Regular Article THROMBOSIS AND HEMOSTASIS Expression of a structurally constrained von Willebrand factor variant triggers acute thrombotic thrombocytopenic purpura in mice

• Introduction of a disulfide bond within the A2 domain renders VWF highly thrombogenic and resistant to proteolysis. • Expression of mVWF/ p.S1494C-p.A1534C in mice triggers an acute onset of thrombotic thrombocytopenic purpura. Thrombotic thrombocytopenic purpura (TTP) is a life-threatening disease that presents with thrombocytopenia, disseminated thrombosis, hemolytic anemia, and organ dysfunction. The etiology of TTP has revealed that patients share a deficiency in plasma protease a disintegrin and metalloproteinase with a thrombospondin type 1 motif, member 13 (ADAMTS13), the enzyme responsible for cleaving ultra-large von Willebrand factor (VWF) multimers into nonthrombogenic fragments. Therefore, existing TTP mouse models were developed by targeted disruption of the ADAMTS13 gene. ADAMTS13 mice are mostly asymptomatic in the absence of a trigger, as redundant proteases appear to take on VWF processing. As an alternative approach to creating one such model,wedevisedastrategybasedon theexpressionof acleavage-resistantVWFmutant inmice. The creationof a disulfidebondwithin theA2domainof VWFwas found to render VWF multimers resistant to proteolysis by plasma proteases under flow. Furthermore, mice expressing the murine VWF/p.S1494C-p.A1534C mutant present with symptoms characteristicsof acuteTTPsuchas thrombocytopenia, redcell shredding, accumulation of VWF-rich thrombi in the microvasculature, and advanced TTP symptoms such as renal dysfunction and splenomegaly. Because this model appears to faithfully emulate the pathophysiology of TTP, it should prove most useful in the study of microangiopathic diseases and their treatment. (Blood. 2014;123(21):3344-3353)