FLI1 level during megakaryopoiesis affects thrombopoiesis and platelet biology

Area of Science:

• Hematology
• Molecular Biology
• Genetics

Background:

• Friend leukemia virus integration 1 (FLI1) is a key transcription factor in megakaryocyte differentiation.
• Hemizygous deletion of FLI1 causes Jacobsen syndrome and Paris-Trousseau syndrome (PTSx), a macrothrombocytopenia.
• Heterozygous FLI1 mutations are increasingly linked to thrombocytopenia.

Purpose of the Study:

• To investigate the role of FLI1 in megakaryopoiesis and platelet function using induced-pluripotent stem cell (iPSC)-derived megakaryocytes (iMegs).
• To understand the molecular mechanisms underlying FLI1 deficiency-related platelet disorders.
• To explore the therapeutic potential of FLI1 modulation.

Main Methods:

• Generated iPSCs from a patient with PTSx and a control line with heterozygous FLI1 knockout (FLI1+/-).
• Differentiated iPSCs into iMegs and analyzed megakaryocyte and platelet characteristics.
• Assessed in vitro and in vivo platelet yield, half-life, and functionality after iMeg infusion.
• Investigated the regulatory relationship between FLI1 and ETS1 in megakaryopoiesis.

Main Results:

• PTSx and FLI1+/- iMegs exhibited reduced yield and fewer released platelets.
• Platelets derived from FLI1-deficient iMegs showed impaired in vivo half-life and functionality.
• Ets1 proto-oncogene 1 (ETS1) was overexpressed in FLI1-deficient iMegs, suggesting negative regulation by FLI1.
• FLI1 overexpression in iMegs significantly increased in vitro and in vivo megakaryocyte and platelet yield, half-life, and functionality.

Conclusions:

• FLI1 heterozygosity leads to significant megakaryocyte and platelet defects, mirroring clinical syndromes like PTSx.
• FLI1 negatively regulates ETS1 expression during megakaryopoiesis.
• FLI1 overexpression demonstrates a unique therapeutic potential, improving platelet production and function, unlike other critical megakaryocyte TFs.