Role of protein kinase C isoforms in rat epididymal microvascular endothelial barrier function

Assessment of Endothelial Barrier Functions in Extra Embryonic Vasculature of Chick Embryo as an Alternative Model

Vascular permeability, a tightly regulated process, is a direct measure of angiogenic and immune responses in the endothelium altered in several acute and chronic diseases such as sepsis, high-altitude pulmonary edema (HAPE), high-altitude cerebral edema (HACE), ischemia, and coronavirus disease 2019 (COVID-19) endotheliitis. Both endogenous and exogenous factors such as cytokines, chemokines, and hormones may affect vascular permeability. The conventional tools available for the measurement of vascular permeability in vitro and in vivo based on collagen-coated Transwell and dye-based spectrophotometric methods are indirect measures of permeability. In this chapter, we present our live in ovo protocols based on dextran-Texas red and avian chorioallantoic membrane assay developed using custom-made equipment to assess leakiness of endothelial cell barrier both in vitro and in vivo. Further, we validate this assay using different stressors such as ischemia and hypoxia known to affect endothelial barrier properties by potentiating actin stress fiber disorganization and disrupting the cell-cell junctions.

Baicalin Protects Vascular Tight Junctions in Piglets During Glaesserella parasuis Infection

Glaesserella parasuis (G. parasuis) can cause Glässer's disease and severely affect swine industry worldwide. This study is an attempt to address the issue of the capability of G. parasuis to damage the vascular barrier and the effects of baicalin on vascular tight junctions (TJ) in order to investigate the interactions between the pathogen and the porcine vascular endothelium. Piglets were challenged with G. parasuis and treated with or without baicalin. The expressions of vascular TJ genes were examined using RT-PCR. The distribution patterns of TJ proteins were detected by immunofluorescence. The involved signaling pathways were determined by Western blot assays on related proteins. G. parasuis can downregulate TJ expression and disrupt the distribution of TJ proteins. Baicalin can alleviate the downregulation of vascular TJ mRNA, maintain the distribution, and prevent the abnormalities of TJ. These results provide ample evidence that baicalin has the capacity to protect vascular TJ damaged by G. parasuis through inhibiting PKC and MLCK/MLC pathway activation. As a result, baicalin is a promising candidate for application as a natural agent for the prevention and control of G. parasuis infection.

Targeting translational read-through of premature termination mutations in BMPR2 with PTC124 for pulmonary arterial hypertension

Pulmonary arterial hypertension is a fatal disorder of the lung circulation in which accumulation of vascular cells progressively obliterates the pulmonary arterioles. This results in sustained elevation in pulmonary artery pressure leading eventually to right heart failure. Approximately, 80% of familial and 20% of sporadic idiopathic pulmonary arterial hypertension cases are caused by mutations in the bone morphogenetic protein receptor type 2 (BMPR2). Nonsense mutations in BMPR2 are amongst the most common mutations found, where the insertion of a premature termination codon causes mRNA degradation via activation of the nonsense-mediated decay pathway leading to a state of haploinsufficiency. Ataluren (PTC124), a compound that permits ribosomal read-through of premature stop codons, has been previously reported to increase BMPR2 protein expression in cells derived from pulmonary arterial hypertension patients harbouring nonsense mutations. In this study, we characterised the effects of PTC124 on a range of nonsense BMPR2 mutations, focusing on the R584X mutation both in vitro and in vivo. Treatment with PTC124 partially restored BMPR2 protein expression in blood outgrowth endothelial cells isolated from a patient harbouring the R584X mutation. Furthermore, a downstream bone morphogenetic protein signalling target, Id1, was rescued by PTC124 treatment. Mutant cells also exhibited increased lipopolysaccharide-induced permeability, which was reversed by PTC124 treatment. Increased proliferation and apoptosis in R584X blood outgrowth endothelial cells were also significantly reduced by PTC124. Moreover, oral PTC124 increased lung BMPR2 protein expression in mice harbouring the R584X mutation (Bmpr2 ^+/R584X ). Our findings provide support for future experimental medicine studies of PTC124 in pulmonary arterial hypertension patients with specific nonsense BMPR2 mutations.

Downregulation of S1P Lyase Improves Barrier Function in Human Cerebral Microvascular Endothelial Cells Following an Inflammatory Challenge

Sphingosine 1-phosphate (S1P) is a key bioactive lipid that regulates a myriad of physiological and pathophysiological processes, including endothelial barrier function, vascular tone, vascular inflammation, and angiogenesis. Various S1P receptor subtypes have been suggested to be involved in the regulation of these processes, whereas the contribution of intracellular S1P (iS1P) through intracellular targets is little explored. In this study, we used the human cerebral microvascular endothelial cell line HCMEC/D3 to stably downregulate the S1P lyase (SPL-kd) and evaluate the consequences on endothelial barrier function and on the molecular factors that regulate barrier tightness under normal and inflammatory conditions. The results show that in SPL-kd cells, transendothelial electrical resistance, as a measure of barrier integrity, was regulated in a dual manner. SPL-kd cells had a delayed barrier build up, a shorter interval of a stable barrier, and, thereafter, a continuous breakdown. Contrariwise, a protection was seen from the rapid proinflammatory cytokine-mediated barrier breakdown. On the molecular level, SPL-kd caused an increased basal protein expression of the adherens junction molecules PECAM-1, VE-cadherin, and β-catenin, increased activity of the signaling kinases protein kinase C, AMP-dependent kinase, and p38-MAPK, but reduced protein expression of the transcription factor c-Jun. However, the only factors that were significantly reduced in TNFα/SPL-kd compared to TNFα/control cells, which could explain the observed protection, were VCAM-1, IL-6, MCP-1, and c-Jun. Furthermore, lipid profiling revealed that dihydro-S1P and S1P were strongly enhanced in TNFα-treated SPL-kd cells. In summary, our data suggest that SPL inhibition is a valid approach to dampenan inflammatory response and augmente barrier integrity during an inflammatory challenge.

Cell chirality regulates intercellular junctions and endothelial permeability

Cell chirality is a newly discovered intrinsic property of the cell, reflecting the bias of the cell to polarize in the left-right axis. Despite increasing evidence on its substantial role in the asymmetric development of embryos, little is known about implications of cell chirality in physiology and disease. We demonstrate that cell chirality accounts for the nonmonotonic, dose-response relationship between endothelial permeability and protein kinase C (PKC) activation. The permeability of the endothelial cell layer is tightly controlled in our body, and dysregulation often leads to tissue inflammation and diseases. Our results show that low-level PKC activation is sufficient to reverse cell chirality through phosphatidylinositol 3-kinase/AKT signaling and alters junctional protein organization between cells with opposite chirality, leading to an unexpected substantial change in endothelial permeability. Our findings suggest that cell chirality regulates intercellular junctions in important ways, providing new opportunities for drug delivery across tightly connected semipermeable cellular sheets.

Regulation of pulmonary endothelial barrier function by kinases

The pulmonary endothelium is the target of continuous physiological and pathological stimuli that affect its crucial barrier function. The regulation, defense, and repair of endothelial barrier function require complex biochemical processes. This review examines the role of endothelial phosphorylating enzymes, kinases, a class with profound, interdigitating influences on endothelial permeability and lung function.

Regulation of Thrombin-Induced Lung Endothelial Cell Barrier Disruption by Protein Kinase C Delta

Protein Kinase C (PKC) plays a significant role in thrombin-induced loss of endothelial cell (EC) barrier integrity; however, the existence of more than 10 isozymes of PKC and tissue-specific isoform expression has limited our understanding of this important second messenger in vascular homeostasis. In this study, we show that PKCδ isoform promotes thrombin-induced loss of human pulmonary artery EC barrier integrity, findings substantiated by PKCδ inhibitory studies (rottlerin), dominant negative PKCδ construct and PKCδ silencing (siRNA). In addition, we identified PKCδ as a signaling mediator upstream of both thrombin-induced MLC phosphorylation and Rho GTPase activation affecting stress fiber formation, cell contraction and loss of EC barrier integrity. Our inhibitor-based studies indicate that thrombin-induced PKCδ activation exerts a positive feedback on Rho GTPase activation and contributes to Rac1 GTPase inhibition. Moreover, PKD (or PKCμ) and CPI-17, two known PKCδ targets, were found to be activated by PKCδ in EC and served as modulators of cytoskeleton rearrangement. These studies clarify the role of PKCδ in EC cytoskeleton regulation, and highlight PKCδ as a therapeutic target in inflammatory lung disorders, characterized by the loss of barrier integrity, such as acute lung injury and sepsis.

Selective enhancement of endothelial BMPR-II with BMP9 reverses pulmonary arterial hypertension

Genetic evidence implicates the loss of bone morphogenetic protein type II receptor (BMPR-II) signaling in the endothelium as an initiating factor in pulmonary arterial hypertension (PAH). However, selective targeting of this signaling pathway using BMP ligands has not yet been explored as a therapeutic strategy. Here, we identify BMP9 as the preferred ligand for preventing apoptosis and enhancing monolayer integrity in both pulmonary arterial endothelial cells and blood outgrowth endothelial cells from subjects with PAH who bear mutations in the gene encoding BMPR-II, BMPR2. Mice bearing a heterozygous knock-in allele of a human BMPR2 mutation, R899X, which we generated as an animal model of PAH caused by BMPR-II deficiency, spontaneously developed PAH. Administration of BMP9 reversed established PAH in these mice, as well as in two other experimental PAH models, in which PAH develops in response to either monocrotaline or VEGF receptor inhibition combined with chronic hypoxia. These results demonstrate the promise of direct enhancement of endothelial BMP signaling as a new therapeutic strategy for PAH.

Mechanisms regulating endothelial permeability

The endothelial monolayer partitioning underlying tissue from blood components in the vessel wall maintains tissue fluid balance and host defense through dynamically opening intercellular junctions. Edemagenic agonists disrupt endothelial barrier function by signaling the opening of the intercellular junctions leading to the formation of protein-rich edema in the interstitial tissue, a hallmark of tissue inflammation that, if left untreated, causes fatal diseases, such as acute respiratory distress syndrome. In this review, we discuss how intercellular junctions are maintained under normal conditions and after stimulation of endothelium with edemagenic agonists. We have focused on reviewing the new concepts dealing with the alteration of adherens junctions after inflammatory stimulus.

ENaC activity and expression is decreased in the lungs of protein kinase C-α knockout mice

We used a PKC-α knockout model to investigate the regulation of alveolar epithelial Na(+) channels (ENaC) by PKC. Primary alveolar type II (ATII) cells were subjected to cell-attached patch clamp. In the absence of PKC-α, the open probability (Po) of ENaC was decreased by half compared with wild-type mice. The channel density (N) was also reduced in the knockout mice. Using in vivo biotinylation, membrane localization of all three ENaC subunits (α, β, and γ) was decreased in the PKC-α knockout lung, compared with the wild-type. Confocal microscopy of lung slices showed elevated levels of reactive oxygen species (ROS) in the lungs of the PKC-α knockout mice vs. the wild-type. High levels of ROS in the knockout lung can be explained by a decrease in both cytosolic and mitochondrial superoxide dismutase activity. Elevated levels of ROS in the knockout lung activates PKC-δ and leads to reduced dephosphorylation of ERK1/2 by MAP kinase phosphatase, which in turn causes increased internalization of ENaC via ubiquitination by the ubiquitin-ligase Nedd4-2. In addition, in the knockout lung, PKC-δ activates ERK, causing a decrease in ENaC density at the apical alveolar membrane. PKC-δ also phosphorylates MARCKS, leading to a decrease in ENaC Po. The effects of ROS and PKC-δ were confirmed with patch-clamp experiments on isolated ATII cells in which the ROS scavenger, Tempol, or a PKC-δ-specific inhibitor added to patches reversed the observed decrease in ENaC apical channel density and Po. These results explain the decrease in ENaC activity in PKC-α knockout lung.

Arginase 1: an unexpected mediator of pulmonary capillary barrier dysfunction in models of acute lung injury

The integrity of epithelial and endothelial barriers in the lower airspaces of the lungs has to be tightly regulated, in order to prevent leakage and to assure efficient gas exchange between the alveoli and capillaries. Both G⁻ and G⁺ bacterial toxins, such as lipopolysaccharide and pneumolysin, respectively, can be released in high concentrations within the pulmonary compartments upon antibiotic treatment of patients suffering from acute respiratory distress syndrome (ARDS) or severe pneumonia. These toxins are able to impair endothelial barrier function, either directly, or indirectly, by induction of pro-inflammatory mediators and neutrophil sequestration. Toxin-induced endothelial hyperpermeability can involve myosin light chain phosphorylation and/or microtubule rearrangement. Endothelial nitric oxide synthase (eNOS) was proposed to be a guardian of basal barrier function, since eNOS knock-out mice display an impaired expression of inter-endothelial junction proteins and as such an increased vascular permeability, as compared to wild type mice. The enzyme arginase, the activity of which can be regulated by the redox status of the cell, exists in two isoforms – arginase 1 (cytosolic) and arginase 2 (mitochondrial) – both of which can be expressed in lung microvascular endothelial cells. Upon activation, arginase competes with eNOS for the substrate l-arginine, as such impairing eNOS-dependent NO generation and promoting reactive oxygen species generation by the enzyme. This mini-review will discuss recent findings regarding the interaction between bacterial toxins and arginase during acute lung injury and will as such address the role of arginase in bacterial toxin-induced pulmonary endothelial barrier dysfunction.

Mini-review: novel therapeutic strategies to blunt actions of pneumolysin in the lungs

Severe pneumonia is the main single cause of death worldwide in children under five years of age. The main etiological agent of pneumonia is the G+ bacterium Streptococcus pneumoniae, which accounts for up to 45% of all cases. Intriguingly, patients can still die days after commencing antibiotic treatment due to the development of permeability edema, although the pathogen was successfully cleared from their lungs. This condition is characterized by a dramatically impaired alveolar epithelial-capillary barrier function and a dysfunction of the sodium transporters required for edema reabsorption, including the apically expressed epithelial sodium channel (ENaC) and the basolaterally expressed sodium potassium pump (Na+-K+-ATPase). The main agent inducing this edema formation is the virulence factor pneumolysin, a cholesterol-binding pore-forming toxin, released in the alveolar compartment of the lungs when pneumococci are being lysed by antibiotic treatment or upon autolysis. Sub-lytic concentrations of pneumolysin can cause endothelial barrier dysfunction and can impair ENaC-mediated sodium uptake in type II alveolar epithelial cells. These events significantly contribute to the formation of permeability edema, for which currently no standard therapy is available. This review focuses on discussing some recent developments in the search for the novel therapeutic agents able to improve lung function despite the presence of pore-forming toxins. Such treatments could reduce the potentially lethal complications occurring after antibiotic treatment of patients with severe pneumonia.

Tight junctions at the blood brain barrier: physiological architecture and disease-associated dysregulation

The Blood–brain barrier (BBB), present at the level of the endothelium of cerebral blood vessels, selectively restricts the blood-to-brain paracellular diffusion of compounds; it is mandatory for cerebral homeostasis and proper neuronal function. The barrier properties of these specialized endothelial cells notably depend on tight junctions (TJs) between adjacent cells: TJs are dynamic structures consisting of a number of transmembrane and membrane-associated cytoplasmic proteins, which are assembled in a multimolecular complex and acting as a platform for intracellular signaling. Although the structural composition of these complexes has been well described in the recent years, our knowledge about their functional regulation still remains fragmentary. Importantly, pericytes, embedded in the vascular basement membrane, and perivascular microglial cells, astrocytes and neurons contribute to the regulation of endothelial TJs and BBB function, altogether constituting the so-called neurovascular unit.

The present review summarizes our current understanding of the structure and functional regulation of endothelial TJs at the BBB. Accumulating evidence points to a correlation between BBB dysfunction, alteration of TJ complexes and progression of a variety of CNS diseases, such as stroke, multiple sclerosis and brain tumors, as well as neurodegenerative diseases like Parkinson’s and Alzheimer’s diseases. Understanding how TJ integrity is controlled may thus help improve drug delivery across the BBB and the design of therapeutic strategies for neurological disorders.

Genetic disruption of protein kinase Cδ reduces endotoxin-induced lung injury

The pathogenesis of acute lung injury and acute respiratory distress syndrome is characterized by sequestration of leukocytes in lung tissue, disruption of capillary integrity, and pulmonary edema. PKCδ plays a critical role in RhoA-mediated endothelial barrier function and inflammatory responses. We used mice with genetic deletion of PKCδ (PKCδ(-/-)) to assess the role of PKCδ in susceptibility to LPS-induced lung injury and pulmonary edema. Under baseline conditions or in settings of increased capillary hydrostatic pressures, no differences were noted in the filtration coefficients (k(f)) or wet-to-dry weight ratios between PKCδ(+/+) and PKCδ(-/-) mice. However, at 24 h after exposure to LPS, the k(f) values were significantly higher in lungs isolated from PKCδ(+/+) than PKCδ(-/-) mice. In addition, bronchoalveolar lavage fluid obtained from LPS-exposed PKCδ(+/+) mice displayed increased protein and cell content compared with LPS-exposed PKCδ(-/-) mice, but similar changes in inflammatory cytokines were measured. Histology indicated elevated LPS-induced cellularity and inflammation within PKCδ(+/+) mouse lung parenchyma relative to PKCδ(-/-) mouse lungs. Transient overexpression of catalytically inactive PKCδ cDNA in the endothelium significantly attenuated LPS-induced endothelial barrier dysfunction in vitro and increased k(f) lung values in PKCδ(+/+) mice. However, transient overexpression of wild-type PKCδ cDNA in PKCδ(-/-) mouse lung vasculature did not alter the protective effects of PKCδ deficiency against LPS-induced acute lung injury. We conclude that PKCδ plays a role in the pathological progression of endotoxin-induced lung injury, likely mediated through modulation of inflammatory signaling and pulmonary vascular barrier function.

The characterization of arachnoid cell transport II: paracellular transport and blood-cerebrospinal fluid barrier formation

We used an immortalized arachnoid cell line to test the arachnoid barrier properties and paracellular transport. The permeabilities of urea, mannitol, and inulin through monolayers were 2.9 ± 1.1 × 10(-6), 0.8 ± .18 × 10(-6), 1.0 ± .29 × 10(-6)cm/s. Size differential permeability testing with dextran clarified the arachnoidal blood-cerebrospinal fluid (CSF) barrier limit and established a rate of transcellular transport to be about two orders of magnitude slower than paracellular transport in a polyester membrane diffusion chamber. The theoretical pore size for paracellular space is 11Å and the occupancy to length ratio is 0.8 and 0.72 cm(-1) for urea and mannitol respectively. The permeability of the monolayer was not significantly different from apical to basal and vice versa. Gap junctions may have a role in contributing to barrier formation. Although the upregulation of claudin by dexamethasone did not significantly alter paracellular transport, increasing intracellular cAMP decreased mannitol permeability. Calcium modulated paracellular transport, but only selectively with the ion chelator, EDTA, and with disruption of intracellular stores. The blood-CSF barrier at the arachnoid is anatomically and physiologically different from the vascular-based blood-brain barrier, but is similarly subject to modulation. We describe the basic paracellular transport characteristics of this CSF "sink" of the brain which will allow for a better description of mass and constitutive balance within the intracranial compartment.

Heterogeneity in apoptotic responses of microvascular endothelial cells to oxidative stress

Oxidative stress contributes to disease and can alter endothelial cell (EC) function. EC from different vascular beds are heterogeneous in structure and function, thus we assessed the apoptotic responses of EC from lung and heart to oxidative stress. Since protein kinase Cδ (PKCδ) is activated by oxidative stress and is an important modulator of apoptosis, experiments assessed the level of apoptosis in fixed lung and heart sections of PKCδ wild-type (PKCδ(+/+)) and null (PKCδ(-/-)) mice housed under normoxia (21% O(2)) or hyperoxia (~95% O(2)). We noted a significantly greater number of TUNEL-positive cells in lungs of hyperoxic PKCδ(+/+) mice, compared to matched hearts or normoxic organs. We found that 33% of apoptotic cells identified in hyperoxic lungs of PKCδ(+/+) mice were EC, compared to 7% EC in hyperoxic hearts. We further noted that EC apoptosis was significantly reduced in lungs of PKCδ(-/-) hyperoxic mice, compared to lungs of PKCδ(+/+) hyperoxic mice. In vitro, both hyperoxia and H(2)O(2) promoted apoptosis in EC isolated from microvasculature of lung (LMVEC), but not from the heart (HMVEC). H(2)O(2) treatment significantly increased p38 activity in LMVEC, but not in HMVEC. Inhibition of p38 attenuated H(2)O(2)-induced LMVEC apoptosis. Baseline expression of total PKCδ protein, as well as the caspase-mediated, catalytically active PKCδ cleavage fragment, was higher in LMVEC, compared to HMVEC. PKCδ inhibition significantly attenuated H(2)O(2)-induced LMVEC p38 activation. Conversely, overexpression of wild-type PKCδ or the catalytically active PKCδ cleavage product greatly increased H(2)O(2)-induced HMVEC caspase and p38 activation. We propose that enhanced susceptibility of lung EC to oxidant-induced apoptosis is due to increased PKCδ→p38 signaling, and we describe a PKCδ-centric pathway which dictates the differential response of EC from distinct vascular beds to oxidative stress.

Mechanisms for vascular cell adhesion molecule-1 activation of ERK1/2 during leukocyte transendothelial migration

BACKGROUND

During inflammation, adhesion molecules regulate recruitment of leukocytes to inflamed tissues. It is reported that vascular cell adhesion molecule-1 (VCAM-1) activates extracellular regulated kinases 1 and 2 (ERK1/2), but the mechanism for this activation is not known. Pharmacological inhibitors of ERK1/2 partially inhibit leukocyte transendothelial migration in a multi-receptor system but it is not known whether VCAM-1 activation of ERK1/2 is required for leukocyte transendothelial migration (TEM) on VCAM-1.

METHODOLOGY/PRINCIPAL FINDINGS

In this study, we identified a mechanism for VCAM-1 activation of ERK1/2 in human and mouse endothelial cells. VCAM-1 signaling, which occurs through endothelial cell NADPH oxidase, protein kinase Cα (PKCα), and protein tyrosine phosphatase 1B (PTP1B), activates endothelial cell ERK1/2. Inhibition of these signals blocked VCAM-1 activation of ERK1/2, indicating that ERK1/2 is activated downstream of PTP1B during VCAM-1 signaling. Furthermore, VCAM-1-specific leukocyte migration under physiological laminar flow of 2 dynes/cm(2) was blocked by pretreatment of endothelial cells with dominant-negative ERK2 K52R or the MEK/ERK inhibitors, PD98059 and U0126, indicating for the first time that ERK regulates VCAM-1-dependent leukocyte transendothelial migration.

CONCLUSIONS/SIGNIFICANCE

VCAM-1 activation of endothelial cell NADPH oxidase/PKCα/PTP1B induces transient ERK1/2 activation that is necessary for VCAM-1-dependent leukocyte TEM.

The Dual Role of TNF in Pulmonary Edema

—Pulmonary edema, a major manifestation of left ventricular heart failure, renal insufficiency, shock, diffuse alveolar damage and lung hypersensitivity states, is a significant medical problem worldwide and can be life-threatening. The proinflammatory cytokine tumor necrosis factor (TNF) has been shown to contribute to the pathogenesis and development of pulmonary edema. However, some recent studies have demonstrated surprisingly that TNF can also promote alveolar fluid reabsorption in vivo and in vitro. This protective effect of the cytokine is mediated by the lectin-like domain of the cytokine, which is spatially distinct from the TNF receptor binding sites. The TIP peptide, a synthetic mimic of the lectin-like domain of TNF, can significantly increase alveolar fluid clearance and improve lung compliance in pulmonary edema models. In this review, we will discuss the dual role of TNF in pulmonary edema.

Interplay between FAK, PKCδ, and p190RhoGAP in the regulation of endothelial barrier function

Disruption of either intercellular or extracellular junctions involved in maintaining endothelial barrier function can result in increased endothelial permeability. Increased endothelial permeability, in turn, allows for the unregulated movement of fluid and solutes out of the vasculature and into the surrounding connective tissue, contributing to a number of disease states, including stroke and pulmonary edema (Ermert et al., 1995; Lee and Slutsky, 2010; van Hinsbergh, 1997; Waller et al., 1996; Warboys et al., 2010). Thus, a better understanding of the molecular mechanisms by which endothelial cell junction integrity is controlled is necessary for development of therapies aimed at treating such conditions. In this review, we will discuss the functions of three signaling molecules known to be involved in regulation of endothelial permeability: focal adhesion kinase (FAK), protein kinase C delta (PKCδ), and p190RhoGAP (p190). We will discuss the independent functions of each protein, as well as the interplay that exists between them and the effects of such interactions on endothelial function.

Length-dependent modulation of cytoskeletal remodeling and mechanical energetics in airway smooth muscle

Actin cytoskeletal remodeling is an important mechanism of airway smooth muscle (ASM) contraction. We tested the hypothesis that mechanical strain modulates the cholinergic receptor-mediated cytoskeletal recruitment of actin-binding and integrin-binding proteins in intact airway smooth muscle, thereby regulating the mechanical energetics of airway smooth muscle. We found that the carbachol-stimulated cytoskeletal recruitment of actin-related protein-3 (Arp3), metavinculin, and talin were up-regulated at short muscle lengths and down-regulated at long muscle lengths, suggesting that the actin cytoskeleton--integrin complex becomes enriched in cross-linked and branched actin filaments in shortened ASM. The mechanical energy output/input ratio during sinusoidal length oscillation was dependent on muscle length, oscillatory amplitude, and cholinergic activation. The enhancing effect of cholinergic stimulation on mechanical energy output/input ratio at short and long muscle lengths may be explained by the length-dependent modulation of cytoskeletal recruitment and crossbridge cycling, respectively. We postulate that ASM functions as a hybrid biomaterial, capable of switching between operating as a cytoskeleton-based mechanical energy store at short muscle lengths to operating as an actomyosin-powered mechanical energy generator at long muscle lengths. This postulate predicts that targeting the signaling molecules involved in cytoskeletal recruitment may provide a novel approach to dilating collapsed airways in obstructive airway disease.

Adenosine protected against pulmonary edema through transporter- and receptor A2-mediated endothelial barrier enhancement

We have previously demonstrated that adenosine plus homocysteine enhanced endothelial basal barrier function and protected against agonist-induced barrier dysfunction in vitro through attenuation of RhoA activation by inhibition of isoprenylcysteine-O-carboxyl methyltransferase. In the current study, we tested the effect of elevated adenosine on pulmonary endothelial barrier function in vitro and in vivo. We noted that adenosine alone dose dependently enhanced endothelial barrier function. While adenosine receptor A(1) or A(3) antagonists were ineffective, an adenosine transporter inhibitor, NBTI, or a combination of DPMX and MRS1754, antagonists for adenosine receptors A(2A) and A(2B), respectively, partially attenuated the barrier-enhancing effect of adenosine. Similarly, inhibition of both A(2A) and A(2B) receptors with siRNA also blunted the effect of adenosine on barrier function. Interestingly, inhibition of both transporters and A(2A)/A(2B) receptors completely abolished adenosine-induced endothelial barrier enhancement. The adenosine receptor A(2A) and A(2B) agonist, NECA, also significantly enhanced endothelial barrier function. These data suggest that both adenosine transporters and A(2A) and A(2B) receptors are necessary for exerting maximal effect of adenosine on barrier enhancement. We also found that adenosine enhanced Rac1 GTPase activity and overexpression of dominant negative Rac1 attenuated adenosine-induced increases in focal adhesion complexes. We further demonstrated that elevation of cellular adenosine by inhibition of adenosine deaminase with Pentostatin significantly enhanced endothelial basal barrier function, an effect that was also associated with enhanced Rac1 GTPase activity and with increased focal adhesion complexes and adherens junctions. Finally, using a non-inflammatory acute lung injury (ALI) model induced by alpha-naphthylthiourea, we found that administration of Pentostatin, which elevated lung adenosine level by 10-fold, not only attenuated the development of edema before ALI but also partially reversed edema after ALI. The data suggest that adenosine deaminase inhibition may be useful in treatment of pulmonary edema in settings of ALI.

Role of protein tyrosine phosphatase SHP2 in barrier function of pulmonary endothelium

Pulmonary edema is mediated in part by disruption of interendothelial cell contacts. Protein tyrosine phosphatases (PTP) have been shown to affect both cell-extracellular matrix and cell-cell junctions. The SH2 domain-containing nonreceptor PTP, SHP2, is involved in intercellular signaling through direct interaction with adherens junction proteins. In this study, we examined the role of SHP2 in pulmonary endothelial barrier function. Inhibition of SHP2 promoted edema formation in rat lungs and increased monolayer permeability in cultured lung endothelial cells. In addition, pulmonary endothelial cells demonstrated a decreased level of p190RhoGAP activity following inhibition of SHP2, events that were accompanied by a concomitant increase in RhoA activity. Furthermore, immunofluorescence microscopy confirmed enhanced actin stress fiber formation and diminished interendothelial staining of adherens junction complex-associated proteins upon SHP2 inhibition. Finally, immunoprecipitation and immunoblot analyses demonstrated increased tyrosine phosphorylation of VE-cadherin, beta-catenin, and p190RhoGAP proteins, as well as decreased association between p120-catenin and VE-cadherin proteins. Our findings suggest that SHP2 supports basal pulmonary endothelial barrier function by coordinating the tyrosine phosphorylation profile of VE-cadherin, beta-catenin, and p190RhoGAP and the activity of RhoA, signaling molecules important in adherens junction complex integrity.

PKCdelta influences p190 phosphorylation and activity: events independent of PKCdelta-mediated regulation of endothelial cell stress fiber and focal adhesion formation and barrier function

BACKGROUND

We have shown that protein kinase Cdelta (PKCdelta) inhibition results in increased endothelial cell (EC) permeability and decreased RhoA activity; which correlated with diminished stress fibers (SF) and focal adhesions (FA). We have also shown co-precipitation of p190RhoGAP (p190) with PKCdelta. Here, we investigated if PKCdelta regulates p190 and whether PKCdelta-mediated changes in SF and FA or permeability were dependent upon p190.

METHODS

Protein-protein interaction and activity analyses were performed using co-precipitation assays. Analysis of p190 phosphorylation was performed using in vitro kinase assays. SF and FA were analyzed by immunofluorescence analyses. EC monolayer permeability was measured using electrical cell impedance sensor (ECIS) technique.

RESULTS

Inhibition of PKCdelta increased p190 activity, while PKCdelta overexpression diminished p190 activity. PKCdelta bound to and phosphorylated both p190FF and p190GTPase domains. p190 protein overexpression diminished SF and FA formation and RhoA activity. Disruption of SF and FA or increased permeability induced upon PKCdelta inhibition, were not attenuated in EC in which the p190 isoforms were suppressed individually or concurrently.

GENERAL SIGNIFICANCE

Our findings suggest that while PKCdelta can regulate p190 activity, possibly at the FF and/or GTPase domains, the effect of PKCdelta inhibition on SF and FA and barrier dysfunction occurs through a pathway independent of p190.

Relationship of p21-activated kinase (PAK) and filopodia to persistence and oncogenic transformation

Previously, we found that oncogenically transformed cells had fewer filopodia and more large, p21-activated kinase (PAK)-dependent features than normal cells. These large protrusions (LPs) were increased in cells expressing RhoA(N19) with Cdc42-associated kinase (ACK). Here, we determine how GTPase-mediated mechanisms of focal contact (FC) regulation affect these protrusions. Constructs encoding various proteins were introduced into cells which were then studied by microscopy and computerized image processing and analysis. Constructs that prevented PAK recruitment by PAK-interacting exchange factor (PIX) or restricted PAK residence time on FCs decreased both protrusions. Thus, filopodia were also PAK-dependent. A comparison of FC distribution in cells expressing PAK in the presence or absence of PAK kinase inhibitor domain (KID) suggested that PAK enlarged FCs without affecting the prevalence of either protrusion. KID or Nck expression increased LPs but not filopodia. Nck failed to synergize with KID or ACK and RhoA(N19) in enhancing LPs. Nck and KID synergistically enhanced filopodia, possibly because Nck recruited PAK to FCs while KID prevented their dissociation by PAK-mediated autophosphorylation. Coexpression of Nck, ACK, and RhoA(N19) abrogated filopodia and replicated the transformed phenotype. Since Nck recruitment of PAK is implicated in persistence of directional movement, we studied the PAK-Nck interface. Filopodia were eliminated by the Nck PAK-binding domain and LPs by the PAK Nck-binding domain. The results suggested that filopodia formation has more stringent requirements than LP formation, and Nck and PAK are used differently in the protrusions. Loss of filopodia in transformed cells may reflect defective regulation of GTPase mechanisms.

Molecular mechanisms of endothelial hyperpermeability: implications in inflammation

Endothelial hyperpermeability is a significant problem in vascular inflammation associated with trauma, ischaemia-reperfusion injury, sepsis, adult respiratory distress syndrome, diabetes, thrombosis and cancer. An important mechanism underlying this process is increased paracellular leakage of plasma fluid and protein. Inflammatory stimuli such as histamine, thrombin, vascular endothelial growth factor and activated neutrophils can cause dissociation of cell-cell junctions between endothelial cells as well as cytoskeleton contraction, leading to a widened intercellular space that facilitates transendothelial flux. Such structural changes initiate with agonist-receptor binding, followed by activation of intracellular signalling molecules including calcium, protein kinase C, tyrosine kinases, myosin light chain kinase, and small Rho-GTPases; these kinases and GTPases then phosphorylate or alter the conformation of different subcellular components that control cell-cell adhesion, resulting in paracellular hypermeability. Targeting key signalling molecules that mediate endothelial-junction-cytoskeleton dissociation demonstrates a therapeutic potential to improve vascular barrier function during inflammatory injury.

Mechanism of C-type natriuretic peptide-induced endothelial cell hyperpolarization

C-type natriuretic peptide (CNP) has a demonstrated hyperpolarizing effect on vascular smooth muscle cells. However, its autocrine function, including its electrophysiological effect on endothelial cells, is not known. Here, we report the effect of CNP on the membrane potential (E(m)) of pulmonary microvascular endothelial cells and describe its target receptors, second messengers, and ion channels. We measured changes in E(m) using fluorescence imaging and perforated patch-clamping techniques. In imaging experiments, samples were preincubated in the potentiometric dye DiBAC(4)(3), and subsequently exposed to CNP in the presence of selective inhibitors of ion channels or second messengers. CNP exposure induced a dose-dependent decrease in fluorescence, indicating that CNP induces endothelial cell hyperpolarization. CNP-induced hyperpolarization was inhibited by the K(+) channel blockers, tetraethylammonium or iberiotoxin, the nonspecific cation channel blocker, La(3+), or by depletion or repletion of extracellular Ca(2+) or K(+), respectively. CNP-induced hyperpolarization was also blocked by pharmacological inhibition of PKG or by small interfering RNA (siRNA)-mediated knockdown of natriuretic peptide receptor-B (NPR-B). CNP-induced hyperpolarization was mimicked by the PKG agonist, 8-bromo-cGMP, and attenuated by both the endothelial nitric oxide synthase (eNOS) inhibitor, N(omega)-nitro-l-arginine methyl ester (l-NAME), and the soluble guanylyl cyclase (sGC) inhibitor, 1H-[1,2,4]oxadiazolo[4,3-a]quinoxalin-1-one. Presence of iberiotoxin-sensitive, CNP-induced outward current was confirmed by perforated patch-clamping experiments. We conclude that CNP hyperpolarizes pulmonary microvascular endothelial cells by activating large-conductance calcium-activated potassium channels mediated by the activation of NPR-B, PKG, eNOS, and sGC.

Regulation of endothelial junctional permeability

The endothelium is a semi-permeable barrier that regulates the flux of liquid and solutes, including plasma proteins, between the blood and surrounding tissue. The permeability of the vascular barrier can be modified in response to specific stimuli acting on endothelial cells. Transport across the endothelium can occur via two different pathways: through the endothelial cell (transcellular) or between adjacent cells, through interendothelial junctions (paracellular). This review focuses on the regulation of the paracellular pathway. The paracellular pathway is composed of adhesive junctions between endothelial cells, both tight junctions and adherens junctions. The actin cytoskeleton is bound to each junction and controls the integrity of each through actin remodeling. These interendothelial junctions can be disassembled or assembled to either increase or decrease paracellular permeability. Mediators, such as thrombin, TNF-alpha, and LPS, stimulate their respective receptor on endothelial cells to initiate signaling that increases cytosolic Ca2+ and activates myosin light chain kinase (MLCK), as well as monomeric GTPases RhoA, Rac1, and Cdc42. Ca2+ activation of MLCK and RhoA disrupts junctions, whereas Rac1 and Cdc42 promote junctional assembly. Increased endothelial permeability can be reversed with "barrier stabilizing agents," such as sphingosine-1-phosphate and cyclic adenosine monophosphate (cAMP). This review provides an overview of the mechanisms that regulate paracellular permeability.

Counter regulatory effects of PKCbetaII and PKCdelta on coronary endothelial permeability

OBJECTIVE

The aim of this study was to examine the endothelial distribution and activity of selected PKC isoforms in coronary vessels with respect to their functional impact on endothelial permeability under the experimental conditions relevant to diabetes.

METHODS AND RESULTS

En face immunohistochemistry demonstrated a significant increase of PKC(betaII) and decrease of PKCdelta expression in coronary arterial endothelium of Zucker diabetic rats. To test whether changes in PKC expression alter endothelial barrier properties, we measured the transcellular electric resistance in human coronary microvascular endothelial monolayers and found that either PKC(betaII) overexpression or PKCdelta inhibition disrupted the cell-cell adhesive barrier. Three-dimensional fluorescence microscopy revealed that hyperpermeability was caused by altered PKC activity in association with distinct translocation of PKC(betaII) to the cell-cell junction and PKCdelta localization to the cytosol. Further analyses in fractionated endothelial lysates confirmed the differential redistribution of these isozymes. Additionally, FRET analysis of PKC subcellular dynamics demonstrated a high PKC(betaII) activity at the cell surface and junction, whereas PKCdelta activity is concentrated in intracellular membrane organelles.

CONCLUSIONS

Taken together, these data suggest that PKC(betaII) and PKCdelta counter-regulate coronary endothelial barrier properties by targeting distinctive subcellular sites. Imbalanced PKC(betaII)/PKCdelta expression and activity may contribute to endothelial hyperpermeability and coronary dysfunction in diabetes.

Rottlerin causes pulmonary edema in vivo: a possible role for PKCδ

In the present study, we assessed the effects of chemical inhibitors shown to be selective for protein kinase C (PKC) isoforms on lung barrier function both in vitro and in vivo. Rottlerin, a purported inhibitor of PKCδ, but not other chemical inhibitors, dose dependently promoted barrier dysfunction in lung endothelial cells in vitro. This barrier dysfunction correlated with structural changes in focal adhesions and stress fibers, which were consistent with functional changes in cell stiffness. To determine whether the effects noted in vitro correlated with changes in intact lungs, we tested the effects of rottlerin in the formation of pulmonary edema in rats using both ex vivo and in vivo models. Isolated, perfused lungs demonstrated a significant increase in filtration coefficients on exposure to rottlerin, compared with vehicle-treated lungs, an effect that correlated with increased extravasation of Evan's blue dye (EBD)-conjugated albumin. Additionally, compared with vehicle, the ratio of the wet lung weights to dry lung weights was significantly greater on exposure of animals to rottlerin; rottlerin also produced a dose-dependent increase in EBD extravasation into the lungs. These effects on lung edema occurred without any increase in right ventricular pressures. Microscopic assessment of edema in the ex vivo lungs demonstrated perivascular cuffing, with no evidence of septal capillary leak, in rottlerin-exposed lungs. Taken together, rottlerin increases barrier dysfunction in pulmonary endothelial cell monolayers and causes pulmonary edema in rats; results suggestive of an important role for PKCδ in maintaining lung endothelial barrier function.

Lipopolysaccharide induces expression of SSeCKS in rat lung microvascular endothelial cell

Src-suppressed C kinase substrate (SSeCKS) plays a role in membrane-cytoskeletal remodeling to regulate mitogenesis, cell differentiation, and motility. Previous study showed that lipopolysaccharide (LPS) induced a selective and strong expression of SSeCKS in the vascular endothelial cells of lung. Here we show that LPS stimulation elevated expression of SSeCKS mRNA and protein in Rat pulmonary microvascular endothelial cell (RPMVEC). LPS potentiated SSeCKS phosphorylation in a time- and dose-dependent manner, and partly induced translocation of SSeCKS from the cytosol to the membrane after LPS challenge. The PKC inhibitor, Calphostin C, significantly decreased LPS-induced phosphorylation of SSeCKS, inhibited SSeCKS translocation and actin cytoskeleton reorganization after LPS challenge, suggesting that PKC may play a role in LPS-induced SSeCKS translocation and actin rearrangement. We conclude that SSeCKS is located downstream of PKC and that SSeCKS and PKC are both necessary for LPS-induced stress fiber formation.

Cell adhesion molecules in chemically-induced renal injury

Cell adhesion molecules are integral cell-membrane proteins that maintain cell-cell and cell-substrate adhesion and in some cases act as regulators of intracellular signaling cascades. In the kidney, cell adhesion molecules, such as the cadherins, the catenins, the zonula occludens protein-1 (ZO-1), occludin and the claudins are essential for maintaining the epithelial polarity and barrier integrity that are necessary for the normal absorption/excretion of fluid and solutes. A growing volume of evidence indicates that these cell adhesion molecules are important early targets for a variety of nephrotoxic substances including metals, drugs, and venom components. In addition, it is now widely appreciated that molecules, such as intracellular adhesion molecule-1 (ICAM-1), integrins, and selectins play important roles in the recruitment of leukocytes and inflammatory responses that are associated with nephrotoxic injury. This review summarizes the results of recent in vitro and in vivo studies indicating that these cell adhesion molecules may be primary molecular targets in many types of chemically-induced renal injury. Some of the specific agents that are discussed include cadmium (Cd), mercury (Hg), bismuth (Bi), cisplatin, aminoglycoside antibiotics, S-(1,2-dichlorovinyl)-l-cysteine (DCVC), and various venom toxins. This review also includes a discussion of the various mechanisms, by which these substances can affect cell adhesion molecules in the kidney.

The vascular endothelium as a target of cadmium toxicity

Cadmium (Cd) is an important industrial and environmental pollutant that can produce a wide variety of adverse effects in humans and animals. A growing volume of evidence indicates that the vascular endothelium may be one of the primary targets of Cd toxicity in vivo. Studies over the past 20 years have shown that Cd, at relatively low, sublethal concentrations, can target vascular endothelial cells at a variety of molecular levels, including cell adhesion molecules, metal ion transporters and protein kinase signaling pathways. The purpose of this review is to summarize the results of these recent studies and to discuss the implications of these findings with regard to the mechanisms of Cd toxicity in specific organs including the lung, liver, kidney, testis and heart. In addition the possible roles of the vascular endothelium in mediating the tumor promoting and anticarcinogenic effects of Cd are discussed.

Regulation of skin microvasculature angiogenesis, cell migration, and permeability by a specific inhibitor of PKCalpha

Activation of protein kinase C (PKC) induces phenotypic changes in the morphology of microvascular endothelial cells that affect major functions of the microvasculature. These functions include the first stages of sprouting in angiogenesis, cell migration following wounding, and vascular permeability. The specific isoform(s) of PKC responsible for each of these changes has not been previously identified. In this study, we used two inflammatory agents, IL-1beta and phorbol myristic acetate, to activate PKC isozymes and specific inhibitors of PKCalpha (Gö6976) and PKCbeta (hispidin) to distinguish how each of these isoform(s) controls angiogenesis, wound healing, and permeability. In all cases, only inhibition of PKCalpha inhibited each of these functions when compared to the inhibition of PKCbeta. Additional analysis of the mechanism of action of Gö6976 (RT-PCR, Western blots, and immunohistochemistry) of the changes in the phosphorylated and nonphosphorylated forms of PKCalpha in the cell membrane and cytoplasm confirmed the specificity of PKCalpha inhibition by Gö6976. These studies therefore indicate a specific and a regulatory role of the PKCalpha isoform in three major endothelial cell functions that are important in the maintenance of microvascular homeostasis.

Natriuretic peptides differentially attenuate thrombin-induced barrier dysfunction in pulmonary microvascular endothelial cells

Previous studies have described a protective effect of atrial natriuretic peptide (ANP) against agonist-induced permeability in endothelial cells derived from various vascular beds. In the current study, we assessed the effects of the three natriuretic peptides on thrombin-induced barrier dysfunction in rat lung microvascular endothelial cells (LMVEC). Both ANP and brain natriuretic peptide (BNP) attenuated the effect of thrombin on increased endothelial monolayer permeability and significantly enhanced the rate of barrier restoration. C-type natriuretic peptide (CNP) had no effect on the degree of thrombin-induced monolayer permeability, but did enhance the restoration of the endothelial barrier, similar to ANP and BNP. In contrast, the non-guanylyl cyclase-linked natriuretic peptide receptor specific ligand, cyclic-atrial natriuretic factor (c-ANF), delayed the rate of barrier restoration following exposure to thrombin. All three natriuretic peptides promoted cGMP production in the endothelial cells; however, 8-bromo-cGMP alone did not significantly affect thrombin modulation of endothelial barrier function. ANP and BNP, but not CNP or c-ANF, blunted thrombin-induced RhoA GTPase activation. We conclude that ANP and BNP protect against thrombin-induced barrier dysfunction in the pulmonary microcirculation by a cGMP-independent mechanism, possibly by attenuation of RhoA activation.

PKCdelta regulates endothelial basal barrier function through modulation of RhoA GTPase activity

We have shown that PKCdelta enhanced microvascular endothelial basal barrier function, correlating with elevated RhoA GTPase activity and increased focal contact formation. In the current study, we investigated signaling pathways important in PKCdelta modulation of barrier function in unstimulated endothelial cell monolayers by assessing the effects of PKCdelta inhibition in endothelial cells (EC) derived from rat pulmonary artery (PAEC) and epididymus (FPEC). Rottlerin exposure or Ad PKCdeltadn infection significantly enhanced monolayer permeability in both EC. Immunofluorescence analyses demonstrated fewer stress fibers and focal contacts in rottlerin-treated or Ad PKCdeltadn-infected EC; yet, PKCdelta inhibition caused no significant changes in microtubule structures. These changes correlated with a reduction in both focal adhesion kinase (FAK) and RhoA GTPase activities. Microfilament stabilization significantly attenuated the focal contact and barrier disruptive effects of rottlerin. FAK overexpression did not blunt the effects of rottlerin-induced barrier dysfunction or stress fiber and focal contact disruption. Conversely, GFP-linked dominant active RhoA overexpression protected EC from stress fiber and focal contact disruption induced by both rottlerin exposure and overexpression of PKCdelta dominant negative protein. Additionally, PKCdelta immunoprecipitated with p190RhoGAP and p120RasGAP, modulators of RhoA activity. Thus, PKCdelta may regulate basal endothelial barrier function by stabilizing microfilaments and focal contacts by regulating RhoA GTPase activity through upstream modulators, p190RhoGAP and p120RasGAP.

RhoA/Rho-associated kinase pathway selectively regulates thrombin-induced intercellular adhesion molecule-1 expression in endothelial cells via activation of I kappa B kinase beta and phosphorylation of RelA/p65

We investigated the involvement of the RhoA/Rho-associated kinase (ROCK) pathway in regulating ICAM-1 expression in endothelial cells by the procoagulant, thrombin. Exposure of HUVECs to C3 exoenzyme, a selective inhibitor of Rho, markedly reduced thrombin-induced ICAM-1 expression. Inhibition of ROCK, the downstream effector of Rho, also prevented thrombin-induced ICAM-1 expression. Blockade of thrombin-induced ICAM-1 expression was secondary to inhibition of NF-kappaB activity, the key regulator of ICAM-1 expression in endothelial cells. In parallel studies we observed that inhibition of the RhoA/ROCK pathway by the same pharmacological and genetic approaches failed to inhibit TNF-alpha-induced NF-kappaB activation and ICAM-1 expression. The effect of RhoA/ROCK inhibition on thrombin-induced NF-kappaB activation was secondary to inhibition of IkappaB kinase activation and subsequent IkappaBalpha degradation and nuclear uptake and the DNA binding of NF-kappaB. Inhibition of the RhoA/ROCK pathway also prevented phosphorylation of Ser(536) within the transactivation domain 1 of NF-kappaB p65/RelA, a critical event conferring transcriptional competency to the bound NF-kappaB. Thus, the RhoA/ROCK pathway signals thrombin-induced ICAM-1 expression through the activation of IkappaB kinase, which promotes NF-kappaB binding to ICAM-1 promoter and phosphorylation of RelA/p65, thus mediating the transcriptional activation of bound NF-kappaB.

Role of protein kinase Cζ in thrombin-induced endothelial permeability changes: inhibition by angiopoietin-1

Endothelial cell leakiness is regulated by mediators such as thrombin, which promotes endothelial permeability, and anti-inflammatory agents, such as angiopoietin-1. Here we define a new pathway involved in thrombin-induced permeability that involves the atypical protein kinase C isoform, PKCζ. Chemical inhibitor studies implicated the involvement of an atypical PKC isoform in thrombin-induced permeability changes in human umbilical vein endothelial cells. Thrombin stimulation resulted in PKCζ, but not the other atypical PKC isoform, PKCλ, translocating to the membrane, an event known to be critical to enzyme activation. The involvement of PKCζ was confirmed by overexpression of constitutively active PKCζ, resulting in enhanced basal permeability. Dominant-negative PKCζ prevented the thrombin-mediated effects on endothelial cell permeability and inhibited thrombin-induced activation of PKCζ. Rho activation does not appear to play a role, either upstream or downstream of PKCζ, as C3 transferase does not block thrombin-induced PKCζ activation and dominant-negative PKCζ does not block thrombin-induced Rho activation. Finally, we show that angiopoietin-1 inhibits thrombin-induced PKCζ activation, Rho activation, and Ca++ flux, thus demonstrating that the powerful antipermeability action of angiopoietin-1 is mediated by its action on a number of signaling pathways induced by thrombin and implicated in permeability changes. (Blood. 2004; 104:1716-1724)

Barrier dysfunction and RhoA activation are blunted by homocysteine and adenosine in pulmonary endothelium

RhoA GTPases modulate endothelial permeability. We have previously shown that adenosine and homocysteine enhance basal barrier function in pulmonary artery endothelial cells by a mechanism involving diminution of RhoA carboxyl methylation and activity. In the current study, we investigated the effects of adenosine and homocysteine on endothelial monolayer permeability in cultured monolayers. Adenosine and homocysteine significantly attenuated thrombin-induced endothelial barrier dysfunction and intercellular gap formation. We found significantly diminished RhoA associated with the membrane subcellular fraction in endothelial cells pretreated with adenosine and homocysteine, compared with vehicle-treated endothelial cells. Additionally, adenosine and homocysteine significantly blunted RhoA activation following thrombin exposure. Incubation with adenosine and homocysteine also enhanced in vitro interactions between RhoA and RhoGDI, as well as subcellular translocation of p190RhoGAP to the cytosol. These data demonstrate that elevated intracellular concentrations of homocysteine and adenosine enhance endothelial barrier function in cultured endothelial cells isolated from the main pulmonary artery and lung microvasculature, suggesting a potentially protective effect against pulmonary edema in response to lung injury. We speculate that homocysteine and adenosine modulate the level of endothelial barrier dysfunction through modulation of RhoA posttranslational processing resulting in diminished GTPase activity through altered interactions with modulators of RhoA activation.

Cholinergic receptor-mediated differential cytoskeletal recruitment of actin- and integrin-binding proteins in intact airway smooth muscle

We tested the hypothesis that cholinergic receptor stimulation recruits actin- and integrin-binding proteins from the cytoplasm to the cytoskeleton-membrane complex in intact airway smooth muscle. We stimulated bovine tracheal smooth muscle with carbachol and fractionated the tissue homogenate into pellet (P) and supernatant (S) by ultracentrifugation. In unstimulated tissues, calponin exhibited the highest basal P-to-S ratio (P/S; 2.74 +/- 0.47), whereas vinculin exhibited the lowest P/S (0.52 +/- 0.09). Cholinergic receptor stimulation increased P/S of the following proteins in descending order of sensitivity: alpha-actinin > talin approximately metavinculin > alpha-smooth muscle actin > vinculin approximately calponin. Carbachol induced ERK1/2 phosphorylation by 300% of basal value. U0126 (10 microM) completely inhibited carbachol-induced ERK1/2 phosphorylation but did not significantly affect the correlation between alpha-actinin P/S and carbachol concentration. This observation indicates that cytoskeletal/membrane recruitment of alpha-actinin is independent of ERK1/2 mitogen-activated protein kinase activation. Metavinculin and vinculin are splice variants of a single gene, but metavinculin P/S was significantly higher than vinculin P/S. Furthermore, the P/S of metavinculin but not vinculin increased significantly in response to cholinergic receptor stimulation. Calponin and alpha-actinin both belong to the family of calponin homology (CH) domain proteins. However, unlike alpha-actinin, the calponin P/S did not change significantly in response to cholinergic receptor stimulation. These findings indicate differential cytoskeletal/membrane recruitment of actin- and integrin-binding proteins in response to cholinergic receptor stimulation in intact airway smooth muscle. alpha-Actinin, talin, and metavinculin appear to be key cytoskeletal proteins involved in the recruitment process.

Isoprenylcysteine Carboxyl Methyltransferase Modulates Endothelial Monolayer Permeability

RhoA and Rac1 regulate formation of stress fibers and intercellular junctions, thus modulating endothelial monolayer permeability. Posttranslational modifications of RhoA and Rac1 regulate enzyme activity and subcellular localization, resulting in altered cellular function. The role of RhoA and Rac1 carboxyl methylation in modulating endothelial monolayer permeability is not known. In this study, we found that inhibition of isoprenylcysteine-O-carboxyl methyltransferase (ICMT) with adenosine plus homocysteine or N-acetyl-S-geranylgeranyl-l-cysteine decreased RhoA carboxyl methylation, RhoA activity, and endothelial monolayer permeability, suggesting that RhoA carboxyl methylation may play a role in the ICMT-modulated monolayer permeability. Similar studies showed no effect of ICMT inhibition on Rac1 carboxyl methylation or localization. Bovine pulmonary artery endothelial cells (PAECs) stably overexpressing ICMT-GFP cDNA were established to determine if increased ICMT expression could alter RhoA or Rac1 carboxyl methylation, activation, and endothelial monolayer permeability. PAECs stably overexpressing ICMT demonstrated increased RhoA carboxyl methylation, membrane-bound RhoA, and RhoA activity. Additionally, PAECs stably overexpressing ICMT had diminished VE-cadherin and beta-catenin at intercellular junctions, with resultant intercellular gap formation, as well as enhanced monolayer permeability. These effects were blunted by adenosine plus homocysteine and by inhibition of RhoA, but not by inhibition of Rac1. These results indicate that ICMT modulates endothelial monolayer permeability by altering RhoA carboxyl methylation and activation, thus changing the organization of intercellular junctions. Therefore, carboxyl methylation of RhoA may modulate endothelial barrier function.

Thrombin and phenotypic modulation of the endothelium

Thrombin signaling in the endothelium is linked to multiple phenotypic changes, including alterations in permeability, vasomotor tone, and leukocyte trafficking. The thrombin signal is transduced, at least in part, at the level of gene transcription. In this review, we focus on the role of thrombin signaling and transcriptional networks in mediating downstream gene expression and endothelial phenotype. In addition, we report the results of DNA microarrays in control and thrombin-treated endothelial cells. We conclude that (1) thrombin induces the upregulation and downregulation of multiple genes in the endothelium, (2) thrombin-mediated gene expression involves a multitude of transcription factors, and (3) future breakthroughs in the field will depend on a better understanding of the spatial and temporal dynamics of these transcriptional networks.

Signal transduction pathways activated in human pulmonary endothelial cells by OxPAPC, a bioactive component of oxidized lipoproteins

The bioactive component of mildly oxidized low-density lipoproteins, oxidized 1-palmitoyl-2-arachidonoyl-sn-glycero-3-phosphorylcholine (OxPAPC), activates tissue factor expression and monocyte adhesion to endothelial cells (EC) from systemic circulation, but blocks expression of inflammatory adhesion molecules (VCAM, E-selectin) and neutrophil adhesion associated with EC acute inflammatory response to bacterial lypopolysacharide (LPS). Due to constant exposure to oxygen free radicals, lipids in the injured lung are especially prone to oxidative modification and increased OxPAPC generation. In this study, we focused on OxPAPC-mediated intracellular signaling mechanisms that lead to physiological responses in pulmonary endothelial cells. Our results demonstrate that OxPAPC treatment activated in a time-dependent fashion protein kinase C (PKC), protein kinase A (PKA), Raf/MEK1,2/Erk-1,2 MAP kinase cascade, JNK MAP kinase and transient protein tyrosine phosphorylation in human pulmonary artery endothelial cells (HPAEC), whereas nonoxidized PAPC was without effect. Pharmacological inhibition of PKC and tyrosine kinases blocked activation of Erk-1,2 kinase cascade upstream of Raf. OxPAPC did not affect myosin light chain (MLC) phosphorylation, but increased phosphorylation of cofillin, a molecular regulator of actin polymerization. Finally, OxPAPC induced p60Src-dependent tyrosine phosphorylation of focal adhesion proteins paxillin and FAK. Our results suggest a critical involvement of PKC and tyrosine phosphorylation in OxPAPC-induced activation of Erk-1,2 MAP kinase cascade associated with regulation of specific gene expression, and demonstrate rapid phosphorylation of cytoskeletal proteins, which indicates OxPAPC-induced EC remodeling.

Involvement of PKCdelta and PKD in pulmonary microvascular endothelial cell hyperpermeability

The involvement of PKC, the isoforms of which are categorized into three subtypes: conventional (alpha, betaI, betaII, and gamma), novel [delta, epsilon, eta, and mu (also known as PKD), theta], and atypical (zeta and iota/lambda), in the regulation of endothelial monolayer integrity is well documented. However, isoform activity varies among different cell types. Our goal was to reveal isoform-specific PKC activity in the microvascular endothelium in response to phorbol 12-myristate 13-acetate (PMA) and diacylglycerol (DAG). Isoform activity was demonstrated by cytosol-to-membrane translocation after PMA treatment and phosphorylation of the myristoylated alanine-rich C kinase substrate (MARCKS) protein after PMA and DAG treatment. Specific isoforms were inhibited by using both antisense oligonucleotides and pharmacological agents. The data showed partial cytosol-to-membrane translocation of isoforms alpha, betaI, and epsilon and complete translocation of PKCdelta and PKD in response to PMA. Furthermore, antisense treatment and pharmacological studies indicated that the novel isoform PKCdelta and PKD are both required for PMA- and DAG-induced MARCKS phosphorylation and hyperpermeability in pulmonary microvascular endothelial cells, whereas isoforms alpha, betaI, and epsilon were dispensable with regard to these same phenomena.