Increased intestinal permeability and tight junction disruption by altered expression and localization of occludin in a murine graft versus host disease model

Chlorogenic acid decreases intestinal permeability and increases expression of intestinal tight junction proteins in weaned rats challenged with LPS

Chlorogenic acid, a natural phenolic acid present in fruits and plants, provides beneficial effects for human health. The objectives of this study were to investigate whether chlorogenic acid (CHA) could improve the intestinal barrier integrity for weaned rats with lipopolysaccharide (LPS) challenge. Thirty-two weaned male Sprague Dawley rats (21±1 d of age; 62.26±2.73 g) were selected and randomly allotted to four treatments, including weaned rat control, LPS-challenged and chlorogenic acid (CHA) supplemented group (orally 20 mg/kg and 50 mg/kg body). Dietary supplementation with CHA decreased (P<0.05) the concentrations of urea and albumin in the serum, compared to the LPS-challenged group. The levels of IFN-γ and TNF-α were lower (P<0.05) in the jejunal and colon of weaned rats receiving CHA supplementation, in comparison with the control group. CHA supplementation increased (P<0.05) villus height and the ratio of villus height to crypt depth in the jejunal and ileal mucosae under condictions of LPS challenge. CHA supplementation decreased (P<0.05) intestinal permeability, which was indicated by the ratio of lactulose to mannitol and serum DAO activity, when compared to weaned rats with LPS challenge. Immunohistochemical analysis of tight junction proteins revealed that ZO-1 and occludin protein abundances in the jejunum and colon were increased (P<0.05) by CHA supplementation. Additionally, results of immunoblot analysis revealed that the amount of occludin in the colon was also increased (P<0.05) in CHA-supplemented rats. In conclusion, CHA decreases intestinal permeability and increases intestinal expression of tight junction proteins in weaned rats challenged with LPS.

The reversible increase in tight junction permeability induced by capsaicin is mediated via cofilin-actin cytoskeletal dynamics and decreased level of occludin

Previous results demonstrated that capsaicin induces the reversible tight junctions (TJ) opening via cofilin activation. The present study investigated the mechanisms underlying the reversible TJ opening and compared the effect to the irreversible opening induced by actin inhibitors. Capsaicin treatment induced the F-actin alteration unique to capsaicin compared to actin-interacting agents such as latrunculin A, which opens TJ irreversibly. Along with TJ opening, capsaicin decreased the level of F-actin at bicellular junctions but increased it at tricellular junctions accompanied with its concentration on the apical side of the lateral membrane. No change in TJ protein localization was observed upon exposure to capsaicin, but the amount of occludin was decreased significantly. In addition, cosedimentation analyses suggested a decrease in the interactions forming TJ, thereby weakening TJ tightness. Introduction of cofilin, LIMK and occludin into the cell monolayers confirmed their contribution to the transepithelial electrical resistance decrease. Finally, exposure of monolayers to capsaicin augmented the paracellular passage of both charged and uncharged compounds, as well as of insulin, indicating that capsaicin can be employed to modulate epithelial permeability. Our results demonstrate that capsaicin induces TJ opening through a unique mechanism, and suggest that it is a new type of paracellular permeability enhancer.

Intestinal epithelial barrier function in liver cirrhosis: an extensive review of the literature

Recent evidence suggests that translocation of bacteria and bacterial products, such as endotoxin from the intestinal lumen into the systemic circulation is a contributing factor in the pathogenesis of chronic liver diseases and the development of complications in cirrhosis. In addition to alterations in the intestinal microbiota and immune system, dysfunction of the intestinal epithelial barrier may be an important factor facilitating bacterial translocation. This review aims to provide an overview of the current evidence of intestinal epithelial barrier dysfunction in human chronic liver diseases and cirrhosis, and to discuss possible contributing factors and mechanisms. Data suggest the presence of intestinal epithelial barrier dysfunction in patients with chronic liver diseases, but are more convincing in patients with cirrhosis, especially in those with complications. The barrier dysfunction can result from both direct and indirect effects of aetiological factors, such as alcohol and obesity, which can cause chronic liver diseases and ultimately cirrhosis. On the other hand characteristics of cirrhosis itself, including portal hypertension, alterations in the intestinal microbiota, inflammation and oxidative stress can affect barrier function of both small and large intestine and may contribute to the development of complications. In conclusion, there are indications for intestinal epithelial barrier dysfunction in patients with chronic liver diseases and especially in patients with cirrhosis, which can be caused by various factors affecting both the small and large intestine.

Regulation of paracellular permeability: factors and mechanisms

Epithelial permeability is composed of transcellular permeability and paracellular permeability. Paracellular permeability is controlled by tight junctions (TJs). Claudins and occludin are two major transmembrane proteins in TJs, which directly determine the paracellular permeability to different ions or large molecules. Intracellular signaling pathways including Rho/Rho-associated protein kinase, protein kinase Cs, and mitogen-activated protein kinase, modulate the TJ proteins to affect paracellular permeability in response for diverse stimuli. Cytokines, growth factors and hormones in organism can regulate the paracellular permeability via signaling pathway. The transcellular transporters such as Na-K-ATPase, Na(+)-coupled transporters and chloride channels, can interact with paracellular transport and regulate the TJs. In this review, we summarized the factors affecting paracellular permeability and new progressions of the related mechanism in recent studies, and pointed out further research areas.

Interleukin-8 regulates endothelial permeability by down-regulation of tight junction but not dependent on integrins induced focal adhesions

Interleukin-8 (IL-8) is a common inflammatory factor, which involves in various non-specific pathological processes of inflammation. It has been found that increased endothelial permeability accompanied with high expression of IL-8 at site of injured endothelium and atherosclerotic plaque at early stages, suggesting that IL-8 participated in regulating endothelial permeability in the developing processes of vascular disease. The purpose of this study is to investigate the regulation effects of IL-8 on the vascular endothelial permeability, and the mRNA and protein expression of tight junction components (i.e., ZO-1, Claudin-5 and Occludin). Endothelial cells were stimulated by IL-8 with the dose of 50, 100 and 200 ng/mL, and duration of 2, 4, 6, 8h, respectively. The mRNA and protein expression level of tight junction components with IL-8 under different concentration and duration was examined by RT-PCR and Western blot, respectively. Meanwhile, the integrins induced focal adhesions event with IL-8 stimulation was also investigated. The results showed that IL-8 regulated the permeability of endothelium by down-regulation of tight junction in a dose- and time-dependence manner, but was not by integrins induced focal adhesions. This finding reveals the molecular mechanism in the increase of endothelial cell permeability induced by IL-8, which is expected to provide a new idea as a therapeutic target in vascular diseases.

Toll-like receptor 4 increases intestinal permeability through up-regulation of membrane PKC activity in alcoholic steatohepatitis

Intestinal hyperpermeability is a causal factor for the development of alcoholic endotoxemia and steatohepatitis. However, the mechanisms governing this link remain unknown. The purpose of this study was to determine whether toll-like receptor 4 (TLR4) is involved in ethanol's deleterious effects on the intestinal barrier. Caco-2 cells were incubated in vitro with 1-10% ethanol. The results indicated that ethanol had a dose-dependent effect in increasing TLR4 expression and intercellular permeability. Then the effects of TLR4 on protein kinase C (PKC) and the intercellular junction protein occludin were assessed with and without pretreatment with a TLR4 inhibitor. The results indicated that TLR4 increased nonspecific PKC activity and reduced the expression of phosphorylated occludin in the membrane, which increased intercellular permeability. These effects were prevented by pretreatment with TLR4 mAb. Wild-type C57BL/6 mice were fed an ethanol or isocaloric liquid diet for 6 weeks. Hepatitis was diagnosed by the presence of an associated elevated blood endotoxin level. Chronic ethanol treatment significantly elevated blood endotoxin levels, intestinal permeability, and the expression of TLR4 in the ileum and colon. Moreover, ethanol exposure reduced the distribution of phosphorylated occludin in the intestinal epithelium because of PKC activation. In conclusion, chronic ethanol exposure induces a high response of TLR4 to lipopolysaccharide (LPS), and TLR4 increases intestinal permeability through down-regulation of phosphorylated occludin expression in the intestinal epithelial barrier, accompanied by membrane PKC hyperactivity.

Effects of rhein on intestinal epithelial tight junction in IgA nephropathy

AIM: To investigate the effects of rhein on intestinal epithelial tight junction proteins in rats with IgA nephropathy (IgAN).

METHODS: Twenty-eight female Sprague-Dawley rats were randomly divided into four groups (7 per group): Control, IgAN, Rhein-treated, and Rhein-prevented. Bovine serum albumin, lipopolysaccharide and CCl₄ were used to establish the rat model of IgA nephropathy. The Rhein-treated group was given rhein from week 7 until the rats were sacrificed. The Rhein-prevented group was given rhein from week 1. Animals were sacrificed at the end of week 10. We observed the changes in the intestinal epithelial tight junctions using transmission electron microscopy, and expression of intestinal epithelial tight junction proteins zona occludens protein (ZO)-1 and occludin by immunofluorescence using laser confocal microscopy. Changes in mRNA and protein expression of ZO-1 and occludin were measured by reverse transcriptase polymerase chain reaction and Western blotting. The ratio of urinary lactulose/mannitol was measured by high performance liquid chromatography (HPLC) for assessing the intestinal permeability.

RESULTS: In the control group, the tight junctions lied between epithelial cells on the top of the outer side of the cell membrane, and appeared in dense dotted crystal structures, the neighboring cells were binded tightly with no significant gap, and the tight junction protein ZO-1 and occludin were evenly distributed in the intestinal epithelial cells at the top of the junction. Compared with the control group, in the IgAN group, the structure of the tight junction became obscured and the dotted crystal structures had disappeared; the fluorescence of ZO-1 and occludin was uneven and weaker (5.37 ± 1.27 vs 10.03 ± 1.96, P < 0.01; 4.23 ± 0.85 vs 12.35 ± 4.17, P < 0.01); the mRNA expression of ZO-1 and occludin decreased (0.42 ± 0.19 vs 0.92 ± 0.24, P < 0.01; 0.40 ± 0.15 vs 0.97 ± 0.25, P < 0.01); protein expression of ZO-1 and occludin was decreased (0.85 ± 0.12 vs 1.98 ± 0.43, P < 0.01; 0.72 ± 0.15 vs 1.38 ± 0.31, P < 0.01); and the ratio of urinary lactulose/mannitol increased (3.55 ± 0.68 vs 2.72 ± 0.21, P < 0.01). In the Rhein-prevented and Rhein-treated groups, compared with the IgAN group, the intestinal epithelial tight junctions were repaired; fluorescence of ZO-1 and occludin was stronger (11.16 ± 3.52 and 8.81 ± 2.30 vs 5.37 ± 1.27, P < 0.01; 10.97 ± 3.40 and 9.46 ± 2.40 vs 4.23 ± 0.85, P < 0.01); mRNA of ZO-1 and occludin increased (0.81 ± 0.17 and 0.64 ± 0.16 vs 0.42 ± 0.19, P < 0.01; 0.82 ± 0.22 and 0.76 ± 0.31 vs 0.40 ± 0.15, P < 0.01); protein expression of ZO-1 and occludin was increased (2.07 ± 0.41 and 1.57 ± 0.23 vs 0.85 ± 0.12, P < 0.01; 1.34 ± 0.21 and 1.15 ± 0.17 vs 0.72 ± 0.15, P < 0.01); and the ratio of urinary lactulose/mannitol decreased (2.83 ± 0.43 and 2.87 ± 0.18 vs 3.55 ± 0.68, P < 0.01).

CONCLUSION: Rhein can enhance the expression of ZO-1 and occludin, repair damaged tight junctions, and protect the intestinal barrier.

Effects of cathepsin K deficiency on intercellular junction proteins, luminal mucus layers, and extracellular matrix constituents in the mouse colon

Cathepsin K has been shown to exhibit antimicrobial and anti-inflammatory activities in the mouse colon. To further elucidate its role, we used Ctsk-/- mice and demonstrated that the absence of cathepsin K was accompanied by elevated protein levels of related cysteine cathepsins (cathepsins B, L, and X) in the colon. In principle, such changes could result in altered subcellular localization; however, the trafficking of cysteine cathepsins was not affected in the colon of Ctsk-/- mice. However, cathepsin K deficiency affected the extracellular matrix constituents, as higher amounts of collagen IV and laminin were observed. Moreover, the localization pattern of the intercellular junction proteins E-cadherin and occludin was altered in the colon of Ctsk-/- mice, suggesting potential impairment of the barrier function. Thus, we used an ex vivo method for assessing the mucus layers and showed that the absence of cathepsin K had no influence on mucus organization and growth. The data of this study support the notion that cathepsin K contributes to intestinal homeostasis and tissue architecture, but the lack of cathepsin K activity is not expected to affect the mucus-depending barrier functions of the mouse colon. These results are important with regard to oral administration of cathepsin K inhibitors that are currently under investigation in clinical trials.

Tumour necrosis factor--induced loss of intestinal barrier function requires TNFR1 and TNFR2 signalling in a mouse model of total parenteral nutrition

Tumour necrosis factor-α (TNF-α) has been reported to play a central role in intestinal barrier dysfunction in many diseases; however, the precise role of the TNF-α receptors (TNFRs) has not been well defined using in vivo models. Our previous data showed that enteral nutrient deprivation or total parenteral nutrition (TPN) led to a loss of intestinal epithelial barrier function (EBF), with an associated upregulation of TNF-α and TNFR1. In this study, we hypothesized that TNF-α plays an important role in TPN-associated EBF dysfunction. Using a mouse TPN model, we explored the relative roles of TNFR1 vs. TNFR2 in mediating this barrier loss. C57/BL6 mice underwent intravenous cannulation and were given enteral nutrition or TPN for 7 days. Tumour necrosis factor-α receptor knockout (KO) mice, including TNFR1KO, TNFR2KO or TNFR1R2 double KO (DKO), were used. Outcomes included small intestine transepithelial resistance (TER) and tracer permeability, junctional protein zonula occludens-1, occludin, claudins and E-cadherin expression. In order to address the dependence of EBF on TNF-α further, exogenous TNF-α and pharmacological blockade of TNF-α (Etanercept) were also performed. Total parenteral nutrition led to a loss of EBF, and this was almost completely prevented in TNFR1R2DKO mice and partly prevented in TNFR1KO mice but not in TNFR2KO mice. The TPN-associated downregulation of junctional protein expression and junctional assembly was almost completely prevented in the TNFR1R2DKO group. Blockade of TNF-α also prevented dysfunction of the EBF and junctional protein losses in mice undergoing TPN. Administration of TPN upregulated the downstream nuclear factor-B and myosin light-chain kinase (MLCK) signalling, and these changes were almost completely prevented in TNFR1R2DKO mice, as well as with TNF-α blockade, but not in TNFR1KO or TNFR2KO TPN groups. Tumour necrosis factor-α is a critical factor for TPN-associated epithelial barrier dysfunction, and both TNFR1 and TNFR2 are involved in EBF loss. Nuclear factor-B and MLCK signalling appear to be important downstream mediators involved in this TNF-α signalling process.

Oral glutamine supplementation improves intestinal permeability dysfunction in a murine acute graft-vs.-host disease model

Although a profound barrier dysfunction has been reported, little is known about the pathophysiological mechanism evoking gastrointestinal graft-vs.-host disease (GI-GvHD) and apparent therapeutic options. The aim of this study was to evaluate the influence of oral glutamine on the course of GI-GvHD in an acute semiallogenic graft-vs.-host disease (GvHD) in irradiated B6D2F1 mice. An acute semiallogenic GvHD was induced by intraperitoneal injection of lymphocytes from C57BL/6 mice to irradiated B6D2F1 mice. Half of the GvHD animals received oral glutamine supplementation for 6 days started at the time of lymphocyte transfer. Six days after induction of the semiallogenic GvHD, jejunum specimens were prepared. The expression of the proinflammatory cytokine TNF-α and the tight junction protein occludin was investigated by PCR. Histological changes along with the apoptotic response were evaluated and intestinal permeability was assessed. Animals with GvHD showed a strong increase in paracellular permeability as a sign of the disturbed barrier function. TNF-α expression was significantly increased and the expression of the tight junction protein occludin decreased. GvHD led to mucosal atrophy, crypt hyperplasia, crypt apoptosis, and a disintegration of the tight junctions. Glutamine-treated mice showed reduced expression of TNF-α, increased occludin expression, fewer histological changes in the jejunum, smaller number of apoptotic cells in the crypt, and reduced gastrointestinal permeability. In conclusion, oral glutamine seems to have beneficial effects on the severity of inflammatory changes in the course of GvHD and might be a therapeutic option.

Effect of calf starter feeding on gut microbial diversity and expression of genes involved in host immune responses and tight junctions in dairy calves during weaning transition

Calf starters are usually offered to dairy calves to facilitate the weaning process, however, the effect of solid feed consumption on gut health has not been well studied. This study aimed to investigate the effect of calf starter feeding on the gut bacterial community and mucosal immune functions in dairy calves during weaning transition. Mucosal tissue and digesta samples were collected from rumen, jejunum, ileum, cecum, and colon upon slaughtering of calves (n=8) after feeding the experimental diets [milk replacer (MR) or milk replacer + calf starter (MR+S)] for 6 wk. Expression of toll-like receptor (TLR) 10 was downregulated along the gut, whereas TLR2 in colon and TLR6 along the gut were upregulated in MR+S-fed calves compared with MR-fed calves. Ileal TLR9 and TLR10 showed higher expression compared with the other regions regardless of the diet. Peptidoglycan recognition protein 1 demonstrated a diet- and gut-regional dependent expression pattern, whereas β-defensin did not. The diet and gut region also affected the expression of tight junction-regulating genes claudin 4 and occludin. Bacterial diversity tended to be different between the 2 diets, whereas the bacterial density was different among gut regions and sample type. The present study revealed that changes in bacterial diversity, expression of genes encoding host mucosal immune responses, and barrier functions were associated with the MR+S diet, and suggests that solid feed consumption may alter gut microbiome and host mucosal functions during weaning transition.

ACF7 regulates colonic permeability

Colonic paracellular permeability is regulated by various factors, including dynamics of the cytoskeleton. Recently, ACF7 has been found to play a critical role in cytoskeletal dynamics as an essential integrator. To elucidate the physiological importance of ACF7 and paracellular permeability, we conditionally knocked out ACF7 in the intestinal mucosa of mice. Histopathological findings indicated that ACF7 deficiency resulted in significant interstitial proliferation and columnar epithelial cell rearrangement. Decreased colonic paracellular permeability was detected using a Ussing chamber and the FITC-inulin method. In order to clarify the underlying mechanism, we further analyzed the expression levels of three important tight junction proteins. Downregulation of ZO-1, occludin and claudin-1 was identified. Immunofluorescence provided strong evidence that ZO-1, occludin and claudin-1 were weakly stained. We hypothesized that ACF7 regulates cytoskeleton dynamics to alter mucosal epithelial arrangement and colonic paracellular permeability.

Targeting α-7 nicotinic acetylcholine receptor in the enteric nervous system: a cholinergic agonist prevents gut barrier failure after severe burn injury

We have previously shown that vagal nerve stimulation prevents intestinal barrier loss in a model of severe burn injury in which injury was associated with decreased expression and altered localization of intestinal tight junction proteins. α-7 Nicotinic acetylcholine receptor (α-7 nAchR) has been shown to be necessary for the vagus nerve to modulate the systemic inflammatory response, but the role of α-7 nAchR in mediating gut protection remained unknown. We hypothesized that α-7 nAchR would be present in the gastrointestinal tract and that treatment with a pharmacological agonist of α-7 nAchR would protect against burn-induced gut barrier injury. The effects of a pharmacological cholinergic agonist on gut barrier integrity were studied using an intraperitoneal injection of nicotine 30 minutes after injury. Intestinal barrier integrity was examined by measuring permeability to 4-kDa fluorescein isothiocyanate-dextran and by examining changes in expression and localization of the intestinal tight junction proteins occludin and ZO-1. Nicotine injection after injury prevented burn-induced intestinal permeability and limited histological gut injury. Treatment with nicotine prevented decreased expression and altered localization of occludin and ZO-1, as seen in animals undergoing burn alone. Defining the interactions among the vagus nerve, the enteric nervous system, and the intestinal epithelium may lead to development of targeted therapeutics aimed at reducing gut barrier failure and intestinal inflammation after severe injury.

Hyperoxia disrupts pulmonary epithelial barrier in newborn rats via the deterioration of occludin and ZO-1

Background

Prolonged exposure to hyperoxia in neonates can cause hyperoxic acute lung injury (HALI), which is characterized by increased pulmonary permeability and diffuse infiltration of various inflammatory cells. Disruption of the epithelial barrier may lead to altered pulmonary permeability and maintenance of barrier properties requires intact epithelial tight junctions (TJs). However, in neonatal animals, relatively little is known about how the TJ proteins are expressed in the pulmonary epithelium, including whether expression of TJ proteins is regulated in response to hyperoxia exposure. This study determines whether changes in tight junctions play an important role in disruption of the pulmonary epithelial barrier during hyperoxic acute lung injury.

Methods

Newborn rats, randomly divided into two groups, were exposed to hyperoxia (95% oxygen) or normoxia for 1–7 days, and the severity of lung injury was assessed; location and expression of key tight junction protein occludin and ZO-1 were examined by immunofluorescence staining and immunobloting; messenger RNA in lung tissue was studied by RT-PCR; transmission electron microscopy study was performed for the detection of tight junction morphology.

Results

We found that different durations of hyperoxia exposure caused different degrees of lung injury in newborn rats. Treatment with hyperoxia for prolonged duration contributed to more serious lung injury, which was characterized by increased wet-to-dry ratio, extravascular lung water content, and bronchoalveolar lavage fluid (BALF):serum FD4 ratio. Transmission electron microscopy study demonstrated that hyperoxia destroyed the structure of tight junctions and prolonged hyperoxia exposure, enhancing the structure destruction. The results were compatible with pathohistologic findings. We found that hyperoxia markedly disrupted the membrane localization and downregulated the cytoplasm expression of the key tight junction proteins occludin and ZO-1 in the alveolar epithelium by immunofluorescence. The changes of messenger RNA and protein expression of occludin and ZO-1 in lung tissue detected by RT-PCR and immunoblotting were consistent with the degree of lung injury.

Conclusions

These data suggest that the disruption of the pulmonary epithelial barrier induced by hyperoxia is, at least in part, due to massive deterioration in the expression and localization of key TJ proteins.