Granule Exocytosis Is Required for Platelet Spreading: Differential Sorting of α-granules Expressing VAMP-7

Blood. 2012 Jul 5;120(1):199-206. doi: 10.1182/blood-2011-10-389247. Epub 2012 May 15.


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.

Publication types

  • Research Support, N.I.H., Extramural
  • Research Support, Non-U.S. Gov't

MeSH terms

  • Animals
  • Blood Platelets / metabolism*
  • Child, Preschool
  • Cytoplasmic Granules / metabolism*
  • Exocytosis / physiology*
  • Female
  • Gray Platelet Syndrome / metabolism*
  • Humans
  • Male
  • Membrane Proteins / genetics
  • Mice
  • Mice, Inbred C57BL
  • Mice, Mutant Strains
  • Middle Aged
  • Protein Transport / physiology
  • Pseudopodia / metabolism
  • R-SNARE Proteins / metabolism*
  • Vesicle-Associated Membrane Protein 3 / metabolism


  • Membrane Proteins
  • R-SNARE Proteins
  • Unc13d protein, mouse
  • VAMP3 protein, human
  • VAMP7 protein, human
  • VAMP8 protein, human
  • Vesicle-Associated Membrane Protein 3