Platelet aggregation at sites of vascular injury is essential for hemostasis and arterial thrombosis. It has long been assumed that platelet aggregation and thrombus growth are initiated by soluble agonists generated at sites of vascular injury. By using high-resolution intravital imaging techniques and hydrodynamic analyses, we show that platelet aggregation is primarily driven by changes in blood flow parameters (rheology), with soluble agonists having a secondary role, stabilizing formed aggregates. We find that in response to vascular injury, thrombi initially develop through the progressive stabilization of discoid platelet aggregates. Analysis of blood flow dynamics revealed that discoid platelets preferentially adhere in low-shear zones at the downstream face of forming thrombi, with stabilization of aggregates dependent on the dynamic restructuring of membrane tethers. These findings provide insight into the prothrombotic effects of disturbed blood flow parameters and suggest a fundamental reinterpretation of the mechanisms driving platelet aggregation and thrombus growth.
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We thank Z. Ruggeri, H.H. Salem, R. Andrews and B. Kile for helpful feedback on the work; H. Blackburn and G. Rosengarten for advice and input on the CFD analysis; C. Nguyen for technical assistance in the analysis of in vivo blood flow rates; SciTech Proprietary Ltd. and Andor Proprietary Ltd. for the generous loan of a DV897CS EMCCD camera; M. Hickey (Monash University Department of Medicine, Monash, Australia) and A. Issekutz (Dalhousie University, Halifax, Canada) for providing the P-selectin–specific antibody; and C. Gachet (INSERM, Strasbourg, France) for P2Y1−/− mice. This work was supported by project funding from the National Health and Medical Research Council of Australia and the Australian Research Council. E.W. was supported by the National Heart Foundation of Australia.
Supplementary Figs. 1–6 and Supplementary Methods (PDF 975 kb)
Rheology-driven platelet aggregation in vivo. (MOV 2808 kb)
Shear microgradient-induced platelet aggregation in vitro. (MOV 2976 kb)
Discoid aggregate formation independent of ADP, TXA2 and thrombin. (MOV 3197 kb)
Discoid platelet aggregation and aggregate consolidation in vivo. (MOV 3433 kb)
Platelet tethering interactions in vivo and in vitro. (MOV 2814 kb)
Intracellular calcium flux during platelet tether restructuring. (MOV 3110 kb)
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Nesbitt, W., Westein, E., Tovar-Lopez, F. et al. A shear gradient–dependent platelet aggregation mechanism drives thrombus formation. Nat Med 15, 665–673 (2009). https://doi.org/10.1038/nm.1955
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