Vo, Karen

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  • Publication
    Fli1 Expression Levels During Megakaryopoiesis Affect Thrombopoiesis And Platelet Biology
    (2017-01-01) Vo, Karen
    Friend Leukemia Virus Integration 1 (FLI1) is a critical transcription factor (TF) in terminal megakaryocyte differentiation. It is amongst the genes missing from an inherited hemizygous deletion on chromosome 11q termed Jacobsen syndrome and often results in a dysmegakaryopoiesis and macrothrombocytopenia termed Paris Trousseau syndrome (PTSx) described as being due to FLI1 allelic exclusion. It has also been reported that heterozygote FLI1 mutations in its DNA-binding domain region cause thrombocytopenia in patients suspected to have inherited platelet defects. To date, there are no reports containing comprehensive in vitro or in vivo characterization of platelet defects due to heterozygous FLI1 deletion or mutations, or that of platelets expressing increased levels of FLI1. We used induced pluripotent stem cell (iPSC)- derived megakaryocytes (iMegs) to determine if the platelet disorder observed in PTSx could be replicated, either with iPSCs generated from a PTSx patient or from a targeted heterozygous knockout of FLI1 (FLI1+/-) in control iPSCs. These studies indicate that PTSx and FLI1+/- iMegs replicate many of the clinical features described in PTSx and showed more in vitro injury to the resulting iMegs with fewer platelets released in vivo. These platelets had shortened half-lives and were functionally defective. We then examined whether increased levels of FLI1 would affect megakaryopoiesis and thrombopoiesis, and found an increased number of iMegs with less in vitro injury compared to control iMegs. FLI1-overexpressing iMegs also released more platelets in recipient mice with increased half-life and functionality. These studies confirm FLI1 heterozygosity results in defects in megakaryopoiesis and thrombopoiesis similar to that noted with other megakaryocyte-specific TFs, but unlike those TFs, FLI1 overexpression is not associated with quality or quantitative platelet deficiencies, but improved yield and functionality that may have clinical applicability.