LIPOPROTEINS CONTAINING APOLIPOPROTEIN A-IV BUT NOT APOLIPOPROTEIN-A-I TAKE UP AND ESTERIFY CELL-DERIVED CHOLESTEROL IN PLASMA

Two-dimensional nondenaturing polyacrplamide gradient gel electrophoresis (2D-PAGGE) identifies distinct apoA-I- or apoE-containing subclasses of high-density lipoproteins (HDLs), each of which plays a different role in reverse cholesterol transport. In this study we used 2D-PAGGE to investigate the role of apoA-IV-containing lipoproteins in reverse cholesterol transport in native plasma. Incubation of 2D electrophoretograms with anti-apoA-IV antibodies identified up to three subclasses of particles. The smaller particle subclasses, LpA-IV-1 and LpA-IV-2, were found in every plasma sample. The largest particle subclass, LpA-IV-3, was observed in fewer than 10% of the plasmas analyzed. 2D-PAGGE of apoA-I-deficient plasma and apoA-I-depleted plasma and anti-apoA-I immunosubtracting 2D-PAGGE of normal plasma revealed that LpA-IV-1 and LpA-IV-2 do not contain apoA-I. The importance of LpA-IV-1 and LpA-IV-2 for uptake and esterification of cell-derived cholesterol was investigated using pulse-chase incubations of plasma with [H-3]cholesterol-labeled fibroblasts followed by anti-apoA-I immunosubtracting 2D-PAGGE. During 1-minute pulse incubation with cells, [H-3]cholesterol was taken up by gamma-LpE > LpA-IV-1 > pre-beta(1)-LpA-I > LpA-IV-2 (''>'' denotes ''more than''). During subsequent chase incubation without cells, proportionately less radioactivity disappeared from LpA-IV-1 and LpA-IV-2, than from pre-beta(1)-LpA-I and gamma-LpE. During 5-minute pulse incubations, radioactive cholesteryl esters were formed in pre-beta(3)-LpA-I > alpha-LpA-I > LpA-IV-1 > LpA-IV-2. The fractional esterification rate was highest in pre-beta(3)-LpA-I and lowest in alpha-LpA-I. Subsequent chase led to the disappearance of [H-3]cholesteryl esters from pre beta(3)-LpA-I and, to a lesser extent, from LpA-IV-1 and LpA-IV-2 but to an increase of [H-3]cholesteryl esters in alpha-LpA-I and LDL. Similar pulse-chase experiments with apoA-I-deficient plasma revealed that LpA-IV-1 and LpA-IV-2 take up and esterify cell-derived cholesterol even more effectively than in normal plasma. We conclude that LpA-IV-1 and LpA-IV-2 are apoA-I-free lipoproteins that are important contributors to reverse cholesterol transport.