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Journal of Lipid Research, Vol. 46, 2143-2150, October 2005
Copyright © 2005 by American Society for Biochemistry and Molecular Biology

SR-BI-mediated selective lipid uptake segregates apoA-I and apoA-II catabolism

Maria C. de Beer^*,, Deneys van der Westhuyzen^*,, Nathan L. Whitaker^*,, Nancy R. Webb^*, and Frederick C. de Beer^1,*,,**

^* Graduate Center for Nutritional Sciences, University of Kentucky Medical Center, Lexington, KY 40536
Departments of Physiology, University of Kentucky Medical Center, Lexington, KY 40536
Internal Medicine, University of Kentucky Medical Center, Lexington, KY 40536
^** Department of Veterans Affair Medical Center, Lexington, KY 40511

Published, JLR Papers in Press, August 1, 2005. DOI 10.1194/jlr.M500068-JLR200

¹ To whom correspondence should be addressed. e-mail: fcdebe1{at}uky.edu

The HDL receptor scavenger receptor class B type I (SR-BI) binds HDL and mediates the selective uptake of cholesteryl ester. We previously showed that remnants, produced when human HDL₂ is catabolized in mice overexpressing SR-BI, become incrementally smaller, ultimately consisting of small -migrating particles, distinct from preß HDL. When mixed with mouse plasma, some remnant particles rapidly increase in size by associating with HDL without the mediation of cholesteryl ester transfer protein, LCAT, or phospholipid transfer protein. Here, we show that processing of HDL₂ by SR-BI-overexpressing mice resulted in the preferential loss of apolipoprotein A-II (apoA-II). Short-term processing generated two distinct, small -migrating particles. One particle (8.0 nm diameter) contained apoA-I and apoA-II; the other particle (7.7 nm diameter) contained only apoA-I. With extensive SR-BI processing, only the 7.7 nm particle remained. Only the 8.0 nm remnants were able to associate with HDL. Compared with HDL₂, this remnant was more readily taken up by the liver than by the kidney.

We conclude that SR-BI-generated HDL remnants consist of particles with or without apoA-II and that only those containing apoA-II associate with HDL in an enzyme-independent manner. Extensive SR-BI processing generates small apoA-II-depleted particles unable to reassociate with HDL and readily taken up by the liver. This represents a pathway by which apoA-I and apoA-II catabolism are segregated.

Abbreviations: apoA-I, apolipoprotein A-I; apoA-I^–/–, apolipoprotein A-I-deficient; CE, cholesteryl ester; CETP, cholesteryl ester transfer protein; DLT, dilactitol tyramine; rHDL, reconstituted high density lipoprotein; SR-BI, scavenger receptor class B type I

Supplementary key words high density lipoprotein • high density lipoprotein receptor • high density lipoprotein size • remnant high density lipoprotein • lipoproteins • lipoprotein metabolism • scavenger receptor class B type I • apolipoprotein A-I • apolipoprotein A-II

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