ZO-1 stabilizes the tight junction solute barrier through coupling to the perijunctional cytoskeleton

ARHGAP12 suppresses F-actin assembly to control epithelial tight junction mechanics and paracellular leak pathway permeability

Tight junctions (TJs) control the paracellular transport of ions, solutes, and macromolecules across epithelial barriers. There is evidence that claudin-based ion transport (the pore pathway) and the paracellular transport of macromolecules (the leak pathway) are controlled independently. However, how leak pathway flux is regulated is unclear. Here, we have identified the Cdc42/Rac GTPase-activating protein ARHGAP12 as a specific activator of the leak pathway. ARHGAP12 is recruited to TJs via an interaction between its Src homology (SH3) domain and the TJ protein ZO-2 to suppress N-WASP-mediated F-actin assembly. This dampens junctional tension and promotes the paracellular transport of macromolecules without affecting ion flux. Mechanistically, we demonstrate that the ARHGAP12 tandem WW domain interacts directly with PPxR motifs in the proline-rich domain of N-WASP and thereby attenuates SH3-domain-mediated N-WASP oligomerization and Arp2/3-driven F-actin assembly. Collectively, our data indicate that branched F-actin networks regulate junctional tension to fine-tune the TJ leak pathway.

The clinical significance and biological function of tropomyosin 3 in ulcerative colitis

BACKGROUND

Ulcerative colitis (UC) is a lifelong chronic inflammatory disease that is characterized by the absence of specific markers for diagnosis and prognosis. TPM3 is an integral component of the thin filament, responsible for the structural stability of actin filaments and modulation of cytoskeletal function. This study investigated the regulatory role of TPM3 in UC and its potential mechanisms.

METHODS

At the clinical level, TPM3 levels were assessed in serum and mucosal tissues of UC and other enteric disease. At the cellular level, the effects of TMP3 overexpressing lentivirus on Caco-2 cell phenotype and the barrier of IL-1β-induced UC model were explored. At the animal level, the effects of TMP3 overexpressing lentivirus on symptoms and colonic damage in a DSS-induced UC model were explored.

RESULTS

TPM3 expression in serum of UC patients was significantly lower than that of other enteric disease, and TPM3 levels in the intestinal mucosa showed a negative correlation with the Mayo score of UC patients. TPM3 overexpression alleviates IL-1β-induced apoptosis and inhibition of invasion and migration in UC model in vitro. In monolayer Caco-2 cells, TPM3 overexpression rescued the IL-1β-induced decrease in transepithelial electrical resistance and tight junction markers (ZO-1 and Occludin) and increase in permeability. In animal experiments, TPM3 overexpression increased body weight and colon length and decreased disease activity index in a DSS-induced UC model. In tissue staining, it alleviated pathological damage and upregulated Occuludin and TPM3 levels in the colon.

CONCLUSION

TPM3 levels correlated with UC disease course and TPM3 overexpression alleviated symptoms/phenotypes and barrier damage in UC models in vivo and in vitro. TPM3 may serve as a potential novel biomarker for UC diagnosis and prognosis.

Oligomerization of 33-mer Gliadin Peptides: Supramolecular Assemblies in Celiac Disease

The 33-mer gliadin peptide and its deamidated derivative, known as 33-mer DGP, are proteolytically resistant peptides central to the pathomechanism of celiac disease (CeD), the autoimmune presentation of gluten-related disorders (GRD). Both peptides can form spontaneous oligomers in the nanomolar concentration, leading to the formation of nanostructures. In other protein-related diseases, oligomers and aggregates are central in their pathomechanism; therefore, it was hypothesized that the oligomerization of proteolytical-resistant 33-mer gliadin peptides could be an underrecognized disease trigger. This review focuses on the current understanding of 33-mer peptides and their oligomers in vitro and cellular experiments. We intend to give the necessary details that incentivize the chemistry community to get involved in the effort to understand the self-assembly of gliadin peptides and the role of their supramolecular structures in CeD and the other GRD. More research is needed to design effective and safe chemical and/or nutritional interventions beyond the gluten-free diet.

A feedback circuitry involving γ-actin, β-actin and nonmuscle myosin-2 A controls tight junction and apical cortex mechanics

Cytoplasmic β- and γ-actin isoforms, along with non-muscle myosin 2 isoforms, are tightly regulated in epithelial cells and compose the actomyosin cytoskeleton at the apical junctional complex. However, their specific role in regulating the mechanics of the membrane cortex and the organization of junctions, and which biomechanical circuitries modulate their expression remain poorly understood. Here, we show that γ-actin depletion in MDCK and other epithelial cells results in increased expression and junctional accumulation of β-actin and increased tight junction membrane tortuosity, both dependent on nonmuscle myosin-2A upregulation. The knock-out of γ-actin also decreases apical membrane stiffness and increases dynamic exchange of the cytoplasmic tight junction proteins like ZO-1 and cingulin, without affecting tight junction organization and barrier function. In summary, our findings uncover a biomechanical circuitry linking γ-actin to β-actin expression through nonmuscle myosin-2A and reveal γ-actin as a key regulator of tight junction and apical membrane cortex mechanics, and the dynamics of cytoskeleton-associated tight junction proteins in epithelial cells.

Harnessing the Potential of Human Breast Milk to Boost Intestinal Permeability for Nanoparticles and Macromolecules

The intricate interplay between human breast milk, nanoparticles, and macromolecules holds promise for innovative nutritional delivery strategies. Compared to bovine milk and infant formula, this study explores human breast milk's role in modulating intestinal permeability and its impact on nanoparticle and macromolecule transport. Comparative analysis with bovine milk and infant formula reveals significant elevations in permeability with human breast milk, accompanied by a decrease in transepithelial electrical resistance, suggesting enhanced paracellular transport. Mechanistically, human breast milk reduces Zonula occludens-1 levels, suggesting a regulatory role in intestinal barrier function. Through in vitro and ex vivo evaluations, we aim to understand better the mechanisms behind enhanced permeability and how human breast milk affects nanoparticle physicochemical properties, potentially modulating their behavior. Specifically, human breast milk improves the intestinal permeability of liposomes in a porcine intestinal model, with associated changes in the composition of milk proteins corona related to liposome charge. These findings underscore the unexploited potential of human breast milk in facilitating transport across the intestinal barrier, offering novel avenues for human nutritional delivery and therapeutic interventions.

Keratin 1 modulates intestinal barrier and immune response via kallikrein kinin system in ulcerative colitis

BACKGROUND

External factors in ulcerative colitis (UC) exacerbate colonic epithelial permeability and inflammatory responses. Keratin 1 (KRT1) is crucial in regulating these alterations, but its specific role in the progression of UC remains to be fully elucidated.

AIM

To explore the role and mechanisms of KRT1 in the regulation of colonic epithelial permeability and inflammation in UC.

METHODS

A KRT1 antibody concentration gradient test, along with a dextran sulfate sodium (DSS)-induced animal model, was implemented to investigate the role of KRT1 in modulating the activation of the kallikrein kinin system (KKS) and the cleavage of bradykinin (BK)/high molecular weight kininogen (HK) in UC.

RESULTS

Treatment with KRT1 antibody in Caco-2 cells suppressed cell proliferation, induced apoptosis, reduced HK expression, and increased BK expression. It further downregulated intestinal barrier proteins, including occludin, zonula occludens-1, and claudin, and negatively impacted the coagulation factor XII. These changes led to enhanced activation of BK and HK cleavage, thereby intensifying KKS-mediated inflammation in UC. In the DSS-induced mouse model, administration of KRT1 antibody mitigated colonic injury, increased colon length, alleviated weight loss, and suppressed inflammatory cytokines such as interleukin (IL)-1, IL-6, tumor necrosis factor-α. It also facilitated repair of the intestinal barrier, reducing DSS-induced injury.

CONCLUSION

KRT1 inhibits BK expression, suppresses inflammatory cytokines, and enhances markers of intestinal barrier function, thus ameliorating colonic damage and maintaining barrier integrity. KRT1 is a viable therapeutic target for UC.

Dynamic behavior of cell-cell adhesion factors in collective cell migration

Collective cell migration is a fundamental process underlying various biological phenomena, including embryonic development and cancer cell invasion. The cohesive yet flexible movement of cell collectives largely depends on the coordinated regulation of cell-cell and cell-substrate adhesions. In this review, we summarize the regulation of key cell-cell junction components, such as cadherins and zonula occludens proteins during collective cell migration, with a particular focus on the recently discovered multifaceted roles of ZO-1 in both cell-cell and cell-substrate interactions.

Myosin light chain kinase-mediated epithelial barrier dysfunction as a potential pathogenic mechanism of afatinib-induced diarrheas: A study in human colonoid model

Diarrheas are an important adverse effect of afatinib, a tyrosine kinase inhibitor (TKI) anti-cancer drug, leading to mortality and morbidity in cancer patients with their pathophysiological mechanisms related to intestinal barrier dysfunctions being poorly understood. This study aimed to investigate the effect of afatinib on intestinal epithelial barrier integrity using a human colon-derived organoid model (colonoids). Afatinib (0.5 μM) significantly decreased the transepithelial electrical resistance (TEER) by ∼60% and increased apical-to-basolateral dextran flux by > 20 folds without causing apparent cytotoxicity in human colonoids. The delocalization of zonula occludens-1 (ZO-1) and a decrease in mRNA and protein expression of claudin-4 and ZO-1 were also observed in the afatinib-treated human colonoids. Afatinib induced nuclear translocation of nuclear factor kappa B (NF-κB) as well as mRNA and protein expression of NF-κB targets including tumor necrosis factor (TNF)-alpha, interleukin-8 (IL-8), and inducible nitric oxide synthase (iNOS) indicating the initiation of the NF-κB-mediated epithelial inflammatory responses. Interestingly, afatinib induced mRNA and protein expression of myosin light chain (MLC) kinase (MLCK) and MLC phosphorylation, a known inducer of intestinal epithelial barrier disruption. Treatment with iNOS inhibitor (1400W) or MLCK inhibitor (ML-7) reversed the effect of afatinib on mRNA expressions of ZO-1 and claudin-4, and TEER. Collectively, our results indicate that afatinib induces intestinal epithelial barrier dysfunction via mechanisms involving NF-κB-iNOS-MLCK pathways. This finding may pave the way for developing therapeutic strategies to reduce adverse effects and enhance efficacy of TKI in cancer patients.

Effects of Zinc Combined with Metformin on Zinc Homeostasis, Blood-Epididymal Barrier, and Epididymal Absorption in Male Diabetic Mice

Diabetes increases the likelihood of germ cell damage, hypogonadism, and male infertility. Diabetes leads to lower zinc (Zn) levels, an important micronutrient for maintaining male fertility, and zinc deficiency can lead to decreased male fertility through multiple mechanisms. The aim of this study was to investigate the effect of combined metformin and zinc administration on epididymis in diabetic mice; 10 of 50 male mice were randomly selected as the control group (group C), and the remaining 40 mice were randomly divided into untreated diabetes group (group D), diabetes + zinc group (group Z), diabetes + metformin group (group M), and diabetes + metformin + zinc group (group ZM) with 10 mice each. Diabetic mice in group Z received oral zinc (10 mg/kg) once daily for 4 weeks; diabetic mice in group M received oral metformin (200 mg/kg) once daily for 4 weeks; diabetic mice in group ZM received oral metformin and zinc once daily for 4 weeks; and groups C and D received the same amount of sterile water by gavage. Overnight fasted mice were sacrificed, and blood samples, mouse epididymides, and sperm were collected for further experiments. In group D, fasting blood glucose and insulin resistance index increased significantly, semen quality, serum insulin, and testosterone decreased, and epididymal structure was disordered. In group D, epididymal tissue zinc, free zinc ions in the caput, and cauda of epididymis and zinc transporter (ZnT2) decreased significantly, while ZIP12, metallothionein (MT), and metal transcription factor (MTF1) increased significantly. In addition, the expressions of blood-epididymal barrier (BEB)-related molecules (including ZO-1 β-catenin and N-cadherin) and aquaporins (AQPs, including AQP3, AQP9, and AQP11) in the epididymis of mice in group D were significantly decreased. In addition, compared with groups D, Z, and M, in the ZM group, the expression of BEB-related molecules (including ZO-1, β-catenin, and N-cadherin) and aquaporins (AQP3, AQP9, and AQP11) in epididymis tissue were significantly increased, and sperm motility and serum testosterone were significantly increased. It was concluded that male diabetic mice have a disturbed epididymal structure and decreased semen quality by causing an imbalance in epididymal zinc homeostasis, BEB, and impaired absorptive function. The combination of zinc and metformin is an effective and safe alternative treatment and provides additional benefits over metformin alone.

Mesenchymal Stem Cells and Their Extracellular Vesicles: Therapeutic Mechanisms for Blood-Spinal Cord Barrier Repair Following Spinal Cord Injury

Spinal cord injury (SCI) disrupts the blood-spinal cord barrier (BSCB) exacerbating damage by allowing harmful substances and immune cells to infiltrate spinal neural tissues from the vasculature. This leads to inflammation, oxidative stress, and impaired axonal regeneration. The BSCB, essential for maintaining spinal cord homeostasis, is structurally similar to the blood-brain barrier. Its restoration is a key therapeutic target for improving outcomes in SCI. Mesenchymal stromal/stem cells (MSCs) and their secreted extracellular vesicles (MSC-EVs) have gained attention for their regenerative, immunomodulatory, and anti-inflammatory properties in promoting BSCB repair. MSCs enhance BSCB integrity by improving endothelial-pericyte association, restoring tight junction proteins, and reducing inflammation. MSC-EVs, which deliver bioactive molecules, replicate many of MSCs' therapeutic effects, and offer a promising cell-free alternative. Preclinical studies have shown that both MSCs and MSC-EVs can reduce BSCB permeability, promote vascular stability, and support functional recovery. While MSC therapy is advancing in clinical trials, MSC-EV therapies require further optimization in terms of production, dosing, and delivery protocols. Despite these challenges, both therapeutic approaches represent significant potential for treating SCI by targeting BSCB repair and improving patient outcomes.

Mechanisms of gut homeostasis regulating Th17/Treg cell balance in PMOP

Postmenopausal osteoporosis (PMOP) is a metabolic bone disease driven by estrogen deficiency, primarily manifesting as reduced bone mass and heightened fracture risk. Its development is intricately linked to the balance between Th17 and Treg cells. Recent studies have highlighted the significant role of gut homeostasis in PMOP. The gut microbiota profoundly impacts bone health by modulating the host's immune system, metabolic pathways, and endocrine functions. In particular, the regulation of Th17 and Treg cell balance by gut homeostasis plays a pivotal role in the onset and progression of PMOP. Th17 cells secrete pro-inflammatory cytokines that stimulate osteoclast activity, accelerating bone resorption, while Treg cells counteract this process through anti-inflammatory mechanisms, preserving bone mass. The gut microbiota and its metabolites can influence Th17/Treg equilibrium, thereby modulating bone metabolism. Furthermore, the integrity of the gut barrier is critical for systemic immune stability, and its disruption can lead to immune dysregulation and metabolic imbalances. Thus, targeting gut homeostasis to restore Th17/Treg balance offers a novel therapeutic avenue for the prevention and treatment of PMOP.

Tight junctions control lumen morphology via hydrostatic pressure and junctional tension

Formation of fluid-filled lumina by epithelial tissues is essential for organ development. How cells control the hydraulic and cortical forces to control lumen morphology is not well understood. Here, we quantified the mechanical role of tight junctions in lumen formation using MDCK-II cysts. We found that the paracellular ion barrier formed by claudin receptors is not required for the hydraulic inflation of a lumen. However, the depletion of the zonula occludens scaffold resulted in lumen collapse and folding of apical membranes. Combining quantitative measurements of hydrostatic lumen pressure and junctional tension with modeling enabled us to explain lumen morphologies from the pressure-tension force balance. Tight junctions promote lumen inflation by decreasing cortical tension via the inhibition of myosin. In addition, our results suggest that excess apical area contributes to lumen opening. Overall, we provide a mechanical understanding of how epithelial cells use tight junctions to modulate tissue and lumen shape.

Loss of intermicrovillar adhesion factor CDHR2 impairs basolateral junctional complexes in transporting epithelia

Transporting epithelial cells in the gut and kidney rely on protocadherin-based apical adhesion complexes to organize microvilli that extend into luminal space. In these systems, CDHR2 and CDHR5 localize to the distal ends of microvilli, where they form an intermicrovillar adhesion complex (IMAC) that links the tips of these structures, promotes the formation of a well-ordered array of protrusions, and thus maximizes apical membrane surface area. Recently, we discovered that IMACs can also form between microvilli that extend from neighboring cells, across cell-cell junctions. As an additional point of physical contact between cells, transjunctional IMACs are well positioned to impact the integrity of canonical tight and adherens junctions that form more basolaterally. To begin to test this idea, we examined cell culture and mouse models that lacked CDHR2 expression and were unable to form IMACs. CDHR2 knockout perturbed cell and junction morphology, reduced key components from tight and adherens junctions, impaired barrier function, and increased the motility of single cells within established monolayers. These results support the hypothesis that, in addition to organizing apical microvilli, IMACs provide a layer of cell-cell contact that functions in parallel with canonical tight and adherens junctions to promote epithelial functions.

Cell line-based in vitro models of normal and chronic bronchitis-like airway mucosa to study the toxic potential of aerosolized palladium nanoparticles

Background

Physiologically relevant cell line-based models of human airway mucosa are needed to assess nanoparticle-mediated pulmonary toxicity for any xenbiotics expsoure study. Palladium nanoparticles (Pd-NP) originating from catalytic converters in vehicles pose health risks. We aimed to develop in vitro airway models to assess the toxic potential of Pd-NP in normal (Non-CB) and chronic bronchitis-like (CB-like) mucosa models.

Methods

Bronchial mucosa models were developed using Epithelial cells (16HBE: apical side) co-cultured with fibroblast (basal side) at an air-liquid interface. Furthermore, both Non-CB and CB-like (IL-13 treatment) models with increased numbers of goblet cells were used. The models were exposed to 3 different doses of aerosolized Pd-NP (0.2, 0.3, and 6 μg/cm2) using XposeALI® and clean air as a control. After 24 h of incubation, the expression of inflammatory (IL6, CXCL8, TNFα, and NFKB), oxidative stress (HMOX1, SOD3, GPx, and GSTA1), and tissue injury/repair (MMP9/TIMP1) markers was assessed using qRT-PCR. The secretion of CXCL-8 and the expression of a tissue injury/repair marker (MMP-9) were measured via ELISA.

Results

Significantly (p < 0.05) increased expressions of CXCL8, IL6, and NFKB were observed at the highest dose of Pd-NP in CB-like models. However, in Non-CB mucosa models, a maximum effect on TNFα and NFKB expression was observed at a medium Pd-NP dose. In Non-CB mucosa models, SOD3 showed a clear dose-dependent response to Pd-NP exposure, while GSTA1 expression was significantly increased (p < 0.05) only at the lowest dose of Pd-NP. The secretion of CXCL-8 increased in a dose-dependent manner in the Non-CB mucosa models following exposure to Pd-NP. In CB-like models, exposure to high concentrations of Pd-NP significantly increased the release of MMP-9 compared to that in other exposure groups.

Conclusion

The combination of our Non-CB and CB-like mucosa models with the XposeALI® system for aerosolized nanoparticle exposure closely mimics in vivo lung environments and cell-particle interactions. Results from these models, utilizing accessible cell lines, will maximize the reliability of in vitro findings in human health risk assessment.

The Scribble-SGEF-Dlg1 complex regulates E-cadherin and ZO-1 stability, turnover and transcription in epithelial cells

SGEF (also known as ARHGEF26), a RhoG specific GEF, can form a ternary complex with the Scribble polarity complex proteins Scribble and Dlg1, which regulates the formation and maintenance of adherens junctions and barrier function of epithelial cells. Notably, silencing SGEF results in a dramatic downregulation of both E-cadherin and ZO-1 (also known as TJP1) protein levels. However, the molecular mechanisms involved in the regulation of this pathway are not known. Here, we describe a novel signaling pathway governed by the Scribble-SGEF-Dlg1 complex. Our results show that the three members of the ternary complex are required to maintain the stability of the apical junctions, ZO-1 protein levels and tight junction (TJ) permeability. In contrast, only SGEF is necessary to regulate E-cadherin levels. The absence of SGEF destabilizes the E-cadherin-catenin complex at the membrane, triggering a positive feedback loop that exacerbates the phenotype through the repression of E-cadherin transcription in a process that involves the internalization of E-cadherin by endocytosis, β-catenin signaling and the transcriptional repressor Slug (also known as SNAI2).

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

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

The gut homeostasis-immune system axis: novel insights into rheumatoid arthritis pathogenesis and treatment

Rheumatoid arthritis is a widely prevalent autoimmune bone disease that imposes a significant burden on global healthcare systems due to its increasing incidence. In recent years, attention has focused on the interaction between gut homeostasis and the immune system, particularly in relation to bone health. Dysbiosis, which refers to an imbalance in the composition and function of the gut microbiota, has been shown to drive immune dysregulation through mechanisms such as the release of pro-inflammatory metabolites, increased gut permeability, and impaired regulatory T cell function. These factors collectively contribute to immune system imbalance, promoting the onset and progression of Rheumatoid arthritis. Dysbiosis induces both local and systemic inflammatory responses, activating key pro-inflammatory cytokines such as tumor necrosis factor-alpha, Interleukin-6, and Interleukin-17, which exacerbate joint inflammation and damage. Investigating the complex interactions between gut homeostasis and immune regulation in the context of Rheumatoid arthritis pathogenesis holds promise for identifying new therapeutic targets, revealing novel mechanisms of disease progression, and offering innovative strategies for clinical treatment.

Intestinal Dysbiosis, Tight Junction Proteins, and Inflammation in Rheumatoid Arthritis Patients: A Cross-Sectional Study

Recent studies point to intestinal permeability as an important factor in the establishment and development of rheumatoid arthritis (RA). Tight junctions (TJs) play a major role in intestinal homeostasis. The alteration of this homeostasis is related to RA. Furthermore, RA patients present dysbiosis and a lower microbiota diversity compared to healthy individuals. A cross-sectional study including RA patients and sex- and age-matched healthy controls was performed. The quantification of TJ proteins was carried out by ELISA. Gut microbiota was evaluated by NGS platform Ion Torrent S. The inflammatory variables included were DAS28, CRP, inflammatory cytokines (IL-6, IL-1, TNF-α) and oxidised LDL. Claudin-1 levels showed significant differences between groups. Results evidenced a correlation between claudin-1 values and age (r: -0.293; p < 0.05), IL6 (r: -0.290; p < 0.05) and CRP (r: -0.327; p < 0.05), and between zonulin values and both age (r: 0.267; p < 0.05) and TNFα (r: 0.266; p < 0.05). Moreover, claudin-1 and CRP levels are related in RA patients (β: -0.619; p: 0.045), and in patients with high inflammatory activity, the abundance of the genus Veillonella is positively associated with claudin-1 levels (β: 39.000; p: 0.004).

Glycyrol Relieves Ulcerative Colitis by Promoting the Fusion of ZO-1 with the Cell Membrane through the Enteric Glial Cells GDNF/RET Pathway

The damage to the mechanical barrier of the intestinal mucosa is the initiating factor and the core link of the progression of ulcerative colitis (UC). Protecting the mechanical barrier of the intestinal mucosa is of great significance for improving the health status of UC patients. ZO-1 is a key scaffold protein of the mechanical barrier of the intestinal mucosa, and its fusion with the membrane of the intestinal epithelium is a necessary condition to maintain the integrity of the mechanical barrier of the intestinal mucosa. Enteric glial cells (EGCs) play an important role in the maintenance of intestinal homeostasis and have become a new target for regulating intestinal health in recent years. In this study, we found that glycyrol (GC), a representative coumarin compound isolated from Licorice (Glycyrrhiza uralensis Fisch, used for medicine and food), can alleviate UC by promoting the production of neurotrophic factor GDNF in mice EGCs. Specifically, we demonstrated that GC promotes the production of GDNF, then activates its receptor RET, promotes ZO-1 fusion with cell membranes, and protects the intestinal mucosal mechanical barrier. The results of this study can provide new ideas for the prevention and treatment of UC.

The relevance of intestinal barrier dysfunction, antimicrobial proteins and bacterial endotoxin in metabolic dysfunction-associated steatotic liver disease

BACKGROUND

Metabolic dysfunction-associated steatotic liver disease (MASLD) is a leading cause of end-stage liver disease associated with increased mortality and cardiovascular disease. Obesity and diabetes are the most important risk factors of MASLD. It is well-established that obesity-associated insulin resistance leads to a situation of tissue lipotoxicity characterized by an accumulation of excess fat in non-fat tissues such as the liver, promoting the development of MASLD, and its progression into metabolic dysfunction-associated steatohepatitis.

METHODS

Here, we aimed to review the impact of disrupted intestinal permeability, antimicrobial proteins and bacterial endotoxin in the development and progression of MASLD.

RESULTS AND CONCLUSION

Recent studies demonstrated that obesity- and obesogenic diets-associated alterations of intestinal microbiota along with the disruption of intestinal barrier integrity, the alteration in antimicrobial proteins and, in consequence, an enhanced translocation of bacterial endotoxin into bloodstream might contribute to this pathological process through to impacting liver metabolism and inflammation.

Buckling forces and the wavy folds between pleural epithelial cells

Cell shapes in tissues are affected by the biophysical interaction between cells. Tissue forces can influence specific cell features such as cell geometry and cell surface area. Here, we examined the 2-dimensional shape, size, and perimeter of pleural epithelial cells at various lung volumes. We demonstrated a 1.53-fold increase in 2-dimensional cell surface area and a 1.43-fold increase in cell perimeter at total lung capacity compared to residual lung volume. Consistent with previous results, close inspection of the pleura demonstrated wavy folds between pleural epithelial cells at all lung volumes. To investigate a potential explanation for the wavy folds, we developed a physical simulacrum suggested by D'Arcy Thompson in On Growth and Form. The simulacrum suggested that the wavy folds were the result of redundant cell membranes unable to contract. To test this hypothesis, we developed a numerical simulation to evaluate the impact of an increase in 2-dimensional cell surface area and cell perimeter on the shape of the cell-cell interface. Our simulation demonstrated that an increase in cell perimeter, rather than an increase in 2-dimensional cell surface area, had the most direct impact on the presence of wavy folds. We conclude that wavy folds between pleural epithelial cells reflects buckling forces arising from the excess cell perimeter necessary to accommodate visceral organ expansion.

The Celiac-Disease Superantigen Oligomerizes and Increases Permeability in an Enterocyte Cell Model

Celiac disease (CeD) is an autoimmune disorder triggered by gluten proteins, affecting approximately 1 % of the global population. The 33-mer deamidated gliadin peptide (DGP) is a metabolically modified wheat-gluten superantigen for CeD. Here, we demonstrate that the 33-mer DGP spontaneously assembles into oligomers with a diameter of approximately 24 nm. The 33-mer DGP oligomers present two main secondary structural motifs-a major polyproline II helix and a minor β-sheet structure. Importantly, in the presence of 33-mer DGP oligomers, there is a statistically significant increase in the permeability in the gut epithelial cell model Caco-2, accompanied by the redistribution of zonula occludens-1, a master tight junction protein. These findings provide novel molecular and supramolecular insights into the impact of 33-mer DGP in CeD and highlight the relevance of gliadin peptide oligomerization.

Long-Term Maintenance of Viable Human Endometrial Epithelial Cells to Analyze Estrogen and Progestin Effects

There are fewer investigations conducted on human primary endometrial epithelial cells (HPEECs) compared to human primary endometrial stromal cells (HPESCs). One of the main reasons is the scarcity of protocols enabling prolonged epithelial cell culture. Even though it is possible to culture HPEECs in 3D over a longer period of time, it is technically demanding. In this study, we successfully established a highly pure, stable, and long-term viable human conditionally reprogrammed endometrial epithelial cell line, designated as eCRC560. These cells stained positive for epithelial markers, estrogen and progesterone receptors, and epithelial cell-cell contacts but negative for stromal and endothelial cell markers. Estradiol (ES) reduced the abundance of ZO-1 in a time- and dose-dependent manner, in contrast to the dose-dependent increase with the progestin dienogest (DNG) when co-cultured with HPESCs. Moreover, ES significantly increased cell viability, cell migration, and invasion of the eCRC560 cells; all these effects were inhibited by pretreatment with DNG. DNG withdrawal led to a significantly disrupted monolayer of eCRC560 cells in co-culture with HPESCs, yet it markedly increased the adhesion of eCRC560 to the human mesothelial MeT-5A cells. The long-term viable eCRC560 cells are suitable for in vitro analysis of HPEECs to study the epithelial compartment of the human endometrium and endometrial pathologies.

T cell infiltration mediates neurodegeneration and cognitive decline in Alzheimer's disease

Alzheimer's disease (AD) is a prevalent neurodegenerative disorder with pathological features of β-amyloid (Aβ) and hyperphosphorylated tau protein accumulation in the brain, often accompanied by cognitive decline. So far, our understanding of the extent and role of adaptive immune responses in AD has been quite limited. T cells, as essential members of the adaptive immune system, exhibit quantitative and functional abnormalities in the brains of AD patients. Dysfunction of the blood-brain barrier (BBB) in AD is considered one of the factors leading to T cell infiltration. Moreover, the degree of neuronal loss in AD is correlated with the quantity of T cells. We first describe the differentiation and subset functions of peripheral T cells in AD patients and provide an overview of the key findings related to BBB dysfunction and how T cells infiltrate the brain parenchyma through the BBB. Furthermore, we emphasize the risk factors associated with AD, including Aβ, Tau protein, microglial cells, apolipoprotein E (ApoE), and neuroinflammation. We discuss their regulation of T cell activation and proliferation, as well as the connection between T cells, neurodegeneration, and cognitive decline. Understanding the innate immune response is crucial for providing comprehensive personalized therapeutic strategies for AD.

Comprehensive analysis of human tissues reveals unique expression and localization patterns of HSF1 and HSF2

Heat shock factors (HSFs) are the main transcriptional regulators of the evolutionarily conserved heat shock response. Beyond cell stress, several studies have demonstrated that HSFs also contribute to a vast variety of human pathologies, ranging from metabolic diseases to cancer and neurodegeneration. Despite their evident role in mitigating cellular perturbations, the functions of HSF1 and HSF2 in physiological proteostasis have remained inconclusive. Here, we analyzed a comprehensive selection of paraffin-embedded human tissue samples with immunohistochemistry. We demonstrate that both HSF1 and HSF2 display distinct expression and subcellular localization patterns in benign tissues. HSF1 localizes to the nucleus in all epithelial cell types, whereas nuclear expression of HSF2 was limited to only a few cell types, especially the spermatogonia and the urothelial umbrella cells. We observed a consistent and robust cytoplasmic expression of HSF2 across all studied smooth muscle and endothelial cells, including the smooth muscle cells surrounding the vasculature and the high endothelial venules in lymph nodes. Outstandingly, HSF2 localized specifically at cell-cell adhesion sites in a broad selection of tissue types, such as the cardiac muscle, liver, and epididymis. To the best of our knowledge, this is the first study to systematically describe the expression and localization patterns of HSF1 and HSF2 in benign human tissues. Thus, our work expands the biological landscape of these factors and creates the foundation for the identification of specific roles of HSF1 and HSF2 in normal physiological processes.

The Scribble/SGEF/Dlg1 complex regulates the stability of apical junctions in epithelial cells

SGEF, a RhoG specific GEF, can form a ternary complex with the Scribble polarity complex proteins Scribble and Dlg1, which regulates the formation and maintenance of adherens junctions and barrier function of epithelial cells. Notably, silencing SGEF results in a dramatic downregulation of the expression of both E-cadherin and ZO-1. However, the molecular mechanisms involved in the regulation of this pathway are not known. Here, we describe a novel signaling pathway governed by the Scribble/SGEF/Dlg1 complex. Our results show that an intact ternary complex is required to maintain the stability of the apical junctions, the expression of ZO-1, and TJ permeability. In contrast, only SGEF is necessary to regulate E-cadherin expression. The absence of SGEF destabilizes the E-cadherin/catenin complex at the membrane, triggering a positive feedback loop that exacerbates the phenotype through the repression of E-cadherin transcription in a process that involves the internalization of E-cadherin by endocytosis, β-catenin signaling and the transcriptional repressor Slug.

Loss of intermicrovillar adhesion impairs basolateral junctional complexes in transporting epithelia

Transporting epithelial cells in the gut and kidney rely on protocadherin-based apical adhesion complexes to organize microvilli that extend into the luminal space. In these systems, CDHR2 and CDHR5 localize to the distal ends of microvilli, where they form an intermicrovillar adhesion complex (IMAC) that links the tips of these structures, promotes the formation of a well-ordered array of protrusions, and in turn maximizes apical membrane surface area. Recently, we discovered that IMACs can also form between microvilli that extend from neighboring cells, across cell-cell junctions. As an additional point of physical contact between cells, transjunctional IMACs are well positioned to impact the integrity of canonical tight and adherens junctions that form more basolaterally. Here, we sought to test this idea using cell culture and mouse models that lacked CDHR2 expression and were unable to form IMACs. CDHR2 knockout perturbed cell and junction morphology, led to loss of key components from tight and adherens junctions, and impaired barrier function and wound healing. These results indicate that, in addition to organizing apical microvilli, IMACs provide a layer of cell-cell contact that functions in parallel with canonical tight and adherens junctions to support the physiological functions of transporting epithelia.

Environmental Toxin Biliatresone-Induced Biliary Atresia-like Abnormal Cilia and Bile Duct Cell Development of Human Liver Organoids

Biliary atresia (BA) is a poorly understood and devastating obstructive bile duct disease of newborns. Biliatresone, a plant toxin, causes BA-like syndrome in some animals, but its relevance in humans is unknown. To validate the hypothesis that biliatresone exposure is a plausible BA disease mechanism in humans, we treated normal human liver organoids with biliatresone and addressed its adverse effects on organoid development, functions and cellular organization. The control organoids (without biliatresone) were well expanded and much bigger than biliatresone-treated organoids. Expression of the cholangiocyte marker CK19 was reduced, while the hepatocyte marker HFN4A was significantly elevated in biliatresone-treated organoids. ZO-1 (a tight junction marker) immunoreactivity was localized at the apical intercellular junctions in control organoids, while it was markedly reduced in biliatresone-treated organoids. Cytoskeleton F-actin was localized at the apical surface of the control organoids, but it was ectopically expressed at the apical and basal sides in biliatresone-treated organoids. Cholangiocytes of control organoids possess primary cilia and elicit cilia mechanosensory function. The number of ciliated cholangiocytes was reduced, and cilia mechanosensory function was hampered in biliatresone-treated organoids. In conclusion, biliatresone induces morphological and developmental changes in human liver organoids resembling those of our previously reported BA organoids, suggesting that environmental toxins could contribute to BA pathogenesis.

PALS1 is a key regulator of the lateral distribution of tight junction proteins in renal epithelial cells

The evolutionarily conserved apical Crumbs (CRB) complex, consisting of the core components CRB3a (an isoform of CRB3), PALS1 and PATJ, plays a key role in epithelial cell-cell contact formation and cell polarization. Recently, we observed that deletion of one Pals1 allele in mice results in functional haploinsufficiency characterized by renal cysts. Here, to address the role of PALS1 at the cellular level, we generated CRISPR/Cas9-mediated PALS1-knockout MDCKII cell lines. The loss of PALS1 resulted in increased paracellular permeability, indicating an epithelial barrier defect. This defect was associated with a redistribution of several tight junction-associated proteins from bicellular to tricellular contacts. PALS1-dependent localization of tight junction proteins at bicellular junctions required its interaction with PATJ. Importantly, reestablishment of the tight junction belt upon transient F-actin depolymerization or upon Ca2+ removal was strongly delayed in PALS1-deficient cells. Additionally, the cytoskeleton regulator RhoA was redistributed from junctions into the cytosol under PALS1 knockout. Together, our data uncover a critical role of PALS1 in the coupling of tight junction proteins to the F-actin cytoskeleton, which ensures their correct distribution along bicellular junctions and the formation of tight epithelial barrier.

The Role of ZO-2 in Modulating JAM-A and γ-Actin Junctional Recruitment, Apical Membrane and Tight Junction Tension, and Cell Response to Substrate Stiffness and Topography

This work analyzes the role of the tight junction (TJ) protein ZO-2 on mechanosensation. We found that the lack of ZO-2 reduced apical membrane rigidity measured with atomic force microscopy, inhibited the association of γ-actin and JAM-A to the cell border, and instead facilitated p114RhoGEF and afadin accumulation at the junction, leading to an enhanced mechanical tension at the TJ measured by FRET, with a ZO-1 tension probe, and increased tricellular TJ tension. Simultaneously, adherens junction tension measured with an E-cadherin probe was unaltered. The stability of JAM-A and ZO-2 binding was assessed by a collaborative in silico study. The absence of ZO-2 also impacted the cell response to the substrate, as monolayers plated in 20 kPa hydrogels developed holes not seen in parental cultures and displayed a retarded elongation and formation of cell aggregates. The absence of ZO-2 was sufficient to induce YAP and Snail nuclear accumulation in cells cultured over glass, but when ZO-2 KD cells were plated in nanostructured ridge arrays, they displayed an increased abundance of nuclear Snail and conspicuous internalization of claudin-4. These results indicate that the absence of ZO-2 also impairs the response of cells to substrate stiffness and exacerbates transformation triggered by substrate topography.

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

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

Peptoniphilus gorbachii alleviates collagen-induced arthritis in mice by improving intestinal homeostasis and immune regulation

Introduction

The intricate connection between gut microbiota and rheumatoid arthritis (RA) pathogenesis has gained prominence, although the specific microbial species contributing to RA development remain largely unknown. Recent studies have sought to comprehensively explore alterations in the human microbiome, focusing on identifying disease-related microbial species through blood analysis. Consequently, this study aimed to identify RA-associated microbial species using a serum microbial array system and to investigate the efficacy and underlying mechanisms of potential microbial species for RA treatment.

Methods

Serum immunoglobulin M levels against 384 intestinal microbial species were assessed using a microbial microarray in patients with RA and healthy individuals. We investigated the therapeutic potential of the identified microbial candidate regarding arthritis development, immune responses, gut barrier function, and gut microbiome using a collagen-induced arthritis (CIA) mouse model.

Results

Our findings revealed significant alterations in antibody levels against 36 microbial species in patients with RA compared to healthy individuals. Notably, the antibody levels against Peptoniphilus gorbachii (PG) were decreased in patients with RA and exhibited an inverse correlation with RA disease activity. In vitro experiments demonstrated that PG produced acetate and butyrate, while exhibiting anti-inflammatory properties. In CIA mice, PG administration suppressed arthritis symptoms, reduced the accumulation of inflammatory monocytes in the mesenteric lymph nodes, and downregulated gene expression of pro-inflammatory cytokines in the ileum. Additionally, PG supplementation restored intestinal barrier integrity and partially resolved gut microbial dysbiosis in CIA mice. The fecal microbiota in PG-treated mice corresponded to improved intestinal barrier integrity and reduced inflammatory responses.

Conclusion

This study highlights the potential of serum-based detection of anti-microbial antibodies to identify microbial targets at the species level for RA treatment. Moreover, our findings suggest that PG, identified through the microbial microarray analysis, holds therapeutic potential for RA by restoring intestinal barrier integrity and suppressing the immunologic response associated with RA.

Intestinal Barrier Dysfunction in Inflammatory Bowel Disease: Underpinning Pathogenesis and Therapeutics

The intestinal barrier is composed of several essential elements including luminal enzymes, bile acids, water layer, epithelial layer, and enterocyte layer. It acts as a dynamic interface between the luminal contents of food, commensal and pathogenic bacteria, and the gastrointestinal tract. The role of barrier dysfunction is of significant research interest in the development and targeted treatment of chronic inflammatory gastrointestinal conditions, such as inflammatory bowel disease. This review aims to examine the role of intestinal barrier dysfunction in the development of inflammatory bowel disease, the pathophysiology of increased barrier permeability in inflammatory bowel disease, and to explore potential treatment targets and clinical applications.

Expression of tight junction proteins in smokers and non-smokers with generalized Stage III periodontitis

OBJECTIVE

This study aims to evaluate the gingival crevicular fluid (GCF) levels of tumor necrosis factor-α (TNF-α), zonula occludens-1 (ZO-1), occludin (Occ), and tricellulin (Tric) in periodontitis, as well as their alterations due to smoking.

BACKGROUND

Tight junctions (TJ), which consist of transmembrane and cytoplasmic scaffolding proteins, connect the epithelial cells of the periodontium. Occ, claudins, junctional adhesion molecules, and Tric are transmembrane TJ proteins found at the cell membrane. The transmembrane TJ proteins and the intracellular cytoskeleton are directly linked by cytoplasmic scaffolding proteins such as ZO-1. Although the functions and locations of these molecules have been defined, their behavior in periodontal inflammation is unknown.

METHODS

The study included four groups: individuals with periodontal health without smoking (C; n = 31), individuals with generalized Stage III periodontitis without smoking (P; n = 28), individuals with periodontal health while smoking (CS; n = 22), and individuals with generalized Stage III periodontitis while smoking (PS; n = 18). Clinical periodontal parameters were recorded, and enzyme-linked immunosorbent assay (ELISA) was used to examine ZO-1, Occ, Tric, and TNF-α levels in GCF.

RESULTS

In the periodontitis groups, clinical parameters were significantly higher (p < .001). The site-specific levels of TNF-α, ZO-1, Tric, and Occ in the P group were statistically higher than those in the other groups (p < .05). TNF-α, probing pocket depth (PPD), and bleeding on probing (BOP) exhibited positive correlations with all TJ proteins (p < .005).

CONCLUSIONS

Smoking could potentially affect the levels of epithelial TJ proteins in the GCF, thereby potentially playing a significant role in the pathogenesis of the periodontal disease.

Cysteine Attenuates the Impact of Bisphenol A-Induced Oxidative Damage on Growth Performance and Intestinal Function in Piglets

Bisphenol A (BPA), a kind of environmental toxin, widely impacts daily life. Cysteine (Cys) is a nutritionally important amino acid for piglets. However, it remains unclear whether Cys can alleviate BPA-induced oxidative damage in piglets. The aim of the present study was to explore the protective effects of Cys in BPA-challenged piglets. A total of twenty-four piglets were divided into four groups that were further subdivided based on the type of exposure (with or without 0.1% BPA) in a basal or Cys diet for a 28 d feeding trial. The results showed that BPA exposure decreased the piglets' average daily weight gain by 14.9%, and decreased dry matter, crude protein and ether extract digestibility by 3.3%, 4.5% and 2.3%, respectively; these decreases were attenuated by Cys supplementation. Additionally, Cys supplementation restored BPA-induced decreases in superoxide dismutase (SOD) and glutathione (GSH), and increases in malondialdehyde (MDA) levels, in the serum and jejunum (p < 0.05). Moreover, BPA decreased the jejunal mRNA expression of antioxidant genes, which were restored by Cys supplementation (p < 0.05). Cys also restored BPA and increased serum D-lactate levels and diamine oxidase (DAO) activity, and BPA decreased jejunal disaccharidase activity (p < 0.05). Further investigations in this study showed that the protective effects of Cys were associated with restoring intestinal barrier integrity by improving the jejunal morphology and enhancing the mRNA expression of tight junction proteins (p < 0.05). Collectively, the results herein demonstrated that Cys supplementation attenuated the impact of BPA-induced oxidative damage on growth performance, nutrient digestibility and intestinal function.

Loss of TJP1 disrupts gastrulation patterning and increases differentiation toward the germ cell lineage in human pluripotent stem cells

Biological patterning events that occur early in development establish proper tissue morphogenesis. Identifying the mechanisms that guide these patterning events is necessary in order to understand the molecular drivers of development and disease and to build tissues in vitro. In this study, we use an in vitro model of gastrulation to study the role of tight junctions and apical/basolateral polarity in modulating bone morphogenic protein-4 (BMP4) signaling and gastrulation-associated patterning in colonies of human pluripotent stem cells (hPSCs). Disrupting tight junctions via knockdown (KD) of the scaffolding tight junction protein-1 (TJP1, also known as ZO1) allows BMP4 to robustly and ubiquitously activate pSMAD1/5 signaling over time, resulting in loss of the patterning phenotype and marked differentiation bias of pluripotent stem cells to primordial germ cell-like cells (PGCLCs). These findings give important insights into how signaling events are regulated and lead to spatial emergence of diverse cell types in vitro.

Identification of Host PDZ-Based Interactions with the SARS-CoV-2 E Protein in Human Monocytes

Proteins containing PDZ (post-synaptic density, PSD-95/disc large, Dlg/zonula occludens, ZO-1) domains assemble signaling complexes that orchestrate cell responses. Viral pathogens target host PDZ proteins by coding proteins containing a PDZ-binding motif (PBM). The presence of a PBM in the SARS-CoV-2 E protein contributes to the virus's pathogenicity. SARS-CoV-2 infects epithelia, but also cells from the innate immune response, including monocytes and alveolar macrophages. This process is critical for alterations of the immune response that are related to the deaths caused by SARS-CoV-2. Identification of E-protein targets in immune cells might offer clues to understanding how SARS-CoV-2 alters the immune response. We analyzed the interactome of the SARS-CoV-2 E protein in human monocytes. The E protein was expressed fused to a GFP tag at the amino terminal in THP-1 monocytes, and associated proteins were identified using a proteomic approach. The E-protein interactome provided 372 partners; only 8 of these harbored PDZ domains, including the cell polarity protein ZO-2, the chemoattractant IL-16, and syntenin. We addressed the expression and localization of the identified PDZ proteins along the differentiation of primary and THP-1 monocytes towards macrophages and dendritic cells. Our data highlight the importance of identifying the functions of PDZ proteins in the maintenance of immune fitness and the viral alteration of inflammatory response.

Knock Out of CGN and CGNL1 in MDCK Cells Affects Claudin-2 but Has a Minor Impact on Tight Junction Barrier Function

Cingulin (CGN) and paracingulin (CGNL1) are cytoplasmic proteins of tight junctions (TJs), where they play a role in tethering ZO-1 to the actomyosin and microtubule cytoskeletons. The role of CGN and CGNL1 in the barrier function of epithelia is not completely understood. Here, we analyzed the effect of the knock out (KO) of either CGN or CGNL1 or both on the paracellular permeability of monolayers of kidney epithelial (MDCK) cells. KO cells displayed a modest but significant increase in the transepithelial resistance (TER) of monolayers both in the steady state and during junction assembly by the calcium switch, whereas the permeability of the monolayers to 3 kDa dextran was not affected. The permeability to sodium was slightly but significantly decreased in KO cells. This phenotype correlated with slightly increased mRNA levels of claudin-2, slightly decreased protein levels of claudin-2, and reduced junctional accumulation of claudin-2, which was rescued by CGN or CGNL1 but not by ZO-1 overexpression. These results confirm previous observations indicating that CGN and CGNL1 are dispensable for the barrier function of epithelia and suggest that the increase in the TER in clonal lines of MDCK cells KO for CGN, CGNL1, or both is due to reduced protein expression and junctional accumulation of the sodium pore-forming claudin, claudin-2.

Zonula Occludens Proteins Signaling in Inflammation and Tumorigenesis

Tight junction (TJ) is the barrier of epithelial and endothelial cells to maintain paracellular substrate transport and cell polarity. As one of the TJ cytoplasmic adaptor proteins adjacent to cell membrane, zonula occludens (ZO) proteins are responsible for connecting transmembrane TJ proteins and cytoplasmic cytoskeleton, providing a binding platform for transmembrane TJ proteins to maintain the barrier function. In addition to the basic structural function, ZO proteins play important roles in signal regulation such as cell proliferation and motility, the latter including cell migration, invasion and metastasis, to influence embryonic development, tissue homeostasis, damage repair, inflammation, tumorigenesis, and cancer progression. In this review, we will focus on the signal regulating function of ZO proteins in inflammation and tumorigenesis, and discuss the limitations of previous research and future challenges in ZO protein research.

Isolation and Characterization of the Primary Marmoset (Callithrix jacchus) Retinal Pigment Epithelial Cells

Marmosets have emerged as a valuable primate model in ophthalmic research due to their similarity to the human visual system and their potential for generating transgenic models to advance the development of therapies. In this study, we isolated and cultured primary retinal pigment epithelium (RPE) cells from marmosets to investigate the mechanisms underlying RPE dysfunction in aging and age-related macular degeneration (AMD). We confirmed that our culture conditions and materials supported the formation of RPE monolayers with functional tight junctions that closely resembled the in vivo RPE. Since serum has been shown to induce epithelial-mesenchymal transition (EMT) in RPE cells, we compared the effects of fetal bovine serum (FBS) with serum-free supplements B27 on transepithelial electrical resistance (TER), cell proliferation, and morphological characteristics. Additionally, we assessed the age-related morphological changes of in vivo and primary RPE cells. Our results indicate that primary marmoset RPE cells exhibit in vivo-like characteristics, while cells obtained from an older donor show evidence of aging, including a failure to form a polarized monolayer, low TER, and delayed cell cycle. In conclusion, our primary marmoset RPE cells provide a reliable in vitro model for developing novel therapeutics for visual-threatening disorders such as AMD, which can be used before animal experiments using marmosets.

Culture Models to Investigate Mechanisms of Milk Production and Blood-Milk Barrier in Mammary Epithelial Cells: a Review and a Protocol

Mammary epithelial cells (MECs) are the only cell type that produces milk during lactation. MECs also form less-permeable tight junctions (TJs) to prevent the leakage of milk and blood components through the paracellular pathway (blood-milk barrier). Multiple factors that include hormones, cytokines, nutrition, and temperature regulate milk production and TJ formation in MECs. Multiple intracellular signaling pathways that positively and negatively regulate milk production and TJ formation have been reported. However, their regulatory mechanisms have not been fully elucidated. In addition, unidentified components that regulate milk production in MECs likely exist in foods, for example plants. Culture models of functional MECs that recapitulate milk production and TJs are useful tools for their study. Such models enable the elimination of indirect effects via cells other than MECs and allows for more detailed experimental conditions. However, culture models of MECs with inappropriate functionality may result in unphysiological reactions that never occur in lactating mammary glands in vivo. Here, I briefly review the physiological functions of alveolar MECs during lactation in vivo and culture models of MECs that feature milk production and less-permeable TJs, together with a protocol for establishment of MEC culture with functional TJ barrier and milk production capability using cell culture inserts.

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.

Mesenteric Adipose Tissue-Derived Klebsiella variicola Disrupts Intestinal Barrier and Promotes Colitis by Type VI Secretion System

Mesenteric adipose tissue (MAT) in Crohn's disease (CD) is associated with transmural inflammation. Extended mesenteric excision can reduce surgical recurrence and improve long-term outcomes, indicating that MAT plays an important role in the pathogenesis of CD. Bacterial translocation has been reported to occur in the MAT of patients with CD (CD-MAT), but the mechanisms by which translocated bacteria lead to intestinal colitis remain unclear. Here it is shown that members of Enterobacteriaceae are highly enriched in CD-MAT compared with non-CD controls. Viable Klebsiella variicola in Enterobacteriaceae is isolated exclusively in CD-MAT and can induce a pro-inflammatory response in vitro and exacerbates colitis both in dextran sulfate sodium (DSS)-induced colitis mice model and IL-10^-/- spontaneous colitis mice model. Mechanistically, active type VI secretion system (T6SS) is identified in the genome of K. variicola, which can impair the intestinal barrier by inhibiting the zonula occludens (ZO-1) expression. Dysfunction of T6SS by CRISPR interference system alleviates the inhibitory effect of K. variicola on ZO-1 expression and attenuated colitis in mice. Overall, these findings demonstrate that a novel colitis-promoting bacteria exist in the mesenteric adipose tissue of CD, opening a new therapeutic avenue for colitis management.

Intestinal barrier functions in hematologic and oncologic diseases

The intestinal barrier is a complex structure that not only regulates the influx of luminal contents into the systemic circulation but is also involved in immune, microbial, and metabolic homeostasis. Evidence implicating disruption in intestinal barrier functions in the development of many systemic diseases, ranging from non-alcoholic steatohepatitis to autism, or systemic complications of intestinal disorders has increased rapidly in recent years, raising the possibility of the intestinal barrier as a potential target for therapeutic intervention to alter the course and mitigate the complications associated with these diseases. In addition to the disease process being associated with a breach in the intestinal barrier functions, patients with hematologic and oncologic diseases are particularly at high risks for the development of increased intestinal permeability, due to the frequent use of broad-spectrum antibiotics and chemoradiation. They also face a distinct challenge of being intermittently severely neutropenic due to treatment of the underlying conditions. In this review, we will discuss how hematologic and oncologic diseases are associated with disruption in the intestinal barrier and highlight the complications associated with an increase in the intestinal permeability. We will explore methods to modulate the complication. To provide a background for our discussion, we will first examine the structure and appraise the methods of evaluation of the intestinal barrier.

Evaluation of toxicity of polystyrene microplastics under realistic exposure levels in human vascular endothelial EA.hy926 cells

Microplastics (MPs) have emerged as a global concern, with a recent study being the first to detect them in the bloodstream of healthy people. However, precise information regarding the toxic effects of MPs on the human vascular system is currently lacking. In this study, we used human vascular endothelial EA. hy926 cells to examine the toxic potential of polystyrene MPs (PSMPs) under realistic blood concentrations. Our findings indicated that PSMPs can cause oxidative stress by reducing the expression of antioxidants, thereby leading to apoptotic cytotoxicity in EA. hy926 cells. Furthermore, the protective potential of heat shock proteins can be reduced by PSMPs. PSMP-induced apoptosis might also lower the expression of rho-associated protein kinase-1 and nuclear factor-κB expression, thus dampening LRR- and pyrin domain-containing protein 3 in EA. hy926 cells. Moreover, we observed that PSMPs induce vascular barrier dysfunction via the depletion of zonula occludens-1 protein. However, although protein expression of the nuclear hormone receptor 77 was inhibited, no significant increase in ectin-like oxidized low-density lipoprotein receptor-1 was noted in PSMP-treated EA. hy926 cells. These results demonstrate that exposure to PSMPs may not sufficiently increase the risk of developing atherosclerosis. Overall, our research signifies that exposure to realistic blood concentrations of PSMPs is associated with low atherosclerotic cardiovascular risk in humans.

Acute Stress Regulates Sex-Related Molecular Responses in the Human Jejunal Mucosa: Implications for Irritable Bowel Syndrome

Irritable bowel syndrome (IBS) is a prevalent gastrointestinal disorder linked to intestinal barrier dysfunction and life stress. We have previously reported that female sex per se determines an increased susceptibility to intestinal barrier dysfunction after cold pain stress (CPS). We aimed to identify sex-related molecular differences in response to CPS in healthy subjects to understand the origin of sex bias predominance in IBS. In 13 healthy males and 21 females, two consecutive jejunal biopsies were obtained using Watson's capsule, at baseline, and ninety minutes after CPS. Total mucosal RNA and protein were isolated from jejunal biopsies. Expression of genes related to epithelial barrier (CLDN1, CLDN2, OCLN, ZO-1, and ZO-3), mast cell (MC) activation (TPSAB1, SERPINA1), and the glucocorticoid receptor (NR3C1) were analyzed using RT-qPCR. NR3C1, ZO-1 and OCLN protein expression were evaluated through immunohistochemistry and western blot, and mucosal inflammation through MC, lymphocyte, and eosinophil numbering. Autonomic, hormonal, and psychological responses to CPS were monitored. We found an increase in jejunal MCs, a reduced CLDN1 and OCLN expression, and an increased CLDN2 and SERPINA1 expression 90 min after CPS. We also found a significant decrease in ZO-1, OCLN, and NR3C1 gene expression, and a decrease in OCLN protein expression only in females, when compared to males. CPS induced a significant increase in blood pressure, plasma cortisol and ACTH, and subjective stress perception in all participants. Specific and independent sex-related molecular responses in epithelial barrier regulation are unraveled by acute stress in the jejunum of healthy subjects and may partially explain female predominance in IBS.

Targeting endothelial tight junctions to predict and protect thoracic aortic aneurysm and dissection

AIMS

Whether changes in endothelial tight junctions (TJs) lead to the formation of thoracic aortic aneurysm and dissection (TAAD) and serve as an early indicator and therapeutic target remains elusive.

METHODS AND RESULTS

Single-cell RNA sequencing analysis showed aberrant endothelial TJ expressions in the thoracic aortas of patients with TAAD. In a β-aminopropionitrile (BAPN)-induced TAAD mouse model, endothelial TJ function was disrupted in the thoracic aortas at an early stage (5 and 10 days) as observed by a vascular permeability assay, while the intercellular distribution of crucial TJ components was significantly decreased by en face staining. For the non-invasive detection of endothelial TJ function, two dextrans of molecular weights 4 and 70 kDa were conjugated with the magnetic resonance imaging (MRI) contrast agent Gd-DOTA to synthesize FITC-dextran-DOTA-Gd and rhodamine B-dextran-DOTA-Gd. MRI images showed that both probes accumulated in the thoracic aortas of the BAPN-fed mice. Particularly, the mice with increased accumulated signals from 5 to 10 days developed TAAD at 14 days, whereas the mice with similar signals between the two time points did not. Furthermore, the protease-activated receptor 2 inhibitor AT-1001, which seals TJs, alleviated the BAPN-induced impairment of endothelial TJ function and expression and subsequently reduced TAAD incidence. Notably, endothelial-targeted ZO-1 conditional knockout increased TAAD incidence. Mechanistically, vascular inflammation and edema were observed in the thoracic aortas of the BAPN-fed mice, whereas these phenomena were attenuated by AT-1001.

CONCLUSION

The disruption of endothelial TJ function is an early event prior to TAAD formation, herein serving as a potential indicator and a promising target for TAAD.

Cellular Distribution Pattern of tjp1 (ZO-1) in Xenopus laevis Oocytes Heterologously Expressing Claudins

Epithelial barriers constitute a fundamental requirement in every organism, as they allow the separation of different environments and set boundaries against noxious and other adverse effectors. In many inflammatory and degenerative diseases, epithelial barrier function is impaired because of a disturbance of the paracellular seal. Recently, the Xenopus laevis oocyte has been established as a heterologous expression model for the analysis of transmembrane tight junction protein interactions and is currently considered to be a suitable screening model for barrier effectors. A prerequisite for this application is a physiological anchoring of claudins to the cytoskeleton via the major scaffolding protein tjp1 (tight junction protein 1, ZO-1). We have analyzed the oocyte model with regard to the interaction of heterologously expressed claudins and tjp1. Our experiments have revealed endogenous tjp1 expression in protein and mRNA analyses of unfertilized Xenopus laevis oocytes expressing human claudin 1 (CLDN1) to claudin 5 (CLDN5). The amphibian cell model can therefore be used for the analysis of claudin interactions.

Protective effects and potential mechanisms of fermented egg-milk peptides on the damaged intestinal barrier

Introduction

Fermented egg-milk peptides (FEMPs) could enhance the colon-intestinal barrier and upgrade the expression of zonula occludens-1 and mucin 2. Besides, the underlying biological mechanism and the targets FEMPs could regulate were analyzed in our study.

Methods

Herein, the immunofluorescence technique and western blot were utilized to evaluate the repair of the intestinal barrier. Network pharmacology analysis and bioinformatics methods were performed to investigate the targets and pathways affected by FEMPs.

Results and discussion

Animal experiments showed that FEMPs could restore intestinal damage and enhance the expression of two key proteins. The pharmacological results revealed that FEMPs could regulate targets related to kinase activity, such as AKT, CASP, RAF, and GSK. The above targets could interact with each other. GO analysis indicated that the targets regulated by FEMPs could participate in the kinase activity of the metabolic process. KEGG enrichment revealed that the core targets were enriched in pathways related to cell apoptosis and other important procedures. Molecular docking demonstrated that FEMPs could bind to the key target AKT via hydrogen bond interactions. Our study combined the experiment in vivo with the method in silico and investigated the interaction between peptides and targets in a pattern of multi-targets and multi-pathways, which offered a new perspective on the functional validation and potential application of bioactive peptides.

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

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

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

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

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