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

suPAR as a biomarker of support in different clinical settings

The urokinase-type plasminogen activator receptor (uPAR) system, which includes protease, receptor and inhibitors, is essential for key cellular functions like immune activation, cell migration, and tissue remodeling. Soluble uPAR (suPAR), released into circulation, serves as a valuable biomarker for systemic inflammation and immune activation. Elevated suPAR levels are associated with disease severity in conditions such as infections, sepsis, cardiovascular diseases, renal injury, cancer, and autoimmune diseases providing prognostic value especially in acute settings. Recent advancements in diagnostic methods, have enhanced the accuracy of suPAR measurement in serum and plasma. New rapid tests, such as suPARnostic Quick Triage, as well as turbidimetric assays, further expand its clinical applicability. In this review, we discuss the suPAR biomarker, focusing on its biochemical structure, biological functions, measurement methods and areas of clinical interest in different fields of medicine.

suPAR in cardiovascular disease

Soluble urokinase plasminogen activator receptor (suPAR), the soluble counterpart of urokinase plasminogen activator receptor, is found in the circulation at various levels. suPAR and its parent molecule, cell surface uPAR, exhibit similar structure and extracellular functional roles facilitating fibrinolysis, cellular adhesion, and migration. Studies have assessed the correlation between suPAR in cardiovascular disease (CVD). It is postulated that suPAR may serve as an indicator of inflammatory activation and burden during CVD progression. Increased suPAR independently predicts poorer outcomes in acute coronary syndromes, in heart failure, as well as in coronary artery disease and atherosclerosis. To guide translation into clinical utization, suPAR has been assessed in numerous CVD settings for improved risk discrimination independently or in association with established traditional risk factors. Whilst the involvement of suPAR has been explored in other diseases such as kidney diseases and cancer, there is only emerging evidence of suPAR's mechanistic involvement in cardiovascular disease. In this review, we provide a background into suPAR and its potential role as a biomarker in CVD.

Prospective Cohort Study of Soluble Urokinase Plasminogen Activation Receptor and Cardiovascular Events in Patients With CKD

Introduction

Soluble urokinase plasminogen activation receptor (suPAR) is an immune-derived pathogenic factor for kidney and atherosclerotic disease. Whether the association between suPAR and cardiovascular (CV) outcomes is dependent on the severity of underlying kidney disease is unclear.

Methods

We measured serum suPAR levels in 4994 participants (mean age 60 years; 60% men; 36% with diabetes mellitus; mean estimated glomerular filtration rate (eGFR) 49 ml/min per 1.73 m2, SD 18) of the German Chronic Kidney Disease (GCKD) cohort and examined its association with all-cause death, CV death, and major CV events (MACE) across the range of eGFR and urine albumin-to-creatinine ratio (UACR).

Results

The median suPAR level was 1771 pg/ml (interquartile range [IQR] 1447-2254 pg/ml). SuPAR levels were positively and independently correlated with age, eGFR, UACR, and parathyroid hormone levels. There were 573 deaths, including 190 CV deaths and 683 MACE events at a follow-up time of 6.5 years. In multivariable analyses, suPAR levels (log2) were associated with all-cause death (hazard ratio [HR] 1.36, 95% confidence interval [CI] 1.21-1.53), CV death (HR 1.27, 95% CI 1.03-1.57), and MACE (HR 1.13, 95% CI 1.00-1.28), and were not found to differ according to diabetes mellitus status, baseline eGFR, UACR, or parathyroid hormone levels. In mediation analysis, suPAR's direct effect on all-cause death, CV death, and MACE accounted for 77%, 67%, and 60% of the total effect, respectively; whereas the effect mediated through eGFR accounted for 23%, 34%, and 40%, respectively.

Conclusion

In a large cohort of individuals with chronic kidney disease (CKD), suPAR levels were associated with mortality and CV outcomes independently of indices of kidney function, consistent with its independent role in the pathogenesis of atherosclerosis.

Comprehensive analysis of atherosclerotic plaques reveals crucial genes and molecular mechanisms associated with plaque progression and rupture

Background

Plaque rupture and acute atherothrombosis, resulting from continued progression of atherosclerotic plaques (APs), are major contributors to acute clinical events such as stroke or myocardial infarction. This article aimed to explore the gene signatures and potential molecular mechanisms in the progression and instability of APs and to identify novel biomarkers and interventional targets for AP rupture.

Methods

The microarray data were downloaded from the Gene Expression Omnibus (GEO) database and grouped into discovery and validation cohorts. In the discovery cohort, Weighted Gene Co-Expression Network Analysis was performed for finding co-expression modules, and the Metascape database was used to perform functional enrichment analysis. Differential Expression Genes analysis subsequently was performed in the validation cohort for verification of the obtained results. Common genes were introduced into Metascape database for protein–protein interaction and functional enrichment analysis. We constructed the miRNAs–mRNAs network with the hub genes. Moreover, gene expression profiles of peripheral blood mononuclear cells (PBMCs) from peripheral blood of patients with plaque rupture were analyzed by high-throughput sequencing, and the diagnostic power of hub genes was verified by receiver operating characteristic (ROC) analysis.

Results

In the discovery cohort, the brown module in GSE28829 and the turquoise module in GSE163154 were the most significant co-expression modules. Functional enrichment analysis of shared genes suggested that “Neutrophil degranulation” was the most significantly enriched pathway. These conclusions were also demonstrated by the validation cohort. A total of 16 hub genes were identified. The miRNA–mRNA network revealed that hsa-miR-665 and hsa-miR-512-3p might regulate the “Neutrophil degranulation” pathway through PLAU and SIRPA, which might play a significant role in AP progression and instability. Five hub genes, including PLAUR, FCER1G, PLAU, ITGB2, and SLC2A5, showed significantly increased expression in PBMCs from patients with plaque rupture compared with controls. ROC analysis finally identified three hub genes PLAUR, FCER1G, and PLAU that could effectively distinguish patients with APs rupture from controls.

Conclusions

The present study demonstrated that the “neutrophil degranulation” signaling pathways and identified novel mRNA and miRNA candidates are closely associated with plaque progression and instability. The hub genes FCER1G, PLAUR, and PLAU may serve as biomarkers for the prospective prediction of AP rupture.

Exogenous Urokinase Inhibits Proteasomal Degradation of Its Cognate Urokinase Plasminogen Activator Receptor

Acute pulmonary embolism (APE) is a debilitating condition with high incidence and mortality rates. APE is widely treated with the serine protease urokinase or urokinase-type plasminogen activator (uPA) that functions by resolving blood clots via catalyzing the conversion of plasminogen to plasmin. Treatment with recombinant uPA has been shown to increase endogenous expression of uPA and its cognate receptor, uPAR; however, the mechanisms for this induction are not known. Using an in vitro hypoxia/reoxygenation model in bronchial epithelial BEAS-2B cells, we show that induction of hypoxia/reoxygenation induces apoptosis and increases secretion of tumor necrosis factor–alpha, brain natriuretic peptide, and fractalkine, which are attenuated when treated with exogenous uPA. Induction of hypoxia/reoxygenation resulted in decreased expression of uPAR on cell surface without any significant changes in its messenger RNA expression, highlighting post-transcriptional regulatory mechanisms. Determination of uPAR protein half-life using cycloheximide showed treatment with uPA significantly increased its half-life (209.6 ± 0.2 min from 48.2 ± 2.3 min). Hypoxia/reoxygenation promoted the degradation of uPAR. Inhibition of proteasome-mediated degradation using MG-132 and lactacystin revealed that uPAR was actively degraded when hypoxia/reoxygenation was induced and that it was reversed when treated with exogenous uPA. Determination of the proteolytic activity of 20S proteasome showed a global increase in ubiquitin–proteasome activation without an increase in proteasome content in cells subjected to hypoxia/reoxygenation. Our results cumulatively reveal that uPAR is actively degraded following hypoxia/reoxygenation, and the degradation was significantly weakened by exogenous uPA treatment. Given the importance of the uPA/uPAR axis in a multitude of pathophysiological contexts, these findings provide important yet undefined mechanistic insights.

Discovery of a novel inhibitor against urokinase-type plasminogen activator, a potential enzyme with a role in atherosclerotic plaque instability

The buildup of lipids, cholesterol, and other substances in and on the walls of the arteries is known as atherosclerosis and deposition is known as atherosclerotic plaque. Urokinase-type plasminogen activator (uPA) has multiple roles in the atherosclerotic plaque formation and even work simultaneously in making the atherosclerotic plaque unstable. Extracellular matrix plays a major role in the plaque remodeling and rapture. In this study, we have accessed that a higher interaction was observed in the molecular interaction score for uPA with ZINC380065722 having a GOLD fitness score of about 67.60, which is much higher as compared to the known standard inhibitor UK 122 which has reported an interaction score of 59.14. Ser217 and Asp192 are found to be the key amino acid residues in almost all the interactions. Protein frustration analysis has shown that these amino acid residues play a crucial role in the retention of the active pocket conformation and any mutation of these two residues can causes serious decrease in the overall function of the protein. It was observed that the molecule ZINC380065722 remained bound to the protein till 100 ns of simulation time. The average SASA for the apo-uPA and uPA-ligand complex was found to be stable. The network of hydrogen bonds for the intramolecular protein secondary structure and with the solvent system for the apo-protein and the uPA-ligand complex was found to be consistent.Communicated by Ramaswamy H. Sarma.

Soluble urokinase-type plasminogen activator receptor predicts peripheral artery disease severity and outcomes

Soluble urokinase-type plasminogen activator receptor (suPAR) is associated with chronic kidney disease (CKD) severity and peripheral artery disease (PAD). We hypothesize an association of PAD severity and suPAR in patients without advanced CKD and further risk stratification according to the Kidney Disease: Improving Global Outcomes (KDIGO) guidelines. For study purposes, suPAR was measured in 334 PAD patients (34% women, age 69 (62-78) years, eGFR 68 ± 20 mL/min/1.72 m2) by commercial ELISA. Patients were followed for 10 years to assess long-term all-cause survival by Cox regression. Higher suPAR levels were associated with lower ankle-brachial index (R = -0.215, p = 0.001) in patients with PAD without media-sclerosis (n = 236). suPAR levels inversely correlated with decreased glomerular filtration rate (R = -0.476, p < 0.001) and directly correlated with urinary albumin-to-creatinine ratio (R = 0.207, p < 0.001). Furthermore, higher suPAR levels associated with a higher KDIGO risk score (p < 0.001). Baseline suPAR was significantly associated with all-cause mortality (HR 1.40 (95% CI 1.16-1.68), p < 0.001) over 10 years. suPAR remained associated with mortality (HR 1.29 (1.03-1.61), p = 0.026) after multivariable adjustment for age, sex, cardiovascular risk factors, and eGFR. Future research may define a standard role for suPAR assessment in PAD's work-up and treatment, especially in patients with CKD.

A critical role for plasminogen in inflammation

Plasminogen and its active form, plasmin, have diverse functions related to the inflammatory response in mammals. Due to these roles in inflammation, plasminogen has been implicated in the progression of a wide range of diseases with an inflammatory component. In this review, we discuss the functions of plasminogen in inflammatory regulation and how this system plays a role in the pathogenesis of diseases spanning organ systems throughout the body.

Molecular imaging of the urokinase plasminogen activator receptor: opportunities beyond cancer

The urokinase plasminogen activator receptor (uPAR) plays a multifaceted role in almost any process where migration of cells and tissue-remodeling is involved such as inflammation, but also in diseases as arthritis and cancer. Normally, uPAR is absent in healthy tissues. By its carefully orchestrated interaction with the protease urokinase plasminogen activator and its inhibitor (plasminogen activator inhibitor-1), uPAR localizes a cascade of proteolytic activities, enabling (patho)physiologic cell migration. Moreover, via the interaction with a broad range of cell membrane proteins, like vitronectin and various integrins, uPAR plays a significant, but not yet completely understood, role in differentiation and proliferation of cells, affecting also disease progression. The implications of these processes, either for diagnostics or therapeutics, have received much attention in oncology, but only limited beyond. Nonetheless, the role of uPAR in different diseases provides ample opportunity to exploit new applications for targeting. Especially in the fields of oncology, cardiology, rheumatology, neurology, and infectious diseases, uPAR-targeted molecular imaging could offer insights for new directions in diagnosis, surveillance, or treatment options.

Soluble urokinase plasminogen activator receptor as a long-term prognostic biomarker in acute coronary syndromes

Purpose: The aim of our study was to analyse the long-term prognostic value of soluble urokinase plasminogen activator receptor (suPAR) in the setting of an acute coronary syndrome (ACS).Methods: We included 340 patients with an ACS who underwent coronary angiography and plasma suPAR concentration was measured. Patients were classified into low suPAR concentrations (<2.6 ng/mL) and high suPAR concentrations (≥2.6 ng/mL) and long-term events were evaluated. suPAR prognostic value was assessed beyond a clinical model that included age, GRACE score, estimated glomerular filtration rate, cardiac troponin-I peak and left ventricular ejection fraction <40%.Results: Higher suPAR concentrations were associated with an increased prevalence of cardiovascular risk factors. After multivariate adjustment, suPAR ≥2.6 ng/mL were independently associated with an increased risk of all-cause death (HR 2.3; 95%CI 1.2-4.4; p = .017), major adverse cardiovascular events (MACE) (HR 1.7; 95%CI 1.1-2.5; p = .020) and heart failure (HR 4.1; 95%CI 1.3-12.6; p = .015), but not with myocardial infarction. For long-term all-cause death significant improvement of reclassification and discrimination were seen after addition of suPAR to a clinical model.Conclusions: In the setting of an ACS, suPAR is associated with long-term all-cause death, heart failure and MACE, and provides incremental prognostic value beyond traditional risks factors.

Soluble Urokinase-Type Plasminogen Activator Receptor and Arterial Stiffness in Patients with COPD

Introduction

Soluble urokinase-type plasminogen activator receptor (suPAR) is upregulated by inflammation and plays a role in the pathogenesis of atherosclerosis. Chronic obstructive pulmonary disease (COPD) is associated with enhanced systemic inflammation and increased risk for atherosclerosis, however, studies analysing the circulating suPAR levels in COPD are contradictory. The aim of the study was to investigate plasma suPAR concentrations together with markers of arterial stiffness in COPD.

Materials and Methods

Twenty-four patients with COPD and 18 non-COPD, control subjects participated in the study. Plasma suPAR was measured, together with lung volumes, symptom burden, exacerbation history, markers of arterial stiffness and soluble inflammatory biomarkers, such as endothelin-1, high-sensitivity C-reactive protein (hsCRP), interleukin-6 (IL-6).

Results

Plasma suPAR levels were higher in COPD (2.84 ± 0.67 ng/ml vs. 2.41 ± 0.57 ng/ml, p = 0.03) and were related to lung function measured with FEV₁ (r = − 0.65, p < 0.01) and symptom burden determined with the modified Medical Research Council questionnaire (r = 0.55, p < 0.05). Plasma suPAR concentrations correlated with various measures of arterial stiffness in all subjects, but only with ejection duration in COPD (r = − 0.44, p = 0.03).

Conclusions

Plasma suPAR levels are elevated in COPD and relate to arterial stiffness. Our results suggest that suPAR may be a potential link between COPD and atherosclerosis.

Soluble urokinase plasminogen activation receptor and long-term outcomes in persons undergoing coronary angiography

Soluble urokinase plasminogen activation receptor (suPAR) is risk factor for kidney disease and biomarker for cardiovascular outcomes but long term longitudinal analyses in a large European cohort have not been perfomed. To hus, we studied suPAR in participants of the Ludwigshafen Risk and Cardiovascular Health study over a very long follow-up time of nearly 10 years. We estimated overall risk of all-cause and cardiovascular death by Cox proportional hazards regression according to quartiles of suPAR, including age, sex, use of lipid-lowering drugs, body mass index, diabetes mellitus, hypertension, smoking, lipids, as well as glomerular filtration rate (eGFR), NT-proBNP, interleukin-6 and high-sensitive CRP as covariates. A total of 2940 participants (age 62.7 ± 10.5years) having a median eGFR of 83.8 mL/min/1.73 m² were included. The median suPAR concentration was 3010 pg/mL (interquartile range, 2250–3988 pg/mL). Using the lowest quartile of suPAR as the reference, crude hazard ratio for cardiovascular mortality were 1.58 (95% CI 1.16–2.16), 1.85 (95% CI 1.37–2.52) and 2.75 (95% CI 2.03–3.71) in the second, third and fourth quartile, respectively. Adjusting for NT-proBNPeGFR or inflammation (interleukin-6 and high-sensitive CRP) confirmed results. suPAR predicts all-cause and cardiovascular death over a period of ten years in persons undergoing coronary angiography, independent of the natriuretic peptide NT-proBNP, kidney function and of markers of systemic inflammation. Future investigation into a potential causal role of suPAR in cardiovascular disease is warranted.

Circulating soluble urokinase plasminogen activator receptor levels and peripheral arterial disease outcomes

BACKGROUND AND AIMS

Circulating soluble urokinase plasminogen activator receptor (suPAR) is a marker of immune activation associated with atherosclerosis. Whether suPAR levels are associated with prevalent peripheral arterial disease (PAD) and its adverse outcomes remains unknown and is the aim of the study.

METHODS

SuPAR levels were measured in 5810 patients (mean age 63 years, 63% male, 77% with obstructive coronary artery disease [CAD]) undergoing cardiac catheterization. The presence of PAD (n = 967, 17%) was classified as carotid (36%), lower/upper extremities (30%), aortic (15%) and multisite disease (19%). Multivariable logistic and Cox regression models were used to determine independent predictors of prevalent PAD and outcomes including all-cause death, cardiovascular death and PAD-related events after adjustment for age, gender, race, body mass index, smoking, diabetes, hypertension, hyperlipidemia, renal function, heart failure history, and obstructive CAD.

RESULTS

Plasma suPAR levels were 22.5% (p < 0.001) higher in patients with PAD compared to those without PAD. Plasma suPAR was higher in patients with more extensive PAD (≥2 compared to single site) p < 0.001. After multivariable adjustment, suPAR was associated with prevalent PAD; odds ratio (OR) for highest compared to lowest tertile of 2.0, 95% CI (1.6-2.5) p < 0.001. In Cox survival analyses adjusted for clinical characteristics and medication regimen, suPAR (in the highest vs. lowest tertile) remained an independent predictor of all-cause death [HR 3.1, 95% CI (1.9-5.3)], cardiovascular death [HR 3.5, 95% CI (1.8-7.0)] and PAD-related events [HR = 1.8, 95% CI (1.3-2.6) p < 0.001 for all].

CONCLUSIONS

Plasma suPAR level is predictive of prevalent PAD and of incident cardiovascular and PAD-related events. Whether SuPAR measurement can help screen, risk stratify, or monitor therapeutic responses in PAD requires further investigation.

Serum Soluble Urokinase-Type Plasminogen Activator Receptor Is Associated with Low Left Ventricular Ejection Fraction and Elevated Plasma Brain-Type Natriuretic Peptide Level

BACKGROUND

Recent studies have suggested that soluble urokinase plasminogen activator receptor (suPAR), a biomarker of subclinical levels of inflammation, is significantly correlated with cardiovascular events.

PURPOSE

We investigated the association between suPAR and left ventricular ejection fraction (LVEF), left ventricular mass index (LVMI), and plasma B-type natriuretic peptide (BNP) among cardiac inpatients.

METHODS AND RESULTS

In total, 242 patients (mean age 71.3 ± 9.8 years; 70 women) admitted to the cardiology department were enrolled in the study. suPAR was significantly correlated with LVEF (R = -0.24, P<0.001), LVMI (R = 0.16, P = 0.014) and BNP (R = 0.46, P<0.001). In logistic regression analysis, the highest suPAR tertile (> 3236 pg/mL) was associated with low LVEF (< 50%) and elevated BNP (> 300 pg/mL) with an odds ratio of 3.84 (95% confidence interval [CI], 1.22-12.1) and 5.36 (95% CI, 1.32-21.8), respectively, after adjusting for age, sex, log-transformed estimated glomerular filtration rate (log(eGFR)), C-reactive protein, and diuretic use. The association between suPAR and LVMI was not statistically significant. In multivariate receiver operating characteristic analysis, addition of log(suPAR) to the combination of age, sex, log(eGFR) and CRP incrementally improved the prediction of low LVEF (area under the curve [AUC], 0.827 to 0.852, P = 0.046) and BNP ≥ 300 pg/mL (AUC, 0.869 to 0.906; P = 0.029).

CONCLUSIONS

suPAR was associated with low LVEF and elevated BNP, but not with left ventricular hypertrophy, independent of CRP, renal function, and diuretic use among cardiac inpatients who were not undergoing chronic hemodialysis.

Cadmium exposure is associated with soluble urokinase plasminogen activator receptor, a circulating marker of inflammation and future cardiovascular disease

BACKGROUND

Diet and smoking are the main sources of cadmium exposure in the general population. Cadmium increases the risk of cardiovascular diseases, and experimental studies show that it induces inflammation. Blood cadmium levels are associated with macrophages in human atherosclerotic plaques. Soluble urokinase-type plasminogen activator receptor (suPAR) is an emerging biomarker for cardiovascular events related to inflammation and atherosclerotic plaques. The aim was to examine whether blood cadmium levels are associated with circulating suPAR and other markers of inflammation.

METHODS

A population sample of 4648 Swedish middle-aged women and men was examined cross-sectionally in 1991-1994. Plasma suPAR was assessed by ELISA, leukocytes were measured by standard methods, and blood cadmium was analysed by inductively coupled plasma mass spectrometry. Prevalent cardiovascular disease, ultrasound-assessed carotid plaque occurrence, and several possible confounding factors were recorded.

RESULTS

After full adjustment for risk factors and confounding variables, a 3-fold increase in blood cadmium was associated with an 10.9% increase in suPAR concentration (p<0.001). In never-smokers, a 3-fold increase in blood cadmium was associated with a 3.7% increase in suPAR concentration (p<0.01) after full adjustment. Blood cadmium was not associated with C-reactive protein, white blood cell count and Lp-PLA2 but with neutrophil/lymphocyte ratio in one of two statistical models.

CONCLUSIONS

Exposure to cadmium was associated with increased plasma suPAR in the general population, independently of smoking and cardiovascular disease. These results imply that cadmium is a possible cause for raised levels of this inflammatory marker.

Increased Urokinase-Type Plasminogen Activator Receptor Expression on Circulating Monocytes Is Correlated with Clinical Instability and Long-Term Adverse Cardiac Events in Patients with Coronary Artery Disease

OBJECTIVES

This study sought to investigate the clinical correlates and prognostic roles of urokinase-type plasminogen activator receptor (uPAR) on circulating monocytes in patients with coronary artery disease (CAD).

METHODS

263 angina patients were included in this study. The percentage of uPAR expressing monocytes (PUEM) and the mean fluorescence intensity (MFI) index of uPAR were measured using flow cytometry. Patient follow-up was on average 604 days. Major adverse cardiac events (MACE) were defined as a composite of cardiac death, reinfarction, acute heart failure and hospitalization for revascularization.

RESULTS

The PUEM and MFI index levels were significantly more elevated in acute coronary syndrome patients than in stable ones. uPAR expressions on circulating monocytes at admission were correlated to inflammatory biomarkers and myocardial necrosis. Logistic regression analysis revealed that PUEM ≥15% (OR 21.96, 95% CI 7.31-65.98, p < 0.001) and uPAR MFI index ≥3.00 (OR 3.54, 95% CI 1.18-10.59, p = 0.024) were independent determinants of clinical instability in patients with CAD. When followed up, a high PUEM level at admission was an independent prognostic parameter for long-term MACE (HR 3.99, 95% CI 1.31-12.11, p = 0.015).

CONCLUSIONS

uPAR expression on circulating monocytes is associated with clinical instability and myocardial necrosis and independently predicts the risk of MACE in patients with CAD.

Hepatic Overexpression of Soluble Urokinase Receptor (uPAR) Suppresses Diet-Induced Atherosclerosis in Low-Density Lipoprotein Receptor-Deficient (LDLR-/-) Mice

Objective

Atherosclerosis, a chronic inflammatory disease, arises from metabolic disorders and is driven by inappropriate recruitment and proliferation of monocytes / macrophages and vascular smooth-muscle-cells. The receptor for the urokinase-type plasminogen activator (uPAR, Plaur) regulates the proteolytic activation of plasminogen. It is also a coactivator of integrins and facilitates leukocyte-endothelial interactions and vascular smooth-muscle-cell migration. The role of uPAR in atherogenesis remains elusive.

Methods and Results

We generated C57Bl6/J low-density lipoprotein receptor (LDL) and uPAR double knockout (uPAR^-/-/LDLR^-/-) mice to test the role of uPAR in two distinct atherosclerosis models. In LDLR^-/- mice, hepatic overexpression following hydrodynamic transfection of soluble uPAR that competes with endogenous membrane-bound uPAR was performed as an interventional strategy. Aortic root atherosclerotic lesions induced by feeding a high-fat diet were smaller and comprised less macrophages and vascular smooth-muscle-cells in double knockout mice and animals overexpressing soluble uPAR when compared to controls. In contrast, lesion size, lipid-, macrophage-, and vascular smooth muscle cell content of guide-wire-induced intima lesions in the carotid artery were not affected by uPAR deficiency. Adhesion of uPAR^-/--macrophages to TNFα-stimulated endothelial cells was decreased in vitro accompanied by reduced VCAM-1 expression on primary endothelial cells. Hepatic overexpression of soluble full-length murine uPAR in LDLR^-/- mice led to a reduction of diet-induced atherosclerotic lesion formation and monocyte recruitment into plaques. Ex vivo incubation with soluble uPAR protein also inhibited adhesion of macrophages to TNFα-stimulated endothelial cells in vitro.

Conclusion

uPAR-deficiency as well as competitive soluble uPAR reduced diet-promoted but not guide-wire induced atherosclerotic lesions in mice by preventing monocyte recruitment and vascular smooth-muscle-cell infiltration. Soluble uPAR may represent a therapeutic tool for the modulation of hyperlipidemia-associated atherosclerotic lesion formation.

Biomarkers of kidney injury and klotho in patients with atherosclerotic renovascular disease

BACKGROUND AND OBJECTIVES

Occlusive renovascular disease and hypertension may progress to CKD. Circulating levels of several biomarkers, including fibroblast growth factor (FGF)-23, Klotho, and soluble urokinase plasminogen activator receptor (suPAR), are altered in patients with CKD, but their role in essential hypertension (EH) and renovascular hypertension (RVH) remains unclear.

DESIGN, SETTING, PARTICIPANTS, & MEASUREMENTS

Levels of FGF-23, Klotho, suPAR, plasminogen activator inhibitor (PAI)-1, tissue factor, and tissue factor pathway inhibitor (TFI) were measured in the inferior vena cava and renal vein of hypertensive patients with atherosclerotic renal artery stenosis (n=12) or age-matched participants with EH (n=12) and relatively preserved renal function. Single-kidney blood flow was measured to calculate renal release of markers. For control, peripheral vein levels were measured in healthy volunteers (HVs; n=12).

RESULTS

FGF-23 levels did not differ among the groups, whereas Klotho levels were lower in participants with RVH and EH than in HVs, and suPAR levels were elevated in patients with RVH compared with HVs and patients with EH (6.1±1.5 versus 4.4±1.9 and 3.2±1.2 ng/ml, P<0.05). PAI-1 levels were higher in patients with RVH than in patients with EH, but tissue factor and TFI levels were not statistically significantly different. After adjustment for GFR, Klotho levels remained decreased in both RVH and EH, and suPAR and PAI-1 levels remained elevated in RVH. eGFR correlated inversely with systemic and renal vein suPAR levels, and directly with systemic Klotho levels.

CONCLUSIONS

Klotho levels are low in hypertensive patients, whereas suPAR and PAI-1 levels are specifically elevated in RVH, correlating with GFR. Klotho, PAI-1, and suPAR may be markers of kidney injury in hypertensive patients.

Circulating intact and cleaved forms of the urokinase-type plasminogen activator receptor: biological variation, reference intervals and clinical useful cut-points

BACKGROUND

High levels of circulating forms of the urokinase-type plasminogen activator receptor (uPAR) are significantly associated to poor prognosis in cancer patients. Our aim was to determine biological variations and reference intervals of the uPAR forms in blood, and in addition, to test the clinical relevance of using these as cut-points in colorectal cancer (CRC) prognosis.

METHODS

uPAR forms were measured in citrated and EDTA plasma samples using time-resolved fluorescence immunoassays. Diurnal, intra- and inter-individual variations were assessed in plasma samples from cohorts of healthy individuals. Reference intervals were determined in plasma from healthy individuals randomly selected from a Danish multi-center cross-sectional study. A cohort of CRC patients was selected from the same cross-sectional study.

RESULTS

The reference intervals showed a slight increase with age and women had ~20% higher levels. The intra- and inter-individual variations were ~10% and ~20-30%, respectively and the measured levels of the uPAR forms were within the determined 95% reference intervals. No diurnal variation was found. Applying the normal upper limit of the reference intervals as cut-point for dichotomizing CRC patients revealed significantly decreased overall survival of patients with levels above this cut-point of any uPAR form.

CONCLUSIONS

The reference intervals for the different uPAR forms are valid and the upper normal limits are clinically relevant cut-points for CRC prognosis.

Soluble urokinase plasminogen activator receptor: a risk factor for carotid plaque, stroke, and coronary artery disease

BACKGROUND AND PURPOSE

Recent studies indicate that the urokinase system could have an important role in atherogenesis and plaque rupture. The relationships among the soluble urokinase plasminogen activator receptor (suPAR), carotid plaque, and incidence of ischemic stroke and coronary artery disease (CAD) events were studied in a prospective cohort.

METHODS

Occurrence of carotid plaque and plasma levels of suPAR were assessed in 5166 men and women, aged 45 to 68 years, participating in the Malmö Diet and Cancer study. Incidences of ischemic stroke and CAD were monitored during a mean follow-up of 15 years.

RESULTS

Subjects with carotid plaque had significantly higher levels of suPAR compared with those without carotid plaque. suPAR was associated with increased incidence of ischemic stroke (hazard ratio [HR] for third versus first tertile, 1.50; 95% confidence interval [CI], 1.06-2.11) and CAD (HR, 1.55; 95% CI, 1.13-2.13) after adjustment for risk factors. The risk factor-adjusted HR for ischemic stroke was 2.21 (95% CI, 1.52-3.22) in subjects with carotid plaque and high suPAR (ie, third tertile) and 1.51 (95% CI, 1.05-2.17) in subjects with carotid plaque and low suPAR compared with those without carotid plaque and low suPAR (reference). High levels of suPAR significantly increased the risk of ischemic stroke and CAD in subjects with carotid plaque.

CONCLUSIONS

suPAR is associated with increased occurrence of carotid plaque and increased incidence of ischemic stroke and CAD. Presence of both elevated levels of suPAR and carotid plaque increases the risk of ischemic stroke in an additive way.

Urokinase receptor counteracts vascular smooth muscle cell functional changes induced by surface topography

Current treatments for human coronary artery disease necessitate the development of the next generations of vascular bioimplants. Recent reports provide evidence that controlling cell orientation and morphology through topographical patterning might be beneficial for bioimplants and tissue engineering scaffolds. However, a concise understanding of cellular events underlying cell-biomaterial interaction remains missing. In this study, applying methods of laser material processing, we aimed to obtain useful markers to guide in the choice of better vascular biomaterials. Our data show that topographically treated human primary vascular smooth muscle cells (VSMC) have a distinct differentiation profile. In particular, cultivation of VSMC on the microgrooved biocompatible polymer E-shell induces VSMC modulation from synthetic to contractile phenotype and directs formation and maintaining of cell-cell communication and adhesion structures. We show that the urokinase receptor (uPAR) interferes with VSMC behavior on microstructured surfaces and serves as a critical regulator of VSMC functional fate. Our findings suggest that microtopography of the E-shell polymer could be important in determining VSMC phenotype and cytoskeleton organization. They further suggest uPAR as a useful target in the development of predictive models for clinical VSMC phenotyping on functional advanced biomaterials.

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.

Plasmin promotes foam cell formation by increasing macrophage catabolism of aggregated low-density lipoprotein

OBJECTIVE

The plasmin/plasminogen system is involved in atherosclerosis. However, the mechanisms by which it stimulates disease are not fully defined. A key event in atherogenesis is the deposition of low-density lipoprotein (LDL) on arterial walls where it is modified, aggregated, and retained. Macrophages are recruited to clear the lipoproteins, and they become foam cells. The goal of this study was to assess the role of plasmin in macrophage uptake of aggregated LDL and foam cell formation.

APPROACH AND RESULTS

Plasminogen treatment of macrophages catabolizing aggregated LDL significantly accelerated foam cell formation. Macrophage interaction with aggregated LDL increased the surface expression of urokinase-type plasminogen activator receptor and plasminogen activator activity, resulting in increased ability to generate plasmin at the cell surface. The high local level of plasmin cleaves cell-associated aggregated LDL, allowing a portion of the aggregate to become sequestered in a nearly sealed, yet extracellular, acidic compartment. The low pH in the plasmin-induced compartment allows lysosomal enzymes, delivered via lysosome exocytosis, greater activity, resulting in more efficient cholesteryl ester hydrolysis and delivery of a large cholesterol load to the macrophage, thereby promoting foam cell formation.

CONCLUSIONS

These findings highlight a critical role for plasmin in the catabolism of aggregated LDL by macrophages and provide a new context for considering the atherogenic role of plasmin.

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.

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.

Urokinase receptor associates with myocardin to control vascular smooth muscle cells phenotype in vascular disease

OBJECTIVE

The urokinase-type plasminogen activator (uPA) and its specific receptor (uPAR) are a potent multifunctional system involved in vascular remodeling. The goal of the study was to unravel the mechanisms of uPA/uPAR-directed vascular smooth muscle cell (VSMC) differentiation.

METHODS AND RESULTS

Using cultured human primary VSMCs, we identified a new molecular mechanism controlling phenotypic modulation in vitro and in vivo. We found that the urokinase-type plasminogen activator receptor (uPAR) acts together with the transcriptional coactivator myocardin to regulate the VSMC phenotype. uPAR, a glycosylphosphatidylinositol-anchored cell-surface receptor family member, undergoes ligand-induced internalization and nuclear transport in VSMCs. Platelet-derived growth factor receptor β and SUMOylated RanGAP1 mediate this trafficking. Nuclear uPAR associates with myocardin, which is then recruited from the promoters of serum response factor target genes and undergoes proteasomal degradation. This chain of events initiates the synthetic VSMC phenotype. Using mouse carotid artery ligation model, we show that this mechanism contributes to adverse vascular remodeling after injury in vivo. We then cultured cells on a microstructured biomaterial and found that substrate topography induced uPAR-mediated VSMC differentiation.

CONCLUSIONS

These findings reveal the transcriptional activity of uPAR, controlling the differentiation of VSMCs in a vascular disease model. They also suggest a new role for uPAR as a therapeutic target and as a marker for VSMC phenotyping on prosthetic biomaterials.

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.

Soluble urokinase plasminogen activator receptor is associated with subclinical organ damage and cardiovascular events

OBJECTIVE

The soluble urokinase plasminogen activator receptor (suPAR) is a plasma marker of low grade inflammation and has been associated with cardiovascular risk. We wanted to investigate whether suPAR was associated with markers of subclinical organ damage.

METHODS

In a population sample of 2038 individuals, aged 41, 51, 61 and 71 years, without diabetes, prior stroke or myocardial infarction, not receiving any cardiovascular, anti-diabetic or lipid-lowering medications, we measured urine albumin/creatinine ratio (UACR), carotid atherosclerotic plaques and carotid/femoral pulse wave-velocity (PWV) together with traditional cardiovascular risk factors and high sensitivity C-reactive protein (hsCRP).

RESULTS

suPAR was significantly associated with the presence of plaques (P = 0.003) and UACR (P < 0.001), but not PWV (P = 0.17) when adjusting for age, gender, systolic blood pressure, cholesterol, plasma glucose, waist/hip ratio, smoking and hsCRP. However, suPAR explained only a small part of the variation in the markers of subclinical organ damage (R(2) 0.02-0.04). During a median follow-up of 12.7 years (5th-95th percentile 5.1-13.4 years) a total of 174 composite endpoints (CEP) of cardiovascular death, non-fatal myocardial infarction and stroke occurred. suPAR was associated with CEP independent of plaques, PWV, UACR, and hsCRP as well as age, gender, systolic blood pressure, cholesterol, plasma glucose, waist/hip ratio and smoking with a standardized hazard ratio of 1.16 (95% confidence interval 1.04-1.28, P = 0.006).

CONCLUSION

suPAR was associated with subclinical organ damage, but predicted cardiovascular events independent of subclinical organ damage, traditional risk factors and hsCRP. Further studies must investigate whether suPAR plays an independent role in the pathogenesis of cardiovascular disease.

Urokinase receptor mediates mobilization, migration, and differentiation of mesenchymal stem cells

AIMS

Multipotent mesenchymal stem cells (MSCs) have regenerative properties and are recognized as putative players in the pathogenesis of cardiovascular diseases. The underlying molecular mechanisms remain, however, sparsely explored. Our study was designed to elucidate a probable role for the multifunctional urokinase (uPA)/urokinase receptor (uPAR) system in MSC regulation. Though uPAR has been implicated in a broad spectrum of pathophysiological processes, nothing is known about uPAR in MSCs.

METHODS AND RESULTS

uPAR was required to mobilize MSCs from the bone marrow (BM) of mice stimulated with granulocyte colony-stimulating factor (G-CSF) in vivo. An insignificant amount of MSCs was mobilized in uPAR(-/-) C57BL/6J mice, whereas in wild-type animals G-CSF induced an eight-fold increase of mobilized MSCs. uPAR(-/-) mice revealed up-regulated expression of G-CSF and stromal cell-derived factor 1 (CXCR4) receptors in BM. uPAR down-regulation leads to inhibition of human MSC migration, as shown in different migration assays. uPAR down- or up-regulation resulted in inhibition or stimulation of MSC differentiation into vascular smooth muscle cells (VSMCs) correspondingly, as monitored by changes in cell morphology and expression of specific marker proteins. Injection of fluorescently labelled MSCs in non-obese diabetic/severe combined immunodeficiency (NOD/SCID) mice after femoral artery wire injury demonstrated impaired engraftment of uPAR-deficient MSCs at the place of injury.

CONCLUSIONS

These data suggest a multifaceted function of uPAR in MSC biology contributing to vascular repair. uPAR might guide and control the trafficking of MSCs to the vascular wall in response to injury or ischaemia and their differentiation towards functional VSMCs at the site of arterial injury.

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.

Urokinase-receptor-mediated phenotypic changes in vascular smooth muscle cells require the involvement of membrane rafts

The cholesterol-enriched membrane microdomains lipid rafts play a key role in cell activation by recruiting and excluding specific signalling components of cell-surface receptors upon receptor engagement. Our previous studies have demonstrated that the GPI (glycosylphosphatidylinositol)-linked uPAR [uPA (urokinase-type plasminogen activator) receptor], which can be found in lipid rafts and in non-raft fractions, can mediate the differentiation of VSMCs (vascular smooth muscle cells) towards a pathophysiological de-differentiated phenotype. However, the mechanism by which uPAR and its ligand uPA regulate VSMC phenotypic changes is not known. In the present study, we provide evidence that the molecular machinery of uPAR-mediated VSMC differentiation employs lipid rafts. We show that the disruption of rafts in VSMCs by membrane cholesterol depletion using MCD (methyl-beta-cyclodextrin) or filipin leads to the up-regulation of uPAR and cell de-differentiation. uPAR silencing by means of interfering RNA resulted in an increased expression of contractile proteins. Consequently, disruption of lipid rafts impaired the expression of these proteins and transcriptional activity of related genes. We provide evidence that this effect was mediated by uPAR. Similar effects were observed in VSMCs isolated from Cav1Z(-/-) (caveolin-1-deficient) mice. Despite the level of uPAR being significantly higher after the disruption of the rafts, uPA/uPAR-dependent cell migration was impaired. However, caveolin-1 deficiency impaired only uPAR-dependent cell proliferation, whereas cell migration was strongly up-regulated in these cells. Our results provide evidence that rafts are required in the regulation of uPAR-mediated VSMC phenotypic modulations. These findings suggest further that, in the context of uPA/uPAR-dependent processes, caveolae-associated and non-associated rafts represent different signalling membrane domains.

A novel signaling pathway: fibroblast nicotinic receptor alpha1 binds urokinase and promotes renal fibrosis

The nicotinic acetylcholine receptor alpha1 (nAChRalpha1) was investigated as a potential fibrogenic molecule in the kidney, given reports that it may be an alternative urokinase (urokinase plasminogen activator; uPA) receptor in addition to the classical receptor uPAR. In a mouse obstructive uropathy model of chronic kidney disease, interstitial fibroblasts were identified as the primary cell type that bears nAChRalpha1 during fibrogenesis. Silencing of the nAChRalpha1 gene led to significantly fewer interstitial alphaSMA(+) myofibroblasts (2.8 times decreased), reduced interstitial cell proliferation (2.6 times decreased), better tubular cell preservation (E-cadherin 14 times increased), and reduced fibrosis severity (24% decrease in total collagen). The myofibroblast-inhibiting effect of nAChRalpha1 silencing in uPA-sufficient mice disappeared in uPA-null mice, suggesting that a uPA-dependent fibroblastic nAChRalpha1 pathway promotes renal fibrosis. To further establish this possible ligand-receptor relationship and to identify downstream signaling pathways, in vitro studies were performed using primary cultures of renal fibroblasts. (35)S-Labeled uPA bound to nAChRalpha1 with a K(d) of 1.6 x 10(-8) m, which was displaced by the specific nAChRalpha1 inhibitor d-tubocurarine in a dose-dependent manner. Pre-exposure of uPA to the fibroblasts inhibited [(3)H]nicotine binding. The uPA binding induced a cellular calcium influx and an inward membrane current that was entirely prevented by d-tubocurarine preincubation or nAChRalpha1 silencing. By mass spectrometry phosphoproteome analyses, uPA stimulation phosphorylated nAChRalpha1 and a complex of signaling proteins, including calcium-binding proteins, cytoskeletal proteins, and a nucleoprotein. This signaling pathway appears to regulate the expression of a group of genes that transform renal fibroblasts into more active myofibroblasts characterized by enhanced proliferation and contractility. This new fibrosis-promoting pathway may also be relevant to disorders that extend beyond chronic kidney disease.

Plasminogen mediates the atherogenic effects of macrophage-expressed urokinase and accelerates atherosclerosis in apoE-knockout mice

Urokinase-type plasminogen activator (uPA) is expressed at elevated levels in atherosclerotic human arteries, primarily in macrophages. Plasminogen (Plg), the primary physiologic substrate of uPA, is present at significant levels in blood and interstitial fluid. Both uPA and Plg have activities that could affect atherosclerosis progression. Moreover, correlations between increased Plg activation and accelerated atherosclerosis are reported in several human studies. However, a coherent picture of the role of the uPA/Plg system in atherogenesis has not yet emerged, with at least one animal study suggesting that Plg is atheroprotective. We used a transgenic mouse model of macrophage-targeted uPA overexpression in apolipoprotein E-deficient mice to investigate the roles of uPA and Plg in atherosclerosis. We found that macrophage-expressed uPA accelerated atherosclerotic plaque growth and promoted aortic root dilation through Plg-dependent pathways. These pathways appeared to affect lesion progression rather than initiation and to include actions that disproportionately increase lipid accumulation in the artery wall. In addition, loss of Plg was protective against atherosclerosis both in the presence and absence of uPA overexpression. Transgenic mice with macrophage-targeted uPA overexpression reveal atherogenic roles for both uPA and Plg and are a useful experimental setting for investigating the molecular mechanisms that underlie clinically established relationships between uPA expression, Plg activation, and atherosclerosis progression.

Fatty acids differentially modify the expression of urokinase type plasminogen activator receptor in monocytes

The urokinase plasminogen activator system with its receptor uPAR contributes to the migratory potential of macrophages, a key event in atherosclerosis. We here investigated whether free fatty acids (FFA) modify the expression for uPAR in the PMA-differentiated human monocyte/macrophage-like cell line U937. Two hundred micromolar palmitate induced a threefold increase of the uPAR mRNA expression. Although the mono- and polyunsaturated fatty acids oleate and linoleate also stimulated uPAR expression, oleate had a significantly lower effect than palmitate. The observed effects were time and dose dependent. Inhibition of PKC-and ERK-pathways resulted in a strong down-regulation of basal uPAR expression whereas the FFA induced up-regulation remained unchanged. In contrast, FFA induced uPAR up-regulation was abolished by the specific inhibition of p38 MAPK. In conclusion we demonstrate that uPAR expression in human monocytes/macrophages is differentially stimulated by FFA. These effects are partially mediated by the p38 MAP-kinase signaling pathway.

Urokinase and its receptors in chronic kidney disease

This review focuses on the role of the serine protease urokinase-type plasminogen activator and its high affinity receptor uPAR/CD87 in chronic kidney disease (CKD) progression. An emerging theme is their organ- and site-specific effects. In addition to tubules, uPA is produced by macrophages and fibroblasts in CKD. By activating hepatocyte growth factor and degrading fibrinogen uPA may have anti-fibrotic effects. However renal fibrosis was similar between uPA wild-type and knockout mice in experimental CKD. The uPAR is expressed by renal parenchymal cells and inflammatory cells in a variety of kidney diseases. Such expression appears anti-fibrotic based on studies in uPAR-deficient mice. In CKD uPAR expression is associated with higher uPA activity but its most important effect appears to be due to effects on cell recruitment and migration that involve interactions with a variety of co-receptors and chemoattractant effects of soluble uPAR. Vitronectin and high molecular weight kininogen are alternate uPAR ligands, and receptors in addition to uPAR may also bind directly to uPA and activate cell signaling pathways.

Rosuvastatin regulates vascular smooth muscle cell phenotypic modulation in vascular remodeling: Role for the urokinase receptor

The urokinase (uPA)/urokinase receptor (uPAR) multifunctional system is an important mediator of migration and proliferation of vascular smooth muscle cells (VSMC). However, whether uPA/uPAR-directed mechanisms are involved in the beneficial effects of 3-hydroxy-3-methylglutaryl-coenzyme A reductase inhibitors on vascular remodeling remains unexplored. In this study, we have investigated the effect of the hydrophilic statin rosuvastatin on neointimal remodeling, and the role of uPAR. Using an ex vivo organ and in vitro cell culture models we demonstrate that rosuvastatin decreases injury-induced neointima formation and proliferation of medial VSMC in porcine coronary arteries, as well as migration and proliferation of human coronary VSMC. Studies on the underlying mechanisms show that rosuvastatin impairs VSMC transition from their physiological contractile to the pathophysiological synthetic phenotype. These effects are mediated, at least in part, via uPAR, as confirmed by means of rosuvastatin-directed uPAR expression and uPAR silencing in both models. Our findings provide evidence that rosuvastatin modulates VSMC phenotypic changes and subsequently their proliferation and migration, and indicate the important role for uPAR in these processes. This mechanism contributes to the beneficial non-lipid lowering effect of rosuvastatin on negative vascular remodeling.

Urokinase-type plasminogen activator and metalloproteinase-2 are independently related to the carotid atherosclerosis in haemodialysis patients

INTRODUCTION

Matrix metalloproteinases (MMPs), their tissue inhibitors (TIMPs) system, and fibrinolytic system, have been implicated as important factors in atherosclerosis and vascular remodeling. However, no data are yet available on the associations between these two systems in relation to carotid atherosclerosis in hemodialysis (HD) patients.

MATERIAL AND METHODS

We compared plasma levels of MMP-2, MMP-9, TIMP-1, TIMP-2; the parameters of fibrinolytic system: tissue-type plasminogen activator (tPA), urokinase-type plasminogen activator (uPAR) and its soluble receptor (suPAR), plasminogen activator inhibitor-1 (PAI-1), plasmin-alpha2-antiplasmin (PAP) complexes; high sensitivity C-reactive protein (hs CRP) as a marker of inflammation and a surrogate of atherosclerotic disease-intima media thickness (IMT) in HD patients and in healthy controls.

RESULTS

The values of the uPA, suPAR, PAP, MMP-2, TIMPs, hs CRP and IMT in the patients significantly exceeded those in controls. The concentrations of MMP-9, tPA and PAI-1 were similar in both investigated groups. uPA, uPAR and PAP were positively associated with MMP-2/TIMPs system; all mentioned above parameters (except TIMP-2) and hsCRP were associated with IMT. Multivariate analysis showed that uPA, MMP-2 and age were the strong independent variables linked to IMT values in HD patients.

CONCLUSIONS

The patients on haemodialysis treatment have evidence of disordered fibrinolysis/proteolysis balance in the plasma, independently associated with IMT on multivariate analysis. These data suggest the importance of uPA and MMP-2 levels in the developing of atherosclerosis in these patients.

Perspectives on endothelial-to-mesenchymal transition: potential contribution to vascular remodeling in chronic pulmonary hypertension

All forms of pulmonary hypertension are characterized by structural changes in pulmonary arteries. Increased numbers of cells expressing α-smooth muscle (α-SM) actin is a nearly universal finding in the remodeled artery. Traditionally, it was assumed that resident smooth muscle cells were the exclusive source of these newly appearing α-SM actin-expressing cells. However, rapidly emerging experimental evidence suggests other, alternative cellular sources of these cells. One possibility is that endothelial cells can transition into mesenchymal cells expressing α-SM actin and that this process contributes to the accumulation of SM-like cells in vascular pathologies. We review the evidence that endothelial-mesenchymal transition is an important contributor to cardiac and vascular development as well as to pathophysiological vascular remodeling. Recent work has provided evidence for the role of transforming growth factor-β, Wnt, and Notch signaling in this process. The potential roles of matrix metalloproteinases and serine proteases are also discussed. Importantly, endothelial-mesenchymal transition may be reversible. Thus insights into the mechanisms controlling endothelial-mesenchymal transition are relevant to vascular remodeling and are important as we consider new therapies aimed at reversing pulmonary vascular remodeling.

Tissue factor and urokinase-type plasminogen activator system are related to the presence of cardiovascular disease in hemodialysis patients

INTRODUCTION

The disturbances of haemostasis and enhanced oxidative stress (SOX) appear to contribute to the cardiovascular disease (CVD) in hemodialysis (HD) patients. The aim of the present study was to investigate if the disorders of coagulation/fibrinolysis system are associated with the presence of CVD in these patients.

MATERIALS AND METHODS

We compared pre-dialysis levels of uPA, suPAR, tissue factor (TF) and its inhibitor (TFPI), prothrombin fragment F1+2 (F1+2); a marker of SOX-Cu/Zn superoxide dismutase (Cu/Zn SOD) and a surrogate of inflammation-high sensitivity C-reactive protein (hs CRP) in HD patients with and without CVD.

RESULTS

The uPA/suPAR system and hs CRP values were significantly greater in patients with CVD than in those without CVD; whereas TF, TFPI, F1+2 and Cu/Zn SOD levels were comparable in both patient groups. TF was positively correlated with both uPA (p<0.001) and suPAR levels (p<0.05). Logistic regression analysis showed that elevated levels of suPAR, TF and uPA were independently associated with the presence of CVD in HD patients.

CONCLUSIONS

The association between TF and uPA/suPAR system is significantly related to the presence of CVD in HD patients.

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.