Prothrombotic phenotype of protein Z deficiency

Physiological and Proteomic Responses of Dairy Buffalo to Heat Stress Induced by Different Altitudes

Buffalo are mainly distributed in low-altitude (LA), medium-altitude (MA), and high-altitude (HA) regions characterised by different thermal and oxygen environments in Yunnan province, China. Due to black skin, sparse hair, and the low density of skin sweat glands, buffalo are more sensitive to heat stress. Here, we used data-independent acquisition (DIA) proteomics to reveal a broad spectrum of proteins that play roles in adaptation to the heat stress of buffalo raised at low altitude or hypoxia at high altitude. LA buffalo showed higher body temperatures than MA- and HA buffalo, and HA buffalo had higher levels of GSH and SOD and lower levels of ROS compared to LA and MA buffalo. In 33 samples, 8476 peptides corresponding to 666 high-confidence proteins were detected. The levels of circulating complement proteins in the immune pathways were lower in LA and MA buffalo than in HA buffalo. There were higher levels of alpha-1 acid glycoprotein in LA buffalo than in MA and HA buffalo. Relative to MA buffalo, levels of blood oxygen delivery proteins were higher in LA and HA buffalo. A higher abundance of apolipoproteins was detected in LA and MA buffalo than in HA buffalo. In summary, buffalo adopted similar adaptation strategies to oxidative stress induced by heat stress or hypoxia, including immunological enhancement, high efficiency of blood oxygen delivery, and the inhibition of lipid oxidation.

Anticoagulant SERPINs: Endogenous Regulators of Hemostasis and Thrombosis

Appropriate activation of coagulation requires a balance between procoagulant and anticoagulant proteins in blood. Loss in this balance leads to hemorrhage and thrombosis. A number of endogenous anticoagulant proteins, such as antithrombin and heparin cofactor II, are members of the serine protease inhibitor (SERPIN) family. These SERPIN anticoagulants function by forming irreversible inhibitory complexes with target coagulation proteases. Mutations in SERPIN family members, such as antithrombin, can cause hereditary thrombophilias. In addition, low plasma levels of SERPINs have been associated with an increased risk of thrombosis. Here, we review the biological activities of the different anticoagulant SERPINs. We further consider the clinical consequences of SERPIN deficiencies and insights gained from preclinical disease models. Finally, we discuss the potential utility of engineered SERPINs as novel therapies for the treatment of thrombotic pathologies.

Protein Z-dependent protease inhibitor (ZPI) is a physiologically significant inhibitor of prothrombinase function

Current thought holds that factor Xa (FXa) bound in the prothrombinase complex is resistant to regulation by protein protease inhibitors during prothrombin activation. Here we provide evidence that, contrary to this view, the FXa-specific serpin inhibitor, protein Z-dependent protease inhibitor (ZPI), complexed with its cofactor, protein Z (PZ), functions as a physiologically significant inhibitor of prothrombinase-bound FXa during prothrombin activation. Kinetics studies showed that the rapid rate of inhibition of FXa by the ZPI-PZ complex on procoagulant membrane vesicles (k_{a (app)} ∼10⁷ m^-1 s^-1) was decreased ∼10-fold when FXa was bound to FVa in prothrombinase and a further ∼3-4-fold when plasma levels of S195A prothrombin were present (k_{a (app)} 2 × 10⁵ m^-1 s^-1). Nevertheless, the ZPI-PZ complex produced a major inhibition of thrombin generation during prothrombinase-catalyzed activation of prothrombin under physiologically relevant conditions. The importance of ZPI-PZ complex anticoagulant regulation of FXa both before and after incorporation into prothrombinase was supported by thrombin generation assays in plasma. These showed enhanced thrombin generation when the inhibitor was neutralized with a PZ-specific antibody and decreased thrombin generation when exogenous ZPI-PZ complex was added whether prothrombin was activated directly by FXa or through extrinsic or intrinsic pathway activators. Moreover, the PZ antibody enhanced thrombin generation both in the absence and presence of activated protein C (APC) anticoagulant activity. Taken together, these results suggest an important anticoagulant role for the ZPI-PZ complex in regulating both free FXa generated in the initiation phase of coagulation as well as prothrombinase-bound FXa in the propagation phase that complement prothrombinase regulation by APC.

Suppressing protein Z-dependent inhibition of factor Xa improves coagulation in hemophilia A

Essentials Protein Z (PZ) catalyzes PZ-dependent proteinase inhibitor (ZPI) inactivation of factor (F)Xa. Gene-deletion of PZ or ZPI improves coagulation in hemophilia (FVIII knockout) mice. A PZ blocking antibody enhances thrombin generation in human hemophilia plasma. Suppression of the PZ/ZPI pathway may ameliorate the phenotype of severe hemophilia. SUMMARY: Background Hemostasis requires a balance between procoagulant and anticoagulant factors. Hemophiliacs bleed because of a procoagulant deficiency. Targeted reduction in the activity of endogenous anticoagulant pathways is currently being investigated as a means of improving hemostasis in hemophilia. Protein Z (PZ) is a cofactor that serves as a catalyst for PZ-dependent protease inhibitor (ZPI) inactivation of activated factor X at phospholipid surfaces. Objectives To evaluate the effects of PZ or ZPI gene deletion in hemophilic mice, and of blocking PZ in human hemophilic plasma. Methods A tail vein rebleeding assay (TVRB) was developed on the basis of the serial disruption of clots forming over a period of 15 min following tail vein laceration in an anesthetized mouse. Wild-type (WT)/FVIII knockout FVIIIKO, PZ knockout PZKO/FVIIIKO and ZPI knockout ZPIKO/FVIIIKO mice were evaluated in this model, and their plasmas were tested in thrombin generation assays. A mAb against PZ was evaluated in human hemophilic plasma thrombin generation assays. Results The numbers of clot disruptions (mean ± standard error of the mean) in the TVRB were: 4.0 ± 0.9 for WT/FVIIIKO mice; 23.8 ± 1.1 for WT/FVIIIKO mice supplemented with 100% FVIII; 15.2 ± 1.1 for PZKO/FVIIIKO mice; and 14.7 ± 1.2 for ZPIKO/FVIIIKO mice. Thrombin generation in PZKO/FVIIIKO and ZPIKO/FVIIIKO mouse plasmas was similar to that in FVIIIKO plasma supplemented with ~ 15% recombinant FVIII. A mAb against PZ added to human hemophilic plasma enhanced thrombin generation to an extent similar to the addition of ~ 15% FVIII. Conclusions Blockade of the PZ/ZPI system may be sufficient to ameliorate the phenotype of severe hemophilia.

High frequency of anti-protein Z antibodies in patients with anticardiolipin antibodies

Protein Z (PZ) is a vitamin K-dependent protein involved in the down-regulation of coagulation by forming a complex with the protein Z-dependent protease inhibitor. The complex inhibits the activated factor X on phospholipid surface. Presence of anti-PZ (aPZ) antibodies was first described in women with pathological pregnancies but the significance of aPZ antibodies in other pathological situations was poorly studied. In this work we analyzed the frequency of aPZ antibodies in a series of 86 consecutive patients with anticardiolipin (aCL) antibodies and studied the association of aPZ with other antiphospholipid (aPL) antibodies [lupus anticoagulant (LAC) and anti-ß2GP-1 antibodies] and the clinical signification of these aPZ antibodies in term of thrombosis or fetal loss. Anti-PZ antibodies (IgG and IgM) were detected using commercially available ELISA assays. The frequency of aPZ antibodies was 40.7% in the patient group versus 6.8% in a group of 59 healthy volunteers (p < 0.0001). The frequency of aPZ antibodies significantly increases (p < 0.05) in patients with a double or triple positivity of aPL antibodies and a higher frequency of aPZ antibodies was observed in patients with LAC (57.7%) than in patients without LAC (25.6%, p = 0.02). There were no significant differences in aPZ antibodies frequency between patients with and without thrombotic events. Interestingly, among the 8 women with recurrent foetal losses, aPZ antibodies were observed in 7 cases, in agreement with previous observations suggesting that aPZ antibodies may be associated with obstetrical complications.

The protein Z/protein Z-dependent protease inhibitor complex

Protein Z (PZ) is a vitamin K-dependent factor identified in human plasma in 1984 but it has no enzymatic activity. It is a cofactor of a serpin, the protein Z-dependent protease inhibitor (ZPI), and the complex PZ/ZPI inhibits activated factor X on phospholipid surfaces. In mice, the disruption of PZ or ZPI gene is asymptomatic, but enhances the thrombotic phenotype and mortality of other thrombotic risk factors. Most of the clinical studies focused on PZ. Despite conflicting results, a recent meta-analysis indicated that PZ deficiency could be a risk for venous and arterial thrombosis and early fetal loss. However, these conclusions are drawn from case-control studies of small size, constituting an important limitation. Recently, it was shown that PZ and/or ZPI are synthesised by normal kidney and different cancer cells, suggesting that the complex PZ/ZPI could play a role in inhibiting the tissue deposition of fibrin. The physiopathological consequences of these observations remain to be established. At this time, the measurement of plasma PZ and ZPI or analysis of their gene polymorphisms should not be performed routinely for the exploration of thrombophilia.

Lipid oxidation inactivates the anticoagulant function of protein Z-dependent protease inhibitor (ZPI)

Lipid oxidation due to oxidative stress plays an important role in the pathogenesis of inflammatory and thrombotic cardiovascular diseases. Several findings suggest that lipid peroxidation can alter the function of coagulation proteins and contribute to a hypercoagulable state, but the molecular mechanisms are unclear. Here, we report that oxidized phospholipids suppress the anticoagulant function of the serpin, protein Z-dependent protease inhibitor (ZPI), a specific inhibitor of membrane-associated factor Xa (FXa) that requires protein Z (PZ), phospholipid, and calcium as cofactors. We found that this suppression arises from a diminished ability of the oxidized membrane to function as a cofactor to promote ZPI inhibition of membrane-bound FXa, due fully or in part to the susceptibility of the bound ZPI-PZ complex to oxidative inactivation. Surprisingly, free ZPI was also susceptible to inactivation by oxidized membrane vesicles in the absence of calcium. Oxidized vesicles containing both phosphatidylserine and polyunsaturated fatty acids were required to promote inactivation of the ZPI-PZ complex or free ZPI, indicating that binding of the PZ-complexed or free ZPI to peroxide-modified phospholipid vesicles mediates the inactivation. Heparin protected the ZPI-PZ complex and free ZPI from inactivation, suggesting that blocking the heparin-binding site on ZPI interferes with ZPI binding to lipid or to PZ. This was confirmed by direct lipid-binding experiments. Native PAGE indicated that oxidization induced dissociation of the ZPI-PZ complex and increased the negative charge of ZPI. We conclude that compromised ZPI anticoagulant function could contribute to thrombus initiation and growth in oxidative stress-induced cardiovascular diseases.

Circulating protein Z concentration, PROZ variants, and unexplained cerebral infarction in young and middle-aged adults

Protein Z (PZ) is a vitamin K-dependent plasma protein that exhibits both pro- and anticoagulant properties. Both low and high PZ levels have been linked to ischaemic stroke. Although PZ-lowering gene variants have been found to be less common in ischaemic stroke, the relationship remains unclear. We investigated PZ levels and PROZ variants in a multi-ethnic case-control study of unexplained stroke in participants aged 18 to 64. Plasma PZ was measured in cases (≥2 months post-stroke) and controls. PZ polymorphisms G79A (rs3024735) and A13G (2273971) were genotyped. A combined genetic score (0-4 minor alleles) was created assuming additive effects. A total of 715 individuals (1:1.4 cases:controls) was included. Analyses revealed evidence of a non-linear association. After adjusting for demographic and clinical covariates, PZ levels >2.5 µg/ml (90^th %ile) were significantly associated with cryptogenic stroke (OR 2.41 [95 % CI 1.34, 4.34]) as compared with lower levels. Higher genetic score was related to progressively lower levels of PZ, and the presence of four minor alleles was associated with lower odds of stroke (adjusted OR 0.26 [95 % CI 0.07, 0.96]) versus 0 minor alleles. In this multi-ethnic study of young and middle-aged adults, there was evidence of a non-linear positive association between PZ level and unexplained stroke, with a directionally consistent association for genetic variants related to PZ levels and cryptogenic stroke. These findings support elevated PZ levels as a risk factor for cryptogenic stroke.

Phosphatidylserine and Phosphatidylethanolamine Bind to Protein Z Cooperatively and with Equal Affinity

Protein Z (PZ) is an anticoagulant that binds with high affinity to Protein Z-dependent protease inhibitor (ZPI) and accelerates the rate of ZPI-mediated inhibition of factor Xa (fXa) by more than 1000-fold in the presence of Ca²⁺ and phospholipids. PZ promotion of the ZPI-fXa interaction results from the anchoring of the Gla domain of PZ onto phospholipid surfaces and positioning the bound ZPI in close proximity to the Gla-anchored fXa, forming a ternary complex of PZ/ZPI/fXa. Although interaction of PZ with phospholipid membrane appears to be absolutely crucial for its cofactor activity, little is known about the binding of different phospholipids to PZ. The present study was conceived to understand the interaction of different phospholipids with PZ. Experiments with both soluble lipids and model membranes revealed that PZ binds to phosphatidylserine (PS) and phosphatidylethanolamine (PE) with equal affinity (K_d~48 μM); further, PS and PE bound to PZ synergistically. Equilibrium dialysis experiments revealed two lipid-binding sites for both PS and PE. PZ binds with weaker affinity to other phospholipids, e.g., phosphatidic acid, phosphatidylglycerol, phosphatidylcholine and binding of these lipids is not synergistic with respect to PS. Both PS and PE -containing membranes supported the formation of a fXa-PZ complex. PZ protection of fXa from antithrombin inhibition were also shown to be comparable in presence of both PS: PC and PE: PC membranes. These findings are particularly important and intriguing since they suggest a special affinity of PZ, in vivo, towards activated platelets, the primary membrane involved in blood coagulation process.

Autoantibodies associated with reproductive failure

Autoimmune factors are involved in some of the cases of reproductive failure. These factors entail several autoantibodies, especially in patients having systemic lupus erythematosus (SLE) or the antiphospholipid syndrome (APS). These autoantibodies include mainly antibodies directed to phospholipid such as cardiolipin, phosphatidylserine, phosphatidylethanolamine or phospholipids binding glycoproteins such as b2glycoprotein-I, annexin V, prothrombin and protein-Z. There are also some other autoantibodies directed to laminin-I, thromboplastin, mitochondrial antibodies of the M5 type, corpus luteum, prolactin, poly (ADP-ribose), thyroglobulin and more, which were also found in SLE or APS patients with reproductive failure. Moreover, the presence of additional autoantibodies directed to actin, enolase, cubilin and others, needs further investigation to support a firm association to reproductive failure in women. Future studies are likely to help to determine and expand the number of autoantibodies screened in these patients, as well as by the use of proteomics technology, to determine peptides resembling the epitope specificities associated with the specific clinical manifestations.

Decreased Protein Z Concentrations Complicating the Hypercoagulable State of Behqet's Disease

Protein Z is a vitamin-K-dependent plasma protein that serves as a cofactor for the inhibition of factor Xa. Although the precise physiologic function of protein Z is still unknown, abnornal plasma protein Z concentrations have been associated with a number of thrombotic disease states. There is the evidence of universal activation of the hemostatic system in Behqet's disease (BD), which represents a hypercoagulable/prothrombotic state. Circulating protein Z levels in patients with BD were evaluated. Plasma protein Z concentrations were assayed in 24 patients with BD (male/female: 13/11, mean age 35.4 years) and in 24 healthy controls (males/females: 14/10, mean age 59.8 years). The disease duration was 10.6 years (range, 1-30 years). None of the subjects in either group had received anticoagulants within 3 weeks before the study, and none of them had liver dysfunction. Patients complicated with vascular disease were also excluded from the study. Mean plasma concentrations of protein Z were 141 ng/mL (range, 56.8-257) in healthy controls and 107.8 ng/mL (range, 21.2-202) in BD patients (p<0.05). There was a positive correlation between the disease duration and protein Z levels in the study group (p<0.05, r=0.448). Alterations of protein Z concentrations could complicate the pathobiology of the prothrombotic state of BD. Furthermore, the tendency of increment in the protein Z with the passage of time may reflect the diminution of the disease activity.

Terminal microdeletions of 13q34 chromosome region in patients with intellectual disability: Delineation of an emerging new microdeletion syndrome

The increasing use of chromosomal microarray studies in patients with intellectual disability has led to the description of new microdeletion and microduplication syndromes. We report terminal microdeletions in 13q34 chromosome region in 5 adult patients of two unrelated families. Patients harboring 13q34 microdeletions display common clinical features, including intellectual disability, obesity, and mild facial dysmorphism. These individuals can become fairly self-sufficient, however they do not live independently, and require community and social support. Further systematic analysis of the genes comprised in the deleted region will allow the identification of genes whose haploinsufficiency is expected to lead to disease manifestations, in particular intellectual disability.

Epidemiology of venous thromboembolism

Thrombosis can affect any venous circulation. Venous thromboembolism (VTE) includes deep-vein thrombosis of the leg or pelvis, and its complication, pulmonary embolism. VTE is a fairly common disease, particularly in older age, and is associated with reduced survival, substantial health-care costs, and a high rate of recurrence. VTE is a complex (multifactorial) disease, involving interactions between acquired or inherited predispositions to thrombosis and various risk factors. Major risk factors for incident VTE include hospitalization for surgery or acute illness, active cancer, neurological disease with leg paresis, nursing-home confinement, trauma or fracture, superficial vein thrombosis, and-in women-pregnancy and puerperium, oral contraception, and hormone therapy. Although independent risk factors for incident VTE and predictors of VTE recurrence have been identified, and effective primary and secondary prophylaxis is available, the occurrence of VTE seems to be fairly constant, or even increasing.

Plasma Concentrations of Protein Z and Protein Z-Dependent Protease Inhibitor in Patients With Essential Thrombocythemia

The pathological consequences of decreased protein Z (PZ) and/or Z-dependent protease inhibitor (ZPI) levels remain as yet unclear, despite a growing body of evidence which supports their involvement in an increased thrombotic risk. The purpose of the present study was 2-fold: to evaluate plasma concentrations of protein Z and ZPI in patients with essential thrombocythemia (ET) and to determine their significance in thrombotic complications. The median (range) plasma concentrations of PZ in our patients with ET were lower, but not significantly, than in healthy individuals: PZ (1.42 µg/mL, 0.36-3.14 µg/mL vs 1.6 µg/mL, 0.75-2.56 µg/mL, P = .08). On the other hand, the median (range) plasma concentrations of ZPI in the said patients with ET were meaningfully lower than in the reference group: ZPI (3.22 µg/mL, 0.85-6.97 µg/mL vs 4.41 µg/mL, 1.63-7.83 µg/mL, P = .0004). More importantly, the study revealed a statistically significant lower concentration of PZ and ZPI in patients with the presence of the JAK2V617F mutation relative to patients without the mutation, for PZ: 1.38 µg/mL, 0.36-2.6 µg/mL versus 1.63 µg/mL, 0.88-3.14 µg/mL, P = .03, and ZPI 2.89 µg/mL, 0.85-5.91 µg/mL versus 3.61 µg/mL, 1.53-6.97 µg/mL, P = .002. Additionally, significant differences between the concentrations of PZ and ZPI were found in patients with venous thrombotic episodes compared to healthy individuals, for PZ: 1.23 µg/mL, 0.82-1.99 µg/mL versus 1.6 µg/mL, 0.75-2.56 µg/mL, P = .043, and ZPI: 2.42 µg/mL, 0.85-4.21 µg/mL versus 4.41 µg/mL, 1.63-7.83 µg/mL, P < .0001. To recapitulate, our results suggest that the deficiency of PZ may increase tendency to thrombosis in patients with ET.

Thermodynamic and kinetic characterization of the protein Z-dependent protease inhibitor (ZPI)-protein Z interaction reveals an unexpected role for ZPI Lys-239

The anticoagulant serpin, protein Z-dependent protease inhibitor (ZPI), circulates in blood as a tight complex with its cofactor, protein Z (PZ), enabling it to function as a rapid inhibitor of membrane-associated factor Xa. Here, we show that N,N'-dimethyl-N-(acetyl)-N'-(7-nitrobenz-3-oxa-1,3-diazol-4-yl)ethylenediamine (NBD)-fluorophore-labeled K239C ZPI is a sensitive, moderately perturbing reporter of the ZPI-PZ interaction and utilize the labeled ZPI to characterize in-depth the thermodynamics and kinetics of wild-type and variant ZPI-PZ interactions. NBD-labeled K239C ZPI bound PZ with ∼3 nM KD and ∼400% fluorescence enhancement at physiologic pH and ionic strength. The NBD-ZPI-PZ interaction was markedly sensitive to ionic strength and pH but minimally affected by temperature, consistent with the importance of charged interactions. NBD-ZPI-PZ affinity was reduced ∼5-fold by physiologic calcium levels to resemble NBD-ZPI affinity for γ-carboxyglutamic acid/EGF1-domainless PZ. Competitive binding studies with ZPI variants revealed that in addition to previously identified Asp-293 and Tyr-240 hot spot residues, Met-71, Asp-74, and Asp-238 made significant contributions to PZ binding, whereas Lys-239 antagonized binding. Rapid kinetic studies indicated a multistep binding mechanism with diffusion-limited association and slow complex dissociation. ZPI complexation with factor Xa or cleavage decreased ZPI-PZ affinity 2-7-fold by increasing the rate of PZ dissociation. A catalytic role for PZ was supported by the correlation between a decreased rate of PZ dissociation from the K239A ZPI-PZ complex and an impaired ability of PZ to catalyze the K239A ZPI-factor Xa reaction. Together, these results reveal the energetic basis of the ZPI-PZ interaction and suggest an important role for ZPI Lys-239 in PZ catalytic action.

Protein z exerts pro-angiogenic effects and upregulates CXCR4

Objective

Protein Z (PZ) is a vitamin K-dependent coagulation factor without catalytic activity. Evidence points towards PZ as an independent risk factor for the occurrence of human peripheral arterial disease. However, the role of PZ in ischemia-driven angiogenesis and vascular healing processes has not been elucidated so far.

Approach

Angiogenic potency of PZ was assessed in established in vitro assays using endothelial cells. PZ-deficient (PZ^−/−) mice and their wild-type littermates (PZ^+/+) were subjected to hindlimb ischemia. Furthermore, PZ^−/− mice were exposed to PZ expressing adenovirus (AdV-PZ) or control adenovirus (AdV-GFP). In an additional set of animals, PZ^−/− mice were exposed to AdV-PZ and AdV-GFP, each in combination with the CXCR4 antagonist AMD3100.

Results

In vitro, PZ stimulated migratory activity and capillary-like tube formation of endothelial cells comparable to SDF-1. PZ^−/− mice exhibited diminished hypoxia-driven neovascularization and reperfusion in post-ischemic hindlimbs, which was restored by adenoviral gene transfer up to levels seen in PZ^+/+ mice. The stimulatory impact of PZ on endothelial cells in vitro was abolished by siRNA targeting against PZ and PZ was not able to restore reduced migration after knock-down of CXCR4. The increased surface expression of CXCR4 on PZ-stimulated endothelial cells and the abrogated restoration of PZ^−/− mice via AdV-PZ after concomitant treatment with the CXCR4 antagonist AMD3100 supports the idea that PZ mediates angiogenesis via a G-protein coupled pathway and involves the SDF-1/CXCR4 axis. This is underlined by the fact that addition of the G-protein inhibitor PTX to PZ-stimulated endothelial cells abolished the effect of PZ on capillary-like tube formation.

Conclusions

The results of the current study reveal a role of PZ in ischemia-induced angiogenesis, which involves a G-protein coupled pathway and a raised surface expression of CXCR4. Our findings thereby extend the involvement of PZ from the coagulation cascade to a beneficial modulation of vascular homeostasis.

Placental vascular pathology and increased thrombin generation as mechanisms of disease in obstetrical syndromes

Obstetrical complications including preeclampsia, fetal growth restriction, preterm labor, preterm prelabor rupture of membranes and fetal demise are all the clinical endpoint of several underlying mechanisms (i.e., infection, inflammation, thrombosis, endocrine disorder, immunologic rejection, genetic, and environmental), therefore, they may be regarded as syndromes. Placental vascular pathology and increased thrombin generation were reported in all of these obstetrical syndromes. Moreover, elevated concentrations of thrombin-anti thrombin III complexes and changes in the coagulation as well as anticoagulation factors can be detected in the maternal circulation prior to the clinical development of the disease in some of these syndromes. In this review, we will assess the changes in the hemostatic system during normal and complicated pregnancy in maternal blood, maternal–fetal interface and amniotic fluid, and describe the contribution of thrombosis and vascular pathology to the development of the great obstetrical syndromes.

Protein Z-deficiency is associated with enhanced neointima formation and inflammatory response after vascular injury in mice

BACKGROUND

Protein Z (PZ) is a vitamin K-dependent coagulation factor without catalytic activity. Evidence points towards PZ as an independent risk factor for the occurrence of human atherosclerotic vascular diseases. The aim of this study was to investigate the role of PZ in vascular arterial disease.

MATERIAL AND METHODS

PZ-deficient (PZ(-/-)) mice and their wild-type littermates (PZ(+/+)) were subjected to unilateral carotid artery injury by using ferric chloride and dissected 21 days thereafter for histological analysis. Human aortic smooth muscle cells (SMC) were used for in vitro wound healing assay to assess the influence of PZ on SMC migration and for cell proliferation studies.

RESULTS

Morphometric analysis of neointima formation revealed a significantly increased area and thickness of the neointima and subsequently increased luminal stenosis in carotid arteries of PZ(-/-) mice compared to PZ(+/+) mice (p < 0.05, n = 9). Immunohistochemical analysis of neointima lesion composition revealed significantly higher numbers of PCNA-positive and α-SMA-positive cells in the neointima of PZ(-/-) mice. Furthermore, PZ showed an anti-migratory potency in in vitro wound healing assay with SMCs, while no effect of PZ on SMC proliferation was detectable. Conclusion: PZ contributes to a reduced neointima formation after vascular injury, underlining the modulatory role of the coagulation cascade in vascular homeostasis.

Contribution of protein Z and protein Z-dependent protease inhibitor in generalized Shwartzman reaction

OBJECTIVE

Sepsis, a leading cause of mortality in critically ill patients, is closely linked to the excessive activation of coagulation and inflammation. Protein Z, a cofactor for the protein Z-dependent protease inhibitor, enhances the inhibition of coagulation factor Xa, and protein Z-dependent protease inhibitor inhibits factor XIa in a protein Z-independent fashion. The functions of protein Z and protein Z-dependent protease inhibitor in the inflammatory and coagulant responses to septic illness have not been evaluated.

DESIGN

For induction of generalized Shwartzman reaction, dorsal skinfold chamber-equipped mice were challenged twice with lipopolysaccharide (0.05 mg/kg on day -1 and 5 mg/kg body weight 24 hr later). Time-matched control animals received equal volumes of saline.

SETTING

University research laboratory.

SUBJECTS, INTERVENTIONS, AND MEASUREMENTS

Using intravital fluorescence microscopy in protein Z-dependent protease inhibitor deficient (ZPI) and protein Z deficient (PZ) mice, as well as their wild-type littermates (ZPI, PZ), kinetics of light/dye-induced thrombus formation and microhemodynamics were assessed in randomly chosen venules. Plasma concentrations of chemokine (C-X-C motif) ligand 1, interleukin-6, and interleukin-10 were measured. Liver and lung were harvested for quantitative analysis of leukocytic tissue infiltration and thrombus formation.

MAIN RESULTS

After induction of generalized Shwartzman reaction, all mice showed significant impairment of microhemodynamics, including blood flow velocity, volumetric blood flow, and functional capillary density, as well as leukocytopenia and thrombocytopenia. Thrombus formation time was markedly prolonged after induction of generalized Shwartzman reaction in all mice, except of ZPI mice, which also had a significantly higher fraction of occluded vessels in liver sections. PZ mice developed the highest concentrations of interleukin-6 and interleukin-10 in response to generalized Shwartzman reaction and showed greater leukocytic tissue infiltration than their wild-type littermates.

CONCLUSIONS

In this murine model of generalized Shwartzman reaction, protein Z-dependent protease inhibitor deficiency enhanced the thrombotic response to vascular injury, whereas protein Z deficiency increased inflammatory response.

The evaluation of protein Z levels of children with acute lymphoblastic leukaemia during induction therapy

The objective of this study was to evaluate the protein Z levels of children with acute lymphoblastic leukaemia (ALL) during induction therapy. Although several studies investigated the association between steroid and L-asparaginase (L-ASP) administration and levels of coagulation proteins such as protein C, protein S and antithrombin in children with ALL, protein Z levels have not been examined in any study yet. Peripheral blood was drawn from the study group before chemotherapy (PZ0) at diagnosis, at 12th day (PZ1), 15th day (PZ2), 18th day (PZ3) and 21st day (PZ4) of treatment wherein L-ASP treatment is given along with steroid administration according to ALL BFM-1995 chemotherapy protocol. Plasma protein Z levels were measured by enzyme immunoassay method. Mean protein Z level at PZ0 was 1.628 ± 0.485 μg/ml in the study group and 1.672 ± 0.662 μg/ml in the control group. No statistical difference was observed. In the study group, there was a slight increase in protein Z levels between the PZ0 and PZ1 periods in which only steroid therapy was administered. Statistically significant decrease was observed between protein Z levels in PZ0-PZ4, PZ1-PZ2, PZ1-PZ3, PZ1-PZ4 and PZ3-PZ4 periods. During the induction treatment, symptomatic haemorrhage or thrombosis was not followed up in any patients. We demonstrated that children with ALL have similar protein Z values to those of the control group at diagnosis. A significant decrease occurs at the end of the induction treatment with steroid and L-ASP administration. However, this deficiency does not result in development of symptomatic thrombosis or bleeding in these patients.

Participation of protein Z-dependent protease inhibitor and protein Z system in the pathomechanism of thrombotic complications

Thrombotic complications of unknown etiology remain a serious diagnostic and therapeutic problem. Occurrence of the inherited polymorphisms of genes encoding proteins involved in the coagulation cascade is one of the possible causes of these complications. In recent years, protein Z (PZ) and PZ-dependent protease inhibitor (ZPI) have been added to the list of prothrombotic factors. PZ is a glycoprotein serving as a cofactor of ZPI, which is responsible for the inhibition of prothrombinase. Expression of the PZ gene is under the control of many transcriptional factors; several polymorphisms alternate the rate of gene expression. The present article describes the significance of the ZPI-PZ system in venous and arterial thrombosis, adverse pregnancy outcomes and antiphospholipid syndrome complications.

Protein Z levels in pregnant Omani women: correlation with pregnancy outcome

Placental insufficiency resulting in fetal loss has been recognized in women with thrombophilic predisposition. Recent studies indicate that there is a high prevalence of protein Z (PZ) deficiency in patients with unexplained fetal loss. The objective of this study was to measure the PZ levels in pregnant Omani women in the first, second and third trimesters and correlate with the pregnancy outcome. The study enrolled 126 consecutive pregnant women after an informed consent prospectively. PZ was estimated in the first, second and third trimester in 15, 97 and 66 pregnant women respectively and they were followed for pregnancy outcomes including live birth, still birth, spontaneous abortion/induced abortion, maternal complications, fetal complications and health risks/complications in the newborn. The median PZ level (Mean ± SD) in the first, second and third trimester were 0.98 (1.07 ± 0.46), 1.3 (1.36 ± 0.61) and 1.44 (1.43 ± 0.69) (P < 0.05, Student's t-test, between first vs. second and first vs. third trimester). PZ deficiency defined as PZ level below 0.54 μg/ml (below 10th centile in the Omani population) was observed in 4 (4.7%) women, but interestingly all had a normal pregnancy outcome. Amongst the 43 subjects in whom paired PZ estimations were available, reducing PZ levels were observed from baseline values in 8 (33%) with normal pregnancy outcome; 5 (55%), with diabetes; 3 (50%) with hypertension and 2 (50%) with low birth weight respectively (P < 0.05, chi square test). PZ values increased progressively during the three trimesters of pregnancy. However, this increase is blunted in patients with abnormal pregnancy outcome like low birth weight babies or pregnancies associated hypertension or diabetes. Isolated PZ deficiency alone did not result in an abnormal outcome in this cohort of subjects.

The risk of occurrence of venous thrombosis: focus on protein Z

Protein Z (PZ) is a vitamin K-dependent factor identified in human plasma in 1984 characterized by an homology with other vitamin K-dependent factors. PZ acts as the cofactor of the PZ dependent inhibitor (ZPI), in the inhibition of activated factor X bound on phospholipid surface. In humans, PZ is characterized by an unusual wide distribution in plasma partly explained by a genetic control. Several PZ gene polymorphisms influencing plasma concentration have been described. In mice, the disruption of PZ gene is asymptomatic, but in association with homozygous FV Leiden produced a severe prothrombotic phenotype. This review analyzes the results obtained from different studies so far published in order to understand whether PZ deficiency could be considered as a risk factor for venous thrombosis. The roles of PZ plasma level and PZ gene polymorphisms remain debated with conflicting results. Many of these studies reported low PZ levels in association with an increased risk of venous thrombosis. On the other side, some studies did not observe an association between low levels of PZ and thrombotic events. A relationship between PZ deficiency and pregnancy complications was also described but not confirmed by all studies. These discrepancies can be explained by the heterogeneity of populations chosen as control, by the PZ interindividual variability and by the small size of the cohorts in mainly retrospective studies. Large prospective studies remain to be done to investigate its possible role in thrombosis.

Role of vitamin K-dependent proteins in the arterial vessel wall

Vitamin K was discovered early last century at the same time as the vitamin K-antagonists. For many years the role of vitamin K was solely ascribed to coagulation and coagulation was thought to be involved only at the venous blood side. This view has dramatically changed with the discovery of vitamin K-dependent proteins outside the coagulation cascade and the role of coagulation factors at the arterial side. Vitamin K-dependent proteins are involved in the regulation of vascular smooth muscle cell migration, apoptosis, and calcification. Vascular calcification has become an important independent predictor of cardiovascular disease. Vitamin K-antagonists induce inactivity of inhibitors of vascular calcification, leading to accelerated calcification. The involvement of vitamin K-dependent proteins such as MGP in vascular calcification make that calcification is amendable for intervention with high intake of vitamin K. This review focuses on the effect of vitamin K-dependent proteins in vascular disease.

Heparin is a major activator of the anticoagulant serpin, protein Z-dependent protease inhibitor

Protein Z-dependent protease inhibitor (ZPI) is a recently identified member of the serpin superfamily that functions as a cofactor-dependent regulator of blood coagulation factors Xa and XIa. Here we provide evidence that, in addition to the established cofactors, protein Z, lipid, and calcium, heparin is an important cofactor of ZPI anticoagulant function. Heparin produced 20-100-fold accelerations of ZPI reactions with factor Xa and factor XIa to yield second order rate constants approaching the physiologically significant diffusion limit (k(a) = 10(6) to 10(7) M(-1) s(-1)). The dependence of heparin accelerating effects on heparin concentration was bell-shaped for ZPI reactions with both factors Xa and XIa, consistent with a template-bridging mechanism of heparin rate enhancement. Maximal accelerations of ZPI-factor Xa reactions required calcium, which augmented the heparin acceleration by relieving Gla domain inhibition as previously shown for heparin bridging of the antithrombin-factor Xa reaction. Heparin acceleration of both ZPI-protease reactions was optimal at heparin concentrations and heparin chain lengths comparable with those that produce physiologically significant rate enhancements of other serpin-protease reactions. Protein Z binding to ZPI minimally affected heparin rate enhancements, indicating that heparin binds to a distinct site on ZPI and activates ZPI in its physiologically relevant complex with protein Z. Taken together, these results suggest that whereas protein Z, lipid, and calcium cofactors promote ZPI inhibition of membrane-associated factor Xa, heparin activates ZPI to inhibit free factor Xa as well as factor XIa and therefore may play a physiologically and pharmacologically important role in ZPI anticoagulant function.

A review of hereditary and acquired coagulation disorders in the aetiology of ischaemic stroke

The diagnostic workup in patients with ischaemic stroke often includes testing for prothrombotic conditions. However, the clinical relevance of coagulation abnormalities in ischaemic stroke is uncertain. Therefore, we reviewed what is presently known about the association between inherited and acquired coagulation disorders and ischaemic stroke, with a special emphasis on the methodological aspects. Good-quality data in this field are scarce, and most studies fall short on epidemiological criteria for causal inference. While inherited coagulation disorders are recognised risk factors for venous thrombosis, there is no substantial evidence for an association with arterial ischaemic stroke. Possible exceptions are the prothrombin G20210A mutation in adults and protein C deficiency in children. There is proof of an association between the antiphospholipid syndrome and ischaemic stroke, but the clinical significance of isolated mildly elevated antiphospholipid antibody titres is unclear. Evidence also suggests significant associations of increased homocysteine and fibrinogen concentrations with ischaemic stroke, but whether these associations are causal is still debated. Data on other acquired coagulation abnormalities are insufficient to allow conclusions regarding causality. For most coagulation disorders, a causal relation with ischaemic stroke has not been definitely established. Hence, at present, there is no valid indication for testing all patients with ischaemic stroke for these conditions. Large prospective population-based studies allowing the evaluation of interactive and subgroup effects are required to appreciate the role of coagulation disorders in the pathophysiology of arterial ischaemic stroke and to guide the management of individual patients.

Antiphospholipid antibody-mediated reproductive failure in antiphospholipid syndrome

The association of elevated titers of circulating antiphospholipid (anti-PL) Abs in antiphospholipid syndrome (APS) and reproductive failure is well established in the literature. The clinical features include recurrent abortions at various stages, including implantation, placentation in the first trimester, miscarriages in the second and third trimesters, intrauterine growth retardation, preeclampsia with placental insufficiency and growth restrictions, arterial and venous thrombosis, and possibly also infertility. APS-mediated recurrent pregnancy loss and other features of reproductive failure might result from diverse autoimmune factors, inflammation, involving different mechanisms, which encompass pathogenic anti-PL Abs. Herein, we discuss the association of anti-PL Abs with reproductive failure with special emphasis on antiphospholipid autoantibodies characterizing APS. This association is evident from either human studies or murine models.

Low levels of protein Z are associated with HELLP syndrome and its severity

Protein Z (PZ) was found to be associated with pregnancy complications. There are no data implying an association between hemolysis (H), elevated liver enzymes (EL), and low platelet counts (LP) (HELLP) syndrome and changes in plasma levels of PZ. The aim of this study is to investigate whether HELLP syndrome is associated with plasma concentrations of PZ. Protein Z levels in 29 women with HELLP syndrome were compared with 29 healthy, nulliparous and 25 normal pregnant women. The median PZ levels in patients with HELLP syndrome were found to be significantly lower than those of pregnant women. No significant difference was found between HELLP and healthy groups. Protein Z levels correlated with platelet counts, lactate dehydrogenase (LDH), and aspartate aminotransferase (AST) levels in patients with HELLP syndrome. Median PZ level was higher in partial HELLP than in complete HELLP. We calculated 1330 ng/mL as a cutoff value for PZ level to discriminate HELLP syndrome from normal pregnancy. Low PZ levels are associated with the pathobiology of HELLP syndrome.

[Protein Z, polymorphisms in the protein Z gene and thrombosis]

Protein Z (PZ) is a vitamin K dependent protein acting as the cofactor of the protein Z dependent inhibitor (ZPI), in the inhibition of activated factor X bound on the phospholipids. Normal plasma protein Z concentrations have wide variations among individuals, partly explained by a genetic control. Several protein Z gene polymorphisms influence plasma concentration, separately and in combination. The role of PZ in blood coagulation regulation has been demonstrated in vitro. The responsibility of low PZ level in the occurrence of thrombosis has been questioned. However, the roles of PZ plasma level and PZ gene polymorphisms remain debated with conflicting results in arterial, venous, or placental thrombosis. These discrepancies can be explained by the heterogeneity of populations chosen as control, by the PZ interindividual variability, by the small size of the cohorts in mainly retrospective studies and perhaps by the lack of real important influence of this protein on coagulation. PZ measurement is not actually considered as a biological marker of thrombophilia. Large prospective studies remain to be done to investigate its possible role in thrombosis.

Maternal anti-protein Z antibodies in pregnancies complicated by pre-eclampsia, SGA and fetal death

OBJECTIVE

Low maternal plasma protein Z (PZ) concentrations were reported in patients with pre-eclampsia (PE), a small for gestational age (SGA) neonate, and a fetal demise (FD). Anti-protein Z antibodies (APZ-AB) have been proposed as a possible underlying mechanism leading to low plasma PZ concentrations. The objective of this study was to determine the maternal plasma concentration of APZ-AB in women with a normal pregnancy, and patients with PE, an SGA neonate or a FD.

STUDY DESIGN

A cross-sectional study included women in the following groups: (1) non-pregnant women (n = 45); and pregnant women with: (2) normal pregnancies (n = 70); (3) PE (n = 123); (4) SGA neonates (n = 51); and (5) a FD (n = 51). Plasma concentrations of anti-protein Z IgM and IgG antibodies were measured by ELISA. Elevated APZ-AB was defined as >75th, 90th and 95th percentile of the normal pregnancy group. Non-parametric statistics were used for analyses.

RESULTS

(1) Patients with an SGA neonate had a higher median maternal plasma IgG APZ-AB concentration than women with normal pregnancies (p < 0.001), and patients with PE (p < 0.001) or with a FD (p = 0.001). (2) The proportion of patients with a maternal plasma IgM APZ-AB concentration >90th percentile was higher in the SGA group than in the PE group (p = 0.01). (3) Patients with PE maternal plasma IgM APZ-AB concentration >90th percentile had a higher rate of villous thrombosis (p = 0.03) and persistent muscularization of basal plate arteries (p = 0.01) than those with IgM APZ-AB concentration <90th percentile; and (5) Patients with FD and maternal plasma IgM APZ-AB concentration >90th percentile had a higher rate of umbilical phlebitis and arteritis than those with IgM APZ-AB concentration <90th percentile (p = 0.003).

CONCLUSIONS

(1) Patients with SGA neonates have a higher median plasma concentration of IgG APZ-AB than normal pregnant women, or patients with PE or FD; and (2) maternal plasma IgM APZ-AB concentration >90th percentile was associated with vascular placental lesions in patients with PE, but not in those with an SGA neonate, suggesting that in a subset of patients, these antibodies can be associated with abnormal placentation and pregnancy complications.

A meta-analysis of potential risks of low levels of protein Z for diseases related to vascular thrombosis

The relationship between protein Z levels and thrombosis is controversial. We performed a systematic review and meta-analysis of the available studies to assess the association between protein Z and vascular thrombotic diseases. We conducted an electronic literature search through MedLine, Embase, Google Scholar, Web of Science, The Cochrane Library, bibliographies of retrieved articles and abstracts of congresses up to October, 2009. Studies were included if they analysed protein Z levels in patients with vascular thrombotic diseases. After the review process, 28 case-control studies (33 patient cohorts), including 4,218 patients with thrombotic diseases and 4,778 controls, were selected for analysis. The overall analysis using a random-effects model showed that low protein Z levels were associated with an increased risk of thrombosis (odds ratio [OR] 2.90, 95% confidence interval [CI] 2.05-4.12; p<0.00001). On subgroup analysis, a significant association was found between low protein Z levels and arterial vascular diseases (OR 2.67, 95%CI 1.60-4.48; p=0.0002), pregnancy complications (OR 4.17, 95%CI 2.31-7.52; p<0.00001), and venous thromboembolic diseases (OR 2.18, 95%CI 1.19-4.00; p=0.01). The results of this meta-analysis are consistent with a role for protein Z deficiency in thrombotic diseases, including arterial thrombosis, pregnancy complications and venous thromboembolism.

Role of protein Z and protein C in neonates with respiratory distress syndrome in Egypt (experience of one centre)

The aim of this study is to evaluate Protein Z (PTZ) and protein C (PTC) levels in newborns suffering from RDS, healthy preterm and full term newborns and to compare PTZ serum levels in RDS preterm infants with healthy preterm before and after recovery. Sixty newborn infants, recruited from the neonatal unit, were enrolled in the study and divided into 3 groups: Group (I): 20 preterm with RDS, Group (II): 20 healthy preterm control newborns (CPT) and Group (III): 20 healthy full term control newborns (CFT). Protein Z and C were measured using ELISA kits. The results of the study showed lower levels of protein Z were obtained in RDS group compared to preterm controls whose levels were significantly lower than in full-term controls. A significant increase in PTZ levels in RDS' group after recovery, when compared to preterm controls. In RDS, no significant correlations existed between PTZ levels (before and after recovery) and routine investigations except for a significant negative correlation with platelets count. No significant differences were found in PTC levels between the 3 studied groups. To conclude: premature newborns suffering from RDS showed decreased serum protein Z levels than normal preterm control newborns with further increase in its pattern after recovery. Further studies are recommended to evaluate the role of PTZ on outcome in premature newborns with RDS and to evaluate the relationship between protein PTZ and PTC and other coagulation factors incriminated in the development of RDS.

Vitamin K, an example of triage theory: is micronutrient inadequacy linked to diseases of aging?

The triage theory posits that some functions of micronutrients (the approximately 40 essential vitamins, minerals, fatty acids, and amino acids) are restricted during shortage and that functions required for short-term survival take precedence over those that are less essential. Insidious changes accumulate as a consequence of restriction, which increases the risk of diseases of aging. For 16 known vitamin K-dependent (VKD) proteins, we evaluated the relative lethality of 11 known mouse knockout mutants to categorize essentiality. Results indicate that 5 VKD proteins that are required for coagulation had critical functions (knockouts were embryonic lethal), whereas the knockouts of 5 less critical VKD proteins [osteocalcin, matrix Gla protein (Mgp), growth arrest specific protein 6, transforming growth factor beta-inducible protein (Tgfbi or betaig-h3), and periostin] survived at least through weaning. The VKD gamma-carboxylation of the 5 essential VKD proteins in the liver and the 5 nonessential proteins in nonhepatic tissues sets up a dichotomy that takes advantage of the preferential distribution of dietary vitamin K1 to the liver to preserve coagulation function when vitamin K1 is limiting. Genetic loss of less critical VKD proteins, dietary vitamin K inadequacy, human polymorphisms or mutations, and vitamin K deficiency induced by chronic anticoagulant (warfarin/coumadin) therapy are all linked to age-associated conditions: bone fragility after estrogen loss (osteocalcin) and arterial calcification linked to cardiovascular disease (Mgp). There is increased spontaneous cancer in Tgfbi mouse knockouts, and knockdown of Tgfbi causes mitotic spindle abnormalities. A triage perspective reinforces recommendations of some experts that much of the population and warfarin/coumadin patients may not receive sufficient vitamin K for optimal function of VKD proteins that are important to maintain long-term health.

Crystal structure of protein Z-dependent inhibitor complex shows how protein Z functions as a cofactor in the membrane inhibition of factor X

Protein Z (PZ) binds to PZ-dependent inhibitor (ZPI) and accelerates the inhibition of the coagulation protease, activated factor X (FXa), in the presence of phospholipids and Ca2+. A 2.3A resolution crystal structure of PZ complexed with ZPI shows that ZPI is a typical serine protease inhibitor and that PZ has a serine protease fold with distorted oxyanion hole and S1 pocket. The 2 molecules bind with fully complementary surfaces spanning over 2400A(2) and involving extensive ionic and hydrophobic interactions. ZPI has an unusual shutter region with a negatively charged residue buried within the hydrophobic core of the molecule. This unique Asp(213) is critical in maintaining the balanced metastability required for optimal protease inhibition, especially when PZ is bound, with its replacement with Asn resulting in increased thermal stability, but decreased efficiency of protease inhibition. The structure of ZPI shows negatively and positively charged surfaces on top of the molecule, in keeping with mutagenesis studies in this work indicating exosite interactions with FXa when it docks on top of ZPI. As modeled in this study, the gamma-carboxy-glutamic acid-containing domains of PZ and FXa enable them to bind to the same phospholipid surfaces on platelet and other membranes, with optimal proximity for the inhibition of FXa by the complexed ZPI.

Protein Z Plasma Levels are Not Elevated in Patients with Non-Arteritic Anterior Ischemic Optic Neuropathy

Background:

Protein Z is a glycoprotein that acts as a co-factor for the inhibition of activated coagulation factor X. Protein Z circulating in abnormal levels has been associated with increased risk for acute ischemic events. Non-arteritic Anterior Ischemic Optic Neuropathy (N-AION) is caused by acute ischemic infarction of the optic nerve head, supplied by the posterior ciliary arteries.

Objectives:

The aim was to investigate whether there is an association between N-AION and plasma protein Z levels.

Patients and Methods:

Twenty-six cases of confirmed N-AION and fifty-two controls were included in the study group. Protein Z was estimated in thawed citrate plasma on both N-AION cases and controls by an enzyme immunoassay. The imprecision of the estimation was satisfactory (CV = 4, 6%).

Results:

The controls’ protein Z values distributed within a range 340 to 4200 ng/ml (median = 1420, mean = 1673, SD = 1040 ng/ml). Patients’ protein Z values distributed within a range 420 to 3600 ng/ml (median = 1030, mean = 1520, SD = 939 ng/ml). There was no statistical difference between the two distributions (Independent t-test, p=0.529).

Conclusion:

In our study, protein Z levels are not implicated in the pathogenesis of non-arteritic anterior ischemic optic neuropathy (N-AION).

Unique secretion mode of human protein Z: its Gla domain is responsible for inefficient, vitamin K–dependent and warfarin-sensitive secretion

Protein Z is a vitamin K–dependent plasma glycoprotein that is involved in the regulation of blood coagulation. Plasma concentrations of protein Z vary widely between subjects and are greatly reduced during warfarin therapy. We developed a sensitive and quantitative assay for protein secretion using a secretory luciferase to explore the mode of secretion of protein Z compared with that of factor X. Protein Z secretion was much less efficient than factor X and was totally dependent upon added vitamin K, while factor X secretion was not. Protein Z secretion was highly sensitive to warfarin treatment of the synthesizing cells. In contrast, although factor X secretion was not precluded by warfarin, its γ-carboxylation was completely blocked. An exchange of the propeptide and/or γ-carboxyglutamic acid domain between protein Z and factor X reproduced the inefficient and warfarin-sensitive secretion pattern of protein Z, and vice versa. Joining of the propeptide and γ-carboxyglutamic acid domain to luciferase also demonstrated that the γ-carboxyglutamic acid domain of protein Z was responsible for its warfarin-sensitive secretion. Thus, it was concluded that the difference observed in secretion patterns of protein Z and factor X was mainly based on the structure of their γ-carboxyglutamic acid domains.

Pregnancy-associated changes in the hemostatic system in wild-type and factor V Leiden mice

BACKGROUND

Pregnancy, oral contraceptive (OC)use and hormone replacement therapy (HRT) are established risk factors for venous thrombosis. Acquired resistance to activated protein C (APC) has been proposed to contribute to the increased thrombosis risk. Mouse models are often used for preclinical testing of newly developed hormone preparations. However, it is not known whether hormone-induced APC resistance is also observed in laboratory animals.

OBJECTIVES

To investigate whether hormonal changes modulate APC resistance in mice, we used pregnant mice as a model of hormone-induced APC resistance. The effect of pregnancy on APC resistance was studied in wild-type and factor (F)V Leiden mice.

METHODS

APC resistance was determined in mouse plasma using a thrombin generation-based APC resistance test. APC resistance determinants,i.e. prothrombin, FV, FX, antithrombin and protein S levels,and of tissue factor pathway inhibitor (TFPI) activity were evaluated in plasma from non-pregnant and pregnant mice.

RESULTS

In contrast to humans, pregnancy induced a decrease in APC resistance in wild-type and in FV Leiden mice.Pregnant mice had higher levels of prothrombin, FV, FX,protein S and TFPI activity as compared with non-pregnant mice.

CONCLUSIONS

Pregnancy causes a decrease in APC resistance in mice, which can be explained by the elevation of protein S levels and increased TFPI activity in plasma. Our findings show species specificity in the effects of pregnancy on the major determinants of the protein C system and suggest that protein S and TFPI play an important role in the development of pregnancy-induced APC resistance in humans.

Pyelonephritis during pregnancy: a cause for an acquired deficiency of protein Z

OBJECTIVE

Pyelonephritis has a more severe course during pregnancy than in the non-pregnant state. This has been attributed to the increased susceptibility of pregnant women to microbial products. An acquired protein Z deficiency has been reported when there is excessive thrombin activity. The aim of this study was to determine whether pyelonephritis during pregnancy is associated with changes in maternal plasma protein Z concentrations.

STUDY DESIGN

A cross-sectional study was conducted to compare plasma protein Z concentrations between normal pregnant women (N = 71) and pregnant women with pyelonephritis (N = 42). Protein Z concentrations were measured by enzyme-linked immunosorbent assay. Parametric and non-parametric statistics were used for analysis.

RESULTS

Patients with pyelonephritis had a significantly lower median plasma concentration of protein Z than did patients with normal pregnancies (median 2.14 microg/mL (0.4-3.4) vs. median 2.36 microg/mL (1.09-3.36); p = 0.03). There was no difference in the median plasma concentration of anti-protein Z antibodies between patients with pyelonephritis and those with normal pregnancies.

CONCLUSION

The median maternal plasma protein Z concentration was significantly lower in patients with pyelonephritis during pregnancy than in patients with normal pregnancies.

Low protein Z levels, but not the intron F G79A polymorphism, are associated with unexplained pregnancy loss

INTRODUCTION

The present case-control study was designed in order to investigate the association between plasma protein Z (PZ) levels, the intron F G79A polymorphism and unexplained pregnancy loss.

MATERIALS AND METHODS

51 women with at least two consecutive or three non-consecutive fetal losses between the 8th and 12th week of gestation and 47 apparently healthy parous women of reproductive age with no history of pregnancy loss (controls) were enrolled. Allele frequencies of the PZ intron F G79A polymorphism and PZ levels were measured.

RESULTS

PZ levels (mg/L) were significantly lower in cases (mean +/- S.D. 1.28 +/- 0.56) than controls (1.97 +/- 0.76, p < 0.001) and in carriers of the A allele (1.46 +/- 0.62), compared to GG homozygous subjects (1.72 +/- 0.81, p = 0.044). A higher proportion of cases (41.2%) were PZ-deficient (<1 mg/L), compared to controls (10.6%, p = 0.001). No significant difference in the frequency of at least one A allele carriers was observed between cases (39.2%) and controls (40.4%).

CONCLUSION(S)

It is possible that low PZ levels are a novel risk factor for unexplained recurrent miscarriage or fetal death. The presence of the F 79A allele is associated with significantly lower PZ levels, but, in the present study, was unrelated to unexplained early pregnancy loss.

Kinetic characterization of the protein Z-dependent protease inhibitor reaction with blood coagulation factor Xa

Protein Z-dependent protease inhibitor (ZPI) is a recently identified member of the serpin superfamily that functions as a cofactor-dependent regulator of blood coagulation factors Xa (FXa) and XIa. Here we show that ZPI and its cofactor, protein Z (PZ), inhibit procoagulant membrane-bound factor Xa by the branched pathway acyl-intermediate trapping mechanism used by other serpins, but with significant variations of this mechanism that are unique to ZPI. Rapid kinetic analyses showed that the reaction proceeded by the initial assembly of a membrane-associated PZ-ZPI-FXa Michaelis complex (K(M) 53+/-5 nM) followed by conversion to a stable ZPI-FXa complex (k(lim) 1.2+/-0.1 s(-1)). Cofactor premixing experiments together with independent kinetic analyses of ZPI-PZ and factor Xa-PZ-membrane complex formation suggested that assembly of the Michaelis complex through either ZPI-PZ-lipid or factor Xa-PZ-lipid intermediates was rate-limiting. Reaction stoichiometry analyses and native PAGE showed that for every factor Xa molecule inhibited by ZPI, two serpin molecules were cleaved. Native PAGE and immunoblotting showed that PZ dissociated from ZPI once ZPI forms a stable complex with FXa, and kinetic analyses confirmed that PZ acted catalytically to accelerate the membrane-dependent ZPI-factor Xa reaction. The ZPI-FXa complex was only transiently stable and dissociated with a rate constant that showed a bell-shaped pH dependence indicative of participation of factor Xa active-site residues. The complex was detectable by SDS-PAGE when denatured at low pH, consistent with it being a kinetically trapped covalent acyl-intermediate. Together our findings show that ZPI functions like other serpins to regulate the activity of FXa but in a manner uniquely dependent on protein Z, procoagulant membranes, and pH.