Correlation between antigenic and functional expression of tissue factor on the surface of cultured human endothelial cells following stimulation by lipopolysaccharide endotoxin

The gut microbiota - a modulator of endothelial cell function and a contributing environmental factor to arterial thrombosis

Introduction: There is emerging evidence linking the commensal gut microbiota with the development of cardiovascular disease and arterial thrombosis. In immunothrombosis, the host clotting system protects against the dissemination of invading microbes, not considering the huge number of microbes that interact with host physiology in a mutualistic fashion. Areas covered: Interestingly, recent research revealed that colonizing gut microbes profoundly influence host innate immune pathways that support arterial thrombus growth. The gut microbiota promotes arterial thrombus formation by enhancing the pro-adhesive capacity of the vascular endothelium, triggering hepatic von Willebrand factor synthesis and its release by Weibel-Palade body exocytosis, resulting in elevated von Willebrand factor levels and enhancing FVIII stability in plasma. Furthermore, the metabolic capacity of gut resident microbes promotes agonist-induced platelet activation and deposition. Here, we give an overview, with a focus on the vascular endothelium, on how this gut-resident microbial ecosystem contributes to arterial thrombus formation. Expert opinion: The gut microbiota and its metabolites not only act on agonist-induced platelet reactivity, but also influence the hepatic endothelial phenotype via remote signaling, facilitating arterial thrombus growth at the arterial injury site.

Tissue factor-bearing microparticles and inflammation: a potential mechanism for the development of venous thromboembolism in cancer

Cancer is associated with an increased risk of venous thromboembolism (VTE); the exact mechanisms for the induction of VTE remain to be fully elucidated, but it is widely acknowledged that tissue factor (TF)-bearing microparticles (TF-MPs) may play a significant role. However, TF-MPs have yet to be accepted as a genuine biomarker for cancer-associated VTE, as the presence of elevated TF-MP levels is not always accompanied by thrombosis; interestingly, in certain cases, particularly in pancreatic cancer, VTE seems to be more likely in the context of acute inflammation. Although several potential mechanisms for the development of VTE in cancer have been postulated, this review explores the homeostatic disruption of TF-MPs, as the main reservoir of bloodborne TF, in the context of cancer and inflammation, and considers the abrogated responses of the activated endothelium and mononuclear phagocyte system in mediating this disruption.

Accumulation of tissue factor in endothelial cells induces cell apoptosis, mediated through p38 and p53 activation

We previously reported that high levels of tissue factor (TF) can induce cellular apoptosis in endothelial cells. In this study, TF-mediated mechanisms of induction of apoptosis were explored. Endothelial cells were transfected to express wild-type TF. Additionally, cells were transfected to express Asp253-substituted, or Ala253-substitued TF to enhance or prevent TF release, respectively. Alternatively, cells were pre-incubated with TF-rich and TF-poor microvesicles. Cell proliferation, apoptosis and the expression of cyclin D1, p53, bax and p21 were measured following activation of cells with PAR2-agonist peptide. Greatest levels of cell proliferation and cyclin D1 expression were observed in cells expressing wild-type or Asp253-substituted TF. In contrast, increased cellular apoptosis was observed in cells expressing Ala253-substituted TF, or cells pre-incubated with TF-rich microvesicles. The level of p53 protein, p53-phosphorylation at ser33, p53 nuclear localisation and transcriptional activity, but not p53 mRNA, were increased in cells expressing wild-type and Ala253-substituted TF, or in cells pre-incubated with TF-rich microvesicles. However, the expression of bax and p21 mRNA, and Bax protein were only increased in cells pre-incubated with TF-rich microvesicle and in cells expressing Ala253-substituted TF. Inhibition of the transcriptional activity of p53 using pifithrin-α suppressed the expression of Bax. Finally, siRNA- mediated suppression of p38α, or inhibition using SB202190 significantly reduced the p53 protein levels, p53 nuclear localisation and transcriptional activity, suppressed Bax expression and prevented cellular apoptosis. In conclusion, accumulation of TF within endothelial cells, or sequestered from the surrounding can induce cellular apoptosis through mechanisms mediated by p38, and involves the stabilisation of p53.

Microparticle-associated tissue factor is recycled by endothelial cells resulting in enhanced surface tissue factor activity

In this study the uptake of tissue factor (TF)-positive microparticles by endothelial cells and the recycling of the TF component were examined. Human dermal blood endothelial cells (HDBEC) were incubated with microparticles derived from cancer cell lines for up to 6 hours. Measurement of HDBEC cell surface TF antigen revealed two distinct peaks at 30 and 180-240 minutes post-incubation with TF-positive, but not TF-deficient microparticles. However, only the second peak was concurrent with high TF activity as determined by a chromogenic thrombin-generation assay. Annexin V-labelling of HDBEC showed phosphatidylserine exposure following 90 minutes incubation with microparticles, which explains the high TF activity associated with the second antigen peak. Analysis of TF mRNA levels revealed no de novo expression of TF mRNA in response to microparticles, and pre-incubation of cells with cycloheximide did not prevent the appearance of TF. However, blocking endocytosis with a dynamin inhibitor prolonged the disappearance and prevented the reappearance of TF antigen on the cell surface. Incubation of HDBEC with microparticles containing TF-GFP revealed the early co-localisation of TF with Rab4 and Rab5, followed by co-localisation with the late endosomal/trans-Golgi network marker Rab9, and the recycling endosome marker Rab11. siRNA-mediated suppression of Rab11 reduced the reappearance of TF on the cell surface. These data suggest a mechanism by which TF-containing microparticles are internalised by endothelial cells and the TF moiety recycled to the cell surface. Together with the exposure of phosphatidylserine, this is capable of inducing a substantial increase in the procoagulant potential of the surface of endothelial cells.

Lipopolysaccharide appears to activate human endometrial endothelial cells through TLR-4-dependent and TLR-4-independent mechanisms

PROBLEM

Uterine innate immunity remains poorly characterized, and while endometrial endothelial cells are known to express Toll-like receptors (TLRs), little is known about their function in these cells. The present study evaluated the effect of Gram-negative bacterial lipopolysaccharide (LPS) on human endometrial endothelial cell (HEECs) cytokine secretion and tissue factor expression, and the role of TLR-4 in these responses.

METHODS

Human endometrial endothelial cells were treated with or without LPS ± LPS-RS, a TLR-4 antagonist, via the binding of MD-2. After 24 hr, cell-free supernatants were evaluated for cytokines by multiplex analysis and cell lysates were analyzed for tissue factor expression by Western blot.

RESULTS

Treatment of HEECs with LPS significantly upregulated the secretion of IL-6, IL-8, and G-CSF, and this was prevented by LPS-RS. LPS also induced tissue factor expression by the HEECs; however, this was unaffected by LPS-RS.

CONCLUSION

These findings suggest that TLR-4 is functional in HEECs and its activation by bacterial LPS induces a specific cytokine/chemokine response. However, bacterial LPS also induced tissue factor expression in what seemed to be a TLR-4-independent fashion, suggesting that this bacterial component can act on the HEECs through TLR-4-dependent and TLR-4-independent pathways. These findings indicate that endometrial endothelial cells may play an active role in uterine innate immunity.

Identification of miRNAs as potential modulators of tissue factor expression in patients with systemic lupus erythematosus and antiphospholipid syndrome

BACKGROUND

Tissue factor (TF) is the main initiator of the coagulation cascade and elements that may upregulate its expression might provoke thrombotic events. Systemic lupus erythematosus (SLE) and antiphospholipid syndrome (APS) are autoimmune diseases characterized by a high TF expression in monocytes.

OBJECTIVES

To examine the role of microRNAs (miRNAs) in TF expression and to evaluate their levels in SLE and APS patients.

METHODS

An in silico search was performed to find potential putative binding sites of miRNAs in TF mRNA. In vitro validation was performed transfecting cells expressing TF (THP-1 and MDA-MB-231) with oligonucleotide miRNA precursors and inhibitors. Additionally, reporter assays were performed to test for the binding of miR-20a to TF mRNA. Levels of miRNAs and TF were measured by quantitative (qRT-PCR) in patients with APS and SLE.

RESULTS

Overexpression of miRNA precursors, but not inhibitors, of two of the members of cluster miR-17∼92, for example miR-19b and miR-20a, in cells expressing TF decreased TF mRNA, protein levels, and procoagulant activity between 30% and 60%. Reporter assays showed that miR-20a binds to TF mRNA. Finally, we measured levels of miR-19b and miR-20a in monocytes from patients with APS and SLE and observed significantly lower miRNAs levels in comparison with healthy subjects inversely correlated with the levels of TF.

CONCLUSIONS

Down-regulation of miR-19b and miR-20a observed in patients with SLE and APS could contribute to increased TF expression and thus provoke the hypercoagulable state characteristic of these patients.

Porcine endothelial cells cocultured with smooth muscle cells became procoagulant in vitro

Endothelial cell (EC) seeding represents a promising approach to provide a nonthrombogenic surface on vascular grafts. In this study, we used a porcine EC/smooth muscle cell (SMC) coculture model that was previously developed to examine the efficacy of EC seeding. Expression of tissue factor (TF), a primary initiator in the coagulation cascade, and TF activity were used as indicators of thrombogenicity. Using immunostaining, primary cultures of porcine EC showed a low level of TF expression, but a highly heterogeneous distribution pattern with 14% of ECs expressing TF. Quiescent primary cultures of porcine SMCs displayed a high level of TF expression and a uniform pattern of staining. When we used a two-stage amidolytic assay, TF activity of ECs cultured alone was very low, whereas that of SMCs was high. ECs cocultured with SMCs initially showed low TF activity, but TF activity of cocultures increased significantly 7-8 days after EC seeding. The increased TF activity was not due to the activation of nuclear factor kappa-B on ECs and SMCs, as immunostaining for p65 indicated that nuclear factor kappa-B was localized in the cytoplasm in an inactive form in both ECs and SMCs. Rather, increased TF activity appeared to be due to the elevated reactive oxygen species levels and contraction of the coculture, thereby compromising the integrity of EC monolayer and exposing TF on SMCs. The incubation of cocultures with N-acetyl-cysteine (2 mM), an antioxidant, inhibited contraction, suggesting involvement of reactive oxygen species in regulating the contraction. The results obtained from this study provide useful information for understanding thrombosis in tissue-engineered vascular grafts.

Contributions of extravascular and intravascular cells to fibrin network formation, structure, and stability

Fibrin is essential for hemostasis; however, abnormal fibrin formation is hypothesized to increase thrombotic risk. We previously showed that in situ thrombin generation on a cell's surface modulates the 3-dimensional structure and stability of the fibrin network. Currently, we compared the abilities of extravascular and intravascular cells to support fibrin formation, structure, and stability. Extravascular cells (fibroblasts, smooth muscle) supported formation of dense fibrin networks that resisted fibrinolysis, whereas unstimulated intravascular (endothelial) cells produced coarse networks that were susceptible to fibrinolysis. All 3 cell types produced a fibrin structural gradient, with a denser network near, versus distal to, the cell surface. Although fibrin structure depended on cellular procoagulant activity, it did not reflect interactions between integrins and fibrin. These findings contrasted with those on platelets, which influenced fibrin structure via interactions between beta3 integrins and fibrin. Inflammatory cytokines that induced prothrombotic activity on endothelial cells caused the production of abnormally dense fibrin networks that resisted fibrinolysis. Blocking tissue factor activity significantly reduced the density and stability of fibrin networks produced by cytokine-stimulated endothelial cells. Together, these findings indicate fibrin structure and stability reflect the procoagulant phenotype of the endogenous cells, and suggest abnormal fibrin structure is a novel link between inflammation and thrombosis.

Tissue factor expression by cells used for sodding of prosthetic vascular grafts

Sodding of vascular grafts involves coating the biomaterial with cells prepared from collagenase-digested fat tissue after removal of the adipocytes by centrifugation. The goal of this study was to investigate the staining characteristics of the sodding cells as well as their ability to express the procoagulant protein tissue factor, and to compare these findings to those found with extensively purified microvascular endothelial cells (MEC) prepared from similar tissue. Sodding cells and MEC, isolated using immunomagnetic separation with anti-PECAM antibodies, were prepared from liposuction material and endothelial-specific staining was compared. The expression of tissue factor on these cells was examined using both an ELISA and a chromogenic assay to assess the rate of generation of factor Xa. Sodding cells expressed significantly more tissue factor than the unstimulated MEC in which the expression was undetectable (sodding cells 2466 +/- 830 pg/mL, P < 0.05). There was no further increase in tissue factor expression in the sodding cells with stimulation with lipopolysaccharide (LPS); however, purified MEC expressed significantly more tissue factor after exposure to LPS (1247 +/- 356 pg/mL, P < 0.05). These results were confirmed by the determination of procoagulant activity of the cells whereby the procoagulant activity on unstimulated MEC was significantly less than that found after stimulation of these cells, and it was also less than stimulated and unstimulated sodding cells (absorbance at 405 nm: 0.423 +/- 0.125, unstimulated MEC; 1.000 +/- 0.438, stimulated MEC; 1.129 +/- 0.396, unstimulated sodding cells; 1.171 +/- 0.254, stimulated sodding cells, P < 0.05). Staining of these two cells types also demonstrated significant uptake of acetylated LDL (Ac-LDL) in the purified MEC which was essentially absent in the sodding cells. Further, vWf staining was found to a greater degree in the purified MEC than in the sodding cells. These experiments demonstrated that the cells prepared for cell sodding express large amounts of tissue factor. The sodding cells do not stain for antigens known to be specific for endothelial cells, whereas MEC do and therefore the concentration of endothelial cells in the sodding cells is small. The significance of the tissue factor expression on the surface of sodded grafts is not yet known.

Signal transduction pathways of bacterial lipopolysaccharide-stimulated bovine vascular endothelial cells

Increased procoagulant activity of vascular endothelial cells may be an important component in the pathogenesis of intravascular coagulation associated with gram-negative bacterial diseases. Two bovine endothelial cell (BEC) lines isolated from pulmonary arteries (ENS-2 and ENT-18) were used in this study to investigate procoagulant signal transduction pathways of endotoxin (lipopolysaccharide, LPS)--stimulated BECs. The endothelial cell line ENS-2 was sensitive to LPS as demonstrated by tissue factor (TF) expression, but in contrast, the ENT-18 endothelial cell line was unusually resistant to the effects of LPS. No remarkable quantitative difference in binding of radiolabeled LPS was detected between the two endothelial cell lines. A protein kinase C (PKC) activator (phorbol 12-myristate 13-acetate, PMA) failed to induce TF expression in either cell line at concentrations ranging from 0.05 to 1.00 microM when used as a sole stimulus for the endothelial cells. However, when PMA was used in combination with LPS, PMA enhanced the stimulatory effect of LPS on the endothelial cells. In parallel experiments, PKC inhibitors (H-7 and GF 109203X) interfered with the stimulatory effect of LPS on the cells by decreasing tissue factor expression. We also found that an activator of adenylate cyclase, forskolin, similarly inhibited LPS-induced tissue factor activity. In contrast, protein tyrosine kinase inhibitors (genistein, lavendustin A) had no inhibitory effect on LPS-induced endothelial cell tissue factor expression. Our results collectively suggest that activation of PKC is an important step in stimulation of endothelial cells by LPS, and that LPS and phorbol esters may synergize to produce an enhanced stimulatory effect. Our results also suggest participation of cAMP in controlling LPS-mediated stimulation of endothelial cells, but fail to demonstrate a role for protein tyrosine kinase activity.

Tissue factor is expressed on monocytes during simulated extracorporeal circulation

Certain forms of extracorporeal circulation exemplified by cardiopulmonary bypass require continuous high-dose anticoagulation to prevent thromboembolic complications. We hypothesized that monocytes may be stimulated to express tissue factor (TF) during prolonged simulated extracorporeal circulation. TF was identified both by flow cytometry by using three TF-specific monoclonal antibodies and functional assay of procoagulant activity (PCA). TF significantly increased between 2 and 6 hours of simulated extracorporeal circulation by both analyses. Relative fluorescence on monocytes increased from a control value of 100 to 313 +/- 79 on cells from the simulated extracorporeal circuit (p < 0.05). PCA increased from 21 +/- 8 to 775 +/- 326 pg TF/10(6) monocytes (p < 0.05) and was blocked 99.6% by preincubation of cells with a mixture of monoclonal antibodies to TF. By 6 hours, the number of leukocytes in the circuit was decreased by 43%. The cells were recovered from the oxygenator membrane by washing with EDTA. Compared with initial values, by 6 hours, both TF antigen at 378 +/- 90 (p < 0.05) and PCA at 1,357 +/- 280 pg TF/10(6) monocytes (p < 0.01) were highest in the recovered cells. Cells incubated for 6 hours and not subjected to simulated extracorporeal circulation did not increase TF. Examination of monocytes for the adhesive receptor CD11b/18 (Mac-1) paralleled TF expression, providing an additional putative receptor for the coagulant proteins, factor X and fibrinogen or fibrin.(ABSTRACT TRUNCATED AT 250 WORDS)

Role of cyclic AMP in promoting the thromboresistance of human endothelial cells by enhancing thrombomodulin and decreasing tissue factor activities

1. The effects of forskolin, prostaglandin E1 (PGE1), dibutyryl cyclic AMP (db cyclic AMP), dibutyryl cyclic GMP (db cyclic GMP) and 3-isobutyl-l-methyl-xanthine (IBMX) were investigated on the expression of tissue factor and thrombomodulin activities on the surface of human saphenous vein endothelial cells (HSVEC) in culture. 2. Forskolin (10(-6) to 10(-4) M), PGE1 (10(-7) to 10(-5) M) and db cyclic AMP (10(-4) to 10(-3) M) caused a concentration-dependent decrease of cytokine-induced tissue factor activity. 3. Similar concentrations of forskolin, PGE1 and db cyclic AMP enhanced significantly constitutive thrombomodulin activity and reversed the decrease of this activity caused by interleukin-1 (IL-1). 4. IBMX (10(-4) M) decreased tissue factor activity and enhanced the effect of forskolin on tissue factor and thrombomodulin activities. 5. Forskolin (10(-4) M) decreased the IL-1-induced tissue factor mRNA and increased the thrombomodulin mRNA level. IL-1 did not change the thrombomodulin mRNA level after 2 h of incubation with HSVEC in culture. 6. Dibutyryl cyclic GMP (10(-4) M to 10(-3) M) did not influence tissue factor or thrombomodulin activity. 7. Our data suggest that elevation of intracellular cyclic AMP levels may participate in the regulation of tissue factor and thrombomodulin expression, thus contributing to promote or restore antithrombotic properties of the endothelium.

Heterogeneous regulation of constitutive thrombomodulin or inducible tissue-factor activities on the surface of human saphenous-vein endothelial cells in culture following stimulation by interleukin-1, tumour necrosis factor, thrombin or phorbol ester

Thrombomodulin and tissue-factor activities were measured on the surface of confluent human saphenous-vein endothelial cells (HSVEC) cultivated in 96-multiwell plates. Thrombomodulin activity was measured in the presence of purified human thrombin (2.2 nM) and protein C (65 nM). Tissue-factor activity was measured with purified human Factor VII (5 nM) and Factor X (400 nM). Generated activated protein C and Factor Xa released in the supernatant were assayed with chromogenic substrates. Resting cells exhibited significant thrombomodulin activity, but no detectable tissue-factor activity. After 4 h of preincubation with tumour necrosis factor (TNF, 22-2200 pM), interleukin-1 (IL-1, 5.7-570 nM) or phorbol myristate acetate (PMA, 1.61-161 nM) there was an increase in tissue-factor activity and a concomitant decrease in thrombomodulin activity. However, the extent of both responses varied according to the nature of the stimulus. Thrombin (0.44-44 nM) also induced an increase in tissue-factor activity, but had no effect on thrombomodulin activity. Kinetic studies showed that for all stimuli the increase in tissue factor was transient, reaching a maximum after 4-8 h of preincubation with the stimulating agent and returning to normal values after 24 h. IL-1 and TNF induced a time-dependent decrease in thrombomodulin, by respectively 47% and 67% of control values after 24 h. However, PMA induced only a transient down-regulation of thrombomodulin, full activity being recovered after 18 h. Hence this simultaneous assay system, using intact HSVEC and purified human coagulation factors, enabled us to observe that the regulation of thrombin generation could be diversely affected by various substances known to stimulate the endothelium. This suggests that the simultaneous and opposite modulation of these proteins does not represent an unified response of the endothelial cells to procoagulant stimuli. These results also confirm the absence of effect of thrombin on the expression of thrombomodulin on the cell surface.

Measurements of tissue factor-like activity in plasma of patients with DIC

Tissue factor-like activity was measured in the plasma of 30 patients with disseminated intravascular coagulation(DIC) and 22 patients without DIC using a chromogenic substrate. Twenty-three of the 30 patients with DIC (77%) exhibited tissue factor-like activity levels above normal range (greater than 3.0 U/L), and in eleven of these patients, the levels were more than 10 U/L. Of the 22 patients without DIC, seven patients had elevated levels (3-10 U/L), and had a possibility to be developing DIC. So, we considered them to be in a pre-DIC state. No correlation was found between tissue factor-like activity and alpha 2 plasmin inhibitor-plasmin complex or FDP-D dimer. In a patient with acute monocytic leukemia, the elevated tissue factor-like activity (84.4 U/L) rapidly decreased after the initiation of chemotherapy, whereas in a patient with pancreatic cancer, the level remained elevated (67.4-79.2 U/L). These results suggested that the plasma tissue factor-like activity is differ from the other parameters reflecting the process of DIC and is a useful indicator of the presence of an initiating factor of blood coagulation in some selected patients with DIC or pre-DIC.

Proteolytic activation of human factors IX and X by recombinant human factor VIIa: effects of calcium, phospholipids, and tissue factor

Previous studies indicated that factor VIIa, in complex with tissue factor, readily activates either factor X or factor IX in the presence of calcium ions. In order to assess the relative physiological importance of the activation of factor IX versus the activation of factor X by recombinant factor VIIa, we have obtained steady-state kinetic parameters for the factor VIIa catalyzed activation of factor IX and factor X under a variety of cofactor conditions that include calcium alone, calcium and phospholipids, calcium, phospholipids, and tissue factor apoprotein, and calcium and cell-surface tissue factor. Calcium alone stimulated the activation of factors IX and X by factor VIIa maximally at 1 and 2.5 mM, respectively. In the presence of 25 microM phospholipids, maximal rates of factor IX and factor X activation were achieved at 2.5-5 mM calcium. With calcium alone, or with phospholipid and calcium, the initial rates of factor IX activation by factor VIIa were significantly higher than that observed for factor X. Kinetic studies revealed that the Km for the factor VIIa catalyzed activation of factor IX was essentially constant in the presence of 5 mM calcium and 1-500 microM phospholipid, whereas the Km for factor X activation varied with phospholipid concentration, reaching a minimum at 7-20 microM phospholipid. At all concentrations of added phospholipid, the kcat/Km ratio for the activation of factor IX by factor VIIa appeared to be considerably greater than that observed for the activation of factor X.(ABSTRACT TRUNCATED AT 250 WORDS)