Exploring the mechanisms of action of anti-ADAMTS 13 antibodies in immune thrombotic thrombocytopenic purpura

项目总结/文摘

Project Summary/Abstract Immune thrombotic thrombocytopenic purpura (iTTP) is a thrombotic microangiopathy caused by autoimmune inhibition of the enzyme ADAMTS13. The only known substrate of ADAMTS13 is von Willebrand factor (VWF). Cleavage of VWF by ADAMTS13 is needed to prevent accumulation of ultralarge VWF multimers in the microvasculature, leading to end-organ damage and potentially life-threatening consequences. Anti-ADAMTS13 IgGs are responsible for the inhibition of the enzyme. The vast majority of inhibitory antibodies target a region of ADAMTS13 that is principally responsible for binding to the domain of VWF cleaved by the enzyme. However, the mechanism of inhibition of these antibodies is currently an area of active research, and it is not known if they primarily prevent substrate binding or decrease catalytic turnover, or if different antibodies inhibit by different mechanisms. Recent work has shown that ADAMTS13 in iTTP patient plasma exists primarily in a conformation that exposes a cryptic epitope otherwise hidden when ADAMTS13 is in its latent state. The current paradigm of ADAMTS13 activity defines this as a so-called “Open” state, and the latent state as “Closed”. A third state also appears to exist in which ADAMTS13 has the cryptic episode exposed, but also is able to cleave VWF; this is referred to here as the “Open and Primed” state. Anti-ADAMTS13 IgGs that target distal domains of the protein appear capable of inducing both the “Open” and “Open and Primed” state. The role of the different conformations of ADAMTS13 in the pathophysiology of iTTP is unclear, as is the potential role of the distal domain-targeting IgGs in the disease. Lastly, it is not known if ADAMTS13 activity can be rescued by introducing moieties capable of competing for the binding of anti-ADAMTS13 IgGs with ADAMTS13. This project aims to elucidate the mechanism(s) of inhibition of anti-ADAMTS13 antibodies, characterize the role of distal domain-targeting anti- ADAMTS13 antibodies in the pathophysiology of the disease, and explore molecular mimics of the binding epitopes of anti-ADAMTS13 IgGs as a rescue strategy for the disease. My career goal is to become an independent investigator as a physician scientist, with a focus on the pathophysiology of iTTP. I am currently on the tenure-track as an Assistant Professor in the Department of Internal Medicine, Division of Hematologic Malignancies and Cellular Therapeutics, at the University of Kansas Medical Center (KUMC), a large academic center. My research mentor is Dr. X. Long Zheng, a world-renowned researcher in iTTP. I am afforded 80% protected time for research under my agreement with the University. My career development plan includes regular meetings with my Career Advisory Committee, hands-on training in the structural biology techniques included in this proposal, and ongoing clinical responsibilities, including a half-day of clinic weekly where I see patients with non-malignant hematologic disorders.