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

• Published in: Blood Vol. 120; no. 1; pp. 199 - 206
• Main Authors: Peters, Christian G., Michelson, Alan D., Flaumenhaft, Robert
• Format: Journal Article
• Language: English
• Published: Washington, DC Elsevier Inc 05.07.2012; Americain Society of Hematology; American Society of Hematology
• Subjects: Animals; Biological and medical sciences; Blood Platelets - metabolism; Child, Preschool; Cytoplasmic Granules - metabolism; Exocytosis - physiology; Female; Gray Platelet Syndrome - metabolism; Hematologic and hematopoietic diseases; Humans; Male; Medical sciences; Membrane Proteins - genetics; Mice; Mice, Inbred C57BL; Mice, Mutant Strains; Middle Aged; Platelets and Thrombopoiesis; Protein Transport - physiology; Pseudopodia - metabolism; R-SNARE Proteins - metabolism; Vesicle-Associated Membrane Protein 3 - metabolism; Platelet; Hematology; Exocytosis; Alpha granule; Sorting
• ISSN: 0006-4971; 1528-0020
• DOI: 10.1182/blood-2011-10-389247

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.