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Mpl expression on megakaryocytes and platelets is dispensable for thrombopoiesis but essential to prevent myeloproliferation.

ABSTRACT: Thrombopoietin (TPO) acting via its receptor, the cellular homologue of the myeloproliferative leukemia virus oncogene (Mpl), is the major cytokine regulator of platelet number. To precisely define the role of specific hematopoietic cells in TPO-dependent hematopoiesis, we generated mice that express the Mpl receptor normally on stem/progenitor cells but lack expression on megakaryocytes and platelets (Mpl(PF4cre/PF4cre)). Mpl(PF4cre/PF4cre) mice displayed profound megakaryocytosis and thrombocytosis with a remarkable expansion of megakaryocyte-committed and multipotential progenitor cells, the latter displaying biological responses and a gene expression signature indicative of chronic TPO overstimulation as the underlying causative mechanism, despite a normal circulating TPO level. Thus, TPO signaling in megakaryocytes is dispensable for platelet production; its key role in control of platelet number is via generation and stimulation of the bipotential megakaryocyte precursors. Nevertheless, Mpl expression on megakaryocytes and platelets is essential to prevent megakaryocytosis and myeloproliferation by restricting the amount of TPO available to stimulate the production of megakaryocytes from the progenitor cell pool.

SUBMITTER: Ng AP

PROVIDER: S-EPMC4000844 | biostudies-literature | 2014 Apr

REPOSITORIES: biostudies-literature

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Mpl expression on megakaryocytes and platelets is dispensable for thrombopoiesis but essential to prevent myeloproliferation.

Ng Ashley P AP Kauppi Maria M Metcalf Donald D Hyland Craig D CD Josefsson Emma C EC Lebois Marion M Zhang Jian-Guo JG Baldwin Tracey M TM Di Rago Ladina L Hilton Douglas J DJ Alexander Warren S WS

Proceedings of the National Academy of Sciences of the United States of America 20140407 16

Thrombopoietin (TPO) acting via its receptor, the cellular homologue of the myeloproliferative leukemia virus oncogene (Mpl), is the major cytokine regulator of platelet number. To precisely define the role of specific hematopoietic cells in TPO-dependent hematopoiesis, we generated mice that express the Mpl receptor normally on stem/progenitor cells but lack expression on megakaryocytes and platelets (Mpl(PF4cre/PF4cre)). Mpl(PF4cre/PF4cre) mice displayed profound megakaryocytosis and thrombocy ...[more]

PMID: 24711413

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Project description:Platelets are essential for hemostatic plug formation and thrombosis. The mechanisms of megakaryocyte (MK) differentiation and subsequent platelet production from stem cells remain only partially understood. The manufacture of megakaryocytes (MKs) and platelets from cell sources including hematopoietic stem cells and pluripotent stem cells have been highlighted for studying the platelet production mechanisms as well as for the development of new strategies for platelet transfusion. The mouse bone marrow stroma cell line OP9 has been widely used as feeder cells for the differentiation of stem cells into MK lineages. OP9 cells are reported to be pre-adipocytes. We previously reported that 3T3-L1 pre-adipocytes differentiated into MKs and platelets. In the present study, we examined whether OP9 cells differentiate into MKs and platelets using MK lineage induction (MKLI) medium previously established to generate MKs and platelets from hematopoietic stem cells, embryonic stem cells, and pre-adipocytes. OP9 cells cultured in MKLI medium had megakaryocytic features, i.e., positivity for surface markers CD41 and CD42b, polyploidy, and distinct morphology. The OP9-derived platelets had functional characteristics, providing the first evidence for the differentiation of OP9 cells into MKs and platelets. We then analyzed gene expressions of critical factors that regulate megakaryopoiesis and thrombopoiesis. The gene expressions of p45NF-E2, FOG, Fli1, GATA2, RUNX1, thrombopoietin, and c-mpl were observed during the MK differentiation. Among the observed transcription factors of MK lineages, p45NF-E2 expression was increased during differentiation. We further studied MK and platelet generation using p45NF-E2-overexpressing OP9 cells. OP9 cells transfected with p45NF-E2 had enhanced production of MKs and platelets. Our findings revealed that OP9 cells differentiated into MKs and platelets in vitro. OP9 cells have critical factors for megakaryopoiesis and thrombopoiesis, which might be involved in a mechanism of this differentiation. p45NF-E2 might also play important roles in the differentiation of OP9 cells into MK lineages cells.

Project description:Normal donors BM CD34+ cells were differentiated in thrombopoietin-treated liquid suspension cultures. Briefly, CD34+ cells (80,000 /mL) were resuspended in a serum-free medium in the presence of 100 ng/mL of human recombinant thrombopoietin (TPO; Genzyme, Boston, MA). Every 3 days, viable cells were scored by Trypan blue dye exclusion and cultures were amplified with fresh serum-free medium. Each well was then supplemented with 100 ng/mL TPO. After 14 to 16 days of liquid culture, CD34-derived megakaryocytes (MKs) were purified by means of an anti-CD41a monoclonal antibody (MoAb) (Dako, Milan, Italy) directed against the glycoproteic *IIb-*3 complex and immunobeads (MPC 450 Dynabeads; Dynal, Oslo, Norway), as previously described (27). The purity of MKs was determined for each isolation by indirect immunofluorescence, using an anti-CD41b MoAb which reacts with a different epitope of *IIb-*3 subunit (Immunotech Inc., Westbrook, ME), followed by a goat anti-mouse IgG, covalently linked to fluorescein (Becton Dickinson, San Jose, CA). Essential Throbocytemia BM CD34+ cells were differentiated in thrombopoietin-treated liquid suspension cultures. Briefly, CD34+ cells (80,000 /mL) were resuspended in a serum-free medium in the presence of 100 ng/mL of human recombinant thrombopoietin (TPO; Genzyme, Boston, MA). Every 3 days, viable cells were scored by Trypan blue dye exclusion and cultures were amplified with fresh serum-free medium. Each well was then supplemented with 100 ng/mL TPO. After 14 to 16 days of liquid culture, CD34-derived megakaryocytes (MKs) were purified by means of an anti-CD41a monoclonal antibody (MoAb) (Dako, Milan, Italy) directed against the glycoproteic *IIb-*3 complex and immunobeads (MPC 450 Dynabeads; Dynal, Oslo, Norway), as previously described (27). The purity of MKs was determined for each isolation by indirect immunofluorescence, using an anti-CD41b MoAb which reacts with a different epitope of *IIb-*3 subunit (Immunotech Inc., Westbrook, ME), followed by a goat anti-mouse IgG, covalently linked to fluorescein (Becton Dickinson, San Jose, CA). Keywords: other

Dataset Information

Mpl expression on megakaryocytes and platelets is dispensable for thrombopoiesis but essential to prevent myeloproliferation.

Publications

Mpl expression on megakaryocytes and platelets is dispensable for thrombopoiesis but essential to prevent myeloproliferation.

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