Protein kinase C beta modulates thrombin-induced Ca2+ signaling and endothelial permeability increase

Interrelation between ROS and Ca2+ in aging and age-related diseases

Calcium (Ca2+) and reactive oxygen species (ROS) are versatile signaling molecules coordinating physiological and pathophysiological processes. While channels and pumps shuttle Ca2+ ions between extracellular space, cytosol and cellular compartments, short-lived and highly reactive ROS are constantly generated by various production sites within the cell. Ca2+ controls membrane potential, modulates mitochondrial adenosine triphosphate (ATP) production and affects proteins like calcineurin (CaN) or calmodulin (CaM), which, in turn, have a wide area of action. Overwhelming Ca2+ levels within mitochondria efficiently induce and trigger cell death. In contrast, ROS comprise a diverse group of relatively unstable molecules with an odd number of electrons that abstract electrons from other molecules to gain stability. Depending on the type and produced amount, ROS act either as signaling molecules by affecting target proteins or as harmful oxidative stressors by damaging cellular components. Due to their wide range of actions, it is little wonder that Ca2+ and ROS signaling pathways overlap and impact one another. Growing evidence suggests a crucial implication of this mutual interplay on the development and enhancement of age-related disorders, including cardiovascular and neurodegenerative diseases as well as cancer.

Effects of preconditioning with sevoflurane on TNF-α-induced permeability and activation of p38 MAPK in rat pulmonary microvascular endothelial cells

Preconditioning with sevoflurane (SPC) diminishes effusion of rat alveolar membrane during inflammation. It is not clear whether this preconditioning directly inhibits permeability of pulmonary microvascular endothelial cell (PMVEC) monolayer. In this article, we evaluated effects of SPC on permeability of PMVEC monolayer and identified signaling pathways involved in these effects. PMVEC monolayer was exposed to different conditions (5-hydroxydecanoate (5-HD), TNF-α, SPC, SPC with subsequent exposure to TNF-α and 5-HD, and SPC with subsequent exposure to TNF-α alone), and the permeability of PMVEC monolayer was assessed using FITC-bovine serum albumin (ELISA). Expression of ICAM-1 (Western blot and RT-PCR) and activation of p38 MAPK (Western blot) were also assessed. Compared to the TNF-α group, permeability of PMVEC monolayer in the SPC + TNF-α group was significantly lower. Activation of p38 MAPK was also diminished in the TNF-α group. Pre-treatment with 5-HD reverted beneficial effects of SPC. Expression of ICAM-1 was not modulated by any of the tested experimental exposures. The results of this study demonstrate that SPC is capable of diminishing the TNF-α-induced increase of permeability of PMVEC monolayer, and that this beneficial effect is partly reversed by 5-HD. Further, SPC suppresses activation of p38 MAPK.

MCP-1: chemoattractant with a role beyond immunity: a review

BACKGROUND

Monocyte Chemoattractant Protein (MCP)-1, a potent monocyte attractant, is a member of the CC chemokine subfamily. MCP-1 exerts its effects through binding to G-protein-coupled receptors on the surface of leukocytes targeted for activation and migration. Role of MCP-1 and its receptor CCR2 in monocyte recruitment during infection or under other inflammatory conditions is well known.

METHOD

A comprehensive literature search was conducted from the websites of the National Library of Medicine (http://www.ncbl.nlm.nih.gov) and Pubmed Central, the US National Library of Medicine's digital archive of life sciences literature (http://www.pubmedcentral.nih.gov/). The data was assessed from books and journals that published relevant articles in this field.

RESULT

Recent and ongoing research indicates the role of MCP-1 in various allergic conditions, immunodeficiency diseases, bone remodelling, and permeability of blood - brain barrier, atherosclerosis, nephropathies and tumors.

CONCLUSION

MCP-1 plays an important role in pathogenesis of various disease states and hence MCP-1 inhibition may have beneficial effects in such conditions.

Diabetic macular oedema: physical, physiological and molecular factors contribute to this pathological process

Diabetic macular oedema (DMO) is an important cause of vision loss in patients with diabetes mellitus. The underlying mechanisms of DMO, on both macrocellular and microcellular levels, are discussed in this review. The pathophysiology of DMO can be described as a process whereby hyperglycaemia leads to overlapping and inter-related pathways that play a role not only in the initial vascular events, but also in the continued tissue insult that leads to chronic DMO. On a macrocellular level, DMO is believed to be in part caused by alterations in hydrostatic pressure, oxygen tension, oncotic pressure and shear stress. Three key components of the microvascular pathways include angiogenic factor expression, inflammation and oxidative stress. These molecular mediators, acting in conjunction with macrocellular factors, which are all stimulated in part by the hyperglycaemia and hypoxia, can have a direct endothelial effect leading to hyperpermeability, disruption of vascular endothelial cell junctions, and leukostasis. The interactions, signalling events and feedback loops between the various molecules are complicated and are not completely understood. However, by attempting to understand the pathways involved in DMO, we can help guide new treatment options targeted towards specific factors or mediators.

Is thrombin a key player in the 'coagulation-atherogenesis' maze?

In addition to its established roles in the haemostatic system, thrombin is an intriguing coagulation protease demonstrating an array of effects on endothelial cells, vascular smooth muscle cells (VSMC), monocytes, and platelets, all of which are involved in the pathophysiology of atherosclerosis. There is mounting evidence that thrombin acts as a powerful modulator of many processes like regulation of vascular tone, permeability, migration and proliferation of VSMC, recruitment of monocytes into the atherosclerotic lesions, induction of diverse pro-inflammatory markers, and all of these are related to the progression of cardiovascular disease. Recent studies in transgenic mice models indicate that the deletion of the natural thrombin inhibitor heparin cofactor II promotes an accelerated atherogenic state. Moreover, the reduction of thrombin activity levels in apolipoprotein E-deficient mice, because of the administration of the direct thrombin inhibitor melagatran, attenuates plaque progression and promotes stability in advanced atherosclerotic lesions. The combined evidence points to thrombin as a pivotal contributor to vascular pathophysiology. Considering the clinical development of selective anticoagulants including direct thrombin inhibitors, it is a relevant moment to review the different thrombin-induced mechanisms that contribute to the initiation, formation, progression, and destabilization of atherosclerotic plaques.

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.

Role of protein kinase C isozymes in the regulation of alpha1-adrenergic receptor-mediated contractions in ovine uterine arteries

Previously, we demonstrated that activation of protein kinase C (PRKC) enhanced alpha(1)-adrenergic receptor-induced contractions in nonpregnant ovine uterine arteries but inhibited the contractions in pregnant ovine uterine arteries. The present study tested the hypothesis that differential regulation of PRKC isozyme activities contributes to the different effects of phorbol 12, 13-dibutyrate (PDBu) on alpha(1)-adrenergic receptor-mediated contractions between the pregnant and nonpregnant ovine uterine arteries. Phenylephrine-induced contractions of ovine nonpregnant and pregnant uterine arteries were determined in the absence or presence of the PRKC activator PDBu and/or in combination with conventional and novel PRKC isozyme inhibitor GF109203X, PRKC isozyme-selective inhibitory peptides for conventional PRKC, PRKCB1, PRKCB2, and PRKCE. GF109203X produced a concentration-dependent inhibition of phenylephrine-induced contractions in both nonpregnant and pregnant uterine arteries, and it reversed the PDBu-mediated potentiation and inhibition of phenylephrine-induced contractions in nonpregnant and pregnant uterine artieries, respectively. In addition, PRKCB1, PRKCB2, and PRKCE inhibitory peptides blocked the PDBu-mediated responses in both nonpregnant and pregnant uterine arteries. Western blot analysis showed that PDBu induced a membrane translocation of PRKCA, PRKCB1, PRKCB2, and PRKCE in pregnant uterine arteries, and PRKCB1, PRKCB2, and PRKCE in nonpregnant uterine arteries. The results disprove the hypothesis that the dichotomy of PRKC mechanisms in the regulation of alpha(1)-adrenergic receptor-induced contractions in nonpregnant and pregnant uterine arteries is caused by the activation of different PRKC isozymes, and suggest downstream mechanisms of differential subcellular distributions for the distinct functional effects of PRKC isozymes in the adaptation of uterine arteries to pregnancy.

Regulation of alpha1-adrenoceptor-mediated contractions of uterine arteries by PKC: effect of pregnancy

Protein kinase C (PKC) plays an important role in the regulation of uterine artery contractility and its adaptation to pregnancy. The present study tested the hypothesis that PKC differentially regulates alpha(1)-adrenoceptor-mediated contractions of uterine arteries isolated from nonpregnant (NPUA) and near-term pregnant (PUA) sheep. Phenylephrine-induced contractions of NPUA and PUA sheep were determined in the absence or presence of the PKC activator phorbol 12,13-dibutyrate (PDBu). In NPUA sheep, PDBu produced a concentration-dependent potentiation of phenylephrine-induced contractions and shifted the dose-response curve to the left. In contrast, in PUA sheep, PDBu significantly inhibited phenylephrine-induced contractions and decreased their maximum response. Simultaneous measurement of contractions and intracellular free Ca(2+) concentrations ([Ca(2+)](i)) in the same tissues revealed that PDBu inhibited phenylephrine-induced [Ca(2+)](i) and contractions in PUA sheep. In NPUA sheep, PDBu increased phenylephrine-induced contractions without changing [Ca(2+)](i). Western blot analysis showed six PKC isozymes, alpha, beta(I), beta(II), delta, epsilon, and zeta, in uterine arteries, among which beta(I), beta(II), and zeta isozymes were significantly increased in PUA sheep. In contrast, PKC-alpha was decreased in PUA sheep. In addition, analysis of subcellular distribution revealed a significant decrease in the particulate-to-cytosolic ratio of PKC-epsilon in PUA compared with that in NPUA sheep. The results suggest that pregnancy induces a reversal of PKC regulatory role on alpha(1)-adrenoceptor-mediated contractions from a potentiation in NPUA sheep to an inhibition in PUA sheep. The differential expression of PKC isozymes and their subcellular distribution in uterine arteries appears to play an important role in the regulation of Ca(2+) mobilization and Ca(2+) sensitivity in alpha(1)-adrenoceptor-mediated contractions and their adaptation to pregnancy.

Roles of protein kinase C in regulation of P2X7 receptor-mediated calcium signalling of cultured type-2 astrocyte cell line, RBA-2

The role of protein kinase C (PKC) on regulation of P2X(7) receptor-mediated Ca(2+) signalling was examined on RBA-2 astrocytes. Activation of PKC decreased the receptor-mediated Ca(2+) signalling and the decrease was restored by PKC inhibitors. Down regulation of PKC also caused a decrease in the Ca(2+) signalling. Thus PKC might play a dual role on the P2X(7) receptor signalling. Successive stimulation of the P2X(7) receptor induced a gradual decline of Ca(2+) signalling but PKC inhibitors failed to restore the decline. Nevertheless, PMA stimulated translocation of PKC-alpha, -betaI, -betaII, and -gamma, but only anti-PKC-gamma co-immunoprecipitated the receptors. To examine the role of PKC-gamma, Ca(2+) signalling was measured by Ca(2+) imaging. Our results revealed that the agonist-stimulated Ca(2+) signalling were reduced in the cells that the transfection of either P2X(7) receptor or PKC-gamma morpholino antisense oligo was identified. Thus, we concluded that PKC-gamma interacted with P2X(7) receptor complex and positively regulated the receptor-mediated Ca(2+) signalling.

Investigation of G protein-initiated, Ca2+-dependent release of ATP from endothelial cells

We investigated G protein-stimulated release of ATP from human umbilical vein endothelial cells (HUVECs) using the G protein stimulant compound 48/80. Application of compound 48/80 resulted in dose-dependent ATP evolution from cultured HUVECs. This release was not cytotoxic as demonstrated by a lactate dehydrogenase assay and the ability of the cells to load and retain the viability dye calcein following stimulation. Mastoparan also stimulated release of ATP, further suggesting the process was G-protein initiated. This G protein was insensitive to pertussis toxin and appeared to be of the Gq-subtype. The ATP efflux was completely abolished in the presence of EGTA and thapsigargin signifying a strict Ca2+ dependence. Furthermore, compound 48/80-induced release was significantly decreased in cells pretreated with the phospholipase C inhibitor U73122. Thus, the release pathway appears to proceed through an increase in intracellular Ca2+ via PLC activation. Additionally, the G protein-initiated release was attenuated by pretreatment of the cells with either phorbol ester or indolactam V, both activators of protein kinase C. Finally, ATP release was not affected by treating HUVECs with nitric oxide synthase (NOS) inhibitors or glybenclamide.

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)

Subcortical Ca2+ waves sneaking under the plasma membrane in endothelial cells

Subplasmalemmal Ca2+, dynamically equilibrated with extracellular Ca2+, affects numerous signaling molecules, effectors, and events within this restricted space. We demonstrated the presence of a novel Ca2+ wave propagating beneath the plasma membrane in response to acute elevation of extracellular [Ca2+], by targeting a Ca2+ sensor, cameleon, to the endothelial plasmalemma. These subcortical waves, spatially distinct from classical cytosolic Ca2+ waves, originated in localized regions and propagated throughout the subplasmalemma. Translocation of an expressed GFP fused with a PH domain of PLC from the plasma membrane to the cytosol accompanied these subcortical waves, and U73122 attenuated not only the GFP-PH translocation, but also the peak amplitude of the subcortical Ca2+ waves; this finding suggests the involvement of local IP3 production through PLC-mediated PIP2 hydrolysis in the initiation of these waves. Changes in NO production as well as PKCbeta-GFP translocation from the cytosol to the plasma membrane, but not of GFP-PLA2 to perinuclear endomembranes, were associated with the subplasmalemmal Ca2+ changes. Thus, extracellular Ca2+ maintains the basal PLC activity of the plasma membrane, is involved in the initiation of compartmentalized subcortical Ca2+ waves, and regulates Ca2+-dependent signaling molecules residing in or translocated to the plasma membrane. The full text of this article is available online at http://circres.ahajournals.org.

Potential role of MCP-1 in endothelial cell tight junction 'opening': signaling via Rho and Rho kinase

The expression of the monocyte chemoattractant protein-1 (MCP-1) receptor CCR2 by brain endothelial cells suggests that MCP-1 may have other functions than purely driving leukocyte migration into brain parenchyma during inflammation. This study examines one of these potential novel roles of MCP-1 regulation of endothelial permeability using primary cultures of mouse brain endothelial cells. MCP-1 induces reorganization of actin cytoskeleton (stress fiber formation) and redistribution of tight junction proteins, ZO-1, ZO-2 occludin and claudin-5, from the Triton X-100-soluble to the Triton X-100-insoluble fractions. These morphological changes are associated with a decrease in transendothelial electrical membrane resistance and an increase in [14C]inulin permeability. MCP-1 did not induce these events in brain endothelial cells prepared from mice genotype CCR2-/-. The Rho kinase inhibitor Y27632 and inhibition of Rho (C3 exoenzyme, and dominant negative mutant of Rho, RhoT19N) prevented MCP-1-induced stress fiber assembly, reorganization of tight junction proteins and alterations in endothelial permeability. In all, this suggests that a small GTPase Rho and Rho kinase have a pivotal role in MCP-1-induced junction disarrangement. These data are the first to strongly suggest that MCP-1, via CCR2 present on brain endothelial cells, contributes to increased brain endothelial permeability.

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.

Involvement of proteinase-activated receptor-2 in mast cell tryptase-induced barrier dysfunction in bovine aortic endothelial cells

We report here a direct modulation by mast cell tryptase of endothelial barrier function through activation of proteinase-activated receptor-2 (PAR-2). In cultured bovine aortic endothelial cells (BAECs), tryptase, trypsin and PAR-2 activating peptide impaired the barrier function as determined by the permeability of protein-conjugated Evans blue. The tryptase-induced barrier dysfunction was completely blocked by U73122, and partially reversed by xestospongin C, calphostin C or Y27632. The intracellular Ca(2+) was elevated by tryptase. It was notable that ioxaglate, a contrast material that degranulates mast cells, markedly increased the permeability when applied to BAECs in combination with mast cells, an action that was blocked by nafamostat, a potent tryptase inhibitor. Immunofluorescence analysis showed that actin stress fibre formation and disruption of VE-cadherin were observed after exposure to tryptase or ioxaglate in combination with mast cells. Therefore, it is suggested that mast cell tryptase impairs endothelial barrier function through activation of endothelial PAR-2 in a manner dependent on the phospholipase C activity.

Inhibition of protein kinase C decreases prostaglandin-induced breakdown of the blood-retinal barrier

Breakdown of the blood-retinal barrier (BRB) occurs in several retinal diseases and is a major cause of visual loss. Vascular endothelial growth factor (VEGF) has been implicated as a cause of BRB breakdown in diabetic retinopathy and other ischemic retinopathies, and there is evidence to suggest that other vasopermeability factors may act indirectly through VEGF. In this study, we investigated the effect of several receptor kinase inhibitors on BRB breakdown resulting from VEGF, tumor necrosis factor-alpha (TNF-alpha), interleukin-1beta (IL-1beta), insulin-like growth factor-1 (IGF-1), prostaglandin E1 (PGE(1)), or PGE(2). Inhibitors of VEGF receptor kinase, including PKC412, PTK787, and SU1498, decreased VEGF-induced breakdown of the BRB. None of the inhibitors blocked leakage caused by TNF-alpha, IL-1beta, or IGF-1 and only PKC412, an inhibitor of protein kinase C (PKC) as well as VEGF and platelet-derived growth factor (PDGF) receptor kinases, decreased leakage caused by prostaglandins. Since the other inhibitors of VEGF and/or PDGF receptor kinases that do not also inhibit PKC had no effect on prostaglandin-induced breakdown of the BRB, these data implicate PKC in retinal vascular leakage caused by prostaglandins. PKC412 may be useful for treatment of post-operative and inflammatory macular edema, in which prostaglandins play a role, as well as macular edema associated with ischemic retinopathies.

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

Endothelial barrier dysfunction is involved in a variety of diseased states. We investigated the role of protein kinase C (PKC) in monolayer permeability using endothelial cells (EC) overexpressing PKC alpha (PKC alpha EC), PKC delta (PKC delta EC) or vector (vector control EC) cDNAs. Thrombin induced permeability changes in all EC, and induced significantly elevated rates of monolayer permeability in PKC alpha EC. Conversely, the basal level of permeability was significantly blunted in PKC delta EC, resulting in diminished thrombin-induced changes in permeability. PKC inhibitors, Gö6976 and rottlerin, reversed the effects of PKC alpha and PKC delta overexpression on permeability, respectively. Immunoblot analyses demonstrated significantly less beta-catenin associated with the cytoskeletal subcellular fraction in thrombin-treated PKC alpha EC, an effect blocked by pretreatment with Gö6976. PKC delta EC contained significantly greater numbers of focal contacts per cell. Thrombin enhanced RhoA GTPase activity in all EC; with a 3-fold greater level of activity in PKC delta EC. Rottlerin significantly blunted RhoA GTPase activity in all EC. Overexpression of RhoA dominant-negative cDNA diminished the size and number of focal contacts in EC, and significantly enhanced the basal rate of PKC delta EC monolayer permeability. These findings demonstrate that monolayer permeability changes are differentially regulated by PKC isoenzymes, suggesting that PKC alpha promotes endothelial barrier dysfunction and PKC delta enhances basal endothelial barrier function.

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.

Critical involvement of p38 MAP kinase in pertussis toxin-induced cytoskeletal reorganization and lung permeability

Bordetella pertussis is an important cause of infection in humans worldwide, with full expression of the syndrome associated with characteristic increases in lung permeability and airway edema. The exact cellular mechanisms by which pertussis toxin (PTX) exerts pulmonary toxicity remain unknown, but may involve its ability to ADP-ribosylate-specific G-proteins. We determined that PTX directly and reproducibly reduced lung endothelial and epithelial cell barrier function in vitro and in vivo assessed by decreases in transmonolayer electrical resistance (TER) and isolated perfused lung preparations. Alterations in lung permeability began approximately 30 min after PTX and were dependent on intrinsic ADP-ribosyltransferase activity, as neither the cell binding beta-oligomer subunit or a genetically engineered PTX mutant (devoid of ADP-ribosyltransferase activity) altered TER. PTX-induced barrier dysfunction was associated with mild increases in F-actin stress fiber formation and causally linked to p38 MAP kinase activities. PTX-mediated p38 MAP kinase activation did not involve either p42/p44 ERK, p60src, Rho family of GTPases, or phosphatidylinositol-3' kinase pathways. PTX-mediated decreases in TER were temporally linked to phosphorylation of the actin binding proteins Hsp27 and caldesmon, known substrates for the Ser/Thr kinase MAPKAP2, whose activity is regulated by p38 MAP kinase. In addition to defining novel signaling pathways involved in PTX-induced respiratory pathophysiology, these data suggest that the direct cell-activating effects of PTX be carefully considered as a potential limitation to its use as a tool in signal transduction analysis.

Intracellular signalling involved in modulating human endothelial barrier function

The endothelium dynamically regulates the extravasation of hormones, macromolecules and other solutes. In pathological conditions, endothelial hyperpermeability can be induced by vasoactive agents, which induce tiny leakage sites between the cells, and by cytokines, in particular vascular endothelial growth factor, which increase the exchange of plasma proteins by vesicles and intracellular pores. It is generally believed that the interaction of actin and non-muscle myosin in the periphery of the endothelial cell, and the destabilization of endothelial junctions, are required for endothelial hyperpermeability induced by vasoactive agents. Transient short-term hyperpermeability induced by histamine involves Ca2+/calmodulin-dependent activation of the myosin light chain (MLC) kinase. Prolonged elevated permeability induced by thrombin in addition involves activation of the small GTPase RhoA and Rho kinase, which inhibits dephosphorylation of MLC. It also involves the action of other protein kinases. Several mechanisms can increase endothelial barrier function, depending on the tissue affected and the cause of hyperpermeability. They include blockage of specific receptors, and elevation of cyclic AMP by agents such as beta2-adrenergic agents. Depending on the vascular bed, nitric oxide and cyclic GMP can counteract or aggravate endothelial hyperpermeability. Finally, inhibitors of RhoA activation and Rho kinase represent a potentially valuable group of agents with endothelial hyperpermeability-reducing properties.

Interleukin-6 causes endothelial barrier dysfunction via the protein kinase C pathway

BACKGROUND

Elevated levels of interleukin-6 (IL-6) have been identified in a variety of systemic inflammatory states that are associated with endothelial barrier dysfunction, but the specific effect of IL-6 on endothelial permeability and the mechanism of action have not been fully examined. The current study evaluated the effect of IL-6 on endothelial permeability and on the distribution of the tight junctional protein ZO-1 and cytoskeletal actin. We also assessed the role of protein kinase C (PKC) in this process.

METHODS

Confluent monolayers of human umbilical vein endothelial cells (n = 6) were exposed to IL-6 (50-500 ng/ml) in the presence or absence of the PKC inhibitor Gö6976 (0.1 microM). Transendothelial electrical resistance (TEER) was measured at the onset of exposure and at 6-h intervals and compared with that of control cells using ANOVA with a Bonferroni multiple comparison test. Additional monolayers were exposed to IL-6, stained for ZO-1 and F-actin, and evaluated via fluorescence microscopy.

RESULTS

Interleukin-6 increased endothelial permeability as measured by TEER in a dose- and time-dependent manner. In the presence of PKC inhibitor, the IL-6-mediated increase in permeability was attenuated (18-h TEER 73% of control with IL-6 exposure vs 95% of control with IL-6 + Gö6976 inhibitor, P < 0.01). Microscopy revealed that permeability changes were accompanied by a redistribution of the tight junctional protein ZO-1 and cytoskeletal actin, increased cell contraction, and disorganization of the intercellular borders. Conclusions. The inflammatory cytokine IL-6 is an important mediator of increased endothelial permeability via alterations in the ultrastructural distribution of tight junctions and morphologic changes in cell shape. PKC is a critical intracellular messenger in these IL-6-mediated changes. A better understanding of this mechanism should allow the determination of rational treatment strategies for endothelial barrier dysfunction which occurs in inflammatory states.

Update on pulmonary edema: the role and regulation of endothelial barrier function

Discovery of the pathophysiologic mechanisms leading to pulmonary edema and identification of effective strategies for prevention remain significant clinical concerns. Endothelial barrier function is a key component for maintenance of the integrity of the vascular boundary in the lung, particularly since the gas exchange surface area of the alveolar-capillary membrane is large. This review is focused on new insights in the pulmonary endothelial response to injury and recovery, reversible activation by edemagenic agents, and the biochemical/structural basis for regulation of endothelial barrier function. This information is discussed in the context of fundamental concepts of lung fluid balance and pulmonary function.

Protein phosphatase 2B inhibitor potentiates endothelial PKC activity and barrier dysfunction

Serine/threonine (Ser/Thr) protein phosphatases (PPs) are implicated in the recovery from endothelial barrier dysfunction caused by inflammatory mediators. We hypothesized that Ser/Thr PPs may regulate protein kinase C (PKC), a critical signaling molecule in barrier dysfunction, in the promotion of barrier recovery. Western analysis indicated that bovine pulmonary microvascular endothelial cells (BPMECs) expressed the three major Ser/Thr PPs, PP1, PP2A, and PP2B. Pretreatment with 100 ng/ml of FK506 (a PP2B inhibitor) but not with the PP1 and PP2A inhibitors calyculin A or okadaic acid potentiated the thrombin-induced increase in PKC phosphotransferase activity. FK506 also potentiated thrombin-induced PKC-alpha but not PKC-beta phosphorylation. FK506 but not calyculin A or okadaic acid inhibited recovery from the thrombin-induced decrease in transendothelial resistance. Neither FK506 nor okadaic acid altered the thrombin-induced resistance decrease, whereas calyculin A potentiated the decrease. Downregulation of PKC with phorbol 12-myristate 13-acetate rescued the FK506-mediated inhibition of recovery, which was consistent with the finding that the thrombin-induced phosphorylation of PKC-alpha was reduced during the recovery phase. These results indicated that PP2B may play a physiologically important role in returning endothelial barrier dysfunction to normal through the regulation of PKC.

Protein transfection of intact microvessels specifically modulates vasoreactivity and permeability

Precise regulation of microvascular tone and barrier function is essential for proper coronary perfusion and performance. Agonist-induced alterations in either or both of these functions ultimately lead to microcirculatory dysfunction and cardiac insufficiency. Two important pathways involved in regulating vasomotor response and barrier function are the activation of nitric oxide synthase (NOS) and upregulation of protein kinase C (PKC). To date, studies of these two signaling proteins have relied mainly on pharmacological approaches. Unfortunately, the specificity of various inhibitors can be cause for concern. In order to address this problem, a protein transfection technique we developed for cultured endothelial cells has been modified and applied to isolated, intact coronary microvessels. Our results from green fluorescent protein transfection in arterioles and venules showed that this procedure could be used to introduce proteins into the microvascular wall. By transfecting inhibitor peptides against NOS and PKC into coronary arterioles and venules, we have been able to determine the specific roles of these two enzymes in vasodilation and hyperpermeability responses.

Protein kinase C-alpha signals rho-guanine nucleotide dissociation inhibitor phosphorylation and rho activation and regulates the endothelial cell barrier function

The Rho-GDP guanine nucleotide dissociation inhibitor (GDI) complexes with the GDP-bound form of Rho and inhibits its activation. We investigated the role of protein kinase C (PKC) isozymes in the mechanism of Rho activation and in signaling the loss of endothelial barrier function. Thrombin and phorbol 12-myristate 13-acetate induced rapid phosphorylation of GDI and the activation of Rho-A in human umbilical venular endothelial cells. Inhibition of PKC by chelerythrine chloride abrogated the thrombin-induced GDI phosphorylation and Rho activation. Depletion of PKC prevented the thrombin-induced GDI phosphorylation and Rho activation, thereby indicating that these events occurred downstream of phorbol ester-sensitive PKC isozyme activation. The depletion of PKC or inhibition of Rho by C3 toxin also prevented the thrombin-induced decrease in transendothelial electrical resistance (a measure of increased transendothelial permeability), thus indicating that PKC-induced barrier dysfunction was mediated through Rho-dependent pathway. Using inhibitors and dominant-negative mutants, we found that Rho activation was regulated by PKC-alpha. Moreover, the stimulation of human umbilical venular endothelial cells with thrombin induced rapid association of PKC-alpha with Rho. Activated PKC-alpha but not PKC-epsilon induced marked phosphorylation of GDI in vitro. Taken together, these results indicate that PKC-alpha is critical in regulating GDI phosphorylation, Rho activation, and in signaling Rho-dependent endothelial barrier dysfunction.

Depletion of protein kinase Cepsilon in normal and scleroderma lung fibroblasts has opposite effects on tenascin expression

OBJECTIVE

To determine whether the extracellular matrix protein tenascin-C (TN-C) is overexpressed in lung fibroblasts from systemic sclerosis (SSc) patients, the molecular mechanisms regulating TN-C secretion in SSc and normal lung fibroblasts, and how these processes might contribute to lung fibrosis in SSc patients.

METHODS

TN-C secretion by SSc and normal fibroblasts was compared in vivo (in bronchoalveolar lavage [BAL] fluid) and in vitro (in culture medium). The ability of thrombin to induce TN-C was confirmed at both the protein and the messenger RNA (mRNA) level. The role of protein kinase Cepsilon (PKCepsilon) in the expression of TN-C was evaluated by determining the effects of thrombin on PKCepsilon levels and by directly manipulating PKCepsilon levels via the use of antisense oligonucleotides.

RESULTS

BAL fluid from SSc patients contained high levels of TN-C, whereas that from normal subjects contained little or no TN-C. In vitro, SSc lung fibroblasts expressed much higher amounts of TN-C than did normal lung fibroblasts. Consistent with the idea that thrombin is a physiologic inducer of TN-C, thrombin stimulated TN-C mRNA and protein expression in both SSc and normal lung fibroblasts by a mechanism that required proteolytic cleavage of the thrombin receptor. Surprisingly, thrombin treatment and antisense oligonucleotide-mediated depletion of PKCepsilon indicated that TN-C expression is regulated via opposite signaling mechanisms in SSc and normal cells. In SSc lung fibroblasts, thrombin decreased PKCepsilon levels, and the decreased PKCepsilon induced TN-C secretion; in normal fibroblasts, thrombin increased PKCepsilon levels, and the increased PKCepsilon induced TN-C secretion. Normal and SSc lung fibroblasts also differed in the subcellular localization of PKCepsilon, both before and after thrombin treatment.

CONCLUSION

These studies are the first to demonstrate that thrombin is a potent simulator of TN-C in lung fibroblasts and that PKCepsilon is a critical regulator of TN-C protein levels in these cells. Furthermore, our results indicate that both the regulation of PKCepsilon levels by thrombin and the regulation of TN-C levels by PKCepsilon are defective in SSc lung fibroblasts.

Oxidant stress and endothelial cell dysfunction

Reactive oxygen species (ROS) are generated at sites of inflammation and injury, and at low levels, ROS can function as signaling molecules participating as signaling intermediates in regulation of fundamental cell activities such as cell growth and cell adaptation responses, whereas at higher concentrations, ROS can cause cellular injury and death. The vascular endothelium, which regulates the passage of macromolecules and circulating cells from blood to tissues, is a major target of oxidant stress, playing a critical role in the pathophysiology of several vascular diseases and disorders. Specifically, oxidant stress increases vascular endothelial permeability and promotes leukocyte adhesion, which are coupled with alterations in endothelial signal transduction and redox-regulated transcription factors such as activator protein-1 and nuclear factor-kappaB. This review discusses recent findings on the cellular and molecular mechanisms by which ROS signal events leading to impairment of endothelial barrier function and promotion of leukocyte adhesion. Particular emphasis is placed on the regulation of cell-cell and cell-surface adhesion molecules, the actin cytoskeleton, key protein kinases, and signal transduction events.

Role of ras-dependent ERK activation in phorbol ester-induced endothelial cell barrier dysfunction

The treatment of endothelial cell monolayers with phorbol 12-myristate 13-acetate (PMA), a direct protein kinase C (PKC) activator, leads to disruption of endothelial cell monolayer integrity and intercellular gap formation. Selective inhibition of PKC (with bisindolylmaleimide) and extracellular signal-regulated kinases (ERKs; with PD-98059, olomoucine, or ERK antisense oligonucleotides) significantly attenuated PMA-induced reductions in transmonolayer electrical resistance consistent with PKC- and ERK-mediated endothelial cell barrier regulation. An inhibitor of the dual-specificity ERK kinase (MEK), PD-98059, completely abolished PMA-induced ERK activation. PMA also produced significant time-dependent increases in the activity of Raf-1, a Ser/Thr kinase known to activate MEK ( approximately 6-fold increase over basal level). Similarly, PMA increased the activity of Ras, which binds and activates Raf-1 ( approximately 80% increase over basal level). The Ras inhibitor farnesyltransferase inhibitor III (100 microM for 3 h) completely abolished PMA-induced Raf-1 activation. Taken together, these data suggest that the sequential activation of Ras, Raf-1, and MEK are involved in PKC-dependent endothelial cell barrier regulation.

Protein kinase C-alpha mediates endothelial barrier dysfunction induced by TNF-alpha

We tested the hypothesis that protein kinase C-alpha (PKC-alpha) mediates tumor necrosis factor-alpha (TNF-alpha)-induced alterations in permeability of pulmonary microvessel endothelial monolayers (PEM). The permeability of PEM was assessed by the clearance rate of Evans blue-labeled albumin. PEM lysates were analyzed for PKC-alpha mRNA (Northern cDNA blot), protein (Western immunoblot), and activity (translocation and phosphorylation of myristoylated arginine-rich C kinase substrate). Incubation of PEM with TNF-alpha (1,000 U/ml) for 4 h resulted in increases in 1) PKC-alpha protein, 2) cytoskeletal-associated PKC-alpha, 3) PKC-alpha activity, and 4) permeability to albumin. The TNF-alpha-induced increase in PKC-alpha protein, PKC-alpha activity, and permeability was prevented by a 4-h pretreatment with PKC-alpha antisense oligonucleotide but not by the scrambled nonsense oligonucleotide. The TNF-alpha-induced increase in permeability to albumin was prevented by myristoylated protein kinase C inhibitor (an inhibitor of PKC-alpha/beta, 100 microM) and calphostin (an inhibitor of the classic and novel PKC isotypes, 200 nM). The treatment with calphostin from 0.5 to 3.0 h after TNF-alpha still prevented barrier dysfunction induced by 4 h of TNF-alpha treatment. The data indicate that prolonged activation of PKC-alpha, maintained by a translation-dependent pool of PKC-alpha protein, mediates TNF-alpha-induced increases in endothelial permeability in PEM.

Staurosporine enhances parathyroid hormone-induced calcium signal in UMR-106 osteoblastic cells

Parathyroid hormone (PTH) treatment of bone and kidney-derived cells not only activates adenylyl cyclase but also increases intracellular free calcium, and translocates protein kinase C (PKC) from cytosol to plasma membranes. We have found that acute phorbol ester pretreatment significantly decreases PTH-induced calcium transients and the effect of phorbol ester was antagonized by staurosporine (ST). Although the major effect of ST in that study was the reversal of the action of phorbol ester, it appeared that ST may also have promoted the effect of PTH directly. To further investigate the observation, we examined the effect of ST on the intracellular calcium transients induced by PTH and alpha-thrombin (alpha-TH). For calcium transient experiments, UMR-106 cells were loaded with 2 mM fluo-acetoxymethylester for 30 min at room temperature. The cells were then washed and suspended in buffer containing 1 mM calcium. Fluorescence was detected at 530 nm, with excitation at 505 nm. ST alone did not cause calcium transients, but enhanced the transients elicited by PTH when added 5 min before the hormone. Another protein kinase inhibitor H-7 likewise enhanced the calcium responses elicited by PTH, while genistein did not affect PTH response. Calcium transients elicited by alpha-TH were also enhanced by ST. The results suggest that there might be tonically activated endogenous protein kinase(s) which inhibit calcium signaling of some calcemic agents.