Exposure of Endothelial Cells to Physiological Levels of Myeloperoxidase-Modified LDL Delays Pericellular Fibrinolysis

Abstract

BackgroundBlood fluidity is maintained by a delicate balance between coagulation and fibrinolysis. The endothelial cell surface is a key player in this equilibrium and cell surface disruptions can upset the balance. We investigated the role of pericellular myeloperoxidase oxidized LDLs (Mox-LDLs) in this balance.Methods and ResultsWe designed a technical device that enabled us to monitor fibrinolysis in real-time at the surface of an endothelial cell line (EA.hy926), and showed that Mox-LDL decreased pericellular fibrinolysis. There were no changes in fibrinolysis when EA.hy926 endothelial cells were exposed to native LDL (24 hours) at doses of 10, 50, 100 and up to 1250 µg/ml. However, treatment of EA.hy926 endothelial cells with 10 and 50 µg/ml of Mox-LDL (physiological serum concentrations) increased the lysis time by 15 and 13%, respectively (p<0.001), although this effect was not present at higher concentrations of 100 µg/ml. This effect was not correlated with any changes in PAI-1 or t-PA or PA Receptor (PAR) expression. No effect was observed at the surface of smooth muscle cells used as controls.ConclusionOur data link the current favorite hypothesis that modified LDL has a causal role in atheroma plaque formation with an old suggestion that fibrin may also play a causal role. Our data help complete the paradigm of atherosclerosis: Modified LDL locally enhances fibrin deposition (present work); fibrin deposits enhance endothelial permeability; this effect allows subendothelial accumulation of lipid and foam cells.

Low-Density Lipoprotein Modified by Myeloperoxidase in Inflammatory Pathways and Clinical Studies

“…This was first mentioned as a key factor in 1998 by Sueishi et al [139] and Mayerl et al [140], and a recent clinical study from our group further confirmed it [141]. However, until 2012, the interplay between Mox-LDL (and more generally ox-LDL), endothelial cells, and fibrinolysis had not been investigated [142]. Our group documented this intriguing subject with the aid of a device which allows us to monitor fibrinolysis in real time [143].…”

“…Previous data described LOX-1 binding to ox-LDL and mediating effects in endothelial cells. However, our first investigations by neutralization of this receptor using antibodies did not impact IL-8 production induced by Mox-LDL, disproving this pathway [142]. Hence, future research on scavenger receptor is required to extend the understanding of Mox-LDL effects on endothelial cells.…”

Myeloperoxidase Oxidized LDL Interferes with Endothelial Cell Motility through miR-22 and Heme Oxygenase 1 Induction: Possible Involvement in Reendothelialization of Vascular Injuries

“…MPO is an enzyme secreted by activated neutrophils; it catalyses the production of hypochlorous acid from hydrogen peroxide and chloride. The generated HOCl is responsible for the modification of LDLs into chlorinated LDLs (HOCl-LDLs) [ 5 ].…”

Macrophage Differentiation from Monocytes Is Influenced by the Lipid Oxidation Degree of Low Density Lipoprotein

“…Oxidized low-density lipoprotein (oxLDL) plays a critical role in atherosclerotic plaque formation, which is triggered by the persistence of lipid-laden macrophages [ 1 ] as well as interfering endothelial cell motility [ 2 ] in arterial wall. The differentiation of monocytes into macrophages, which accumulate oxLDL to form foam cells, is induced by oxLDL [ 1 , 3 ].…”