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Localization of an apolipoprotein A-I epitope critical for lipoprotein-mediated cholesterol efflux from monocytic
C L Banka1, A S Black, L K Curtiss
1Scripps Research Institute, Department of Immunology, La Jolla, California 92037.
Insights
Two antibodies targeting human apolipoprotein A-I (apoA-I) significantly inhibited cellular cholesterol efflux, a key process in reverse cholesterol transport and cardiovascular disease prevention. This suggests specific apoA-I domains are crucial for this function.
Area of Science:
- Biochemistry
- Cardiovascular Biology
- Immunology
Background:
- High-density lipoprotein (HDL) levels inversely correlate with cardiovascular disease risk.
- HDL facilitates reverse cholesterol transport, moving cholesterol from peripheral cells to the liver.
- Apolipoprotein A-I (apoA-I) is a major HDL component involved in this process.
Purpose of the Study:
- To investigate the role of human apoA-I in cellular cholesterol efflux.
- To determine if specific structural domains of apoA-I mediate cholesterol removal from cells.
Main Methods:
- Utilized an immunochemical approach with monoclonal antibodies against apoA-I.
- Assessed the impact of antibodies on in vitro cholesterol efflux from THP-1 cells to HDL or apoA-I proteoliposomes.
Main Results:
- Two apoA-I specific monoclonal antibodies, AI-11 and AI-14, inhibited cholesterol efflux by approximately 50%.
- Antibody AI-11 binds apoA-I residues 96-111; AI-14 binds residues 74-105.
- These antibodies target overlapping yet distinct regions of apoA-I.
Conclusions:
- Specific structural domains within apoA-I are critical for mediating cellular cholesterol efflux.
- These findings provide insights into the mechanism of reverse cholesterol transport and potential therapeutic targets for cardiovascular disease.
Abstract:
The inverse correlation between plasma high density lipoprotein (HDL) levels and the risk for cardiovascular disease has been attributed in part to the role of HDL in facilitating the transport of cholesterol to the liver for catabolism. One component of this reverse cholesterol transport is removal of excess cholesterol from peripheral cells. An immunochemical approach was employed to evaluate the role of human apolipoprotein (apo) A-I in cellular cholesterol efflux and to test the hypothesis that discrete structural domains of the molecule mediate this function. Two apoA-I-specific monoclonal antibodies (AI-11 and AI-14) inhibited in vitro cellular cholesterol efflux from THP-1 monocytic cells to HDL or apoA-I proteoliposomes by approximately 50%. Six other antibodies had no effect although three of these bound significant proportions of the apoA-I proteoliposomes. Antibody AI-11 binds apoA-I amino acid residues 96-111 (Banka, C. L., Bonnet, D. J., Black, A. S., Smith, R. S., and Curtiss, L. K. (1991) J. Biol. Chem. 266, 23886-23892). The AI-14 epitope was localized to residues 74-105. Therefore, the two antibodies that inhibited HDL promotion of cellular cholesterol efflux bound overlapping but distinct regions of the apoA-I molecule.