Knock-in mice bearing constitutively active αIIb(R990W) mutation develop macrothrombocytopenia with severe platelet
Keigo Akuta1, Kazunobu Kiyomizu1, Hirokazu Kashiwagi1
1Department of Hematology and Oncology, Graduate School of Medicine, Osaka University, Suita, Japan.
Background:
To date, several mutations that induce constitutive activation of integrin αIIbβ3 have been identified in congenital macrothrombocytopenia. Of these, αIIb(R995W) is the most prevalent mutation observed in Japanese patients with αIIbβ3-related congenital macrothrombocytopenia.
Objective And Methods:
The present study aimed to explore the effects of constitutive activation of the αIIb(R995W) mutation on platelet production, morphology, and function. We generated αIIb(R990W) knock-in (KI) mice corresponding to human αIIb(R995W).
Results:
Platelet counts of heterozygous (hetero) and homozygous (homo) KI mice were decreased by ~10% and ~25% relative to those of wild-type (WT) mice, respectively, with increase in platelet size. Decrease in absolute reticulated platelet numbers in steady state, delayed recovery from thrombocytopenia induced by anti-platelet antibody and impaired response to exogenous thrombopoietin administration suggested impaired platelet production in KI mice. WT and KI mice showed no significant differences in the number of megakaryocytes and ploidy of megakaryocytes, whereas proplatelet formation was significantly impaired in homo mice. We observed a slight but significant reduction in platelet lifespan in homo mice. The homo mice showed dramatic reduction in αIIbβ3 expression in platelets, which was accompanied by severe in vivo and in vitro platelet dysfunction.
Conclusion:
The αIIb(R990W) KI mice developed macrothrombocytopenia, which was primarily attributed to impaired proplatelet formation. In addition, homo KI mice showed marked downregulation in αIIbβ3 expression in platelets with severe impaired platelet function, similar to Glanzmann thrombasthenia.
Insights
Constitutive activation of integrin αIIbβ3, specifically the R995W mutation, causes congenital macrothrombocytopenia. This study in knock-in mice reveals impaired platelet production and function, leading to macrothrombocytopenia.
Area of Science:
- Hematology
- Molecular Biology
- Genetics
Background:
- Congenital macrothrombocytopenia is linked to mutations causing constitutive activation of integrin αIIbβ3.
- The αIIb(R995W) mutation is the most common cause in Japanese patients.
Purpose of the Study:
- To investigate the impact of the αIIb(R995W) mutation on platelet production, morphology, and function.
- To model human αIIb(R995W) congenital macrothrombocytopenia using αIIb(R990W) knock-in mice.
Main Methods:
- Generation of αIIb(R990W) knock-in (KI) mouse models.
- Analysis of platelet counts, size, reticulated platelet numbers, and recovery from induced thrombocytopenia.
- Assessment of megakaryocyte number, ploidy, and proplatelet formation.
- Evaluation of platelet lifespan, αIIbβ3 expression, and in vivo/in vitro platelet function.
Main Results:
- KI mice exhibited macrothrombocytopenia with decreased platelet counts and increased size.
- Impaired proplatelet formation in homozygous KI mice was a primary cause of macrothrombocytopenia.
- Homozygous KI mice showed significantly reduced platelet lifespan and severe platelet dysfunction due to decreased αIIbβ3 expression.
Conclusions:
- The αIIb(R990W) KI mouse model accurately reflects human αIIbβ3-related congenital macrothrombocytopenia.
- Impaired proplatelet formation and severe platelet dysfunction, resembling Glanzmann thrombasthenia, characterize this condition.
