Abstract 1910: Shear Stress Modulates Endothelial Microparticles Shedding
Background : Microparticles are bioactive submicron membrane vesicles released upon cell activation and characterized by phosphatidyserine (PS) exposure. Plasma levels of endothelial microparticles (EMPs) are markers of cardiovascular diseases and may contribute to the pathogenesis of atherosclerosis. Laminar shear stress (SS) is known to protect against plaque formation contrarily to oscillatory and low SS. We thus investigated whether different flow patterns (laminar, low or static) could affect EMP release.
Results : Human Umbilical Vein Endothelial Cells (HUVECs, passage 1–2) were subjected to high and low SS (15, 1.5 dynes /cm2) for 24 hours or maintained under static conditions. EMPs were isolated from the cell culture medium by differential centrifugation, and characterized by annexin V labelling and surface markers using flow cytometry analysis. HUVECs exposed to high SS for 24 hours emitted 4 fold less AnnexinV+ EMPs compared to static (p<0.001) and 3 fold less compared to low SS (p<0.01) conditions. Treatment of HUVECs with the NO synthase inhibitor L-NAME (10 – 4M) significantly increased EMPs in all conditions when compared to untreated cells. Furthermore, static-derived EMPs were not only more abundant, but they also expressed at their surface a significant increase in negatively charged PS per EMP (vs low SS and high SS,p<0.001). These data suggest that low-sheared and specially static- derived EMPs have high thrombogenic properties. We further characterized EMPs by determining their surface expression of ICAM-1 and VCAM-1. EMP expression of ICAM-1 was increased in low SS and inhibited by high SS compared to static conditions, whereas VCAM-1 expressed by EMPs significantly decreased in a SS dependent manner, ie, 1 fold less in low SS vs static (p<0.05), 10 fold less in high SS vs static (p<0.05) and 5 fold less in high SS vs low SS (p<0.05).
Conclusions : Altogether, these findings indicate that high SS decreased the thrombotic and adhesive properties of EMPs, which might in part explain their anti-atherogenic effects, whereas low SS induced the shedding of prothrombotic, ICAM-1 and VCAM-1 positive EMPs, suggesting a novel way by which low SS might induce the formation and progression of atherosclerotic plaques.