Abstract Number: PB0362
Meeting: ISTH 2022 Congress
Background: Thrombocytopenia is a common platelet disorder with a variety of etiologies, including antibody-mediated platelet activation and clearance, aberrant megakaryocyte (MK) development, infection and trauma. Clinical outcomes vary from mild purpura and bruising to severe, life-threatening bleeding. Mice lacking the immunoreceptor tyrosine-based inhibition motif-containing co-inhibitory receptor G6b-B (Mpig6b, G6b knockout, KO) are born with a complex MK/platelet phenotype characterized by severe macrothrombocytopenia, expansion of the MK population and myelofibrosis. Platelets are almost completely devoid of the GPVI-FcR gamma-chain collagen receptor complex and a subset have increased surface immunoglobulins. A strikingly similar phenotype has been recently reported in patients with null and loss-of-function mutations in MPIG6B.
Aims: To better understand the cause and treatment of macrothrombocytopenia and GPVI down-regulation in G6b KO mice.
Methods: G6b KO mice were either treated with standard therapies for macrothrombocytopenia, or crossed with mice Rag1 KO or Syk R41A loss-of-function mice to rescue the phenotype. Platelet count and volume were measured using a blood analyzer. Platelet surface receptor expression and activation were measured by flow cytometry. Platelet aggregation and secretion were measured by lumi-aggregometry.
Results: Intravenous-immunoglobulin resulted in a transient partial recovery of platelet counts in G6b KO mice, whereas crossing these mice with Rag1 KO mice, lacking B and T cells, had no effect. Treatment with the thrombopoietin mimetic Romiplostim rescued platelet count, GPVI expression and the response of G6b KO platelets to the GPVI-specific agonist collagen-related peptide. Loss-of-function of Syk tyrosine kinase (R41A) and treatment with the Syk kinase inhibitor BI1002494 rescued platelet counts and GPVI expression in G6b KO mice, whereas the Src family kinase inhibitor dasatinib did not.
Conclusion(s): These findings provide mechanistic insights into the cause of the disease and mode of action of Syk inhibitors in the treatment of congenital macrothrombocytopenia caused by mutations in G6b.
To cite this abstract in AMA style:MAZHARIAN A, Maître B, Hennequin D, Lourenco-Rodrigues M, Heising S, De la salle H, Watson S, GACHET C, Senis Y. Molecular insights into the cause and treatment of congenital thrombocytopenia in mice lacking the co-inhibitory receptor G6b-B [abstract]. https://abstracts.isth.org/abstract/molecular-insights-into-the-cause-and-treatment-of-congenital-thrombocytopenia-in-mice-lacking-the-co-inhibitory-receptor-g6b-b/. Accessed September 26, 2022.
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