Abnormal megakaryocyte development and platelet function in Nbeal2−/− mice

WHA Kahr, RW Lo, L Li, FG Pluthero… - Blood, The Journal …, 2013 - ashpublications.org
WHA Kahr, RW Lo, L Li, FG Pluthero, H Christensen, R Ni, N Vaezzadeh, CE Hawkins
Blood, The Journal of the American Society of Hematology, 2013ashpublications.org
Gray platelet syndrome (GPS) is an inherited bleeding disorder associated with
macrothrombocytopenia and α-granule-deficient platelets. GPS has been linked to loss of
function mutations in NEABL2 (neurobeachin-like 2), and we describe here a murine GPS
model, the Nbeal2−/− mouse. As in GPS, Nbeal2−/− mice exhibit splenomegaly,
macrothrombocytopenia, and a deficiency of platelet α-granules and their cargo, including
von Willebrand factor (VWF), thrombospondin-1, and platelet factor 4. The platelet α-granule …
Abstract
Gray platelet syndrome (GPS) is an inherited bleeding disorder associated with macrothrombocytopenia and α-granule-deficient platelets. GPS has been linked to loss of function mutations in NEABL2 (neurobeachin-like 2), and we describe here a murine GPS model, the Nbeal2−/− mouse. As in GPS, Nbeal2−/− mice exhibit splenomegaly, macrothrombocytopenia, and a deficiency of platelet α-granules and their cargo, including von Willebrand factor (VWF), thrombospondin-1, and platelet factor 4. The platelet α-granule membrane protein P-selectin is expressed at 48% of wild-type levels and externalized upon platelet activation. The presence of P-selectin and normal levels of VPS33B and VPS16B in Nbeal2−/− platelets suggests that NBEAL2 acts independently of VPS33B/VPS16B at a later stage of α-granule biogenesis. Impaired Nbeal2−/− platelet function was shown by flow cytometry, platelet aggregometry, bleeding assays, and intravital imaging of laser-induced arterial thrombus formation. Microscopic analysis detected marked abnormalities in Nbeal2−/− bone marrow megakaryocytes, which when cultured showed delayed maturation, decreased survival, decreased ploidy, and developmental abnormalities, including abnormal extracellular distribution of VWF. Our results confirm that α-granule secretion plays a significant role in platelet function, and they also indicate that abnormal α-granule formation in Nbeal2−/− mice has deleterious effects on megakaryocyte survival, development, and platelet production.
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