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Objective: Plasminogen activator inhibitor-1 (PAI-1) has previously been shown to be key to the formation of myoendothelial junctions (MEJs) in normal and pathological states (eg, obesity). We therefore sought to identify the mechanism whereby PAI-1 could be selectively accumulated at the MEJ., Methods and Results: We identified PAI-1 protein enrichment at the MEJ in obese mice and in response to tumor necrosis factor (TNF-α) with a vascular cell coculture. However, PAI-1 mRNA was also found at the MEJ and transfection with a PAI-1-GFP with TNF-α did not demonstrate trafficking of the protein to the MEJ. We therefore hypothesized the PAI-1 mRNA was being locally translated and identified serpine binding protein-1, which stabilizes PAI-1 mRNA, as being enriched in obese mice and after treatment with TNF-α, whereas Staufen, which degrades PAI-1 mRNA, was absent in obese mice and after TNF-α application. We identified nicotinamide phosphoribosyl transferase as a serpine binding protein-1 binding partner with a functional τ-like microtubule binding domain. Application of peptides against the microtubule binding domain significantly decreased the number of MEJs and the amount of PAI-1 at the MEJ., Conclusions: We conclude that PAI-1 can be locally translated at the MEJ as a result of a unique mRNA binding protein complex.

Plasminogen activator inhibitor-1 (PAI-1) plays a pivotal role in the regulation of the fibrinolytic system and in the modulation of extracellular proteolysis. Increased PAI-1 was found in atherosclerotic lesions, and high PAI-1 plasma levels were associated with coronary heart disease. Smooth muscle cells (SMC) are a major source of PAI-1 within the vascular wall, and PAI-1 was implicated in SMC migration, proliferation, and apoptosis. We treated human coronary artery SMC (HCASMC) and human aortic SMC (HASMC) with the glycoprotein 130 (gp130) ligands cardiotrophin-1, interleukin-6 (IL-6), leukemia inhibitory factor (LIF), or oncostatin M (OSM). Only OSM increased PAI-1 antigen and activity production significantly in these cells up to 20-fold. OSM upregulated mRNA specific for PAI-1 up to 4.5-fold in these cells. HCASMC and HASMC express gp130, OSM receptor, IL-6 receptor, and LIF receptor. OSM induced extracellular signal-regulated kinase (ERK) 1/2 and Akt phosphorylations in HASMC. A phosphatidylinositol 3-kinase inhibitor and a mitogen-activated protein/extracellular signal-regulated kinase inhibitor reduced Akt and ERK1/2 phosphorylation, respectively, and abolished OSM-induced PAI-1 upregulation. A janus kinase/signal transducer and activator of transcription inhibitor, a p38 mitogen-activated protein kinase inhibitor, or c-Jun NH(2)-terminal kinase inhibitor I did not inhibit the OSM-dependent PAI-1 induction. OSM enhanced proliferation of both HCASMC and HASMC by 77 and 90%, respectively. We hypothesize that, if the effect of OSM on PAI-1 expression in smooth muscle cells is operative in vivo, it could, via modulation of fibrinolysis and extracellular proteolysis, be involved in the development of vascular pathologies such as plaque progression, destabilization and subsequent thrombus formation, and restenosis and neointima formation.

Background: Atherosclerosis is considered to be a chronic inflammatory disorder. Activation of the complement cascade is a major aspect of chronic inflammatory diseases. Complement components were identified in atherosclerotic plaques, and a correlation between adverse events and C5a plasma levels was found. These findings support the notion that complement activation contributes to development and progression of atherosclerotic lesions., Objectives: We investigated whether complement components C3a and C5a regulate plasminogen activator inhibitor (PAI-1) in human macrophages., Methods: Human monocyte-derived macrophages (MDM) and human plaque macrophages were cultured and incubated with the complement component C5a., Results: C5a increased PAI-1 up to 11-fold in human MDM and up to 2.7-fold in human plaque macrophages. These results were confirmed at the mRNA level using real time-polymerase chain reaction. Pertussis toxin or anti-C5aR/CD88 antibody completely abolished the effect of recombinant human C5a on PAI-1 production, suggesting a role of the C5a receptor. Experiments with antitumor necrosis factor (TNF)-alpha antibodies and tiron showed that the effect of C5a was not mediated by TNF-alpha or oxidative burst. Furthermore C5a induced NF-kappaB binding to the cis element in human macrophages and the C5a-induced increase in PAI-1 was completely abolished by an NF-kappaB inhibitor., Conclusions: We conclude that C5a upregulates PAI-1 in macrophages via NF-kappaB activation. We hypothesize that - if operative in vivo- this effect could favor thrombus development and thrombus stabilization in the lesion area. On the other hand one could speculate that C5a-induced upregulation of PAI-1 in plaque macrophages could act as a defense mechanism against plaque destabilization and rupture.

Background: Adipose tissue is a prominent source of plasminogen activator inhibitor-1 (PAI-1), the primary physiological inhibitor of plasminogen activation. Increased PAI-1 expression acts as a cardiovascular risk factor, and plasma levels of PAI-1 strongly correlate with body mass index (BMI). Elevated serum levels of interleukin-6 (IL-6), an inflammatory cytokine and a member of the glycoprotein 130 (gp130) ligand family, are found in obese patients and might indicate low-grade systemic inflammation. Another gp130 ligand, oncostatin M (OSM), upregulates PAI-1 in cardiac myocytes, astrocytes, and endothelial cells. We used tissue explants and primary cultures of preadipocytes and adipocytes from human subcutaneous and visceral adipose tissue to investigate whether IL-6 and OSM affect PAI-1 expression in fat., Methods and Results: Human subcutaneous and visceral adipose tissue responded to treatment with IL-6 and OSM with a significant increase in PAI-1 production. Human preadipocytes were isolated from subcutaneous and visceral adipose tissue. Adipocyte differentiation was induced by hormone supplementation. All cell types expressed receptors for IL-6 and OSM and produced up to 12-fold increased levels of PAI-1 protein and up to 9-fold increased levels of PAI-1 mRNA on stimulation with IL-6 and OSM. AG-490, a janus kinase/signal transducer and activator of transcription inhibitor, abolished the OSM-dependent PAI-1 induction almost completely., Conclusions: We have for the first time established a link between the gp130 ligands, the proinflammatory mediators IL-6 and OSM, and the expression of PAI-1 in human adipose tissue. Thus, we speculate that IL-6 and OSM, by upregulating PAI-1 in adipose tissue, can contribute to the increased cardiovascular risk of obese patients.

Accumulating evidence points towards a role for proteases and protease inhibitors in tissue remodelling and repair in a variety of organs. In particular-besides the matrix metalloprotease system-the plasminogen activator (PA)/plasmin system has been implicated in these processes in the heart. Urokinase type PA (u-PA) and PA inhibitor type 1 (PAI-1) seem to modulate cardiac rupture and infarct healing. In this study we aimed to investigate whether inflammatory mediators can regulate the expression of components of the PA/plasmin system in human adult cardiac myocytes (HACM). We could demonstrate that HACM, isolated from pieces of myocardial tissue by mechanical dispersion and characterized by positive immunostaining for the cardiac markers troponin I, tropomyosin, cardiotin and myocardial muscle-actin, in vitro express PAI-1 and tissue type PA (t-PA) whereas u-PA was not detectable in these cells. PAI-1 protein production was increased up to twofold by interleukin-1alpha (IL-1alpha) and tumor necrosis factor-alpha (TNF-alpha) and up to fivefold by transforming growth factor-beta (TGF-beta) and oncostatin M (OSM). Similar changes were observed in PAI-1 transcript levels after cytokine treatment. t-PA production in HACM was not affected by these agonists. No effect of these cytokines on PAI-1 production in fibroblasts isolated from human myocardial tissue was seen. In an ex vivo model we could show that incubation of pieces of human myocardial tissue with these cytokines also resulted in an increase in PAI-1 in cardiac myocytes as evidenced by immuno-histochemistry. Furthermore we found increased PAI-1 expression in myocardial tissue from a patient suffering from acute myocarditis. Thus for the first time we provide evidence that inflammatory mediators modulate PAI-1 expression in human adult cardiac myocytes in vitro and ex vivo and could demonstrate that PAI-1 expression is increased in the in vivo setting under inflammatory conditions. If the effect on PAI-1 expression brought about by IL-1alpha, TNF-alpha, TGF-beta and OSM is not only operative under in vitro and ex vivo conditions but also in the in vivo setting one could speculate that these cytokines contribute to upregulation of PAI-1 in myocardial tissue and that PAI-1, when upregulated in myocardial tissue during inflammatory processes, could serve as a defence mechanism against excessive matrix degradation by proteases. Thus we propose a role for PAI-1 produced in the heart by cardiac myocytes in cardiac remodelling and repair processes.

We have recently shown that resting human mast cells (MCs) produce tissue-type plasminogen activator (t-PA) without simultaneously expressing plasminogen activator inhibitor 1 (PAI-1). In the present study we have identified the anaphylatoxin rhC5a as a potent inducer of PAI-1 expression in human MCs and basophils. In primary human skin MCs and primary blood basophils, exposure to rhC5a was followed by an increase from undetectable to significant levels of PAI-1. In addition, rhC5a induced a concentration- and time-dependent increase in PAI-1 antigen in the MC line HMC-1 and the basophil cell line KU-812 and increased the expression of PAI-1 mRNA in HMC-1. In conditioned media of HMC-1 treated with rhC5a, active PAI-1 could be detected. A simultaneous loss of t-PA activity in conditioned media from the same cells indicated that rhC5a-induced PAI-1 was capable of inhibiting the enzymatic activity of coproduced t-PA. Correspondingly, the levels of t-PA-PAI-1 complexes increased in rhC5a-treated cells. When HMC-1 cells were incubated with pertussis toxin or anti-C5a receptor antibodies, the effect of rhC5a on PAI-1 production was completely abolished. Treatment of C5a with plasmin resulted in loss of its ability to induce PAI-1 production in MCs. Considering the suggested role for MCs and components of the complement system in the development of cardiovascular diseases, we hypothesize that MCs, by producing t-PA in a resting state and by expressing PAI-1 when activated by C5a, might participate in the modulation of the balance between proteases and protease inhibitors regulating tissue injury and repair in such disease processes.

In this study we aimed to investigate whether the therapeutic efficacy of anisodamine in the treatment of bacteraemic shock could--at least in part--be brought about by its direct interference with the lipopolysaccharide (LPS)-induced activation of endothelial cells. Thus, we investigated the effect of anisodamine on LPS-induced expression of plasminogen activator inhibitor-1 (PAI-1) and tissue factor (TF), two major markers of endothelial activation. PAI-1 was measured in the conditioned media of human umbilical vein endothelial cells (HUVEC) by a specific enzyme-linked immunosorbent assay (ELISA) whereas TF activity was measured in the lysates of these cells by using a single step clotting assay. Results obtained in these assays were confirmed on the level of specific mRNA expression by Northern blotting using specific probes for human PAI-1 or TF. In order to evaluate a possible contribution of the NF-kappa B pathway on the effects observed, electrophoretic mobility shift assays (EMSA) were performed using nuclear extracts from HUVEC and NF-kappa B-binding oligonucleotides. When HUVEC were treated with 1 microg/ml LPS a significant increase in PAI-1 and TF activity was observed compared with cells incubated without LPS. Anisodamine dose-dependently inhibited this LPS-induced upregulation of PAI-1 and TF. Anisodamine alone had no effect on the constitutive expression of PAI-1 and TF in these cells. These effects were also confirmed on the level of specific PAI-1 and TF mRNA expression by Northern blotting. Furthermore, we could show by EMSA that anisodamine completely abolished LPS-induced NF-kappa B DNA binding activity in nuclear extracts from HUVEC treated with LPS together with anisodamine. Thus, we provide evidence that anisodamine counteracts endothelial cell activation by inhibiting LPS-induced PAI-1 and TF expression in these cells. Its interference with the NF-kappa B pathway might - at least in part - contribute to this effect. The ability of anisodamine to counteract LPS effects on endothelial cells might be one underlying mechanism explaining its efficacy in the treatment of bacteraemic shock., (Copyright 2001 S. Karger AG, Basel)

The pleiotropic growth factor hepatocyte growth factor/scatter factor (HGF/SF) has been implicated by clinical and experimental studies in repair mechanisms in different organs and tissues. However, no data on the impact of HGF/SF in wound healing in the skin are yet available. Proliferating and migrating keratinocytes play a major role in repair processes in the skin by closing the wound. Recent evidence gathered from studies that used gene-deficient mice has implicated the plasminogen activator (PA)/plasmin system in wound healing, which depends on controlled matrix degradation and deposition during cell migration and proliferation. Furthermore, keratinocytes are an important source of vascular endothelial growth factor (VEGF), which is a potent inducer of angiogenesis. In this study, we show that in human keratinocytes HGF/SF but not the related cytokine macrophage stimulating protein (MSP) significantly increases expression of VEGF and plasminogen activator inhibitor-1 (PAI-1) on the level of protein and mRNA. Furthermore, we demonstrate that HGF/SF increases the expression of the VEGF receptor flk-1 in human endothelial cells and that, in an angiogenesis co-culture assay of endothelial cells and keratinocytes, HGF/SF increases endothelial cell tube formation significantly. Therefore, we propose a role for HGF/SF in wound repair in the skin: HGF/SF--produced by activated fibroblasts--increases in keratinocytes the expression of PAI-1, which leads to increased matrix stability during the repair process and which could also limit activation of HGF/SF by proteases such as urokinase-type PA (u-PA) or tissue-type PA (t-PA). Furthermore HGF/SF also increases the expression of VEGF in these cells, thereby initiating angiogenesis in a paracrine manner. This effect would be enhanced by an increased responsiveness of endothelial cells toward VEGF, resulting from the HGF/SF-induced up-regulation of flk-1 on these cells.

Increased expression of plasminogen activator inhibitor-1 (PAI-1) mRNA in atherosclerotic human arteries suggests a linkage between PAI-1 gene expression and cellular proliferation, the fundamental feature of atherosclerosis. To investigate whether smooth muscle cell (SMC) proliferation influences overall fibrinolytic properties of the vascular wall, we examined the effect of serial in vitro passaging of human SMCs on tissue plasminogen activator (TPA) and PAI-1 synthesis levels as well as the ability to modulate TPA and PAI-1 synthesis of human umbilical vein endothelial cells (HUVECs). As in vivo correlates for such late-passage cells in culture, SMCs derived from human atherosclerotic plaques were used, because they are thought to have already undergone numerous cell doublings. We observed an increase of PAI-1 secretion (from 591 +/- 106 to 2952 +/- 290 ng PAI-1.10(5) cells-1.24 h-1) with a concomitant fourfold to fivefold increase of PAI-1 mRNA levels, as well as a decrease of TPA secretion (from 118 +/- 34 to 8 +/- 1.3 ng TPA.10(5) cells-1.24 h-1) and a twofold to threefold decrease of TPA mRNA levels with increasing in vitro passage number (from passage 3 to 11) of normal pulmonary artery smooth muscle cells (PASMCs) (P < .05). SMCs derived from atherosclerotic plaques of coronary arteries (CASMCs) displayed higher levels of PAI-1 antigen synthesis (3093 +/- 507 ng PAI-1.10(5) cells-1.24 h-1) with an approximately twofold increase of PAI-1 mRNA levels, as well as decreased levels of TPA antigen synthesis (10 +/- 1.6 ng TPA.10(5) cells-1.24 h-1) with an approximately 1.5- to 2-fold decrease of TPA mRNA levels in passage 1, compared with their counterparts derived from normal-appearing arterial tissue of the same vessel (1794 +/- 525 ng PAI-1.10(5) cells-1.24 h-1; 17 +/- 5 ng TPA.10(5) cells-1.24 h-1) (P < .001; P < .01). Incubation of HUVEC cultures with the 24-hour conditioned media (CM) of early-passage PASMCs decreased endothelial PAI-1 antigen synthesis by approximately 42% (P < .001) and endothelial PAI-1 mRNA levels about twofold to threefold (P < .001), whereas by incubation with the 24-hour CM of late-passage PASMCs, endothelial PAI-1 antigen synthesis was upregulated by 68% (P = .001), with a concomitant twofold increase of endothelial PAI-1 mRNA levels (P < .001). The apparent MW of this heat- and acid-stable PAI-1 upregulating factor appears to be between 50 and 100 kD, as judged by ultrafiltration. Incubation of HUVEC cultures with the 24-hour CM of early-passage CASMCs derived from normal-appearing arterial tissue showed no significant influence on endothelial PAI-1 synthesis, whereas incubation with late-passage normal CASMCs, as well as early-passage atherosclerotic CASMCs from the same vessel, increased endothelial PAI-1 antigen secretion by 45% and 48% (P < .001), with a concomitant 1.5 fold to 2-fold increase of endothelial PAI-1 mRNA levels (P < .05). No significant change in endothelial TPA synthesis was observed by incubation with CM of either PASMCs (early or late passage) or CASMCs (atherosclerotic or normal). These data suggest that SMC proliferation is associated with (1) increased SMC PAI-1 synthesis as well as decreased TPA synthesis and (2) upregulation of endothelial PAI-1 synthesis by SMC CM. This phenomenon is observed with either late passages of normal PASMCs and CASMCs or early passages of atherosclerotic plaque CASMCs. This suggests that proliferating SMCs are a major regulator of the fibrinolytic potential within the vessel wall, thereby contributing to the thrombotic risk associated with the development of atherosclerosis.