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Updated: Jun 21, 2026
Quantification of Atherosclerosis in Mice
Published on: June 12, 2019
Macrophage reverse cholesterol transport in mice expressing ApoA-I Milano
Eric T Alexander1, Ginny L Weibel, Michelle R Joshi
1Lipid Research Group, Children's Hospital of Philadelphia, Philadelphia, PA, USA.
Objective:
To compare the abilities of human wild-type apoA-I (WT apoA-I) and human apoA-I(Milano) (apoA-I(M)) to promote macrophage reverse cholesterol transport (RCT) in apoA-I-null mice infected with adeno-associated virus (AAV) expressing either WT apoA-I or apoA-I(M).
Methods And Results:
WT apoA-I- or apoA-I(M)-expressing mice were intraperitoneally injected with [H(3)]cholesterol-labeled J774 mouse macrophages. After 48 hours, no significant difference was detected in the amount of cholesterol removed from the macrophages and deposited in the feces via the RCT pathway between the WT apoA-I and apoA-I(M) groups. Analysis of the individual components of the RCT pathway demonstrated that the apoA-I(M)-expressing mice promoted ATP-binding cassette transporter A1 (ABCA1)-mediated cholesterol efflux as efficiently as WT apoA-I but that apoA-I(M) had a reduced ability to promote cholesterol esterification via lecithin cholesterol-acyltransferase (LCAT). This resulted in reduced cholesteryl ester (CE) and increased free cholesterol (FC) levels in the plasma of mice expressing apoA-I(M) compared to WT apoA-I. These differences did not affect the rate of delivery of labeled cholesterol to the liver via SR-BI-mediated selective uptake or its subsequent excretion in the feces.
Conclusions:
Within the limits of the in vivo assay, WT apoA-I and apoA-I(M) are equally efficient at promoting macrophage RCT, suggesting that if apoA-I(M) is more atheroprotective than WT apoA-I it is not attributable to an enhancement of macrophage RCT.
Insights
Human wild-type apoA-I and apoA-I(Milano) equally promote macrophage reverse cholesterol transport (RCT). ApoA-I(Milano) shows reduced cholesterol esterification, impacting plasma lipid levels but not overall RCT efficiency.
Area of Science:
- Cardiovascular Biology
- Lipid Metabolism
- Apolipoprotein Research
Background:
- Apolipoprotein A-I (apoA-I) plays a crucial role in reverse cholesterol transport (RCT), a key process in preventing atherosclerosis.
- The apoA-I(Milano) variant is associated with reduced cardiovascular risk, but its precise mechanisms, particularly concerning macrophage RCT, require further elucidation.
- Understanding the comparative efficacy of wild-type apoA-I (WT apoA-I) and apoA-I(Milano) (apoA-I(M)) in RCT is vital for developing targeted therapies.
Purpose of the Study:
- To directly compare the abilities of WT apoA-I and apoA-I(M) to facilitate macrophage RCT in vivo.
- To investigate the impact of apoA-I(M) on specific steps of the RCT pathway, including cholesterol efflux, esterification, and hepatic uptake.
- To determine if any observed differences in RCT efficiency contribute to the potential atheroprotective effects of apoA-I(M).
Main Methods:
- Adeno-associated virus (AAV) vectors were used to express either WT apoA-I or apoA-I(M) in apoA-I-null mice.
- Mice received intraperitoneal injections of [H(3)]cholesterol-labeled J774 mouse macrophages to track cholesterol movement.
- Analysis included quantification of cholesterol deposition in feces, assessment of ATP-binding cassette transporter A1 (ABCA1)-mediated efflux, lecithin cholesterol-acyltransferase (LCAT)-mediated esterification, and scavenger receptor class B type I (SR-BI)-mediated hepatic uptake.
Main Results:
- No significant difference was observed in the overall efficiency of macrophage RCT between mice expressing WT apoA-I and apoA-I(M).
- ApoA-I(M) effectively promoted ABCA1-mediated cholesterol efflux, similar to WT apoA-I.
- However, apoA-I(M) demonstrated a reduced capacity for LCAT-mediated cholesterol esterification, leading to increased plasma free cholesterol (FC) and decreased cholesteryl ester (CE) levels compared to WT apoA-I. These changes did not impede cholesterol delivery to the liver or fecal excretion.
Conclusions:
- Within the limitations of this in vivo model, WT apoA-I and apoA-I(M) exhibit comparable efficacy in promoting macrophage RCT.
- The potential enhanced atheroprotective properties of apoA-I(M) over WT apoA-I are unlikely to be mediated by a superior ability to promote macrophage RCT.
- The observed alterations in plasma lipid profiles due to apoA-I(M) warrant further investigation into their broader cardiovascular implications.
