Atherosclerosis affects calcium signalling in endothelial cells from apolipoprotein E knockout mice before plaque formation

Abstract

Little is known about how hypercholesterolaemia affects Ca ²⁺ signalling in the vasculature of ApoE ^−/− mice, a model of atherosclerosis. Our objectives were therefore to determine (i) if hypercholesterolaemia alters Ca ²⁺ signalling in aortic endothelial cells before overt atherosclerotic lesions occur, (ii) how Ca ²⁺ signals are affected in older plaque-containing mice, and (iii) whether Ca ²⁺ signalling changes were translated into contractility differences. Using confocal microscopy we found agonist-specific Ca ²⁺ changes in endothelial cells. ATP responses were unchanged in ApoE ^−/− cells and methyl-β-cyclodextrin, which lowers cholesterol, was without effect. In contrast, Ca ²⁺ signals to carbachol were significantly increased in ApoE ^−/− cells, an effect methyl-β-cyclodextrin reversed. Ca ²⁺ signals were more oscillatory and store-operated Ca ²⁺ entry decreased as mice aged and plaques formed. Despite clearly increased Ca ²⁺ signals, aortic rings pre-contracted with phenylephrine had impaired relaxation to carbachol. This functional deficit increased with age, was not related to ROS generation, and could be partially rescued by methyl-β-cyclodextrin. In conclusion, carbachol-induced calcium signalling and handling are significantly altered in endothelial cells of ApoE ^−/− mice before plaque development. We speculate that reduction in store-operated Ca ²⁺ entry may result in less efficient activation of eNOS and thus explain the reduced relaxatory response to CCh, despite the enhanced Ca ²⁺ response.