Regulation of Thrombopoiesis by the Inhibitor of MyoD Family A (I-mfa)

Abstract The differentiation of megakaryocytes (Mk) from hematopoietic stem and progenitor cells (HSPC) is crucial to homeostasis and requires tight regulation. Cell-intrinsic factors skew HSPCs towards the Mk lineage and promote terminal differentiation, but this regulatory network is not yet well understood. The Inhibitor of MyoD Family A (I-mfa) is a protein which interacts with multiple pathways, including β-catenin/TCF/LEF and JNK which have known roles in HSPC differentiation. This led us to examine the role of I-mfa in hematopoiesis, hypothesizing that it promotes Mk differentiation by regulating cellular signaling events. Mice which completely lack I-mfa expression (I-mfa KO) had reduced percentages of Mk/Erythroid Progenitors (MEPs) in the bone marrow compared to WT animals by flow cytometry, as well as reduced platelet counts in peripheral blood. To examine the potential role for I-mfa in thrombopoiesis, K562 cells (which show PMA-induced Mk differentiation) were transfected with a vector for doxycycline-induced overexpression of I-mfa, and differentiation was assessed by flow cytometry for Mk surface markers. Cells overexpressing I-mfa showed increased differentiation with a higher proportion of CD61+, CD71− cells compared to parent. The mechanism underlying this effect is being examined by analyzing cellular signaling after PMA stimulation and identifying I-mfa binding partners over time. This work demonstrates a role for I-mfa in the regulatory control of hematopoiesis and lineage commitment through its regulation of thrombopoiesis. These results may also suggest that I-mfa could be an important cellular regulator in hematopoietic disorders including anemia, bone marrow failure, or hematological malignancies. Supported by NIH T32 Immunology Training Grant AI00763316A1