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Papers In Press, published online ahead of print May 1, 2007
J. Lipid Res., doi:10.1194/jlr.M600390-JLR200

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Journal of Lipid Research, Vol. 48, 1012-1021, May 2007
Copyright © 2007 by American Society for Biochemistry and Molecular Biology

Effects of cellular cholesterol loading on macrophage foam cell lysosome acidification

Brian E. Cox^*, Evelyn E. Griffin^*, Jody C. Ullery^* and W. Gray Jerome^1,*,

^* Department of Pathology, Vanderbilt University Medical Center, Nashville, TN 37232
Department of Cancer Biology, Vanderbilt University Medical Center, Nashville, TN 37232

The online version of this article (available at http://www.jlr.org) contains supplementary data in the form of four figures.

Published, JLR Papers in Press, February 16, 2007.

¹ To whom correspondence should be addressed. e-mail: jay.jerome{at}vanderbilt.edu

Macrophages incubated with mildly oxidized low density lipoprotein (OxLDL), aggregated low density lipoprotein (AggLDL), or cholesteryl ester-rich lipid dispersions (DISPs) accumulate cholesterol in lysosomes followed by an inhibition of lysosomal cholesteryl ester (CE) hydrolysis. The variety of cholesterol-containing particles producing inhibition of hydrolysis suggests that inhibition may relate to general changes in lysosomes. Lysosome pH is a key mediator of activity and thus is a potential mechanism for lipid-induced inhibition. We investigated the effects of cholesterol accumulation on THP-1 macrophage lysosome pH. Treatment with OxLDL, AggLDL, and DISPs resulted in inhibition of the lysosome's ability to maintain an active pH and concomitant decreases in CE hydrolysis. Consistent with an overall disruption of lysosome function, exposure to OxLDL or AggLDL reduced lysosomal apolipoprotein B degradation. The lysosomal cholesterol sequestration and inactivation are not observed in cholesterol-equivalent cells loaded using acetylated low density lipoprotein (AcLDL). However, AcLDL-derived cholesterol in the presence of progesterone (to block cholesterol egression from lysosomes) inhibited lysosome acidification. Lysosome inhibition was not attributable to a decrease in the overall levels of vacuolar ATPase. However, augmentation of membrane cholesterol in isolated lysosomes inhibited vacuolar ATPase-dependent pumping of H⁺ ions into lysosomes. These data indicate that lysosomal cholesterol accumulation alters lysosomes in ways that could exacerbate foam cell formation and influence atherosclerotic lesion development.

Supplementary key words atherosclerosis • microscopy • vacuolar H⁺-adenosine 5'-triphosphatase

Abbreviations: AcLDL, acetylated low density lipoprotein; AggLDL, aggregated low density lipoprotein; apoB, apolipoprotein B; CD, methyl-ß-cyclodextrin; CE, cholesteryl ester; DISP, cholesteryl ester-rich lipid dispersion; FC, free cholesterol; LAMP-1, lysosome-associated membrane protein-1; OxLDL, oxidized low density lipoprotein; TBARS, thiobarbituric acid-reactive substances; v-ATPase, vacuolar H⁺-ATPase

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