Thrombopoiesis is spatially regulated by the bone marrow vasculature
David Stegner1, Judith M M vanEeuwijk2, Oğuzhan Angay3
1Institute of Experimental Biomedicine, University Hospital Würzburg, Josef-Schneider-Str. 2, D15, 97080, Würzburg, Germany. stegner@virchow.uni-wuerzburg.de.
Abstract:
In mammals, megakaryocytes (MKs) in the bone marrow (BM) produce blood platelets, required for hemostasis and thrombosis. MKs originate from hematopoietic stem cells and are thought to migrate from an endosteal niche towards the vascular sinusoids during their maturation. Through imaging of MKs in the intact BM, here we show that MKs can be found within the entire BM, without a bias towards bone-distant regions. By combining in vivo two-photon microscopy and in situ light-sheet fluorescence microscopy with computational simulations, we reveal surprisingly slow MK migration, limited intervascular space, and a vessel-biased MK pool. These data challenge the current thrombopoiesis model of MK migration and support a modified model, where MKs at sinusoids are replenished by sinusoidal precursors rather than cells from a distant periostic niche. As MKs do not need to migrate to reach the vessel, therapies to increase MK numbers might be sufficient to raise platelet counts.Megakaryocyte maturation is thought to occur as the cells migrate from a vessel-distant (endosteal) niche to the vessel within the bone. Here, the authors show that megakaryocytes represent largely sessile cells in close contact with the vasculature and homogeneously distributed in the bone marrow.
Insights
Megakaryocytes (MKs), crucial for platelet production, are not confined to distant niches but are evenly distributed throughout bone marrow. This finding challenges current models and suggests therapies targeting MK numbers may boost platelet counts.
Area of Science:
- Hematology
- Cell Biology
- Biophysics
Background:
- Megakaryocytes (MKs) in bone marrow (BM) produce platelets essential for hemostasis.
- Current models propose MKs migrate from endosteal niches to vascular sinusoids during maturation.
- This migration is believed to be crucial for thrombopoiesis.
Purpose of the Study:
- To investigate the in vivo migration patterns of MKs within the intact BM.
- To challenge and refine the existing model of MK migration during thrombopoiesis.
- To understand the spatial distribution and dynamics of MKs in relation to bone marrow vasculature.
Main Methods:
- In vivo two-photon microscopy for imaging MKs in intact BM.
- In situ light-sheet fluorescence microscopy for detailed cellular visualization.
- Computational simulations to analyze MK migration and spatial distribution.
Main Results:
- MKs are found homogeneously distributed throughout the BM, not biased towards endosteal regions.
- MK migration is surprisingly slow, with limited movement observed.
- A significant pool of MKs is located in close proximity to vascular sinusoids, suggesting a vessel-biased distribution.
Conclusions:
- The traditional model of MK migration from distant niches to sinusoids is challenged.
- A modified model suggests MKs at sinusoids are replenished by local precursors, not distant migration.
- Therapeutic strategies to increase platelet counts may focus on augmenting MK numbers rather than promoting migration.
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