Combined tissue factor pathway inhibitor and thrombomodulin deficiency produces an augmented hypercoagulable state with tissue-specific fibrin deposition

Plasma tissue factor pathway inhibitor levels in coronavirus disease 2019 patients: a systematic review and meta-analysis

Studies have suggested a relationship between tissue factor pathway inhibitor (TFPI) and coronavirus disease 2019 (COVID-19) severity. However, there is inconsistency in the findings of the studies. To enhance comprehension of this relationship, a meta-analysis was conducted. PubMed, Web of Science, and Scopus databases were searched to identify eligible studies. The mean difference was employed as effect measures and the standardized mean difference (SMD) and the 95% confidence interval (CI) were utilized as a summary statistic. Heterogeneity was assessed through the application of the chi-square test and the I2 statistic. The included studies' quality and risk of bias were assessed using the Newcastle-Ottawa assessment scale, adapted for case-control studies. A total of six studies were included with 684 cases and healthy controls (180 healthy controls and 504 COVID-19 patients with different severity, 76 mild, 292 moderate, and 136 severe). The analysis revealed a significant increase in the TFPI level in COVID-19 patients with moderate severity compared with healthy controls (SMD = 0.95 ng/ml, 95% confidence interval (CI) 0.27, 1.63 ng/ml; I2 : 87.2%). The increased TFPI level in mild and moderate COVID-19 was not significant, SMD = 0.68 ng/ml, 95% CI -0.64 to 2.0 ng/ml; I2 92.9% and SMD = 0.62 ng/ml, 95% CI -0.62 to 1.86 ng/ml; I2 91.5%, respectively. In addition, most studies indicate an association of the increased TFPI concentrations with increased markers of inflammation, endothelial damage, and hypercoagulation. Considering the anticoagulant and anti-inflammatory roles of TFPI, its increase seems to be aimed at modulating COVID-19-induced hyper-inflammation and hyper-coagulation state.

SYSTEMATIC REVIEW REGISTRATION

PROSPERO CRD42023437353.

Defective fibrin deposition and thrombus stability in Bambi-/- mice are mediated by elevated anticoagulant function

BACKGROUND

Bone morphogenetic and activin membrane-bound inhibitor (BAMBI) is a transmembrane protein related to the type I transforming growth factor- β (TGF-β) receptor family that is present on both platelets and endothelial cells (ECs). Bambi-deficient mice exhibit reduced hemostatic function and thrombus stability characterized by an increased embolization.

OBJECTIVE

We aimed to delineate how BAMBI influences endothelial function and thrombus stability.

METHODS

Bambi-deficient mice were subjected to the laser-induced thrombosis model where platelet and fibrin accumulation was evaluated. Expression of thrombomodulin and tissue factor pathway inhibitor (TFPI) was also assessed in these mice.

RESULTS

Thrombus instability in Bambi-/- mice was associated with a profound defect in fibrin deposition. Injection of hirudin into Bambi+/+ mice prior to thrombus formation recapitulated the Bambi-/- thrombus instability phenotype. In contrast, hirudin had no additional effect upon thrombus formation in Bambi-/- mice. Deletion of Bambi in ECs resulted in mice with defective thrombus stability caused by decreased fibrin accumulation. Increased levels of the anticoagulant proteins TFPI and thrombomodulin were detected in Bambi-/- mouse lung homogenates. Endothelial cells isolated from Bambi-/- mouse lungs exhibited enhanced ability to activate protein C due to elevated thrombomodulin levels. Blocking thrombomodulin and TFPI in vivo fully restored fibrin accumulation and thrombus stability in Bambi-/- mice.

CONCLUSIONS

We demonstrate that endothelial BAMBI influences fibrin generation and thrombus stability by modulating thrombomodulin and TFPI anticoagulant function of the endothelium; we also highlight the importance of these anticoagulant proteins in the laser-induced thrombosis model.

New insights into the biology of tissue factor pathway inhibitor

Tissue factor pathway inhibitor (TFPI) dampens the initiation of blood coagulation by inhibiting two potent procoagulant complexes, tissue factor-factor VIIa (TF-FVIIa) and early forms of prothrombinase. TFPI isoforms, TFPIα and TFPIβ, result from alternative splicing of mRNA, producing distinct C-terminal ends of the two proteins. Both isoforms inhibit TF-FVIIa, but only TFPIα can inhibit early forms of prothrombinase by binding of its positively charged C-terminus with high affinity to the acidic B-domain exosite of FVa, which is generated upon activation by FXa. TFPIα and TFPIβ are produced in cultured human endothelial cells, while platelets contain only TFPIα. Knowledge of the anticoagulant mechanisms and tissue expression patterns of TFPIα and TFPIβ have improved our understanding of the phenotypes observed in different mouse models of TFPI deficiency, the east Texas bleeding disorder, and the development of pharmaceutical agents that block TFPI function to treat hemophilia.

A balance between TFPI and thrombin-mediated platelet activation is required for murine embryonic development

Tissue factor pathway inhibitor (TFPI) is a critical anticoagulant protein present in endothelium and platelets. Mice lacking TFPI (Tfpi(-/-)) die in utero from disseminated intravascular coagulation. They are rescued by concomitant tissue factor (TF) deficiency, demonstrating that TFPI modulates TF function in vivo. Recent studies have found TFPI inhibits prothrombinase activity during the initiation of coagulation and limits platelet accumulation during thrombus formation, implicating TFPI in modulating platelet procoagulant activity. To examine whether altered platelet function would compensate for the lack of TFPI and rescue TFPI-null embryonic lethality, Tfpi(+/-) mice lacking the platelet thrombin receptor, protease activated receptor 4 (PAR4; Par4(-/-)), or its coreceptor, PAR3, were mated. PAR3 deficiency did not rescue Tfpi(-/-) embryos, but >40% of expected Tfpi(-/-):Par4(-/-) offspring survived to adulthood. Adult Tfpi(-/-):Par4(-/-) mice did not exhibit overt thrombosis. However, they had focal sterile inflammation with fibrin(ogen) deposition in the liver and elevated plasma thrombin-antithrombin complexes, indicating activation of coagulation at baseline. Tfpi(-/-):Par4(-/-) mice have platelet and fibrin accumulation similar to Par4(-/-) mice following venous electrolytic injury but were more susceptible than Par4(-/-) mice to TF-induced pulmonary embolism. In addition, ∼30% of the Tfpi(-/-):Par4(-/-) mice were born with short tails. Tfpi(-/-):Par4(-/-) mice are the first adult mice described that lack TFPI with unaltered TF. They demonstrate that TFPI physiologically modulates thrombin-dependent platelet activation in a manner that is required for successful embryonic development and identify a role for TFPI in dampening intravascular procoagulant stimuli that lead to thrombin generation, even in the absence of thrombin-mediated platelet activation.

Coagulation in liver toxicity and disease: role of hepatocyte tissue factor

The liver is the primary source of a number of circulating coagulation factors, and acute liver injury and chronic liver disease are each associated with alterations in blood coagulation. Current views of the connection between liver injury and coagulation extend beyond the impact of liver disease on synthesis of coagulation factors to include a role for coagulation factor activity in the initiation and progression of liver disease. Mechanisms of coagulation initiation in liver disease are not completely understood. Compared to other tissues, liver expresses very low levels of tissue factor (TF). Recent studies indicate that expression of TF by hepatocytes comprises the majority of liver procoagulant activity, and that hepatocyte TF activates coagulation induced by liver injury. This review will briefly cover the expression and regulation of TF by hepatocytes, the role of TF in coagulation triggered by liver toxicity, and the contribution of coagulation activity to the progression of liver disease.

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.

Cellular expression and biological activities of alternatively spliced forms of tissue factor pathway inhibitor

PURPOSE OF REVIEW

Tissue factor pathway inhibitor (TFPI) is an anticoagulant protein that inhibits tissue factor-factor VIIa (TF-fVIIa) and factor Xa (fXa). Recent studies revealed distinct cellular expression patterns for TFPIα and TFPIβ and spurred additional experiments to define unique functions for these alternatively spliced TFPI isoforms.

RECENT FINDINGS

TFPIα is produced by endothelial cells, localizes to an intracellular granule, and is released following cellular stimulation with thrombin or heparin. TFPIα also is produced by megakaryocytes and released from activated platelets. Platelet TFPIα limits clot growth following vessel injury and alters bleeding in hemophilia, suggesting that its primary physiological role is modulation of clot development. TFPIβ is made by endothelial cells, localizes to the endothelium surface, and is not in platelets. TFPIβ is an effective inhibitor of TF-mediated cellular migration and may act to dampen the adverse effects of intravascular TF expressed during inflammation.

SUMMARY

Knowledge of TFPI isoform expression and activity provides new insights into the biochemical regulation of TF-mediated thrombotic and inflammatory disease. Recent findings have therapeutic implications for use of recombinant TFPI to treat severe sepsis in community-acquired pneumonia or to achieve improved engraftment of hematopoietic stem cells, and for development of TFPI-blocking pharmaceuticals to treat hemophilia.

Loss of endothelial protein C receptors links coagulation and inflammation to parasite sequestration in cerebral malaria in African children

Cerebral malaria (CM) is a major cause of mortality in African children and the mechanisms underlying its development, namely how malaria-infected erythrocytes (IEs) cause disease and why the brain is preferentially affected, remain unclear. Brain microhemorrhages in CM suggest a clotting disorder, but whether this phenomenon is important in pathogenesis is debated. We hypothesized that localized cerebral microvascular thrombosis in CM is caused by a decreased expression of the anticoagulant and protective receptors thrombomodulin (TM) and endothelial protein C receptor (EPCR) and that low constitutive expression of these regulatory molecules in the brain make it particularly vulnerable. Autopsies from Malawian children with CM showed cerebral fibrin clots and loss of EPCR, colocalized with sequestered IEs. Using a novel assay to examine endothelial phenotype ex vivo using subcutaneous microvessels, we demonstrated that loss of EPCR and TM at sites of IE cytoadherence is detectible in nonfatal CM. In contrast, although clotting factor activation was seen in the blood of CM patients, this was compensated and did not disseminate. Because of the pleiotropic nature of EPCR and TM, these data implicate disruption of the endothelial protective properties at vulnerable sites and particularly in the brain, linking coagulation and inflammation with IE sequestration.

Use of topical bovine thrombin in an anti-coagulated rat model of hepatic injury

The need for surgical hemostasis in patients treated with anticoagulant medications is a concern. This study assessed a bovine-derived topical hemostat (FastAct, FA) using a partial hepatectomy hemorrhage model in anticoagulated rats. Ninety rats were randomly assigned to receive preoperative heparin, warfarin, or nothing (n=30/treatment). Within each treatment group, FA, saline, direct pressure (DP), electrocautery, or nothing (n=6/group) was applied to the hepatectomy site. Eight additional rats were used for assessment of the preoperative anticoagulant regimen. Rats that were not anticoagulated and received FA had faster clot times and less hemorrhage than those receiving DP (P<0.05). In warfarin-pretreated rats, FA resulted in faster coagulation times than saline or DP and less hemorrhage than saline (P<0.05). No differences were detected in heparinized rats. Across all groups, rats receiving FA lost less blood and formed clots more frequently than saline (P<0.05). FA may be useful to treat hemorrhage from hepatic lacerations in anticoagulated patients.

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.

Procoagulant activity in hemostasis and thrombosis: Virchow's triad revisited

Virchow's triad is traditionally invoked to explain pathophysiologic mechanisms leading to thrombosis, alleging concerted roles for abnormalities in blood composition, vessel wall components, and blood flow in the development of arterial and venous thrombosis. Given the tissue-specific bleeding observed in hemophilia patients, it may be instructive to consider the principles of Virchow's triad when investigating mechanisms operant in hemostatic disorders as well. Blood composition (the function of circulating blood cells and plasma proteins) is the most well studied component of the triad. For example, increased levels of plasma procoagulant proteins such as prothrombin and fibrinogen are established risk factors for thrombosis, whereas deficiencies in plasma factors VIII and IX result in bleeding (hemophilia A and B, respectively). Vessel wall (cellular) components contribute adhesion molecules that recruit circulating leukocytes and platelets to sites of vascular damage, tissue factor, which provides a procoagulant signal of vascular breach, and a surface upon which coagulation complexes are assembled. Blood flow is often characterized by 2 key variables: shear rate and shear stress. Shear rate affects several aspects of coagulation, including transport rates of platelets and plasma proteins to and from the injury site, platelet activation, and the kinetics of fibrin monomer formation and polymerization. Shear stress modulates adhesion rates of platelets and expression of adhesion molecules and procoagulant activity on endothelial cells lining the blood vessels. That no one abnormality in any component of Virchow's triad fully predicts coagulopathy a priori suggests coagulopathies are complex, multifactorial, and interactive. In this review, we focus on contributions of blood composition, vascular cells, and blood flow to hemostasis and thrombosis, and suggest that cross-talk among the 3 components of Virchow's triad is necessary for hemostasis and determines propensity for thrombosis or bleeding. Investigative models that permit interplay among these components are necessary to understand the operant pathophysiology, and effectively treat and prevent thrombotic and bleeding disorders.

Hydration-sensitive gene expression in brain

Dehydration has a profound influence on neuroexcitability. The mechanisms remained, however, incompletely understood. The present study addressed the effect of water deprivation on gene expression in the brain. To this end, animals were exposed to a 24 hours deprivation of drinking water and neuronal gene expression was determined by microarray technology with subsequent confirmation by RT-PCR. As a result, water deprivation was followed by significant upregulation of clathrin (light polypeptide Lcb), serum/glucocorticoid-regulated kinase (SGK) 1, and protein kinase A (PRKA) anchor protein 8-like. Water deprivation led to downregulation of janus kinase and microtubule interacting protein 1, neuronal PAS domain protein 4, thrombomodulin, purinergic receptor P2Y - G-protein coupled 13 gene, gap junction protein beta 1, neurotrophin 3, hyaluronan and proteoglycan link protein 1, G protein-coupled receptor 19, CD93 antigen, forkhead box P1, suppressor of cytokine signaling 3, apelin, immunity-related GTPase family M, serine (or cysteine) peptidase inhibitor clade B member 1a, serine (or cysteine) peptidase inhibitor clade H member 1, glutathion peroxidase 8 (putative), discs large (Drosophila) homolog-associated protein 1, zinc finger and BTB domain containing 3, and H2A histone family member V. Western blotting revealed the downregulation of forkhead box P1, serine (or cysteine) peptidase inhibitor clade H member 1, and gap junction protein beta 1 protein abundance paralleling the respective alterations of transcript levels. In conclusion, water deprivation influences the transcription of a wide variety of genes in the brain, which may participate in the orchestration of brain responses to water deprivation.

Amelioration effects of berberine on diabetic microendothelial injury model by the combination of high glucose and advanced glycation end products in vitro

Microvascular complications are much earlier and common in diabetes. Advanced glycation end products (AGEs), together with high glucose, play a key role in the endothelial dysfunction of diabetic vascular complications. So it is of more significance to expedite the therapies to block the formation and/or the effects of AGEs. Berberine has been showed to have anti-diabetic effects, however the effects on diabetic complications were less explored, especially the effects on the microvascular complications and the formation and pathways of AGEs which have not been reported. Therefore, the present study established an in vitro model of diabetic microendothelial (microEC) injury by the combination of high glucose and AGEs to mimic the clinical situations and examine the effects and mechanisms of berberine on high glucose-AGEs-induced microEC injuries and on the formation of AGEs. We prepared AGEs, established the high glucose-AGEs injured microEC models by MTT assay, which was further supported by significantly decreased nitric oxide (NO) release, NO synthase (NOS) and thrombomodulin production with ELISA, western blot and RT-PCR analysis. Berberine treatments showed significant improvements as indicated by significantly increased NO release, NOS and thrombomodulin production. Moreover, we also observed significant inhibition effects of berberine on AGEs formation. We concluded that the in vitro model of diabetic microEC injury could be established by the combination treatments of high glucose and AGEs, while berberine could improve the diabetic microvascular injury in vitro and inhibit the formation of AGEs, suggesting the potential clinical therapies with berberine for diabetes and its vascular complications.

Mitogen-activated protein kinases pathway is involved in physiological testosterone-induced tissue factor pathway inhibitor expression in endothelial cells

The mechanism of testosterone inducing the tissue factor pathway inhibitor (TFPI) in protecting against thrombosis is unknown. We aimed to elucidate the mechanisms involved in the induction by observing, in human umbilical vein endothelial cells (HUVECs), the phosphorylation of mitogen-activated protein kinases (MAPKs), a major cell signaling system. The level of testosterone regulating several signaling pathways, including extracellular signal-regulated kinases 1/2 (ERK1/2), c-Jun-N-terminal kinase (JNK), and p38 MAPK, was measured by western blot in HUVECs. ELISA and quantitative real-time reverse transcriptase-PCR were used to analyze TFPI expression after blocking ERK1/2 (with PD98059) or JNK (with SP600125) pathway in HUVECs. Testosterone-induced a rapid phosphorylation of ERK1/2, JNK and p38 MAPK in HUVECs, which could not be inhibited by androgen receptor antagonist flutamide. Blocking ERK1/2 or JNK pathway could significantly impair testosterone-induced TFPI at both translational and transcriptional levels in HUVECs. Testosterone at a physiological concentration may help to prevent thrombosis development by stimulating TFPI expression in HUVECs, partly through the ERK1/2 and JNK MAPK pathway.

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.

Influence of cellular and plasma procoagulant activity on the fibrin network

At the nexus of cellular and plasma procoagulant activities lies fibrin, which is necessary to provide a clot's structural support. Abnormalities in fibrin network formation or function can result in either bleeding or thrombotic complications. Understanding relationships between procoagulant activity and normal fibrin formation, as well as pathophysiologic mechanisms leading to abnormal fibrin deposition, is essential for the continued development of hemostatic and antithrombotic therapies.

Testosterone alleviates tumor necrosis factor-alpha-mediated tissue factor pathway inhibitor downregulation via suppression of nuclear factor-kappa B in endothelial cells

We have observed earlier that testosterone at physiological concentrations can stimulate tissue factor pathway inhibitor (TFPI) gene expression through the androgen receptor in endothelial cells. This study further investigated the impact of testosterone on TFPI levels in response to inflammatory cytokine tumor necrosis factor-alpha (TNF-alpha). Cultured human umbilical vein endothelial cells were incubated in the presence or absence of testosterone or TNF-alpha. TFPI protein and mRNA levels were assessed by enzyme-linked immunosorbent assay and quantitative real-time reverse transcription polymerase chain reaction. To study the cellular mechanism of testosterone's action, nuclear factor-kappa B (NF-kappaB) translocation was confirmed by electrophoretic mobility shift assays. We found that after NF-kappaB was activated by TNF-alpha, TFPI protein levels declined significantly by 37.3% compared with controls (P < 0.001), and the mRNA levels of TFPI also decreased greatly (P < 0.001). A concentration of 30 nmol L(-1) testosterone increased the secretion of TFPI compared with the TNF-alpha-treated group. NF-kappaB DNA-binding activity was significantly suppressed by testosterone (P < 0.05). This suggests that physiological testosterone concentrations may exert their antithrombotic effects on TFPI expression during inflammation by downregulating NF-kappaB activity.

Cellular procoagulant activity dictates clot structure and stability as a function of distance from the cell surface

BACKGROUND

Thrombin concentration modulates fibrin structure and fibrin structure modulates clot stability; however, the impact of localized, cell surface-driven in situ thrombin generation on fibrin structure and stability has not previously been evaluated.

METHODS AND RESULTS

Human fibroblasts were incubated with factors Xa, Va, prothrombin and fibrinogen, or plasma. Fibrin formation, structure, and lysis were examined using laser scanning confocal microscopy and transmission electron microscopy. In situ thrombin generation on the cell surface produced clots with a significantly denser fiber network in a 10-microm region proximal versus distal to (40 to 50 microm) the cell surface. This morphology was not altered by addition of integrin-blocking RGDS peptide and was not apparent in clots made by exogenous thrombin addition, suggesting that spatial morphology was dictated predominantly by localized thrombin generation on the fibroblast surface. The fibrin network lysed more rapidly distal versus proximal to the cell surface, suggesting that the structural heterogeneity of the clot affected its fibrinolytic stability.

CONCLUSIONS

In situ thrombin generation on the cell surface modulates the three-dimensional structure and stability of the clot. Thrombus formation in vivo may reflect the ability of the local cell population to support thrombin generation and, therefore, the three-dimensional structure and stability of the fibrin network.

Tissue factor pathway inhibitor-gamma is an active alternatively spliced form of tissue factor pathway inhibitor present in mice but not in humans

BACKGROUND

Tissue factor pathway inhibitor (TFPI) is a potent inhibitor of tissue factor procoagulant activity produced as two alternatively spliced isoforms, TFPIalpha and TFPIbeta, which differ in domain structure and mechanism for cell surface association. 3' Rapid amplification of cDNA ends was used to search for new TFPI isoforms. TFPIgamma, a new alternatively spliced form of TFPI, was identified and characterized.

METHODS

The tissue expression, cell surface association and anticoagulant activity of TFPIgamma were characterized and compared to those of TFPIalpha and TFPIbeta through studies of mouse and human tissues and expression of recombinant proteins in Chinese hamster ovary (CHO) cells.

RESULTS

TFPIgamma is produced by alternative splicing using the same 5'-splice donor site as TFPIbeta and a 3'-splice acceptor site 276 nucleotides beyond the stop codon of TFPIbeta in exon 8. The resulting protein has the first two Kunitz domains connected to an 18 amino acid C-terminal region specific to TFPIgamma. TFPIgamma mRNA is differentially produced in mouse tissues but is not encoded within the human TFPI gene. When expressed in CHO cells, TFPIgamma is secreted into conditioned media and effectively inhibits tissue factor procoagulant activity.

CONCLUSIONS

TFPIgamma is a third alternatively spliced form of TFPI that is widely expressed in mouse tissues but not made by human tissues. It contains the first two Kunitz domains and is a secreted, rather than a cell surface-associated, protein. It is a functional anticoagulant and may partially explain the resistance of mice to coagulopathy in tissue factor-mediated models of disease.