Platelet α‐granule cargo packaging and release are affected by the luminal proteoglycan, serglycin. (8th February 2021)

• Record Type: Journal Article
• Authors: Chanzu, Harry; Lykins, Joshua; Wigna‐Kumar, Subershan; Joshi, Smita; Pokrovskaya, Irina; Storrie, Brian; Pejler, Gunnar; Wood, Jeremy P.; Whiteheart, Sidney W.
• Is Part Of: Journal of thrombosis and haemostasis. Volume 19:Number 4(2021)
• Page Start: 1082
• Page End: 1095
• Publication Date: 2021-02-08
• Subjects: exocytosis -- granule biogenesis -- megakaryocytes -- secretion -- shedding; Thrombosis -- Periodicals; Hemostasis -- Periodicals; Blood coagulation disorders -- Periodicals; 616.1
• DOI: 10.1111/jth.15243
• Languages: English
• ISSNs: 1538-7933

Abstract

Abstract: Background: Serglycin (SRGN) is an intragranular, sulfated proteoglycan in hematopoietic cells that affects granule composition and function. Objective: To understand how SRGN affects platelet granule packaging, cargo release, and extra‐platelet microenvironments. Methods: Platelets and megakaryocytes from SRGN −/− mice were assayed for secretion kinetics, cargo levels, granule morphology upon activation, and receptor shedding. Results: Metabolic, 35 SO4 labeling identified SRGN as a major sulfated macromolecule in megakaryocytes. SRGN colocalized with α‐granule markers (platelet factor 4 [PF4], von Willebrand factor [VWF], and P‐selectin), but its deletion did not affect α‐granule morphology or number. Platelet α‐granule composition was altered, with a reduction in basic proteins (pI ≥8; e.g., PF4, SDF‐1, angiogenin) and constitutive release of PF4 from SRGN −/− megakaryocytes. P‐Selectin, VWF, and fibrinogen were unaffected. Serotonin (5‐HT) uptake and β‐hexosaminidase (HEXB) were slightly elevated. Thrombin‐induced exocytosis of PF4 from platelets was defective; however, release of RANTES/CCL5 was normal and osteopontin secretion was more rapid. Release of 5‐HT and HEXB (from dense granules and lysosomes, respectively) were unaffected. Ultrastructural studies showed distinct morphologies in activated platelets. The α‐granule lumen of SRGN −/− platelet had a grainy staining pattern, whereas that of wild‐type granules had only fibrous material remaining. α‐Granule swelling and decondensation were reduced in SRGN −/− platelets. Upon stimulation of platelets, a SRGN/PF4 complex was released in a time‐ and agonist‐dependent manner. Shedding of GPVI from SRGN −/− platelets was modestly enhanced. Shedding of GP1b was unaffected. Conclusion: The polyanionic proteoglycan SRGN influences α‐granule packaging, cargo release, and shedding of platelet membrane proteins.