Exposure of plasminogen and a novel plasminogen receptor, Plg-RKT, on activated human and murine platelets

Claire S. Whyte, Gael B. Morrow, Nagyung Baik, Nuala A. Booth, Mohammed M. Jalal, Robert Parmer, Lindsey Miles, Nicola J Mutch* (Corresponding Author)

*Corresponding author for this work

Research output: Contribution to journalArticlepeer-review

4 Citations (Scopus)

Abstract

Plasminogen activation rates are enhanced by cell surface binding. We have previously demonstrated that exogenous plasminogen binds to phosphatidylserine-exposing and spread platelets. Platelets contain plasminogen in their α-granules but secretion of plasminogen from platelets
has not been studied. Recently, a novel transmembrane lysine-dependent plasminogen receptor, Plg-RKT , has been described on macrophages. Here, we analyzed the pool of plasminogen in platelets and examined whether platelets express Plg-RKT. Plasminogen content of the supernatant of resting and collagen/thrombin-stimulated platelets was similar. Pre-treatment with the lysine analogue, εACA, significantly increased platelet-derived plasminogen (0.33 nmol/10 8 plts vs. 0.08 nmol/10 8 plts) in the stimulated supernatant, indicating a lysine-dependent mechanism of membrane retention. Lysine-dependent, platelet-derived plasminogen retention on thrombin and convulxin activated human platelets was confirmed by flow cytometry. Platelets initiated fibrinolytic activity in fluorescently labelled plasminogen-deficient clots and in turbidimetric clot lysis assays. A 17 kDa band, consistent with Plg-RKT, was detected in the platelet membrane fraction by Western blotting. Confocal microscopy of stimulated platelets revealed Plg-RKT co-localized with platelet-derived plasminogen on the activated platelet membrane.
Plasminogen exposure was significantly attenuated in thrombin and convulxin stimulated platelets from Plg-RKT -/- mice compared to wild type (WT) littermates. Membrane exposure of Plg-RKT was not dependent on plasminogen, as similar levels of the receptor were detected in plasminogen -/- platelets. These data highlight Plg-RKT as a novel plasminogen receptor in human and murine platelets. We show for the first time that platelet-derived plasminogen is retained on the activated platelet membrane and drives local fibrinolysis, by enhancing cell-surface mediated plasminogen activation.
Original languageEnglish
Pages (from-to)248–257
Number of pages26
JournalBlood
Volume137
Issue number2
Early online date25 Aug 2020
DOIs
Publication statusPublished - 14 Jan 2021

Keywords

  • plasminogen
  • Plg-RKT
  • platelets
  • fibrinolysis
  • ALPHA-GRANULES
  • FIBRINOLYSIS INHIBITOR
  • FACTOR-XIII-A
  • LYSIS
  • CLOT RETRACTION
  • INDUCED BINDING-SITES
  • SYSTEMS-APPROACH
  • SURFACE
  • GLYCOPROTEIN-IB
  • MONOCLONAL-ANTIBODIES

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