Soluble tissue factor has unique angiogenic activities that selectively promote migration and differentiation but not proliferation of endothelial cells

High expression of CCR5 in melanoma enhances epithelial-mesenchymal transition and metastasis via TGFβ1

Chemokine receptors are highly expressed in various cancers and play crucial roles in tumor progression. However, their expression patterns and functions in melanoma are unclear. The present study aimed to identify the chemokine receptors that play critical roles in melanoma progression and unravel the underlying molecular mechanisms. We found that CCR5 was more abundant in melanoma cells than normal cells and was positively associated with tumor malignancy in clinical patients. Animal experiments suggested that CCR5 deficiency in B16/F10 or A375 cells suppressed primary tumor growth and lung metastasis, whereas CCR5 overexpression in B16/F0 cells enhanced primary tumor growth and lung metastasis. CCR5 played a critical role in proliferation and migration of melanoma cells in vitro. Importantly, CCR5 was required for maintenance of the mesenchymal phenotype of metastatic melanoma cells. Mechanistically, CCR5 positively regulated expression of TGFβ1, which in turn induced epithelial-mesenchymal transition and migration via PI3K/AKT/GSK3β signaling. Collectively, our results establish a critical role of CCR5 expressed by melanoma cells in cancer progression and reveal the novel mechanisms controlling this process, which suggests the prognostic value of CCR5 in melanoma patients and provides novel insights into CCR5-targeted strategies for melanoma treatment. Copyright © 2018 Pathological Society of Great Britain and Ireland. Published by John Wiley & Sons, Ltd.

Dgcr8 deletion in the primitive heart uncovered novel microRNA regulating the balance of cardiac-vascular gene program

Primitive mammalian heart transforms from a single tube to a four-chambered muscular organ during a short developmental window. We found that knocking out global microRNA by deleting Dgcr8 microprocessor in Mesp1 cardiovascular progenitor cells lead to the formation of extremely dilated and enlarged heart due to defective cardiomyocyte (CM) differentiation. Transcriptome analysis revealed unusual upregulation of vascular gene expression in Dgcr8 cKO hearts. Single cell RNA sequencing study further confirmed the increase of angiogenesis genes in single Dgcr8 cKO CM. We also performed global microRNA profiling of E9.5 heart for the first time, and identified that miR-541 was transiently highly expressed in E9.5 hearts. Interestingly, introducing miR-541 back into microRNA-free CMs partially rescued their defects, downregulated angiogenesis genes and significantly upregulated cardiac genes. Moreover, miR-541 can target Ctgf and inhibit endothelial function. Our results suggest that microRNAs are required to suppress abnormal angiogenesis gene program to maintain CM differentiation.

Cellular prion protein and γ-synuclein overexpression in LS 174T colorectal cancer cell drives endothelial proliferation-to-differentiation switch

Background

Tumor-induced angiogenesis is an imperative event in pledging new vasculature for tumor metastasis. Since overexpression of neuronal proteins gamma-synuclein (γ-Syn) and cellular prion protein (PrP^C) is always detected in advanced stages of cancer diseases which involve metastasis, this study aimed to investigate whether γ-Syn or PrP^C overexpression in colorectal adenocarcinoma, LS 174T cells affects angiogenesis of endothelial cells, EA.hy 926 (EA).

Methods

EA cells were treated with conditioned media (CM) of LS 174T-γ-Syn or LS 174T-PrP, and their proliferation, invasion, migration, adhesion and ability to form angiogenic tubes were assessed using a range of biological assays. To investigate plausible background mechanisms in conferring the properties of EA cells above, nitrite oxide (NO) levels were measured and the expression of angiogenesis-related factors was assessed using a human angiogenesis antibody array.

Results

EA proliferation was significantly inhibited by LS 174T-PrP CM whereas its telomerase activity was reduced by CM of LS 174T-γ-Syn or LS 174T-PrP, as compared to EA incubated with LS 174T CM. Besides, LS 174T-γ-Syn CM or LS 174T-PrP CM inhibited EA invasion and migration in Boyden chamber assay. Furthermore, LS 174T-γ-Syn CM significantly inhibited EA migration in scratch wound assay. Gelatin zymography revealed reduced secretion of MMP-2 and MMP-9 by EA treated with LS 174T-γ-Syn CM or LS 174T-PrP CM. In addition, cell adhesion assay showed lesser LS 174T-γ-Syn or LS 174T-PrP cells adhered onto EA, as compared to LS 174T. In tube formation assay, LS 174T-γ-Syn CM or LS 174T-PrP CM induced EA tube formation. Increased NO secretion by EA treated with LS 174T-γ-Syn CM or LS 174T-PrP CM was also detected. Lastly, decreased expression of pro-angiogenic factors like CXCL16, IGFBP-2 and amphiregulin in LS 174T-γ-Syn CM or LS 174T-PrP CM was detected using the angiogenesis antibody array.

Discussion

These results suggest that overexpression of γ-Syn or PrP^C could possibly be involved in colorectal cancer-induced angiogenesis by inducing an endothelial proliferation-differentiation switch. NO could be the main factor in governing this switch, and modulation on the secretion patterns of angiogenesis-related proteins could be the strategy of colorectal cancer cells overexpressing γ-Syn or PrP^C in ensuring this transition.

Endostatin has ATPase activity, which mediates its antiangiogenic and antitumor activities

Endostatin is an endogenous angiogenesis inhibitor with broad-spectrum antitumor activities. Although the molecular mechanisms of endostatin have been extensively explored, the intrinsic biochemical characteristics of endostatin are not completely understood. Here, we revealed for the first time that endostatin embedded novel ATPase activity. Moreover, mutagenesis study showed that the ATPase activity of endostatin mutants positively correlated with effects on endothelial cell activities and tumor growth. E-M, an endostatin mutant with higher ATPase activity than that of wild-type (WT) endostatin, significantly increased endostatin-mediated inhibitory effects on endothelial cell proliferation, migration, tube formation, and adhesion. In vivo study showed that E-M displayed enhanced antitumor effects compared with WT. On the other hand, K96A, K96R, and E176A, endostatin mutants with lower ATPase activities than that of WT, showed reduced or comparable effects on targeting both in vitro endothelial cell activities and in vivo tumor angiogenesis and tumor growth. Furthermore, endostatin and its mutants exhibited distinct abilities in regulations of gene expression (Id1, Id3), cell signaling (Erk, p38, and Src phosphorylation), and intracellular ATP levels. Collectively, our study demonstrates that endostatin has novel ATPase activity, which mediates its antiangiogenic and antitumor activities, suggesting that construction of endostatin analogues with high ATPase activity may provide a new direction for the development of more potent antiangiogenic drugs.

MicroRNA-542-3p inhibits tumour angiogenesis by targeting angiopoietin-2

Angiopoietin-2 (Angpt2) plays a critical role in angiogenesis and tumour progression. Therapeutic targeting of Angpt2 has been implicated as a promising strategy for cancer treatment. Whereas miRNAs are emerging as important modulators of angiogenesis, regulation of Angpt2 by miRNAs has not been established. Here we firstly report that Ang2 is targeted by a microRNA, miRNA-542-3p, which inhibits tumour progression by impairing Ang2's pro-angiogenic activity. In cultured endothelial cells, miR-542-3p inhibited translation of Angpt2 mRNA by binding to its 3' UTR, and addition of miR-542-3p to cultured endothelial cells attenuated angiogenesis. Administration of miR-542-3p to tumour-bearing mice reduced tumour growth, angiogenesis and metastasis. Furthermore, the level of miR-542-3p in primary breast carcinomas correlated inversely with clinical progression in primary tumour samples from stage III and IV patients. Together, these findings uncover a novel regulatory pathway whereby an anti-angiogenic miR-542-3p directly targets the key angiogenesis-promoting protein Angpt2, suggesting that miR-542-3p may represent a promising target for anti-angiogenic therapy and a potential marker for monitoring disease progression.

A role for trans-caryophyllene in the moderation of insulin secretion

Glucose-stimulated insulin secretion (GSIS) is essential for the control of metabolic fuel homeostasis and its impairment is a key element in the failure of β-cells in type 2 diabetes. Trans-caryophyllene (TC), an important constituent of the essential oil of several species of plants, has been reported to activate the type 2 cannabinoid receptor (CB2R). The effects of TC on GSIS are still unknown. Our results demonstrate that administration of TC in MIN6 cells promotes GSIS in a dose dependent manner. However, inhibition of CB2R by a specific inhibitor or specific RNA interference abolished the effects of TC on GSIS, which suggests that the effects of TC on GSIS are dependent on activation of CB2R. Further study demonstrated that treatment with TC leads to the activation of small G protein Arf6 as well as Rac1 and Cdc42. Importantly, Arf6 silencing abolished the effects of TC on GSIS, which suggests that Arf6 participates in mediating the effects of TC on GSIS. We conclude from these data that TC has a novel role in regulating GSIS in pancreatic β-cells.

Adiponectin offers protection against L166P mutant DJ-1-induced neuronal cytotoxicity mediated by APPL1-dependent AMPK activation

Parkinson's disease (PD) is the second most common neurodegenerative disease in the world. L166P mutant DJ-1 has been linked with a genetic form of the disease. Preventing neurotoxicity of DJ-1 familial mutations has become a new therapeutic target for PD. Adiponectin, the most abundantly secreted adipokine, has displayed its protective roles in pathologies of various types of diseases. In this study, we investigate whether adiponectin is protective against neurotoxicity induced by familial L166P mutant DJ-1 in PD. Our results demonstrate that adiponectin treatment could attenuate increased levels of reactive oxygen species and nitric oxide induced by the DJ-1L166P mutation. In addition, adiponectin could rescue impaired mitochondrial membrane potential induced by DJ-1L166P. Importantly, we verified that both adiponectin receptors, type 1 (AdipoR1) and type 2 (AdipoR2), are expressed in human neuroblastoma M17 cells. Our results also demonstrate that the protective effects of adiponectin against DJ-1L166P-induced neuronal cytotoxicity under 1-methyl-4-phenylpyridinium ion (MPP+) treatment require binding of adiponectin to its cell surface receptors. Finally, we found that the protective effects of adiponectin against DJ-1L166P depend on AMP-activated protein kinase (AMPK) activation mediated by the endosomal adaptor protein, APPL1 (adaptor protein with phosphotyrosine binding, pleckstrin homology domains and leucine zipper motif). These data suggest that adiponectin may have potential for implementation in novel therapies against PD.

Resistin protection against endogenous Aβ neuronal cytotoxicity from mitochondrial pathway

Neurotoxicity of amyloid β (Aβ) plays an important role in Alzheimer's disease (AD) pathogenesis. In this study, we researched the potential protective effects of resistin against Aβ neurotoxicity in mouse Neuro2a (N2a) cells transfected with the Swedish amyloid precursor protein (Sw-APP) mutant and Presenilin exon 9 deletion mutant (N2a/D9), which overproduced Aβ with abnormal intracellular Aβ accumulation. The results show increased levels of ROS, NO, protein carbonyls, and 4HNE in N2a/D9 cells, which were attenuated by resistin treatment in a dose dependent manner. We also found that resistin could improve mitochondrial function in N2a/D9 cells through increasing the level of ATP and mitochondrial membrane potential. MTT and LDH assay indicated that N2a/D9 cells show increased vulnerability to H2O2-induced insult, which could be ameliorated by resistin. Mechanically, we found that resistin prevented apoptosis signals through reducing the ratio of Bax/Bcl2, the level of cleaved caspase-3, and attenuating cytochrome C release. Finally, the results demonstrated that resistin did not change the production of Aβ1-40 and Aβ1-42 in N2a/D9 cells, which suggests that the protective effects of resistin are independent of APP metabolism. This raises the possibility of novel AD therapies using resistin.

Cilostazol promotes mitochondrial biogenesis in human umbilical vein endothelial cells through activating the expression of PGC-1α

Mitochondrial dysfunction is frequently observed in vascular diseases. Cilostazol is a drug approved by the US Food and Drug Administration for the treatment of intermittent claudication. Cilostazol increases intracellular cyclic adenosine monophosphate (cAMP) levels through inhibition of type III phosphodiesterase. The effects of cilostazol in mitochondrial biogenesis in human umbilical vein endothelial cells (HUVECs) were investigated in this study. Cilostazol treated HUVECs displayed increased levels of ATP, mitochondrial DNA/nuclear DNA ratio, expressions of cytochrome B, and mitochondrial mass, suggesting an enhanced mitochondrial biogenesis induced by cilostazol. The promoted mitochondrial biogenesis could be abolished by Protein kinase A (PKA) specific inhibitor H-89, implying that PKA pathway played a critical role in increased mitochondrial biogenesis after cilostazol treatment. Indeed, expression levels of peroxisome proliferator activator receptor gamma-coactivator 1α (PGC-1α), NRF 1 and mitochondrial transcription factor A (TFAM) were significantly increased in HUVECs after incubation with cilostazol at both mRNA levels and protein levels. Importantly, knockdown of PGC-1α could abolish cilostazol-induced mitochondrial biogenesis. Enhanced expression of p-CREB and PGC-1α induced by cilostazol could be inhibited by H-89. Moreover, the increased expression of PGC-1α induced by cilostazol could be inhibited by downregulation of CREB using CREB siRNA at both mRNA and protein levels. All the results indicated that cilostazol promoted mitochondrial biogenesis through activating the expression of PGC-1α in HUVECs, which was mediated by PKA/CREB pathway.

Angiogenesis: A Target in Solid Tumors, Also in Leukemia?

Targeting angiogenesis has become an established therapeutic approach to fighting solid tumor growth in cancer patients. Even though increased angiogenesis has long been recognized in various types of hematologic malignancies, the molecular basis underlying this angiogenic switch in leukemias remains poorly understood. The BM stroma is gaining increasing attention for its role in promoting leukemia growth and resistance against current treatments with tyrosine kinase inhibitors. This article provides a brief overview of the role of angiogenesis in leukemias, discusses recent insights into the role of placenta growth factor (PlGF), a VEGF family member, as a novel disease candidate in chronic myeloid leukemia (CML), and highlights the therapeutic potential of PlGF blockade for imatinib-resistant CML.

Cholesterol sequestration by nystatin enhances the uptake and activity of endostatin in endothelium via regulating distinct endocytic pathways

Specific internalization of endostatin into endothelial cells has been proved to be important for its biologic functions. However, the mechanism of endostatin internalization still remains elusive. In this study, we report for the first time that both caveolae/lipid rafts and clathrin-coated pits are involved in endostatin internalization. Inhibition of either the caveolae pathway or the clathrin pathway with the use of chemical inhibitors, small interfering RNAs, or dominant-negative mutants alters endostatin internalization in vitro. Intriguingly, cholesterol sequestration by nystatin, a polyene antifungal drug, significantly enhances endostatin uptake by endothelial cells through switching endostatin internalization predominantly to the clathrin-mediated pathway. Nystatin-enhanced internalization of endostatin also increases its inhibitory effects on endothelial cell tube formation and migration. More importantly, combined treatment with nystatin and endostatin selectively enhances endostatin uptake and biodistribution in tumor blood vessels and tumor tissues but not in normal tissues of tumor-bearing mice, ultimately resulting in elevated antiangiogenic and antitumor efficacies of endostatin in vivo. Taken together, our data show a novel mechanism of endostatin internalization and support the potential application of enhancing the uptake and therapeutic efficacy of endostatin via regulating distinct endocytic pathways with cholesterol-sequestering agents.

Gene expression analysis of HUVEC in response to TF-binding

INTRODUCTION

Tissue factor (TF), the cofactor for factor VII/VIIa (FVII/FVIIa) and initiator of the extrinsic pathway, is transiently expressed on intravascular cells under control of cytokines and growth factors. In addition, endothelial cells express a binding site for external TF. In the present study, we investigated gene expression of endothelial cells derived from human umbilical veins (HUVEC) in response to TF-binding to identify differentially expressed genes.

MATERIALS AND METHODS

HUVEC were treated with recombinant relipidated TF (Innovin) versus nontreated cells, as well as TF/FVIIa versus FVIIa alone. TF binding was measured by ELISA. Gene expression profiles were examined using HG-U133 plus 2.0 arrays (Affymetrix).

RESULTS

Gene expression analysis of HUVEC showed 148 up-regulated and 29 down-regulated genes 4h after TF binding. Notably, the genes, which were significantly up- and down-regulated, either by TF alone or by the complex of TF/FVIIa, exhibited a complete overlap, indicating that activation of endothelial cells after binding of external added TF does not depend on FVIIa as has been demonstrated for TF-expressing cells. TF-mediated regulation of gene expression of several genes, involved in regulation of apoptosis, cell adhesion, cell motility, and angiogenesis, was confirmed by qPCR. Furthermore, in case of SELE, TGFB2, TNFAIP3, TNFSF4, TNFSF18, TAGLN, CXCL1, PCF11 antibodies directed to TF clearly inhibited TF-mediated regulation of gene expression.

CONCLUSIONS

The results demonstrate that interaction of TF with HUVEC via a binding site, independent from FVIIa, may result in regulation of a variety of genes involved in arteriosclerosis, cancer, and cardiovascular diseases.

Anti-tissue factor short hairpin RNA inhibits breast cancer growth in vivo

In breast cancer, there is a correlation between tissue factor (TF) expression, angiogenesis and disease progression. TF stimulates tumour angiogenesis, in part, through up-regulation of vascular endothelial growth factor (VEGF). Therefore, this study aimed to establish whether TF stimulates angiogenesis and tumour progression directly and independent of VEGF up-regulation. Initially, the effects of TF and VEGF were assessed on endothelial cell migration (Boyden chamber) and differentiation (tubule formation on Matrigel). Subsequently, MDA-MB-436 breast cancer cells, which produce high levels of both TF and VEGF (western blot analysis), were established in vivo, following which tumours were treated three times per week for 3 weeks with intra-tumoural injections of either anti-VEGF siRNA, anti-TF shRNA, the two treatments combined, or relevant controls. Both VEGF and TF significantly stimulated endothelial cell migration and tubule formation (P < 0.02). Breast cancer xenografts (MDA-MB-436) treated with TF or VEGF-specific agents demonstrated significant inhibition in tumour growth (VEGFsiRNA 61%; final volume: 236.2 ± 23.2 mm(3) vs TFshRNA 89%; 161.9 ± 17.4 mm(3) vs combination 93%; 136.3 ± 9.2 mm(3) vs control 400.4 ± 32.7 mm(3); P < 0.005). Microvessel density (MVD), a measure of angiogenesis, was also significantly inhibited in all groups (MVD in control = 29 ± 2.9; TFshRNA = 18 ± 1.1; VEGFsiRNA = 16.7 ± 1.5; both = 12 ± 2.1; P < 0.004), whereas the proliferative index of the tumours was only reduced in the TFshRNA-treated groups (control = 0.51 ± 0.011; TFshRNA = 0.41 ± 0.014; VEGFsiRNA = 0.49 ± 0.013; both = 0.41 ± 0.004; P < 0.008). These data suggest that TF has a direct effect on primary breast cancer growth and angiogenesis, and that specific inhibition of the TF-signalling pathway has potential for the treatment of primary breast cancer.

Influence of silica particle internalization on adhesion and migration of human dermal fibroblasts

In spite of significant advantages exhibiting in the applications of silicon dioxide particles in biological and medicine fields, their adverse effects still remain a big concern. Herein monodisperse spherical SiO(2) particles with diameters of 80 nm and 500 nm were used to study their interactions with human dermal fibroblasts. Both the particles were readily internalized into the fibroblasts within a short time. The 500 nm particles were taken up in a larger amount through macropinocytosis and clathrin-mediated endocytosis pathways, whereas uptake of the 80 nm SiO(2) particles was mediated corporately by macropinocytosis, clathrin-mediated and caveolae-mediated endocytosis. The particles mainly dispersed in the cytoplasm or resided within the lysosomal vesicles, but could not enter into the cell nucleus within 24 h culture in vitro. Treatment with the 80 nm SiO(2) particles caused apparently decrease of cell viability and also weakened the mitochondrial membrane potential. Further experiments demonstrated that the cell adhesion and migration were greatly affected by uptake of the SiO(2) particles regardless of their size. RT-PCR results indicated down regulation of the mRNA expression of adhesion relevant genes, i.e. fibronectin, laminin and focal adhesion kinase (FAK).

The regulatory mechanism of Hsp90alpha secretion from endothelial cells and its role in angiogenesis during wound healing

Heat shock protein 90alpha (Hsp90alpha) is a ubiquitously expressed molecular chaperone, which is essential for the maintenance of eukaryote homeostasis. Hsp90alpha can also be secreted extracellularly and is associated with several physiological and pathological processes including wound healing, cancer, infectious diseases and diabetes. Angiogenesis, defined as the sprouting of new blood vessels from pre-existing capillaries via endothelial cell proliferation and migration, commonly occurs in and contributes to the above mentioned processes. However, the secretion of Hsp90alpha from endothelial cells and also its function in angiogenesis are still unclear. Here we investigated the role of extracellular Hsp90alpha in angiogenesis using dermal endothelial cells in vitro and a wound healing model in vivo. We find that the secretion of Hsp90alpha but not Hsp90beta is increased in activated endothelial cells with the induction of angiogenic factors and matrix proteins. Secreted Hsp90alpha localizes on the leading edge of endothelial cells and promotes their angiogenic activities, whereas Hsp90alpha neutralizing antibodies reverse the effect. Furthermore, using a mouse skin wound healing model in vivo, we demonstrate that extracellular Hsp90alpha localizes on blood vessels in granulation tissues of wounded skin and promotes angiogenesis during wound healing. Taken together, our study reveals that Hsp90alpha can be secreted by activated endothelial cells and is a positive regulator of angiogenesis, suggesting the potential application of Hsp90alpha as a stimulator for wound repair.

Evaluation of thrombogenic potential of electrospun bioresorbable vascular graft materials: acute monocyte tissue factor expression

The purpose of this study was to quantify the acute expression of tissue factor (TF) by monocytes on interaction with electrospun bioresorbable constructs. A minimal expression of TF will demonstrate the potential for scaffolds to be used as a vascular graft without enhanced risk of failure from acute thrombotic occlusion. Polydioxanone (PDO) (60, 80, 120, and 160 mg/mL) and polycaprolactone (PCL) (80, 10, and 160 mg/mL) dissolved in 1,1,1,3,3,3 hexafluoro-2-propanol (HFP) were electrospun to form fibrous scaffolds. Circular discs (10 mm diameter) of each scaffold were disinfected and seeded with human monocytes (50,000 cells/well). The discs were statically cultured under standard conditions (37 degrees C and 5% CO2), and removed after 24 h for TF analysis with an In-Cell Western assay. Fiber diameter was calculated through ImageTool analysis of scanning electron micrographs. Acute monocyte interaction with scaffolds of PCL (120 mg/mL) resulted in the lowest amount of TF expressed (4 ng/disc), whereas scaffolds of 160 mg/mL PDO elicited the highest amount of TF expressed (51 ng/disc). TF levels expressed on all scaffolds were comparable with the amount expressed on e-PTFE (20 ng/disc). Preliminary data for TF expression on scaffolds of silk (70 mg/mL and 150 mg/mL) and silk:PCL (100 mg/mL, v/v) blends (50:50 and 70:30) resulted in values of TF expression ranging from 0 to 24 ng. Results from this study reveal electrospun grafts composed of PDO and PCL provide no greater risk of failure from an acute thrombotic occlusion due to TF expression when compared with that of the standard e-PTFE graft.

Modified C-reactive protein is expressed by stroke neovessels and is a potent activator of angiogenesis in vitro

Native C-reactive protein (nCRP) is a pentameric oligo-protein and an acute phase reactant whose serum expression is increased in patients with inflammatory disease. We have identified by immunohistochemistry, significant expression of a tissue-binding insoluble modified version or monomeric form of CRP (mCRP) associated with angiogenic microvessels in peri-infarcted regions of patients studied with acute ischaemic stroke. mCRP, but not nCRP was expressed in the cytoplasm and nucleus of damaged neurons. mCRP co-localized with CD105, a marker of angiogenesis in regions of revascularisation. In vitro investigations demonstrated that mCRP was preferentially expressed in human brain microvessel endothelial cells following oxygen-glucose deprivation and mCRP (but not column purified nCRP) associated with the endothelial cell surface, and was angiogenic to vascular endothelial cells, stimulating migration and tube formation in matrigel more strongly than fibroblast growth factor-2. The mechanism of signal transduction was not through the CD16 receptor. Western blotting showed that mCRP stimulated phosphorylation of the key down-stream mitogenic signalling protein ERK1/2. Pharmacological inhibition of ERK1/2 phosphorylation blocked the angiogenic effects of mCRP. We propose that mCRP may contribute to the neovascularization process and because of its abundant presence, be important in modulating angiogenesis in both acute stroke and later during neuro-recovery.

Tissue factor in cardiovascular disease pathophysiology and pharmacological intervention

Tissue factor (TF) is the major trigger of the coagulation cascade and thereby crucially involved in the maintenance of vascular hemostasis. By binding factor VIIa, the resulting TF:VIIa complex activates the coagulation factors IX and X ultimately leading to fibrin and clot formation. In the vessel wall, TF expression and activity is detectable in vascular smooth muscle cells and fibroblasts and, at a much lower level, in endothelial cells and can be induced by various stimuli including cytokines. In addition, TF is found in the bloodstream in circulating cells such as monocytes, in TF containing microparticles, and as a soluble splicing isoform. Besides its well-known extracellular role as a trigger of coagulation, TF also functions as a transmembrane receptor, and TF-dependent intracellular signaling events regulate the expression of genes involved in cellular responses such as proliferation and migration. TF indeed appears to be involved in the pathogenesis of neointima formation and tumor growth, and increased levels of TF have been detected in patients with cardiovascular risk factors or coronary artery disease as well as in those with cancer. Therefore, pharmacological or genetic inhibition of TF may be an attractive target for the treatment of cardiovascular disease and cancer. Different strategies for inhibition of TF have been developed such as inhibition of TF synthesis and blockade of TF action. Clinical applications of such strategies need to be tested in appropriate trials, in particular for evaluating the advantages of targeted versus systemic delivery of the inhibitors.

Tissue factor and cardiovascular disease: quo vadis?

The coagulation cascade represents a system of proteases responsible to maintain vascular integrity and to induce rapid clot formation after vessel injury. Tissue factor (TF), the key initiator of the coagulation cascade, binds to factor VIIa and thereby activates factor IX and factor X, resulting in thrombus formation. Different stimuli enhance TF gene expression in endothelial and vascular smooth muscle cells. In addition to these vascular cells, TF has recently been detected in the bloodstream in circulating cells such as leukocytes and platelets, as a component of microparticles, and as a soluble, alternatively spliced form of TF. Various cardiovascular risk factors like hypertension, diabetes, and dyslipidemia, increase levels of TF. In line with this observation, enhanced vascular TF expression occurs during atherogenesis, particularly in patients with acute coronary syndromes. (Circ J 2010; 74: 3 - 12).

Tissue factor: beyond coagulation in the cardiovascular system

TF (tissue factor) is the main trigger of the coagulation cascade; by binding Factor VIIa it activates Factor IX and Factor X, thereby resulting in fibrin formation. Various stimuli, such as cytokines, growth factors and biogenic amines, induce TF expression and activity in vascular cells. Downstream targets of these mediators include diverse signalling molecules such as MAPKs (mitogen-activated protein kinases), PI3K (phosphoinositide 3-kinase) and PKC (protein kinase C). In addition, TF can be detected in the bloodstream, known as circulating or blood-borne TF. Many cardiovascular risk factors, such as hypertension, diabetes, dyslipidaemia and smoking, are associated with increased expression of TF. Furthermore, in patients presenting with acute coronary syndromes, elevated levels of circulating TF are found. Apart from its role in thrombosis, TF has pro-atherogenic properties, as it is involved in neointima formation by inducing vascular smooth muscle cell migration. As inhibition of TF action appears to be an attractive target for the treatment of cardiovascular disease, therapeutic strategies are under investigation to specifically interfere with the action of TF or, alternatively, promote the effects of TFPI (TF pathway inhibitor).

Human peripheral blood endothelial progenitor cells synthesize and express functionally active tissue factor

INTRODUCTION

Endothelial progenitor cells are circulating cells able to home to sites of vascular damage and to contribute to the revascularization of ischemic areas. We evaluated whether endothelial progenitor cells synthesize tissue factor, a procoagulant protein also involved in angiogenesis.

MATERIALS AND METHODS

Endothelial progenitor cells were obtained from the peripheral blood mononuclear fraction of normal donors and cultured in endothelial medium supplemented with specific growth factors. The procoagulant activity expressed by cells disrupted by freeze-thaw cycles was assessed by a one stage clotting assay. Tissue factor mRNA expression was evaluated by RT-PCR.

RESULTS

Endothelial progenitor cells do not express procoagulant activity in baseline conditions. However, lipopolysaccharide induces the expression of procoagulant activity. The effect is dose-dependent and reaches statistical significance at 100 ng/mL lipopolysaccharide. Inhibition with an anti-tissue factor antibody and amplification of cDNA with primers based on the tissue factor sequence confirm the identity of this activity with tissue factor. The kinetics of tissue factor expression by endothelial progenitor cells is identical to that of human umbilical vein endothelial cells showing maximal activity within 4 hours, and then decreasing; in contrast, tissue factor expression by mononuclear cells lasts for longer times. Both 5,6-dichloro-beta D-ribofuranosyl-benzimidazole and cycloheximide prevented the expression of procoagulant activity. Stimulation of endothelial progenitor cells with tumor necrosis factor-alpha did not elicit any detectable procoagulant activity.

CONCLUSIONS

Endothelial progenitor cells can be stimulated by lipopolysaccharide to synthesize tissue factor. This protein might be involved in thrombotic phenomena and might contribute to endothelial progenitor cells related neovascularization.

Increased bone marrow microvascular density in haematological malignancies is associated with differential regulation of angiogenic factors

Antiangiogenic drugs are currently tested in haematological malignancies. As these drugs target different angiogenic regulators, and as cancers are inherently heterogeneous, a detailed characterization of angiogenesis in individual cancers is needed. Hence, we measured bone marrow microvessel density (MVD), plasma concentrations of eight angiogenesis-related parameters and the expression in blood mononuclear cells of 40 angiogenesis-related mRNAs in 93 patients with haematological neoplasias (acute myeloid leukaemia; chronic lymphatic leukaemia; multiple myeloma (MM); or non-Hodgkin's lymphoma (NHL)) before start and after completion of cancer therapy. Compared with healthy individuals, the patients had significantly increased bone marrow MVD, especially patients with advanced stage disease. A novel finding was that patients with NHL also had increased bone marrow MVD. The plasma levels of vascular endothelial growth factor (VEGF), interleukin (IL)-6 and IL-8 were significantly increased. VEGF levels were highest in those who did not achieve complete remission after cancer therapy. The mRNA expression of IL-8 was upregulated 15-fold. Our data show that patients with haematological malignancies have increased bone marrow MVD; hence, supporting the notion that bone marrow angiogenesis plays a role in the pathogenesis and progression of these cancers. VEGF, IL-6 and IL-8 seem to contribute to the malignant phenotype.