Cabelof Diane C, Raffoul Julian J, Yanamadala Sunitha, Ganir Cirlette, Guo ZhongMao, Heydari Ahmad R
Department of Nutrition and Food Science, Wayne State University, Detroit, MI 48202, USA.
Mutat Res. 2002 Mar 20;500(1-2):135-45. doi: 10.1016/s0027-5107(02)00003-9.
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.
导致衰老的生物学机制仍未得到充分理解。我们提出，随着年龄增长而出现的DNA损伤和突变增加是由于修复DNA损伤的能力下降所致。为了验证这一假设，我们通过碱基切除修复（BER）途径，测量了年轻（4个月大）和年老（24个月大）的C57BL/6小鼠组织中体外修复DNA损伤的能力。我们发现在所有测试的组织（脑、肝、脾和睾丸）中，随着年龄增长，修复损伤的能力显著降低（50 - 75%；P<0.01），并且随着年龄增长观察到的修复能力下降与DNA聚合酶β（β-pol）酶活性、蛋白质和mRNA水平的降低相关。为了确定这种与年龄相关的BER下降的生物学相关性，我们测量了年轻和年老动物中自发的和化学诱导的lacI突变频率。与之前的研究结果一致，我们观察到老年动物的自发突变频率增加了三倍。有趣的是，年轻动物对硫酸二甲酯（DMS）的反应中lacI突变频率没有显著增加，而老年动物相同的暴露导致突变频率增加了五倍。由于DMS诱导由BER途径处理的DNA损伤，因此表明DMS随着年龄增长的致突变性增加与随着年龄增长发生的BER能力下降有关。BER途径无法修复随着年龄积累的损伤，这可能为随着年龄增长DNA损伤积累这一已确立的表型提供一个机制解释。
