Hormone-sensitive lipase overexpression increases cholesteryl ester hydrolysis in macrophage foam cells

Abstract

Atherosclerosis is a complex physiopathologic process initiated by the formation of cholesterol-rich lesions in the arterial wall. Macrophages play a crucial role in this process because they accumulate large amounts of cholesterol esters (CEs) to form the foam cells that initiate the formation of the lesion and participate actively in the development of the lesion. Therefore, prevention or reversal of CE accumulation in macrophage foam cells could result in protection from multiple pathological effects. In this report, we show that the CE hydrolysis catalyzed by neutral cholesterol ester hydrolase (nCEH) can be modulated by overexpression of hormone-sensitive lipase (HSL) in macrophage foam cells. For these studies, RAW 264.7 cells, a murine macrophage cell line, were found to be a suitable model of foam cell formation. HSL expression and nCEH activity in these cells and in peritoneal macrophages were comparable. In addition, antibody titration showed that essentially all nCEH activity in murine macrophages was accounted for by HSL. To examine the effect of HSL overexpression on foam cell formation, RAW 264.7 cells were stably transfected with a rat HSL cDNA. The resulting HSL overexpression increased hydrolysis of cellular CEs 2- to 3-fold in lipid-laden cells in the presence of an acyl coenzyme A:cholesterol acyltransferase (ACAT) inhibitor. Furthermore, addition of cAMP produced a 5-fold higher rate of CE hydrolysis in cholesterol-laden, HSL-overexpressing cells than in control cells and resulted in nearly complete hydrolysis of cellular CEs in only 9 hours, compared with <50% hydrolysis in control cells. Thus, HSL overexpression stimulated the net hydrolysis of CEs, leading to faster hydrolysis of lipid deposits in model foam cells. These data suggest that HSL overexpression in macrophages, alone or in combination with ACAT inhibitors, may constitute a useful therapeutic approach for impeding CE accumulation in macrophages in vivo.