Modulation of vascular integrity and neuroinflammation by peroxiredoxin 4 following cerebral ischemia-reperfusion injury.

Ischemic stroke is a leading cause of morbidity and mortality worldwide, with oxidative stress playing a key role in the injury mechanism of thrombolytic therapy. There is increasing evidence that oxidative stress damages endothelial cells (ECs), degrades tight junction proteins (TJs), and contributes to increased blood-brain barrier (BBB) permeability. It has been demonstrated that the breakdown of BBB could increase the risk of intracerebral hemorrhagic transformation in ischemic stroke. And an episode of cerebral ischemia/reperfusion (I/R) also initiates oxidative stress-mediated inflammatory processes in ECs, which further promotes BBB disruption and the progression of brain injury. Previous studies have revealed that antioxidants could inhibit ROS generation and attenuate BBB disruption after cerebral I/R. Peroxiredoxin 4 (Prx4) is a member of the antioxidant enzymes family (Prx1-6) and has been characterized to be an efficient H2O2 scavenger. It should be noted that Prx4 may be directly involved in the protection of ECs from the effects of ROS and function in ECs as a membrane-associated peroxidase. This paper reviewed the implication of Prx4 on vascular integrity and neuroinflammation following a cerebral I/R injury.

A prebiotic fructo-oligosaccharide promotes tight junction assembly in intestinal epithelial cells via an AMPK-dependent pathway.

Tight junctions play an important role in maintaining barrier integrity of intestinal epithelia. Activation of AMP-activated protein kinase (AMPK) promotes tight junction assembly in intestinal epithelial cells (IEC). Fructo-oligosaccharides (FOS), well-known prebiotics, have previously been shown to alleviate inflammation-associated intestinal epithelial disruption although the mechanisms were unclear. This study aimed to investigate any effect of FOS on AMPK activity and tight junction assembly under non-inflammatory and inflammatory conditions using T84 cells as an IEC model. As analyzed by western blot, FOS induced AMPK activation through a calcium sensing receptor (CaSR)-phospholipase C (PLC)- Ca2+/calmodulin-dependent protein kinase kinase-ß (CaMKKß) pathway. Calcium switch assays and immunofluorescence staining of zonula occludens-1 (ZO-1) revealed that FOS induced tight junction assembly via an CaMKKß-AMPK-dependent mechanism in IEC. Interestingly, FOS reversed the suppressive effect of lipopolysaccharide (LPS) on AMPK activity and tight junction assembly via a CaMKKß pathway. Taken together, these findings uncover a prebiotic-independent effect of FOS in promoting intestinal epithelial tight junction assembly through AMPK activation, which may have implications for the treatment of diseases whose pathogenesis involves impaired intestinal barrier function.

Mechanisms involved in AMPK-mediated deposition of tight junction components to the plasma membrane.

AMP-activated protein kinase (AMPK) activation promotes early stages of epithelial junction assembly. AMPK activation in MDCK renal epithelial cells facilitates localization of the junction-associated proteins aPKCζ and Par3 to the plasma membrane and promotes conversion of Cdc42, a key regulator of epithelial polarization and junction assembly, to its active GTP bound state. Furthermore, Par3 is an important regulator of AMPK-mediated aPKCζ localization. Both aPKCζ and Par3 serve as intermediates in AMPK-mediated junction assembly, with inhibition of aPKCζ activity or Par3 knockdown disrupting AMPK's ability to facilitate zonula occludens (ZO-1) localization. AMPK phosphorylates the adherens junction protein afadin and regulates its interaction with the tight-junction protein zonula occludens-1. Afadin is phosphorylated at two critical sites, S228 (residing within an aPKCζ consensus site) and S1102 (residing within an AMPK consensus site), that are differentially regulated during junction assembly and that exert different effects on the process. Expression of phospho-defective mutants (S228A and S1102A) perturbed ZO-1 localization to the plasma membrane during AMPK-induced junction assembly. Expression of S228A increased the ZO-1/afadin interaction, while S1102A reduced this interaction during extracellular calcium-induced junction assembly. Inhibition of aPKCζ activity also increased the ZO-1/afadin interaction. Taken together, these data suggest that aPKCζ phosphorylation of afadin terminates the ZO-1/afadin interaction and thus permits the later stages of junction assembly.

APOC3 promotes TNF-α-induced expression of JAM-1 in endothelial cell via PI3K-IKK2-p65 pathway.

Atherosclerosis is a chronic inflammatory disease with lipid accumulation. Apolipoprotein C3 (APOC3), which is an important regulator of human lipid metabolism, is associated with multiple vascular mechanisms in atherosclerosis and proinflammatory responses. We have previously reported that the expression of inflammatory cytokine TNF-α is elevated in human endothelial cells (HUVECs) after APOC3 treatment. This study investigates the APOC3 signaling pathway involved in TNF-α-mediated expression of JAM-1 in HUVECs. Cultured HUVECs were exposed to APOC3 (50 µg/ml) for 16 h. Mechanistic studies were carried out by silencing TNF-α gene with lentiviral TNF-α-shRNA. Our study was based on the eight signaling pathway inhibitors to block the effect of APOC3 in HUVECs. The expression of JAM-1 was determined by qRT-PCR, Western blotting, and flow cytometry. IKK2 degradation and NF-κB p65 phosphorylation were determined by Western blotting. Our results showed that APOC3 significantly promoted the TNF-α-induced expression of JAM-1 in HUVECs. Inhibiting APOC3 reversed the TNF-α-induced overexpression of JAM-1. Moreover, APOC3 induced the expression of NF-κB p65 and degraded IκB. In conclusion, APOC3 promoted the expression of JAM-1 via the NF-κB, IKK2, and PI3K signaling pathway.

Transient High Pressure in Pancreatic Ducts Promotes Inflammation and Alters Tight Junctions via Calcineurin Signaling in Mice.

BACKGROUND & AIMS: Pancreatitis after endoscopic retrograde cholangiopancreatography (PEP) is thought to be provoked by pancreatic ductal hypertension, via unknown mechanisms. We investigated the effects of hydrostatic pressures on the development of pancreatitis in mice. METHODS: We performed studies with Swiss Webster mice, B6129 mice (controls), and B6129 mice with disruption of the protein phosphatase 3, catalytic subunit, ßisoform gene (Cnab-/- mice). Acute pancreatitis was induced in mice by retrograde biliopancreatic ductal or intraductal infusion of saline with a constant hydrostatic pressure while the proximal common bile duct was clamped -these mice were used as a model of PEP. Some mice were given pancreatic infusions of adeno-associated virus 6-nuclear factor of activated T-cells-luciferase to monitor calcineurin activity or the calcineurin inhibitor FK506. Blood samples and pancreas were collected at 6 and 24 hours and analyzed by enzyme-linked immunosorbent assay, histology, immunohistochemistry, or fluorescence microscopy. Ca2+ signaling and mitochondrial permeability were measured in pancreatic acinar cells isolated 15 minutes after PEP induction. Ca2+-activated phosphatase calcineurin within the pancreas was tracked in vivo over 24 hours. RESULTS: Intraductal pressures of up to 130 mm Hg were observed in the previously reported model of PEP; we found that application of hydrostatic pressures of 100 and 150 mm Hg for 10 minutes consistently induced pancreatitis. Pancreatic tissues had markers of inflammation (increased levels of interleukin [IL] 6, IL1B, and tumor necrosis factor), activation of signal transducer and activator of transcription 3, increased serum amylase and IL6, and loss of tight junction integrity. Transiently high pressures dysregulated Ca2+ processing (reduced Ca2+ oscillations and an increased peak plateau Ca2+ signal) and reduced the mitochondrial membrane potential. We observed activation of pancreatic calcineurin in the pancreas in mice. Cnab-/- mice, which lack the catalytic subunit of calcineurin, and mice given FK506 did not develop pressure-induced pancreatic inflammation, edema, or loss of tight junction integrity. CONCLUSIONS: Transient high ductal pressure produces pancreatic inflammation and loss of tight junction integrity in a mouse model of PEP. These processes require calcineurin signaling. Calcineurin inhibitors might be used to prevent acute pancreatitis that results from obstruction.

Inhibition of mTOR protects the blood-brain barrier in models of Alzheimer's disease and vascular cognitive impairment.

An intact blood-brain barrier (BBB) limits entry of proinflammatory and neurotoxic blood-derived factors into the brain parenchyma. The BBB is damaged in Alzheimer's disease (AD), which contributes significantly to the progression of AD pathologies and cognitive decline. However, the mechanisms underlying BBB breakdown in AD remain elusive, and no interventions are available for treatment or prevention. We and others recently established that inhibition of the mammalian/mechanistic target of rapamycin (mTOR) pathway with rapamycin yields significant neuroprotective effects, improving cerebrovascular and cognitive function in mouse models of AD. To test whether mTOR inhibition protects the BBB in neurological diseases of aging, we treated hAPP(J20) mice modeling AD and low-density lipoprotein receptor-null (LDLR-/-) mice modeling vascular cognitive impairment with rapamycin. We found that inhibition of mTOR abrogates BBB breakdown in hAPP(J20) and LDLR-/- mice. Experiments using an in vitro BBB model indicated that mTOR attenuation preserves BBB integrity through upregulation of specific tight junction proteins and downregulation of matrix metalloproteinase-9 activity. Together, our data establish mTOR activity as a critical mediator of BBB breakdown in AD and, potentially, vascular cognitive impairment and suggest that rapamycin and/or rapalogs could be used for the restoration of BBB integrity. NEW & NOTEWORTHY This report establishes mammalian/mechanistic target of rapamycin as a critical mediator of blood-brain barrier breakdown in models of Alzheimer's disease and vascular cognitive impairment and suggests that drugs targeting the target of rapamycin pathway could be used for the restoration of blood-brain barrier integrity in disease states.

Matrix Metalloproteinase-8 Inhibition Prevents Disruption of Blood-Spinal Cord Barrier and Attenuates Inflammation in Rat Model of Spinal Cord Injury.

After spinal cord injury (SCI), tight junction (TJ) protein degradation increases permeability and disrupts the blood-spinal cord barrier (BSCB). The BSCB is primarily formed of endothelial cell, which forms a specialized tight seal due to the presence of TJs. BSCB disruption after SCI allows neutrophil infiltration. Matrix metalloproteinase (MMP)-8 is believed to be mainly expressed by neutrophils and is quickly released upon neutrophil activation. Here, we determined whether MMP-8 is involved in the TJ protein degradation in endothelial cells and also determined its role in the neuroinflammation after SCI. MMP-8 recombinant protein treatment increases the TNF-α expression and decreased the TJ (occludin and zonula occludens-1) protein expression in the endothelial cells. Likewise, specific MMP-8 inhibitor (MMP-8I) significantly prevented the TNF-α-induced decrease in the expression of TJ protein in endothelial cells. Furthermore, MMP-8 expression was significantly increased 1 and 3 days after moderate compression (35 g for 5 min at T10 level) SCI, whereas TJ protein levels decreased as determined qRT-PCR, western blotting, and immunohistochemistry. MMP-8 was inhibited directly using a MMP-8I (5 mg/kg) and indirectly by reducing neutrophil infiltration with sivelestat sodium (50 mg/kg) or using the antioxidant N-acetyl-L-cysteine (100 mg/kg). The MMP-8I significantly decreased TNF-α expression, IL-6, and iNOS expression and increased TJ protein expression after SCI. In addition, MMP-8I significantly lessens the amount of Evans blue dye extravasation observed after injury. Thus, our result suggests that MMP-8 plays an imperative role in inflammation and degradation of TJ proteins. Increased MMP-8 expression was associated with the early inflammatory phase of SCI. Inhibiting MMP-8 significantly attenuated SCI-induced inflammation, BSCB breakdown, and cell injury.

Statin regulated ERK5 stimulates tight junction formation and reduces permeability in human cardiac endothelial cells.

The MEKK3/MEK5/ERK5 signaling axis is required for cardiovascular development in vivo. We analyzed the physiological role of ERK5 in cardiac endothelial cells and the consequence of activation of this kinase by the statin class of HMG Co-A reductase inhibitor drugs. We utilized human cardiac microvascular endothelial cells (HCMECs) and altered ERK5 expression using siRNA mediated gene silencing or overexpression of constitutively active MEK5 and ERK5 to reveal a role for ERK5 in regulating endothelial tight junction formation and cell permeability. Statin treatment of HCMECs stimulated activation of ERK5 and translocation to the plasma membrane resulting in co-localization with the tight junction protein ZO-1 and a concomitant reduction in endothelial cell permeability. Statin mediated activation of ERK5 was a consequence of reduced isoprenoid synthesis following HMG Co-A reductase inhibition. Statin pretreatment could overcome the effect of doxorubicin in reducing endothelial tight junction formation and prevent increased permeability. Our data provide the first evidence for the role of ERK5 in regulating endothelial tight junction formation and endothelial cell permeability. Statin mediated ERK5 activation and the resulting decrease in cardiac endothelial cell permeability may contribute to the cardioprotective effects of statins in reducing doxorubicin-induced cardiotoxicity.

The RING finger- and PDZ domain-containing protein PDZRN3 controls localization of the Mg2+ regulator claudin-16 in renal tube epithelial cells.

Ion exchange in the renal tubules is fundamental to the maintenance of physiological ion levels. Claudin-16 (CLDN16) regulates the paracellular reabsorption of Mg2+ in the thick ascending limb of Henle's loop in the kidney, with dephosphorylation of CLDN16 increasing its intracellular distribution and decreasing paracellular Mg2+ permeability. CLDN16 is located in the tight junctions, but the mechanism regulating its localization is unclear. Using yeast two-hybrid systems, we found that CLDN16 binds to PDZRN3, a protein containing both RING-finger and PDZ domains. We also observed that the carboxyl terminus of the cytoplasmic CLDN16 region was required for PDZRN3 binding. PZDRN3 was mainly distributed in the cytosol of rat kidney cells and upon cell treatment with the protein kinase A inhibitor H-89, colocalized with CLDN16. H-89 also increased mono-ubiquitination and the association of CLDN16 with PDZRN3. Mono-ubiquitination levels of a K275A mutant were lower, and its association with PDZRN3 was reduced compared with wild-type (WT) CLDN16 and a K261A mutant, indicating that Lys-275 is the major ubiquitination site. An S217A mutant, a dephosphorylated form of CLDN16, localized to the cytosol along with PDZRN3 and the endosomal marker Rab7. PDZRN3 siRNA increased cell-surface localization of WT CLDN16 in H-89-treated cells or containing the S217A mutant and also suppressed CLDN16 endocytosis. Of note, H-89 decreased paracellular Mg2+ flux in WT CLDN16 cells, and PDZRN3 siRNA increased Mg2+ flux in the H-89-treated WT CLDN16 and S217A mutant cells. These results suggest that PDZRN3 mediates endocytosis of dephosphorylated CLDN16 and represents an important component of the CLDN16-trafficking machinery in the kidney.

Rebeccamycin Attenuates TNF-α-Induced Intestinal Epithelial Barrier Dysfunction by Inhibiting Myosin Light Chain Kinase Production.

BACKGROUND/AIMS: Although proinflammatory cytokine-induced disruption of intestinal epithelial barrier integrity is associated with intestinal inflammatory disease, effective treatment for barrier dysfunction is lacking. Previously, we demonstrated that rebeccamycin alleviates epithelial barrier dysfunction induced by inflammatory cytokines in Caco-2 cell monolayers; however, the underlying mechanism remained unclear. Here, we investigated the mechanism by which rebeccamycin protects the epithelial barrier function of Caco-2 cells exposed to TNF-α. METHODS: To confirm the epithelial barrier function of Caco-2 cell monolayers, transepithelial electrical resistance (TER) and paracellular permeability were measured. Production levels and localization of tight junction (TJ) proteins were analyzed by immunoblot and immunofluorescence, respectively. Phosphorylated myosin light chain (pMLC) and MLC kinase (MLCK) mRNA expression levels were determined by immunoblot and quantitative RT-PCR, respectively. RESULTS: Rebeccamycin attenuated the TNF-α-induced reduction in TER and increase in paracellular permeability. Rebeccamycin increased claudin-5 expression, but not claudin-1, -2, -4, occludin or ZO-1 expression, and prevented the TNF-α-induced changes in ZO-1 and occludin localization. Rebeccamycin suppressed the TNF-α-induced increase in MLCK mRNA expression, thus suppressing MLC phosphorylation. The rebeccamycin-mediated reduction in MLCK production and protection of epithelial barrier function were alleviated by Chk1 inhibition. CONCLUSION: Rebeccamycin attenuates TNF-α-induced disruption of intestinal epithelial barrier integrity by inducing claudin-5 expression and suppressing MLCK production via Chk1 activation.

Early Activation of MAPK p44/42 Is Partially Involved in DON-Induced Disruption of the Intestinal Barrier Function and Tight Junction Network.

Deoxynivalenol (DON), produced by the plant pathogens Fusarium graminearum and Fusarium culmorum, is one of the most common mycotoxins, contaminating cereal and cereal-derived products. Although worldwide contamination of food and feed poses health threats to humans and animals, pigs are particularly susceptible to this mycotoxin. DON derivatives, such as deepoxy-deoxynivalenol (DOM-1), are produced by bacterial transformation of certain intestinal bacteria, which are naturally occurring or applied as feed additives. Intestinal epithelial cells are the initial barrier against these food- and feed-borne toxins. The present study confirms DON-induced activation of MAPK p44/42 and inhibition of p44/42 by MAPK-inhibitor U0126 monoethanolate. Influence of DON and DOM-1 on transepithelial electrical resistance (TEER), viability and expression of seven tight junction proteins (TJ), as well as the potential of U0126 to counteract DON-induced effects, was assessed. While DOM-1 showed no effect, DON significantly reduced TEER of differentiated IPEC-J2 and decreased expression of claudin-1 and -3, while leaving claudin-4; ZO-1, -2, and -3 and occludin unaffected. Inhibition of p44/42 counteracted DON-induced TEER decrease and restored claudin-3, but not claudin-1 expression. Therefore, effects of DON on TEER and claudin-3 are at least partially p44/42 mediated, while effects on viability and claudin-1 are likely mediated via alternative pathways.

ß1-Na(+),K(+)-ATPase gene therapy upregulates tight junctions to rescue lipopolysaccharide-induced acute lung injury.

Acute lung injury (ALI) and acute respiratory distress syndrome (ARDS) are associated with diverse disorders and characterized by disruption of the alveolar-capillary barrier, leakage of edema fluid into the lung, and substantial inflammation leading to acute respiratory failure. Gene therapy is a potentially powerful approach to treat ALI/ARDS through repair of alveolar epithelial function. Herein, we show that delivery of a plasmid expressing ß1-subunit of the Na(+),K(+)-ATPase (ß1-Na(+),K(+)-ATPase) alone or in combination with epithelial sodium channel (ENaC) α1-subunit using electroporation not only protected from subsequent lipopolysaccharide (LPS)-mediated lung injury, but also treated injured lungs. However, transfer of α1-subunit of ENaC (α1-ENaC) alone only provided protection benefit rather than treatment benefit although alveolar fluid clearance had been remarkably enhanced. Gene transfer of ß1-Na(+),K(+)-ATPase, but not α1-ENaC, not only enhanced expression of tight junction protein zona occludins-1 (ZO-1) and occludin both in cultured cells and in mouse lungs, but also reduced pre-existing increase of lung permeability in vivo. These results demonstrate that gene transfer of ß1-Na(+),K(+)-ATPase upregulates tight junction formation and therefore treats lungs with existing injury, whereas delivery of α1-ENaC only maintains pre-existing tight junction but not for generation. This indicates that the restoration of epithelial/endothelial barrier function may provide better treatment of ALI/ARDS.

Matrix metalloproteinase 9-induced increase in intestinal epithelial tight junction permeability contributes to the severity of experimental DSS colitis.

Recent studies have implicated a pathogenic role for matrix metalloproteinases 9 (MMP-9) in inflammatory bowel disease. Although loss of epithelial barrier function has been shown to be a key pathogenic factor for the development of intestinal inflammation, the role of MMP-9 in intestinal barrier function remains unclear. The aim of this study was to investigate the role of MMP-9 in intestinal barrier function and intestinal inflammation. Wild-type (WT) and MMP-9(-/-) mice were subjected to experimental dextran sodium sulfate (DSS) colitis by administration of 3% DSS in drinking water for 7 days. The mouse colonic permeability was measured in vivo by recycling perfusion of the entire colon using fluorescently labeled dextran. The DSS-induced increase in the colonic permeability was accompanied by an increase in intestinal epithelial cell MMP-9 expression in WT mice. The DSS-induced increase in intestinal permeability and the severity of DSS colitis was found to be attenuated in MMP-9(-/-) mice. The colonic protein expression of myosin light chain kinase (MLCK) and phospho-MLC was found to be significantly increased after DSS administration in WT mice but not in MMP-9(-/-) mice. The DSS-induced increase in colonic permeability and colonic inflammation was attenuated in MLCK(-/-) mice and MLCK inhibitor ML-7-treated WT mice. The DSS-induced increase in colonic surface epithelial cell MLCK mRNA was abolished in MMP-9(-/-) mice. Lastly, increased MMP-9 protein expression was detected within the colonic surface epithelial cells in ulcerative colitis cases. These data suggest a role of MMP-9 in modulation of colonic epithelial permeability and inflammation via MLCK.

RhoGTPase signalling at epithelial tight junctions: Bridging the GAP between polarity and cancer.

The establishment and maintenance of epithelial polarity must be correctly controlled for normal development and homeostasis. Tight junctions (TJ) in vertebrates define apical and basolateral membrane domains in polarized epithelia via bi-directional, complex signalling pathways between TJ themselves and the cytoskeleton they are associated with. RhoGTPases are central to these processes and evidence suggests that their regulation is coordinated by interactions between GEFs and GAPs with junctional, cytoplasmic adapter proteins. In this InFocus review we determine that the expression, localization or stability of a variety of these adaptor proteins is altered in various cancers, potentially representing an important mechanistic link between loss of polarity and cancer. We focus here, on two well characterized RhoGTPases Cdc42 and RhoA who's GEFs and GAPs are predominantly localized to TJ via cytoplasmic adaptor proteins.

12/15-Lipoxygenase-dependent ROS production is required for diet-induced endothelial barrier dysfunction.

To understand the mechanisms of 15(S)-HETE-induced endothelial cell (EC) barrier dysfunction, we examined the role of xanthine oxidase (XO). 15(S)-HETE induced junction adhesion molecule A (JamA) phosphorylation on Y164, Y218, and Y280 involving XO-mediated reactive oxygen species production and Src and Pyk2 activation, resulting in its dissociation from occludin, thereby causing tight junction (TJ) disruption, increased vascular permeability, and enhanced leukocyte and monocyte transmigration in vitro using EC monolayer and ex vivo using arteries as models. The phosphorylation of JamA on Y164, Y218, and Y280 appears to be critical for its role in 15(S)-HETE-induced EC barrier dysfunction, as mutation of any one of these amino acid residues prevented its dissociation from occludin and restored TJ integrity and barrier function. In response to high-fat diet (HFD) feeding, WT, but not 12/15-lipoxygenase (LO)(-/-), mice showed enhanced XO expression and its activity in the artery, which was correlated with increased aortic TJ disruption and barrier permeability with enhanced leukocyte adhesion and these responses were inhibited by allopurinol. These observations provide novel insights on the role of XO in 12/15-LO-induced JamA tyrosine phosphorylation and TJ disruption leading to increased vascular permeability in response to HFD.

c-Jun N-terminal kinase inhibitor SP600125 enhances barrier function and elongation of human pancreatic cancer cell line HPAC in a Ca-switch model.

c-Jun N-terminal kinase (JNK), known as a stress-activated protein kinase, regulates normal epithelial biological processes, including assembly of adherens and tight junctions, and it is involved in the development of several cancers. The JNK inhibitor SP600125 enhances epithelial barrier function through modulation of tight junction molecules in normal human pancreatic epithelial cells. Furthermore, this JNK inhibitor suppresses the growth of human pancreatic cancer cells. However, the effects of SP600125 on the epithelial barrier in human pancreatic cancer cells remain unknown. In the present study, the JNK inhibitor SP600125 markedly enhanced the barrier function and cell elongation of well-differentiated human pancreatic cancer cell line HPAC in a Ca-switch model. The epithelial barrier function induced by SP600125 was regulated by phosphorylated ß-catenin without changes in the tight junction molecules. The cell elongation induced by SP600125 was closely related to the expression of the F-actin-binding protein DrebrinE. These findings suggest that JNK is involved in the regulation of the epithelial barrier function and cell shape during remodeling of pancreatic cancer cells. The JNK inhibitor SP600125 may have potential as a therapeutic drug for pancreatic cancer via induction of differentiation.

Extracellular signal-regulated kinase1/2-dependent changes in tight junctions after ischemic preconditioning contributes to tolerance induction after ischemic stroke.

Less disruption of the blood-brain barrier (BBB) after severe ischemic stroke is one of the beneficial outcomes of ischemic preconditioning (IP). However, the effect of IP on tight junctions (TJs), which regulate paracellular permeability of the BBB, is not well understood. In the present study, we examined IP-induced changes in TJs before and after middle cerebral artery occlusion (MCAO) in mice, and the association between changes in TJs and tolerance to a subsequent insult. After IP, we found decreased levels of transmembrane TJ proteins occludin and claudin-5, and widened gaps of TJs with perivascular swelling at the ultrastructural level in the brain. An inflammatory response was also observed. These changes were reversed by inhibition of extracellular signal-regulated kinase1/2 (ERK1/2) via the specific ERK1/2 inhibitor U0126. After MCAO, reduced brain edema and inflammatory responses were associated with altered levels of angiogenic factors and cytokines in preconditioned brains. Pretreatment with U0126 reversed the neuroprotective effects of IP against MCAO. These findings suggest that ERK1/2 activation has a pivotal role in IP-induced changes in TJs and inflammatory response, which serve to protect against BBB breakdown and inflammation after ischemic stroke.

Involvement of RhoA/ROCK1 signaling pathway in hyperglycemia-induced microvascular endothelial dysfunction in diabetic retinopathy.

Diabetic retinopathy (DR) is a well-known serious complication of diabetes mellitus (DM), and can eventually advance to end-stage blindness. In the early stage of DR, endothelial cell barrier disorganized primarily and tight junction (TJ) protein composition transformed subsequently. The small GTPase RhoA and its downstream effector Rho-associated coiled-coil containing protein kinase 1 (ROCK1) regulate a mass of cellular processes, including cell adherence, proliferation, permeability and apoptosis. Although RhoA inhibitors have provided substantial clinical benefit as hypertonicity therapeutics, their use is limited by complex microenvironment as DR. While ample evidence indicates that TJ can be influenced by the RhoA/ROCK1 signaling, the underlying mechanisms remain incompletely understood. Here, we have uncovered a significant signaling network involved in diabetic retinal microvascular endothelial dysfunction (RMVED). Our results indicated that the activation of RhoA/ROCK1 pathway due to high glucose played a key role in microvascular endothelial cell dysfunction (MVED) by way of directly inducing TJ proteins over-expression during DR. We demonstrated that inhibition of RhoA/ROCK1 may attenuate the hypertonicity of endothelial cell caused by high glucose microenvironment meanwhile. Besides, chemical and pharmacological inhibitors of RhoA/ROCK1 pathway may partly block inflammation due to DR. Simultaneously, the apoptosis aroused by high glucose was also prevented considerably by fasudil, a kind of pharmacological inhibitor of RhoA/ROCK1 pathway. These findings indicate that RhoA/ROCK1 signaling directly modulates MVED, suggesting a novel therapeutic target for DR.

Potent and specific inhibition of the biological activity of the type-II transmembrane serine protease matriptase by the cyclic microprotein MCoTI-II.

Matriptase is a type-II transmembrane serine protease involved in epithelial homeostasis in both health and disease, and is implicated in the development and progression of a variety of cancers. Matriptase mediates its biological effects both via as yet undefined substrates and pathways, and also by proteolytic cleavage of a variety of well-defined protein substrates, several of which it shares with the closely-related protease hepsin. Development of targeted therapeutic strategies will require discrimination between these proteases. Here we have investigated cyclic microproteins of the squash Momordica cochinchinensis trypsin-inhibitor family (generated by total chemical synthesis) and found MCoTI-II to be a high-affinity (Ki 9 nM) and highly selective (> 1,000-fold) inhibitor of matriptase. MCoTI-II efficiently inhibited the proteolytic activation of pro-hepatocyte growth factor (HGF) by matriptase but not by hepsin, in both purified and cell-based systems, and inhibited HGF-dependent cell scattering. MCoTI-II also selectively inhibited the invasion of matriptase-expressing prostate cancer cells. Using a model of epithelial cell tight junction assembly, we also found that MCoTI-II could effectively inhibit the re-establishment of tight junctions and epithelial barrier function in MDCK-I cells after disruption, consistent with the role of matriptase in regulating epithelial integrity. Surprisingly, MCoTI-II was unable to inhibit matriptase-dependent proteolytic activation of prostasin, a GPI-anchored serine protease also implicated in epithelial homeostasis. These observations suggest that the unusually high selectivity afforded by MCoTI-II and its biological effectiveness might represent a useful starting point for the development of therapeutic inhibitors, and further highlight the role of matriptase in epithelial maintenance.

Role of MMP-9 in the breakdown of barrier integrity of the corneal endothelium in response to TNF-α.

TNF-α induces loss of barrier integrity of the corneal endothelium through mechanisms involving the activation of p38 MAP kinase. This study has investigated the role of matrix metalloproteinase-9 (MMP-9), known to be activated by mechanisms downstream of p38 MAP kinase, on the breakdown of the barrier integrity. Experiments were performed with primary cultures of bovine corneal endothelium. Changes in the trans-endothelial electrical resistance (TER), a measure of barrier integrity, were measured by electric cell-substrate impedance sensing. The integrity of the apical junctional assembly was imaged by immunolocalization of ZO-1. MMP-9 activity in the conditioned medium of cells treated with TNF-α was visualized by gelatin zymography. Transcriptional activation of MMP-9 was assessed by real-time RT-PCR. Exposure to TNF-α led to significant disruption of ZO-1 and also caused a continuous decline in TER for more than 20 h. These effects were opposed by cycloheximide (protein synthesis inhibitor), GM-6001 (broad spectrum inhibitor of MMPs), minocycline (MMP-2 and MMP-9 inhibitor), and MMP-9 inhibitor I (selective MMP-9 inhibitor). Cycloheximide, GM-6001, and MMP-9 inhibitor I also attenuated the increase in permeability to FITC-dextran (10 kDa). In addition, TNF-α led to an increased MMP-9 activity in the conditioned medium as well as a nearly 20-fold increase in mRNA for MMP-9 but not for MMP-2. The functional activity and increase in mRNA levels of MMP-9 were blocked by SB-203580 (selective p38 MAP kinase inhibitor) and cycloheximide. In conclusion, transcriptional and translational activation of MMP-9, downstream of p38 MAP kinase signaling, is involved in the (TNF-α)-induced loss of corneal endothelial barrier integrity.