and passive diffusion. The barrier-crossing efficiency depends on the structural properties and state of FPs and coexisting substances. Absorption efficiency can be significantly improved with permeability enhancers, nano-delivery systems, and chemical modifications. These insights provide a scientific basis and practical guidance for optimizing the bioactivity and health benefits of food-derived peptides.

Progress in the mechanism of functional dyspepsia: roles of mitochondrial autophagy in duodenal abnormalities

Mitochondria are the main source of energy for cellular activity. Their functional damage or deficiency leads to cellular deterioration, which in turn triggers autophagic reactions. Taking mitochondrial autophagy as a starting point, the present review explored the mechanisms of duodenal abnormalities in detail, including mucosal barrier damage, release of inflammatory factors, and disruption of intracellular signal transduction. We summarized the key roles of mitochondrial autophagy in the abnormal development of the duodenum and examined the in-depth physiological and pathological mechanisms involved, providing a comprehensive theoretical basis for understanding the pathogenesis of functional dyspepsia. At present, it has been confirmed that an increase in the eosinophil count and mast cell degranulation in the duodenum can trigger visceral hypersensitive reactions and cause gastrointestinal motility disorders. In the future, it is necessary to continue exploring the molecular mechanisms and signaling pathways of mitochondrial autophagy in duodenal abnormalities. A deeper understanding of mitochondrial autophagy provides important references for developing treatment strategies for functional dyspepsia, thereby improving clinical efficacy and patient quality of life.

Perturbation of mammary epithelial cell apicobasal polarity by RHBDF1-facilitated nuclear translocation of PKCζ

BACKGROUND

The establishment of apicobasal polarity in epithelial cells is of critical importance in morphogenesis of mammary gland and other secretive gland tissues. The demise of the polarity is a critical step in early stages of tumorigenesis such as in breast ductal carcinoma in situ. The underlying molecular mechanism thus warrants in-depth investigations.

RESULTS

Protein kinase C isoform ζ (PKCζ), which is highly expressed in breast cancer cells, accumulates in the nuclei of human mammary epithelial cells overexpressing human rhomboid family-1 (RHBDF1), an endoplasmic reticulum membrane protein. Nuclear translocation of PKCζ results in the failure of the formation of the cytosolic apicobasal polarity complex Par, of which PKCζ is an essential component. Additionally, enhanced nuclear translocation of PKCζ is accompanied by an inhibition of the expression of cell tight junction and adherens junction proteins and an increase of cell mobility. Mechanistically, RHBDF1 is able to interact with importin β1 and PKCζ and promote PKCζ phosphorylation. Consistently, treatment of RHBDF1-overexpressing cells with an inhibitor of PKCζ phosphorylation leads to restoration of apicobasal polarity and cell-cell junctions, as well as suppressed cell mobility.

CONCLUSIONS

RHBDF1-facilitated nuclear translocation of PKCζ is critically responsible for the dismantlement of epithelial cell apicobasal polarity, and thus may serve as a target in the development of therapeutic approaches against early stages of breast cancer.

Hyperglycemic environments directly compromise intestinal epithelial barrier function in an organoid model and hyaluronan (∼35 kDa) protects via a layilin dependent mechanism

BACKGROUND

Metabolic syndrome and diabetes in obese individuals are strong risk factors for development of inflammatory bowel disease (IBD) and colorectal cancer. The pathogenic mechanisms of low-grade metabolic inflammation, including chronic hyperglycemic stress, in disrupting gut homeostasis are poorly understood. In this study, we sought to understand the impact of a hyperglycemic environment on intestinal barrier integrity and the protective effects of small molecular weight (35 kDa) hyaluronan on epithelial barrier function.

METHODS

Intestinal organoids derived from mouse colon were grown in normal glucose media (5 mM) or high glucose media (25 mM) to study the impact of hyperglycemic stress on the intestinal barrier. Additionally, organoids were pretreated with 35 kDa hyaluronan (HA35) to investigate the effect of hyaluronan on epithelial barrier under high glucose stress. Immunoblotting as well as confocal imaging was used to understand changes in barrier proteins, quantitative as well as spatial distribution, respectively. Alterations in barrier function were measured using trans-epithelial electrical resistance and fluorescein isothiocyanate flux assays. Untargeted proteomics analysis was performed to elucidate mechanisms by which HA35 exerts a protective effect on the barrier. Intestinal organoids derived from receptor knockout mice specific to various HA receptors were utilized to understand the role of HA receptors in barrier protection under high glucose conditions.

RESULTS

We found that high glucose stress decreased the protein expression as well as spatial distribution of two key barrier proteins, zona occludens-1 (ZO-1) and occludin. HA35 prevented the degradation or loss of ZO-1 and maintained the spatial distribution of both ZO-1 and occludin under hyperglycemic stress. Functionally, we also observed a protective effect of HA35 on the epithelial barrier under high glucose conditions. We found that HA receptor, layilin, was involved in preventing barrier protein loss (ZO-1) as well as maintaining spatial distribution of ZO-1 and occludin. Additionally, proteomics analysis showed that cell death and survival was the primary pathway upregulated in organoids treated with HA35 under high glucose stress. We found that XIAP associated factor 1 (Xaf1) was modulated by HA35 thereby regulating apoptotic cell death in the intestinal organoid system. Finally, we observed that spatial organization of both focal adhesion kinase (FAK) as well as F-actin was mediated by HA35 via layilin.

CONCLUSION

Our results highlight the impact of hyperglycemic stress on the intestinal barrier function. This is of clinical relevance, as impaired barrier function has been observed in individuals with metabolic syndrome. Additionally, we demonstrate barrier protective effects of HA35 through its receptor layilin and modulation of cellular apoptosis under high glucose stress.

Claudin-4 polymerizes after a small extracellular claudin-3-like substitution

Tight junctions play a pivotal role in the functional integrity of the human body by forming barriers that compartmentalize tissues and protect the body from external threats. Essential components of tight junctions are the transmembrane claudin proteins, which can polymerize into tight junction strands and meshworks. This study delves into the structural determinants of claudin polymerization, using the close homology yet strong difference in polymerization capacity between claudin-3 and claudin-4. Through a combination of sequence alignment and structural modeling, critical residues in the second extracellular segment are pinpointed. Molecular dynamics simulations provide insights into the interactions of and the conformational changes induced by the identified extracellular segment 2 residues. Live-stimulated emission depletion imaging demonstrates that introduction of these residues from claudin-3 into claudin-4 significantly enhances polymerization in nonepithelial cells. In tight junction-deficient epithelial cells, mutated claudin-4 not only influences tight junction morphology but also partially restores barrier function. Understanding the structural basis of claudin polymerization is crucial, as it offers insights into the dynamic nature of tight junctions. This knowledge could be applied to targeted therapeutic interventions, offer insight to repair or prevent barrier defects associated with pathological conditions, or introduce temporary barrier openings during drug delivery.

Early Radiation-Induced Changes in Lung Tissue and Intercellular Junctions: Implications for Tissue Repair and Fibrosis

Early changes in lung tissue following ionizing radiation (IR) initiate processes that may lead to either regeneration or fibrosis. Intercellular junction proteins play a crucial role in the organization and function of epithelial tissues, both under normal conditions and after injuries. Alterations in the expression and localization of these proteins can influence the fate of epithelial cells. This study aims to investigate the effects of IR on lung tissue structure, as well as on the levels and distribution of intercellular junction proteins. Wistar rats were subjected to total X-ray irradiation at doses of 2 and 10 Gy. Lung tissue samples were collected for Western blot and histological analysis 72 h post-IR. IR at doses of 2 and 10 Gy led to structural changes in lung tissue and elevated levels of E-cadherin. The 10 Gy IR resulted in increased claudin-4 and occludin in lung parenchyma, decreased claudin-8 and claudin-12 in bronchial epithelium and endothelium, and suppression of apoptosis. Data evaluation indicated that alterations in the protein composition of intercellular junctions are essential processes in lung tissue at early stages after IR, and at least some of these alterations are associated with adaptation.

Gastrointestinal Permeation Enhancers Beyond Sodium Caprate and SNAC - What is Coming Next?

Oral peptide delivery is trending again. Among the possible reasons are the recent approvals of two oral peptide formulations, which represent a huge stride in the field. For the first time, gastrointestinal (GI) permeation enhancers (PEs) are leveraged to overcome the main limitation of oral peptide delivery-low permeability through the intestinal epithelium. Despite some success, the application of current PEs, such as salcaprozate sodium (SNAC), sodium caprylate (C8), and sodium caprate (C10), is generally resulting in relatively low oral bioavailabilities (BAs)-even for carefully selected therapeutics. With several hundred peptide-based drugs presently in the pipeline, there is a huge unmet need for more effective PEs. Aiming to provide useful insights for the development of novel PEs, this review summarizes the biological hurdles to oral peptide delivery with special emphasis on the epithelial barrier. It describes the concepts and action modes of PEs and mentions possible new targets. It further states the benchmark that is set by current PEs, while critically assessing and evaluating emerging PEs regarding translatability, safety, and efficacy. Additionally, examples of novel PEs under preclinical and clinical evaluation and future directions are discussed.

The preclinical discovery and development of zolbetuximab for the treatment of gastric cancer

INTRODUCTION

Gastric cancer remains a formidable challenge in oncology with high mortality rates and few advancements in treatment. Claudin-18.2 (CLDN18.2) is a tight junction protein primarily expressed in the stomach and is frequently overexpressed in certain subsets of gastric cancers. Targeting CLDN18.2 with monoclonal antibodies, such as zolbetuximab (IMAB362), has shown promising efficacy results in combination with chemotherapy.

AREAS COVERED

The molecular cell biology of CLDN18.2 is discussed along with studies demonstrating the utility of CLDN18.2 expression as a biomarker and therapeutic target. Important clinical studies are reviewed, including Phase III trials, SPOTLIGHT and GLOW, which demonstrate the efficacy of zolbetuximab in combination with chemotherapy in patients with CLDN18.2-positive advanced gastric cancer.

EXPERT OPINION

CLDN18.2 is involved in gastric differentiation through maintenance of epithelial barrier function and coordination of signaling pathways, and its expression in gastric cancers reflects a 'gastric differentiation' program. Targeting Claudin-18.2 represents the first gastric cancer specific 'targeted' treatment. Further studies are needed to determine its role within current gastric cancer treatment sequencing, including HER2-targeted therapies and immunotherapies. Management strategies will also be needed to better mitigate zolbetuximab-related treatment side effects, including gastrointestinal (GI) toxicities.

Bacillus coagulans restores pathogen-induced intestinal dysfunction via acetate-FFAR2-NF-κB-MLCK-MLC axis in Apostichopus japonicus

Skin ulceration syndrome (SUS) is currently the main disease threatening Apostichopus japonicus aquaculture due to its higher mortality rate and infectivity, which is caused by Vibrio splendidus. Our previous studies have demonstrated that SUS is accompanied by intestinal microbiota (IM) dysbiosis, alteration of short-chain fatty acids (SCFAs) content and the damage to the intestinal barrier. However, the mediating effect of IM on intestine dysfunction is largely unknown. Herein, we conducted comprehensive intestinal microbiota transplantation (IMT) to explore the link between IM and SUS development. Furthermore, we isolated and identified a Bacillus coagulans strain with an ability to produce acetic acid from both healthy individual and SUS individual with IM from healthy donors. We found that dysbiotic IM and intestinal barrier function in SUS recipients A. japonicus could be restored by IM from healthy donors. The B. coagulans strain could restore IM community and intestinal barrier function. Consistently, acetate supply also restores intestinal homeostasis of SUS-diseased and V. splendidus-infected A. japonicus. Mechanically, acetate was found to specifically bind to its receptor-free fatty acid receptor 2 (FFAR2) to mediate IM structure community and intestinal barrier function. Knockdown of FFAR2 by transfection of specific FFAR2 siRNA could hamper acetate-mediated intestinal homeostasis in vivo. Furthermore, we confirmed that acetate/FFAR2 could inhibit V. splendidus-activated NF-κB-MLCK-MLC signaling pathway to restore intestinal epithelium integrity and upregulated the expression of ZO-1 and Occludin. Our findings provide the first evidence that B. coagulans restores pathogen-induced intestinal barrier dysfunction via acetate/FFAR2-NF-κB-MLCK-MLC axis, which provides new insights into the control and prevention of SUS outbreak from an ecological perspective.IMPORTANCESkin ulceration syndrome (SUS) as a main disease in Apostichopus japonicus aquaculture has severely restricted the developmental A. japonicus aquaculture industry. Intestinal microbiota (IM) has been studied extensively due to its immunomodulatory properties. Short-chain fatty acids (SCFAs) as an essential signal molecule for microbial regulation of host health also have attracted wide attention. Therefore, it is beneficial to explore the link between IM and SUS for prevention and control of SUS. In the study, the contribution of IM to SUS development has been examined. Additionally, our research further validated the restoration of SCFAs on intestinal barrier dysfunction caused by SUS via isolating SCFAs-producing bacteria. Notably, this restoration might be achieved by inhibition of NF-κB-MLCK-MLC signal pathway, which could be activated by V. splendidus. These findings may have important implications for exploration of the role of IM in SUS occurrence and provide insight into the SUS treatment.

Pharmacological inhibition of the Src homology phosphatase 2 confers partial protection in a mouse model of alcohol-associated liver disease

Alcohol-associated liver disease (ALD) is a leading factor of liver-related death worldwide. ALD has various manifestations that include steatosis, hepatitis, and cirrhosis and is currently without approved pharmacotherapies. The Src homology phosphatase 2 (Shp2) is a drug target in some cancers due to its positive regulation of Ras-mitogen-activated protein kinase signaling and cell proliferation. Shp2 pharmacological inhibition yields beneficial outcomes in animal disease models, but its impact on ALD remains unexplored. This study aims to investigate the effects of Shp2 inhibition and its validity using a preclinical mouse model of ALD. We report that the administration of SHP099, a potent and selective allosteric inhibitor of Shp2, partially ameliorated ethanol-induced hepatic injury, inflammation, and steatosis in mice. Additionally, Shp2 inhibition was associated with reduced ethanol-evoked activation of extracellular signal-regulated kinase (ERK), oxidative, and endoplasmic reticulum (ER) stress in the liver. Besides the liver, excessive alcohol consumption induces multi-organ injury and dysfunction, including the intestine. Notably, Shp2 inhibition diminished ethanol-induced intestinal inflammation and permeability, abrogated the reduction in tight junction protein expression, and the activation of ERK and stress signaling in the ileum. Collectively, Shp2 pharmacological inhibition mitigates the deleterious effects of ethanol in the liver and intestine in a mouse model of ALD. Given the multifactorial aspects underlying ALD pathogenesis, additional studies are needed to decipher the utility of Shp2 inhibition alone or as a component in a multitherapeutic regimen to combat this deadly malady.

Beneficial effect of heat-killed Lactiplantibacillus plantarum L-137 on intestinal barrier function of rat small intestinal epithelial cells

Heat-killed Lactiplantibacillus plantarum L-137 (HK L-137) has been suggested to enhance the intestinal barrier in obese mice, leading to improvement of metabolic abnormalities and adipose tissue inflammation, and in healthy humans with overweight, leading to improvement of systemic inflammation. However, its detailed mechanism of action has not been clarified. Therefore, this study investigated the effects of HK L-137 on the permeability of rat small intestinal epithelial IEC-6 cells, tight junction-related gene and protein expression and localization, and intracellular signaling pathways involved in barrier function. Treatment of IEC-6 cells with HK L-137 for 26 h significantly reduced the permeability to fluorescein isothiocyanate-dextran (FD-4). HK L-137 also increased gene and protein expression of zonula occludens-1 (ZO-1), an important tight junction protein, without affecting the localization. Furthermore, inhibition of the extracellular signal-regulated kinase (ERK)1/2 pathway in IEC-6 cells canceled the HK L-137-related reduction in permeability to FD-4. Phosphorylation of ERK in IEC-6 cells was induced 15 min after the addition of HK L-137. These results suggest that HK L-137 reduces intestinal permeability partly through activating the ERK pathway and increasing expression of the ZO-1 gene and protein. Enhancement of intestinal barrier function with HK L-137 might be effective in preventing and treating leaky gut, for which no specific therapeutic tool has been established.

Protective effect of zinc gluconate on intestinal mucosal barrier injury in antibiotics and LPS-induced mice

Objective

The aim of the study is to investigate the function and mechanism of Zinc Gluconate (ZG) on intestinal mucosal barrier damage in antibiotics and Lipopolysaccharide (LPS)-induced mice.

Methods

We established a composite mouse model by inducing intestinal mucosal barrier damage using antibiotics and LPS. The animals were divided into five groups: Control (normal and model) and experimental (low, medium, and high-dose ZG treatments). We evaluated the intestinal mucosal barrier using various methods, including monitoring body weight and fecal changes, assessing pathological damage and ultrastructure of the mouse ileum, analyzing expression levels of tight junction (TJ)-related proteins and genes, confirming the TLR4/NF-κB signaling pathway, and examining the structure of the intestinal flora.

Results

In mice, the dual induction of antibiotics and LPS led to weight loss, fecal abnormalities, disruption of ileocecal mucosal structure, increased intestinal barrier permeability, and disorganization of the microbiota structure. ZG restored body weight, alleviated diarrheal symptoms and pathological damage, and maintained the structural integrity of intestinal epithelial cells (IECs). Additionally, ZG reduced intestinal mucosal permeability by upregulating TJ-associated proteins (ZO-1, Occludin, Claudin-1, and JAM-A) and downregulating MLCK, thereby repairing intestinal mucosal barrier damage induced by dual induction of antibiotics and LPS. Moreover, ZG suppressed the TLR4/NF-κB signaling pathway, demonstrating anti-inflammatory properties and preserving barrier integrity. Furthermore, ZG restored gut microbiota diversity and richness, evidenced by increased Shannon and Observed features indices, and decreased Simpson's index. ZG also modulated the relative abundance of beneficial human gut bacteria (Bacteroidetes, Firmicutes, Verrucomicrobia, Parabacteroides, Lactobacillus, and Akkermansia) and harmful bacteria (Proteobacteria and Enterobacter), repairing the damage induced by dual administration of antibiotics and LPS.

Conclusion

ZG attenuates the dual induction of antibiotics and LPS-induced intestinal barrier damage and also protects the intestinal barrier function in mice.

Systematic-Narrative Hybrid Literature Review: Crosstalk between Gastrointestinal Renin-Angiotensin and Dopaminergic Systems in the Regulation of Intestinal Permeability by Tight Junctions

In the first part of this article, the role of intestinal epithelial tight junctions (TJs), together with gastrointestinal dopaminergic and renin-angiotensin systems, are narratively reviewed to provide sufficient background. In the second part, the current experimental data on the interplay between gastrointestinal (GI) dopaminergic and renin-angiotensin systems in the regulation of intestinal epithelial permeability are reviewed in a systematic manner using the PRISMA methodology. Experimental data confirmed the copresence of DOPA decarboxylase (DDC) and angiotensin converting enzyme 2 (ACE2) in human and rodent enterocytes. The intestinal barrier structure and integrity can be altered by angiotensin (1-7) and dopamine (DA). Both renin-angiotensin and dopaminergic systems influence intestinal Na+/K+-ATPase activity, thus maintaining electrolyte and nutritional homeostasis. The colocalization of B0AT1 and ACE2 indicates the direct role of the renin-angiotensin system in amino acid absorption. Yet, more studies are needed to thoroughly define the structural and functional interaction between TJ-associated proteins and GI renin-angiotensin and dopaminergic systems.

Ziziphus jujuba Miller Ethanol Extract Restores Disrupted Intestinal Barrier Function via Tight Junction Recovery and Reduces Inflammation

Inflammatory bowel disease (IBD) is a chronic inflammatory condition caused by the disruption of the intestinal barrier. The intestinal barrier is maintained by tight junctions (TJs), which sustain intestinal homeostasis and prevent pathogens from entering the microbiome and mucosal tissues. Ziziphus jujuba Miller (Z. jujuba) is a natural substance that has been used in traditional medicine as a therapy for a variety of diseases. However, in IBD, the efficacy of Z. jujuba is unknown. Therefore, we evaluated ZJB in Caco2 cells and a dextran sodium sulfate (DSS)-induced mouse model to demonstrate its efficacy in IBD. Z. jujuba extracts were prepared using 70% ethanol and were named ZJB. ZJB was found to be non-cytotoxic and to have excellent antioxidant effects. We confirmed its anti-inflammatory properties via the down-regulation of inflammatory factors, including inducible nitric oxide synthase (iNOS) and cyclooxygenase-2 (COX-2). To evaluate the effects of ZJB on intestinal barrier function and TJ improvement, the trans-epithelial electrical resistance (TEER) and fluorescein isothiocyanate-dextran 4 kDa (FITC-Dextran 4) permeability were assessed. The TEER value increased by 61.389% and permeability decreased by 27.348% in the 200 μg/mL ZJB group compared with the 50 ng/mL IL-6 group after 24 h. Additionally, ZJB alleviated body weight loss, reduced the disease activity index (DAI) score, and induced colon shortening in 5% DSS-induced mice; inflammatory cytokines, tumor necrosis factor (TNF)-α, and interleukin (IL)-6 were down-regulated in the serum. TJ proteins, such as Zonula occludens (ZO)-1 and occludin, were up-regulated by ZJB in an impaired Caco2 mouse model. Additionally, according to the liquid chromatography results, in tandem with mass spectrometry (LC-MS/MS) analysis, seven active ingredients were detected in ZJB. In conclusion, ZJB down-regulated inflammatory factors, protected intestinal barrier function, and increased TJ proteins. It is thus a safe, natural substance with the potential to be used as a therapeutic agent in IBD treatment.

Tight junction membrane proteins regulate the mechanical resistance of the apical junctional complex

Epithelia must be able to resist mechanical force to preserve tissue integrity. While intercellular junctions are known to be important for the mechanical resistance of epithelia, the roles of tight junctions (TJs) remain to be established. We previously demonstrated that epithelial cells devoid of the TJ membrane proteins claudins and JAM-A completely lack TJs and exhibit focal breakages of their apical junctions. Here, we demonstrate that apical junctions fracture when claudin/JAM-A-deficient cells undergo spontaneous cell stretching. The junction fracture was accompanied by actin disorganization, and actin polymerization was required for apical junction integrity in the claudin/JAM-A-deficient cells. Further deletion of CAR resulted in the disruption of ZO-1 molecule ordering at cell junctions, accompanied by severe defects in apical junction integrity. These results demonstrate that TJ membrane proteins regulate the mechanical resistance of the apical junctional complex in epithelial cells.

Tight Junction Proteins as Therapeutic Targets to Treat Liver Fibrosis and Hepatocellular Carcinoma

In the last decade tight junction proteins exposed at the surface of liver or cancer cells have been uncovered as mediators of liver disease biology: Claudin-1 and Occludin are host factors for hepatitis C virus entry and Claudin-1 has been identified as a driver for liver fibrosis and hepatocellular carcinoma (HCC). Moreover, Claudins have emerged as therapeutic targets for liver disease and HCC. CLDN1 expression is upregulated in liver fibrosis and HCC. Monoclonal antibodies (mAbs) targeting Claudin-1 have completed preclinical proof-of-concept studies for treatment of liver fibrosis and HCC and are currently in clinical development for advanced liver fibrosis. Claudin-6 overexpression is associated with an HCC aggressive phenotype and treatment resistance. Claudin-6 mAbs or chimeric antigen receptor-T cells therapies are currently being clinically investigated for Claudin-6 overexpressing tumors. In conclusion, targeting Claudin proteins offers a novel clinical opportunity for the treatment of patients with advanced liver fibrosis and HCC.

Sphingosine-1-phosphate receptor 1/5 selective agonist alleviates ocular vascular pathologies

Ocular abnormal angiogenesis and edema are featured in several ocular diseases. S1P signaling via S1P1 likely is part of the negative feedback mechanism necessary to maintain vascular health. In this study, we conducted pharmacological experiments to determine whether ASP4058, a sphingosine 1-phosphate receptor 1/5 (S1P1/5) agonist, is useful in abnormal vascular pathology in the eye. First, human retinal microvascular endothelial cells (HRMECs) were examined using vascular endothelial growth factor (VEGF)-induced cell proliferation and hyperpermeability. ASP4058 showed high affinity and inhibited VEGF-induced proliferation and hyperpermeability of HRMECs. Furthermore, S1P1 expression and localization changes were examined in the murine laser-induced choroidal neovascularization (CNV) model, a mouse model of exudative age-related macular degeneration, and the efficacy of ASP4058 was verified. In the CNV model mice, S1P1 tended to decrease in expression immediately after laser irradiation and colocalized with endothelial cells and Müller glial cells. Oral administration of ASP4058 also suppressed vascular hyperpermeability and CNV, and the effect was comparable to that of the intravitreal administration of aflibercept, an anti-VEGF drug. Next, efficacy was also examined in a retinal vein occlusion (RVO) model in which retinal vascular permeability was increased. ASP4058 dose-dependently suppressed the intraretinal edema. In addition, it suppressed the expansion of the perfusion area observed in the RVO model. ASP4058 also suppressed the production of VEGF in the eye. Collectively, ASP4058 can be a potential therapeutic agent that normalizes abnormal vascular pathology, such as age-related macular degeneration and RVO, through its direct action on endothelial cells.

Lactiplantibacillus plantarum ST-III and Lacticaseibacillus rhamnosus KF7 Enhance the Intestinal Epithelial Barrier in a Dual-Environment In Vitro Co-Culture Model

Intestinal barrier hyperpermeability, which is characterised by impaired tight junction proteins, is associated with a variety of gastrointestinal and systemic diseases. Therefore, maintaining intestinal barrier integrity is considered one of the effective strategies to reduce the risk of such disorders. This study aims to investigate the potential benefits of two probiotic strains (Lactiplantibacillus plantarum ST-III and Lacticaseibacillus rhamnosus KF7) on intestinal barrier function by using a physiologically relevant in vitro model of the intestinal epithelium. Our results demonstrate that both strains increased transepithelial electrical resistance, a measure of intestinal barrier integrity. Immunolocalisation studies indicated that this improvement in barrier function was not due to changes in the co-localisation of the tight junction (TJ) proteins ZO-1 and occludin. However, we observed several modifications in TJ-related genes in response to the probiotics, including the upregulation of transmembrane and cytosolic TJ proteins, as well as TJ signalling proteins. Gene expression modulation was strain- and time-dependent, with a greater number of differentially expressed genes and higher fold-change being observed in the L. plantarum ST-III group and at the latter timepoint. Further studies to investigate how the observed gene expression changes can lead to enhanced barrier function will aid in the development of probiotic foods to help improve intestinal barrier function.

Calcitriol modulates epidermal tight junction barrier function in human keratinocytes

BACKGROUND

The aberrant expression of tight junction (TJ) proteins play an important role in several diseases with impaired skin barriers, including atopic dermatitis, psoriasis, and chronic wounds. The evidence provided thus far suggests an important role of calcitriol in skin homeostasis. However, it is not known whether calcitriol improves the impaired skin barrier.

OBJECTIVE

To investigate the effect of calcitriol on TJ barrier function in human primary keratinocytes.

METHODS

Normal human primary keratinocytes were stimulated with calcitriol, and the expression of TJ-related proteins was measured by real-time PCR and Western blotting. Immunofluorescence was used to examine the intercellular distribution of TJ-related proteins. TJ barrier function was assessed by the transepithelial electrical resistance (TER) assay.

RESULTS

We demonstrated that calcitriol increased the expression levels of TJ-related proteins, including claudin-4, claudin-7, occludin, and zonula occludens (ZO)- 1. Calcitriol enhanced the distribution of TJ-related proteins at cellcell borders and induced the phosphorylation of pathways involved in the regulation of TJ barrier function, such as atypical protein kinase C (aPKC), Ras-related C3 botulinum toxin substrate 1 (Rac1), phosphoinositide 3-kinase (PI3K), and protein kinase B (Akt), as evidenced by the effects of specific inhibitors on the above pathways. Indeed, we confirmed that calcitriol enhanced TER in keratinocyte monolayers.

CONCLUSION

These findings showed that calcitriol could modify the expression of keratinocyte TJ proteins, contributing to the maintenance of homeostatic barrier function.

Molecular mechanisms of saliva secretion and hyposecretion

The exocrine salivary gland secretes saliva, a fundamental body component to maintain oral homeostasis. Saliva is composed of water, ions, and proteins such as amylase, mucins, and immunoglobulins that play essential roles in the digestion of food, lubrication, and prevention of dental caries and periodontitis. An increasing number of people experience saliva hyposecretion due to aging, medications, Sjögren's syndrome, and radiation therapy for head and neck cancer. However, current treatments are mostly limited to temporary symptomatic relief. This review explores the molecular mechanisms underlying saliva secretion and hyposecretion to provide insight into putative therapeutic targets for treatment. Proteins implicated in saliva secretion pathways, including Ca2+ -signaling proteins, aquaporins, soluble N-ethylmaleimide-sensitive factor attachment protein receptors, and tight junctions, are aberrantly expressed and localized in patients with saliva hyposecretion, such as Sjögren's syndrome. Analysis of studies on the mechanisms of saliva secretion and hyposecretion suggests that crosstalk between fluid and protein secretory pathways via Ca2+ /protein kinase C and cAMP/protein kinase A regulates saliva secretion. Impaired crosstalk between the two secretory pathways may contribute to saliva hyposecretion. Future research into the detailed regulatory mechanisms of saliva secretion and hyposecretion may provide information to define novel targets and generate therapeutic strategies for saliva hyposecretion.

Diversity of Intercellular Communication Modes: A Cancer Biology Perspective

From the moment a cell is on the path to malignant transformation, its interaction with other cells from the microenvironment becomes altered. The flow of molecular information is at the heart of the cellular and systemic fate in tumors, and various processes participate in conveying key molecular information from or to certain cancer cells. For instance, the loss of tight junction molecules is part of the signal sent to cancer cells so that they are no longer bound to the primary tumors and are thus free to travel and metastasize. Upon the targeting of a single cell by a therapeutic drug, gap junctions are able to communicate death information to by-standing cells. The discovery of the importance of novel modes of cell-cell communication such as different types of extracellular vesicles or tunneling nanotubes is changing the way scientists look at these processes. However, are they all actively involved in different contexts at the same time or are they recruited to fulfill specific tasks? What does the multiplicity of modes mean for the overall progression of the disease? Here, we extend an open invitation to think about the overall significance of these questions, rather than engage in an elusive attempt at a systematic repertory of the mechanisms at play.

Integrating network pharmacology and experimental verification to explore the mucosal protective effect of Chimonanthus nitens Oliv. Leaf Granule on ulcerative colitis

ETHNOPHARMACOLOGICAL RELEVANCE

Chimonanthus nitens Oliv. Leaf Granule (COG) is a commonly used clinical preparation of traditional Chinese medicine for the treatment of cold, but there are folk reports that it can treat diarrhea and other gastrointestinal diseases. Therefore, the mechanism of COG in the treatment of ulcerative colitis with diarrhea as the main symptom needs to be studied.

AIM OF THE STUDY

Combined network pharmacology and experimental validation to explore the mechanism of COG in the treatment of ulcerative colitis.

MATERIALS AND METHODS

First, the main components of COG were characterized by liquid chromatography-mass spectrometry (LC-MS); subsequently, a network pharmacology approach was used to screen the effective chemical components and action targets of COG to construct a target network of COG for the treatment of ulcerative colitis (UC). The protein-protein interaction network (PPI) and literature reports were combined to identify the potential targets of COG for the treatment of UC. Finally, the predicted results of network pharmacology were validated by animal and cellular experiments.

RESULTS

19 components of COG were characterized by LC-MS, among which 10 bioactive components could act on 377 potential targets of UC. Key therapeutic targets were collected, including SRC, HSP90AA1, PIK3RI, MAPK1 and ESR1. KEGG results are enriched in pathways related to oxidative stress. Molecular docking analysis showed good binding activity of main components and target genes. Animal experiments showed that COG significantly relieved the colitis symptoms in mice, regulated the Treg/Th17 balance, and promoted the secretion of IL-10 and IL-4, along with the inhibition of IL-1β and TNF-α. Additionally, COG reduced the apoptosis of colon epithelial cells, and significantly improved the levels of SOD, MAO, GSH-px, and inhibited MDA, iNOS, eNOS in colon. Also, it increased the expression of tight junction proteins such as ZO-1, Claudin1, Occludin and E-cadherin. In vitro experiments, COG inhibited the oxidative stress and inflammatory injury of HCT116 cells induced by LPS.

CONCLUSIONS

Combining network pharmacology and in vitro and in vivo experiments, COG was verified to have a good protective effect in UC, which may be related to enhancing antioxidation in colon tissues.

MUC13 negatively regulates tight junction proteins and intestinal epithelial barrier integrity via protein kinase C

Glycosylated mucin proteins contribute to the essential barrier function of the intestinal epithelium. The transmembrane mucin MUC13 is an abundant intestinal glycoprotein with important functions for mucosal maintenance that are not yet completely understood. We demonstrate that in human intestinal epithelial monolayers, MUC13 localized to both the apical surface and the tight junction (TJ) region on the lateral membrane. MUC13 deletion resulted in increased transepithelial resistance (TEER) and reduced translocation of small solutes. TEER buildup in ΔMUC13 cells could be prevented by addition of MLCK, ROCK or protein kinase C (PKC) inhibitors. The levels of TJ proteins including claudins and occludin were highly increased in membrane fractions of MUC13 knockout cells. Removal of the MUC13 cytoplasmic tail (CT) also altered TJ composition but did not affect TEER. The increased buildup of TJ complexes in ΔMUC13 and MUC13-ΔCT cells was dependent on PKC. The responsible PKC member might be PKCδ (or PRKCD) based on elevated protein levels in the absence of full-length MUC13. Our results demonstrate for the first time that a mucin protein can negatively regulate TJ function and stimulate intestinal barrier permeability.

Claudins and hepatocellular carcinoma

Hepatocellular carcinoma (HCC) has a high incidence and dismal prognosis, making it a significant global health burden. To change this, the development of new therapeutic strategies is imminent. The claudin (CLDN) family, as key components of tight junctions (TJs), plays an important role in the initiation and development of cancer. Dysregulated expression of CLDNs leads to loss of intercellular adhesion and aberrant cell signaling, which are closely related to cancer cell invasion, migration, and epithelial-mesenchymal transition (EMT). CLDN1, CLDN3, CLDN4, CLDN5, CLDN6, CLDN7, CLDN9, CLDN10, CLDN11, CLDN14, and CLDN17 are aberrantly expressed in HCC, which drives the progression of the disease. Consequently, they have tremendous potential as prognostic indicators and therapeutic targets. This article summarizes the aberrant expression, molecular mechanisms, and clinical application studies of different subtypes of CLDNs in HCC, with a particular emphasis on CLDN1.

Fentanyl dysregulates neuroinflammation and disrupts blood-brain barrier integrity in HIV-1 Tat transgenic mice

Opioid overdose deaths have dramatically increased by 781% from 1999 to 2021. In the setting of HIV, opioid drug abuse exacerbates neurotoxic effects of HIV in the brain, as opioids enhance viral replication, promote neuronal dysfunction and injury, and dysregulate an already compromised inflammatory response. Despite the rise in fentanyl abuse and the close association between opioid abuse and HIV infection, the interactive comorbidity between fentanyl abuse and HIV has yet to be examined in vivo. The HIV-1 Tat-transgenic mouse model was used to understand the interactive effects between fentanyl and HIV. Tat is an essential protein produced during HIV that drives the transcription of new virions and exerts neurotoxic effects within the brain. The Tat-transgenic mouse model uses a glial fibrillary acidic protein (GFAP)-driven tetracycline promoter which limits Tat production to the brain and this model is well used for examining mechanisms related to neuroHIV. After 7 days of fentanyl exposure, brains were harvested. Tight junction proteins, the vascular cell adhesion molecule, and platelet-derived growth factor receptor-β were measured to examine the integrity of the blood brain barrier. The immune response was assessed using a mouse-specific multiplex chemokine assay. For the first time in vivo, we demonstrate that fentanyl by itself can severely disrupt the blood-brain barrier and dysregulate the immune response. In addition, we reveal associations between inflammatory markers and tight junction proteins at the blood-brain barrier.

Citric Acid Promotes Immune Function by Modulating the Intestinal Barrier

Amidst increasing concern about antibiotic resistance resulting from the overuse of antibiotics, there is a growing interest in exploring alternative agents. One such agent is citric acid, an organic compound commonly used for various applications. Our research findings indicate that the inclusion of citric acid can have several beneficial effects on the tight junctions found in the mouse intestine. Firstly, the study suggests that citric acid may contribute to weight gain by stimulating the growth of intestinal epithelial cells (IE-6). Citric acid enhances the small intestinal villus-crypt ratio in mice, thereby promoting intestinal structural morphology. Additionally, citric acid has been found to increase the population of beneficial intestinal microorganisms, including Bifidobacterium and Lactobacillus. It also promotes the expression of important protein genes such as occludin, ZO-1, and claudin-1, which play crucial roles in maintaining the integrity of the tight junction barrier in the intestines. Furthermore, in infected IEC-6 cells with H9N2 avian influenza virus, citric acid augmented the expression of genes closely associated with the influenza virus infection. Moreover, it reduces the inflammatory response caused by the viral infection and thwarted influenza virus replication. These findings suggest that citric acid fortifies the intestinal tight junction barrier, inhibits the replication of influenza viruses targeting the intestinal tract, and boosts intestinal immune function.

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.

Functional Analysis of Membrane-Associated Scaffolding Tight Junction (TJ) Proteins in Tumorigenic Characteristics of B16-F10 Mouse Melanoma Cells

Tight junction (TJ) proteins (Tjps), Tjp1 and Tjp2, are tight junction-associated scaffold proteins that bind to the transmembrane proteins of tight junctions and the underlying cytoskeleton. In this study, we first analyzed the tumorigenic characteristics of B16-F10 melanoma cells, including cell proliferation, migration, invasion, metastatic potential, and the expression patterns of related proteins, after the CRISPR-Cas9-mediated knockout (KO) of Tjp genes. The proliferation of Tjp1 and Tjp2 KO cells significantly increased in vitro. Other tumorigenic characteristics, including migration and invasion, were significantly enhanced in Tjp1 and Tjp2 KO cells. Zonula occludens (ZO)-associated protein Claudin-1 (CLDN-1), which is a major component of tight junctions and functions in controlling cell-to-cell adhesion, was decreased in Tjp KO cells. Additionally, Tjp KO significantly stimulated tumor growth and metastasis in an in vivo mouse model. We performed a transcriptome analysis using next-generation sequencing (NGS) to elucidate the key genes involved in the mechanisms of action of Tjp1 and Tjp2. Among the various genes affected by Tjp KO-, cell cycle-, cell migration-, angiogenesis-, and cell-cell adhesion-related genes were significantly altered. In particular, we found that the Ninjurin-1 (Ninj1) and Catenin alpha-1 (Ctnna1) genes, which are known to play fundamental roles in Tjps, were significantly downregulated in Tjp KO cells. In summary, tumorigenic characteristics, including cell proliferation, migration, invasion, tumor growth, and metastatic potential, were significantly increased in Tjp1 and Tjp2 KO cells, and the knockout of Tjp genes significantly affected the expression of related proteins.

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.

Dietary methionine sources and levels modulate the intestinal health status of broiler chickens

Given the key role of methionine in biological processes, adequate methionine should be provided to meet the nutritional requirements. DL-2-hydroxy-4-(methylthio)-butanoic acid (DL-HMTBA) has been considered as an important source of methionine. However, the effects of different sources and levels of methionine on the intestinal health status have not been clarified yet. An experiment was carried out to investigate the effects of different dietary sources and levels of methionine on the intestinal epithelial barrier, inflammatory cytokines expression, ileal morphology, microbiota composition, and cecal short chain fatty acids (SCFA) profiles. For this purpose, 720 male Arbor Acre broiler chicks at 1 d old were randomly assigned to a 2 × 3 factorial arrangement with 2 methionine sources (DL-methionine and DL-HMTBA) and 3 total sulfur amino acids (TSAA) levels (80%, 100%, and 120% of Arbor Acre recommendation). The results showed that DL-HMTBA supplementation promoted intestinal physical barrier at both gene expression level of claudin-1 and serum diamine oxidase level (P < 0.05), and the inflammatory cytokine IL-6 mRNA expression was down-regulated by dietary DL-HMTBA supplementation compared with the DL-methionine group (P < 0.05). Meanwhile, an upregulated gene expression of claudin-1 and zonula occluden-1 (ZO-1) were observed in the low-TSAA treatment on d 14 (P < 0.05), whereas this treatment increased the expression of IL-1β and IL-6 (P < 0.05). Villus height to crypt depth ratio was high (P < 0.05) in the middle-level TSAA group. Furthermore, DL-HMTBA supplementation optimized the microbiota of the ileum especially the relative abundance of Lactobacillus, where the digestion and absorption were completed, and elevated the concentrations of SCFA (acetate, propionate, and butyrate) in the cecal content on d 21 (P < 0.01). In conclusion, dietary DL-HMTBA supplementation improved the intestinal barrier function, immune homeostasis and optimized the microbiota to promote intestinal health status in broiler chickens.

An emerging role of arecoline on growth performance, intestinal digestion and absorption capacities and intestinal structural integrity of adult grass carp (Ctenopharyngodon idella)

Arecoline is an alkaloid with important pharmacological effects in the plant areca nut, which has been demonstrated to be an agonist of muscarinic receptors (M receptor). This study explored the influences of dietary arecoline on growth performance, intestinal digestion and absorption abilities, antioxidant capacity, and the apical junction complex (AJC) of adult grass carp (Ctenopharyngodon idella). Adult grass carp (608 to 1512 g) were fed at 6 graded levels of dietary arecoline (0, 0.5, 1.0, 1.5, 2.0, and 2.5 mg/kg diet) for 9 weeks. The results suggested that appropriate dietary supplementation of arecoline (1.0 mg/kg) increased growth parameters and intestinal growth in adult grass carp (P < 0.05), enhanced digestion and absorption capacities (P < 0.05), up-regulated muscarinic receptor 3 (M3) mRNA level (P < 0.05), increased the content of neuropeptide fish substance P (P < 0.05), improved antioxidant capacity by activating the Keap1a/Nrf2 signaling pathway (P < 0.05), reduced intestinal mucosal permeability (P < 0.05), and increased mRNA levels of tight junction (TJ) and adherent junction AJ-related proteins in fish by inhibiting the RhoA/ROCK signaling pathway (RhoA/ROCK/MLCK/NMII) (P < 0.05). In addition, the appropriate arecoline supplementation for adult grass carp was determined to be 1.20, 1.21, 1.07, and 1.19 mg/kg based on percentage weight gain, lipase activity, serum diamine oxidase, and protein carbonyl, respectively. Overall, to the best of our knowledge, we investigated for the first time the effects and possible mechanisms of dietary arecoline on intestinal digestive and absorptive capacities and structural integrity in fish and evaluated the appropriate level of supplementation.

Nanocarriers transport across the gastrointestinal barriers: The contribution to oral bioavailability via blood circulation and lymphatic pathway

Oral administration is the preferred route of drug delivery in clinical practice due to its noninvasiveness, safety, convenience, and high patient compliance. The gastrointestinal tract (GIT) plays a crucial role in facilitating the targeted delivery of oral drugs. However, the GIT presents multiple barriers that impede drug absorption, including the gastric barrier in the stomach and the mucus and epithelial barriers in the intestine. In recent decades, nanotechnology has emerged as a promising approach for overcoming these challenges by utilizing nanocarrier-based drug delivery systems such as liposomes, micelles, polymeric nanoparticles, solid lipid nanoparticles, and inorganic nanoparticles. Encapsulating drugs within nanocarriers not only protects them from degradation but also enhances their transport and absorption across the GIT, ultimately improving oral bioavailability. The aim of this review is to elucidate the mechanisms underlying nanocarrier-mediated transportation across the GIT into systemic circulation via both the blood circulation and lymphatic pathway.

β(2 → 1)-β(2 → 6) and β(2 → 1) fructans protect from impairment of intestinal tight junction's gene expression and attenuate human dendritic cell responses in a fructan-dependent fashion

β(2 → 1)-β(2 → 6) branched graminan-type fructans (GTFs) and β(2 → 1) linear fructans (ITFs) possess immunomodulatory properties and protect human intestinal barrier function, however the mechanisms underlying these effects are not well studied. Herein, GTFs and ITFs effects with different degree of polymerization (DP) values on tight junctions (TJs) genes CLDN-1, -2 and -3, CDH1, OCLN and TJP1 were studied in Caco-2 gut epithelial cells, under homeostatic and inflammatory conditions. Also, cytokine production in dendritic cells (DCs) was studied. Higher DP fructans decreased the expression of the pore forming CLDN-2. Higher DP GTFs enhanced CLDN-3, OCLN, and TJP-1. Fructans prevented mRNA dysregulation of CLDN-1, -2 and -3 induced by the barrier disruptors A23187 and deoxynivalenol in a fructan-type dependent fashion. The production of pro-inflammatory cytokines MCP-1/CCL2, MIP-1α/CCL3 and TNFα by DCs was also attenuated in a fructan-type dependent manner and was strongly attenuated by DCs cultured with medium of Caco-2 cells which were pre-exposed to fructans. Our data show that specific fructans have TJs and DCs modulating effects and contribute to gut homeostasis. This might serve to design effective dietary means to prevent intestinal inflammation.

D-2-hydroxyglutarate regulates human brain vascular endothelial cell proliferation and barrier function

Gain-of-function mutations in isocitrate dehydrogenase (IDH) genes result in excessive production of (D)-2-hydroxyglutarate (D-2HG) which intrinsically modifies tumor cell epigenetics and impacts surrounding noncancerous cells through nonepigenetic pathways. However, whether D-2HG has a paracrine effect on endothelial cells in the tumor microenvironment needs further clarification. We quantified microvessel density by immunohistochemistry using tissue sections from 60 high-grade astrocytic gliomas with or without IDH mutation. Microvessel density was found to be reduced in tumors carrying an IDH mutation. Ex vivo experiments showed that D-2HG inhibited endothelial cell migration, wound healing, and tube formation by suppressing cell proliferation but not viability, possibly through reduced activation of the mTOR/STAT3 pathway. Further, D-2HG reduced fluorescent dextran permeability and decreased paracellular T-cell transendothelial migration by augmenting expression of junctional proteins thereby collectively increasing endothelial barrier function. These results indicate that D-2HG may influence the tumor vascular microenvironment by reducing the intratumoral vasculature density and by inhibiting the transport of metabolites and extravasation of circulating cells into the astrocytoma microenvironment. These observations provide a rationale for combining IDH inhibition with antitumor immunological/angiogenic approaches and suggest a molecular basis for resistance to antiangiogenic drugs in patients whose tumors express a mutant IDH allele.

Inhibiting PI3K/Akt-Signaling Pathway Improves Neurobehavior Changes in Anti-NMDAR Encephalitis Mice by Ameliorating Blood-Brain Barrier Disruption and Neuronal Damage

The disruption of the blood-brain barrier (BBB) is hypothesized to be involved in the progression of anti-N-methyl-D-aspartate receptor (NMDAR) encephalitis, but its mechanism is still unclear. Recently, the phosphatidylinositol 3-kinase (PI3K)/threonine kinase (Akt) pathway is involved in the regulation of the BBB in various diseases. This study is aimed to investigate the mechanism of BBB damage and neurobehavior changes in anti-NMDAR encephalitis mice. Female C57BL/6J mice were actively immunized to establish an anti-NMDAR encephalitis mouse model and evaluate the neurobehavior changes of mice. To study its potential mechanism, LY294002 (PI3K inhibitor, 8 mg/kg) and Recilisib (PI3K agonist, 10 mg/kg) were treated by intraperitoneal injection, respectively. Anti-NMDAR encephalitis mice showed neurological deficits, increased BBB permeability, open endothelial tight junctions (TJs), and decreased expression of TJ-related proteins zonula occludens (ZO)-1 and Claudin-5. However, administration of PI3K inhibitor significantly reduced the expression of p-PI3K and p-Akt, improved neurobehavior function, decreased BBB permeability, and upregulated the expressions of ZO-1 and Claudin-5. Furthermore, PI3K inhibition reversed the decline of NMDAR NR1 in the membranes of hippocampal neurons, which reduced the loss of neuron-specific nucleoprotein (NeuN) and microtubule-associated protein 2 (MAP2). In contrast, administration of the PI3K agonist Recilisib showed a tendency to exacerbate BBB breakdown and neurological deficits. Our results showed that the activation of PI3K/Akt, along with the changes in TJ-related proteins ZO-1 and Claudin-5, may be closely related to BBB damage and neurobehavior changes in anti-NMDAR encephalitis mice. PI3K inhibition attenuates BBB disruption and neuronal damage in mice, thereby improving neurobehavior.

Protective Effects of Alginate and Chitosan Oligosaccharides against Clostridioides difficile Bacteria and Toxin

Clostridioides difficile infection is expected to become the most common healthcare-associated infection worldwide. C. difficile-induced pathogenicity is significantly attributed to its enterotoxin, TcdA, which primarily targets Rho-GTPases involved in regulating cytoskeletal and tight junction (TJ) dynamics, thus leading to cytoskeleton breakdown and ultimately increased intestinal permeability. This study investigated whether two non-digestible oligosaccharides (NDOs), alginate (AOS) and chitosan (COS) oligosaccharides, possess antipathogenic and barrier-protective properties against C. difficile bacteria and TcdA toxin, respectively. Both NDOs significantly reduced C. difficile growth, while cell cytotoxicity assays demonstrated that neither COS nor AOS significantly attenuated the TcdA-induced cell death 24 h post-exposure. The challenge of Caco-2 monolayers with increasing TcdA concentrations increased paracellular permeability, as measured by TEER and LY flux assays. In this experimental setup, COS completely abolished, and AOS mitigated, the deleterious effects of TcdA on the monolayer's integrity. These events were not accompanied by alterations in ZO-1 and occludin protein levels; however, immunofluorescence microscopy revealed that both AOS and COS prevented the TcdA-induced occludin mislocalization. Finally, both NDOs accelerated TJ reassembly upon a calcium-switch assay. Overall, this study established the antipathogenic and barrier-protective capacity of AOS and COS against C. difficile and its toxin, TcdA, while revealing their ability to promote TJ reassembly in Caco-2 cells.

Long-Term Exposure to Microcystin-LR Induces Gastric Toxicity by Activating the Mitogen-Activated Protein Kinase Signaling Pathway

Previous studies have primarily concentrated on the hepatotoxicity of MC-LR, whereas its gastric toxicity effects and mechanisms of long-term exposure under low dosage remain unknown. Herein, the gastric tissue from C57BL/6 mice fed with drinking water contaminated by low-dose MC-LR (including 1, 60, and 120 μg/L) was investigated. The results obtained showed that exposure to different concentrations of MC-LR resulted in significant shedding and necrosis of gastric epithelial cells in mice, and a down-regulation of tight junction markers, including ZO-1, Claudin1, and Occludin in the stomach, which might lead to increased permeability of the gastric mucosa. Moreover, the protein expression levels of p-RAF/RAF, p-ERK1/2/ERK1/2, Pink1, Parkin, and LC3-II/LC-3-I were increased in the gastric tissue of mice exposed to 120 μg/L of MC-LR, while the protein expression level of P62 was significantly decreased. Furthermore, we found that pro-inflammatory factors, including IL-6 and TNF-ɑ, were dramatically increased, while the anti-inflammatory factor IL-10 was significantly decreased in the gastric tissue of MC-LR-exposed mice. The activation of the MAPK signaling pathway and mitophagy might contribute to the development of gastric damage by promoting inflammation. We first reported that long-term exposure to MC-LR induced gastric toxicity by activating the MAPK signaling pathway, providing a new insight into the gastric toxic mechanisms caused by MC-LR.

Claudin-2 in hyperproliferative migrating keratinocytes and migration inhibition via siRNA knockdown

Claudin-2 is a tight junction protein found in various tissues including the epidermis of the skin. Intracellular signalling via claudin-2 may have an effect on cell proliferation and migration. While the role of claudin-2 in the epidermis has not been established, here we show an increase in claudin-2 expression in hyperproliferative archival skin samples. To further examine the role of claudin-2 in cell migration we examined its expression in cultured keratinocytes and found it was increased in wound margins in an in vitro scratch test assay. We then used a claudin-2 knockdown assay using small interfering ribonucleic acid (siRNA) with a 77% transfection efficiency and decrease in claudin-2 protein via Western blot analysis to examine cell migration, which was inhibited following claudin-2 knockdown over a 5-day period. Cells transfected with claudin-2 siRNA also showed a decreased size compared to controls and a more diffuse staining pattern. Lastly we examined claudin-2 expression in migrating keratinocytes by Western blot analysis and found a significant decrease in protein staining in scratch-test assay cultures after 4 h, followed by a significant increase in claudin-2 protein after 24 h. Taken together these results indicate a role for claudin-2 signalling in proliferation and cell migration in the epidermis of the skin.

cAMP: A master regulator of cadherin-mediated binding in endothelium, epithelium and myocardium

Regulation of cadherin-mediated cell adhesion is crucial not only for maintaining tissue integrity and barrier function in the endothelium and epithelium but also for electromechanical coupling within the myocardium. Therefore, loss of cadherin-mediated adhesion causes various disorders, including vascular inflammation and desmosome-related diseases such as the autoimmune blistering skin dermatosis pemphigus and arrhythmogenic cardiomyopathy. Mechanisms regulating cadherin-mediated binding contribute to the pathogenesis of diseases and may also be used as therapeutic targets. Over the last 30 years, cyclic adenosine 3',5'-monophosphate (cAMP) has emerged as one of the master regulators of cell adhesion in endothelium and, more recently, also in epithelial cells as well as in cardiomyocytes. A broad spectrum of experimental models from vascular physiology and cell biology applied by different generations of researchers provided evidence that not only cadherins of endothelial adherens junctions (AJ) but also desmosomal contacts in keratinocytes and the cardiomyocyte intercalated discs are central targets in this scenario. The molecular mechanisms involve protein kinase A- and exchange protein directly activated by cAMP-mediated regulation of Rho family GTPases and S665 phosphorylation of the AJ and desmosome adaptor protein plakoglobin. In line with this, phosphodiesterase 4 inhibitors such as apremilast have been proposed as a therapeutic strategy to stabilize cadherin-mediated adhesion in pemphigus and may also be effective to treat other disorders where cadherin-mediated binding is compromised.