Cholesterol Efflux, Lecithin−Cholesterol Acyltransferase Activity, and Pre-β Particle Formation by Serum from Human Apolipoprotein A-I and Apolipoprotein A-I/Apolipoprotein A-II Transgenic Mice Consistent with the Latter Being Less Effective for Reverse Cholesterol Transport

Abstract

Studies assessing fatty streak formation in mice have revealed that human apolipoprotein A-I (apoAI) transgenic mice (TgAI) have 15-fold less atherosclerosis susceptibility than combined human apolipoprotein A-I/human apolipoprotein A-II (apoAI:AII) transgenics (TgAI:AII) and 40-fold less than nontransgenic control mice. In order to examine the biochemical mechanisms underlying those in vivo observations, we have compared in vitro properties of serum from the different groups of animals for participation in cholesterol efflux, LCAT activation, and pre-β particle formation. Analysis of cholesterol efflux from both Fu5AH hepatoma and Ob1771 adipose cells revealed serum from the TgAI to be the most efficient in promoting efflux. The two-dimensional electrophoresis of mouse serum shows that control mice have exclusively apoAI in α particles. TgAI and TgAI:AII mice have 30 and 38% of total apoAI in particles with pre-β electrophoretic mobility, respectively. The distribution of cell-derived cholesterol between these apoAI-containing lipoprotein subspecies after 1 and 60 min of incubation with Fu5AH hepatoma cells was examined. This revealed after a 1 min incubation 66 ± 8 and 83 ± 9% of the counts in particles with pre-β mobility for TgAI and TgAI:AII mice, respectively; while after 60 min of incubation, only 6 ± 2% of counts remained in pre-β particles from the TgAI and 30 ± 3% for the TgAI:AII. This suggests faster movement of cholesterol from pre-β to α particles in plasma from the TgAI. Consistent with this is the observation that LCAT activity with both exogenous and endogenous substrate increased in the TgAI versus the TgAI:AII mice. The previously observed decrease in fatty streak formation in the TgAI versus the TgAI:AII and control mice is consistent with the in vitro studies presented here and suggests that HDL containing human apoAI is a more effective participant in the postulated early steps in reverse cholesterol transport than HDL containing both human apoAI and human apoAII, and/or murine HDL.