Thrombin-mediated permeability of human microvascular pulmonary endothelial cells is calcium dependent

Purification and characterization of a novel thermostable anticoagulant protein from medicinal leech Whitmania pigra Whitman

ETHNOPHARMACOLOGICAL RELEVANCE

The prevalence of cardiovascular disease (CVD) is increasing worldwide. Despite significant improvements in novel targeted treatment agents, natural products purified from medicinal animals with minimal side effects have attracted much attention. Several native proteins explored from suck-blood leeches, such as non-thermostable hirudin and its variants, revealed potent anticoagulant activity. Traditional Chinese medicine clinics have proved that non-suck-blood leech Whitmania pigra Whitman (W. pigra) also played notable roles in CVD treatments even after decoction. However, only a few natural proteins and peptides have been identified from the fresh material of this medicinal species.

AIM OF THE STUDY

We aimed to purify and characterize thermostable anticoagulant proteins from W. pigra for further development of a therapeutic agent for thrombosis.

MATERIALS AND METHODS

W. pigra crude extract was prepared by decoction in water. Anticoagulant proteins were purified by DEAE cellulose DE-52, Sephadex G-75, and reversed-phase liquid chromatography sequentially and analyzed by SDS-PAGE and LC-MS/MS for structural information. In addition, we conducted in vitro anticoagulant experiments, including plasma recalcification time (PRT) assay, fibrinolytic assay, activated partial thromboplastin time (APTT), prothrombin time (PT), thrombin time (TT), fibrinogen (Fib) assay, and cell viability assays. Furthermore, a carrageenan-induced chronic thromboembolism model was employed in ICR mice, and four coagulation factors (APTT, PT, TT, and Fib) activities were determined after intragastric administration.

RESULTS

The anticoagulant protein WP-77 has a relative molecular weight of ca. 20.8 kDa. It was effective over a broad temperature range from 20 °C to 100 °C and a pH 2-8 condition. The anticoagulant activity of WP-77 was retained after incubation with pepsin but was greatly inhibited by trypsin (P < 0.01). It significantly prolonged APTT and TT (P < 0.05) but had little effect on PT and Fib in vitro. Furthermore, WP-77 of a low concentration resulted in the recovery of injured EA.hy926 by thrombin. The protein also significantly prolonged APTT and TT (P < 0.01) and inhibited thrombus formation in carrageenan-induced thrombosis mice, demonstrating its antithrombotic effect in vivo.

CONCLUSION

Our results suggest that WP-77 from W. pigra plays a distinct role in treating thrombotic diseases, and it is an essential substance of anticoagulant activity of non-suck-blood medicinal leeches. This thermostable anticoagulant protein could be a promising candidate for the development of clinical antithrombosis medicines.

Endothelial Dysfunction in Patients with Severe Acute Pancreatitis: Improved by Continuous Blood Purification Therapy

Objectives.

Endothelium dysfunction is one of the critical pathophysiologic disorders in patients with severe acute pancreatitis (SAP). To investigate the effect of continuous blood purification (CBP) on endothelial function, we conducted a prospective study of 20 patients with SAP, 9 of whom had evidence of sepsis.

Methods.

All patients underwent CVVH for 72 h. Soluble E-selectin (sE-selectin), soluble thrombomodulin, permeability of the endothelial monolayer, and endothelial intracellular calcium ([Ca2+]i) levels were used as the markers for the assessment of endothelial function and the effect of CBP therapy in patients with SAP. Blood samples were taken from the patients at 0, 2, 12, 24, 48, and 72 h during CVVH therapy. sE-selectin and thrombomoduiln were measured by ELISA. The endothelial permeability and activation were evaluated using cultured endothelial monolayer and intracellular Ca2+ concentration.

Results.

The results showed that during CVVH treatment, the hemodynamics and mean arterial pressure (MAP) were stable. The Acute Physiology and Chronic Health Evaluation (APACHE) II score was improved significantly after CVVH. Endothelial dysfunction was evident in patients with SAP as compared to normal controls. Patients with SAP had increased levels of sE-selectin, endothelial permeability and intracellular [Ca2+]i, which was higher in patients with sepsis than in those without sepsis. The level of thrombomodulin showed a tendency to increase; however, these changes were not significant between SAP patients and controls. After CBP treatment, sE-selectin levels substantially decreased in all patients. CBP treatment also significantly diminished the endothelial permeability and decreased the intracellular [Ca2+] concentration.

Conclusions.

These data demonstrate that endothelial dysfunction is present in patients with SAP and the degree of endothelial damage may be correlated with the disease severity. CBP therapy can not only improve the general conditions, as measured by the APACHE II score, but also effectively improve endothelial dysfunction.

Protective role of FKBP51 in calcium entry-induced endothelial barrier disruption

Pulmonary artery endothelial cells (PAECs) express a cation current, I_SOC (store-operated calcium entry current), which when activated permits calcium entry leading to inter-endothelial cell gap formation. The large molecular weight immunophilin FKBP51 inhibits I_SOC but not other calcium entry pathways in PAECs. However, it is unknown whether FKBP51-mediated inhibition of I_SOC is sufficient to protect the endothelial barrier from calcium entry-induced disruption. The major objective of this study was to determine whether FKBP51-mediated inhibition of I_SOC leads to decreased calcium entry-induced inter-endothelial gap formation and thus preservation of the endothelial barrier. Here, we measured the effects of thapsigargin-induced I_SOC on the endothelial barrier in control and FKBP51 overexpressing PAECs. FKBP51 overexpression decreased actin stress fiber and inter-endothelial cell gap formation in addition to attenuating the decrease in resistance observed with control cells using electric cell-substrate impedance sensing. Finally, the thapsigargin-induced increase in dextran flux was abolished in FKBP51 overexpressing PAECs. We then measured endothelial permeability in perfused lungs of FKBP51 knockout (FKBP51^–/–) mice and observed increased calcium entry-induced permeability compared to wild-type mice. To begin to dissect the mechanism underlying the FKBP51-mediated inhibition of I_SOC, a second goal of this study was to determine the role of the microtubule network. We observed that FKBP51 overexpressing PAECs exhibited increased microtubule polymerization that is critical for inhibition of I_SOC by FKBP51. Overall, we have identified FKBP51 as a novel regulator of endothelial barrier integrity, and these findings are significant as they reveal a protective mechanism for endothelium against calcium entry-induced disruption.

Thrombin Induces Inositol Trisphosphate-Mediated Spatially Extensive Responses in Lung Microvessels

Activation of plasma membrane receptors initiates compartmentalized second messenger signaling. Whether this compartmentalization facilitates the preferential intercellular diffusion of specific second messengers is unclear. Toward this, the receptor-mediated agonist, thrombin, was instilled into microvessels in a restricted region of isolated blood-perfused mouse lungs. Subsequently, the thrombin-induced increase in endothelial F-actin was determined using confocal fluorescence microscopy. Increased F-actin was evident in microvessels directly treated with thrombin and in those located in adjoining thrombin-free regions. This increase was abrogated by inhibiting inositol trisphosphate-mediated calcium release with Xestospongin C (XeC). XeC also inhibited the thrombin-induced increase in the amplitude of endothelial cytosolic Ca²⁺ oscillations. Instillation of thrombin and XeC into adjacent restricted regions increased F-actin in microvessels in the thrombin-treated and adjacent regions but not in those in the XeC-treated region. Thus, inositol trisphosphate, and not calcium, diffused interendothelially to the spatially remote thrombin-free microvessels. Thus, activation of plasma membrane receptors increased the ambit of inflammatory responses via a second messenger different from that used by stimuli that induce cell-wide increases in second messengers. Thrombin however failed to induce the spatially extensive response in microvessels of mice lacking endothelial connexin43, suggesting a role for connexin43 gap junctions. Compartmental second messenger signaling and interendothelial communication define the specific second messenger involved in exacerbating proinflammatory responses to receptor-mediated agonists.

Low anticoagulant heparin blocks thrombin-induced endothelial permeability in a PAR-dependent manner

Acute lung injury and acute respiratory distress syndrome are accompanied by thrombin activation and fibrin deposition that enhance lung inflammation, activate endothelial cells and disrupt lung paracellular permeability. Heparin possesses anti-inflammatory properties but its clinical use is limited by hemorrhage and heparin induced thrombocytopenia. We studied the effects of heparin and low anticoagulant 2-O, 3-O desulfated heparin (ODSH) on thrombin-induced increases in paracellular permeability of cultured human pulmonary endothelial cells (ECs). Pretreatment with heparin or ODSH blocked thrombin-induced decrease in the EC transendothelial electrical resistance (TER), attenuated thrombin-stimulated paracellular gap formation and actin cytoskeletal rearrangement. Our data demonstrated that heparin and ODSH had inhibitory effects on thrombin-induced RhoA activation and intracellular calcium elevation. Thrombin-stimulated phosphorylation of the cytoskeletal regulatory proteins, myosin light chain and ezrin/radixin/moesin was also reduced. In these effects, low anticoagulant ODSH was more potent than heparin. Heparin or ODSH alone produced decreases in the EC TER that were abolished by siRNA-mediated depletion of the thrombin receptor, PAR-1. We also demonstrated that, in contrast to heparin, ODSH did not possess thrombin-binding activity. Results suggest that heparin and low anticoagulant ODSH can interfere with thrombin-activated signaling.

Platelet-mediated vascular dysfunction during acute lung injury

CONTEXT

Platelets have significant roles in initiating and mediating reduced alveolar blood flow, microvascular leak, and ventilation/perfusion mismatch caused by metabolic changes and altered signal transduction caused by ischemia-reperfusion.

OBJECTIVE

This review focuses on platelet mechanisms of vascular dysfunction in the lung and presents a hypothesis for interplay between platelet activation, endothelial damage and fibrinogen. The purpose is to discuss current knowledge regarding mechanisms of platelet-mediated endothelial injury and implications for new strategies to treat vascular dysfunction associated with acute lung injury (ALI).

METHODS

Literature from a number of fields was searched using Medline and Google Scholar.

RESULTS

Activated platelets contribute to redox imbalance through reactive oxygen species production, pro-leak molecules such as PAF and serotonin, and recruitment of inflammatory cytokines and leukocytes to the damaged endothelium.

CONCLUSION

Platelets are a critical component of pulmonary ALI, acting in conjunction with fibrinogen to mediate endothelial damage through multiple signal transduction pathways.

Rab1 GTPase promotes expression of beta-adrenergic receptors in rat pulmonary microvascular endothelial cells

It is known that Rab1 regulates the expression and function of beta-adrenoceptors (beta-ARs) in many cells. However, the effect of these changes in rat pulmonary microvascular endothelial cells (RPMVECs) is not known. In the present study, we investigated the role of Rab1, a Ras-like GTPase that coordinates protein transport from the endoplasmic reticulum (ER) to the Golgi body and regulates the cell-surface targeting and function of endogenous beta-ARs in RPMVECs in the presence of lipopolysaccharide (LPS). We found that lentivirus-driven expression of wild-type Rab1 (Rab1WT) in RPMVECs strongly enhanced the amount of beta-ARs on the cell surface, whereas the dominant-negative mutant Rab1N124I significantly attenuated beta-ARs expression on the cell surface. In addition, LPS stimulation significantly reduced beta-ARs expression on the cell surface in RPMVECs; however, this effect was reversed by over-expression of wild-type Rab1WT. Fluorescent microscopy analysis demonstrated that expression of Rab1N124I and Rab1 small interfering RNA (siRNA) significantly induced the accumulation of green fluorescent protein (GFP)-tagged beta(2)-AR in the ER. Consistent with their effects on beta-ARs export, Rab1WT and Rab1N124I differentially modified the beta-AR-mediated activation of extracellular signal-regulated kinase1/2 (ERK1/2). Importantly, over-expression of Rab1WT markedly reduced LPS-induced hyper-permeability of RPMVECs by increasing the expression of beta(2)-AR on the cell surface. These data reveal that beta-ARs function in RPMVECs could be modulated by manipulating beta-ARs traffic from the ER to the Golgi body. We propose the ER-to-Golgi transport as a regulatory site for control of permeability of RPMVECs.

Role of calcium/calmodulin signaling pathway in Vibrio vulnificus cytolysin-induced hyperpermeability

Endothelial hyperpermeability, a hallmark of septicemia, is induced by stress fiber formation, which is primarily regulated by the calcium/calmodulin signaling pathway in endothelial cells. We previously reported that trifluoperazine, a calcium/calmodulin antagonist, blocks Vibrio vulnificus cytolysin (VVC) -induced lethality at in vivo animal model. The object of this study was therefore to examine whether VVC induces stress fiber formation through calcium/calmodulin signaling in endothelial cells. Here, we monitored calcium-influx after treatment of VVC using confocal microscopy in CPAE cells, pulmonary endothelial cell line. Interestingly, we found that VVC-induced dose-dependently increases of [Ca(2+)](i) in CPAE cells. Moreover, VVC-induced stress fiber formation as well as phosphorylation of myosin light chain (MLC) in a dose- and time-dependent manner, which was completely blocked by trifluoperazine. These results suggest that the calcium/calmodulin signaling pathway plays a pivotal role in VVC-induced hyperpermeability.

Thrombin enhances the barrier function of rat microvascular endothelium in a PAR-1-dependent manner

Thrombin is a multifunctional coagulation protease with pro- and anti-inflammatory vascular effects. We questioned whether thrombin may have segmentally differentiated effects on pulmonary endothelium. In cultured rat endothelial cells, rat thrombin (10 U/ml) recapitulated the previously reported decrease in transmonolayer electrical resistance (TER), F-actin stress fiber formation, paracellular gap formation, and increased permeability. In contrast, in rat pulmonary microvascular endothelial cells (PMVEC), isolated on the basis of Griffonia simplicifolia lectin recognition, thrombin increased TER, induced fewer stress fibers, and decreased permeability. To assess for differential proteinase-activated receptor (PAR) expression as a basis for the different responses, PAR family expression was analyzed. Both pulmonary artery endothelial cells and PMVEC expressed PAR-1 and PAR-2; however, only PMVEC expressed PAR-3, as shown by both RT-PCR and Western analysis. PAR-1 activating peptides (PAR-APs: SFLLRN-NH(2) and TFLLRN-NH(2)) were used to confirm a role for the PAR-1 receptor. PAR-APs (25-250 muM) also increased TER, formed fewer stress fibers, and did not induce paracellular gaps in PMVEC in contrast to that shown in pulmonary artery endothelial cells. These results were confirmed in isolated perfused rat lung preparations. PAR-APs (100 mug/ml) induced a 60% increase in the filtration coefficient over baseline. However, by transmission electron microscopy, perivascular fluid cuffs were seen only along conduit veins and arteries without evidence of intra-alveolar edema. We conclude that thrombin exerts a segmentally differentiated effect on endothelial barrier function in vitro, which corresponds to a pattern of predominant perivascular fluid cuff formation in situ. This may indicate a distinct role for thrombin in the microcirculation.

New functions for a vertebrate Rho guanine nucleotide exchange factor in ciliated epithelia

Human ARHGEF11, a PDZ-domain-containing Rho guanine nucleotide exchange factor (RhoGEF), has been studied primarily in tissue culture, where it exhibits transforming ability, associates with and modulates the actin cytoskeleton, regulates neurite outgrowth, and mediates activation of Rho in response to stimulation by activated Galpha12/13 or Plexin B1. The fruit fly homolog, RhoGEF2, interacts with heterotrimeric G protein subunits to activate Rho, associates with microtubules, and is required during gastrulation for cell shape changes that mediate epithelial folding. Here, we report functional characterization of a zebrafish homolog of ARHGEF11 that is expressed ubiquitously at blastula and gastrula stages and is enriched in neural tissues and the pronephros during later embryogenesis. Similar to its human homolog, zebrafish Arhgef11 stimulated actin stress fiber formation in cultured cells, whereas overexpression in the embryo of either the zebrafish or human protein impaired gastrulation movements. Loss-of-function experiments utilizing a chromosomal deletion that encompasses the arhgef11 locus, and antisense morpholino oligonucleotides designed to block either translation or splicing, produced embryos with ventrally-curved axes and a number of other phenotypes associated with ciliated epithelia. Arhgef11-deficient embryos often exhibited altered expression of laterality markers, enlarged brain ventricles, kidney cysts, and an excess number of otoliths in the otic vesicles. Although cilia formed and were motile in these embryos, polarized distribution of F-actin and Na(+)/K(+)-ATPase in the pronephric ducts was disturbed. Our studies in zebrafish embryos have identified new, essential roles for this RhoGEF in ciliated epithelia during vertebrate development.

Dynamic and label-free cell-based assays using the real-time cell electronic sensing system

Cell-based assays have become an integral part of the preclinical drug development process. Recently, noninvasive label-free cell-based assay technologies have taken center stage, offering important and distinct advantages over and in addition to traditional label-based endpoint assays. Dynamic monitoring of live cells, the preclusion of label, and kinetics are some of the fundamental features of cell-based label-free technologies. In this article we will discuss the real-time cell electronic sensing (RT-CES, ACEA Biosciences Inc., San Diego, CA) system and some of its key applications for cell-based assays such as cell proliferation and cytotoxicity, functional assays for receptor-ligand analysis, cell adhesion and spreading assays, dynamic monitoring of endothelial barrier function, and dynamic monitoring of cell migration and invasion. Also, where appropriate we will briefly discuss other label-free technologies in an application-specific manner.

Thrombin and histamine induce stiffening of alveolar epithelial cells

The mechanical properties of alveolar epithelial cells play a central role in maintaining the physical integrity of the alveolar epithelium. We studied the viscoelastic properties of alveolar epithelial cells (A549) in response to thrombin and histamine with optical magnetic twisting cytometry. Ferrimagnetic beads coated with Arg-Gly-Asp (RGD)-peptide or acetylated low-density lipoprotein were bound to cell surface receptors and subsequently twisted in an oscillatory magnetic field (0.1–100 Hz). The cell storage (G′) and loss (G″) moduli were computed from twisting torque and bead displacement. In measurements with RGD-coated beads, thrombin (0.5 U/ml) induced a rapid and sustained threefold increase in G′ and G″ at ∼100 s after challenge. Histamine (100 μM) induced a rapid but transient twofold increase in G′ and G″ with maximum values 60 s after challenge. Posttreatment with cytochalasin D abolished thrombin-induced cell stiffening. G′ increased with frequency following a power law with exponent 0.214. G″ increased proportionally to G′ up to 10 Hz but showed a steeper rise at higher frequencies. Thrombin caused a fall in the power-law exponent (0.164). In measurements with acetylated low-density lipoprotein-coated beads, minor changes (<20%) were observed in G′ and G″ after the addition of thrombin and histamine. F-actin staining revealed that thrombin and histamine induced a profound reorganization of the actin cytoskeleton at the cell periphery and formation of actin bundles. In the mechanically dynamic environment of the lung, cell stiffening induced by thrombin and histamine increases centripetal tension, which could contribute to alveolar barrier dysfunction.

P2Y receptor-mediated Ca(2+) signaling increases human vascular endothelial cell permeability

We investigated the effects of P2-receptor agonists on cell size, intracellular calcium levels ([Ca(2+)](i)), and permeation of FITC-labeled dextran (FD-4) as well as the relationship between these effects in human umbilical vein endothelial cells (HUVEC). FD-4 concentration, cell size, and [Ca(2+)](i) were analyzed by HPLC with fluorescence, phase contrast microscopic imaging, and fluorescent confocal microscopic imaging, respectively. The P2Y(1)-receptor agonists 2-methylthio ATP (2meS-ATP) and ADP decreased cell size and increased [Ca(2+)](i) in HUVEC. The P2Y(2)-receptor agonist UTP increased [Ca(2+)](i), but did not influence cell size. The P2X-receptor agonist alpha,beta-methylene ATP did not induce either response. The decrease in size and increase in [Ca(2+)](i) by 2meS-ATP were blocked by pyridoxalphosphate-6-azophenyl-2',4'-disulphonic acid (PPADS, P2Y(1)-antagonist), thapsigargin (Ca(2+)-pump inhibitor), and U73122 (phospholipase C inhibitor). Furthermore, 2meS-ATP (P2Y(1)-receptor agonist) enhanced permeation of FD-4 through the endothelial cell monolayer. The 2meS-ATP-induced enhancement of the permeation was also prevented by PPADS, thapsigargin, and U73122. These results indicate that activation of P2Y receptors induces a decrease in cell size, an increase in [Ca(2+)](i), and may participate in facilitating macromolecular permeability in HUVEC.

Differential Ca2+ signaling by thrombin and protease-activated receptor-1-activating peptide in human brain microvascular endothelial cells

Thrombin and related protease-activated receptors 1, 2, 3, and 4 (PAR1-4) play a multifunctional role in many types of cells including endothelial cells. Here, using RT-PCR and immunofluorescence staining, we showed for the first time that PAR1-4 are expressed on primary human brain microvascular endothelial cells (HBMEC). Digital fluorescence microscopy and fura 2 were used to monitor intracellular Ca2+ concentration ([Ca2+]i) changes in response to thrombin and PAR1-activating peptide (PAR1-AP) SFFLRN. Both thrombin and PAR1-AP induced a dose-dependent [Ca2+]i rise that was inhibited by pretreatment of HBMEC with the phospholipase C inhibitor U-73122 and the sarco(endo)plasmic reticulum Ca2+-ATPase inhibitor thapsigargin. Thrombin induced transient [Ca2+]i increase, whereas PAR1-AP exhibited sustained [Ca2+]i rise. The PAR1-AP-induced sustained [Ca2+]i rise was significantly reduced in the absence of extracellular calcium or in the presence of an inhibitor of store-operated calcium channels, SKF-96365. Restoration of extracellular Ca2+ to the cells that were initially activated by PAR1-AP in the absence of extracellular Ca2+ resulted in significant [Ca2+]i rise; however, this effect was not observed after thrombin stimulation. Pretreatment of the cells with a low thrombin concentration (0.1 nM) prevented [Ca2+]i rise in response to high thrombin concentration (10 nM), but pretreatment with PAR1-AP did not prevent subsequent [Ca2+]i rise to high PAR1-AP concentration. Additionally, treatment with thrombin decreased transendothelial electrical resistance in HBMEC, whereas PAR1-AP was without significant effect. These findings suggest that, in contrast to thrombin, stimulation of PAR1 by untethered peptide SFFLRN results in stimulation of store-operated Ca2+ influx without significantly affecting brain endothelial barrier functions.

The role of oxidant-mediated pathways in the cytotoxicity of endothelial cells exposed to mesenteric lymph from rats subjected to trauma-hemorrhagic shock

Because gut-derived factors carried in mesenteric lymph are implicated in multiple organ dysfunction syndrome and have been shown to injure endothelial cells, we investigated several cellular pathways by which this process could occur. To accomplish this, mesenteric lymph (5%, v/v) collected at 1 to 3 h postshock from male rats undergoing trauma (5-cm laparotomy) and hemorrhagic shock (90 min of mean arterial pressure [MAP] of 30 mmHg; T/HS) was tested for endothelial cell cytotoxicity on human umbilical vein endothelial cells (HUVECs). Over 30 pharmacologic agents that had been reported to inhibit endothelial cell death were tested for their ability to prevent T/HS lymph-induced HUVEC cell death. These included agents documented to protect against oxidant-mediated, calcium-mediated, and arachidonic acid pathway-mediated endothelial cell injury and death. These pharmacologic inhibitors were preincubated with HUVECs for 1 h or were added to the HUVECs simultaneously with lymph, and were then incubated for 18 h. Controls were lymph alone, inhibitor alone, or medium alone. Mitochondrial tetrazolium (MTT) and LDH release assays were used to determine cell viability. The inhibitors that significantly protected HUVECs from the cytotoxicity of T/HS lymph (P < 0.001) included the antioxidant combination of vitamins C and E and the antioxidant-lipooxygenase inhibitor nordihydroguaretic acid (NDGA). These agents were equally effective when added simultaneously with lymph or preincubated with the HUVECs, suggesting an extracellular or membrane-bound process. In summary, the inhibitors that provided protection from toxic lymph appear to work at the membrane and are involved in limiting membrane peroxidation. Based on this study, it appears that an oxidant pathway is involved in T/HS lymph-induced endothelial cell injury and death.

P2Y-receptor regulates size of endothelial cells in an intracellular Ca2+ dependent manner

The effects of P2 receptor agonists on cell size and intracellular calcium levels, [Ca(2+)](i), was investigated using cultured endothelial cells isolated from the caudal artery of male Wistar rats. Cell size and [Ca(2+)](i) were measured using a phase-contrast and fluorescent confocal microscopic image analyzer and a Calcium Green fluorescence probe. P2Y receptor agonists, 2-methylthio ATP (2meS-ATP), ADP, UTP and ATP decreased the cell size and increased [Ca(2+)](i) in endothelial cells from rat caudal artery. However, alpha,beta-methylene ATP, a P2X receptor agonist, did not induce these responses. The decrease in size and the increase in [Ca(2+)](i), by 2meS-ATP were blocked by PPADS (P2-antagonist), suramin (P2-antagonist), thapsigargin (Ca(2+) pump inhibitor) and U-73122 (phospholipase C inhibitor). The present results show that activation of P2Y receptors, not P2X receptors, induces a decrease in cell size and an increase in [Ca(2+)](i), and the pharmacological properties of these two responses are the same. We concluded that the size of endothelial cells is regulated by P2Y receptors via intracelluar Ca(2+) derived from Ca(2+) stores.

ZO-1 redistribution and F-actin stress fiber formation in pulmonary endothelial cells after thermal injury

BACKGROUND

In response to isolated inflammatory stimuli, changes in endothelial cell morphology that enhance paracellular flow of solutes result from F-actin stress fiber formation, myosin phosphorylation, and actin anchoring protein (ZO-1) modifications. We hypothesized that myosin light chain kinase inhibition would diminish burn-enhanced endothelial monolayer permeability by secondarily preventing F-actin and actin anchoring protein rearrangements.

METHODS

Human pulmonary microvascular endothelial cells were treated for 4 hours with 20% human burn serum (isolated from patients with > 45% total body surface area thermal injury or healthy volunteers). Select cultures were pretreated with myosin light chain kinase inhibitors (ML-9). Permeability was assessed by migration of bovine serum albumin across cell monolayers. Cells were stained with rhodamine-phalloidin and anti-ZO-1 antisera and examined by means of confocal microscopy.

RESULTS

Burn serum significantly enhanced monolayer permeability to albumin, whereas pretreatment with ML-9 limited this effect. Control cells maintained cortical F-actin and peripheral ZO-1 distributions (1a, b), whereas burn serum induced transcellular F-actin stress fiber formation and a diffuse ZO-1 staining (2a, b). ML-9 prevented burn-induced actin rearrangements, but not the diffuse redistribution of ZO-1.

CONCLUSION

These data demonstrate that endothelial F-actin stress fiber formation and ZO-1 redistribution contribute to postburn loss of pulmonary endothelial monolayer integrity. Although myosin phosphorylation appears to be required for endothelial F-actin stress fiber formation, redistribution of actin-membrane anchoring proteins appears to be regulated independently after thermal injury.

Thrombin receptors activate G(o) proteins in endothelial cells to regulate intracellular calcium and cell shape changes

Thrombin receptors couple to G(i/o), G(q), and G(12/13) proteins to regulate a variety of signal transduction pathways that underlie the physiological role of endothelial cells in wound healing or inflammation. Whereas the involvement of G(i), G(q), G(12), or G(13) proteins in thrombin signaling has been investigated extensively, the role of G(o) proteins has largely been ignored. To determine whether G(o) proteins could contribute to thrombin-mediated signaling in endothelial cells, we have developed minigenes that encode an 11-amino acid C-terminal peptide of G(o1) proteins. Previously, we have shown that use of the C-terminal minigenes can specifically block receptor activation of G protein families (). In this study, we demonstrate that G(o) proteins are present in human microvascular endothelial cells (HMECs). Moreover, we show that thrombin receptors can stimulate [(35)S]guanosine-5'-O-(3-thio)triphosphate binding to G(o) proteins when co-expressed in Sf9 membranes. The potential coupling of thrombin receptors to G(o) proteins was substantiated by transfection of the G(o1) minigene into HMECs, which led to a blockade of thrombin-stimulated release of [Ca(2+)](i) from intracellular stores. Transfection of the beta-adrenergic kinase C terminus blocked the [Ca(2+)](i) response to the same extent as with G(o1) minigene peptide, suggesting that this G(o)-mediated [Ca(2+)](i) transient was caused by Gbetagamma stimulation of PLCbeta. Transfection of a G(i1/2) minigene had no effect on thrombin-stimulated [Ca(2+)](i) signaling in HMEC, suggesting that Gbetagamma derived from G(o) but not G(i) could activate PLCbeta. The involvement of G(o) proteins on events downstream from calcium signaling was further evidenced by investigating the effect of G(o1) minigenes on thrombin-stimulated stress fiber formation and endothelial barrier permeability. Both of these effects were sensitive to pertussis toxin treatment and could be blocked by transfection of G(o1) minigenes but not G(i1/2) minigenes. We conclude that the G(o) proteins play a role in thrombin signaling distinct from G(i1/2) proteins, which are mediated through their Gbetagamma subunits and involve coupling to calcium signaling and cytoskeletal rearrangements.

Extracellular matrix, junctional integrity and matrix metalloproteinase interactions in endothelial permeability regulation

Vascular endothelial permeability is maintained by the regulated apposition of adherens and tight junctional proteins whose organization is controlled by several pharmacological and physiological mediators. Endothelial permeability changes are associated with: (1) the spatial redistribution of surface cadherins and occludin, (2) stabilization of focal adhesive bonds and (3) the progressive activation of matrix metalloproteinases (MMPs). In response to peroxide, histamine and EDTA, endothelial cells sequester VE-cadherin and alter its cytoskeletal binding. Simultaneously, these mediators enhance focal adhesion to the substratum. Oxidants, cytokines and pharmacological mediators also trigger the activation of matrix metalloproteinases (MMPs) in a cytoskeleton and tyrosine phosphorylation dependent manner to degrade occludin, a well-characterized tight junction element. These related in vitro phenomena appear to co-operate during inflammation, to increase endothelial permeability, structurally stabilize cells while also remodelling cell junctions and substratum.