Thermolabile 8-hydroxyguanine DNA glycosylase with low activity in senescence-accelerated mice due to a single-base mutation

8-hydroxyguanine (8-oxoguanine; oh8Gua) DNA glycosylase (OGG1) repairs oh8Gua, a highly mutagenic oxidative DNA damage. In the present study, we compared two strains of senescence-accelerated mouse (SAM) expressing senescence-prone phenotypes, SAMP1 and SAMP8, with one strain of SAM expressing senescence-resistant phenotype, SAMR1. We found three distinct characteristics of OGG1 in SAMPs: (i) low activity (10–40% of the SAMR1 enzyme in all organs and ages observed), (ii) thermolability, and (iii) mutation from Arg (CGG) in SAMR1 to Trp (TGG) at codon 304. There was no difference in the levels of mRNA and protein. As expected, oh8Gua level in tissues was higher in the SAMPs. In contrast, O6-methylguanine-DNA methyltransferase, which repairs alkylated DNA, showed no difference in its activity. The impairment of oh8Gua repair activity caused by the 304 mutation in OGG1 may be one of the factors contributing to the high somatic mutation rate and the accelerated senescence observed in these strains.