Structure of von Willebrand factor-cleaving protease (ADAMTS13), a metalloprotease involved in thrombotic thrombocytopenic purpura

Role of reduced ADAMTS13 in arterial ischemic stroke: a pediatric cohort study

OBJECTIVE

Previous studies in adults and mice have implicated ADAMTS13 (a disintegrin and metalloproteinase with a thrombospondin type 1 motif, member 13), also known as von Willebrand factor (VWF)-cleaving protease, as a protective factor for stroke. Here we investigated ADAMTS13 in 208 pediatric patients with arterial ischemic stroke (AIS) and 125 population-based control children in a frequency-matched case-control study.

METHODS

The proportion of patients/controls with ADAMTS13 activity levels below and above the 10th percentile was compared. Additionally, in a quintile comparison, the proportion of patients versus controls in the lowest ADAMTS13 quintile was compared to those in the 2nd to 5th quintiles. Adjustment was performed for VWF antigen (VWF:Ag), factor VIII activity (FVIII:C), blood group, and age.

RESULTS

Forty-six of 208 patients (22%) showed ADAMTS13 levels below the 10th percentile, compared with 5 of 125 controls (4%; p < 0.001). Odds ratios/95% confidence intervals were 7.30/2.73-19.50 for the lowest percentile and 2.44/1.15-5.16 in the quintile comparison after adjustment for VWF:Ag, FVIII:C, blood group, and age. Comparing the proportion of patients with ADAMTS13 activity below the 10th percentile within the different stroke subtypes (undetermined, cardioembolic, steno-occlusive arteriopathies), no statistically significant differences were found (undetermined, 16 of 89; cardioembolic, 6 of 40; steno-occlusive arteriopathies, 24 of 79; p = 0.08). ADAMTS13 levels did not significantly differ among stroke subtypes (p = 0.29).

INTERPRETATION

Our findings implicate reduced ADAMTS13 activity as a risk factor for pediatric AIS, and support the concept that ADAMTS13 has a role in the pathogenesis of pediatric AIS.

Emerging Roles of ADAMTSs in Angiogenesis and Cancer

A Disintegrin-like And Metalloproteinase with ThromboSpondin motifs—ADAMTSs—are a multi-domain, secreted, extracellular zinc metalloproteinase family with 19 members in humans. These extracellular metalloproteinases are known to cleave a wide range of substrates in the extracellular matrix. They have been implicated in various physiological processes, such as extracellular matrix turnover, melanoblast development, interdigital web regression, blood coagulation, ovulation, etc. ADAMTSs are also critical in pathological processes such as arthritis, atherosclerosis, cancer, angiogenesis, wound healing, etc. In the past few years, there has been an explosion of reports concerning the role of ADAMTS family members in angiogenesis and cancer. To date, 10 out of the 19 members have been demonstrated to be involved in regulating angiogenesis and/or cancer. The mechanism involved in their regulation of angiogenesis or cancer differs among different members. Both angiogenesis-dependent and -independent regulation of cancer have been reported. This review summarizes our current understanding on the roles of ADAMTS in angiogenesis and cancer and highlights their implications in cancer therapeutic development.

Hypercoagulability and cardiovascular disease in diabetic nephropathy

Diabetic nephropathy is the leading cause of end stage renal disease (ESRD) and an important risk factor for cardiovascular disease. Recent studies have shown that increased plasma levels of Von Willebrand factor (VWF) and reduced plasma levels of enzyme ADAMTS13 are associated with diabetic nephropathy and an increased risk of developing cardiovascular disease, suggesting that these markers of hypercoagulability may contribute to an increased risk of cardiovascular disease in diabetic patients with impaired renal function. However, it is still not clear whether VWF and ADAMTS13 are only markers of cardiovascular events or whether they play an active role in the development of these events. It is also unclear how renal injury may affect ADAMTS13 levels, leading consequently to hypercoagulability. The association of diabetic nephropathy, atherosclerotic cardiovascular disease and these hypercoagulability markers is discussed in this review. Insights on the role that renal dysfunction and other possible mechanisms may have in ADAMTS13 metabolism, leading to reduced levels of this enzyme and increased hypercoagulability are also presented.

Presence of anti-ADAMTS13 antibodies in obesity

BACKGROUND

The low-grade chronic inflammation present in obesity has been recognized as a risk factor for thrombosis, atherosclerosis and cardiovascular complications. In this context, production by adipose organ of a number of inflammatory adipokines could play a crucial role. It has been reported that obesity represents a risk factor for acquired thrombotic thrombocytopenic purpura (TTP), a disease caused by ADAMTS13 deficiency because of anti-ADAMTS13 antibodies, but the pathophysiological link between obesity and TTP is still unknown. We aimed to investigate mechanisms linking obesity to risk of TTP.

MATERIALS AND METHODS

Eighty obese patients consecutively admitted to Bariatric Unit of Padua between 2006 and 2009, and 39 lean subjects were characterized by anthropometric, metabolic and inflammatory parameters. ADAMTS13 autoantibodies, activity and antigen levels, and several cytokines including thrombospondin-1 were measured.

RESULTS

21.3% of obese patients were positive for noninhibitory ADAMTS13 autoantibodies, while all lean subjects were negative (P<0.01). No differences in ADAMTS13 activity and antigen levels were found. Thrombospondin-1 levels were significantly higher in obese than in lean subjects (974.4 ± 592.7 vs. 318.9 ± 202.1 ng/mL; P<0.001) and were inversely correlated with ADAMTS13 activity (R=-0.4853; P<0.001). Dot blot suggests that anti-ADAMTS13 antibodies in obese patients bind recombinant thrombospondin-1.

CONCLUSIONS

We suggest that anti-ADAMTS13 antibodies are directed against thrombospondin domains shared between ADAMTS13 and thrombospondin-1 and that their generation may be sustained by high levels of thrombospondin-1. This phenomenon could be of relevance, because little is known on the pathogenesis of TTP and its possible link with obesity.

Age dependency of coagulation parameters during childhood and puberty

BACKGROUND

Use of age-adjusted reference values is crucial for correct diagnosis and management of thrombotic and hemorrhagic disease in children. They vary with utilized reagents and analyzers.

OBJECTIVES

We established reference values with the Sysmex CA-1500 System and in parallel with the Behring BCS System using reagents from Siemens Healthcare Diagnostics Products GmbH.

METHODS

After informed consent, blood samples were obtained from 218 healthy children and 52 healthy adults, grouped as 1-6 months (n = 29), 7-12 months (n = 25), 1-5 years (n = 57), 6-10 years (n = 57), 11-18 years (n = 50) and > 19 years (n = 52).

RESULTS

Most coagulation parameters demonstrate good comparability between analyzers with the exception of PT and APTT. Single coagulation factors fibrinogen, factor (F) II, FIX, FXI and XII were significantly decreased in the youngest children; the strongest age dependency was found for coagulation inhibitors Protein C and S, both significantly decreased in infancy and young childhood. We confirmed that high levels of von Willebrand factor are found in the youngest children without increased levels of FVIII followed by decreased von Willebrand levels in the subsequent age group. In children with blood group O a less distinct increase in time was found, compared with individuals with one of the other blood groups.

CONCLUSIONS

The correlation between the CA-1500 and the BCS system was remarkable. Differences were most pronounced between children < 12 months and older children and adults, confirming the phenomenon of developmental hemostasis. The rationale for age-related changes in the hemostatic system remains unraveled. Our results underline the need for age-specific reference ranges.

ADAMTS13 and Von Willebrand factor in patients undergoing hemodialysis

Hemodialysis (HD) is associated with increasing thrombotic trend. Vascular access thrombosis (VAT) increases morbidity in HD patients. The aim of this study was to evaluate ADAMTS13 and VWF plasma levels from patients undergoing HD as putative biomarkers of the hypercoagulability state, as well the association between these markers and VAT occurrence. This study included 195 patients on HD for more than 6 months. HD patients were allocated into two groups according to the occurrence or not of previous episode of VAT; HD with VAT (N = 46) and HD without VAT (N = 149). ADAMTS13 and VWF were performed by ELISA. There was no significant difference between HD patients with and without VAT for ADAMTS13 and VWF levels. However, VWF levels were higher (P < 0.001) and ADAMTS13 were lower (P < 0.001) in HD patients, comparing to the control group composed by healthy subjects without kidney disease, age and sex-matched (N = 80). Taken together our data suggest a potential role of the kidneys function compromised on ADAMTS13 synthesis or metabolism, regardless other known sources of ADAMTS13. The imbalance between ADAMTS13 and VWF levels does not explain the development of VAT in HD patients by itself, although it should contribute for the hypercoagulability state. Therefore, additional studies to identify other risk factors are warranted and essential for better management of HD patients.

Unwinding the von Willebrand factor strings puzzle

von Willebrand factor (VWF) is amongst others synthesized by endothelial cells and stored as ultra-large (UL) VWF multimers in Weibel-Palade bodies. Although UL-VWF is proteolysed by ADAMTS13 (a disintegrin-like and metalloprotease domain with thrombospondin type-1 motif, number 13) on secretion from endothelial cells, in vitro experiments in the absence of ADAMTS13 have demonstrated that a proportion of these UL-VWF multimers remain anchored to the activated endothelium. These multimers unravel, bind platelets, and wave in the direction of the flow. These so-called VWF "strings" have also been visualized in vivo, lining the lumen of activated mesenteric veins of Adamts13(-/-) mice. Various studies have demonstrated the extraordinary length of these VWF strings, the availability of their platelet binding and ADAMTS13 cleavage sites, and the possible nature of their endothelial attachment. VWF strings are also capable of tethering leukocytes and parasite-infected red blood cells. However, the majority of studies have been performed in the absence of ADAMTS13, a condition only experienced in thrombotic thrombocytopenic purpura. A normal functional role of VWF strings in healthy persons or in other disease pathologies remains unclear. In this review, we discuss some of the puzzling characteristics of VWF strings, and we debate whether the properties of VWF strings in the absence of ADAMTS13 might be relevant for understanding (patho)physiologic mechanisms.

The unfolded von Willebrand factor response in bloodstream: the self-association perspective

von Willebrand factor (vWF) is a multimeric glycoprotein essential for hemostasis after vascular injury, which modulates platelet-surface and platelet–platelet interactions by linking platelet receptors to the extracellular matrix and to each other. The crucial role of vWF in platelet function is particularly apparent when hemodynamic conditions create blood flow with high shear stress. Through multiple functional domains, vWF mediates the attachment of platelets to exposed tissues, where immobilized vWF is able to support a homotypic and/or heterotypic self-association. The self-association of vWF is also supported by a rapidly expanding reservoir of novel evidences that the thiol/disulfide exchange regulates vWF multimer size in the blood circulation. Moreover, in addition to proteolysis and reduction of ADAMTS13 (a disintegrin and metalloproteinase with a thrombospondin type 1 motif, member 13), the regulation of vWF multimer size and self-association may depend on a disulfide bond reductase activity ascribed to thrombospondin-1 (TSP-1). Along with the classical signaling pathways in activated platelets, evidence is emerging that lipid rafts also play important roles in various phases of hemostasis and thrombosis and facilitate the interaction between the key signaling molecules. Developments in these areas will refine our understanding of the role played by vWF self-association in physiological hemostasis and pathological thrombosis.

A disintegrin-like and metalloprotease domain containing thrombospondin type 1 motif-like 5 (ADAMTSL5) is a novel fibrillin-1-, fibrillin-2-, and heparin-binding member of the ADAMTS superfamily containing a netrin-like module

ADAMTS-like proteins are related to ADAMTS metalloproteases by their similarity to ADAMTS ancillary domains. Here, we have characterized ADAMTSL5, a novel member of the superfamily with a unique modular organization that includes a single C-terminal netrin-like (NTR) module. Alternative splicing of ADAMTSL5 at its 5' end generates two transcripts that encode different signal peptides, but the same mature protein. These transcripts differ in their translational efficiency. Recombinant ADAMTSL5 is a secreted, N-glycosylated 60kDa glycoprotein located in the subcellular matrix, on the cell-surface, and in the medium of transfected cells. RT-PCR and western blot analysis of adult mouse tissues showed broad expression. Western blot analysis suggested proteolytic release of the NTR module in transfected cells as well as in some mouse tissues. Immunostaining during mouse organogenesis identified ADAMTSL5 in musculoskeletal tissues such as skeletal muscle, cartilage and bone, as well as in many epithelia. Affinity-chromatography demonstrated heparin-binding of ADAMTSL5 through its NTR-module. Recombinant ADAMTSL5 bound to both fibrillin-1 and fibrillin-2, and co-localized with fibrillin microfibrils in the extracellular matrix of cultured fibroblasts, but without discernible effect on microfibril assembly. ADAMTSL5 is the first family member shown to bind both fibrillin-1 and fibrillin-2. Like other ADAMTS proteins implicated in microfibril biology through identification of human and animal mutations, ADAMTSL5 could have a role in modulating microfibril functions.

Endothelial cells and thrombotic microangiopathy

Thrombotic microangiopathy represents the clinical picture of thrombocytopenia and hemolytic anemia in the setting of small blood vessel thrombosis, accompanied by varying degrees of organ dysfunction. Well known to both nephrologists and hematologists alike, among the most common and best-studied thrombotic microangiopathy are hemolytic-uremic syndrome and thrombotic thrombocytopenic purpura. Despite sharing a strong clinical and historical relationship, these disorders represent distinct clinical and pathophysiological entities. This article reviews recent progress into the pathogenesis of thrombotic thrombocytopenic purpura and hemolytic-uremic syndrome, focusing on events taking place at the endothelial surface.

A phenotype-genotype correlation of ADAMTS13 mutations in congenital thrombotic thrombocytopenic purpura patients treated in the United Kingdom

BACKGROUND

ADAMTS13 mutations play a role in thrombotic thrombocytopenic purpura (TTP) pathogenesis.

OBJECTIVES

To establish a phenotype-genotype correlation in a cohort of congenital TTP patients.

PATIENTS/METHODS

Clinical history and ADAMTS13 activity, antigen and anti-ADAMTS13 antibody assays were used to diagnose congenital TTP, and DNA sequencing and in vitro expression were performed to identify the functional effects of the ADAMTS13 mutations responsible.

RESULTS

Seventeen (11 novel) ADAMTS13 mutations were identified in 17 congenital TTP patients. All had severely reduced ADAMTS13 activity and antigen levels at presentation. Six patients with pregnancy-associated TTP and six patients with childhood TTP were homozygous or compound heterozygous for ADAMTS13 mutations located in the metalloprotease (MP), cysteine-rich, spacer and/or distal thrombospondin type 1 domains. The adults had TTP precipitated by pregnancy, and had overall higher antigen levels (median, 30 ng mL(-1) ; range, < 10-57 ng mL(-1) ) than the children (median, 14 ng mL(-1) ; range, < 10-40 ng mL(-1)). Presentation in the neonatal period was associated with more intensive treatment requirements. The two neonates with the most severe phenotype had mutations in the first thrombospondin type 1 motif of ADAMTS13 (p.R398C, p.R409W, and p.Q436H). Using transfected HEK293T cells, we have shown that p.R398C and p.R409W block ADAMTS13 secretion, whereas p.Q436H allows secretion at reduced levels.

CONCLUSIONS

This study confirms the heterogeneity of ADAMTS13 defects and an association between ADAMTS13 genotypes and TTP phenotype.

Relationship between ABO blood groups and von Willebrand factor, ADAMTS13 and factor VIII in patients undergoing hemodialysis

Several studies have demonstrated that non-O blood groups subjects present an increased VTE risk as compared to those carrying O blood group. The aim of this study was to investigate the ABO blood groups influence on factor VIII (FVIII) activity, von Willebrand factor (VWF), and ADAMTS13 plasma levels in patients undergoing hemodialysis (HD). Patients undergoing HD (N=195) and 80 healthy subjects (control group) were eligible for this cross-sectional study. The ABO blood group phenotyping was performed by the reverse technique. FVIII activity was measured through coagulometric method, and VWF and ADAMTS13 antigens were assessed by ELISA. FVIII activity and VWF levels were significantly higher and ADAMTS13 levels was decreased in HD patients, as compared to healthy subjects (P < 0.001, in three cases). HD patients carrying non-O blood groups showed a significant increase in FVIII activity (P = 0.001) and VWF levels (P < 0.001) when compared to carriers of O blood group. However, no significant difference was observed in ADAMTS13 levels (P = 0.767). In the control group, increased in FVIII activity (P = 0.001) and VWF levels (P = 0.002) and decreased in ADAMTS13 levels (P = 0.005) were observed in subjects carrying non-O blood groups as compared to carriers of O blood group.Our data confirmed that ABO blood group is an important risk factor for increased procoagulant factors in plasma, as FVIII and VWF. Admitting the possible role of kidneys in ADAMTS13 synthesis or on its metabolism, HD patients were not able to increase ADAMTS13 levels in order to compensate the increase of VWF levels mediated by ABO blood groups. Considering that non-O blood groups constitute a risk factor for thrombosis, it is reasonable to admit that A, B and AB HD patients need a careful and continuous follow-up in order to minimize thrombotic events.

ADAMTS-13 activity and autoantibodies classes and subclasses as prognostic predictors in acquired thrombotic thrombocytopenic purpura

BACKGROUND

Thrombotic thrombocytopenic purpura (TTP) is a rare life-threatening disease. Of surviving patients, 45% develops an exacerbation or a late recurrence. Severe ADAMTS-13 deficiency, both during the acute episode and remission, is a well-established predictor of recurrence. The predictive value of anti-ADAMTS-13 antibodies, their inhibitory activity and Ig class subtype for disease recurrence is still to be established.

OBJECTIVES

To analyze ADAMTS-13-related biomarkers (ADAMTS-13 and anti-ADAMTS-13 immunoglobulins, classes and subclasses) and their potential relationship with prognosis.

PATIENTS/METHODS

In 115 patients with TTP, we assessed the association between levels of these biomarkers and the severity of acute episodes; we analysed also the hazard ratio (HR) and 95% confidence interval (CI) of recurrence in association with biomarkers levels retrieved at the previous acute episode or during remission, using Cox regression models.

RESULTS

During the acute phase, higher IgA, IgG1 and IgG3 titers showed the strongest association with acute episode severity. In the survival analyzes, the only biomarker significantly associated with a high hazard of recurrence after an acute episode was the presence of IgG. Conversly, low ADAMTS-13 activity or antigen levels (<10%), the presence of ADAMTS-13 inhibitor or IgG during remission were all significantly associated with a higher hazard of recurrence.

CONCLUSIONS

Both the Ig class and subclass are of predictive value for acute episode severity in patients with TTP. Although markers that could predict the risk of recurrence in the acute phase are limited, a thorough assessment of ADAMTS-13-related parameters during remission is warranted.

G, Shapiro A, Okunji C, Kosti I, Shomron N, Grigoryan V, Przytycka TM, Sauna ZE, Salari R, Mandel-Gutfreund Y, Komar AA, Kimchi-Sarfaty C. Characterization of coding synonymous and non-synonymous variants in ADAMTS13 using ex vivo and in silico approaches

Synonymous variations, which are defined as codon substitutions that do not change the encoded amino acid, were previously thought to have no effect on the properties of the synthesized protein(s). However, mounting evidence shows that these “silent” variations can have a significant impact on protein expression and function and should no longer be considered “silent”. Here, the effects of six synonymous and six non-synonymous variations, previously found in the gene of ADAMTS13, the von Willebrand Factor (VWF) cleaving hemostatic protease, have been investigated using a variety of approaches. The ADAMTS13 mRNA and protein expression levels, as well as the conformation and activity of the variants have been compared to that of wild-type ADAMTS13. Interestingly, not only the non-synonymous variants but also the synonymous variants have been found to change the protein expression levels, conformation and function. Bioinformatic analysis of ADAMTS13 mRNA structure, amino acid conservation and codon usage allowed us to establish correlations between mRNA stability, RSCU, and intracellular protein expression. This study demonstrates that variants and more specifically, synonymous variants can have a substantial and definite effect on ADAMTS13 function and that bioinformatic analysis may allow development of predictive tools to identify variants that will have significant effects on the encoded protein.

Identification of epitopes on ADAMTS13 recognized by a panel of monoclonal antibodies with functional or non-functional effects on catalytic activity

INTRODUCTION

von Willebrand factor (VWF) cleavage by ADAMTS13 is mediated by multi-step interactions between their multi-domain structures. To clarify the relationship between inhibitory effects of monoclonal antibodies and epitopes on each ADAMTS13 domain, we analyzed how each ADAMTS13 domain contributes to catalyze VWF using a mouse anti-ADAMTS13 monoclonal antibody panel.

MATERIALS AND METHODS

FRETS-VWF73 assay was used to examine the effects of 14 anti-ADAMTS13 monoclonal antibodies on the catalytic activity of plasma ADAMTS13. Epitope mapping was performed using phage surface display. Libraries expressing peptide fragments of ADAMTS13 were screened with the monoclonal antibodies.

RESULTS

Eleven epitopes of 14 monoclonal antibodies were successfully defined. Three monoclonal antibodies recognizing metalloprotease or disintegrin-like domains strongly inhibited the catalytic activity and their epitopes were on Gln159-Asp166, Tyr 305-Glu327, and Asn308-Glu376. Five monoclonal antibodies recognizing TSP1-3 to -7 repeats showed weak inhibitory effects, and their epitopes were on Pro744-Ala806, Pro856-Cys864, Gln892-Gly940, Cys1007-Cys1072, and Gln1163-Asn1185. Four monoclonal antibodies recognizing the TSP1-1, TSP1-2, CUB1 or CUB2 domains had no inhibitory effects, and their epitopes, except that for TSP1-1, were Pro682-Cys742, Thr1200-Cys1213, and Gln1409-Glu1414. Two monoclonal antibodies recognizing cysteine-rich and spacer domains showed moderate inhibitory effects, but their epitopes were not determined.

CONCLUSIONS

We revealed the epitopes of 11 monoclonal anti-ADAMTS13 antibodies on each of the domains and clarified their association with inhibitory effects on VWF catalysis under static conditions. Catalytic activity correlated strongly with the epitopes on metalloprotease and disintegrin-like domains, weakly with those on TSP1-3 to -7 repeats, and negatively with those on TSP1-1, -2, and CUB domains.

Genetic ablation of Adamts13 gene dramatically accelerates the formation of early atherosclerosis in a murine model

OBJECTIVE

ADAMTS13 (a disintegrin and metalloprotease with thrombospondin type 1 repeats-13) cleaves von Willebrand factor, thereby modulating thrombosis and inflammation. Low plasma ADAMTS13 activity is associated with cardiovascular events, including myocardial and cerebral infarction. Here, we investigated the role of ADAMTS13 in the development of early atherosclerosis in a murine model.

METHODS AND RESULTS

Apolipoprotein E-null (ApoE(-/-)) and Adamts13-null (Adamts13(-/-)) ApoE(-/-) mice were fed with a high-fat Western diet for 12 weeks. Atherosclerotic lesions in the aorta and aortic roots were quantified after staining. Leukocyte rolling and adhesion onto cremaster venules after oxidative injury were determined by intravital microscopy. Although plasma cholesterol levels were largely similar in both groups, the extent of atherosclerotic lesions in the aorta en face and in the aortic roots in the Adamts13(-/-)ApoE(-/-) mice increased ≈ 5.5-fold (P=0.0017) and ≈ 6.1-fold (P=0.0037), respectively. In addition, the ratio of plasma high- to low-molecular-weight von Willebrand factor multimers increased ≈ 3-fold. The leukocyte rolling velocities were significantly reduced (P<0.001), with an increased number of leukocyte rolling (P=0.0026) and macrophage infiltration into the atherosclerotic lesions in the Adamts13(-/-)ApoE(-/-) mice.

CONCLUSIONS

Our results suggest that ADAMTS13 plays a critical role in modulating the development of early atherosclerosis, likely through the proteolytic cleavage of ultra-large von Willebrand factor multimers, thereby inhibiting platelet deposition and inflammation.

ADAMTS13 promotes angiogenesis and modulates VEGF-induced angiogenesis

Plasma ADAMTS13 deficiency results in the clinical disorder thrombotic thrombocytopenic purpura. However, other potential pathophysiological roles of ADAMTS13 in endothelial cell biology remain unexplored. To assess the possible role of ADAMTS13 and its interactions with VEGF-mediated angiogenesis, the effects of ADAMTS13 on human umbilical vein endothelial cell (HUVEC) were studied in Matrigel tube formation, proliferation, cell migration, and scratch wound assays. Treatment of endothelial cells with exogenous recombinant full-length ADAMTS13 alone promoted angiogenesis in a dose-dependent manner. HUVEC incubated with 200 ng/mL ADAMTS13 (1.4 nM) resulted in a 65% increase in cell tube formation when compared to the EBM-2 control. HUVEC treated with 30 ng/mL ADAMTS13 (204.1 pM) resulted in an 83% increase in proliferation in a visual counting assay, whereas HUVEC treated with 10 ng/mL ADAMTS13 (68.0 pM) yielded a 295% increase in EC migration in a Boyden chamber assay. In contrast, ADAMTS13 inhibited VEGF-induced angiogenesis in a dose-dependent manner, with 200ng/mL inhibiting tube formation by 35%. HUVEC co-incubated with ADAMTS13 and an antibody to the ADAMTS13 thrombospondin domains 5-7 reversed the inhibition of tube formation. HUVEC treated with 30 ng/mL ADAMTS13 and 6.2 ng/mL (323.0 pM) VEGF proliferated 40% slower than the VEGF control after 24 h of incubation as measured by visual counting assay. Treatment of HUVEC with 6.2 ng/mL VEGF and 10 ng/mL ADAMTS13 inhibited cell migration by 48%, compared to the VEGF control. Substitution of ADAMTS13 with truncated ADAMTS13 (deletion of C-terminal TSP1 domain) did not significantly increase angiogenesis or suppress VEGF-induced angiogenesis, suggesting that the TSP1 domain is involved in ADAMTS13 angiogenic activities. Co-immunoprecipitation experiments provided further evidence that ADAMTS13 binds to VEGF via its TSP1 domain.

Donor age affects liver regeneration during early period in the graft liver and late period in the remnant liver after living donor liver transplantation

BACKGROUND

The aim of the present study was to evaluate the influence of donor age on liver regeneration and surgical outcomes in recipients and donors.

PATIENTS AND METHODS

Among 101 cases of adult-to-adult living donor liver transplantation (LDLT) between March 2002 and March 2011, according to donor age: younger (Y) <50 years of age or older (O) ≥ 50 years of age, the donors and recipients using right (R) or left (L) graft were divided into groups Y/R (n = 51) and O/R (n = 17), and groups Y/L (n = 26) and O/L (n = 7), respectively. Remnant liver volume (RemLV) and graft liver volume (GLV) were estimated by computed tomography (CT) volumetry. A disintegrin and metalloprotease with thrombospondin type I domain 13 (ADAMTS13) activities and von Willebrand factor (vWF) antigen levels were measured as factors reflecting thrombotic microangiopathy.

RESULTS

Among the donors, RemLV/total liver volume (TLV) was lower in group O/R than in group Y/R, although there were no significant differences by t-test with the Bonferroni correction (rough p value = 0.02 at 6 months and rough p value > 0.05 at 1, 3, and 12 months). Donor age (≥ 50 years) was independently correlated with impaired remnant liver regeneration at 6 months in right lobe LDLT (p = 0.04). Among the recipients, GLV/standard liver volume (SLV) was lower during the first month, although there were no significant differences between the two groups by t-test with the Bonferroni correction (rough p value = 0.03 at 1 week and rough p value >0.05 at 2 weeks and 1 and 3 months). Donor age (≥ 50 years) was independently correlated with impaired graft liver regeneration at 1 week in both right and left lobe LDLT (p < 0.05). ADAMTS13 activities were lower in group O/R than in group Y/R, although there were no significant differences by t-test with the Bonferroni correction (rough p value = 0.049 on postoperative days (POD) 1 and 28 and rough p value >0.05 on POD 7 and 14). vWF/ADAMTW13 ratios were higher on POD 14, although there were no significant differences between the two groups by t-test with the Bonferroni correction (rough p value = 0.044 on POD 14 and rough p value >0.05 on POD 1, 7, 14, and 28).

CONCLUSIONS

The surgical outcomes using older donor livers for LDLT were comparable to those using younger donor livers. When using older donor livers, however, we should pay attention to the liver volume for recipients as well as donors, because older donor livers might have impaired regenerative ability.

Residual plasmatic activity of ADAMTS13 is correlated with phenotype severity in congenital thrombotic thrombocytopenic purpura

The quantification of residual plasmatic ADAMTS13 activity in congenital thrombotic thrombocytopenic purpura (TTP) patients is constrained by limitations in sensitivity and reproducibility of commonly used assays at low levels of ADAMTS13 activity, blunting efforts to establish genotype-phenotype correlations. In the present study, the residual plasmatic activity of ADAMTS13 was measured centrally by surface-enhanced laser desorption/ionization time-of-flight mass spectrometry (limit of detection = 0.5%) in 29 congenital TTP patients. The results were used to study correlations among ADAMTS13 genotype, residual plasmatic activity, and clinical phenotype severity. An ADAMTS13 activity above 0.5% was measured in 26 (90%) patients and lower levels of activity were associated with earlier age at first TTP episode requiring plasma infusion, more frequent recurrences, and prescription of fresh-frozen plasma prophylaxis. Receiver operating characteristic curve analysis showed that activity levels of less than 2.74% and 1.61% were discriminative of age at first TTP episode requiring plasma infusion < 18 years, annual rate of TTP episodes > 1, and use of prophylaxis. Mutations affecting the highly conserved N-terminal domains of the protein were associated with lower residual ADAMTS13 activity and a more severe phenotype in an allelic-dose dependent manner. The results of the present study show that residual ADAMTS13 activity is associated with the severity of clinical phenotype in congenital TTP and provide insights into genotype-phenotype correlations.

ADAMTS-13 is produced by glial cells and upregulated after spinal cord injury

ADAMTS-13, a member of the family of disintegrins and metalloproteinases with thrombospondin motifs, is produced primarily in the liver, particularly by hepatic stellate cells. This metalloproteinase cleaves von Willebrand factor multimers and thereby regulates blood coagulation. Here, we investigated the expression of ADAMTS-13 in the central nervous system. ADAMTS-13 mRNA was expressed in cultured astrocytes and microglia but not in neurons. The protein production of ADAMTS-13 was also detected in these cultured glial cells. Furthermore, we found that the expression of ADAMTS-13 was significantly increased in the rat spinal cord after injury. Supporting the in vivo data, ADAMTS-13 protein was detected in GFAP- and CD11b-positive glial cells in injured spinal cord. Consistent with this, the proteolytic activity of ADAMTS-13 was increased after spinal cord injury. Our data suggest that ADAMTS-13 may have a critical role in the central nervous system, particularly after neuronal injuries.

Left atrial blood stasis and Von Willebrand factor-ADAMTS13 homeostasis in atrial fibrillation

OBJECTIVE

Left atrial blood stasis is associated with increased risk for left atrial appendage thrombus (LAAT) and stroke in atrial fibrillation (AF). Von Willebrand factor (VWF) is associated with thromboembolism in AF. VWF thrombogenic activity is proportional to multimer size, which is regulated by VWF-cleaving protease (ADAMTS13).

METHODS AND RESULTS

To assess the association between left atrial blood stasis and VWF-ADAMTS13 system, plasma VWF antigen (VWF:Ag), VWF activity (VWF:Act), and ADAMTS13 activity were measured in 414 consecutive patients with nonvalvular AF (age 63±13 years; 25% women) and in 100 patients (age 64±14 years; 39% women) with normal sinus rhythm. Spontaneous echocardiographic contrast (SEC), left atrial appendage emptying velocity, and LAAT were assessed by transesophageal echocardiography. Presence and intensity of SEC varied directly with VWF:Ag and VWF:Act but not with ADAMTS13 activity. AF patients with LAAT had higher VWF:Ag (200±61 versus 155±52, P=0.0006) and VWF:Act (179±57 versus 141±51 P=0.0026) compared with those without LAAT. VWF:Ag and VWF:Act were independent predictors of LAAT after adjustment for CHADS2 score (P=0.0179 and P=0.0497, respectively).

CONCLUSION

The association between VWF and SEC may explain the thrombotic propensity in AF. Elevated VWF:Ag may help identify AF patients at risk for LAAT.

Paradigm shift of childhood thrombotic thrombocytopenic purpura with severe ADAMTS13 deficiency

Thrombotic thrombocytopenic purpura (TTP) is a life-threatening generalized disease with pathological conditions termed thrombotic microangiopathy (TMA). TTP is thought to predominantly affect adults and to rarely occur in children. Currently, TTP is defined by a severe deficiency in the activity of ADAMTS13, a metalloprotease that specifically cleaves unusually large von Willebrand factor multimers under high shear stress. Genetic mutations in and acquired autoantibodies to ADAMTS13 cause congenital TTP (termed Upshaw-Schulman syndrome [USS]) and acquired TTP, respectively. Because of very few overt clinical signs for TTP, USS is often misdiagnosed as chronic idiopathic thrombocytopenic purpura or overlooked during childhood. However, in women with USS, pregnancy can induce thrombocytopenia followed by the development of TTP. Furthermore, early childhood cases of acquired idiopathic TTP have not been characterized. From 1998 to 2008, our institution at Nara Medical University functioned as a TMA referral center in Japan and collected a large dataset on 919 TMA patients (Intern Med 2010;49:7-15). This registry contains 324 patients with a severe deficiency in ADAMTS13 activity, including 41 patients with USS and 283 patients with acquired TTP. Of note, the latter population contains 17 patients who were enrolled as children (≤ 15years old), including 14 children with idiopathic TTP and three with connective tissue disease-associated TTP. Of the 14 patients with idiopathic TTP, five were very young children (under 2 years old). This study focused on these 58 patients (41 USS and 17 acquired TTP) who were diagnosed with a severe deficiency in ADAMTS13 activity during childhood, causing a paradigm shift in our concept of TTP.

Advantages and limits of ADAMTS13 testing in the prognostic assessment of thrombotic thrombocytopenic purpura

Thrombotic thrombocytopenic purpura (TTP) is a rare but severe disease characterized by mechanical hemolytic anemia and consumptive thrombocytopenia leading to disseminated microvascular thrombosis that causes signs and symptoms of organ ischemia and functional damage. After the elucidation of the pathophysiology of TTP, thanks to the demonstration of the congenital or acquired (autoimmune) plasma deficiency of the von Willebrand factor cleaving metalloprotease A Disintegrin And Metalloprotease with ThromboSpondin 1 repeats (ADAMTS13), a number of laboratory assays for measuring ADAMTS13 and related autoantibodies have been developed. Current knowledge on the diagnostic and prognostic value of ADAMTS13 and anti-ADAMTS13 assays is summarized in this review.

Essential domains of a disintegrin and metalloprotease with thrombospondin type 1 repeats-13 metalloprotease required for modulation of arterial thrombosis

OBJECTIVE

A disintegrin and metalloprotease with thrombospondin type 1 repeats-13 (ADAMTS13) inhibits platelet aggregation and arterial thrombosis by cleavage of von Willebrand factor. However, the structural components of ADAMTS13 required for inhibition of arterial thrombosis are not fully defined.

METHODS AND RESULTS

Using recombinant proteins and a murine model, we demonstrated that an ADAMTS13 variant truncated after either the eighth thrombospondin type 1 repeat or the spacer domain inhibits ferric chloride-induced arterial thrombosis in ADAMTS13(-/-) mice with efficacy similar to that of full-length ADAMTS13. The results obtained from monitoring thrombus formation in carotid and mesenteric arteries were highly concordant. Further analyses by site-directed mutagenesis and human monoclonal antibody inhibition assay revealed that the Cys-rich and spacer domains of ADAMTS13, particularly the amino acid residues between Arg559 and Glu664 in the spacer domain, may be critical for modulation of arterial thrombosis in vivo. Finally, the thrombosis-modulating function of ADAMTS13 and variants/mutants was highly correlated with the von Willebrand factor-cleavage activity under fluid shear stress.

CONCLUSIONS

Our results suggest that the amino terminus of ADAMTS13, specifically the variable region of the spacer domain, is crucial for modulation of arterial thromboses under (patho)physiological conditions. These findings shed more light on the structure-function relationship of ADAMTS13 in vivo and may be applicable for rational design of protein- or gene-based therapy of arterial thromboses.

Unraveling the scissile bond: how ADAMTS13 recognizes and cleaves von Willebrand factor

von Willebrand factor (VWF) is a large adhesive glycoprotein with established functions in hemostasis. It serves as a carrier for factor VIII and acts as a vascular damage sensor by attracting platelets to sites of vessel injury. VWF size is important for this latter function, with larger multimers being more hemostatically active. Functional imbalance in multimer size can variously cause microvascular thrombosis or bleeding. The regulation of VWF multimeric size and platelet-tethering function is carried out by ADAMTS13, a plasma metalloprotease that is constitutively active. Unusually, protease activity of ADAMTS13 is controlled not by natural inhibitors but by conformational changes in its substrate, which are induced when VWF is subject to elevated rheologic shear forces. This transforms VWF from a globular to an elongated protein. This conformational transformation unfolds the VWF A2 domain and reveals cryptic exosites as well as the scissile bond. To enable VWF proteolysis, ADAMTS13 makes multiple interactions that bring the protease to the substrate and position it to engage with the cleavage site as this becomes exposed by shear. This article reviews recent literature on the interaction between these 2 multidomain proteins and provides a summary model to explain proteolytic regulation of VWF by ADAMTS13.

Prediction of hepatocellular carcinoma development by plasma ADAMTS13 in chronic hepatitis B and C

BACKGROUND

Chronic liver injury evokes a wound healing response, promoting fibrosis and finally hepatocellular carcinoma (HCC), in which hepatic stellate cells play an important role. Although a blood marker of hepatic stellate cells is not known, those cells importantly contribute to the regulation of plasma a disintegrin-like and metalloproteinase with thrombospondin type-1 motifs 13 (ADAMTS13) activity, a defect of which causes thrombotic thrombocytopenic purpura.

METHODS

Plasma ADAMTS13 was evaluated in chronic hepatitis B or C patients with or without HCC.

RESULTS

Plasma ADAMTS13 activity significantly correlated with serum aspartate aminotransferase and alanine aminotransferase, liver stiffness value, and aspartate aminotransferase-to-platelet ratio index, irrespective of the presence of HCC, suggesting that it may reflect hepatocellular damage and subsequent wound healing and fibrosis as a result of hepatic stellate cell action. During the three-year follow-up period for patients without HCC, it developed in 10 among 81 patients. Plasma ADAMTS13 activity was significantly higher in patients with HCC development than in those without and was a significant risk for HCC development by univariate and multivariate analyses. Furthermore, during the one-year follow-up period for patients with HCC treated with radiofrequency ablation, HCC recurred in 55 among 107 patients. Plasma ADAMTS13 activity or antigen level was significantly higher in patients with HCC recurrence than in those without and was retained as a significant risk for HCC recurrence by multivariate analysis.

CONCLUSIONS

Higher plasma ADAMTS13 activity and antigen level was a risk of HCC development in chronic liver disease.

IMPACT

Plasma ADAMTS13 as a potential marker of hepatic stellate cells may be useful in the prediction of hepatocarcinogenesis.

von Willebrand disease

von Willebrand disease is a common inherited bleeding disorder characterized by excessive mucocutaneous bleeding. Characteristic bleeding symptoms include epistaxis, easy bruising, oral cavity bleeding, menorrhagia, bleeding after dental extraction, surgery, and/or childbirth, and in severe cases, bleeding into joints and soft tissues. There are three subtypes: types 1 and 3 represent quantitative variants and type 2 is a group of four qualitative variants: (1) type 2A-characterized by defective von Willebrand factor-dependent platelet adhesion because of decreased high-molecular-weight von Willebrand factor multimers, (2) type 2B-caused by pathologically increased von Willebrand factor-platelet interactions, (3) type 2M-caused by decreased von Willebrand factor-platelet interactions not based on the loss of high-molecular-weight multimers, and (4) type 2N-characterized by reduced binding of von Willebrand factor to factor VIII. The diagnosis of von Willebrand disease requires specialized assays of von Willebrand factor and/or molecular genetic testing of von Willebrand factor. Severe bleeding episodes can be prevented or controlled with intravenous infusions of virally inactivated plasma-derived clotting factor concentrates containing both von Willebrand factor and factor VIII. Depending on the von Willebrand disease type, mild bleeding episodes usually respond to intravenous or subcutaneous treatment with desmopressin, a vasopressin analog. Other treatments that can reduce symptoms include fibrinolytic inhibitors and hormones for menorrhagia.

ADAMTS13, FVIII, von Willebrand factor, ABO blood group assessment in preeclampsia

INTRODUCTION

Preeclampsia (PE) is a multifactorial disease characterized by high blood pressure and proteinuria after the 20th week of pregnancy. PE is associated with fibrin deposition in placental microcirculation and intrauterine fetal growth retardation. We evaluated FVIII activity, VWF and ADAMTS13 plasma levels, according to O and "non O" blood groups, in women with severe PE (sPE).

METHODS

This case-control study included 140 women; 55 pregnant with sPE, 35 normotensive pregnant and 50 non-pregnant women. VWF and ADAMTS13 antigen levels were assessed by ELISA (American Diagnostica). FVIII activity was measured by automated coagulometric method (Dade Behring) and ABO blood groups phenotyping was performed by indirect technique.

RESULTS

FVIII activity and VWF levels were significantly higher comparing either sPE to normotensive pregnant (P=0.01; P=0.05) and to non-pregnant women (P=0.00 in both cases) or normotensive pregnant and non-pregnant women (P=0.00 in both cases). A significant decrease in ADAMTS13 levels was observed comparing either sPE to normotensive pregnant (P=0.02) and non-pregnant women (P=0.00) or normotensive pregnant and non-pregnant women (P=0.00). FVIII activity and VWF levels were associated to O and "non O" blood groups only in non-pregnant women.

CONCLUSIONS

The increase of FVIII activity and VWF levels and the decrease of ADAMTS13 in sPE are not associated to O and "non O" blood groups. These alterations in hemostatic markers in sPE largely surpass those physiologically determined by ABO blood groups influence and may have masked the effect of O and "non O" groups in this disease. A concomitant analysis of VWF levels and ADAMTS13 activity and antigenic levels will be important to clarify the imbalance between these parameters found in sPE in the present study.

SNPs in ADAMTS13

The multidomain metalloprotease ADAMTS13 limits thrombus formation via the cleavage of large multimeric forms of von Willebrand factor. Deficiency of functional ADAMTS13 is associated with a number of disease pathologies including thrombotic thrombocytopenic purpura, cardiovascular disease and inflammation. To date, deficiency is known to result from mutations in the ADAMTS13 gene or from inhibitory and non-neutralizing antibodies. The exact contributory effect of genetic variation in ADAMTS13 on observable pathology is unclear, and specifically, polymorphisms of ADAMTS13 have not been the focus of much systematic study. Here we have amassed an up-to-date collection of ADAMTS13 polymorphisms described in the literature and from the National Center for Biotechnology Information’s SNP database. This article considers the effect that these polymorphisms may have on the expression and function of ADAMTS13 and speculates on their relevance in future therapies based on pharmacogenomics.

Structure and proteolytic properties of ADAMTS13, a metalloprotease involved in the pathogenesis of thrombotic microangiopathies

ADAMTS13 is a 190-kDa zinc protease encoded by a gene located on chromosome 9q34. This protease specifically hydrolyzes von Willebrand factor (VWF) multimers, thus causing VWF size reduction. ADAMTS13 belongs to the A Disintegrin And Metalloprotease with ThromboSpondin type 1 repeats (ADAMTS) family, involved in proteolytic processing of many matrix proteins. ADAMTS13 consists of numerous domains, including a metalloprotease domain, a disintegrin domain, several thrombospondin type 1 (TSP1) repeats, a cysteine-rich domain, a spacer domain, and two CUB (Complement c1r/c1s, sea Urchin epidermal growth factor, and Bone morphogenetic protein) domains. ADAMTS13 cleaves a single peptide bond (Tyr(1605)-Met(1606)) in the central A2 domain of the VWF molecule. This proteolytic cleavage is essential to reduce the size of ultralarge VWF polymers, which, when exposed to high shear stress in the microcirculation, are prone to form platelets clumps, which cause severe syndromes called thrombotic microangiopathies (TMAs). In this chapter, we (a) discuss the current knowledge of structure-function aspects of ADAMTS13 and its involvement in the pathogenesis of TMAs, (b) address the ongoing controversies, and (c) indicate the direction of future investigations.

Determination of ADAMTS13 and Its Clinical Significance for ADAMTS13 Supplementation Therapy to Improve the Survival of Patients with Decompensated Liver Cirrhosis

The liver plays a central role in hemostasis by synthesizing clotting factors, coagulation inhibitors, and fibrinolytic proteins. Liver cirrhosis (LC), therefore, impacts on both primary and secondary hemostatic mechanisms. ADAMTS13 is a metalloproteinase, produced exclusively in hepatic stellate cells, and specifically cleaves unusually large von Willebrand factor multimers (UL-VWFM). Deficiency of ADAMTS13 results in accumulation of UL-VWFM, which induces platelet clumping or thrombi under high shear stress, followed by sinusoidal microcirculatory disturbances and subsequent progression of liver injuries, eventually leading to multiorgan failure. The marked imbalance between decreased ADAMTS13 activity (ADAMTS13 : AC) and increased production of UL-VWFM indicating a high-risk state of platelet microthrombi formation was closely related to functional liver capacity, hepatic encephalopathy, hepatorenal syndrome, and intractable ascites in advanced LC. Some end-stage LC patients with extremely low ADAMTS13 : AC and its IgG inhibitor may reflect conditions similar to thrombotic thrombocytopenic purpura (TTP) or may reflect "subclinical TTP." Hence, cirrhotic patients with severe to moderate deficiency of ADAMTS13 : AC may be candidates for FFP infusion as a source of ADAMTS13 or for recombinant ADAMTS13 supplementation. Such treatments may improve the survival of patients with decompensated LC.

Mechanism of von Willebrand factor scissile bond cleavage by a disintegrin and metalloproteinase with a thrombospondin type 1 motif, member 13 (ADAMTS13)

The platelet-tethering function of von Willebrand factor (VWF) is proteolytically regulated by ADAMTS13 (a disintegrin and metalloproteinase with a thrombospondin type 1 motif, member 13), which cleaves the Tyr1605-Met1606 (P1-P1') bond in the VWF A2 domain. To date, most of the functional interactions between ADAMTS13 and VWF that have been characterized involve VWF residues that are C terminal to the scissile bond. We now demonstrate that the substrate P3 position in VWF, Leu1603, is a critical determinant of VWF proteolysis. When VWF Leu1603 was substituted with Ser, Ala, Asn, or Lys in a short VWF substrate, VWF115, proteolysis was either greatly reduced or ablated (up to 400-fold reduction in k(cat)/K(m)). As Leu1603 must interact with residues proximate to the Zn(2+) ion coordinated in the active center of ADAMTS13, we sought the corresponding S3 interacting residues. Substitution of 10 candidate residues in the metalloprotease domain of ADAMTS13 identified two spatially separated clusters centered on Leu198 or Val195 (acting with Leu232 and Leu274, or with Leu151, respectively), as possible subsites interacting with VWF. These experimental findings using the short VWF115 substrate were replicated using full-length VWF. It is hypothesized that VWF Leu1603 interacts with ADAMTS13 Leu198/Leu232/Leu274 and that Val195/Leu151 may form part of a S1 subsite. The recognition of VWF Leu1603 by ADAMTS13, in conjunction with previously reported remote exosites C terminal of the cleavage site, suggests a mechanism whereby the VWF P1-P1' scissile bond is brought into position over the active site for cleavage. Together with recently characterized remote exosite interactions, these findings provide a general framework for understanding the ADAMTS family substrate interactions.

A Case of Thrombotic Thrombocytopenia Purpura Associated with Systemic Lupus Erythematosus: Diagnostic Utility of ADAMTS-13 Activity

Thrombotic thrombocytopenia purpura (TTP) caused by a deficiency in ADAMTS-13 activity is considered to involve a subset of thrombotic microangiopathy (TMA). Although concept of TTP is included under the umbrella of TMA, discrimination of TTP from TMA is occasionally difficult in an autoimmune disorder. Herein, we report a case with TTP associated with systemic lupus erythematosus (SLE). In this case, it was difficult to discriminate TTP from TMA and the measurement of ADAMTS-13 activity was useful for obtaining an accurate diagnosis. SLE patients having thrombocytopenia in complication with anemia should be considered a monitoring of ADAMTS-13 activity even though the patients lacked symptoms of TTP related to the microvascular coagulation.

IL-1β down-regulates ADAMTS-13 mRNA expression in cells of the central nervous system

ADAMTS-13 is the Von Willebrand factor (vWF) cleaving protease, responsible for the cleavage and down-regulation of the pro-thrombotic properties of ultra large VWF multimers. It is expressed predominantly by the hepatic stellate cells of the liver, but is also found to be expressed in other tissues, including brain. Reduced ADAMTS-13 is associated with a variety of thrombotic microangiopathies. Since the cellular origin and regulation of ADAMTS-13 expression in the brain is unknown, we aimed to investigate this in four different central nervous system (CNS)-derived cell lines, SHSY-5Y (human neuroblastoma), U373 (human astroglioma), CHME-3 (human foetal microglia) and hCMEC/D3 (adult human brain endothelial cells). All cell lines expressed ADAMTS-13 mRNA constitutively with neuroblastoma cells showing the highest expression. Interleukin (IL)-1β down-regulated ADAMTS-13 mRNA expression in astroglioma cells and microglial cells whereas TNF and IL-6 treatment showed no significant differences in ADAMTS-13 mRNA expression in any cell line tested. ADAMTS-13 protein expression was reduced in a dose-dependent manner only in astroglioma cells following stimulation by IL-1β. The ability of IL-1β to significantly reduce ADAMTS-13 mRNA expression in human microglia and astroglioma cells suggests a role in the haemostasis of the local microenvironment under inflammatory conditions. This is the first report of ADAMTS-13 expression in cells of the CNS; however, its function remains to be determined.

Molecular cloning, in vitro expression and functional characterization of canine ADAMTS13

A disintegrin and metalloproteinase with thrombospondin type 1 motifs, number 13 (ADAMTS13) is a plasma zinc metalloprotease also known as von Willebrand factor (VWF)-cleaving protease. Deficiency of ADAMTS13 activity is known to cause thrombotic thrombocytopenic purpura (TTP) in humans. We isolated the canine ADAMTS13 cDNA, which encodes 1502 amino acids, and expressed the recombinant protein to evaluate VWF-cleaving ability. Although the propeptide domain was longer and the TSP1 repeat domain was shorter than those in other species, the overall structures were similar to human and mouse ADAMTS13. Recombinant canine ADAMTS13 cleaved the 250-kDa VWF monomer into two fragments of 150 kDa and 120 kDa. Furthermore, high molecular weight VWF multimers were abolished based on the activity of ADAMTS13. These results could facilitate research into hemostatic disorders such as TTP in dogs.

A shear-based assay for assessing plasma ADAMTS13 activity and inhibitors in patients with thrombotic thrombocytopenic purpura

BACKGROUND

Severe deficiency of plasma ADAMTS13 activity is a frequent finding in patients with hereditary and acquired thrombotic thrombocytopenic purpura (TTP). To date, plasma ADAMTS13 activity is determined by cleavage of either predenatured von Willebrand factor (VWF) or small peptides derived from the VWF-A2 domain. The physiologic relevance of the assay results is uncertain.

STUDY DESIGN AND METHODS

We sought to develop a novel shear-based assay to assess plasma ADAMTS13 activity and inhibitors. We also compared this assay with a fluorogenic peptide assay.

RESULTS

We found that an incubation of purified plasma VWF with 0.5 to 1.0 µL of citrated plasma under constant vortexing at 2500 rpm for 60 minutes in the presence of 5 mmol/L CaCl(2) and 1.7 µmol/L ZnCl(2) and low concentration of NaCl resulted in the maximal cleavage of VWF. The cleavage product could be separated by a 2.5% agarose gel and detected by Western blotting. The assay revealed that plasma and recombinant ADAMTS13 are highly sensitive to inhibition by zinc and chloride ions. Under the optimal conditions, the shear-based assay appeared to be more sensitive than the guanidine-denaturization assay for determining plasma ADAMTS13 activity.

CONCLUSIONS

Our fluid shear-based assay may be useful for investigating basic biologic function and regulation of ADAMTS13 metalloprotease. It may also be applicable for assessing plasma ADAMTS13 activity and inhibitors in TTP patients.

Natural history of Upshaw-Schulman syndrome based on ADAMTS13 gene analysis in Japan

Upshaw-Schulman syndrome (USS) is an extremely rare hereditary deficiency of ADAMTS13 activity, termed congenital TTP. The clinical signs are usually mild during childhood, often with isolated thrombocytopenia. But their symptoms become more evident when patients have infections or get pregnant. We identified 43 USS-patients in Japan, who ranged in age from early childhood to 79 years of age. Analysing the natural history of these USS patients based on ADAMTS13 gene mutations may help characterise their clinical phenotypes. Severe neonatal jaundice that requires exchange blood transfusion, a hallmark of USS, was found in 18 of 43 patients (42%). During childhood, 25 of 43 patients were correctly diagnosed with USS without gender disparity. These 25 patients were categorised as having 'the early-onset phenotype'. Between 15 and 45 years of age, 15 were correctly diagnosed, and, interestingly, they were all female. The remaining three patients were male and were diagnosed when they were older than 45 years of age, suggesting that they were 'the late-onset phenotype'. Two of these three males developed sudden overt TTP when they were 55 and 63 years old, respectively. These two men had two different homozygous ADAMTS13 gene mutations, p.R193W/p.R193W and p.C1024R/p.C1024R, respectively. Both of which were not discovered in the US or Western countries. In vitro expression studies showed that these two proteins were consistently secreted into the culture medium but to a lesser extent and with reduced activity compared to the wild-type protein. Our results indicate that 'the late-onset phenotype' of USS is formed with ethnic specificity.

Native multimer analysis of plasma and platelet von Willebrand factor compared to denaturing separation: implication for the interpretation of satellite bands

Blue native electrophoresis (BNE) was applied to analyze the von Willebrand factor (vWF) multimers in their native state and to present a methodology to perform blue native electrophoresis on human plasma proteins, which has not been done before. The major difference between this method and the commonly used SDS-agarose gel electrophoresis is the lack of satellite bands in the high-resolution native gel. To further analyze this phenomenon, a second dimension was performed under denaturing conditions. Thereby, we obtained a pattern in which each protein sub-unit from the first dimension dissociates into three distinct sub-bands. These bands confirm the triplet structure, which consists of an intermediate band and two satellite bands. By introducing the second dimension, our novel method separates the triplet structure into a higher resolution than the commonly used SDS-agarose gel electrophoresis does. This helps considerably in the classification of ambiguous von Willebrand's disease subtypes. In addition, our method has the additional advantage of being able to resolve the triplet structure of platelet vWF multimers, which has not been identified previously through conventional SDS-agarose electrophoresis multimer analysis. This potential enables us to compare the triplet structure from platelet and plasmatic vWF, and may help to find out whether structural abnormalities concern the vWF molecule in the platelet itself, or whether they are due to the physiological processing of vWF shed into circulation. Owing to its resolution and sensitivity, this native separation technique offers a promising tool for the analysis and detection of von Willebrand disorder, and for the classification of von Willebrand's disease subtypes.