Abstract
LPL and endothelial lipase (EL) are associated with macrophages in human atherosclerotic lesions, and overexpression of LPL in mouse macrophages is associated with a greater extent of atherosclerosis. To investigate potential mechanisms by which macrophage-derived lipase expression may mediate proatherogenic effects, we used lentivirus-mediated RNA interference to suppress the expression of either LPL or EL within THP-1 macrophages. After suppression of either LPL or EL, significant decreases in the concentration of interleukin-1beta, interleukin-6, monocyte chemoattractant protein-1, and tumor necrosis factor-alpha were observed. Incubation of THP-1 macrophages with either mildly or extensively oxidized LDL consistently decreased cytokine expression, which was additive to that contributed by lipase suppression. Decreased lipase expression was also associated with an altered lipid composition, with reduced percentages of cholesterol (unesterified and esterified), triglycerides, and lysophosphatidylcholine. Microarray data indicated a decreased expression of proinflammatory genes, growth factors, and antiapoptotic genes. By contrast, there was an increased expression of lipoprotein receptors (scavenger receptor 1, low density lipoprotein receptor, scavenger receptor class B type I, and CD36). Thus, we conclude that the suppression of either LPL or EL decreases proinflammatory cytokine expression and influences the lipid composition of THP-1 macrophages. These results provide further insight into the specific metabolic and potential pathological roles of LPL and EL in human macrophages.
Highlights
LPL and endothelial lipase (EL) are associated with macrophages in human atherosclerotic lesions, and overexpression of LPL in mouse macrophages is associated with a greater extent of atherosclerosis
It is well recognized that a variety of proinflammatory cytokines are expressed in activated macrophages, including tumor necrosis factor-a (TNF-a), interleukin-6 (IL-6), IL-8, IL-1b, and monocyte chemoattractant protein-1 (MCP-1)
The specific roles of these lipases in atherosclerosis likely depend on their tissue localization, accumulating evidence supports a proatherogenic role of macrophage-derived lipases
Summary
LPL and endothelial lipase (EL) are associated with macrophages in human atherosclerotic lesions, and overexpression of LPL in mouse macrophages is associated with a greater extent of atherosclerosis. We conclude that the suppression of either LPL or EL decreases proinflammatory cytokine expression and influences the lipid composition of THP-1 macrophages. These results provide further insight into the specific metabolic and potential pathological roles of LPL and EL in human macrophages.—Qiu, G., A. It is well recognized that a variety of proinflammatory cytokines are expressed in activated macrophages, including tumor necrosis factor-a (TNF-a), interleukin-6 (IL-6), IL-8, IL-1b, and monocyte chemoattractant protein-1 (MCP-1) These cytokines have been shown to promote lesion progression by aggravating endothelial dysfunction, recruiting additional inflammatory cells, or stimulating smooth muscle proliferation [1]. This article is available online at http://www.jlr.org
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