Abstract
Cholesteryl ester (CE) accumulation in macrophages represents a crucial event during foam cell formation, a hallmark of atherogenesis. Here we investigated the role of two previously described CE hydrolases, hormone-sensitive lipase (HSL) and KIAA1363, in macrophage CE hydrolysis. HSL and KIAA1363 exhibited marked differences in their abilities to hydrolyze CE, triacylglycerol (TG), diacylglycerol (DG), and 2-acetyl monoalkylglycerol ether (AcMAGE), a precursor for biosynthesis of platelet-activating factor (PAF). HSL efficiently cleaved all four substrates, whereas KIAA1363 hydrolyzed only AcMAGE. This contradicts previous studies suggesting that KIAA1363 is a neutral CE hydrolase. Macrophages of KIAA1363−/− and wild-type mice exhibited identical neutral CE hydrolase activity, which was almost abolished in tissues and macrophages of HSL−/− mice. Conversely, AcMAGE hydrolase activity was diminished in macrophages and some tissues of KIAA1363−/− but unchanged in HSL−/− mice. CE turnover was unaffected in macrophages lacking KIAA1363 and HSL, whereas cAMP-dependent cholesterol efflux was influenced by HSL but not by KIAA1363. Despite decreased CE hydrolase activities, HSL−/− macrophages exhibited CE accumulation similar to wild-type (WT) macrophages. We conclude that additional enzymes must exist that cooperate with HSL to regulate CE levels in macrophages. KIAA1363 affects AcMAGE hydrolase activity but is of minor importance as a direct CE hydrolase in macrophages.
Highlights
Cholesteryl ester (CE) accumulation in macrophages represents a crucial event during foam cell formation, a hallmark of atherogenesis
Overexpression of hormonesensitive lipase (HSL) in COS-7 cells resulted in markedly increased neutral CE- (17-fold) (Fig. 2A), TG- (22-fold) (Fig. 2B), and DG- (13-fold) (Fig. 2C) hydrolase activities compared with LacZ-transfected cells
We compared neutral CE hydrolase activities in HSL- and KIAA1363-transfected COS-7 cells using alternative mixed micelles as substrates. By using both PC/PI and PC/Na-taurocholate, we found significantly increased neutral CE hydrolase activity in cell lysates overexpressing HSL compared with LacZ-transfected cells, whereas
Summary
Cholesteryl ester (CE) accumulation in macrophages represents a crucial event during foam cell formation, a hallmark of atherogenesis. In RAW264.7 macrophages, neutral CE hydrolase activity was nearly completely blocked with an antiHSL antibody, whereas overexpression of HSL increased CE hydrolysis in these cells [5]. Enhanced CE hydrolysis, in macrophages of transgenic mice overexpressing HSL, led to accumulation of free cholesterol (FC) and an increased incidence and severity of aortic fatty lesions [7]. These results suggested that HSL plays a major role in the hydrolysis of CE stores in macrophages. Since CEL is expressed in human but not in murine macrophages, it was proposed that CEL plays a similar role in human macrophages as does HSL in mouse macrophages [16]
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