Expression of tissue factor pathway inhibitor in vascular smooth muscle cells and its regulation by growth factors

TFPI from erythroblasts drives heme production in central macrophages promoting erythropoiesis in polycythemia

Bleeding and thrombosis are known as common complications of polycythemia for a long time. However, the role of coagulation system in erythropoiesis is unclear. Here, we discover that an anticoagulant protein tissue factor pathway inhibitor (TFPI) plays an essential role in erythropoiesis via the control of heme biosynthesis in central macrophages. TFPI levels are elevated in erythroblasts of human erythroblastic islands with JAK2V617F mutation and hypoxia condition. Erythroid lineage-specific knockout TFPI results in impaired erythropoiesis through decreasing ferrochelatase expression and heme biosynthesis in central macrophages. Mechanistically, the TFPI interacts with thrombomodulin to promote the downstream ERK1/2-GATA1 signaling pathway to induce heme biosynthesis in central macrophages. Furthermore, TFPI blockade impairs human erythropoiesis in vitro, and normalizes the erythroid compartment in mice with polycythemia. These results show that erythroblast-derived TFPI plays an important role in the regulation of erythropoiesis and reveal an interplay between erythroblasts and central macrophages.

The contribution of TFPIα to the hemostatic response to injury in mice

BACKGROUND

Tissue factor pathway inhibitor (TFPI) is an essential regulator of coagulation, limiting thrombin generation and preventing thrombosis. In humans and mice, TFPIα is the sole isoform present in platelets.

OBJECTIVE

Here, we asked whether TFPIα, because of its release from platelets at sites of injury, has a unique role in limiting the hemostatic response.

METHODS

TFPIα-mutant (TfpiΔα/Δα ) mice were generated by introducing a stop codon in the C-terminus. Platelet accumulation, platelet activation, and fibrin accumulation were measured following penetrating injuries in the jugular vein and cremaster muscle arterioles, and imaged by fluorescence and scanning electron microscopy. Time to bleeding cessation was recorded in the jugular vein studies.

RESULTS

TfpiΔα/Δα mice were viable and fertile. Plasma TFPI levels were normal in the TfpiΔα/Δα mice, no TFPI protein or activity was present in their platelets and thrombin-antithrombin complex levels were indistinguishable from Tfpi+/+ littermates. There was a small, but statistically significant reduction in the time to bleeding cessation following jugular vein puncture injury in the TfpiΔα/Δα mice, but no measurable changes in platelet or fibrin accumulation or in hemostatic plug architecture following injury of the micro- or macrovasculature.

CONCLUSION

Loss of TFPIα expression does not produce a global prothrombotic state in mice. Platelet TFPIα is expected to be released or displayed in a focal manner at the site of injury, potentially accumulating to high concentrations in the narrow gaps between platelets. If so, the data from the vascular injury models studied here indicate this is not essential for a normal hemostatic response in mice.

Knockdown screening of chromatin binding and regulatory proteins in zebrafish identified Suz12b as a regulator of tfpia and an antithrombotic drug target

Tissue factor pathway inhibitor (TFPI) is an anticoagulant protein that inhibits factor VIIa and Xa in the coagulation cascade. It has been shown that forkhead box P3 protein is a TFPI transcriptional repressor. However, there are no studies on chromatin remodeling that control TFPI expression. We hypothesized that the genome-wide knockdowns of the chromatin binding and regulatory proteins (CBRPs) in zebrafish could identify novel tfpia gene regulators. As an initial step, we selected 69 CBRP genes from the list of zebrafish thrombocyte-expressed genes. We then performed a 3-gene piggyback knockdown screen of these 69 genes, followed by quantification of tfpia mRNA levels. The results revealed that knockdown of brd7, ing2, ing3, ing4, and suz12b increased tfpia mRNA levels. The simultaneous knockdown of these 5 genes also increased tfpia mRNA levels. We also performed individual gene and simultaneous 5-gene knockdowns on the 5 genes in zebrafish larvae. We found that after laser injury, it took a longer time for the formation of the thrombus to occlude the caudal vessel compared to the control larvae. We then treated the larvae and adults with a chemical UNC6852 known to proteolytically degrade polycomb repressor complex 2, where SUZ12 is a member, and observed prolongation of time to occlude (TTO) the caudal vein after laser injury and increased tfpia mRNA levels in larvae and adults, respectively. In summary, our results have identified novel epigenetic regulators for tfpia and exploited this information to discover a drug that enhances tfpia mRNA levels and prolongation of TTO. This discovery provides the basis for testing whether UNC6852 could be used as an antithrombotic drug. This approach could be used to study the regulation of other plasma proteins, including coagulant and anticoagulant factors.

Post-transcriptional, post-translational and pharmacological regulation of tissue factor pathway inhibitor

: Tissue factor (TF) pathway inhibitor (TFPI) is an endogenous natural anticoagulant that readily inhibits the extrinsic coagulation initiation complex (TF-FVIIa-Xa) and prothrombinase (FXa, FVa and calcium ions). Alternatively, spliced TFPI isoforms (α, β and δ) are expressed by vascular and extravascular cells and regulate thrombosis and haemostasis, as well as cell signalling functions of TF complexes via protease-activated receptors (PARs). Proteolysis of TFPI plays an important role in regulating physiological roles of the TF pathway in host defense and possibly haemostasis. Elimination of TFPI inhibition has therefore been proposed as an approach to improve haemostasis in haemophilia patients. In this review, we focus on posttranscription and translational modification of TFPI and its function in thrombosis and how pharmacological inhibitors and endogenous proteases interfere with TFPI and alter haemostasis.

PDGF Restores the Defective Phenotype of Adipose-Derived Mesenchymal Stromal Cells from Diabetic Patients

Diabetes is a chronic metabolic disorder that affects 415 million people worldwide. This pathology is often associated with long-term complications, such as critical limb ischemia (CLI), which increases the risk of limb loss and mortality. Mesenchymal stromal cells (MSCs) represent a promising option for the treatment of diabetes complications. Although MSCs are widely used in autologous cell-based therapy, their effects may be influenced by the constant crosstalk between the graft and the host, which could affect the MSC fate potential. In this context, we previously reported that MSCs derived from diabetic patients with CLI have a defective phenotype that manifests as reduced fibrinolytic activity, thereby enhancing the thrombotic risk and compromising patient safety. Here, we found that MSCs derived from diabetic patients with CLI not only exhibit a prothrombotic profile but also have altered multi-differentiation potential, reduced proliferation, and inhibited migration and homing to sites of inflammation. We further demonstrated that this aberrant cell phenotype is reversed by the platelet-derived growth factor (PDGF) BB, indicating that PDGF signaling is a key regulator of MSC functionality. These findings provide an attractive approach to improve the therapeutic efficacy of MSCs in autologous therapy for diabetic patients.

Endogenous tissue factor pathway inhibitor in vascular smooth muscle cells inhibits arterial thrombosis

Tissue factor pathway inhibitor (TFPI) is the main inhibitor of tissue factor-mediated coagulation. TFPI is expressed by endothelial and smooth muscle cells in the vasculature. Endothelium-derived TFPI has been reported to play a regulatory role in arterial thrombosis. However, the role of endogenous TFPI in vascular smooth muscle cells (VSMCs) in thrombosis and vascular disease development has yet to be elucidated. In this TFPI^Flox mice crossbred with Sma-Cre mice were utilized to establish TFPI conditional knockout mice and to examine the effects of VSMC-directed TFPI deletion on development, hemostasis, and thrombosis. The mice with deleted TFPI in VSMCs (TFPI^Sma) reproduced viable offspring. Plasma TFPI concentration was reduced 7.2% in the TFPI^Sma mice compared with TFPI^Flox littermate controls. Plasma TFPI concentration was also detected in the TFPI^Tie2 (mice deleted TFPI in endothelial cells and cells of hematopoietic origin) mice. Plasma TFPI concentration of the TFPI^Tie2 mice was 80.4% lower (P < 0.001) than that of the TFPI^Flox mice. No difference in hemostatic measures (PT, APTT, and tail bleeding) was observed between TFPI^Sma and TFPI^Flox mice. However, TFPI^Sma mice had increased ferric chloride-induced arterial thrombosis compared with TFPI^Flox littermate controls. Taken together, these data indicated that endogenous TFPI from VSMCs inhibited ferric chloride-induced arterial thrombosis without causing hemostatic effects.

Increased expression of TFPI in human carotid stenosis

INTRODUCTION

Tissue factor (TF) pathway inhibitor (TFPI) is the physiological inhibitor of TF induced blood coagulation and two isoforms exists, TFPIα and TFPIβ. In atherosclerotic plaques, TFPI may inhibit TF activity and thrombus formation, which is the main cause of ischemic stroke in carotid artery disease. We aimed to identify the isoforms of TFPI present in human carotid plaques and potential sources of TFPI.

MATERIALS AND METHODS

Human atherosclerotic plaques from carotid endarterectomies were used for mRNA and immunohistochemistry analyses. hPBMCs isolated from buffy coats and THP-1 cells were differentiated and polarized into M1 or M2 macrophages, and subsequently cultured with or without cholesterol crystals (CC). mRNA and protein expression were measured with qRT-PCR and ELISA, respectively, and procoagulant activity was assessed using a two-stage chromogenic assay.

RESULTS

TFPIα and TFPIβ mRNA levels were significantly increased in carotid plaques, whereas TF levels were unchanged as compared to healthy arteries. Antibodies against total TFPI showed elevated levels compared to antibodies against free TFPIα, both by immunohistochemical and ELISA detection in plaques. The antibody against total TFPI also co-localized with CD68 and the M1 and M2 markers CD80 and CD163, respectively. The TFPI mRNA expression was elevated and the procoagulant activity was decreased in M2 compared to M1 polarized human macrophages. TFPI was present in early foam cell formation and CC treatment increased the TFPI mRNA expression even further in M2 macrophages.

CONCLUSIONS

Our data indicate that both isoforms of TFPI are present in advanced plaques and that anti-inflammatory M2 macrophages may be a potential source of TFPI.

Leveraging cell type specific regulatory regions to detect SNPs associated with tissue factor pathway inhibitor plasma levels

Tissue factor pathway inhibitor (TFPI) regulates the formation of intravascular blood clots, which manifest clinically as ischemic heart disease, ischemic stroke, and venous thromboembolism (VTE). TFPI plasma levels are heritable, but the genetics underlying TFPI plasma level variability are poorly understood. Herein we report the first genome-wide association scan (GWAS) of TFPI plasma levels, conducted in 251 individuals from five extended French-Canadian Families ascertained on VTE. To improve discovery, we also applied a hypothesis-driven (HD) GWAS approach that prioritized single nucleotide polymorphisms (SNPs) in (1) hemostasis pathway genes, and (2) vascular endothelial cell (EC) regulatory regions, which are among the highest expressers of TFPI. Our GWAS identified 131 SNPs with suggestive evidence of association (P-value < 5 × 10^-8 ), but no SNPs reached the genome-wide threshold for statistical significance. Hemostasis pathway genes were not enriched for TFPI plasma level associated SNPs (global hypothesis test P-value = 0.147), but EC regulatory regions contained more TFPI plasma level associated SNPs than expected by chance (global hypothesis test P-value = 0.046). We therefore stratified our genome-wide SNPs, prioritizing those in EC regulatory regions via stratified false discovery rate (sFDR) control, and reranked the SNPs by q-value. The minimum q-value was 0.27, and the top-ranked SNPs did not show association evidence in the MARTHA replication sample of 1,033 unrelated VTE cases. Although this study did not result in new loci for TFPI, our work lays out a strategy to utilize epigenomic data in prioritization schemes for future GWAS studies.

Conditional knockout of TFPI-1 in VSMCs of mice accelerates atherosclerosis by enhancing AMOT/YAP pathway

BACKGROUND

Tissue factor pathway inhibitor-1 (TFPI-1) has multiple functions and its precise role and molecular mechanism during the development of atherosclerosis are not clear.

OBJECTIVES

To determine the effect and molecular mechanism of TFPI-1 deficiency in vascular smooth muscle cells (VSMCs) in atherosclerosis in the apolipoprotein E knockout (ApoE^-/-) mouse.

METHODS AND RESULTS

A mouse model with a conditional knockout of TFPI-1 in VSMCs in an atherosclerosis-prone background (ApoE^-/-) was generated. Mice were fed a high fat diet for 18weeks and were then euthanized. Arterial trees and aortas were stained with Sudan IV and were labeled via immunohistochemistry. Cell proliferation and migration of VSMCs in atherosclerotic plaques were assessed. More atherosclerotic lesions and higher levels of proliferation and migration of VSMCs were observed in TFPI-1^fl/fl/Sma-Cre⁺ApoE^-/-mice. An interaction between TFPI-1 and angiomotin (AMOT) was identified in human VSMCs by mass spectrometry, immunoprecipitation and co-localization analyses. Signal pathway changes were detected by Western blot analysis, and the expression levels of target genes were determined by real-time PCR. Decreased phosphorylation of AMOT and Yes-associated protein 1 (YAP) in TFPI-1^fl/fl/Sma-Cre⁺ApoE^-/- mice resulted in increased expression levels of snail family zinc finger 2 (SLUG) and connective tissue growth factor (CTGF), which are target genes of the Hippo signaling pathway that have been verified as atherosclerosis candidate genes.

CONCLUSION

Deficiency in TFPI-1 in the VSMCs of ApoE^-/- mice accelerated the development of atherosclerosis by promoting the proliferation and migration of VSMCs which may be caused by the decreased phosphorylation of AMOT and YAP.

SIGNIFICANCE

TFPI-1 has been found to has an anticoagulant activity, induce cell apoptosis and prevent cell proliferation. For the first time, we constructed a line of conditional knockout mice in which the TPFI-1 gene is deleted in VSMCs. We found that TFPI-1 deficiency clearly promoted the development of atherosclerosis when these mice were crossed into an ApoE^-/-background. One notable feature of atherosclerosis is the proliferation and migration of smooth muscle cells. Previous reports involved TFPI-1 do not completely explain the proliferation and migration of VSMCs because heterozygous TF deficient (TF^±) mice bred in an ApoE^-/- background did not show diminished atherosclerosis compared to TF^+/+ mice bred in the same background. Our results first confirmed that TFPI-1 interacts with AMOT, which led to a decrease in the phosphorylation of YAP and further increased the genes expression of the proliferation and migration involved. Our results further confirmed that atherosclerosis was a localized disease.

EPAS1/HIF-2 alpha-mediated downregulation of tissue factor pathway inhibitor leads to a pro-thrombotic potential in endothelial cells

Neovascularization and hemorrhaging are evident in advanced atherosclerotic plaques due to hypoxic conditions, and mediate the accumulation of metabolic substrates, inflammatory cells, lipids, and other blood born factors inside the plaque. Tissue factor (TF) pathway inhibitor (TFPI) is mainly expressed by endothelial cells and is the endogenous inhibitor of the coagulation activator TF, which together with the downstream product thrombin can drive plaque progression and atherogenesis. We aimed to investigate the effect of hypoxic conditions on endothelial cell expression and activity of TFPI and TF that are important in coagulation initiation. Hypoxia was induced in primary human umbilical vein endothelial cells using chemicals or 1% oxygen tension, and mRNA and protein expressions were measured using qRT-PCR, ELISA, and Western blot analysis. Microscopy of fluorescence-labeled cells was used to visualize cell-associated TFPI. Cell-surface factor Xa (FXa) activity was measured using a two-stage chromogenic substrate method. We found that hypoxia reduced the TFPI mRNA and protein levels and increased the TF mRNA expression in a dose-dependent manner. The effect on TFPI was apparent on all the protein pools of TFPI, i.e., secreted TFPI, cell-surface associated TFPI, and intracellular TFPI, and seemed to be dependent upon hypoxia inducible factor-2α (HIF-2α). An increase in FXa activity was also observed on the endothelial cell surface, reflecting an increase in pro-thrombotic potential of the cells. Our findings indicate that hypoxic conditions may enhance the pro-coagulant activity of endothelial cells, which may promote atherogenesis in addition to clinical events and thus the severity of atherosclerotic disorders.

Syndecan-3 and TFPI colocalize on the surface of endothelial-, smooth muscle-, and cancer cells

Background

Tissue factor (TF) pathway inhibitor (TFPI) exists in two isoforms; TFPIα and TFPIβ. Both isoforms are cell surface attached mainly through glycosylphosphatidylinositol (GPI) anchors. TFPIα has also been proposed to bind other surface molecules, like glycosaminoglycans (GAGs). Cell surface TFPIβ has been shown to exert higher anticoagulant activity than TFPIα, suggesting alternative functions for TFPIα. Further characterization and search for novel TFPI binding partners is crucial to completely understand the biological functions of cell associated TFPI.

Methods and Results

Potential association of TFPI to heparan sulphate (HS) proteoglycans in the syndecan family were evaluated by knock down studies and flow cytometry analysis. Cell surface colocalization was assessed by confocal microscopy, and native PAGE or immunoprecipitation followed by Western blotting was used to test for protein interaction. Heparanase was used to enzymatically degrade cell surface HS GAGs. Anticoagulant potential was evaluated using a factor Xa (FXa) activity assay. Knock down of syndecan-3 in endothelial,- smooth muscle- and breast cancer cells reduced the TFPI surface levels by 20-50%, and an association of TFPIα to syndecan-3 on the cell surface was demonstrated. Western blotting indicated that TFPIα was found in complex with syndecan-3. The TFPI bound to syndecan-3 did not inhibit the FXa generation. Removal of HS GAGs did not release TFPI antigen from the cells.

Conclusions

We demonstrated an association between TFPIα and syndecan-3 in vascular cells and in cancer cells, which did not appear to depend on HS GAGs. No anticoagulant activity was detected for the TFPI associated with syndecan-3, which may indicate coagulation independent functions for this cell associated TFPI pool. This will, however, require further investigation.

Biology of tissue factor pathway inhibitor

Recent studies of the anticoagulant activities of the tissue factor (TF) pathway inhibitor (TFPI) isoforms, TFPIα and TFPIβ, have provided new insight into the biochemical and physiological mechanisms that underlie bleeding and clotting disorders. TFPIα and TFPIβ have tissue-specific expression patterns and anticoagulant activities. An alternative splicing event in the 5' untranslated region allows for translational regulation of TFPIβ expression. TFPIα has 3 Kunitz-type inhibitor domains (K1, K2, K3) and a basic C terminus, whereas TFPIβ has the K1 and K2 domains attached to a glycosylphosphatidyl inositol-anchored C terminus. TFPIα is the only isoform present in platelets, whereas endothelial cells produce both isoforms, secreting TFPIα and expressing TFPIβ on the cell surface. TFPIα and TFPIβ inhibit both TF-factor VIIa-dependent factor Xa (FXa) generation and free FXa. Protein S enhances FXa inhibition by TFPIα. TFPIα produces isoform-specific inhibition of prothrombinase during the initiation of coagulation, an anticoagulant activity that requires an exosite interaction between its basic C terminus and an acidic region in the factor Va B domain. Platelet TFPIα may be optimally localized to dampen initial thrombin generation. Similarly, endothelial TFPIβ may be optimally localized to inhibit processes that occur when endothelial TF is present, such as during the inflammatory response.

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.

Adenovirus-mediated tissue factor pathway inhibitor gene transfer induces apoptosis by blocking the phosphorylation of JAK-2/STAT-3 pathway in vascular smooth muscle cells

OBJECTIVE

In our previous study, we have demonstrated that tissue factor pathway inhibitor (TFPI) gene could induce vascular smooth muscle cell (VSMC) apoptosis. This study was conducted to investigate whether the overexpression of the TFPI gene can induce VSMC apoptosis by inhibiting JAK-2/STAT-3 pathway phosphorylation and thereby inhibiting the expression of such downstream targets as the apoptotic protein Bcl-2 and cell cycle protein cyclin D1. The effect of TFPI on the expression of survivin, a central molecule in cell survival, was also investigated.

METHODS

Rat VSMCs were infected with recombinant adenovirus containing either the TFPI (Ad-TFPI) or LacZ (Ad-LacZ) gene or DMEM in vitro. TFPI expression was detected by ELISA. TUNEL staining and electron microscope were carried out to determine the apoptosis of VSMCs. The expression levels of JAK-2, p-JAK-2, STAT-3, p-STAT-3, cyclin D1, Bcl-2 and survivin were examined by western blot analysis.

RESULTS

TFPI protein was detected in the TFPI group after gene transfer and the peak expression was at the 3rd day. At the 3rd, 5th and 7th days after gene transfer, the apoptotic rates by TUNEL assay in the TFPI group were 10.91 ± 1.66%, 13.46 ± 1.28% and 17.04 ± 1.95%, respectively, whereas those in the LacZ group were 3.28 ± 0.89%, 4.01 ± 0.72% and 4.89 ± 1.17%, respectively. We observed cell contraction, slight mitochondrial swelling, nuclear pyknosis and apoptotic body formation in TFPI-treated VSMCs using electron microscopy. JAK-2, p-JAK-2, STAT-3, p-STAT-3, cyclin D1 and Bcl-2, which are all involved in the JAK-2/STAT-3 pathway, were detected in the VSMCs on the 3rd, 5th and 7th days after gene transfer, which is consistent with previously demonstrated time points when VSMCs apoptosis occurred. The expression levels of p-JAK-2, p-STAT-3, cyclin D1 and Bcl-2 were significantly decreased over time in the TFPI group (each P<0.05) but not in the Ad-LacZ and DMEM groups. However, this attenuation of expression was not observed for JAK-2 and STAT-3 in any of the groups at any time points after gene transfer (each P>0.05). The expression level of survivin in the TFPI group also weakened significantly over time compared with the levels in the Ad-LacZ and DMEM groups (each P<0.05) at the 3rd, 5th and 7th days after gene transfer.

CONCLUSION

The results demonstrated that TFPI played an apoptosis-inducing role in VSMCs in a manner that involves both the suppression of JAK-2/STAT-3 pathway phosphorylation and the down-regulation of survivin. Our data show for the first time that targeting the JAK-2/STAT-3 pathway and survivin by overexpressing TFPI may be a new avenue for the treatment of restenosis.

Hemostatic effect of a monoclonal antibody mAb 2021 blocking the interaction between FXa and TFPI in a rabbit hemophilia model

Hemophilia is treated by IV replacement therapy with Factor VIII (FVIII) or Factor IX (FIX), either on demand to resolve bleeding, or as prophylaxis. Improved treatment may be provided by drugs designed for subcutaneous and less frequent administration with a reduced risk of inhibitor formation. Tissue factor pathway inhibitor (TFPI) down-regulates the initiation of coagulation by inhibition of Factor VIIa (FVIIa)/tissue factor/Factor Xa (FVIIa/TF/FXa). Blockage of TFPI inhibition may facilitate thrombin generation in a hemophilic setting. A high-affinity (KD = 25pM) mAb, mAb 2021, against TFPI was investigated. Binding of mAb 2021 to TFPI effectively prevented inhibition of FVIIa/TF/FXa and improved clot formation in hemophilia blood and plasma. The binding epitope on the Kunitz-type protease inhibitor domain 2 of TFPI was mapped by crystallography, and showed an extensive overlap with the FXa contact region highlighting a structural basis for its mechanism of action. In a rabbit hemophilia model, an intravenous or subcutaneous dose significantly reduced cuticle bleeding. mAb 2021 showed an effect comparable with that of rFVIIa. Cuticle bleeding in the model was reduced for at least 7 days by a single intravenous dose of mAb 2021. This study suggests that neutralization of TFPI by mAb 2021 may constitute a novel treatment option in hemophilia.

Absence of hematopoietic tissue factor pathway inhibitor mitigates bleeding in mice with hemophilia

Tissue factor pathway inhibitor (TFPI) blocks thrombin generation via the extrinsic blood coagulation pathway. Because the severe bleeding in patients with hemophilia occurs from deficiency of intrinsic blood coagulation pathway factor VIII or IX, pharmacological agents that inactivate TFPI and, therefore, restore thrombin generation via the extrinsic pathway, are being developed for treatment of hemophilia. Murine models of combined TFPI and factor VIII deficiency were used to examine the impact of TFPI deficiency on bleeding and clotting in hemophilia. In breeding studies, Factor VIII null (F8(-/-)) did not rescue the embryonic death of TFPI null (Tfpi(-/-)) mice. Tfpi(+/-) did not alter the bleeding phenotype of F8(-/-) mice. However, total inhibition of intravascular TFPI through injection of anti-TFPI antibody mitigated tail vein bleeding. Interestingly, tail blood loss progressively decreased at doses greater than needed to totally inhibit plasma TFPI, suggesting that inhibition of a sequestered pool of TFPI released at the injury site mitigates bleeding. Because TFPI is sequestered within platelets and released following their activation, the function of platelet TFPI was examined in F8(-/-) mice lacking hematopoietic cell TFPI that was generated by fetal liver transplantation. Blood loss after tail transection significantly decreased in Tfpi(+/-);F8(-/-) mice with hematopoietic Tfpi(-/-) cells compared with Tfpi(+/-);F8(-/-) mice with Tfpi(+/+) hematopoietic cells. Additionally, following femoral vein injury, Tfpi(+/-);F8(-/-) mice with Tfpi(-/-) hematopoietic cells had increased fibrin deposition compared with identical-genotype mice with Tfpi(+/+) hematopoietic cells. These findings implicate platelet TFPI as a primary physiological regulator of bleeding in hemophilia.

Tissue factor pathway inhibitor: structure-function

TFPI is a multivalent, Kunitz-type proteinase inhibitor, which, due to alternative mRNA splicing, is transcribed in three isoforms: TFPIalpha, TFPIdelta, and glycosyl phosphatidyl inositol (GPI)-anchored TFPIbeta. The microvascular endothelium is thought to be the principal source of TFPI and TFPIalpha is the predominant isoform expressed in humans. TFPIalpha, apparently attached to the surface of the endothelium in an indirect GPI-anchor-dependent fashion, represents the greatest in vivo reservoir of TFPI. The Kunitz-2 domain of TFPI is responsible for factor Xa inhibition and the Kunitz-1 domain is responsible for factor Xa-dependent inhibition of the factor VIIa/tissue factor catalytic complex. The anticoagulant activity of TFPI in one-stage coagulation assays is due mainly to its inhibition of factor Xa through a process that is enhanced by protein S and dependent upon the Kunitz-3 and carboxyterminal domains of full-length TFPIalpha. Carboxyterminal truncated forms of TFPI as well as TFPIalpha in plasma, however, inhibit factor VIIa/tissue factor in two-stage assay systems. Studies in gene-disrupted mice demonstrate the physiological importance of TFPI.

Peroxisome proliferator-activated receptor-gamma agonists suppress tissue factor overexpression in rat balloon injury model with paclitaxel infusion

The role and underlying mechanisms of rosiglitazone, a peroxisome proliferator-activated receptor-gamma (PPAR-γ) agonist, on myocardial infarction are poorly understood. We investigated the effects of this PPAR-γ agonist on the expression of tissue factor (TF), a primary molecule for thrombosis, and elucidated its underlying mechanisms. The PPAR-γ agonist inhibited TF expression in response to TNF-α in human umbilical vein endothelial cells, human monocytic leukemia cell line, and human umbilical arterial smooth muscle cells. The overexpression of TF was mediated by increased phosphorylation of mitogen-activated protein kinase (MAPK), which was blocked by the PPAR-γ agonist. The effective MAPK differed depending on each cell type. Luciferase and ChIP assays showed that transcription factor, activator protein-1 (AP-1), was a pivotal target of the PPAR-γ agonist to lower TF transcription. Intriguingly, two main drugs for drug-eluting stent, paclitaxel or rapamycin, significantly exaggerated thrombin-induced TF expression, which was also effectively blocked by the PPAR-γ agonist in all cell types. This PPAR-γ agonist did not impair TF pathway inhibitor (TFPI) in three cell types. In rat balloon injury model (Sprague-Dawley rats, n = 10/group) with continuous paclitaxel infusion, the PPAR-γ agonist attenuated TF expression by 70±5% (n = 4; P<0.0001) in injured vasculature. Taken together, rosiglitazone reduced TF expression in three critical cell types involved in vascular thrombus formation via MAPK and AP-1 inhibitions. Also, this PPAR-γ agonist reversed the paclitaxel-induced aggravation of TF expression, which suggests a possibility that the benefits might outweigh its risks in a group of patients with paclitaxel-eluting stent implanted.

Endothelial-derived tissue factor pathway inhibitor regulates arterial thrombosis but is not required for development or hemostasis

The antithrombotic surface of endothelium is regulated in a coordinated manner. Tissue factor pathway inhibitor (TFPI) localized at the endothelial cell surface regulates the production of FXa by inhibiting the TF/VIIa complex. Systemic homozygotic deletion of the first Kunitz (K1) domain of TFPI results in intrauterine lethality in mice. Here we define the cellular sources of TFPI and their role in development, hemostasis, and thrombosis using TFPI conditional knockout mice. We used a Cre-lox strategy and generated mice with a floxed exon 4 (TFPI(Flox)) which encodes for the TFPI-K1 domain. Mice bred into Tie2-Cre and LysM-Cre lines to delete TFPI-K1 in endothelial (TFPI(Tie2)) and myelomonocytic (TFPI(LysM)) cells resulted in viable and fertile offspring. Plasma TFPI activity was reduced in the TFPI(Tie2) (71% ± 0.9%, P < .001) and TFPI(LysM) (19% ± 0.6%, P < .001) compared with TFPI(Flox) littermate controls. Tail and cuticle bleeding were unaffected. However, TFPI(Tie2) mice but not TFPI(LysM) mice had increased ferric chloride-induced arterial thrombosis. Taken together, the data reveal distinct roles for endothelial- and myelomonocytic-derived TFPI.

Alternatively spliced isoforms of tissue factor pathway inhibitor

Tissue factor pathway inhibitor (TFPI) is the major regulator of tissue factor (TF)-induced coagulation. It down regulates coagulation by binding to the TF/fVIIa complex in a fXa dependent manner. It is predominantly produced by microvascular endothelial cells, though it is also found in platelets, monocytes, smooth muscle cells, and plasma. Its physiological importance is demonstrated by the embryonic lethality observed in TFPI knockout mice and by the increase in thrombotic burden that occurs when heterozygous TFPI mice are bred with mice carrying genetic risk factors for thrombotic disease, such as factor V Leiden. Multiple TFPI isoforms, termed TFPIalpha, TFPIbeta, and TFPIdelta in humans and TFPIalpha, TFPIbeta, and TFPIgamma in mice, have been described, which differ in their domain structure and method for cell surface attachment. A significant functional difference between these isoforms has yet to be described in vivo. Both human and mouse tissues produce, on average, approximately 10 times more TFPIalpha message when compared to that of TFPIbeta. Consistent with this finding, several lines of evidence suggest that TFPIalpha is the predominant protein isoform in humans. In contrast, recent work from our laboratory demonstrates that TFPIbeta is the major protein isoform produced in adult mice, suggesting that TFPI isoform production is translationally regulated.

Vascular-directed tissue factor pathway inhibitor overexpression regulates plasma cholesterol and reduces atherosclerotic plaque development

RATIONALE

Tissue factor pathway inhibitor (TFPI) is a potent regulator of the tissue factor pathway and is found in plasma in association with lipoproteins.

OBJECTIVE

To determine the role of TFPI in the development of atherosclerosis, we bred mice which overexpress TFPI into the apolipoprotein E-deficient (apoE(-/-)) background.

METHODS AND RESULTS

On a high-fat diet, smooth muscle 22alpha (SM22alpha)-TFPI/apoE(-/-) mice were shown to have less aortic plaque burden compared to apoE(-/-) mice. Unexpectedly, SM22alpha-TFPI/apoE(-/-) had lower plasma cholesterol levels compared to apoE(-/-) mice. Furthermore, SM22alpha-TFPI mice fed a high-fat diet had lower cholesterol levels than did wild-type mice. Because TFPI is associated with lipoproteins and its carboxyl terminus (TFPIct) has been shown to be a ligand for the very-low-density lipoprotein (VLDL) receptor, we hypothesized that TFPI overexpression may regulate lipoprotein distribution. We quantified VLDL binding and uptake in vitro in mouse aortic smooth muscle cells from SM22alpha-TFPI and wild-type mice. Mouse aortic smooth muscle cells from SM22alpha-TFPI mice demonstrated higher VLDL binding and internalization compared to those from wild-type mice. Because SM22alpha-TFPI mice have increased circulating levels of TFPI antigen, we examined whether TFPIct may act to alter lipoprotein distribution. In vitro, TFPIct increased VLDL binding, uptake, and degradation in murine embryonic fibroblasts. Furthermore, this effect was blocked by heparinase treatment. In vivo, systemic administration of TFPIct reduced plasma cholesterol levels in apoE(-/-) mice.

CONCLUSIONS

These studies suggest that overexpression of TFPI lowers plasma cholesterol through the interaction of its carboxyl terminus with lipoproteins and heparan sulfate proteoglycans.

Tissue factor expression in the symptomatic carotid plaque

Background

The aims of this study were to identify that the differences in the natural history of patients with symptomatic and asymptomatic carotid stenosis may be reflected in differences in the expression of procoagulant protein factors.

Methods

Carotid artery plaques were obtained from 33 symptomatic and 4 asymptomatic patients with internal carotid artery stenosis of greater than 70%. These plaques were stained with monoclonal antibody against human tissue factor. Areas of staining for the cap and core were analysed using the analySIS computer programme.

Results

There were 37 patients, of whom 27 were male with a mean age 69.3 years and a range of 53 to 83 years. Statistical analysis using non-parametric tests revealed a significant increase in the area of positive staining for tissue factor in plaques taken from symptomatic patients when compared to those who were asymptomatic (P = 0001). Within the symptomatic patients group there was significantly increased tissue factor in the plaque core of those who were the most recently symptomatic (P = 0.003).

Conclusions

The unstable carotid artery plaque is associated with significantly increased tissue factor expression in the cap and core. Plaques from the most recently symptomatic patients have significantly more tissue factor in the core and this may represent part of the mechanism responsible for plaque destabilisation. More research is needed in this important area.

Keywords

Tissue Factor; Carotid stenosis; Stroke; Plaque stability

Temporal expression of alternatively spliced forms of tissue factor pathway inhibitor in mice

BACKGROUND

Mouse tissue factor pathway inhibitor (TFPI) is produced in three alternatively spliced isoforms that differ in domain structure and mechanism for cell surface binding. Tissue expression of TFPI isoforms in mice was characterized as an initial step for identification of their physiological functions.

METHODS AND RESULTS

Sequence homology demonstrates that TFPIalpha existed over 430 Ma while TFPIbeta and TFPIgamma evolved more recently. In situ hybridization studies of heart and lung did not reveal any cells exclusively expressing a single isoform. Although our previous studies have demonstrated that TFPIalpha mRNA is more prevalent than TFPIbeta or TFPIgamma mRNA in mouse tissues, western blot studies demonstrated that TFPIbeta is the primary protein isoform produced in adult tissues, while TFPIalpha is expressed during embryonic development and in placenta. Consistent with TFPIbeta as the primary isoform produced within adult vascular beds, the TFPI isoform in mouse plasma migrates like TFPIbeta in SDS-PAGE and mice have a much smaller heparin-releasable pool of plasma TFPIalpha than humans.

CONCLUSIONS

The data demonstrate that alternatively spliced isoforms of TFPI are temporally expressed in mouse tissues at the level of protein production. TFPIalpha and TFPIbeta are produced in embryonic tissues and in placenta while adult tissues produce almost exclusively TFPIbeta.

Murine strain differences in hemostasis and thrombosis and tissue factor pathway inhibitor

INTRODUCTION

Differences among murine strains often lead to differential responses in models of human disease. The aim of the current study was to investigate whether differences exist among strains in models of hemostasis and thrombosis and whether these differences are reflected in differences in the tissue factor (TF) pathway.

METHODS

We examined baseline hemostatic parameters and the response to FeCl3-induced arterial thrombosis and a tail vein bleeding model in C57BL/6J (C57), 129S1/SvImJ (129S), and Balb/cJ (BalbC) mice. Finally, we examined TF and tissue factor pathway inhibitor (TFPI) activities in blood and expression in vascular tissue to determine whether these factors covary with a thrombotic phenotype.

RESULTS

No differences were observed in PT or aPTT among strains. 129S mice had lower platelet counts (p<0.001). BalbC had an increased rate of occlusion (mean occlusion time of 330+/-45 sec) in a FeCl(3)-induced model of thrombosis when compared to C57 (1182+/-349 sec) or 129 S (1442+/-281 sec) (p<0.05). Similarly, BalbC demonstrated reduced blood loss in tail bleeding experiments when compared to C57 and 129S. Vascular expression of TF and TFPI content did not correlate with the thrombotic phenotype of BalbC. However, circulating TFPI activities were lower in BalbC compared to both C57 and 129S mice. When normalized to circulating TF activities, BalbC had lower circulating TFPI activity than C57 and 129S, and there was a significant correlation between tail bleeding and normalized TFPI activity (r=0.67).

CONCLUSIONS

These data suggest that there are significant differences among strains in thrombosis and hemostasis and that circulating TFPI activity correlates with these differences.

Porphyromonas gingivalis infection and prothrombotic effects in human aortic smooth muscle cells

INTRODUCTION

Accumulating evidence has demonstrated an association between periodontal infectious agents, such as Porphyromonas gingivalis, and vascular disease. Tissue factor (TF) and its specific tissue factor pathway inhibitor (TFPI) are produced by vascular cells and are important regulators of the coagulation cascade.

MATERIALS AND METHODS

To assess the role of P. gingivalis in atherothrombosis, we infected primary human aortic smooth muscle cells (HASMC) with either P. gingivalis 381, its non-invasive mutant DPG3, or heat-killed P. gingivalis 381. Levels and activity of TF and TFPI were measured 8 and 24 hours after infection in cell extracts and cell culture supernatants.

RESULTS

P. gingivalis 381 did not affect total TF antigen or TF activity in HASMC, but it significantly suppressed TFPI levels and activity compared to uninfected control cells, and those infected with the non-invasive mutant strain or the heat-killed bacteria. Further, P. gingivalis' LPS (up to a concentration of 5 microg/ml) failed to induce prothrombotic effects in HASMC, suggesting a significant role for the ability of whole viable bacteria to invade this cell type.

CONCLUSION

These data demonstrate for the first time that infection with a periodontal pathogen induces a prothrombotic response in HASMC.

Recombinant tissue factor pathway inhibitor induces apoptosis in cultured rat mesangial cells via its Kunitz-3 domain and C-terminal through inhibiting PI3-kinase/Akt pathway

Tissue factor pathway inhibitor (TFPI) is an endogenous inhibitor of tissue factor (TF) induced coagulation. In addition to its anticoagulation activity, TFPI has other functions such as antiproliferation and inducing apoptosis. In the present study, we investigated whether or not TFPI induced apoptosis in cultured rat mesangial cells (MsCs) and the possible signal pathway that involved in the apoptotic process. We demonstrated that recombinant TFPI (rTFPI) induced apoptosis in cultured MsCs via its Kunitz-3 domain and C-terminal in a dose- and time-dependent manner by Hoechst 33258 assay, flow cytometry, nucleosomal laddering of DNA, caspase 3 assay. Because the serine/threonine protein kinase Akt has attracted attention as a mediator of survival (anti-apoptotic) signal in MsCs, we investigated the expression of phosphospecific-Akt and its downstream signal phospho-IkappaB-alpha and some other signal molecules like Fas and bcl-2. The results indicated that the process of apoptosis triggered by rTFPI is, at least in part, actively conducted by rat MsCs possibly through PI3-Kinase-Akt signal pathway not by binding to tissue factor. Our findings suggest that rTFPI has the potential usefulness in inducing apoptosis of MsCs under inflammatory conditions.

Tissue factor pathway inhibitor is highly susceptible to chymase-mediated proteolysis

Tissue factor pathway inhibitor (TFPI) is a multivalent Kunitz-type protease inhibitor that primarily inhibits the extrinsic pathway of blood coagulation. It is synthesized by various cells and its expression level increases in inflammatory environments. Mast cells and neutrophils accumulate at sites of inflammation and vascular disease where they release proteinases as well as chemical mediators of these conditions. In this study, the interactions between TFPI and serine proteinases secreted from human mast cells and neutrophils were examined. TFPI inactivated human lung tryptase, and its inhibitory activity was stronger than that of antithrombin. In contrast, mast cell chymase rapidly cleaved TFPI even at an enzyme to substrate molar ratio of 1:500, resulting in markedly decreased TFPI anticoagulant and anti-(factor Xa) activities. N-terminal amino-acid sequencing and MS analyses of the proteolytic fragments revealed that chymase preferentially cleaved TFPI at Tyr159-Gly160, Phe181-Glu182, Leu89-Gln90, and Tyr268-Glu269, in that order, resulting in the separation of the three individual Kunitz domains. Neutrophil-derived proteinase 3 also cleaved TFPI, but the reaction was much slower than the chymase reaction. In contrast, alpha-chymotrypsin, which shows similar substrate specificities to those of chymase, resulted in a markedly lower level of TFPI degradation. These data indicate that TFPI is a novel and highly susceptible substrate of chymase. We propose that chymase-mediated proteolysis of TFPI may induce a thrombosis-prone state at inflammatory sites.

Caveolin-1 enhances tissue factor pathway inhibitor exposure and function on the cell surface

Tissue factor pathway inhibitor (TFPI) blocks tissue factor-factor VIIa (TF-FVIIa) activation of factors X and IX through the formation of the TF-FVIIa-FXa-TFPI complex. Most TFPI in vivo associates with caveolae in endothelial cells (EC). The mechanism of this association and the anticoagulant role of caveolar TFPI are not yet known. Here we show that expression of caveolin-1 (Cav-1) in 293 cells keeps TFPI exposed on the plasmalemma surface, decreases the membrane lateral mobility of TFPI, and increases the TFPI-dependent inhibition of TF-FVIIa. Caveolae-associated TFPI supports the co-localization of the quaternary complex with caveolae. To investigate the significance of these observations for EC we used RNA interference to deplete the cells of Cav-1. Functional assays and fluorescence microscopy revealed that the inhibitory properties of TFPI were diminished in EC lacking Cav-1, apparently through deficient assembly of the quaternary complex. These findings demonstrate that caveolae regulate the inhibition by cell-bound TFPI of the active protease production by the extrinsic pathway of coagulation.

Oncostatin M induces procoagulant activity in human vascular smooth muscle cells by modulating the balance between tissue factor and tissue factor pathway inhibitor

Oncostatin M (OSM) is a cytokine of the interleukin-6 (IL-6) family secreted by activated monocytes, and is expressed in atherosclerotic plaque. Smooth muscle cells (SMC), by expressing tissue factor (TF) and tissue factor pathway inhibitor (TFPI) can contribute to the thrombogenicity of atherosclerotic plaque. Consequently, the aim of this study was to evaluate the effects of OSM on the procoagulant activity of SMC. We observed that OSM induced in a concentration-dependent manner a potent procoagulant activity (PCA) that was related in part to an increased synthesis of TF, both at the cell membrane and in SMC lysates. The increased expression of TF on SMC membrane induced by OSM was sustained and was still observed 24 h after stimulation by OSM. IL-6 and leukaemia inhibitory factor (LIF), two OSM-related cytokines, did not significantly modify TF expression at the surface of SMC. In addition to its effects on TF, OSM decreased the secretion of TFPI in the supernatants of SMC, as well as in the lysates, but was devoid of effect on TFPI bound at the membrane of SMC. IL-6 and LIF reduced also TFPI secretion, which could explain why the PCA of SMC lysates treated by IL-6 or LIF was increased, despite an absence of effect on TF expression. In conclusion, these data support the hypothesis that by increasing the PCA of SMC, OSM might be involved in the thrombotic complications associated with plaque rupture.

A tissue-engineered stent for cell-based vascular gene transfer

Cell-based gene transfer using a stent platform would provide a significant advantage in terms of site-specific gene expression in the vasculature. The current study presents a novel stent design that allows stable in vivo transgene expression over a 4-week period in the vasculature. A mesh-stent coated with fibronectin provided an excellent platform for adherent porcine smooth muscle cells (SMC). Autologous porcine SMC were stably transduced with a plasmid encoding green fluorescence protein (GFP), seeded at high density in the mesh-stent, and deployed in the porcine coronary artery. Stable in vivo GFP expression within the mesh-stent (5.2 x 10(5) GFP-positive cells/cm(2) mesh) was demonstrated 1 month after implantation in the porcine coronary artery by fluorescence microscopy and flow cytometry. No significant change in GFP positive cell number within the stent occurred over a 1-month period in vivo when compared to preinsertion. Angiographic and histologic analysis revealed mild neointimal proliferation and no inflammatory infiltrate in the stented segment. This study has implications for treatment of cardiovascular and other diseases where long-term cell-based delivery of transgene is a desirable therapeutic option.

Lipoprotein (a) binds and inactivates tissue factor pathway inhibitor: a novel link between lipoproteins and thrombosis

Lipoprotein (a) [Lp(a)] has been associated with both anti-fibrinolytic and atherogenic effects. However, no direct link currently exists between this atherogenic lipoprotein and intravascular coagulation. The current study examined the binding and functional effects of Lp(a), its lipoprotein constituents, apoliprotein (a) [apo(a)] and low-density lipoprotein (LDL), and lysine-plasminogen (L-PLG), which shares significant homology with apo(a), on tissue factor pathway inhibitor (TFPI), a major regulator of tissue factor-mediated coagulation. Results indicate that Lp(a), apo(a), and PLG but not LDL bound recombinant TFPI (rTFPI) in vitro and that apo(a) bound to a region spanning the last 37 amino acid residues of the c-terminus of TFPI. The apparent binding affinity for TFPI was much higher for Lp(a) (KD approximately 150 nM) compared to PLG (KD approximately 800 nM) and nanomolar concentrations of apo(a) (500 nM) inhibited PLG binding to TFPI. Lp(a) also inhibited in a concentration-dependent manner rTFPI activity and endothelial cell surface TFPI activity in vitro, whereas PLG had no such effect. Moreover physiologic concentrations of PLG (2 microM) had no effect on the concentration-dependent inhibition of TFPI activity induced by Lp(a). In human atherosclerotic plaque, apo(a) and TFPI immunostaining were shown to coexist in smooth muscle cell-rich areas of the intima. These data suggest a novel mechanism whereby Lp(a) through its apo(a) moiety may promote thrombosis by binding and inactivating TFPI.

Expression of exogenous tissue factor pathway inhibitor in vivo suppresses thrombus formation in injured rabbit carotid arteries

OBJECTIVES

The aim of the present study was to test the hypothesis that retrovirus-mediated in vivo tissue factor pathway inhibitor (TFPI) gene transfer to the arterial wall would efficiently inhibit thrombosis without causing significant changes in systemic hemostatic variables.

BACKGROUND

Acute coronary syndromes (unstable angina and acute myocardial infarction) are usually caused by atherosclerotic plaque rupture, with consequent activation of the coagulation cascade and circulating platelets. Tissue factor (TF) exposure represents an early event in this pathophysiologic sequence, leading to activation of the extrinsic coagulation pathway and thrombin formation. Tissue factor pathway inhibitor is a naturally occurring inhibitor of the extrinsic pathway.

METHODS

In the present study, the gene coding for rabbit TFPI was inserted in a retroviral vector under control of a tetracycline-inducible promoter. Replication-defective, infectious, recombinant retroviruses were used to transfect rabbit carotid arteries with either TFPI or a reporter gene--green fluorescent protein (GFP).

RESULTS

Retroviral-mediated arterial gene transfer of TFPI resulted in potent inhibition of intravascular thrombus formation in stenotic and injured rabbit carotid arteries, whereas transfection of the contralateral carotid artery with GFP had no effect on thrombosis. No significant changes in systemic hemostatic variables (prothrombin time and partial thromboplastin time) were observed when thrombosis was inhibited.

CONCLUSIONS

These data suggest that retroviral-mediated transfection of the arterial wall with TFPI might represent an attractive approach for the treatment of thrombotic disorders.

Regulation of monocyte procoagulant activity in acute myocardial infarction: role of tissue factor and tissue factor pathway inhibitor-1

In acute myocardial infarction (AMI), monocyte procoagulant activity is increased and may contribute to the risk for recurrence and other thrombotic events. This study sought to investigate the role tissue factor (TF) and tissue factor pathway inhibitor-1 (TFPI-1) in the regulation of monocyte procoagulant activity in AMI. Serial venous blood samples were obtained from 40 patients with AMI undergoing revascularization by stent placement. Twenty patients with elective stenting for stable angina served as control subjects. TF proteolytic activity was measured with spectrozyme factor Xa (FXa), TF and TFPI-1 surface expression on monocytes by flow cytometry, RNA expression in whole blood by reverse transcription-polymerase chain reaction, and concentrations of plasma prothrombin fragments F(1 + 2) by immunoassay. Forty-eight hours after AMI, an increase was found in TF RNA, followed by an increase in TF surface expression by 24% +/- 4% and in plasma concentration of F(1 + 2) by 103% +/- 17% (P <.05). These changes could not be attributed to the intervention because they did not occur in the control group. TFPI-1 RNA and binding to the monocyte surface remained unchanged. FXa generation by monocytes of patients with AMI increased 53.6% +/- 9% in the presence of polyclonal antibodies to TFPI-1, indicating that cell-associated TFPI-1 inhibits monocyte TF activity. The increased monocyte procoagulant activity in AMI was caused by an up-regulation of TF that was partially inhibited by surface-bound TFPI-1. Anticoagulant therapy by direct inhibition of TF activity may, thus, be particularly effective in AMI. (Blood. 2001;97:3721-3726)

Endogenous mediators and thrombophilia

Platelets are one of the most important components of primary haemostasis. Since they lack a nucleus, their functional characteristics are determined at the time of production. The role of platelets in thrombosis is further modified by the interaction with vascular mediators that are endogenously produced in response to a variety of stimuli. This chapter discusses the factors that influence platelet production, the interaction with endogenous mediators, and the potential therapeutic benefits achieved by modifying this interaction in the clinical setting.

Regulation of Tissue Factor Pathway Inhibitor Expression in Smooth Muscle Cells

Tissue factor pathway inhibitor (TFPI) is the primary physiological inhibitor that regulates tissue factor-induced blood coagulation. TFPI is thought to be synthesized, in vivo, primarily by microvascular endothelial cells. Little is known about how TFPI is regulated under pathophysiological conditions. In this study, we determined mechanisms by which TFPI expression is regulated by human pulmonary artery smooth muscle cells (PASMC), because these cells contribute to remodeling of the pulmonary vasculature in disease. PASMC in culture constitutively synthesize and secrete TFPI. Exposure of PASMC to phorbol myristate acetate, lipopolysaccharide, tumor necrosis factor , thrombin, interleukin-1, and transforming growth factor-β had no significant effect on expression of TFPI by PASMC. By contrast, treatment of PASMC with serum and basic fibroblast growth factor (bFGF)/heparin markedly upregulated the expression of TFPI activity and antigen. On Western blot analysis, a protein consistent with full-length TFPI (42 kD) was identified in the conditioned media of PASMC, and the levels of the protein were much higher in the conditioned media of serum and bFGF/heparin-treated cells. Northern blot analysis showed that PASMC constitutively express TFPI mRNA, and treatment of cells with serum and bFGF/heparin had a minimal effect on the steady-state levels of TFPI mRNA. Nuclear run-on analysis did not show a significant increase in the transcriptional rate of TFPI gene in PASMC treated with serum or bFGF/heparin. Cycloheximide, but not actinomycin-D, treatment inhibited the serum and bFGF/heparin-induced increase in TFPI activity in PASMC. In conclusion, our data demonstrate that PASMC constitutively synthesize and secrete TFPI and serum or bFGF upregulate its expression, suggesting that growth factors that can stimulate the vessel wall in vivo might locally regulate TFPI expression. Our study also suggests that control of TFPI expression by serum or bFGF occurs via translational rather than transcriptional regulation.

Regulation of Tissue Factor Pathway Inhibitor Expression in Smooth Muscle Cells

Tissue factor pathway inhibitor (TFPI) is the primary physiological inhibitor that regulates tissue factor-induced blood coagulation. TFPI is thought to be synthesized, in vivo, primarily by microvascular endothelial cells. Little is known about how TFPI is regulated under pathophysiological conditions. In this study, we determined mechanisms by which TFPI expression is regulated by human pulmonary artery smooth muscle cells (PASMC), because these cells contribute to remodeling of the pulmonary vasculature in disease. PASMC in culture constitutively synthesize and secrete TFPI. Exposure of PASMC to phorbol myristate acetate, lipopolysaccharide, tumor necrosis factor , thrombin, interleukin-1, and transforming growth factor-β had no significant effect on expression of TFPI by PASMC. By contrast, treatment of PASMC with serum and basic fibroblast growth factor (bFGF)/heparin markedly upregulated the expression of TFPI activity and antigen. On Western blot analysis, a protein consistent with full-length TFPI (42 kD) was identified in the conditioned media of PASMC, and the levels of the protein were much higher in the conditioned media of serum and bFGF/heparin-treated cells. Northern blot analysis showed that PASMC constitutively express TFPI mRNA, and treatment of cells with serum and bFGF/heparin had a minimal effect on the steady-state levels of TFPI mRNA. Nuclear run-on analysis did not show a significant increase in the transcriptional rate of TFPI gene in PASMC treated with serum or bFGF/heparin. Cycloheximide, but not actinomycin-D, treatment inhibited the serum and bFGF/heparin-induced increase in TFPI activity in PASMC. In conclusion, our data demonstrate that PASMC constitutively synthesize and secrete TFPI and serum or bFGF upregulate its expression, suggesting that growth factors that can stimulate the vessel wall in vivo might locally regulate TFPI expression. Our study also suggests that control of TFPI expression by serum or bFGF occurs via translational rather than transcriptional regulation.