Attenuated superoxide dismutase 2 activity induces atherosclerotic plaque instability during aging in hyperlipidemic mice

Background--Atherosclerosis progression during aging culminates in the development of vulnerable plaques, which may increase the risk of cardiovascular events. Increased generation and/or decreased scavenging of reactive oxygen species in the vascular wall are major contributors to atherogenesis. We previously showed that superoxide dismutase 2 deficiency increased vascular oxidative stress and reduced aortic compliance in aged wild-type mice and that young Apoe^-/-/Sod2^+/- had increased mitochondrial DNA damage and atherosclerosis versus young Apoe^-/- mice. Here we investigated the effects of superoxide dismutase 2 deficiency on atherosclerosis progression and plaque morphology in middle-aged Apoe^-/- mice. Methods and Results--Compared with Apoe^-/-, middle-aged Apoe^-/-/Sod2^+/- mice had increased vascular wall reactive oxygen species (P<0.05) and higher atherosclerotic lesion area (P < 0.001). The atherosclerotic plaques in middle-aged Apoe^-/-/ Sod2^+/- mice had an increased necrotic core with higher inflammatory cell infiltration, a thinned fibrous cap with depleted smooth muscle content, and intraplaque hemorrhage. In addition, the plaque shoulder area had higher levels of calpain-2, caspase-3, and matrix metalloproteinase-2 in intimal smooth muscle cells and depleted fibrous cap collagen. Targeting mitochondrial reactive oxygen species with MitoTEMPO attenuated features of atherosclerotic plaque vulnerability in middle-aged Apoe^-/-/Sod2^+/- mice by lowering expression of calpain-2, caspase-3, and matrix metalloproteinase-2 and decreasing smooth muscle cell apoptosis and matrix degradation. Conclusions--Enhanced mitochondrial oxidative stress under hyperlipidemic conditions in aging induces plaque instability, in part by increasing smooth muscle cell apoptosis, necrotic core expansion, and matrix degradation. Targeting mitochondrial reactive oxygen species or its effectors may be a viable therapeutic strategy to prevent aging-associated and oxidative stress-related atherosclerosis complications.