The Inflammatory Chemokine CXC Motif Ligand 16 Triggers Platelet Activation and Adhesion Via CXC Motif Receptor 6–Dependent Phosphatidylinositide 3-Kinase/Akt Signaling

Abstract

Rationale: The recently discovered chemokine CXC motif ligand 16 (CXCL16) is highly expressed in atherosclerotic lesions and is a potential pathogenic mediator in coronary artery disease. Objective: The aim of this study was to test the role of CXCL16 on platelet activation and vascular adhesion, as well as the underlying mechanism and signaling pathway. Methods and Results: Reverse-transcriptase polymerase chain reaction, Western blotting, confocal microscopy, and flow cytometry revealed that CXCL16-specific receptor, CXC motif receptor 6, is highly expressed in platelets. According to flow cytometry and confocal microscopy, stimulation of platelets with CXCL16 induced platelet degranulation, integrin α IIb β 3 activation, and shape change. CXCL16 increased Akt phosphorylation (Thr 308 /Ser 473 ), an effect abrogated by phosphatidylinositide 3-kinase inhibitors wortmannin (100 nmol/L) and LY294002 (25 µmol/L). The phosphatidylinositide 3-kinase inhibitors and Akt inhibitor SH-6 (20 µmol/L) further diminished CXCL16-induced platelet activation. CXCL16-mediated platelet degranulation, integrin α IIb β 3 activation, and Akt phosphorylation were blunted in platelets lacking CXCL16-specific receptor CXC motif receptor 6. CXCL16-induced platelet activation was abrogated in Akt1- or Akt2-deficient platelets. CXCL16 enhanced platelet adhesion to endothelium in vitro after high arterial shear stress (2000 −s ) and to injured vascular wall in vivo after carotid ligation. CXCL16-induced stimulation of platelet adhesion again was prevented by phosphatidylinositide 3-kinase and Akt inhibitors. Apyrase and antagonists of platelet purinergic receptors P 2 Y 1 (MRS2179, 100 µmol/L) and especially P 2 Y 12 (Cangrelor, 10 µmol/L) blunted CXCL16-triggered platelet activation as well as CXCL16-induced platelet adhesion under high arterial shear stress in vitro and after carotid ligation in vivo. Conclusions: The inflammatory chemokine CXCL16 triggers platelet activation and adhesion via CXC motif receptor 6–dependent phosphatidylinositide 3-kinase/Akt signaling and paracrine activation, suggesting a decisive role for CXCL16 in linking vascular inflammation and thrombo-occlusive diseases.

Platelets Mediate Oxidized Low-Density Lipoprotein–Induced Monocyte Extravasation and Foam Cell Formation

“…The observed effects of OxLDL on platelet-monocyte interactions were dependent on the concentration and the degree of oxidative modification of LDL. Although platelet-monocyte interactions involve a variety of receptor-counter-receptor pairs, such as CD147/basigin or CD11b/CD18-glycoprotein Ib α (GPIbα), 29,30 and are also modulated by secreted soluble mediators, such as CXC motif ligand 16 (CXCL16) or CX3-C motif ligand 1 (CX3CL1), 31,32 our findings reinforce P-selectin as the key initial mediator for platelet-leukocyte interactions because blocking P-selectin-PSGL-1 interactions virtually abrogated platelet interaction with monocytes. P-selectin has previously been shown to be involved in the development and exacerbation of atherosclerotic lesions by bridging platelets to leukocytes.…”

PDK1 Determines Collagen-Dependent Platelet Ca 2+ Signaling and Is Critical to Development of Ischemic Stroke In Vivo

“…5,31,32 Acute myocardial infarction and ischemic stroke represent the leading causes of death and permanent disability in industrialized countries, despite ongoing improvements in antithrombotic therapy. 1,33 By understanding the multifaceted intracellular signaling involved in platelet activation underlying hemostasis as well as arterial thrombosis, new approaches can be tailored to selectively inhibit pathways most relevant to pathological thrombus formation.…”

CXCL16 in Vascular Pathology Research: from Macro Effects to microRNAs

“…Human monocytederived macrophages express CXCL16 on activation and in atherosclerotic lesions 10,[23][24][25] . CXCL16 expression at the mRNA level was also confirmed in B-cells 8) , 1) C-X-C motif chemokine domain with N-terminal signal sequence, 2) Mucin stalk, 3) Hydrophobic transmembrane domain, 4) Cytoplasmic tail with YXPV motif platelets 43) . The soluble form of CXCL16 acts as a chemoattractant for nearly all cells that express its "private" receptor, at least in vitro 8,9,29,44) .…”

“…Therefore, the culture of HUVECs became one of the best in vitro models in vascular pathology research 50,53,59,60) . A recent study has shown for the first time that CXCL16 increases platelet adhesion to the HUVEC monolayer under conditions of high arterial shear stress in in vitro flow chamber experiments 43) . Moreover, the authors verified this process in vivo after carotis ligation by intravital microscopy.…”

“…Therefore, the authors concluded that CXCL16 expression in atherosclerotic lesions and release from inflammatory cells could be an additional local proadhesive stimulus for circulating platelets that could lead to increased platelet adhesion at the sites of vascular injury. Thus, CXCL16 could play a decisive role in linking inflammatory vascular diseases and thrombosis 43) .…”