Novel Function of Tenascin-C, a Matrix Protein Relevant to Atherosclerosis, in Platelet Recruitment and Activation Under Flow

Abstract

Objective-The identification of platelet-reactive proteins exclusively present in atherosclerotic plaques could provide interesting targets for effective and safe antithrombotic strategies. In this context, we explored platelet adhesion and activation to tenascin-C (TN-C), a matrix protein preferentially found within atheroma. Methods and Results-We show that platelets efficiently adhere to TN-C under both static and flow conditions.Videomicroscopy revealed a unique behavior under flow, with platelets exhibiting stationary adhesion to TN-C; in contrast, platelets rolled over von Willebrand factor and detached from fibrinogen. Platelet interaction with TN-C was predominantly supported by integrin ␣ 2 ␤ 1 under static conditions, whereas under high shear, it was dependent on both the ␣ 2 ␤ 1 integrin and the glycoprotein Ib-IX complex. Integrin ␣ IIb ␤ 3 appeared to play a secondary role but only at low shear rates. The glycoprotein Ib-IX-dependent interaction was indirect, relying on von Willebrand factor, and increased as a function of wall shear rate. Von Willebrand factor bound directly to TN-C, as shown by ELISA and coimmunoprecipitation, suggesting that it acts as a bridge between TN-C and platelets. The adhesion of platelets to TN-C triggered their activation, as demonstrated by a shape change and increases in intracellular calcium level. Key Words: blood flow Ⅲ platelets Ⅲ receptors Ⅲ thrombosis Ⅲ tenascin-C T he central role of platelets in arterial thrombosis renders them attractive targets for antithrombotic drugs. Clopidogrel and integrin ␣ IIb ␤ 3 blockers, 2 antiplatelet agents widely used in clinical practice, have greatly reduced cardiovascular-associated death; however, because they directly target the hemostatic function of platelets, their use is linked to an increased bleeding risk. The development of more selective antithrombotic drugs causing minimal perturbation of hemostasis could pave the way to new and more effective strategies in the treatment of ischemic events. This task is challenged by the fact that the main cellular and molecular events implicated in thrombosis are also those regulating hemostasis. Nevertheless, differences exist between these 2 conditions, such as the rheological microenvironment and the nature of the vascular material exposed to platelets. Thrombosis occurs in advanced atherosclerotic arteries that present abnormal luminal narrowing or stenosis inducing local disturbance of blood flow. 1 In addition, the marked inflammation and active tissue remodeling found in atheroma profoundly modify the composition of the subendothelium. Atherosclerotic plaques are rich in highly reactive platelet-adhesive materials, such as collagens or lipids, and overexpress extracellular matrix proteins that are essentially absent from the healthy vessel wall. The identification of platelet-adhesive proteins preferentially expressed in diseased vessels could provide novel targets for more selective antithrombotic therapies. Conclusion-ThisIn this context, tenascin-C (TN-C) appears to be a...

Tenascin-C: Its functions as an integrin ligand

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Role and regulation of phosphatidylinositol 3-kinase β in platelet integrin α2β1 signaling

“…15,16 Although some controversies persist, the role of integrin ␣2␤1 in adhesion to collagen, platelet activation, and thrombus formation is well documented. 14,[17][18][19] Recruitment of integrin ␣2␤1 initiates an outside-in signaling pathway leading to platelet spreading on the extracellular matrix and to activation of integrin ␣IIb␤3, thus allowing binding of soluble fibrinogen to adherent platelets.…”

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