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Journal of Lipid Research, Vol. 46, 1433-1439, July 2005
Copyright © 2005 by American Society for Biochemistry and Molecular Biology

The recycling of apolipoprotein E in macrophages

Alyssa H. Hasty^1,*, Michelle R. Plummer^*, Karl H. Weisgraber, MacRae F. Linton^,**, Sergio Fazio^, and Larry L. Swift

^* Departments of Molecular Physiology and Biophysics, Vanderbilt University Medical Center, Nashville, TN 37232
Medicine, Vanderbilt University Medical Center, Nashville, TN 37232
^** Pharmacology, Vanderbilt University Medical Center, Nashville, TN 37232
Pathology, Vanderbilt University Medical Center, Nashville, TN 37232
Gladstone Institute of Cardiovascular Disease, Cardiovascular Research Institute, and Department of Pathology, University of California, San Francisco, CA 94141

Published, JLR Papers in Press, April 1, 2005. DOI 10.1194/jlr.M400418-JLR200

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

The ability of apolipoprotein E (apoE) to be spared degradation in lysosomes and to recycle to the cell surface has been demonstrated by our group and others, but its physiologic relevance is unknown. In this study, we characterized apoE recycling in primary murine macrophages and probed the effects of HDL and apoA-I on this process. In cells pulsed with ¹²⁵I·apoE bound to VLDL, intact apoE was found in the chase medium for up to 24 h after the pulse. Approximately 27 ± 5% of the apoE internalized during the pulse was recycled after 4 h of chase. Addition of apoA-I and HDL increased apoE recycling to 45 ± 3% and 46 ± 3%, respectively, similar to the amount of apoE recycled after pulsing the cells with ¹²⁵I·apoE·HDL. In addition, apoA-I-producing macrophages from transgenic mice showed increased apoE recycling at 4 h (38 ± 3%). Increased ABCA1 expression potentiated apoE recycling, suggesting that recycling occurs via ABCA1. Finally, in the presence of apoA-I, recycled apoE exited the cells on HDL-like particles.

These results suggest that apoE recycling in macrophages may be part of a larger signaling loop activated by HDL and directed at maximizing cholesterol losses from the cell.

Supplementary key words cholesterol • efflux • atherosclerosis • high density lipoprotein • apolipoprotein E • macrophage

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