Optimization of plasma-based BioID identifies plasminogen as a ligand of ADAMTS13

ADAMTS13, a disintegrin and metalloprotease with a thrombospondin type 1 motif, member 13, regulates the length of Von Willebrand factor (VWF) multimers and their platelet-binding activity. ADAMTS13 is constitutively secreted as an active protease and is not inhibited by circulating protease inhibitors. Therefore, the mechanisms that regulate ADAMTS13 protease activity are unknown. We performed an unbiased proteomics screen to identify ligands of ADAMTS13 by optimizing the application of BioID to plasma. Plasma BioID identified 5 plasma proteins significantly labeled by the ADAMTS13-birA* fusion, including VWF and plasminogen. Glu-plasminogen, Lys-plasminogen, mini-plasminogen, and apo(a) bound ADAMTS13 with high affinity, whereas micro-plasminogen did not. None of the plasminogen variants or apo(a) bound to a C-terminal truncation variant of ADAMTS13 (MDTCS). The binding of plasminogen to ADAMTS13 was attenuated by tranexamic acid or ε-aminocaproic acid, and tranexamic acid protected ADAMTS13 from plasmin degradation. These data demonstrate that plasminogen is an important ligand of ADAMTS13 in plasma by binding to the C-terminus of ADAMTS13. Plasmin proteolytically degrades ADAMTS13 in a lysine-dependent manner, which may contribute to its regulation. Adapting BioID to identify protein-interaction networks in plasma provides a powerful new tool to study protease regulation in the cardiovascular system.

Proteolytic inactivation of ADAMTS13 by plasmin in human plasma: risk of thrombotic thrombocytopenic purpura

Thrombotic thrombocytopenic purpura (TTP) is caused by inactivation of a von Willebrand factor (VWF)-cleaving enzyme, a disintegrin and metalloproteinase with a thrombospondin type 1 motif, member 13 (ADAMTS13), which leads to platelet-rich thrombi comprising unusually large VWF multimers. We have found that ADAMTS13 can bind to the inactivated form of plasmin. In addition, plasmin cleaves purified ADAMTS13 into several fragments and inactivates it. Hence, we hypothesized that activation of plasminogen to plasmin becomes a new-onset factor for TTP due to ADAMTS13 inactivation. Plasmin was added exogenously or activated from plasminogen by streprokinase addition in human plasma (HP). ADAMTS13 digestion and effects of the digestion on ADAMTS13 activity were evaluated. Exogenous plasmin cleaved ADAMTS13 into several fragments, but a portion of ADAMTS13 remained in full-length form. Digestion profile of ADAMTS13 with streprokinase added exogenously in HP was similar to that of ADAMTS13 with exogenous plasmin. ADAMTS13 activity measured using FRETS-VWF73 decreased to ∼40% compared with that for normal plasma. Endogenous VWF multimer-cleaving activity was attenuated more severely (∼10%). These data suggest that endogenous plasmin cleaves ADAMTS13 into fragments and reduces its activity to ∼10%. We suggest that endogenous plasmin activation alone is not sufficient to cause TTP, but plasmin activation with ADAMTS13 deficiency might increase the risk of TTP onset.

ADAMTS13 activity and genetic mutations in Japan

Thrombotic thrombocytopenic purpura (TTP), a life threatening disease, can be induced by congenital or acquired deficiency of plasma metalloprotease ADAMTS13. Since the publication of the first genetic analysis in patients with congenital ADAMTS13 deficiency in 2001, more than 100 genetic defects in the ADAMTS13 gene have been reported worldwide. Genetic analysis in patients with ADAMTS13 deficiency has greatly contributed to the understanding of the etiology of TTP. A rapid and quantitative assay method for the plasma ADAMTS13 activity was developed recently in 2005 and opened a new area of TTP research – namely genetic research using a general population to evaluate age and gender differences of ADAMTS13 activity as well as phenotype – genotype correlations of genetic polymorphisms and estimation of a homozygote or a compound heterozygote ADAMTS13 deficiencies. The Japanese general population study included 3616 individuals with an age between 30 – 80 years confirming other studies that while ADAMTS13 activity decreased with age, VWF antigen increased and VWF antigen levels are lowest in blood group O indviduals, whereas ADAMTS13 activity levels were not associated with the AB0 blood group. 25 polymorphisms with a minor allele frequency of more than 0.01 were found, among them 6 missense mutations and 19 synonymous mutations, except P475S missense polymorphisms that was only idenitified in an East Asian population, characterized by reduced ADAMTS13 activity. Prevalence of congenital ADAMTS13 deficiency in the Japanese population was estimated about one individual in 1.1 × 106 to be homozygote or compound heterozygote for ADAMTS13 deficiency. So far more than 40 mutations in Japanese congenital TTP patients were found, but R193W, Q449*, C754Afs*24 (c.2259delA) and C908Y were identified in more than four patients suggesting the precipitaion of these mutations in the Japanese population.

A role for tissue plasminogen activator in thrombotic thrombocytopenic purpura

Thrombotic thrombocytopenic purpura (TTP) is a life-threatening disease characterized by generalized microvascular occlusion. TTP has been related to severe deficiency of ADAMTS13, an enzyme that cleaves von Willebrand factor multimers into less adhesive molecules. However, ADAMTS13 deficiency correlates poorly with severity of thrombocytopenia or microangiopathic hemolysis, with the frequency of neurologic complications or the response to plasma exchange. Also, some patients with severe hereditary ADAMTS13 deficiency consistently relapse every few weeks, whereas others remain asymptomatic into their forties. Taken together, these findings suggest that an additional element is missing in the pathophysiology of TTP. We postulate that both low ADAMTS13 activity and low tissue-plasminogen activator activity are required to trigger TTP attacks. Tissue-plasminogen activator end product, plasmin, extensively degrades von Willebrand factor, breaking-down the bonds between platelets and the blood vessel wall, so that low tissue-plasminogen activator activity prevents a mechanism similar to that of ADAMTS13. The hypothesis that low tissue-plasminogen activator activity plays an important role in TTP pathogenesis is further substantiated by TTP comorbidity. Problems prevalent in patients with TTP attacks or with long-term TTP remission, including increased body mass index, major depression, cognitive abnormalities, hypertension, and premature death, are somehow associated with low tissue-plasminogen activator activity.

ADAMTS13 unbound to larger von Willebrand factor multimers in cryosupernatant: implications for selection of plasma preparations for thrombotic thrombocytopenic purpura treatment

BACKGROUND

Thrombotic thrombocytopenic purpura (TTP) is characterized by deficient ADAMTS13 activity. Treatment involves plasma exchange (PE). Both fresh-frozen plasma (FFP) and cryosupernatant (CSP) are used, but it remains to be determined which is more effective.

STUDY DESIGN AND METHODS

To analyze the interaction between von Willebrand factor (VWF) and ADAMTS13, we used large-pore isoelectric focusing (IEF) analysis followed by detection with anti-ADAMTS13 monoclonal antibody. FFP, CSP, cryoprecipitate (CP), and purified ADAMTS13 were analyzed for their effects on high shear stress-induced platelet aggregation (H-SIPA).

RESULTS

IEF analysis of normal plasma revealed three groups of ADAMTS13 bands with pI of 4.9 to 5.6, 5.8 to 6.7, and 7.0 or 7.5. Two band groups (pI 4.9-5.6 and 5.8-6.7) were found in plasma of a patient with Type 3 von Willebrand disease, in which VWF is absent, whereas no bands were found in plasma of a patient with congenital ADAMTS13 deficiency. Mixing these plasmas generated the bands at pI 7.0 or 7.5, representing the VWF-ADAMTS13 complex; these bands were absent in CSP. FFP and purified ADAMTS13 down regulated H-SIPA in a dose-dependent manner. However, CP did not inhibit H-SIPA in the initial phase, and the degree of inhibition at the endpoint was almost indistinguishable from those of the other two plasma products.

CONCLUSION

Both plasma products (FFP and CSP) are effective for PE in TTP patients. However, CSP may be more favorable, because it has lower levels of VWF and almost normal ADAMTS13 activity, but lower levels of ADAMTS13 in complex with larger VWF multimers.