Intracellular MLCK1 diversion reverses barrier loss to restore mucosal homeostasis

Protein isoform-centric therapeutics: expanding targets and increasing specificity

Most protein-coding genes produce multiple protein isoforms; however, these isoforms are commonly neglected in drug discovery. The expression of protein isoforms can be specific to a disease, tissue and/or developmental stage, and this specific expression can be harnessed to achieve greater drug specificity than pan-targeting of all gene products and to enable improved treatments for diseases caused by aberrant protein isoform production. In recent years, several protein isoform-centric therapeutics have been developed. Here, we collate these studies and clinical trials to highlight three distinct but overlapping modes of action for protein isoform-centric drugs: isoform switching, isoform introduction or depletion, and modulation of isoform activity. In addition, we discuss how protein isoforms can be used clinically as targets for cell type-specific drug delivery and immunotherapy, diagnostic biomarkers and sources of cancer neoantigens. Collectively, we emphasize the value of a focus on isoforms as a route to discovering drugs with greater specificity and fewer adverse effects. This approach could enable the targeting of proteins for which pan-inhibition of all isoforms is toxic and poorly tolerated.

Bifidobacterium bifidum Strain BB1 Inhibits Tumor Necrosis Factor-α-Induced Increase in Intestinal Epithelial Tight Junction Permeability via Toll-Like Receptor-2/Toll-Like Receptor-6 Receptor Complex-Dependent Stimulation of Peroxisome Proliferator-Activated Receptor γ and Suppression of NF-κB p65

Bifidobacterium bifidum strain BB1 causes a strain-specific enhancement in intestinal epithelial tight junction (TJ) barrier. Tumor necrosis factor (TNF)-α induces an increase in intestinal epithelial TJ permeability and promotes intestinal inflammation. The major purpose of this study was to delineate the protective effect of BB1 against the TNF-α-induced increase in intestinal TJ permeability and to unravel the intracellular mechanisms involved. TNF-α produces an increase in intestinal epithelial TJ permeability in Caco-2 monolayers and in mice. Herein, the addition of BB1 inhibited the TNF-α increase in Caco-2 intestinal TJ permeability and mouse intestinal permeability in a strain-specific manner. BB1 inhibited the TNF-α-induced increase in intestinal TJ permeability by interfering with TNF-α-induced enterocyte NF-κB p50/p65 and myosin light chain kinase (MLCK) gene activation. The BB1 protective effect against the TNF-α-induced increase in intestinal permeability was mediated by toll-like receptor-2/toll-like receptor-6 heterodimer complex activation of peroxisome proliferator-activated receptor γ (PPAR-γ) and PPAR-γ pathway inhibition of TNF-α-induced inhibitory kappa B kinase α (IKK-α) activation, which, in turn, resulted in a step-wise inhibition of NF-κB p50/p65, MLCK gene, MLCK kinase activity, and MLCK-induced opening of the TJ barrier. In conclusion, these studies unraveled novel intracellular mechanisms of BB1 protection against the TNF-α-induced increase in intestinal TJ permeability. The current data show that BB1 protects against the TNF-α-induced increase in intestinal epithelial TJ permeability via a PPAR-γ-dependent inhibition of NF-κB p50/p65 and MLCK gene activation.

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.

IBD Matchmaking - Rational Combination Therapy

A growing number of patients with Crohn's disease and ulcerative colitis have disease that is refractory to multiple advanced therapies, have undergone multiple surgeries, and require further treatment options. For this reason, there has been increasing use of multiple simultaneous advanced targeted therapies. Although the knowledge on combined advanced targeted therapy (CATT) in inflammatory bowel disease (IBD) has been largely limited to observational data and early-phase randomized controlled trials, combination of therapies is commonplace in many other diseases. This review discusses conceptual frameworks of CATT in IBD, provides context of combined therapies in other diseases, provides current evidence for CATT in IBD, and projects future applications and positioning of CATT using existing, novel, and orthogonal mechanisms of action. CATT aims to address the need to overcome low efficacy rates and frequent loss of response of current individual therapies. Both treatment exposure and disease duration are major determinants of response to therapy. Identification of safe and effective CATT may impact positioning of this strategy to apply to a broader IBD population.

The Effect of Protein Nutritional Support on Inflammatory Bowel Disease and Its Potential Mechanisms

Inflammatory bowel disease (IBD), a complex chronic inflammatory bowel disorder that includes Crohn's disease (CD) and Ulcerative Colitis (UC), has become a globally increasing health concern. Nutrition, as an important factor influencing the occurrence and development of IBD, has attracted more and more attention. As the most important nutrient, protein can not only provide energy and nutrition required by patients, but also help repair damaged intestinal tissue, enhance immunity, and thus alleviate inflammation. Numerous studies have shown that protein nutritional support plays a significant role in the treatment and remission of IBD. This article presents a comprehensive review of the pathogenesis of IBD and analyzes and summarizes the potential mechanisms of protein nutritional support in IBD. Additionally, it provides an overview of the clinical effects of protein nutritional support in IBD and its impact on clinical complications. Research findings reveal that protein nutritional support demonstrates significant benefits in improving clinical symptoms, reducing the risk of complications, and improving quality of life in IBD patients. Therefore, protein nutritional support is expected to provide a new approach for the treatment of IBD.

Lactobacillus acidophilus inhibits the TNF-α-induced increase in intestinal epithelial tight junction permeability via a TLR-2 and PI3K-dependent inhibition of NF-κB activation

Background

Defective intestinal epithelial tight junction (TJ), characterized by an increase in intestinal TJ permeability, has been shown to play a critical role in the pathogenesis of inflammatory bowel disease (IBD). Tumor necrosis factor-α (TNF-α) is a key pro-inflammatory cytokine involved in the immunopathology of IBD and has been shown to cause an increase in intestinal epithelial TJ permeability. Although TNF-α antibodies and other biologics have been advanced for use in IBD treatment, these therapies are associated with severe side effects and have limited efficacy, and there is an urgent need for therapies with benign profiles and high therapeutic efficacy. Probiotic bacteria have beneficial effects and are generally safe and represent an important class of potential therapeutic agents in IBD. Lactobacillus acidophilus (LA) is one of the most used probiotics for wide-ranging health benefits, including in gastrointestinal, metabolic, and inflammatory disorders. A specific strain of LA, LA1, was recently demonstrated to have protective and therapeutic effects on the intestinal epithelial TJ barrier. However, the mechanisms of actions of LA1 remain largely unknown.

Methods

The primary aim of this study was to investigate microbial-epithelial interactions and novel signaling pathways that regulate the effect of LA1 on TNF-α-induced increase in intestinal epithelial TJ permeability, using cell culture and animal model systems.

Results and Conclusion

Pre-treatment of filter-grown Caco-2 monolayers with LA1 prevented the TNF-α-induced increase in intestinal epithelial TJ permeability by inhibiting TNF-α-induced activation of NF-κB p50/p65 and myosin light chain kinase (MLCK) gene and kinase activity in a TLR-2-dependent manner. LA1 produced a TLR-2- and MyD88-dependent activation of NF-κB p50/p65 in immune cells; however, LA1, in intestinal cells, inhibited the NF-κB p50/p65 activation in a TLR-2-dependent but MyD88-independent manner. In addition, LA1 inhibition of NF-κB p50/p65 and MLCK gene was mediated by TLR-2 pathway activation of phosphatidylinositol 3-kinase (PI3K) and IKK-α phosphorylation. Our results demonstrated novel intracellular signaling pathways by which LA1/TLR-2 suppresses the TNF-α pathway activation of NF-κB p50/p65 in intestinal epithelial cells and protects against the TNF-α-induced increase in intestinal epithelial TJ permeability.

Effects of proton pump inhibitors on inflammatory bowel disease: An updated review

Inflammatory bowel disease (IBD) is believed to be caused by various factors, including abnormalities in disease susceptibility genes, environmental factors, immune factors, and intestinal bacteria. Proton pump inhibitors (PPIs) are the primary drugs used to treat acid-related diseases. They are also commonly prescribed to patients with IBD. Recent studies have suggested a potential association between the use of certain medications, such as PPIs, and the occurrence and progression of IBD. In this review, we summarize the potential impact of PPIs on IBD and analyze the underlying mechanisms. Our findings may provide insights for conducting further investigations into the effects of PPIs on IBD and serve as an important reminder for physicians to exercise caution when prescribing PPIs to patients with IBD.

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.

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.

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.

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.

Deciphering internal and external factors influencing intestinal junctional complexes

The intestinal barrier, an indispensable guardian of gastrointestinal health, mediates the intricate exchange between internal and external environments. Anchored by evolutionarily conserved junctional complexes, this barrier meticulously regulates paracellular permeability in essentially all living organisms. Disruptions in intestinal junctional complexes, prevalent in inflammatory bowel diseases and irritable bowel syndrome, compromise barrier integrity and often lead to the notorious "leaky gut" syndrome. Critical to the maintenance of the intestinal barrier is a finely orchestrated network of intrinsic and extrinsic factors that modulate the expression, composition, and functionality of junctional complexes. This review navigates through the composition of key junctional complex components and the common methods used to assess intestinal permeability. It also explores the critical intracellular signaling pathways that modulate these junctional components. Lastly, we delve into the complex dynamics between the junctional complexes, microbial communities, and environmental chemicals in shaping the intestinal barrier function. Comprehending this intricate interplay holds paramount importance in unraveling the pathophysiology of gastrointestinal disorders. Furthermore, it lays the foundation for the development of precise therapeutic interventions targeting barrier dysfunction.

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.

Activation of the 5-hydroxytryptamine 4 receptor ameliorates tight junction barrier dysfunction in the colon of type 1 diabetic mice

Hyperglycemia drives dysfunction of the intestinal barrier. 5-Hydroxytryptaine 4 receptor (5-HT 4R) agonists have been considered therapeutics for constipation in clnic. However, the roles of 5-HT 4R activation in mucosa should be fully realized. Here, we investigate the effects of 5-HT 4R activation on diabetes-induced disruption of the tight junction (TJ) barrier in the colon. Not surprisingly, the TJ barrier in diabetic mice with or without 5-HT 4R is tremendously destroyed, as indicated by increased serum fluorescein isothiocyanate (FITC)-dextran and decreased transepithelial electrical resistance (TER). Simultaneously, decreased expressions of TJ proteins are shown in both wild-type (WT) and 5-HT 4R knockout (KO) mice with diabetes. Notably, chronic treatment with intraperitoneal injection of a 5-HT 4R agonist in WT mice with diabetes repairs the TJ barrier and promotes TJ protein expressions, including occludin, claudin-1 and ZO-1, in the colon, whereas a 5-HT 4R agonist does not improve TJ barrier function or TJ protein expressions in 5-HT 4R KO mice with diabetes. Furthermore, stimulation of 5-HT 4R inhibits diabetes-induced upregulation of myosin light chain kinase (MLCK), Rho-associated coiled coil protein kinase 1 (ROCK1), and phosphorylated myosin light chain (p-MLC), which are key molecules that regulate TJ integrity, in the colonic mucosa of WT mice. However, such action induced by a 5-HT 4R agonist is not observed in 5-HT 4R KO mice with diabetes. These findings indicate that 5-HT 4R activation may restore TJ integrity by inhibiting the expressions of MLCK, ROCK1 and p-MLC, improving epithelial barrier function in diabetes.

The function of alternative splicing in the proteome: rewiring protein interactomes to put old functions into new contexts

Alternative splicing affects more than 95% of multi-exon genes in the human genome. These changes affect the proteome in a myriad of ways. Here, we review our understanding of the breadth of these changes from their effect on protein structure to their influence on interactions. These changes encompass effects on nucleic acid binding in the nucleus to protein-carbohydrate interactions in the extracellular milieu, altering interactions involving all major classes of biological molecules. Protein isoforms have profound influences on cellular and tissue physiology, for example, by shaping neuronal connections, enhancing insulin secretion by pancreatic beta cells and allowing for alternative viral defense strategies in stem cells. More broadly, alternative splicing enables repurposing proteins from one context to another and thereby contributes to both the evolution of new traits as well as the creation of disease-specific interactomes that drive pathological phenotypes. In this Review, we highlight this universal character of alternative splicing as a central regulator of protein function with implications for almost every biological process.

Cannabidiol attenuates inflammatory impairment of intestinal cells expanding biomaterial-based therapeutic approaches

Cannabis-based biomaterials have the potential to deliver anti-inflammatory therapeutics specifically to desired cells, tissues, and organs, enhancing drug delivery and the effectiveness of anti-inflammatory treatment while minimizing toxicity. As a major component of Cannabis, Cannabidiol (CBD) has gained major attention in recent years because of its potential therapeutic properties, e.g., for restoring a disturbed barrier resulting from inflammatory conditions. The aim of this study was to test the hypothesis that CBD has beneficial effects under normal and inflammatory conditions in the established non-transformed intestinal epithelial cell model IPEC-J2. CBD induced a significant increase in transepithelial electrical resistance (TER) values and a decrease in the paracellular permeability of [³H]-D-Mannitol, indicating a strengthening effect on the barrier. Under inflammatory conditions induced by tumor necrosis factor alpha (TNFα), CBD stabilized the TER and mitigated the increase in paracellular permeability. Additionally, CBD prevented the barrier-disrupting effects of TNFα on the distribution and localization of sealing TJ proteins. CBD also affected the expression of TNF receptors. These findings demonstrate the potential of CBD as a component of Cannabis-based biomaterials used in the development of novel therapeutic approaches against inflammatory pathogenesis.

Intestinal barrier in inflammatory bowel disease: A bibliometric and knowledge-map analysis

BACKGROUND

Barrier surfaces composed of specialized epithelial cells separate the host body from the external environment, and are essential for maintaining proper intestinal physiologic and immune homeostasis.

AIM

To explore the development trends and research hotspots of intestinal barrier research in inflammatory bowel disease (IBD).

METHODS

The publications related to the intestinal barrier in IBD were obtained from the Web of Science Core Collection database. Bibliometric analysis and visualization were conducted using VOSviewer, CiteSpace and R software.

RESULTS

A total of 4482 articles published between 2002 and 2022 were identified. The United States is dominant in intestinal barrier research, whereas the University of Chicago is the most active institution. Jerrold from Harvard Medical School was the most productive authors with the most citations. The journals Inflammatory Bowel Disease and Gastroenterology have made significant contributions in this field. The keywords appearing at high frequency related to the intestinal barrier in IBD were detected, including nuclear factor kappa B, tumor necrosis factor-α, apoptosis, oxidative stress and probiotics. Among them, antioxidants, Akkermansia muciniphila, nanoparticles, short-chain fatty acids and extracellular vesicles have received growing interest in recent research.

CONCLUSION

The intestinal barrier field is developing rapidly with extensive cooperation. Targeting the gut microbiota and dietary metabolism to regulate the intestinal barrier has shown promising prospective applications and has generated broad interest. The importance of the intestinal barrier in IBD is gradually being fully recognized, providing a new therapeutic perspective for improving inflammation and prognosis.

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.

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

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

Transcription factor Krüppel-like factor 4 upregulated G protein-coupled receptor 30 alleviates intestinal inflammation and apoptosis, and protects intestinal integrity from intestinal ischemia-reperfusion injury

INTRODUCTION

Intestinal ischemia/reperfusion (I/R) injury is a common clinical event occurring during multiple clinical pathological processes. Here, we designed this paper to discuss the role of G protein-coupled receptor 30 (GPR30) playing in intestinal I/R injury.

METHODS

An oxygen-glucose deprivation/reoxygenation (OGD/R) cell model was established to simulate the pathological process of I/R injury. With the application of enzyme-linked immunosorbent assay, TUNEL, and transepithelial electrical resistance (TEER) assays, the levels of inflammatory cytokines, cell apoptosis, and intestinal integrity were estimated. The corresponding proteins were estimated by applying western blot. Immunofluorescence was conducted to examine N-terminal Gasdermin D (GSDMD-N) expression. The interplay between KLF4 and GPR30 was demonstrated by dual-luciferase reporter assay and chromatin immunoprecipitation.

RESULTS

The results showed that GPR30 was downregulated in Caco-2 cells exposed to OGD/R. GPR30 overexpression reduced the production of TNF-α, IL-6, IL-1β, and IL-18, the TUNEL-positive cells, as well as the contents of p-p65, Cox-2, Inos, Bax, and cleaved-PARP, but elevated the expression of Bcl-2 in OGD/R-induced Caco-2 cells. In addition, OGD/R-induced the reduction of TEER value and reduced expression of tight junction proteins in Caco-2 cells, which was partially restored by GPR30 overexpression. Furthermore, GPR30 suppressed nod-like receptor pyrin 3 inflammasome and GSDMD-N expression. It was evidenced that Krüppel-like factor 4 (KLF4) could directly bind to GPR30 promoter and positively regulate GPR30 expression. The regulation of GPR30 overexpression above was weakened by KLF4 knockdown.

CONCLUSION

Collectively, our findings suggested that KLF4 could transcriptionally upregulate GPR30, and GPR30 prevented intestine I/R injury by inhibiting inflammation and apoptosis, and maintaining intestinal integrity that provides potential targets for mitigating the I/R injury.

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.

Cytokines and intestinal epithelial permeability: A systematic review

BACKGROUND

The intestinal mucosa is composed of a well-organized epithelium, acting as a physical barrier to harmful luminal contents, while simultaneously ensuring absorption of physiological nutrients and solutes. Increased intestinal permeability has been described in various chronic diseases, leading to abnormal activation of subepithelial immune cells and overproduction of inflammatory mediators. This review aimed to summarize and evaluate the effects of cytokines on intestinal permeability.

METHODS

A systematic review of the literature was performed in the Medline, Cochrane and Embase databases, up to 01/04/2022, to identify published studies assessing the direct effect of cytokines on intestinal permeability. We collected data on the study design, the method of assessment of intestinal permeability, the type of intervention and the subsequent effect on gut permeability.

RESULTS

A total of 120 publications were included, describing a total of 89 in vitro and 44 in vivo studies. TNFα, IFNγ or IL-1β were the most frequently studied cytokines, inducing an increase in intestinal permeability through a myosin light-chain-mediated mechanism. In situations associated with intestinal barrier disruption, such as inflammatory bowel diseases, in vivo studies showed that anti-TNFα treatment decreased intestinal permeability while achieving clinical recovery. In contrast to TNFα, IL-10 decreased permeability in conditions associated with intestinal hyperpermeability. For some cytokines (e.g. IL-17, IL-23), results are conflicting, with both an increase and a decrease in gut permeability reported, depending on the study model, methodology, or the studied conditions (e.g. burn injury, colitis, ischemia, sepsis).

CONCLUSION

This systematic review provides evidence that intestinal permeability can be directly influenced by cytokines in numerous conditions. The immune environment probably plays an important role, given the variability of their effect, according to different conditions. A better understanding of these mechanisms could open new therapeutic perspectives for disorders associated with gut barrier dysfunction.

MYOSIN LIGHT CHAIN KINASE DELETION WORSENS LUNG PERMEABILITY AND INCREASES MORTALITY IN PNEUMONIA-INDUCED SEPSIS

ABSTRACT

Increased epithelial permeability in sepsis is mediated via disruptions in tight junctions, which are closely associated with the perijunctional actin-myosin ring. Genetic deletion of myosin light chain kinase (MLCK) reverses sepsis-induced intestinal hyperpermeability and improves survival in a murine model of intra-abdominal sepsis. In an attempt to determine the generalizability of these findings, this study measured the impact of MLCK deletion on survival and potential associated mechanisms following pneumonia-induced sepsis. MLCK -/- and wild-type mice underwent intratracheal injection of Pseudomonas aeruginosa . Unexpectedly, survival was significantly worse in MLCK -/- mice than wild-type mice. This was associated with increased permeability to Evans blue dye in bronchoalveolar lavage fluid but not in tissue homogenate, suggesting increased alveolar epithelial leak. In addition, bacterial burden was increased in bronchoalveolar lavage fluid. Cytokine array using whole-lung homogenate demonstrated increases in multiple proinflammatory and anti-inflammatory cytokines in knockout mice. These local pulmonary changes were associated with systemic inflammation with increased serum levels of IL-6 and IL-10 and a marked increase in bacteremia in MLCK -/- mice. Increased numbers of both bulk and memory CD4 + T cells were identified in the spleens of knockout mice, with increased early and late activation. These results demonstrate that genetic deletion of MLCK unexpectedly increases mortality in pulmonary sepsis, associated with worsened alveolar epithelial leak and both local and systemic inflammation. This suggests that caution is required in targeting MLCK for therapeutic gain in sepsis.

Prospects for macrolide therapy of asthma and COPD

Macrolide compounds, many of which are derived from natural sources, all share a lactone ring structure, but of varying sizes. Their biological activities differ with structure and size but tend to overlap. Marketed macrolide drugs include immunosuppressives and antibiotics. Some of the latter have been shown to exert anti-inflammatory activities, due to direct effects on inflammatory cells and processes when used for respiratory infections. Consequently, azithromycin is included in clinical guidelines for COPD and asthma treatment, though it has the disadvantage, as an antibiotic, of increasing bacterial resistance. COPD and asthma, however, like several chronic inflammatory diseases involving other organs, are driven to a large extent by epithelial barrier dysfunction. Recently, azithromycin was shown to directly enhance epithelial barrier function and a new class of derivatives, barriolides, is under development with the lead indication COPD. It is thus likely that by circumventing antibiosis and acting on a crucial etiological disease process, this type of agent will open up a new, safer approach to COPD and asthma therapy with macrolides.

IBD disease-modifying therapies: insights from emerging therapeutics

Inflammatory bowel disease (IBD) pathogenesis is associated with gut mucosal inflammation, epithelial damage, and dysbiosis leading to a dysregulated gut mucosal barrier. However, the extent and underlying mechanisms remain largely unknown. Current treatment regimens have focused mainly on treating IBD symptoms; however, such treatment strategies do not address mucosal epithelial repair, barrier homeostasis, or intestinal dysbiosis. Although attempts have been made to identify new therapeutic modalities to enhance gut barrier functions, these are at an early developmental stage and have not been wholly successful. We review conventional therapies, the possible relevant role of gut barrier-protecting agents, and biomaterial strategies relating to combination therapies that may pave the way towards developing new therapeutic approaches for IBD.

Phase separation of an actin nucleator by junctional microtubules regulates epithelial function

Liquid-liquid phase separation (LLPS) is involved in various dynamic biological phenomena. In epithelial cells, dynamic regulation of junctional actin filaments tethered to the apical junctional complex (AJC) is critical for maintaining internal homeostasis against external perturbations; however, the role of LLPS in this process remains unknown. Here, after identifying a multifunctional actin nucleator, cordon bleu (Cobl), as an AJC-enriched microtubule-associated protein, we conducted comprehensive in vitro and in vivo analyses. We found that apical microtubules promoted LLPS of Cobl at the AJC, and Cobl actin assembly activity increased upon LLPS. Thus, microtubules spatiotemporally regulated junctional actin assembly for epithelial morphogenesis and paracellular barriers. Collectively, these findings established that LLPS of the actin nucleator Cobl mediated dynamic microtubule-actin cross-talk in junctions, which fine-tuned the epithelial barrier.

Epithelial RAC1-dependent cytoskeleton dynamics controls cell mechanics, cell shedding and barrier integrity in intestinal inflammation

OBJECTIVE

Increased apoptotic shedding has been linked to intestinal barrier dysfunction and development of inflammatory bowel diseases (IBD). In contrast, physiological cell shedding allows the renewal of the epithelial monolayer without compromising the barrier function. Here, we investigated the role of live cell extrusion in epithelial barrier alterations in IBD.

DESIGN

Taking advantage of conditional GGTase and RAC1 knockout mice in intestinal epithelial cells (Pggt1b ^iΔIEC and Rac1 ^iΔIEC mice), intravital microscopy, immunostaining, mechanobiology, organoid techniques and RNA sequencing, we analysed cell shedding alterations within the intestinal epithelium. Moreover, we examined human gut tissue and intestinal organoids from patients with IBD for cell shedding alterations and RAC1 function.

RESULTS

Epithelial Pggt1b deletion led to cytoskeleton rearrangement and tight junction redistribution, causing cell overcrowding due to arresting of cell shedding that finally resulted in epithelial leakage and spontaneous mucosal inflammation in the small and to a lesser extent in the large intestine. Both in vivo and in vitro studies (knockout mice, organoids) identified RAC1 as a GGTase target critically involved in prenylation-dependent cytoskeleton dynamics, cell mechanics and epithelial cell shedding. Moreover, inflamed areas of gut tissue from patients with IBD exhibited funnel-like structures, signs of arrested cell shedding and impaired RAC1 function. RAC1 inhibition in human intestinal organoids caused actin alterations compatible with arresting of cell shedding.

CONCLUSION

Impaired epithelial RAC1 function causes cell overcrowding and epithelial leakage thus inducing chronic intestinal inflammation. Epithelial RAC1 emerges as key regulator of cytoskeletal dynamics, cell mechanics and intestinal cell shedding. Modulation of RAC1 might be exploited for restoration of epithelial integrity in the gut of patients with IBD.

Glutamine supplementation attenuates intestinal apoptosis by inducing heat shock protein 70 in heatstroke rats

BACKGROUND

Heatstroke is the most hazardous heat-related illness and has a high fatality rate. We investigated whether glutamine supplementation could have a protective effect on heatstroke rats.

METHODS

Twenty-five 12-week-old male Wistar rats (weight 305±16 g) were randomly divided into a control group (n=5), heatstroke (HS) group (n=10), and heatstroke+glutamine (HSG) group (n=10). Seven days before heat exposure, glutamine (0.4 g/[kg·d]) was administered to the rats in the HSG group by gavage every day. Three hours after heat exposure, serum samples were collected to detect white blood cells, coagulation indicators, blood biochemical indicators, and inflammatory cytokines in the rats. The small intestine tissue was stained to analyze pathological structural changes and apoptosis. Finally, immunohistochemistry and Western blotting were used to analyze the expression levels of heat shock protein 70 (HSP70). Multiple comparisons were analyzed by using one-way analysis of variance, and the Bonferroni test was conducted for the post hoc comparisons.

RESULTS

After heat exposure, the core temperature of the HS group (40.65±0.31 °C) was higher than the criterion of heatstroke, whereas the core temperature of the HSG group (39.45±0.14 °C) was lower than the criterion. Glutamine supplementation restored the increased white blood cells, coagulation indicators, blood biochemical indicators, and inflammatory cytokines that were induced by heatstroke to normal levels. The intestinal mucosa was injured, and the structure of tight junctions was damaged in the HS group; however, the structure of intestinal mucosal epithelial cells was stable in the HSG group. Glutamine supplementation alleviated intestinal apoptosis and up-regulated HSP70 expression.

CONCLUSION

Glutamine supplementation may alleviate intestinal apoptosis by inducing the expression of HSP70 and have a protective effect on heatstroke rats.

New insights into bacterial mechanisms and potential intestinal epithelial cell therapeutic targets of inflammatory bowel disease

The global incidence of inflammatory bowel disease (IBD) has increased rapidly in recent years, but its exact etiology remains unclear. In the past decade, IBD has been reported to be associated with dysbiosis of gut microbiota. Although not yet proven to be a cause or consequence of IBD, the common hypothesis is that at least some alterations in the microbiome are protective or pathogenic. Furthermore, intestinal epithelial cells (IECs) serve as a protective physical barrier for gut microbiota, essential for maintaining intestinal homeostasis and actively contributes to the mucosal immune system. Thus, dysregulation within the intestinal epithelium increases intestinal permeability, promotes the entry of bacteria, toxins, and macromolecules, and disrupts intestinal immune homeostasis, all of which are associated with the clinical course of IBD. This article presents a selective overview of recent studies on bacterial mechanisms that may be protective or promotive of IBD in biological models. Moreover, we summarize and discuss the recent discovery of key modulators and signaling pathways in the IECs that could serve as potential IBD therapeutic targets. Understanding the role of the IECs in the pathogenesis of IBD may help improve the understanding of the inflammatory process and the identification of potential therapeutic targets to help ameliorate this increasingly common disease.

Differential Response to the Course of Cryptosporidium parvum Infection and Its Impact on Epithelial Integrity in Differentiated versus Undifferentiated Human Intestinal Enteroids

Cryptosporidium is a leading cause of diarrhea and death in young children and untreated AIDS patients and causes waterborne outbreaks. Pathogenic mechanisms underlying diarrhea and intestinal dysfunction are poorly understood. We previously developed stem-cell derived human intestinal enteroid (HIE) models for Cryptosporidium parvum which we used in this study to investigate the course of infection and its effect on intestinal epithelial integrity. By immunofluorescence and confocal microscopy, there was robust infection of undifferentiated and differentiated HIEs in two and three-dimensional (2D, 3D) models. Infection of differentiated HIEs in the 2D model was greater than that of undifferentiated HIEs but lasted only for 3 days, whereas infection persisted for 21 days and resulted in completion of the life cycle in undifferentiated HIEs. Infection of undifferentiated HIE monolayers suggest that C. parvum infects LGR5+ stem cells. Transepithelial electrical resistance measurement of HIEs in the 2D model revealed that infection resulted in decreased epithelial integrity which persisted in differentiated HIEs but recovered in undifferentiated HIEs. Compromised epithelial integrity was reflected in disorganization of the tight and adherens junctions as visualized using the markers ZO-1 and E-cadherin, respectively. Quantitation using the image analysis tools Tight Junction Organizational Rate and Intercellular Junction Organization Quantification, measurement of monolayer height, and RNA transcripts of both proteins by quantitative reverse transcription PCR confirmed that disruption persisted in differentiated HIEs but recovered in undifferentiated HIEs. These models, which more accurately recapitulate human infection, will be useful tools to dissect pathogenic mechanisms underlying diarrhea and intestinal dysfunction in cryptosporidiosis.

Mitochondria-Targeted Antioxidant SkQ1 Prevents the Development of Experimental Colitis in Mice and Impairment of the Barrier Function of the Intestinal Epithelium

Mitochondria-targeted antioxidants have become promising candidates for the therapy of various pathologies. The mitochondria-targeted antioxidant SkQ1, which is a derivative of plastoquinone, has been successfully used in preclinical studies for the treatment of cardiovascular and renal diseases, and has demonstrated anti-inflammatory activity in a number of inflammatory disease models. The present work aimed to investigate the therapeutic potential of SkQ1 and C12TPP, the analog of SkQ1 lacking the antioxidant quinone moiety, in the prevention of sodium dextran sulfate (DSS) experimental colitis and impairment of the barrier function of the intestinal epithelium in mice. DSS-treated animals exhibited weight loss, bloody stool, dysfunction of the intestinal epithelium barrier (which was observed using FITC-dextran permeability), reduced colon length, and histopathological changes in the colon mucosa. SkQ1 prevented the development of clinical and histological changes in DSS-treated mice. SkQ1 also reduced mRNA expression of pro-inflammatory molecules TNF, IL-6, IL-1β, and ICAM-1 in the proximal colon compared with DSS-treated animals. SkQ1 prevented DSS-induced tight junction disassembly in Caco-2 cells. Pretreatment of mice by C12TPP did not protect against DSS-induced colitis. Furthermore, C12TPP did not prevent DSS-induced tight junction disassembly in Caco-2 cells. Our results suggest that SkQ1 may be a promising therapeutic agent for the treatment of inflammatory bowel diseases, in particular ulcerative colitis.

How Nanoparticles Open the Paracellular Route of Biological Barriers: Mechanisms, Applications, and Prospects

Biological barriers are essential physiological protective systems and obstacles to drug delivery. Nanoparticles (NPs) can access the paracellular route of biological barriers, either causing adverse health impacts on humans or producing therapeutic opportunities. This Review introduces the structural and functional influences of NPs on the key components that govern the paracellular route, mainly tight junctions, adherens junctions, and cytoskeletons. Furthermore, we evaluate their interaction mechanisms and address the influencing factors that determine the ability of NPs to open the paracellular route, which provides a better knowledge of how NPs can open the paracellular route in a safer and more controllable way. Finally, we summarize limitations in the research models and methodologies of the existing research in the field and provide future research direction. This Review demonstrates the in-depth causes for the reversible opening or destruction of the integrity of barriers generated by NPs; more importantly, it contributes insights into the design of NP-based medications to boost paracellular drug delivery efficiency.

Genetic polymorphisms of muscular fitness in young healthy men

The effects of genetic polymorphisms on muscle structure and function remain elusive. The present study tested for possible associations of 16 polymorphisms (across ten candidate genes) with fittness and skeletal muscle phenotypes in 17- to 37-year-old healthy Caucasian male endurance (n = 86), power/strength (n = 75) and team athletes (n = 60), and non-athletes (n = 218). Skeletal muscle function was measured with eight performance tests covering multiple aspects of muscular fitness. Along with body mass and height, the upper arm and limb girths, and maximal oxygen uptake were measured. Genotyping was conducted on DNA extracted from blood. Of the 16 polymorphisms studied, nine (spanning seven candidate genes and four gene families/signalling pathways) were independently associated with at least one skeletal muscle fitness measure (size or function, or both) measure and explained up to 4.1% of its variation. Five of the studied polymorphisms (activin- and adreno-receptors, as well as myosine light chain kinase 1) in a group of one to three combined with body height, age and/or group explained up to 20.4% of the variation of muscle function. ACVR1B (rs2854464) contributed 2.0–3.6% to explain up to 14.6% of limb proximal girths. The G allele (genotypes AG and GG) of the ACVR1B (rs2854464) polymorphism was significantly overrepresented among team (60.4%) and power (62.0%) athletes compared to controls (52.3%) and endurance athletes (39.2%), and G allele was also most consistently/frequently associated with muscle size and power. Overall, the investigated polymorphisms determined up to 4.1% of the variability of muscular fitness in healthy young humans.

Contribution of Innate Lymphoid Cells in Supplementing Cytokines Produced by CD4+ T Cells During Acute and Chronic SIV Infection of the Colon

HIV/SIV (simian immunodeficiency virus) infection leads to a loss of CD4+ T helper (Th) cells in number and function that begins during the acute phase and persists through the chronic phase of infection. In particular, there is a drastic decrease of Th17 and Th22 cells in the HIV/SIV-infected gastrointestinal (GI) tract as a source of interleukin (IL)-17 and IL-22. These cytokines are vital in the immune response to extracellular pathogens and maintenance of the GI tract. However, innate lymphoid cells (ILCs) are a source of IL-17 and IL-22 during the early stages of an immune response in mucosal tissue and remain vital cytokine producers when the immune response is persistent. Here, we wanted to determine whether ILCs are a source of IL-17 and IL-22 in the SIV-infected colon and could compensate for the loss of Th17 and Th22 cells. As a control, we evaluated the frequency and number of ILCs expressing interferon-gamma (IFNγ) and tumor necrosis factor-alpha (TNFα). We determined the frequency and number of cytokine expressing ILC subsets and T cell subsets within leukocytes from the colons of uninfected as well as acute and chronic SIV-infected colons without in vitro mitogenic stimulation. In the present study, we find that: (1) the frequency of IL-22, IFNγ, and TNFα but not IL-17 producing ILCs is increased in the acutely infected colon and remains high during the chronically infected colon relative to cytokine expressing ILCs in the uninfected colon, (2) ILCs are a significant source of IL-22, IFNγ, and TNFα but not IL-17 when CD4+ T lymphocytes in the gut lose their capacity to secrete these cytokines during SIV infection, and (3) the changes in the cytokines expressed by ILCs relative to CD4+ T cells in the infected colon were not due to increases in the frequency or number of ILCs in relation to T lymphocytes found in the tissue.

Streptococcal autolysin promotes dysfunction of swine tracheal epithelium by interacting with vimentin

Streptococcus suis serotype 2 (SS2) is a major zoonotic pathogen resulting in manifestations as pneumonia and septic shock. The upper respiratory tract is typically thought to be the main colonization and entry site of SS2 in pigs, but the mechanism through which it penetrates the respiratory barrier is still unclear. In this study, a mutant with low invasive potential to swine tracheal epithelial cells (STECs) was screened from the TnYLB-1 transposon insertion mutant library of SS2, and the interrupted gene was identified as autolysin (atl). Compared to wild-type (WT) SS2, Δatl mutant exhibited lower ability to penetrate the tracheal epithelial barrier in a mouse model. Purified Atl also enhanced SS2 translocation across STEC monolayers in Transwell inserts. Furthermore, Atl redistributed the tight junctions (TJs) in STECs through myosin light chain kinase (MLCK) signaling, which led to increased barrier permeability. Using mass spectrometry, co-immunoprecipitation (co-IP), pull-down, bacterial two-hybrid and saturation binding experiments, we showed that Atl binds directly to vimentin. CRISPR/Cas9-targeted deletion of vimentin in STECs (VIM KO STECs) abrogated the capacity of SS2 to translocate across the monolayers, SS2-induced phosphorylation of myosin II regulatory light chain (MLC) and MLCK transcription, indicating that vimentin is indispensable for MLCK activation. Consistently, vimentin null mice were protected from SS2 infection and exhibited reduced tracheal and lung injury. Thus, MLCK-mediated epithelial barrier opening caused by the Atl-vimentin interaction is found to be likely the key mechanism by which SS2 penetrates the tracheal epithelium.

Streptococcus suis serotype 2 (SS2), an emerging zoonotic agent, can breach the respiratory barrier and cause invasive disease in pigs. Here, we identified the novel role of autolysin Atl in penetration of the respiratory barrier by SS2 and its systemic dissemination and identified its binding partner, vimentin, a type III intermediate filament protein. Atl contributed to the MLCK-triggered redistribution of tight junctions to open the tracheal epithelial barrier. Knockout of vimentin abolished the ability of SS2 to penetrate the monolayer barrier and the activation of MLCK. Furthermore, vimentin null mice were protected from infection by intranasally administered SS2. This study is the first to demonstrate that the interaction between the GBS Bsp-like domain of Atl and vimentin promotes MLCK-mediated dysfunction of the epithelial barrier, which may provide theoretical information for prophylactic and/or therapeutic treatments against diseases caused by similar respiratory pathogens.

Mechanisms of mucosal healing: treating inflammatory bowel disease without immunosuppression?

Almost all currently available treatments for inflammatory bowel disease (IBD) act by inhibiting inflammation, often blocking specific inflammatory molecules. However, given the infectious and neoplastic disease burden associated with chronic immunosuppressive therapy, the goal of attaining mucosal healing without immunosuppression is attractive. The absence of treatments that directly promote mucosal healing and regeneration in IBD could be linked to the lack of understanding of the underlying pathways. The range of potential strategies to achieve mucosal healing is diverse. However, the targeting of regenerative mechanisms has not yet been achieved for IBD. Stem cells provide hope as a regenerative treatment and are used in limited clinical situations. Growth factors are available for the treatment of short bowel syndrome but have not yet been applied in IBD. The therapeutic application of organoid culture and stem cell therapy to generate new intestinal tissue could provide a novel mechanism to restore barrier function in IBD. Furthermore, blocking key effectors of barrier dysfunction (such as MLCK or damage-associated molecular pattern molecules) has shown promise in experimental IBD. Here, we review the diversity of molecular targets available to directly promote mucosal healing, experimental models to identify new potential pathways and some of the anticipated potential therapies for IBD.

Differential mRNA expression in ileal and colonic biopsies in irritable bowel syndrome with diarrhea or constipation

Altered mucosal functions are documented in jejunal or colorectal mucosa from patients with irritable bowel syndrome (IBS). Our aim was to quantify ileal, ascending, and rectosigmoid colon mucosal expression of genes in IBS-diarrhea (D) and IBS-constipation (C). Forty-four patients with IBS-D, 30 with IBS-C, and 30 healthy volunteers underwent colonoscopic ileal, ascending, and rectosigmoid colon biopsies. Biopsies were stored in RNA_later at -80 °C, purified with on-column DNase, cDNA libraries prepared from 100-200 ng of total RNA, sequenced on Illumina NovaSeq 6000, and analyzed on Illumina's RTA version 3.4.4. Normalized mRNA expression was obtained using MAP-RSeq bioinformatics pipeline. Differential expressions in the groups (Log2-fold change) were measured using the bioinformatics package edgeR 2.6.2, corrected for false discovery rate (P_ADJ <0.05). There were 30 females with IBS-C and 31 females and 13 males with IBS-D. In IBS-D and IBS-C groups, there were differential expressions of 181 genes in ascending colon and 199 genes in rectosigmoid colon. The majority were gene upregulations in IBS-D with functions reflecting activation of inflammation genes, TRPV1 (visceral hypersensitivity) and neurotransmitters/receptors (specifically purinergic, GABA, and cannabinoid). Although gene differential expressions in the ascending and rectosigmoid colon mucosa of the two groups were different, the diverse upregulated genes involved immune functions, receptors, transmitters, ion channels, and transporters. Conversely, there was reduced expression of PI15 and PI16 genes that inhibit proteases. In patients with IBS-D and IBS-C, differential expressions of genes related to immune, transmitter, nociceptive, protease inhibition, channel, and transporter functions suggest opportunities to reverse the pathobiology and treat patients with IBS.NEW & NOTEWORTHY This study compares gene expression in mucosa of the terminal ileum, right colon, and left colon in patients with diarrhea- or constipation-predominant irritable bowel syndrome (IBS) and contrasts expression between these two disease entities and also between each entity and mucosa from healthy controls. The study shows there is differential expression of genes related to immune, transmitter, nociceptive, ion channel, and transporter functions, as well as reduced serine protease inhibition, in patients with IBS.

Mechanisms of mucosal healing: treating inflammatory bowel disease without immunosuppression?

Almost all currently available treatments for inflammatory bowel disease (IBD) act by inhibiting inflammation, often blocking specific inflammatory molecules. However, given the infectious and neoplastic disease burden associated with chronic immunosuppressive therapy, the goal of attaining mucosal healing without immunosuppression is attractive. The absence of treatments that directly promote mucosal healing and regeneration in IBD could be linked to the lack of understanding of the underlying pathways. The range of potential strategies to achieve mucosal healing is diverse. However, the targeting of regenerative mechanisms has not yet been achieved for IBD. Stem cells provide hope as a regenerative treatment and are used in limited clinical situations. Growth factors are available for the treatment of short bowel syndrome but have not yet been applied in IBD. The therapeutic application of organoid culture and stem cell therapy to generate new intestinal tissue could provide a novel mechanism to restore barrier function in IBD. Furthermore, blocking key effectors of barrier dysfunction (such as MLCK or damage-associated molecular pattern molecules) has shown promise in experimental IBD. Here, we review the diversity of molecular targets available to directly promote mucosal healing, experimental models to identify new potential pathways and some of the anticipated potential therapies for IBD.

PLGA microspheres carrying miR-20a-5p improved intestinal epithelial barrier function in patients with Crohn's disease through STAT3-mediated inhibition of Th17 differentiation

BACKGROUND

Recent studies have shown that microRNAs (miRNAs) are aberrantly expressed in patients with Crohn's disease (CD). This suggests that the aberrant expression of miRNAs may contribute to the development of CD. Currently, the specific miRNAs involved in CD development have not been clearly identified. Therefore, we aimed to identify CD-associated miRNAs and explore their functions.

METHODS

miRNA microarray analysis was performed to screen for differentially expressed miRNAs in colon tissues from normal controls (NC) and CD patients. The identified miRNAs were validated using quantitative real-time PCR (qPCR). The therapeutic roles of miR-20a-5p mimics via the delivery of poly(lactic-co-glycolic acid) microspheres (PLGA MSs) were further investigated in IL-10^-/- mice with spontaneous chronic colitis that were used as a model of CD. The target genes of miR-20a-5p and the associated signaling pathways were identified through bioinformatic analysis and experimental verification of the interactions between the targets predicted by the algorithms and dysregulated mRNAs.

RESULTS

The analysis showed that miR-20a-5p was the most significantly downregulated miRNA in patients with CD. Treatment with PLGA MSs carrying miR-20a-5p significantly ameliorated the colitis, decreased mucosal inflammation, and improved epithelial barrier function. Bioinformatic analysis and experimental studies showed that miR-20a-5p inhibition enhanced Th17 differentiation and improved intestinal epithelial barrier function by targeting STAT3.

CONCLUSIONS

Downregulation of miR-20a-5p improved the intestinal epithelial barrier function and prevented CD development through the STAT3/IL-17 signaling pathway. Therefore, the delivery of miR-20a-5p by PLGA MSs may serve as a potential therapeutic strategy for CD treatment.

Mechanisms and prevention of intestinal barrier function damage in traumatic hemorrhagic shock

The intestinal barrier is composed of mechanical barrier, chemical barrier, immune barrier, and microbial barrier, which has an important role in defense against microbial invasion. The components of intestinal barrier coordinate with each other under physiological conditions to maintain the homeostasis of intestinal internal and external environment. In traumatic hemorrhagic shock, intestinal barrier function is prone to be impaired by intestinal hypoperfusion, intestinal ischemia-reperfusion injury, and many other factors. Bacterial translocation and endotoxin entry into the blood may occur, leading to enterogenic infection, multiple organ dysfunction, and even death. At present, there are many conceptual updates and technical progress on the mechanisms, prevention, and treatment of intestinal barrier function injury in traumatic hemorrhagic shock both at home and abroad. This paper intends to make a literature review in this field based on the previous research of our team, in order to provide a systematic and comprehensive theoretical system for the clinical prevention and treatment of post-traumatic intestinal dysfunction related diseases.

Nutraceuticals for the Treatment of IBD: Current Progress and Future Directions

Inflammatory bowel disease (IBD) is a chronic relapsing-remitting inflammatory disease of the gastrointestinal tract. Patients are usually diagnosed in adolescence and early adulthood and need lifelong treatment. In recent years, it has been found that diet plays an important role in the pathogenesis of IBD. Diet can change intestinal barrier function, affect the structure and function of intestinal flora, and promote immune disorder, thus promoting inflammation. Many patients believe that diet plays a role in the onset and treatment of the disease and changes their diet spontaneously. This review provides some insights into how nutraceuticals regulate intestinal immune homeostasis and improve intestinal barrier function. We reviewed the research results of dietary fiber, polyphenols, bioactive peptides, and other nutraceuticals in the prevention and treatment of IBD and sought better alternative or supplementary treatment methods for IBD patients.

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.