Premium
Intramedullary megakaryocytes internalize released platelet factor 4 and store it in alpha granules
Author(s) -
Lambert M. P.,
Meng R.,
Xiao L.,
Harper D. C.,
Marks M. S.,
Kowalska M. A.,
Poncz M.
Publication year - 2015
Publication title -
journal of thrombosis and haemostasis
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.947
H-Index - 178
eISSN - 1538-7836
pISSN - 1538-7933
DOI - 10.1111/jth.13069
Subject(s) - platelet factor 4 , bone marrow , microbiology and biotechnology , haematopoiesis , megakaryocyte , biology , stem cell factor , stem cell , platelet , cancer research , chemistry , immunology
Summary Background Megakaryocytes express and store platelet factor 4 ( PF 4) in alpha granules. In vivo , PF 4 is a clinically relevant, negative regulator of megakaryopoiesis and hematopoietic stem cell replication. These findings would suggest a regulated source of free intramedullary PF 4. Objectives Define the source of free intramedullary PF 4 and its intramedullary life cycle. Methods We interrogated both murine and human bone marrow–derived cells during megakaryopoiesis in vitro by using confocal microscopy and enzyme‐linked immunosorbent assay. With immunohistochemistry, we examined in vivo free PF 4 in murine bone marrow before and after radiation injury and in the setting of megakaryocytopenia and thrombocytopenia. Results Exogenously added human PF 4 is internalized by murine megakaryocytes. Human megakaryocytes similarly take up murine PF 4 but not the related chemokine, platelet basic protein. Confocal microscopy shows that internalized PF 4 colocalizes with endogenous PF 4 in alpha granules and is available for release on thrombin stimulation. Immunohistochemistry shows free PF 4 in the marrow, but not another alphagranule protein, von Willebrand factor. Free PF 4 increases with radiation injury and decreases with megakaryocytopenia. Consistent with the known role of low‐density lipoprotein receptor–related protein 1 in the negative paracrine effect of PF 4 on megakaryopoiesis, PF 4 internalization is at least partially low‐density lipoprotein receptor–related protein 1 dependent. Conclusions PF 4 has a complex intramedullary life cycle with important implications in megakaryopoiesis and hematopoietic stem cell replication not seen with other tested alpha granule proteins.