Oxidation of apolipoprotein A-I by myeloperoxidase impairs the initial interactions with ABCA1 required for signaling and cholesterol export

Baohai Shao,Chongren Tang,Jay W Heinecke,John F Oram

doi:10.1194/jlr.m004085

Abstract

A key cardioprotective effect of high-density lipoprotein involves the interaction of its major protein, apolipoprotein A-I (apoA-I) with ATP-binding cassette transporter A1 (ABCA1), a macrophage cholesterol exporter. ApoA-I is thought to remove cholesterol from macrophages by a cascade of events. First it binds directly to ABCA1, activating signaling pathways, and then it binds to and solubilizes lipid domains generated by ABCA1. HDL isolated from human atherosclerotic lesions and blood of subjects with established coronary artery disease contains elevated levels of 3-chlorotyrosine and 3-nitrotyrosine, two characteristic products of myeloperoxidase (MPO), a heme protein secreted by macrophages. Here we show that chlorination (but not nitration) of apoA-I by the MPO pathway impairs its ability to interact directly with ABCA1, to activate the Janus kinase 2 signaling pathway, and to promote efflux of cellular cholesterol. In contrast, oxidation of apoA-I has little effect on its ability to stabilize ABCA1 protein or to solubilize phospholipids. Our results indicate that chlorination of apoA-I by the MPO pathway selectively inhibits two critical early events in cholesterol efflux: (1) the binding of apoA-I to ABCA1 and (2) the activation of a key signaling pathway. Therefore, oxidation of apoA-I in the artery wall by MPO-generated chlorinating intermediates may contribute to atherogenesis by impairing cholesterol efflux from macrophages.

Highlights

A key cardioprotective effect of high-density lipoprotein involves the interaction of its major protein, apolipoprotein A-I with ATP-binding cassette transporter A1 (ABCA1), a macrophage cholesterol exporter
Many lines of evidence support the hypothesis that apolipoproteins remove lipids from cells in three steps: [1] the apolipoprotein binds directly to ABCA1;(2) it binds to exovesiculated lipid domains formed by ABCA1; and [3] it solubilizes the lipids [12, 19, 21, 45]
Exposing apolipoprotein A-I (apoA-I) to increasing concentrations of hydrogen peroxide (H2O2) in the presence of MPO and NaCl progressively and severely impaired its ability to remove cellular cholesterol from Baby hamster kidney (BHK) cells transfected with ABCA1 (Fig.1A)

Summary

Introduction

A key cardioprotective effect of high-density lipoprotein involves the interaction of its major protein, apolipoprotein A-I (apoA-I) with ATP-binding cassette transporter A1 (ABCA1), a macrophage cholesterol exporter. Oxidation ClϪ system selectively impairs of apoA-I by the MPO-H2O2the apolipoprotein interactions with ABCA1 that are required for lipid removal and signaling. Exposing apoA-I to increasing concentrations of H2O2 in the presence of MPO and NaCl progressively and severely impaired its ability to remove cellular cholesterol from BHK cells transfected with ABCA1 (Fig.1A).

Results

Conclusion