Unfolded protein response involved in oxidized ldl-evoked endothelial dysfunction

Abstract

Accumulation of cholesterol in the endoplasmatic reticulum (ER) contributes to apoptosis of macrophages and smooth muscle cells in atherosclerotic lesions. The present study was designed to investigate whether unfolded protein response (UPR) is activated in endothelial cells in atherosclerotic aortae and cells exposed to oxidized low density lipoprotein (ox-LDL). Immunohistochemistry was performed for glucose-regulated protein (Grp78) and measurements of nitric oxide (NO) and calcium in human umbilical vein endothelial cells (HUVEC). Grp78, as marker for UPR activation, was extensively expressed in atherosclerotic plaques, in endothelium and adventitia localised in the ascending part of aorta (ApoE-/- mice (n=8)). GRP78 expression was also increased in HUVEC exposed to a component of ox-LDL, lysophosphatidyl choline (LPC), and a chemical inducer of ER stress tunicamycin (TM). In HUVEC, endothelial NO synthase (eNOS) expression was unaltered, while eNOS phosphorylation at serine1177 was unaltered after incubation with LPC and increased with tunicamycin. However, histamine (1 μM)-induced increases in NO concentration (ΔNO, 22.9±5.9 nM) were decreased after incubation with LPC (7.8±1.7) and TM (7.9±2.1), and inhibited in the presence of asymmetric dimetylarginine. Our results indicate activation of the UPR system associated with reduced NO release, suggesting involvement in endothelial dysfunction caused by Ox-LDL. [...].