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

The molecular mechanisms of cuproptosis and its relevance to cardiovascular disease

Recently, cuproptosis has been demonstrated to be a new non-apototic cell death mode that is characterized by copper dependence and the regulation of mitochondrial respiration. Cuproptosis is distinct from known cell death modes such as apoptosis, necrosis, pyroptosis, or ferroptosis. Excessive copper induces cuproptosis by promoting protein toxic stress reactions via copper-dependent anomalous oligomerization of lipoylation proteins in the tricarboxylic acid (TCA) cycle and reducing iron-sulfur cluster protein levels. Ferredoxin1 (FDX1) promotes dihydrolipoyl transacetylase (DLAT) lipoacylation and abates iron-sulfur cluster proteins by reducing Cu²⁺ to Cu⁺, inducing cell death. Copper homeostasis depends on the copper transporter, and disturbances to this homeostasis cause cuproptosis. Recent evidence has shown that cuproptosis plays a significant role in the occurrence and development of many cardiovascular diseases, such as myocardial ischemia/reperfusion (I/R) injury, heart failure, atherosclerosis, and arrhythmias. Copper chelators, such as ammonium tetrathiomolybdate(VI) and DL-Penicillamine, may ease the above cardiovascular diseases by inhibiting the cuproptosis pathway. Oxidative phosphorylation inhibitors may inhibit cuproptosis by inhibiting protein stress response. In conclusion, cuproptosis plays an essential role in cardiovascular disease pathogenesis. Inhibition of cardiovascular cuproptosis is expected to become a potential treatment. Here, we will thoroughly review the molecular mechanisms involved in cuproptosis and its significance in cardiovascular disease.

Human umbilical cord mesenchymal stem cell-derived exosomal microRNA-148a-3p inhibits neointimal hyperplasia by targeting Serpine1

BACKGROUND

Restenosis is inevitable when patients undergo percutaneous transluminal angioplasty due to neointimal hyperplasia (NIH). Human umbilical cord mesenchymal stem cell-derived exosomes (hucMSC-Exos) have been studied in the field of cardiovascular diseases. However, the effects and mechanisms of hucMSC-Exos on NIH are unclear. We aimed to investigate whether MSC-Exos regulate vascular smooth muscle cell (VSMC) functions to inhibit NIH and explore the underlying mechanisms.

METHODS

HucMSCs and mouse VSMCs were isolated and characterized by flow cytometry and immunofluorescence. HucMSC-Exos were identified by transmission electron microscopy, nanoparticle tracking analysis and western blots. Exosomes (Exos) were intravenously injected into mice with left common carotid artery ligation, and their effects on NIH were assessed by haematoxylin and eosin (H&E) and immunohistochemistry staining. The effects of hucMSC-Exos on VSMCs were evaluated by Cell Counting Kit-8, scratch wound, Transwell and Western blot assays. MicroRNA sequencing data in the Gene Expression Omnibus and mRNA sequencing results were used to identify potential molecules in hucMSC-Exos and target genes in VSMCs, respectively. We tested the regulatory effect of microRNAs in Exos and target genes in VSMCs using overexpression and knockdown experiments.

RESULTS

Primary hucMSCs, VSMCs and hucMSC-Exos were isolated and characterized. Administration of hucMSC-Exos suppressed NIH after artery ligation. H&E and immunohistochemistry results showed that hucMSC-Exos decreased the intima and media area and intima/media ratio, increased the contractile phenotype protein SM22a in the media layer and downregulated Serpine1 expression in the carotid artery. Exos were ingested by VSMCs, which inhibited migration and upregulated SM22a expression by suppressing Serpine1 expression in vitro. MiR-148a-3p was enriched in hucMSC-Exos and repressed Serpine1 by targeting its 3' untranslated region. Moreover, exosomal miR-148a-3p suppressed VSMC phenotypic switching and migration by targeting Serpine1.

CONCLUSIONS

We found that hucMSC-Exos inhibited NIH in a mouse carotid artery ligation model and that the inhibitory effects on VSMC phenotypic switching and migration were mediated by delivery of miR-148a-3p to VSMCs to target Serpine1.

Pharmacological Targeting of Plasminogen Activator Inhibitor-1 Decreases Vascular Smooth Muscle Cell Migration and Neointima Formation

OBJECTIVE

Plasminogen activator inhibitor-1 (PAI-1), a serine protease inhibitor that promotes and inhibits cell migration, plays a complex and important role in adverse vascular remodeling. Little is known about the effects of pharmacological PAI-1 inhibitors, an emerging drug class, on migration of vascular smooth muscle cells (SMCs) and endothelial cells (ECs), crucial mediators of vascular remodeling. We investigated the effects of PAI-039 (tiplaxtinin), a specific PAI-1 inhibitor, on SMC and EC migration in vitro and vascular remodeling in vivo.

APPROACH AND RESULTS

PAI-039 inhibited SMC migration through collagen gels, including those supplemented with vitronectin and other extracellular matrix proteins, but did not inhibit migration of PAI-1-deficient SMCs, suggesting that its antimigratory effects were PAI-1-specific and physiologically relevant. However, PAI-039 did not inhibit EC migration. PAI-039 inhibited phosphorylation and nuclear translocation of signal transducers and activators of transcription-1 in SMCs, but had no discernable effect on signal transducer and activator of transcription-1 signaling in ECs. Expression of low-density lipoprotein receptor-related protein 1, a motogenic PAI-1 receptor that activates Janus kinase/signal transducers and activators of transcription-1 signaling, was markedly lower in ECs than in SMCs. Notably, PAI-039 significantly inhibited intimal hyperplasia and inflammation in murine models of adverse vascular remodeling, but did not adversely affect re-endothelialization after endothelium-denuding mechanical vascular injury.

CONCLUSIONS

PAI-039 inhibits SMC migration and intimal hyperplasia, while having no inhibitory effect on ECs, which seems to be because of differences in PAI-1-dependent low-density lipoprotein receptor-related protein 1/Janus kinase/signal transducer and activator of transcription-1 signaling between SMCs and ECs. These findings suggest that PAI-1 may be an important therapeutic target in obstructive vascular diseases characterized by neointimal hyperplasia.

Fibrinolytic system related to pulmonary arterial pressure and lung function of patients with idiopathic pulmonary fibrosis

OBJECTIVES AND AIMS

To investigate urokinase-(uPA) and tissue-type (tPA) plasminogen activator and plasminogen activator inhibitor type-1 (PAI-1) levels in patients with idiopathic pulmonary fibrosis (IPF) and to determine the relationship between fibrinolytic system and pulmonary arterial pressure and pulmonary function.

METHODS

Seventy-nine patients with IPF were included. Bronchoalveolar lavage fluid (BALF) and blood samples were collected. The concentrations of tPA, uPA and PAI-1 were measured using enzyme-linked immunosorbent assay. Doppler echocardiography was used to detect tricuspid regurgitation pressure gradient (TRPG) to estimate pulmonary arterial pressure.

RESULTS

BALF tPA elevated (P < 0.005), circulatory PAI-1 decreased (P = 0.05) and the ratio of uPA and PAI-1 decreased (P = 0.01) in BALF in IPF patients with pulmonary hypertension (PH) compared to those without PH. Positive linear correlations were found: BALF tPA and TRPG (r = 0.558, P = 0.013); the predicted percentage of diffusion capacity of lung for carbon monoxide adjustments for alveolar volume and BALF uPA (r = 0.319, P = 0.035). Negative linear correlations were as follows: BALF PAI-1 and the predicted percentage of VC_max (r = -0.325, P = 0.020), or total lung capacity (r = -0.312, P = 0.033); circulatory PAI-1 and TRPG (r = -0.697, P = 0.003).

CONCLUSIONS

The change of alveolar fibrolytic system in IPF, especially the uPA reduction and the PAI-1elevation, contributes to the deterioration of lung function. During the lung injury initiating fibrosis, tPA and PAI-1 might be leaked out of the pulmonary capillaries into alveoli, resulting in their elevation in alveoli and reduction in circulation, and finally contributing to the development of PH in IPF.

Effects of altered plasminogen activator inhibitor-1 expression on cardiovascular disease

Plasminogen Activator Inhibitor-1 (PAI-1) is a multifunctional protein with the ability to not only regulate fibrinolysis through inhibition of plasminogen activation, but also cell signaling events which have direct downstream effects on cell function. Elevated plasma levels of this protein have been shown to have profound effects on the development and progression of cardiovascular diseases. However, results from a number of studies, especially those using PAI-1 deficient mouse models, have demonstrated that its function is ambiguous, with evidence of both preventing and enhancing various disease states. A number of lifestyle changes and pharmacological reagents have been identified that can regulate PAI-1 levels or function. Those reagents that target function are focused on its ability to regulate plasmin formation, and have been studied in in vivo models of thrombosis. Further investigations involving regulation of cell function could potentially resolve paradoxical issues associated with the function of this protein in regulating cardiovascular disease.

Low Molecular Weight Antagonists of Plasminogen Activator Inhibitor-1: Therapeutic Potential in Cardiovascular Disease

Plasminogen activator inhibitor-1 (PAI-1; SERPINE1) is the major physiologic regulator of the plasmin-based pericellular proteolytic cascade, a modulator of vascular smooth muscle cell (VSMC) migration and a causative factor in cardiovascular disease and restenosis, particularly in the context of increased vessel transforming growth factor- β1 (TGF-β1) levels. PAI-1 limits conversion of plasminogen to plasmin (and, thereby, fibrin degradation) by inhibiting its protease targets urokinase and tissue-type plasminogen activators (uPA, tPA). PAI-1 also has signaling functions and binds to the low density lipoprotein receptor-related protein 1 (LRP1) to regulate LRP1-dependent cell motility that, in turn, contributes to neointima formation. PAI-1/uPA/uPA receptor/LRPI/integrin complexes are endocytosed with subsequent uPAR/LRP1/integrin redistribution to the leading edge, initiating an "adhesion-detachment-readhesion" cycle to promote cell migration. PAI-1 also interacts with LRP1 in a uPA/uPAR-independent manner triggering Jak/Stat1 pathway activation to stimulate cell motility. PAI-1 itself is a substrate for extracellular proteases and exists in a "cleaved" form which, while unable to interact with uPA and tPA, retains LRP1-binding and migratory activity. These findings suggest that there are multiple mechanisms through which inhibition of PAI-1 may promote cardiovascular health. Several studies have focused on the design, synthesis and preclinical assessment of PAI-1 antagonists including monoclonal antibodies, peptides and low molecular weight (LMW) antagonists. This review discusses the translational impact of LMW PAI-1 antagonists on cardiovascular disease addressing PAI-1-initiated signaling, PAI-1 structure, the design and characteristics of PAI-1-targeting drugs, results of in vitro and in vivo studies, and their clinical implications.

Multifaceted role of plasminogen activator inhibitor-1 in regulating early remodeling of vein bypass grafts

OBJECTIVE

The role of plasminogen activator inhibitor-1 (PAI-1) in vein graft (VG) remodeling is undefined. We examined the effect of PAI-1 on VG intimal hyperplasia and tested the hypothesis that PAI-1 regulates VG thrombin activity.

METHODS AND RESULTS

VGs from wild-type (WT), Pai1(-/-), and PAI-1-transgenic mice were implanted into WT, Pai1(-/-), or PAI-1-transgenic arteries. VG remodeling was assessed 4 weeks later. Intimal hyperplasia was significantly greater in PAI-1-deficient mice than in WT mice. The proliferative effect of PAI-1 deficiency was retained in vitronectin-deficient mice, suggesting that PAI-1's antiproteolytic function plays a key role in regulating intimal hyperplasia. Thrombin-induced proliferation of PAI-1-deficient venous smooth muscle cells (SMC) was significantly greater than that of WT SMC, and thrombin activity was significantly higher in PAI-1-deficient VGs than in WT VGs. Increased PAI-1 expression, which has been associated with obstructive VG disease, did not increase intimal hyperplasia.

CONCLUSIONS

Decreased PAI-1 expression (1) promotes intimal hyperplasia by pathways that do not require vitronectin and (2) increases thrombin activity in VG. PAI-1 overexpression, although it promotes SMC migration in vitro, did not increase intimal hyperplasia. These results challenge the concept that PAI-1 drives nonthrombotic obstructive disease in VG and suggest that PAI-1's antiproteolytic function, including its antithrombin activity, inhibits intimal hyperplasia.

An assessment of transcriptional changes in porcine skin exposed to bromine vapor

Bromine is an industrial chemical that can cause severe cutaneous burns. This study was a preliminary investigation into the effect of cutaneous exposure to bromine vapor using a weanling swine burn model and microarray analysis. Ventral abdominal sites were exposed to a mean calculated bromine vapor concentration of 0.69 g L(-1) for 10 or 20 min. At 48 h postexposure, total RNA from skin samples was isolated, processed, and hybridized to Affymetrix GeneChip Porcine Genome Arrays. Expression analysis revealed that bromine vapor exposure for 10 or 20 min promoted similar transcriptional changes in the number of significantly modulated probe sets. A minimum of 83% of the probe sets was similar for both exposure times. Ingenuity pathways analysis revealed eight common biological functions among the top 10 functions of each experimental group, in which 30 genes were commonly shared among 19 significantly altered signaling pathways. Transcripts encoding heme oxygenase 1, interleukin-1β, interleukin 2 receptor gamma chain, and plasminogen activator inhibitor-1 were identified as common potential therapeutic targets for Phase II/III clinical trial or FDA-approved drugs. The present study is an initial assessment of the transcriptional responses to cutaneous bromine vapor exposure identifying molecular networks and genes that could serve as targets for developing therapeutics for bromine-induced skin injury.

Use of mouse models to study plasminogen activator inhibitor-1

Plasminogen activator inhibitor-1 (PAI-1) is the main inhibitor of tissue-type plasminogen activator (t-PA) and urokinase-type plasminogen activator (u-PA) and therefore plays an important role in the plasminogen/plasmin system. PAI-1 is involved in a variety of cardiovascular diseases (mainly through inhibition of t-PA) as well as in cell migration and tumor development (mainly through inhibition of u-PA and interaction with vitronectin). PAI-1 is a unique member of the serpin superfamily, exhibiting particular unique conformational and functional properties. Since its involvement in various biological and pathophysiological processes PAI-1 has been the subject of many in vivo studies in mouse models. We briefly discuss structural and physiological differences between human and mouse PAI-1 that should be taken into account prior to extrapolation of data obtained in mouse models to the human situation. The current review provides an overview of the various models, with a focus on cardiovascular disease and cancer, using wild-type mice or genetically modified mice, either deficient in PAI-1 or overexpressing different variants of PAI-1.

Plasminogen activator inhibitor-1 and vitronectin expression level and stoichiometry regulate vascular smooth muscle cell migration through physiological collagen matrices

BACKGROUND

Vascular smooth muscle cell (VSMC) migration is a critical process in arterial remodeling. Purified plasminogen activator inhibitor-1 (PAI-1) is reported to both promote and inhibit VSMC migration on two-dimensional (D) surfaces.

OBJECTIVE

To determine the effects of PAI-1 and vitronectin (VN) expressed by VSMC themselves on migration through physiological collagen matrices.

METHODS

We studied migration of wild-type (WT), PAI-1-deficient, VN-deficient, PAI-1/VN doubly-deficient (DKO) and PAI-1-transgenic (Tg) VSMC through three-D collagen gels.

RESULTS

WT VSMC migrated significantly slower than PAI-1- and VN-deficient VSMC, but significantly faster than DKO VSMC. Experiments with recombinant PAI-1 suggested that basal VSMC PAI-1 expression inhibits migration by binding VN, which is secreted by VSMC and binds collagen. However, PAI-1-over-expressing Tg VSMC migrated faster than WT VSMC. Reconstitution experiments with recombinant PAI-1 mutants suggested that the pro-migratory effect of PAI-1 over-expression required its anti-plasminogen activator (PA) and LDL receptor-related protein (LRP) binding functions, but not VN binding. While promoting VSMC migration in the absence of PAI-1, VN inhibited the pro-migratory effect of active PAI-1.

CONCLUSIONS

In isolation, VN and PAI-1 are each pro-migratory. However, via formation of a high-affinity, non-motogenic complex, PAI-1 and VN each buffers the other's pro-migratory effect. The level of PAI-1 expression by VSMC and the concentration of VN in extracellular matrix are critical determinants of whether PAI-1 and VN promote or inhibit migration. These findings help to rectify previously conflicting reports and suggest that PAI-1/VN stoichiometry plays an important role in VSMC migration and vascular remodeling.

Review: Therapeutic potential of plasminogen activator inhibitor-1 inhibitors

Plasminogen activator inhibitor-1 (PAI-1) is the major physiological inhibitor of fibrinolysis and regulates cell migration and fibrosis. Preclinical studies using genetically altered mice and biological or small molecule inhibitors have elucidated a role for PAI-1 in the pathogenesis of thrombosis, vascular remodeling, renal injury, and initiation of diabetes. Inhibition of PAI-1 is a potential therapeutic strategy in these diseases.

Recombinant plasminogen activator inhibitor-1 inhibits intimal hyperplasia

OBJECTIVE

Plasminogen activator inhibitor-1 (PAI-1) overexpression is implicated in vascular disease. However, the effects of a primary increase in PAI-1 expression on arterial remodeling are poorly defined. We tested the hypothesis that recombinant PAI-1 inhibits intimal hyperplasia after vascular injury.

METHODS AND RESULTS

Rats underwent carotid artery injury and received intraperitoneal injections of saline or mutant forms of PAI-1 for 14 days, including an active stable mutant (PAI-1-14-1b), a mutant lacking anti-PA activity (PAI-1-R), or a mutant defective in vitronectin (VN) binding (PAI-1-K). All forms of PAI-1 significantly inhibited neointima formation, whereas elastase-cleaved PAI-1, which lacks both anti-PA and VN-binding functions, did not. Similar effects were observed in a murine model. However, the antiproliferative effect of PAI-1-R was lost in Vn(-/-) mice, suggesting that PAI-1 can inhibit intimal hyperplasia in vivo by a VN-dependent pathway not involving direct inhibition of proteases. In vitro, recombinant PAI-1 inhibited wild-type vascular smooth muscle cell (VSMC) proliferation, promoted apoptosis, and inhibited migration. These effects were lost in VN-deficient VSMCs.

CONCLUSIONS

Recombinant PAI-1 inhibits intimal hyperplasia by inhibiting proteases and binding VN. VN is a key determinant of the antiproliferative effect of PAI-1 overexpression. PAI-1-R has therapeutic potential to inhibit vascular restenosis without promoting thrombosis.

Plasminogen activator inhibitor-1 and asthma: role in the pathogenesis and molecular regulation

Plasminogen activator inhibitor (PAI)-1 is a major inhibitor of the fibrinolytic system. PAI-1 levels are markedly increased in asthmatic airways, and mast cells (MCs), a pivotal cell type in the pathogenesis of asthma, are one of the main sources of PAI-1 production. Recent studies suggest that PAI-1 may promote the development of asthma by regulating airway remodelling, airway hyperresponsiveness (AHR), and allergic inflammation. The single guanosine nucleotide deletion/insertion polymorphism (4G/5G) at -675 bp of the PAI-1 gene is the major genetic determinant of PAI-1 expression. Plasma PAI-1 level is higher in people with the 4G/4G genotype than in those with the 5G/5G genotype. A strong association between the 4G/5G polymorphism and the risk and the severity of asthma has been suggested. Levels of plasma IgE and PAI-1 and severity of AHR are greater in asthmatic patients with the 4G/4G genotype than in those with the 5G/5G genotype. The PAI-1 promoter with the 4G allele renders higher transcription activity than the PAI-1 promoter with the 5G allele in stimulated MCs. The molecular mechanism for the 4G allele-mediated higher PAI-1 expression is associated with greater binding of upstream stimulatory factor-1 to the E-box adjacent to the 4G site (E-4G) than to the E-5G. In summary, PAI-1 may play an important role in the pathogenesis of asthma. Further studies evaluating the mechanisms of PAI-1 action and regulation may lead to the development of a novel prognostic factor and therapeutic target for the treatment and prevention of asthma and other PAI-1-associated diseases.

Cuff-induced vascular intima thickening is influenced by titration of the Ace gene in mice

We tested the hypothesis that small changes in angiotensin I-converting enzyme (ACE) expression can alter the vascular response to injury. Male mice containing one, two, three, and four copies of the Ace gene with no detectable vascular abnormality or changes in blood pressure were submitted to cuff-induced femoral artery injury. Femoral thickening was higher in 3- and 4-copy mice (42.4 ± 4.3% and 45.7 ± 6.5%, respectively) compared with 1- and 2-copy mice (8.3 ± 1.3% and 8.5 ± 0.9%, respectively). Femoral ACE levels from control and injured vessels were assessed in 1- and 3-copy Ace mice, which represent the extremes of the observed response. ACE vascular activity was higher in 3- vs. 1-copy Ace mice (2.4-fold, P < 0.05) in the control uninjured vessel. Upon injury, ACE activity significantly increased in both groups [2.41-fold and 2.14-fold ( P < 0.05) for 1- and 3-copy groups, respectively] but reached higher levels in 3- vs. 1-copy Ace mice ( P < 0.05). Pharmacological interventions were then used as a counterproof and to indirectly assess the role of angiotensin II (ANG II) on this response. Interestingly, ACE inhibition (enalapril) and ANG II AT1 receptor blocker (losartan) reduced intima thickening in 3-copy mice to 1-copy mouse values ( P < 0.05) while ANG II treatment significantly increased intima thickening in 1-copy mice to 3-copy mouse levels ( P < 0.05). Together, these data indicate that small physiologically relevant changes in ACE, not associated with basal vascular abnormalities or blood pressure levels, do influence the magnitude of cuff-induced neointima thickening in mice.

Severe deficiency of coagulation Factor VII results in spontaneous cardiac fibrosis in mice

Mice genetically modified to produce low levels (approximately 1% of wild-type) of coagulation FVII presented with echocardiographic evidence of heart abnormalities. Decreases in ventricular size and reductions in systolic and diastolic functions were found, suggestive of a restrictive cardiomyopathy and consistent with an infiltrative myopathic process. Microscopic analysis of mouse hearts showed severe patchy fibrosis in the low-FVII mice. Haemosiderin deposition was discovered in hearts of these mice, along with increases in inflammatory cell number, ultimately resulting in widespread collagen deposition. Significant increases in mRNA levels of TGFbeta, TNFalpha and several matrix metalloproteinases in low-FVII mice, beginning at early ages, supported a state of cardiac remodelling associated with the fibrotic pathology. Mechanistic time-course studies suggested that cardiac fibrosis in low-FVII mice originated from bleeding in heart tissue, resulting in the recruitment of leukocytes, which released inflammatory mediators and induced collagen synthesis and secretion. These events led to necrosis of cardiomyocytes and collagen deposition, characteristics of cardiac fibrosis. The results of this study demonstrated that haemorrhagic and inflammatory responses to a severe FVII deficiency resulted in the development of cardiac fibrosis, observed echocardiographically as a restrictive cardiomyopathy, with compromised ventricular diastolic and systolic functions.

Integration of non-SMAD and SMAD signaling in TGF-beta1-induced plasminogen activator inhibitor type-1 gene expression in vascular smooth muscle cells

Overexpression of plasminogen activator inhibitor-1 (SERPINE1, PAI-1), the major physiological inhibitor of pericellular plasmin generation, is a significant causative factor in the progression of vascular disorders (e.g. arteriosclerosis, thrombosis, perivascular fibrosis) as well as a biomarker and a predictor of cardiovascular-disease associated mortality. PAI-1 is a temporal/spatial regulator of pericellular proteolysis and ECM accumulation impacting, thereby, vascular remodeling, smooth muscle cell migration, proliferation and apoptosis. Within the specific context of TGF-beta1-initiated vascular fibrosis and neointima formation, PAI-1 is a member of the most prominently expressed subset of TGF-beta1-induced transcripts. Recent findings implicate EGFR/pp60c-src-->MEK/ERK1/2 and Rho/ROCK-->SMAD2/3 signaling in TGF-beta1-stimulated PAI-1 expression in vascular smooth muscle cells. The EGFR is a direct upstream regulator of MEK/ERK1/2 while Rho/ROCK modulate both the duration of SMAD2/3 phosphorylation and nuclear accumulation. E-box motifs (CACGTG) in the PE1/PE2 promoter regions of the human PAI-1 gene, moreover, are platforms for a MAP kinase-directed USF subtype switch (USF-1-->USF-2) in response to growth factor addition suggesting that the EGFR-->MEK/ERK axis impacts PAI-1 expression, at least partly, through USF-dependent transcriptional controls. This paper reviews recent data suggesting the essential cooperativity among the EGFR-->MAP kinase cascade, the Rho/ROCK pathway and SMADs in TGF-beta1-initiated PAI-1 expression. The continued clarification of mechanistic controls on PAI-1 transcription may lead to new targeted therapies and clinically-relevant options for the treatment of vascular diseases in which PAI-1 dysregulation is a major underlying pathogenic feature.

Vitronectin inhibits plasminogen activator inhibitor-1-induced signalling and chemotaxis by blocking plasminogen activator inhibitor-1 binding to the low-density lipoprotein receptor-related protein

We have previously reported that the serpin plasminogen activator inhibitor-1 activates the Janus kinase (Jak)/signal transducer and activator of transcription (Stat) signalling pathway and stimulates cell migration by binding to the low-density lipoprotein receptor-related protein. All the free forms (cleaved, latent or active) of this inhibitor were shown to be motogenic. However, the plasminogen activator inhibitor-1 can also interact with vitronectin which acts as a cofactor by increasing the half-life of the active form of the serpin. Since vitronectin influences most of the biological functions of the plasminogen activator inhibitor-1, we explored the effects of vitronectin on signalling and cell migration induced by this serpin. We found that the interaction between vitronectin and the plasminogen activator inhibitor-1 suppressed signalling and cell migration. In fact, a purified vitronectin(1-97)/plasminogen activator inhibitor-1 complex was not chemotactic. Vitronectin interaction with the plasminogen activator inhibitor-1 blocks the binding of this serpin to its motogenic receptor, the low-density lipoprotein receptor-related protein. Consequently, vitronectin inhibits the activation of the Janus kinase/signal transducer and activator of transcription signalling pathway by the plasminogen activator inhibitor-1 and subsequent cell migration. In conclusion, we have unveiled a new inhibitory role of vitronectin, which turns off the intracellular signalling and migration-promoting activity of the plasminogen activator inhibitor-1. Thus, the motogenic (cleaved, latent or active) and non-motogenic (in complex with vitronectin) forms of the plasminogen activator inhibitor-1 have different properties that may explain the rather contrasting physiological and pathological roles of this serpin.

Adiponectin Mediates the Suppressive Effect of Rosiglitazone on Plasminogen Activator Inhibitor-1 Production

Objective— The purpose of this study was to examine the effects of PPAR-γ agonist rosiglitazone, relative to sulfonylureas, on circulating levels of adiponectin and the prothrombotic factor, plasminogen activator inhibitor (PAI)-1, in type 2 diabetic patients, and to investigate, in animal models, whether the antithrombotic action of rosiglitazone was mediated through adiponectin.

Methods and Results— Our clinical study (n=64) showed that after 24-week add-on therapy, the rosiglitazone group had a greater mean reduction in plasma PAI-1 levels (25%, versus 12% in sulfonylurea group, P =0.002). Stepwise multiple linear regression analysis identified the reduction in plasma fasting glucose and the rise in adiponectin levels to be independently associated with the reduction in PAI-I concentration in the rosiglitazone-treated patients. Rosiglitazone (20 mg/kg/d) reduced adipose tissue PAI-1 mRNA expression and its plasma levels in wild-type C57 mice with diet-induced obesity ( P <0.001), but this suppressive effect was attenuated in adiponectin knockout mice. Adenovirus-mediated overexpression of adiponectin led to a significant suppression of adipose tissue PAI-1 expression and its circulating concentrations in db/db diabetic mice. Our in vitro study demonstrated that recombinant adiponectin directly inhibited PAI-1 production in 3T3-L1 adipocytes.

Conclusions— The antithrombotic effect of rosiglitazone is mediated, at least in part, through the suppressive effect of adiponectin on PAI-1 production.

Vascular Functions of the Plasminogen Activation System

The plasminogen activator (PA) system, which controls the formation and activity of plasmin, plays a key role in modulating hemostasis, thrombosis, and several other biological processes. While a great deal is known about the function of the PA system, it remains a focus of intensive investigation, and the list of biological pathways and human diseases that are modulated by normal and pathologic function of its components continues to lengthen. Because of remarkable advances in molecular genetics, the laboratory mouse has become the most useful animal system to study the normal and pathologic functions of the PA system. The purpose of this review is to summarize studies that have used genetically modified mice to examine the functions of the PA system in hemostasis and thrombosis, intimal hyperplasia after vascular injury, and atherosclerosis. Particular emphasis is placed on the vascular functions of PA inhibitor-1, a key regulator of the PA system, and the multiple variables that appear to account for the complex role of PA inhibitor-1 in regulating vascular remodeling. Lastly, the strengths and limitations of using mice to model human vascular disease processes are discussed.

A guide to murine fibrinolytic factor structure, function, assays, and genetic alterations

The components and functions of the murine fibrinolytic system are quite similar to those of humans. Because of these similarities and the adaptability of mice to genetic manipulation, murine fibrinolysis has been studied extensively. These studies have yielded important information regarding the function of the several components of fibrinolysis. This review presents information on the structure, function and assay of mouse fibrinolytic parameters and it discusses the results of the extensive studies of genetically modified mice. It is intended to be a convenient reference resource for investigators of fibrinolysis.

Orally administered penicillamine is a potent inhibitor of neointimal and medial thickening in porcine saphenous vein–carotid artery interposition grafts

OBJECTIVE

In patients who have undergone coronary artery bypass grafting, blood copper levels are elevated for 6 weeks after surgery. Copper is an established risk factor for cardiovascular disease and atherogenesis and promotes oxidative stress, lipid oxidation, cell proliferation, and matrix formation, all components of vein graft disease. This project therefore examined the effect of the copper chelator penicillamine on saphenous vein graft thickening in a pig model.

METHODS

Saphenous vein-carotid artery interposition grafts were carried out in Landrace pigs. Penicillamine (10 mg/kg once daily, n = 8) was administered orally incorporated into small amounts of mashed potato for 1 month (n = 8 controls). Vein grafts were then excised and fixed at 100 mm Hg, histologic sections were prepared, and morphometry and measurement of proliferating cell nuclear antigen count were carried out. In vitro studies on the effect of copper or penicillamine on human vascular smooth muscle cell replication was carried out with bromodeoxyuridine incorporation.

RESULTS

Administration of penicillamine had a potent inhibitory effect on both neointimal and medial thickness and proliferating cell nuclear antigen count but elicited a marked increase in luminal area and reduced serum copper concentrations. In vitro, copper augmented vascular smooth muscle cell proliferation, an effect blocked by penicillamine. Penicillamine alone also inhibited in vitro vascular smooth muscle cell replication.

CONCLUSION

The administration of penicillamine reduces vein graft thickening and promotes positive remodeling through negation of copper-induced cell proliferation. Copper chelators may therefore be therapeutically useful in preventing late vein graft failure in patients undergoing reconstructive arterial surgery.

Haemostasis

When the continuity of the vascular endothelium is disrupted, platelets and fibrin seal off the defect. Haemostatic processes are classified as primary (mainly involving platelets) and secondary (mainly related to fibrin formation or blood coagulation). When the blood clot is no longer required for haemostasis, the fibrinolytic system will dissolve it. The pivotal ligand for initial platelet recruitment to injured vessel wall components is von Willebrand factor (vWF), a multimeric protein present in the subendothelium and in plasma, where it is conformationally activated by shear forces. Adhering activated platelets recruit additional platelets, which are in turn activated and form a platelet aggregate. Coagulation is initiated by a reaction, activating factors IX and X. Once critical amounts of factor Xa are generated, thrombin generation is initiated and soluble fibrinogen is converted into insoluble fibrin. Excessive thrombin generation is prevented via inhibition by antithrombin and also via downregulation of its further generation by activation of the protein C pathway. Activation of the fibrinolytic system results from conversion of the proenzyme plasminogen into the active serine proteinase plasmin by tissue-type or urokinase-type plasminogen activators. Plasmin digests the fibrin component of a blood clot. Inhibition of the fibrinolytic system occurs at the level of the plasminogen activator (by plasminogen activator inhibitors) or at the level of plasmin (by alpha2-antiplasmin). Together, these physiological processes act to maintain normal functioning blood vessels and a non-thrombotic state.

Genetic background determines response to hemostasis and thrombosis

Background

Thrombosis is the fatal and disabling consequence of cardiovascular diseases, the leading cause of mortality and morbidity in Western countries. Two inbred mouse strains, C57BL/6J and A/J, have marked differences in susceptibility to obesity, atherosclerosis, and vessel remodeling. However, it is unclear how these diverse genetic backgrounds influence pathways known to regulate thrombosis and hemostasis. The objective of this study was to evaluate thrombosis and hemostasis in these two inbred strains and determine the phenotypic response of A/J chromosomes in the C57BL/6J background.

Methods

A/J and C57Bl/6J mice were evaluated for differences in thrombosis and hemostasis. A thrombus was induced in the carotid artery by application of the exposed carotid to ferric chloride and blood flow measured until the vessel occluded. Bleeding and rebleeding times, as surrogate markers for thrombosis and hemostasis, were determined after clipping the tail and placing in warm saline. Twenty-one chromosome substitution strains, A/J chromosomes in a C57BL/6J background, were screened for response to the tail bleeding assay.

Results

Thrombus occlusion time was markedly decreased in the A/J mice compared to C57BL/6J mice. Tail bleeding time was similar in the two strains, but rebleeding time was markedly increased in the A/J mice compared to C57BL/6J mice. Coagulation times and tail morphology were similar, but tail collagen content was higher in A/J than C57BL/6J mice. Three chromosome substitution strains, B6-Chr5^A/J, B6-Chr11^A/J, and B6-Chr17^A/J, were identified with increased rebleeding time, a phenotype similar to A/J mice. Mice heterosomic for chromosomes 5 or 17 had rebleeding times similar to C57BL/6J mice, but when these two chromosome substitution strains, B6-Chr5^A/J and B6-Chr17^A/J, were crossed, the A/J phenotype was restored in these doubly heterosomic progeny.

Conclusion

These results indicate that susceptibility to arterial thrombosis and haemostasis is remarkably different in C57BL/and A/J mice. Three A/J chromosome substitution strains were identified that expressed a phenotype similar to A/J for rebleeding, the C57Bl/6J background could modify the A/J phenotype, and the combination of two A/J QTL could restore the phenotype. The diverse genetic backgrounds and differences in response to vascular injury induced thrombosis and the tail bleeding assay, suggest the potential for identifying novel genetic determinants of thrombotic risk.

Vascular effects of TZDs: New implications

The incidence of diabetes, now affecting more than 170 million individuals is growing rapidly. Type 2 diabetes, which accounts for 90% of all diabetes cases, is associated with increased cardiovascular morbidity and mortality. Thiazolidinediones (TZDs), used for the treatment of patients with type 2 diabetes improve insulin sensitivity and endothelial dysfunction and exert beneficial effects on the lipid profile by activating the peroxisome proliferator-activated receptor gamma (PPAR-gamma). Moreover, a large body of evidence indicates that TZDs exhibit antiatherogenic effects independent of their antidiabetic and lipid-lowering properties by modulating inflammatory processes. This review will focus on the role of PPAR-gamma agonists in the vessel wall and summarize their effects on C-reactive protein (CRP), plasminogen activator inhibitor type-1 (PAI-1), matrix metalloproteinase-9 (MMP-9), adiponectin and ATP-binding cassette transporter A1 (ABCA1) and their implications for treatment of advanced stages of atherosclerosis, particularly in a setting of type 2 diabetes.

Plasminogen Activator Inhibitor-1 From Bone Marrow–Derived Cells Suppresses Neointimal Formation After Vascular Injury in Mice

Objective— To investigate the ability of bone marrow (BM)–derived cells to modulate neointimal growth after injury by expressing plasminogen activator inhibitor-1 (PAI-1).

Methods and Results— We performed BM transplantation (BMT) in lethally irradiated wild-type (WT) and PAI-1−/− mice. Three weeks after carotid injury with ferric chloride, analysis of Y-chromosome DNA expression in the vessel wall of female hosts revealed that 20.8±6.0% of the cells in the neointima and 37.6±5.7% of those in the media were of BM origin. Lack of PAI-1 in either the host or the donor cells did not affect recruitment of BM-derived cells into sites of vascular injury. The neointima consisted predominantly of smooth muscle cells, and a proportion of these cells expressed PAI-1. Overall, lack of PAI-1 was associated with enhanced neointimal formation. However, importantly, BMT WT→PAI-1−/− mice exhibited reduced neointimal area ( P =0.05) and luminal stenosis ( P =0.04) compared with BMT PAI-1−/−→PAI-1−/− mice. Although PAI-1–expressing cells were shown to be present in BMT WT→PAI-1−/− lesions, these mice did not exhibit detectable levels of the inhibitor in the circulation, suggesting that local production of PAI-1 by cells in the neointima and media was sufficient to reduce luminal stenosis.

Conclusions— PAI-1 from BM-derived cells appears capable of suppressing neointimal growth after vascular injury.

Phenotypic and genetic characterization of the Atp7a(Mo-Tohm) mottled mouse: a new murine model of Menkes disease

Mottled Tohoku (Atp7a(Mo-Tohm) or Mo(Tohm)) is an X-linked mutation with mottled pigmentation in heterozygous (Mo(Tohm)/+) females and is embryonic lethal at E11 in hemizygous (Mo(Tohm)/Y) males. Copper levels were low in the brain and high in the intestine of Mo(Tohm) mice. Two congenic strains with ICR or C57BL/6 (B6) background were produced for genetic and phenotypic analyses and revealed that Mo(Tohm)/+ females with ICR background survived until adulthood, while most with B6 background died within 2 days after birth. The Mo(Tohm)/Y males with both backgrounds died at around E11. Massive hemorrhage was shown in the yolk sac cavity with irregular attachment between the mesoderm and the endothelial cells of blood vessels in the embryos at E10.5, suggesting that this irregular attachment causes embryonic lethality. The Mo(Tohm) mutant had a 1440-bp deletion between intron 22 and exon 23 of the Atp7a gene. Mo(Tohm)/Y males with the wild-type Atp7a cDNA transgene were rescued from embryonic lethality, confirming that the Mo(Tohm) mutant is caused by the defect in the Atp7a gene. This mutant mouse is the most severe model of human Menkes disease in mottled mice established to date and one of the useful models for understanding the gene function of Menkes disease.

Apo(a) promotes thrombosis in a vascular injury model by a mechanism independent of plasminogen

OBJECTIVE

Structural similarity between apolipoprotein(a) [apo(a)], the unique apoprotein of lipoprotein(a), and plasminogen (Plg), the zymogen for plasmin, results in inhibition of functions of Plg by apo(a) in vitro. The objective of this study was to evaluate the interaction of Plg and apo(a) in vivo.

METHODS AND RESULTS

Vascular injury was induced in the carotid artery with a perivascular cuff in: (i) wild-type (WT); (ii) Plg deficient (Plg-/-); (iii) apo(a) (6 KIV construct) transgenic [apo(a)tg]; and (iv) apo(a) transgenic and Plg deficient [apo(a):Plg-/-] mice. At 10 days after cuff placement, the media and adventitia area were increased in the injured carotids compared with the uninjured carotids, and collagen deposition was greater in apo(a)tg, Plg-/- and apo(a):Plg-/- mice compared with WT mice. The incidence of a thrombus was greater (P < 0.05) in apo(a):Plg-/- mice (83%) than WT (20%), Plg-/- (12%), and apo(a)tg mice (9%). In the thrombi from apo(a)tg and apo(a):Plg-/- mice, P-selectin and von Willebrand factor immunostaining, indicating a platelet-rich thrombi, was greater than in WT and Plg-/- mice. The presence of fibrin(ogen) in the thrombi was greater in Plg-/- and apo(a):Plg-/- mice than apo(a)tg and WT mice. Of the four genotypes, only the apo(a):Plg-/- mice had both increased platelet and increased fibrin(ogen) deposition.

CONCLUSIONS

The major finding of this study is the high incidence of thrombosis after vascular injury in apo(a)transgenic mice in a Plg deficient background, providing strong evidence for a prothrombotic role of apo(a) independent of Plg in vivo.

The effects of the overexpression of recombinant uncoupling protein 2 on proliferation, migration and plasminogen activator inhibitor 1 expression in human vascular smooth muscle cells

AIMS/HYPOTHESIS

Increased oxidative stress in vascular smooth muscle cells (VSMCs) has been implicated in the pathogenesis of accelerated atherosclerosis in patients with diabetes mellitus. Uncoupling protein 2 (UCP-2) is an important regulator of intracellular reactive oxygen species (ROS) production. We hypothesised that UCP-2 functions as an inhibitor of the atherosclerotic process in VSMCs.

METHODS

Overexpression of human UCP-2 was performed in primary cultured human VSMCs (HVSMCs) via adenovirus-mediated gene transfer. Its effects on ROS production, AP-1 activity, plasminogen activator inhibitor 1 (PAI-1) gene expression, and cellular proliferation and migration were measured in response to high glucose and angiotensin II (Ang II) concentrations, two major factors in the pathogenesis of atherosclerosis in patients with diabetes and hypertension. Mitochondrial membrane potential and NAD(P)H oxidase activity were also measured.

RESULTS

High glucose and Ang II caused transient mitochondrial membrane hyperpolarisation. They also significantly stimulated ROS production, NAD(P)H oxidase activity, mitochondrial membrane potential, AP-1 activity, PAI-1 mRNA expression, and proliferation and migration of HVSMCs. Adenovirus-mediated transfer of the UCP-2 gene reversed all of these effects.

CONCLUSIONS/INTERPRETATION

The present study demonstrates that UCP-2 can modify atherosclerotic processes in HVSMCs in response to high glucose and Ang II. Our data suggest that agents increasing UCP-2 expression in vascular cells may help prevent the development and progression of atherosclerosis in patients with diabetes and hypertension.

Adipose Tissue and Atherothrombosis

Obesity is associated with increased cardiovascular mortality and morbidity mainly through insulin resistance. Dysregulation of protein secretion by adipose tissue is involved in obesity-related diseases. Adipose tissue contributes to create a subinflammatory status which could explain the disturbances in the haemostatic and fibrinolytic systems observed in obesity. Elevated plasma levels of PAI-1 demonstrated the strongest association with the degree of insulin resistance and could be an underlying mechanism for the thrombotic tendency and the progression of atherothrombosis during obesity. The effect of PAI-1 was examined on adipose tissue growth in several mouse models as well as on adipocyte differentiation in vitro. Most of the data indicate that PAI-1 can effectively modulate weight gain and may be a potential therapeutic target for controlling cardiovascular morbidity in obese subjects.

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.

Plasminogen activator inhibitor 1, fibrin, and the vascular response to injury

Intravascular fibrin deposition is believed to play an important role in the development of intimal hyperplasia, which is a hallmark of several human vascular disorders, including atherosclerosis and restenosis after balloon angioplasty. Plasminogen activator inhibitor-1 (PAI-1), the primary inhibitor or tissue- and urinary-type plasminogen activator, plays a key role in fibrin homeostasis by controlling plasmin formation. PAI-1 may also modulate vascular pathology via alternative pathways, such as inhibiting activated protein C and altering interactions between vascular smooth muscle cells and the extracellular matrix. The diverse functional profile of PAI-1 likely accounts for the variation observed in its impact on intimal hyperplasia in different disease models. This review examines recent studies addressing the vascular function of PAI-1, and those assessing the role of fibrin as a downstream mediator of PAI-1's effects.

Tiplaxtinin, a novel, orally efficacious inhibitor of plasminogen activator inhibitor-1: design, synthesis, and preclinical characterization

Indole oxoacetic acid derivatives were prepared and evaluated for in vitro binding to and inactivation of human plasminogen activator inhibitor-1 (PAI-1). SAR based on biochemical, physiological, and pharmacokinetic attributes led to identification of tiplaxtinin as the optimal selective PAI-1 inhibitor. Tiplaxtinin exhibited in vivo oral efficacy in two different models of acute arterial thrombosis. The remarkable preclinical safety and metabolic stability profiles of tiplaxtinin led to advancing the compound to clinical trials.

Conservation of critical functional domains in murine plasminogen activator inhibitor-1

Plasminogen activator inhibitor-1 is the main physiological regulator of tissue-type plasminogen activator in normal plasma. In addition to its critical function in fibrinolysis, plasminogen activator inhibitor-1 has been implicated in roles in other physiological and pathophysiological processes. To investigate structure-function aspects of mouse plasminogen activator inhibitor-1, the recombinant protein was expressed in Escherichia coli and purified. Five variant recombinant murine proteins (R76E, Q123K, R346A, R101A, and Q123K/R101A) were also generated using site-directed mutagenesis. The variant (R346A) was found to be defective in its inhibitory activity against tissue plasminogen activator relative to its wild-type counterpart. Enzyme-linked immunosorbent assay and surface plasmon resonance experiments demonstrated reduced vitronectin-binding affinity of the (Q123K) variant (K(D) = 1800 nm) relative to the wild-type protein (K(D) = 5.4 nm). Kinetic analyses indicated that the (Q123K) variant had a slower association (k(on) = 2.92 x 10(4) m(-1) s(-1)) to, and a faster dissociation from, vitronectin (k(off) = 5.3 x 10(-2) s(-1)), (wild-type k(on) = 1.03 x 10(6) m(-1) s(-1) and k(off) = 5.27 x 10(-3) s(-1)). The Q123K/R101A variant demonstrated an even lower vitronectin-binding ability. Low density lipoprotein receptor-related protein binding was decreased for the (R76E) variant. It was also demonstrated that the plasminogen activator inhibitor-1/vitronectin complex decreased the interaction of plasminogen activator inhibitor-1 with low density lipoprotein receptor-related protein. These results indicate that the complex interactions traditionally associated with different plasminogen activator inhibitor-1 functions apply to the murine system, thus showing a commonality of subtle functions among different species and evolutionary conservation of this protein. Further, this study provides additional evidence that the human hemostasis system can be studied effectively in the mouse, which is a great asset for investigations with gene-altered mice.

Enhanced in Vitro Proliferation of Aortic Endothelial Cells from Plasminogen Activator Inhibitor-1-deficient Mice

A number of studies have identified a role for plasminogen activator inhibitor-1 (PAI-1) in regulating angiogenesis, although results from these investigations have been controversial. Among key cellular components of an angiogenic vessel are endothelial cells (ECs), which are known to express several components of the fibrinolytic system, including PAI-1. Thus, alterations in expression of this protein may have direct effects on cell functions involved in vascular development. In this study, ECs were isolated from sections of murine arterial trees from wild-type and PAI-1-deficient mice, and low passage (passages 3-4) homogeneous subpopulations of these cells were obtained by immunomagnetic absorption to antibodies against CD105/CD106. The homogeneity of these cells was further assessed by immunohistochemistry and quantitative real-time reverse transcription-PCR analysis of a number of EC markers. Comparative analyses of EC proliferation (one event associated with angiogenesis) in wild-type and PAI-1-deficient ECs demonstrated enhanced rates of cell growth for PAI-1-deficient cells relative to wild-type cells. Additional studies demonstrated similar levels of both vascular endothelial growth factor (VEGF) mRNA and protein and enhanced levels of VEGF receptor-1 (Flt-1) mRNA in PAI-1-deficient cells relative to wild-type cells. Immunohistochemical analyses indicated that phosphorylation of Akt was also enhanced in PAI-1-deficient cells, implicating VEGF-induced cell signaling alterations in PAI-1-deficient cells, the result of which may contribute to alterations in cell proliferation.

Neointima formation and thrombosis after vascular injury in transgenic mice overexpressing plasminogen activator inhibitor-1 (PAI-1)

The controversial role of plasminogen activator inhibitor-1 (PAI-1) in neointima formation and restenosis was studied with the use of a vascular injury model in transgenic mice overexpressing murine PAI-1 (PAI-1 Tg) and in wild-type (WT) controls. Despite the high circulating PAI-1 levels in the PAI-1 Tg mice (52 +/- 9.8 ng mL-1 vs. 0.76 +/- 0.17 ng mL-1 in WT mice), no significant fibrin deposition was observed in non-injured femoral arteries of 8- to 12-week-old mice. Two weeks after severe electric injury, extensive and comparable fibrin deposition was observed in both genotypes, despite a significantly reduced in situ fibrinolytic activity in arterial sections of the PAI-1 Tg mice. The neointimal and medial areas were similar in WT and PAI-1 Tg mice, resulting in comparable intima/media ratios (e.g. 0.94 +/- 0.25 and 1.04 +/- 0.17 at the center of the injury). Nuclear cell counts in cross-sectional areas of the neointima of the injured region were also comparable in arteries from WT and PAI-1 Tg mice (224 +/- 63, 233 +/- 20), and the distribution pattern of alpha-actin-positive smooth muscle cells was similar. These findings indicate that in a vascular injury model that induces extensive and persistent fibrin deposition in femoral arteries of mice, overexpression of PAI-1 does not affect neointima formation.

Cause-effect relation between hyperfibrinogenemia and vascular disease

Elevated plasma levels of fibrinogen are associated with the presence of cardiovascular disease, but it is controversial whether elevated fibrinogen causally imparts an increased risk, and as such is a true modifier of cardiovascular disease, or is merely associated with disease. By investigating a transgenic mouse model of hyperfibrinogenemia, we show that elevated plasma fibrinogen concentration (1) elicits augmented fibrin deposition in specific organs, (2) interacts with an independent modifier of hemostatic activity to regulate fibrin turnover/deposition, (3) exacerbates neointimal hyperplasia in an experimental model of stasis-induced vascular remodeling, yet (4) may suppress thrombin generation in response to a procoagulant challenge. These findings provide direct experimental evidence that hyperfibrinogenemia is more than a by-product of cardiovascular disease and may function independently or interactively to modulate the severity and/or progression of vascular disease.

Intramural plasminogen activator inhibitor type-1 and coronary atherosclerosis

Altered expression of plasminogen activator inhibitor type-1 in vessel walls, reviewed here, might affect coronary atherogenesis. Upregulation might exacerbate vasculopathy by potentiating thrombosis and by inhibiting vascular smooth muscle cell migration, resulting in attenuation of thickness of elaborated fibrous caps implicated in the vulnerability of atheroma to rupture.

Fibrinolysis in LPS-induced chronic airway disease

To examine the role of the fibrinolytic system in LPS-induced airway disease, we compared the effect of a chronic LPS challenge in plasminogen activator inhibitor-deficient (C57BL/6JPAI-1-/-) mice and wild-type (WT) C57BL/6J mice. Physiological and biological assessments were performed, immediately after, and 4 wk after an 8-wk exposure to LPS or saline. Immediately after the LPS exposure, WT mice had increased estimates of airway reactivity to methacholine compared with C57BL/6JPAI-1-/- mice; however, airway inflammation was similar in both LPS-exposed groups. Significant increases in both active transforming growth factor (TGF)-beta1 and active matrix metalloproteinase (MMP)-9 was detected after LPS exposure in WT but not C57BL/6JPAI-1-/- mice. C57BL/6JPAI-1-/- mice showed significantly less TGF-beta1 in the lavage and higher MMP-9 in the lung tissue than WT mice at the end of exposure and 4 wk later. After LPS exposure, both WT and C57BL/6JPAI-1-/- mice had substantial expansion of the subepithelial area of the medium [diameter (d) = 90-129 microm]- and large (d > 129 microm)-size airways when compared with saline-exposed mice. Subepithelial fibrin deposition was prevalent in WT mice but diminished in C57BL/6JPAI-1-/-. PAI-1 expression by nonciliated bronchial epithelial cells was enhanced in LPS-exposed WT mice compared with the saline-exposed group. Four weeks after LPS inhalation, airway hyperreactivity and the expansion of the subepithelial area in the medium and large airways persisted in WT but not C57BL/6JPAI-1-/- mice. We conclude that an active fibrinolytic system can substantially alter the development and resolution of the postinflammatory airway remodeling observed after chronic LPS inhalation.

Serine protease inhibitor Serp-1 strongly impairs atherosclerotic lesion formation and induces a stable plaque phenotype in ApoE-/-mice

The myxoma virus protein Serp-1 is a member of the serine protease inhibitor superfamily. Serp-1 potently inhibits human serum proteases including plasmin, urokinase-type plasminogen activator (uPA), and tissue-type plasminogen activator (tPA). Serp-1 also displays a high antiinflammatory activity, rendering it a promising candidate for antiatherosclerotic therapy. In this study, we have thus examined the effect of Serp-1 on de novo atherosclerotic plaque formation and on advanced lesions. Perivascular collars were placed around carotid arteries of ApoE-/- mice to induce atherosclerotic plaques and Serp-1 treatment started at week 1 and week 5 after collar placement. Effects of Serp-1 on de novo atherogenesis were characterized by a significantly lower plaque size than that of control mice (18+/-5x10(3) versus 57+/-12x10(3) microm2, respectively; P=0.007). Immunostaining showed a 50% (P=0.004) decrease in the MOMA-2-stained lesion area of Serp-1-treated mice. Treatment of advanced lesions with Serp-1 resulted in a decrease in plaque size and lumen stenosis (P=0.028). Alpha-actin staining of these lesions was significantly increased compared with the control (P=0.017). In both studies, a higher cellularity of the plaque and increased collagen content was observed in Serp-1-treated mice. In vitro studies showed that Serp-1 induces proliferation and migration of vascular smooth muscle cells. In conclusion, Serp-1 inhibits carotid artery plaque growth and progression in ApoE-/- mice. Equally relevant, it enhances cellularity of the plaque core potentially leading to improved plaque stability. The above results indicate that Serp-1 constitutes a promising lead in antiatherosclerotic therapy.

Fibrinogen, inflammation and concentric left ventricular hypertrophy in chronic renal failure

BACKGROUND

We investigated the relationship between fibrinogen and echocardiographic measurements of left ventricular (LV) geometry and LV function in a group of 192 patients with end stage renal disease (ESRD).

RESULTS

Patients in the third fibrinogen tertile had higher mean wall thickness (MWT), relative wall thickness (RWT) and left ventricular mass index (LVMI) and lower LV end diastolic diameter and LV ejection fraction than those in the other tertiles. On multivariate analysis fibrinogen resulted to be an independent correlate of MWT (P = 0.001) and RWT (P = 0.0001) and the first factor in rank explaining the variance in LV ejection fraction (P = 0.0001). Left ventricular concentric hypertrophy was more prevalent (P = 0.001) in patients in the third fibrinogen tertile (n = 35, 54%) than in those in the second (n = 24, 37%) and first (n = 13, 21%) tertiles. In a multiple logistic regression model patients in the third tertile of fibrinogen had a risk for left ventricular concentric hypertrophy that was 3.56 (95% CI: 1.56-8.14) fold higher than in those in the first tertile (P = 0.003).

CONCLUSIONS

Elevated fibrinogen is independently associated with LV concentric hypertrophy and systolic dysfunction in ESRD patients. These relationships may contribute to the negative prognostic impact of elevated fibrinogen levels in ESRD.

The susceptibility of lipoprotein(a) to copper oxidation is correlated with the susceptibility of autologous low density lipoprotein to oxidation

OBJECTIVES

Lipoprotein(a) [Lp(a)] can be oxidized by copper in vitro in a way comparable to low-density lipoprotein (LDL). We sought to determine whether the susceptibility of Lp(a) to oxidation is correlated with the susceptibility of autologous heterogeneous LDL, with apolipoprotein(a) [apo(a)] molecular size, or with both factors.

DESIGN AND METHODS

We examined shifts in electrophoretic mobility of Lp(a) and LDL caused by copper oxidation in plasma samples from 81 healthy men. The effect of copper oxidation on different-sized apo(a) was also evaluated.

RESULTS

There was a close correlation between the relative electrophoretic mobilities of oxidized Lp(a) and oxidized LDL in subjects, especially with small-sized apo(a) (n = 25, r = 0.72, p < 0.0001). Oxidative processes in Lp(a) resulted in the degradation of large-, but not small-sized apo(a).

CONCLUSIONS

The susceptibility of Lp(a) to oxidation is correlated with that of autologous LDL. Large-sized apo(a) may be involved in the Lp(a) oxidation.

Plasminogen activator inhibitor 1 and vitronectin protect against stenosis in a murine carotid artery ligation model

OBJECTIVE

We previously reported that plasminogen activator inhibitor 1 (PAI-1), in the presence of vitronectin (VN), inhibits thrombin activity in vitro. Furthermore, we demonstrated in human atherosclerotic plaques the colocalization of thrombin, PAI-1, and VN, as well as activity of thrombin and PAI-1. Here, we show that PAI-1 is a local thrombin inhibitor in vivo.

METHODS AND RESULTS

We used the murine carotid artery ligation model to assess the role of PAI-1 and VN in stenosis by using PAI-1-deficient (PAI-1(-/-)) and VN(-/-) mice. Ligation resulted in a smooth muscle cell (SMC)-rich intima without infiltrating cells. We show that PAI-1(-/-) and VN(-/-) mice generate a larger intima than wild-type mice as the result of more extensive SMC proliferation, as evidenced by cell counting and staining for proliferating cell-nuclear antigen.

CONCLUSIONS

In PAI-1(-/-) mice, excessive intima formation is prevented by the thrombin-specific inhibitor hirudin. Finally, immunohistochemical analysis revealed PAI-1, VN, and (pro)thrombin antigen in intimal lesions. Our observations are compatible with inhibition of thrombin-mediated SMC proliferation by PAI-1/VN complexes.

Different mechanisms of increased luminal stenosis after arterial injury in mice deficient for urokinase- or tissue-type plasminogen activator

BACKGROUND

Tissue-type plasminogen activator (tPA) and urokinase-type plasminogen activator (uPA) are thought to play critical roles in vascular remodeling after injury, with tPA mediating intravascular clot lysis and uPA modulating cell migration within the vessel wall. In human vascular disease, however, thrombus organization and neointimal formation are closely interrelated processes. This study examines the differential roles of tPA and uPA in these processes in mice.

METHODS AND RESULTS

Carotid artery injury and thrombosis were induced in wild-type (WT), uPA-deficient (uPA(-/-)), and tPA-deficient (tPA(-/-)) mice with the use of ferric chloride. The expression of uPA and tPA was significantly upregulated in the vessel wall of WT mice 1 week after injury, and compared with WT mice, uPA(-/-) and tPA(-/-) mice had lower carotid patency rates after injury. At 3 weeks, only 55% of uPA(-/-) mouse vessels were patent compared with 81% in tPA(-/-) mice and 100% in WT mice (P=0.014). Morphometric analysis of injured arterial segments revealed severe luminal stenosis (62+/-28%) in uPA(-/-) mice compared with their tPA(-/-) (16+/-12%) and WT (6.3+/-3.6%, P<0.001) counterparts. Moreover, although the vascular walls of WT mice and, particularly, tPA(-/-) mice developed a cell-rich multilayered neointima and media, the lumen of uPA(-/-) vessels remained obstructed with acellular unorganized thrombotic material, and their medial areas did not expand.

CONCLUSIONS

These results indicate that the roles of uPA and tPA in the arterial response to injury are different and more complex than previously assumed and emphasize the critical role of thrombus organization and resolution in neointimal formation and vascular pathology.