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

Whyte, Claire S.; Morrow, Gael B.; Baik, Nagyung; Booth, Nuala A.; Jalal, Mohammed M.; Parmer, Robert J.; Miles, Lindsey A.; Mutch, Nicola J.

Abstract

Plasminogen activation rates are enhanced by cell surface binding. We 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. Pretreatment with the lysine analog, ε-aminocaproic acid, significantly increased platelet-derived plasminogen (0.33 vs 0.08 nmol/108platelets) 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 labeled 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-RKTcolocalized with plateletderived plasminogen on the activated platelet membrane. Plasminogen exposure was significantly attenuated in thrombin- and convulxin-stimulated platelets from Plg-RKT-/-mice compared with Plg-RKT+/+littermates. Membrane exposure of Plg-RKTwas not dependent on plasminogen, as similar levels of the receptor were detected in plasminogen-/-platelets. These data highlight Plg-RKTas 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.

Citation

WHYTE, C.S., MORROW, G.B., BAIK, N., BOOTH, N.A., JALAL, M.M., PARR, R.J. and MUTCH, N.J. 2021. Exposure of plasminogen and a novel plasminogen receptor, Plg-RKT, on activated human and murine platelets. Blood [online], 137(2), pages 248-257. Available from: https://doi.org/10.1182/blood.2020007263

• Journal Article Type: Article
• Acceptance Date: Aug 15, 2020
• Online Publication Date: Aug 25, 2020
• Publication Date: Jan 14, 2021
• Deposit Date: Aug 7, 2023
• Publicly Available Date: Aug 14, 2023
• Journal: Blood
• Print ISSN: 0006-4971
• Electronic ISSN: 1528-0020
• Publisher: American Society of Hematology
• Peer Reviewed: Peer Reviewed
• Volume: 137
• Issue: 2
• Pages: 248-257
• DOI: https://doi.org/10.1182/blood.2020007263
• Keywords: Platelets and thrombopoiesis; Thrombosis and hemostasis; Plasminogen; Plg-RKT; Platelets; Fibrinolysis
• Public URL: https://rgu-repository.worktribe.com/output/2034912