Suppression of EC-SOD by oxLDL During Vascular Smooth Muscle Cell Proliferation

Reactive oxygen species (ROS) produced by endothelial cells and macrophages play important roles in atherogenesis because they promote the formation of oxidized low-density lipoproteins (oxLDL). Extracellular-superoxide dismutase (EC-SOD) is mainly produced by vascular smooth muscle cells (VSMCs), is secreted into the extracellular space, and protects cells from the damaging effects of the superoxide anion. Thus, the expression of EC-SOD in VSMCs is crucial for protecting cells against atherogenesis; however, oxLDL-induced changes in the expression of EC-SOD in VSMCs have not yet been examined. We herein showed that oxLDL decreased EC-SOD mRNA and protein levels by binding to lectin-like oxidized LDL receptor-1 (LOX-1). Moreover, we demonstrated the significant role of mitogen-activated protein kinase (MEK)/extracellular-regulated protein kinase (ERK) signaling in oxLDL-elicited reductions in the expression of EC-SOD and proliferation of VSMCs. The results obtained with the FCS treatment indicate that oxLDL-elicited reductions in the expression of EC-SOD are related to the proliferation of VSMCs. We herein showed for the first time that luteolin, a natural product, restored oxLDL-induced decreases in the expression of EC-SOD and proliferation of VSMCs. Collectively, the results of the present study suggest that oxLDL accelerates the development of atherosclerosis by suppressing the expression of EC-SOD and also that luteolin has potential as a treatment for atherosclerosis. J. Cell. Biochem. 117: 2496-2505, 2016. © 2016 Wiley Periodicals, Inc.