Abstract
Platelet alpha-granules constitute the major rapidly releasable reservoir of thrombospondin-1 in higher animals. Although some fragments and peptides derived from thrombospondin-1 stimulate or inhibit platelet aggregation, its physiologic function in platelets has remained elusive. We now show that endogenous thrombospondin-1 is necessary for platelet aggregation in vitro in the presence of physiologic levels of nitric oxide (NO). Exogenous NO or elevation of cGMP delays thrombin-induced platelet aggregation under high shear and static conditions, and exogenous thrombospondin-1 reverses this delay. Thrombospondin-1-null murine platelets fail to aggregate in response to thrombin in the presence of exogenous NO or 8Br-cGMP. At physiologic concentrations of the NO synthase substrate arginine, thrombospondin-1-null platelets have elevated basal cGMP. Ligation of CD36 or CD47 is sufficient to block NO-induced cGMP accumulation and mimic the effect of thrombospondin-1 on aggregation. Exogenous thrombospondin-1 also reverses the suppression by NO of alphaIIb/beta3 integrin-mediated platelet adhesion on immobilized fibrinogen, mediated in part by increased GTP loading of Rap1. Thrombospondin-1 also inhibits cGMP-mediated activation of cGMP-dependent protein kinase and thereby prevents phosphorylation of VASP. Thus, release of thrombospondin-1 from alpha-granules during activation provides positive feedback to promote efficient platelet aggregation and adhesion by overcoming the antithrombotic activity of physiologic NO.
Publication types
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Research Support, N.I.H., Extramural
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Research Support, N.I.H., Intramural
MeSH terms
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Animals
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Arginine / genetics
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Arginine / metabolism
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Blood Platelets / cytology
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Blood Platelets / metabolism*
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CD36 Antigens / genetics
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CD36 Antigens / metabolism
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CD47 Antigen / genetics
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CD47 Antigen / metabolism
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Cell Adhesion Molecules / genetics
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Cell Adhesion Molecules / metabolism
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Cyclic GMP / antagonists & inhibitors
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Cyclic GMP / genetics
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Cyclic GMP / metabolism*
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Cyclic GMP / pharmacology
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Fibrinolytic Agents / metabolism*
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Fibrinolytic Agents / pharmacology
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Immunologic Capping / drug effects
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Immunologic Capping / physiology
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Mice
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Mice, Knockout
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Microfilament Proteins / genetics
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Microfilament Proteins / metabolism
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Nitric Oxide / antagonists & inhibitors
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Nitric Oxide / genetics
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Nitric Oxide / metabolism*
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Peptides / genetics
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Peptides / metabolism
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Peptides / pharmacology
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Phosphoproteins / genetics
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Phosphoproteins / metabolism
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Platelet Adhesiveness / drug effects
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Platelet Adhesiveness / genetics
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Platelet Aggregation / drug effects
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Platelet Aggregation / physiology*
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Platelet Glycoprotein GPIIb-IIIa Complex / genetics
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Platelet Glycoprotein GPIIb-IIIa Complex / metabolism
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Secretory Vesicles / genetics
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Secretory Vesicles / metabolism
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Shear Strength
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Thrombin / genetics
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Thrombin / metabolism
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Thrombin / pharmacology
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Thrombospondin 1 / genetics
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Thrombospondin 1 / metabolism*
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Thrombospondin 1 / pharmacology
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Vasodilator-Stimulated Phosphoprotein
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rap1 GTP-Binding Proteins / genetics
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rap1 GTP-Binding Proteins / metabolism
Substances
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CD36 Antigens
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CD47 Antigen
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Cd47 protein, mouse
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Cell Adhesion Molecules
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Fibrinolytic Agents
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Microfilament Proteins
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Peptides
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Phosphoproteins
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Platelet Glycoprotein GPIIb-IIIa Complex
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Thrombospondin 1
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Vasodilator-Stimulated Phosphoprotein
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Nitric Oxide
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Arginine
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Thrombin
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rap1 GTP-Binding Proteins
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Cyclic GMP