Abstract P321: Oxidative Stress Induces DNA Double-Strand Breaks and Activates DNA Damage Responses in Vascular Smooth Muscle Cells: A Possible Mechanism for Atherosclerosis Progression

Backgrounds: Oxidative stress is thought to be a pathogenic mediator of atherosclerosis. Oxidative stress induces DNA damage, and the unrepaired or improperly repaired DNA damage increases genomic instability, which cause cell death, senescence, or dysregulation of cellular functions. Pathogenesis of both Hutchinson-Gilford Progeria syndrome and Werner syndrome, which feature prominent atherosclerotic disease at young age, involves impaired DNA repair and the resultant genomic instability. The purpose of this study is to determine whether oxidative stress causes DNA damage in vascular smooth muscle cells (VSMC) and to elucidate the role of DNA damage responses in atherosclerosis and the fate of VSMC. Methods and Results: Immunoreactivity against gamma-H2AX, a sensitive marker for DNA double-strand breaks (DSBs), which is the most severe form of DNA damage, was increased in human atherosclerotic plaques, but not in the adjacent normal areas. gamma-H2AX staining was observed in almost same regions where 8-oxo-dG immunoreactivity, an oxidative modification of DNA, was observed. Apoptotic cells were abundant in atherosclerotic lesions, but not in normal areas. In cultured human aortic smooth muscle cells (HASM), 15 min incubation with H2O2 (100 microM) induced foci formation of gamma-H2AX in the nuclei. H2O2 activated various signaling molecules involved in DNA damage responses, including ATM, Chk2, DNA-PK and p53 in HASM. Some H2O2-induced DSBs persisted after 24 hours, at which point apoptosis was induced in 7.1 ± 1.3 % of HASM, as detected by TUNEL method. Knockdown experiments using siRNA revealed that ATM-, DNA-PK-, or Chk2-deficient VSMC were more resistant to H2O2-induced apoptosis. Conclusions: In summary, 1) DNA double-strand breaks were accumulated in human atherosclerotic plaques, 2) oxidative stress induced double-strand breaks and activation of DNA damage response in vascular smooth muscle cells, and 3) impairment of DNA damage responses modulated damage-induced cell fate such as apoptosis. Thus, DNA damage itself or alteration in DNA damage responses may be involved in the mechanisms for progression of atherosclerosis.