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Megakaryocytes regulate hematopoietic stem cell quiescence through CXCL4 secretion


In the bone marrow, hematopoietic stem cells (HSCs) lodge in specialized microenvironments that tightly control the proliferative state of HSCs to adapt to the varying needs for replenishment of blood cells while also preventing HSC exhaustion1. All putative niche cells suggested thus far have a nonhematopoietic origin2,3,4,5,6,7,8. Thus, it remains unclear how feedback from mature cells is conveyed to HSCs to adjust their proliferation. Here we show that megakaryocytes (MKs) can directly regulate HSC pool size in mice. Three-dimensional whole-mount imaging revealed that endogenous HSCs are frequently located adjacent to MKs in a nonrandom fashion. Selective in vivo depletion of MKs resulted in specific loss of HSC quiescence and led to a marked expansion of functional HSCs. Gene expression analyses revealed that MKs are the source of chemokine C-X-C motif ligand 4 (CXCL4, also named platelet factor 4 or PF4) in the bone marrow, and we found that CXCL4 regulates HSC cell cycle activity. CXCL4 injection into mice resulted in a reduced number of HSCs because of their increased quiescence. By contrast, Cxcl4−/− mice exhibited an increased number of HSCs and increased HSC proliferation. Combined use of whole-mount imaging and computational modeling was highly suggestive of a megakaryocytic niche capable of independently influencing HSC maintenance by regulating quiescence. These results indicate that a terminally differentiated cell type derived from HSCs contributes to the HSC niche, directly regulating HSC behavior.

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Figure 1: The spatial relationship of HSCs and MKs in the bone marrow.
Figure 2: MKs maintain the quiescence of HSCs in vivo.
Figure 3: MKs control HSC quiescence through CXCL4.
Figure 4: MKs regulate HSC quiescence independently of the arteriolar niche.

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We thank C. Prophete and P. Ciero for mouse husbandry and L. Tesfa, O. Uche and J. Zhang for technical assistance with sorting. I.B. was supported by the American Society of Hematology–European Hematology Association (ASH-EHA) research exchange award and the University of Düsseldorf. S.P. is a New York Stem Cell Foundation–Druckenmiller Fellow. J.A. was supported by the Integrated Training in Pharmacological Science program, NIGMS T32 063754. This work was supported by the New York Stem Cell Foundation and the New York State Department of Health (NYSTEM Program) and by grants from the US National Institutes of Health (NIH; R01 grants DK056638 and HL069438 to P.S.F., CA164468 and DA033788 to A.B. and P01 HL110860 and U01 HL099656 to M.P.).

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Authors and Affiliations



I.B., D.L. and S.P. designed the study, performed the majority of the experiments and analyzed data. J.A. and A.B. performed computational modeling and statistical analysis of the data. M.P.L. performed imaging of CXCL4 in MKs and provided mice. C.S. and Y.K. contributed to the processing and imaging of whole-mount bone marrow tissues. L.S. genotyped mice. M.P. provided mice and interpreted data. P.S.F. and A.B. supervised the study. I.B., D.L., S.P., A.B. and P.S.F. wrote the manuscript. All authors discussed the results and commented on the manuscript.

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Correspondence to Aviv Bergman or Paul S Frenette.

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The authors declare no competing financial interests.

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Bruns, I., Lucas, D., Pinho, S. et al. Megakaryocytes regulate hematopoietic stem cell quiescence through CXCL4 secretion. Nat Med 20, 1315–1320 (2014).

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