Plasmin cleavage of von Willebrand factor as an emergency bypass for ADAMTS13 deficiency in thrombotic microangiopathy.
BACKGROUND
Von Willebrand factor (VWF) multimer size is controlled through continuous proteolysis by ADAMTS13 (a disintegrin and metalloproteinase with a thrombospondin type I motif, member 13). This prevents spontaneous platelet agglutination and microvascular obstructions. ADAMTS13 deficiency is associated with thrombotic thrombocytopenic purpura, in which life-threatening episodes of microangiopathy damage kidneys, heart, and brain. Enigmatically, a complete ADAMTS13 deficiency does not lead to continuous microangiopathy. We hypothesized that plasmin, the key enzyme of the fibrinolytic system, serves as a physiological backup enzyme for ADAMTS13 in the degradation of pathological platelet-VWF complexes.


RESULTS
Using real-time microscopy, we determined that plasmin rapidly degrades platelet-VWF complexes on endothelial cells in absence of ADAMTS13, after activation by urokinase-type plasminogen activator or the thrombolytic agent streptokinase. Similarly, plasmin degrades platelet-VWF complexes in platelet agglutination studies. Plasminogen directly binds to VWF and its A1 domain in a lysine-dependent manner, as determined by enzyme-linked immunosorbent assay. Plasma levels of plasmin-α2-antiplasmin complexes increase with the extent of thrombocytopenia in patients with acute episodes of thrombotic thrombocytopenic purpura, independent of ADAMTS13 activity. This indicates that plasminogen activation takes place during microangiopathy. Finally, we show that the thrombolytic agent streptokinase has therapeutic value for Adamts13(-/-) mice in a model of thrombotic thrombocytopenic purpura.


CONCLUSIONS
We propose that plasminogen activation on endothelial cells acts as a natural backup for ADAMTS13 to degrade obstructive platelet-VWF complexes. Our findings indicate that thrombolytic agents may have therapeutic value in the treatment of microangiopathies and may be useful to bypass inhibitory antibodies against ADAMTS13 that cause thrombotic thrombocytopenic purpura.
Laboratory of Clinical Chemistry and Haematology (C.T., S.d.M., M.W.J.S., A.D.B., M.R., R.F., P.G.d.G., C.M.) and Laboratory of Experimental Cardiology (C.T., G.P.), UMC Utrecht, Utrecht, The Netherlands; and Laboratory for Thrombosis Research, IRF Life Sciences, KU Leuven Kulak, Kortrijk, Belgium (S.F.D.M., K.V.).
Claudia
C
Tersteeg
Steven
S
de Maat
Simon F
SF
De Meyer
Michel W J
MW
Smeets
Arjan D
AD
Barendrecht
Mark
M
Roest
Gerard
G
Pasterkamp
Rob
R
Fijnheer
Karen
K
Vanhoorelbeke
Philip G
PG
de Groot
Coen
C
Maas
D051722:ADAM Proteins / Q000235:genetics / Q000276:immunology / Q000378:metabolism*; D000071120:ADAMTS13 Protein; D000818:Animals; D001323:Autoantibodies / Q000378:metabolism; D001792:Blood Platelets / Q000378:metabolism; D004195:Disease Models, Animal; D042783:Endothelial Cells / Q000378:metabolism; D005341:Fibrinolysin / Q000378:metabolism*; D005342:Fibrinolysis / Q000502:physiology*; D005343:Fibrinolytic Agents / Q000378:metabolism / Q000494:pharmacology; D061307:Human Umbilical Vein Endothelial Cells; D006801:Humans; D051379:Mice; D008810:Mice, Inbred C57BL; D018345:Mice, Knockout; D008970:Molecular Weight; D010958:Plasminogen / Q000378:metabolism; D011697:Purpura, Thrombotic Thrombocytopenic / Q000378:metabolism; D013300:Streptokinase / Q000378:metabolism / Q000494:pharmacology; D057049:Thrombotic Microangiopathies / Q000188:drug therapy / Q000378:metabolism*; D014841:von Willebrand Factor / Q000737:chemistry / Q000378:metabolism*
D001323:Autoantibodies; D005343:Fibrinolytic Agents; D014841:von Willebrand Factor; D010958:Plasminogen; D013300:Streptokinase; D005341:Fibrinolysin; D051722:ADAM Proteins; D000071120:ADAMTS13 Protein; C099604:ADAMTS13 protein, human
fibrinolysis; plasminogen; platelets; streptokinase; urokinase; von Willebrand factor