Quantification of plasminogen activators and their inhibitors in the aortic vessel wall in relation to the presence and severity of atherosclerotic disease

The Paradigm Change of IL-33 in Vascular Biology

In this review, we focus on the actual understanding of the role of IL-33 in vascular biology in the context of the historical development since the description of IL-33 as a member of IL-1 superfamily and the ligand for ST2 receptor in 2005. We summarize recent data on the biology, structure and signaling of this dual-function factor with both nuclear and extracellular cytokine properties. We describe cellular sources of IL-33, particularly within vascular wall, changes in its expression in different cardio-vascular conditions and mechanisms of IL-33 release. Additionally, we summarize the regulators of IL-33 expression as well as the effects of IL-33 itself in cells of the vasculature and in monocytes/macrophages in vitro combined with the consequences of IL-33 modulation in models of vascular diseases in vivo. Described in murine atherosclerosis models as well as in macrophages as an atheroprotective cytokine, extracellular IL-33 induces proinflammatory, prothrombotic and proangiogenic activation of human endothelial cells, which are processes known to be involved in the development and progression of atherosclerosis. We, therefore, discuss that IL-33 can possess both protective and harmful effects in experimental models of vascular pathologies depending on experimental conditions, type and dose of administration or method of modulation.

Attenuation of Neointimal Vascular Smooth Muscle Cellularity in Atheroma by Plasminogen Activator Inhibitor Type 1 (PAI-1)

Rupture of vulnerable atheroma often underlies acute coronary syndromes. Vulnerable plaques exhibit a paucity of vascular smooth muscle cells (VSMCs) in the cap. Therefore, decreased VSMC migration into the neointima may predispose to vulnerability. The balance between cell surface plasminogen activator activity and its inhibition [mediated primarily by plasminogen activator inhibitor type 1 (PAI-1)] modulates migration of diverse types of cells. We sought to determine whether increased expression of PAI-1 would decrease migration of VSMCs in vitro and neointimal cellularity in vivo in apolipo-protein E knockout (ApoE−-/–) mice fed a high-fat diet. Increased vessel wall expression of PAI-1 in transgenic mice was induced with the SM22α promoter. VSMC migration through Matrigel in vitro was quantified with laser scanning cytometry. Expression of PAI-1 was increased threefold in the aortic wall of SM22-PAI transgene-positive mice. Neointimal cellularity of vascular lesions was decreased by 26% ( p=0.01; n=5 each) in ApoE−-/– mice with the SM22-PAI transgene compared with ApoE−-/– mice. VSMCs explanted from transgene-positive mice exhibited twofold greater expression of PAI-1 and their migration was attenuated by 27% ( p=0.03). Accordingly, increased expression of PAI-1 protein by VSMCs reduces their migration in vitro and their contribution to neointimal cellularity in vivo.

What causes intracerebral bleeding after thrombolysis for acute ischaemic stroke? Recent insights into mechanisms and potential biomarkers

The overall population benefit of intravascular recombinant tissue plasminogen activator (rtPA) on functional outcome in ischaemic stroke is clear, but there are some treated patients who are harmed by early symptomatic intracranial haemorrhage (ICH). Although several clinical and radiological factors increase the risk of rtPA-related ICH, none of the currently available risk prediction tools are yet useful for practical clinical decision-making, probably reflecting our limited understanding of the underlying mechanisms. Finding new methods to identify patients at highest risk of rtPA-related ICH, or new measures to limit risk, are urgent challenges in acute stroke therapy research. In this article, we focus on the potential underlying mechanisms of rtPA-related ICH, highlight promising candidate risk biomarkers and suggest future research directions.

Interleukin-33 induces urokinase in human endothelial cells--possible impact on angiogenesis

BACKGROUND

Urokinase-type plasminogen activator (u-PA) plays a pivotal role in extracellular proteolysis and is thought to be critically involved in the modulation of angiogenesis. Interleukin (IL)-33 is a member of the IL-1 cytokine family, which is thought to act as danger signal that is released from cells after injury. IL-33 is involved in the pathogenesis of various inflammatory diseases and previously was shown to induce angiogenesis and inflammatory activation of endothelial cells.

OBJECTIVE

We investigated the impact of IL-33 on u-PA in endothelial cells as a new possible function for IL-33.

METHODS AND RESULTS

We could demonstrate that IL-33 upregulated u-PA mRNA expression and protein production in human coronary artery and human umbilical vein endothelial cells in a time- and concentration-dependent manner via interaction with its receptor ST2 and activation of the nuclear factor-κB pathway but independent of autocrine IL-1-induced effects. The hydroxymethylglutaryl-coenzyme A reductase inhibitor simvastatin abrogated the IL-33-induced increase in u-PA, thus providing further evidence for pleiotropic effects of statins. IL-33 induced u-PA-dependent capillary-like tube formation and vessel sprouting. In human carotid atherosclerotic plaques (n = 16), u-PA mRNA positively correlated with IL-33 mRNA expression (r = 0.780, P < 0.001). Furthermore, IL-33 and u-PA protein were detected in endothelial cells in these samples using fluorescence immunohistochemistry.

CONCLUSIONS

We hypothesize that IL-33, representing a danger signal that is released after tissue damage, in addition to its role in the inflammatory activation of endothelial cells, is involved in u-PA-driven angiogenesis, a process that has been shown before to be linked to inflammation in various pathologies.

UPA promotes lipid-loaded vascular smooth muscle cell migration through LRP-1

AIM

Migration of vascular smooth muscle cells (VSMCs) is a crucial event in atherosclerosis and vascular repair. Low-density lipoprotein (LDL) infiltrated in the vessel wall become aggregated (agLDL) and internalized by VSMC through the LDL receptor-related protein LRP1, deriving in lipid-loaded cells with reduced motility capacity. The urokinase-plasminogen activator (UPA)/UPA receptor (UPAR) system plays a relevant role in vascular remodelling. Here, we investigated whether UPA-ligand binding is involved in the detrimental effects of lipid loading in VSMC migration.

METHODS AND RESULTS

Animals fed a high-fat diet had 10-fold higher cholesterol-LDL plasma levels, >60% decrease in aortic UPA-protein expression, and VSMC showed impaired outgrowth from aortic explants. Angiotensin II infusion significantly increased aortic UPA expression and accelerated VSMC migration. Using an in vitro model of wound repair, we showed that agLDL inhibits UPA-mediated VSMC migration. UPA silencing reduced migration in control cells to levels observed in lipid-loaded VSMC. UPA silencing did not affect migration in lipid-loaded VSMC. UPA expression was significantly decreased in agLDL-exposed VSMC. agLDL also induced changes in the subcellular localization of UPA, with a reduction in colocalization with UPAR strongly evident at the front edge of agLDL-treated migrating cells. Rescue experiments showed that UPA acting as UPAR ligand restored migration capacity of agLDL-VSMC to control levels. The effects of UPA/UPAR on migration of lipid-loaded cells occurred through the binding to LRP-1.

CONCLUSION

UPA-ligand binding regulates VSMC migration, a process that is interfered by LDL. Thus, tissue infiltrated LDL through the abrogation of UPA function reduces VSMC-regulated vascular repair.

The Renin-Angiotensin and fibrinolytic systems co-conspirators in the pathogenesis of ischemic cardiovascular disease

In vitro and in vivo data provide evidence for an interaction between the renin-angiotensin and fibrinolytic systems. Angiotensin-converting enzyme (ACE) is strategically poised to regulate this interaction. ACE catalyzes the conversion of angiotensin I to angiotensin II (Ang), and Ang II stimulates release of PAI-1, the major inhibitor of tissue-type plasminogen activator (t-PA) and urokinase in the vasculature. Conversely, ACE catalyzes the breakdown of bradykinin, a potent stimulus of t-PA secretion. This interaction between the renin-angiotensin and fibrinolytic systems may partially explain the clinical observation that stimulation or suppression of the renin-angiotensin system can alter the risk of ischemic cardiovascular events. © 1996, Elsevier Science Inc. (Trends Cardiovasc Med 1996;6:239-243).

Aggregated low-density lipoprotein induce impairment of the cytoskeleton dynamics through urokinase-type plasminogen activator/urokinase-type plasminogen activator receptor in human vascular smooth muscle cell

BACKGROUND

Urokinase-type plasminogen activator (UPA) regulates vascular smooth muscle cell (VSMC) functions relevant in vascular remodeling by facilitating proteolysis at the cell surface and inducing cell signaling pathways. Our previous results demonstrated that aggregated low-density lipoprotein (agLDL) impair cytoskeleton dynamics, a key event contributing to VSMC behavior during progression of atherosclerotic plaques.

OBJECTIVES

To investigate whether mechanisms underlying inhibition of cytoskeleton dynamics in lipid-loaded VSMC occurs through a UPA-mediated process.

METHODS

Adhesion assay was performed in lipid-loaded human VSMC after 16-h exposition to agLDL (100 μg mL(-1)). Protein subcellular localization and actin-fiber formation were assessed by confocal microscopy. For analysis of protein expression western blots were carried out. Co-immunoprecipitates of UPAR were examined by one-dimensional- or two-dimensional electrophoresis (1-DE or 2-DE), mass spectrometry MALDI-TOF and western blot.

RESULTS

agLDL induced UPA subcellular delocalization and significantly decreased UPA levels during attachment of VSMC. UPA (enhanced endogenous-expression or exogenous added) acting as a urokinase-type plasminogen activator receptor (UPAR)-ligand restored actin-cytoskeleton organization and adhesion capacity of lipid-loaded cells to control levels. UPAR co-immunoprecipitated with the unphosphorylated form of myosin regulatory light chain (MRLC) in lipid-loaded cells. The detrimental effects of agLDL on MRLC phosphorylation were reversed by high levels of UPA. The UPA effects on VSMC exposed to agLDL involved FAK phosphorylation.

CONCLUSIONS

The detrimental effects of atherogenic LDL on VSMC are mediated by a decrease and delocalization of the UPA-UPAR interaction that result in an impairment of cytoskeleton dynamics and adhesion capacity affecting cell phenotype and function.

Fibulin-5 binds urokinase-type plasminogen activator and mediates urokinase-stimulated β1-integrin-dependent cell migration

uPA (urokinase-type plasminogen activator) stimulates cell migration through multiple pathways, including formation of plasmin and extracellular metalloproteinases, and binding to the uPAR (uPA receptor; also known as CD87), integrins and LRP1 (low-density lipoprotein receptor-related protein 1) which activate intracellular signalling pathways. In the present paper we report that uPA-mediated cell migration requires an interaction with fibulin-5. uPA stimulates migration of wild-type MEFs (mouse embryonic fibroblasts) (Fbln5+/+ MEFs), but has no effect on fibulin-5-deficient (Fbln5-/-) MEFs. Migration of MEFs in response to uPA requires an interaction of fibulin-5 with integrins, as MEFs expressing a mutant fibulin-5 incapable of binding integrins (Fbln(RGE/RGE) MEFs) do not migrate in response to uPA. Moreover, a blocking anti-(human β1-integrin) antibody inhibited the migration of PASMCs (pulmonary arterial smooth muscle cells) in response to uPA. Binding of uPA to fibulin-5 generates plasmin, which excises the integrin-binding N-terminal cbEGF (Ca2+-binding epidermal growth factor)-like domain, leading to loss of β1-integrin binding. We suggest that uPA promotes cell migration by binding to fibulin-5, initiating its cleavage by plasmin, which leads to its dissociation from β1-integrin and thereby unblocks the capacity of integrin to facilitate cell motility.

The urokinase system in the pathogenesis of atherosclerosis

Atherogenesis refers to the development of atheromatous plaques in the inner lining of the arteries. These atherosclerotic lesions are characterized by accumulation of monocyte-derived macrophage-foam cells loaded with cholesterol, which eventually undergo apoptotic death, leading finally to formation of the necrotic core of the plaque. Atheroma formation also involves the recruitment of smooth muscle cells (SMC) from the media into the intima, where they proliferate and form the neointima in a process called "remodeling". Cells in the advanced atherosclerotic plaques express high levels of the serine protease urokinase-type plasminogen activator (uPA) and its receptor (uPAR). uPA is a multi-functional multi-domain protein that is not only a regulator of fibrinolysis, but it is also associated with several acute and chronic pathologic conditions. uPA mediate the extracellular matrix (ECM) degradation, and plays a pivotal role in cell adhesion, migration and proliferation, during tissue remodeling. On cell surface uPA binds to the high affinity urokinase receptor, providing a strictly localized proteolysis of ECM proteins. The uPA/uPAR complex also activates intracellular signaling, thus regulating cellular function. An imbalance in the uPA/uPAR system leads to dis-orders in tissue structure and function. This review summarizes recent progress in understanding the role and mechanisms of the uPA/uPAR system in atherogenesis.

Mechanisms of urokinase plasminogen activator (uPA)-mediated atherosclerosis: role of the uPA receptor and S100A8/A9 proteins

Data from clinical studies, cell culture, and animal models implicate the urokinase plasminogen activator (uPA)/uPA receptor (uPAR)/plasminogen system in the development of atherosclerosis and aneurysms. However, the mechanisms through which uPA/uPAR/plasminogen stimulate these diseases are not yet defined. We used genetically modified, atherosclerosis-prone mice, including mice with macrophage-specific uPA overexpression and mice genetically deficient in uPAR to elucidate mechanisms of uPA/uPAR/plasminogen-accelerated atherosclerosis and aneurysm formation. We found that macrophage-specific uPA overexpression accelerates atherosclerosis and causes aortic root dilation in fat-fed Ldlr(-/-) mice (as we previously reported in Apoe(-/-) mice). Macrophage-expressed uPA accelerates atherosclerosis by stimulation of lesion progression rather than initiation and causes disproportionate lipid accumulation in early lesions. uPA-accelerated atherosclerosis and aortic dilation are largely, if not completely, independent of uPAR. In the absence of uPA overexpression, however, uPAR contributes modestly to both atherosclerosis and aortic dilation. Microarray studies identified S100A8 and S100A9 mRNA as the most highly up-regulated transcripts in uPA-overexpressing macrophages; up-regulation of S100A9 protein in uPA-overexpressing macrophages was confirmed by Western blotting. S100A8/A9, which are atherogenic in mice and are expressed in human atherosclerotic plaques, are also up-regulated in the aortae of mice with uPA-overexpressing macrophages, and macrophage S100A9 mRNA is up-regulated by exposure of wild-type macrophages to medium from uPA-overexpressing macrophages. Macrophage microarray data suggest significant effects of uPA overexpression on cell migration and cell-matrix interactions. Our results confirm in a second animal model that macrophage-expressed uPA stimulates atherosclerosis and aortic dilation. They also reveal uPAR independence of these actions and implicate specific pathways in uPA/Plg-accelerated atherosclerosis and aneurysmal disease.

Association of putative functional variants in the PLAU gene and the PLAUR gene with myocardial infarction

uPA (urokinase-plasminogen activator) and its receptor (uPAR) have been implicated in a broad spectrum of pathophysiological processes, including fibrinolysis, proteolysis, inflammation, atherogenesis and plaque destabilization, all of which are involved in the pathogenesis of MI (myocardial infarction). We hypothesized that putative functional genetic variation in the two genes encoding uPA and uPAR (PLAU and PLAUR respectively) might influence the susceptibility to MI. We genotyped rs4065 [3'-UTR (untranslated region) *141C>T) and rs2227564 (Pro141Leu) in the PLAU gene as well as rs344781 (-516T>C) in the PLAUR gene in 633 MI patients and 1237 gender- and age-matched control subjects. Our results showed that the T allele of rs4065 was significantly associated with an increased risk of MI, with an adjusted OR (odds ratio) of 1.38 [95% CI (confidence interval), 1.07-1.78; P=0.012) under the dominant model, 1.4 (95% CI, 1.12-1.75; P=0.003) under the additive model and 2.5 (95% CI, 1.15-5.41; P=0.02) under the recessive model. The findings were then replicated in another independent case-control study including 545 MI patients and 597 control subjects. In conclusion, our results suggest that rs4065 might be a previously unknown genetic risk factor for MI in the Chinese Han population.

Constriction of carotid arteries by urokinase-type plasminogen activator requires catalytic activity and is independent of NH(2)-terminal domains

Urokinase-type plasminogen activator (uPA) is expressed at increased levels in stenotic, atherosclerotic human arteries. However, the biological roles of uPA in the artery wall are poorly understood. Previous studies associate uPA with both acute vasoconstriction and chronic vascular remodeling and attribute uPA-mediated vasoconstriction to the kringle - not the catalytic - domain of uPA. We used an in-vivo uPA overexpression model to test the hypothesis that uPA-induced vasoconstriction is a reversible vasomotor process that can be prevented - and uPA fibrinolytic activity preserved - by: 1) removing the growth factor and kringle domains; or 2) anchoring uPA to the endothelial surface. To test this hypothesis we constructed adenoviral vectors that express: wild-type rabbit uPA (AduPA); a uPA mutant lacking the NH(2)-terminal growth-factor and kringle domains (AduPAdel); a mutant lacking catalytic activity (AduPAS-->A), and a cell-surface anchored mutant (AdTMuPA). uPA mutants were expressed and characterised in vitro and in carotid arteries in vivo. uPAS-->A had no plasminogen activator activity. Activity was similar for uPA and uPAdel, whereas AdTMuPA had only cell-associated activity. AduPAS-->A arteries were not constricted. AduPA, AduPAdel, and AdTM-uPA arteries were constricted (approximately 30% smaller lumens; p< or =0.008 vs. AdNull arteries). Papaverine reversed constriction of AduPA arteries. uPA-mediated arterial constriction is a vasomotor process that is mediated by uPA catalytic activity, not by the NH(2)-terminal domains. Anchoring uPA to the endothelial surface does not prevent vasoconstriction. uPA catalytic activity, generated by artery wall cells, may contribute to lumen loss in human arteries. Elimination of uPA vasoconstrictor activity requires concomitant loss of fibrinolytic activity.

Inflammatory stress and idiosyncratic hepatotoxicity: hints from animal models

Adverse drug reactions (ADRs) present a serious human health problem. They are major contributors to hospitalization and mortality throughout the world (Lazarou et al., 1998; Pirmohamed et al., 2004). A small fraction (less than 5%) of ADRs can be classified as "idiosyncratic." Idiosyncratic ADRs (IADRs) are caused by drugs with diverse pharmacological effects and occur at various times during drug therapy. Although IADRs affect a number of organs, liver toxicity occurs frequently and is the primary focus of this review. Because of the inconsistency of clinical data and the lack of experimental animal models, how IADRs arise is largely undefined. Generation of toxic drug metabolites and induction of specific immunity are frequently cited as causes of IADRs, but definitive evidence supporting either mechanism is lacking for most drugs. Among the more recent hypotheses for causation of IADRs is that inflammatory stress induced by exogenous or endogenous inflammagens is a susceptibility factor. In this review, we give a brief overview of idiosyncratic hepatotoxicity and the inflammatory response induced by bacterial lipopolysaccharide. We discuss the inflammatory stress hypothesis and use as examples two drugs that have caused IADRs in human patients: ranitidine and diclofenac. The review focuses on experimental animal models that support the inflammatory stress hypothesis and on the mechanisms of hepatotoxic response in these models. The need for design of epidemiological studies and the potential for implementation of inflammation interaction studies in preclinical toxicity screening are also discussed briefly.

Expression of annexin II in experimental abdominal aortic aneurysms

Annexin II is a receptor of tissue-type plasminogen activator (t-PA). We have previously identified annexin II by immunolocalization in human atherosclerotic abdominal aortic aneurysms (AAAs). To investigate possible interactions between annexin II and AAA development, we examined annexin II mRNA and protein expression in a rat model of experimental AAA. AAAs were induced in rats by transient aortic infusion of elastase. The rats were divided into three groups: a saline-treated control group, a group with 15-min elastase infusion, and a group with 30-min elastase infusion. The 15-min elastase-infused group had smaller aneurysms and more preserved media than the 30-min elastase-infused group. Immunohistochemistry showed that annexin II expression was increased in the thickened intima and media of AAA rats as compared with the media of control rats. Furthermore, annexin II was colocalized with macrophages and smooth muscle cells. Quantitative real-time polymerase chain reaction showed that annexin II mRNA levels were up-regulated only in the smaller aneurysm group compared with the control group. In contrast, t-PA mRNA levels were increased in both the 15- and 30-min elastase-infused groups as compared with the control group. These results demonstrate various levels of annexin II expression within the aortic wall of rats with experimental AAAs. It has been suggested that alteration of fibrinolytic activity regulated by annexin II within the aortic wall may be associated with aneurysm formation.

Insulin acts through FOXO3a to activate transcription of plasminogen activator inhibitor type 1

Plasminogen activator inhibitor-1 (PAI-1) is an important regulator of fibrinolysis. PAI-1 levels are elevated in type 2 diabetes, and this elevation correlates with macro- and microvascular complications of diabetes. However, the mechanistic link between insulin and up-regulation of PAI-1 is unclear. Here we demonstrate that overexpression of Forkhead-related transcription factor (Fox)O1, FoxO3a, and FoxC1 augment insulin's ability to activate the PAI-1 promoter. In addition, insulin treatment promotes the phosphorylation of nuclear and cytoplasmic Fox03a and an increase of cytoplasmic Fox03a. In contrast, insulin treatment led to the accumulation of phospho-Fox01 only in the cytoplasm. Furthermore, insulin also increased the ability of chimeric LexA-FoxO1, LexA-FoxO3a, and LexA-FoxC1 proteins to increase the activity of a LexA reporter, suggesting that the effect of insulin on FoxO3a was direct. Using small interfering RNA to specifically deplete each of the Fox transcription factors tested, we demonstrate that only reduction of FoxO3a inhibits insulin-increased PAI-1-Luc expression and PAI-1 mRNA accumulation. Finally, chromatin immunoprecipitation assays confirm the presence of FoxO3a on the PAI-1 promoter. These results suggest that FoxO3a mediates insulin-increased PAI-1 gene expression.

Urokinase activates macrophage PON2 gene transcription via the PI3K/ROS/MEK/SREBP-2 signalling cascade mediated by the PDGFR-beta

AIMS

We have recently shown that urokinase plasminogen activator (uPA) increases oxidative stress (OS), cholesterol biosynthesis, and paraoxonase 2 (PON2) expression in macrophages via binding to its receptor, the uPAR. Since PON2 is regulated by both OS and cholesterol content, we hypothesized that uPA elicits a cascade of signal transduction events shared by NADPH oxidase and cholesterol biosynthesis that culminates in PON2 gene expression. Here, we investigated the signalling pathway that leads to the expression of PON2 in macrophages in response to uPA.

METHODS AND RESULTS

The increase in macrophage PON2 mRNA levels in response to uPA was shown to depend on PON2 gene promoter activation and mRNA transcription. LDL abolished these effects, suggesting a possible role for a transcription factor involved in cellular cholesterogenesis. Indeed, uPA upregulated PON2 expression in a sterol regulatory binding protein-2 (SREBP-2)-dependent manner, since blocking SREBP-2 maturation by 4-(2-aminoethyl)-benzenesulfonyl fluoride abolished uPA-stimulation of PON2, whereas inhibition of SREBP-2 catabolism by N-acetyl-leucyl-norleucinal had an opposite effect. The upstream signalling mechanisms include uPA activation of extracellular signal-regulated kinases (ERK1/2), which was dependent on NADPH oxidase and phosphatidylinositol 3-kinase activation, and these latter effects were mediated by the tyrosine kinase activity of the platelet-derived growth factor receptor-beta.

CONCLUSION

These findings provide a framework linking interactions among cellular signalling pathways associated with reactive oxygen species production, macrophage cholesterol biosynthesis, and cellular PON2 expression in vascular pathophysiology.

Elevated tissue expression of thrombomodulatory factors correlates with acute symptomatic carotid plaque phenotype

OBJECTIVES

Thrombomodulatory factors have been implicated in plaque instability. The aim was to examine the relationship between thrombomodulatory gene expression, timing of clinical events and plaque histology.

DESIGN OF STUDY

Plaques were obtained from 40 consecutive patients undergoing carotid endarterectomy and divided into three groups (group 1, early symptomatic, within 1 month; group 2, late symptomatic, 1-6 months and group 3, asymptomatic). Total RNA was isolated to determine the expression of tissue plasminogen activator (t-PA), urokinase plasminogen activator (u-PA), plasminogen activator inhibitor-1 (PAI-1), tissue factor (TF), tissue factor pathway inhibitor (TFPI), thrombomodulin (TM), CD68 and vascular endothelial-cadherin (VE-Cadherin).

RESULTS

Expression of t-PA, PAI-1, TF, TFPI, TM, CD68 and VE-cadherin were significantly increased in the early symptomatic group (p=0.019, 0.028, 0.018, 0.025, 0.038, 0.016 and 0.027 respectively), but the level of gene expression in the late symptomatic group was indistinguishable from the asymptomatic group. The incidence of plaque rupture and intraplaque haemorrhage was significantly increased in the early symptomatic groups (58% versus 18%/18% group 2/3, and 55% versus 6%/9% respectively, p<0.05 for both).

CONCLUSIONS

Expression of thrombomodulatory genes is increased in unstable plaques, though levels after 1 month are comparable to asymptomatic plaques. This transient rise may influence plaque instability, and rapid resolution mirrors the clinical reduction in risk of further thrombo-embolic events.

Regulation of arterial remodeling and angiogenesis by urokinase-type plasminogen activatorThis article is one of a selection of papers from the NATO Advanced Research Workshop on Translational Knowledge for Heart Health (published in part 2 of a 2-part Special Issue)

A wide variety of disorders are associated with an imbalance in the plasminogen activator system, including inflammatory diseases, atherosclerosis, intimal hyperplasia, the response mechanism to vascular injury, and restenosis. Urokinase-type plasminogen activator (uPA) is a multifunctional protein that in addition to its fibrinolytic and matrix degradation capabilities also affects growth factor bioavailability, cytokine modulation, receptor shedding, cell migration and proliferation, phenotypic modulation, protein expression, and cascade activation of proteases, inhibitors, receptors, and modulators. uPA is the crucial protein for neointimal growth and vascular remodeling. Moreover, it was recently shown to be implicated in the stimulation of angiogenesis, which makes it a promising multipurpose therapeutic target. This review is focused on the mechanisms by which uPA can regulate arterial remodeling, angiogenesis, and cell migration and proliferation after arterial injury and the means by which it modulates gene expression in vascular cells. The role of domain specificity of urokinase in these processes is also discussed.

Endothelial dysfunction: from molecular mechanisms to measurement, clinical implications, and therapeutic opportunities

Endothelial dysfunction has been implicated as a key factor in the development of a wide range of cardiovascular diseases, but its definition and mechanisms vary greatly between different disease processes. This review combines evidence from cell-culture experiments, in vitro and in vivo animal models, and clinical studies to identify the variety of mechanisms involved in endothelial dysfunction in its broadest sense. Several prominent disease states, including hypertension, heart failure, and atherosclerosis, are used to illustrate the different manifestations of endothelial dysfunction and to establish its clinical implications in the context of the range of mechanisms involved in its development. The size of the literature relating to this subject precludes a comprehensive survey; this review aims to cover the key elements of endothelial dysfunction in cardiovascular disease and to highlight the importance of the process across many different conditions.

Expression of annexin II in human atherosclerotic abdominal aortic aneurysms

BACKGROUND

Annexin II is a receptor for tissue-type plasminogen activator (t-PA) that converts plasminogen to plasmin. Although the fibrinolytic system is known to play an important role in the pathogenesis of abdominal aortic aneurysms (AAAs), the relationship between annexin II and AAA development is unknown. Therefore, we examined annexin II localization in the wall of human atherosclerotic AAAs.

METHODS AND RESULTS

Specimens from 13 patients undergoing elective repair of an AAA were taken. Annexin II expression was evaluated by immunohistochemical analysis. Immunostaining results were semiquantitatively analyzed using histology scores and WinROOF software based on staining intensity. The expression of annexin II was increased and the histology score was higher in the shoulder region of the atheromatous plaque than in the atheroma and fibrous plaque regions. Annexin II appeared to have greater expression and the histology score was higher in regions where the media was preserved. Furthermore, there was a significant inverse correlation between AAA size and histology score in the fibrous plaque region.

CONCLUSIONS

The present work demonstrates various levels of annexin II expression within the aneurysm wall. Therefore, we suggest that alteration of annexin II expression within the aortic wall may be associated with the development of an aneurysm.

Inhibition of plasminogen activator inhibitor-1 expression in vascular smooth muscle cells by protoporphyrins through a heme oxygenase-independent mechanism

Heme oxygenase-1 (HO-1), a rate-limiting enzyme in heme catabolism, has been shown to play a regulatory role in the expression of plasminogen activator inhibitor-1 (PAI-1), a risk factor for vascular disease. Accordingly, we examined the effect of protoporphyrins, both HO inhibitors and activators, on PAI-1 expression in human vascular smooth muscle cells (VSMCs). Tin-protoporphyrin (SnPP) markedly inhibited the transforming growth factor beta1 (TGFbeta1)-induced expression of PAI-1 protein. Protoporphyrins, whether they are inhibitors or activators of HO, produced a similar inhibitory effect. However, SnPP had no effect on the level of PAI-1 mRNA transcripts. Knockdown of human HO-1 with a specific siRNA did not reduce the PAI-1 protein level in TGFbeta1-treated cells. In addition, the proteasome inhibitor lactacystin reversed the inhibitory effect of SnPP on PAI-1 protein expression. Both cobalt-protoporphyrin (CoPP) and CoCl2 markedly induced HO-1 expression. However, CoPP did not affect PAI-1 gene expression, whereas CoCl2 upregulated PAI-1 mRNA in a dose-dependent manner. Our results demonstrate that protoporphyrins can block the TGFbeta1-mediated induction of PAI-1 protein in VSMCs and that this inhibitory effect is independent of HO activity.

The inflammatory cytokine oncostatin M induces PAI-1 in human vascular smooth muscle cells in vitro via PI 3-kinase and ERK1/2-dependent pathways

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 NH2-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.

Urokinase plasminogen activator (uPA) stimulates cholesterol biosynthesis in macrophages through activation of SREBP-1 in a PI3-kinase and MEK-dependent manner

Urokinase plasminogen activator (uPA) is expressed in human atherosclerotic lesions, predominantly in macrophages, and contributes to atherosclerosis progression. Since atherogenesis is characterized by the formation of cholesterol-loaded macrophage foam cells, we questioned whether uPA atherogenicity may involve macrophage cholesterol accumulation, and by what mechanisms. uPA increased cellular cholesterol content by 44% (mainly unesterified cholesterol) in THP-1 macrophages, and this effect was inhibited by statins. This effect was associated with 172% elevated cholesterol biosynthesis, which required the binding of uPA to its receptor. An upregulation of HMGCoA reductase (HMGCR) expression (protein and mRNA) was noted. Since HMGCR expression is controlled by sterol regulatory element-binding proteins (SREBPs), we next analyzed this issue. Indeed, treatment of macrophages with uPA increased SREBP-1 processing, and mature SEREBP-1 content (by 5.7-fold) in the nucleus. These latter effects were mediated by uPA-induced activation of the mitogen-activated protein kinase/extracellular signal-regulated kinase (MEK). Finally, uPA was found to activate MAP-kinase through PI3 kinase (PI3K), as PI3K inhibition abrogated both uPA-induced ERK phosphorylation and cholesterol biosynthesis. In conclusion, uPA-induced macrophage cholesterol accumulation is a novel pathway by which uPA may contribute to accelerated atherosclerosis development. These findings provide new insight into the atherogenicity of uPA and may suggest new novel therapeutic means.

Notoginsenoside R1 from Panax notoginseng inhibits TNF-alpha-induced PAI-1 production in human aortic smooth muscle cells

Notoginsenoside R1 is the main ingredient with cardiovascular activity in Panax notoginseng. We reported that notoginsenoside R1 significantly decreased tumor necrosis factor-alpha (TNF-alpha)-induced plasminogen activator inhibitor-1 (PAI-1) mRNA, protein level and secretion in human aortic smooth muscle cells (HASMCs) in a dose-dependent manner. TNF-alpha significantly increased extracellular signal-related kinases (ERK) and protein kinase B (PKB) activation and, which was blocked by notoginsenoside R1, PD098059, U0126 or wortmannin. Our data demonstrates that TNF-alpha-induced up-regulation of PAI-1 mRNA and protein levels and secretion occur via activation of ERK and PKB, which was prevented by treatment of notoginsenoside R1, PD098059, U0126 or wortmannin. These results suggest that notoginsenoside R1 inhibits TNF-alpha-induced PAI-1 overexpression in HASMCs by suppressing ERK and PKB signaling pathways.

Downregulated Expression of Plasminogen Activator Inhibitor-1 Augments Myocardial Neovascularization and Reduces Cardiomyocyte Apoptosis After Acute Myocardial Infarction

OBJECTIVES

The aim of this study was to examine whether selective plasminogen activator inhibitor type 1 (PAI-1) downregulation in the acutely ischemic heart increases the myocardial microvasculature and improves cardiomyocyte (CM) survival.

BACKGROUND

Endogenous myocardial neovascularization is an important process enabling cardiac functional recovery after acute myocardial infarction. Expression of PAI-1, a potent inhibitor of angiogenesis, is induced in ischemic heart tissue.

METHODS

A sequence-specific catalytic deoxyribonucleic acid (DNA) enzyme was used to reduce PAI-1 levels in cultured endothelial cells and in ischemic myocardium. At the time of coronary artery ligation, rats were randomized into three groups, each receiving an intramyocardial injection (IMI) of a single dose at three different sites of the peri-infarct region consisting, respectively, of DNA enzyme E2 targeting rat PAI-1 (E2), scrambled control DNA enzyme (E0), or saline. Cardiomyocyte apoptosis, capillary density, and echocardiography were studied two weeks following infarction.

RESULTS

The E2 DNA enzyme, which efficiently inhibited rat PAI-1 expression in vitro, induced prolonged suppression (>2 weeks) of PAI-1 messenger ribonucleic acid and protein in rat heart tissues after a single IMI. At two weeks, hearts from experimental rats had over five-fold greater capillary density, 70% reduction in apoptotic CMs, and four-fold greater functional recovery compared with controls.

CONCLUSIONS

These results imply a causal relationship between elevated PAI-1 levels in ischemic hearts and adverse outcomes, and they suggest that strategies to reduce cardiac PAI-1 activity may augment neovascularization and improve functional recovery.

The status of plasminogen activator inhibitor-1 as a therapeutic target

Plasminogen activator inhibitor-1 (PAI-1) is the major physiological inhibitor of tissue-type plasminogen activator (tPA). An increase in the plasma concentration of PAI-1 has been proposed as a risk factor in thrombotic disease and elevated PAI-1 is associated with a poor prognosis in a variety of cancers. These observations have led to numerous studies addressing the physiological and pathophysiological role of PAI-1 and to the proposal that manipulation of PAI-1 activity presents a new therapeutic target. Recent experimental studies with anti-PAI-1 antibodies and low molecular weight inhibitors have demonstrated efficacy in both arterial and venous thrombosis models. These studies have confirmed the potential clinical benefit of reducing PAI-1 activity. As it is now possible to manipulate PAI-1 activity in vivo, future studies should be aimed at confirming the importance of PAI-1 as a major therapeutic target.

Role of oxidatively modified low density lipoproteins and anti-oxidants in atherothrombosis

Retrospective studies have demonstrated an association between coronary artery disease (CAD) and increased plasma levels of oxidised low density lipoproteins (LDL). A very recent prospective study in heart transplant patients has demonstrated that oxidised LDL is an independent risk factor for transplant CAD, thus further supporting the hypothesis that oxidised LDL is actively involved in the development of CAD. The increase of circulating oxidised LDL is most probably caused by back-diffusion from the atherosclerotic arterial wall in the blood, independent of plaque rupture. Indeed, plasma levels of oxidised LDL were very similar in patients with stable CAD and in patients with acute coronary syndromes. These were, however, associated with increased release of malondialdehyde (MDA)-modified LDL. Oxidised LDL may be generated by radical-mediated or by lipoxygenase or phospholipase catalysed lipid oxidation, and by myeloperoxidase catalysed protein and lipid oxidation. Prostaglandin synthesis by endothelial cells under oxidative stress and platelet activation are associated with the release of aldehydes; these induce the oxidative modification of the apolipoprotein B-100 moiety of LDL in the absence of lipid peroxidation, and thus generate MDA-modified LDL. Efficient prevention of in vivo oxidation may involve efficient cholesterol lowering, improving the anti-oxidative status of LDL by increasing the anti-oxidant content and increasing the oleate content of LDL, and by shifting the LDL away from phenotype B (characterised by small dense LDL particles). Anti-oxidative and anti-inflammatory enzymes associated with HDL may inhibit the oxidation of LDL or reverse the atherothrombotic effects of LDL.

Down-regulation of plasminogen activator inhibitor 1 expression promotes myocardial neovascularization by bone marrow progenitors

Human adult bone marrow–derived endothelial progenitors, or angioblasts, induce neovascularization of infarcted myocardium via mechanisms involving both cell surface urokinase-type plasminogen activator, and interactions between β integrins and tissue vitronectin. Because each of these processes is regulated by plasminogen activator inhibitor (PAI)-1, we selectively down-regulated PAI-1 mRNA in the adult heart to examine the effects on postinfarct neovascularization and myocardial function. Sequence-specific catalytic DNA enzymes inhibited rat PAI-1 mRNA and protein expression in peri-infarct endothelium within 48 h of administration, and maintained down-regulation for at least 2 wk. PAI-1 inhibition enhanced vitronectin-dependent transendothelial migration of human bone marrow–derived CD34⁺ cells, and resulted in a striking augmentation of angioblast-dependent neovascularization. Development of large, thin-walled vessels at the peri-infarct region was accompanied by induction of proliferation and regeneration of endogenous cardiomyocytes and functional cardiac recovery. These results identify a causal relationship between elevated PAI-1 levels and poor outcome in patients with myocardial infarction through mechanisms that directly inhibit bone marrow–dependent neovascularization. Strategies that reduce myocardial PAI-1 expression appear capable of enhancing cardiac neovascularization, regeneration, and functional recovery after ischemic insult.

Differential regulation of urokinase-type plasminogen activator expression by fluid shear stress in human coronary artery endothelial cells

Atherosclerotic plaques preferentially localize at arterial regions exposed to turbulent low-shear flow. Urokinase-type plasminogen activator (uPA) plays a role in vascular remodeling by facilitating smooth muscle cell migration and proliferation in addition to the proteolysis of extracellular matrix, and the expression of uPA is elevated in atherosclerotic lesions. In this study, we analyzed the effects of laminar and turbulent shear stress on uPA expression in cultured human coronary artery endothelial cells. The application of laminar shear stress (1.5 or 15 dyn/cm2) significantly decreased the amount of uPA mRNA as well as the secretion of uPA protein. In contrast, turbulent shear stress (average intensity, 1.5 dyn/cm2) markedly increased uPA gene expression and protein secretion. Laminar shear stress downregulated uPA gene expression transcriptionally and posttranscriptionally; laminar shear stress activated transcription factor GATA6, which binds to a GATA consensus element located between -692 and -687 bp in the uPA promoter, thereby inhibiting uPA gene transcription. Laminar shear stress also accelerated the degradation of uPA mRNA; the half-life of uPA mRNA decreased to about half of the static control's half-life. Although turbulent shear stress had no effect on the transcription of uPA, it significantly increased uPA mRNA stability; the half-life of uPA mRNA increased by about two times the static control's half-life. Our results suggest that endothelial uPA expression is flow sensitive and differentially regulated by laminar and turbulent shear stress in vitro. We speculate that this effect may contribute to the local nature of atherosclerosis.

Overexpression of urokinase receptor and cell surface urokinase-type plasminogen activator in the human vessel wall with different types of atherosclerotic lesions

Urokinase-type plasminogen activator (UPA) has been implicated in a broad spectrum of pathogenic processes involved in the formation and disruption of atherosclerotic lesions. Up to now, there is no consensus on the contribution of membrane-bound UPA and its receptor CD87 (UPAR) to the development of atherosclerosis. In this study, we determined comparatively the levels of UPAR and UPAR-bound UPA in segments of human coronary and aortic vessels with different degrees of atherosclerotic lesions (macroscopically normal areas, early atherosclerotic lesions, fibrous and calcified plaques). The UPAR content increased progressively with the severity of atherosclerosis. In aortic segments, in which intima and media layers were analyzed separately, the content of UPAR in the intima significantly exceeded the levels measured in the media. Using a detergent-phase separation method with a Triton X-114-containing buffer, we could demonstrate that the levels of membrane (glycosylphosphatidylinositol)-anchored UPAR were significantly higher in the intima of early atherosclerotic lesions as well as in the cap areas of fibrous plaques compared with macroscopically normal areas. However, only 20-25% of the intimal and 30-50% of the medial glycosylphosphatidylinositol-UPAR was occupied by UPA as determined on a molar basis. These data confirm that the overexpression of UPAR in advanced atherosclerotic lesions contributes to lesion development. Whether UPAR's excess over cell surface UPA provides an additional role for this receptor in atherogenesis besides UPA-mediated proteolysis remains to be elucidated.

Smoking as a crucial independent determinant of stroke

Background

Although smoking is known to be powerful risk factor for other vascular diseases, such as cardiac and peripheral vascular disease, only relatively recently has evidence for the role of smoking in the development of stroke been established. The reasons for this advance lie in the acknowledgement that stroke is a heterogeneous disease, in which its subtypes are associated with different risk factors. Furthermore, improvements in the stringency of epidemiological studies and the greater use of CT scanning have enabled the role of smoking in the development of stroke to be elucidated.

Summary of review

This is a qualitative examination of high quality epidemiological studies in which the role of smoking and passive smoking, as a risk factor for cerebral infarction, intracerebral haemorrhage and subarachnoid haemorrhage, is examined. In addition, the pathological mechanisms by which smoking or passive smoking may contribute to the development of stroke are reviewed.

Conclusion

Smoking is a crucial independent determinant of cerebral infarction and subarachnoid haemorrhage, however its role in intracerebral haemorrhage is unclear. Although studies are limited, there is evidence that exposure to passive smoking may also increase the risk of stroke. Smoking appears to be involved in the pathogenesis of stroke via direct injury to the vasculature and also by altering haemodynamic factors within the circulation. Importantly, smoking is modifiable risk factor for stroke. Therefore, the encouragement of smoking cessation may result in a substantial reduction in the incidence of this devastating disease.

Oxidative stress activates the plasminogen activator inhibitor type 1 (PAI-1) promoter through an AP-1 response element and cooperates with insulin for additive effects on PAI-1 transcription

Oxidative stress is one of the characteristics of diabetes and is thought to be responsible for many of the pathophysiological changes caused by the disease. We previously identified an insulin response element in the promoter of plasminogen activator inhibitor 1 (PAI-1) that was activated by an unidentified member of the forkhead/winged helix (Fox) family of transcription factors. This element mediated a 5-7-fold increase in PAI-1 transcription because of insulin. Here we report that oxidative stress also caused a 3-fold increase in PAI-1 transcription and that the effect was additive with that of insulin. Antioxidants prevent this response. Mutational analysis of the PAI-1 promoter revealed that oxidative stress acted at an AP-1 site at -60/52 of the promoter. Gel mobility shift analysis demonstrated that binding to an AP-1 oligonucleotide was increased 4-fold by oxidative stress. Jun levels were increased by oxidants as assessed by reverse transcriptase-PCR. Western blotting demonstrated that a rapid and prolonged nuclear accumulation of phospho-c-Jun followed oxidant stimulation. The nuclear c-Jun phosphorylation was not observed in cells treated with reduced glutathione. Finally, JNK/SAPK activity was found to increase in response to oxidants, and inhibition of JNK/SAP blocked TBHQ-increased PAI-1-luciferase expression. Thus, oxidative stress stimulated AP-1 and activated the PAI-1 promoter.

MEK1,2 response element mediates angiotensin II-stimulated plasminogen activator inhibitor-1 promoter activation

The MEK1,2 (MAPK/ERK kinase 1 and 2) pathway mediates the up-regulation of plasminogen activator inhibitor-1 (PAI-1) expression in vascular smooth muscle cells by a variety of hormones, including angiotensin II. Transfection of constitutively active MEKK-1, an upstream activator of the mitogen-activated protein (MAP) kinase pathways, was used to isolate an enhancer element located between -89 and -50 bp in PAI-1 promoter that was activated by MEKK-1 and selectively blocked by the MEK1,2 inhibitor PD98059. Mutational analysis revealed that the MEKK-1 response element (MRE) contained 2 cis-acting Sp1- and AP-1-like sequences, located between -75 to -70 and -63 to -52 bp, respectively. Overexpression of Sp1 enhanced MEKK-1-induced MRE promoter activity and a dominant-negative c-Fos blocked this Sp1 response. The combination of Sp1 and c-Jun or c-Fos was required to activate this MRE. Angiotensin II (Ang II) stimulation increased c-Fos, c-Jun, and Sp1 binding to the MRE by 100-, 4.9-, and 1.9-fold, respectively, and these responses were inhibited by PD98059 and AT1 receptor antagonist candesartan. Intravenous Ang II infusion in rats increased aortic c-Fos binding to the MRE. This MRE sequence mediated a 4-fold increase of MEK1,2-dependent PAI-1/luciferase mRNA expression by angiotensin II stimulation. This report identifies the MEK1,2 response element that mediates angiotensin II-stimulated PAI-1 promoter activation and shows that activation of this element requires Sp1 and AP-1 co-activation.

Functional regulation of tissue plasminogen activator on the surface of vascular smooth muscle cells by the type-II transmembrane protein p63 (CKAP4)

We have demonstrated that tissue plasminogen activator (tPA) binds specifically to human vascular smooth muscle cells (VSMC) in a functionally relevant manner, both increasing plasminogen activation and decreasing tPA inhibition (Ellis, V., and Whawell, S. A. (1997) Blood 90, 2312-2322; Werner, F., Razzaq, T. M., and Ellis, V. (1999) J. Biol. Chem. 274, 21555-21561). To further understand this system we have now identified and characterized the protein responsible for this binding. Rat VSMC were surface-labeled with 125I, and cell lysates were subjected to an affinity chromatography scheme based on the previously identified tPA binding characteristics. A single radiolabeled protein of 63 kDa bound specifically and was eluted at low pH. This protein was isolated from large scale preparations of VSMC and unambiguously identified as the rat homologue of the human type-II transmembrane protein p63 (CKAP4) by matrix-assisted laser desorption ionization and nano-electrospray tandem mass spectrometry of tryptic fragments. In confirmation of this, a monoclonal antibody raised against authentic human p63 recognized the isolated protein in Western blotting. Immunofluorescence microscopy demonstrated that p63 was located principally in the endoplasmic reticulum but was also detected in significant quantities on the surface of human VSMC. In support of the hypothesis that p63 is the functional tPA binding site on VSMC, an anti-p63 monoclonal antibody was found to block tPA binding. Furthermore, heterologous expression of an N-terminally truncated mutant of p63, which targets exclusively to the plasma membrane, led to an increase in tPA-catalyzed plasminogen activation. Therefore, p63 on the surface of VSMC may contribute to the functional regulation of the plasminogen activation system in the vessel wall.

Donor PAI-1 expression inhibits the intimal response of early allograft vascular disease

BACKGROUND

The development of allograft vascular disease (AVD) may be related to altered expression of the fibrinolytic system. We determined the extent to which plasminogen activator inhibitor type 1 (PAI-1) expression in donor tissue influences intimal proliferation (IP) in a mouse model of AVD.

METHODS

We utilized an end-to-end abdominal aortic transplant model in mice to investigate the development of IP in 3 groups of 6 recipients. Group A (negative control) utilized C57BL/6J strain mice as both donors and recipients. In Groups B (positive control) and C, C57BL/6J mice were vessel donors and CBA/J mice were recipients. Both groups received intraperitoneal anti-CD4 and anti-CD8 monoclonal antibodies (250 microg/week for 5 weeks). Group C recipients, however, were transplanted with vessels from C57BL/6J PAI-1 knockout mice. Animals were killed at 50 days. Transplanted aortas were removed and intimal areas calculated using morphometric analysis.

RESULTS

Group A (mean intimal area 6421 +/- 8507 microm(2)) demonstrated very little IP in comparison to the other groups. IP was significantly higher in Group B (mean intimal area 56357 +/- 35629 microm(2)) than Group A (p = 0.008). Group C (mean intimal area 288195 +/- 123279 microm(2)) demonstrated significantly more intimal proliferation than either Groups A or B (vs B, p = 0.003; vs A, p < 0.001). The significance of these results is maintained if intimal thickness is measured as a stand-alone reference for the intimal response.

CONCLUSIONS

Lack of PAI-1 expression in donor tissue greatly exaggerates the extent of IP after allogeneic transplantation and suggests that PAI-1 is important in limiting the early phase of AVD.

Plasminogen activator inhibitor type-1 inhibits insulin signaling by competing with alphavbeta3 integrin for vitronectin binding

Functional cooperation between integrins and growth factor receptors has been reported for several systems, one of which is the modulation of insulin signaling by alphavbeta3 integrin. Plasminogen activator inhibitor type-1 (PAI-1), competes with alphavbeta3 integrin for vitronectin (VN) binding. Here we report that PAI-1, in a VN-dependent manner, prevents the cooperation of alphavbeta3 integrin with insulin signaling in NIH3T3 fibroblasts, resulting in a decrease in insulin-induced protein kinase B (PKB) phosphorylation, vascular endothelial growth factor (VEGF) expression and cell migration. Insulin-induced HUVEC migration and angiotube formation was also enhanced in the presence of VN and this enhancement is inhibited by PAI-1. By using specific PAI-1 mutants with either VN binding or plasminogen activator (PA) inhibiting activities ablated, we have shown that the PAI-1-mediated interference with insulin signaling occurs through its direct interaction with VN, and not through its PA neutralizing activity. Moreover, using cells deficient for uPA receptor (uPAR) we have demonstrated that the inhibition of PAI-1 on insulin signaling is independent of uPAR-VN binding. These results constitute the first demonstration of the interaction of PAI-1 with the insulin response.

Increased expression of urokinase during atherosclerotic lesion development causes arterial constriction and lumen loss, and accelerates lesion growth

Overexpression of urokinase plasminogen activator (uPA) in endothelial cells can decrease intravascular thrombosis. However, expression of uPA is increased in atherosclerotic human arteries, which suggests that uPA might accelerate atherogenesis. To investigate whether elevated uPA expression accelerates atherogenesis, we cloned a rabbit uPA cDNA and expressed it in carotid arteries of cholesterol-fed rabbits. uPA gene transfer increased artery-wall uPA activity for at least 1 week, with a return to baseline by 2 weeks. One week after gene transfer, uPA-transduced arteries were constricted, with significantly smaller lumens and thicker walls, but no difference in intimal or medial mass. Two weeks after gene transfer, uPA- and control-transduced arteries were morphologically indistinguishable. By 4 weeks, however, uPA-transduced arteries had 70% larger intimas than control-transduced arteries (P < 0.01) and smaller lumens (P < 0.05). Intimal lesions appeared to be of similar composition in uPA- and control-transduced arteries, except that degradation of elastic laminae was evident in uPA-transduced arteries. These data suggest that elevated uPA expression in atherosclerotic arteries contributes to intimal growth and constrictive remodeling leading to lumen loss. Antagonists of uPA activity might, therefore, be useful in limiting intimal growth and preventing constrictive remodeling. Overexpression of uPA in endothelial cells to prevent intravascular thrombosis must be reconsidered, because this intervention could worsen underlying vascular disease.

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.

Regulation of plasminogen activator inhibitor-1 secretion by urokinase and tissue plasminogen activator in rat epithelioid-type smooth muscle cells

Tissue plasminogen activator (tPA) and urokinase (uPA) are targets of plasminogen activator inhibitor-1 (PAI-1) inhibition. We have previously shown that both proteases can also induce PAI-1 secretion in rat smooth muscle cells (SMCs). We now report that both proteases appear to use very similar cellular mechanisms for signal transduction. They induced PAI-1 secretion using a pathway(s) involving protein kinase C (PKC). They also activated the Raf/Mek/mitogen-activated protein kinase (MAPK) pathway, which lies downstream of PKC activation. Activation of protein kinase A (PKA), however, lowered PAI-1 secretion induced by uPA and tPA, as a result of an inhibition of the PKC pathway and inhibition of Raf, Mek and MAPK phosphorylations. Src and syk family non-receptor tyrosine kinases (TK) were also involved in PAI-1 induction. The mechanisms of interaction of these tyrosine kinases with other pathways appeared to be quite different: src appeared to act within the PKC and PKA pathways, while syk operated independently of these pathways. Furthermore, whereas src inhibition resulted in inhibition of Raf/Mek/Erk phosphorylations, syk inhibition could only inhibit Mek and Erk phosphorylations but not the phosphorylation of Raf. These multiple pathways utilized by uPA and tPA to modulate PAI-1 secretion might be involved in determining the proteolytic or antiproteolytic potential of the SMCs under different pathophysiological conditions.

Vimentin exposed on activated platelets and platelet microparticles localizes vitronectin and plasminogen activator inhibitor complexes on their surface

Type 1 plasminogen activator inhibitor (PAI-1), the primary inhibitor of tissue-type plasminogen activator (t-PA), is found in plasma and platelets. PAI-1 circulates in complex with vitronectin (Vn), an interaction that stabilizes PAI-1 in its active conform. In this study, we examined the binding of platelet-derived Vn and PAI-1 to the surface of isolated platelets. Flow cytometry indicate that, like P-selectin, PAI-1, and Vn are found on the surface of thrombin- or calcium ionophore-activated platelets and platelet microparticles. The binding of PAI-1 to the activated platelet surface is Vn-dependent. Vn mediates the binding of PAI-1 to platelet surfaces through a high affinity (K(d) of 80 nm) binding interaction with the NH(2) terminus of vimentin, and this Vn-binding domain is expressed on the surface of activated platelets and platelet microparticles. Immunological and functional assays indicate that only -5% of the total PAI-1 in platelet releasates is functionally active, and it co-precipitates with Vn, and the vimentin-enriched cytoskeleton fraction of activated platelet debris. The remaining platelet PAI-1 is inactive, and does not associate with the cytoskeletal debris of activated platelets. Confocal microscopic analysis of platelet-rich plasma clots confirm the co-localization of PAI-1 with Vn and vimentin on the surface of activated platelets, and platelet microparticles. These findings suggest that platelet vimentin may regulate fibrinolysis in plasma and thrombi by binding platelet-derived Vn.PAI-1 complexes.

Urokinase plasminogen activator augments cell proliferation and neointima formation in injured arteries via proteolytic mechanisms

Urokinase plasminogen activator (uPA) has been implicated in the healing responses of injured arteries, but the importance of its various properties that influence smooth muscle cell (SMC) proliferation and migration in vivo is unclear. We used three recombinant (r-) forms of uPA, which differ markedly in their proteolytic activities and abilities to bind to the uPA receptor (uPAR), to determine, which property most influences the healing responses of balloon catheter injured rat carotid arteries. After injury, uPA and uPAR expression increased markedly throughout the period when medial SMCs were rapidly proliferating and migrating to form the neointima. Perivascular application of uPA neutralizing antibodies immediately after injury attenuated the healing response, significantly reducing neointima size and neointimal SMC numbers. Perivascular application of r-uPAwt (wild type uPA) or r-uPA/GDF (r-uPA with multiple mutations in its growth factor-like domain) doubled the size of the neointima. Four days after injury these two uPAs nearly doubled neointimal and medial SMC numbers in the vessels, and induced greater reductions in lumen size than injury alone. Proteolytically inactive r-uPA/H/Q (containing glutamine rather than histidine-204 in its catalytic site) did not affect neointima or lumen size. Also, in contrast to the actions of proteolytically active uPAs, tissue plasminogen activator (tPA) did not affect the rate of neointima development. We conclude that uPA is an important factor regulating the healing responses of balloon catheter injured arteries, and its proteolytic property, which cannot be mimicked by tPA, greatly influences SMC proliferation and early neointima formation.

Remnant lipoproteins induce endothelial plasminogen activator inhibitor-1

Remnant lipoproteins (RLPs) accumulate in type III hyperlipoproteinemia, a condition associated with significant cardiovascular morbidity. The effect of RLPs on fibrinolysis is unknown. Our aim was to study the effect of RLPs on endothelial expression of plasminogen activator inhibitor-1 (PAI-1). After 24-h culture of human aortic endothelial cells with RLPs at concentrations of 0 (control), 0.038, or 0.076 mg triglyceride/mL, postculture PAI-1 antigen concentrations were: 870 +/- 80, 1963 +/- 183 (P = 0.005), and 3551 +/- 177 ng/mL (P < 0.001), respectively. Furthermore, after 24-h incubation of endothelial cells with RLPs (0 or 0.076 mg triglyceride/mL), PAI-1 activity increased from 0.667 +/- 0.144 to 1.268 +/- 0.198 U/mL, respectively (P = 0.008) and endothelial PAI-1 mRNA increased to 2.7 +/- 0.66 that of control (P = 0.048). In conclusion, RLPs from patients with type III hyperlipoproteinemia induce endothelial cell PAI-1 expression, which may contribute to a prothrombotic state.

Effective lysis of model thrombi by a t-PA mutant (A473S) that is resistant to alpha2-antiplasmin

This study used two mutants of tissue-type plasminogen activator (t-PA) with resistance to inhibitors of fibrinolysis to define the contribution of plasminogen activator inhibitor (PAI)-1 and alpha2-antiplasmin (alpha2-AP) to the control of fibrin lysis. Wild-type t-PA was compared with KHRR296-299AAAA, which is resistant to PAI-1, and with A473S, which is resistant to alpha2-AP. We examined these forms of t-PA in model systems that are physiologically relevant. Neutralization of alpha2-AP was essential for lysis of plasma clots, irrespective of their platelet content, by either wild-type t-PA or KHRR296-299AAAA. In marked contrast, A473S lysed plasma clots without neutralization of alpha2-AP. Model thrombi, with structures similar to in vivo thrombi, were lysed slowly by wild-type t-PA; the rate and extent of lysis were enhanced by the addition of antibodies to alpha2-AP or PAI-1. A473S was more effective than wild-type t-PA without the addition of antibodies by virtue of its resistance to alpha2-AP. This resistance was remarkable, in that no complex formed between A473S t-PA and alpha2-AP, even after extended incubation, when 50% of wild-type t-PA could be converted to complex. Comparison of A473S and KHRR296-299AAAA mutants showed their similar effectiveness in lysis of platelet-rich model thrombi. Thus, PAI-1 and alpha2-AP contribute approximately equally to the inhibition of thrombus lysis. This study underlines the functional significance of alpha2-AP as a direct inhibitor of t-PA and further explains the basis of the accepted role of alpha2-AP as a regulator of fibrin persistence and thrombus resistance to lysis.

Plasmin-mediated macrophage reversal of low density lipoprotein aggregation

Evidence suggests that aggregated low density lipoprotein (AgLDL) accumulates in atherosclerotic lesions. Previously, we showed that AgLDL induces and enters surface-connected compartments (SCC) in human monocyte-derived macrophages by a process we have named patocytosis. Most AgLDL taken up by these macrophages in the absence of serum is stored in SCC and remains undegraded. We now show that macrophages released AgLDL (prepared by vortexing or treatment with phospholipase C or sphingomyelinase) from their SCC when exposed to 10% human lipoprotein-deficient serum (LPDS). Macrophages also took up AgLDL in the presence of LPDS, but subsequently released it. In both cases, the released AgLDL was disaggregated. Although the AgLDL that macrophages took up could not pass through a 0.45-micrometer filter, >60% of AgLDL could pass this filter after release from the macrophages. Disaggregation of AgLDL was verified by gel-filtration chromatography and electron microscopy that also showed particles larger than LDL, reflecting fusion of LDL that aggregates. The factor in serum that mediated AgLDL release and disaggregation was plasmin generated from plasminogen by macrophage urokinase plasminogen activator. AgLDL release was decreased >90% by inhibitors of plasmin (epsilon-amino caproic acid and anti-plasminogen mAb), and also by inhibitors of urokinase plasminogen activator (plasminogen activator inhibitor-1 and anti-urokinase plasminogen activator mAb). Moreover, plasminogen could substitute for LPDS and produce similar macrophage release and disaggregation of AgLDL. Because only plasmin bound to the macrophage surface is protected from serum plasmin inhibitors, interaction of AgLDL with macrophages was necessary for reversal of its aggregation by LPDS. The released disaggregated LDL particles were competent to stimulate LDL receptor-mediated endocytosis in cultured fibroblasts. Macrophage-mediated disaggregation of aggregated and fused LDL is a mechanism for transforming LDL into lipoprotein structures size-consistent with lipid particles found in atherosclerotic lesions.

New insights into the size and stoichiometry of the plasminogen activator inhibitor type-1.vitronectin complex

Plasminogen activator inhibitor-type 1 (PAI-1) is the primary inhibitor of endogenous plasminogen activators that generate plasmin in the vicinity of a thrombus to initiate thrombolysis, or in the pericellular region of cells to facilitate migration and/or tissue remodeling. It has been shown that the physiologically relevant form of PAI-1 is in a complex with the abundant plasma glycoprotein, vitronectin. The interaction between vitronectin and PAI-1 is important for stabilizing the inhibitor in a reactive conformation. Although the complex is clearly significant, information is vague regarding the composition of the complex and consequences of its formation on the distribution and activity of vitronectin in vivo. Most studies have assumed a 1:1 interaction between the two proteins, but this has not been demonstrated experimentally and is a matter of some controversy since more than one PAI-1-binding site has been proposed within the sequence of vitronectin. To address this issue, competition studies using monoclonal antibodies specific for separate epitopes confirmed that the two distinct PAI-1-binding sites present on vitronectin can be occupied simultaneously. Analytical ultracentrifugation was used also for a rigorous analysis of the composition and sizes of complexes formed from purified vitronectin and PAI-1. The predominant associating species observed was high in molecular weight (M(r) approximately 320,000), demonstrating that self-association of vitronectin occurs upon interaction with PAI-1. Moreover, the size of this higher order complex indicates that two molecules of PAI-1 bind per vitronectin molecule. Binding of PAI-1 to vitronectin and association into higher order complexes is proposed to facilitate interaction with macromolecules on surfaces.