Thrombospondin-1 stimulates platelet aggregation by blocking the antithrombotic activity of nitric oxide/cGMP signaling

• Published in: Blood 2008-01, Vol.111 (2), p.613-623
• Main Authors: Isenberg, Jeff S., Romeo, Martin J., Yu, Christine, Yu, Christine K., Nghiem, Khauh, Monsale, Jude, Rick, Margaret E., Wink, David A., Frazier, William A., Roberts, David D.
• Format: Article
• Language: English
• Subjects: Animals; Arginine - genetics; Arginine - metabolism; Blood Platelets - cytology; Blood Platelets - metabolism; CD36 Antigens - genetics; CD36 Antigens - metabolism; CD47 Antigen - genetics; CD47 Antigen - metabolism; Cell Adhesion Molecules - genetics; Cell Adhesion Molecules - metabolism; Cyclic GMP - antagonists & inhibitors; Cyclic GMP - genetics; Cyclic GMP - metabolism; Cyclic GMP - pharmacology; Fibrinolytic Agents - metabolism; Fibrinolytic Agents - pharmacology; Hemostasis, Thrombosis, and Vascular Biology; Immunologic Capping - drug effects; Immunologic Capping - physiology; Mice; Mice, Knockout; Microfilament Proteins - genetics; Microfilament Proteins - metabolism; Nitric Oxide - antagonists & inhibitors; Nitric Oxide - genetics; Nitric Oxide - metabolism; Peptides - genetics; Peptides - metabolism; Peptides - pharmacology; Phosphoproteins - genetics; Phosphoproteins - metabolism; Platelet Adhesiveness - drug effects; Platelet Adhesiveness - genetics; Platelet Aggregation - drug effects; Platelet Aggregation - physiology; Platelet Glycoprotein GPIIb-IIIa Complex - genetics; Platelet Glycoprotein GPIIb-IIIa Complex - metabolism; rap1 GTP-Binding Proteins - genetics; rap1 GTP-Binding Proteins - metabolism; Secretory Vesicles - genetics; Secretory Vesicles - metabolism; Shear Strength; Thrombin - genetics; Thrombin - metabolism; Thrombin - pharmacology; Thrombospondin 1 - genetics; Thrombospondin 1 - metabolism; Thrombospondin 1 - pharmacology
• ISSN: 0006-4971; 1528-0020
• DOI: 10.1182/blood-2007-06-098392

Platelet α-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 αIIb/β3 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 α-granules during activation provides positive feedback to promote efficient platelet aggregation and adhesion by overcoming the antithrombotic activity of physiologic NO.