Inactivation of ADAMTS13 by plasmin as a potential cause of thrombotic thrombocytopenic purpura.
BACKGROUND
ADAMTS13 deficiency causes accumulation of unusually large von Willebrand factor molecules, which cross-link platelets in the circulation or on the endothelial surface. This process of intravascular agglutination leads to the microangiopathy thrombotic thrombocytopenic purpura (TTP). Most TTP patients have acquired anti-ADAMTS13 autoantibodies that inhibit enzyme function and/or clear it from the circulation. However, the reason for ADAMTS13 deficiency is not always easily identified in a subset of patients.


OBJECTIVE
To determine the origin of ADAMTS13 deficiency in a case of acquired TTP.


METHODS
Western blotting of ADAMTS13 in plasmas from acute and remission phases was used.


RESULTS
The ADAMTS13 deficiency was not caused by mutations or (detectable) autoantibodies; however, an abnormal ADAMTS13 truncated fragment (100 kDa) was found in acute-phase but not remission-phase plasma. This fragment resulted from enzymatic proteolysis, as recombinant ADAMTS13 was also cleaved when in the presence of acute-phase but not remission-phase plasma. Inhibitor screening showed that ADAMTS13 was cleaved by a serine protease that could be dose-dependently inhibited by addition of exogenous α₂ -antiplasmin. Examination of the endogenous α₂-antiplasmin antigen and activity confirmed deficiency of α₂ -antiplasmin function in acute-phase but not remission-phase plasma. To investigate the possibility of ADAMTS13 cleavage by plasmin in plasma, urokinase-type plasminogen activator was added to an (unrelated) congenital α₂ -antiplasmin-deficient plasma sample to activate plasminogen. This experiment confirmed cleavage of endogenous ADAMTS13 similar to that observed in our TTP patient.


CONCLUSIONS
We report the first acquired TTP patient with cleaved ADAMTS13 and show that plasmin is involved.
Feys
H B
HB
Laboratory for Thrombosis Research, Katholieke Universiteit Leuven Campus Kortrijk, Kortrijk, Belgium.
Vandeputte
N
N
Palla
R
R
Peyvandi
F
F
Peerlinck
K
K
Deckmyn
H
H
Lijnen
H R
HR
Vanhoorelbeke
K
K
D051722:ADAM Proteins / Q000037:antagonists & inhibitors* / Q000502:physiology; D000071120:ADAMTS13 Protein; D000328:Adult; D001323:Autoantibodies / Q000737:chemistry; D015551:Autoimmunity; D015153:Blotting, Western; D005341:Fibrinolysin / Q000378:metabolism; D006801:Humans; D008297:Male; D009154:Mutation; D017434:Protein Structure, Tertiary; D011697:Purpura, Thrombotic Thrombocytopenic / Q000097:blood* / Q000378:metabolism; D012074:Remission Induction; D000979:alpha-2-Antiplasmin / Q000378:metabolism*
D001323:Autoantibodies; D000979:alpha-2-Antiplasmin; D005341:Fibrinolysin; D051722:ADAM Proteins; D000071120:ADAMTS13 Protein; C099604:ADAMTS13 protein, human