Singlet oxygen mediates the UVA-induced generation of the photoaging-associated mitochondrial common deletion

Mutations of mitochondrial (mt) DNA accumulate during normal aging. The mos t frequent mutation is a 4,977-base pair deletion also called the common de letion, which is increased in photoaged skin. Oxidative stress may play a m ajor role in the generation of large scale mtDNA deletions, but direct proo f for this has been elusive. We therefore assessed whether the common delet ion can be generated in vitro through UV irradiation and whether reactive o xygen species are involved in this process, Normal human fibroblasts were r epetitively exposed to sublethal doses of UVA radiation and assayed for the common deletion employing a semiquantitative polymerase chain reaction tec hnique. There was a time/dose-dependent generation of the common deletion, attributable to the generation of singlet oxygen, since the common deletion was diminished when irradiating in the presence of singlet oxygen quencher s, but increased when enhancing singlet oxygen half-life by deuterium oxide . The induction of the common deletion by UVA irradiation was mimicked by t reatment of unirradiated cells with singlet oxygen produced by the thermode composition of an endoperoxide. These studies provide evidence for the invo lvement of reactive oxygen species in the generation of aging-associated mt DNA lesions in human cells and indicate a previously unrecognized role of s inglet oxygen in photoaging of human skin.