RATIONALE:DNA damage is present in both genomic and mitochondrial DNA in atherosclerosis. However, whether DNA damage itself promotes atherosclerosis, or is simply a byproduct of the risk factors that promote atherosclerosis, is unknown. OBJECTIVE:To examine the effect of DNA damage on atherosclerosis, we studied apolipoprotein (Apo)E mice that were haploinsufficient for the protein kinase ATM (ataxia telangiectasia mutated), which coordinates DNA repair. METHODS AND RESULTS:ATM/ApoE mice developed accelerated atherosclerosis and multiple features of the metabolic syndrome, including hypertension, hypercholesterolemia, obesity, steatohepatitis, and glucose intolerance. Transplantation with ATM bone marrow attenuated atherosclerosis but not the metabolic syndrome. ATM smooth muscle cells and macrophages showed increased nuclear DNA damage and defective DNA repair signaling, growth arrest, and apoptosis. Metabolomic screening of ATM/ApoE mouse tissues identified metabolic changes compatible with mitochondrial defects, with increased β-hydroxybutyrate but reduced lactate, reduced glucose, and alterations in multiple lipid species. ATM/ApoE mouse tissues showed an increased frequency of a mouse mitochondrial “common” deletion equivalent and reduced mitochondrial oxidative phosphorylation. CONCLUSIONS:We propose that failure of DNA repair generates defects in cell proliferation, apoptosis, and mitochondrial dysfunction. This in turn leads to ketosis, hyperlipidemia, and increased fat storage, promoting atherosclerosis and the metabolic syndrome. Prevention of mitochondrial dysfunction may represent a novel target in cardiovascular disease.