Tissue factor cytoplasmic domain exacerbates post-infarct left ventricular remodeling via orchestrating cardiac inflammation and angiogenesis

Introduction

The coagulation protein tissue factor (TF) regulates inflammation and angiogenesis via its cytoplasmic domain in infection, cancer and diabetes. While TF is highly abundant in the heart and implicated in cardiac injuries and dysfunction, the contribution of its cytoplasmic domain in cardiac pathology remains unclear.

Purpose

We aimed to investigate the contribution of the cytoplasmic domain of TF to post-infarct myocardial injury and adverse left ventricular (LV) remodeling.

Methods and results

Myocardial infarction was induced by permanent occlusion of the left anterior descending coronary artery. Male mice with C57BL/Jax background were used for the study. Compared with wild-type mice, mice lacking the TF cytoplasmic domain (TFΔCT) had a higher survival rate (90.5% versus 70%, p=0.0298) during a 28-day follow-up after myocardial infarction. Among surviving mice, TFΔCT mice had better cardiac function and less LV remodeling (ESV: 114.5±13.1mL for WT, 67.06±10.8mL for TFΔCT, p<0.001; EDV: 146.6±12.4mL for WT, 99.97±11.71mL for TFΔCT, p<0.001) than wild-type mice. Bone marrow chimerism indicated that deletion of the TF cytoplasmic domain in either bone marrow-derived cells or cardiac resident cells could alleviate post-infarct cardiac dysfunction. Speckle-tracking strain analysis revealed that the overall improvement of post-infarct cardiac performance in TFΔCT mice was attributed to reduced myocardial deformation in the peri-infarct region (strain-%: 11.14±0.97 for WT, 15.34±1.10 for TFΔCT, p=0.007; strain rate-/s: 3.89±0.26 for WT, 5.18±0.21 for TFΔCT, p=0.0005). Histological analysis demonstrated that TFΔCT hearts had in the infarct area greater proliferation of endothelial cells and myofibroblasts accompanied with better scar formation. Compared with wild-type hearts, infarcted TFΔCT hearts showed less infiltration of proinflammatory cells with concomitant lower expression of protease-activated receptor-1 (PAR1)-Rac1 axis. Furthermore, infarcted TFΔCT hearts presented markedly higher peri-infarct vessel density associated with enhanced endothelial cell proliferation and higher expression of PAR2 and PAR2-associated pro-angiogenic pathway factors.

Conclusions

Our findings demonstrate that the TF cytoplasmic domain exacerbates post-infarct cardiac injury and adverse LV remodeling via differential regulation of inflammation and angiogenesis. Targeted inhibition of the TF cytoplasmic domain-mediated intracellular signaling may ameliorate post-infarct LV remodeling without perturbing coagulation.

Funding Acknowledgement

Type of funding sources: Public Institution(s). Main funding source(s): National University Health System of Singapore

Characterization and Targeting of the Murine α2-Antiplasmin Gene

α2-Antiplasmin (α2-AP) is the main physiological plasmin inhibitor in mammalian plasma. As a first step toward the generation of α2-AP deficient mice, the murine α2-AP 1 gene was characterized and a targeting vector for homologous recombination in embryonic stem (ES) cells constructed. Alignment of nucleotide sequences obtained from genomic subclones allowed location of exons 2 through 10 of the α2-AP 1gene, but failed to identify the 5’ boundary of exon 1. Compared to the human gene, exons 2 through 9 in the murine gene have identical size and intron-exon boundaries obeying the GT/AG rule. The 5’ boundary of exon 10 is identical in both genes while the 3’ non-coding region is 64 bp longer in the human gene. Introns 2,3,6 and 8 have similar sizes in the mouse and human genes; intron 1 is 6-fold smaller, introns 5, 7 and 9 are 2- to 3-fold smaller, whereas intron 4 is about 2-fold larger in the mouse gene. Compared to the human 5’ flanking sequence, an insertion of a simple repeat region with sequence (TGG)n has occurred. The open reading frame of the mouse α2-AP gene encodes a 491-amino acid protein comprising the experimentally determined NH2-terminus of the mature protein Val-Asp-Leu-Pro-Gly-.

A targeting vector, ppPNT.α2-AP, was constructed by introducing a homologous sequence of 8.3 kb in total in the parental pPNT vector. In pPNT.α2-AP, the neomycin resistance expression cassette replaces a 7 kb genomic fragment comprising exon 2 through part of exon 10 (including the stop codon), which represents the entire sequence encoding the mature protein, including the fibrin-binding domain, the reactive site peptide bond and the plasmin(ogen)-binding region. Electroporation of 129R1 embryonic stem (ES) cells with the linearized vector pPNT.α2-AP yielded three targeted clones with correct homologous recombination at the 5’- and 3’-ends, as confirmed by Southern blot analysis of purified genomic DNA with appropriate restriction enzymes and probes. These targeted clones will be used to generate α2-AP deficient mice.

Thrombolytic and Pharmacokinetic Properties of a Recombinant Chimeric Plasminogen Activator Consisting of a Fibrin Fragment D-Dimer Specific Humanized Monoclonal Antibody and a Truncated Single-Chain Urokinase

A recombinant chimeric plasminogen activator consisting of a humanized monoclonal antibody specific for cross-linked human fibrin (MA-15C5Hu) and a 32 kDa single-chain urokinase-type plasminogen activator (scu-PA-32k) comprising amino acids Leu144-Leu411, MA-15C5Hu/scu-PA-32k, was previously found to have a 12-fold higher fibrinolytic potency than recombinant scu-PA-32k towards a human plasma clot in a human plasma milieu in vitro (Vandamme et al., Eur J Biochem 1992; 205: 139–46). Therefore, the thrombolytic and pharmacokinetic properties of MA-15C5Hu/scu-PA-32k were compared with those of recombinant single-chain urokinase-type plasminogen activator (scu-PA) in 3 different venous thrombosis models in vivo. In hamsters with a pulmonary embolus consisting of a human plasma clot, the thrombolytic potency (% lysis per dose in mg/kg administered) of MA-15C5Hu/scu-PA-32k was 23-fold higher than that of scu-PA (p <0.0005). In rabbits with a jugular vein clot prepared from human plasma, the thrombolytic potency of MA-15C5Hu/scu-PA-32k was 11-fold higher than that of scu-PA (p = 0.012). In baboons with an autologous whole blood clot in the femoral vein, the chimera had a 5-fold higher thrombolytic potency than scu-PA. In all three animal species, the clearance of the chimera was 10- to 27-fold reduced as compared to scu-PA. The specific thrombolytic activity (% lysis per µg/ml steady-state plasma u-PA antigen) was increased up to 7-fold with MA-15C5Hu/scu-PA-32k as compared with scu-PA, which is indicative of targeting of the chimera to the clot. No fibrinogen breakdown or α2-antiplasmin depletion was observed during thrombolysis with the chimera.

Thus, MA-15C5Hu/scu-PA-32k constitutes a recombinant chimeric plasminogen activator with a significantly enhanced thrombolytic potency in 3 different animal models of venous thrombosis.

Enhanced Fibrinolytic Potential in Mice with Combined Homozygous Deficiency of α2-antiplasmin and PAI-1

α2-antiplasmin (α2-AP) and plasminogen activator inhibitor-1 (PAI-1) are the main physiological inhibitors of the plasminogen/ plasmin system in mammalian plasma. In the present study, the relative importance of both inhibitors was evaluated with the use of mice with single or combined deficiency of α2-AP and PAI-1 in the same genetic background. Mice with combined deficiency (α2-AP–/–:PAI-1–/–) are viable, develop normally and are fertile. After amputation of the tail, bleeding times are prolonged (>15 min) in α2-AP–/–:PAI-1–/– mice, as compared to double wild-type or single deficient mice (4.6 to 10 min). Spontaneous lysis after 4 h of intravenously injected 125I-fibrin labeled plasma clots is significantly higher in mice with α2-AP deficiency both in the PAI-1+/+ background (89 ± 2% versus 42 ± 3%; p = 0.002) and in the PAI-1–/– background (83 ± 4% versus 53 ± 5%; p = 0.002). PAI-1 deletion in the α2-AP+/+ or α2-AP–/– background, however, has no significant effect (p = 0.13 or 0.18, respectively). Four hours after endotoxin injection, fibrin deposition in the kidneys is not significantly affected by PAI-1 deletion in mice with α2-AP+/+ or α2-AP–/– background (p = 0.07 and 0.19, respectively). In contrast, α2-AP deletion causes significantly reduced fibrin deposition in the PAI-1+/+ background (p = 0.01). Endotoxin injection causes a dramatic increase in PAI-1 antigen levels in kidney extracts of PAI-1+/+ animals, without effect on α2-AP levels.

Taken together, these data indicate that the higher endogenous fibrinolytic capacity observed in mice with combined deficiency is mainly due to the lack of α2-AP and suggest a less important role for PAI-1.

Increased human dermal microvascular endothelial cell survival induced by cysteamine

BACKGROUND

Cystinosis is an autosomal recessive disease caused by intralysosomal cystine accumulation, treated with cysteamine. Recently, new adverse effects of cysteamine were reported. Skin biopsies showed microvascular proliferation (angioendotheliomatosis). To examine the mechanism of angioendotheliomatosis associated with cysteamine toxicity, we examined the effect of cysteamine on human dermal microvascular endothelial cells (HDMVEC).

METHODS

After cysteamine exposure (range 0-3.0 mM) during 24 h, cell viability was measured using water soluble tetrazolium salt-1 (WST-1) in both control HDMVEC and fibroblasts. Cell proliferation and apoptosis rate were measured in HDMVEC by bromodeoxyuridine (BrdU) incorporation and caspase 3 and caspase 7 activity, respectively. Intracellular glutathione (GSH) was measured in HDMVEC after cysteamine exposure of 0, 0.1 or 1.0 mM. Medium and cysteamine were refreshed every 6 h to mimic the in vivo situation. Next, cell viability in HDMVEC was measured after 24 h of GSH exposure (range 0-10.0 mM).

RESULTS

HDMVEC viability and proliferation increased after cysteamine exposure 0.03-3.0 mM (p < 0.01) and 0.03-1.0 mM (p = 0.01) respectively; cell viability in fibroblasts was not affected by incubation with cysteamine. Apoptosis remained unaffected by incubation with 0-1.0 mM cysteamine, 3.0 mM caused increased apoptosis. Intracellular GSH was significantly increased after incubation with cysteamine 0.1 mM (p = 0.02) and 1.0 mM (p < 0.01). HDMVEC viability increased after exposure to GSH 1.0-5.0 mM (p < 0.01).

CONCLUSION

Cysteamine concentrations, similar to those described in plasma of cystinosis patients, stimulate HDMVEC viability and proliferation and increase intracellular GSH content. We postulate that this mechanism might underlie angioendotheliomatosis induced by cysteamine.

Clinical and fundamental aspects of angiogenesis and anti-angiogenesis

Insight into the fundamental physiological mechanisms of blood vessel development and neoformation has led to the discovery of multiple angiogenic growth factors and inhibitors. To date, at least 5 angiogenesis inhibitors are readily available for clinical use, mainly in the treatment of cancers and age-related macular degeneration. More inhibitors are yet to come and the indications for their clinical use are expected to broaden. Conversely, the use of angiogenic stimulators, although initially promising in animal models and in small uncontrolled pilot studies in patients with ischaemic heart disease or peripheral arterial occlusive disease, could thus far not show any convincing therapeutic improvement. Challenges still remain as to which angiogenic factor or combination of factors should be administered and in which form (protein versus gene), and what route and duration of administration should be used. Further clinical perspective might come from the recent identification of vascular endothelial growth factor (VEGF) as a modifier of the neurodegenerative disease amyotrophic lateral sclerosis (ALS), and as a promising therapy in the treatment of ALS in preclinical animal models. This review discusses the different clinical trials of angiogenic inhibitors and stimulators, preceded by some fundamental aspects of angiogenesis, giving the clinician a brief overview of the most relevant angiogenic topics.

Variable region heavy chain glycosylation determines the anticoagulant activity of a factor VIII antibody

BACKGROUND

N-glycosylation occurs in the variable region of about 10% of antibodies but the role of carbohydrate at this location is still poorly understood.

OBJECTIVES

We investigated the function of N-glycosylation in the variable region of the heavy chain of a human monoclonal antibody, mAb-LE2E9, that partially inhibits factor VIII (FVIII) activity during coagulation.

METHODS AND RESULTS

Enzymatic deglycosylation indicated that the oligosaccharides do not determine the affinity of the antibody but enhance its FVIII neutralizing activity. A mutant antibody lacking the N-glycosylation site in the variable region of the heavy chain inhibited FVIII activity by up to 40%, while inhibition by the native antibody was 80%. To evaluate the physiological effect of such a FVIII inhibition, we investigated the ability of the mutant antibody devoid of N-glycosylation in the variable region to prevent thrombosis in mice with a strong prothombotic phenotype resulting from a type II deficiency mutation in the heparin binding site of antithrombin. Despite its moderate inhibition of FVIII activity, the mutant antibody significantly prevented thrombosis in treated animals. We also carried out glycan analysis of native and mutant antibodies.

CONCLUSIONS

Modification of glycosylation in the variable region of antibodies contributes to the diversity of FVIII type II inhibition possibly by steric hindrance of the active site of FVIII by glycans, and may provide a novel strategy to modulate the functional activity of therapeutic antibodies.

Inhibition of factor VIII with a partially inhibitory human recombinant monoclonal antibody prevents thrombotic events in a transgenic model of type II HBS antithrombin deficiency in mice

Venous thromboembolic disease is a major cause of morbidity and mortality, necessitating antithrombotic therapy. A human monoclonal anti-factor (F)VIII antibody, LCL-mAb-LE2E9, produced by a lymphoblastoid cell line derived from a hemophilia A patient with inhibitor to wild-type but not mutant self FVIII, was previously reported to achieve efficient inhibition of thrombosis in an experimental vena cava thrombosis model in mice. Here, the antithrombotic efficacy of a recombinant DNA-derived version of this anti-FVIII antibody (rec-mAb-LE2E9) was tested in mice which carry a type II heparin binding site antithrombin deficiency mutation and display spontaneous chronic thrombosis in several sites including the penile vein of sexually active males. The recombinant anti-FVIII antibody (100 microg, repeated after 3 days) prevented thrombotic priapism in all treated males, whereas all control animals treated with saline (group of four animals) developed priapism within 6 days after mating (P < 0.05 for treated vs. saline). The rec-mAb-LE2E9 and the original LCL-mAb-LE2E9 were equally effective (five and seven males/group, respectively). These results confirm that FVIII inhibition represents a potent antithrombotic strategy, and show that both LCL-mAb-LE2E9 and rec-mAb-LE2E9 efficiently prevent thrombosis in a physiological model representative of thrombosis in patients with a severe prothrombotic risk.

Endogenous alpha2-antiplasmin does not enhance glomerular fibrin deposition or injury in glomerulonephritis

BACKGROUND

Fibrin deposition is an important mechanism of glomerular injury in crescentic glomerulonephritis (GN), a severe form of immune renal injury. Both coagulation and fibrinolysis (via the plasminogen-plasmin system) are important in net glomerular fibrin accumulation in GN. alpha2-Antiplasmin (alpha2-AP) is the major circulating inhibitor of plasmin and is expressed in the renal tubulointerstitium.

OBJECTIVE

To determine whether endogenous alpha2-AP contributes to glomerular fibrin accumulation in GN.

METHODS

Crescentic autologous phase antiglomerular basement membrane GN was induced in mice with intact and deficient endogenous alpha2-AP (alpha2-AP+/+ and alpha2-AP-/- mice).

RESULTS

In mice with crescentic GN, alpha2-AP was detected in the tubulointerstitium and in segmental deposits within some glomeruli. alpha2-AP+/+ mice developed crescentic GN (38 +/- 9% glomeruli affected) with glomerular fibrin deposition and renal impairment (serum creatinine 30 +/- 1 micro mol L-1, normal without GN 11 +/- 1 micro mol L-1). Genetic deficiency of alpha2-AP did not result in attenuated glomerular fibrin deposition, crescent formation (39 +/- 8% glomeruli affected), glomerular leukocyte infiltration or renal impairment (serum creatinine 33 +/- 7 micro mol L-1). alpha2-AP was unmeasurable in kidneys from alpha2-AP-/- mice, which did not develop compensatory changes in plasminogen, tissue type plasminogen activator (tPA), urokinase type PA (uPA) or plasminogen activator inhibitor-1 proteins, or changes in tPA or uPA activity. alpha2-AP-/- mice did have enhanced total renal fibrinolytic capacity as assessed by in situ fibrin overlay (alpha2-AP+/+ 0.19 +/- 0.01, alpha2-AP-/- 0.36 +/- 0.03 lyzed area/total area).

CONCLUSIONS

alpha2-AP is not important to net glomerular fibrin deposition, crescent formation or renal impairment in crescentic GN.

Duodenal calcium absorption in vitamin D receptor-knockout mice: functional and molecular aspects

Rickets and hyperparathyroidism caused by a defective vitamin D receptor (VDR) can be prevented in humans and animals by high calcium intake, suggesting that intestinal calcium absorption is critical for 1,25(OH)(2) vitamin D [1,25(OH)(2)D(3)] action on calcium homeostasis. We assessed the rate of serum (45)Ca accumulation within 10 min of oral gavage in two strains of VDR-knockout (KO) mice (Leuven and Tokyo KO) and observed a 3-fold lower area under the curve in both KO strains. Moreover, we evaluated the expression of intestinal candidate genes involved in transcellular calcium transport. The calcium transport protein1 (CaT1) was more abundantly expressed at mRNA level than the epithelial calcium channel (ECaC) in duodenum, but both were considerably reduced (CaT1>90%, ECaC>60%) in the two VDR-KO strains on a normal calcium diet. Calbindin-D(9K) expression was decreased only in the Tokyo KO, whereas plasma membrane calcium ATPase (PMCA(1b)) expression was normal in both VDR-KOs. In Leuven wild-type mice, a high calcium diet inhibited (>90%) and 1,25(OH)(2)D(3) injection or low calcium diet induced (6-fold) duodenal CaT1 expression and, to a lesser degree, ECaC and calbindin-D(9K) expression. In Leuven KO mice, however, high or low calcium intake decreased calbindin-D(9K) and PMCA(1b) expression, whereas CaT1 and ECaC expression remained consistently low on any diet. These results suggest that the expression of the novel duodenal epithelial calcium channels (in particular CaT1) is strongly vitamin D-dependent, and that calcium influx, probably interacting with calbindin-D(9K), should be considered as a rate-limiting step in the process of vitamin D-dependent active calcium absorption.

Replacement of the muscle-specific sarcoplasmic reticulum Ca(2+)-ATPase isoform SERCA2a by the nonmuscle SERCA2b homologue causes mild concentric hypertrophy and impairs contraction-relaxation of the heart

The cardiac sarco(endo)plasmic reticulum Ca(2+)-ATPase gene (ATP2A2) encodes the following two different protein isoforms: SERCA2a (muscle-specific) and SERCA2b (ubiquitous). We have investigated whether this isoform specificity is required for normal cardiac function. Gene targeting in mice successfully disrupted the splicing mechanism responsible for generating the SERCA2a isoform. Homozygous SERCA2a(-/-) mice displayed a complete loss of SERCA2a mRNA and protein resulting in a switch to the SERCA2b isoform. The expression of SERCA2b mRNA and protein in hearts of SERCA2a(-/-) mice corresponded to only 50% of wild-type SERCA2 levels. Cardiac phospholamban mRNA levels were unaltered in SERCA2a(-/-) mice, but total phospholamban protein levels increased 2-fold. The transgenic phenotype was characterized by a approximately 20% increase in embryonic and neonatal mortality (early phenotype), with histopathologic evidence of major cardiac malformations. Adult SERCA2a(-/-) animals (adult phenotype) showed a reduced spontaneous nocturnal activity and developed a mild compensatory concentric cardiac hypertrophy with impaired cardiac contractility and relaxation, but preserved beta-adrenergic response. Ca(2+) uptake levels in SERCA2a(-/-) cardiac homogenates were reduced by approximately 50%. In isolated cells, relaxation and Ca(2+) removal by the SR were significantly reduced. Comparison of our data with those obtained in mice expressing similar cardiac levels of SERCA2a instead of SERCA2b indicate the importance of the muscle-specific SERCA2a isoform for normal cardiac development and for the cardiac contraction-relaxation cycle.

Hypoxia-inducible factor-2alpha (HIF-2alpha) is involved in the apoptotic response to hypoglycemia but not to hypoxia

Deprivation of oxygen (hypoxia) and/or glucose (hypoglycemia) represents a serious stress that affects cellular survival. The hypoxia-inducible transcription factor-1alpha (HIF-1alpha), which has been implicated in the cellular response to hypoxia (Semenza, G. L. (1999) Annu. Rev. Cell Dev. Biol. 15, 551-578), mediates apoptosis during hypoxia (Halterman, M. W., Miller, C. C., and Federoff, H. J. (1999) J. Neurosci. 19, 6818-6824 and Carmeliet, P., Dor, Y., Herbert, J. M., Fukumura, D., Brusselmans, K., Dewerchin, M., Neeman, M., Bono, F., Abramovitch, R., Maxwell, P., Koch, C. J., Ratcliffe, P., Moons, L., Jain, R. K., Collen, D., and Keshet, E. (1998) Nature 394, 485-490), but the function of its homologue HIF-2alpha remains unknown. Therefore, the role of HIF-2alpha in cellular survival was studied by targeted inactivation of the HIF-2alpha gene (HIF-2alpha(-/-)) in murine embryonic stem (ES) cells. In contrast to HIF-1alpha deficiency, loss of HIF-2alpha did not protect ES cells against apoptosis during hypoxia. Both HIF-1alpha(-/-) and HIF-2alpha(-/-) ES cells were, however, resistant to apoptosis in response to hypoglycemia. When co-cultured with wild type ES cells, HIF-2alpha(-/-) ES cells became rapidly and progressively enriched in hypoglycemia but not in hypoxia. Thus, HIF-1alpha and HIF-2alpha may have distinct roles in responses to environmental stress, and despite its name, HIF-2alpha may be more important in the survival response to environmental variables other than the level of oxygen.

Abrupt rate accelerations or premature beats cause life-threatening arrhythmias in mice with long-QT3 syndrome

Deletion of amino-acid residues 1505-1507 (KPQ) in the cardiac SCN5A Na(+) channel causes autosomal dominant prolongation of the electrocardiographic QT interval (long-QT syndrome type 3 or LQT3). Excessive prolongation of the action potential at low heart rates predisposes individuals with LQT3 to fatal arrhythmias, typically at rest or during sleep. Here we report that mice heterozygous for a knock-in KPQ-deletion (SCN5A(Delta/+)) show the essential LQT3 features and spontaneously develop life-threatening polymorphous ventricular arrhythmias. Unexpectedly, sudden accelerations in heart rate or premature beats caused lengthening of the action potential with early afterdepolarization and triggered arrhythmias in Scn5a(Delta/+) mice. Adrenergic agonists normalized the response to rate acceleration in vitro and suppressed arrhythmias upon premature stimulation in vivo. These results show the possible risk of sudden heart-rate accelerations. The Scn5a(Delta/+) mouse with its predisposition for pacing-induced arrhythmia might be useful for the development of new treatments for the LQT3 syndrome.

Targeted deletion of the cytosolic domain of tissue factor in mice does not affect development

The role of the cytosolic domain of tissue factor (TF) in signal transduction and gene regulation was studied in mice with a targeted deletion of the 18 carboxy-terminal intracellular amino acids. This deletion was introduced in exon 6 along with a floxed neo(R) selection cassette in intron 5 using homologous recombination in embryonic stem cells. Removal of the floxed neo(R) cassette by in vivo Cre-mediated loxP recombination yielded TF(+/deltaCT) and TF(deltaCT/deltaCT) mice. In contrast to TF(-/-) mice, TF(+/deltaCT) and TF(deltaCT/deltaCT) mice displayed normal embryonic development, survival, fertility, and blood coagulation. Factor VIIa or factor Xa stimulation produced similar p44/42 MAPK activation in TF(+/+) and TF(deltaCT/deltaCT) fibroblasts. These data, based on expression of a TF(deltaCT) molecule from the endogenous TF locus, provide conclusive proof that the cytosolic domain of TF is not essential for signal transduction in embryogenesis and in physiological postnatal processes.

Enhanced fibrinolytic potential in mice with combined homozygous deficiency of alpha2-antiplasmin and PAI-1

Alpha2-antiplasmin (alpha2-AP) and plasminogen activator inhibitor-1 (PAI-1) are the main physiological inhibitors of the plasminogen/plasmin system in mammalian plasma. In the present study, the relative importance of both inhibitors was evaluated with the use of mice with single or combined deficiency of alpha2-AP and PAI-1 in the same genetic background. Mice with combined deficiency (alpha2-AP-/-:PAI-1-/-) are viable, develop normally and are fertile. After amputation of the tail, bleeding times are prolonged (>15 min) in alpha2-AP-/-: PAI-1-/- mice, as compared to double wild-type or single deficient mice (4.6 to 10 min). Spontaneous lysis after 4 h of intravenously injected 125I-fibrin labeled plasma clots is significantly higher in mice with alpha2-AP deficiency both in the PAI-1+/+ background (89+/-2% versus 42+/-3%; p = 0.002) and in the PAI-1-/- background (83+/-4% versus 53+/-5%; p = 0.002). PAI-1 deletion in the alpha2-AP+/+ or alpha2-AP-/- background, however, has no significant effect (p = 0.13 or 0.18, respectively). Four hours after endotoxin injection, fibrin deposition in the kidneys is not significantly affected by PAI-1 deletion in mice with alpha2-AP+/+ or alpha2-AP-/- background (p = 0.07 and 0.19, respectively). In contrast, alpha2-AP deletion causes significantly reduced fibrin deposition in the PAI-1+/+ background (p = 0.01). Endotoxin injection causes a dramatic increase in PAI-1 antigen levels in kidney extracts of PAI-1+/+ animals, without effect on alpha2-AP levels. Taken together, these data indicate that the higher endogenous fibrinolytic capacity observed in mice with combined deficiency is mainly due to the lack of alpha2-AP and suggest a less important role for PAI-1.

Bmx tyrosine kinase has a redundant function downstream of angiopoietin and vascular endothelial growth factor receptors in arterial endothelium

The Bmx gene, a member of the Tec tyrosine kinase gene family, is known to be expressed in subsets of hematopoietic and endothelial cells. In this study, mice were generated in which the first coding exon of the Bmx gene was replaced with the lacZ reporter gene by a knock-in strategy. The homozygous mice lacking Bmx activity were fertile and had a normal life span without an obvious phenotype. Staining of their tissues using beta-galactosidase substrate to assess the sites of Bmx expression revealed strong signals in the endothelial cells of large arteries and in the endocardium starting between days 10.5 and 12.5 of embryogenesis and continuing in adult mice, while the venular endothelium showed a weak signal only in the superior and inferior venae cavae. Of the five known endothelial receptor tyrosine kinases tested, activated Tie-2 induced tyrosyl phosphorylation of the Bmx protein and both Tie-2 and vascular endothelial growth factor receptor 1 (VEGFR-1) stimulated Bmx tyrosine kinase activity. Thus, the Bmx tyrosine kinase has a redundant role in arterial endothelial signal transduction downstream of the Tie-2 and VEGFR-1 growth factor receptors.

Deletion of the hypoxia-response element in the vascular endothelial growth factor promoter causes motor neuron degeneration

Hypoxia stimulates angiogenesis through the binding of hypoxia-inducible factors to the hypoxia-response element in the vascular endothelial growth factor (Vegf) promotor. Here, we report that deletion of the hypoxia-response element in the Vegf promotor reduced hypoxic Vegf expression in the spinal cord and caused adult-onset progressive motor neuron degeneration, reminiscent of amyotrophic lateral sclerosis. The neurodegeneration seemed to be due to reduced neural vascular perfusion. In addition, Vegf165 promoted survival of motor neurons during hypoxia through binding to Vegf receptor 2 and neuropilin 1. Acute ischemia is known to cause nonselective neuronal death. Our results indicate that chronic vascular insufficiency and, possibly, insufficient Vegf-dependent neuroprotection lead to the select degeneration of motor neurons.

Synergism between vascular endothelial growth factor and placental growth factor contributes to angiogenesis and plasma extravasation in pathological conditions

Vascular endothelial growth factor (VEGF) stimulates angiogenesis by activating VEGF receptor-2 (VEGFR-2). The role of its homolog, placental growth factor (PlGF), remains unknown. Both VEGF and PlGF bind to VEGF receptor-1 (VEGFR-1), but it is unknown whether VEGFR-1, which exists as a soluble or a membrane-bound type, is an inert decoy or a signaling receptor for PlGF during angiogenesis. Here, we report that embryonic angiogenesis in mice was not affected by deficiency of PlGF (Pgf-/-). VEGF-B, another ligand of VEGFR-1, did not rescue development in Pgf-/- mice. However, loss of PlGF impaired angiogenesis, plasma extravasation and collateral growth during ischemia, inflammation, wound healing and cancer. Transplantation of wild-type bone marrow rescued the impaired angiogenesis and collateral growth in Pgf-/- mice, indicating that PlGF might have contributed to vessel growth in the adult by mobilizing bone-marrow-derived cells. The synergism between PlGF and VEGF was specific, as PlGF deficiency impaired the response to VEGF, but not to bFGF or histamine. VEGFR-1 was activated by PlGF, given that anti-VEGFR-1 antibodies and a Src-kinase inhibitor blocked the endothelial response to PlGF or VEGF/PlGF. By upregulating PlGF and the signaling subtype of VEGFR-1, endothelial cells amplify their responsiveness to VEGF during the 'angiogenic switch' in many pathological disorders.

Mouse carotid artery ligation induces platelet-leukocyte-dependent luminal fibrin, required for neointima development

The relationship between platelet and leukocyte activation, coagulation, and neointima development was investigated in noninjured murine blood vessels subjected to blood stasis. The left common carotid artery of C57BL/6J mice was ligated proximal to the bifurcation. Tissue-factor expression in luminal leukocytes progressively increased over 2 weeks. On day 3 after ligation, in addition to infiltrated granulocytes, platelet microthrombi and platelet-covered leukocytes as well as tissue-factor-positive fibrin deposits lined the endothelium. Maximal neointima formation in carotid artery cross sections of control mice equaled 28+/-3.7% (n=11) and 42+/-5.1% (n=8) of the internal elastic lamina cross-sectional area 1 and 2 weeks after ligation. In FVIII(-/-) mice, stenosis was significantly lower 1 (11+/-3.6%, n=8) and 2 (21+/-4.7%, n=7) weeks after ligation (both P:<0.01 versus background-matched controls). In u-PA(-/-) mice, luminal stenosis was significantly higher 1 (38+/-7.0%, n=7) and 2 (77+/-5.6%, n=6) weeks after ligation (P:<0.05 and P:<0.01, respectively, versus matched controls). In alpha(2)-AP(-/-) mice, stenosis was lower at 1 week (14+/-2.6%, n=7, P:<0.01) but not at 2 weeks. Responses in tissue-type plasminogen activator or plasminogen activator inhibitor-1 gene-deficient mice equaled that in controls. Reducing plasma fibrinogen levels in controls with ancrod or inducing partial thrombocytopenia with busulfan resulted in significantly less neointima, but inflammation was inhibited only in busulfan-treated mice. We conclude that stasis induces platelet activation, leading to microthrombosis and platelet-leukocyte conjugate formation, triggering inflammation and tissue-factor accumulation on the carotid artery endothelium. Delayed coagulation then results in formation of a fibrin matrix, which is used by smooth muscle cells to migrate into the lumen.

Deficiency or inhibition of Gas6 causes platelet dysfunction and protects mice against thrombosis

The growth arrest-specific gene 6 product (Gas6) is a secreted protein related to the anticoagulant protein S but its role in hemostasis is unknown. Here we show that inactivation of the Gas6 gene prevented venous and arterial thrombosis in mice, and protected against fatal collagen/epinephrine-induced thrombo embolism. Gas6-/- mice did not, however, suffer spontaneous bleeding and had normal bleeding after tail clipping. In addition, we found that Gas6 antibodies inhibited platelet aggregation in vitro and protected mice against fatal thrombo embolism without causing bleeding in vivo. Gas6 amplified platelet aggregation and secretion in response to known agonists. Platelet dysfunction in Gas6-/- mice resembled that of patients with platelet signaling transduction defects. Thus, Gas6 is a platelet-response amplifier that plays a significant role in thrombosis. These findings warrant further evaluation of the possible therapeutic use of Gas6 inhibition for prevention of thrombosis.

Disruption of the protein C inhibitor gene results in impaired spermatogenesis and male infertility

Protein C inhibitor (PCI) is a nonspecific, heparin-binding serpin (serine protease inhibitor) that inactivates many plasmatic and extravascular serine proteases by forming stable 1:1 complexes. Proteases inhibited by PCI include the anticoagulant activated protein C, the plasminogen activator urokinase, and the sperm protease acrosin. In humans PCI circulates as a plasma protein but is also present at high concentrations in organs of the male reproductive tract. The biological role of PCI has not been defined so far. However, the colocalization of high concentrations of PCI together with several of its target proteases in the male reproductive tract suggests a role of PCI in reproduction. We generated mice lacking PCI by homologous recombination. Here we show that PCI(-/-) mice are apparently healthy but that males of this genotype are infertile. Infertility was apparently caused by abnormal spermatogenesis due to destruction of the Sertoli cell barrier, perhaps due to unopposed proteolytic activity. The resulting sperm are malformed and are morphologically similar to abnormal sperm seen in some cases of human male infertility. This animal model might therefore be useful for analyzing the molecular bases of these human conditions.

The role of proteinases in angiogenesis, heart development, restenosis, atherosclerosis, myocardial ischemia, and stroke: insights from genetic studies

The development of novel gene technologies in mice has provided an elegant tool to identify gene products that are causally linked to certain physiologic processes as well as the pathogenesis of numerous disorders. Using these techniques, three major proteolytic systems -- the plasminogen, the matrix metalloproteinase (MMP) and the coagulation systems -- have been shown to be involved in cardiovascular diseases, which still constitute the leading cause of death in Western societies. This overview summarizes the role of these proteolytic systems in angiogenesis, arterial stenosis, allograft transplant stenosis, vein graft stenosis, atherosclerosis, myocardial infarction, cardiac development and ischemic stroke and discusses possible therapeutic implications.

Vascular release of plasminogen activator inhibitor-1 impairs fibrinolysis during acute arterial thrombosis in mice

The role of plasminogen activator inhibitor-1 (PAI-1) in the plasma, blood platelets, and vessel wall during acute arterial thrombus formation was investigated in gene-deficient mice. Photochemically induced thrombosis in the carotid artery was analyzed via transillumination. In comparison to thrombosis in C57BL/6J wild-type (wt) mice (113 +/- 19 x 10(6) arbitrary light units [AU] n = 15, mean +/- SEM), thrombosis in PAI-1(-/-) mice (40 +/- 10 x 10(6) AU, n = 13) was inhibited (P <.01), indicating that PAI-1 controls fibrinolysis during thrombus formation. Systemic administration of murine PAI-1 into PAI-1(-/-) mice led to a full recovery of thrombotic response. Occurrence of fibrinolytic activity was confirmed in alpha(2)-antiplasmin (alpha(2)-AP)-deficient mice. The sizes of thrombi developing in wt mice, in alpha(2)-AP(+/-) and alpha(2)-AP(-/-) mice were 102 +/- 35, 65 +/- 8.1, and 13 +/- 6.1 x 10(6) AU, respectively (n = 6 each) (P <.05), compatible with functional plasmin inhibition by alpha(2)-AP. In contrast, thrombi in wt mice, t-PA(-/-) and u-PA(-/-) mice were comparable, substantiating efficient inhibition of fibrinolysis by the combined PAI-1/alpha(2)-AP action. Platelet depletion and reconstitution confirmed a normal thrombotic response in wt mice, reconstituted with PAI-1(-/-) platelets, but weak thrombosis in PAI-1(-/-) mice reconstituted with wt platelets. Accordingly, murine (wt) PAI-1 levels in platelet lysates and releasates were 0.43 +/- 0.09 ng/10(9) platelets and plasma concentrations equaled 0.73 +/- 0.13 ng/mL. After photochemical injury, plasma PAI-1 rose to 2.9 +/- 0.7 ng/mL (n = 9, P <.01). The plasma rise was prevented by ligating the carotid artery. Hence, during acute thrombosis, fibrinolysis is efficiently prevented by plasma alpha(2)-AP, but also by vascular PAI-1, locally released into the circulation after endothelial injury.

Transcription factor hepatocyte nuclear factor 6 regulates pancreatic endocrine cell differentiation and controls expression of the proendocrine gene ngn3

Hepatocyte nuclear factor 6 (HNF-6) is the prototype of a new class of cut homeodomain transcription factors. During mouse development, HNF-6 is expressed in the epithelial cells that are precursors of the exocrine and endocrine pancreatic cells. We have investigated the role of HNF-6 in pancreas differentiation by inactivating its gene in the mouse. In hnf6(-/-) embryos, the exocrine pancreas appeared to be normal but endocrine cell differentiation was impaired. The expression of neurogenin 3 (Ngn-3), a transcription factor that is essential for determination of endocrine cell precursors, was almost abolished. Consistent with this, we demonstrated that HNF-6 binds to and stimulates the ngn3 gene promoter. At birth, only a few endocrine cells were found and the islets of Langerhans were missing. Later, the number of endocrine cells increased and islets appeared. However, the architecture of the islets was perturbed, and their beta cells were deficient in glucose transporter 2 expression. Adult hnf6(-/-) mice were diabetic. Taken together, our data demonstrate that HNF-6 controls pancreatic endocrine differentiation at the precursor stage and identify HNF-6 as the first positive regulator of the proendocrine gene ngn3 in the pancreas. They also suggest that HNF-6 is a candidate gene for diabetes mellitus in humans.

Alpha(2)-antiplasmin gene deficiency in mice does not affect neointima formation after vascular injury

The hypothesis that alpha(2)-antiplasmin (alpha(2)-AP), the main physiological plasmin inhibitor, plays a role in neointima formation was tested with use of a vascular injury model in wild-type (alpha(2)-AP(+/+)) and alpha(2)-AP-deficient (alpha(2)-AP(-/-)) mice. The neointimal and medial areas were similar 1 to 3 weeks after electric injury of the femoral artery in alpha(2)-AP(+/+) and alpha(2)-AP(-/-) mice, resulting in comparable intima/media ratios (eg, 0.43+/-0.12 and 0.42+/-0.11 2 weeks after injury). Nuclear cell counts in cross-sectional areas of the intima of the injured region were also comparable in arteries from alpha(2)-AP(+/+) and alpha(2)-AP(-/-) mice (78+/-19 and 69+/-8). Fibrin deposition was not significantly different in arteries of both genotypes 1 day after injury, and no mural thrombosis was detected 1 week after injury. Fibrinolytic activity in femoral arterial sections, as monitored by fibrin zymography, was higher in alpha(2)-AP(-/-) mice 1 week after injury (P<0.001) but was comparable in both genotypes 2 and 3 weeks after injury. Staining for elastin did not reveal significant degradation of the internal elastica lamina in either genotype. Immunocytochemical analysis revealed a comparable distribution pattern of alpha-actin-positive smooth muscle cells in both genotypes. These findings indicate that the endogenous fibrinolytic system of alpha(2)-AP(+/+) mice is capable of preventing fibrin deposition after vascular injury and suggest that alpha(2)-AP does not play a major role in smooth muscle cell migration and neointima formation in vivo.

Blood coagulation factor X deficiency causes partial embryonic lethality and fatal neonatal bleeding in mice

Mice with a total deficiency in blood coagulation Factor X (FX) were generated by targeted replacement of an 18-kb fragment of the FX gene, comprising all exons encoding the mature FX protein, with a neo(r) cassette. The genotype distribution among the offspring from heterozygous breeding pairs suggested that FX deficiency resulted in partial embryonic lethality, with approximately one-third of the FX-/- embryos dying around embryonic day (E) 11.5-12.5. Two of 44 non-resorbed FX-/- embryos analyzed at these stages showed signs of massive bleeding, one of which into the brain ventricles, but no histological defects in the vasculature of these embryos or their yolk sac were observed. The remainder of the FX-/- embryos appeared normal and survived to term, but the majority of neonates (90%) died within 5 days, most frequently from intraabdominal bleeding. The remaining FX-/- animals succumbed between postnatal day (P)5 and P20 with intraabdominal, subcutaneous, or intracranial bleeding or a combination thereof. The lethal phenotype of the FX-/- mice illustrates the importance of FX function in embryonic and postnatal survival and demonstrates that these mice serve as effective models of the bleeding disorders observed in severe FX deficiency in humans.

Targeted deficiency or cytosolic truncation of the VE-cadherin gene in mice impairs VEGF-mediated endothelial survival and angiogenesis

Vascular endothelial cadherin, VE-cadherin, mediates adhesion between endothelial cells and may affect vascular morphogenesis via intracellular signaling, but the nature of these signals remains unknown. Here, targeted inactivation (VEC-/-) or truncation of the beta-catenin-binding cytosolic domain (VECdeltaC/deltaC) of the VE-cadherin gene was found not to affect assembly of endothelial cells in vascular plexi, but to impair their subsequent remodeling and maturation, causing lethality at 9.5 days of gestation. Deficiency or truncation of VE-cadherin induced endothelial apoptosis and abolished transmission of the endothelial survival signal by VEGF-A to Akt kinase and Bcl2 via reduced complex formation with VEGF receptor-2, beta-catenin, and phosphoinositide 3 (PI3)-kinase. Thus, VE-cadherin/ beta-catenin signaling controls endothelial survival.

Alpha2-antiplasmin gene deficiency in mice is associated with enhanced fibrinolytic potential without overt bleeding

alpha2-antiplasmin (alpha2-AP) is the main physiologic plasmin inhibitor in mammalian plasma. Inactivation of the murine alpha2-AP gene was achieved by replacing, through homologous recombination in embryonic stem cells, a 7-kb genomic sequence encoding the entire murine protein (exon 2 through part of exon 10, including the stop codon) with the neomycin resistance expression cassette. Germline transmission of the mutated allele was confirmed by Southern blot analysis. Mendelian inheritance of the inactivated alpha2-AP allele was observed, and homozygous deficient (alpha2-AP-/-) mice displayed normal fertility, viability, and development. Reverse transcription-polymerase chain reaction confirmed the absence of alpha2-AP mRNA in kidney and liver from alpha2-AP-/- mice, in contrast to wild-type (alpha2-AP+/+) mice. Immunologic and functional alpha2-AP levels were undetectable in plasma of alpha2-AP-/- mice, and were about half of wild-type in heterozygous littermates (alpha2-AP+/-). Other hemostasis parameters, including plasminogen activator inhibitor-1, plasminogen, fibrinogen, hemoglobin, hematocrit, and blood cell counts were comparable for alpha2-AP+/+, alpha2-AP+/-, and alpha2-AP-/- mice. After amputation of tail or toe tips, bleeding stopped spontaneously in alpha2-AP+/+, as well as in alpha2-AP+/- and alpha2-AP-/- mice. Spontaneous lysis after 4 hours of intravenously injected 125I-fibrin-labeled plasma clots was significantly higher in alpha2-AP-/- than in alpha2-AP+/+ mice when injecting clots prepared from alpha2-AP+/+ plasma (78% +/- 5% v 46% +/- 9%; mean +/- SEM, n = 6 to 7; P =.02) or from alpha2-AP-/- plasma (81% +/- 5% v 46% +/- 5%; mean +/- SEM, n = 5; P =.008). Four to 8 hours after endotoxin injection, fibrin deposition in the kidneys was significantly reduced in alpha2-AP-/- mice, as compared with alpha2-AP+/+ mice (P </=.005). Thus, alpha2-AP-/- mice develop and reproduce normally; they have an enhanced endogenous fibrinolytic capacity without overt bleeding.

Role of HIF-1alpha in hypoxia-mediated apoptosis, cell proliferation and tumour angiogenesis

As a result of deprivation of oxygen (hypoxia) and nutrients, the growth and viability of cells is reduced. Hypoxia-inducible factor (HIF)-1alpha helps to restore oxygen homeostasis by inducing glycolysis, erythropoiesis and angiogenesis. Here we show that hypoxia and hypoglycaemia reduce proliferation and increase apoptosis in wild-type (HIF-1alpha+/+) embryonic stem (ES) cells, but not in ES cells with inactivated HIF-1alpha genes (HIF-1alpha-/-); however, a deficiency of HIF-1alpha does not affect apoptosis induced by cytokines. We find that hypoxia/hypoglycaemia-regulated genes involved in controlling the cell cycle are either HIF-1alpha-dependent (those encoding the proteins p53, p21, Bcl-2) or HIF-1alpha-independent (p27, GADD153), suggesting that there are at least two different adaptive responses to being deprived of oxygen and nutrients. Loss of HIF-1alpha reduces hypoxia-induced expression of vascular endothelial growth factor, prevents formation of large vessels in ES-derived tumours, and impairs vascular function, resulting in hypoxic microenvironments within the tumour mass. However, growth of HIF-1alpha tumours was not retarded but was accelerated, owing to decreased hypoxia-induced apoptosis and increased stress-induced proliferation. As hypoxic stress contributes to many (patho)biological disorders, this new role for HIF-1alpha in hypoxic control of cell growth and death may be of general pathophysiological importance.

Receptor-independent role of urokinase-type plasminogen activator in pericellular plasmin and matrix metalloproteinase proteolysis during vascular wound healing in mice

It has been proposed that the urokinase receptor (u-PAR) is essential for the various biological roles of urokinase-type plasminogen activator (u-PA) in vivo, and that smooth muscle cells require u-PA for migration during arterial neointima formation. The present study was undertaken to evaluate the role of u-PAR during this process in mice with targeted disruption of the u-PAR gene (u-PAR-/-). Surprisingly, u-PAR deficiency did not affect arterial neointima formation, neointimal cell accumulation, or migration of smooth muscle cells. Indeed, topographic analysis of arterial wound healing after electric injury revealed that u-PAR-/- smooth muscle cells, originating from the uninjured borders, migrated over a similar distance and at a similar rate into the necrotic center of the wound as wild-type (u-PAR+/+) smooth muscle cells. In addition, u-PAR deficiency did not impair migration of wounded cultured smooth muscle cells in vitro. There were no genotypic differences in reendothelialization of the vascular wound. The minimal role of u-PAR in smooth muscle cell migration was not because of absent expression, since wild-type smooth muscle cells expressed u-PAR mRNA and functional receptor in vitro and in vivo. Pericellular plasmin proteolysis, evaluated by degradation of 125I-labeled fibrin and activation of zymogen matrix metalloproteinases, was similar for u-PAR-/- and u-PAR+/+ cells. Immunoelectron microscopy of injured arteries in vivo revealed that u-PA was bound on the cell surface of u-PAR+/+ cells, whereas it was present in the pericellular space around u-PAR-/- cells. Taken together, these results suggest that binding of u-PA to u-PAR is not required to provide sufficient pericellular u-PA-mediated plasmin proteolysis to allow cellular migration into a vascular wound.

Characterization and targeting of the murine alpha2-antiplasmin gene

Alpha2-Antiplasmin (alpha2-AP) is the main physiological plasmin inhibitor in mammalian plasma. As a first step toward the generation of alpha2-AP deficient mice, the murine alpha2-AP gene was characterized and a targeting vector for homologous recombination in embryonic stem (ES) cells constructed. Alignment of nucleotide sequences obtained from genomic subclones allowed location of exons 2 through 10 of the alpha2-AP gene, but failed to identify the 5' boundary of exon 1. Compared to the human gene, exons 2 through 9 in the murine gene have identical size and intron-exon boundaries obeying the GT/AG rule. The 5' boundary of exon 10 is identical in both genes while the 3' non-coding region is 64 bp longer in the human gene. Introns 2, 3, 6 and 8 have similar sizes in the mouse and human genes; intron 1 is 6-fold smaller, introns 5, 7 and 9 are 2- to 3-fold smaller, whereas intron 4 is about 2-fold larger in the mouse gene. Compared to the human 5' flanking sequence, an insertion of a simple repeat region with sequence (TGG)n has occurred. The open reading frame of the mouse alpha2-AP gene encodes a 491-amino-acid protein comprising the experimentally determined NH2-terminus of the mature protein Val-Asp-Leu-Pro-Gly-. A targeting vector, pPNT.alpha2-AP, was constructed by introducing a homologous sequence of 8.3 kb in total in the parental pPNT vector. In pPNT.alpha2-AP, the neomycin resistance expression cassette replaces a 7 kb genomic fragment comprising exon 2 through part of exon 10 (including the stop codon), which represents the entire sequence encoding the mature protein, including the fibrin-binding domain, the reactive site peptide bond and the plasmin(ogen)-binding region. Electroporation of 129R1 embryonic stem (ES) cells with the linearized vector pPNT.alpha2-AP yielded three targeted clones with correct homologous recombination at the 5'- and 3'-ends, as confirmed by Southern blot analysis of purified genomic DNA with appropriate restriction enzymes and probes. These targeted clones will be used to generate alpha2-AP deficient mice.

Insights in vessel development and vascular disorders using targeted inactivation and transfer of vascular endothelial growth factor, the tissue factor receptor, and the plasminogen system

VEGF has been proposed to participate in normal and pathological vessel formation. Surprisingly, lack of only a single VEGF allele resulted in embryonic lethality due to abnormal formation of intra- and extra-embryonic vessels. Homozygous VEGF-deficient embryos, generated by tetraploid aggregation, revealed an even more severe defect in vessel formation. These results (1) suggest a tight regulation of early vessel development by VEGF and, indirectly, the presence of other VEGF-like molecules; (2) reveal an unprecedented lethal phenotype associated with heterozygous deficiency of an autosomal gene, and (3) demonstrate that tetraploid aggregation was a valid and the only method to study the phenotype of the homozyogous VEGF-deficient embryos. The dominant and strict dose-dependent role of VEGF in vivo renders this molecule a desirable therapeutic target for promoting or preventing angiogenesis. Tissue factor (TF) is the principal cellular initiator of coagulation and its deregulated expression has been related to thrombogenesis in sepsis, cancer, and inflammation. However, TF appears to be also involved in a variety of non-hemostatic functions including inflammation, cancer, brain function, immune response, and tumor-associated angiogenesis. Surprisingly, TF deficiency resulted in embryonic lethality due to abnormal extra-embryonic vessel development and defective vitelloembryonic circulation. The abnormal yolk sac vasculature is reminiscent of that observed in embryos lacking VEGF, possibly suggesting that both gene functions are interconnected. These targeting studies extend the recently documented role of TF in tumor-associated angiogenesis and warrant further study of its role in angiogenesis during other pathological disorders. The plasminogen system, via its triggers, tissue-type plasminogen activator (t-PA) and urokinase-type plasminogen activator (u-PA) and its inhibitor, plasminogen activator inhibitor-1 (PAI-1), has been implicated in thrombosis, arterial neointima formation, and atherosclerosis. Studies in mice with targeted gene inactivation of t-PA, u-PA, PAI-1, the urokinase receptor (u-PAR), and plasminogen (Plg) revealed (1) that deficiency of t-PA or u-PA increase the susceptibility to thrombosis associated with inflammation and that combined deficiency of t-PA:u-PA or deficiency of Plg induces severe spontaneous thrombosis; (2) that vascular injury-induced neointima formation is reduced in mice lacking u-PA-mediated plasmin proteolysis, unaltered in t-PA- or u-PAR-deficient mice and accelerated in PAI-1-deficient mice, but that it can be reverted by adenoviral PAI-1 gene transfer; and (3) that atherosclerosis in mice doubly deficient in apolipoprotein E (apoE) and PAI-1 is reduced after 10 weeks of cholesterol-rich diet. Thus, the plasminogen system significantly affects thrombosis, restenosis, and atherosclerosis.

Generation and characterization of urokinase receptor-deficient mice

Mice homozygously deficient for the urokinase-type plasminogen activator (u-PA) receptor (u-PAR-1-) were generated by homologous recombination in D3, embryonic stem cells. The genomic sequences comprising exon 2 through 5 of the u-PAR gene were replaced by the neomycin resistance gene, resulting in inactivation of both u-PAR splice variants. The inactivated u-PAR allele was transmitted via mendelian inheritance, and fertility. Inactivation of u-PAR was confirmed by the absence of binding of rabbit anti-murine u-PAR or of an aminoterminal fragment of murine u-PA (mu-PA.1-48) to u-PAR-1- embryonic fibroblasts and macrophages. u-PAR-1- mice displayed normal lysis of a murine plasma clot injected via the jugular vein. Invasion of macrophages into the peritoneal cavity after thioglycollate stimulation was similar in u-PAR-1- and u-PAR-1- mice. u-PAR-1- peritoneal macrophages had a threefold decreased initial rate of u-PA-mediated plasminogen activation in vitro but degraded extracellular matrix proteins in vitro as efficiently as u-PAR-1- macrophages.

Vaccination with recombinant vaccinia viruses expressing ICP27 induces protective immunity against herpes simplex virus through CD4+ Th1+ T cells

This study was designed to evaluate the efficacy and mechanisms of protection mediated by recombinant vaccinia viruses encoding immediate-early (IE) proteins of herpes simplex virus type 2 (HSV-2). Three mouse strains were immunized against the IE proteins ICP27, ICP0, and ICP4, and mice were challenged intracutaneously in the zosteriform model with HSV-2 strain MS. Protection was observed only following immunization with the ICP27 construct and then only in the BALB/c mouse strain. Protection in BALB/c mice was ablated by CD4+ T-cell suppression but remained intact in animals depleted of CD8+ T cells. Moreover, protection could be afforded to SCID nude recipients with CD4+ but not CD8+ T cells from ICP27-immunized mice. Only BALB/c mice developed a delayed-type hypersensitivity reaction to HSV-2, and in vitro measurements of humoral and cell-mediated immunity revealed response patterns to ICP27 and HSV that differed between protected BALB/c and unprotected mouse strains. Accordingly, BALB/c responses showed antigen-induced cytokine profiles dominated by type 1 cytokines, whereas C57BL/6 and C3H/HeN mice generated cytokine responses mainly of the type 2 variety. Our results may indicate that protection against zosterification is mainly mediated by CD4+ T cells that express a type 1 cytokine profile and that protective vaccines against HSV which effectively induce such T-cell responses should be chosen.

Thrombolytic profiles of clot-targeted plasminogen activators. Parameters determining potency and initial and maximal rates

BACKGROUND

Targeting of plasminogen activators to the thrombus by means of fibrin-specific monoclonal antibodies may enhance their thrombolytic potency. The kinetics of clot binding of two human fibrin-specific monoclonal antibodies (MA-12B3 and MA-15C5) and of clot lysis with their chemical 1:1 stoichiometric complexes with recombinant single-chain urokinase-type plasminogen activator (rscu-PA) (rscu-PA/MA-12B3 and rscu-PA/MA-15C5) were determined in hamsters and rabbits. Thrombolytic potencies, maximal rates of clot lysis, and the duration of the lag phases before clot lysis of the antibody/rscu-PA conjugates were compared with those of rscu-PA and tissue-type plasminogen activator (rt-PA).

METHODS AND RESULTS

Bolus injection of 7.5 micrograms of 125I-labeled antibody in rabbits with an extracorporeal arteriovenous loop containing a 0.3-mL human plasma clot produced clot-to-blood ratios of 6.6 +/- 1.0 (mean +/- SEM) for MA-12B3 and 1.1 +/- 0.15 for MA-15C5 (p < 0.001 versus MA-12B3) within 6 hours. Progressive digestion of the clot did not alter the binding of MA-12B3 but resulted in as much as a 10-fold increase of the binding of MA-15C5. The conjugates infused intravenously over 90 minutes in hamsters with a human plasma clot in the pulmonary artery produced dose-related in vivo clot lysis. Thrombolytic potencies (maximal slope of the percent lysis versus dose in milligrams of u-PA equivalent per kilogram body weight) were 2,500 +/- 440 for rscu-PA/MA-12B3, 3,600 +/- 640 for rscu-PA/MA-15C5 (p = NS vs. rscu-PA/MA-12B3), 60 +/- 8 for rscu-PA (p < 0.001 versus both conjugates), and 380 +/- 66 for rt-PA (p < 0.001 versus both conjugates). The plasma clearances of the conjugates were fourfold to sixfold slower than those of rscu-PA and rt-PA. Maximal rates of clot lysis, determined by continuous external radioisotope scanning over the thorax, were 0.90 +/- 0.13%, 0.91 +/- 0.17%, 0.84 +/- 0.12%, and 1.1 +/- 0.16% lysis per minute for rscu-PA/MA-12B3, rscu-PA/MA-15C5, rscu-PA, and rt-PA, respectively; these maximal rates were obtained with 0.016, 0.016, 1.0, and 0.25 mg/kg, respectively, and were associated with minimal lag phases of 18 +/- 3.2, 28 +/- 4.9, 34 +/- 3.7, and 25 +/- 3.9 minutes, respectively.

CONCLUSIONS

The thrombolytic potency of the rscu-PA/antifibrin conjugates is determined by their clearance, as well as by rate and extent of initial binding to clots and by changes in binding during clot lysis. Clot targeting of rscu-PA with fibrin-specific antibodies increases its thrombolytic potency but does not alter the maximal rate or the minimal lag phase of clot lysis. These parameters appear to be independent of the nature of the plasminogen activator and of targeting.

Thrombolytic and pharmacokinetic properties of a recombinant chimeric plasminogen activator consisting of a fibrin fragment D-dimer specific humanized monoclonal antibody and a truncated single-chain urokinase

A recombinant chimeric plasminogen activator consisting of a humanized monoclonal antibody specific for cross-linked human fibrin (MA-15C5Hu) and a 32 kDa single-chain urokinase-type plasminogen activator (scu-PA-32k) comprising amino acids Leu144-Leu411, MA-15C5Hu/scu-PA-32k, was previously found to have a 12-fold higher fibrinolytic potency than recombinant scu-PA-32k towards a human plasma clot in a human plasma milieu in vitro (Vandamme et al., Eur J Biochem 1992; 205: 139-46). Therefore, the thrombolytic and pharmacokinetic properties of MA-15C5Hu/scu-PA-32k were compared with those of recombinant single-chain urokinase-type plasminogen activator (scu-PA) in 3 different venous thrombosis models in vivo. In hamsters with a pulmonary embolus consisting of a human plasma clot, the thrombolytic potency (% lysis per dose in mg/kg administered) of MA-15C5Hu/scu-PA-32k was 23-fold higher than that of scu-PA (p less than 0.0005). In rabbits with a jugular vein clot prepared from human plasma, the thrombolytic potency of MA-15C5Hu/scu-PA-32k was 11-fold higher than that of scu-PA (p = 0.012). In baboons with an autologous whole blood clot in the femoral vein, the chimera had a 5-fold higher thrombolytic potency than scu-PA. In all three animal species, the clearance of the chimera was 10- to 27-fold reduced as compared to scu-PA. The specific thrombolytic activity (% lysis per micrograms/ml steady-state plasma u-PA antigen) was increased up to 7-fold with MA-15C5Hu/scu-PA-32k as compared with scu-PA, which is indicative of targeting of the chimera to the clot. No fibrinogen breakdown or alpha 2-antiplasmin depletion was observed during thrombolysis with the chimera. Thus, MA-15C5Hu/scu-PA-32k constitutes a recombinant chimeric plasminogen activator with a significantly enhanced thrombolytic potency in 3 different animal models of venous thrombosis.

Characterization of a recombinant chimeric plasminogen activator composed of a fibrin fragment-D-dimer-specific humanized monoclonal antibody and a truncated single-chain urokinase

A recombinant chimeric plasminogen activator, MA-15C5Hu/scu-PA-32k, composed of a humanized fibrin fragment-D-dimer-specific monoclonal antibody (MA-15C5Hu) and a recombinant low-molecular-mass single-chain urokinase-type plasminogen activator, comprising amino acids Leu144-Leu411 (scu-PA-32k), was produced by cotransfecting Chinese hamster ovary (CHO) cells with the cDNA encoding the MA-15C5Hu light-chain sequence and the cDNA encoding the MA-15C5Hu heavy-chain sequence fused with the cDNA encoding scu-PA-32k. Purified MA-15C5Hu/scu-PA-32k migrated as a 215-kDa band on non-reducing SDS/PAGE, which is consistent with a molecule composed of one antibody and two scu-PA-32k moieties. However, the chimera was obtained as a mixture of single-chain u-PA-32k (37%) and amidolytically inactive (50%) and active (13%) two-chain u-PA-32k, the latter of which was removed by immunoadsorption on a monoclonal antibody specific for two-chain urokinase. The fragment-D-dimer affinity and enzymatic properties of MA-15CHu/scu-PA-32k were similar to those of MA-15C5Hu or of scu-PA-32k. In an in vitro system composed of a 125I-fibrin-labeled human plasma clot submerged in citrated human plasma, MA-15C5Hu/scu-PA-32k had a 12-fold higher fibrinolytic potency than scu-PA-32k: 50% lysis in 2 h required 0.43 +/- 0.12 micrograms u-PA-32k equivalent of the chimera/ml versus 5.4 +/- 0.3 micrograms/ml of scu-PA-32k (mean +/- SEM, n = 4). Addition of purified fibrin fragment-D dimer reduced the fibrinolytic potency of MA-15C5Hu/scu-PA-32k in a concentration-dependent way, indicating that the increased potency is the result of antibody targeting. Thus, a recombinant humanized antifibrin antibody/u-PA chimera has been obtained in which only the variable domains of the antibody moiety are of non-human origin. The chimera has intact antigen-binding capacity, u-PA enzymatic activity and a significantly increased fibrinolytic potency in a plasma medium in vitro.

Effect of chemical conjugation of recombinant single-chain urokinase-type plasminogen activator with monoclonal antiplatelet antibodies on platelet aggregation and on plasma clot lysis in vitro and in vivo

The murine monoclonal antiplatelet antibodies MA-TSPI-1 (directed against human thrombospondin) and MA-PMI-2, MA-PMI-1, and MA-LIBS-1 (directed against ligand-induced binding sites [LIBS] on human platelet glycoprotein IIb/IIIa) were conjugated with recombinant single-chain urokinase-type plasminogen activator (rscu-PA) using the cross-linking reagent N-succinimidyl 3-(2-pyridyldithio)propionate (SPDP). The conjugates (rscu-PA/MA-TSPI-1, rscu-PA/MA-PMI-2, rscu-PA/MA-PMI-1, and rscu-PA/MA-LIBS-1), purified by immunoadsorption and gel filtration, were obtained with recoveries of 34% to 45%, with an average stoichiometry of 1.6 to 1.8 IgG molecules per rscu-PA molecule, and with unaltered specific activities and affinities. Preincubation of human platelet-rich plasma with rscu-PA/MA-PMI-2, rscu-PA/MA-PMI-1, or unconjugated rscu-PA resulted in partial inhibition of ADP-induced aggregation; 25% inhibition was obtained with 63 micrograms/mL rscu-PA and with 6 micrograms u-PA/mL rscu-PA/MA-PMI-2 or 1.2 micrograms u-PA/mL rscu-PA/MA-PMI-1. In an in vitro system composed of a 125I-fibrin-labeled platelet-rich human plasma clot immersed in normal human plasma, the conjugates had threefold to greater than 15-fold less fibrinolytic potency than unconjugated rscu-PA. The thrombolytic potency of rscu-PA/MA-PMI-1 and rscu-PA/MA-LIBS-1 was compared with that of rscu-PA and that of a control conjugate rscu-PA/MA-1C8 in a pulmonary embolism model in the hamster, using clots prepared from platelet-poor or platelet-rich human plasma. Lysis was measured 30 minutes after the end of a 60-minute intravenous infusion of the thrombolytic agents. rscu-PA, rscu-PA/MA-PMI-1, rscu-PA/MA-LIBS-1, as well as rscu-PA/MA-1C8 had comparable thrombolytic potencies (percent lysis per dose administered) towards platelet-poor human plasma clots. In contrast, the thrombolytic potency of rscu-PA/MA-PMI-1 and of rscu-PA/MA-LIBS-1 towards platelet-rich clots was 2.3- to 3-fold higher than that of rscu-PA (P less than .005) and fivefold to sevenfold higher than that of the control conjugate (P less than .01).

Thrombolytic and pharmacokinetic properties of a conjugate of recombinant single-chain urokinase-type plasminogen activator with a monoclonal antibody specific for cross-linked fibrin in a baboon venous thrombosis model

Chemical conjugates between recombinant single-chain urokinase-type plasminogen activator (rscu-PA) and a murine monoclonal antibody directed against fragment D-dimer of cross-linked human fibrin (MA-15C5), rscu-PA/MA-15C5, and between rscu-PA and a control monoclonal antibody (MA-1C8), rscu-PA/MA-1C8, were produced by cross-linking with N-succinimidyl 3-(2-pyridyldithio) propionate (SPDP). In an in vitro system composed of a [125 I]fibrin-labeled baboon plasma clot immersed in autologous citrated plasma, dose- and time-dependent lysis was obtained with a ratio of the potencies of free and conjugated rscu-PA similar to that in human plasma: 50% lysis in 2 hours required 4.3 micrograms/ml rscu-PA, 1.0 microgram/ml urokinase-type plasminogen activator (u-PA) equivalent rscu-PA/MA-15C5, or 15 micrograms/ml u-PA equivalent rscu-PA/MA-1C8. The thrombolytic and pharmacokinetic properties of rscu-PA and of rscu-PA/MA-15C5 were compared in baboons with a 0.8-1.0 ml [125 I]fibrin-labeled autologous blood clot produced in a femoral vein. Continuous intravenous infusion of these compounds during a 2-hour period resulted in dose- and time-dependent lysis. The thrombolytic potency of rscu-PA/MA-15C5 was 3.0 +/- 0.5 times higher (50% lysis with 0.3 +/- 0.02 mg u-PA equivalent/kg body wt) than that of rscu-PA measured by ex vivo isotope recovery from the femoral vein segment (p less than 0.001) and was 2.7 +/- 0.5 times higher (50% lysis with 0.35 +/- 0.02 mg/kg rscu-PA/MA-15C5) by external radioisotope counting (p less than 0.001). A dose of 0.5 mg/kg of rscu-PA/MA-1C8 was much less active than rscu-PA. After the end of the infusion, u-PA-related antigen disappeared from plasma in a biphasic manner with an initial half-time of 2.7 +/- 0.5 for rscu-PA, 24 +/- 1.2 for rscu-PA/MA-15C5, and 21 +/- 0.5 minutes for rscu-PA/MA-1C8 with corresponding plasma clearances of 340 +/- 40, 20 +/- 3, and 24 +/- 2 ml/min, respectively. In conclusion, the increased thrombolytic potency of rscu-PA/MA-15C5 is the result of a reduction of the thrombolytic potency due to coupling of rscu-PA to the antibody molecule, which is counter-balanced by an enhancement of the thrombolytic potency due to fibrin targeting by the specific idiotype.

TEC1, a gene involved in the activation of Ty1 and Ty1-mediated gene expression in Saccharomyces cerevisiae: cloning and molecular analysis

Ty and Ty-mediated gene expression observed in haploid cells of Saccharomyces cerevisiae depends on several determinants, some of which are required for the expression of haploid-specific genes. We report here the cloning and molecular analysis of TEC1. TEC1 encodes a 486-amino-acid protein that is a trans-acting factor required for full Ty1 expression and Ty1-mediated gene activation. However, mutation or deletion of the TEC1 gene had little effect on total Ty2 transcript levels. Our analysis provides clear evidence that TEC1 is not involved in mating or sporulation processes. Unlike most of the proteins involved in Ty and adjacent gene expression, the product of TEC1 has no known cellular function. Although there was no mating-type effect on TEC1 expression, our results indicate that the TEC1 and the a/alpha diploid controls on Ty1 expression are probably not cumulative.

Effect of fibrin-targeting on clot lysis with urokinase-type plasminogen activator

The effect of fibrin-targeting of urokinase-type plasminogen activator (u-PA) on its fibrinolytic potency was studied using recombinant fusion proteins of u-PA with the NH2-terminal region of tissue-type plasminogen activator (t-PA/u-PA) and chemical complexes of u-PA with F(ab')2 fragments of a fibrin specific monoclonal antibody (u-PA/MA-15C5-F(ab')2). Two chain derivatives of a low Mr variant of u-PA comprising amino acids Leu144-Leu411 (tcu-PA-32k), obtained by cleavage of recombinant single-chain u-PA (rscu-PA-32k) with thrombin (rtcu-PA-32k/T) or plasmin (rtcu-PA-32k/P) were investigated. The plasmin-derived two chain u-PA moieties, rtcu-PA-32k/P, rt-PA/tcu-PA-32k/P and rtcu-PA-32k/MA-15C5-F(ab')2/P had high specific activities in amidolytic and fibrin plate assays (130,000 and 150,000 IU/mg u-PA, 43,000 and 71,000 IU/mg u-PA and 32,000 and 56,000 IU/mg u-PA respectively). The thrombin-derived two chain u-PA moieties had a very low amidolytic activity, corresponding to less than or equal to 1 percent of that of their plasmin-derived counterparts. On fibrin plates, however, rtcu-PA-32k/T had a negligible activity, whereas rt-PA/tcu-PA-32k/T and rtcu-PA-32k/MA-15C5-F(ab')2/T had specific activities of 12,000 and 25,000 IU/mg u-PA respectively. The catalytic efficiency for plasminogen activation of rtcu-PA-32k/MA-15C5-F(ab')2/T is 4,000-fold lower than that of rtcu-PA-32k/MA-15C5-F(ab')2/P, but its concentration required for 50 percent lysis in 2 hours of a 125I-fibrin labeled plasma clot in human plasma (C50) is only 25-fold higher. The catalytic efficiency of rt-PA/tcu-PA-32k/T is 1,600-fold lower and the C50 100-fold higher than that of rt-PA/tcu-PA-32k/P. The catalytic efficiency and the fibrinolytic potential of rtcu-PA-32k/T are negligible as compared to that of rtcu-PA-32k/P. These observations may be explained by conversion of the thrombin derived two chain u-PA moieties to their plasmin-derived analogues at the fibrin surface. This conversion appears to be most efficient for the antibody conjugate which has a high fibrin-affinity, less efficient for the t-PA/u-PA chimera which has only moderate fibrin-affinity, and negligible for the unconjugated u-PA moiety which has no fibrin-affinity. These findings illustrate the importance of plasmin-mediated positive feedback mechanisms in u-PA mediated clot lysis.