Heterogeneity in platelet differentiation pathways

<p dir="ltr">Hematopoietic stem cells replenish billions of mature blood cells every day through a series of increasingly lineage-restricted progenitor cells and are therefore vital for immune response, oxygen transport and hemostasis. Upon acute depletion of the hematopoietic system, such as after cytotoxic treatment for blood cancer, one of the most troublesome complications is bleeding due to thrombocytopenia.</p><p dir="ltr">Through mouse models, our lab has characterized a novel and direct pathway of platelet generation, initiated by a hitherto unrecognized subset of HSCs, that are activated in response to cytotoxic stress. Study I investigates the emergence of lineage restriction and bias in perinatal HSCs. Study II describes the non- hierarchical relationship of two distinct types of HSCs, von Willebrand factor positive platelet-restricted and -biased HSCs (P-HSCs) and von Willebrand factor negative multilineage HSCs (M-HSCs). The transcriptional expression of FMS-like tyrosine kinase (Flt-3) was found to be a marker that distinguishes the differentiation pathways of P-HSCs and M-HSCs. This finding was validated by fate mapping using a Flt3-Cre/Rosa26-tdTomato mouse model. Furthermore, we performed molecular characterization of the megakaryocyte progenitors, the unilineage progenitors responsible for platelet generation, finding distinct molecular profiles depending on the type of HSC that generated them. We therefore speculate that the different pathways can in part explain platelet heterogeneity, an issue that has gained interest due to expansion of prothrombotic subsets upon aging. To this end, Study III describes a protocol for RNA-seq of sorted platelet populations allowing for molecular studies of platelet heterogeneity within the same individual.</p><p dir="ltr">Taken together, these studies show that a mature cell can be generated through more than one differentiation pathway, suggesting a revision of the established hematopoietic hierarchy that currently posits only one unique sequence of differentiation steps for each mature cell type.</p><h3>List of scientific papers</h3><p dir="ltr">I. Platelet and myeloid lineage biases of transplanted single perinatal mouse hematopoietic stem cells. (Cell Research. 2023, 33, 883-886). Karin Belander Strålin*, Joana Carrelha*, <b>Axel Winroth</b>, Christoph Ziegenhain, Michael Hagemann-Jensen, Laura M. Kettyle, Amy Hillen, Kari Högstrand, Ellen Markljung, Francesca Grasso, Masafumi Seki, Stefania Mazzi, Yiran Meng, Bishan Wu, Edwin Chari, Madeleine Lehander, Rickard Sandberg, Petter S. Woll, Sten Eirik W. Jacobsen. <a href="https://doi.org/10.1038/s41422-023-00866-4" rel="noreferrer" target="_blank">https://doi.org/10.1038/s41422-023-00866-4</a></p><p dir="ltr">II. Alternative platelet differentiation pathways initiated by non-hierarchically related hematopoietic stem cells. (Nature Immunology. 2024, 25, 1007-1019). Joana Carrelha*, Stefania Mazzi*, <b>Axel Winroth</b>*, Michael Hagemann-Jensen, Christoph Ziegenhain, Kari Högstrand, Masafumi Seki, Margs S. Brennan, Madeleine Lehander, Bishan Wu, Yiran Meng, Ellen Markljung, Ruggiero Norfo, Hisahi Ishida, Karin Belander Strålin, Francesca Grasso, Christina Simoglu Karali, Affaf Aliouat, Amy Hillen, Edwin Chari, Kimberly SiIletti, Supat Thongjuea, Adam J. Mead, Sten Linnarsson, Claus Nerlov, Rickard Sandberg, Tetsuichi Yoshizato, Petter S. Woll, Sten Eirik W. Jacobsen. <a href="https://doi.org/10.1038/s41590-024-01845-6" rel="noreferrer" target="_blank">https://doi.org/10.1038/s41590-024-01845-6</a></p><p dir="ltr">III. The platelet transcriptome is stable across age and is minimally responsive to spontaneous CD62 externalization. Masafumi Seki*, <b>Axel Winroth</b>*, Margs Brennan, Kari Högstrand, Tetsuichi Yoshizato, Michael Hagemann-Jensen, Christoph Ziegenhain, Amie Waller, Holly Foster, John W. Semple, Cedric Ghevaert, Sten Eirik W. Jacobsen^, Petter S. Woll^. [Manuscript]</p><p dir="ltr">(*Equal contribution, ^Shared senior authorship)</p>