Studies on the role of microtubule and actin filament regulatory proteins in megakaryo- and thrombopoiesis

• Applicant: Professor Dr. Markus Bender
• Subject Area: Hematology, Oncology
• Term: from 2015 to 2022
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 268521205

The cytoskeleton plays a fundamental role in platelet production and function. During platelet spreading, the actin cytoskeleton undergoes rapid rearrangement, forming filopodia and lamellipodia. Controversial data have been published on the role of lamellipodia in thrombus formation. The WAVE (WASp family verprolin-homologous protein) regulatory complex, which has been shown in other cells to drive lamellipodia formation by enhancing actin nucleation via the Arp2/3 complex, is activated by Rac1 interaction with the WAVE complex subunit Cyfip1 (Cytoplasmic FMR1 Interacting Protein). In preliminary work, we analyzed Cyfip1 flox/flox Pf4-Cre mice to investigate the role of Cyfip1 in platelet function. Lamellipodia formation of mutant platelets was completely abolished on different matrices. Nevertheless, Cyfip1-deficient platelets formed stable thrombi on collagen fibers ex vivo and in two models of occlusive arterial thrombosis in vivo. Similarly, the hemostatic function and maintenance of vascular integrity during inflammation of the skin and lung were unaltered in the mutant mice. Herewith, we can show that platelet lamellipodia formation is not required for stable thrombus formation.However, one open question remains: what is the role of lamellipodia in platelet function? In this proposal, we will address this question by analyzing Cyfip1 flox/flox Pf4-Cre and Fam49b flox/flox Pf4-Cre mice. Recently, it was identified in other cells that Fam49b is a negative regulator of the WAVE complex, and that Fam49 binds activated Rac1 via a domain shared with Cyfip. Knockdown or overexpression of Fam49b strongly affected cell migration. We hypothesize that the inability of platelets to form lamellipodia structures will impair platelet migration. Thus, we will focus our studies on whether platelet lamellipodia formation is essential for platelet migration and platelet-bacteria interaction.The proposed experiments will provide new insights into the role of lamellipodia in platelet function.

• DFG Programme: Independent Junior Research Groups