Translational Studies of Lipoprotein-Associated Phospholipase A2 in Inflammation and Atherosclerosis

Abstract

This study sought to examine the role of lipoprotein-associated phospholipase A₂ (Lp-PLA₂/PLA2G7) in human inflammation and coronary atherosclerosis. Lp-PLA₂ has emerged as a potential therapeutic target in coronary heart disease. Data supporting Lp-PLA₂ are indirect and confounded by species differences; whether Lp-PLA₂ is causal in coronary heart disease remains in question. We examined inflammatory regulation of Lp-PLA₂ during experimental endotoxemia in humans, probed the source of Lp-PLA₂ in human leukocytes under inflammatory conditions, and assessed the relationship of variation in PLA2G7, the gene encoding Lp-PLA₂, with coronary artery calcification. In contrast to circulating tumor necrosis factor-alpha and C-reactive protein, blood and monocyte Lp-PLA₂ messenger ribonucleic acid decreased transiently, and plasma Lp-PLA₂ mass declined modestly during endotoxemia. In vitro, Lp-PLA₂ expression increased dramatically during human monocyte to macrophage differentiation and further in inflammatory macrophages and foamlike cells. Despite only a marginal association of single nucleotide polymorphisms in PLA2G7 with Lp-PLA₂ activity or mass, numerous PLA2G7 single nucleotide polymorphisms were associated with coronary artery calcification. In contrast, several single nucleotide polymorphisms in CRP were significantly associated with plasma C-reactive protein levels but had no relation with coronary artery calcification. Circulating Lp-PLA₂ did not increase during acute phase response in humans, whereas inflammatory macrophages and foam cells, but not circulating monocytes, are major leukocyte sources of Lp-PLA₂. Common genetic variation in PLA2G7 is associated with subclinical coronary atherosclerosis. These data link Lp-PLA₂ to atherosclerosis in humans while highlighting the challenge in using circulating Lp-PLA₂ as a biomarker of Lp-PLA₂ actions in the vasculature.