Expression Of Tight Junction Proteins Occludin Research Articles

MATRIX METALLOPROTEINASE (MMP-9) INDUCED INCREASE IN INTESTINAL EPITHELIAL TIGHT JUNCTION BARRIER IS MEDIATED BY EGFR ACTIVATION

Abstract BACKGROUND The defective intestinal tight junction (TJ) barrier has a key pathogenic factor in Crohn’s disease (CD) and other inflammatory conditions of the gut. Clinical studies in CD patients have shown that a persistent increase in intestinal permeability is predictive of poor clinical outcome. Matrix metalloproteinase-9 (MMP-9) has been shown to be markedly increased in intestinal tissues of patients with CD and it has been postulated that MMP-9 plays an important role on the pathogenesis of intestinal inflammation in CD. Our recent studies suggested that MMP-9 at clinically relevant concentrations causes an increase in intestinal epithelial TJ permeability in-vitro and in-vivo by inducing intracellular signaling pathways via activating distinct basolateral membrane receptors. However, the specific protein receptors and the intracellular signaling cascades involved have not been fully identified. One of the potential protein receptors that might be a target of MMP-9 on the basolateral membrane of the intestinal epithelial cells is the epidermal growth factor receptor (EGFR), which has been shown to have opposing roles in the pathophysiology of CD. AIMS Therefore, our aims in this study were to examine the effect of MMP-9 on EGFR activation and delineate the role of EGRF in MMP-9 induced increase in intestinal epithelial TJ permeability by using Caco-2 monolayers as an in-vitro model system. RESULTS MMP-9 (400 ng/ml) caused a time-dependent increase in EGFR activation as assessed by EGFR phosphorylation, and by in-vitro kinase activity measurement of EGFR in filter-grown Caco-2 monolayers. Inhibition of EGFR by pharmacologic inhibitor, PD 153035, prevented the MMP-9 induced increase in Caco-2 TJ permeability measured by trans-epithelial resistance (TER) and mucosal-to-serosal flux of a paracellular marker dextran 10kd. MMP-9 caused a decrease in the TJ protein occludin expression. Inhibition of EGFR by PD 153035 prevented the MMP-9 induced degradation of occludin expression. In addition, the effect of EGFR activation by a known activator, NSC 228155 25, in the absence of MMP-9, caused an increase in Caco-2 TJ permeability and a decrease in occludin expression. CONCLUSION Our data showed that MMP-9 induced increase in intestinal epithelial TJ permeability is mediated in part by the activation of EGFR and the subsequent degradation of occludin expression. Identifying the specific membrane receptors that mediate the MMP-9 induced increase in intestinal TJ permeability could be important in developing future therapeutic strategies in IBD.

Selenium-enriched Bifidobacterium longum DD98 attenuates irinotecan-induced intestinal and hepatic toxicity in vitro and in vivo

Irinotecan (CPT-11) is a camptothecin chemotherapy drug largely used in treating cancers. However, its strong adverse effects, such as gastrointestinal and hepatic toxicities, tend to reduce the patients’ life qualities and to limit the clinical use of CPT-11. The protective roles of selenium (Se) and probiotics against CPT-11-induced toxicity have been widely reported. However, the application of Se-enriched probiotics in the adjuvant therapy of CPT-11 has not been well explored. The purpose of this study is to evaluate the in-vitro and in-vivo effects of Se-enriched Bifidobacterium longum DD98 (Se-B. longum DD98) as a chemotherapy preventive agent on alleviating intestinal and hepatic toxicities induced by CPT-11 chemotherapy. The results showed that Se-B. longum DD98 positively regulated the aberrant cell viability and oxidative stress induced by CPT-11 both in human normal liver (L-02) and rat small intestinal epithelial (IEC-6) cell lines. In vivo experiment revealed that Se-B. longum DD98 significantly attenuated intestinal and hepatic toxicities by ameliorating symptoms such as body weight loss and diarrhea, and by improving the biochemical indicators of hepatotoxicity and oxidative stress. Furthermore, we discovered that the protective effects of Se-B. longum DD98 based largely upon decreasing the pro-inflammatory cytokines IL-1β and IL-18 and enhancing the expression of tight-junction proteins occludin and ZO-1, as well as restoring the composition and diversity of gut microbiota. Results suggested that Se-B. longum DD98 effectively protected livers and intestines against the CPT-11-induced damages, and therefore, could be considered as a promising adjuvant therapeutic agent with CPT-11 for the cancer treatment.

Potential mechanistic pathways underlying intestinal and hepatic effects of kefir in high-fructose-fed rats

Excess intake of fructose may contribute to the high prevalence of metabolic disorder. In this study, we investigated the effects of kefir supplementation on the intestine-liver-adipose tissue axis in metabolic disorder induced by high-fructose diet in rats to describe mechanistic action and potential therapeutic value of kefir. Fructose was given to the rats as a 20% solution in drinking water for 15 weeks. Kefir was administrated by gastric gavage once a day during the final six weeks. Kefir supplementation improved metabolic parameters, including plasma triglyceride and insulin levels; hepatic weight, triglyceride content and fatty degeneration; omental fat mass in fructose-fed rats. Kefir supplementation decreased the ratio of Firmicutes/Bacteroidetes in feces, as well as necrotic degeneration, expression levels of nuclear factor-kappa B (NF-κB), and inducible nitric oxide synthase (iNOS), but increased expression of tight-junction proteins occludin and claudin-1, in the ileum of the fructose-fed rats. Kefir treatment also reduced the mRNA levels of key lipogenic genes sterol regulatory element-binding protein (SREBP-1c) and fatty acid synthase (FASN) together with a decline in expression of tumor necrosis factor-alpha (TNF-α), NF-κB, and glycosylated glycoprotein (CD68) in the liver. Moreover, kefir treatment improved insulin signaling at the level of insulin receptor substrate 1 (IRS-1) and phospho-endothelial nitric oxide synthase (peNOS) as well as fructose transporters (GLUT2 and GLUT5) in the liver, but not in the adipose tissue, of high-fructose-fed rats. Consequently, kefir supplementation suppresses hepatic lipogenesis and inflammatory status, but promotes insulin signaling, in association with a change of the fecal microbiota and attenuation of the intestinal permeability factors in high-fructose-fed rats. Thus, we propose that kefir has favorable effects on the hepatic and intestinal irregularities induced by fructose overconsumption.

Hydrogen-rich saline protects intestinal epithelial tight junction barrier in rats with intestinal ischemia–reperfusion injury by inhibiting endoplasmic reticulum stress-induced apoptosis pathway

AimTo investigate the effects of hydrogen-rich saline (HRS) on intestinal epithelial tight junction (TJ) barrier in rats with intestinal ischemia–reperfusion injury (IIRI). Materials and methodsThirty-two healthy male Sprague–Dawley (SD) rats were randomly divided into four groups (n = 8 each): Sham group, I/R group, HRS group and 4-PBA group. After 45 min of ischemia and 6 h of reperfusion, the rats were sacrificed to collect serum and ileum for detection. Hematoxylin and eosin (H&E) staining was used to observe the morphology of small intestine. The serum expression levels of intestinal fatty acid binding protein (IFABP), tumor necrosis factor-α (TNF-α), and interleukin-1β (IL-1β) were determined by enzyme linked immunosorbent assay (ELISA). Imunohistochemistry, immunofluorescence and Western blot were used to detect key proteins in intestinal epithelial TJs, ERS, and ERS-induced apoptosis, including occludin, zonula occludens-1 (ZO-1), glucose-regulated protein 78 (GRP78), X-box binding protein-1 (XBP1), C/EBP-homologous protein (CHOP) and caspase-3. Data was presented as mean ± SEM and compared using one-way ANOVA. A p-value <0.05 was considered significant. ResultsCompared with rats in the I/R group, the Chiu score of ileum damage in the HRS group and 4-PBA group were lower. The levels of serum IFABP, TNF-α, and IL-1β were statistically significant among the groups. Increased expression of TJ proteins occludin and ZO-1 by reducing various parameters of ERS and ERS-induced apoptosis evidenced by down-regulation of the protein levels of GRP78, XBP1, CHOP and caspase-3 were shown in the HRS and 4-PBA groups. ConclusionHRS had potential protective effects on intestinal barrier in IIRI rats. This study suggested that inhibition of excessive ERS and ERS-induced apoptosis by HRS may reduce intestinal epithelial cells damage and maintain the integrity of intestinal epithelial TJ barrier in rats with IIRI.

Progesterone decreases gut permeability through upregulating occludin expression in primary human gut tissues and Caco-2 cells

Progesterone plays a protective role in preventing inflammation and preterm delivery during pregnancy. However, the mechanism involved is unknown. Microbial product translocation from a permeable mucosa is demonstrated as a driver of inflammation. To study the mechanism of the protective role of progesterone during pregnancy, we investigated the effect of physiologic concentrations of progesterone on tight junction protein occludin expression and human gut permeability in vitro and systemic microbial translocation in pregnant women in vivo. Plasma bacterial lipopolysaccharide (LPS), a representative marker of in vivo systemic microbial translocation was measured. We found that plasma LPS levels were significantly decreased during 24 to 28 weeks of gestation compared to 8 to 12 weeks of gestation. Moreover, plasma LPS levels were negatively correlated with plasma progesterone levels but positively correlated with plasma tumor necrosis factor-alpha (TNF-α) levels at 8 to 12 weeks of gestation but not at 24 to 28 weeks of gestation. Progesterone treatment increased intestinal trans-epithelial electrical resistance (TEER) in primary human colon tissues and Caco-2 cells in vitro through upregulating tight junction protein occludin expression. Furthermore, progesterone exhibited an inhibitory effect on nuclear factor kappa B (NF-κB) activation following LPS stimulation in Caco-2 cells. These results reveal a novel mechanism that progesterone may play an important role in decreasing mucosal permeability, systemic microbial translocation, and inflammation during pregnancy.

MTOR/STAT-3 pathway mediates mesenchymal stem cell-secreted hepatocyte growth factor protective effects against lipopolysaccharide-induced vascular endothelial barrier dysfunction and apoptosis.

Mesenchymal stem cells (MSCs) protect the endothelial barrier complex and survival, implicated in the pathogenesis of acute lung injury (ALI) via paracrine hepatocyte growth factor (HGF). However, the mechanism of HGF in endothelial regulation remains unclear. Here, we introduced a coculture protocol of pulmonary microvascular endothelial cells (PMVECs) and overexpression of the HGF gene of MSCs (MSC-HGF). Immunofluorescence and endothelial permeability analysis revealed that MSC-HGF protected endothelial tight junction protein occludin expression and attenuated cellular permeability as well as endothelial apoptosis. To investigate the novel mechanism mammalian TOR (mTOR)/ signal transducer and activator of transcription 3 (STAT-3) signaling in HGF protective effects against endothelial barrier and apoptosis, we used recombinant mouse HGF in endothelial cells. In addition, we used mTOR inhibitor rapamycin to inhibit the mTOR pathway. Our study demonstrated that rapamycin decreased the protective effects of HGF on the endothelium by decreasing tight junction protein occludin expression and cell proliferation, and raising lipopolysaccharide (LPS)-induced endothelial permeability, endothelial cell injury factors ET-1 and vWF. Similarly, the protective effects of HGF on reducing endothelial barrier and apoptosis were weakened when PMVECs were treated with the STAT-3 inhibitor S3I-201. Moreover, mTOR/STAT-3 were activated by HGF demonstrated as raising mTOR (Ser2448) and STAT3 (Ser727) phosphorylation proteins, leading to endothelial barrier improvement and survival. Reversely, rapamycin or S3I-201 inhibited mTOR/STAT-3 activation. Taken together, our findings highlight that the activation of the mTOR/STAT-3 pathway provides novel mechanistic insights into MSC-secreted HGF protection against LPS-induced vascular endothelial permeability dysfunction and apoptosis, which contributes to decreasing microvascular loss and lung injury.

Role of nuclear factor E2 related factor/heme oxygenase-1 pathway in hydrogen sulfide-induced reduction of blood brain barrier damage in rats with cardiac arrest

Objective To investigate whether the nuclear factor E2 related factor/heme synthase-1(Nrf2/HO-1) pathway is involved in the mechanism of hydrogen sulfide-induced reduction of blood brain barrier(BBB) injury in rats with cardiac arrest and the possible mechanism involved in the effect. Methods Cardiac arrest was induced with transoesophageal cardiac pacing followed by cardiopulmonary resuscitation to establish the cardiac arrest model and the time of ischemia was 4 min. 140 adult male SD rats were randomly divided into five groups: sham operation group(Sham group, n=20), cardiac arrest model group (CPR group, n=30), sodium hydrogen sulfide(NaHS) group(n=30), NaHS+solvent group[NaHS+dimethyl sulfoxide(DMSO) group, n=30], NaHS+Nrf2 inhibitor retinoic acid(RA) group(NaHS+RA group, n=30). In Sham group, only anesthesia was performed, and the trachea was inserted through the mouth, and the catheters were performed via femoral artery and vein. The other four groups were all induced cardiac arrest by electrical stimulation. NaHS group and NaHS+RA group, rats received NaHS (0.5 mg/kg) at the start of CPR intravenously, followed by a continuous infusion of NaHS(1.5 mg·kg-1·h-1) for 3 h. NaHS+RA group, RA was given i.p. daily at 10 mg/kg for 1 week before experiment and immediately after recovery. NaHS+DMSO group was given the same amount of solvent daily for 1 week before experiment and immediately after recovery. CPR group was given the same amount of normal saline at the start of CPR intravenously. After recovery, 7 days were observed continuously and the survival condition was recorded, and neurological function were evaluated at 1, 3 d, and 7 d after recovery, brain water content, BBB permeability and Nrf2, HO-1, BBB tight junction protein occludin expression was detected at 24 h after resuscitation, and the expression of matrix metalloproteinase-9(MMP-9) was detected by immunohistochemical staining. Results The survival rates, neurologic deficit scores(NDS), Nrf2 and HO-1 expression, and occludin expression in NaHS group were higher than CPR group(P 0.05). Conclusions Hydrogen sulfide could reduce the BBB damage in rats with cardiac arrest, which may be related to the activation of Nrf2/HO-1 pathway, inhibiting the expression of MMP-9 and decreasing the loss of occludin protein. Key words: Nuclear factor E2 related factor/heme oxygenase-1 pathway; Blood-brain barrier; Hydrogen sulfide; Cardiac arrest; Cardiopulmonary resuscitation

Effect of tight junction protein Occludin expression and permeability in blood-brain barrier of rats after heat stress

Effect of tight junction protein Occludin expression and permeability in blood-brain barrier of rats after heat stress

Pretreatment with Xuebijing injection alleviates systemic inflammatory response induced by severe heat-stroke via ameliorating intestinal injury in rats

To observe the effect of Xuebijing injection pretreatment on systemic inflammatory response induced by severe heat-stroke, and to investigate the mechanism of alleviation of intestinal injury in rats. Thirty-six healthy adult male Wistar rats with grade SPF were randomly assigned into three groups with randomized number method, namely sham group, severe heat-stroke model group, and Xuebijing pretreatment group ( XBJ group ), with 12 rats in each group. The animals were placed in a pre-warm chamber [ temperature ( 40±2 ) centigrade, humidity ( 65±5 )% ] in order to induce typical heat-stroke. The duration of heat-stress was 60 minutes, while the animals in sham group were exposed to ambient temperature of 25 centigrade. Arterial blood samples were collected at the beginning and the end of heat-stress, the concentrations of tumor necrosis factor-α( TNF-α), interleukins ( IL-1β, IL-6 ), and lipopolysaccharide ( LPS ) in peripheral blood were determined by enzyme linked immunosorbent assay ( ELISA ). The intestinal tissues were harvested after heat-stress, and the pathological changes in intestine tissues were observed after hematoxylin-eosin ( HE ) staining and under optical microscope. The pathological injury scores were calculated. Immunohistochemistry was performed to determine inducible nitric oxide synthase ( iNOS ) expression in intestinal tissue. Apoptosis was determined by terminal deoxynucleotidyl transferase-mediated dUTP nick end labeling ( TUNEL ) staining. Western Blot was used to measure the tight junction protein occludin expression. The concentrations of TNF-α, IL-1β, IL-6 and LPS in blood of the rats after heat-stress in model group were significantly higher than those of sham group [ TNF-α ( μg/L ): 443.00±110.10 vs. 98.36±44.61, IL-1β ( μg/L ): 436.37±163.64 vs.64.24±16.15, IL-6 ( μg/L ): 342.70±92.42 vs. 54.40±13.22, LPS ( μg/L ): 0.68±0.22 vs. 0.09±0.02, all P < 0.01 ], but the levels of these parameters in XBJ group were significantly lower than those of model group [ TNF-α ( μg/L ): 340.45±68.57 vs. 443.00±110.10, IL-1β ( μg/L ): 191.33±82.78 vs. 436.37±163.64, IL-6 ( μg/L ): 192.21±37.89 vs. 342.70±92.42, LPS ( μg/L ): 0.43±0.17 vs. 0.68±0.22, all P < 0.01 ]. Infiltration of inflammatory cells, necrosis and hemorrhage in intestinal mucosa were found in the intestine of heat-stroke animals in model group. The pathological lesions in XBJ group were milder than those of model group, with a decreased pathological injury score compared with model group ( 2.10±1.15 vs. 3.20±0.67, P < 0.01 ). The expression of iNOS and apoptosis of cells in intestinal tissue in model group were increased compared with that of sham group, but they were significantly less marked in XBJ group compared with model group [ iNOS ( adjusted A value ): 0.32±0.15 vs. 0.74±0.17, apoptotic index: 0.23±0.08 vs. 0.56±0.07, both P < 0.01 ]. The order of expression for occludin protein from high to low was sham group, XBJ group and model group ( A value was 0.96±0.25, 0.62±0.20, 0.33±0.11, respectively ). Furthermore, there was significant difference in the expression of occludin protein between model group and both XBJ group and sham group ( both P < 0.01 ). Xuebijing injection alleviates inflammation and endotoxemia produced by severe heat-stroke in rats. The mechanism may be related to amelioration of oxidative injury, apoptosis, and dysfunction of tight junction protein occludin expression.

Somatostatin ameliorates lipopolysaccharide-induced tight junction damage via the ERK–MAPK pathway in Caco2 cells

Dysfunction of the epithelial barrier is an important pathogenic factor of inflammatory bowel disease and other inflammatory conditions of the gut. Somatostatin (SST) has been demonstrated to reduce local and systemic inflammation reactions and maintain the integrity of the blood–brain barrier (BBB). To determine the beneficial effect of SST on lipopolysaccharide (LPS)-induced damage of the tight junction (TJ) and its mechanisms, Caco2 cells pretreated with SST (1nM) or MEK inhibitor U0126 (10μM) were exposed to LPS. LPS significantly reduced the expression of TJ proteins in a dose-dependent way. LPS (100μg/ml) greatly induced Caco2 monolayer barrier dysfunction by decreasing transepithelial resistance and increasing epithelial permeability. Pretreatment with SST effectively improved the barrier dysfunction of Caco2 cells. SST significantly increased the expression of TJ proteins occludin and ZO-1 and inhibited the redistribution of TJ proteins due to LPS stimulation. Furthermore, SST decreased the LPS-induced phosphorylation of ERK1/2, and a selective MEK inhibitor markedly protected the barrier function against LPS disturbance by blocking the activation of the ERK–MAPK pathway in Caco2 cells. Besides, LPS significantly increased the mRNA level of SSTR5, which was partly inhibited by pretreatment with SST. In conclusion, the present study indicates that SST protects the Caco2 monolayer barrier against LPS-induced tight junction breakdown by down-regulating the activation of the ERK–MAPK pathway and suppression the activation of SSTR5.

NADPH oxidase is involved in polychlorinated biphenyl‐mediated alterations of tight junction proteins in cells of the gastrointestinal tract

Exposure to polychlorinated biphenyls (PCBs) can contribute to numerous disease states. The main route of exposure to PCBs is through the gastrointestinal tract; however, little is known about the effects of PCBs on intestinal epithelial barrier functions. In the present study, we evaluated the effects of several highly‐chlorinated PCBs using human intestinal Caco‐2 cell line as an in vitro epithelial model system. Epithelial cells are comprised of tight junction (TJ) proteins that form an intricate assembly of membrane, cytoplasmic and accessory proteins linked to an actin cytoskeleton and which contribute to limited paracellular diffusion between adjacent epithelium. We demonstrated that exposure to PCBs increased permeability of FITC‐labeled dextran (4 kDa) across Caco‐2 monolayers. Consistent with permeability results, PCB disrupted expression of TJ proteins occludin and ZO‐1. These effects were associated with upregulation of the expressions of NADPH oxidase subunits as detected by immunoblotting. In addition, inhibition of NAPDH oxidase by apocynin significantly blocked PCB‐mediated increase in epithelial permeability and alterations of TJ protein expression. Similar effects were exerted by pretreatment with Rho kinase and Ras inhibitors suggesting that PCBs can disrupt epithelial barrier integrity through induction of redox‐regulated mechanisms. Supported by NIH/NIEHS (P42 ES 07380).

Effect of Oxidative Stress on the Junctional Proteins of Cultured Cerebral Endothelial Cells

(1) There is increasing evidence that the cerebral endothelium and the blood-brain barrier (BBB) plays an important role in the oxidative stress-induced brain damage. The aim of the present study was to investigate the role of interendothelial junctional proteins in the BBB permeability increase induced by oxidative stress. (2) For the experiments, we have used cultured cerebral endothelial cells exposed to hypoxia/reoxygenation or treated with the redox cycling quinone 2,3-Dimethoxy-1,4-naphthoquinone (DMNQ) in the presence or absence of glucose. The expression of junctional proteins and activation of mitogen activated protein kinases (MAPK) was followed by Western-blotting, the interaction of junctional proteins was investigated using coimmunoprecipitation. (3) Oxidative stress induces a downregulation of the tight junction protein occludin expression which is more pronounced in the absence of glucose. Furthermore, oxidative stress leads to disruption of the cadherin-beta-catenin complex and an activation of extracellular signal-regulated kinase (ERK1/2), which is more intense in the absence of glucose. (4) We have shown that one of the causes of the BBB breakdown is probably the structural alteration of the junctional complex caused by oxidative stress, a process in which ERK1/2 may play an important role.