SIRT1 and atherosclerosis: However, SIRT1 is downregulated in human atherosclerotic plaques and in plaque and senescent VSMCs compared with normal VSMCs in culture,10 suggesting that SIRT1 regulation of OGG1 may be particularly relevant in normal arteries as a way of deactivating OGG1 when oxidative DNA repair is complete, but it may be less important in atherosclerosis in which the reduced p300 expression results in reduced acetylated OGG1.