Angiopoietin-1 (Ang1) and -2 (Ang2) are endothelial growth factors that bind to the tyrosine kinase receptor Tie2 and contribute to orchestrate blood vessel formation during angiogenesis. Ang1 mediates vessel maturation and integrity by the recruitment of pericytes. In contrast, Ang2 is classically considered as a Tie2 antagonist, counteracting the stabilizing action of Ang1. Inflammation exists in a mutually dependent association with angiogenesis and we have therefore studied the capacity of angiopoietins to modulate proinflammatory activities, namely Pselectin translocation and neutrophil adhesion onto endothelial cells. We observed that both Ang1 and Ang2 increased these biologic activities. Furthermore, combination of Ang1/Ang2 induced an additive effect on neutrophil adhesion but not on P-selectin translocation. In an attempt to clarify this phenomenon, we found that angiopoietins can directly activate neutrophils through

Objective-CD40 ligand is a thromboinflammatory molecule that predicts cardiovascular events. Platelets constitute the major source of soluble CD40 ligand (sCD40L), which has been shown to influence platelet activation, although its exact functional impact on platelets and the underlying mechanisms remain undefined. We aimed to determine the impact and the signaling mechanisms of sCD40L on platelets. Methods and Results-sCD40L strongly enhances platelet activation and aggregation. Human platelets treated with a mutated form of sCD40L that does not bind CD40, and CD40 Ϫ/Ϫ mouse platelets failed to elicit such responses. Furthermore, sCD40L stimulation induces the association of the tumor necrosis factor receptor-associated factor-2 with platelet CD40. Notably, sCD40L primes platelets through activation of the small GTPase Rac1 and its downstream target p38 mitogen-activated protein kinase, which leads to platelet shape change and actin polymerization. Moreover, sCD40L exacerbates thrombus formation and leukocyte infiltration in wild-type mice but not in CD40 Ϫ/Ϫ mice. Conclusion-sCD40L enhances agonist-induced platelet activation and aggregation through a CD40-dependent tumor necrosis factor receptor-associated factor-2/Rac1/p38 mitogen-activated protein kinase signaling pathway. Thus, sCD40L is an important platelet primer predisposing platelets to enhanced thrombus formation in response to vascular injury. This may explain the link between circulating levels of sCD40L and cardiovascular diseases. M ultiple lines of evidence now support a plethora of inflammatory mediators potentially involved in the pathogenesis of vascular disease. Among these, the CD40 ligand (CD40L)/CD40 dyad has been the focus of much attention, and circulating levels of soluble CD40L (sCD40L) are now considered reliable predictors of cardiovascular events. [1][2][3][4] CD40L is a 48-kDa trimeric transmembrane protein belonging to the tumor necrosis factor superfamily originally identified on cells of the immune system. 5,6 Interaction of CD40L with its respective receptor on B cells, CD40, a 39-kDa glycoprotein from the tumor necrosis factor receptor family, is of critical importance for immunoglobulin isotype switching during the immune response. 7 Today, we know that these 2 molecules are also present on cells of the vascular system, including endothelial cells, monocytes/macrophages, smooth muscle cells, and platelets, 8,9 and have important implications in inflammatory reactions, through upregulation of cell adhesion molecules and production of proinflammatory cytokines, chemokines, growth factors, matrix metalloproteinases, and procoagulants. 8,10 -12 The involvement of the CD40L/CD40 dyad in thromboinflammation has been highlighted in all pathogenic phases of atherosclerosis, including endothelial dysfunction, platelet activation, thrombosis, and neointima formation. [13][14][15][16][17][18][19][20] Platelets are highly specialized blood cells of paramount importance in normal hemostasis and thromboinflammatory complications. The pio...

Background-P-selectin mediates leukocyte recruitment to activated platelets and endothelium through its high-affinity receptor P-selectin glycoprotein ligand-1 (PSGL-1). Platelet and leukocyte activation and binding have been reported after coronary angioplasty and were correlated with restenosis. We investigated the effect of a recombinant soluble PSGL-1 (rPSGL-Ig) on the adhesion of platelets and neutrophils and the development of restenosis after double arterial injury. Methods and Results-Four weeks after angioplasty of both carotid arteries in pigs, a second angioplasty was performed at the same sites, 15 minutes after a single administration of vehicle or rPSGL-1 (1 mg/kg IV). Animals were euthanized 1 hour, 4 hours, 1 week, or 4 weeks later. Adhesion of autologous 51 Cr-platelets and 111 In-neutrophils was quantified and histological/morphometric analyses were performed. Although rPSGL-Ig did not affect adherence of these cells 1 hour after injury, it significantly reduced the adhesion of platelets (50% at 4 hours and 85% at 1 week) and neutrophils (50% at 4 hours and 78% at 1 week) to deeply injured arteries. At 4 weeks, the residual lumen was 63% larger in rPSGL-Ig-treated arteries as compared with control arteries (6.1Ϯ0.6 versus 3.8Ϯ0.1 mm 2 ; PϽ0.002). The neointimal area was slightly reduced (0.5 in rPSGL-Ig versus 0.7 mm 2 in control). The ratio of the external elastic lamina of injured to uninjured reference segments was Ͼ1 in treated arteries and Ͻ1 in control arteries. Conclusions-P-selectin antagonism with rPSGL-Ig inhibits early platelet/leukocyte adhesion on injured arteries and reduces restenosis through a positive impact on vascular remodeling. Hence, rPSGL-Ig may have potential in the prevention of restenosis.