title: Attenuation of DNA polymerase beta-dependent base excision repair and increased DMS-induced mutagenicity in aged mice.
abstract: The biological mechanisms responsible for aging remain poorly understood. We propose that increases in DNA damage and mutations that occur with age result from a reduced ability to repair DNA damage. To test this hypothesis, we have measured the ability to repair DNA damage in vitro by the base excision repair (BER) pathway in tissues of young (4-month-old) and old (24-month-old) C57BL/6 mice. We find in all tissues tested (brain, liver, spleen and testes), the ability to repair damage is significantly reduced (50-75%; P<0.01) with age, and that the reduction in repair capacity seen with age correlates with decreased levels of DNA polymerase beta (beta-pol) enzymatic activity, protein and mRNA. To determine the biological relevance of this age-related decline in BER, we measured spontaneous and chemically induced lacI mutation frequency in young and old animals. In line with previous findings, we observed a three-fold increase in spontaneous mutation frequency in aged animals. Interestingly, lacI mutation frequency in response to dimethyl sulfate (DMS) does not significantly increase in young animals whereas identical exposure in aged animals results in a five-fold increase in mutation frequency. Because DMS induces DNA damage processed by the BER pathway, it is suggested that the increased mutagenicity of DMS with age is related to the decline in BER capacity that occurs with age. The inability of the BER pathway to repair damages that accumulate with age may provide a mechanistic explanation for the well-established phenotype of DNA damage accumulation with age.
authors.affiliation: Department of Nutrition and Food Science, Wayne State University, Detroit, MI 48202, USA.
authors.forename: Diane C
authors.initials: DC
authors.lastname: Cabelof
authors.forename: Julian J
authors.initials: JJ
authors.lastname: Raffoul
authors.forename: Sunitha
authors.initials: S
authors.lastname: Yanamadala
authors.forename: Cirlette
authors.initials: C
authors.lastname: Ganir
authors.forename: ZhongMao
authors.initials: Z
authors.lastname: Guo
authors.forename: Ahmad R
authors.initials: AR
authors.lastname: Heydari
mesh_terms: D000375:Aging / Q000235:genetics*; D000818:Animals; D001483:Base Sequence; D001921:Brain / Q000187:drug effects; D004252:DNA Mutational Analysis; D019951:DNA Polymerase beta / Q000378:metabolism*; D017931:DNA Primers; D004260:DNA Repair / Q000187:drug effects; D008099:Liver / Q000187:drug effects; D008297:Male; D051379:Mice; D008810:Mice, Inbred C57BL; D008969:Molecular Sequence Data; D009153:Mutagens / Q000494:pharmacology*; D013154:Spleen / Q000187:drug effects; D013463:Sulfuric Acid Esters / Q000494:pharmacology*; D013737:Testis / Q000187:drug effects
chemical_list: D017931:DNA Primers; D009153:Mutagens; D013463:Sulfuric Acid Esters; D019951:DNA Polymerase beta; C007482:dimethyl sulfate