title: Flt3/Flk-2-ligand in synergy with thrombopoietin delays megakaryocyte development and increases the numbers of megakaryocyte progenitor cells in serum-free cultures initiated with CD34+ cells.
abstract: Megakaryocytopoiesis involves proliferation and maturation of committed precursors that increase their size by polyploidy, a process that is believed to be critical for the efficient production and release of platelets. Thrombopoietin has been shown to act on proliferation, maturation, and survival pathways in megakaryocytopoiesis. Less is known about the role of Flt3/Flk-2-ligand in this development. Apoptosis has an important role in hematopoiesis in general. It has been shown to have an effect on senescent megakaryocytes but not megakaryocyte progenitor cells. In this study, a serum-free culture model was developed, differentiating bone marrow CD34(+) hematopoietic stem cells into megakaryocytes, using thrombopoietin and Flt3/Flk-2-ligand. The model was used to study the effect of these growth factors on expansion of megakaryocyte progenitor cells, differentiation of megakaryocytes, and ploidy. Our results demonstrate that bone marrow CD34(+) cells cultured with thrombopoietin and Flt3/Flk-2-ligand show a lower developmental rate into MK cells compared to cells cultured with thrombopoietin alone. Cells cultured with thrombopoietin and Flt3/Flk-2-ligand expressed less CD41, the ploidy level was lower, and they appeared less mature. On the other hand, the cells showed up to 10-fold increase in cell numbers compared to five-fold increase when cultured with thrombopoietin alone. These results suggest that Flt3/Flk-2-ligand in synergy with thrombopoietin may slow down megakaryocyte development by causing increased proliferation of megakaryocyte progenitor cells.
authors: The Blood Bank, Department of Basic Research, Landspitali-University Hospital, 101 Reykjavík, Iceland. oes@landspitali.is
authors: Olafur Eysteinn
authors: OE
authors: Sigurjónsson
authors: Kristbjörn Orri
authors: KO
authors: Gudmundsson
authors: Vilhelmína
authors: V
authors: Haraldsdóttir
authors: Thorunn
authors: T
authors: Rafnar
authors: Sveinn
authors: S
authors: Gudmundsson
authors: Kristbjörn Orri
authors: KO
authors: Guomundsson
authors: Sveinn
authors: S
authors: Guomundsson
mesh_terms: D018952:Antigens, CD34; D001854:Bone Marrow Cells / Q000166:cytology; D002452:Cell Count; D018929:Cell Culture Techniques; D002454:Cell Differentiation / Q000187:drug effects; D016895:Culture Media, Serum-Free; D004357:Drug Synergism; D015672:Erythroid Precursor Cells / Q000166:cytology / Q000187:drug effects*; D006410:Hematopoiesis / Q000187:drug effects; D006801:Humans; D008533:Megakaryocytes / Q000166:cytology / Q000187:drug effects*; D008565:Membrane Proteins / Q000494:pharmacology*; D011518:Proto-Oncogene Proteins / Q000494:pharmacology*; D020794:Receptor Protein-Tyrosine Kinases / Q000494:pharmacology*; D013926:Thrombopoietin / Q000494:pharmacology*; D051941:fms-Like Tyrosine Kinase 3
chemical_list: D018952:Antigens, CD34; D016895:Culture Media, Serum-Free; D008565:Membrane Proteins; D011518:Proto-Oncogene Proteins; C084881:flt3 ligand protein; D013926:Thrombopoietin; C497970:FLT3 protein, human; D020794:Receptor Protein-Tyrosine Kinases; D051941:fms-Like Tyrosine Kinase 3