Non-hematopoietic deficiency of proprotein convertase subtilisin/kexin type 9 deficiency leads to more severe anemia in a murine model of sickle cell disease.

Proprotein convertase subtilisin/kexin type 9 (PCSK9) deficiency leads to lower cholesterol and is associated with reduced vascular complications in the general population. Cholesterol lowering may also have beneficial effects in sickle cell disease (SCD). The objective of this study was to determine effects of PCSK9 deficiency in a mouse model of SCD. Bone marrow transplantation (BMT) was performed from donor SCD mice to wild-type, PCSK9-deficient, and LDLR-deficient recipients to generate SCD controls (Pcsk9+/+, SCDbmt) with preserved PCSK9 status, SCD mice with deficiency of PCSK9 (Pcsk9-/-, SCDbmt), and SCD mice with deficiency of LDLR (Ldlr-/-, SCDbmt). Although cholesterol levels were lower in Pcsk9-/-, SCDbmt mice compared to Pcsk9+/+, SCDbmt mice, anemia was more severe in Pcsk9-/-, SCDbmt mice. Increased reticulocytosis, enhanced ex vivo erythrocyte sickling, and increased erythrocyte phosphatidylserine exposure was also observed. Livers, spleens, and kidneys contained increased iron in Pcsk9-/-, SCDbmt mice compared to Pcsk9+/+, SCDbmt mice consistent with greater hemolysis. SCD mice with deficiency of LDLR (Ldlr-/-, SCDbmt mice) had similar anemia as Ldlr+/+, SCDbmt mice despite higher serum cholesterol. In conclusion, deficiency of PCSK9 is associated with worsened anemia in SCD mice due to increased hemolysis. These findings may have implications for lipid-lowering strategies in patients with SCD, as well as for potential novel modifiers of anemia severity.

Bleomycin-induced pulmonary fibrosis in transgenic mice that either lack or overexpress the murine plasminogen activator inhibitor-1 gene.

Impaired fibrinolytic activity within the lung is a common manifestation of acute and chronic inflammatory lung diseases. Because the fibrinolytic system is active during repair processes that restore injured tissues to normal, reduced fibrinolytic activity may contribute to the subsequent development of pulmonary fibrosis. To examine the relationship between the fibrinolytic system and pulmonary fibrosis, lung inflammation was induced by bleomycin in transgenic mice that either overexpressed or were completely deficient in murine plasminogen activator inhibitor-1 (PAI-1). 2 wk after 0.075 U of bleomycin, the lungs of transgenic mice overexpressing PAI-1 contained significantly more hydroxyproline (118 +/- 8 micrograms) than littermate controls (70.5 +/- 8 micrograms, P < 0.005). 3 wk after administration of a higher dose of bleomycin (0.15 U), the lung hydroxyproline content of mice completely deficient in PAI-1 (49 +/- 8 micrograms) was not significantly different (P = 0.63) than that of control animals receiving saline (37 +/- 1 micrograms), while hydroxyproline content was significantly increased in heterozygote (77 +/- 12 micrograms, P = 0.06) and wild-type (124 +/- 19 micrograms, P < 0.001) littermates. These data demonstrate a direct correlation between the genetically determined level of PAI-1 expression and the extent of collagen accumulation that follows inflammatory lung injury. These results strongly support the hypothesis that alterations in fibrinolytic activity influence the extent of pulmonary fibrosis that occurs after inflammatory injury.

Peptide-mediated inactivation of recombinant and platelet plasminogen activator inhibitor-1 in vitro.

Plasminogen activator inhibitor-1 (PAI-1), the primary inhibitor of tissue-type plasminogen activator (t-PA) and urokinase plasminogen activator, is an important regulator of the blood fibrinolytic system. Elevated plasma levels of PAI-1 are associated with thrombosis, and high levels of PAI-1 within platelet-rich clots contribute to their resistance to lysis by t-PA. Consequently, strategies aimed at inhibition of PAI-1 may prove clinically useful. This study was designed to test the hypothesis that a 14-amino acid peptide, corresponding to the PAI-1 reactive center loop (residues 333-346), can rapidly inhibit PAI-1 function. PAI-1 (0.7 microM) was incubated with peptide (55 microM) at 37 degrees C. At timed intervals, residual PAI-1 activity was determined by addition of reaction mixture samples to t-PA and chromogenic substrate. The T1/2 of PAI-1 activity in the presence of peptide was 4 +/- 3 min compared to a control T1/2 of 98 +/- 18 min. The peptide also inhibited complex formation between PAI-1 and t-PA as demonstrated by SDS-PAGE analysis. However, the capacity of the peptide to inhibit PAI-1 bound to vitronectin, a plasma protein that stabilizes PAI-1 activity, was markedly attenuated. Finally, the peptide significantly enhanced in vitro lysis of platelet-rich clots and platelet-poor clots containing recombinant PAI-1. These results indicate that a 14-amino acid peptide can rapidly inactivate PAI-1 and accelerate fibrinolysis in vitro. These studies also demonstrate that PAI-1 function can be directly attenuated in a physiologic setting and suggest a novel approach for augmenting fibrinolysis in vivo.

Generation of soluble P- and E-selectins in vivo is dependent on expression of P-selectin glycoprotein ligand-1.

BACKGROUND: Factors contributing to the generation of soluble P- and E-selectins remain unclear. RESULTS: This work demonstrates that mice lacking P-selectin glycoprotein ligand-1 (Psgl-1(-/-)) are deficient in soluble P-selectin (sP-sel), which is due to a defective binding interaction between PSGL-1 and P-sel, because mice lacking alpha(1,3)-fucosyltransferase-VII are also deficient in sP-sel. Psgl-1(-/-) mice are also deficient in soluble E-selectin (sE-sel) indicating that leukocyte interactions with endothelial cells lead to the generation of sE-sel. The generation of sE-sel requires an interaction between PSGL-1 and P-sel, as deficiency of sE-sel is observed in both Psgl-1(-/-) and P-sel(-/-) mice. Bone marrow transplantation from Psgl-1(-/-) to Psgl-1(+/+) mice leads to deficiency of sP-sel and sE-sel in recipient mice, establishing the importance of bone marrow-derived PSGL-1 toward the generation of sP-sel and sE-sel. Bone marrow transplantation from P-sel(-/-) to P-sel1(+/+) mice does not lead to a significant reduction in sP-sel, confirming the importance of the endothelium toward the liberation of sP-sel. CONCLUSION: sP-sel and sE-sel reflect an interaction between leukocyte PSGL-1 and endothelial P-sel.

Deficiency of tissue factor pathway inhibitor promotes atherosclerosis and thrombosis in mice.

BACKGROUND: Tissue factor initiates blood coagulation after atherosclerotic plaque disruption. Tissue factor pathway inhibitor (TFPI) inhibits tissue factor activity and may reduce thrombus formation in this setting. We evaluated the effect of heterozygous TFPI deficiency on the development of atherosclerosis and thrombosis in atherosclerosis-prone mice. METHODS AND RESULTS: Mice with a combined heterozygous TFPI deficiency and homozygous apolipoprotein E deficiency (TFPI(+/-)/apoE(-/-)) were generated by crossbreeding, and they were analyzed for atherosclerosis throughout the vascular tree. Compared with mice with a normal TFPI genotype (TFPI(+/+)/apoE(-/-)), mice with a TFPI deficiency exhibited a greater atherosclerotic burden involving the carotid and common iliac arteries. Staining for active tissue factor within the plaque revealed more activity in TFPI(+/-)/apoE(-/-) mice compared with TFPI(+/+)/apoE(-/-) mice. Consistent with increased plaque tissue factor activity, the time to occlusive thrombosis after photochemical carotid plaque injury was significantly decreased in TFPI(+/-)/apoE(-/-) mice. CONCLUSIONS: These observations indicate that TFPI protects from atherosclerosis and is an important regulator of the thrombosis that occurs in the setting of atherosclerosis.

Nifedipine administered after reperfusion ablates systolic contractile dysfunction of postischemic "stunned" myocardium.

Recent evidence suggests that postischemic contractile dysfunction of viable myocardium salvaged by reperfusion ("stunned myocardium") may be a consequence of abnormal calcium flux within the previously ischemic cells. Calcium channel blocking agents have been shown to enhance contractile function of stunned postischemic tissue, but it is not certain whether these improvements in function are due to the profound hemodynamic and vasodilator effects of these agents or to a direct effect on calcium flux within the stunned myocytes. Therefore, the effects of 1) high doses of nifedipine, given intravenously at 30 min after reperfusion, and 2) minute doses of nifedipine, infused directly into the coronary circulation at 30 min after reflow, were assessed and compared in anesthetized open chest dogs subjected to 15 min of transient coronary artery occlusion. As anticipated, intravenous nifedipine significantly reduced arterial pressure and increased regional myocardial blood flow. In addition, intravenous nifedipine restored systolic contractile function of the stunned, previously ischemic tissue to essentially normal preocclusion values: segment shortening averaged 102 +/- 8% versus 26 +/- 11% of baseline at 2 h after treatment in treated versus control dogs, respectively (p less than 0.003). Low dose intracoronary infusion of nifedipine did not alter hemodynamic variables or myocardial blood flow, but did improve segment shortening (90 +/- 9% versus 37 +/- 10% of preocclusion values at 1 h after treatment versus 25 min after reperfusion [that is, pretreatment], respectively; p less than 0.03). These data indicate that the calcium channel blocking agent nifedipine, given 30 min after reperfusion, enhances systolic contractile function of postischemic stunned myocardium.(ABSTRACT TRUNCATED AT 250 WORDS)

Pioglitazone protects against thrombosis in a mouse model of obesity and insulin resistance.

BACKGROUND: As arterial thrombosis accounts for the vast majority of cardiovascular complications in obese, insulin resistant patients, we hypothesized that improving insulin sensitivity may be effective in reducing the thrombotic response following vascular injury. OBJECTIVES: We investigated the effect of the thiazolidinedione drug, pioglitazone, on the thrombotic response to injury in obese, insulin resistant mice. METHODS: Insulin-resistant, obesity-prone mice (KK strain) were treated with pioglitazone, placebo, or the sulfonylurea compound, glipizide, for 2.5 weeks and then subjected to photochemical injury of the carotid artery. RESULTS: KK mice have a significant increase in adiposity (7 weeks: 25.6%; 15 weeks: 34.4%; P < 0.0001) and thrombotic tendency (7 weeks: 21.2 +/- 1.9 min; 15 weeks: 13.7 +/- 1.7 min; P < 0.01) with age. Pioglitazone provided significant protection from thrombosis at both time points, prolonging the time to occlusive thrombosis by 40% and 68%, at 7 and 15 weeks of age, respectively (P < 0.05). Similarly, following a diet-challenge to promote diabetes, pioglitazone provided protection from occlusive thrombus formation (Placebo: 11.3 +/- 1.0 min; Pioglitazone: 22.3 +/- 3.9 min; P < 0.05). However, despite a salient effect of glipizide on the hyperglycemia of the mice, there was no effect on the time to occlusive thrombus formation (13.2 +/- 0.9 min, n = 4) compared with placebo-treated mice. The pioglitazone protection was paralleled by significantly lower soluble P-selectin and platelet P-selectin expression providing evidence of an antiplatelet effect. CONCLUSIONS: We conclude that pioglitazone treatment provides protection against arterial thrombosis in an obese, insulin resistant, prothrombotic mouse model.

Deficiency of P-selectin glycoprotein ligand-1 is protective against the prothrombotic effects of interleukin-1ß.

BACKGROUND: Proinflammatory cytokines are associated with cardiovascular diseases, including acute and recurrent myocardial infarction. However, the causal role of cytokines in thrombotic complications of atherosclerosis remains unclear. Interleukin-1ß (IL-1ß) is currently being targeted in a human clinical trial for the prevention of ischemic events. OBJECTIVES: The purpose of the present study was to test the role of IL-1ß in arterial thrombosis and a potential protective effect of P-selectin glycoprotein ligand-1 (Psgl-1) deficiency. METHODS AND RESULTS: Wild-type and Psgl-1-deficient mice were treated with IL-1ß and then subjected to carotid photochemical injury to induce thrombosis. IL-1ß shortened the time to thrombosis in wild-type mice, while Psgl-1(-/-) mice were protected from the prothrombotic effects of IL-1ß. A neutralizing antibody to Psgl-1 was also effective in protecting against the prothrombotic effects of IL-1ß. The protective effect of Psgl-1 deficiency was associated with reduced plasma levels of soluble P-selectin and collagen-stimulated whole blood aggregation. CONCLUSIONS: Our data demonstrate that Psgl-1 deficiency is protective against the prothrombotic effects of IL-1ß and suggest that Psgl-1 inhibition may be a useful treatment strategy for targeting vascular thrombosis associated with enhanced inflammatory states.

Pulmonary fibrosis is increased in mice carrying the factor V Leiden mutation following bleomycin injury.

Increased fibrin deposition following inflammatory lung injury has been proposed to facilitate the development of pulmonary fibrosis. Therefore, factors predisposing to thrombosis may affect the fibrotic response to injury. Activated protein C (aPC) resistance due to the factor V Leiden mutation (FvL) is a common genetic risk factor for vascular thrombosis. To examine the relationship between aPC resistance and the development of pulmonary fibrosis, lung inflammation was induced by bleomycin in mice carrying the FvL mutation. Three weeks following the instillation of 0.0375 U of bleomycin, the lungs of mice homozygous and heterozygous for FvL contained significantly more hydroxyproline (35 +/- 4 and 36 +/- 7 ug hydroxyproline/mg total protein, respectively) than wild-type mice (26 +/- 6 ug/mg protein, p <0.01 for both comparisons). These data demonstrate a strong relationship between aPC resistance and the pulmonary fibrosis that occurs following inflammatory lung injury.

Spontaneous coronary artery dissection in a pregnant woman.

BACKGROUND: Spontaneous coronary dissection is a rare condition occurring more often in women, with a higher frequency during the peripartum period. No specific etiology has been defined to describe this uncommon, yet often fatal phenomenon. CASE: A young woman presented at 36 weeks of a noncomplicated pregnancy with recent onset of diaphoresis, dyspnea, and tingling substernal chest discomfort. Upon evaluation, she developed cardiovascular collapse and ventricular fibrillation requiring aggressive resuscitative measures, eventually leading to extracorporeal membrane oxygenation. Right coronary artery dissection was ultimately diagnosed and treated with intracoronary angioplasty and stent placement. CONCLUSION: Spontaneous coronary dissection must be considered when evaluating a patient with a similar clinical presentation, given its overall mortality of more than 50% at presentation, particularly in the peripartum period.

Eustachian valve endocarditis caused by Streptococcus viridans.

A 76-year-old man was admitted for ethanol detoxification. He was found to be in atrial fibrillation with a rapid ventricular response that was refractory to electrical and chemical cardioversion attempts. The patient subsequently developed respiratory distress. A transesophageal echocardiogram revealed a vegetation attached to the eustachian valve and blood cultures grew Streptococcus viridans. After treatment with appropriate antibiotics, the patient converted to sinus rhythm with sotalol hydrochloride, and the eustachian valve vegetation resolved. This is the first reported case of eustachian valve endocarditis caused by S viridans.

Perivascular visceral adipose tissue induces atherosclerosis in apolipoprotein E deficient mice.

OBJECTIVE: Epicardial adipose tissue is associated with coronary artery disease, however the causal relationship between perivascular adipose tissue and local atherogenesis is unclear. METHODS AND RESULTS: Apolipoprotein E deficient (ApoE(-/-)) mice underwent transplantation of visceral or subcutaneous adipose tissue immediately adjacent to the right common carotid artery. Carotid arteries with fat transplants were analyzed for atherosclerosis by surface oil-red-O staining and cross-sectional analysis. Vascular function of the carotid arteries was assessed using pressure myography. Visceral fat transplants were also performed to ApoE(-/-) mice with neutralization of P-selectin glycoprotein ligand-1 (Psgl-1). Atherosclerosis surface area and lesion thickness were greater in mice receiving the perivascular visceral fat compared to the subcutaneous fat. Mice with visceral fat transplants also displayed more complicated atherosclerotic lesions with evidence of atherothrombosis. Serum Mcp-1 was higher in mice receiving visceral fat transplants compared to subcutaneous transplants. Visceral fat transplantation also caused impaired endothelial-dependent relaxation of the carotid artery. Psgl-1 deficiency or neutralization of Psgl-1 with an anti-Psgl-1 antibody was protective against perivascular visceral adipose tissue-induced atherosclerosis and was associated with reduced Mcp-1 levels. CONCLUSIONS: Perivascular visceral fat leads to endothelial dysfunction and accelerated atherosclerosis. This proatherogenic effect of perivascular adipose tissue is blocked by neutralization of Psgl-1.

Hyperlipidemia promotes thrombosis after injury to atherosclerotic vessels in apolipoprotein E-deficient mice.

The increased risk of hyperlipidemia on the development of complications of atherosclerosis is well established. Cholesterol-lowering therapies lead to a decrease in the incidence of vascular thrombotic events that is out of proportion to the reduction in plaque size. This suggests that the occurrence of acute thrombosis overlying a disrupted plaque is influenced by changes in lipid levels. The influence of acute hyperlipidemia on the development of thrombosis overlying an atherosclerotic plaque in vivo has not been extensively studied. We used a murine model of vascular injury induced by a photochemical reaction to elicit thrombus formation overlying an atherosclerotic plaque. Fifteen apolipoprotein E-deficient mice were maintained on normal chow until the age of 30 weeks. Five days before the induction of thrombosis, 6 mice were started on a high fat diet, and 9 mice were continued on normal chow. Mice then underwent photochemical injury to the common carotid artery immediately proximal to the carotid bifurcation, where an atherosclerotic plaque is consistently present. Mice maintained on normal chow developed occlusive thrombi, determined by cessation of blood flow, 44+/-5 minutes (mean+/-SEM) after photochemical injury, whereas mice fed a high fat chow developed occlusive thrombosis at 27+/-3 minutes (P<0.02). Histological analysis confirmed the presence of acute thrombus formation overlying an atherosclerotic plaque. These studies demonstrate a useful model for assessing the determinants of thrombosis in the setting of atherosclerosis and show that acute elevations in plasma cholesterol facilitate thrombus formation at sites of atherosclerosis after vascular injury.

Plasminogen activator inhibitor-1 deficiency protects against atherosclerosis progression in the mouse carotid artery.

Dissolution of the fibrin blood clot is regulated in large part by plasminogen activator inhibitor-1 (PAI-1). Elevated levels of plasma PAI-1 may be an important risk factor for atherosclerotic vascular disease and are associated with premature myocardial infarction. The role of the endogenous plasminogen activation system in limiting thrombus formation following atherosclerotic plaque disruption is unknown. This study found that genetic deficiency for PAI-1, the primary physiologic regulator of tissue-type plasminogen activator (tPA), prolonged the time to occlusive thrombosis following photochemical injury to carotid atherosclerotic plaque in apolipoprotein E-deficient (apoE(-/-)) mice. However, anatomic analysis revealed a striking difference in the extent of atherosclerosis at the carotid artery bifurcation between apoE(-/-) mice and mice doubly deficient for apoE and PAI-1 (PAI-1(-/-)/apoE(-/-)). Consistent with a previous report, PAI-1(+/+)/apoE(-/-)and PAI-1(-/-)/apoE(-/-) mice developed similar atherosclerosis in the aortic arch. The marked protection from atherosclerosis progression at the carotid bifurcation conferred by PAI-1 deficiency suggests a critical role for PAI-1 in the pathogenesis of atherosclerosis at sites of turbulent flow, potentially through the inhibition of fibrin clearance. Consistent with this hypothesis, intense fibrinogen/fibrin staining was observed in atherosclerotic lesions at the carotid bifurcation compared to the aortic arch. These observations identify significant differences in the pathogenesis of atherosclerosis at varying sites in the vascular tree and suggest a previously unappreciated role for the plasminogen activation system in atherosclerosis progression at sites of turbulent flow. (Blood. 2000;96:4212-4215)

Lack of plasminogen activator inhibitor-1 effect in a transgenic mouse model of metastatic melanoma.

Tumor cell invasion and metastasis is a complex, multistep process that is postulated to require degradation of extracellular matrix at several steps. Urokinase-type plasminogen activator (uPA) is expressed on the cell surface of B16 murine melanoma cells and is thought to contribute to the pericellular proteolysis necessary for tumor cell migration. In vitro modification of B16 melanoma cell surface uPA activity has been shown to alter the invasive and metastatic potential of these murine melanoma cells in vivo. Plasminogen activator inhibitor-1 (PAI-1), a rapid inhibitor of both uPA and tissue-type plasminogen activator (tPA) is the major physiologic regulator of plasminogen activator activity. To test the role of host PAI-1 in the invasive and metastatic capacity of B16 melanoma cells we analyzed local tumor growth and pulmonary metastasis in transgenic mice engineered to overexpress murine PAI-1 in multiple tissues including lung, and in mice completely deficient in PAI-1. No significant difference in the number of pulmonary metastases was observed after intravenous inoculation of tumor cells into PAI-1-overexpressing and PAI-1-deficient mice when compared with wild-type controls. Similarly, in a spontaneous metastasis model, PAI-1-overexpressing and PAI-1-deficient mice demonstrated no difference in primary tumor size or overall survival. These data demonstrate that wide variations of host PAI-1 expression, from complete absence to marked overexpression, does not significantly influence the metastatic potential of B16 melanoma cells in a murine model.

Plasminogen activator inhibitor-1 and vitronectin promote vascular thrombosis in mice.

Occlusive thrombosis depends on the net balance between platelets, coagulation, and fibrinolytic factors. Epidemiologic information suggests that plasminogen activator inhibitor-1 (PAI-1), a central regulator of the fibrinolytic system, plays an important role in determining the overall risk for clinically significant vascular thrombosis. Vitronectin (VN), an abundant plasma and matrix glycoprotein, binds PAI-1 and stabilizes its active conformation. This study assessed the role of PAI-1 and VN expression in the formation of occlusive vascular thrombosis following arterial or venous injury. The common carotid arteries of 17 wild-type (WT) mice and 8 mice deficient in PAI-1 were injured photochemically while blood flow was continuously monitored. WT mice developed occlusive thrombi at 52.0 +/- 3.8 minutes (mean +/- SEM) following injury; mice deficient in PAI-1 developed occlusive thrombosis at 127 +/- 15 minutes (P <.0001). Mice deficient in VN (n = 12) developed vascular occlusion 77 +/- 11 minutes after injury, intermediate between the values observed for WT mice (P <.03) and mice deficient in PAI-1 (P <.01). PAI-1 and VN also affected the time to occlusion after injury to the jugular vein. Three WT mice developed occlusive venous thrombosis an average of 39.7 +/- 1 minutes following the onset of injury, whereas the jugular veins of 4 mice deficient in PAI-1 and 4 deficient in VN occluded 56.7 +/- 5 and 58.7 +/- 2 minutes, respectively, following injury (P <.04 and P <.01 compared to WT mice). These results suggest that endogenous fibrinolysis and its regulation by PAI-1 and VN have important roles in the development of occlusive vascular thrombosis after vascular injury. (Blood. 2000;95:577-580)

Atherosclerosis progression in LDL receptor-deficient and apolipoprotein E-deficient mice is independent of genetic alterations in plasminogen activator inhibitor-1.

Impaired fibrinolysis has been linked to atherosclerosis in a number of experimental and clinical studies. Plasminogen activator inhibitor type 1 (PAI-1) is the primary inhibitor of plasminogen activation and has been proposed to promote atherosclerosis by facilitating fibrin deposition within developing lesions. We examined the contribution of PAI-1 to disease progression in 2 established mouse models of atherosclerosis. Mice lacking apolipoprotein E (apoE-/-) and mice lacking the low density lipoprotein receptor (LDLR-/-) were crossbred with transgenic mice overexpressing PAI-1 (resulting in PAI-1 Tg(+)/apoE-/- and PAI-1 Tg(+)/LDLR-/-, respectively) or were crossbred with mice completely deficient in PAI-1 gene expression (resulting in PAI-1-/-/apoE-/- and PAI-1-/-/LDLR-/-, respectively). All animals were placed on a western diet (21% fat and 0.15% cholesterol) at 4 weeks of age and analyzed for the extent of atherosclerosis after an additional 6, 15, or 30 weeks. Intimal and medial areas were determined by computer-assisted morphometric analysis of standardized microscopic sections from the base of the aorta. Atherosclerotic lesions were also characterized by histochemical analyses with the use of markers for smooth muscle cells, macrophages, and fibrin deposition. Typical atherosclerotic lesions were observed in all experimental animals, with greater severity at the later time points and generally more extensive lesions in apoE-/- than in comparable LDLR-/- mice. No significant differences in lesion size or histological appearance were observed among PAI-1-/-, PAI-1 Tg(+), or PAI-1 wild-type mice at any of the time points on either the apoE-/- or LDLR-/- genetic background. We conclude that genetic modification of PAI-1 expression does not significantly alter the progression of atherosclerosis in either of these well-established mouse models. These results suggest that fibrinolytic balance (as well as the potential contribution of PAI-1 to the regulation of cell migration) plays only a limited role in the pathogenesis of the simple atherosclerotic lesions observed in the mouse.