Deletion of the Arp2/3 complex in megakaryocytes leads to microthrombocytopenia in mice

Actin reorganization regulates key processes in platelet activation. Here we examined the role of the Arp2/3 complex, an essential component in actin filament branching, in platelet function. The Arpc2 gene, encoding the p34 subunit of the Arp2/3 complex, was deleted in the megakaryocyte lineage (Arpc2(fl/fl)PF4-Cre). Deletion of the Arp2/3 complex resulted in marked microthrombocytopenia in mice, caused by premature platelet release into the bone marrow compartment and impaired platelet survival in circulation. Arpc2(fl/fl)PF4-Cre platelets exhibited alterations in their actin cytoskeleton and their peripheral microtubule coil. Thrombocytopenia was alleviated following clodronate liposome-induced macrophage depletion in Arpc2(fl/fl)PF4-Cre mice. Arpc2(fl/fl)PF4-Cre platelets failed to spread and showed a mild defect in integrin activation and aggregation; however, no significant differences in hemostasis or thrombosis were observed between Arpc2(fl/fl)PF4-Cre and control mice. Thus, Arp2/3 is critical for platelet homeostasis but plays only a minor role for vascular hemostasis.