ACAT1 Deficiency Disrupts Cholesterol Efflux and Alters Cellular Morphology in Macrophages

Objective— Acyl-coenzyme A: cholesterol acyltransferase (ACAT) converts intracellular free cholesterol (FC) into cholesteryl esters (CE) for storage in lipid droplets. Recent studies in our laboratory have shown that the deletion of the macrophage ACAT1 gene results in apoptosis and increased atherosclerotic lesion area in the aortas of hyperlipidemic mice. The objective of the current study was to elucidate the mechanism of the increased atherosclerosis. Methods and Results— CE storage and FC efflux were studied in ACAT1(−/−) peritoneal macrophages that were treated with acetylated low-density lipoprotein (acLDL). Our results show that efflux of cellular cholesterol was reduced by 25% in ACAT1-deficient cells compared with wild-type controls. This decrease occurred despite the upregulated expression of ABCA1, an important mediator of cholesterol efflux. In contrast, ACAT1 deficiency increased efflux of the cholesterol derived from acLDL by 32%. ACAT1-deficient macrophages also showed a 26% increase in the accumulation of FC derived from acLDL, which was associated with a 75% increase in the number of intracellular vesicles. Conclusions— Together, these data show that macrophage ACAT1 influences the efflux of both cellular and lipoprotein-derived cholesterol and propose a pathway for the pro-atherogenic transformation of ACAT1(−/−) macrophages.

[1]  S. Yokoyama,et al.  An inhibitor of acylCoA: cholesterol acyltransferase increases expression of ATP-binding cassette transporter A1 and thereby enhances the ApoA-I-mediated release of cholesterol from macrophages. , 2004, Biochimica et biophysica acta.

[2]  D. Ory.  The niemann-pick disease genes; regulators of cellular cholesterol homeostasis. , 2004, Trends in cardiovascular medicine.

[3]  George Kuriakose,et al.  The endoplasmic reticulum is the site of cholesterol-induced cytotoxicity in macrophages , 2003, Nature Cell Biology.

[4]  M. Linton,et al.  Rapid quantification of murine ABC mRNAs by real time reverse transcriptase-polymerase chain reaction Published, JLR Papers in Press, September 1, 2002. DOI 10.1194/jlr.D200020-JLR200 , 2002, Journal of Lipid Research.

[5]  I. Tabas,et al.  ABCA1-mediated Cholesterol Efflux Is Defective in Free Cholesterol-loaded Macrophages , 2002, The Journal of Biological Chemistry.

[6]  O. Francone,et al.  Increased Atherosclerosis in Hyperlipidemic Mice With Inactivation of ABCA1 in Macrophages , 2002, Arteriosclerosis, thrombosis, and vascular biology.

[7]  Carrie M. Welch,et al.  Preferential ATP-binding Cassette Transporter A1-mediated Cholesterol Efflux from Late Endosomes/Lysosomes* , 2001, The Journal of Biological Chemistry.

[8]  M. Linton,et al.  Increased Cholesterol Efflux in Apolipoprotein AI (ApoAI)–Producing Macrophages as a Mechanism for Reduced Atherosclerosis in ApoAI(−/−) Mice , 2001, Arteriosclerosis, thrombosis, and vascular biology.

[9]  A. Tall,et al.  ATP-binding Cassette Transporter A1 (ABCA1) Functions as a Cholesterol Efflux Regulatory Protein* , 2001, The Journal of Biological Chemistry.

[10]  B. McHendry-Rinde,et al.  Evidence that newly synthesized esterified cholesterol is deposited in existing cytoplasmic lipid inclusions. , 2001, Journal of lipid research.

[11]  P. Yancey,et al.  Lysosomal cholesterol derived from mildly oxidized low density lipoprotein is resistant to efflux. , 2001, Journal of lipid research.

[12]  Robert V Farese,et al.  Increased atherosclerosis in LDL receptor-null mice lacking ACAT1 in macrophages. , 2001, The Journal of clinical investigation.

[13]  Robert V Farese,et al.  Mammalian acyl-CoA:cholesterol acyltransferases. , 2000, Biochimica et biophysica acta.

[14]  J. Mcneish,et al.  The Correlation of ATP-binding Cassette 1 mRNA Levels with Cholesterol Efflux from Various Cell Lines* , 2000, The Journal of Biological Chemistry.

[15]  C. Gabel,et al.  High density lipoprotein deficiency and foam cell accumulation in mice with targeted disruption of ATP-binding cassette transporter-1. , 2000, Proceedings of the National Academy of Sciences of the United States of America.

[16]  P. Bachorik,et al.  Novel effects of the acyl-coenzyme A:Cholesterol acyltransferase inhibitor 58-035 on foam cell development in primary human monocyte-derived macrophages. , 1999, Arteriosclerosis, thrombosis, and vascular biology.

[17]  T. Mazzone,et al.  Apolipoprotein E-dependent cholesterol efflux from macrophages: kinetic study and divergent mechanisms for endogenous versus exogenous apolipoprotein E. , 1999, Journal of lipid research.

[18]  P. Yancey,et al.  Crystallization of free cholesterol in model macrophage foam cells. , 1999, Arteriosclerosis, thrombosis, and vascular biology.

[19]  F. Maxfield,et al.  Cholesterol distribution in living cells: fluorescence imaging using dehydroergosterol as a fluorescent cholesterol analog. , 1998, Biophysical journal.

[20]  P. Yancey,et al.  Lysosomal sequestration of free and esterified cholesterol from oxidized low density lipoprotein in macrophages of different species. , 1998, Journal of lipid research.

[21]  D. Small,et al.  Effects of intracellular free cholesterol accumulation on macrophage viability: a model for foam cell death. , 1998, Arteriosclerosis, thrombosis, and vascular biology.

[22]  H. Kruth,et al.  Apolipoprotein E Produced by Human Monocyte-derived Macrophages Mediates Cholesterol Efflux That Occurs in the Absence of Added Cholesterol Acceptors* , 1996, The Journal of Biological Chemistry.

[23]  W. J. Johnson,et al.  Cell Toxicity Induced by Inhibition of Acyl Coenzyme A:Cholesterol Acyltransferase and Accumulation of Unesterified Cholesterol * , 1995, The Journal of Biological Chemistry.

[24]  S. Fazio,et al.  Prevention of atherosclerosis in apolipoprotein E-deficient mice by bone marrow transplantation , 1995, Science.

[25]  J. Guyton,et al.  Development of the atherosclerotic core region. Chemical and ultrastructural analysis of microdissected atherosclerotic lesions from human aorta. , 1994, Arteriosclerosis and thrombosis : a journal of vascular biology.

[26]  T. Mazzone,et al.  Expression of heterologous human apolipoprotein E by J774 macrophages enhances cholesterol efflux to HDL3. , 1994, Journal of lipid research.

[27]  I. Tabas,et al.  Free cholesterol loading of macrophages stimulates phosphatidylcholine biosynthesis and up-regulation of CTP: phosphocholine cytidylyltransferase. , 1994, The Journal of biological chemistry.

[28]  W. J. Johnson,et al.  The efflux of lysosomal cholesterol from cells. , 1990, The Journal of biological chemistry.

[29]  G. Schmitz,et al.  Ca++ Antagonists and ACAT Inhibitors Promote Cholesterol Efflux from Macrophages by Different Mechanisms: II. Characterization of Intracellular Morphologic Changes , 1988, Arteriosclerosis.

[30]  M. Brown,et al.  Degradation of cationized low density lipoprotein and regulation of cholesterol metabolism in homozygous familial hypercholesterolemia fibroblasts. , 1976, Proceedings of the National Academy of Sciences of the United States of America.

[31]  E. Weibel,et al.  PRACTICAL STEREOLOGICAL METHODS FOR MORPHOMETRIC CYTOLOGY , 1966, The Journal of cell biology.

[32]  W. J. Dyer,et al.  A rapid method of total lipid extraction and purification. , 1959, Canadian journal of biochemistry and physiology.

[33]  S. Horiuchi,et al.  Localization of human acyl-coenzyme A: cholesterol acyltransferase-1 (ACAT-1) in macrophages and in various tissues. , 2000, The American journal of pathology.