Abstract 8: Oxidized LDL Induces Macrophage Production of Prothrombotic Microparticles

Abstract

Background: Microparticles (MP) are submicron vesicles produced by activated or apoptotic vascular cells. Agonist proteins borne by MPs enables them to function as mediators of inflammation and thrombosis. Atherosclerotic plaques contain high levels of MPs, and plasma MP levels increase during acute coronary syndromes. The thrombotic consequences of plaque rupture may involve macrophage (MΦ) MPs. The activation pathways that promote MΦMP production remain poorly defined, and this study therefore tested the hypothesis that signals implicated in atherogenesis stimulates MΦMP production. Methods and Results: We stimulated human primary MΦs with pro-inflammatory cytokines and atherogenic lipids, and assessed MΦMP production using light- and impedance-based flow cytometry. Oxidized LDL (oxLDL, 6-17 moles MDA/mg protein), but not IFN-γ, IL-1β, LPS or TNF, induced MΦMP production in a concentration- and time-dependent manner (293% increase, 16h peak, p<0.001). Non-oxidized LDL and minimally oxidized LDL components (POV-PC and PG-PC) did not augment MΦMP generation. oxLDL stimulation increased MΦMP tissue factor (TF) content by 78% (p<0.05), and oxLDL-induced MΦMP production correlated with activation of PI-3K/Akt signaling pathways. Inhibition of Akt signaling with the Akt inhibitor, KP372-1, reduced MΦMP release by 29% (p<0.01). Because statins inhibit inflammatory signaling that promotes MP production, we also examined the ability of mevastatin to reduce ox-LDL-stimulated MΦMP generation. Mevastatin treatment (10μM) reduced oxLDL-stimulated MΦMP production by 60% (p<0.01), MΦMP TF content by 43% (p<0.05), and attenuated oxLDL-stimulated Akt activation. Conclusion: oxLDL induces Akt-dependent production of prothrombotic MPs, a process inhibited by pretreatment with mevastatin. These findings link atherogenic signaling pathways, inflammation, and plaque thrombogenicity, and identify a novel potential mechanism for the LDL-independent antithrombotic effects of statins.