Author:

Keywords:

Science & Technology, Life Sciences & Biomedicine, Hematology, Peripheral Vascular Disease, Cardiovascular System & Cardiology, ADAMTS-13 protein, antibodies, epitopes, protein conformation, thrombotic thrombocytopenic purpura, VON-WILLEBRAND-FACTOR, CLEAVING PROTEASE ADAMTS13, SPACER DOMAIN, ANTI-ADAMTS13 ANTIBODIES, BINDING-SITE, DEFICIENCY, ACTIVATION, PLATELET-FACTOR-4, REMISSION, EPITOPE, ADAMTS13 Protein, Autoantibodies, Case-Control Studies, Enzyme-Linked Immunosorbent Assay, Epitope Mapping, Epitopes, Humans, Protein Binding, Protein Conformation, Protein Folding, Purpura, Thrombotic Thrombocytopenic, Structure-Activity Relationship, PROFILE - 675746;info:eu-repo/grantAgreement/EC/H2020/675746, 1102 Cardiorespiratory Medicine and Haematology, 1103 Clinical Sciences, Cardiovascular System & Hematology, 3201 Cardiovascular medicine and haematology, 3202 Clinical sciences

Abstract:

UNLABELLED: Essentials Conformational changes in ADAMTS-13 are part of its mode-of-action. The murine anti-ADAMTS-13 antibody 1C4 discriminates between folded and open ADAMTS-13. ADAMTS-13 conformation is open in acute acquired thrombotic thrombocytopenic purpura (TTP). Our study forms an important basis to fully elucidate the pathophysiology of TTP. SUMMARY: Background Acquired thrombotic thrombocytopenic purpura (aTTP) is an autoimmune disorder characterized by absent ADAMTS-13 activity and the presence of anti-ADAMTS-13 autoantibodies. Recently, it was shown that ADAMTS-13 adopts a folded or an open conformation. Objectives As conformational changes in self-antigens play a role in the pathophysiology of different autoimmune diseases, we hypothesized that the conformation of ADAMTS-13 changes during acute aTTP. Methods Antibodies recognizing cryptic epitopes in the spacer domain were generated. Next, the conformation of ADAMTS-13 in 40 healthy donors (HDs), 99 aTTP patients (63 in the acute phase versus 36 in remission), 12 hemolytic-uremic syndrome (HUS) patients and 63 sepsis patients was determined with ELISA. Results The antibody 1C4 recognizes a cryptic epitope in ADAMTS-13. Therefore, we were able to discriminate between a folded and an open ADAMTS-13 conformation. We showed that ADAMTS-13 in HDs does not bind to 1C4, indicating that ADAMTS-13 circulates in a folded conformation. Similar results were obtained for HUS and sepsis patients. In contrast, ADAMTS-13 of acute aTTP patients bound to 1C4 in 92% of the cases, whereas, in most cases, this binding was abolished during remission, showing that the conformation of ADAMTS-13 is open during an acute aTTP episode. Conclusions Our study shows that, besides absent ADAMTS-13 activity and the presence of anti-ADAMTS-13 autoantibodies, an open ADAMTS-13 conformation is also a hallmark of acute aTTP. Demonstrating this altered ADAMTS-13 conformation in acute aTTP will help to further unravel the pathophysiology of aTTP and lead to improved therapy and diagnosis.