Coagulation factors X, Xa, and protein S as potent mitogens of cultured aortic smooth muscle cells

Lipoprotein(a) in Atherosclerotic Diseases: From Pathophysiology to Diagnosis and Treatment

Lipoprotein(a) (Lp(a)) is a low-density lipoprotein (LDL) cholesterol-like particle bound to apolipoprotein(a). Increased Lp(a) levels are an independent, heritable causal risk factor for atherosclerotic cardiovascular disease (ASCVD) as they are largely determined by variations in the Lp(a) gene (LPA) locus encoding apo(a). Lp(a) is the preferential lipoprotein carrier for oxidized phospholipids (OxPL), and its role adversely affects vascular inflammation, atherosclerotic lesions, endothelial function and thrombogenicity, which pathophysiologically leads to cardiovascular (CV) events. Despite this crucial role of Lp(a), its measurement lacks a globally unified method, and, between different laboratories, results need standardization. Standard antilipidemic therapies, such as statins, fibrates and ezetimibe, have a mediocre effect on Lp(a) levels, although it is not yet clear whether such treatments can affect CV events and prognosis. This narrative review aims to summarize knowledge regarding the mechanisms mediating the effect of Lp(a) on inflammation, atherosclerosis and thrombosis and discuss current diagnostic and therapeutic potentials.

Efferocytosis of vascular cells in cardiovascular disease

Cell death and the clearance of apoptotic cells are tightly regulated by various signaling molecules in order to maintain physiological tissue function and homeostasis. The phagocytic removal of apoptotic cells is known as the process of efferocytosis, and abnormal efferocytosis is linked to various health complications and diseases, such as cardiovascular disease, inflammatory diseases, and autoimmune diseases. During efferocytosis, phagocytic cells and/or apoptotic cells release signals, such as "find me" and "eat me" signals, to stimulate the phagocytic engulfment of apoptotic cells. Primary phagocytic cells are macrophages and dendritic cells; however, more recently, other neighboring cell types have also been shown to exhibit phagocytic character, including endothelial cells and fibroblasts, although they are comparatively slower in clearing dead cells. In this review, we focus on macrophage efferocytosis of vascular cells, such as endothelial cells, smooth muscle cells, fibroblasts, and pericytes, and its relation to the progression and development of cardiovascular disease. We also highlight the role of efferocytosis-related molecules and their contribution to the maintenance of vascular homeostasis.

Roles of Factor XII in Innate Immunity

Factor XII (FXII) is the zymogen of serine protease, factor XIIa (FXIIa). FXIIa enzymatic activities have been extensively studied and FXIIa inhibition is emerging as a promising target to treat or prevent thrombosis without creating a hemostatic defect. FXII and plasma prekallikrein reciprocally activate each other and result in liberation of bradykinin. Due to its unique structure among coagulation factors, FXII exerts mitogenic activity in endothelial and smooth muscle cells, indicating that zymogen FXII has activities independent of its protease function. A growing body of evidence has revealed that both FXII and FXIIa upregulate neutrophil functions, contribute to macrophage polarization and induce T-cell differentiation. In vivo, these signaling activities contribute to host defense against pathogens, mediate the development of neuroinflammation, influence wound repair and may facilitate cancer maintenance and progression. Here, we review the roles of FXII in innate immunity as they relate to non-sterile and sterile immune responses.

TAM receptors in cardiovascular disease

The TAM receptors are a distinct family of three receptor tyrosine kinases, namely Tyro3, Axl, and MerTK. Since their discovery in the early 1990s, they have been studied for their ability to influence numerous diseases, including cancer, chronic inflammatory and autoimmune disorders, and cardiovascular diseases. The TAM receptors demonstrate an ability to influence multiple aspects of cardiovascular pathology via their diverse effects on cells of both the vasculature and the immune system. In this review, we will explore the various functions of the TAM receptors and how they influence cardiovascular disease through regulation of vascular remodelling, efferocytosis and inflammation. Based on this information, we will suggest areas in which further research is required and identify potential targets for therapeutic intervention.

Antiplatelet and anticoagulant for prevention of reocclusion in patients with atrial fibrillation undergoing endovascular treatment for low extremity ischemia

Background

The purpose of this study is to report the efficacy of the mono antiplatelet plus anticoagulation therapy for prevention of reocclusion in patients with atrial fibrillation (AF) undergoing endovascular treatment for lower extremity ischemia.

Methods

From March 2014 to July 2016, 32 (21 males; range, 68-84 years) patients were submitted to endovascular therapy for low extremity ischemia with AF and all were treated with endovascular treatments to correct underlying lesions. Then 20 patients receive aspirin plus rivaroxaban post-operation and 12 patients receive aspirin plus warfarin to prevent reocclusion.

Results

Complete reconstruction of occluded femopopliteal arteries with unimpeded blood flow to legs were successfully obtained in all 32 patients; 12 (37.5%) patients had acute ischemia, 17 (53.1%) patients had chronic ischemia, 3 (9.4%) patients had acute on chronic ischemia. Endovascular treatments including percutaneous transluminal angioplasty (PTA) and stenting were performed to correct residual lesions after the thrombolytic/thrombectomy procedure or to correct native lesions for chronic patients. All 32 patients showed significant improvements in symptoms and 4 patients improved completely. The mean ankle-brachial index (ABI) had risen from 0.43±0.21 preoperatively to 0.81±0.16 postoperatively (P<0.01), and the primary patency rates were 88.9% at 12 months, and 81.5% at 24 months. No episodes of major bleeding and only one patient showed positive fecal occult blood tests during the follow-up.

Conclusions

The mono antiplatelet plus anticoagulation therapy offers a safe and effective alternative for prevention of reocclusion in patients with AF undergoing endovascular treatment for lower extremity ischemic.

A direct oral factor Xa inhibitor edoxaban ameliorates neointimal hyperplasia following vascular injury and thrombosis in apolipoprotein E-deficient mice

Vascular injury activates the coagulation cascade. Some studies report that coagulation factor Xa and thrombin are implicated in proliferation of vascular smooth muscle cells and neointimal hyperplasia after vascular injury. The aim of this study was to determine the effect of an oral direct factor Xa inhibitor, edoxaban, on neointimal hyperplasia following the carotid artery injury in apolipoprotein E (ApoE)-deficient mice. Vascular injury was induced by the application of 10% ferric chloride to the carotid artery for 3 min in ApoE-deficient mice. After vascular injury, all animals were fed with high-cholesterol chow for 6 weeks. Edoxaban at 15 mg/kg was orally administered to the mice 1 h before (n = 10) or 1 h after (n = 9) ferric chloride injury, and thereafter 10 mg/kg edoxaban was orally administered b.i.d. for 6 weeks. Thrombus formation and neointimal hyperplasia were evaluated. Treatment with 15 mg/kg edoxaban before vascular injury almost completely inhibited thrombus formation, and following chronic administration of edoxaban significantly suppressed neointimal hyperplasia. In the mice treated with edoxaban after vascular injury, there was wide interindividual variability. In some mice (four out of nine) the neointimal hyperplasia was inhibited like in edoxaban-pretreated mice, but there was no statistical difference compared with control. This study demonstrated that inhibition of the coagulation and thrombosis by edoxaban ameliorated neointimal hyperplasia caused by vascular injury and high-cholesterol diets in ApoE-deficient mice. This suggests that factor Xa has a crucial role in the formation of neointima following vascular injury.The abstract should be followed by 3-4 bullet points that highlight major findings. The final bullet point should emphasize future directions for research.

The Journey of Protein S from an Anticoagulant to a Signaling Molecule

Protein S (PS), a γ-carboxyglutamate-containing serum protein, was unexpectedly discovered in 1977. Soon after its discovery, PS gained the attention of researchers because of its physiological importance, acting as a multifunctional protein at the intersection of blood coagulation, inflammation, and other cellular processes. Protein S functions as an anticoagulant by directly inhibiting procoagulants, such as Factor Xa (FXa), FVa, and FIXa, while also serving as a cofactor for anticoagulants such as Activated Protein C and Tissue Factor Pathway Inhibitor. By associating with C4b binding protein (C4BP), PS has also been shown to minimize the effect of inflammation. Finally, PS promotes efferocytosis through TAM family protein kinase receptors. Mutations in the PS gene cause pathological conditions such as deep vein thrombosis and hereditary ischemia. In this review, we summarize studies regarding the multiple functions of PS.

TAM receptor signaling in immune homeostasis

The TAM receptor tyrosine kinases (RTKs)-TYRO3, AXL, and MERTK-together with their cognate agonists GAS6 and PROS1 play an essential role in the resolution of inflammation. Deficiencies in TAM signaling have been associated with chronic inflammatory and autoimmune diseases. Three processes regulated by TAM signaling may contribute, either independently or collectively, to immune homeostasis: the negative regulation of the innate immune response, the phagocytosis of apoptotic cells, and the restoration of vascular integrity. Recent studies have also revealed the function of TAMs in infectious diseases and cancer. Here, we review the important milestones in the discovery of these RTKs and their ligands and the studies that underscore the functional importance of this signaling pathway in physiological immune settings and disease.

Biology of the TAM receptors

The TAM receptors--Tyro3, Axl, and Mer--comprise a unique family of receptor tyrosine kinases, in that as a group they play no essential role in embryonic development. Instead, they function as homeostatic regulators in adult tissues and organ systems that are subject to continuous challenge and renewal throughout life. Their regulatory roles are prominent in the mature immune, reproductive, hematopoietic, vascular, and nervous systems. The TAMs and their ligands--Gas6 and Protein S--are essential for the efficient phagocytosis of apoptotic cells and membranes in these tissues; and in the immune system, they act as pleiotropic inhibitors of the innate inflammatory response to pathogens. Deficiencies in TAM signaling are thought to contribute to chronic inflammatory and autoimmune disease in humans, and aberrantly elevated TAM signaling is strongly associated with cancer progression, metastasis, and resistance to targeted therapies.

Protein S: A multifunctional anticoagulant vitamin K-dependent protein at the crossroads of coagulation, inflammation, angiogenesis, and cancer

Since its discovery in 1970, protein S (PS) has emerged as a key vitamin K-dependent natural anticoagulant protein at the crossroads of multiple biological processes, including coagulation, apoptosis, atherosclerosis, angiogenesis/vasculogenesis, and cancer progression. Following the binding to a unique family of protein tyrosine kinase receptors referred to as Tyro-3, Axl and Mer (TAM) receptors, PS can lead to regulation of coagulation, phagocytosis of apoptotic cells, cell survival, activation of innate immunity, vessel integrity and angiogenesis, and local invasion and metastasis. Because of these dynamics and multiple functions of PS, which are largely lost following invalidation of the mouse PROS1 gene, this molecule is currently intensively studied in biomedical research. The purpose of this review is to provide a brief chronicle of the discovery and current understanding of the mechanisms of PS signaling, and how PS and their signaling partners regulate various cellular functions, with a particular focus on TAM receptors.

Factor-Xa-induced mitogenesis and migration require sphingosine kinase activity and S1P formation in human vascular smooth muscle cells

AIMS

Sphingosine-1-phosphate (S1P) is a cellular signalling lipid generated by sphingosine kinase-1 (SPHK1). The aim of the study was to investigate whether the activated coagulation factor-X (FXa) regulates SPHK1 transcription and the formation of S1P and subsequent mitogenesis and migration of human vascular smooth muscle cells (SMC).

METHODS AND RESULTS

FXa induced a time- (3-6 h) and concentration-dependent (3-30 nmol/L) increase of SPHK1 mRNA and protein expression in human aortic SMC, resulting in an increased synthesis of S1P. FXa-stimulated transcription of SPHK1 was mediated by the protease-activated receptor-1 (PAR-1) and PAR-2. In human carotid artery plaques, expression of SPHK1 was observed at SMC-rich sites and was co-localized with intraplaque FX/FXa content. FXa-induced SPHK1 transcription was attenuated by inhibitors of Rho kinase (Y27632) and by protein kinase C (PKC) isoforms (GF109203X). In addition, FXa rapidly induced the activation of the small GTPase Rho A. Inhibition of signalling pathways which regulate SPHK1 expression, inhibition of its activity or siRNA-mediated SPHK1 knockdown attenuated the mitogenic and chemotactic response of human SMC to FXa.

CONCLUSION

These data suggest that FXa induces SPHK1 expression and increases S1P formation independent of thrombin and that this involves the activation of Rho A and PKC signalling. In addition to its key function in coagulation, this direct effect of FXa on human SMC may increase cell proliferation and migration at sites of vessel injury and thereby contribute to the progression of vascular lesions.

The role of tissue factor pathway inhibitor in atherosclerosis and arterial thrombosis

Tissue factor pathway inhibitor (TFPI) is the main inhibitor of tissue factor (TF)-mediated coagulation. In atherosclerotic plaques TFPI co-localizes with TF, where it is believed to play an important role in attenuating TF activity. Findings in animal models such as TFPI knockout models and gene transfer models are consistent on the role of TFPI in arterial thrombosis as they reveal an active role for TFPI in attenuating arterial thrombus formation. In addition, ample experimental evidence exists indicating that TFPI has inhibitory effects on both smooth muscle cell migration and proliferation, both which are recognized as important pathological features in atherosclerosis development. Nonetheless, the clinical relevance of these antithrombotic and atheroprotective effects remains unclear. Paradoxically, the majority of clinical studies find increased instead of decreased TFPI antigen and activity levels in atherothrombotic disease, particularly in atherosclerosis and coronary artery disease (CAD). Increased TFPI levels in cardiovascular disease might result from complex interactions with established cardiovascular risk factors, such as hypercholesterolemia, diabetes and smoking. Moreover, it is postulated that increased TFPI levels reflect either the amount of endothelial perturbation and platelet activation, or a compensatory mechanism for the increased procoagulant state observed in cardiovascular disease. In all, the prognostic value of plasma TFPI in cardiovascular disease remains to be established. The current review focuses on TFPI in clinical studies of asymptomatic and symptomatic atherosclerosis, coronary artery disease and ischemic stroke, and discusses potential atheroprotective actions of TFPI.

The use of antithrombotic therapies in reducing synthetic small-diameter vascular graft thrombosis

BACKGROUND

Thrombosis of synthetic small-diameter bypass grafts remains a major problem. The aim of this article is to review the antithrombotic strategies that have been used in an attempt to reduce graft thrombogenicity.

METHODS

A PubMed/MEDLINE search was performed using the search terms "vascular graft thrombosis," "small-diameter graft thrombosis," "synthetic graft thrombosis" combined with "antithrombotic," "antiplatelet," "anticoagulant," "Dacron," "PTFE," and "polyurethane."

RESULTS

The majority of studies on antithrombotic therapies have used either in vitro models or in vivo animal experiments. Many of the therapies used in these settings do show antithrombotic efficacy against synthetic graft materials. There is however, a distinct lack of human in vivo studies to further delineate the performance and limitations of therapies displaying good antithrombotic characteristics.

CONCLUSION

Very few antithrombotic therapies have translated into clinical use. More human in vivo studies are required to assess the efficacy and safety of such therapies.

Evaluation of plaque stability of advanced atherosclerotic lesions in apo E-deficient mice after treatment with the oral factor Xa inhibitor rivaroxaban

Aim. Thrombin not only plays a central role in thrombus formation and platelet activation, but also in induction of inflammatory processes. Activated factor X (FXa) is traditionally known as an important player in the coagulation cascade responsible for thrombin generation. We assessed the hypothesis that rivaroxaban, a direct FXa inhibitor, attenuates plaque progression and promotes stability of advanced atherosclerotic lesions in an in vivo model. Methods and Results. Rivaroxaban (1 or 5 mg/kg body weight/day) or standard chow diet was administered for 26 weeks to apolipoprotein E-deficient mice (n = 20 per group) with already established atherosclerotic lesions. There was a nonsignificant reduction of lesion progression in the high-concentration group, compared to control mice. FXa inhibition with 5 mg Rivaroxaban/kg/day resulted in increased thickness of the protective fibrous caps (12.3 ± 3.8 μm versus 10.1 ± 2.7 μm; P < .05), as well as in fewer medial erosions and fewer lateral xanthomas, indicating plaque stabilizing properties. Real time-PCR from thoracic aortas revealed that rivaroxaban (5 mg/kg/day) treatment reduced mRNA expression of inflammatory mediators, such of IL-6, TNF-α, MCP-1, and Egr-1 (P < .05). Conclusions. Chronic administration of rivaroxaban does not affect lesion progression but downregulates expression of inflammatory mediators and promotes lesion stability in apolipoprotein E-deficient mice.

Protein S blocks the extrinsic apoptotic cascade in tissue plasminogen activator/N-methyl D-aspartate-treated neurons via Tyro3-Akt-FKHRL1 signaling pathway

Background

Thrombolytic therapy with tissue plasminogen activator (tPA) benefits patients with acute ischemic stroke. However, tPA increases the risk for intracerebral bleeding and enhances post-ischemic neuronal injury if administered 3-4 hours after stroke. Therefore, combination therapies with tPA and neuroprotective agents have been considered to increase tPA's therapeutic window and reduce toxicity. The anticoagulant factor protein S (PS) protects neurons from hypoxic/ischemic injury. PS also inhibits N-methyl-D-aspartate (NMDA) excitotoxicity by phosphorylating Bad and Mdm2 which blocks the downstream steps in the intrinsic apoptotic cascade. To test whether PS can protect neurons from tPA toxicity we studied its effects on tPA/NMDA combined injury which in contrast to NMDA alone kills neurons by activating the extrinsic apoptotic pathway. Neither Bad nor Mdm2 which are PS's targets and control the intrinsic apoptotic pathway can influence the extrinsic cascade. Thus, based on published data one cannot predict whether PS can protect neurons from tPA/NMDA injury by blocking the extrinsic pathway. Neurons express all three TAM (Tyro3, Axl, Mer) receptors that can potentially interact with PS. Therefore, we studied whether PS can activate TAM receptors during a tPA/NMDA insult.

Results

We show that PS protects neurons from tPA/NMDA-induced apoptosis by suppressing Fas-ligand (FasL) production and FasL-dependent caspase-8 activation within the extrinsic apoptotic pathway. By transducing neurons with adenoviral vectors expressing the kinase-deficient Akt mutant Akt^K179A and a triple FKHRL1 Akt phosphorylation site mutant (FKHRL1-TM), we show that Akt activation and Akt-mediated phosphorylation of FKHRL1, a member of the Forkhead family of transcription factors, are critical for FasL down-regulation and caspase-8 inhibition. Using cultured neurons from Tyro3, Axl and Mer mutants, we show that Tyro3, but not Axl and Mer, mediates phosphorylation of FHKRL1 that is required for PS-mediated neuronal protection after tPA/NMDA-induced injury.

Conclusions

PS blocks the extrinsic apoptotic cascade through a novel mechanism mediated by Tyro3-dependent FKHRL1 phosphorylation which inhibits FasL-dependent caspase-8 activation and can control tPA-induced neurotoxicity associated with pathologic activation of NMDA receptors. The present findings should encourage future studies in animal stroke models to determine whether PS can increase the therapeutic window of tPA by reducing its post-ischemic neuronal toxicity.

Increased preoperative thrombin generation and low protein S level associated with unfavorable postoperative hemodynamics after coronary artery bypass grafting

In a previous study, preoperative levels of activated protein C (APC) were associated with unfavorable postoperative hemodynamics after coronary artery bypass grafting (CABG). Protein C is activated by thrombin. Protein S, the cofactor of activated protein C, has activated protein C-independent anticoagulant activity and cytoprotective effects. Therefore, the objective of this study was to test whether preoperative, baseline levels of either thrombin or protein S were associated with hemodynamic performance or markers of myocardial damage after CABG. One hundred patients undergoing elective on-pump CABG were prospectively studied. Prothrombin fragment F1+2 (a marker of thrombin generation) and free protein S were measured preoperatively and cardiac index, systemic vascular resistance index (SVRI), and pulmonary vascular resistance index (PVRI) were measured serially thereafter at fixed time points. Cardiac biomarkers CK-MBm and TnT were measured postoperatively. There was an inverse correlation between preoperative F1+2 and free protein S levels (r= —0.30, p=0.003). High preoperative F1+2 and low preoperative protein S levels were associated with a less favorable hemodynamic profile postoperatively. Patients with F1+2 in the highest decile (≥0.85 nmol/l) and patients with preoperative protein S in the lowest decile (≤63%) had lower CI values, and higher pulmonary and systemic vascular resistance index values postoperatively than comparison patients. Preoperative F1+2 or protein S did not correlate with postoperative cardiac biomarker levels. Baseline activation of coagulation and the balance between pro-coagulant and anti-coagulant factors preoperatively might have implications for postoperative hemodynamic recovery after CABG.

The endothelial protein C receptor supports tissue factor ternary coagulation initiation complex signaling through protease-activated receptors

Protease-activated receptor (PAR) signaling is closely linked to the cellular activation of the pro- and anticoagulant pathways. The endothelial protein C receptor (EPCR) is crucial for signaling by activated protein C through PAR1, but EPCR may have additional roles by interacting with the 4-carboxyglutamic acid domains of procoagulant coagulation factors VII (FVII) and X (FX). Here we show that soluble EPCR regulates the interaction of FX with human or mouse tissue factor (TF)-FVIIa complexes. Mutagenesis of the FVIIa 4-carboxyglutamic acid domain and dose titrations with FX showed that EPCR interacted primarily with FX to attenuate FX activation in lipid-free assay systems. In human cell models of TF signaling, antibody inhibition of EPCR selectively blocked PAR activation by the ternary TF-FVIIa-FXa complex but not by the non-coagulant TF-FVIIa binary complex. Heterologous expression of EPCR promoted PAR1 and PAR2 cleavage by FXa in the ternary complex but did not alter PAR2 cleavage by TF-FVIIa. In murine smooth muscle cells that constitutively express EPCR and TF, thrombin and FVIIa/FX but not FVIIa alone induced PAR1-dependent signaling. Although thrombin signaling was unchanged, cells with genetically reduced levels of EPCR no longer showed a signaling response to the ternary complex. These results demonstrate that EPCR interacts with the ternary TF coagulation initiation complex to enable PAR signaling and suggest that EPCR may play a role in regulating the biology of TF-expressing extravascular and vessel wall cells that are exposed to limited concentrations of FVIIa and FX provided by ectopic synthesis or vascular leakage.

Protein S protects neurons from excitotoxic injury by activating the TAM receptor Tyro3-phosphatidylinositol 3-kinase-Akt pathway through its sex hormone-binding globulin-like region

The anticoagulant factor protein S (PS) protects neurons from hypoxic/ischemic injury. However, molecular mechanisms mediating PS protection in injured neurons remain unknown. Here, we show mouse recombinant PS protects dose-dependently mouse cortical neurons from excitotoxic NMDA-mediated neuritic bead formation and apoptosis by activating the phosphatidylinositol 3-kinase (PI3K)-Akt pathway (EC(50) = 26 ± 4 nm). PS stimulated phosphorylation of Bad and Mdm2, two downstream targets of Akt, which in neurons subjected to pathological overstimulation of NMDA receptors (NMDARs) increased the antiapoptotic Bcl-2 and Bcl-X(L) levels and reduced the proapoptotic p53 and Bax levels. Adenoviral transduction with a kinase-deficient Akt mutant (Ad.Akt(K179A)) resulted in loss of PS-mediated neuronal protection, Akt activation, and Bad and Mdm2 phosphorylation. Using the TAM receptors tyrosine kinases Tyro3-, Axl-, and Mer-deficient neurons, we showed that PS protected neurons lacking Axl and Mer, but not Tyro3, suggesting a requirement of Tyro3 for PS-mediated protection. Consistent with these results, PS dose-dependently phosphorylated Tyro3 on neurons (EC(50) = 25 ± 3 nm). In an in vivo model of NMDA-induced excitotoxic lesions in the striatum, PS dose-dependently reduced the lesion volume in control mice (EC(50) = 22 ± 2 nm) and protected Axl(-/-) and Mer(-/-) transgenic mice, but not Tyro3(-/-) transgenic mice. Using different structural PS analogs, we demonstrated that the C terminus sex hormone-binding globulin-like (SHBG) domain of PS is critical for neuronal protection in vitro and in vivo. Thus, our data show that PS protects neurons by activating the Tyro3-PI3K-Akt pathway via its SHGB domain, suggesting potentially a novel neuroprotective approach for acute brain injury and chronic neurodegenerative disorders associated with excessive activation of NMDARs.

TWEAK-Fn14 interaction enhances plasminogen activator inhibitor 1 and tissue factor expression in atherosclerotic plaques and in cultured vascular smooth muscle cells

AIMS

atherosclerotic plaque development can conclude with a thrombotic acute event triggered by plaque rupture/erosion. Tumour necrosis factor-like weak inducer of apoptosis (TWEAK) is a member of the tumour necrosis factor superfamily that, through its receptor, fibroblast growth factor-inducible 14 (Fn14), participates in vascular remodelling, increasing vascular inflammatory responses and atherosclerotic lesion size in ApoE knockout mice. However, the role of the TWEAK-Fn14 axis in thrombosis has not been previously investigated.

METHODS AND RESULTS

we have examined whether TWEAK regulates expression of prothrombotic factors such as tissue factor (TF) and plasminogen activator inhibitor 1 (PAI-1) in atherosclerotic plaques as well as in human aortic vascular smooth muscle cells (hASMCs) in culture. Expression of TF and PAI-1 was colocalized and positively correlated with Fn14 in human carotid atherosclerotic plaques. In vitro, TWEAK increased TF and PAI-1 mRNA, protein expression and activity in hASMCs. All these effects were reversed using blocking anti-TWEAK monoclonal antibody, anti-Fn14 antibody or Fn14 small interfering RNA, indicating that TWEAK increased the prothrombotic state through its receptor, Fn14. Finally, ApoE(-/-) mice were fed a hyperlipidaemic diet for 10 weeks, then randomized and treated with saline (controls), TWEAK (10 microg/kg/day), anti-TWEAK neutralizing monoclonal antibody (1000 µg/kg/day), or non-specific immunoglobulin G (1000 microg/kg/day) daily for 9 days. Systemic TWEAK injection increased TF and PAI-1 protein expression in the aortic root of ApoE(-/-) mice. Conversely, TWEAK blocking antibodies diminished both TF and PAI-1 protein expression compared with non-specific immunoglobulin G-treated mice.

CONCLUSIONS

our results indicate that the TWEAK-Fn14 axis can regulate activation of TF and PAI-1 expression in vascular cells. TWEAK-Fn14 may be a therapeutic target in the prothrombotic complications associated with atherosclerosis.

Protein S controls hypoxic/ischemic blood-brain barrier disruption through the TAM receptor Tyro3 and sphingosine 1-phosphate receptor

The anticoagulant factor protein S (PS) has direct cellular activities. Lack of PS in mice causes lethal coagulopathy, ischemic/thrombotic injuries, vascular dysgenesis, and blood-brain barrier (BBB) disruption with intracerebral hemorrhages. Thus, we hypothesized that PS maintains and/or enhances the BBB integrity. Using a BBB model with human brain endothelial cells, we show PS inhibits time- and dose-dependently (half maximal effective concentration [EC(50)] = 27 +/- 3 nM) oxygen/glucose deprivation-induced BBB breakdown, as demonstrated by measurements of the transmonolayer electrical resistance, permeability of endothelial monolayers to dextran (40 kDa), and rearrangement of F-actin toward the cortical cytoskeletal ring. Using Tyro-3, Axl, and Mer (TAM) receptor, tyrosine kinase silencing through RNA interference, specific N-terminus-blocking antibodies, Tyro3 phosphorylation, and Tyro3-, Axl- and Mer-deficient mouse brain endothelial cells, we show that Tyro3 mediates PS vasculoprotection. After Tyro3 ligation, PS activated sphingosine 1-phosphate receptor (S1P(1)), resulting in Rac1-dependent BBB protection. Using 2-photon in vivo imaging, we show that PS blocks postischemic BBB disruption in Tyro3(+/+), Axl(-/-), and Mer(-/-) mice, but not in Tyro3(-/-) mice or Tyro3(+/+) mice receiving low-dose W146, a S1P(1)-specific antagonist. Our findings indicate that PS protects the BBB integrity via Tyro3 and S1P(1), suggesting potentially novel treatments for neurovascular dysfunction resulting from hypoxic/ischemic BBB damage.

Lack of protein S in mice causes embryonic lethal coagulopathy and vascular dysgenesis

Protein S (ProS) is a blood anticoagulant encoded by the Pros1 gene, and ProS deficiencies are associated with venous thrombosis, stroke, and autoimmunity. These associations notwithstanding, the relative risk that reduced ProS expression confers in different disease settings has been difficult to assess without an animal model. We have now described a mouse model of ProS deficiency and shown that all Pros1-/- mice die in utero,from a fulminant coagulopathy and associated hemorrhages. Although ProS is known to act as a cofactor for activated Protein C (aPC), plasma from Pros1+/- heterozygous mice exhibited accelerated thrombin generation independent of aPC, and Pros1 mutants displayed defects in vessel development and function not seen in mice lacking protein C. Similar vascular defects appeared in mice in which Pros1 was conditionally deleted in vascular smooth muscle cells. Mutants in which Pros1 was deleted specifically in hepatocytes, which are thought to be the major source of ProS in the blood, were viable as adults and displayed less-severe coagulopathy without vascular dysgenesis. Finally, analysis of mutants in which Pros1 was deleted in endothelial cells indicated that these cells make a substantial contribution to circulating ProS. These results demonstrate that ProS is a pleiotropic anticoagulant with aPC-independent activities and highlight new roles for ProS in vascular development and homeostasis.

Species-specific anticoagulant and mitogenic activities of murine protein S

BACKGROUND

The protein C pathway down-regulates thrombin generation and promotes cytoprotection during inflammation and stress. In preclinical studies using models of murine injury (e.g., sepsis and ischemic stroke), murine protein S may be required because of restrictive species specificity.

DESIGN AND METHODS

We prepared and characterized recombinant murine protein S using novel coagulation assays, immunoassays, and cell proliferation assays.

RESULTS

Purified murine protein S had good anticoagulant co-factor activity for murine activated protein C, but not for human activated protein C, in mouse or rat plasma. In human plasma, murine protein S was a poor co-factor for murine activated protein C and had no anticoagulant effect with human activated protein C, suggesting protein S species specificity for factor V in addition to activated protein C. We estimated that mouse plasma contains 22+/-1 microg/mL protein S and developed assays to measure activated protein C co-factor activity of the protein S in murine plasma. Activated protein C-independent anticoagulant activity of murine protein S was demonstrable and quantifiable in mouse plasma, and this activity was enhanced by exogenous murine protein S. Murine protein S promoted the proliferation of mouse and human smooth muscle cells. The potency of murine protein S was higher for mouse cells than for human cells and similarly, human protein S was more potent for human cells than for mouse cells.

CONCLUSIONS

The spectrum of bioactivities of recombinant murine protein S with mouse plasma and smooth muscle cells is similar to that of human protein S. However, in vitro and in vivo studies of the protein C pathway in murine disease models are more appropriately performed using murine protein S. This study extends previous observations regarding the remarkable species specificity of protein S to the mouse.

Human protein S inhibits the uptake of AcLDL and expression of SR-A through Mer receptor tyrosine kinase in human macrophages

Human protein S is an anticoagulation protein. However, it is unknown whether protein S could regulate the expression and function of macrophage scavenger receptor A (SR-A) in macrophages. Human THP-1 monocytes and peripheral blood monocytes were differentiated into macrophages and then treated with physiological concentrations of human protein S. We found that protein S significantly reduced acetylated low-density lipoprotein (AcLDL) uptake and binding by macrophages and decreased the intracellular cholesteryl ester content. Protein S suppressed the expression of the SR-A at both mRNA and protein levels. Protein S reduced the SR-A promoter activity primarily through inhibition in the binding of transcription factors to the AP-1 promoter element in macrophages. Furthermore, human protein S could bind and induce phosphorylation of Mer receptor tyrosine kinase (Mer RTK). Soluble Mer protein or tyrosine kinase inhibitor herbimycin A effectively blocked the effects of protein S on AcLDL uptake. Immunohistochemical analysis revealed that the level of protein S was substantially increased in human atherosclerotic arteries. Thus, human protein S can inhibit the expression and activity of SR-A through Mer RTK in macrophages, suggesting that human protein S is a modulator for macrophage functions in uptaking of modified lipoproteins.

Blood coagulation and fibrinolysis in male patients with hypogonadotropic hypogonadism: plasma factor V and factor X activities increase in hypogonadotropic hypogonadism

BACKGROUND AND OBJECTIVES

In men, androgens have both pro- and anti-thrombotic effects. Androgen deficiency in men is associated with an increased incidence of cardiovascular disease (CVD). However, the influence of hypogonadism on hemostasis is controversial. Little is known about hemostatic features of male patients with idiopathic hypogonadotropic hypogonadism (IHH). Thus, the aim of the present study was to evaluate the markers of endogenous coagulation and fibrinolysis, and to investigate the relationships between endogenous sex hormones and hemostatic parameters and serum lipid profile in men with IHH.

DESIGN AND METHODS

Seventeen patients with IHH and 20 age-matched healthy controls were included in the study. Prothrombin time (PT), activated partial thromboplastin time (aPTT), fibrinogen, factors (F) V, VII, VIII, IX, and X activities, von Willebrand factor (vWF), antithrombin III (AT III), protein C, protein S, tissue plasminogen activator (t-PA), and tissue plasminogen activator inhibitor (PAI-1), as well as common lipid variables, were measured. The relationships between serum sex hormones and these hemostatic parameters were examined.

RESULTS

Compared with the control subjects, platelet count, FV, FX, and protein C activities were significantly increased in patients with IHH (p<0.01, p<0.05, p<0.01, and p<0.05, respectively), whereas AT III was decreased (p<0.05). Fibrinogen, FVIII, vWF, t-PA, PAI-1, and the other coagulation/fibrinolysis parameters and lipid profile in patients with IHH were not different from the controls. In patients with IHH, we showed that serum LH level was negatively correlated with fibrinogen (r: -0.78, p<0.01) and protein C (r: -0.55, p<0.05) and positively correlated with t-PA (r: 0.53, p<0.05). Serum FSH levels inversely correlated with fibrinogen (r: -0.75, p<0.01).

INTERPRETATION AND CONCLUSIONS

We found some differences in the hemostatic parameters between the patients with IHH and healthy controls. Increased platelet count, FV and FX activities and decreased AT III levels in patients with IHH represent a potential hypercoagulable state, which might augment the risk for atherosclerotic and atherothrombotic complications. Therefore, IHH may be associated with an increased risk of CVD. However, sex hormones may play a role at different levels of the complex hemostatic system in patients with IHH.

Role of coagulation factor Xa and protease-activated receptor 2 in human mesangial cell proliferation

BACKGROUND

Fibrin deposition and mesangial cell proliferation are frequently observed in the active type of mesangioproliferative glomerulonephritis. Coagulation factors, such as factor V and factor Xa are colocalized with fibrin in the mesangial areas in active type of IgA nephropathy with mesangial cell proliferation. In this study, therefore, we studied the role of factor Xa and its receptor, protease-activated receptor 2 (PAR2) in mesangial cell proliferation and fibrin deposition, and examined ant-proliferative effects of a specific factor Xa inhibitor, DX-9065a, in cultured human mesangial cells.

METHODS

To examine the effect of DX-9065a on the factor Xa-induced proliferation of cultured human mesangial cells, we measured thymidine incorporation and cell numbers. We also examined the effect of DX-9065a on extracellular regulated kinase (ERK) activation and fibrin production induced by factor Xa in human mesangial cells.

RESULTS

Factor Xa increased [(3)H]-thymidine incorporation and cell numbers in a dose-dependent manner in mesangial cells, which was inhibited by DX-9065a. DX-9065a also suppressed factor Xa-triggered fibrin deposition on mesangial cell surface. Factor Xa induced the activation of ERK in mesangial cells and this activation was also completely inhibited by DX-9065a, but not inhibited by PAR1 antagonist. Factor Xa-induced cell proliferation and ERK activation were inhibited by PD98059.

CONCLUSION

There results suggest that factor Xa can induce mesangial cell proliferation through the activation of ERK via PAR2 in mesangial cells and that PAR2 may play a crucial role in the cell proliferation induced by factor Xa. Our results implicate that DX-9065a may be a promising agent to regulate proliferation of mesangial cellss and inhibit the coagulation process in mesangium.

Coagulation cascade activation causes CC chemokine receptor-2 gene expression and mononuclear cell activation in hemodialysis patients

Priming of the coagulation cascade during hemodialysis (HD) leads to the release of activated factor X (FXa). The binding of FXa to its specific receptors, effector protease receptor-1 (EPR-1) and protease-activated receptor-2 (PAR-2), may induce the activation of peripheral blood mononuclear cells (PBMC) and promote a chronic inflammatory state that is responsible for several HD-related morbidities. In the attempt to elucidate the mechanisms underlying the coagulation-associated inflammation in HD, 10 HD patients were randomized to be treated subsequently with a cellulose acetate membrane (CA) and Ethylen-vinyl-alcohol (EVAL), a synthetic membrane that has been shown to reduce FXa generation. At the end of each experimental period, surface FXa and thrombin receptors (EPR-1 and PAR-1, -2, and -4) and CCR2 (monocyte chemoattractant protein-1 receptor) gene expression in isolated PBMC were examined. the ability of dialytic membranes to activate protein-tyrosine kinases and the stress-activated kinase JNK and to modulate the generation of terminal complement complex (TCC) was also investigated. EPR-1 and PAR-2 and -4 mRNA expression, barely detectable in normal PBMC, were significantly upregulated in HD patients, particularly in those who were treated with CA. A striking increase of tyrosine-phosphorylated proteins and JNK activation was observed at the end of HD only in CA-treated patients. Simultaneously, an increased gene expression for both splicing isoforms of CCR2, A and B, only in PBMC from CA-treated patients was demonstrated. The increased CCR-2 mRNA abundance was followed by a significant increase in its protein synthesis. The high expression of CCR2 was associated with an increased generation of plasma TCC and a significant drop in leukocyte and monocyte count. By contrast, EVAL treatment slightly lowered TCC generation and normalized leukocyte count. In vitro FXa induced CCR2 A and B expression and JNK activation in freshly isolated PBMC. FXa-induced CCR2 mRNA expression was completely abolished by JNK and tyrosine kinase inhibition. In conclusion, these data suggest that subclinical clotting activation may cause an increased CCR2 gene and protein expression on uremic PBMC, contributing to HD-related chronic microinflammation. The use of the less coagulation-activating membrane, EVAL, may reduce PBMC activation through the modulation of the stress-activated kinase JNK.

The intriguing world of prothrombin activators from snake venom

Activation of prothrombin to mature thrombin occurs by the proteolytic action of the prothrombinase complex consisting of a serine proteinase factor Xa, and cofactors factor Va, Ca(2+) ions and phospholipids. Several exogenous prothrombin activators are found in snake venom. They are classified into four groups based on their cofactor requirements. Group A and B prothrombin activators are metalloproteinases whereas group C and D prothrombin activators are serine proteinases. Group C prothrombin activators resemble the mammalian factor Xa-factor Va complex, while Group D activators are structurally and functionally similar to factor Xa. This review provides a detailed description of the current knowledge on all prothrombin activators and highlights several intriguing questions that are yet to be answered.

Synthetic and recombinant antithrombin drugs

As the final enzyme in the activation of the coagulation system, the serine protease, thrombin, is believed to be an important target for the development of new anticoagulant/antithrombotic drugs. Direct thrombin inhibitors are either derived from natural sources, such as hirudin or are chemically synthesised, such as argatroban. The coupling of hirudin or parts of it with other entities leads to novel agents with different pharmacokinetic and pharmacodynamic characteristics, such as polyethylene glycol (PEG)-hirudin or the hirulogs. Due to the reversible or irreversible inactivation of the enzyme, thrombin inhibitors exert strong anticoagulant effects that can be measured in global clotting assays. Furthermore, these compounds inhibit thrombin-induced platelet reactions and influence other cellular, receptor-mediated actions of thrombin, e.g., on vascular cells. Directly acting thrombin inhibitors prevent blood clotting and are also capable of inhibiting clot-associated thrombin; however, they do not effectively block the further generation of the enzyme. Comprehensive experimental studies suggest that thrombin inhibitors may be effective drugs in a wide range of intravascular thrombus formation, also including the inhibition of vascular restenosis. Recent clinical trials revealed the effectiveness of direct thrombin inhibitors in various thrombotic and cardiovascular indications, but also a tendency to an increased risk of bleeding complications. At present, thrombin inhibitors are the most promising class of drugs for the initial therapy of patients with heparin-induced thrombocytopaenia (HIT) or the heparin-induced thrombocytopaenia and thrombosis syndrome (HITTS). They are also useful for the management of venous thrombosis and for acute ischaemic syndromes as well as for invasive procedures. However, with regard to the long-term outcome, a superiority of thrombin inhibitors over heparin has not yet been demonstrated. Several important issues, such as monitoring, pharmacological antagonism and drug interactions will also play an important role in the development of these new drugs. Further clinical trials are required to confirm the effectiveness of direct thrombin inhibitors in the prophylaxis and treatment of various thromboembolic and cardiovascular disorders.

The physiology of vitamin K nutriture and vitamin K-dependent protein function in atherosclerosis

Recent advances in the discovery of new functions for vitamin K-dependent (VKD) proteins and in defining vitamin K nutriture have led to a substantial revision in our understanding of vitamin K physiology. The only unequivocal function for vitamin K is as a cofactor for the carboxylation of VKD proteins which renders them active. While vitamin K was originally associated only with hepatic VKD proteins that participate in hemostasis, VKD proteins are now known to be present in virtually every tissue and to be important to bone mineralization, arterial calcification, apoptosis, phagocytosis, growth control, chemotaxis, and signal transduction. The development of improved methods for analyzing vitamin K has shed considerable insight into the relative importance of different vitamin K forms in the diet and their contribution to hepatic vs. non-hepatic tissue. New assays that measure the extent of carboxylation in VKD proteins have revealed that while the current recommended daily allowance for vitamin K is sufficient for maintaining functional hemostasis, the undercarboxylation of at least one non-hemostatic protein is frequently observed in the general population. The advances in defining VKD protein function and vitamin K nutriture are described, as is the potential impact of VKD proteins on atherosclerosis. Many of the VKD proteins contribute to atherogenesis. Recent studies suggest involvement in arterial calcification, which may be influenced by dietary levels of vitamin K and by anticoagulant drugs such as warfarin that antagonize vitamin K action.

Tissue factor-factor VIIa signaling

How does tissue factor (TF), whose principle role is to support clotting factor VIIa (FVIIa) in triggering the coagulation cascade, affect various pathophysiological processes? One of the answers is that TF interaction with FVIIa not only initiates clotting but also induces cell signaling via activation of G-protein-coupled protease activated receptors (PARs). Recent studies using various cell model systems and limited in vivo systems are beginning to define how TF-VIIa-induced signaling regulates cellular behavior. Signaling pathways initiated by both TF-VIIa protease activation of PARs and phosphorylation of the TF-cytoplasmic domain appear to regulate cellular functions. In the present article, we review the emerging data on the mechanism of TF-mediated cell signaling and how it regulates various cellular responses, with particular focus on TF-VIIa protease-dependent signaling.

Regulation of tissue factor-factor VIIa expression on cell surfaces: a role for tissue factor-factor VIIa endocytosis

Tissue factor (TF) is the cellular receptor for plasma clotting factor VIIa (FVIIa) and the formation of TF-VIIa complexes on cell surfaces triggers the coagulation cascade. Further, TF-VIIa, either directly or indirectly, influences various biological processes, such as development, inflammation and tumor metastasis. Therefore, a proper regulation of TF-VIIa expression is critical for the maintenance of hemostatic balance and health in general. TF-VIIa functional expression on cell surfaces is regulated primarily by transcriptional regulation of TF gene or by specific plasma inhibitors, particularly tissue factor pathway inhibitor (TFPI). However, a number of other mechanisms that are yet to be well defined also regulate TF-VIIa functional expression. One such mechanism is the endocytosis of TF-VIIa. In this article, we provide a comprehensive review on the regulation of TF-VIIa functional expression by these other mechanisms, with a particular emphasis on TF-VIIa endocytosis, and our perspective of these studies.

Activated protein C and ischemic stroke

OBJECTIVE

To summarize clinical observations, animal model experimentation, and in vitro studies that advance knowledge of the protein C system, including activated protein C (APC), in the setting of ischemic stroke.

DATA SOURCE

Narrative review of selected published primary basic and clinical literature from MEDLINE for 2000-2003.

DATA SYNTHESIS

Low levels of plasma APC and a poor response to APC in clotting assays may be markers or risk factors for ischemic stroke. Ischemia during routine endarterectomy causes APC generation in the affected region of the human brain. The prospective epidemiologic Atherosclerosis Risk in Communities (ARIC) study reported that plasma protein C may be protective for ischemic stroke. In murine models of focal cerebral ischemia, APC provided remarkable anti-inflammatory and neuroprotective effects in vivo and increased survival at 24 hrs. Recent in vitro and in vivo studies provide remarkable insights into mechanisms of the neuroprotective activities of APC. Independent of its well-known anticoagulant activity, APC acts directly on cells and alters gene expression profiles, inhibits apoptosis, and down-regulates inflammation. These effects require protease-activated receptor-1 and the endothelial protein C receptor. In an in vitro model involving hypoxia-induced apoptosis of human brain endothelial cells, protease-activated receptor-1 and endothelial protein C receptor were required for APC to exert its anti-apoptotic effects. In these cells, APC blunts hypoxia-induced increases in p53 messenger RNA and protein, reduces pro-apoptotic Bax, and increases anti-apoptotic Bcl-2, thereby inhibiting mitochondrial-dependent apoptosis. Murine ischemic stroke model studies have provided in vivo evidence for the physiologic roles of protease-activated receptor-1 and endothelial protein C receptor in the neuroprotective activities of APC. Because the low doses required for recombinant murine APC to provide neuroprotection do not cause observable anticoagulant effects, the in vivo neuroprotective action of APC seems, at least in part, to be independent of its anticoagulant activity and is likely to involve its anti-apoptotic activity.

CONCLUSIONS

There is compelling evidence that ischemic stroke is an attractive target for therapy with APC.

Macrophage Migration Inhibitory Factor Is Induced by Thrombin and Factor Xa in Endothelial Cells

Macrophage migration inhibitory factor (MIF), a proinflammatory cytokine, has been shown to play a role in wound-healing processes. In this study, we investigated whether protease-activated receptor (PAR)-1 and PAR-2 mediated MIF expression in human endothelial cells. Thrombin, factor Xa (FXa), and trypsin induced MIF expression in human dermal microvascular endothelial cells and human umbilical vein endothelial cells, but other proteases, including kallikrein and urokinase, failed to do so. Thrombin-induced MIF mRNA expression was significantly reduced by the thrombin-specific inhibitor hirudin. Thrombin receptor activation peptide-6, a synthetic PAR-1 peptide, induced MIF mRNA expression, suggesting that PAR-1 mediates MIF expression in response to thrombin. The effects of FXa were blocked by antithrombin III, but not by hirudin, indicating that FXa might enhance MIF production directly rather than via thrombin stimulation. The synthetic PAR-2 peptide SLIGRL-NH(2) induced MIF mRNA expression, showing that PAR-2 mediated MIF expression in response to FXa. Concerning the signal transduction, a mitogen-activated protein kinase kinase inhibitor (PD98089) and a nuclear factor (NF)-kappaB inhibitor (SN50) suppressed the up-regulation of MIF mRNA in response to thrombin, FXa, and PAR-2 agonist stimulation, whereas a p38 inhibitor (SB203580) had little effect. These facts indicate that up-regulation of MIF by thrombin or FXa is regulated by p44/p42 mitogen-activated protein kinase-dependent pathways and NF-kappaB-dependent pathways. Moreover, we found that PAR-1 and PAR-2 mRNA expression in endothelial cells was enhanced by MIF. Furthermore, we examined the inflammatory response induced by PAR-1 and PAR-2 agonists injected into the mouse footpad. As shown by footpad thickness, an indicator of inflammation, MIF-deficient mice (C57BL/6) were much less sensitive to either PAR-1 or PAR-2 agonists than wild-type mice. Taken together, these results suggest that MIF contributes to the inflammatory phase of the wound healing process in concert with thrombin and FXa via PAR-1 and PAR-2.

Factor VII activating protease (FSAP) inhibits growth factor‐mediated cell proliferation and migration of vascular smooth muscle cells

The factor VII activating protease (FSAP) is a serine-protease present in human plasma that serves to activate single-chain plasminogen activators, as well as coagulation factor VII. FSAP was localized within atherosclerotic lesions, and a genetic polymorphism in FSAP is associated with carotid stenosis. Hence, this study was conducted to gain broader insights into the cellular effects of FSAP on vascular smooth muscle cells (VSMC). DNA synthesis and cell proliferation assays revealed an inhibitory action of FSAP on platelet-derived growth factor BB (PDGF-BB)-mediated proliferation of VSMC. FSAP also inhibited PDGF-BB-induced migration of VSMC. These cellular effects of FSAP could be neutralized by an anti-FSAP mAb as well as by protease inhibitors such as aprotinin or a chloromethylketone inhibitor. Moreover, unfractionated heparin promoted the antiproliferative effect of FSAP on VSMC and was essential for the inhibition of VSMC migration. FSAP inhibited PDGF-BB binding to human VSMC and concomitantly blocked PDGF-BB-dependent phosphorylation of mitogen activated protein kinase p42/p44 and tyrosine phosphorylation of other proteins. These results unravel a new function of FSAP as an inhibitor of the proatherogenic phenotype of vascular smooth muscle.

Thrombin- and Factor Xa–Induced DNA Synthesis Is Mediated by Transactivation of Fibroblast Growth Factor Receptor-1 in Human Vascular Smooth Muscle Cells

Thrombin and factor Xa (FXa) are agonists for G protein–coupled receptors (GPRCs) and may contribute to vascular lesion formation by stimulating proliferation of vascular smooth muscle cells (SMCs). Mitogenic signaling of GPCRs requires transactivation of receptor tyrosine kinases (RTKs). In rat SMCs, thrombin transactivates the epidermal growth factor receptor (EGFR) via a pathway that involves heparin-binding EGF-like growth factor (HB-EGF) as ligand for EGFR. The purpose of this study was to investigate in human SMCs the role of receptor transactivation in the mitogenic response to thrombin and FXa. Thrombin (10 nmol/L) and FXa (100 nmol/L) cause a 3.3- and 2.6-fold increase in DNA synthesis, respectively. In human SMCs, neither thrombin nor FXa causes EGFR phosphorylation, and blockade of EGFR kinase does not inhibit DNA synthesis. However, DNA synthesis and phosphorylation of fibroblast growth factor receptor-1 (FGFR-1) induced by thrombin or FXa are inhibited by antibodies neutralizing basic fibroblast growth factor (bFGF) or by heparin. Hirudin inhibits thrombin-, but not FXa-induced mitogenesis, indicating that FXa acts independently of thrombin. We further demonstrate by ELISA that upon thrombin and FXa stimulation, bFGF is released and binds to the extracellular matrix. Our data suggest that in human vascular SMCs, both thrombin and FXa rapidly release bFGF into the pericellular matrix. This is followed by transactivation of the FGFR-1 and increased proliferation. Heparin may inhibit the mitogenic effects of thrombin and FXa in human SMCs by preventing bFGF binding to FGFR-1.

Trocarin, a blood coagulation factor Xa homologue from snake venom, causes inflammation and mitogenesis

Trocarin, a Group D prothrombin activator from Tropidechis carinatus snake venom, has high sequence similarity to blood coagulation factor Xa (FXa). Both trocarin and FXa activate prothrombin to mature thrombin and have similar requirements for cofactors, such as factor Va, Ca2+ ions and phospholipids. In addition to its hemostatic functions, human FXa causes inflammation and induces mitogenesis in several cell types due to its interaction with effector protease receptor-1 (EPR-1). The inter-EGF domain region (L83FTKRL88) of FXa implicated in EPR-1-binding is distinctly different in trocarin (K83VLYQS88). Here we show that, interestingly, trocarin also causes edema in the mouse footpad; the inflammation, accompanied by a large purplish clot, is more persistent than the transient edema caused by FXa. Histological examination indicates significant differences between edema induced by FXa and trocarin. Moreover, trocarin-induced edema is not inhibited by a synthetic peptide based on the FXa-binding region of EPR-1, indicating that the inflammation is probably mediated by a mechanism independent of EPR-1-binding. Trocarin, like FXa, also has a mitogenic effect on bronchial smooth muscle cells mediated by an EPR-1-independent mechanism. Hence trocarin, being closely related to FXa, has similar non-hemostatic functions in mediating inflammation and mitogenesis, yet appears to act by distinctly different mechanisms.

Factor Xa induces mitogenesis of vascular smooth muscle cells via autocrine production of epiregulin

Factor Xa has been reported to elicit smooth muscle cell proliferation via autocrine release of platelet-derived growth factor. However, this study has shown that factor Xa-induced mitogenesis of rat aortic smooth muscle cell is independent of platelet-derived growth factor. We also could not observe any platelet-derived growth factor isoforms in the cultured medium of factor Xa-stimulated cells. Our finding that the cultured medium of factor Xa-stimulated cells strongly induces rat aortic smooth muscle cell mitogenesis in the absence of factor Xa activity led us to explore the existence of a novel autocrine pathway. The autocrine growth factor was purified from the cultured medium and was identified to be epiregulin. Recombinant epiregulin was also able to induce the mitogenesis. The secretion of epiregulin from factor Xa-stimulated rat aortic smooth muscle cell required mRNA expression and protein synthesis of the growth factor. The mitogenic effect of factor Xa on rat aortic smooth muscle cell was significantly reduced by anti-epiregulin antibody or by antisense oligodeoxynucleotide to epiregulin. Several lines of experimental evidence clearly indicate that the autocrine production of epiregulin, an epidermal growth factor-related ligand, is induced in the factor Xa-stimulated mitogenic process of rat aortic smooth muscle cell.

Coagulation activators and inhibitors in the neointima of polyester vascular grafts

The surface of synthetic vascular grafts is thrombogenic, which implies a risk for their occlusion. The aim of the study was to evaluate expression of coagulation components in the polyester vascular grafts neointima. The study was carried out on 18 dogs, which underwent replacement of the abdominal aorta with a polyester prosthesis. Grafts were removed after 1, 4 and 12 months. Immunohistochemical labeling for von Willebrand factor, tissue factor, factor XII, tissue factor pathway inhibitor, thrombomodulin, protein C, protein S and prothrombin activation fragment F1 + 2 was performed. Increasing intensity of von Willebrand factor expression was found in successive periods of the study. Factor XII was shown in the whole neointima after 1 month, whereas in the following periods its presence was limited to the luminal surface. Tissue factor expression was demonstrated after 1 month and its intensity increased in later periods. Tissue factor pathway inhibitor and thrombomodulin expression was demonstrated after 4 and 12 months. Protein C and protein S were present in all observation periods, as well as prothrombin activation fragment F1 + 2. Results indicate a high thrombotic potential of the graft neointima early after prosthesis implantation, whereas in the late postoperative follow-up increasing expression of coagulation inhibitors reduces thrombotic properties of the graft neointima.

Intralumenal tissue-engineered therapeutic stent using endothelial progenitor cell-inoculated hybrid tissue and in vitro performance

Rapid reendothelialization at an atherosclerotic lesion after balloon or stent inflation may be essential for maintaining homeostatic tissue function, which could reduce or prevent restenosis. We devised an endothelial progenitor cell (EPC)-enriched tubular hybrid tissue and mounted it on a small-diameter metallic stent (outer diameter, 1.5 mm), which is used for intravascular angioplasty to atherosclerotic lesions. This study addressed the fabrication technique and in vitro performance to verify lumenal endothelialization. A thin collagenous tubular tissue was prepared by contraction of collagen fibers by inoculated EPCs, which were isolated from canine peripheral blood and expanded ex vivo, in a collagen gel formed in a mold. An EPC-inoculated hybrid tissue-covered stent, loaded on a balloon catheter, was inserted into a tubular hybrid vascular medial tissue inoculated with smooth muscle cells (SMCs) as an arterial media mimic, and subjected to balloon inflation for enlargement (outer diameter, 3 mm), followed by balloon deflation. The EPC-inoculated hybrid tissue-covered stent tightly adhered to the lumenal surface of the hybrid medial tissue. On culture, EPCs in the hybrid tissue migrated and proliferated to form a completely endothelialized lumenal surface at stented sites as well as sites adjacent to the vascular hybrid medial tissue with the prolongation of culture. This in vitro pilot study before in vivo experiments suggests that an EPC-inoculated hybrid tissue-covered stent may be a novel therapeutic device for reendothelialization or paving with EPC-enriched tissue at an atherosclerotic arterial wall, resulting in the prevention of restenosis and the rapid formation of normal tissue.

Protein S confers neuronal protection during ischemic/hypoxic injury in mice

BACKGROUND

Protein S is an antithrombotic factor that also exhibits mitogenic activity. Thus, we hypothesized that protein S may control cerebrovascular thrombosis in stroke and protect brain tissue from ischemic injury.

METHODS AND RESULTS

We studied protein S in a murine in vivo model of stroke and an in vitro model of neuronal hypoxia/reoxygenation injury. Animals received purified human plasma-derived protein S or vehicle intravenously 10 minutes after initiation of middle cerebral artery occlusion followed by reperfusion. Protein S at 0.2 to 2 mg/kg significantly improved the motor neurological deficit by 3.8- to 3.2-fold and reduced infarction and edema volumes by 45% to 54% and 45% to 62%, respectively. Protein S at 2 mg/kg improved postischemic cerebral blood flow by 21% to 26% and reduced brain fibrin deposition and infiltration with neutrophils by 40% and 53%, respectively. Intracerebral bleeding was not observed with protein S. Protein S protected ischemic neurons in vivo and cultured neurons from hypoxia/reoxygenation-induced apoptosis in a time- and dose-dependent manner. Recombinant human protein S exerted protective effects from hypoxia-induced damage similar to the plasma-derived protein S both in vivo and in vitro.

CONCLUSIONS

Protein S is a significant neuroprotectant during ischemic brain injury with direct effects on neurons and antithrombotic effects. Thus, protein S could be a prototype of a new class of agents for clinical stroke with combined direct neuronal protective effects and systemic antithrombotic and antiinflammatory activities.

Coagulation factor Xa synergistically interacts with serotonin in inducing vascular smooth muscle cell proliferation

INTRODUCTION

Initial events following vascular interventions include activation of platelets and coagulation cascade. Activated platelets release several vasoactive mediators including serotonin. Activation of coagulation cascade results in conversion of inactive zymogens such as factor X to its active form (factor Xa). So this study designed to examine the effect of factor Xa on rabbit vascular smooth muscle cell (VSMC) proliferation and its interaction with serotonin.

METHODS

Growth-arrested VSMCs were incubated in a serum-free medium with different concentrations of factor Xa with or without serotonin. VSMC proliferation was examined by increase in incorporation of [3H]thymidine into DNA and by increase in cell number.

RESULTS

Factor Xa and serotonin stimulated DNA synthesis in a dose-dependent manner. Factor Xa had a maximal effect at 100 nM (1180+/-110%) and serotonin at 50 microM (345+/-21%). When added together, at nonmitogenic concentrations, factor Xa (0.1 nM) and serotonin (1 micoM) synergistically induced DNA synthesis (312+/-12%). These increases in DNA synthesis were paralleled by an increase in cell number. Serine protease inhibitors, active site blockers and platelet-derived growth factor receptor tyrosine kinase inhibitor blocked the mitogenic effect of factor Xa and its interaction with serotonin. Similarly, serotonin type 2 receptor inhibitor and Gi-protein-coupled receptor inhibitor inhibited the mitogenic effect of serotonin and its interaction with factor Xa. When used in combination, they blocked the interaction between factor Xa and serotonin.

CONCLUSION

Coagulation factor Xa and serotonin are mitogenic to VSMCs and also function as amplification factors to each other, suggesting that inhibition of neointimal proliferation after vascular injury may require the combined use of multiple growth factor inhibitors to simultaneously block several critical cellular activation pathways.

Prolonged procoagulant activity on overstretch-injured coronary arteries in pigs

This study was designed to assess the time course and nature of the vascular procoagulant response after 1.5-fold balloon overstretch injury of the coronary arteries in pigs. Arteries were excised for chromogenic assay of bound factor (F)Xa and thrombin at 24 h, 3 days, 1 week, or 2 weeks after injury. FXa at the site of injury remained elevated for 1 week (4.9 +/- 5.9 microg cm(-2), n = 10), compared with non-injured control arteries (0.4 +/- 0.2 microg cm(-2), n = 18, P = 0.00025), while thrombin was increased only at 24 h. Tissue factor protein was abundant in non-injured coronaries (10 +/- 6 ng microg(-1) total protein, n = 9) and levels were unchanged by injury (13 +/- 11 ng microg(-1), n = 6) or 24-h administration of tissue factor pathway inhibitor (16 +/- 6 ng microg(-1), n = 6). Persistent tissue factor-mediated procoagulant activity may explain the need for prolonged anticoagulation to attenuate neointimal formation after balloon-induced coronary injury.

Extrahepatic synthesis of factor VII in human atherosclerotic vessels

OBJECTIVE

Coagulation is initiated by the interaction of tissue factor (TF) with plasma coagulation factors VII (FVII) and X (FX). TF is highly expressed in atherosclerotic lesions, but little is known about the synthesis of FX or FVII outside of the liver. Previous studies suggested that macrophages synthesize FVII. We therefore hypothesized that macrophages within atherosclerotic lesions may produce FVII, leading to partial activation of the coagulation cascade.

METHODS AND RESULTS

Immunohistochemistry was performed using antibodies against FVII, FX, and TF on normal and atherosclerotic vessels. In atherosclerotic lesions, FVII immunostaining was colocalized with TF in macrophages and spindle-shaped smooth muscle cells. FVII mRNA was also detected in these cells using in situ hybridization, suggesting the local synthesis of FVII in atherosclerosis. Reverse transcriptase-polymerase chain reaction confirmed the presence of FVII mRNA in normal and atherosclerotic vessels as well as smooth muscle cells, fibroblasts, and keratinocytes in vitro.

CONCLUSIONS

The localization of FVII synthesis outside the liver may be indicative of other cellular functions for this coagulation protein. The observed coexpression of TF and FVII may contribute to autocrine signaling via thrombin-independent mechanisms and may represent a novel mechanism contributing to growth in the setting of vascular disease.

Factor Xa induces mitogenesis of coronary artery smooth muscle cell via activation of PAR-2

Factor Xa-induced stimulation of coronary artery smooth muscle cells (CASMC) was investigated by analyzing [(3)H]thymidine incorporation, cell proliferation, and ERK-1/2 activation. Exposure of the cells to factor Xa evoked a time-dependent activation of ERK-1/2 with increased [(3)H]thymidine incorporation and cell proliferation. The factor Xa-induced ERK-1/2 activation was not desensitized by preincubation of the cells with thrombin. However, ERK-1/2 activation was markedly attenuated by prior exposure of the cells to protease-activated receptor-2 (PAR-2) activating peptide, SLIGKV. The mitogenic effect of factor Xa was significantly reduced in the presence of anti-PAR-2 monoclonal antibody. Several lines of experimental evidence indicate that factor Xa-induced mitogenesis of CASMC is a cellular process mediated by PAR-2 activation.

Beta-cyclodextrin tetradecasulfate, a novel cyclic oligosaccharide, inhibits thrombus and neointimal formation after coronary vascular injury

BACKGROUND

Neointimal formation is a major cause of restenosis after interventional vascular procedures. Beta-cyclodextrin tetradecasulfate (beta-CDT) has been shown to inhibit fibroblast growth factor activity and we hypothesized that beta-CDT would reduce intimal formation.

DESIGN

Three studies were performed: (1) pharmacokinetics of oral and intravenous beta-CDT and determination of optimal dose, (2) determination of efficacy of oral and intravenous beta-CDT in reducing neointimal formation after balloon-overstretch injury and (3) determination of the effect of beta-CDT on cellular proliferation, factor Xa activity, activated clotting time, activated partial thromboplastin time and thrombus formation.

METHODS

Pharmacokinetics were determined in eight domestic swine following administration of oral beta-CDT and intravenous beta-CDT at three doses each. In the efficacy study, balloon-overstretch injury of 37 pigs (69 arteries) was performed and randomized into three groups (n = 23 arteries/group): control, oral administration of 300 mg beta-CDT/kg per day or intravenous infusion of 100 mg beta-CDT/kg per day. Animals were sacrificed 14 days later. Cellular proliferation and mural thrombus were determined in six arteries/group at 5 days and endothelial coverage was evaluated at 5 and 14 days.

RESULTS

Oral and intravenous beta-CDT reduced the intimal hyperplasia area normalized to injury index by 24 and 48%, respectively: control, 3.03 +/- 0.75 mm2, oral, 2.31 +/- 0.83 mm2 (P = 0.004) and intravenous, 1.67 +/- 0.73 mm2 (P = 0.0000002). beta-CDT reduced cellular proliferation (control, 55 +/- 18%, oral, 35 +/- 7%, P = 0.03 and intravenous, 30 +/- 12%, P = 0.01) and mural thrombus formation (control, 0.84 +/- 0.4 mm2, oral, 0.44 +/- 0.14 mm2, P = 0.04, intravenous, 0.42 +/- 0.09 mm2, P = 0.03). Endothelial coverage was increased in the experimental groups (P = 0.008, oral versus control, P < 0.0001, intravenous versus control). Factor Xa activity was inhibited 9-10 fold following intravenous administration while oral administration demonstrated no effect.

CONCLUSIONS

Both oral and intravenous formation of beta-CDT reduced intimal hyperplasia with the greatest reduction in the intravenous group. We postulate that beta-CDT was effective by the combination of increasing endothelial coverage, reducing mural thrombus formation, inhibiting factor Xa activity and reducing cellular proliferation.

Extrahepatic synthesis of FVII in human atheroma and smooth muscle cells in vitro

The present series of experiments provide evidence that FVII is synthesized outside of the liver and is found in a variety of cells in normal and atherosclerotic vessels. In normal vessels FVII was localized to the endothelial cell layer and in adventitial fibroblasts at sites where tissue factor (TF) is also found. In early and advanced atherosclerotic lesions, FVII was mostly found in macrophage- rich regions colocalized with TF. Foam cells and macrophages in the necrotic core adjacent to the cholesterol clefts and foamy macrophages in early intimal thickenings all showed strong cytoplasmic staining with FVII antibodies. Although it is possible that FVII protein staining found in normal and atherosclerotic vessels originated from the blood, the finding of FVII mRNA by both in situ hybridization and RT-PCR suggests that these tissues are sites of FVII synthesis. Additional work demonstrated synthesis of FVII in a variety of tissues and smooth muscle cells and fibroblasts in vitro. The distribution of FVII synthesis in extrahepatic tissues and more recent data regarding thrombin-independent signaling as a consequence of FVII/TF binding may suggest the possibility of other cellular functions for this coagulation factor.

Active tissue factor shed from human arterial smooth muscle cells adheres to artificial surfaces

Through a series of in vitro assays, this study outlines a flow-mediated process by which active tissue factor (TF), the prime initiator of coagulation, may be transferred from the plasma membrane of vascular smooth muscle cells (VSMCs) to that of artificial surfaces such as those typically associated with intravascular implants. Studies with quiescent and activated rat VSMCs demonstrated that pathologically high shear stresses (tau(w) = 250 dyn cm(-2)) resulted in the loss of TF activity from the cell surface. Subsequent experiments with human VSMCs showed that VSMCs continuously release active TF into their extracellular medium, presumably in the form of lipid vesicles or microparticles, and that fluid shear stress (tauw = 50 dyncm(-2)) or chemical agonists (A23187) can significantly accelerate this release. Experiments with a wide array of polymeric and metallic materials showed that the TF shed from VSMCs was able to adhere to these surfaces and promote the activation of coagulation factor X (FX) at the material surface. Extracellular TF bound strongly to both uncoated and human plasma coated surfaces under a wide range of hemodynamic shear stresses (0-20 dyncm(-2)). When an extracellular, VSMC-derived TF mixture was perfused over Ti 6-4 surfaces, the adhesion of TF was found to be time-dependent, gradually accumulating on the material surface over time. Thus an important criterion in the design or success of intravascular devices may be related to their ability to interact with TF, shed from cell surfaces. This is especially important as TF may lead to thrombotic complications, the products of which may also increase cellular proliferation.