Genotype profiles of loci encoding DNA repair enzymes in newborn and elderly populations: no evidence of association with longevity

1936A→G (I646 V) polymorphism in the AKAP10 gene encoding A-kinase-anchoring protein 10 in very long-lived poles is similar to that in newborns

BACKGROUND/STUDY CONTEXT: The common 1936A→G transition (rs203462) in the AKAP10 gene encoding the A-kinase-anchoring protein 10 has been recently associated with negative prognosis in the aging European American population (60 to 79 years old). The aim of this study was to see the effects of this transition on allele frequency in very long-lived Poles.

METHODS

AKAP10 genotype and allele distributions were analyzed in Polish subjects: 148 nonagenarians (95 to 103 years old) and 200 healthy newborn controls, using polymerase chain reaction-restriction fragment length polymorphism (PCR-RFLP). Distributions were separated according to gender and χ(2) tests used to analyze possible differences.

RESULTS

No significant differences were found in genotype or allele distribution between the age groups, for either gender. Percentages of GG AKAP10 homozygotes were slightly greater in the very old subjects than in the newborns (12.2% vs. 9.0%, respectively), and the G allele percentages were very similar (males, 30.7% and 33.0%; females, 34.1% and 35.8%; respectively).

CONCLUSION

The authors conclude that differences in study results between European Americans (60 to 79 years old) and Poles (≥95 years old) result from either (1) geographical location; or (2) the influence of this polymorphism on groups of people differing in genetic background or environmental history; or (3) the time window affected, including extreme age. Further studies with full age-frequency distributions are needed to clarify these results.

Progress & prospects: gene therapy in aging

Studies performed on various experimental model systems indicate that genetic interventions can increase longevity, even if in a highly protected laboratory condition. Generally, such interventions required partial or complete switching off of the gene and inhibiting the activity of its gene products, which normally have other well-defined roles in metabolic processes. Overexpression of some genes, such as stress response and antioxidant genes, in some model systems also extends their longevity. Such genetic interventions may not be easily applicable to humans without knowing their effects on human growth, development, maturation, reproduction and other characteristics. Studies on the association of single nucleotide polymorphisms and multiple polymorphisms (haplotype) in genes with human longevity have identified several genes whose frequencies increase or decrease with age. Whether genetic redesigning can be achieved in the wake of numerous and complex epigenetic factors that effectively determine the life course and the life span of an individual still appears to be a 'mission impossible'.

Base excision repair of oxidative DNA damage and association with cancer and aging

Aging has been associated with damage accumulation in the genome and with increased cancer incidence. Reactive oxygen species (ROS) are produced from endogenous sources, most notably the oxidative metabolism in the mitochondria, and from exogenous sources, such as ionizing radiation. ROS attack DNA readily, generating a variety of DNA lesions, such as oxidized bases and strand breaks. If not properly removed, DNA damage can be potentially devastating to normal cell physiology, leading to mutagenesis and/or cell death, especially in the case of cytotoxic lesions that block the progression of DNA/RNA polymerases. Damage-induced mutagenesis has been linked to various malignancies. The major mechanism that cells use to repair oxidative damage lesions, such as 8-hydroxyguanine, formamidopyrimidines, and 5-hydroxyuracil, is base excision repair (BER). The BER pathway in the nucleus is well elucidated. More recently, BER was shown to also exist in the mitochondria. Here, we review the association of BER of oxidative DNA damage with aging, cancer and other diseases.

Influence of polymorphisms at loci encoding DNA repair proteins on cancer susceptibility and G2 chromosomal radiosensitivity

Sixteen candidate polymorphisms (13 SNPs and 3 microsatellites) in nine genes from four DNA repair pathways were examined in 83 subjects, comprising 23 survivors of childhood cancer, their 23 partners, and 37 offspring, all of whom had previously been studied for G(2) chromosomal radiosensitivity. Genotype at the Asp148Glu SNP site in the APEX gene of the base excision repair (BER) pathway was associated with childhood cancer in survivors (P = 0.001, significant even after multiple test adjustment), due to the enhanced frequency of the APEX Asp148 allele among survivors in comparison to that of their partners. Analysis of variance (ANOVA) of G(2) radiosensitivity in the pooled sample, as well as family-based association test (FBAT) of the family-wise data, showed sporadic suggestions of associations between G(2) radiosensitivity and polymorphisms at two sites (the Thr241Met SNP site in the XRCC3 gene of the homologous recombinational pathway by ANOVA, and the Ser326Cys site in the hOGG1 gene of the BER pathway by FBAT analysis), but neither of these remained significant after multiple-test adjustment. This pilot study provides an intriguing indication that DNA repair gene polymorphisms may underlie cancer susceptibility and variation in radiosensitivity.