title: Thrombospondin-1 stimulates platelet aggregation by blocking the antithrombotic activity of nitric oxide/cGMP signaling.
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.
authors: Laboratory of Pathology, Center for Cancer Research, National Cancer Institute, National Institutes of Health, Bethesda, MD 20892, USA.
authors: Jeff S
authors: JS
authors: Isenberg
authors: Martin J
authors: MJ
authors: Romeo
authors: Christine
authors: C
authors: Yu
authors: Christine K
authors: CK
authors: Yu
authors: Khauh
authors: K
authors: Nghiem
authors: Jude
authors: J
authors: Monsale
authors: Margaret E
authors: ME
authors: Rick
authors: David A
authors: DA
authors: Wink
authors: William A
authors: WA
authors: Frazier
authors: David D
authors: DD
authors: Roberts
mesh_terms: D000818:Animals; D001120:Arginine / Q000235:genetics / Q000378:metabolism; D001792:Blood Platelets / Q000166:cytology / Q000378:metabolism*; D018955:CD36 Antigens / Q000235:genetics / Q000378:metabolism; D051928:CD47 Antigen / Q000235:genetics / Q000378:metabolism; D015815:Cell Adhesion Molecules / Q000235:genetics / Q000378:metabolism; D006152:Cyclic GMP / Q000037:antagonists & inhibitors / Q000235:genetics / Q000378:metabolism* / Q000494:pharmacology; D005343:Fibrinolytic Agents / Q000378:metabolism* / Q000494:pharmacology; D007152:Immunologic Capping / Q000187:drug effects / Q000502:physiology; D051379:Mice; D018345:Mice, Knockout; D008840:Microfilament Proteins / Q000235:genetics / Q000378:metabolism; D009569:Nitric Oxide / Q000037:antagonists & inhibitors / Q000235:genetics / Q000378:metabolism*; D010455:Peptides / Q000235:genetics / Q000378:metabolism / Q000494:pharmacology; D010750:Phosphoproteins / Q000235:genetics / Q000378:metabolism; D010973:Platelet Adhesiveness / Q000187:drug effects / Q000235:genetics; D010974:Platelet Aggregation / Q000187:drug effects / Q000502:physiology*; D019039:Platelet Glycoprotein GPIIb-IIIa Complex / Q000235:genetics / Q000378:metabolism; D022142:Secretory Vesicles / Q000235:genetics / Q000378:metabolism; D033081:Shear Strength; D013917:Thrombin / Q000235:genetics / Q000378:metabolism / Q000494:pharmacology; D019700:Thrombospondin 1 / Q000235:genetics / Q000378:metabolism* / Q000494:pharmacology; D020827:rap1 GTP-Binding Proteins / Q000235:genetics / Q000378:metabolism; D000098662:Vasodilator-Stimulated Phosphoprotein
chemical_list: D018955:CD36 Antigens; D051928:CD47 Antigen; C497895:Cd47 protein, mouse; D015815:Cell Adhesion Molecules; D005343:Fibrinolytic Agents; D008840:Microfilament Proteins; D010455:Peptides; D010750:Phosphoproteins; D019039:Platelet Glycoprotein GPIIb-IIIa Complex; D019700:Thrombospondin 1; D000098662:Vasodilator-Stimulated Phosphoprotein; D009569:Nitric Oxide; D001120:Arginine; D013917:Thrombin; D020827:rap1 GTP-Binding Proteins; D006152:Cyclic GMP