Age-associated modifications of Base Excision Repair activities in human skin fibroblast extracts

Base Excision Repair (BER) is the predominant repair pathway responsible for removal of so-called small DNA lesions such as abasic sites (AP site), uracil (U), 8-oxo-7,8-dihydroguanine (8oxoG), thymine glycol (Tg). In this study, we investigated effect of aging on excision efficacy of several endogenous base lesions and AP sites using an in vitro multiplexed fluorescent approach on support (parallelized oligonucleotide cleavage assay). Human fibroblasts nuclear extracts from 29 donors of different ages were characterized in their ability to simultaneously excise the different lesions. Clearly, three different groups of lesions emerged according to the efficiency of their cleavage: one exhibited very high cleavage efficiency (AP sites and U paired with G), one showed intermediate cleavage efficiency (U paired with A and Tg). The third group included 8oxoG, A paired with 8oxoG, T at CpG site and hypoxanthine (Hx) and displayed poor repair. Aging was significantly associated with modification of excision efficiency for AP sites, uracil, Tg and 8oxoG. Repair rate decreased for the first three lesions and the most drastic effects were observed for repair of U:A. Surprisingly, excision of 8oxoG increased with aging suggesting a completely different regulation or adaptation for the initiation step of this related specific repair pathway.