Plasminogen activator expression in human atherosclerotic lesions

Post-Translational Oxidative Modifications of Hemostasis Proteins: Structure, Function, and Regulation

Reactive oxygen species (ROS) are constantly generated in a living organism. An imbalance between the amount of generated reactive species in the body and their destruction leads to the development of oxidative stress. Proteins are extremely vulnerable targets for ROS molecules, which can cause oxidative modifications of amino acid residues, thus altering structure and function of intra- and extracellular proteins. The current review considers the effect of oxidation on the structural rearrangements and functional activity of hemostasis proteins: coagulation system proteins such as fibrinogen, prothrombin/thrombin, factor VII/VIIa; anticoagulant proteins - thrombomodulin and protein C; proteins of the fibrinolytic system such as plasminogen, tissue plasminogen activator and plasminogen activator inhibitor-1. Structure and function of the proteins, oxidative modifications, and their detrimental consequences resulting from the induced oxidation or oxidative stress in vivo are described. Possible effects of oxidative modifications of proteins in vitro and in vivo leading to disruption of the coagulation and fibrinolysis processes are summarized and systematized, and the possibility of a compensatory mechanism in maintaining hemostasis under oxidative stress is analyzed.

Circulating Biomarkers for Laboratory Diagnostics of Atherosclerosis-Literature Review

Atherosclerosis is still considered a disease burden with long-term damaging processes towards the cardiovascular system. Evaluation of atherosclerotic stages requires the use of independent markers such as those already considered traditional, that remain the main therapeutic target for patients with atherosclerosis, together with emerging biomarkers. The challenge is finding models of predictive markers that are particularly tailored to detect and evaluate the evolution of incipient vascular lesions. Important advances have been made in this field, resulting in a more comprehensible and stronger linkage between the lipidic profile and the continuous inflammatory process. In this paper, we analysed the most recent data from the literature studying the molecular mechanisms of biomarkers and their involvement in the cascade of events that occur in the pathophysiology of atherosclerosis.

Elevated expression of urokinase plasminogen activator in rodent models and patients with cerebral amyloid angiopathy

AIMS

The aim of this work is to study the association of urokinase plasminogen activator (uPA) with development and progression of cerebral amyloid angiopathy (CAA).

MATERIALS AND METHODS

We studied the expression of uPA mRNA by quantitative polymerase chain reaction (qPCR) and co-localisation of uPA with amyloid-β (Aβ) using immunohistochemistry in the cerebral vasculature of rTg-DI rats compared with wild-type (WT) rats and in a sporadic CAA (sCAA) patient and control subject using immunohistochemistry. Cerebrospinal fluid (CSF) uPA levels were measured in rTg-DI and WT rats and in two separate cohorts of sCAA and Dutch-type hereditary CAA (D-CAA) patients and controls, using enzyme-linked immunosorbent assays (ELISA).

RESULTS

The presence of uPA was clearly detected in the cerebral vasculature of rTg-DI rats and an sCAA patient but not in WT rats or a non-CAA human control. uPA expression was highly co-localised with microvascular Aβ deposits. In rTg-DI rats, uPA mRNA expression was highly elevated at 3 months of age (coinciding with the emergence of microvascular Aβ deposition) and sustained up to 12 months of age (with severe microvascular CAA deposition) compared with WT rats. CSF uPA levels were elevated in rTg-DI rats compared with WT rats (p = 0.03), and in sCAA patients compared with controls (after adjustment for age of subjects, p = 0.05 and p = 0.03). No differences in CSF uPA levels were found between asymptomatic and symptomatic D-CAA patients and their respective controls (after age-adjustment, p = 0.09 and p = 0.44). Increased cerebrovascular expression of uPA in CAA correlates with increased quantities of CSF uPA in rTg-DI rats and human CAA patients, suggesting that uPA could serve as a biomarker for CAA.

Plasminogen activator receptor assemblies in cell signaling, innate immunity, and inflammation

Tissue-type plasminogen activator (tPA) and urokinase-type plasminogen activator (uPA) are serine proteases and major activators of fibrinolysis in mammalian systems. Because fibrinolysis is an essential component of the response to tissue injury, diverse cells, including cells that participate in the response to injury, have evolved receptor systems to detect tPA and uPA and initiate appropriate cell-signaling responses. Formation of functional receptor systems for the plasminogen activators requires assembly of diverse plasma membrane proteins, including but not limited to: the urokinase receptor (uPAR); integrins; N-formyl peptide receptor-2 (FPR2), receptor tyrosine kinases (RTKs), the N-methyl-d-aspartate receptor (NMDA-R), and low-density lipoprotein receptor-related protein-1 (LRP1). The cell-signaling responses elicited by tPA and uPA impact diverse aspects of cell physiology. This review describes rapidly evolving knowledge regarding the structure and function of plasminogen activator receptor assemblies. How these receptor assemblies regulate innate immunity and inflammation is then considered.

Single-Cell Transcriptomic Atlas of Different Human Cardiac Arteries Identifies Cell Types Associated With Vascular Physiology

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Parallel Murine and Human Plaque Proteomics Reveals Pathways of Plaque Rupture

RATIONALE

Plaque rupture is the proximate cause of most myocardial infarctions and many strokes. However, the molecular mechanisms that precipitate plaque rupture are unknown.

OBJECTIVE

By applying proteomic and bioinformatic approaches in mouse models of protease-induced plaque rupture and in ruptured human plaques, we aimed to illuminate biochemical pathways through which proteolysis causes plaque rupture and identify substrates that are cleaved in ruptured plaques.

METHODS AND RESULTS

We performed shotgun proteomics analyses of aortas of transgenic mice with macrophage-specific overexpression of urokinase (SR-uPA^+/0 mice) and of SR-uPA^+/0 bone marrow transplant recipients, and we used bioinformatic tools to evaluate protein abundance and functional category enrichment in these aortas. In parallel, we performed shotgun proteomics and bioinformatics studies on extracts of ruptured and stable areas of freshly harvested human carotid plaques. We also applied a separate protein-analysis method (protein topography and migration analysis platform) to attempt to identify substrates and proteolytic fragments in mouse and human plaque extracts. Approximately 10% of extracted aortic proteins were reproducibly altered in SR-uPA^+/0 aortas. Proteases, inflammatory signaling molecules, as well as proteins involved with cell adhesion, the cytoskeleton, and apoptosis, were increased. ECM (Extracellular matrix) proteins, including basement-membrane proteins, were decreased. Approximately 40% of proteins were altered in ruptured versus stable areas of human carotid plaques, including many of the same functional categories that were altered in SR-uPA^+/0 aortas. Collagens were minimally altered in SR-uPA^+/0 aortas and ruptured human plaques; however, several basement-membrane proteins were reduced in both SR-uPA^+/0 aortas and ruptured human plaques. Protein topography and migration analysis platform did not detect robust increases in proteolytic fragments of ECM proteins in either setting.

CONCLUSIONS

Parallel studies of SR-uPA^+/0 mouse aortas and human plaques identify mechanisms that connect proteolysis with plaque rupture, including inflammation, basement-membrane protein loss, and apoptosis. Basement-membrane protein loss is a prominent feature of ruptured human plaques, suggesting a major role for basement-membrane proteins in maintaining plaque stability.

Impact of bariatric surgery on subclinical atherosclerosis in patients with morbid obesity

BACKGROUND

The main cause of death in obese individuals is cardiovascular disease precipitated by atherosclerosis. Endothelial dysfunction and inflammation are considered early events in the development of the disease.

OBJECTIVES

The aim of this study was to identify biomarkers of subclinical atherosclerosis in patients with morbid obesity by comparing clinical, vascular, and biochemical parameters indicative of endothelial dysfunction in patients with and without atheromatous plaque and monitoring changes after bariatric surgery.

SETTINGS

Multicenter collaboration between Biochemistry and Biomedicine Department in Barcelona University and University Hospital Arnau de Vilanova in Lleida.

METHODS

Plasma samples from 66 patients with morbid obesity were obtained before bariatric surgery and at 6 and 12 months after. Patients were divided into 2 groups based on the presence of atheromatous plaque. We used contrast-enhanced carotid ultrasound, enzyme-linked immunosorbent assay, Griess, and EndoPAT-2000 methods.

RESULTS

Patients with plaque showed the worst profile of cardiovascular risk factors. Carotid intima-media thickness and plasminogen activator inhibitor-1 were higher in plaque group (P < .0001). After bariatric surgery, vasa vasorum, oxidized low-density lipoprotein, and plasminogen activator inhibitor-1 decreased (P < .0001 in all cases).

CONCLUSIONS

Obesity promotes atherogenesis, leading to vascular endothelial damage. Bariatric surgery reduces cardiovascular risk and the prognosis is better for patients without plaque. The increase in plasminogen activator inhibitor-1, carotid intima-media thickness, and vasa vasorum proliferation might be the first alterations in the atheromatous process in obesity and could serve as good biomarkers of subclinical atherosclerosis.

Mechanisms of plasminogen activator inhibitor 1 action in stromal remodeling and related diseases

Plasminogen activator inhibitor type 1 (PAI-1) is the main physiologic inhibitor of fibrinolysis. However, it is also involved in many physiological processes such as extracellular matrix (ECM) proteolysis and remodeling, cell adhesion, motility, and apoptosis, angiogenesis, etc. The aim of the study was to summarize current knowledge and gain insights into the mechanisms of PAI-1 action in the processes of stromal remodeling and diseases with considerable matrix pathologies (atherosclerosis, tissue fibrosis, cancer metastasis, pregnancy related complications, etc). As a component of an early cellular response to injury, PAI-1 reacts with membrane surface proteins and participates in the initiation of intracellular signaling, specifically cytoskeletal reorganization and motility. Complexity of ECM homeostasis resides in varying relation of the plasminogen system components and other matrix constituents. Inflammatory mediators (transforming growth factor-β and interferon-γ) and hormones (angiotensin II) are in the close interdependent relation with PAI-1. Also, special attention is devoted to the role of increased PAI-1 concentrations due to the common 4G/5G polymorphism. Some of the novel mechanisms of ECM modification consider PAI-1 dependent stabilization of urokinase mediated cell adhesion, control of the vascular endothelial cadherin trafficking and interaction with endothelial cells proteasome, its relation to matrix metalloproteinase 2 and osteopontin, and oxidative inhibition by myeloperoxidase. Targeting and/or alteration of PAI-1 functions might bring benefit to the future therapeutic approaches in diseases where ECM undergoes substantial remodeling.

Urban air pollution increases plasma fibrinogen and plasminogen activator inhibitor-1 levels in susceptible patients

BACKGROUND

The cardiovascular effects on fibrinolytic activity by urban air pollution are still unknown.

METHODS

Paired fasting blood samples during high and low air pollution days in Taipei were taken from a panel of 49 patients with coronary heart disease or multiple risk factors to study their fibrinolytic and inflammatory response to urban air pollution. Paired t-tests and mixed-effects models were used to determine the air pollution effects.

RESULTS

Patients' plasma plasminogen activator inhibitor-1 levels were significantly increased when hourly concentrations of particulate matter with diameters less than 10 microm (PM10) were greater than 100 microg/m during the period 0800 to 1800 h.

CONCLUSION

Urban air pollution has an adverse effect on plasma fibrinolytic function in a susceptible population.

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.

Regulatory role of microRNA-30b and plasminogen activator inhibitor-1 in the pathogenesis of cognitive impairment

The present study aimed to investigate the role of plasminogen activator inhibitor-1 (PAI-1) in drug-induced early cognitive impairment and the underlying mechanism concerning microRNA (miR)-30b. A mouse model of cognitive impairment was established by intraperitoneal injection of scopolamine (2 mg/kg body weight) for 13 days. Behavioral performance was assessed using the Morris water maze (MWM) test. The mRNA expression levels of PAI-1 and miR-30b were detected using quantitative polymerase chain reaction (qPCR). The protein expression levels of PAI-1 in the hippocampus and blood were determined using western blot analysis and enzyme-linked immunosorbent assays. The MWM test demonstrated that, on days 3 and 4, the escape latency was significantly elevated in the model mice in comparison with control group (P<0.05). In addition, the length of swimming path was significantly increased (P<0.05), while the number of times of crossing the platform location was significantly reduced in the model mouse group (P<0.05) in comparison with the control group. qPCR demonstrated that the mRNA expression levels of PAI-1 in the model mice was significantly elevated in the hippocampus and blood in comparison with the control group (P<0.01). Furthermore, western blot analysis and enzyme-linked immunosorbent assay demonstrated that the protein expression levels of PAI-1 were significantly elevated in the hippocampus and blood in the model group, in comparison with the control group (P<0.05). Notably, the levels of miR-30b in the hippocampus and blood were significantly decreased in the model mice in comparison with the control group (P<0.01). To conclude, the expression levels of PAI-1 were significantly elevated in mice with scopolamine-induced cognitive impairment, which may be associated with the downregulation of miR-30b. The findings from the present study suggest that miR-30b may be involved in the regulation of PAI-1, which would contribute to the pathogenesis of cognitive impairment.

Co-localization of fibrinolytic activators and inhibitors with macrophages in atherosclerotic vessels

The plasmin system is involved in hemostasis and tissue remodelling. The accumulation of plasminogen activators and their inhibitors in atherosclerotic lesions may be due to invasion of inflammatory cells in the vessel wall. High concentrations of macrophages are associated with increased risk of atherosclerotic plaque rupture. By immunohistochemistry on circumferential serial sections of atherosclerotic and healthy vessels the morphological association of plasminogen activators and inhibitors with macrophages was studied. Urokinase plasminogen activator (u-PA), plasminogen activator inhibitor type 2 (PAI-2), and macrophages were mainly expressed within plaques while tissue plasminogen activator (t-PA) and plasminogen activator inhibitor type 1 (PAI-1) were also expressed outside plaque lesions. Computer assisted image analysis on diseased vessels showed that regulatory proteins of the fibrinolytic system were found more often in areas positive for macrophages than in other parts of the sections (p < 0.001). u-PA was significantly more defined to areas positive for macrophages than tissue plasminogen activator (t-PA) and plasminogen activator inhibitor type 1 (PAI-1) (p < 0.05). Similarly, PAI-2 expression was more associated with macrophage distribution than PAI-1 (p < 0.05). Tumor necrosis factor α (TNFα), an inflammatoric mediator of macrophages, had the same levels of co-localization with macrophages as u-PA and PAI-2. These results suggest that u-PA and PAI-2 might be key factors for inflammatory regulation of plasmin mediated proteolysis in the vessel walls.

Role of plasminogen activator inhibitor-1 in senescence and aging

The average age of the US population continues to increase. Age is the most important determinant of disease and disability in humans, but the fundamental mechanisms of aging remain largely unknown. Many age-related diseases are associated with an impaired fibrinolytic system. Elevated plasminogen activator inhibitor-1 (PAI-1) levels are reported in age-associated clinical conditions including cardiovascular diseases, type 2 diabetes, obesity and inflammation. PAI-1 levels are also elevated in animal models of aging. While the association of PAI-1 with physiological aging is well documented, it is only recently that its critical role in the regulation of aging and senescence has become evident. PAI-1 is synthesized and secreted in senescent cells and contributes directly to the development of senescence by acting downstream of p53 and upstream of insulin-like growth factor binding protein-3. Pharmacologic inhibition or genetic deficiency of PAI-1 was shown to be protective against senescence and the aging-like phenotypes in kl/kl and N(ω)-nitro-l-arginine methyl ester-treated wild-type mice. Further investigation into PAI-1's role in senescence and aging will likely contribute to the prevention and treatment of aging-related pathologies.

Integrative analysis of ocular complications in atherosclerosis unveils pathway convergence and crosstalk

Atherosclerosis is a life-threatening disease and a major cause of mortalities worldwide. While many of the atherosclerotic sequelae are reflected as microvascular effects in the eye, the molecular mechanisms of their development is not yet known. In this study, we employed a systems biology approach to unveil the most significant events and key molecular mediators of ophthalmic sequelae caused by atherosclerosis. Literature mining was used to identify the proteins involved in both atherosclerosis and ophthalmic diseases. A protein-protein interaction (PPI) network was prepared using the literature-mined seed nodes. Network topological analysis was carried out using Cytoscape, while network nodes were annotated using database for annotation, visualization and integrated discovery in order to identify the most enriched pathways and processes. Network analysis revealed that mitogen-activated protein kinase 1 (MAPK1) and protein kinase C occur with highest betweenness centrality, degree and closeness centrality, thus reflecting their functional importance to the network. Our analysis shows that atherosclerosis-associated ophthalmic complications are caused by the convergence of neurotrophin signaling pathways, multiple immune response pathways and focal adhesion pathway on the MAPK signaling pathway. The PPI network shares features with vasoregression, a process underlying multiple vascular eye diseases. Our study presents a first clear and composite picture of the components and crosstalk of the main pathways of atherosclerosis-induced ocular diseases. The hub bottleneck nodes highlight the presence of molecules important for mediating the ophthalmic complications of atherosclerosis and contain five established drug targets for future therapeutic modulation efforts.

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.

Urokinase plasminogen activator gene deficiency inhibits fracture cartilage remodeling

Urokinase plasminogen activator (uPA) regulates a proteolytic cascade of extracellular matrix degradation that functions in tissue development and tissue repair. The development and remodeling of the skeletal extracellular matrix during wound healing suggests that uPA might regulate bone development and repair. To determine whether uPA functions regulate bone development and repair, we examined the basal skeletal phenotype and endochondral bone fracture repair in uPA-deficient mice. The skeletal phenotype of uPA knockout mice was compared with that of control mice under basal conditions by dual-energy X-ray absorptiometry and micro-CT analysis, and during femur fracture repair by micro-CT and histological examination of the fracture callus. No effects of uPA gene deficiency were observed in the basal skeletal phenotype of the whole body or the femur. However, uPA gene deficiency resulted in increased fracture callus cartilage abundance during femur fracture repair at 14 days healing. The increase in cartilage corresponded to reduced tartrate-resistant acid phosphatase (TRAP) staining for osteoclasts in the uPA knockout fracture callus at this time, consistent with impaired osteoclast-mediated remodeling of the fracture cartilage. CD31 staining was reduced in the knockout fracture tissues at this time, suggesting that angiogenesis was also reduced. Osteoclasts also colocalized with CD31 expression in the endothelial cells of the fracture tissues during callus remodeling. These results indicate that uPA promotes remodeling of the fracture cartilage by osteoclasts that are associated with angiogenesis and suggest that uPA promotes angiogenesis and remodeling of the fracture cartilage at this time of bone fracture repair.

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.

Plasminogen activator inhibitor-1 inhibitors: a patent review (2006-present)

INTRODUCTION

Plasminogen activator inhibitor-1 (PAI-1), the serine protease inhibitor (serpin), binds to and inhibits the plasminogen activators-tissue-type plasminogen activator (tPA) and the urokinase-type plasminogen activator (uPA). This results in both a decrease in plasmin production and a decrease in the dissolution of fibrin clots. Elevated levels of PAI-1 are correlated with an increased risk for cardiovascular disease and have been linked to obesity and metabolic syndrome. Consequently, the pharmacological suppression of PAI-1 might prevent or treat vascular disease.

AREAS COVERED

This article provides an overview of the patenting activity on PAI-1 inhibitors. Patents filed by pharmaceutical companies or individual research groups are described, and the biological and biochemical evaluation of the inhibitors, including in vitro and in vivo studies, is discussed. An overview of patents pertaining to using these inhibitors for treating various diseases is also included.

EXPERT OPINION

Although there is still no PAI-1 inhibitor being evaluated in a clinical setting or approved for human therapy, research in this field has progressed, and promising new compounds have been designed. Most research has focused on improving the pharmacological profile of these compounds, which will hopefully allow them to proceed to clinical studies. Despite the need for further testing and research, the potential use of PAI-1 inhibitors for treating cardiovascular disease appears quite promising.

Inflammation in atherosclerosis: a cause or a result of vascular disorders?

Sound data support the concept that in atherosclerosis, inflammation and dyslipidemia intersect each other and that irrespective of the initiator, both participate from the early stages to the ultimate fate of the atheromatous plaque. The two partakers manoeuvre a vicious circle in atheroma formation: dyslipidaemia triggers an inflammatory process and inflammation elicits dyslipidaemia. Independent of the initial cause, the atherosclerotic lesions occur focally, in particular arterial-susceptible sites, by a process that, although continuous, can be arbitrarily divided into a sequence of consecutive stages that lead from fatty streak to the fibro-lipid plaque and ultimately to plaque rupture and thrombosis. In the process, the initial event is a change in endothelial cells (EC) constitutive properties. Then, the molecular alarm signals send by dysfunctional EC are decoded by specific blood immune cells (monocytes, T lymphocytes, neutrophils, mast cells) and by the resident vascular cells, that respond by initiating a robust inflammatory process, in which the cells and the factors they secrete hasten the atheroma development. Direct and indirect crosstalk between the cells housed within the nascent plaque, complemented by the increase in risk factors of atherosclerosis lead to atheroma development and outcome. The initial inflammatory response can be regarded as a defense/protective reaction mechanism, but its further amplification, speeds up atherosclerosis. In this review, we provide an overview on the role of inflammation and dyslipidaemia and their intersection in atherogenesis. The data may add to the foundation of a novel attitude in the diagnosis and treatment of atherosclerosis.

Analysis of stromal cell secretomes reveals a critical role for stromal cell-derived hepatocyte growth factor and fibronectin in angiogenesis

OBJECTIVE

Angiogenesis requires tightly coordinated crosstalk between endothelial cells (ECs) and stromal cells, such as fibroblasts and smooth muscle cells. The specific molecular mechanisms moderating this process are still poorly understood.

METHODS AND RESULTS

Stromal cell-derived factors are essential for EC sprouting and lumen formation. We therefore compared the abilities of 2 primary fibroblast isolates and a primary smooth muscle cell isolate to promote in vitro angiogenesis, and analyzed their secretomes using a combination of nano liquid chromatography-mass spectrometry/mass spectrometry, quantitative PCR, and ELISA. Each isolate exhibited a different level of angiogenic ability. Using quantitative MS, we then compared the secretomes of a fibroblast isolate exhibiting low angiogenic activity, a fibroblast isolate exhibiting high angiogenic activity, and human umbilical vein ECs. High angiogenic fibroblast supernatants exhibited an overabundance of proteins associated with extracellular matrix constituents compared with low angiogenic fibroblasts or ECs. Finally, small interfering RNA technology and purified protein were used to confirm a role for stromal cell-derived hepatocyte growth factor and fibronectin in inducing EC sprouting.

CONCLUSIONS

Differences in stromal cell ability to induce angiogenesis are a result of differences in the secreted proteomes of both extracellular matrix proteins and proangiogenic growth factors.

Soluble urokinase plasminogen activator receptor is associated with inflammation in the vulnerable human atherosclerotic plaque

BACKGROUND AND PURPOSE

Recently, plasma soluble urokinase plasminogen activator receptor (suPAR) has gained interest as a marker of cardiovascular risk. suPAR is released through the cleavage of urokinase plasminogen activator receptor (uPAR), which is found in monocytes, activated T-lymphocytes and endothelial cells, all involved in atherosclerosis. suPAR levels have been well studied in plasma, but no studies have focused on suPAR in human atherosclerotic plaques. The aim of this study was to determine whether suPAR measured in the plaque is associated with symptomatic plaques and plaque inflammation.

METHODS

Plasma and carotid plaques from 162 patients were analyzed. Lipids, collagen, uPAR, and macrophages were measured histologically. Cytokines and suPAR were measured in homogenized plaque extracts using multiplex immunoassay and ELISA, respectively. Plasma levels of suPAR were analysed with ELISA. CD3, CD4, as well as uPAR mRNA expression were assessed with quantitative real-time polymerase chain reaction in plaque homogenates from 123 patients.

RESULTS

Plaque and plasma suPAR levels were higher in symptomatic patients compared with asymptomatic patients. Plaque suPAR levels correlated with plaque content of lipids and macrophages and with proinflammatory chemokines and cytokines monocyte chemoattractant protein 1, tumor necrosis factor α, interleukin 1β, interleukin 6, platelet-derived growth factor AB/BB, monocyte inflammatory protein 1β, regulated on activation normal T-cell expressed and secreted, and s-CD40L. uPAR mRNA and histological staining for uPAR correlated with plaque content of suPAR.

CONCLUSIONS

This study shows that suPAR in human carotid plaques and plasma is associated with the presence of symptoms and that plaque suPAR is associated with the vulnerable inflammatory plaque. These findings strengthen the hypothesis of suPAR as a future marker of vulnerable atherosclerotic plaques.

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.

Overexpression of urokinase by plaque macrophages causes histological features of plaque rupture and increases vascular matrix metalloproteinase activity in aged apolipoprotein e-null mice

BACKGROUND

The mechanisms of atherosclerotic plaque rupture are poorly understood. Urokinase-type plasminogen activator (uPA) is expressed at elevated levels by macrophages in advanced human plaques. Patients with evidence of increased plasminogen activation have an elevated risk of major cardiovascular events. We used atherosclerotic mice to test the hypothesis that increased macrophage uPA expression in advanced plaques would cause histological features similar to those in ruptured human plaques.

METHODS AND RESULTS

Bone marrow from transgenic mice with increased macrophage uPA expression or nontransgenic controls (all apolipoprotein E-null [Apoe(-/-)]) was transplanted into 35-week-old Apoe(-/-) recipients, and innominate lesions and aortas were examined 8 to 13 weeks later. Donor macrophages accumulated in innominate lesions adjacent to plaque caps and in aortas, increasing uPA expression at both sites. Recipients of uPA-overexpressing macrophages had an increased prevalence of intraplaque hemorrhage (61% versus 13%; P=0.002) as well as increased lesion fibrin staining and fibrous cap disruption (P=0.06 for both). Transplantation of uPA-overexpressing macrophages increased aortic matrix metalloproteinase activity (40%; P=0.02). This increase was independent of matrix metalloproteinase-9.

CONCLUSIONS

In advanced plaques of Apoe(-/-) mice, macrophage uPA overexpression causes intraplaque hemorrhage and fibrous cap disruption, features associated with human plaque rupture. uPA overexpression also increases vascular matrix metalloproteinase activity. These data provide a mechanism that connects macrophage uPA expression, matrix metalloproteinase activity, and plaque rupture features in mice. The data also suggest that elevated plaque plasminogen activator expression and plasminogen activation in humans may be causally linked to plaque rupture and cardiovascular events.

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.

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.

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.

The effect of urban air pollution on inflammation, oxidative stress, coagulation, and autonomic dysfunction in young adults

RATIONALE

The biological mechanisms linking air pollution to cardiovascular events still remain largely unclear.

OBJECTIVES

To investigate whether biological mechanisms linking air pollution to cardiovascular events occurred concurrently in human subjects exposed to urban air pollutants.

METHODS

We recruited a panel of 76 young, healthy students from a university in Taipei. Between April and June of 2004 or 2005, three measurements were made in each participant of high-sensitivity C-reactive protein (hs-CRP), 8-hydroxy-2'-deoxyguanosine (8-OHdG), plasminogen activator fibrinogen inhibitor-1 (PAI-1), tissue-type plasminogen activator (tPA) in plasma, and heart rate variability (HRV). Gaseous air pollutants were measured at one air-monitoring station inside their campus, and particulate air pollutants were measured at one particulate matter supersite monitoring station 1 km from their campus. We used linear mixed-effects models to associate biological endpoints with individual air pollutants averaged over 1- to 3-day periods before measurements were performed.

MEASUREMENTS AND MAIN RESULTS

We found that increases in hs-CRP, 8-OHdG, fibrinogen, and PAI-1, and decreases in HRV indices were associated with increases in levels of particles with aerodynamic diameters less than 10 microm and 2.5 microm, sulfate, nitrate, and ozone (O(3)) in single-pollutant models. The increase in 8-OHdG, fibrinogen, and PAI-1, and the reduction in HRV remained significantly associated with 3-day averaged sulfate and O(3) levels in two-pollutant models. There were moderate correlations (r = -0.3) between blood markers of hs-CRP, fibrinogen, PAI-1, and HRV indices.

CONCLUSIONS

Urban air pollution is associated with inflammation, oxidative stress, blood coagulation and autonomic dysfunction simultaneously in healthy young humans, with sulfate and O(3) as two major traffic-related pollutants contributing to such effects.

Proteinase systems and thoracic aortic aneurysm progression

Thoracic aortic aneurysms (TAAs) are a rare but potentially devastating condition. Current surgical treatment of TAAs usually involves a major operation, which conveys many risks to the patient. Better knowledge of the cellular events that lead to aneurysm formation may elucidate less morbid treatment options for this condition. A number of recent studies have identified that the relative abundance and activity of extracellular matrix (ECM) proteolytic systems are increased with TAAs. Specifically, the matrix metalloproteinases (MMPs) have been linked through numerous studies to TAA formation. MMPs comprise a family of ECM-degrading proteinases. Endogenous tissue inhibitors (TIMPs) normally regulate MMP activity, and the activation of MMPs is complex and tightly controlled. Aneurysm formation may be related to relative changes in the balance between MMP/TIMP abundance favoring proteolysis. Through ECM degradation, the medial layer will undergo structural remodeling and a loss of structural integrity, leading to TAA formation. The goals of this review are to examine the structure of the normal and aneurysmal thoracic aorta and to place the new findings regarding ECM proteolysis in perspective with regard to TAA formation and progression. Through an integration of basic and clinical studies regarding the underlying molecular basis for proteolysis of the thoracic aorta, improved diagnostic, prognostic, and therapeutic strategies for this disease process are likely to be realized.

Elevated Plasma Plasminogen Activator Inhibitor Type-1 is an Independent Predictor of Coronary Microvascular Dysfunction in Hypertension

BACKGROUND

Elevated plasma plasminogen activator inhibitor-1 (PAI-1) is related to cardiovascular events, but its role in subclinical coronary microvascular dysfunction remains unknown. Thus, in the present study it was investigated whether elevated plasma PAI-1 activity is associated with coronary microvascular dysfunction in hypertensive patients.

METHODS AND RESULTS

Thirty patients with untreated essential hypertension and 10 age-matched healthy controls were studied prospectively. Myocardial blood flow (MBF) was measured by using (15)O-water positron emission tomography. Clinical variables associated with atherosclerosis (low-density lipoprotein-cholesterol, high-density lipoprotein (HDL)-cholesterol, triglyceride, homeostasis model assessment (HOMA-IR), and PAI-1 activity) were assessed to determine their involvement in coronary microvascular dysfunction. Adenosine triphosphate (ATP)-induced hyperemic MBF and coronary flow reserve (CFR) were significantly lower in hypertensive patients than in healthy controls (ATP-induced MBF: 2.77+/-0.82 vs 3.49+/-0.71 ml x g(-1) x min(-1); p<0.02 and CFR: 2.95 +/-1.06 vs 4.25+/-0.69; p<0.001). By univariate analysis, CFR was positively correlated with HDL-cholesterol (r=0.46, p<0.02), and inversely with HOMA-IR (r=-0.39, p<0.05) and PAI-1 activity (r=-0.61, p<0.001). By multivariate analysis, elevated PAI-1 activity remained a significant independent determinant of diminished CFR.

CONCLUSIONS

Elevated plasma PAI-1 activity was independently associated with coronary microvascular dysfunction, which suggests that plasma PAI-1 activity is an important clue linking hypofibrinolysis to the development of atherosclerosis.

The plasminogen activator system modulates sympathetic nerve function

Sympathetic neurons synthesize and release tissue plasminogen activator (t-PA). We investigated whether t-PA modulates sympathetic activity. t-PA inhibition markedly reduced contraction of the guinea pig vas deferens to electrical field stimulation (EFS) and norepinephrine (NE) exocytosis from cardiac synaptosomes. Recombinant t-PA (rt-PA) induced exocytotic and carrier-mediated NE release from cardiac synaptosomes and cultured neuroblastoma cells; this was a plasmin-independent effect but was potentiated by a fibrinogen cleavage product. Notably, hearts from t-PA–null mice released much less NE upon EFS than their wild-type (WT) controls (i.e., a 76.5% decrease; P < 0.01), whereas hearts from plasminogen activator inhibitor-1 (PAI-1)–null mice released much more NE (i.e., a 275% increase; P < 0.05). Furthermore, vasa deferentia from t-PA–null mice were hyporesponsive to EFS (P < 0.0001) but were normalized by the addition of rt-PA. In contrast, vasa from PAI-1–null mice were much more responsive (P < 0.05). Coronary NE overflow from hearts subjected to ischemia/reperfusion was much smaller in t-PA–null than in WT control mice (P < 0.01). Furthermore, reperfusion arrhythmias were significantly reduced (P < 0.05) in t-PA–null hearts. Thus, t-PA enhances NE release from sympathetic nerves and contributes to cardiac arrhythmias in ischemia/reperfusion. Because the risk of arrhythmias and sudden cardiac death is increased in hyperadrenergic conditions, targeting the NE-releasing effect of t-PA may have valuable therapeutic potential.

The complement component C5a induces the expression of plasminogen activator inhibitor-1 in human macrophages via NF-kappaB activation

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.

Topology of protease activities reflects atherothrombotic plaque complexity

The pathological remodeling of the arterial wall in atherosclerosis involves protease activities, which play a major role in complications, through plaque rupture. Here, we investigated the release of active proteases by human carotid plaques in relation to (1) the degree of lesion complexity and (2) their compartmentalization between cap, core and media. Eighty human carotid endarterectomy specimens were dissected into culprit stenosing (CPs) and adjacent non-complicated/non-stenosing plaques (NPs). Thirty-five additional CPs were microdissected into cap, core and media. All specimens were compared to control non-atherosclerotic endarteries for the release of components of the plasminogen/plasmin system and matrix metalloproteinases (MMPs). Results show a greater release of the plasminogen activators (PAs), plasmin and active MMPs by CPs compared to NPs, whereas healthy arteries released even lower levels. Furthermore, we highlight a functional interaction between these proteases in human atherosclerotic tissues and more importantly, we demonstrate that the core constitutes the main source of protease activities within CPs. Together, these results suggest that CPs generate plasmin, mainly in the core, which could in turn participate in MMP activation and the onset of complications.

Vascular and fibrinolytic effects of intra-arterial tumour necrosis factor-alpha in patients with coronary heart disease

Elevated plasma t-PA (tissue plasminogen activator) and serum CRP (C-reactive protein) concentrations are associated with an adverse cardiovascular risk. In the present study, we investigated whether acute local inflammation causes vascular dysfunction and influences t-PA release in patients with stable coronary heart disease. Serum CRP, plasma t-PA and PAI-1 (plasminogen activator inhibitor type 1) concentrations were determined in 95 patients with stable coronary heart disease. A representative subpopulation of 12 male patients received an intra-brachial infusion of TNF-alpha (tumour necrosis factor-alpha) and saline placebo using a randomized double-blind cross-over study design. Forearm blood flow and plasma fibrinolytic and inflammatory variables were measured. Serum CRP concentrations correlated with plasma t-PA concentrations (r=0.37, P<0.001) and t-PA/PAI-1 ratio (r=-0.21, P<0.05). Intra-arterial TNF-alpha caused a rise in t-PA concentrations (P<0.001) without affecting blood flow or PAI-1 concentrations. TNF-alpha pretreatment impaired acetylcholine- and sodium nitroprusside-induced vasodilatation (P<0.001 for both) whilst doubling bradykinin-induced t-PA release (P=0.006). In patients with stable coronary heart disease, plasma fibrinolytic factors correlate with a systemic inflammatory marker and local vascular inflammation directly impairs vasomotor function whilst enhancing endothelial t-PA release. We suggest that the adverse prognosis associated with elevated plasma t-PA concentrations relates to the underlying causative association with vascular inflammation and injury.

Plasminogen activation: a mediator of vascular smooth muscle cell apoptosis in atherosclerotic plaques

BACKGROUND

Apoptosis of vascular cells is considered to be a major determinant of atherosclerotic plaque vulnerability and potential rupture. Plasmin can be generated in atherosclerotic plaques and recent in vitro data suggest that plasminogen activation may trigger vascular smooth muscle cell (VSMC) apoptosis.

AIM

To determine whether plasminogen activation may induce aortic VSMC apoptosis ex vivo and in vivo.

METHODS AND RESULTS

Mice with single or combined deficiencies of apolipoprotein E (ApoE) and plasminogen activator inhibitor-1 (PAI-1) were used. Ex vivo incubation with plasminogen of isolated aortic tunica media from PAI-1-deficient mice induced plasminogen activation and VSMC apoptosis, which was inhibited by alpha2-antiplasmin. In vivo, levels of plasmin, active caspase 3 and VSMC apoptotic index were significantly higher in atherosclerotic aortas from mice with combined ApoE and PAI-1 deficiencies than in those from littermates with single ApoE deficiency. A parallel decrease in VSMC density was observed.

CONCLUSIONS

These data strongly suggest that plasminogen activation may contribute to VSMC apoptosis in atherosclerotic plaques.

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.

Arterial Wall Response to ex vivo Exposure to Oscillatory Shear Stress

BACKGROUND

The aim of this study was to analyze the arterial wall response to plaque-prone hemodynamic environments, known to occur mainly in areas of arterial trees such as bifurcations and branching points. In these areas, the vasculature is exposed to cyclically reversing flow that induces an endothelial dysfunction predisposing thus arteries to local development of atherosclerotic plaques.

METHODS

We used an ex vivo perfusion system that allows culturing arterial segments under different hemodynamic conditions. Porcine carotid arteries were exposed for 3 days to unidirectional high and low shear stress (6 +/- 3 and 0.3 +/- 0.1 dyn/cm(2)) as well as to oscillatory shear stress (0.3 +/- 3 dyn/cm(2)). This latter condition mimics the hemodynamics present at plaque-prone areas. At the end of the perfusion, the influence of different flow patterns on arterial metabolism was assessed in terms of matrix turnover as well as of smooth muscle cell function, differentiation and migration.

RESULTS

Our results show that after 3 days of perfusion none of the applied conditions influence smooth muscle cell phenotype retaining their full contraction capacity. However, an increase in the expression level of matrix metalloproteinase-2 and -9, as well as a decrease in plasminogen activator inhibitor-1 expression were observed in arteries exposed to oscillatory shear stress when compared to arteries exposed to unidirectional shear stress.

CONCLUSION

These observations suggest that plaque-prone hemodynamic environment triggers a vascular wall remodelling process and promotes changes in arterial wall metabolism, with important implication in atherogenesis.

Alteplase treatment affects circulating matrix metalloproteinase concentrations in patients with ST segment elevation acute myocardial infarction

INTRODUCTION

Matrix metalloproteinases (MMPs) are expressed in atherosclerotic plaques. Acute coronary syndromes may be precipitated by MMPs through degradation of the fibrous cap and subsequent plaque disruption. Serine proteases such as plasmin activate MMPs and may contribute to plaque events. Thrombolysis with recombinant tissue plasminogen activator (rtPA) is widely used for treatment of acute ST segment elevation myocardial infarction (STEMI). In the present study we assessed whether thrombolytic therapy with rtPA in patients with STEMI influences serum levels of MMP-2 and MMP-9.

METHODS

We recruited 108 patients (92 men, mean age 64 +/- 12 years) with STEMI, of whom 84 (78%) received thrombolytic treatment with rtPA and 24 (22%) did not. MMP-2 and MMP-9 levels were assessed at hospital admission (baseline), and at 24 and 72 h after admission, using a commercially available ELISA.

RESULTS

Overall, MMP-9 levels were higher in the thrombolysis group compared to patients without thrombolysis (p < 0.001). Thrombolysis treatment significantly affected the change in MMP-9 levels during the 72-h study period (p < 0.001).

CONCLUSIONS

The present study showed that thrombolysis could affect circulating levels of MMP-9 in STEMI patients. Whether this effect may lead to plaque instability deserves further investigation.

Immunization with plasmid DNA encoding a truncated, secreted form of the bovine viral diarrhea virus E2 protein elicits strong humoral and cellular immune responses

The major protective antigen of bovine viral diarrhea virus (BVDV), the E2 protein, is cell-associated and not expressed on the cell surface. In this study we evaluated a DNA vaccine encoding various secreted versions of E2. In vitro analysis demonstrated that deletion of the transmembrane anchor and addition of the signal sequence of bovine herpesvirus-1 (BHV-1) (gDsDeltaE2) resulted in efficient secretion of E2 into the culture medium. In contrast, full-length E2, either without or with gDs (gDsE2), as well as truncated E2 without gDs (DeltaE2), remained entirely cell-associated. Mice immunized with plasmid encoding gDsDeltaE2 developed significantly higher IgG and virus neutralizing antibody titres compared to animals vaccinated with plasmid encoding E2, DeltaE2 or gDsE2. To optimize secretion of E2, the efficiency of gDs was compared with that of the tissue plasminogen activator signal (tPAs) sequence. In addition, the effect of the plasmid backbone was assessed by comparing two vectors. Four plasmids, pMASIA-gDsDeltaE2, pMASIA-tPAsDeltaE2, pSLKIA-gDsDeltaE2 and pSLKIA-tPAsDeltaE2, were constructed and administered intradermally to mice. The mice immunized with pMASIA-tPAsDeltaE2 developed the strongest and most balanced immune responses. Vaccination of cattle confirmed that pMASIA-tPAsDeltaE2 elicited both strong humoral and cellular immune responses and thus could be a candidate DNA vaccine against BVDV.

Metalloproteinases in Development and Progression of Vascular Disease

Remodeling of the vascular wall plays a role in many physiological processes, but also in the pathogenesis of major cardiovascular diseases such as restenosis and atherosclerosis. Remodeling requires proteolytic activity to degrade components of the extracellular matrix; this can be generated by the matrix metalloproteinase(MMP) system alone or in concert with the fibrinolytic (plasminogen/plasmin) system. Several lines of evidence suggest that the MMP system plays a role in vascular smooth muscle cell migration and neointima formation after vascular injury. In atherosclerotic lesions, active MMPs may contribute to plaque destabilisation by degrading extracellular matrix components, but may also promote aneurysm formation by proteolytic degradation of the elastic lamina. The MMP system may therefore represent a potential therapeutic target for treatment of restenosis or atherosclerosis.

Modulation of smooth muscle cell proliferation and migration: role of smooth muscle cell heterogeneity

Proliferation and migration of smooth muscle cells (SMCs) from the media towards the intima are key events in atherosclerosis and restenosis. During these processes, SMC undergo phenotypic modulations leading to SMC dedifferentiation. The identification and characterization of factors controlling these phenotypic changes are crucial in order to prevent the formation of intimal thickening. One of the questions which presently remains open, is to know whether any SMCs of the media are capable of accumulating into the intima or whether only a predisposed medial SMC subpopulation is involved in this process. The latter hypothesis implies that arterial SMCs are phenotypically heterogenous. In this chapter, we will describe the distinct SMC phenotypes identified in arteries of various species, including humans. Their role in the formation of intimal thickening will be discussed.

Pleiotropic functions of plasminogen activator inhibitor-1

Plasminogen activator inhibitor-1 (PAI-1), a 45-kDa serine proteinase inhibitor with reactive site peptide bond Arg345-Met346, is the main physiological plasminogen activator inhibitor. It occurs in human plasma at an antigen concentration of about 20 ng mL(-1). Besides the active inhibitory form of PAI-1 that spontaneously converts to a latent form, also a substrate form exists that is cleaved at the P1-P1' site by its target enzymes, but does not form stable complexes. Besides its role in regulating hemostasis, PAI-1 plays a role in several biological processes dependent on plasminogen activator or plasmin activity. Studies with transgenic mice have revealed a functional role for PAI-1 in wound healing, atherosclerosis, metabolic disturbances such as obesity and insulin resistance, tumor angiogenesis, chronic stress, bone remodeling, asthma, rheumatoid arthritis, fibrosis, glomerulonephritis and sepsis. It is not always clear if these functions depend on the antiproteolytic activity of PAI-1, on its binding to vitronectin or on its intereference with cellular migration or matrix binding.

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.

Interrelationships between the fibrinolytic system and lipoproteins in the pathogenesis of coronary atherosclerosis

The fibrinolytic system is comprised of a series of serine proteases and serine protease inhibitors which are involved in the dissolution of fibrin in the vascular lumen, but also in the migration of cells and in the remodeling of the extracellular matrix of the vascular wall. The transcription, expression and degradation of the various fibrinolytic enzymes by cells in the vascular wall is influenced by lipoproteins and this interrelationship may play a significant role in the development of the atherosclerotic plaque: the transcription of plasminogen activator inhibitor-1 is influenced by very low-density lipoproteins, the expression of both tissue plasminogen activator and plasminogen activator inhibitor-1 is influenced by low-density lipoproteins and lipoprotein(a) (Lp(a)) and the internalization of the urokinase: plasminogen activator inhibitor-1 complex occurs via the low-density lipoprotein related protein. Several clinical studies have shown correlations between fibrinolytic parameters and lipoproteins in healthy populations and in patients with dyslipidemia, but the correlation between single plasma fibrinolytic enzymes and the severity of coronary atherosclerosis is less well documented. The reduction of plasma lipids with lipid-lowering drugs also affects the concentration of fibrinolytic enzymes, although this may also be due to direct effects of the drugs on the expression of the various fibrinolytic enzymes. The reduction of fibrinolytic and proteolytic activity in the atherosclerotic plaque by their lipid-lowering effect and by their direct action on the fibrinolytic system may be one of the mechanisms by which some lipid-lowering drugs achieve plaque stabilization.