title: Granule exocytosis is required for platelet spreading: differential sorting of α-granules expressing VAMP-7.
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 Unc13d(Jinx) 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.
authors.affiliation: Division of Hemostasis and Thrombosis, Department of Medicine, Beth Israel Deaconess Medical Center, Harvard Medical School, Boston, MA 02215, USA.
authors.forename: Christian G
authors.initials: CG
authors.lastname: Peters
authors.forename: Alan D
authors.initials: AD
authors.lastname: Michelson
authors.forename: Robert
authors.initials: R
authors.lastname: Flaumenhaft
mesh_terms: D000818:Animals; D001792:Blood Platelets / Q000378:metabolism*; D002675:Child, Preschool; D003594:Cytoplasmic Granules / Q000378:metabolism*; D005089:Exocytosis / Q000502:physiology*; D005260:Female; D055652:Gray Platelet Syndrome / Q000378:metabolism*; D006801:Humans; D008297:Male; D008565:Membrane Proteins / Q000235:genetics; D051379:Mice; D008810:Mice, Inbred C57BL; D008817:Mice, Mutant Strains; D008875:Middle Aged; D021381:Protein Transport / Q000502:physiology; D011554:Pseudopodia / Q000378:metabolism; D050683:R-SNARE Proteins / Q000378:metabolism*; D051040:Vesicle-Associated Membrane Protein 3 / Q000378:metabolism
chemical_list: D008565:Membrane Proteins; D050683:R-SNARE Proteins; C520225:Unc13d protein, mouse; C494946:VAMP3 protein, human; C121241:VAMP7 protein, human; C112938:VAMP8 protein, human; D051040:Vesicle-Associated Membrane Protein 3