Epithelial myosin light chain kinase-dependent barrier dysfunction mediates T cell activation-induced diarrhea in vivo

Solanum melongena L. Extract Promotes Intestinal Tight Junction Re-Assembly via SIRT-1-Dependent Mechanisms

Tight junction disruption can lead to pathogenesis of various diseases without therapeutic strategy to recover intestinal barrier integrity. The main objective of this study is to demonstrate the effect of Solanum melongena L. extract (SMLE) on intestinal tight junction recovery and its underlying mechanism. Intestinal barrier function is attenuated by Ca2+ depletion. SMLE treatment increased TER value across T84 cell monolayers. Permeability assay reveals that Ca2+ depletion promotes 4-kDa FITC-dextran permeability, but not 70-kDa FITC-dextran. SMLE suppresses the rate of 4-kDa FITC-dextran permeability, indicating that SMLE inhibits paracellular leak pathway permeability. SMLE-mediated TER increase and leak pathway suppression are abolished by neither calcium/calmodulin-dependent protein kinase kinase β (CaMKKβ) inhibitor nor AMP-activated protein kinase (AMPK) inhibitor. Furthermore, mammalian target of rapamycin (mTOR) and extracellular signal-regulated kinase (ERK) inhibitors have no effects on SMLE-mediated TER increase and leak pathway suppression. Interestingly, SMLE is unable to enhance TER value and diminish leak pathway permeability in T84 cell monolayers pre-treated with sirtuin-1 (SIRT-1) inhibitor. Immunofluorescence staining reveals that SMLE enhances re-assembly of tight junction proteins, including occludin and ZO-1 to intercellular space but this effect is abolished by SIRT-1 inhibitor. These data suggest that SMLE promotes intestinal tight junction re-assembly via SIRT-1-dependent manner.

Endoplasmic reticulum stress in the pathogenesis of chemotherapy-induced mucositis: Physiological mechanisms and therapeutic implications

Chemotherapy is a common and effective treatment for cancer, but these drugs are also associated with significant side effects affecting patients' well-being. One such debilitating side effect is mucositis, characterized by inflammation, ulcerations, and altered physiological functions of the gastrointestinal (GI) tract's mucosal lining. Understanding the mechanisms of chemotherapy-induced intestinal mucositis (CIM) is crucial for developing effective preventive measures and supportive care. Chemotherapeutics not only target cancer cells but also rapidly dividing cells in the GI tract. These drugs disrupt endoplasmic reticulum (ER) homeostasis, leading to ER-stress and activation of the unfolded protein response (UPR) in various intestinal epithelial cell types. The UPR triggers signaling pathways that exacerbate tissue inflammation and damage, influence the differentiation and fate of intestinal epithelial cells, and compromise the integrity of the intestinal mucosal barrier. These factors contribute significantly to mucositis development and progression. In this review, we aim to give an in-depth overview of the role of ER-stress in mucositis and its impact on GI function. This will provide valuable insights into the underlying mechanisms and highlighting potential therapeutic interventions that could improve treatment-outcomes and the quality of life of cancer patients.

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.

Challenges in IBD Research 2024: Preclinical Human IBD Mechanisms

Preclinical human inflammatory bowel disease (IBD) mechanisms is one of 5 focus areas of the Challenges in IBD Research 2024 document, which also includes environmental triggers, novel technologies, precision medicine, and pragmatic clinical research. Herein, we provide a comprehensive overview of current gaps in inflammatory bowel diseases research that relate to preclinical research and deliver actionable approaches to address them with a focus on how these gaps can lead to advancements in IBD interception, remission, and restoration. The document is the result of multidisciplinary input from scientists, clinicians, patients, and funders and represents a valuable resource for patient-centric research prioritization. This preclinical human IBD mechanisms section identifies major research gaps whose investigation will elucidate pathways and mechanisms that can be targeted to address unmet medical needs in IBD. Research gaps were identified in the following areas: genetics, risk alleles, and epigenetics; the microbiome; cell states and interactions; barrier function; IBD complications (specifically fibrosis and stricturing); and extraintestinal manifestations. To address these gaps, we share specific opportunities for investigation for basic and translational scientists and identify priority actions.

Molecular mechanism of MLCK1 inducing 5-Fu resistance in colorectal cancer cells through activation of TNFR2/NF-κB pathway

BACKGROUND AND AIMS

Chemotherapy resistance in colorectal cancer have been faced with significant challenges in recent years. Particular interest is directed to tumor microenvironment function. Recent work has, identified a small molecule named Divertin that prevents myosin light chain kinase 1(MLCK1) recruitment to the perijunctional actomyosin ring(PAMR), restores barrier function after tumor necrosis factor(TNF)-induced barrier loss and prevents disease progression in experimental inflammatory bowel disease. Studies have shown that MLCK is a potential target for affecting intestinal barrier function, as well as for tumor therapy. However, the relative contributions of MLCK expression and chemotherapy resistance in colorectal cancers have not been defined.

METHODS

Statistical analysis of MYLK gene expression differences in colorectal cancer patients and normal population and prognosis results from The Cancer Genome Atlas(TCGA) data. Cell activity was detected by Cell counting Kit-8. Cell proliferation was detected by monoclonal plate. The apoptosis was detected by flow cytometry and western blot. Determine the role of MLCK1 in inducing 5-Fluorouracil(5-Fu) resistance in colorectal cancer cells was detected by overexpression of MLCK1 and knock-down expression of MLCK1.

RESULTS

MLCK1 is expressed at different levels in different colorectal cancer cells, high MLCK1 expressing cell lines are less sensitive to 5-Fu, and low MLCK1 expressing cell lines are more sensitive to 5-Fu. MLCK1 high expression enhances resistance to 5-Fu in colorectal cancer cells and the sensitivity to 5-Fu was increased after knocking down the expression of MLCK1, that might be closely correlated to TNFR2/NF-κB pathway.

CONCLUSIONS

MLCK1 high expression can enhance resistance to 5-Fu in colorectal cancer cells and the sensitivity to 5-Fu was increased after knocking down the expression of MLCK1, that might be closely correlated to TNFR2/NF-κB pathway, which will provide a new method for the treatment of colorectal cancer patients who are resistant to 5-Fu chemotherapy.

A short guide to the tight junction

Tight junctions (TJs) are specialized regions of contact between cells of epithelial and endothelial tissues that form selective semipermeable paracellular barriers that establish and maintain body compartments with different fluid compositions. As such, the formation of TJs represents a critical step in metazoan evolution, allowing the formation of multicompartmental organisms and true, barrier-forming epithelia and endothelia. In the six decades that have passed since the first observations of TJs by transmission electron microscopy, much progress has been made in understanding the structure, function, molecular composition and regulation of TJs. The goal of this Perspective is to highlight the key concepts that have emerged through this research and the future challenges that lie ahead for the field.

The barrier-protective effect of β-eudesmol against type 2-inflammatory cytokine-induced tight junction disassembly in airway epithelial cells

Allergic inflammation, which is the pathogenesis of allergic rhinitis and asthma, is associated with disruption of the airway epithelial barrier due to the effects of type 2 inflammatory cytokines, i.e. interleukin-4 and interleukin-13 (IL-4/13). The anti-allergic inflammatory effect of β-eudesmol (BE) on the tight junction (TJ) of the airway epithelium has not previously been reported. Herein, the barrier protective effect of BE was determined by measurement of transepithelial electrical resistance and by paracellular permeability assay in an IL-4/13-treated 16HBE14o- monolayer. Pre-treatment of BE concentration- and time- dependently inhibited IL-4/13-induced TJ barrier disruption, with the most significant effect observed at 20 μM. Cytotoxicity analyses showed that BE, either alone or in combination with IL-4/13, had no effect on cell viability. Western blot and immunofluorescence analyses showed that BE inhibited IL-4/13-induced mislocalization of TJ components, including occludin and zonula occludens-1 (ZO-1), without affecting the expression of these two proteins. In addition, the mechanism of the TJ-protective effect of BE was mediated by inhibition of IL-4/13-induced STAT6 phosphorylation, in which BE might serve as an antagonist of cytokine receptors. In silico molecular docking analysis demonstrated that BE potentially interacted with the site I pocket of the type 2 IL-4 receptor, likely at Asn-126 and Tyr-127 amino acid residues. It can therefore be concluded that BE is able to prevent IL-4/13-induced TJ disassembly by interfering with cytokine-receptor interaction, leading to suppression of STAT6-induced mislocalization of occludin and ZO-1. BE is a promising candidate for a therapeutic intervention for inflammatory airway epithelial disorders driven by IL-4/13.

Inter-claudin antagonism of paracellular pore function: mechanism and beyond

Claudin-2-dependent pore function mediates paracellular cation permeability and can result in pathogenesis of many diseases. Although existing various types of claudins, including barrier-forming and pore-forming claudins, their heterodimeric interaction affecting barrier and pore functions has never been fully elucidated yet. Recently, Shashikanth and colleagues demonstrated that expression of claudin-4 was able to antagonize paracellular pore activity of claudin-2. This commentary will emphasize the mechanism underlying claudin-4-mediated claudin-2-dependent pore inhibition and discuss its potential therapeutic and prognostic applications.

Listeria adhesion protein orchestrates caveolae-mediated apical junctional remodeling of epithelial barrier for Listeria monocytogenes translocation

The cellular junctional architecture remodeling by Listeria adhesion protein-heat shock protein 60 (LAP-Hsp60) interaction for Listeria monocytogenes (Lm) passage through the epithelial barrier is incompletely understood. Here, using the gerbil model, permissive to internalin (Inl) A/B-mediated pathways like in humans, we demonstrate that Lm crosses the intestinal villi at 48 h post-infection. In contrast, the single isogenic (lap- or ΔinlA) or double (lap-ΔinlA) mutant strains show significant defects. LAP promotes Lm translocation via endocytosis of cell-cell junctional complex in enterocytes that do not display luminal E-cadherin. In comparison, InlA facilitates Lm translocation at cells displaying apical E-cadherin during cell extrusion and mucus expulsion from goblet cells. LAP hijacks caveolar endocytosis to traffic integral junctional proteins to the early and recycling endosomes. Pharmacological inhibition in a cell line and genetic knockout of caveolin-1 in mice prevents LAP-induced intestinal permeability, junctional endocytosis, and Lm translocation. Furthermore, LAP-Hsp60-dependent tight junction remodeling is also necessary for InlA access to E-cadherin for Lm intestinal barrier crossing in InlA-permissive hosts.

IMPORTANCE

Listeria monocytogenes (Lm) is a foodborne pathogen with high mortality (20%-30%) and hospitalization rates (94%), particularly affecting vulnerable groups such as pregnant women, fetuses, newborns, seniors, and immunocompromised individuals. Invasive listeriosis involves Lm's internalin (InlA) protein binding to E-cadherin to breach the intestinal barrier. However, non-functional InlA variants have been identified in Lm isolates, suggesting InlA-independent pathways for translocation. Our study reveals that Listeria adhesion protein (LAP) and InlA cooperatively assist Lm entry into the gut lamina propria in a gerbil model, mimicking human listeriosis in early infection stages. LAP triggers caveolin-1-mediated endocytosis of critical junctional proteins, transporting them to early and recycling endosomes, facilitating Lm passage through enterocytes. Furthermore, LAP-Hsp60-mediated junctional protein endocytosis precedes InlA's interaction with basolateral E-cadherin, emphasizing LAP and InlA's cooperation in enhancing Lm intestinal translocation. This understanding is vital in combating the severe consequences of Lm infection, including sepsis, meningitis, encephalitis, and brain abscess.

The epithelium takes the stage in asthma and inflammatory bowel diseases

The epithelium is a dynamic barrier and the damage to this epithelial layer governs a variety of complex mechanisms involving not only epithelial cells but all resident tissue constituents, including immune and stroma cells. Traditionally, diseases characterized by a damaged epithelium have been considered "immunological diseases," and research efforts aimed at preventing and treating these diseases have primarily focused on immuno-centric therapeutic strategies, that often fail to halt or reverse the natural progression of the disease. In this review, we intend to focus on specific mechanisms driven by the epithelium that ensure barrier function. We will bring asthma and Inflammatory Bowel Diseases into the spotlight, as we believe that these two diseases serve as pertinent examples of epithelium derived pathologies. Finally, we will argue how targeting the epithelium is emerging as a novel therapeutic strategy that holds promise for addressing these chronic diseases.

Claudin-2 upregulation enhances intestinal permeability, immune activation, dysbiosis, and mortality in sepsis

Intestinal epithelial expression of the tight junction protein claudin-2, which forms paracellular cation and water channels, is precisely regulated during development and in disease. Here, we show that small intestinal epithelial claudin-2 expression is selectively upregulated in septic patients. Similar changes occurred in septic mice, where claudin-2 upregulation coincided with increased flux across the paracellular pore pathway. In order to define the significance of these changes, sepsis was induced in claudin-2 knockout (KO) and wild-type (WT) mice. Sepsis-induced increases in pore pathway permeability were prevented by claudin-2 KO. Moreover, claudin-2 deletion reduced interleukin-17 production and T cell activation and limited intestinal damage. These effects were associated with reduced numbers of neutrophils, macrophages, dendritic cells, and bacteria within the peritoneal fluid of septic claudin-2 KO mice. Most strikingly, claudin-2 deletion dramatically enhanced survival in sepsis. Finally, the microbial changes induced by sepsis were less pathogenic in claudin-2 KO mice as survival of healthy WT mice injected with cecal slurry collected from WT mice 24 h after sepsis was far worse than that of healthy WT mice injected with cecal slurry collected from claudin-2 KO mice 24 h after sepsis. Claudin-2 upregulation and increased pore pathway permeability are, therefore, key intermediates that contribute to development of dysbiosis, intestinal damage, inflammation, ineffective pathogen control, and increased mortality in sepsis. The striking impact of claudin-2 deletion on progression of the lethal cascade activated during sepsis suggests that claudin-2 may be an attractive therapeutic target in septic patients.

Eosinophilic Asthma: Pathophysiology and Therapeutic Horizons

Asthma is a prevalent chronic non-communicable disease, affecting approximately 300 million people worldwide. It is characterized by significant airway inflammation, hyperresponsiveness, obstruction, and remodeling. Eosinophilic asthma, a subtype of asthma, involves the accumulation of eosinophils in the airways. These eosinophils release mediators and cytokines, contributing to severe airway inflammation and tissue damage. Emerging evidence suggests that targeting eosinophils could reduce airway remodeling and slow the progression of asthma. To achieve this, it is essential to understand the immunopathology of asthma, identify specific eosinophil-associated biomarkers, and categorize patients more accurately based on the clinical characteristics (phenotypes) and underlying pathobiological mechanisms (endotypes). This review delves into the role of eosinophils in exacerbating severe asthma, exploring various phenotypes and endotypes, as well as biomarkers. It also examines the current and emerging biological agents that target eosinophils in eosinophilic asthma. By focusing on these aspects, both researchers and clinicians can advance the development of targeted therapies to combat eosinophilic pathology in severe asthma.

Mechanisms underlying distinct subcellular localization and regulation of epithelial long myosin light-chain kinase splice variants

Intestinal epithelia express two long myosin light-chain kinase (MLCK) splice variants, MLCK1 and MLCK2, which differ by the absence of a complete immunoglobulin (Ig)-like domain 3 within MLCK2. MLCK1 is preferentially associated with the perijunctional actomyosin ring at steady state, and this localization is enhanced by inflammatory stimuli including tumor necrosis factor (TNF). Here, we sought to identify MLCK1 domains that direct perijunctional MLCK1 localization and their relevance to disease. Ileal biopsies from Crohn's disease patients demonstrated preferential increases in MLCK1 expression and perijunctional localization relative to healthy controls. In contrast to MLCK1, MLCK2 expressed in intestinal epithelia is predominantly associated with basal stress fibers, and the two isoforms have distinct effects on epithelial migration and barrier regulation. MLCK1(Ig1-4) and MLCK1(Ig1-3), but not MLCK2(Ig1-4) or MLCK1(Ig3), directly bind to F-actin in vitro and direct perijunctional recruitment in intestinal epithelial cells. Further study showed that Ig1 is unnecessary, but that, like Ig3, the unstructured linker between Ig1 and Ig2 (Ig1/2us) is essential for recruitment. Despite being unable to bind F-actin or direct recruitment independently, Ig3 does have dominant negative functions that allow it to displace perijunctional MLCK1, increase steady-state barrier function, prevent TNF-induced MLCK1 recruitment, and attenuate TNF-induced barrier loss. These data define the minimal domain required for MLCK1 localization and provide mechanistic insight into the MLCK1 recruitment process. Overall, the results create a foundation for development of molecularly targeted therapies that target key domains to prevent MLCK1 recruitment, restore barrier function, and limit inflammatory bowel disease progression.

Analysis of risk factors and prognosis of diarrhea after renal transplantation

BACKGROUND

Diarrhea is a prevalent complication after renal transplantation.

OBJECTIVE

To examine the risk factors for diarrhea after renal transplantation, evaluate their combined predictive values, and analyze the prognosis.

METHODS

Clinical data of patients who underwent allogeneic renal transplantation in the Second People's Hospital of Shanxi Province from January 2019 to March 2020 were retrospectively analyzed, cases were screened and grouped, independent risk factors for diarrhea after renal transplantation were analyzed by univariate analysis and multivariate analysis, and their predictive value was evaluated by receiver operating characteristic (ROC) curve. The survival time of recipient grafts in diarrhea and non-diarrhea groups were evaluated by Kaplan-Meier and log-rank test.

RESULTS

We included 166 recipients in the study and the incidence of diarrhea was 25.9%; univariate and logistic regression multivariate analyses revealed that independent risk factors for diarrhea in recipients were that the type of renal transplant donor was DCD (donation after circulatory death), immunity induction was onducted with basiliximab + antithymocyte globulin (ATG), and ATG alone, the type of mycophenolic acid (MPA) used was mycophenolate mofetil capsules, and delayed graft function (DGF) occurred after transplantation. The ROC curve indicated that the combination of the four factors had good accuracy in predicting the occurrence of diarrhea in recipients. The graft survival rate two years after the operation in the diarrhea group was significantly lower than that in the non-diarrhea group.

CONCLUSION

Diarrhea affected the two-year survival rate of the graft. The type of donor, immunity induction scheme, and the type of MPA and DGF were independent risk factors for diarrhea in recipients, and the combination of the four factors had good prognostic prediction value.

Sleep Deprivation Impairs Intestinal Mucosal Barrier by Activating Endoplasmic Reticulum Stress in Goblet Cells

Sleep deficiency is associated with intestinal inflammatory conditions and is increasingly recognized as a public health concern worldwide. However, the effects of sleep deficiency on intestinal goblet cells (GCs), which play a major role in intestinal barrier formation, remain elusive. Herein, the effects of sleep deprivation on intestinal GCs were determined using a sleep-deprivation mouse model. Sleep deprivation impaired the intestinal mucosal barrier and decreased the expression of tight junction proteins. According to single-cell RNA sequencing and histologic assessments, sleep deprivation significantly reduced GC numbers and mucin protein levels in intestinal tissues. Furthermore, sleep deprivation initiated endoplasmic reticulum stress by activating transcription factor 6 and binding Ig protein. Treatment with melatonin, an endoplasmic reticulum stress regulator, significantly alleviated endoplasmic reticulum stress responses in intestinal GCs. In addition, melatonin increased the villus length, reduced the crypt depth, and restored intestinal barrier function in mice with sleep deprivation. Overall, the findings revealed that sleep deprivation could impair intestinal mucosal barrier integrity and GC function. Targeting endoplasmic reticulum stress could represent an ideal strategy for treating sleep deficiency-induced gastrointestinal disorders.

Intestinal Membrane Function in Inflammatory Bowel Disease

Inflammatory bowel disease is a set of chronic inflammatory diseases that mainly develop in the gastrointestinal mucosa, including ulcerative colitis and Crohn's disease. Gastrointestinal membrane permeability is an important factor influencing the pharmacological effects of pharmaceuticals administered orally for treating inflammatory bowel disease and other diseases. Understanding the presence or absence of changes in pharmacokinetic properties under a disease state facilitates effective pharmacotherapy. In this paper, we reviewed the gastrointestinal membrane function in ulcerative colitis and Crohn's disease from the perspective of in vitro membrane permeability and electrophysiological parameters. Information on in vivo permeability in humans is summarized. We also overviewed the inflammatory bowel disease research using gut-on-a-chip, in which some advances have recently been achieved. It is expected that these findings will be exploited for the development of therapeutic drugs for inflammatory bowel disease and the optimization of treatment options and regimens.

High Diversity but Monodominance of Multidrug-Resistant Bacteria in Immunocompromised Pediatric Patients with Acute Lymphoblastic Leukemia Developing GVHD Are Not Associated with Changes in Gut Mycobiome

Graft-versus-host disease (GvHD) is a severe complication after hematopoietic stem cell transplantation (HSCT). Our study focused on identifying multidrug-resistant (MDR) gut bacteria associated with GvHD-prone guts and association with gut microbiota (GM) diversity, bacteriome, and mycobiome composition in post-HSCT patients. We examined 11 pediatric patients with acute lymphoblastic leukemia (ALL), including six with GvHD, within three time points: seven days pre-HSCT, seven days post-, and 28 days post-HSCT. The gut microbiome and its resistome were investigated using metagenomic sequencing, taxonomically classified with Kraken2, and statistically evaluated for significance using appropriate tests. We observed an increase in the abundance of MDR bacteria, mainly Enterococcus faecium strains carrying msr(C), erm(T), aac(6')-li, dfrG, and ant(6)-la genes, in GvHD patients one week post-HSCT. Conversely, non-GvHD patients had more MDR beneficial bacteria pre-HSCT, promoting immunosurveillance, with resistance genes increasing one-month post-HSCT. MDR beneficial bacteria included the anti-inflammatory Bacteroides fragilis, Ruminococcus gnavus, and Turicibacter, while most MDR bacteria represented the dominant species of GM. Changes in the gut mycobiome were not associated with MDR bacterial monodominance or GvHD. Significant α-diversity decline (Shannon index) one week and one month post-HSCT in GvHD patients (p < 0.05) was accompanied by increased Pseudomonadota and decreased Bacteroidota post-HSCT. Our findings suggest that MDR commensal gut bacteria may preserve diversity and enhance immunosurveillance, potentially preventing GvHD in pediatric ALL patients undergoing HSCT. This observation has therapeutic implications.

Role of Stress on Driving the Intestinal Paracellular Permeability

The gut epithelium is a polarized monolayer that exhibits apical and basolateral membrane surfaces. Monolayer cell components are joined side by side via protein complexes known as tight junction proteins (TJPs), expressed at the most apical extreme of the basolateral membrane. The gut epithelium is a physical barrier that determinates intestinal permeability, referred to as the measurement of the transit of molecules from the intestinal lumen to the bloodstream or, conversely, from the blood to the gut lumen. TJPs play a role in the control of intestinal permeability that can be disrupted by stress through signal pathways triggered by the ligation of receptors with stress hormones like glucocorticoids. Preclinical studies conducted under in vitro and/or in vivo conditions have addressed underlying mechanisms that account for the impact of stress on gut permeability. These mechanisms may provide insights for novel therapeutic interventions in diseases in which stress is a risk factor, like irritable bowel syndrome. The focus of this study was to review, in an integrative context, the neuroendocrine effects of stress, with special emphasis on TJPs along with intestinal permeability.

Caveolin-1: A Review of Intracellular Functions, Tissue-Specific Roles, and Epithelial Tight Junction Regulation

Caveolin-1 (Cav1) is a vital protein for many cellular processes and is involved in both the positive and negative regulation of these processes. Cav1 exists in multiple cellular compartments depending on its role. Of particular interest is its contribution to the formation of plasma membrane invaginations called caveolae and its involvement in cytoskeletal interactions, endocytosis, and cholesterol trafficking. Cav1 participates in stem cell differentiation as well as proliferation and cell death pathways, which is implicated in tumor growth and metastasis. Additionally, Cav1 has tissue-specific functions that are adapted to the requirements of the cells within those tissues. Its role has been described in adipose, lung, pancreatic, and vascular tissue and in epithelial barrier maintenance. In both the intestinal and the blood brain barriers, Cav1 has significant interactions with junctional complexes that manage barrier integrity. Tight junctions have a close relationship with Cav1 and this relationship affects both their level of expression and their location within the cell. The ubiquitous nature of Cav1 both within the cell and within specific tissues is what makes the protein important for ongoing research as it can assist in further understanding pathophysiologic processes and can potentially be a target for therapies.

Targeting sting to reduce sepsis-induced acute intestinal injury

BACKGROUND

Sepsis is a dysregulated host response to infection syndrome leading to life-threatening organ dysfunction. Sepsis-induced intestinal dysfunction is a key element in the progression to multisystem organ failure. The stimulator of interferon genes is an intracellular protein implicated in intestinal injury in sepsis. H151, a small molecule inhibitor of stimulator of interferon genes, has not yet been studied as a potential therapeutic in sepsis. We hypothesize that H151 therapeutically reduces sepsis-induced acute intestinal injury.

METHODS

Male mice underwent cecal ligation and puncture and were treated with intraperitoneal H151 (10 mg/kg body weight) or vehicle. Intestines and serum were collected for analysis 20 hours after cecal ligation and puncture. Oral gavage of mice with FITC-dextran was performed 15 hours after cecal ligation and puncture. Five hours after gavage, serum was collected, and intestinal permeability was assessed. Mice were monitored for 10 days after cecal ligation and puncture to assess survival.

RESULTS

Zonula occludens 1 tight junctional protein expression was reduced after cecal ligation and puncture and recovered with H151 treatment. This was associated with a 62.3% reduction in intestinal permeability as assessed by fluorimetry. After cecal ligation and puncture, treatment with H151 was associated with a 58.7% reduction in intestinal histopathologic injury (P < .05) and a 56.6% reduction in intestinal apoptosis (P < .05). Intestinal myeloperoxidase activity was decreased by 70.8% after H151 treatment (P < .05). Finally, H151 improved 10-day survival from 33% to 80% after cecal ligation and puncture (P = .011).

CONCLUSION

H151, a novel stimulator of interferon genes inhibitor, reduces intestinal injury, inflammation, and permeability when administered as a treatment for cecal ligation and puncture-induced sepsis. Thus, targeting stimulator of interferon genes shows promise as a therapeutic strategy to ameliorate sepsis-induced acute intestinal injury.

The panda-derived Lactiplantibacillus plantarum BSG201683 improves LPS-induced intestinal inflammation and epithelial barrier disruption in vitro

Captive pandas are suffering from intestinal infection due to intestinal microbiota characterized by a high abundance of Enterobacteriaceae induced by long-term captivity. Probiotic supplements showed improvement in intestinal barrier function and inflammation. However, the effects of panda-derived probiotics on the intestinal epithelium and inflammation have not been elucidated. In the present study, lipopolysaccharide (LPS) impaired Caco-2 and RAW264.7 inflammatory models were applied to assess the protection of Lactiplantibacillus plantarum BSG201683 (L. plantarum G83) on barrier disruption and inflammation. The results showed that treatment with L. plantarum G83 significantly decreased the paracellular permeability to fluorescein isothiocyanate conjugated dextran (MW 4000, FITC-D4) after LPS induction. Meanwhile, L. plantarum G83 alleviated the reduction in tight junction (TJ) proteins and downregulated proinflammatory cytokines caused by LPS in Caco-2 cells. L. plantarum G83 also significantly decreased the expression and secretion of pro-inflammatory cytokines in LPS-induced RAW264.7 cells. In addition, the IL-10 increased in both Caco-2 and RAW264.7 cells after L. plantarum G83 treatment. The phagocytosis activity of RAW264.7 cells was significantly increased after L. plantarum G83 treatment. Toll-like receptor 4/ nuclear factor kappa-B (TLR4/NF-κB) signaling pathways were significantly down-regulated after L. plantarum G83 intervention, and the phosphorylation of NF-κB/p65 was consistent with this result. Our findings suggest that L. plantarum G83 improves intestinal inflammation and epithelial barrier disruption in vitro.

Improving intestinal inflammaging to delay aging? A new perspective

Greying population is becoming an increasingly critical issue for social development. In advanced aging context, organismal multiple tissues and organs experience a progressive deterioration, initially presenting with functional decline, followed by structural disruption and eventually organ failure. The aging of the gut is one of the key links. Decreased gut function leads to reduced nutrient absorption and can perturb systemic metabolic rates. The degeneration of the intestinal structure causes the migration of harmful components such as pathogens and toxins, inducing pathophysiological changes in other organs through the "brain-gut axis" and "liver-gut axis". There is no accepted singular underlying mechanism of aged gut. While the inflamm-aging theory was first proposed in 2000, the mutual promotion of chronic inflammation and aging has attracted much attention. Numerous studies have established that gut microbiome composition, gut immune function, and gut barrier integrity are involved in the formation of inflammaging in the aging gut. Remarkably, inflammaging additionally drives the development of aging-like phenotypes, such as microbiota dysbiosis and impaired intestinal barrier, via a broad array of inflammatory mediators. Here we demonstrate the mechanisms of inflammaging in the gut and explore whether aging-like phenotypes in the gut can be negated by improving gut inflammaging.

METTL3-mediated m6 A modification of circPRKAR1B promotes Crohn's colitis by inducing pyroptosis via autophagy inhibition

BACKGROUND

The roles of circRNA and N6-methyladenosine (m6 A) methylation in Crohn's disease (CD) have drawn much attention. Therefore, this investigation aimed to discover how the m6 A modification of circRNAs contributes to CD progression.

METHODS

The study performed circRNA sequencing on colon samples from four CD patients and four normal controls (NCs) to screen for dysregulated circRNAs. Quantitative real-time polymerase chain reaction (qRT-PCR) was performed to validate the candidate circRNA expression and determine its correlation to CD-associated inflammatory indicators. In vivo and in vitro investigations were conducted to examine the functions and pathways of circPRKAR1B in CD, besides investigating the m6 A modification role in circRNA expression modulation.

RESULTS

The RNA-seq revealed that hsa_circ_0008039 (circPRKAR1B) was the most significant upregulated circRNA and was identified as the candidate circRNA for further examinations. Relative circPRKAR1B expression was significantly upregulated in CD colon tissues and closely related to CD-associated inflammatory indices. The circPRKAR1B expression and function were regulated by methyltransferase-like 3 (METTL3)-mediated m6 A methylation. In vitro studies indicated that circPRKAR1B promoted pyroptosis mediated by NLRP3 inflammasome (NLRP3; nucleotide-binding oligomerization domain, leucine-rich repeat and pyrin domain-containing 3) and impaired autophagy by interacting with the RNA-binding protein (RBP) SPTBN1, (SPTBN1; spectrin beta, non-erythrocytic 1). The in vivo investigations revealed the treatment effects of si-circPRKAR1B and si-METTL3 in colitis models of IL-10-deficient mice.

CONCLUSION

Our study reveals that METTL3-mediated m6 A modification of circPRKAR1B promotes Crohn's colitis by aggravating NLRP3 inflammasome-mediated pyroptosis via autophagy impairment in colonic epithelial cells.

CHRONIC ETHANOL USE WORSENS GUT PERMEABILITY AND ALTERS TIGHT JUNCTION EXPRESSION IN A MURINE SEPSIS MODEL

ABSTRACT

Alcohol use disorder is associated with increased mortality in septic patients. Murine studies demonstrate that ethanol/sepsis is associated with changes in gut integrity. This study examined intestinal permeability after ethanol/sepsis and investigated mechanisms responsible for alterations in barrier function. Mice were randomized to drink either 20% ethanol or water for 12 weeks and then were subjected to either sham laparotomy or cecal ligation and puncture (CLP). Intestinal permeability was disproportionately increased in ethanol/septic mice via the pore, leak, and unrestricted pathways. Consistent with increased permeability in the leak pathway, jejunal myosin light chain (MLC) kinase (MLCK) expression and the ratio of phospho-MLC to total MLC were both increased in ethanol/CLP. Gut permeability was altered in MLCK -/- mice in water/CLP; however, permeability was not different between WT and MLCK -/- mice in ethanol/CLP. Similarly, jejunal IL-1β levels were decreased while systemic IL-6 levels were increased in MLCK -/- mice in water/CLP but no differences were identified in ethanol/CLP. While we have previously shown that mortality is improved in MLCK -/- mice after water/CLP, mortality was significantly worse in MLCK -/- mice after ethanol/CLP. Consistent with an increase in the pore pathway, claudin 4 levels were also selectively decreased in ethanol/CLP WT mice. Furthermore, mRNA expression of jejunal TNF and IFN-γ were both significantly increased in ethanol/CLP. The frequency of CD4 + cells expressing TNF and IL-17A and the frequency of CD8 + cells expressing IFN-γ in Peyer's Patches were also increased in ethanol/CLP. Thus, there is an ethanol-specific worsening of gut barrier function after CLP that impacts all pathways of intestinal permeability, mediated, in part, via changes to the tight junction. Differences in the host response in the setting of chronic alcohol use may play a role in future precision medicine approaches toward the treatment of sepsis.

Tacrolimus-binding protein FKBP8 directs myosin light chain kinase-dependent barrier regulation and is a potential therapeutic target in Crohn's disease

OBJECTIVE

Intestinal barrier loss is a Crohn's disease (CD) risk factor. This may be related to increased expression and enzymatic activation of myosin light chain kinase 1 (MLCK1), which increases intestinal paracellular permeability and correlates with CD severity. Moreover, preclinical studies have shown that MLCK1 recruitment to cell junctions is required for tumour necrosis factor (TNF)-induced barrier loss as well as experimental inflammatory bowel disease progression. We sought to define mechanisms of MLCK1 recruitment and to target this process pharmacologically.

DESIGN

Protein interactions between FK506 binding protein 8 (FKBP8) and MLCK1 were assessed in vitro. Transgenic and knockout intestinal epithelial cell lines, human intestinal organoids, and mice were used as preclinical models. Discoveries were validated in biopsies from patients with CD and control subjects.

RESULTS

MLCK1 interacted specifically with the tacrolimus-binding FKBP8 PPI domain. Knockout or dominant negative FKBP8 expression prevented TNF-induced MLCK1 recruitment and barrier loss in vitro. MLCK1-FKBP8 binding was blocked by tacrolimus, which reversed TNF-induced MLCK1-FKBP8 interactions, MLCK1 recruitment and barrier loss in vitro and in vivo. Biopsies of patient with CD demonstrated increased numbers of MLCK1-FKBP8 interactions at intercellular junctions relative to control subjects.

CONCLUSION

Binding to FKBP8, which can be blocked by tacrolimus, is required for MLCK1 recruitment to intercellular junctions and downstream events leading to immune-mediated barrier loss. The observed increases in MLCK1 activity, MLCK1 localisation at cell junctions and perijunctional MLCK1-FKBP8 interactions in CD suggest that targeting this process may be therapeutic in human disease. These new insights into mechanisms of disease-associated barrier loss provide a critical foundation for therapeutic exploitation of FKBP8-MLCK1 interactions.

Paracellular permeability and tight junction regulation in gut health and disease

Epithelial tight junctions define the paracellular permeability of the intestinal barrier. Molecules can cross the tight junctions via two distinct size-selective and charge-selective paracellular pathways: the pore pathway and the leak pathway. These can be distinguished by their selectivities and differential regulation by immune cells. However, permeability increases measured in most studies are secondary to epithelial damage, which allows non-selective flux via the unrestricted pathway. Restoration of increased unrestricted pathway permeability requires mucosal healing. By contrast, tight junction barrier loss can be reversed by targeted interventions. Specific approaches are needed to restore pore pathway or leak pathway permeability increases. Recent studies have used preclinical disease models to demonstrate the potential of pore pathway or leak pathway barrier restoration in disease. In this Review, we focus on the two paracellular flux pathways that are dependent on the tight junction. We discuss the latest evidence that highlights tight junction components, structures and regulatory mechanisms, their impact on gut health and disease, and opportunities for therapeutic intervention.

Effects of GBT1118, a voxelotor analog, on intestinal pathophysiology in sickle cell disease

Voxelotor is an allosteric haemoglobin (Hb) modulator that binds covalently and reversibly to Hb alpha chain to facilitate improved Hb-O₂ affinity and arterial oxygen. It, therefore, reduces the susceptibility of erythrocytes carrying Haemoglobin S to sickle. In this study, we have used GBT1118, an analog of voxelotor, to treat male Townes sickle cell disease (SCD) mice to investigate whether the Hb modulator could attenuate the intestinal pathophysiologic changes associated with SCD. Compared with mice fed with control chow, GBT1118-treated mice showed improvement in the intestinal pathophysiology. These mice exhibited improved small intestinal barrier functions, reduced intestinal microbial density, reduced enterocyte injury, lower serum lipopolysaccharides and smaller spleens. These improvements were observed after only 3 weeks of GBT1118 treatment. Benefits were also observed after experimentally-induced vaso-occlusive crisis (VOC). Recovery from the VOC-induced changes was faster in mice that were treated with GBT1118. The improved small intestinal barrier function was associated with higher expression of genes encoding enterocyte E-cadherin, JAM-A, ZO-1, MUC-2 and occludin while the lower intestinal microbial density associated with higher expression of genes encoding the antimicrobial peptides defensin-α 1 and defensin-α 4. Our findings provide the evidence to support the beneficial effects of GBT1118 in SCD-related intestinal pathophysiology.

Increased intestinal permeability and downregulation of absorptive ion transporters Nhe3, Dra, and Sglt1 contribute to diarrhea during Clostridioides difficile infection

BACKGROUND & AIM

Clostridioides difficile infection (CDI) is the leading cause of hospital-acquired diarrhea and pseudomembranous colitis. Two protein toxins, TcdA and TcdB, produced by C. difficile are the major determinants of disease. However, the pathophysiological causes of diarrhea during CDI are not well understood. Here, we investigated the effects of C. difficile toxins on paracellular permeability and apical ion transporters in the context of an acute physiological infection.

METHODS

We studied intestinal permeability and apical membrane transporters in female C57BL/6J mice. Üssing chambers were used to measure paracellular permeability and ion transporter function across the intestinal tract. Infected intestinal tissues were analyzed by immunofluorescence microscopy and RNA-sequencing to uncover mechanisms of transporter dysregulation.

RESULTS

Intestinal permeability was increased through the size-selective leak pathway in vivo during acute CDI in a 2-day-post infection model. Chloride secretory activity was reduced in the cecum and distal colon during infection by decreased CaCC and CFTR function, respectively. SGLT1 activity was significantly reduced in the cecum and colon, accompanied by ablated SGLT1 expression in colonocytes and increased luminal glucose concentrations. SGLT1 and DRA expression was ablated by either TcdA or TcdB during acute infection, but NHE3 was decreased in a TcdB-dependent manner. The localization of key proteins that link filamentous actin to the ion transporters in the apical plasma membrane was unchanged. However, Sglt1, Nhe3, and Dra were drastically reduced at the transcript level, implicating downregulation of ion transporters in the mechanism of diarrhea during CDI.

CONCLUSIONS

CDI increases intestinal permeability and decreases apical abundance of NHE3, SGLT1, and DRA. This combination likely leads to dysfunctional water and solute absorption in the large bowel, causing osmotic diarrhea. These findings provide insights into the pathophysiological mechanisms underlying diarrhea and may open novel avenues for attenuating CDI-associated diarrhea.

Redox and Metabolic Regulation of Intestinal Barrier Function and Associated Disorders

The intestinal epithelium forms a physical barrier assembled by intercellular junctions, preventing luminal pathogens and toxins from crossing it. The integrity of tight junctions is critical for maintaining intestinal health as the breakdown of tight junction proteins leads to various disorders. Redox reactions are closely associated with energy metabolism. Understanding the regulation of tight junctions by cellular metabolism and redox status in cells may lead to the identification of potential targets for therapeutic interventions. In vitro and in vivo models have been utilized in investigating intestinal barrier dysfunction and in particular the free-living soil nematode, Caenorhabditis elegans, may be an important alternative to mammalian models because of its convenience of culture, transparent body for microscopy, short generation time, invariant cell lineage and tractable genetics.

Direct Action of Non-Digestible Oligosaccharides against a Leaky Gut

The epithelial monolayer is the primary determinant of mucosal barrier function, and tight junction (TJ) complexes seal the paracellular space between the adjacent epithelial cells and represent the main "gate-keepers" of the paracellular route. Impaired TJ functionality results in increased permeation of the "pro-inflammatory" luminal contents to the circulation that induces local and systemic inflammatory and immune responses, ultimately triggering and/or perpetuating (chronic) systemic inflammatory disorders. Increased gut leakiness is associated with intestinal and systemic disease states such as inflammatory bowel disease and neurodegenerative diseases such as Parkinson's disease. Modulation of TJ dynamics is an appealing strategy aiming at inflammatory conditions associated with compromised intestinal epithelial function. Recently there has been a growing interest in nutraceuticals, particularly in non-digestible oligosaccharides (NDOs). NDOs confer innumerable health benefits via microbiome-shaping and gut microbiota-related immune responses, including enhancement of epithelial barrier integrity. Emerging evidence supports that NDOs also exert health-beneficial effects on microbiota independently via direct interactions with intestinal epithelial and immune cells. Among these valuable features, NDOs promote barrier function by directly regulating TJs via AMPK-, PKC-, MAPK-, and TLR-associated pathways. This review provides a comprehensive overview of the epithelial barrier-protective effects of different NDOs with a special focus on their microbiota-independent modulation of TJs.

circSMAD4 promotes experimental colitis and impairs intestinal barrier functions by targeting JAK2 through sponging miR-135a-5p

BACKGROUND

Numerous studies have explored the association between circular RNAs (circRNAs) and Crohn's disease (CD). However, the pathological role, biological functions, and molecular mechanisms of circRNAs in CD have not been fully elucidated.

METHODS

The circRNA microarray analysis was performed to identify deregulated circRNAs in colon tissues. The identified circRNA were verified through quantitative real time-polymerase chain reaction (qRT-PCR). In vivo and in vitro functional studies were performed to verify the role of circSMAD4 in CD and investigate the mechanisms involved.

RESULTS

We found that circSMAD4 was the most significantly upregulated circRNA. The expression level of circSMAD4 was positively correlated with levels of inflammatory factors. Overexpression of circSMAD4 impaired tight junction (TJ) proteins and enhanced apoptosis of epithelial cells. These effects were reversed by treatment with miR-135a-5p mimic. Mechanistic studies showed that circSMAD4 exerts its effects on CD by "sponging" miR-135a-5p to regulate Janus kinase 2 (JAK2). Si-circSMAD4 delivery through microspheres ameliorated experimental colitis and protected the intestinal barrier function in IL-10 knock-out mice.

CONCLUSION

This study shows that circSMAD4 regulates the progression of experimental colitis via the miR-135a-5p/JAK2 signaling axis and it may be a potential therapeutic target.

Loss of NKCC1 function increases epithelial tight junction permeability by upregulating claudin-2 expression

Conditions that cause the loss of epithelial barrier integrity are often accompanied by dysregulation of tight junction protein expression and/or localization. Recently, we have reported that patients with mutations in SLC12A2, the gene encoding the basolateral Na+-K+-2Cl- cotransporter (NKCC1), suffer from severe gastrointestinal deficits, including chronic gastrointestinal inflammation, gastrointestinal hemorrhage, intestinal obstruction, and constipation. Although the intestinal inflammation observed in patients with loss of NKCC1 function may or may not be due to tight junction dysfunction, we investigated whether the loss of NKCC1 function affects paracellular ion transport and epithelial barrier function. Wild-type HT29-MTX-E12 and CRISPR/Cas9-mediated NKCC1 knockout (KO) HT29 clones were tested for tight junction protein expression and localization. Tightness of epithelial cell monolayer was assessed by measurement of transepithelial electrical resistance and permeability of molecular tracers in transwell filters. Tight junction protein localization was assessed by immunofluorescence. Loss of NKCC1 expression strongly increases the expression of claudin-2 and occludin in epithelial cell monolayers. Loss of NKCC1 significantly reduces the transepithelial electrical resistance (TER) indicating an increase in paracellular ions flux, consistent with upregulation of the cation-selective and channel-forming claudin-2. In addition, NKCC1-KO monolayers showed a significant increase in the paracellular flux of small molecules like fluorescein (0.33 kDa), whereas the permeability of higher molecular weight TRITC-Dextran (4 kDa and 70 kDa) remained unchanged. Thus, NKCC1 regulates tight junction protein expression and loss of NKCC1 function affects epithelial barrier integrity.

Chondrogenic primed extracellular vesicles activate miR-455/SOX11/FOXO axis for cartilage regeneration and osteoarthritis treatment

Osteoarthritis (OA) is the leading cause of disability worldwide. Considerable progress has been made using stem-cell-derived therapy. Increasing evidence has demonstrated that the therapeutic effects of BMSCs in chondrogenesis could be attributed to the secreted small extracellular vesicles (sEVs). Herein, we investigated the feasibility of applying engineered EVs with chondrogenic priming as a biomimetic tool in chondrogenesis. We demonstrated that EVs derived from TGFβ3-preconditioned BMSCs presented enriched specific miRNAs that could be transferred to native BMSCs to promote chondrogenesis. In addition, We found that EVs derived from TGFβ3-preconditioned BMSCs rich in miR-455 promoted OA alleviation and cartilage regeneration by activating the SOX11/FOXO signaling pathway. Moreover, the designed T3-EV hydrogel showed great potential in cartilage defect treatment. Our findings provide new means to apply biosafe engineered EVs from chondrogenic primed-BMSCs for cartilage repair and OA treatment, expanding the understanding of chondrogenesis and OA development modulated by EV-miRNAs in vivo.

Mannose ameliorates experimental colitis by protecting intestinal barrier integrity

Metabolite alteration has been associated with the pathogenesis of inflammatory bowel disease (IBD), including colitis. Mannose, a natural bioactive monosaccharide that is involved in metabolism and synthesis of glycoproteins, exhibits anti-inflammatory and anti-oxidative activities. We show here that the circulating level of mannose is increased in patients with IBD and mice with experimental colitis. Mannose treatment attenuates intestinal barrier damage in two mouse colitis models, dextran sodium sulfate (DSS)-induced colitis and spontaneous colitis in IL-10-deficient mice. We demonstrate that mannose treatment enhanced lysosomal integrity and limited the release of cathepsin B, preventing mitochondrial dysfunction and myosin light chain kinase (MLCK)-induced tight junction disruption in the context of intestinal epithelial damage. Mannose exerts a synergistic therapeutic effect with mesalamine on mouse colitis. Cumulatively, the results indicate that mannose supplementation may be an optional approach to the treatment of colitis and other diseases associated with intestinal barrier dysfunction.

Proanthocyanidins at the gastrointestinal tract: mechanisms involved in their capacity to mitigate obesity-associated metabolic disorders

The prevalence of overweight and obesity is continually increasing worldwide. Obesity is a major public health concern given the multiple associated comorbidities. Finding dietary approaches to prevent/mitigate these conditions is of critical relevance. Proanthocyanidins (PACs), oligomers or polymers of flavan-3-ols that are extensively distributed in nature, represent a major part of total dietary polyphenols. Although current evidence supports the capacity of PACs to mitigate obesity-associated comorbidities, the underlying mechanisms remain speculative due to the complexity of PACs' structure. Given their limited bioavailability, the major site of the biological actions of intact PACs is the gastrointestinal (GI) tract. This review discusses the actions of PACs at the GI tract which could underlie their anti-obesity effects. These mechanisms include: i) inhibition of digestive enzymes at the GI lumen, including pancreatic lipase, α-amylase, α-glucosidase; ii) modification of gut microbiota composition; iii) modulation of inflammation- and oxidative stress-triggered signaling pathways, e.g. NF-κB and MAPKs; iv) protection of the GI barrier integrity. Further understanding of the mechanisms and biological activities of PACs at the GI tract can contribute to develop nutritional and pharmacological strategies oriented to mitigate the serious comorbidities of obesity.

Tight junctions: from molecules to gastrointestinal diseases

Intestinal epithelium functions as a tissue barrier to prevent interaction between the internal compartment and the external milieu. Intestinal barrier function also determines epithelial polarity for the absorption of nutrients and the secretion of waste products. These vital functions require strong integrity of tight junction proteins. In fact, intestinal tight junctions that seal the paracellular space can restrict mucosal-to-serosal transport of hostile luminal contents. Tight junctions can form both an absolute barrier and a paracellular ion channel. Although defective tight junctions potentially lead to compromised intestinal barrier and the development and progression of gastrointestinal (GI) diseases, no FDA-approved therapies that recover the epithelial tight junction barrier are currently available in clinical practice. Here, we discuss the impacts and regulatory mechanisms of tight junction disruption in the gut and related diseases. We also provide an overview of potential therapeutic targets to restore the epithelial tight junction barrier in the GI tract.

Food as Treatment of Inflammatory Bowel Diseases

Inflammatory bowel diseases (IBD), namely, Crohn's disease (CD) and ulcerative colitis (UC), are lifelong and incurable chronic inflammatory diseases affecting 6.8 million people worldwide. By 2030, the prevalence of IBD is estimated to reach 1% of the population in Western countries, and thus there is an urgent need to develop effective therapies to reduce the burden of this disease. Microbiome dysbiosis is at the heart of the IBD pathophysiology, and current research and development efforts for IBD treatments have been focused on gut microbiome regulation. Diet can shape the intestinal microbiome. Diet is also preferred over medication, is safe, and has been proven to be an effective strategy for the management of IBD. Therefore, although often overlooked, dietary interventions targeting the microbiome represent ideal treatments for IBD. Here, I summarize the latest research on diet as a treatment for IBD from infancy to adulthood, compile evidence of the mechanisms of action behind diet as treatment, and, lastly, provide insights into future research focusing on culturally tailored diets for ethnic minority groups with increased incidence of IBD yet underrepresented in nutrition research.

Pattern Recognition Receptor Signaling and Cytokine Networks in Microbial Defenses and Regulation of Intestinal Barriers: Implications for Inflammatory Bowel Disease

Inflammatory bowel disease is characterized by defects in epithelial function and dysregulated inflammatory signaling by lamina propria mononuclear cells including macrophages and dendritic cells in response to microbiota. In this review, we focus on the role of pattern recognition receptors in the inflammatory response as well as epithelial barrier regulation. We explore cytokine networks that increase inflammation, regulate paracellular permeability, cause epithelial damage, up-regulate epithelial proliferation, and trigger restitutive processes. We focus on studies using patient samples as well as speculate on pathways that can be targeted to more holistically treat patients with inflammatory bowel disease.

Intestinal Barrier Dysfunction in Fatty Liver Disease: Roles of Microbiota, Mucosal Immune System, and Bile Acids

Nonalcoholic fatty liver disease (NAFLD) describes a spectrum of progressive liver diseases ranging from simple steatosis to steatohepatitis and fibrosis. Globally, NAFLD is the leading cause of morbidity and mortality associated with chronic liver disease, and NAFLD patients are at a higher risk of developing cirrhosis and hepatocellular carcinoma. While there is a consensus that inflammation plays a key role in promoting NAFLD progression, the underlying mechanisms are not well understood. Recent clinical and experimental evidence suggest that increased hepatic translocation of gut microbial antigens, secondary to diet-induced impairment of the intestinal barrier may be important in driving hepatic inflammation in NAFLD. Here, we briefly review various endogenous and exogenous factors influencing the intestinal barrier and present recent advances in our understanding of cellular and molecular mechanisms underlying intestinal barrier dysfunction in NAFLD.

Modulation of Intestinal Epithelial Permeability via Protease-Activated Receptor-2-Induced Autophagy

Protease-activated receptor 2 (PAR2) alleviates intestinal inflammation by upregulating autophagy. PAR2 also modulates tight junctions through β-arrestin signaling. Therefore, we investigated the effect of PAR2-induced autophagy on intestinal epithelial tight junctions and permeability. RT-PCR, Western blot analysis, and immunoprecipitation were performed to investigate the underlying molecular mechanisms by which PAR2 regulates autophagy and intestinal epithelial tight junctions. Inhibition of PAR2 by GB83, a PAR2 antagonist, decreased the expression of autophagy-related and tight-junction-related factors in Caco-2 cells. Moreover, inhibition of PAR2 decreased intestinal transepithelial electrical resistance. When PAR2 was activated, intestinal permeability was maintained, but when autophagy was suppressed by chloroquine, intestinal permeability was significantly increased. In addition, the prolongation of ERK1/2 phosphorylation by PAR2–ERK1/2–β-arrestin assembly was reduced under autophagy inhibition conditions. Therefore, PAR2 induces autophagy to regulate intestinal epithelial permeability, suggesting that it is related to the β-arrestin–ERK1/2 pathway. In conclusion, regulating intestinal epithelial permeability through PAR2-induced autophagy can help maintain mucosal barrier integrity. Therefore, these findings suggest that the regulation of PAR2 can be a suitable strategy to treat intestinal diseases caused by permeability dysfunction.

Characterization and Analysis of the Temporal and Spatial Dynamic of Several Enteritis Modeling Methodologies

Inflammatory bowel disease (IBD), such as Crohn’s disease and ulcerative colitis, is a complex disease involving genetic, immune, and microbiological factors. A variety of animal models of IBD have been developed to study the pathogenesis of human IBD, but there is no model that can fully represent the complexity of IBD. In this study, we established two acute enteritis models by oral 3% DSS or intraperitoneal injection of anti-CD3 antibody, and two chronic enteritis models by feeding 3 cycles of 1.5% DSS or 3 months of the high-fat diet, respectively, and then examined the clinical parameters, histological changes, and cytokine expression profiles after the successful establishment of the models. Our results indicated that in 3% DSS-induced acute enteritis, the colorectal injury was significantly higher than that of the small intestine, while in anti-CD3 antibody-induced acute enteritis, the small intestine injury was significantly higher than that of colorectal damage. Besides, in the 1.5% DSS-induced chronic enteritis, the damage was mainly concentrated in the colorectal, while the damage caused by long-term HFD-induced chronic enteritis was more focused on the small intestine. Therefore, our work provides a reference for selecting appropriate models when conducting research on factors related to the pathogenesis of IBD or evaluating the potential diagnosis and treatment possibilities of pharmaceuticals.

Oral nanomedicine for modulating immunity, intestinal barrier functions, and gut microbiome

The gastrointestinal tract (GIT) affects not only local diseases in the GIT but also various systemic diseases. Factors that can affect the health and disease of both GIT and the human body include 1) the mucosal immune system composed of the gut-associated lymphoid tissues and the lamina propria, 2) the intestinal barrier composed of mucus and intestinal epithelium, and 3) the gut microbiota. Selective delivery of drugs, including antigens, immune-modulators, intestinal barrier enhancers, and gut-microbiome manipulators, has shown promising results for oral vaccines, immune tolerance, treatment of inflammatory bowel diseases, and other systemic diseases, including cancer. However, physicochemical and biological barriers of the GIT present significant challenges for successful translation. With the advances of novel nanomaterials, oral nanomedicine has emerged as an attractive option to not only overcome these barriers but also to selectively deliver drugs to the target sites in GIT. In this review, we discuss the GIT factors and physicochemical and biological barriers in the GIT. Furthermore, we present the recent progress of oral nanomedicine for oral vaccines, immune tolerance, and anti-inflammation therapies. We also discuss recent advances in oral nanomedicine designed to fortify the intestinal barrier functions and modulate the gut microbiota and microbial metabolites. Finally, we opine about the future directions of oral nano-immunotherapy.

Arbutin ameliorated ulcerative colitis of mice induced by dextran sodium sulfate (DSS)

Accumulating evidence has revealed the anti-inflammatory effects of arbutin against various diseases. However, the effects of arbutin are not clarified in ulcerative colitis. This study was intended to investigate the protective effects and mechanisms of arbutin on DSS-induced colitis. Hematoxylin eosin staining was performed to determine the pathological damage of intestinal tissue in mice. Inflammatory factors levels in intestinal tissue were detected by enzyme linked immunosorbent assay (ELISA) assay. TUNEL staining showed the apoptosis levels of cells. Intestinal permeability was analyzed using the application of Fluorescein isothiocyanate Dextran (FD) 4. The levels of Zona Occludens 1 (ZO-1), occluding and claudin-1, and the related proteins in MAPK/ELK1 pathway were analyzed by Western blot. DSS promotes pathological injury, the levels of pro-inflammatory factors containing tumor necrosis factor alpha (TNF-α), Interleukin- 6 (IL-6) and myeloperoxidase (MPO), and cell apoptosis in the mouse colon. Additionally, intestinal permeability was increased and the levels of tight function-related proteins were increased following DSS induction. Its effects could be greatly improved by arbutin. Arbutin exerted effects by eliciting anti-inflammatory effects and maintaining normal intestinal mucosal barrier function, the action mechanism of which could be associated with MAPK/ELK1 pathway.

The Tight Junction Protein ZO-1 Is Dispensable for Barrier Function but Critical for Effective Mucosal Repair

BACKGROUNDS & AIMS

Increased permeability is implicated in the pathogenesis of intestinal disease. In vitro and in vivo studies have linked down-regulation of the scaffolding protein ZO-1, encoded by the TJP1 gene, to increased tight junction permeability. This has not, however, been tested in vivo. Here, we assessed the contributions of ZO-1 to in vivo epithelial barrier function and mucosal homeostasis.

METHODS

Public Gene Expression Omnibus data sets and biopsy specimens from patients with inflammatory bowel disease (IBD) and healthy control individuals were analyzed. Tjp1f/f;vil-CreTg mice with intestinal epithelial-specific ZO-1 knockout (ZO-1KO.IEC) mice and Tjp1f/f mice littermates without Cre expression were studied using chemical and immune-mediated models of disease as well as colonic stem cell cultures.

RESULTS

ZO-1 transcript and protein expression were reduced in biopsy specimens from patients with IBD. Despite mildly increased intestinal permeability, ZO-1KO.IEC mice were healthy and did not develop spontaneous disease. ZO-1KO.IEC mice were, however, hypersensitive to mucosal insults and displayed defective repair. Furthermore, ZO-1-deficient colonic epithelia failed to up-regulate proliferation in response to damage in vivo or Wnt signaling in vitro. ZO-1 was associated with centrioles in interphase cells and mitotic spindle poles during division. In the absence of ZO-1, mitotic spindles failed to correctly orient, resulting in mitotic catastrophe and abortive proliferation. ZO-1 is, therefore, critical for up-regulation of epithelial proliferation and successful completion of mitosis.

CONCLUSIONS

ZO-1 makes critical, tight junction-independent contributions to Wnt signaling and mitotic spindle orientation. As a result, ZO-1 is essential for mucosal repair. We speculate that ZO-1 down-regulation may be one cause of ineffective mucosal healing in patients with IBD.

Vitamin D Deficiency Exacerbates Colonic Inflammation Due to Activation of the Local Renin-Angiotensin System in the Colon

BACKGROUND

The renin-angiotensin system (RAS) is activated in inflammatory bowel disease (IBD), and vitamin D deficiency aggravates the development of colitis, but the relationship between the local colonic RAS and vitamin D is unclear with regard to the pathogenesis of IBD.

AIMS

To investigate whether vitamin D suppresses the local colonic RAS to prevent colonic mucosal inflammation in a mouse model of experimental colitis.

METHODS

C57BL/6 mice fed vitamin D-deficient (VDD) diet for 8 weeks were induced to colitis by 2,4,6-trinitrobenzenesulfonic acid (TNBS), with mice fed vitamin D-sufficient (VDS) diet as controls. Colitis severity was assessed by histology, and pro-inflammatory cytokines, RAS components, and signaling pathways were quantified by real-time RT-PCR and Western blotting.

RESULTS

C57BL/6 mice fed the VDD diet for 8 weeks exhibited significantly lower serum 25(OH)D₃ concentrations compared to mice fed the VDS diet. When these VDD mice were induced to colitis by TNBS, they exhibited more severe colonic inflammation and developed more severe colitis compared to the VDS counterparts. VDD diet feeding resulted in higher production of mucosal pro-inflammatory cytokines, higher activation of the myosin light chain kinase-tight junction regulatory pathway, and greater increases in mucosal permeability. VDD diet feeding also enhanced colonic RAS activation. Treatment with angiotensin II receptor blocker losartan markedly alleviated colitis in TNBS-induced VDD mice.

CONCLUSION

Vitamin D deficiency promotes colonic inflammation at least in part due to over activation of the local RAS in the colon.

Keratin 1 maintains the intestinal barrier in ulcerative colitis

BACKGROUND

The intestinal mechanical barrier plays a key role in the pathogenesis of ulcerative colitis (UC). Our previous study showed keratin 1 (KRT1) was downregulated in UC, but the mechanism by which KRT1 affects the intestinal barrier remains unknown.

OBJECTIVES

To explore the mechanism of KRT1 in the intestinal barrier in UC.

METHODS

Colonic tissues were collected from 20 UC patients before and after mucosal healing (MH) and 15 healthy controls. The expression of KRT1 was measured by PCR, western blotting and immunohistochemistry (IHC). A dextran sulfate sodium (DSS)-induced colitis model was established in krt1 transgenic (TG) mice, and the mice were treated with methylprednisolone (MP) to explore the role of KRT1 in the intestinal barrier. Inflammation was evaluated through the DAI score, colon, spleen and H&E. The expression of KRT1 and tight junction (TJ) proteins in mouse was analysed by the same methods.

RESULTS

The transcription and expression of KRT1 in UC was decreased and recovered after MH but did not reach the level of the healthy controls. Similar to the clinical results, the expression of krt1 was decreased in DSS-induced colitis and upregulated after MP. Moreover, the krt1 TG group exhibited less inflammation than wild-type (WT) group. The expression of Occludin and ZO-1 decreased after DSS induction, the decreases in Occludin and ZO-1 in the krt1 TG group were lower than WT group, which was significantly increased after MP, while the expression of Claudin-2 exhibited the opposite effect.

CONCLUSIONS

Keratin 1 maintains the intestinal barrier by upregulating TJ proteins in UC.

Foxo1 controls gut homeostasis and commensalism by regulating mucus secretion

Mucus produced by goblet cells in the gastrointestinal tract forms a biological barrier that protects the intestine from invasion by commensals and pathogens. However, the host-derived regulatory network that controls mucus secretion and thereby changes gut microbiota has not been well studied. Here, we identify that Forkhead box protein O1 (Foxo1) regulates mucus secretion by goblet cells and determines intestinal homeostasis. Loss of Foxo1 in intestinal epithelial cells (IECs) results in defects in goblet cell autophagy and mucus secretion, leading to an impaired gut microenvironment and dysbiosis. Subsequently, due to changes in microbiota and disruption in microbiome metabolites of short-chain fatty acids, Foxo1 deficiency results in altered organization of tight junction proteins and enhanced susceptibility to intestinal inflammation. Our study demonstrates that Foxo1 is crucial for IECs to establish commensalism and maintain intestinal barrier integrity by regulating goblet cell function.

Culture of Intestinal Epithelial Cell Monolayers and Their Use in Multiplex Macromolecular Permeability Assays for In Vitro Analysis of Tight Junction Size Selectivity

Tight junctions form a selectively permeable barrier that limits paracellular flux across epithelial-lined surfaces. Small molecules (less than ∼8 Å diameter) can traverse the junction via the size- and charge-selective, high-conductance pore pathway. In contrast, the low-conductance leak pathway accommodates larger macromolecules (up to ∼100 Å diameter) and is not charge-selective. Flux across the tight junction-independent, high-conductance, non-selective, unrestricted pathway occurs at sites of epithelial damage. Cytokines can regulate each of these pathways, but commonly used measures of barrier function cannot discriminate between tight junction regulation and epithelial damage. This article describes methods for culturing intestinal epithelial cell monolayers and assessing the impact of cytokine treatment on leak and unrestricted pathway permeabilities. © 2020 Wiley Periodicals LLC. Basic Protocol 1: Generation and culture of cell monolayers in Transwells Basic Protocol 2: Assessment of cytokine (IFNγ and TNF) treatment effects on barrier function Support Protocol: Immunofluorescent staining of monolayers Basic Protocol 3: Multiplex flux assay.

Role of MicroRNA in Inflammatory Bowel Disease: Clinical Evidence and the Development of Preclinical Animal Models

The dysregulation of microRNA (miRNA) is implicated in cancer, inflammation, cardiovascular disorders, drug resistance, and aging. While most researchers study miRNA's role as a biomarker, for example, to distinguish between various sub-forms or stages of a given disease of interest, research is also ongoing to utilize these small nucleic acids as therapeutics. An example of a common pleiotropic disease that could benefit from miRNA-based therapeutics is inflammatory bowel disease (IBD), which is characterized by chronic inflammation of the small and large intestines. Due to complex interactions between multiple factors in the etiology of IBD, development of therapies that effectively maintain remission for this disease is a significant challenge. In this review, we discuss the role of dysregulated miRNA expression in the context of clinical ulcerative colitis (UC) and Crohn's disease (CD)-the two main forms of IBD-and the various preclinical mouse models of IBD utilized to validate the therapeutic potential of targeting these miRNA. Additionally, we highlight advances in the development of genetically engineered animal models that recapitulate clinical miRNA expression and provide powerful preclinical models to assess the diagnostic and therapeutic promise of miRNA in IBD.