Stabilizing Role of Platelet P2Y12 Receptors in Shear-Dependent Thrombus Formation on Ruptured Plaques

Background

In most models of experimental thrombosis, healthy blood vessels are damaged. This results in the formation of a platelet thrombus that is stabilized by ADP signaling via P2Y₁₂ receptors. However, such models do not predict involvement of P2Y₁₂ in the clinically relevant situation of thrombosis upon rupture of atherosclerotic plaques. We investigated the role of P2Y₁₂ in thrombus formation on (collagen-containing) atherosclerotic plaques in vitro and in vivo, by using a novel mouse model of atherothrombosis.

Methodology

Plaques in the carotid arteries from Apoe ^−/− mice were acutely ruptured by ultrasound treatment, and the thrombotic process was monitored via intravital fluorescence microscopy. Thrombus formation in vitro was assessed in mouse and human blood perfused over collagen or plaque material under variable conditions of shear rate and coagulation. Effects of two reversible P2Y₁₂ blockers, ticagrelor (AZD6140) and cangrelor (AR-C69931MX), were investigated.

Principal Findings

Acute plaque rupture by ultrasound treatment provoked rapid formation of non-occlusive thrombi, which were smaller in size and unstable in the presence of P2Y₁₂ blockers. In vitro, when mouse or human blood was perfused over collagen or atherosclerotic plaque material, blockage or deficiency of P2Y₁₂ reduced the thrombi and increased embolization events. These P2Y₁₂ effects were present at shear rates >500 s⁻¹, and they persisted in the presence of coagulation. P2Y₁₂-dependent thrombus stabilization was accompanied by increased fibrin(ogen) binding.

Conclusions/Significance

Platelet P2Y₁₂ receptors play a crucial role in the stabilization of thrombi formed on atherosclerotic plaques. This P2Y₁₂ function is restricted to high shear flow conditions, and is preserved in the presence of coagulation.