Platelet α-granule cargo packaging and release are affected by the luminal proteoglycan, serglycin

Harry Chanzu, Joshua Lykins, Subershan Wigna-Kumar, Smita Joshi, Irina Pokrovskaya, Brian Storrie, Gunnar Pejler, Jeremy P. Wood, Sidney W. Whiteheart

Research output: Contribution to journalArticlepeer-review

5 Scopus citations

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, 35SO4 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.

Original languageEnglish
Pages (from-to)1082-1095
Number of pages14
JournalJournal of Thrombosis and Haemostasis
Volume19
Issue number4
DOIs
StatePublished - Apr 2021

Bibliographical note

Funding Information:
The authors thank the members of Wood and Whiteheart Laboratories for their careful perusal of this manuscript. The authors thank the University of Kentucky Flow Cytometry Core Facility and the Imaging Core Facility for their technical assistance with experiments. This work is supported by grants from the National Institutes of Health, National Heart, Lung, and Blood Institute (HL56652, HL138179, and HL150818), and a Department of Veterans Affairs Merit Award to S.W.W.

Funding Information:
The authors thank the members of Wood and Whiteheart Laboratories for their careful perusal of this manuscript. The authors thank the University of Kentucky Flow Cytometry Core Facility and the Imaging Core Facility for their technical assistance with experiments. This work is supported by grants from the National Institutes of Health, National Heart, Lung, and Blood Institute (HL56652, HL138179, and HL150818), and a Department of Veterans Affairs Merit Award to S.W.W.

Publisher Copyright:
© 2021 International Society on Thrombosis and Haemostasis

Keywords

  • exocytosis
  • granule biogenesis
  • megakaryocytes
  • secretion
  • shedding

ASJC Scopus subject areas

  • Hematology

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