Modifying Apolipoprotein A-I by Malondialdehyde,but Not by an Array of Other Reactive Carbonyls,Blocks Cholesterol Efflux by the ABCA1 Pathway |
| |
Authors: | Baohai Shao Subramaniam Pennathur Ioanna Pagani Michael N Oda Joseph L Witztum John F Oram Jay W Heinecke |
| |
Institution: | From the ‡Department of Medicine, University of Washington, Seattle, Washington 98195.;the §Department of Internal Medicine, University of Michigan, Ann Arbor, Michigan 48109.;the ¶Children''s Hospital Oakland Research Institute, Oakland, California 94609, and ;the ‖Department of Medicine, University of California at San Diego, La Jolla, California 92093 |
| |
Abstract: | Dysfunctional high density lipoprotein (HDL) is implicated in the pathogenesis of cardiovascular disease, but the underlying pathways remain poorly understood. One potential mechanism involves covalent modification by reactive carbonyls of apolipoprotein A-I (apoA-I), the major HDL protein. We therefore determined whether carbonyls resulting from lipid peroxidation (malondialdehyde (MDA) and hydroxynonenal) or carbohydrate oxidation (glycolaldehyde, glyoxal, and methylglyoxal) covalently modify lipid-free apoA-I and inhibit its ability to promote cellular cholesterol efflux by the ABCA1 pathway. MDA markedly impaired the ABCA1 activity of apoA-I. In striking contrast, none of the other four carbonyls were effective. Liquid chromatography-electrospray ionization-tandem mass spectrometry of MDA-modified apoA-I revealed that Lys residues at specific sites had been modified. The chief adducts were MDA-Lys and a Lys-MDA-Lys cross-link. Lys residues in the C terminus of apoA-I were targeted for cross-linking in high yield, and this process may hinder the interaction of apoA-I with lipids and ABCA1, two key steps in reverse cholesterol transport. Moreover, levels of MDA-protein adducts were elevated in HDL isolated from human atherosclerotic lesions, suggesting that lipid peroxidation might render HDL dysfunctional in vivo. Taken together, our observations indicate that MDA damages apoA-I by a pathway that generates lysine adducts at specific sites on the protein. Such damage may facilitate the formation of macrophage foam cells by impairing cholesterol efflux by the ABCA1 pathway. |
| |
Keywords: | Atherosclerosis Mass Spectrometry (MS) Protein Chemical Modification Protein Cross-linking Protein Structure 4-Hydroxynonenal Advanced Glycation End Products Advanced Lipoxidation End Products Glycolaldehyde Methylglyoxal |
|
|