Granule exocytosis is required for platelet spreading: differential sorting of α-granules expressing VAMP-7

CG Peters, AD Michelson… - Blood, The Journal of …, 2012 - ashpublications.org
CG Peters, AD Michelson, R Flaumenhaft
Blood, The Journal of the American Society of Hematology, 2012ashpublications.org
There has been recent controversy as to whether platelet α-granules represent a single
granule population or are composed of different subpopulations that serve discrete
functions. To address this question, we evaluated the localization of vesicle-associated
membrane proteins (VAMPs) in spread platelets to determine whether platelets actively sort
a specific subpopulation of α-granules to the periphery during spreading.
Immunofluorescence microscopy demonstrated that granules expressing VAMP-3 and …
Abstract
There has been recent controversy as to whether platelet α-granules represent a single granule population or are composed of different subpopulations that serve discrete functions. To address this question, we evaluated the localization of vesicle-associated membrane proteins (VAMPs) in spread platelets to determine whether platelets actively sort a specific subpopulation of α-granules to the periphery during spreading. Immunofluorescence microscopy demonstrated that granules expressing VAMP-3 and VAMP-8 localized to the central granulomere of spread platelets along with the granule cargos von Willebrand factor and serotonin. In contrast, α-granules expressing VAMP-7 translocated to the periphery of spread platelets along with the granule cargos TIMP2 and VEFG. Time-lapse microscopy demonstrated that α-granules expressing VAMP-7 actively moved from the granulomere to the periphery during spreading. Platelets from a patient with gray platelet syndrome lacked α-granules and demonstrated only minimal spreading. Similarly, spreading was impaired in platelets obtained from Unc13dJinx mice, which are deficient in Munc13-4 and have an exocytosis defect. These studies identify a new α-granule subtype expressing VAMP-7 that moves to the periphery during spreading, supporting the premise that α-granules are heterogeneous and demonstrating that granule exocytosis is required for platelet spreading.
ashpublications.org