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Published on: October 12, 2017
Oxidized Low-Density Lipoprotein Induces Macrophage Production of Prothrombotic Microparticles
Julio F Marchini1,2, Andre Manica1,3, Paulo Crestani1
1Cardiovascular Division Department of Medicine Brigham and Women's HospitalHarvard Medical School Boston MA.
Abstract:
Background Activated vascular cells produce submicron prothrombotic and proinflammatory microparticle vesicles. Atherosclerotic plaques contain high levels of microparticles. Plasma microparticle levels increase during acute coronary syndromes and the thrombotic consequences of plaque rupture likely involve macrophage-derived microparticles (MΦMPs). The activation pathways that promote MΦMP production remain poorly defined. This study tested the hypothesis that signals implicated in atherogenesis also stimulate MΦMP production. Methods and Results We stimulated human primary MΦs with proinflammatory cytokines and atherogenic lipids, and measured MΦMP production by flow cytometry. Oxidized low-density lipoprotein (oxLDL; 25 µg/mL) induced MΦMP production in a concentration-dependent manner (293% increase; P<0.001), and these oxLDL MΦMP stimulatory effects were mediated by CD36. OxLDL stimulation increased MΦMP tissue factor content by 78% (P<0.05), and oxLDL-induced MΦMP production correlated with activation of caspase 3/7 signaling pathways. Salvionolic acid B, a CD36 inhibitor and a CD36 inhibitor antibody reduced oxLDL-induced MΦMP by 67% and 60%, respectively. Caspase 3/7 inhibition reduced MΦMP release by 52% (P<0.01) and caspase 3/7 activation increased MΦMP production by 208% (P<0.01). Mevastatin pretreatment (10 µM) decreased oxLDL-induced caspase 3/7 activation and attenuated oxLDL-stimulated MΦMP production and tissue factor content by 60% (P<0.01) and 43% (P<0.05), respectively. Conclusions OxLDL induces the production of prothrombotic microparticles in macrophages. This process depends on caspases 3 and 7 and CD36 and is inhibited by mevastatin pretreatment. These findings link atherogenic signaling pathways, inflammation, and plaque thrombogenicity and identify a novel potential mechanism for antithrombotic effects of statins independent of LDL lowering.
Insights
Oxidized LDL (oxLDL) stimulates macrophages to produce prothrombotic microparticles, a process involving CD36 and caspase 3/7 pathways. Mevastatin pretreatment inhibits this production, suggesting a novel statin mechanism against plaque thrombogenicity.
Area of Science:
- Cardiovascular Biology
- Cellular Biology
- Immunology
Background:
- Activated vascular cells, particularly macrophages, release prothrombotic and proinflammatory microparticle vesicles.
- Atherosclerotic plaques and acute coronary syndromes are associated with elevated microparticle levels, with macrophage-derived microparticles (MΦMPs) implicated in plaque rupture thrombotic events.
- The precise signaling pathways driving MΦMP production remain largely undefined.
Purpose of the Study:
- To investigate whether key atherogenesis-related signals stimulate MΦMP production.
- To elucidate the molecular mechanisms, including specific proteins and signaling pathways, involved in oxLDL-induced MΦMP generation.
- To assess the potential inhibitory effects of mevastatin on oxLDL-induced MΦMP production and associated prothrombotic markers.
Main Methods:
- Human primary macrophages were stimulated with proinflammatory cytokines and atherogenic lipids, specifically oxidized low-density lipoprotein (oxLDL).
- Macrophage-derived microparticle (MΦMP) production and tissue factor content were quantified using flow cytometry.
- Inhibitors of CD36, caspase 3/7, and mevastatin pretreatment were employed to investigate mechanistic pathways and potential therapeutic interventions.
Main Results:
- Oxidized low-density lipoprotein (oxLDL) significantly increased MΦMP production in a concentration-dependent manner, mediated by CD36.
- OxLDL stimulation elevated MΦMP tissue factor content and correlated with caspase 3/7 pathway activation.
- CD36 inhibition, caspase 3/7 inhibition, and mevastatin pretreatment markedly reduced oxLDL-induced MΦMP production and/or tissue factor content.
Conclusions:
- Oxidized LDL is a potent inducer of prothrombotic microparticles from macrophages.
- The production of these microparticles is critically dependent on CD36 and caspase 3/7 signaling pathways.
- Mevastatin pretreatment demonstrates an inhibitory effect on oxLDL-induced MΦMP production, suggesting a potential LDL-independent antithrombotic mechanism for statins in atherosclerosis.
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