Investigation of the roles of Tropomyosin 4 and Tropomyosin 1 in hematopoiesis, platelet production and function

• Applicant: Dr. Irina Pleines
• Subject Area: Hematology, Oncology ; Cell Biology
• Term: from 2016 to 2019
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 315312020

Inherited platelet disorders are characterized by defects in megakaryopoiesis, platelet production or platelet function, and are often associated with an increased bleeding risk. It is accepted that platelet count (PLT) and platelet volume (MPV) are to a large extent genetically controlled. Genome-wide association studies (GWAS) recently identified two genes encoding the actin filament-binding proteins Tropomyosin 1 (TPM1) and Tropomyosin 4 (TPM4) as potential regulators of PLT and MPV. Virtually nothing is known about the roles of tropomyosins in hematopoietic cells. We have isolated a mouse line with an ENU-induced missense mutation in the Tpm4 gene, which results in a premature STOP codon. Tpm4 mutant mice exhibited gene dose-dependent macrothrombocytopenia, while other blood cell counts were barely affected. Strikingly, in collaboration with the BRIDGE bleeding and platelet disorders (BPD) consortium, we identified a family, in which a STOP mutation in the TPM4 gene is segregated that likewise results in macrothrombocytopenia. Remarkably, TPM4 insufficiency reduced the ability of murine and human megakaryocytes (MKs) to form proplatelets in a dose-dependent manner. Mechanistically, our results indicate that TPM4-association with actin filaments serves as a local platform regulating activation, localization and stability of multiple actin cytoskeletal regulators, which together drive the terminal stages of platelet production. In contrast to Tpm4 mutant mice, very mild thrombocytopenia with normal platelet size was observed in mice with a MK- and platelet-specific Tpm1 deficiency. In this project we will take advantage of different Tpm-transgenic mouse models to in detail investigate the roles of TPM4 and TPM1 in platelet production and platelet function in vitro and in vivo. A focus will lie on elucidating the network of TPMs and their interacting proteins in MKs and platelets by expression and localization studies in combination with cutting edge imaging techniques. Furthermore, the potential functional redundancy of TPM1 and TPM4 in the hematopoietic system will be investigated. We are confident that this strategy will enable us to gain new insights into the roles of tropomyosins, and the actin cytoskeletal network in general, in platelet production and function in both mice and humans.

• DFG Programme: Research Grants