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Oxidized membrane vesicles and blebs from apoptotic cells contain biologically active oxidized phospholipids that
Joakim Huber1, Anja Vales, Goran Mitulovic
1Department of Vascular Biology and Thrombosis Research, University of Vienna, Austria.
Abstract:
Membrane vesicles (MVs) released from activated cells and blebs from apoptotic cells are increased in patients with vascular disease and in those with atherosclerotic lesions, and their contribution to inflammatory reactions has been suggested. At sites of inflammation, MVs could serve as rapidly available substrates for peroxidation, carry oxidized compounds to activate other cells, and amplify inflammation. Here, we show that MVs released from tert-butyl hydroperoxide-treated endothelial cells (ECs) and apoptotic blebs, but not MVs from Ca(2+) ionophore-treated ECs, stimulate monocyte adhesion to ECs, an important step in atherogenesis. We show that oxidized phospholipids, such as the previously identified 1-palmitoyl-2-(5-oxovaleroyl)-sn-glycero-3-phosphorylcholine (POVPC), are responsible for biological activity in MVs and apoptotic blebs. Natural antibodies from apolipoprotein E-null mice that recognize POVPC also recognize oxidized MVs, and pretreatment of MVs with these antibodies inhibits their ability to activate ECs. Furthermore, the biological activity of oxidized MVs is inhibited by platelet-activating factor receptor antagonists, which have been shown to inhibit the action of POVPC. Taken together, we show that oxidized MVs and apoptotic blebs stimulate ECs to specifically bind monocytes, with oxidized phospholipids (POVPC) being the active principle. In addition to oxidized lipoproteins, oxidized MVs and apoptotic blebs may play an important role in chronic inflammatory diseases, such as atherosclerosis.
Insights
Oxidized membrane vesicles (MVs) and apoptotic blebs promote monocyte adhesion to endothelial cells, a key step in atherosclerosis. Oxidized phospholipids like POVPC are responsible for this inflammatory activity.
Area of Science:
- Cardiovascular Biology
- Cell Biology
- Inflammation Research
Background:
- Membrane vesicles (MVs) and apoptotic blebs are elevated in vascular disease and atherosclerosis.
- These extracellular vesicles may contribute to inflammatory processes and disease progression.
Purpose of the Study:
- To investigate the role of MVs and apoptotic blebs in monocyte adhesion to endothelial cells.
- To identify the active components within MVs and blebs responsible for stimulating inflammatory responses.
Main Methods:
- Treatment of endothelial cells (ECs) with tert-butyl hydroperoxide or Ca(2+) ionophore to generate MVs.
- Assessing monocyte adhesion to ECs stimulated by MVs and apoptotic blebs.
- Identifying oxidized phospholipids using mass spectrometry and testing their biological activity.
- Utilizing natural antibodies and receptor antagonists to block MV activity.
Main Results:
- MVs from peroxide-treated ECs and apoptotic blebs, but not ionophore-treated MVs, enhanced monocyte adhesion to ECs.
- Oxidized phospholipids, specifically 1-palmitoyl-2-(5-oxovaleroyl)-sn-glycero-3-phosphorylcholine (POVPC), were identified as the active mediators.
- Antibodies recognizing POVPC and platelet-activating factor receptor antagonists inhibited the pro-inflammatory effects of oxidized MVs.
Conclusions:
- Oxidized MVs and apoptotic blebs stimulate endothelial cells to bind monocytes, mediated by oxidized phospholipids like POVPC.
- These findings highlight a novel mechanism by which oxidized MVs contribute to chronic inflammatory diseases, such as atherosclerosis.