Evidence for Oxidative Activation of c-Myc–Dependent Nuclear Signaling in Human Coronary Smooth Muscle Cells and in Early Lesions of Watanabe Heritable Hyperlipidemic Rabbits

Abstract

Background —Oxidized LDL (oxLDL) promotes atherogenesis, and antioxidants reduce lesions in experimental models. OxLDL-mediated effects on c-Myc are poorly characterized, and those on c-Myc nuclear pathways are completely unknown. c-Myc stimulates smooth muscle cell (SMC) proliferation and could be involved in atherosclerosis. We investigated the early effects of oxLDL and α-tocopherol on c-Myc, its binding partner Max, and the carboxy-terminal domain–binding factors activator protein-2 and elongation 2 factor in human coronary SMCs. We also investigated whether 9-week treatment of Watanabe heritable hyperlipidemic (WHHL) rabbits with diet-enriched α-tocopherol reduces c-Myc expression and oxLDL in the left coronary artery. Methods and Results —OxLDL enhanced c-Myc/Max expression and transcription by cotransfection assay and the nuclear activities of E2F and activator protein-2 by binding shift and supershift in coronary SMCs. α-Tocopherol significantly reduced these molecular events. Furthermore, α-tocopherol reduced early lesions, SMC density, and the immunohistochemical presence of c-Myc, which colocalized with oxLDL/foam cells in the coronaries of WHHL rabbits. Conclusions —We provide the first evidence that oxLDL and α-tocopherol may influence c-Myc activation and several c-Myc–dependent signaling pathways in human coronary SMCs. The observation that in vivo, an antioxidant reduces both c-Myc and oxLDL in early coronary lesions of rabbits is consistent with, but does not prove, the hypothesis that c-Myc–dependent factors activated by oxidative processes contribute to atherogenesis and coronary heart disease.