Efficacy of Laurus nobilis L. for Tight Junction Protein Imbalance in Leaky Gut Syndrome.

Laurus nobilis L. (LNL) belongs to the evergreen Lauraceae family. It is native to the Mediterranean and widely distributed in the southern United States, Europe, and the Middle East. LNL is rich in active ingredients of the sesquiterpene lactone series and has been reported to have antioxidant, anti-inflammatory, and anticancer effects. And parthenolide, known as a sesquiterpene lactone-based compound, inhibits the activation of lipopolysaccharide-binding protein (LBP), which is a major trigger for leaky gut syndrome. However, the effectiveness of LNL in improving the state of increased intestinal permeability has not yet been reported. Therefore, we demonstrated the efficacy of LNL, which is known to be rich in parthenolide, in improving intestinal permeability induced by IL-13. We investigated the improvement in permeability and analyzed major tight junction proteins (TJs), permeability-related mechanisms, weight and disease activity indices, and corresponding cytokine mechanisms. LNL maintained TJs homeostasis and clinical improvement by reducing increased claudin-2 through the inhibition of IL-13/STAT6 activation in TJ-damaged conditions. These results are expected to be effective in preventing leaky gut syndrome through the TJ balance and to further improve intestinal-related diseases, such as inflammatory bowel disease.

Investigation of the Relationship of Nesfatin-1, Adropin Levels and Claudin-2, Renalase Immunoreactivity with Kidney Function in an Experimental Hypertension Model.

OBJECTIVE: Hypertension is one of the cardiovascular diseases that causes the most mortality, and 95% of the causes are unknown. The aim of the study was to examine the possible correlation of nesfatin-1 levels, adropin levels, claudin-2 immunoreactivity (claudin-2 expression in the renal proximal tubule), and renalase immunoreactivity (renalase expression in the renal proximal tubule) with arterial blood pressure, kidney function, and kidney damage. METHODS: Adult male Sprague Dawley rats were divided into control and hypertension groups (8 per group). Angiotensin II vehicle was given to the control group and angiotensin II (0.7 mg/kg/day) to the hypertension group, both via an osmotic mini pump for 7 days. The animals blood pressures were measured by tail cuff plethysmography on days 1, 3, 5, and 7. On day 7, 24-hour urine, blood, and tissues were collected from the rats. RESULTS: In the hypertension group compared with the control group, there was an increase in systolic blood pressure levels after day 1. While claudin-2 immunoreactivity was reduced in the kidneys, renalase immunoreactivity was increased. There was a decrease in creatinine clearance and an increase in fractional potassium excretion (P < .05). CONCLUSION: Our results showed that claudin-2 and renalase are associated with renal glomerular and tubular dysfunction and may play discrete roles in the pathogenesis of hypertension. We believe that these potential roles warrant further investigation.

Identification of claudin-2 as a promising biomarker for early diagnosis of pre-diabetes.

Introduction: Pre-diabetes, a high-risk metabolic state, is situated between normal glucose homeostasis and diabetes. Early identification of pre-diabetes offers opportunities for intervention and diabetes reversal, highlighting the crucial need to investigate reliable biomarkers for this condition. Methods: We conducted an in-depth bioinformatics analysis of clinical samples from non-diabetic (ND), impaired glucose tolerance (IGT), and type 2 diabetes mellitus (T2DM) categories within the GSE164416 dataset. Thereafter the HFD and STZ treated mice were used for validation. Results: This analysis identified several codifferentially expressed genes (Co-DEGs) for IGT and T2DM, including CFB, TSHR, VNN2, APOC1, CLDN2, SLPI, LCN2, CXCL17, FAIM2, and REG3A. Validation of these genes and the determination of ROC curves were performed using the GSE76895 dataset. Thereafter, CLDN2 was selected for further verification. Gene expression analysis and immunofluorescence analysis revealed a significant upregulation of CLDN2 expression in the pancreas islets of mice in the high-fat diet and T2DM groups compared to the control group. Similarly, serum level of CLDN2 in patients with IGT and T2DM were significantly higher than those in the healthy group. Discussion: These results suggest that CLDN2 can serve as a novel biomarker for pre-diabetes, providing a new direction for future research in the prevention of type 2 diabetes.

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 Roles and Regulatory Mechanisms of Tight Junction Protein Cingulin and Transcription Factor Forkhead Box Protein O1 in Human Lung Adenocarcinoma A549 Cells and Normal Lung Epithelial Cells.

Tight junction (TJ) protein cingulin (CGN) and transcription factor forkhead box protein O1 (FOXO1) contribute to the development of various cancers. Histone deacetylase (HDAC) inhibitors have a potential therapeutic role for some cancers. HDAC inhibitors affect the expression of both CGN and FOXO1. However, the roles and regulatory mechanisms of CGN and FOXO1 are unknown in non-small cell lung cancer (NSCLC) and normal human lung epithelial (HLE) cells. In the present study, to investigate the effects of CGN and FOXO1 on the malignancy of NSCLC, we used A549 cells as human lung adenocarcinoma and primary human lung epithelial (HLE) cells as normal lung tissues and performed the knockdown of CGN and FOXO1 by siRNAs. Furthermore, to investigate the detailed mechanisms in the antitumor effects of HDAC inhibitors for NSCLC via CGN and FOXO1, A549 cells and HLE cells were treated with the HDAC inhibitors trichostatin A (TSA) and Quisinostat (JNJ-2648158). In A549 cells, the knockdown of CGN increased bicellular TJ protein claudin-2 (CLDN-2) via mitogen-activated protein kinase/adenosine monophosphate-activated protein kinase (MAPK/AMPK) pathways and induced cell migration, while the knockdown of FOXO1 increased claudin-4 (CLDN-4), decreased CGN, and induced cell proliferation. The knockdown of CGN and FOXO1 induced cell metabolism in A549 cells. TSA and Quisinostat increased CGN and tricellular TJ protein angulin-1/lipolysis-stimulated lipoprotein receptor (LSR) in A549. In normal HLE cells, the knockdown of CGN and FOXO1 increased CLDN-4, while HDAC inhibitors increased CGN and CLDN-4. In conclusion, the knockdown of CGN via FOXO1 contributes to the malignancy of NSCLC. Both HDAC inhibitors, TSA and Quisinostat, may have potential for use in therapy for lung adenocarcinoma via changes in the expression of CGN and FOXO1.

Claudin-2 Mediates the Proximal Tubular Epithelial Cell-Fibroblast Crosstalk via Paracrine CTGF.

Purpose: Proximal tubular epithelial cell (PTEC) is vulnerable to injury in diabetic kidney disease (DKD) due to high energy expenditure. The injured PTECs-derived profibrotic factors are thought to be driving forces in tubulointerstitial fibrosis (TIF) as they activate surrounding fibroblasts. However, the mechanisms remain unclear. Methods: The diabetes with uninephrectomy (DKD) rats were used to evaluated renal histological changes and the expression of Claudin-2 by immunofluorescence staining. Then, Claudin-2 expression in PTECs were modulated and subsequently determined the proliferation and activation of fibroblasts by building a transwell co-culture system in normal glucose (NG)or high glucose (HG) condition. Results: Decreased expression of Claudin-2 in PTECs accompanied by tight junction disruption and increased interstitial fibrosis, were detected in DKD rats. In vitro, downregulated Claudin-2 in PTECs promoted proliferation and activation of fibroblasts, which coincided with elevated expression of profibrotic connective tissue growth factor (CTGF) in PTECs. Silenced CTGF inhibited the profibrotic of PTECs via Claudin-2 inhibition. Fibroblasts co-cultured with PTECs transitioned more to myofibroblasts and generated extracellular matrix (ECM) significantly in response to high glucose (HG) stimulation whereas overexpression of Claudin-2 in PTECs reversed the above results. Upregulating CTGF disrupted the beneficial anti-fibrosis effects obtained by overexpression of Claudin-2 in HG condition. Conclusion: Our study suggested that Claudin-2 in PTECs, a key mediator of paracellular cation and water transport, promotes the activation and proliferation of surrounding fibroblasts significantly via CTGF in a paracrine manner.

Plasma-activated medium ameliorates the chemoresistance of human lung adenocarcinoma cells mediated via downregulation of claudin-2 expression.

Plasma-activated medium (PAM) has various biological activities including anticancer and antimicrobial. However, the effect on chemoresistance in cancer cells has not been clarified in detail. Solid cancer cells form a microenvironment in the body and acquire resistance against anticancer drugs. So far, we reported that claudin-2 (CLDN2), a component of tight junctions, suppresses the anticancer drug-induced cytotoxicity of spheroids that mimic in vivo tumors. Here, we found that the protein level of CLDN2 is downregulated by the sublethal concentration of PAM in human lung adenocarcinoma-derived A549 and PC-3 cells. A cycloheximide pulse-chase assay showed that PAM accelerates the degradation of CLDN2 protein. The PAM-induced reduction of CLDN2 protein was inhibited by a lysosome inhibitor, indicating PAM may enhance the lysosomal degradation of CLDN2. The paracellular permeability to doxorubicin (DXR), an anthracycline antitumor drug, was enhanced by PAM. In the spheroids, the accumulation and toxicity of DXR were enhanced by PAM. In addition, oxidative stress and the expression of nuclear factor erythroid 2-related factor 2, one of the key factors for the acquisition of chemoresistance, were attenuated by PAM. The improvement effect of PAM on chemoresistance was suppressed by the exogenous CLDN2 overexpression. These results indicate that PAM has the ability to downregulate CLDN2 expression and may become an adjuvant drug against lung adenocarcinoma.

A Colonic Organoid Model Challenged with the Large Toxins of Clostridioides difficile TcdA and TcdB Exhibit Deregulated Tight Junction Proteins.

BACKGROUND: Clostridioides difficile toxins TcdA and TcdB are responsible for diarrhea and colitis. Lack of functional studies in organoid models of the gut prompted us to elucidate the toxin's effects on epithelial barrier function and the molecular mechanisms for diarrhea and inflammation. METHODS: Human adult colon organoids were cultured on membrane inserts. Tight junction (TJ) proteins and actin cytoskeleton were analyzed for expression via Western blotting and via confocal laser-scanning microscopy for subcellular localization. RESULTS: Polarized intestinal organoid monolayers were established from stem cell-containing colon organoids to apply toxins from the apical side and to perform functional measurements in the organoid model. The toxins caused a reduction in transepithelial electrical resistance in human colonic organoid monolayers with sublethal concentrations. Concomitantly, we detected increased paracellular permeability fluorescein and FITC-dextran-4000. Human colonic organoid monolayers exposed to the toxins exhibited redistribution of barrier-forming TJ proteins claudin-1, -4 and tricellulin, whereas channel-forming claudin-2 expression was increased. Perijunctional F-actin cytoskeleton organization was affected. CONCLUSIONS: Adult stem cell-derived human colonic organoid monolayers were applicable as a colon infection model for electrophysiological measurements. The TJ changes noted can explain the epithelial barrier dysfunction and diarrhea in patients, as well as increased entry of luminal antigens triggering inflammation.

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.

Alpha-tocopherylquinone differentially modulates claudins to enhance intestinal epithelial tight junction barrier via AhR and Nrf2 pathways.

Defects in intestinal epithelial tight junctions (TJs) allow paracellular permeation of noxious luminal antigens and are important pathogenic factors in inflammatory bowel disease (IBD). We show that alpha-tocopherylquinone (TQ), a quinone-structured oxidation product of vitamin E, consistently enhances the intestinal TJ barrier by increasing barrier-forming claudin-3 (CLDN3) and reducing channel-forming CLDN2 in Caco-2 cell monolayers (in vitro), mouse models (in vivo), and surgically resected human colons (ex vivo). TQ reduces colonic permeability and ameliorates colitis symptoms in multiple colitis models. TQ, bifunctionally, activates both aryl hydrocarbon receptor (AhR) and nuclear factor erythroid 2-related factor 2 (Nrf2) pathways. Genetic deletion studies reveal that TQ-induced AhR activation transcriptionally increases CLDN3 via xenobiotic response element (XRE) in the CLDN3 promoter. Conversely, TQ suppresses CLDN2 expression via Nrf2-mediated STAT3 inhibition. TQ offers a naturally occurring, non-toxic intervention for enhancement of the intestinal TJ barrier and adjunct therapeutics to treat intestinal inflammation.

Digested Cinnamon (Cinnamomum verum J. Presl) Bark Extract Modulates Claudin-2 Gene Expression and Protein Levels under TNFα/IL-1ß Inflammatory Stimulus.

Epigenetic changes, host-gut microbiota interactions, and environmental factors contribute to inflammatory bowel disease (IBD) onset and progression. A healthy lifestyle may help to slow down the chronic or remitting/relapsing intestinal tract inflammation characteristic of IBD. In this scenario, the employment of a nutritional strategy to prevent the onset or supplement disease therapies included functional food consumption. Its formulation consists of the addition of a phytoextract enriched in bioactive molecules. A good candidate as an ingredient is the Cinnamon verum aqueous extract. Indeed, this extract, subjected to a process of gastrointestinal digestion simulation (INFOGEST), exhibits beneficial antioxidant and anti-inflammatory properties in an in vitro model of the inflamed intestinal barrier. Here, we deepen the study of the mechanisms related to the effect of digested cinnamon extract pre-treatment, showing a correlation between transepithelial electrical resistance (TEER) decrement and alterations in claudin-2 expression under Tumor necrosis factor-α/Interleukin-1ß (TNF-α/IL-1) ß cytokine administration. Our results show that pre-treatment with cinnamon extract prevents TEER loss by claudin-2 protein level regulation, influencing both gene transcription and autophagy-mediated degradation. Hence, cinnamon polyphenols and their metabolites probably work as mediators in gene regulation and receptor/pathway activation, leading to an adaptive response against renewed insults.

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

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

Solasodine suppresses the metastasis of gastric cancer through claudin-2 via the AMPK/STAT3/NF-κB pathway.

Gastric cancer (GC) is one of the most common malignancies, and it has become the third most common malignant tumour in the world. Targeting metastasis has also become a key and difficult point in the treatment of GC. Solasodine is an active ingredient isolated from Solanum nigrum L. for the treatment of various cancers, such as breast cancer, pancreatic cancer and lung cancer. In the present study, we investigated the role and mechanism of solasodine in inhibiting GC. In vitro, we found that solasodine not only promoted cell death but also inhibited the migration and invasion of HGC27 and AGS cells. Solasodine regulated epithelial-mesenchymal transition (EMT) and reduced the expression of claudin-2 (CLDN2). Moreover, overexpression of CLDN2 inhibited the prometastatic phenotype and EMT of GC, and solasodine recovered this phenotype. Furthermore, the knockdown of CLDN2 had the opposite effect. We also found that the AMPK activators metformin and AICAR activated phosphorylation of AMPK and downregulated the expression of RhoA and CLDN2, indicating that AMPK was the upstream regulator of CLDN2. Solasodine could also activate AMP-activated protein kinase (AMPK) and inhibit the phosphorylation of STAT3 and the nuclear translocation of NF-κB. Therefore, solasodine may have prevented EMT by modulating the AMPK/STAT3/NF-κB/CLDN2 signalling pathway. In vivo, we established a xenograft model to investigate the phosphorylation of AMPK and the expression of CLDN2 from tumour tissues, and we found that solasodine inhibited tumour growth through AMPK-CLDN2 pathway. To sum up, solasodine prevented EMT by modulating the AMPK/STAT3/NF-κB/CLDN2 signalling pathway, becoming a new solution for inhibiting GC metastasis.

Alleviation of cholestatic liver injury and intestinal permeability by lubiprostone treatment in bile duct ligated rats: role of intestinal FXR and tight junction proteins claudin-1, claudin-2, and occludin.

Gut barrier disintegrity and endotoxin translocation to the liver and systemic circulation are serious clinical complications associated with the stoppage of intestinal bile flow. There is no precise pharmacological option to prevent increased intestinal permeability after bile duct ligation (BDL). Lubiprostone, a chloride channel-2 agonist, has been shown to accelerate restoration of epithelial barrier dysfunction caused by injury, but the exact mechanisms underlying the beneficial effects of lubiprostone on intestine barrier integrity remain unknown. Here, we assessed the beneficial effect of lubiprostone on cholestasis caused by BDL and relevant mechanisms. Male rats were subjected to BDL for 21 days. Seven days after BDL induction, lubiprostone was administered twice daily (10 µg/kg of body weight). Intestinal permeability was assessed through measurements of serum lipopolysaccharide (LPS) concentration. Real-time PCR was conducted to assess expression of intestinal claudin-1 occludin and FXR genes, which are important in preserving the intestinal epithelial barrier integrity, as well as claudin-2 being involved in a leaky gut barrier. Histopathological alterations were also monitored for liver injury. Lubiprostone significantly decreased BDL-induced systemic LPS elevation in rats. BDL induced a significant reduction in FXR, occludin, and claudin-1 genes expression, while increased claudin-2 expression in rat colon. Treatment with lubiprostone significantly restored expression of these genes to the control values. BDL also increased the level of hepatic enzymes ALT, ALP, AST, and total bilirubin, while lubiprostone could preserve the hepatic enzymes and total bilirubin in the treated BDL rats. Lubiprostone also caused a significant reduction in BDL-induced liver fibrosis and intestinal damage in rats. Our results suggest that lubiprostone favorably prevents BDL-induced alterations in intestinal epithelial barrier integrity possibly via modulating intestinal FXRs and tight junction gene expression.

Downregulation of angulin-1/LSR induces malignancy via upregulation of EGF-dependent claudin-2 and TGF-ß-dependent cell metabolism in human lung adenocarcinoma A549 cells.

Abnormal expression of bicellular tight junction claudins, including claudin-2 are observed during carcinogenesis in human lung adenocarcinoma. However, little is known about the role of tricellular tight junction molecule angulin-1/lipolysis-stimulated lipoprotein receptor (LSR). In the lung adenocarcinoma tissues examined in the present study, expression of claudin-2 was higher than in normal lung tissues, while angulin-1/LSR was poorly or faintly expressed. We investigated how loss of angulin-1/LSR affects the malignancy of lung adenocarcinoma cell line A549 and normal human lung epithelial (HLE) cells. The EGF receptor tyrosine kinase inhibitor AG1478 prevented the increase of claudin-2 expression induced by EGF in A549 cells. Knockdown of LSR induced expression of claudin-2 at the protein and mRNA levels and AG1478 prevented the upregulation of claudin-2 in A549 cells. Knockdown of LSR induced cell proliferation, cell migration and cell metabolism in A549 cells. Knockdown of claudin-2 inhibited the cell proliferation but did not affect the cell migration or cell metabolism of A549 cells. The TGF-ß type I receptor inhibitor EW-7197 prevented the decrease of LSR and claudin-2 induced by TGF-ß1 in A549 cells and 2D culture of normal HLE cells. EW-7197 prevented the increase of cell migration and cell metabolism induced by TGF-ß1 in A549 cells. EW-7197 prevented the increase of epithelial permeability of FITC-4kD dextran induced by TGF-ß1 in 2.5D culture of normal HLE cells. In conclusion, downregulation of angulin-1/LSR induces malignancy via EGF-dependent claudin-2 and TGF-ß-dependent cell metabolism in human lung adenocarcinoma.

Efficacy of Qifu Lizhong enema prescription on intestinal mucosal tight junction function modulation of ulcerative colitis rat model.

OBJECTIVE: To investigate the efficacy and mechanism of Qifu Lizhong enema prescription(, QFLZ) on intervening ulcerative colitis (UC) rat model with TCM spleen and kidney insufficiency syndrome. METHODS: Seventy-two male Sprague-Dawley rats were randomly assigned to six groups: normal model, mesalazine, and QFLZ high, medium, and low dose groups, each with 12 rats. After 3 d of adaptation feeding, all groups except the normal group were induced using rhubarb decoction in combination with trinitrobenzene sulfonic acid (TNBS)/55 % ethanol to establish a UC rat model. Following successful modeling, the normal and model groups received daily saline enema, while the Chinese medicine and Western medicine groups received daily QFLZ and Mesalazine enema for 2 weeks respectively. The disease activity index score, hematoxylin and eosin staining, immunohistochemistry, and Western blotting were used to determine the expression of claudin 1, claudin 2, zonula occludens-1 protein (ZO-1), and F-actin proteins in each rat colon tissue following treatment. RESULTS: QFLZ significantly alleviated the structural disorganization in the form of epithelial glands in the intestinal mucosa of rats with UC and retarded the progression of the disease. The intestinal mucosal epithelial cells of UC rats showed decreased expression of claudin 1, ZO-1, F-actin ( 0.05), claudin 2 appeared elevated ( 0.05), which resulted in impaired TJ. Treatment with QFLZ resulted in elevated expression of claudin 1 ( 0.05), ZO-1 ( 0.05) and F-actin ( 0.05) and decreased expression of claudin 2 ( 0.05), which allowed for repair of the intestinal mucosal TJ, which in turn served as a treatment for UC. CONCLUSIONS: The mechanism of repairing TJ function and repairing the intestinal mucosal barrier by QFLZ may be associated with up-regulation of claudin 1, ZO-1, and F-actin levels, and down-regulation of claudin 2 expression level.

Elevation of Anticancer Drug Toxicity by Caffeine in Spheroid Model of Human Lung Adenocarcinoma A549 Cells Mediated by Reduction in Claudin-2 and Nrf2 Expression.

Claudin-2 (CLDN2), a component of tight junctions, is abnormally expressed in human lung adenocarcinoma tissue. CLDN2 contributes to chemoresistance in human lung adenocarcinoma-derived A549 cells, and it may be a target for cancer therapy. Here, we found that coffee ingredients, namely caffeine and theobromine, decreased the protein level of CLDN2 in human lung adenocarcinoma-derived A549 cells. In contrast, other components, such as theophylline and chlorogenic acid, had no effect. These results indicate that the 7-methyl group in methylxanthines may play a key role in the reduction in CLDN2 expression. The caffeine-induced reduction in the CLDN2 protein was inhibited by chloroquine, a lysosome inhibitor. In a protein-stability assay using cycloheximide, CLDN2 protein levels decreased faster in caffeine-treated cells than in vehicle-treated cells. These results suggest that caffeine accelerates the lysosomal degradation of CLDN2. The accumulation and cytotoxicity of doxorubicin were dose-dependently increased, which was exaggerated by caffeine but not by theophylline in spheroids. Caffeine decreased nuclear factor-erythroid 2-related factor 2 (Nrf2) levels without affecting hypoxia-inducible factor-1α levels. Furthermore, caffeine decreased the expression of Nrf2-targeted genes. The effects of caffeine on CLDN2 expression and anticancer-drug-induced toxicity were also observed in lung adenocarcinoma RERF-LC-MS cells. We suggest that caffeine enhances doxorubicin-induced toxicity in A549 spheroids mediated by the reduction in CLDN2 and Nrf2 expression.

IL-22 regulates endometrial regeneration by enhancing tight junctions and orchestrating extracellular matrix.

The uterine endometrium uniquely regenerates after menses, postpartum, or after breaks in the uterine layer integrity throughout women's lives. Direct cell-cell contacts ensured by tight and adherens junctions play an important role in endometrial integrity. Any changes in these junctions can alter the endometrial permeability of the uterus and have an impact on the regeneration of uterine layers. Interleukin 22 (IL-22) is a cytokine that is recognized for its role in epithelial regeneration. Moreover, it is crucial in controlling the inflammatory response in mucosal tissues. Here, we studied the role of IL-22 in endometrial recovery after inflammation-triggered abortion. Fecundity of mice was studied in consecutive matings of the same animals after lipopolysaccharide (LPS) (10 µg per mouse)-triggered abortion. The fecundity rate after the second mating was substantially different between IL-22 knockout (IL-22-/-) (9.1%) and wild-type (WT) (71.4%) mice (p < 0.05), while there was no difference between the groups in the initial mating, suggesting that IL-22 deficiency might be associated with secondary infertility. A considerable difference was observed between IL-22-/- and WT mice in the uterine clearance following LPS-triggered abortion. Gross examination of the uteri of IL-22-/- mice revealed non-viable fetuses retained inside the horns (delayed clearance). In contrast, all WT mice had completed abortion with total clearance after LPS exposure. We also discovered that IL-22 deficiency is associated with a decreased expression of tight junctions (claudin-2 and claudin-10) and cell surface pathogen protectors (mucin-1). Moreover, IL-22 has a role in the remodeling of the uterine tissue in the inflammatory environment by regulating epithelial-mesenchymal transition markers called E- and N-cadherin. Therefore, IL-22 contributes to the proper regeneration of endometrial layers after inflammation-triggered abortion. Thus, it might have a practical significance to be utilized as a treatment option postpartum (enhanced regeneration function) and in secondary infertility caused by inflammation (enhanced barrier/protector function).

Increase in Anticancer Drug-Induced Toxicity by Fisetin in Lung Adenocarcinoma A549 Spheroid Cells Mediated by the Reduction of Claudin-2 Expression.

Claudin-2 (CLDN2), a component of tight junction, is involved in the reduction of anticancer drug-induced toxicity in spheroids of A549 cells derived from human lung adenocarcinoma. Fisetin, a dietary flavonoid, inhibits cancer cell growth, but its effect on chemosensitivity in spheroids is unknown. Here, we found that fisetin (20 µM) decreases the protein level of CLDN2 to 22.3%. Therefore, the expression mechanisms were investigated by real-time polymerase chain reaction and Western blotting. Spheroids were formed in round-bottom plates, and anticancer drug-induced toxicity was measured by ATP content. Fisetin decreased the phosphorylated-Akt level, and CLDN2 expression was decreased by a phosphatidylinositol 3-kinase (PI3K) inhibitor, suggesting the inhibition of PI3K/Akt signal is involved in the reduction of CLDN2 expression. Hypoxia level, one of the hallmarks of tumor microenvironment, was reduced by fisetin. Although fisetin did not change hypoxia inducible factor-1α level, it decreased the protein level of nuclear factor erythroid 2-related factor 2, a stress response factor, by 25.4% in the spheroids. The toxicity of doxorubicin (20 µM) was enhanced by fisetin from 62.8% to 40.9%, which was rescued by CLDN2 overexpression (51.7%). These results suggest that fisetin can enhance anticancer drug toxicity in A549 spheroids mediated by the reduction of CLDN2 expression.

Role of CB1 receptors in the acute regulation of small intestinal permeability: effects of high-fat diet.

The endocannabinoid system of the gastrointestinal tract is involved in the control of intestinal barrier function. Whether the cannabinoid 1 (CB1) receptor is expressed on the intestinal epithelium and acutely regulates barrier function has not been determined. Here, we tested the hypothesis that ligands of the CB1 receptor acutely modulate small intestinal permeability and that this is associated with altered distribution of tight junction proteins. We examined the acute effects of CB1 receptor ligands on small intestinal permeability both in chow-fed and 2-wk high-fat diet (HFD)-fed mice using Ussing chambers. We assessed the distribution of CB1 receptor and tight junction proteins using immunofluorescence and the expression of CB1 receptor using PCR. A low level of CB1 expression was found on the intestinal epithelium. CB1 receptor was highly expressed on enteric nerves in the lamina propria. Neither the CB1/CB2 agonist CP55,940 nor the CB1 neutral antagonist AM6545 altered the flux of 4kDa FITC dextran (FD4) across the jejunum or ileum of chow-fed mice. Remarkably, both CP55,940 and AM6545 reduced FD4 flux across the jejunum and ileum in HFD-fed mice that have elevated baseline intestinal permeability. These effects were absent in CB1 knockout mice. CP55,940 reduced the expression of claudin-2, whereas AM6545 had little effect on claudin-2 expression. Neither ligand altered the expression of ZO-1. Our data suggest that CB1 receptor on the intestinal epithelium regulates tight junction protein expression and restores barrier function when it is increased following exposure to a HFD for 2 wk.NEW & NOTEWORTHY The endocannabinoid system of the gastrointestinal tract regulates homeostasis by acting as brake on motility and secretion. Here we show that when exposed to a high fat diet, intestinal permeability is increased and activation of the CB1 receptor on the intestinal epithelium restores barrier function. This work further highlights the role of the endocannabinoid system in regulating intestinal homeostasis when it is perturbed.