Non-Activating Integrin β3(R734C) Mutation Associated with Macrothrombocytopenia and Impaired Platelet Function

• Published in: Blood 2023-11, Vol.142 (Supplement 1), p.2564-2564
• Main Authors: Nakata, Keiichi, Akuta, Keigo, Endo, Takaya, Koike, Midori, Kato, Hisashi, Tomiyama, Yoshiaki, Hosen, Naoki, Kashiwagi, Hirokazu
• Format: Article
• Language: English
• ISSN: 0006-4971; 1528-0020
• DOI: 10.1182/blood-2023-178475

Introduction We and others identified several mutations in ITGA2B or ITGB3 associated with congenital macrothrombocytopenia. These mutations are located around transmembrane domains of αIIb or β3, and basically induce constitutive activation of αIIbβ3. Recently, we identified a mutation, β3(R734C), which is located in cytoplasmic tail of β3 without inducing αIIbβ3 activation in a Japanese family with macrothrombocytopenia. We analyzed the effect of the mutation on platelet production and function using knock-in (KI) mice. Cases and Transfection assay The proband was a 14-year-old Japanese girl, who showed macrothrombocytopenia with 60-90 x 10 9/L platelet counts and mild bleeding tendency. Her mother, her maternal aunt and a cousin also showed macrothrombocytopenia. The expression of αIIbβ3 on their platelets was decreased to ~50% of healthy control. GPVI expression was decreased, whereas GPIb expression was increased probably due to the increase in platelet size. Genetic analysis revealed that all affected subjects were heterozygous of β3(R734C) mutation. No PAC-1 binding was observed to the platelets of the affected subjects or αIIbβ3(R734C)-transfected 293T cells, indicating that the mutation does not cause αIIbβ3 activation. Methods and Results of mouse studies We generated β3(R734C) KI mouse (C57BL6/J background) by CRISPR/Cas9-mediated genome editing. The β3(R734C) KI mice were viable with no apparent bleeding tendency. Platelet counts of heterozygous (Hetero), and homozygous (Homo) KI mice were decreased relative to those of wild-type (WT) mice [WT: 1095 ± 52 (x10 9/L), Hetero: 834 ± 93**, Homo: 445 ± 30** (mean±SD, **P