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Abstract 42: Monocyte Tissue Factor-Dependent Activation of Coagulation in Hypercholesterolemic Mice and Monkeys Is Inhibited by Simvastatin

Hyperlipidemia is associated with a prothrombotic state that includes activation of platelets. However, the molecular pathway that leads to the activation of the coagulation cascade has not been defined. Hyperlipidemia leads to the presence of low levels of oxidized lipoproteins, such as oxidized LDL (oxLDL), in the circulation and the accumulation of oxLDL in atherosclerotic lesions.. Monocytes and macrophages are activated by oxLDL binding to a TLR4/TLR6/CD36 receptor complex. We hypothesized that oxLDL induction of monocyte tissue factor (TF) expression and the release of TF-positive microparticles (MPs) produces a prothrombotic state. In support of this hypothesis, we found that oxLDL induced TF expression in human monocytic cells and monocytes. In addition, patients with familial hypercholesterolemia had elevated levels of plasma MP TF activity. Furthermore, a western diet induced a time-dependent increase in plasma MP TF activity and activation of coagulation in both LDL receptor-deficient mice and African green monkeys. Inhibition of TF or a genetic deficiency of TF in bone marrow cells reduced coagulation in hypercholesterolemic mice, consistent with a major role for monocyte TF in the activation of coagulation. Similarly, a deficiency of either TLR4 or TLR6 reduced levels of MP TF activity consistent with a role of the TLR4/TLR6/CD36 complex in oxLDL induction of monocyte TF expression. Importantly, simvastatin treatment of hyperlipidemic mice and monkeys reduced oxLDL, monocyte TF expression, MP TF activity, activation of coagulation, and inflammation without affecting total cholesterol levels. Our results suggest that the prothrombotic state associated with hyperlipidemia is caused by oxLDL-mediated induction of TF expression in monocytes via engagement of a TLR4/TLR6/CD36 receptor complex. Furthermore, simvastatin appears to act at multiple levels to reduce the prothrombotic state.