Augmented arterial wall expression of type-1 plasminogen activator inhibitor induced by thrombosis

Plasminogen activator inhibitor-1 regulates the vascular expression of vitronectin

Essentials Vitronectin (VN) is produced by smooth muscle cells (SMCs) and promotes neointima formation. We studied the regulation of vascular VN expression by plasminogen activator inhibitor-1 (PAI-1). PAI-1 stimulates VN gene expression in SMCs by binding LDL receptor-related protein 1. Stimulation of VN gene expression may be a mechanism by which PAI-1 controls vascular remodeling.

SUMMARY

Background Increased expression of vitronectin (VN) by smooth muscle cells (SMCs) promotes neointima formation after vascular injury, and may contribute to chronic vascular diseases, such as atherosclerosis. However, the molecular regulation of vascular VN expression is poorly defined. Given the overlapping expression profiles and functions of VN and plasminogen activator inhibitor (PAI)-1, we hypothesized that PAI-1 regulates vascular VN expression. Objectives To determine whether PAI-1 regulates VN expression in SMCs and in vivo. Methods The effects of genetic alterations in PAI-1 expression, pharmacologic PAI-1 inhibition and recombinant PAI-1 on SMC VN expression were studied, and vascular VN expression in wild-type (WT) and PAI-1-deficient mice was assessed. Results VN expression was significantly lower in PAI-1-deficient SMCs and significantly increased in PAI-1-overexpressing SMCs. PAI-1 small interfering RNA and pharmacologic PAI-1 inhibition significantly decreased SMC VN expression. Recombinant PAI-1 stimulated VN expression by binding LDL receptor-related protein-1 (LRP1), but another LRP1 ligand, α2 -macroglobulin, did not. As compared with WT controls, carotid artery VN expression was significantly lower in PAI-1-deficient mice and significantly higher in PAI-1-transgenic mice. In a vein graft (VG) model of intimal hyperplasia, VN expression was significantly attenuated in PAI-1-deficient VGs as compared with WT controls. The plasma VN concentration was significantly decreased in PAI-1-deficient mice versus WT controls at 4 weeks, but not at 5 days or 8 weeks, after surgery. Conclusions PAI-1 stimulates SMC VN expression by binding LRP1, and controls vascular VN expression in vivo. Autocrine regulation of vascular VN expression by PAI-1 may play important roles in vascular homeostasis and pathologic vascular remodeling.

Coagulation and the vessel wall in pulmonary embolism

Venous thromboembolism comprises deep-vein thrombosis, thrombus in transit, acute pulmonary embolism, and chronic thromboembolic pulmonary hypertension (CTEPH). Pulmonary thromboemboli commonly resolve, with restoration of normal pulmonary hemodynamics. When they fail to resorb, permanent occlusion of the deep veins and/or CTEPH are the consequences. Apart from endogenous fibrinolysis, venous thrombi resolve by a process of mechanical fragmentation, through organization of the thromboembolus by invasion of endothelial cells, leukocytes, and fibroblasts leading to recanalization. Recent data utilizing various models have contributed to a better understanding of venous thrombosis and the resolution process that is directed at maintaining vascular patency. This review summarizes the plasmatic and cellular components of venous thrombus formation and resolution.

A Forkhead/winged helix-related transcription factor mediates insulin-increased plasminogen activator inhibitor-1 gene transcription

Plasminogen activator inhibitor-1 (PAI-1) is an important regulator of fibrinolysis by its inhibition of both tissue-type and urokinase plasminogen activators. PAI-1 levels are elevated in type II diabetes and this elevation correlates with macro- and microvascular complications of diabetes. Insulin increases PAI-1 production in several experimental systems, but the mechanism of insulin-activated PAI-1 transcription remains to be determined. Deletion analysis of the PAI-1 promoter revealed that the insulin response element is between -117 and -7. Mutation of the AT-rich site at -52/-45 abolished the insulin responsiveness of the PAI-1 promoter. This sequence is similar to the inhibitory sequence found in the phosphoenolpyruvate carboxylkinase/insulin-like growth factor-I-binding protein I promoters. Gel-mobility shift assays demonstrated that the forkhead bound to the PAI-1 promoter insulin response element. Expression of the DNA-binding domain of FKHR acted as a dominant negative to block insulin-increased PAI-1-CAT expression. A LexA-FKHR construct was also insulin responsive. These data suggested that a member of the Forkhead/winged helix family of transcription factors mediated the effect of insulin on PAI-1 transcription. Inhibition of phosphatidylinositol 3-kinase reduced the effect of insulin on PAI-1 gene expression, a result consistent with activation through FKHR. However, it was likely that a different member of the FKHR family (not FKHR) mediated this effect since FKHR was present in both insulin-responsive and non-responsive cell lines.

Remodeling of the vessel wall after copper-induced injury is highly attenuated in mice with a total deficiency of plasminogen activator inhibitor-1

Clinical studies have indicated that high plasma levels of fibrinogen, or decreased fibrinolytic potential, are conducive to an increased risk of cardiovascular disease. Other investigations have shown that insoluble fibrin promotes atherosclerotic lesion formation by affecting smooth muscle cell proliferation, collagen deposition, and cholesterol accumulation. To directly assess the physiological impact of an imbalanced fibrinolytic system on both early and late stages of this disease, mice deficient for plasminogen activator inhibitor-1 (PAI-1(-/-)) were used in a model of vascular injury/repair, and the resulting phenotype compared to that of wild-type (WT) mice. A copper-induced arterial injury was found to generate a lesion with characteristics similar to many of the clinical features of atherosclerosis. Fibrin deposition in the injured arterial wall at early (7 days) and late (21 days) times after copper cuff placement was prevalent in WT mice, but was greatly diminished in PAI-1(-/-) mice. A multilayered neointima with enhanced collagen deposition was evident at day 21 in WT mice. In contrast, only diffuse fibrin was identified in the adventitial compartments of arteries from PAI-1(-/-) mice, with no evidence of a neointima. Neovascularization was observed in the adventitia and was more extensive in WT arteries, relative to PAI-1(-/-) arteries. Additionally, enhanced PAI-1 expression and fat deposition were seen only in the arterial walls of WT mice. The results of this study emphasize the involvement of the fibrinolytic system in vascular repair processes after injury and indicate that alterations in the fibrinolytic balance in the vessel wall have a profound effect on the development and progression of vascular lesion formation.

Cellular and molecular mechanisms of inflammation and thrombosis

In the last 20 years, the cellular and molecular mechanisms of inflammation and thrombosis have been characterised. These are essentially cell adhesion processes which are regulated by vascular endothelium. Many of the cell adhesion molecules and leucocyte chemoattractants expressed and generated at sites of inflammation have been sequenced and cloned. These inflammatory molecules work together in concert to mediate the adhesion between leucocytes, platelets and vascular endothelium which occurs during the occlusive, thromboembolic, reperfusion and septic complications of atherosclerotic and diabetic vascular diseases. This review aims to summarise our current understanding of the molecular basis of these disorders and the therapeutic implications.

Coronary vessel perforation during balloon angioplasty: a case report

Coronary perforation can be managed with prolonged balloon inflations, covered stents, or embolization of the vessel. We report on a case of a balloon-induced perforation of the distal left anterior descending artery, that was sealed by injecting preclotted autologous blood through the balloon catheter lumen at the site of the perforation. The patency of the distal vessel was maintained.

Thrombosis, antithrombotic agents, and the antithrombotic approach in cardiac disease

To develop a rational approach to antithrombotic therapy, in cardiac disease, a sound understanding is required (1) of the hemostatic processes leading to thrombosis, (2) of the various antithrombotic agents, and (3) of the relative risks of thrombosis and thromboembolism in the various cardiac disease entities. With the understanding of pathogenesis and risk of thrombus formation, a rational approach to the use of antiplatelet and anticoagulant agents can be formulated. Those at high risk of thrombus formation should generally receive a high degree of antithrombotics and, depending on the pathophysiology of the thrombus, may benefit from the concomitant use of antiplatelet and anticoagulant agents. Those with a medium risk of thrombus formation may benefit with the use of an antiplatelet agent alone or anticoagulants alone. Patients at low risk of thrombus formation should not receive antithrombotics. Such rational approach to antithrombotic therapy serves as the basis of this article.

Insights in vessel development and vascular disorders using targeted inactivation and transfer of vascular endothelial growth factor, the tissue factor receptor, and the plasminogen system

VEGF has been proposed to participate in normal and pathological vessel formation. Surprisingly, lack of only a single VEGF allele resulted in embryonic lethality due to abnormal formation of intra- and extra-embryonic vessels. Homozygous VEGF-deficient embryos, generated by tetraploid aggregation, revealed an even more severe defect in vessel formation. These results (1) suggest a tight regulation of early vessel development by VEGF and, indirectly, the presence of other VEGF-like molecules; (2) reveal an unprecedented lethal phenotype associated with heterozygous deficiency of an autosomal gene, and (3) demonstrate that tetraploid aggregation was a valid and the only method to study the phenotype of the homozyogous VEGF-deficient embryos. The dominant and strict dose-dependent role of VEGF in vivo renders this molecule a desirable therapeutic target for promoting or preventing angiogenesis. Tissue factor (TF) is the principal cellular initiator of coagulation and its deregulated expression has been related to thrombogenesis in sepsis, cancer, and inflammation. However, TF appears to be also involved in a variety of non-hemostatic functions including inflammation, cancer, brain function, immune response, and tumor-associated angiogenesis. Surprisingly, TF deficiency resulted in embryonic lethality due to abnormal extra-embryonic vessel development and defective vitelloembryonic circulation. The abnormal yolk sac vasculature is reminiscent of that observed in embryos lacking VEGF, possibly suggesting that both gene functions are interconnected. These targeting studies extend the recently documented role of TF in tumor-associated angiogenesis and warrant further study of its role in angiogenesis during other pathological disorders. The plasminogen system, via its triggers, tissue-type plasminogen activator (t-PA) and urokinase-type plasminogen activator (u-PA) and its inhibitor, plasminogen activator inhibitor-1 (PAI-1), has been implicated in thrombosis, arterial neointima formation, and atherosclerosis. Studies in mice with targeted gene inactivation of t-PA, u-PA, PAI-1, the urokinase receptor (u-PAR), and plasminogen (Plg) revealed (1) that deficiency of t-PA or u-PA increase the susceptibility to thrombosis associated with inflammation and that combined deficiency of t-PA:u-PA or deficiency of Plg induces severe spontaneous thrombosis; (2) that vascular injury-induced neointima formation is reduced in mice lacking u-PA-mediated plasmin proteolysis, unaltered in t-PA- or u-PAR-deficient mice and accelerated in PAI-1-deficient mice, but that it can be reverted by adenoviral PAI-1 gene transfer; and (3) that atherosclerosis in mice doubly deficient in apolipoprotein E (apoE) and PAI-1 is reduced after 10 weeks of cholesterol-rich diet. Thus, the plasminogen system significantly affects thrombosis, restenosis, and atherosclerosis.

Impaired fibrinolysis early after percutaneous transluminal coronary angioplasty is associated with restenosis

This study examined the role of fibrinolytic components in the process of restenosis after percutaneous transluminal coronary angioplasty (PTCA). Seventy-two patients with single-vessel disease who underwent successful PTCA were prospectively selected. Tissue plasminogen activator (TPA), free plasminogen activator inhibitor-1 (free PAI-1), TPA/PAI-1 complex, and total PAI-1 antigen levels were measured before, at 1 week after, and at 3 months after PTCA. Six months after PTCA, the study patients were divided into two groups: 41 patients without restenosis and 31 patients with restenosis. There were no significant differences with regard to sex, age, coronary risk factors, or morphologic changes in the target lesions between the two groups. There were no significant differences in plasma TPA, TPA/PAI-1 complex, or total PAI-1 levels at each sampling period, or in the time courses between the two groups, except for total PAI-1 levels at 1 week after PTCA. Although no significant differences in free PAI-1 levels before PTCA were observed, free PAI-1 levels after PTCA in the patients with restenosis were significantly higher than those in the patients without restenosis. In addition, each group had a significant change in the time course of free PAI-1 levels. The results suggest that impaired fibrinolysis early after PTCA might affect the repair process of vascular injury, which leads to restenosis, and also that serial determination of free PAI-1 levels could help predict restenosis.

Mechanisms of physiological fibrinolysis

The fibrinolytic system comprises an inactive proenzyme, plasminogen, that is converted by plasminogen activators to the active enzyme, plasmin, which degrades fibrin. Two immunologically distinct plasminogen activators (PA) have been identified: tissue-type plasminogen activator (t-PA) and urokinase-type plasminogen activator (u-PA). t-PA mediated plasminogen activation is mainly involved in the dissolution of fibrin in the circulation, whereas u-PA mediated plasminogen activation mainly plays a role in pericellular proteolysis. Plasminogen activation is regulated by specific molecular interactions between its main components, such as binding of plasminogen and t-PA to fibrin, or to specific cellular receptors resulting in enhanced plasminogen activation, inhibition of t-PA and u-PA by plasminogen activator inhibitors (PAI) and inhibition of plasmin by alpha 2-antiplasmin. Controlled synthesis and release of PAs and PAIs primarily from endothelial cells also contributes to the regulation of physiological fibrinolysis. The lysine binding sites situated in the kringle structures of plasminogen play a crucial role in the regulation of fibrinolysis by modulating its binding to fibrin and to cell surfaces, and by controlling the inhibition rate of plasmin by alpha 2-antiplasmin.

Physiological consequences of over- or under-expression of fibrinolytic system components in transgenic mice

Studies with transgenic mice over- or under-expressing components of the fibrinolytic system, have revealed a significant role of this system in fibrin clot surveillance, reproduction, (vascular) wound healing, brain function, health and survival. The distinct phenotypes associated with single loss and the more severe phenotype associated with combined loss of plasminogen activator gene function suggest that through evolution, both plasminogen activators have evolved with specific but overlapping biological properties. Interestingly, the role of the fibrinolytic system in thrombosis and vascular wound healing became more apparent after challenging mice single deficiencies of plasminogen activators with an inflammatory, or traumatic challenge, respectively. It therefore seems warranted to examine possible consequences of loss of plasminogen activator gene function in other processes including atherosclerosis, neoangiogenesis, inflammatory lung and kidney disease and malignancy. The plasminogen activator knock-out mice with their thrombotic phenotypes are also valuable models to evaluate whether adenoviral mediated gene-transfer of wild-type or mutant plasminogen activator genes is able to restore normal thrombolytic function and to prevent thrombosis. Preliminary evidence suggests that impaired thrombolysis of t-PA deficient mice can be completely restored using adenoviral-mediated gene transfer of rt-PA (Carmeliet et al, 1994c). In addition, analysis of neointima formation in plasminogen activator deficient mice suggests that controlled reduction of fibrinolytic activity in the vessel wall might be beneficial for the prevention or reduction of restenosis. Whether this can be achieved with gene transfer methodologies remains to be defined.

Increased intramural expression of plasminogen activator inhibitor type 1 after balloon injury: a potential progenitor of restenosis

OBJECTIVES

This study was performed to determine whether altered gene expression of plasminogen activator inhibitor type 1 (PAI-1) occurs within the arterial wall after experimentally induced balloon injury.

BACKGROUND

PAI-1, known to inhibit fibrinolysis in the circulation and to be present within atherosclerotic vessels, may influence proteolysis in the arterial wall and neointimal formation after angioplasty.

METHODS

In rabbit carotid arteries subjected to balloon injury, both PAI-1 gene and protein expression were assayed sequentially with the use of Northern blotting, in situ hybridization and immunohistochemical studies.

RESULTS

In uninjured, normal vessels PAI-1 messenger ribonucleic acid (mRNA) was not detectable by Northern blotting or in situ hybridization. However, injury was followed within 3 h by increases in PAI-1 mRNA (3.2 kb) of 5.9-fold compared with that in contralateral control carotid arteries (Northern blots). PAI-1 mRNA was detectable by in situ hybridization early after injury first in adventitia; after 24 h it was particularly prominent in the media. From 1 to 4 weeks after injury it was consistently detectable and was localized in neointimal vascular smooth muscle and endothelial cells at a time when neointimal thickening was marked. Cells of both types exhibited PAI-1 protein detected immunohistochemically. In vessels maintained in organ culture after balloon injury in vivo, sustained increases in PAI-1 activity appeared in conditioned media as well.

CONCLUSIONS

Our results indicate that balloon injury simulating angioplasty in patients induces intramural expression of PAI-1 in vascular smooth muscle and endothelial cells. The decreased cell surface fibrinolytic activity likely to result from the increased PAI-1 expression may initiate or exacerbate mural thrombosis. Accordingly, excessive stimulation with clot-associated mitogens may stimulate vascular smooth muscle cell proliferation, which, coupled with increased accumulation of extracellular matrix attributable to decreased plasmin-mediated degradation, may contribute to restenosis.

In vivo kinetics of 99mTc labeled recombinant tissue plasminogen activator in rabbits

Our previous studies demonstrated that 99mTc labeled recombinant tissue plasminogen activator (rt-PA) retained high affinity with fibrin in vitro but showed unexpectedly low uptake in fresh thrombi in vivo. The present study was performed to determine the in vivo kinetics of radiolabeled t-PA in the rabbit. Sequential images and blood samples after the intravenous administration of 99mTc labeled rt-PA in thrombus-bearing rabbits were taken. The radioactivity and immunological level of t-PA and PAI-1 in the solution eluted to each fraction by gel permeation chromatography were measured by means of a well scintillation counter and enzyme-linked immunosorbent assay (ELISA). Most of the radioactivity was eluted in the fraction (Fr. 7) of larger molecular weight than that (Fr. 9) of intact t-PA. The level of intact rt-PA was increased with a regimen involving the preadministration of cold rt-PA which was followed by the administration of hot rt-PA. The level of PAI-1 in plasma showed an increased rebound 15 minutes after the intravenous injection. These results suggest two possible reasons why rt-PA retains high affinity with fibrin in vitro, once radiolabeled, but was ineffective in delineating fresh thrombi with a gamma camera: 1) some plasma components such as PAI-1 combine with circulating radiolabeled rt-PA and form a larger molecule immediately and/or 2) radiolabeled rt-PA is modulated as a consequence of the radiolabeling and forms a larger molecule than intact rt-PA.

Timing of surgery influences survival in receptor-negative as well as receptor-positive breast cancer

Analysis of oestrogen and progesterone receptor (ER, PR) status was interpreted in relation to menstrual phase at the time of surgery and survival in 84 women diagnosed with breast cancer between 1975 and 1988. We showed previously (Br J Surgery 1994, 81, 217-220) that long-term survival was significantly poorer when surgery was performed during the follicular phase of the menstrual cycle compared to luteal phase; we now demonstrate that this effect on survival is at least as important in receptor-negative as receptor-positive patients. At 10 years, overall survival (OS) of ER-positive patients who had their biopsy during the follicular phase was significantly poorer than for those whose biopsy was performed during the luteal phase of their menstrual cycle (52 versus 88%, P = 0.02). OS for the ER-negative follicular phase group was also significantly poorer than that for the ER-negative luteal phase group (33 versus 76%, P = 0.009). The OS difference between the PR-positive follicular phase group and PR-positive luteal phase group was of borderline significance (60 versus 87%, P = 0.06), while the difference in OS between the PR-negative follicular phase group and that of the PR-negative luteal phase group was highly significant (13 versus 76%, P = 0.001). Disease-free survival for these groups followed a similar trend. The survival differences in receptor-negative women suggest that hormonal fluctuations at the time of surgery may have complex indirect effects on tumour growth and metastasis. The mechanism, if indeed independent of the tumour steroid receptors, could also apply in other cancers.