Genetic and Pharmacological Modifications of Thrombin Formation in Apolipoprotein E-deficient Mice Determine Atherosclerosis Severity and Atherothrombosis Onset in a Neutrophil-Dependent Manner

Abstract

BackgroundVariations in the blood coagulation activity, determined genetically or by medication, may alter atherosclerotic plaque progression, by influencing pleiotropic effects of coagulation proteases. Published experimental studies have yielded contradictory findings on the role of hypercoagulability in atherogenesis. We therefore sought to address this matter by extensively investigating the in vivo significance of genetic alterations and pharmacologic inhibition of thrombin formation for the onset and progression of atherosclerosis, and plaque phenotype determination.Methodology/Principal FindingsWe generated transgenic atherosclerosis-prone mice with diminished coagulant or hypercoagulable phenotype and employed two distinct models of atherosclerosis. Gene-targeted 50% reduction in prothrombin (FII−/WT:ApoE−/−) was remarkably effective in limiting disease compared to control ApoE−/− mice, associated with significant qualitative benefits, including diminished leukocyte infiltration, altered collagen and vascular smooth muscle cell content. Genetically-imposed hypercoagulability in TMPro/Pro:ApoE−/− mice resulted in severe atherosclerosis, plaque vulnerability and spontaneous atherothrombosis. Hypercoagulability was associated with a pronounced neutrophilia, neutrophil hyper-reactivity, markedly increased oxidative stress, neutrophil intraplaque infiltration and apoptosis. Administration of either the synthetic specific thrombin inhibitor Dabigatran etexilate, or recombinant activated protein C (APC), counteracted the pro-inflammatory and pro-atherogenic phenotype of pro-thrombotic TMPro/Pro:ApoE−/− mice.Conclusions/SignificanceWe provide new evidence highlighting the importance of neutrophils in the coagulation-inflammation interplay during atherogenesis. Our findings reveal that thrombin-mediated proteolysis is an unexpectedly powerful determinant of atherosclerosis in multiple distinct settings. These studies suggest that selective anticoagulants employed to prevent thrombotic events may also be remarkably effective in clinically impeding the onset and progression of cardiovascular disease.

Loss of Biglycan Enhances Thrombin Generation in Apolipoprotein E -Deficient Mice

“…29,30 Mechanistically, this reduced expression of HCII may lead to increased thrombin-mediated activation of platelets, which in turn stimulate macrophage-mediated inflammation. 31,32 As shown here, the absence of biglycan in ApoE mice did, however, not lead to changes in hemostasis or an overt thrombotic phenotype. However, because thrombosis models involve endothelial injury and denudation, this leads …”

Factor XI Regulates Pathological Thrombus Formation on Acutely Ruptured Atherosclerotic Plaques

“…Several clotting factors, including thrombin, contribute to atherosclerotic plaque formation. 30 Therefore, it would be interesting to study the role of factor XI during this long-term process. Our current observations are that inhibition of factor XI prevents thrombosis on acutely ruptured atherosclerotic plaques without impairment of normal clot formation and indicates that targeting factor XI could be a safe alternative for the prevention of atherothrombotic disease.…”

Atherosclerotic Plaque Destabilization

“…67 A more recent study proposed a model combining perivascular collar placement with a mouse model of genetically imposed hypercoagulability. 68 Hypercoagulability induces vulnerable plaques characterized by increased lesion sizes, outward remodeling, larger NCs, thinner fibrous caps, enhanced neointimal apoptosis, and increased macrophage and neutrophil infiltration. Unlike in other mouse models of plaque vulnerability, events such as plaque disruption with superimposed thrombosis, repeated plaque disruptions, and intramural thrombi were evidenced.…”

“…Unlike in other mouse models of plaque vulnerability, events such as plaque disruption with superimposed thrombosis, repeated plaque disruptions, and intramural thrombi were evidenced. 68 A variant of the perivascular collar model was developed where, consequent to ligation of the common carotid artery, a polyethylene cuff was placed close to the ligation site, 69 thereby generating advanced lesions with a SMC-rich fibrous cap and a high prevalence of intraplaque hemorrhages. Moreover, disruptions of fibrous cap integrity with superimposed mural or occlusive thrombosis were observed.…”