Hypoxia/aglycemia increases endothelial permeability: role of second messengers and cytoskeleton

Pathological changes within the cerebral vasculature in Alzheimer's disease: New perspectives

Cerebrovascular disease underpins vascular dementia (VaD), but structural and functional changes to the cerebral vasculature contribute to disease pathology and cognitive decline in Alzheimer's disease (AD). In this review, we discuss the contribution of cerebral amyloid angiopathy and non‐amyloid small vessel disease in AD, and the accompanying changes to the density, maintenance and remodelling of vessels (including alterations to the composition and function of the cerebrovascular basement membrane). We consider how abnormalities of the constituent cells of the neurovascular unit – particularly of endothelial cells and pericytes – and impairment of the blood‐brain barrier (BBB) impact on the pathogenesis of AD. We also discuss how changes to the cerebral vasculature are likely to impair Aβ clearance – both intra‐periarteriolar drainage (IPAD) and transport of Aβ peptides across the BBB, and how impaired neurovascular coupling and reduced blood flow in relation to metabolic demand increase amyloidogenic processing of APP and the production of Aβ. We review the vasoactive properties of Aβ peptides themselves, and the probable bi‐directional relationship between vascular dysfunction and Aβ accumulation in AD. Lastly, we discuss recent methodological advances in transcriptomics and imaging that have provided novel insights into vascular changes in AD, and recent advances in assessment of the retina that allow in vivo detection of vascular changes in the early stages of AD.

A reciprocal feedback of miR-548ac/YB-1/Snail induces EndMT of HUVECs during acidity microenvironment

Background

Researches indicated the process of Endothelial-Mesenchymal-Transition (EndMT) of vascular endothelial cells (ECs) was critically involved in the progression of tumor. ECs demonstrated functional and phenotypic heterogeneity when located under different microenvironments. The extracellular pH of tumor tissues was acidic compared to that of normal tissues. However, there was still unclear whether the acidic microenvironment affected the EndMT of vascular ECs.

Methods

Human Umbilical Vein Endothelial Cell (HUVECs) was cultured under the normal or acidic medium to evaluate the alteration of morphology, migration, permeability, and EndMT markers. Microarray assay was adopted to analyze the differential expression of miRNAs in the acidity-treated HUVECs. Gain- and loss- of function experiments were performed to evaluate the functional role of miRNA-548ac on acidity-induced EndMT of HUVECs. Luciferase reporter and Chromatin-immunoprecipitation assays were conducted to assess the downstream pathway of miRNA-548ac in acidity-induced EndMT of HUVECs.

Results

Our results showed that HUVECs demonstrated mesenchymal transition under acidic conditions with the increase of migration, permeability, and expression of α-SMA and Vimentin, but the expression of vascular endothelial cadherin (VE-cadherin) and CD31 were reduced. In addition, the acidity-treated HUVECs remarkably facilitated the transmigration of pancreatic cancer cells. The expression of miRNA-548ac was significantly decreased in the acidity-treated HUVECs. Moreover, overexpression of miR-548ac inhibited the EndMT of HUVECs and consequently impeded the transmigration of pancreatic cancer cells. The miR-548ac inhibited the expression of YB-1 by binding to the 3’UTR of its mRNA, and YB-1 promoted the translation of Snail which was a critical regulator of EndMT. What’s more, Snail transcriptionally inhibited the expression of miR-548ac through binding to the promoter of its host gene.

Conclusions

Our data implicated that the acidic microenvironment promoted the EndMT of HUVECs by the miR-548ac/YB-1/Snail axis, which could contribute to the metastasis of pancreatic cancer.

Supplementary Information

The online version contains supplementary material available at 10.1186/s12935-021-02388-8.

Mechanisms of cardiovascular toxicity induced by PM2.5: a review

An increasing number of studies have shown that exposure to particulate matter with a diameter ≤ 2.5 μm (PM_2.5) could affect the onset and development of cardiovascular diseases. To explore the underlying mechanisms, the studies conducted in vitro investigations using different cell lines. In this review, we examined recently published reports cited by PubMed or Web of Science on the topic of cardiovascular toxicity induced by PM_2.5 that carried the term in vitro. Here, we summarized the suggested mechanisms of PM_2.5 leading to adverse effects and cardiovascular toxicity including oxidative stress; the increase of vascular endothelial permeability; the injury of vasomotor function and vascular reparative capacity in vascular endothelial cell lines; macrophage polarization and apoptosis in macrophage cell lines; and hypermethylation and apoptosis in the AC16 cell line and the related signaling pathways, which provided a new research direction of cardiovascular toxicity of PM_2.5.

Novel HIF-1-target gene isthmin1 contributes to hypoxia-induced hyperpermeability of pulmonary microvascular endothelial cells monolayers

Hypoxia-induced pulmonary microvascular endothelial cell (PMVEC) monolayers hyperpermeability is vital for vascular leakage, which participates in vascular diseases, such as acute lung injury (ALI) and high-altitude pulmonary edema (HAPE). We previously observed that PMVEC permeability was markedly elevated in hypoxia when cocultured with primary type II alveolar epithelial cells (AECII) in which isthmin1 (ISM1) was highly upregulated. However, whether the upregulation of ISM1 plays a role in hypoxia-induced PMVEC hyperpermeability is unclear. In this study, we assessed the role of AECII-derived ISM1 in hypoxia-induced PMVEC hyperpermeability with an AECII/PMVEC coculture system and uncovered the underlying mechanism whereby hypoxia stimulates ISM1 gene expression. We found that ISM1 gene expression was upregulated in cultured AECII cells exposed to hypoxia (3% O2) and that AECII-derived ISM1 participated in hypoxia-induced hyperpermeability of PMVEC monolayers, as small interference RNA (siRNA)-mediated knockdown of ISM1 in AECII markedly attenuated the increase in PMVEC permeability in coculture system under hypoxia. In addition, we confirmed that ISM1 was regulated by hypoxia-inducible factor-1α (HIF1α) according to the evidence that silencing of HIF1α inhibited the hypoxia-mediated upregulation of ISM1. Mechanismly, overexpression of HIF1α transcriptionally activated ISM1 gene expression by directly binding to the conserved regulatory elements upstream of the ism1 locus. We identified a novel HIF-1-target gene ISM1, which involves in hyperpermeability of pulmonary microvascular endothelial cell monolayers under hypoxia. Our in vitro cell experiments implied that the upregulated ISM1 derived from alveolar epithelium might be a vital modulator in hypoxia-induced endothelial hyperpermeability and thereby implicates with hypoxic pulmonary-related diseases.

Blast-induced temporal alterations in blood-brain barrier properties in a rodent model

The consequences of blast-induced traumatic brain injury (bTBI) on the blood–brain barrier (BBB) and components of the neurovascular unit are an area of active research. In this study we assessed the time course of BBB integrity in anesthetized rats exposed to a single blast overpressure of 130 kPa (18.9 PSI). BBB permeability was measured in vivo via intravital microscopy by imaging extravasation of fluorescently labeled tracers (40 kDa and 70 kDa molecular weight) through the pial microvasculature into brain parenchyma at 2–3 h, 1, 3, 14, or 28 days after the blast exposure. BBB structural changes were assessed by immunostaining and molecular assays. At 2–3 h and 1 day after blast exposure, significant increases in the extravasation of the 40 kDa but not the 70 kDa tracers were observed, along with differential reductions in the expression of tight junction proteins (occludin, claudin-5, zona occluden-1) and increase in the levels of the astrocytic water channel protein, AQP-4, and matrix metalloprotease, MMP-9. Nearly all of these measures were normalized by day 3 and maintained up to 28 days post exposure. These data demonstrate that blast-induced changes in BBB permeability are closely coupled to structural and functional components of the BBB.

Human placental mesenchymal stem cells improve stroke outcomes via extracellular vesicles-mediated preservation of cerebral blood flow

Background

Besides long-term trans-differentiation into neural cells, benefits of stem cell therapy (SCT) in ischemic stroke may include secretion of protective factors, which partly reflects extracellular vesicle (EVs) released by stem cell. However, the mechanism(s) by which stem cells/EVs limit stroke injury have yet to be fully defined.

Methods

We evaluated the protection effect of human placenta mesenchymal stem cells (hPMSC) as a potential form of SCT in experimental ischemic stroke ‘transient middle cerebral artery occusion (MCAO)/reperfusion’ mice model.

Findings

We found for the first time that intraperitoneal administration of hPMSCs or intravenous hPMSC-derived EVs, given at the time of reperfusion, significantly protected the ipsilateral hemisphere from ischemic injury. This protection was associated with significant restoration of normal blood flow to the post-MCAO brain. More importantly, EVs derived from hPMSC promote paracrine-based protection of SCT in the MCAO model in a cholesterol/lipid-dependent manner.

Interpretation

Together, our results demonstrated beneficial effects of hPMSC/EVs in experimental stroke models which could permit the rapid “translation” of these cells into clinical trials in the near-term.

Validation of a Miniaturized Permeability Assay Compatible with CRISPR-Mediated Genome-Wide Screen

The impermeability of the luminal endothelial cell monolayer is crucial for the normal performance of the vascular and lymphatic systems. A key to this function is the integrity of the monolayer's intercellular junctions. The known repertoire of junction-regulating genes is incomplete. Current permeability assays are incompatible with high-throughput genome-wide screens that could identify these genes. To overcome these limitations, we designed a new permeability assay that consists of cell monolayers grown on ~150 μm microcarriers (MCs). Each MC functions as a miniature individual assay of permeability (MAP). We demonstrate that false-positive results can be minimized, and that MAP sensitivity to thrombin-induced increase in monolayer permeability is similar to the sensitivity of impedance measurement. We validated the assay by showing that the expression of single guide RNAs (sgRNAs) that target genes encoding known thrombin signaling proteins blocks effectively thrombin-induced junction disassembly, and that MAPs carrying such cells can be separated effectively by fluorescence-assisted sorting from those that carry cells expressing non-targeting sgRNAs. These results indicate that MAPs are suitable for high-throughput experimentation and for genome-wide screens for genes that mediate the disruptive effect of thrombin on endothelial cell junctions.

Vascular Dysfunction in Alzheimer's Disease: A Prelude to the Pathological Process or a Consequence of It?

Alzheimer's disease (AD) is the most prevalent form of dementia. Despite decades of research following several theoretical and clinical lines, all existing treatments for the disorder are purely symptomatic. AD research has traditionally been focused on neuronal and glial dysfunction. Although there is a wealth of evidence pointing to a significant vascular component in the disease, this angle has been relatively poorly explored. In this review, we consider the various aspects of vascular dysfunction in AD, which has a significant impact on brain metabolism and homeostasis and the clearance of β-amyloid and other toxic metabolites. This may potentially precede the onset of the hallmark pathophysiological and cognitive symptoms of the disease. Pathological changes in vessel haemodynamics, angiogenesis, vascular cell function, vascular coverage, blood-brain barrier permeability and immune cell migration may be related to amyloid toxicity, oxidative stress and apolipoprotein E (APOE) genotype. These vascular deficits may in turn contribute to parenchymal amyloid deposition, neurotoxicity, glial activation and metabolic dysfunction in multiple cell types. A vicious feedback cycle ensues, with progressively worsening neuronal and vascular pathology through the course of the disease. Thus, a better appreciation for the importance of vascular dysfunction in AD may open new avenues for research and therapy.

Exposure to concentrated ambient fine particulate matter disrupts vascular endothelial cell barrier function via the IL-6/HIF-1α signaling pathway

Exposure to concentrated ambient fine particulate matter (PM2.5) has been associated with cardiovascular diseases (CVDs). The barrier function of vascular endothelial cells is critical for the development of CVDs. Here, we employed human umbilical vein endothelial cells to clarify the function of ambient PM2.5 pollution in the regulation of membrane permeability of vascular endothelial cells. The results show that a high concentration of PM2.5, which mainly includes heavy metals and polycyclic aromatic hydrocarbons, induces barrier dysfunction of vascular endothelial cells. This was mediated in part by promoting IL‐6 expression, which then increases the transcriptional activity of HIF‐1α by promoting its translocation to the nucleus. Our findings indicate that concentrated PM2.5 can destroy membrane integrity and promote permeability in vascular endothelial cells, thereby contributing to the development of CVDs.

Human Sulfatase-1 Improves the Effectiveness of Cytosine Deaminase Suicide Gene Therapy with 5-Fluorocytosine Treatment on Hepatocellular Carcinoma Cell Line HepG2 In Vitro and In Vivo

BACKGROUND

Human sulfatase-1 (Hsulf-1) is an endosulfatase that selectively removes sulfate groups from heparan sulfate proteoglycans (HSPGs), altering the binding of several growth factors and cytokines to HSPG to regulate cell proliferation, cell motility, and apoptosis. We investigated the role of combined cancer gene therapy with Hsulf-1 and cytosine deaminase/5-fluorocytosine (CD/5-FC) suicide gene on a hepatocellular carcinoma (HCC) cell line, HepG2, in vitro and in vivo.

METHODS

Reverse transcription polymerase chain reaction and immunohistochemistry were used to determine the expression of Hsulf-1 in HCC. Cell apoptosis was observed through flow cytometry instrument and mechanism of Hsulf-1 to enhance the cytotoxicity of 5-FC against HCC was analyzed in HCC by confocal microscopy. We also establish a nude mice model of HCC to address the effect of Hsulf-1 expression on the CD/5-FC suicide gene therapy in vivo.

RESULTS

A significant decrease in HepG2 cell proliferation and an increase in HepG2 cell apoptosis were observed when Hsulf-1 expression was combined with the CD/5-FC gene suicide system. A noticeable bystander effect was observed when the Hsulf-1 and CD genes were co-expressed. Intracellular calcium was also increased after HepG2 cells were infected with the Hsulf-1 gene. In vivo studies showed that the suppression of tumor growth was more pronounced in animals treated with the Hsulf-1 plus CD than those treated with either gene therapy alone, and the combined treatment resulted in a significant increase in survival.

CONCLUSIONS

Hsulf-1 expression combined with the CD/5-FC gene suicide system could be an effective treatment approach for HCC.

G protein-coupled estrogen receptor-mediated effects on cytosolic calcium and nanomechanics in brain microvascular endothelial cells

G protein-coupled estrogen receptor (GPER) is a relatively recently identified non-nuclear estrogen receptor, expressed in several tissues, including brain and blood vessels. The mechanisms elicited by GPER activation in brain microvascular endothelial cells are incompletely understood. The purpose of this work was to assess the effects of GPER activation on cytosolic Ca(2+) concentration, [Ca(2+)](i), nitric oxide production, membrane potential and cell nanomechanics in rat brain microvascular endothelial cells (RBMVEC). Extracellular but not intracellular administration of G-1, a selective GPER agonist, or extracellular administration of 17-β-estradiol and tamoxifen, increased [Ca(2+)](i) in RBMVEC. The effect of G-1 on [Ca(2+)](i) was abolished in Ca(2+) -free saline or in the presence of a L-type Ca(2+) channel blocker. G-1 increased nitric oxide production in RBMVEC; the effect was prevented by NG-nitro-l-arginine methyl ester. G-1 elicited membrane hyperpolarization that was abolished by the antagonists of small and intermediate-conductance Ca(2+) -activated K(+) channels, apamin, and charibdotoxin. GPER-mediated responses were sensitive to G-36, a GPER antagonist. In addition, atomic force microscopy studies revealed that G-1 increased the modulus of elasticity, indicative of cytoskeletal changes and increase in RBMVEC stiffness. Our results unravel the mechanisms underlying GPER-mediated effects in RBMVEC with implications for the effect of estrogen on cerebral microvasculature. Activation of the G protein-coupled estrogen receptor (GPER) in rat brain microvascular endothelial cells (RBMVEC) increases [Ca(2+)](i) by promoting Ca(2+) influx. The increase in [Ca(2+)](i) leads to membrane hyperpolarization, nitric oxide (NO) production, and to cytoskeletal changes and increased cell stiffness. Our results unravel the mechanisms underlying GPER-mediated effects in RBMVEC with implications for the effect of estrogen on cerebral microvasculature.

Blood-letting punctures at twelve Jing-Well points of the hand can treat cerebral ischemia in a similar manner to mannitol

A rat model of middle cerebral artery permanent occlusion was established using the modified Longa method. Successfully established model animals were treated by blood-letting puncture at twelve Jing-Well points of the hand, and/or by injecting mannitol into the caudal vein twice daily. Brain tissue was collected at 24, 48 and 72 hours after modeling, and blood was collected through the retinal vein before Evans blue was injected, approximately 1 hour prior to harvesting of brain tissue. Results showed that Evans blue leakage into brain tissue and serum nitric oxide synthase activity were significantly increased in model rats. Treatment with blood-letting punctures at twelve Jing-Well points of the hand and/or injection of mannitol into the caudal vein reduced the amount of Evans blue leakage into the brain tissue and serum nitric oxide synthase activity to varying degrees. There was no significant difference between single treatment and combined treatment. Experimental findings indicate that blood-letting punctures at twelve Jing-Well points of the hand can decrease blood-brain barrier permeability and serum nitric oxide synthase activity in rats following middle cerebral artery occlusion, and its effect is similar to that of mannitol injection alone and Jing-Well points plus mannitol injection.

Disruption of kv1.3 channel forward vesicular trafficking by hypoxia in human T lymphocytes

Hypoxia in solid tumors contributes to decreased immunosurveillance via down-regulation of Kv1.3 channels in T lymphocytes and associated T cell function inhibition. However, the mechanisms responsible for Kv1.3 down-regulation are not understood. We hypothesized that chronic hypoxia reduces Kv1.3 surface expression via alterations in membrane trafficking. Chronic hypoxia decreased Kv1.3 surface expression and current density in Jurkat T cells. Inhibition of either protein synthesis or degradation and endocytosis did not prevent this effect. Instead, blockade of clathrin-coated vesicle formation and forward trafficking prevented the Kv1.3 surface expression decrease in hypoxia. Confocal microscopy revealed an increased retention of Kv1.3 in the trans-Golgi during hypoxia. Expression of adaptor protein-1 (AP1), responsible for clathrin-coated vesicle formation at the trans-Golgi, was selectively down-regulated by hypoxia. Furthermore, AP1 down-regulation increased Kv1.3 retention in the trans-Golgi and reduced Kv1.3 currents. Our results indicate that hypoxia disrupts AP1/clathrin-mediated forward trafficking of Kv1.3 from the trans-Golgi to the plasma membrane thus contributing to decreased Kv1.3 surface expression in T lymphocytes.

Occludin protein family: oxidative stress and reducing conditions

The occludin-like proteins belong to a family of tetraspan transmembrane proteins carrying a marvel domain. The intrinsic function of the occludin family is not yet clear. Occludin is a unique marker of any tight junction and is found in polarized endothelial and epithelial tissue barriers, at least in the adult vertebrate organism. Occludin is able to oligomerize and to form tight junction strands by homologous and heterologous interactions, but has no direct tightening function. Its oligomerization is affected by pro- and antioxidative agents or processes. Phosphorylation of occludin has been described at multiple sites and is proposed to play a regulatory role in tight junction assembly and maintenance and, hence, to influence tissue barrier characteristics. Redox-dependent signal transduction mechanisms are among the pathways modulating occludin phosphorylation and function. This review discusses the novel concept that occludin plays a key role in the redox regulation of tight junctions, which has a major impact in pathologies related to oxidative stress and corresponding pharmacologic interventions.

Mitogen-activated protein kinase signalling and ERK1/2 bistability in asthma

Mitogen-activated protein kinases (MAPKs) integrate signals from numerous receptors and translate these signals into cell functions. MAPKs are critical for immune cell metabolism, migration, production of pro-inflammatory mediators, survival and differentiation. We provide a concise review of the involvement of MAPK in important cells of the immune system. Certain cell functions, e.g. production of pro-inflammatory mediators resolve quickly and may require a transient MAPK activation, other processes such as cell differentiation and long-term survival may require persistent MAPK signal. The persistent MAPK signal is frequently a consequence of positive feedback loops or double negative feedback loops which perpetuate the signal after removal of an external cell stimulus. This self-perpetuated activation of a signalling circuit is a manifestation of its bistability. Bistable systems can exist in 'on' and 'off' states and both states are stable. We have demonstrated the existence of self-perpetuated activation mechanism for ERK1/2 in bronchial epithelial cells. This sustained activation of ERK1/2 supports long-term survival of these cells and primes them for cytokine transcription. ERK1/2 bistability arises from repetitive stimulation of the cell. The repeated stimulation (e.g. repeated viral infection or repeated allergen exposure) seems to be a common theme in asthma and other chronic illnesses. We thus hypothesize that the self-perpetuated ERK1/2 signal plays an important role in the pathogenesis of asthma.

Up-regulation of caveolin-1 and blood-brain barrier breakdown are attenuated by N-acetylcysteine in thiamine deficiency

Wernicke's encephalopathy is a cerebral metabolic disorder caused by thiamine (vitamin B1) deficiency (TD). Neuropathologic consequences of TD include region-selective neuronal cell loss and blood-brain barrier (BBB) breakdown. Caveolin-1 is involved in the regulation of tight junction proteins and BBB permeability, and is modulated by oxidative stress, a feature of vulnerable brain regions in TD. We hypothesized that TD-related oxidative stress alters BBB integrity via induction of the caveolin-1 pathway. TD was induced in C57BL6 mice by treatment with a thiamine-deficient diet and administration of the thiamine antagonist pyrithiamine, in the absence or presence of the antioxidant N-acetylcysteine (NAC). A significant and focal increase in both caveolin-1 gene and protein expression was detected in the thalamus of thiamine-deficient mice, concomitant with IgG extravasation. Reduction of oxidative stress by NAC, as shown by normalization of reduced glutathione levels and attenuation of endothelial heme oxygenase-1 and nitric oxide synthase expression, resulted in prevention of the up-regulation of caveolin-1 in TD. Normalization of caveolin-1 levels by NAC was accompanied by a reduction in BBB breakdown, indicated by decreased IgG extravasation, normalization of occludin levels and prevention of matrix metalloproteinase-9 up-regulation. These findings demonstrate a role for caveolin-1 in TD pathogenesis, and suggest that oxidative stress contributes to BBB alterations in TD via modulation of this pathway.

TRPC-mediated actin-myosin contraction is critical for BBB disruption following hypoxic stress

Hypoxia-induced disruption of the blood-brain barrier (BBB) is the result of many different mechanisms, including alterations to the cytoskeleton. In this study, we identified actin-binding proteins involved in cytoskeletal dynamics with quantitative proteomics and assessed changes in subcellular localization of two proteins involved in actin polymerization [vasodilator-stimulated phosphoprotein (VASP)] and cytoskeleton-plasma membrane cross-linking (moesin). We found significant redistribution of both VASP and moesin to the cytoskeletal and membrane fractions of BBB endothelial cells after 1-h hypoxic stress. We also investigated activation of actin-myosin contraction through assessment of phosphorylated myosin light chain (pMLC) with confocal microscopy. Hypoxia caused a rapid and transient increase in pMLC. Blocking MLC phosphorylation through inhibition of myosin light chain kinase (MLCK) with ML-7 prevented hypoxia-induced BBB disruption and relocalization of the tight junction protein ZO-1. Finally, we implicate the transient receptor potential (TRP)C family of channels in mediating these events since blockade of TRPC channels and the associated calcium influx with SKF-96365 prevents hypoxia-induced permeability changes and the phosphorylation of MLC needed for actin-myosin contraction. These data suggest that hypoxic stress triggers alterations to cytoskeletal structure that contribute to BBB disruption and that calcium influx through TRPC channels contributes to these events.

Interleukin-25 expressed by brain capillary endothelial cells maintains blood-brain barrier function in a protein kinase Cepsilon-dependent manner

Interleukin (IL)-25, a member of the IL-17 family of cytokines, is expressed in the brains of normal mice. However, the cellular source of IL-25 and its function in the brain remain to be elucidated. Here, we show that IL-25 plays an important role in preventing infiltration of the inflammatory cells into the central nervous system. Brain capillary endothelial cells (BCECs) express IL-25. However, it is down-regulated by inflammatory cytokines, including tumor necrosis factor (TNF)-alpha, IL-17, interferon-gamma, IL-1beta, and IL-6 in vitro, and is also reduced in active multiple sclerosis (MS) lesions and in the inflamed spinal cord of experimental autoimmune encephalomyelitis, an animal model of MS. Furthermore, IL-25 restores the reduced expression of tight junction proteins, occludin, junction adhesion molecule, and claudin-5, induced by TNF-alpha in BCECs and consequently repairs TNF-alpha-induced blood-brain barrier (BBB) permeability. IL-25 induces protein kinase Cepsilon (PKCepsilon) phosphorylation, and up-regulation of claudin-5 is suppressed by PKCepsilon inhibitor peptide in the IL-25-stimulated BCECs. These results suggest that IL-25 is produced by BCECs and protects against inflammatory cytokine-induced excessive BBB collapse through a PKCepsilon-dependent pathway. These novel functions of IL-25 in maintaining BBB integrity may help us understand the pathophysiology of inflammatory brain diseases such as MS.

Occludin oligomeric assemblies at tight junctions of the blood-brain barrier are altered by hypoxia and reoxygenation stress

Hypoxic (low oxygen) and reperfusion (post-hypoxic reoxygenation) phases of stroke promote an increase in microvascular permeability at tight junctions (TJs) of the blood-brain barrier (BBB) that may lead to cerebral edema. To investigate the effect of hypoxia (Hx) and reoxygenation on oligomeric assemblies of the transmembrane TJ protein occludin, rats were subjected to either normoxia (Nx, 21% O(2), 60 min), Hx (6% O(2), 60 min), or hypoxia/reoxygenation (H/R, 6% O(2), 60 min followed by 21% O(2), 10 min). After treatment, cerebral microvessels were isolated, fractionated by detergent-free density gradient centrifugation, and occludin oligomeric assemblies associated with plasma membrane lipid rafts were solubilized by perfluoro-octanoic acid (PFO) exclusively as high molecular weight protein complexes. Analysis by non-reducing and reducing sodium dodecyl sulfate (SDS)-polyacrylamide gel electrophoresis/western blot of PFO-solubilized occludin revealed that occludin oligomeric assemblies co-localizing with 'TJ-associated' raft domains contained a high molecular weight 'structural core' that was resistant to disassembly by either SDS or a hydrophilic reducing agent ex vivo, and by Hx and H/R conditions in vivo. However, exposure of PFO-solubilized occludin oligomeric assemblies to SDS ex vivo revealed the non-covalent association of a significant amount of dimeric and monomeric occludin isoforms to the disulfide-bonded inner core, and dispersal of these non-covalently attached occludin subunits to lipid rafts of higher density in vivo was differentially promoted by Hx and H/R. Our data suggest a model of isoform interaction within occludin oligomeric assemblies at the BBB that enables occludin to simultaneously perform a structural role in inhibiting paracellular diffusion, and a signaling role involving interactions of dimeric and monomeric occludin isoforms with a variety of regulatory molecules within different plasma membrane lipid raft domains.

Cellular functions and X-ray structure of anthrolysin O, a cholesterol-dependent cytolysin secreted by Bacillus anthracis

Anthrolysin O (ALO) is a pore-forming, cholesterol-dependent cytolysin (CDC) secreted by Bacillus anthracis, the etiologic agent for anthrax. Growing evidence suggests the involvement of ALO in anthrax pathogenesis. Here, we show that the apical application of ALO decreases the barrier function of human polarized epithelial cells as well as increases intracellular calcium and the internalization of the tight junction protein occludin. Using pharmacological agents, we also found that barrier function disruption requires increased intracellular calcium and protein degradation. We also report a crystal structure of the soluble state of ALO. Based on our analytical ultracentrifugation and light scattering studies, ALO exists as a monomer. Our ALO structure provides the molecular basis as to how ALO is locked in a monomeric state, in contrast to other CDCs that undergo antiparallel dimerization or higher order oligomerization in solution. ALO has four domains and is globally similar to perfringolysin O (PFO) and intermedilysin (ILY), yet the highly conserved undecapeptide region in domain 4 (D4) adopts a completely different conformation in all three CDCs. Consistent with the differences within D4 and at the D2-D4 interface, we found that ALO D4 plays a key role in affecting the barrier function of C2BBE cells, whereas PFO domain 4 cannot substitute for this role. Novel structural elements and unique cellular functions of ALO revealed by our studies provide new insight into the molecular basis for the diverse nature of the CDC family.

Blood-brain barrier tight junction permeability and ischemic stroke

The blood-brain barrier (BBB) is formed by the endothelial cells of cerebral microvessels, providing a dynamic interface between the peripheral circulation and the central nervous system. The tight junctions (TJs) between the endothelial cells serve to restrict blood-borne substances from entering the brain. Under ischemic stroke conditions decreased BBB TJ integrity results in increased paracellular permeability, directly contributing to cerebral vasogenic edema, hemorrhagic transformation, and increased mortality. This loss of TJ integrity occurs in a phasic manner, which is contingent on several interdependent mechanisms (ionic dysregulation, inflammation, oxidative and nitrosative stress, enzymatic activity, and angiogenesis). Understanding the inter-relation of these mechanisms is critical for the development of new therapies. This review focuses on those aspects of ischemic stroke impacting BBB TJ integrity and the principle regulatory pathways, respective to the phases of paracellular permeability.

AKAP12 in astrocytes induces barrier functions in human endothelial cells through protein kinase Czeta

Interactions between astrocytes and blood vessels are essential for the formation and maintenance of the blood-neural barrier (BNB). Astrocyte-derived A-kinase anchor protein 12 (AKAP12) influences BNB formation, but the mechanism of regulation of BNB functions by AKAP12 is not fully understood. We have defined a new pathway of barriergenesis in human retina microvascular endothelial cells (HRMECs) involving astrocytic AKAP12. Treatment of HRMECs with conditioned media from AKAP12-overexpressing astrocytes reduced phosphorylation of protein kinase Czeta (PKCzeta), decreased the levels of vascular endothelial growth factor (VEGF) mRNA and protein, and increased thrombospondin-1 (TSP-1) levels, which led to antiangiogenesis and barriergenesis. Transfection of a small interference RNA targeting PKCzeta decreased VEGF levels and increased TSP-1 levels in HRMECs. Rho is a putative downstream signal of PKCzeta, and inhibition of Rho kinase with a specific inhibitor, Y27632, decreased VEGF levels and increased TSP-1 levels. We therefore suggest that AKAP12 in astrocytes differentially regulates the expression of VEGF and TSP-1 via the inhibition of PKCzeta phosphorylation and Rho kinase activity in HRMECs.

MgcRacGAP interacts with HIF-1alpha and regulates its transcriptional activity

HIF-1alpha is the inducible subunit of the dimeric transcription factor HIF-1 (Hypoxia Inducible Factor 1). It is induced by hypoxia and hypoxia-mimetics in most cell types, as well as non-hypoxic signals such as growth factors, cytokines and oncogenes, often in a cell specific manner. HIF-1 is present in virtually all cells of higher eukaryotes and its function is of great biomedical relevance since it is highly involved in development, tumor progression and tissue ischemia. Intracellular signaling to HIF-1alpha, as well as its further action, involves its participation in numerous protein complexes. Using the yeast two-hybrid system we have identified MgcRacGAP (male germ cell Rac GTPase Activating Protein) as a HIF-1alpha interacting protein. The MgcRacGAP protein is a regulator of Rho proteins, which are principally involved in cytoskeletal organization. We have verified specific binding of HIF-1alpha and MgcRacGAP in vitro and in vivo in mammalian cells. We have additionally shown that MgcRacGAP overexpression inhibits HIF-1alpha transcriptional activity, without lowering HIF-1alpha protein levels, or altering its subcellular localization. Moreover, this inhibition is dependent on the MgcRacGAP domain that interacts with HIF-1alpha. In conclusion, our findings demonstrate that HIF-1alpha function is negatively affected by its interaction with MgcRacGAP.

AKAP12 regulates human blood-retinal barrier formation by downregulation of hypoxia-inducible factor-1alpha

Many diseases of the eye such as retinoblastoma, diabetic retinopathy, and retinopathy of prematurity are associated with blood-retinal barrier (BRB) dysfunction. Identifying the factors that contribute to BRB formation during human eye development and maintenance could provide insights into such diseases. Here we show that A-kinase anchor protein 12 (AKAP12) induces BRB formation by increasing angiopoietin-1 and decreasing vascular endothelial growth factor (VEGF) levels in astrocytes. We reveal that AKAP12 downregulates the level of hypoxia-inducible factor-1alpha (HIF-1alpha) protein by enhancing the interaction of HIF-1alpha with pVHL (von Hippel-Lindau tumor suppressor protein) and PHD2 (prolyl hydroxylase 2). Conditioned media from AKAP12-overexpressing astrocytes induced barriergenesis by upregulating the expression of tight junction proteins in human retina microvascular endothelial cells (HRMECs). Compared with the retina during BRB maturation, AKAP12 expression in retinoblastoma patient tissue was markedly reduced whereas that of VEGF was increased. These findings suggest that AKAP12 may induce BRB formation through antiangiogenesis and barriergenesis in the developing human eye and that defects in this mechanism can lead to a loss of tight junction proteins and contribute to the development of retinal pathologies such as retinoblastoma.

Hypoxia inducible factor-1 modulates hemin-induced IL-8 secretion in microvascular endothelium

Ischemia/Reperfusion injury and hemolysis are characterized by erythrocyte lysis and release of free heme into the microcirculation. Following substantial erythrocyte lysis, heme overwhelms circulatory heme-binding protein networks rapidly forming hemin, the oxidized form of iron protoporphyrin IX. Hemin's role in modulating inflammatory responses in microvascular endothelium (MVEC) remains ill-defined. We studied the impact of hemin exposure on human MVEC interleukin-8 (IL-8) expression. Hemin significantly up-regulated MVEC IL-8 secretion and was associated with cellular iron loading. Hemin-induced IL-8 up-regulation was significantly attenuated by increasing environmental serum concentrations. As well, hemin-induced IL-8 secretion was significantly reduced in a concentration-dependent fashion following pyrrolidine dithiocarbamate exposure, suggesting that induction occurred via an oxidant-sensitive mechanism. Interestingly, transfection studies revealed that oxidant-driven transcription factors NF-kappaB and AP-1 played no role in hemin-induced IL-8 transcription. In studies employing actinomycin D, hemin was found to dramatically lengthen IL-8 mRNA half-life. Of major importance in the current report was the finding that hypoxia inducible factor-1 (HIF-1), a powerful transcription factor mediating tissue responses to hypoxia, potently regulated hemin-induced IL-8 secretion in human MVEC. Activation of HIF-1 via the prolyl hydroxylase inhibitor dimethyloxalylglycine attenuated hemin-induced IL-8 secretion. These studies were confirmed via DNA-directed siRNA silencing of HIF-1alpha. In conclusion, hemin induces a serum protein-sensitive pro-inflammatory phenotype in MVEC via an oxidant-sensitive mechanism that is powerfully regulated by HIF-1.

Homogeneity of mesothelial cells with lymphatic endothelium: expression of lymphatic endothelial markers by mesothelial cells

BACKGROUND

Mesothelial cell monolayers cover the serous cavities and internal organs, and provide a protective low-friction interface between apposed organs and tissues. The mesothelium also regulates inflammation, fluid and cell exchange, and tissue repair in these compartments and possibly tumor metastasis. In the present study, a stable pleural mesothelial cell line (MIM) was isolated and characterized, and the expression of several lymphatic specific markers by these cells examined.

METHODS AND RESULTS

MIM were isolated from mice stably expressing a temperature-sensitive SV40 large T antigen ('Immortomouse', strain: H-2K(b)-tsA58). These cells were compared with lymphatic endothelial cells (LEC) derived from the mesenteric adventitia of the Immortomouse. MIM and LEC expression of lymphatic-specific markers (Flt-4, LYVE-1, and Prox-1) was examined, and the tight junction protein (ZO-1) was studied by immunofluorescence and immunoblotting in these cells.

RESULTS

LYVE-1, Prox-1, and Flt-4 were detected in both MIM and LEC, with Prox-1 and LYVE-1 more strongly expressed on LEC than MIM. Conversely, Flt-4 was more densely expressed on MIM than on LEC. Spatially, ZO-1 was prominent at MIM junctions, but was less well organized in LEC.

CONCLUSION

MIM and LEC share several characteristic markers usually associated with lymphatic endothelium. MIM might be useful for studying the biology and pathology of mesothelial cells in vitro and help in the development of therapies for mesothelial-related diseases, such as mesothelioma and pleural effusion.

Astrocytes are more resistant than cerebral endothelial cells toward geno- and cytotoxicity mediated by short-term oxidative stress

Evidence is accumulating that capillary endothelial cells (cEC) and astrocytes play a pivotal role in neuroprotection, in particular with respect to counteract oxidative injury. Furthermore, differences among both cell types in response to oxidative stress have been shown and astrocytes seem to be more tolerant in terms of cytotoxicity, however, no reports exist on oxidative stress mediated genotoxicity in astrocytes. We investigated genotoxic and cytotoxic effects of oxidative stress in astrocytes and cECs induced by hypoxia/reoxygenation or by the redox cycling quinone DMNQ. Additionally, the dependence of these effects on glucose availabilty was also studied. On exposure to Hy/Re or 10 muM DMNQ for 24 hr, the frequency of micronucleated and apoptotic cells was significantly increasing, however, astrocytes proved to be more resistant to apoptosis induction, in particular on use of DMNQ. In astrocytes, the low background rates of necrotic cells were not affected and a significant necrosis induction was only detectable in cECs exposed to DMNQ for 24 hr. Short-term exposure to DMNQ (1 hr) had no effect in astrocytes but exerted significant geno- and cytotoxicity in cECs. Increasing the glucose concentration markedly reduced oxidative stress mediated geno- and cytotoxicity in astrocytes. Surprisingly, glucose deprivation (aglycemia) suppressed DMNQ induced micronucleus formation in astrocytes without affecting the frequency of apoptotic cells. Our results indicate that astrocytes are more resistant to oxidative stress than cECs, in particular regarding the potential to counteract genotoxicity as well as apoptosis induction mediated by a short term oxidative insult.

Reactive oxygen species production by mitochondria in endothelial cells exposed to reoxygenation after hypoxia and glucose depletion is mediated by ceramide

In endothelium, reoxygenation after hypoxia (H/R) has been shown to induce production of reactive oxygen species (ROS) by complex III of the mitochondrial respiratory chain. The purpose of the present study was to test the involvement of ceramide in this phenomenon. Human umbilical vein endothelial cells underwent 2 h of hypoxia (Po2, ∼20 mmHg) without glucose and 1 h of reoxygenation (Po2, ∼120 mmHg) with glucose. ROS production was measured by the fluorescent marker 2′,7′-dichlorodihydrofluorescein diacetate, and cell death by propidium iodide. We showed that 1) after 1 h of reoxygenation, fluorescence had risen and that ROS production was inhibited by desipramine, an inhibitor of sphingomyelinase, an enzyme responsible for ceramide production (126 ± 7% vs. 48 ± 12%, P < 0.05); 2) administration of ceramide ( N-acetylsphingosine) per se (i.e., in the absence of H/R) induced ROS production (65 ± 3%), which was inhibited by complex III inhibitor: antimycin A (24 ± 3%, P < 0.0001), or stigmatellin (31 ± 2%, P < 0.0001); 3) hypoxia/reoxygenation-induced ROS production was not affected by either ceramide-activated protein kinase inhibitor dimethyl aminopurine or mitochondrial permeability transition inhibitor cyclosporin A but was significantly inhibited by the antiapoptotic protein Bcl-2 (82 ± 8%, P < 0.05); 4) ceramide-induced ROS production was also inhibited by Bcl-2 (41 ± 4%, P < 0.0001). These results demonstrate that in endothelial cells submitted to hypoxia and glucose depletion followed by reoxygenation with glucose, the pathway implicated in mitochondrial complex III ROS production is ceramide dependent and is decreased by the antiapoptotic protein Bcl-2.

Isolation and Characterization of A Novel Mouse Lymphatic Endothelial Cell Line: SV-LEC

BACKGROUND

The lymphatic system regulates interstitial fluid and protein balance and modulates immune responses by regulating leukocyte and antigen traffic to lymph nodes. The present article describes a stable mouse lymphatic endothelial cell line from mesenteric adventitial tissue (SV-LEC) which is distinct from blood aortic (AEC) and venous (VEC) endothelial cells, based on expression of several lymphatic markers (e.g., Prox-1, LYVE-1, Flt-4). SV-LEC also expresses MAdCAM-1 in response to TNF-alpha, an effect seen in VEC, but not AEC.

METHODS AND RESULTS

Lymphatic endothelial cells (SV-LEC) were isolated from mesenteric adventitia from mice expressing temperature-sensitive SV40 large T ('Immortomouse', H-2K(b)tsA58) selected with hypoxia culture in D-valine-substituted MEM supplemented with VEGFC in a low oxygen atmosphere (0% O2, 5% CO2, and 95% N2) with 5 mM thioglycolate. Expression of lymphatic-specific markers (Flt-4, LYVE-1, Prox-1) and the tight junction proteins (ZO-1) were examined by RT-PCR, immunoblotting, and fluorescent microscopy. MAdCAM-1 (a high endothelial venular marker) expression was also examined in response to TNF-alpha IL-1beta and IFN-gamma.

RESULTS

Message for Flt-4 and LYVE-1 was detected on SV-LEC. Immunoblotting for LYVE-1 and Prox-1 showed strong expression on SV-LEC and VEC, but not AEC. Occludin expression was seen in all cell types, junctional ZO-1 was detected at SV-LEC and VEC junctions, not AEC.

CONCLUSION

SV-LEC expresses several lymphatic endothelial markers, some of which are shared with VEC, but not AEC, and may represent a useful system for modeling lymphatic function in vitro.

HIGH GLUCOSE-INDUCED HUMAN UMBILICAL VEIN ENDOTHELIAL CELL HYPERPERMEABILITY IS DEPENDENT ON PROTEIN KINASE C ACTIVATION AND INDEPENDENT OF THE Ca2+-NITRIC OXIDE SIGNALLING PATHWAY

1. Endothelial barrier dysfunction plays a pivotal role in the pathogenesis of diabetic vascular complications. The precise molecular mechanisms by which hyperglycaemia causes the increased permeability in endothelial cells are not yet well understood. In the present study, we investigated whether high concentrations of glucose induce endothelial permeability through the activation of protein kinase C (PKC) and/or the calcium-nitric oxide (NO) signalling pathway in human umbilical vein endothelial cells (HUVEC). 2. Endothelial permeability was measured by albumin diffusion across endothelial monolayers under the stimuli of high glucose (HG; 20 mmol/L), 100 nmol/L phorbol-myristate-acetate (PMA) or 100 nmol/L histamine. The intracellular calcium concentration ([Ca2+]i) was detected in HUVEC using the fluorescent probe fura-2 AM. The effects of PKC inhibitors (LY379196 and hypocrellin A) and the NO synthase (NOS) inhibitor NG-monomethyl-L-arginine (L-NMMA) on endothelial permeability and [Ca2+]i were determined. 3. High glucose and PMA increased endothelial permeability associated with decreased [Ca2+]i, whereas histamine triggered significant increases in endothelial permeability, accompanied by increases in [Ca2+]i in HUVEC. Hypocrellin A (HA) and LY379196 reversed both HG- and histamine-induced endothelial permeability. The NOS inhibitor L-NMMA only abolished histamine- and not HG-induced endothelial permeability. Neither LY379196, HA nor L-NMMA had any significant effects on alterations in [Ca2+]i caused by HG and histamine. 4. These results indicate that increased endothelial permeability in HUVEC induced by HG is dependent on PKC activity and is independent of the [Ca2+]i-NO pathway. Increased endothelial permeability due to other inflammatory factors, such as histamine, may also be mediated by the PKC pathway. Thus, PKC inhibitors would be a potential therapeutic approach to endothelial dysfunction induced by hyperglycaemia, as well as other inflammatory factors, in diabetes.

Disrupting tumour blood vessels

Low-molecular-weight vascular-disrupting agents (VDAs) cause a pronounced shutdown in blood flow to solid tumours, resulting in extensive tumour-cell necrosis, while they leave the blood flow in normal tissues relatively intact. The largest group of VDAs is the tubulin-binding combretastatins, several of which are now being tested in clinical trials. DMXAA (5,6-dimethylxanthenone-4-acetic acid) - one of a structurally distinct group of drugs - is also being tested in clinical trials. A full understanding of the action of these and other VDAs will provide insights into mechanisms that control tumour blood flow and will be the basis for the development of new therapeutic drugs for targeting the established tumour vasculature for therapy.

Regulation of Sertoli-germ cell adherens junction dynamics in the testis via the nitric oxide synthase (NOS)/cGMP/protein kinase G (PRKG)/beta-catenin (CATNB) signaling pathway: an in vitro and in vivo study

During spermatogenesis, extensive restructuring of cell junctions takes place in the seminiferous epithelium to facilitate germ cell movement. However, the mechanism that regulates this event remains largely unknown. Recent studies have shown that nitric oxide (NO) likely regulates tight junction (TJ) dynamics in the testis via the cGMP/protein kinase G (cGMP-dependent protein kinase, PRKG) signaling pathway. Due to the proximity of TJ and adherens junctions (AJ) in the testis, in particular at the blood-testis barrier, it is of interest to investigate if NO can affect AJ dynamics. Studies using Sertoli-germ cell cocultures in vitro have shown that the levels of NOS (nitric oxide synthase), cGMP, and PRKG were induced when anchoring junctions were being established. Using an in vivo model in which adult rats were treated with adjudin [a molecule that induces adherens junction disruption, formerly called AF-2364, 1-(2,4-dichlorobenzyl)-IH-indazole-3-carbohydrazide], the event of AJ disruption was also associated with a transient iNOS (inducible nitric oxide synthase, NOS2) induction. Immunohistochemistry has illustrated that NOS2 was intensely accumulated in Sertoli and germ cells in the epithelium during adjudin-induced germ cell loss, with a concomitant accumulation of intracellular cGMP and an induction of PRKG but not cAMP or protein kinase A (cAMP-dependent protein kinase, PRKA). To identify the NOS-mediated downstream signaling partners, coimmunoprecipitation was used to demonstrate that NOS2 and eNOS (endothelial nitric oxide synthase, NOS3) were structurally associated with the N-cadherin (CDH2)/beta-catenin (CATNB)/actin complex but not the nectin-3 (poliovirus receptor-related 3, PVRL 3)/afadin (myeloid/lymphoid or mixed lineage-leukemia tranlocation to 4 homolog, MLLT4) nor the integrin beta1 (ITB1)-mediated protein complexes, illustrating the spatial vicinity of NOS with selected AJ-protein complexes. Interestingly, CDH2 and CATNB were shown to dissociate from NOS during the adjudin-mediated AJ disruption, implicating the CDH2/CATNB protein complex is the likely downstream target of the NO signaling. Furthermore, PRKG, the downstream signaling protein of NOS, was shown to interact with CATNB in the rat testis. Perhaps the most important of all, pretreatment of testes with KT5823, a specific PRKG inhibitor, can indeed delay the adjudin-induced germ cell loss, further validating NOS/NO regulates Sertoli-germ cell AJ dynamics via the cGMP/PRKG pathway. These results illustrate that the CDH2/CATNB-mediated adhesion function in the testis is regulated, at least in part, via the NOS/cGMP/PRKG/CATNB pathway.

Hypoxia/aglycemia alters expression of occludin and actin in brain endothelial cells

The blood-brain barrier (BBB) serves as a critical organ in the maintenance of central nervous system homeostasis and is disrupted in a number of neurological disorders, including stroke. We examined the effects of hypoxia/aglycemia on the expression and localization of tight junction proteins, and on the function of the BBB in an in vitro model system. A receptor-operated/store-operated calcium channel blocker, SKF 96365, was used to determine if calcium flux was important in mediating hypoxia/aglycemia effects on the BBB. Expression of the tight junction protein occludin increased after hypoxic/aglycemic stress when cells were exposed to SKF 96365; this was correlated with partial protection of membrane localization of occludin and inhibition of the hypoxia-induced increase in permeability. Actin expression was dramatically reduced by hypoxia/aglycemia. Treatment with SKF 96365 during hypoxic stress protected monolayer permeability of sucrose, but transendothelial electrical resistances decreased with exposure to hypoxic stress regardless of treatment. Therefore, the presence of occludin at the membrane is dependent in part on calcium-sensitive signaling cascades; this provides a target for therapeutic intervention to minimize BBB disruption after stroke.

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.

LSP1 is an endothelial gatekeeper of leukocyte transendothelial migration

Leukocyte-specific protein 1 (LSP1), an F-actin binding protein and a major downstream substrate of p38 mitogen-activated protein kinase as well as protein kinase C, has been reported to be important in leukocyte chemotaxis. Although its distribution has been thought to be restricted to leukocytes, herein we report that LSP1 is expressed in endothelium and is essential to permit neutrophil emigration. Using intravital microscopy to directly visualize leukocyte rolling, adhesion, and emigration in postcapillary venules in LSP1-deficient (Lsp1^−/−) mice, we found that LSP1 deficiency inhibits neutrophil extravasation in response to various cytokines (tumor necrosis factor-α and interleukin-1β) and to neutrophil chemokine keratinocyte-derived chemokine in vivo. LSP1 deficiency did not affect leukocyte rolling or adhesion. Generation of Lsp1^−/− chimeric mice using bone marrow transplantation revealed that in mice with Lsp1^−/− endothelial cells and wild-type leukocytes, neutrophil transendothelial migration out of postcapillary venules is markedly restricted. In contrast, Lsp1^−/− neutrophils in wild-type mice were able to extravasate normally. Consistent with altered endothelial function was a reduction in vascular permeability to histamine in Lsp1^−/− animals. Western blot analysis and immunofluorescence microscopy examination confirmed the presence of LSP1 in wild-type but not in Lsp1^−/− mouse microvascular endothelial cells. Cultured human endothelial cells also stained positive for LSP1. Our results suggest that LSP1 expressed in endothelium regulates neutrophil transendothelial migration.

Cell column chromatography: a new research tool to quantify cerebral cell volume changes following chemically-induced anoxia/re-oxygenation

OBJECTIVE

The roles of individual types of cerebral cells in contributing to brain edema are undefined. The objective of this study was to determine the role of cerebral cell-column chromatography in quantifying cell volumes of individual cerebral cell lines, under chemically-induced anoxia/re-oxygenation (A/R).

METHODS

Cerebral endothelial cells (4 experiments) or type II astrocytes (4 experiments) were cultured to confluence on microcarrier beads. A chromatographic cell-column of 1.5 cm height was filled with non-treated cell-covered beads. The column was perfused at 1 ml/min with a balanced perfusate for one hour (Baseline). The perfusate was then switched to that containing 5 mM thioglycolic acid for one hour (Anoxia). Then the column was perfused with the normal perfusate for another two hours (Re-oxygenation). The total free space in the column, reversely reflecting cell volumes, was determined by averaged transit time (TTa) of a non-permeable flow tracer blue dextran. Decreased TTa means that cells swell, and vice versa.

RESULTS

TTa in endothelial cell columns increased with a peak at 60 minutes of re-oxygenation. TTa in astrocyte columns decreased with a nadir at 30 minutes of re-oxygenation.

CONCLUSION

Cell column chromatography can be used to determine the cerebral cell volume changes following chemically-induced anoxia/re-oxygenation.

Reoxygenation after hypoxia and glucose depletion causes reactive oxygen species production by mitochondria in HUVEC

In hemorrhagic shock, local hypoxia is present and followed by reoxygenation during the therapeutic process. In endothelium, reactive oxygen species (ROS) have been identified as a cause of inflammatory reactions and tissular lesions in ischemic territory during reoxygenation. This study was designed to identify the enzymatic mechanisms of ROS formation during reoxygenation after hypoxia. Because severe shock, in vivo, can affect both O2and nutriments, we combined hypoxia at a level close to that found in terminal vessels during shock, with glucose depletion, which induces a relevant additional stress. Human umbilical vein endothelial cells (HUVEC) underwent 2 h of hypoxia (Po2∼20 mmHg) without glucose and 1 h of reoxygenation (Po2∼120 mmHg) with glucose. ROS production was measured by the fluorescent marker 2′,7′-dichlorodihydrofluorescein diacetate, and cell death by propidium iodide. After 1 h of reoxygenation, fluorescence had risen by 143 ± 17%. Cell death was equal to 8.6 ± 2.4%. Antimycin A and stigmatellin, which inhibits the type III mitochondrial respiratory chain complex, reduced ROS production to values of 61 ± 10 and 59 ± 7%, respectively, but inhibitors of other chain complexes did not affect it. In addition, the increase in fluorescence was not affected by inhibition of NADPH oxidase, xanthine oxidase, NOS, cyclooxygenase, cytochrome P-450 monooxygenase, or monoamine oxidase. We did not observe any increase in cell death. These results show that, in HUVEC, mitochondria are responsible for ROS production after hypoxia and reoxygenation and suggest that a ROS release site is activated in the cytochrome b of the type III respiratory chain complex.

A novel four transmembrane spanning protein, CLP24. A hypoxically regulated cell junction protein

A novel hypoxically regulated intercellular junction protein (claudin-like protein of 24 kDa, CLP24) has been identified that shows homology to the myelin protein 22/epithelial membrane protein 1/claudin family of cell junction proteins, which are involved in the modulation of paracellular permeability. The CLP24 protein contains four predicted transmembrane domains and a C-terminal protein-protein interaction domain. These domains are characteristic of the four transmembrane spanning (tetraspan) family of proteins, which includes myelin protein 22, and are involved in cell adhesion at tight, gap and adherens junctions. Expression profiling analyses show that CLP24 is highly expressed in lung, heart, kidney and placental tissues. Cellular studies confirm that the CLP24 protein localizes to cell-cell junctions and co-localizes with the beta-catenin adherens junction-associated protein but not with tight junctions. Over-expression of CLP24 results in decreased adhesion between cells, and functional paracellular flux studies confirm that over-expression of the CLP24 protein modulates the junctional barrier function. These data therefore suggest that CLP24 is a novel, hypoxically regulated tetraspan adherens junction protein that modulates cell adhesion, paracellular permeability and angiogenesis.

Evidence for injurious effect of cocaethylene in human microvascular endothelial cells

BACKGROUND

Cocaethylene (CE) is a conjugate of cocaine and ethanol that may contribute to the pathogenesis of systemic vascular diseases. This study was conducted to investigate the effect of CE on human microvascular endothelial cells (HMEC-1) in culture.

METHODS

Proliferating and confluent monolayers of HMEC-1 were used for assessing growth kinetics, viability, cytotoxicity, and morphologic/barrier alterations after CE treatment (0-1 mmol/l) for up to 7 days. The Trypan blue exclusion, lactate dehydrogenase (LDH) release assay, manual cell counts, and silver nitrate staining technique were used.

RESULTS

The doubling times of 30.0 and 31.4 h for the 0.5 and 1.0 mmol/l CE-treated HMEC-1, respectively, were significantly longer than the 28.6 h for the control group (p < 0.05). The viabilities of 90.4 +/- 3.8% (control) and 93.1 +/- 1.9% (CE-treated) from the Trypan blue exclusion-staining experiments indicated non-lethality of CE. LDH activities of 173 +/- 33 U/l (control) and 157 +/- 43 U/l (CE-treated) confirmed the absence of CE cytotoxicity. Silver staining results indicated increased monolayer permeability as demonstrated by the formation of intercellular gaps after 1 h of exposure.

CONCLUSIONS

HMEC-1 exposure to CE induced cellular injury that could affect the permeability of small blood vessels. These cellular changes could in part be the pivotal point for studies to explain the edema and inflammation in surrounding tissues of individuals exposed to CE.

Protection against hypoxia-induced blood-brain barrier disruption: changes in intracellular calcium

Tissue damage after stroke is partly due to disruption of the blood-brain barrier (BBB). Little is known about the role of calcium in modulating BBB disruption. We investigated the effect of hypoxic and aglycemic stress on BBB function and intracellular calcium levels. Bovine brain microvessel endothelial cells were treated with A-23187 to increase intracellular calcium without hypoxia or treated with a calcium chelator (BAPTA) or calcium channel blockers (nifedipine or SKF-96365) and 6 h of hypoxia. A-23187 alone did not increase paracellular permeability. Hypoxia increased intracellular calcium, and hypoxia or hypoxia-aglycemia increased paracellular permeability. Treatment with nifedipine and SKF-96365 increased intracellular calcium under normoglycemic conditions, instead of blocking calcium influx, and was protective against hypoxia-induced BBB disruption under normoglycemia. Protection by nifedipine and SKF-96365 was not due to antioxidant properties of these compounds. These data indicate that increased intracellular calcium alone is not enough to disrupt the BBB. However, increased intracellular calcium after drug treatment and hypoxia suggests a potential mechanism for these drugs in BBB protection; nifedipine and SKF-96365 plus hypoxic stress may trigger calcium-mediated signaling cascades, altering BBB integrity.

p38mapk and MEK1/2 inhibition contribute to cellular oxidant injury after hypoxia

Lung epithelial cells produce increased reactive oxygen species (ROS) after hypoxia exposure, and they are more susceptible after hypoxia to injury by agents that generate superoxide [O2-; e.g., 2,3-dimethoxy-1,4-naphthoquinone (DMNQ)]. Cellular GSH and MnSOD both decrease in hypoxic lung epithelial cells, altering the redox state. Because ROS participate in signaling pathways involved in cell death or survival, we tested the hypothesis that mitogen-activated protein kinases (MAPK) were involved in a protective response against cellular injury during reoxygenation. Human lung epithelial A549 cells were incubated in hypoxia (<1% O2 for 24 h) and then reoxygenated by return to air. p38mapk and MKK3 phosphorylation both decreased after hypoxia. During reoxygenation, cells were incubated with DMNQ (0-50 microM), a redox cycling quinone that produces O2-. Hypoxia preexposure significantly increased epithelial cell lysis resulting from DMNQ. Addition of the p38mapk inhibitors SB-202190 or SB-203580 markedly increased cytotoxicity, as did the mitogen/extracellular signal-regulated kinase (MEK) 1/2 inhibitor PD-98059 (all 10 microM), suggesting a protective effect of downstream molecules activated by the kinases. Transfection of A549 cells with a dominant active MKK3 plasmid (MKK3[Glu]) partially inhibited cytolysis resulting from DMNQ, whereas the inactive MKK3 plasmid (MKK3[Ala]) had less evident protective effects. Stress-related signaling pathways in epithelial cells are modulated by hypoxia and confer protection from reoxygenation, since hypoxia and chemical inhibition of p38mapk and MEK1/2 similarly increase cytolysis resulting from O2-.

Neuropeptide Y enhances permeability across a rat aortic endothelial cell monolayer

Previously, in vivo studies showed that neuropeptide Y (NPY) elevates vascular permeability in isolated lung perfusion preparations, possibly through binding to the NPY Y(3) receptor. The present study used monolayers in a double-chamber culture method under conditions of normoxia (5% CO(2)-20% O(2)-75% N(2)) or hypoxia (5% CO(2)-5% O(2)-90% N(2)) to test the hypothesis that NPY directly affects rat aortic endothelial cells (RAECs). RAECs were cultured on the base of the upper chamber, into which FITC-labeled albumin was introduced, and permeation into the lower chamber was measured. The RAEC monolayer was treated with 10(-8)-3 x 10(-7) M NPY for 2 h in normoxia or hypoxia. In hypoxia, NPY concentration dependently increased the permeability of the RAEC monolayer, whereas in normoxia no significant change was observed. Peptide YY, NPY Y(1), and NPY Y(2) receptor agonists and NPY Y(1) receptor antagonist exerted no significant effects under hypoxic conditions. NPY-(18-36), an NPY Y(3) receptor antagonist, elicited an inhibitory action on the NPY-induced increase in monolayer permeability. Furthermore, neither N-monomethyl-l-arginine, a nitric oxide synthase inhibitor, the bradykinin B(2) receptor antagonist FK-3657, nor the vascular endothelial growth factor receptor-coupled tyrosine kinase inhibitor tyrphostin SU-1498, injected into the medium of the upper chamber, affected the NPY-induced permeability changes under hypoxic conditions. The results suggest that the NPY-induced increase in permeability across the RAEC monolayer is closely related to low O(2) tension, possibly mediated by direct action on the NPY Y(3) receptor expressed on the endothelial cell membrane. Furthermore, this NPY-induced increase is not likely due to nitric oxide, bradykinin, or vascular endothelial growth factor.

Regulation of Sertoli cell tight junction dynamics in the rat testis via the nitric oxide synthase/soluble guanylate cyclase/3',5'-cyclic guanosine monophosphate/protein kinase G signaling pathway: an in vitro study

Nitric oxide (NO) synthase (NOS) catalyzes the oxidation of L-arginine to NO. NO plays a crucial role in regulating various physiological functions, possibly including junction dynamics via its effects on cAMP and cGMP, which are known modulators of tight junction (TJ) dynamics. Although inducible NOS (iNOS) and endothelial NOS (eNOS) are found in the testis and have been implicated in the regulation of spermatogenesis, their role(s) in TJ dynamics, if any, is not known. When Sertoli cells were cultured at 0.5-1.2 x 10(6) cells/cm(2) on Matrigel-coated dishes or bicameral units, functional TJ barrier was formed when the barrier function was assessed by quantifying transepithelial electrical resistance across the cell epithelium. The assembly of the TJ barrier was shown to associate with a significant plummeting in the levels of iNOS and eNOS, seemingly suggesting that their presence by producing NO might perturb TJ assembly. To further confirm the role of NOS on the TJ barrier function in vitro, zinc (II) protoporphyrin-IX (ZnPP), an NOS inhibitor and a soluble guanylate cyclase inhibitor, was added to the Sertoli cell cultures during TJ assembly. Indeed, ZnPP was found to facilitate the assembly and maintenance of the Sertoli cell TJ barrier, possibly by inducing the production of TJ-associated proteins, such as occludin. Subsequent studies by immunoprecipitation and immunoblotting have shown that iNOS and eNOS are structurally linked to TJ-integral membrane proteins, such as occludin, and cytoskeletal proteins, such as actin, vimentin, and alpha-tubulin. When the cAMP and cGMP levels in these ZnPP-treated samples were quantified, a ZnPP-induced reduction of intracellular cGMP, but not cAMP, was indeed detected. Furthermore, 8-bromo-cGMP, a cell membrane-permeable analog of cGMP, could also perturb the TJ barrier dose dependently similar to the effects of 8-bromo-cAMP. KT-5823, a specific inhibitor of protein kinase G, was shown to facilitate the Sertoli cell TJ barrier assembly. Cytokines, such as TGF-beta and TNF-alpha, known to perturb the Sertoli cell TJ barrier, were also shown to stimulate Sertoli cell iNOS and eNOS expression dose dependently in vitro. Collectively, these results illustrate NOS is an important physiological regulator of TJ dynamics in the testis, exerting its effects via the NO/soluble guanylate cyclase/cGMP/protein kinase G signaling pathway.

Protein kinase C modulates pulmonary endothelial permeability: a paradigm for acute lung injury

The intracellular serine/threonine kinase protein kinase C (PKC) has an important role in the genesis of pulmonary edema. This review discusses the PKC-mediated mechanisms that participate in the pulmonary endothelial response to agents involved in lung injury characteristic of the respiratory distress syndrome. Thus the paradigms of PKC-induced lung injury are discussed within the context of pulmonary transvascular fluid exchange. We focus on the signal transduction pathways that are modulated by PKC and their effect on lung endothelial permeability. Specifically, alpha-thrombin, tumor necrosis factor (TNF)-alpha, and reactive oxygen species are discussed because of their well-established roles in both human and experimental lung injury. We conclude that PKC, most likely PKC-alpha, is a primary supporter for lung endothelial injury in response to alpha-thrombin, TNF-alpha, and reactive oxygen species.