Abstract
Foam cells formed from receptor-mediated uptake of lipoprotein cholesterol by macrophages in the arterial intima are critical in the initiation, progression, and stability of atherosclerotic lesions. Macrophages accumulate cholesterol when conditions favor esterification by acyl-CoA:cholesterol acyltransferase (ACAT) over cholesterylester hydrolysis by a neutral cholesteryl-ester hydrolase, such as hormone-sensitive lipase (HSL), and subsequent cholesterol efflux mediated by extracellular acceptors. We recently made stable transfectants of a murine macrophage cell line, RAW 264.7, that overexpressed a rat HSL cDNA and had a 5-fold higher rate of cholesteryl-ester hydrolysis than control cells. The current study examined the effect of macrophage-specific HSL overexpression on susceptibility to diet-induced atherosclerosis in mice. A transgenic line overexpressing the rat HSL cDNA regulated with a macrophage-specific scavenger receptor promoter-enhancer was established by breeding with C57BL/6J mice. Transgenic peritoneal macrophages exhibited macrophage-specific 7-fold overexpression of HSL cholesterol esterase activity. Total plasma cholesterol levels in transgenic mice fed a chow diet were modestly elevated 16% compared to control littermates. After 14 weeks on a high-fat, high-cholesterol diet, total cholesterol increased 3-fold, with no difference between transgenics and controls. However, HSL overexpression resulted in thicker aortic fatty lesions that were 2.5-times larger in transgenic mice. HSL expression in the aortic lesions was shown by immunocytochemistry. Atherosclerosis was more advanced in transgenic mice exhibiting raised lesions involving the aortic wall, along with lipid accumulation in coronary arteries occurring only in transgenics. Thus, increasing cholesteryl-ester hydrolysis, without concomitantly decreasing ACAT activity or increasing cholesterol efflux, is not sufficient to protect against atherosclerosis.—Escary, J-L., H. A. Choy, K. Reue, X-P. Wang, L. W. Castellani, C. K. Glass, A. J. Lusis, and M. C. Schotz. Paradoxical effect on atherosclerosis of hormone-sensitive lipase overexpression in macrophages. J. Lipid Res. 1999. 40: 397–404.
Highlights
Foam cells formed from receptor-mediated uptake of lipoprotein cholesterol by macrophages in the arterial intima are critical in the initiation, progression, and stability of atherosclerotic lesions
The intracellular deposition of cholesteryl esters is thought to result from an imbalance favoring cholesterol esterification by acyl-CoA:cholesterol acyltransferase (ACAT) in the endoplasmic reticulum over its release by a neutral cholesteryl-ester hydrolase and subsequent efflux via the plasma membrane mediated by extracellular acceptors, such as high density lipoprotein (HDL) [3,4,5]
To examine the effect of hormone-sensitive lipase (HSL) overexpression in macrophages on cholesterol metabolism and susceptibility to atherosclerosis, transgenic mice were designed to express a rat HSL cDNA regulated by a human macrophage scavenger receptor promoter-enhancer
Summary
Foam cells formed from receptor-mediated uptake of lipoprotein cholesterol by macrophages in the arterial intima are critical in the initiation, progression, and stability of atherosclerotic lesions. Macrophages accumulate cholesterol when conditions favor esterification by acylCoA:cholesterol acyltransferase (ACAT) over cholesterylester hydrolysis by a neutral cholesteryl-ester hydrolase, such as hormone-sensitive lipase (HSL), and subsequent cholesterol efflux mediated by extracellular acceptors. We recently made stable transfectants of a murine macrophage cell line, RAW 264.7, that overexpressed a rat HSL cDNA and had a 5-fold higher rate of cholesteryl-ester hydrolysis than control cells. Atherogenesis involves receptor-mediated uptake of lipoproteins by macrophages in the arterial intima, leading to cellular accumulation of cholesterol and formation of the foam cells characteristic of aortic fatty lesions [1, 2]. Macrophage cell line that stably overexpresses rat HSL [14] These cells exhibited a 5-fold higher rate of hydrolysis with cAMP activation compared to control RAW cells, and a dramatic reduction in cholesteryl-ester accumulation [14]
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