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813 Platelet ERO1α Is Crucial for Ca2+ Mobilization and Platelet Activation in Atherothrombosis

Program: Oral and Poster Abstracts
Type: Oral
Session: 301. Vasculature, Endothelium, Thrombosis and Platelets: Basic and Translational: Mechanistic Insights That Suggest Novel Diagnostic or Therapeutic Strategies
Hematology Disease Topics & Pathways:
Bleeding and Clotting, Fundamental Science, Research, platelet disorders, Diseases, thrombotic disorders
Monday, December 12, 2022: 3:15 PM

Vishwanath Jha, PhD1*, Tripti Kumari2*, Bei Xiong3*, Kyungho Kim, PhD4*, Jingzhi Wang, Ph.D5*, Gavriel Brown, BS6*, Nathan Asquith, PhD7*, John Gallagher, BS6*, Lillian Asherman8*, Yanyan Bai9*, Xiaoping Du, MD, PhD10*, Jeong-Ki Min11*, Babak Razani12*, Joseph E. Italiano Jr., Ph.D.13, Jin-Moo Lee, MD, PhD14* and Jaehyung Cho, PhD15

1Division of Hematology, Washington University in St. Louis, SAINT LOUIS, MO
2Washington University in St. Louis, St. Louis, MO
3Department of Hematology, Zhongnan Hospital of Wuhan University, Wuhan, China
4Department of Pharmacology, University of Illinois At Chicago, Chicago, IL
5Washington University, St. Louis
6Washington University School of Medicine, Washington University, Saint Louis, MO
7Boston Childrens Hospital, Boston, MA
8Washington University, Saint Louis, MO
9University of Illinois at Chicago, Chicago, IL
10Department of Pharmacology, The University of Illinois, Chicago, IL
115Biotherapeutics Translational Research Center, Korea Research Institute of Bioscience and Biotechnology (KRIBB), Daejeon, Korea, Republic of (South)
12Department of Pathology and Immunology, Washington university, St. Louis, MO
13Department of Medicine, Harvard Medical School and Boston Childrens Hospital, Boston, MA
14Mallinckrodt Institute of Radiology, Washington University School of Medicine, Saint Louis, MO
15Division of Hematology, Department of Medicine, Washington University School of Medicine, Saint Louis, MO

Endoplasmic reticulum oxidoreductase 1α (ERO1α) is a key oxidase of protein disulfide isomerase (PDI) during protein folding in the ER. Platelet ERO1α was reported to interact with PDI and αIIbβ3 integrin and regulate platelet function. However, the regulatory mechanism and pathophysiological role remain unknown. In the present study, we demonstrate that platelet ERO1α orchestrates intracellular Ca2+ signaling during platelet activation and contributes to thrombogenesis. Intravital microscopy using megakaryocyte-specific Ero1α conditional knockout (CKO) and KO mice reveals that platelet ERO1α is crucial for platelet thrombus formation in mouse models of laser-induced cremaster arteriolar thrombosis and FeCl3-induced carotid arterial thrombosis. Deletion of Ero1α does not affect bleeding times and blood loss at the site of tail amputation, implying that ERO1α is not required for hemostasis. Studies using Ero1α-null platelets, novel function-blocking antibodies, and small-molecule inhibitors reveal that intracellular, but not extracellular, ERO1α promotes P-selectin exposure, αIIbβ3 integrin activation, and platelet aggregation induced by multiple agonists, such as thrombin and collagen-related peptide. Importantly, the regulatory function of ERO1α is independent of PDI activity. Mass spectrometry and immunoprecipitation assays identify stromal interaction molecule 1 (STIM1) and sarco/endoplasmic reticulum Ca2+-ATPase 2 (SERCA2) as ERO1α binding partners. We have found that ERO1α-STIM1 binding is enhanced during platelet activation, whereas ERO1α-SERCA2 binding is reduced. Intriguingly, platelet ERO1α interacts with STIM1 through Cys49 and Cys56 residues and promotes its function by oxidizing the Cys49-Cys56 disulfide bond, contributing to Ca2+ store content and enhancing Ca2+ mobilization during platelet activation. Using a high throughput screen, we identify a small-molecule ERO1α inhibitor, B20, which inhibits ERO1α activity with an IC50 value of 10.0 μM but does not affect the activities of H2O2 and PDI. Treatment of platelets with B20 recapitulates the functional defects as seen in Ero1α-null platelets. Intravenous injection of B20 and eptifibatide, an αIIbβ3 integrin antagonist, into WT mice significantly inhibits platelet thrombus formation following laser- or FeCl3-induced vascular injury. While treatment of mice with eptifibatide markedly prolongs tail bleeding times and causes blood loss, B20 does not impair hemostatic function. Furthermore, treatment with B20 reduces the infarct volume in ischemic stroke. These results indicate that platelet ERO1α is a novel regulator of Ca2+ signaling and promotes platelet activation and aggregation in a PDI-independent manner, contributing to the pathogenesis of arterial thrombosis and thromboinflammation. Targeting ERO1α may be an attractive therapeutic strategy for treating patients with thrombotic disease.

Disclosures: No relevant conflicts of interest to declare.

*signifies non-member of ASH