Overview of murine thrombosis models

Developing human tissue engineered arterial constructs to simulate human in vivo thrombus formation

Thrombus formation is highly dependent upon the physico-chemical environment in which it is triggered. Our ability to understand how thrombus formation is initiated, regulated, and resolved in the human body is dependent upon our ability to replicate the mechanical and biological properties of the arterial wall. Current in vitro thrombosis models principally use reductionist approaches to model the complex biochemical and cellular milieu present in the arterial wall, and so researcher have favored the use of in vivo models. The field of vascular tissue engineering has developed a range of techniques for culturing artificial human arteries for use as vascular grafts. These techniques therefore provide a basis for developing more sophisticated 3D replicas of the arterial wall that can be used in in vitro thrombosis models. In this review, we consider how tissue engineering approaches can be used to generate 3D models of the arterial wall that improve upon current in vivo and in vitro approaches. We consider the current benefits and limitations of reported 3D tissue engineered models and consider what additional evidence is required to validate them as alternatives to current in vivo models.

High Contrast Detection of Carotid Neothrombus with Strong Near-Infrared Absorption Selenium Nanosphere Enhanced Photoacoustic Imaging

Background

Carotid artery thrombosis is the leading cause of stroke. Since there are no apparent symptoms in the early stages of carotid atherosclerosis onset, it causes a more significant clinical diagnosis. Photoacoustic (PA) imaging provides high contrast and good depth information, which has been used for the early detection and diagnosis of many diseases.

Methods

We investigated thrombus formation by using 20% ferric chloride (FeCl3) in the carotid arteries of KM mice for the thrombosis model. The near-infrared selenium/polypyrrole (Se@PPy) nanomaterials are easy to synthesize and have excellent optical absorption in vivo, which can be used as PA contrast agents to obtain thrombosis information.

Results

In vitro experiments showed that Se@PPy nanocomposites have fulfilling PA ability in the 700 nm to 900 nm wavelength range. In the carotid atherosclerosis model, maximum PA signal enhancement up to 3.44, 4.04, and 5.07 times was observed by injection of Se@PPy nanomaterials, which helped to diagnose the severity of carotid atherosclerosis.

Conclusion

The superior PA signal of Se@PPy nanomaterials can identify the extent of atherosclerotic carotid lesions, demonstrating the feasibility of PA imaging technology in diagnosing carotid thrombosis lesion formation. This study demonstrates nanocomposites and PA techniques for imaging and diagnosing carotid thrombosis in vivo.

Developing Biomimetic Hydrogels of the Arterial Wall as a Prothrombotic Substrate for In Vitro Human Thrombosis Models

Current in vitro thrombosis models utilise simplistic 2D surfaces coated with purified components of the subendothelial matrix. The lack of a realistic humanised model has led to greater study of thrombus formation in in vivo tests in animals. Here we aimed to develop 3D hydrogel-based replicas of the medial and adventitial layers of the human artery to produce a surface that can optimally support thrombus formation under physiological flow conditions. These tissue-engineered medial- (TEML) and adventitial-layer (TEAL) hydrogels were developed by culturing human coronary artery smooth muscle cells and human aortic adventitial fibroblasts within collagen hydrogels, both individually and in co-culture. Platelet aggregation upon these hydrogels was studied using a custom-made parallel flow chamber. When cultured in the presence of ascorbic acid, the medial-layer hydrogels were able to produce sufficient neo-collagen to support effective platelet aggregation under arterial flow conditions. Both TEML and TEAL hydrogels possessed measurable tissue factor activity and could trigger coagulation of platelet-poor plasma in a factor VII-dependent manner. Biomimetic hydrogel replicas of the subendothelial layers of the human artery are effective substrates for a humanised in vitro thrombosis model that could reduce animal experimentation by replacing current in vivo models.

Indoleamine 2,3-dioxygenase-1, a Novel Therapeutic Target for Post-Vascular Injury Thrombosis in CKD

BACKGROUND

CKD, characterized by retained uremic solutes, is a strong and independent risk factor for thrombosis after vascular procedures . Urem ic solutes such as indoxyl sulfate (IS) and kynurenine (Kyn) mediate prothrombotic effect through tissue factor (TF). IS and Kyn biogenesis depends on multiple enzymes, with therapeutic implications unexplored. We examined the role of indoleamine 2,3-dioxygenase-1 (IDO-1), a rate-limiting enzyme of kynurenine biogenesis, in CKD-associated thrombosis after vascular injury.

METHODS

IDO-1 expression in mice and human vessels was examined. IDO-1-/- mice, IDO-1 inhibitors, an adenine-induced CKD, and carotid artery injury models were used.

RESULTS

Both global IDO-1-/- CKD mice and IDO-1 inhibitor in wild-type CKD mice showed reduced blood Kyn levels, TF expression in their arteries, and thrombogenicity compared with respective controls. Several advanced IDO-1 inhibitors downregulated TF expression in primary human aortic vascular smooth muscle cells specifically in response to uremic serum. Further mechanistic probing of arteries from an IS-specific mouse model, and CKD mice, showed upregulation of IDO-1 protein, which was due to inhibition of its polyubiquitination and degradation by IS in vascular smooth muscle cells. In two cohorts of patients with advanced CKD, blood IDO-1 activity was significantly higher in sera of study participants who subsequently developed thrombosis after endovascular interventions or vascular surgery.

CONCLUSION

Leveraging genetic and pharmacologic manipulation in experimental models and data from human studies implicate IS as an inducer of IDO-1 and a perpetuator of the thrombotic milieu and supports IDO-1 as an antithrombotic target in CKD.

Microvascular thrombosis: experimental and clinical implications

A significant amount of clinical and research interest in thrombosis is focused on large vessels (eg, stroke, myocardial infarction, deep venous thrombosis, etc.); however, thrombosis is often present in the microcirculation in a variety of significant human diseases, such as disseminated intravascular coagulation, thrombotic microangiopathy, sickle cell disease, and others. Further, microvascular thrombosis has recently been demonstrated in patients with COVID-19, and has been proposed to mediate the pathogenesis of organ injury in this disease. In many of these conditions, microvascular thrombosis is accompanied by inflammation, an association referred to as thromboinflammation. In this review, we discuss endogenous regulatory mechanisms that prevent thrombosis in the microcirculation, experimental approaches to induce microvascular thrombi, and clinical conditions associated with microvascular thrombosis. A greater understanding of the links between inflammation and thrombosis in the microcirculation is anticipated to provide optimal therapeutic targets for patients with diseases accompanied by microvascular thrombosis.

Fe3O4-based PLGA nanoparticles as MR contrast agents for the detection of thrombosis

Thrombotic disease is a great threat to human health, and early detection is particularly important. Magnetic resonance (MR) molecular imaging provides noninvasive imaging with the potential for early disease diagnosis. In this study, we developed Fe₃O₄-based poly(lactic-co-glycolic acid) (PLGA) nanoparticles (NPs) surface-modified with a cyclic Arg-Gly-Asp (cRGD) peptide as an MR contrast agent for the detection of thrombosis. The physical and chemical characteristics, biological toxicity, ability to target thrombi, and biodistribution of the NPs were studied. The Fe₃O₄-PLGA-cRGD NPs were constructed successfully, and hematologic and pathologic assays indicated no in vivo toxicity of the NPs. In a rat model of FeCl₃-induced abdominal aorta thrombosis, the NPs readily and selectively accumulated on the surface of the thrombosis and under vascular endothelial cells ex vivo and in vivo. In the in vivo experiment, the biodistribution of the NPs suggested that the NPs might be internalized by the macrophages of the reticuloendothelial system in the liver and the spleen. The T2 signal decreased at the mural thrombus 10 min after injection and then gradually increased until 50 min. These results suggest that the NPs are suitable for in vivo molecular imaging of thrombosis under high shear stress conditions and represent a very promising MR contrast agent for sensitive and specific detection of thrombosis.

A rapid pro-hemostatic approach to overcome direct oral anticoagulants

Direct inhibitors of coagulation factor Xa (FXa) or thrombin are promising oral anticoagulants that are becoming widely adopted. The ability to reverse their anticoagulant effects is important when serious bleeding occurs or urgent medical procedures are needed. Here, using experimental mouse models of hemostasis, we show that a variant coagulation factor, FXa(I16L), rapidly restores hemostasis in the presence of the anticoagulant effects of these inhibitors. The ability of FXa(I16L) to reverse the anticoagulant effects of FXa inhibitor depends, at least in part, on the ability of the active site inhibitor to hinder antithrombin-dependent FXa inactivation, paradoxically allowing uninhibited FXa to persist in plasma. Because of its inherent catalytic activity, FXa(I16L) is more potent (by >50-fold) in the hemostasis models tested than a noncatalytic antidote that is currently in clinical development. FXa(I16L) also reduces the anticoagulant-associated bleeding in vivo that is induced by the thrombin inhibitor dabigatran. FXa(I16L) may be able to fill an important unmet clinical need for a rapid, pro-hemostatic agent to reverse the effects of several new anticoagulants.

Blood coagulation and metabolic profiles in middle-aged male and female ob/ob mice

Obese and diabetic states in humans are associated with an increased incidence of thrombotic diseases caused by various coagulation abnormalities. Genetically obese ob/ob mice produce metabolic abnormalities similar to those associated with type 2 diabetes. However, little is known about their coagulation features or sex differences. The present study aimed to determine the effects of obese and diabetic complications on blood coagulation and vascular diseases by exploring correlations between blood coagulation and metabolic profiles in middle-aged male and female ob/ob mice. Plasma levels of plasminogen activator inhibitor 1 (PAI-1) were significantly increased, whereas those that of platelet factor-4 (PF-4) was slightly, but significantly increased in male and female ob/ob mice compared with lean counterparts. Prothrombin time (PT) was significantly shortened in female ob/ob mice and activated partial thrombin time (APTT) significantly differed between male and female ob/ob mice. Plasma levels of antithrombin (AT) were significantly increased in male and female ob/ob mice. None of the other coagulation and fibrinolytic factors examined significantly differed between ob/ob mice and lean counterparts. On the contrary, factors such as body weight and cholesterol levels significantly differed between ob/ob and lean mice, whereas glucose, fructosamine and insulin levels significantly differed only in one sex of each strain. These results provided fundamental information about blood coagulation and metabolic features for exploring the function of altered blood coagulation states in ob/ob mice.

Allosterism-based simultaneous, dual anticoagulant and antiplatelet action: allosteric inhibitor targeting the glycoprotein Ibα-binding and heparin-binding site of thrombin

BACKGROUND

Allosteric inhibition is a promising approach for developing a new group of anticoagulants with potentially reduced bleeding consequences. Recently, we designed sulfated β-O4 lignin (SbO4L) as an allosteric inhibitor that targets exosite 2 of thrombin to reduce fibrinogen cleavage through allostery and compete with glycoprotein Ibα to reduce platelet activation.

OBJECTIVE

To assess: (i) the antithrombotic potential of a novel approach of simultaneous exosite 2-dependent allosteric inhibition of thrombin and competitive inhibition of platelet activation; and (ii) the promise of SbO4L as the first-in-class antithrombotic agent.

METHODS

A combination of whole blood thromboelastography, hemostasis analysis, mouse arterial thrombosis models and mouse tail bleeding studies were used to assess antithrombotic potential.

RESULTS AND CONCLUSIONS

SbO4L extended the clot initiation time, and reduced maximal clot strength, platelet contractile force, and the clot elastic modulus, suggesting dual anticoagulant and antiplatelet effects. These effects were comparable to those observed with enoxaparin. A dose of 1 mg of SbO4L per mouse prevented occlusion in 100% of arteries, and lower doses resulted in a proportionally reduced response. Likewise, the time to occlusion increased by ~ 70% with a 0.5-mg dose in the mouse Rose Bengal thrombosis model. Finally, tail bleeding studies demonstrated that SbO4L does not increase bleeding propensity. In comparison, a 0.3-mg dose of enoxaparin increased the bleeding time and blood volume loss. Overall, this study highlights the promise of the allosteric inhibition approach, and presents SbO4L as a novel anticoagulant with potentially reduced bleeding side effects.

Antiplatelet Aggregation and Antithrombosis Efficiency of Peptides in the Snake Venom of Deinagkistrodon acutus: Isolation, Identification, and Evaluation

Two peptides of Pt-A (Glu-Asn-Trp 429 Da) and Pt-B (Glu-Gln-Trp 443 Da) were isolated from venom liquor of Deinagkistrodon acutus. Their antiplatelet aggregation effects were evaluated with platelet-rich human plasma in vitro; the respective IC₅₀ of Pt-A and Pt-B was 66 μM and 203 μM. Both peptides exhibited protection effects on ADP-induced paralysis in mice. After ADP administration, the paralysis time of different concentration of Pt-A and Pt-B lasted as the following: 80 mg/kg Pt-B (152.8 ± 57.8 s) < 40 mg/kg Pt-A (163.5 ± 59.8 s) < 20 mg/kg Pt-A (253.5 ± 74.5 s) < 4 mg/kg clopidogrel (a positive control, 254.5 ± 41.97 s) < 40 mg/kg Pt-B (400.8 ± 35.9 s) < 10 mg/kg Pt-A (422.8 ± 55.4 s), all of which were statistically shorter than the saline treatment (666 ± 28 s). Pulmonary tissue biopsy confirmed that Pt-A and Pt-B prevented the formation of thrombi in the lung. Unlike ADP injection alone, which caused significant reduction of peripheral platelet count, Pt-A treatment prevented the drop of peripheral platelet counts; interestingly, Pt-B could not, even though the same amount of Pt-B also showed protection effects on ADP-induced paralysis and thrombosis. More importantly, intravenous injection of Pt-A and Pt-B did not significantly increase the hemorrhage risks as clopidogrel.

New insights into the spatiotemporal localization of prothrombinase in vivo

The membrane-dependent interaction of factor Xa (FXa) with factor Va (FVa) forms prothrombinase and drives thrombin formation essential for hemostasis. Activated platelets are considered to provide the primary biological surface to support prothrombinase function. However, the question of how other cell types may cooperate within the biological milieu to affect hemostatic plug formation remains unaddressed. We used confocal fluorescence microscopy to image the distribution of site-specific fluorescent derivatives of FVa and FXa after laser injury in the mouse cremaster arteriole. These proteins bound to the injury site extend beyond the platelet mass to the surrounding endothelium. Although bound FVa and FXa may have been present on the platelet core at the nidus of the injury, bound proteins were not evident on platelets adherent even a small distance from the injury site. Manipulations to drastically reduce adherent platelets yielded a surprisingly modest decrease in bound FXa and FVa with little impact on fibrin formation. Thus, platelets adherent to the site of vascular injury do not play the presumed preeminent role in supporting prothrombinase assembly and thrombin formation. Rather, the damaged/activated endothelium and possibly other blood cells play an unexpectedly important role in providing a procoagulant membrane surface in vivo.

Construction and evaluation of Fe₃O₄-based PLGA nanoparticles carrying rtPA used in the detection of thrombosis and in targeted thrombolysis

Thrombotic disease is extremely harmful to human health, but early detection and treatment can help improve prognoses and reduce mortality. To date, few studies have used MR molecular imaging in the early detection of thrombi and in the dynamic monitoring of the thrombolytic efficiency. In this article, we construct Fe3O4-based poly(lactic-co-glycolic acid) (PLGA) nanoparticles to use in the detection of thrombi and in targeted thrombolysis using MRI monitoring. Cyclic arginine-glycine-aspartic peptide (cRGD) was grafted onto the chitosan (CS) surface to synthesize a CS-cRGD film using carbodiimide-mediated amide bond formation. A double emulsion solvent evaporation method (water in oil in water [W/O/W]) was used to construct Fe3O4-based PLGA nanoparticles carrying recombinant tissue plasminogen activator (rtPA) (Fe3O4-PLGA-rtPA/CS-cRGD). Fe3O4-PLGA, Fe3O4-PLGA-rtPA, and Fe3O4-PLGA-rtPA/CS nanoparticles were constructed using the same W/O/W method. The results showed that the Fe3O4-based nanoparticles were constructed successfully and have a regular shape, a relatively uniform size, a high carrier rate of Fe3O4 and encapsulation efficiency of rtPA, and a relatively high activity of released rtPA. Transmission electron microscope (TEM) images revealed that the iron oxide particles were relatively uniformly distributed in the nano-spherical shell. The Fe3O4-based nanoparticles could be imaged using a clinical MRI scanner, and there were no significant differences in the transverse relaxation rate (R2*) or in the signal-to-noise ratio (SNR) values between the Fe3O4-based nanoparticles and an Fe3O4 solution with the same concentration of Fe3O4. In vitro and in vivo experiments confirmed that the Fe3O4-PLGA-rtPA/CS-cRGD nanoparticles specifically accumulated on the edge of the thrombus and that they had a significant effect on the thrombolysis compared with the Fe3O4-PLGA, Fe3O4-PLGA-rtPA, and Fe3O4-PLGA-rtPA/CS nanoparticles and with free rtPA solution. These results suggest the potential of the Fe3O4-PLGA-rtPA/CS-cRGD nanoparticles as a dual-function tool in the early detection of a thrombus and in the dynamic monitoring of the thrombolytic efficiency using MRI.

Preparation and characterization of gadolinium-loaded PLGA particles surface modified with RGDS for the detection of thrombus

Thrombotic disease is a leading cause of death and disability worldwide. The development of magnetic resonance molecular imaging provides potential promise for early disease diagnosis. In this study, we explore the preparation and characterization of gadolinium (Gd)-loaded poly (lactic-co-glycolic acid) (PLGA) particles surface modified with the Arg-Gly-Asp-Ser (RGDS) peptide for the detection of thrombus. PLGA was employed as the carrier-delivery system, and a double emulsion solvent-evaporation method (water in oil in water) was used to prepare PLGA particles encapsulating the magnetic resonance contrast agent Gd diethylenetriaminepentaacetic acid (DTPA). To synthesize the Gd-PLGA/chitosan (CS)-RGDS particles, carbodiimide-mediated amide bond formation was used to graft the RGDS peptide to CS to form a CS-RGDS film that coated the surface of the PLGA particles. Blank PLGA, Gd-PLGA, and Gd-PLGA/CS particles were fabricated using the same water in oil in water method. Our results indicated that the RGDS peptide successfully coated the surface of the Gd-PLGA/CS-RGDS particles. The particles had a regular shape, smooth surface, relatively uniform size, and did not aggregate. The high electron density of the Gd-loaded particles and a translucent film around the particles coated with the CS and CS-RGDS films could be observed by transmission electron microscopy. In vitro experiments demonstrated that the Gd-PLGA/CS-RGDS particles could target thrombi and could be imaged using a clinical magnetic resonance scanner. Compared with the Gd-DTPA solution, the longitudinal relaxation time of the Gd-loaded particles was slightly longer, and as the Gd-load concentration increased, the longitudinal relaxation time values decreased. These results suggest the potential of the Gd-PLGA/CS-RGDS particles for the sensitive and specific detection of thrombus at the molecular level.

Thrombodynamics of microvascular repairs: effects of antithrombotic therapy on platelets and fibrin

PURPOSE

To evaluate the hypothesis that platelets and fibrin differentially accrue at microvascular anastomoses in arteries versus veins and under different pharmacologic conditions.

METHODS

We evaluated mouse arterial and venous anastomoses with intravital fluorescence imaging, using fluorophore-labeled platelets and anti-fibrin antibodies to measure the extent of thrombus component development in the intraluminal anastomotic site. We evaluated systemic heparin or eptifibatide (platelet aggregation inhibitor) to determine their relative influences on thrombus composition.

RESULTS

Platelets accumulated rapidly in both arterial and venous repairs, and then fell in number after 10 to 30 minutes of reflow. Fibrin had a relatively steady development over 60 minutes in veins, with a more variable increase in arteries. Heparin reduced platelet accumulation in arteries and fibrin development in veins. Eptifibatide reduced platelets in both arteries and veins and had an apparent effect on lowering the amount of fibrin in veins.

CONCLUSIONS

These findings show that platelets have a rapid, transient response, whereas fibrin has a slower, more sustained accrual in both arterial and venous anastomoses. Furthermore, inhibition of either coagulation or platelet aggregation can influence presumably non-targeted components of thrombosis in vascular repairs of both arteries and veins.

CLINICAL RELEVANCE

Preventing replantation failure using antithrombotic therapies requires a better understanding of the effect of each pharmacologic compound on the various aspects of thrombogenesis.

Enhanced platelet activity and thrombosis in a murine model of type I diabetes are partially insulin-like growth factor 1-dependent and phosphoinositide 3-kinase-dependent

OBJECTIVES

To determine whether dysregulation of platelet signaling mechanisms contributes to the increased risk of thrombosis associated with diabetes, using a type I diabetes mouse model.

METHODS AND RESULTS

Type I diabetes was induced in C57Bl6 mice following streptozotocin injection. Arterial thrombosis, platelet signaling and function were assessed 4 weeks later in comparison with non-diabetic control mice. Fifty-seven per cent of diabetic mice (glucose level of > 250 mg dL(-1) ) developed stable occlusive thrombi after FeCl3 injury, as compared with 5% of their non-diabetic counterparts, suggesting that diabetic mice are more sensitive to arterial injury (P ≤ 0.02). Platelets from diabetic mice were more sensitive to protease-activated receptor 4 (PAR4) agonist-induced fibrinogen binding than platelets from non-diabetic mice, and the average Akt phosphorylation induced by PAR4 agonist peptide was greater (P ≤ 0.01) in platelets from diabetic mice. Recent studies suggest that insulin-like growth factor 1 (IGF-1) potentiates Akt phosphorylation in platelets. To determine whether IGF-1 signaling contributes to the increase in PAR4 sensitivity in platelets from diabetic mice, platelet signaling and function were evaluated in the presence of inhibitors of the IGF-1 receptor. IGF-1 receptor inhibition reduced Akt phosphorylation and fibrinogen binding in platelets from diabetic mice to levels consistent with those seen in normoglycemic platelets, but had no significant effect on platelets from non-diabetic mice.

CONCLUSIONS

The results suggest that platelets from mice with streptozotocin-induced diabetes show enhanced platelet Akt phosphorylation and activity resulting from IGF-1-dependent mechanisms. Increases in platelet Akt activation may explain the enhanced sensitivity to thrombotic insult seen in diabetic mice.

Ferric chloride-induced murine carotid arterial injury: A model of redox pathology

Ferric chloride (FeCl₃) induced vascular injury is a widely used model of occlusive thrombosis that reports platelet activation in the context of an aseptic closed vascular system. This model is based on redox-induced endothelial cell injury, which is simple and sensitive to both anticoagulant and anti-platelets drugs. The time required for platelet aggregation to occlude blood flow gives a quantitative measure of vascular damage that is pathologically relevant to thrombotic disease. We have refined the traditional FeCl₃-induced carotid artery model making the data highly reproducible with lower variation. This paper will describe our artifices and report the role of varying the oxidative damage by varying FeCl₃ concentrations and exposure. To explore a maximum difference between experimental groups, adjustment of the selected FeCl₃ dose and exposure duration may be necessary.

Model systems of genetically modified platelets

Although platelets are the smallest cells in the blood, they are implied in various processes ranging from immunology and oncology to thrombosis and hemostasis. Many large-scale screening programs, genome-wide association, and "omics" studies have generated lists of genes and loci that are probably involved in the formation or physiology of platelets under normal and pathologic conditions. This creates an increasing demand for new and improved model systems that allow functional assessment of the corresponding gene products in vivo. Such animal models not only render invaluable insight in the platelet biology, but in addition, provide improved test systems for the validation of newly developed anti-thrombotics. This review summarizes the most important models to generate transgenic platelets and to study their influence on platelet physiology in vivo. Here we focus on the zebrafish morpholino oligonucleotide technology, the (platelet-specific) knockout mouse, and the transplantation of genetically modified human or murine platelet progenitor cells in myelo-conditioned mice. The various strengths and pitfalls of these animal models are illustrated by recent examples from the platelet field. Finally, we highlight the latest developments in genetic engineering techniques and their possible application in platelet research.

Overexpression of the cell cycle inhibitor p16INK4a promotes a prothrombotic phenotype following vascular injury in mice

OBJECTIVE

Age-associated cellular senescence is thought to promote vascular dysfunction. p16(INK4a) is a cell cycle inhibitor that promotes senescence and is upregulated during normal aging. In this study, we examine the contribution of p16(INK4a) overexpression to venous thrombosis.

METHODS AND RESULTS

Mice overexpressing p16(INK4a) were studied with 4 different vascular injury models: (1) ferric chloride (FeCl(3)) and (2) Rose Bengal to induce saphenous vein thrombus formation; (3) FeCl(3) and vascular ligation to examine thrombus resolution; and (4) lipopolysaccharide administration to initiate inflammation-induced vascular dysfunction. p16(INK4a) transgenic mice had accelerated occlusion times (13.1 ± 0.4 minutes) compared with normal controls (19.7 ± 1.1 minutes) in the FeCl(3) model and 12.7 ± 2.0 and 18.6 ± 1.9 minutes, respectively in the Rose Bengal model. Moreover, overexpression of p16(INK4a) delayed thrombus resolution compared with normal controls. In response to lipopolysaccharide treatment, the p16(INK4a) transgenic mice showed enhanced thrombin generation in plasma-based calibrated automated thrombography assays. Finally, bone marrow transplantation studies suggested increased p16(INK4a) expression in hematopoietic cells contributes to thrombosis, demonstrating a role for p16(INK4a) expression in venous thrombosis.

CONCLUSIONS

Venous thrombosis is augmented by overexpression of the cellular senescence protein p16(INK4a).

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.