Abstract 252: Impact of Endothelial Microparticles on Endothelial Cell Signaling and Endothelium-dependent Vasorelaxation

Abstract

Microparticles (MPs), fragments of membrane shed from stressed/damaged cells, are found in the plasma of healthy individuals with levels increased in vascular disease. However, whether MPs themselves contribute to endothelial dysfunction and damage is unclear. We examined the effects of endothelial MPs (eMPs) on cultured endothelial cells (ECs) in vitro and on the function of isolated mesenteric arteries ex vivo . eMPs were isolated from the media of cultured mouse aortic ECs and quantified by flow cytometry. ECs were treated with eMPs (10 5 /ml) and effects on kinase signaling pathways (Akt, c-Src, ERK1/2, p38 MAPK), superoxide anion generation (dihydroethidium) and NO production (diaminofluorescin) were examined. eMPs increased phosphorylation of ERK1/2 at 5, 15, and 30 minutes post-treatment (P<0.05) and increased phosphorylation of c-Src at 2, 4, and 8 hours post-treatment (P<0.05). Phosphorylation of p38 MAPK and Akt were not altered by eMP exposure. eMPs increased superoxide anion production (208% of control, P<0.05) and decreased ionomycin-induced NO production (39% of control, P<0.05) in ECs after 4 hours. Additionally, the sensitivity to acetylcholine was impaired in MP-treated vessels (pD2: 5.6±0.2) compared to untreated vessels (pD2: 6.7±0.1, P<0.01), assessed in 2nd order mesenteric arteries using wire myography. Finally, we explored mechanisms by which MPs achieve their effects. Co-treatment with an epidermal growth factor receptor inhibitor (AG1478, 10 μM), but not a platelet-derived growth factor receptor inhibitor (Tyrphostin AG1296, 10 μM), blocked microparticle-mediated effects on superoxide generation, and NO production in ECs. In summary, we demonstrate that eMPs impair vasorelaxation ex vivo and activate kinase signaling pathways, promote superoxide production and inhibit endothelial NO production in vitro . These effects may be mediated, at least in part, through EGFR.