Apolipoprotein A-II inhibits high density lipoprotein remodeling and lipid-poor apolipoprotein A-I formation.
The high density lipoproteins (HDL) in human plasma are classified on the basis of apolipoprotein composition into those containing apolipoprotein (apo) A-I but not apoA-II, (A-I)HDL, and those containing both apoA-I and apoA-II, (A-I/A-II)HDL. Cholesteryl ester transfer protein (CETP) transfers core lipids between HDL and other lipoproteins. It also remodels (A-I)HDL into large and small particles in a process that generates lipid-poor, pre-beta-migrating apoA-I. Lipid-poor apoA-I is the initial acceptor of cellular cholesterol and phospholipids in reverse cholesterol transport. The aim of this study is to determine whether lipid-poor apoA-I is also formed when (A-I/A-II)rHDL are remodeled by CETP. Spherical reconstituted HDL that were identical in size had comparable lipid/apolipoprotein ratios and either contained apoA-I only, (A-I)rHDL, or (A-I/A-II)rHDL were incubated for 0-24 h with CETP and Intralipid(R). At 6 h, the apoA-I content of the (A-I)rHDL had decreased by 25% and there was a concomitant formation of lipid-poor apoA-I. By 24 h, all of the (A-I)rHDL were remodeled into large and small particles. CETP remodeled approximately 32% (A-I/A-II)rHDL into small but not large particles. Lipid-poor apoA-I did not dissociate from the (A-I/A-II)rHDL. The reasons for these differences were investigated. The binding of monoclonal antibodies to three epitopes in the C-terminal domain of apoA-I was decreased in (A-I/A-II)rHDL compared with (A-I)rHDL. When the (A-I/A-II)rHDL were incubated with Gdn-HCl at pH 8.0, the apoA-I unfolded by 15% compared with 100% for the apoA-I in (A-I)rHDL. When these incubations were repeated at pH 4.0 and 2.0, the apoA-I in the (A-I)rHDL and the (A-I/A-II)rHDL unfolded completely. These results are consistent with salt bridges between apoA-II and the C-terminal domain of apoA-I, enhancing the stability of apoA-I in (A-I/A-II)rHDL and possibly contributing to the reduced remodeling and absence of lipid poor apoA-I in the (A-I/A-II)rHDL incubations.
Rye
Kerry-Anne
KA
Lipid Research Laboratory, Hanson Institute, Adelaide, South Australia 5000, Australia. karye@ozemail.com.au
Wee
Kevin
K
Curtiss
Linda K
LK
Bonnet
David J
DJ
Barter
Philip J
PJ
D000911:Antibodies, Monoclonal; D016632:Apolipoprotein A-I / Q000096:biosynthesis / Q000737:chemistry / Q000172:deficiency*; D016633:Apolipoprotein A-II / Q000494:pharmacology*; D002352:Carrier Proteins / Q000097:blood / Q000494:pharmacology; D053480:Cholesterol Ester Transfer Proteins; D004591:Electrophoresis, Polyacrylamide Gel; D005217:Fat Emulsions, Intravenous / Q000494:pharmacology; D006023:Glycoproteins; D006801:Humans; D007700:Kinetics; D008075:Lipoproteins, HDL / Q000378:metabolism*; D011485:Protein Binding; D011489:Protein Denaturation; D011994:Recombinant Proteins / Q000494:pharmacology
D000911:Antibodies, Monoclonal; D016632:Apolipoprotein A-I; D016633:Apolipoprotein A-II; C506642:CETP protein, human; D002352:Carrier Proteins; D053480:Cholesterol Ester Transfer Proteins; D005217:Fat Emulsions, Intravenous; D006023:Glycoproteins; D008075:Lipoproteins, HDL; D011994:Recombinant Proteins