Participation of ATP7A in macrophage mediated oxidation of LDL

Zhenyu Qin,Eddy S Konaniah,Bonnie Neltner,Raphael A Nemenoff,David Y Hui,Neal L Weintraub

doi:10.1194/jlr.m003426

Abstract

ATP7A primarily functions to egress copper from cells, thereby supplying this cofactor to secreted copper-accepting enzymes. This ATPase has attracted significant attention since the discovery of its mutation leading to human Menkes disease and the demonstration of its distribution in various tissues. Recently, we reported that ATP7A is expressed in the human vasculature. In the present study, we investigated the cellular expression of ATP7A in atherosclerotic lesions of LDL receptor (-/-) mice. Subsequently, we examined the role of ATP7A in regulating the oxidation of LDL in a macrophage cell model. We observed that ATP7A is expressed in atherosclerotic murine aorta and colocalizes with macrophages. To investigate the function of ATP7A, we downregulated ATP7A expression in THP-1 derived macrophages using small interfering RNA (siRNA). ATP7A downregulation attenuated cell-mediated oxidation of LDL. Moreover, downregulation of ATP7A resulted in decreased expression and enzymatic activity of cytosolic phospholipase A(2) alpha (cPLA(2)alpha), a key intracellular enzyme involved in cell-mediated LDL oxidation. In addition, cPLA(2)alpha promoter activity was decreased after downregulation of ATP7A, suggesting that ATP7A transcriptionally regulates cPLA(2)alpha expression. Finally, cPLA(2)alpha overexpression increased LDL oxidation, which was blocked by coadministration of ATP7A siRNA oligonucleotides. These findings suggest a novel mechanism linking ATP7A to cPLA(2)alpha and LDL oxidation, suggesting that this copper transporter could play a previously unrecognized role in the pathogenesis of atherosclerosis.

Highlights

ATP7A primarily functions to egress copper from cells, thereby supplying this cofactor to secreted copperaccepting enzymes
Cell viability was similar between ATP7A-downregulated macrophages and control cells, as assessed by MTT assay. These observations suggest that endogenous ATP7A contributes to LDL oxidation in THP-1-derived macrophages
Because our results suggested that downregulation of ATP7A in THP-1 macrophages inhibits cell-mediated LDL oxidation and because ablation of cPLA2␣ inhibits macrophage-mediated LDL oxidation [19], we examined whether ATP7A regulates cPLA2␣ expression and activity in macrophages

Summary

Introduction

ATP7A primarily functions to egress copper from cells, thereby supplying this cofactor to secreted copperaccepting enzymes This ATPase has attracted significant attention since the discovery of its mutation leading to human Menkes disease and the demonstration of its distribution in various tissues. ATP7A egresses copper from cells, and supplying copper to secreted copper-accepting enzymes This P-type ATPase has attracted significant attention since the discovery of its mutation leading to human Menkes disease and the demonstration of its distribution in various tissues, including placenta, brain, testes, kidney, and lung [4,5,6]. We identified a novel vascular function of ATP7A to modulate the expression and activity of a copper-accepting enzyme, extracellular superoxide dismutase [8] This finding suggests that ATP7A is closely associated with its copper-accepting enzymes in the vasculature [2] and raises the possibility that the ATPase could regulate other important functions in the blood vessel wall.

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Results

Conclusion