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Blood, 15 May 2007, Vol. 109, No. 10, pp. 4237-4244. Prepublished online as a Blood First Edition Paper on January 18, 2007; DOI 10.1182/blood-2006-10-050740.
HEMATOPOIESIS A novel role for PECAM-1 in megakaryocytokinesis and recovery of platelet counts in thrombocytopenic mice1 Centre for Cardiovascular Sciences, Institute of Biomedical Research, Division of Medical Sciences, The Medical School, University of Birmingham, Birmingham, United Kingdom; 2 Rheumatology Research Group, Institute of Biomedical Research, Division of Immunity & Infection, Medical Research Council (MRC) Centre for Immune Regulation, The Medical School, University of Birmingham, Birmingham, United Kingdom During thrombopoiesis, maturing megakaryocytes (MKs) migrate within the complex bone marrow stromal microenvironment from the proliferative osteoblastic niche to the capillary-rich vascular niche where proplatelet formation and platelet release occurs. This physiologic process involves proliferation, differentiation, migration, and maturation of MKs before platelet production occurs. In this study, we report a role for the glycoprotein PECAM-1 in thrombopoiesis. We show that following induced thrombocytopenia, recovery of the peripheral platelet count is impaired in PECAM-1deficient mice. Whereas MK maturation, proplatelet formation, and platelet production under in vitro conditions were unaffected, we identified a migration defect in PECAM-1deficient MKs in response to a gradient of stromal cellderived factor 1 (SDF1), a major chemokine regulating MK migration within the bone marrow. This defect could be explained by defective PECAM-1/ MK polarization of the SDF1 receptor CXCR4 and an increase in adhesion to immobilized bone marrow matrix proteins that can be explained by an increase in integrin activation. The defect of migration and polarization was confirmed in vivo with demonstration of altered spatial localization of MKs within the bone marrow in PECAM-1deficient mice, following immune-induced thrombocytopenia. This study identifies a novel role for PECAM-1 in regulating MK migration and thrombopoiesis.
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