Altered B-lymphopoiesis in mice with deregulated thrombopoietin signaling

Amanda E Au,Emma C Josefsson,Pradnya Gangatirkar,Marion Lebois,Ashley P Ng,Kylie D Mason,Warren S Alexander,Diane Moujalled,Starling A Sim,Craig D Hyland,Fatme Yassinson,Benjamin T Kile,Ping Cannon,Angelika Rutgersson,Jason Corbin

doi:10.1038/s41598-017-15023-2

Abstract

Thrombopoietin (TPO) is the master cytokine regulator of megakaryopoiesis. In addition to regulation of megakaryocyte and platelet number, TPO is important for maintaining proper hematopoietic stem cell (HSC) function. It was previously shown that a number of lymphoid genes were upregulated in HSCs from Tpo−/− mice. We investigated if absent or enhanced TPO signaling would influence normal B-lymphopoiesis. Absent TPO signaling in Mpl−/− mice led to enrichment of a common lymphoid progenitor (CLP) signature in multipotential lineage-negative Sca-1+c-Kit+ (LSK) cells and an increase in CLP formation. Moreover, Mpl−/− mice exhibited increased numbers of PreB2 and immature B-cells in bone marrow and spleen, with an increased proportion of B-lymphoid cells in the G1 phase of the cell cycle. Conversely, elevated TPO signaling in TpoTg mice was associated with reduced B-lymphopoiesis. Although at steady state, peripheral blood lymphocyte counts were normal in both models, Mpl−/− Eµ-myc mice showed an enhanced preneoplastic phase with increased numbers of splenic PreB2 and immature B-cells, a reduced quiescent fraction, and augmented blood lymphocyte counts. Thus, although Mpl is not expressed on lymphoid cells, TPO signaling may indirectly influence B-lymphopoiesis and the preneoplastic state in Myc-driven B-cell lymphomagenesis by lineage priming in multipotential progenitor cells.

Highlights

B-cells in bone marrow and spleen, with an increased proportion of B-lymphoid cells in the G1 phase of the cell cycle
Mpl is not expressed on lymphoid cells, absent TPO signaling in Mpl−/− mice led to lineage priming of lineage-negative Sca-1+c-Kit+ (LSK) cells with increased numbers of common lymphoid progenitors (CLPs), PreB2 and immature B-cells
In accordance with previous findings reported in adult mice[7,15], in the setting of increased TPO signaling, we found that 4–5 week old TpoTg mice had a 4-fold increase in numbers of LSK cells and corresponding LSK subpopulations long-term hematopoietic stem cell (HSC) (LTHSCs), short-term HSCs (STHSCs) and lymphoid-primed multipotent progenitors (LMPPs) in the bone marrow when compared to wild-type mice (Fig. 1a)

Summary

Introduction

B-cells in bone marrow and spleen, with an increased proportion of B-lymphoid cells in the G1 phase of the cell cycle. Thrombopoietin (TPO), produced mainly in the liver, stimulates both megakaryocyte colony formation and enhances megakaryocyte maturation in the bone marrow leading to increased platelet production. TPO binds to its receptor, TPOR/MPL, which is expressed on hematopoietic stem cells (HSCs), megakaryocytes and platelets[2]. A low level of TPO leads to reductions in total HSCs, but with more of them in active cycle This is evident in Mpl deficient mice, which exhibit thrombocytopenia, and have increased cycling and a decline in the number of HSCs with age[8,9,10]. It has previously been reported that down-regulation of Mpl marks the transition from pluripotent to lymphoid-primed multipotent hematopoietic progenitor cells[11] and that a number of lymphoid genes are upregulated in HSCs from Tpo−/− mice[12]. We compared the effects of absent or enhanced TPO signaling on www.nature.com/scientificreports/

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