Regulation of arterial thrombolysis by plasminogen activator inhibitor-1 in mice

A Reliable Nonhuman Primate Model of Ischemic Stroke with Reproducible Infarct Size and Long-term Sensorimotor Deficits

A nonhuman primate model of ischemic stroke is considered as an ideal preclinical model to replicate various aspects of human stroke because of their similarity to humans in genetics, neuroanatomy, physiology, and immunology. However, it remains challenging to produce a reliable and reproducible stroke model in nonhuman primates due to high mortality and variable outcomes. Here, we developed a focal cerebral ischemic model induced by topical application of 50% ferric chloride (FeCl₃) onto the MCA-M1 segment through a cranial window in the cynomolgus monkeys. We found that FeCl₃ rapidly produced a stable intraarterial thrombus that caused complete occlusion of the MCA, leading to the quick decrease of the regional cerebral blood flow in 10 min. A typical cortical infarct was detected 24 hours by magnetic resonance imaging (MRI) and was stable at least for 1 month after surgery. The sensorimotor deficit assessed by nonhuman primate stroke scale was observed at 1 day and up to 3 months after ischemic stroke. No spontaneous revascularization or autolysis of thrombus was observed, and vital signs were not affected. All operated cynomolgus monkeys survived. Our data suggested that FeCl₃-induced stroke in nonhuman primates was a replicable and reliable model that is necessary for the correct prediction of the relevance of experimental therapeutic approaches in human beings.

A Thrombin-Responsive Nanoprobe for In Vivo Visualization of Thrombus Formation through Three-Dimensional Optical/Computed Tomography Hybrid Imaging

Early spontaneous detection of thrombin activation benefits precise theranostics for thrombotic vascular disease. Herein, a thrombin-responsive nanoprobe conjugated by a FITC dye, PEGylated Fe₃O₄ nanoparticles, and a thrombin-sensitive peptide (LASG) was constructed to visualize thrombin activation and subsequent thrombosis in vivo. The FITC dye was linked to the LASG coated on the Fe₃O₄ nanoparticles for sensing the thrombin activity via the Förster resonance energy transfer effect. In vitro fluorescence imaging showed that the fluorescence signal intensity increased significantly after incubation with thrombin in contrast to that of the control group (p < 0.05), and the signal intensity was enhanced with the increase in thrombin concentration. Further in vivo fluorescence imaging also revealed that the signal elevated markedly in the left common carotid artery (LCCA) lesion of the mice thrombosis model after nanoprobe injection, in contrast to that of the control + nanoprobe group (p < 0.05). Moreover, the thrombin inhibitor bivalirudin could decrease the filling defect of the LCCA. Three-dimensional fusion images of micro-CT and fluorescence confirmed that filling defects in the LCCA were nicely colocalized with fluorescence signal caused by nanoprobes. The nanoplatform based on a thrombin-activatable visualization system could provide smart responsive and dynamic imaging of thrombosis in vivo.

Plasmin and Plasminogen System in the Tumor Microenvironment: Implications for Cancer Diagnosis, Prognosis, and Therapy

Simple Summary

In this review, we present a detailed discussion of how the plasminogen-activation system is utilized by tumor cells in their unrelenting attack on the tissues surrounding them. Plasmin is an enzyme which is responsible for digesting several proteins that hold the tissues surrounding solid tumors together. In this process tumor cells utilize the activity of plasmin to digest tissue barriers in order to leave the tumour site and spread to other parts of the body. We specifically focus on the role of plasminogen receptor—p11 which is an important regulatory protein that facilitates the conversion of plasminogen to plasmin and by this means promotes the attack by the tumour cells on their surrounding tissues.

Abstract

The tumor microenvironment (TME) is now being widely accepted as the key contributor to a range of processes involved in cancer progression from tumor growth to metastasis and chemoresistance. The extracellular matrix (ECM) and the proteases that mediate the remodeling of the ECM form an integral part of the TME. Plasmin is a broad-spectrum, highly potent, serine protease whose activation from its precursor plasminogen is tightly regulated by the activators (uPA, uPAR, and tPA), the inhibitors (PAI-1, PAI-2), and plasminogen receptors. Collectively, this system is called the plasminogen activation system. The expression of the components of the plasminogen activation system by malignant cells and the surrounding stromal cells modulates the TME resulting in sustained cancer progression signals. In this review, we provide a detailed discussion of the roles of plasminogen activation system in tumor growth, invasion, metastasis, and chemoresistance with specific emphasis on their role in the TME. We particularly review the recent highlights of the plasminogen receptor S100A10 (p11), which is a pivotal component of the plasminogen activation system.

Identification and Characterization of Plasmin-Independent Thrombolytic Enzymes

Supplemental Digital Content is available in the text.

Rationale:

Current thrombolytic agents activate plasminogen to plasmin which triggers fibrinolysis to dissolve thrombi. Since plasmin is a nonspecific proteolytic enzyme, all of the current plasmin-dependent thrombolytics lead to serious hemorrhagic complications, demanding a new class of fibrinolytic enzymes independent from plasmin activation and undesirable side effects. We speculated that the mammalian version of bacterial heat-shock proteins could selectively degrade intravascular thrombi, a typical example of a highly aggregated protein mixture.

Objective:

The objective of this study is to identify enzymes that can dissolve intravascular thrombi specifically without affecting fibrinogen and fibronectin so that the wound healing processes remain uninterrupted and tissues are not damaged. In this study, HtrA (high-temperature requirement A) proteins were tested for its specific proteolytic activity on intravascular thrombi independently from plasmin activation.

Methods and Results:

HtrA1 and HtrA2/Omi proteins, collectively called as HtrAs, lysed ex vivo blood thrombi by degrading fibrin polymers. The thrombolysis by HtrAs was plasmin-independent and specific to vascular thrombi without causing the systemic activation of plasminogen and preventing nonspecific proteolysis of other proteins including fibrinogen and fibronectin. As expected, HtrAs did not disturb clotting and wound healing of excised wounds from mouse skin. It was further confirmed in a tail bleeding and a rebleeding assay that HtrAs allowed normal clotting and maintenance of clot stability in wounds, unlike other thrombolytics. Most importantly, HtrAs completely dissolved blood thrombi in tail thrombosis mice, and the intravenous injection of HtrAs to mice with pulmonary embolism completely dissolved intravascular thrombi and thus rescued thromboembolism.

Conclusions:

Here, we identified HtrA1 and HtrA2/Omi as plasmin-independent and highly specific thrombolytics that can dissolve intravascular thrombi specifically without bleeding risk. This work is the first report of a plasmin-independent thrombolytic pathway, providing HtrA1 and HtrA2/Omi as ideal therapeutic candidates for various thrombotic diseases without hemorrhagic complications.

VAMP3 and SNAP23 as Potential Targets for Preventing the Disturbed Flow-Accelerated Thrombus Formation

Disturbed blood flow has been recognized to promote platelet aggregation and thrombosis via increasing accumulation of von Willebrand factor (VWF) at the arterial post-stenotic sites. The mechanism underlying the disturbed-flow regulated endothelial VWF production remains elusive. Here we described a mouse model, in which the left external carotid artery (LECA) is ligated to generate disturbed flow in the common carotid artery. Ligation of LECA increased VWF accumulation in the plasma. Carotid arterial thrombosis was induced by ferric chloride (FeCl₃) application and the time to occlusion in the ligated vessels was reduced in comparison with the unligated vessels. In vitro, endothelial cells were subjected to oscillatory shear (OS, 0.5 ± 4 dynes/cm²) or pulsatile shear (PS, 12 ± 4 dynes/cm²). OS promoted VWF secretion as well as the cell conditioned media-induced platelet aggregation by regulating the intracellular localization of vesicle-associated membrane protein 3 (VAMP3) and synaptosomal-associated protein 23 (SNAP23). Disruption of vimentin intermediate filaments abolished the OS-induced translocation of SNAP23 to the cell membrane. Knockdown of VAMP3 and SNAP23 reduced the endothelial secretion of VWF. Systemic inhibition of VAMP3 and SNAP23 by treatment of mice with rapamycin significantly ameliorated the FeCl₃-induced thrombogenesis, whereas intraluminal overexpression of VAMP3 and SNAP23 aggravated it. Our findings demonstrate VAMP3 and SNAP23 as potential targets for preventing the disturbed flow-accelerated thrombus formation.

Histamine deficiency facilitates coronary microthrombosis after myocardial infarction by increasing neutrophil-platelet interactions

Neutrophil‐platelet interactions are responsible for thrombosis as well as inflammatory responses following acute myocardial infarction (AMI). While histamine has been shown to play a crucial role in many physiological and pathological processes, its effects on neutrophil‐platelet interactions in thromboinflammatory complications of AMI remain elusive. In this study, we show a previously unknown mechanism by which neutrophil‐derived histamine protects the infarcted heart from excessive neutrophil‐platelet interactions and redundant arterial thrombosis. Using histamine‐deficient (histidine decarboxylase knockout, HDC^−/−) and wild‐type murine AMI models, we demonstrate that histamine deficiency increases the number of microthrombosis after AMI, in accordance with depressed cardiac function. Histamine‐producing myeloid cells, mainly Ly6G⁺ neutrophils, directly participate in arteriole thrombosis. Histamine deficiency elevates platelet activation and aggregation by enhancing Akt phosphorylation and leads to dysfunctional characteristics in neutrophils which was confirmed by high levels of reactive oxygen species production and CD11b expression. Furthermore, HDC^−/− platelets were shown to elicit neutrophil extracellular nucleosomes release, provoke neutrophil‐platelet interactions and promote HDC‐expressing neutrophils recruitment in arteriole thrombosis in vivo. In conclusion, we provide evidence that histamine deficiency promotes coronary microthrombosis and deteriorates cardiac function post‐AMI, which is associated with the enhanced platelets/neutrophils function and neutrophil‐platelet interactions.

SerpinB2 inhibits migration and promotes a resolution phase signature in large peritoneal macrophages

SerpinB2 (plasminogen activator inhibitor type 2) has been called the "undecided serpin" with no clear consensus on its physiological role, although it is well described as an inhibitor of urokinase plasminogen activator (uPA). In macrophages, pro-inflammatory stimuli usually induce SerpinB2; however, expression is constitutive in Gata6+ large peritoneal macrophages (LPM). Interrogation of expression data from human macrophages treated with a range of stimuli using a new bioinformatics tool, CEMiTool, suggested that SerpinB2 is most tightly co- and counter-regulated with genes associated with cell movement. Using LPM from SerpinB2-/- and SerpinB2R380A (active site mutant) mice, we show that migration on Matrigel was faster than for their wild-type controls. Confocal microscopy illustrated that SerpinB2 and F-actin staining overlapped in focal adhesions and lamellipodia. Genes associated with migration and extracellular matrix interactions were also identified by RNA-Seq analysis of migrating RPM from wild-type and SerpinB2R380A mice. Subsequent gene set enrichment analyses (GSEA) suggested SerpinB2 counter-regulates many Gata6-regulated genes associated with migration. These data argue that the role of SerpinB2 in macrophages is inhibition of uPA-mediated plasmin generation during cell migration. GSEA also suggested that SerpinB2 expression (likely via ensuing modulation of uPA-receptor/integrin signaling) promotes the adoption of a resolution phase signature.

SerpinB2 deficiency in mice reduces bleeding times via dysregulated platelet activation

SerpinB2, also known as plasminogen activation inhibitor type 2 (PAI-2), is classically viewed as an inhibitor of fibrinolysis. However, we show herein a distinct, hitherto unrecognized role for SerpinB2 in hemostasis. Mice deficient in SerpinB2 expression and mice with an active site mutation in SerpinB2, both showed significant reductions in tail bleeding times. This hemostatic phenotype was associated with platelets, with SerpinB2 and SerpinB2-urokinase complexes clearly present in platelet fractions, and immunohistochemistry of blood clots suggesting SerpinB2 is associated with platelet aggregates. Thromboelastography illustrated faster onset of clot formation in blood from SerpinB2 deficient mice, whereas clotting of platelet-free plasma was unaffected. The results appear consistent with the low circulating SerpinB2 levels and hypercoagulation seen during pre-eclampsia; however, SerpinB2 was not detected in human platelets.

Thrombocytopenia-associated mutations in Ser/Thr kinase MASTL deregulate actin cytoskeletal dynamics in platelets

MASTL, a Ser/Thr kinase that inhibits PP2A-B55 complexes during mitosis, is mutated in autosomal dominant thrombocytopenia. However, the connections between the cell-cycle machinery and this human disease remain unexplored. We report here that, whereas Mastl ablation in megakaryocytes prevented proper maturation of these cells, mice carrying the thrombocytopenia-associated mutation developed thrombocytopenia as a consequence of aberrant activation and survival of platelets. Activation of mutant platelets was characterized by hyperstabilized pseudopods mimicking the effect of PP2A inhibition and actin polymerization defects. These aberrations were accompanied by abnormal hyperphosphorylation of multiple components of the actin cytoskeleton and were rescued both in vitro and in vivo by inhibiting upstream kinases such as PKA, PKC, or AMPK. These data reveal an unexpected role of Mastl in actin cytoskeletal dynamics in postmitotic cells and suggest that the thrombocytopenia-associated mutation in MASTL is a pathogenic dominant mutation that mimics decreased PP2A activity resulting in altered phosphorylation of cytoskeletal regulatory pathways.

Optimizing outcome measurement with murine ferric chloride-induced thrombosis

: The murine FeCl3 model is a widely used model for studying arterial thrombosis, yet provides limited information from each mouse, often only a single time point for the onset of occlusion (defined as the time to occlusion; TTO). To optimize data from the murine ferric chloride model of thrombosis. FeCl3 injury was induced in the carotid arteries of wild-type and Factor IX (FIX) knockout mice, with infusion of recombinant FIX (rFIX) to normalize FIX deficiency at various times around FeCl3 injury. The TTO was recorded as a percentage of baseline flow as occlusion continued to zero flow, with identification of reflow events. The TTO among the treatment groups of FIX-deficient mice showed no statistical differences, except with physiological saline-treated FIX-deficient mice and those receiving delayed treatment. Incidences of occlusion were 100% for wild-type mice and FIX-deficient mice receiving slow infusions of rFIX at early times around the FeCl3 application. In contrast, only 68% of FIX-deficient mice achieved occlusion with preinfusion of rFIX and none occluded with delayed rFIX infusion. A majority of occluded vessels exhibited reflow events, with significantly lower incidence for slow infusion of rFIX starting 4 min after FeCl3 application in comparison with preinjury bolus, demonstrating characterization of a differential response to timing and infusion rates of treatment. Simple use of the time to occlusion may not maximize data available from the FeCl3 arterial thrombosis model. Inclusion of documenting reflow events can extend the useful data obtained with application of this model.

Increased Thrombogenicity in Chronic Renal Failure in a Rat Model Induced by 5/6 Ablation/Infarction

PURPOSE

Abnormalities in hemostasis and coagulation have been suggested in chronic renal failure (CRF). In this study, we compared processes of thrombus formation between rats with CRF and those with normal kidney function.

MATERIALS AND METHODS

CRF was induced by 5/6 ablation/infarction of the kidneys in Sprague-Dawley rats, and surviving rats after 4 weeks were used. Ferric chloride (FeCl₃)-induced thrombosis in the carotid artery was induced to assess thrombus formation. Whole blood clot formation was evaluated using rotational thromboelastometry (ROTEM). Platelet aggregation was assessed with impedance platelet aggregometry.

RESULTS

FeCl₃-induced thrombus formation was initiated faster in the CRF group than in the control group (13.2±1.1 sec vs. 17.8±1.0 sec, p=0.027). On histological examination, the maximal diameters of thrombi were larger in the CRF group than in the control group (394.2±201.1 μm vs. 114.0±145.1 μm, p=0.039). In extrinsic pathway ROTEM, the CRF group showed faster clot initiation (clotting time, 59.0±7.3 sec vs. 72.8±5.0 sec, p=0.032) and increased clot growth kinetics (α angle, 84.8±0.2° vs. 82.0±0.6°, p=0.008), compared to the control group. Maximal platelet aggregation rate was higher in the CRF group than in the control group (58.2±0.2% vs. 44.6±1.2%, p=0.006).

CONCLUSION

Our study demonstrated that thrombogenicity is increased in rats with CRF. An activated extrinsic coagulation pathway may play an important role in increasing thrombogenicity in CRF.

Role of the chemokine receptors CCR2 and CX3CR1 in an experimental model of thrombotic stroke

Stroke is the second cause of mortality worldwide and occurs following the interruption of cerebral blood circulation by cerebral vessel burst or subsequent to a local thrombus formation. Ischemic lesion triggers an important inflammatory response, characterized by massive infiltration of leukocytes, activation of glial cells and neurovascular reorganization. Chemokines and their receptors, such as CCR2 and CX3CR1, play an important role in leukocyte recruitment in the damaged area. Mice genetically depleted for the two receptors CCR2 and CX3CR1 underwent focal cerebral ischemia, based on the topical application of ferric chloride to truncate the distal middle cerebral artery. The infarct, limited only to the cortical area, remained stable in WT mice, while it is reduced overtime in the transgenic mice. Moreover, we did not observe any significant changes in the level of the inflammatory response in the infarcted areas while immune cell infiltration and neurovascularization are modulated according to genotype. Our results show that the genetic deletion of both CCR2 and CX3CR1 receptors has neuroprotective effects in response to a cerebral permanent ischemia. This study underlines a key role of CCR2- and CX3CR1-expressing immune cells in the neuropathology associated with ischemic injuries.

Plasminogen activator inhibitor-1: a risk factor for deep vein thrombosis after total hip arthroplasty

Background

The onset of deep vein thrombosis (DVT) in patients after total hip arthroplasty (THA) may expand or enlarge and subsequently lead to significant mortality. The objective of this study was to investigate potential risk factors for DVT in patients after THA.

Methods

Eligible patients with hip joint diseases who were scheduled for unilateral primary THA at our hospital were prospectively included into this study. The demographic and clinical features, preoperative plasma biomarkers were detailed, recorded, and compared. The multiple logistic regression analysis was used to evaluate potential risk factors for DVT.

Results

A total of 214 subjects were enrolled into our study cohort for the final analysis, and 23 of them have suffered DVT with an incidence of 9.5%. The performance of logistic regression analysis showed that preoperative expression of plasminogen activator inhibitor-1 (PAI-1) was an independent risk factor for the onset of DVT in patients after THA (OR 1.18, 95% CI 1.04–1.29; p = 0.011).

Conclusions

Our study indicated preoperative plasma PAI-1 expression as an independent risk factor for DVT in patients who underwent THA.

A long-acting PAI-1 inhibitor reduces thrombus formation

Plasminogen activator inhibitor 1 (PAI-1) is the main inhibitor of tissue-type and urokinase-type plasminogen activators (t/uPA) and plays an important role in fibrinolysis. Inhibition of PAI-1 activity prevents thrombosis and accelerates fibrinolysis, indicating that PAI-1 inhibitors may be used as effective antithrombotic agents. We previously designed a PAI-1 inhibitor (PAItrap) which is a variant of inactivated urokinase protease domain. In the present study, we fused PAItrap with human serum albumin (HSA) to develop a long-acting PAI-1 inhibitor. Unfortunately, the fusion protein PAItrap-HSA lost some potency compared to PAItrap (33 nM vs 10 nM). Guided by computational method, we carried out further optimisation to enhance inhibitory potency for PAI-1. The new PAItrap, denominated PAItrap(H37R)-HSA, which was the H37R variant of PAItrap fused to HSA, gave a six-fold improvement of IC50 (5 nM) for human active PAI-1 compared to PAItrap-HSA, and showed much longer plasma half-life (200-fold) compared to PAItrap. We further demonstrated that the PAItrap(H37R)-HSA inhibited exogenous or endogenous PAI-1 to promote fibrinolysis in fibrin-clot lysis assay. PAItrap(H37R)-HSA inhibits murine PAI-1 with IC50 value of 12 nM, allowing the inhibitor to be evaluated in murine models. Using an intravital microscopy, we demonstrated that PAItrap(H37R)-HSA blocks thrombus formation and platelet accumulation in vivo in a laser-induced vascular injury mouse model. Additionally, mouse tail bleeding assay showed that PAItrap(H37R)-HSA did not affect the global haemostasis. These results suggest that PAItrap(H37R)-HSA have the potential benefit to prevent thrombosis and accelerates fibrinolysis.

Novel Thrombolytic Drug Based on Thrombin Cleavable Microplasminogen Coupled to a Single-Chain Antibody Specific for Activated GPIIb/IIIa

Background

Thrombolytic therapy for acute thrombosis is limited by life‐threatening side effects such as major bleeding and neurotoxicity. New treatment options with enhanced fibrinolytic potential are therefore required. Here, we report the development of a new thrombolytic molecule that exploits key features of thrombosis. We designed a recombinant microplasminogen modified to be activated by the prothrombotic serine‐protease thrombin (HtPlg), fused to an activation‐specific anti–glycoprotein IIb/IIIa single‐chain antibody (SCE5), thereby hijacking the coagulation system to initiate thrombolysis.

Methods and Results

The resulting fusion protein named SCE5‐HtPlg shows in vitro targeting towards the highly abundant activated form of the fibrinogen receptor glycoprotein IIb/IIIa expressed on activated human platelets. Following thrombin formation, SCE5‐HtPlg is activated to contain active microplasmin. We evaluate the effectiveness of our targeted thrombolytic construct in two models of thromboembolic disease. Administration of SCE5‐HtPlg (4 μg/g body weight) resulted in effective thrombolysis 20 minutes after injection in a ferric chloride–induced model of mesenteric thrombosis (48±3% versus 92±5% for saline control, P<0.01) and also reduced emboli formation in a model of pulmonary embolism (P<0.01 versus saline). Furthermore, at these effective therapeutic doses, the SCE5‐HtPlg did not prolong bleeding time compared with saline (P=0.99).

Conclusions

Our novel fusion molecule is a potent and effective treatment for thrombosis that enables in vivo thrombolysis without bleeding time prolongation. The activation of this construct by thrombin generated within the clot itself rather than by a plasminogen activator, which needs to be delivered systemically, provides a novel targeted approach to improve thrombolysis.

Palladin is involved in platelet activation and arterial thrombosis

The dynamics of actin cytoskeleton have been shown to play a critical role during platelet activation. Palladin is an actin-associated protein, serving as a cytoskeleton scaffold to bundle actin fibers and actin cross linker. The functional role of palladin on platelet activation has not been investigated. Here, we characterized heterozygous palladin knockout (palladin^+/-) mice to elucidate the platelet-related functions of palladin. The results showed that palladin was expressed in platelets and moderate palladin deficiency accelerated hemostasis and arterial thrombosis. The aggregation of palladin^+/- platelets was increased in response to low levels of thrombin, U46619, and collagen. We also observed enhanced spreading of palladin^+/- platelets on immobilized fibrinogen (Fg) and increased rate of clot retraction in platelet-rich plasma (PRP) containing palladin^+/- platelets. Furthermore, the activation of the small GTPase Rac1 and Cdc42, which is associated with cytoskeletal dynamics and platelet activation signalings, was increased in the spreading and aggregating palladin^+/- platelets compared to that in wild type platelets. Taken together, these findings indicated that palladin is involved in platelet activation and arterial thrombosis, implying a potent role of palladin in pathophysiology of thrombotic diseases.

Hyperglycaemia-induced reciprocal changes in miR-30c and PAI-1 expression in platelets

Type 2 diabetic mellitus (DM2) is associated with accelerated thrombotic complications and is characterized by high levels of plasminogen activator inhibitor-1 (PAI-1). Recent studies show that human platelets have high levels of miR-30c and synthesize considerable active PAI-1. The underlying mechanism of how PAI-1 expression is upregulated in DM2 is poorly understood. We now report that hyperglycaemia-induced repression of miR-30c increases PAI-1 expression and thrombus formation in DM2. Bioinformatic analysis and identification of miRNA targets were assessed using luciferase assays, quantitative real-time PCR and western blots invitro and in vivo. The changes in miR-30c and PAI-1 levels were identified in platelets from healthy and diabetic individuals. We found that miR-30c directly targeted the 3′ UTR of PAI-1 and negatively regulated its expression. miR-30c was negatively correlated with glucose and HbA1c levels in DM2. In HFD-fed diabetic mice, increasing miR-30c expression by lenti-miR-30c significantly decreased the PAI-1 expression and prolonged the time to occlusion in an arterial thrombosis model. Platelet depletion/reinfusion experiments generating mice with selective ablation of PAI-1 demonstrate a major contribution by platelet-derived PAI-1 in the treatment of lenti-miR-30c to thrombus formation. These results provide important implications regarding the regulation of fibrinolysis by platelet miRNA under diabetic mellitus.

Ferric Chloride-induced Murine Thrombosis Models

Arterial thrombosis (blood clot) is a common complication of many systemic diseases associated with chronic inflammation, including atherosclerosis, diabetes, obesity, cancer and chronic autoimmune rheumatologic disorders. Thrombi are the cause of most heart attacks, strokes and extremity loss, making thrombosis an extremely important public health problem. Since these thrombi stem from inappropriate platelet activation and subsequent coagulation, targeting these systems therapeutically has important clinical significance for developing safer treatments. Due to the complexities of the hemostatic system, in vitro experiments cannot replicate the blood-to-vessel wall interactions; therefore, in vivo studies are critical to understand pathological mechanisms of thrombus formation. To this end, various thrombosis models have been developed in mice. Among them, ferric chloride (FeCl3) induced vascular injury is a widely used model of occlusive thrombosis that reports platelet activation and aggregation 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 the development of a thrombus that occludes blood flow gives a quantitative measure of vascular injury, platelet activation and aggregation that is relevant to thrombotic diseases. We have significantly refined this FeCl3-induced vascular thrombosis model, which makes the data highly reproducible with minimal variation. Here we describe the model and present representative data from several experimental set-ups that demonstrate the utility of this model in thrombosis research.

Role of the CD39/CD73 Purinergic Pathway in Modulating Arterial Thrombosis in Mice

OBJECTIVE

Circulating blood cells and endothelial cells express ectonucleoside triphosphate diphosphohydrolase-1 (CD39) and ecto-5'-nucleotidase (CD73). CD39 hydrolyzes extracellular ATP or ADP to AMP. CD73 hydrolyzes AMP to adenosine. The goal of this study was to examine the interplay between CD39 and CD73 cascade in arterial thrombosis.

APPROACH AND RESULTS

To determine how CD73 activity influences in vivo thrombosis, the time to ferric chloride-induced arterial thrombosis was measured in CD73-null mice. In response to 5% FeCl3, but not to 10% FeCl3, there was a significant decrease in the time to thrombosis in CD73-null mice compared with wild-type mice. In mice overexpressing CD39, ablation of CD73 did not inhibit the prolongation in the time to thrombosis conveyed by CD39 overexpression. However, the CD73 inhibitor α-β-methylene-ADP nullified the prolongation in the time to thrombosis in human CD39 transgenic (hC39-Tg)/CD73-null mice. To determine whether hematopoietic-derived cells or endothelial cell CD39 activity regulates in vivo arterial thrombus, bone marrow transplant studies were conducted. FeCl3-induced arterial thrombosis in chimeric mice revealed a significant prolongation in the time to thrombosis in hCD39-Tg reconstituted wild-type mice, but not on wild-type reconstituted hCD39-Tg mice. Monocyte depletion with clodronate-loaded liposomes normalized the time to thrombosis in hCD39-Tg mice compared with hCD39-Tg mice treated with control liposomes, demonstrating that increased CD39 expression on monocytes protects against thrombosis.

CONCLUSIONS

These data demonstrate that ablation of CD73 minimally effects in vivo thrombosis, but increased CD39 expression on hematopoietic-derived cells, especially monocytes, attenuates in vivo arterial thrombosis.

Plasma L5 levels are elevated in ischemic stroke patients and enhance platelet aggregation

L5, the most electronegative and atherogenic subfraction of low-density lipoprotein (LDL), induces platelet activation. We hypothesized that plasma L5 levels are increased in acute ischemic stroke patients and examined whether lectin-like oxidized LDL receptor-1 (LOX-1), the receptor for L5 on endothelial cells and platelets, plays a critical role in stroke. Because amyloid β (Aβ) stimulates platelet aggregation, we studied whether L5 and Aβ function synergistically to induce prothrombotic pathways leading to stroke. Levels of plasma L5, serum Aβ, and platelet LOX-1 expression were significantly higher in acute ischemic stroke patients than in controls without metabolic syndrome (P < .01). In mice subjected to focal cerebral ischemia, L5 treatment resulted in larger infarction volumes than did phosphate-buffered saline treatment. Deficiency or neutralizing of LOX-1 reduced infarct volume up to threefold after focal cerebral ischemia in mice, illustrating the importance of LOX-1 in stroke injury. In human platelets, L5 but not L1 (the least electronegative LDL subfraction) induced Aβ release via IκB kinase 2 (IKK2). Furthermore, L5+Aβ synergistically induced glycoprotein IIb/IIIa receptor activation; phosphorylation of IKK2, IκBα, p65, and c-Jun N-terminal kinase 1; and platelet aggregation. These effects were blocked by inhibiting IKK2, LOX-1, or nuclear factor-κB (NF-κB). Injecting L5+Aβ shortened tail-bleeding time by 50% (n = 12; P < .05 vs L1-injected mice), which was prevented by the IKK2 inhibitor. Our findings suggest that, through LOX-1, atherogenic L5 potentiates Aβ-mediated platelet activation, platelet aggregation, and hemostasis via IKK2/NF-κB signaling. L5 elevation may be a risk factor for cerebral atherothrombosis, and downregulating LOX-1 and inhibiting IKK2 may be novel antithrombotic strategies.

Kaempferol suppresses collagen-induced platelet activation by inhibiting NADPH oxidase and protecting SHP-2 from oxidative inactivation

Reactive oxygen species (ROS) generated upon collagen stimulation act as second messengers to propagate various platelet-activating events. Among the ROS-generating enzymes, NADPH oxidase (NOX) plays a prominent role in platelet activation. Thus, NOX has been suggested as a novel target for anti-platelet drug development. Although kaempferol has been identified as a NOX inhibitor, the influence of kaempferol on the activation of platelets and the underlying mechanism have never been investigated. Here, we studied the effects of kaempferol on NOX activation, ROS-dependent signaling pathways, and functional responses in collagen-stimulated platelets. Superoxide anion generation stimulated by collagen was significantly inhibited by kaempferol in a concentration-dependent manner. More importantly, kaempferol directly bound p47(phox), a major regulatory subunit of NOX, and significantly inhibited collagen-induced phosphorylation of p47(phox) and NOX activation. In accordance with the inhibition of NOX, ROS-dependent inactivation of SH2 domain-containing protein tyrosine phosphatase-2 (SHP-2) was potently protected by kaempferol. Subsequently, the specific tyrosine phosphorylation of key components (Syk, Vav1, Btk, and PLCγ2) of collagen receptor signaling pathways was suppressed by kaempferol. Kaempferol also attenuated downstream responses, including cytosolic calcium elevation, P-selectin surface exposure, and integrin-αIIbβ3 activation. Ultimately, kaempferol inhibited platelet aggregation and adhesion in response to collagen in vitro and prolonged in vivo thrombotic response in carotid arteries of mice. This study shows that kaempferol impairs collagen-induced platelet activation through inhibition of NOX-derived ROS production and subsequent oxidative inactivation of SHP-2. This effect suggests that kaempferol has therapeutic potential for the prevention and treatment of thrombovascular diseases.

Resolving the multifaceted mechanisms of the ferric chloride thrombosis model using an interdisciplinary microfluidic approach

The mechanism of action of the widely used in vivo ferric chloride (FeCl3) thrombosis model remains poorly understood; although endothelial cell denudation is historically cited, a recent study refutes this and implicates a role for erythrocytes. Given the complexity of the in vivo environment, an in vitro reductionist approach is required to systematically isolate and analyze the biochemical, mass transfer, and biological phenomena that govern the system. To this end, we designed an "endothelial-ized" microfluidic device to introduce controlled FeCl3 concentrations to the molecular and cellular components of blood and vasculature. FeCl3 induces aggregation of all plasma proteins and blood cells, independent of endothelial cells, by colloidal chemistry principles: initial aggregation is due to binding of negatively charged blood components to positively charged iron, independent of biological receptor/ligand interactions. Full occlusion of the microchannel proceeds by conventional pathways, and can be attenuated by antithrombotic agents and loss-of-function proteins (as in IL4-R/Iba mice). As elevated FeCl3 concentrations overcome protective effects, the overlap between charge-based aggregation and clotting is a function of mass transfer. Our physiologically relevant in vitro system allows us to discern the multifaceted mechanism of FeCl3-induced thrombosis, thereby reconciling literature findings and cautioning researchers in using the FeCl3 model.

Unfractionated heparin-clopidogrel combination in ST-elevation myocardial infarction not receiving reperfusion therapy

OBJECTIVE

We sought explore the relative benefits of unfractionated heparin (UFH) compared with enoxaparin, alone or in combination with clopidogrel, in ST-segment elevation myocardial infarction (STEMI) patients not undergoing reperfusion therapy.

METHODS

This is a propensity score study from The International Survey on Acute Coronary Syndromes in Transition Countries (ISACS-TC/NCT01218776) on patients admitted between October 2010-June 2013. There were a total of 1175 STEMI patients who did not receive mechanical or pharmacological reperfusion. Of these, 1063 were eligible for the aim of the study, being treated with UFH (522/1175; 44.4%) or enoxaparin (541/1175; 46%). Clopidogrel in combination with UFH or enoxaparin was given to 751 (63.9%) patients. The primary endpoint was in-hospital mortality. Secondary endpoints were intracranial hemorrhages, and clinically relevant bleedings.

RESULTS

After adjustment for any confounders, UFH was associated with a lower risk of in-hospital mortality in clopidogrel users (multivariate adjusted regression analysis: odds ratio [OR]: 0.62, 95% Confidence Interval [CI] 0.41-0.94) as compared with clopidogrel non-users (OR: 0.94, 95% CI 0.55-1.60). The observed effect was not associated with combined enoxaparin and clopidogrel therapy. Major bleeding events were comparable in the enoxaparin group and UFH group (0.4% and 1.5% respectively, p = 0.06). The risk of major hemorrhage was nearly similar with combined UFH-clopidogrel therapy (1.4%) as compared with UFH alone (1.9%), p = 0.67.

CONCLUSION

UFH - Clopidogrel combination was associated with a large mortality reduction in STEMI patients not undergoing reperfusion therapy and did not significantly increase the risk of major bleeding.

Chelation of dietary iron prevents iron accumulation and macrophage infiltration in the type I diabetic kidney

We previously reported that the functional deletion of p21, a cyclin-dependent kinase inhibitor, in mice attenuated renal cell senescence in streptozotocin (STZ)-induced type 1 diabetic mice. In the present study, we investigated the effect of iron chelation on renal cell senescence and inflammation in the type 1 diabetic kidney. STZ-treated mice showed increase in iron accumulation, tubular cell senescence and macrophage infiltration at week 28 in the kidney. Administering deferasirox, which removes only dietary iron, significantly attenuated iron accumulation in proximal tubules and the number of infiltrating F4/80-positive cells without effecting blood glucose, hematocrit or hemoglobin levels. In contrast however, deferasirox did not influence renal cell senescence. The lack of p21 decreased the renal tubular iron accumulation and did not change tubular cell senescence. Interestingly, the STZ-treated animals showed an increase in p16, another cyclin-dependent kinase inhibitor. The results suggest that type 1 diabetes increases renal tubular iron accumulation and macrophage infiltration through a p21-dependent mechanism, and that the chelation of dietary iron attenuates these responses.

Peroxiredoxin II is an antioxidant enzyme that negatively regulates collagen-stimulated platelet function

Collagen-induced platelet signaling is mediated by binding to the primary receptor glycoprotein VI (GPVI). Reactive oxygen species produced in response to collagen have been found to be responsible for the propagation of GPVI signaling pathways in platelets. Therefore, it has been suggested that antioxidant enzymes could down-regulate GPVI-stimulated platelet activation. Although the antioxidant enzyme peroxiredoxin II (PrxII) has emerged as having a role in negatively regulating signaling through various receptors by eliminating H2O2 generated upon receptor stimulation, the function of PrxII in collagen-stimulated platelets is not known. We tested the hypothesis that PrxII negatively regulates collagen-stimulated platelet activation. We analyzed PrxII-deficient murine platelets. PrxII deficiency enhanced GPVI-mediated platelet activation through the defective elimination of H2O2 and the impaired protection of SH2 domain-containing tyrosine phosphatase 2 (SHP-2) against oxidative inactivation, which resulted in increased tyrosine phosphorylation of key components for the GPVI signaling cascade, including Syk, Btk, and phospholipase Cγ2. Interestingly, PrxII-mediated antioxidative protection of SHP-2 appeared to occur in the lipid rafts. PrxII-deficient platelets exhibited increased adhesion and aggregation upon collagen stimulation. Furthermore, in vivo experiments demonstrated that PrxII deficiency facilitated platelet-dependent thrombus formation in injured carotid arteries. This study reveals that PrxII functions as a protective antioxidant enzyme against collagen-stimulated platelet activation and platelet-dependent thrombosis.

Murine arterial thrombus induction mechanism influences subsequent thrombodynamics

BACKGROUND

The mechanism of thrombotic induction in experimental models can vary greatly, as can the applied evaluative measures, making comparisons among models difficult.

OBJECTIVES

This study comparatively evaluated the arterial thrombodynamic response among injury mechanisms.

METHODS

Thrombotic responses were induced in mouse carotid arteries, with subsequent intravital imaging using rhodamine-6G-labeled platelets to quantitate platelet accumulation over 30minutes. Nine induction methods were evaluated: brief pinch, temporary hard ligation, cautery/heat, needle puncture, intralumenal wire (scratch), intralumenal adventitia/collagen (2 different models), and brief exposures to either iron-based surface electrolytic injury or ferric chloride.

RESULTS

The accumulation of platelets was variable among induction methods, with a greater response to more severe injury mechanisms, free radical injury, and exposed collagen. Temporal profiles were generated by normalizing data to peak platelet accumulation for each run; rapid platelet development and subsequent detachment were found for mechanical injuries that maintained vessel integrity (pinch and ligation injuries), with more sustained growth for more severe mechanical (wire) injury or breach of the vessel (needle puncture or intralumenal collagen). A delayed but extended temporal response was seen with free radical injury (both electrolytic and ferric chloride).

CONCLUSIONS

These findings demonstrate a dependence of platelet thrombodynamics on the method of induction, with collagen exposure causing greater, more prolonged activity, while free-radical injury effected a delayed but sustained platelet thrombus formation with slower resolution. A better understanding of how these various injury models relate to clinical causes of arterial thrombosis is needed for optimal translational interpretation of murine models of thrombosis.

Ferric chloride-induced arterial thrombosis in mice

Because of its high sensitivity and reproducibility, the FeCl3 -induced arterial thrombosis mouse model is widely used to study molecular mechanisms as well as the efficacy of antithrombotic agents. The model also carries the additional advantages of being relatively easy to establish and requiring minimal instrumentation. However, the various parameters that influence the outcome must be optimized to the experimental requirements and the individual laboratory conditions. Here, we describe a standard protocol for FeCl3 -induced common carotid artery thrombosis, parameters that influence thrombus growth, ways to optimize the experiment, and interpretation of the data.

Evaluation of antithrombotic activity of thrombin DNA aptamers by a murine thrombosis model

Aptamers are nucleic acid based molecular recognition elements with a high potential for the theranostics. Some of the aptamers are under development for therapeutic applications as promising antithrombotic agents; and G-quadruplex DNA aptamers, which directly inhibit the thrombin activity, are among them. RA-36, the 31-meric DNA aptamer, consists of two thrombin binding pharmacophores joined with the thymine linker. It has been shown earlier that RA-36 directly inhibits thrombin in the reaction of fibrinogen hydrolysis, and also it inhibits plasma and blood coagulation. Studies of both inhibitory and anticoagulation effects had indicated rather high species specificity of the aptamer. Further R&D of RA-36 requires exploring its efficiency in vivo. Therefore the development of a robust and adequate animal model for effective physiological studies of aptamers is in high current demand. This work is devoted to in vivo study of the antithrombotic effect of RA-36 aptamer. A murine model of thrombosis has been applied to reveal a lag and even prevention of thrombus formation when RA-36 was intravenous bolus injected in high doses of 1.4–7.1 µmol/kg (14–70 mg/kg). A comparative study of RA-36 aptamer and bivalirudin reveals that both direct thrombin inhibitors have similar antithrombotic effects for the murine model of thrombosis; though in vitro bivalirudin has anticoagulation activity several times higher compared to RA-36. The results indicate that both RA-36 aptamer and bivalirudin are direct thrombin inhibitors of different potency, but possible interactions of the thrombin-inhibitor complex with other components of blood coagulation cascade level the physiological effects for both inhibitors.

Endothelial cells but not platelets are the major source of Toll-like receptor 4 in the arterial thrombosis and tissue factor expression in mice

It is known that Toll-like receptor (TLR)-4 plays an important role in myocardial infarction and atherothrombosis. The role of TLR-4 in arterial thrombosis is undefined. Both TLR-4-deficient (TLR-4(-/-)) and wild-type (WT) mice were subjected to FeCl3 carotid artery injury, and the time required to form an occlusive thrombus was measured. The mean time to occlusion in TLR-4(-/-) mice was significantly greater than that in WT mice after injury (303 ± 32 vs. 165 ± 34 s, P < 0.05). Furthermore, when we used a WT or TLR-4(-/-)-derived platelet reinfusion in a platelet depletion/reinfusion procedure, there was no significant change in the occlusion time and tissue factor (TF) activity in injured arteries between WT mice and platelet-depleted WT mice. Similarly, no significant difference was observed between TLR-4(-/-) mice and platelet-depleted TLR-4(-/-) mice for the WT or TLR-4(-/-)-derived platelet reinfusion. However, TF expression and activity were significantly reduced in the vascular wall of TLR-4(-/-) mice compared with WT mice. In vivo, lipopolysaccharide accelerated the occlusion time in WT mice but not TLR-4(-/-) mice. In vitro, LPS-induced TF activity was reduced in endothelial cells of TLR-4(-/-) mice relative to WT mice. The data demonstrate that TLR-4 contributes to arterial thrombosis formation in vivo and causes increased TF expression and activity in vitro. The results further suggest that the stimulation is mainly derived by endothelial cells but is not due to platelet-derived TLR-4.

High-density lipoprotein from patients with coronary heart disease loses anti-thrombotic effects on endothelial cells: impact on arterial thrombus formation

Thrombus formation is determined by the balance between pro- thrombotic mediators and anti-thrombotic factors.High-density lipoprotein (HDL) from healthy subjects exerts anti-thrombotic properties. Whether this is also the case for HDL from patients with stable coronary heart disease (CHD) or acute coronary syndrome (ACS) is unknown.In human aortic endothelial cells in culture,HDL (50 µg/ml) from healthy subjects (HS) inhibited thrombin-induced tissue factor (TF) expression and activity, while HDL (50 µg/ml) from CHD and ACS patients did not. Similarly, only healthy HDL increased endothelial tissue factor pathway inhibitor (TFPI) expression and tissue plasminogen activator (tPA) release, while HDL from CHD and ACS patients had no effect. Healthy HDL inhibited thrombin-induced plasminogen activator inhibitor type 1 (PAI-1) expression, while HDL from ACS patients enhanced endothelial PAI-1 expression. Inhibition of nitric oxide (NO) formation with L-NAME (100 µmol/l) abolished the anti-thrombotic effects of healthy HDL on TF, TFPI, and tPA expression. The exogenous nitric oxide donor, DETANO, mimicked the effects of healthy HDL and counterbalanced the loss of anti-thrombotic effects of HDL from CHD and ACS patients in endothelial cells. In line with this observation, healthy HDL, in contrast to HDL from CHD and ACS patients, increased endothelial NO production. In the laser-injured carotid artery of the mouse, thrombus formation was delayed in animals treated with healthy HDL compared with mice treated with vehicle or HDL from patients with CHD or ACS. In conclusion, HDL from CHD and ACS patients loses the ability of healthy HDL to suppress TF and to increase TFPI and t-PA and instead enhances PAI-1 and arterial thrombus formation.

Reactive oxygen species play a critical role in collagen-induced platelet activation via SHP-2 oxidation

AIMS

The collagen-stimulated generation of reactive oxygen species (ROS) regulates signal transduction in platelets, although the mechanism is unclear. The major targets of ROS include protein tyrosine phosphatases (PTPs). ROS-mediated oxidation of the active cysteine site in PTPs abrogates the PTP catalytic activity. The aim of this study was to elucidate whether collagen-induced ROS generation leads to PTP oxidation, which promotes platelet stimulation.

RESULTS

SH2 domain-containing PTP-2 (SHP-2) is oxidized in platelets by ROS produced upon collagen stimulation. The oxidative inactivation of SHP-2 leads to the enhanced tyrosine phosphorylation of spleen tyrosine kinase (Syk), Vav1, and Bruton's tyrosine kinase (Btk) in the linker for the activation of T cells signaling complex, which promotes the tyrosine phosphorylation-mediated activation of phospholipase Cγ2 (PLCγ2). Moreover, we found that, relative to wild-type platelets, platelets derived from glutathione peroxidase 1 (GPx1)/catalase double-deficient mice showed enhanced cellular ROS levels, oxidative inactivation of SHP-2, and tyrosine phosphorylation of Syk, Vav1, Btk, and PLCγ2 in response to collagen, which subsequently led to increased intracellular calcium levels, degranulation, and integrin αIIbβ3 activation. Consistent with these findings, GPx1/catalase double-deficiency accelerated the thrombotic response in FeCl3-injured carotid arteries.

INNOVATION

The present study is the first to demonstrate that SHP-2 is targeted by ROS produced in collagen-stimulated platelets and suggests that a novel mechanism for the regulation of platelet activation by ROS is due to oxidative inactivation of SHP-2.

CONCLUSION

We conclude that collagen-induced ROS production leads to SHP-2 oxidation, which promotes platelet activation by upregulating tyrosine phosphorylation-based signal transduction.

The extrinsic coagulation cascade and tissue factor pathway inhibitor in macrophages: a potential therapeutic opportunity for atherosclerotic thrombosis

OBJECTIVES

The coagulation protease cascade plays the central requisite role in initiation of arterial atherothrombosis. However, the relative participation of the extrinsic as compared to the intrinsic pathway is incompletely resolved. We have investigated in vivo the relative importance of the extrinsic and intrinsic pathways to define which is more essential to atherothrombosis and therefore the preferable prophylactic therapeutic target. We further addressed which type of plaque associated macrophage population is associated with the thrombotic propensity of atherosclerotic plaques.

METHODS

Both photochemical injury and ferric chloride vascular injury models demonstrated arterial thrombosis formation in ApoE deficient mice. We found that direct interference with the extrinsic pathway, but not the intrinsic pathway, markedly diminished the rate of thrombus formation and occlusion of atherosclerotic carotid arteries following experimental challenge. To explore which plaque macrophage subtype may participate in plaque thrombosis in regard to expression tissue factor pathway inhibitor (TFPI), bone marrow derived macrophages of both M and GM phenotypes expressed tissue factor (TF), but the level of TFPI was much greater in M- type macrophages, which exhibited diminished thrombogenic activity, compared to type GM-macrophages.

RESULTS AND CONCLUSIONS

Our works support the hypothesis that the TF-initiated and direct extrinsic pathway provides the more significant contribution to arterial plaque thrombogenesis. Activation of the TF driven extrinsic pathway can be influenced by differing colony-stimulating factor influenced macrophage TFPI-1 expression. These results advance our understanding of atherothrombosis and identify potential therapeutic targets associated with the extrinsic pathway and with macrophages populating arterial atherosclerotic plaques.

Extract of Ulmus macrocarpa Hance prevents thrombus formation through antiplatelet activity

Ulmus macrocarpa Hance (Ulmaceae) has been used as a traditional oriental medicine for the treatment of edema, mastitis, gastric cancer and inflammation. The aim of this study was to investigate the effects of Ulmus macrocarpa extract (UME) on thrombus formation in vivo, platelet activation ex vivo and fibrinolytic activity in vitro. To identify the antithrombotic activity of UME in vivo, we used an arterial thrombosis model. UME delayed the occlusion time by 13.4 and 13.9 min at doses of 300 and 600 mg/kg, respectively. UME significantly inhibited ex vivo platelet aggregation induced by collagen and adenosine 5'-diphosphate (ADP), respectively, but did not affect the coagulation times following activated partial thromboplastin and prothrombin activation. Therefore, to investigate the antiplatelet effect of UME, the effect of UME on collagen and ADP-induced platelet aggregation in vitro was examined. UME exhibited antiplatelet aggregation activity, induced by ADP and collagen. Furthermore, the fibrinolytic activity of UME was investigated. The results showed that UME significantly increased fibrinolysis at 1,000 mg/ml. In conclusion, the results suggested that UME may significantly inhibit artery thrombus formation in vivo, potentially due to antiplatelet activity, and also exhibits potential as a clot‑dissolving agent for thrombolytic therapy.

PDK1 regulates platelet activation and arterial thrombosis

The effects of phosphoinositide-dependent protein kinase 1 (PDK1), a master kinase in the phosphoinositide 3-kinase/Akt pathway, on platelet activation are unknown. Accordingly, platelet-specific PDK1-deficient mice were characterized to elucidate the platelet-related function(s) of PDK1. We found that PDK1 deficiency caused mild thrombocytopenia. The aggregation of PDK1(-/-) platelets was diminished in response to low levels of thrombin, U46619, and adenosine 5'-diphosphate. Further results demonstrated that PDK1 regulates thrombin-induced platelet activation by affecting αIIbβ3-mediated outside-in signaling. This result provided an explanation for the diminished spreading of PDK1(-/-) platelets on immobilized fibrinogen (Fg) and the decreased rate of clot retraction in platelet-rich plasma (PRP) containing PDK1(-/-) platelets. PDK1 deficiency diminished agonist-induced Akt Ser473 phosphorylation and thoroughly abolished Akt Thr308 and Gsk3β Ser9 phosphorylation in response to agonist treatment and platelet spreading, respectively. A Gsk3β inhibitor fully restored the aggregation of PDK1(-/-) platelets in response to low levels of thrombin, normal spreading of PDK1(-/-) platelets on Fg, and normal clot retraction in PRP containing PDK1(-/-) platelets. Those results indicated that Gsk3β is one of the major downstream effectors of PDK1 in thrombin-induced platelet activation and αIIbβ3-mediated outside-in signaling. In addition, in vivo data demonstrated that PDK1 is an important regulator in arterial thrombosis formation.

The hyperfibrinolytic state of mice with combined thrombin-activatable fibrinolysis inhibitor (TAFI) and plasminogen activator inhibitor-1 gene deficiency is critically dependent on TAFI deficiency

BACKGROUND

Mice with single gene deficiency of thrombin-activatable fibrinolysis inhibitor (TAFI) or plasminogen activator inhibitor-1 (PAI-1) have an enhanced fibrinolytic capacity.

OBJECTIVES

To unravel the function and relevance of both antifibrinolytic proteins through the generation and characterization of mice with combined TAFI and PAI-1 gene deficiency.

RESULTS

Mating of TAFI knockout (KO) mice with PAI-1 KO mice resulted in the production of TAFI/PAI-1 double-KO mice that were viable, were fertile, and developed normally. In a tail vein bleeding model, the bleeding time and hemoglobin content of the TAFI/PAI-1 double-KO mice did not deviate significantly from those of the single-KO mice or of the wild-type (WT) counterparts. Interestingly, in ex vivo rotational thromboelastometry measurements with whole blood samples, TAFI KO mice and TAFI/PAI-1 double-KO mice were more sensitive to fibrinolytic activation with tissue-type plasminogen activator than WT or PAI-1 KO mice. This enhanced fibrinolytic capacity was confirmed in vivo in a mouse thromboembolism model, as shown by decreased fibrin deposition in the lungs of TAFI KO mice and TAFI/PAI-1 double-KO mice as compared with WT or PAI-1 KO mice.

CONCLUSIONS

TAFI gene inactivation predominantly contributes to the increased fibrinolytic capacity of TAFI and PAI-1 double-gene-deficient mice, as observed in some basic thrombosis models.

Dronedarone reduces arterial thrombus formation

Dronedarone has been associated with a reduced number of first hospitalisation due to acute coronary syndromes. Whether this is only due to the reduction in ventricular heart rate and blood pressure or whether other effects of dronedarone may be involved is currently elusive. This study was designed to investigate the role of dronedarone in arterial thrombus formation. C57Bl/6 mice were treated with dronedarone and arterial thrombosis was investigated using a mouse photochemical injury model. Dronedarone inhibited carotid artery thrombus formation in vivo (P < 0.05). Thrombin- and collagen-induced platelet aggregation was impaired in dronedarone-treated mice (P < 0.05), and expression of plasminogen activator inhibitor-1 (PAI1), an inhibitor of the fibrinolytic system, was reduced in the arterial wall (P < 0.05). In contrast, the level of tissue factor (TF), the main trigger of the coagulation cascade, and that of its physiological inhibitor, TF pathway inhibitor, did not differ. Similarly, coagulation times as measured by prothrombin time and activated partial thromboplastin time were comparable between the two groups. Dronedarone inhibits thrombus formation in vivo through inhibition of platelet aggregation and PAI1 expression. This effect occurs within the range of dronedarone concentrations measured in patients, and may represent a beneficial pleiotropic effect of this drug.

Critical review of mouse models of venous thrombosis

Deep vein thrombosis and pulmonary embolism are a significant health care concern, representing a major source of mortality and morbidity. In order to understand the pathophysiology of thrombogenesis and thrombus resolution, animal models are necessary. Mouse models of venous thrombosis contribute to our understanding of the initiation, propagation, and resolution of venous thrombus, as well as allow for the evaluation of new pharmaceutical approaches to prophylaxis and treatment of deep vein thrombosis. In this work we review the ferric chloride model, the inferior vena cava ligation model, the inferior vena cava stenosis models, and the electrolytic inferior vena cava model and compare their advantages and disadvantages.

Animal models of hemophilia

The X-linked bleeding disorder hemophilia is caused by mutations in coagulation factor VIII (hemophilia A) or factor IX (hemophilia B). Unless prophylactic treatment is provided, patients with severe disease (less than 1% clotting activity) typically experience frequent spontaneous bleeds. Current treatment is largely based on intravenous infusion of recombinant or plasma-derived coagulation factor concentrate. More effective factor products are being developed. Moreover, gene therapies for sustained correction of hemophilia are showing much promise in preclinical studies and in clinical trials. These advances in molecular medicine heavily depend on availability of well-characterized small and large animal models of hemophilia, primarily hemophilia mice and dogs. Experiments in these animals represent important early and intermediate steps of translational research aimed at development of better and safer treatments for hemophilia, such a protein and gene therapies or immune tolerance protocols. While murine models are excellent for studies of large groups of animals using genetically defined strains, canine models are important for testing scale-up and for long-term follow-up as well as for studies that require larger blood volumes.

Mannose-binding lectin-associated serine protease-1 is a significant contributor to coagulation in a murine model of occlusive thrombosis

Bleeding disorders and thrombotic complications constitute a major cause of death and disability worldwide. Although it is known that the complement and coagulation systems interact, no studies have investigated the specific role or mechanisms of lectin-mediated coagulation in vivo. FeCl(3) treatment resulted in intra-arterial occlusive thrombogenesis within 10 min in wild-type (WT) and C2/factor B-null mice. In contrast, mannose-binding lectin (MBL)-null and MBL-associated serine protease (MASP)-1/-3 knockout (KO) mice had significantly decreased FeCl(3)-induced thrombogenesis. Reconstitution with recombinant human (rh) MBL restored FeCl(3)-induced thrombogenesis in MBL-null mice to levels comparable to WT mice, suggesting a significant role of the MBL/MASP complex for in vivo coagulation. Additionally, whole blood aggregation demonstrated increased MBL/MASP complex-dependent platelet aggregation. In vitro, MBL/MASP complexes were captured on mannan-coated plates, and cleavage of a chromogenic thrombin substrate (S2238) was measured. We observed no significant differences in S2238 cleavage between WT, C2/factor B-null, MBL-A(-/-), or MBL-C(-/-) sera; however, MBL-null or MASP-1/-3 KO mouse sera demonstrated significantly decreased S2238 cleavage. rhMBL alone failed to cleave S2238, but cleavage was restored when rMASP-1 was added to either MASP-1/-3 KO sera or rhMBL. Taken together, these findings indicate that MBL/MASP complexes, and specifically MASP-1, play a key role in thrombus formation in vitro and in vivo.

Inducible nitric oxide synthase provides protection against injury-induced thrombosis in female mice

Nitric oxide (NO) is an important vasoactive molecule produced by three NO synthase (NOS) enzymes: neuronal (nNOS), inducible (iNOS), and endothelial NOS (eNOS). While eNOS contributes to blood vessel dilation that protects against the development of hypertension, iNOS has been primarily implicated as a disease-promoting isoform during atherogenesis. Despite this, iNOS may play a physiological role via the modulation of cyclooxygenase and thromboregulatory eicosanoid production. Herein, we examined the role of iNOS in a murine model of thrombosis. Blood flow was measured in carotid arteries of male and female wild-type (WT) and iNOS-deficient mice following ferric chloride-induced thrombosis. Female WT mice were more resistant to thrombotic occlusion than male counterparts but became more susceptible upon iNOS deletion. In contrast, male mice (with and without iNOS deletion) were equally susceptible to thrombosis. Deletion of iNOS was not associated with a change in the balance of thromboxane A(2) (TxA(2)) or antithrombotic prostacyclin (PGI(2)). Compared with male counterparts, female WT mice exhibited increased urinary nitrite and nitrate levels and enhanced ex vivo induction of iNOS in hearts and aortas. Our findings suggest that iNOS-derived NO in female WT mice may attenuate the effects of vascular injury. Thus, although iNOS is detrimental during atherogenesis, physiological iNOS levels may contribute to providing protection against thrombotic occlusion, a phenomenon that may be enhanced in female mice.

Vitronectin dictates intraglomerular fibrinolysis in immune-mediated glomerulonephritis

During human glomerulonephritis, the severity of injuries correlates with glomerular fibrin deposits, which are tightly regulated by the intraglomerular fibrinolytic system. Here, we evaluated the role of vitronectin (VTN; also known as complement S protein), the principal cofactor of the plasminogen activator inhibitor-1 (PAI-1), in a mouse model of acute glomerulonephritis. We found that in mice subjected to nephrotoxic serum, the absence of VTN resulted in a lower glomerular PAI-1 activity and a higher glomerular fibrinolytic activity. Challenged VTN(-/-) mice displayed significantly less fibrin deposits, proteinuria, and renal failure than their wild-type counterparts. Notably, this protective effect afforded by VTN deficiency was still observed after a C3 depletion. Finally, the injection of VTN(+/+) serum in VTN(-/-) mice induced the glomerular deposition of VTN, increased PAI-1 deposition, decreased glomerular fibrinolytic activity, and aggravated glomerular injury. As in mice, abundant glomerular VTN deposits were also observed in patients with severe glomerulonephritis. Here, we show that plasma-exchange therapy, admittedly beneficial in this clinical context, induces a significant depletion in circulating VTN, which might modulate PAI-1 activity locally and accelerate the clearance of fibrin deposits in the glomeruli. Collectively, these results demonstrate that VTN exerts a deleterious role independently from complement, by directing PAI-dependent fibrinolysis in the glomerular compartment.

Thrombotic distal middle cerebral artery occlusion produced by topical FeCl(3) application: a novel model suitable for intravital microscopy and thrombolysis studies

Intravital or multiphoton microscopy and laser-speckle imaging have become popular because they allow live monitoring of several processes during cerebral ischemia. Available rodent models have limitations for these experiments; e.g., filament occlusion of the proximal middle cerebral artery (MCA) is difficult to perform under a microscope, whereas distal occlusion methods may damage the MCA and the peri-arterial cortex. We found that placement of a 10% FeCl(3)-soaked filter paper strip (0.3 × 1 mm(2)) on the duramater over the trunk of the distal MCA through a cranial window for 3 minutes induced intraarterial thrombus without damaging the peri-arterial cortex in the mouse. This caused a rapid regional cerebral blood flow decrease within 10 minutes and total occlusion of the MCA segment under the filter paper in 17±2 minutes, which resulted in a typical cortical infarct of 27±4 mm(3) at 24 hours and moderate sensorimotor deficits. There was no significant hemispheric swelling or hemorrhage or mortality at 24 hours. Reperfusion was obtained in half of the mice with tissue plasminogen activator, which allowed live monitoring of clot lysis along with restoration of tissue perfusion and MCA flow. In conclusion, this relatively simple and noninvasive stroke model is easy to perform under a microscope, making it suitable for live imaging and thrombolysis studies.

Intravenous low redox potential saline attenuates FeCl3-induced vascular dysfunction via downregulation of endothelial H2O2, CX3CL1, intercellular adhesion molecule-1, and p53 expression

Exaggerated reactive oxygen species (ROS) may contribute to vascular injury by the enhancement of CX3CL1, intercellular adhesion molecule-1 (ICAM-1), and pro-apoptotic p53 expression. Reduced water with safely antioxidant activity may protect vascular tissue against oxidative injury. We established reduced water (RW) by using a modified magnesium alloy and evaluated the effects of an RW-made culture medium on TNF-α-induced endothelial damage in vitro and intravenous RW-made saline (0.9%NaCl) infusion on FeCl(3)-induced arterial injury in rats in vivo. Several oxidative stresses were evaluated by using a chemiluminescence analyzer, Western blot, and immunohistochemistry. We found that the established RW, RW-culture medium, and RW saline displayed a lower redox potential (<-150 mV) and efficient H(2)O(2) scavenging activity compared with distilled-water-made solutions. The RW-culture medium significantly depressed TNF-α-enhanced endothelial H(2)O(2) production; improved CX3CL1, ICAM-1, and p53 expression; and inhibited activated monocyte adhesion to endothelial cells as well as to the CX3CL1 or the ICAM-1 coated plate when compared with the distilled-water-culture medium. In the in vivo study, the time required for FeCl(3)-induced occlusion in the urethane anesthetized rat's carotid and femoral arteries was significantly extended by intravenous RW saline infusion compared with distilled-water saline. FeCl(3) stimulation significantly enhanced vascular NADPH oxidase activity, ROS production, as well as CX3CL1, ICAM-1, p53, 3-nitrotyrosine, and 4-hydroxynonenal expression in the damaged arteries. Intravenous RW saline significantly reduced all the FeCl(3)-enhanced oxidative parameters when compared with intravenous distilled-water-saline infusion. We conclude that the RW-culture medium and saline made from magnesium alloy confer cardiovascular protection by the antioxidant capability.