Impaired DNA double-strand break repair contributes to the age-associated rise of genomic instability in humans

Abstract

Failing to repair DNA double-strand breaks by either nonhomologous end joining (NHEJ) or homologous recombination (HR) poses a threat to genome integrity, and may have roles in the onset of aging and age-related diseases. Recent work indicates an age-related decrease of NHEJ efficiency in mouse models, but whether NHEJ and HR change with age in humans and the underlying mechanisms of such a change remain uncharacterized. Here, using 50 eyelid fibroblast cell lines isolated from healthy donors at the age of 16-75 years, we demonstrate that the efficiency and fidelity of NHEJ, and the efficiency of HR decline with age, leading to increased IR sensitivity in cells isolated from old donors. Mechanistic analysis suggests that decreased expression of XRCC4, Lig4 and Lig3 drives the observed, age-associated decline of NHEJ efficiency and fidelity. Restoration of XRCC4 and Lig4 significantly promotes the fidelity and efficiency of NHEJ in aged fibroblasts. In contrast, essential HR-related factors, such as Rad51, do not change in expression level with age, but Rad51 exhibits a slow kinetics of recruitment to DNA damage sites in aged fibroblasts. Further rescue experiments indicate that restoration of XRCC4 and Lig4 may suppress the onset of stress-induced premature cellular senescence, suggesting that improving NHEJ efficiency and fidelity by targeting the NHEJ pathway holds great potential to delay aging and mitigate aging-related pathologies. Cell Death and Differentiation (2016) 23, 1765-1777; doi:10.1038/cdd.2016.65; published online 8 July 2016Aging in mammals is a complex biological process, characterized by several major hallmarks.1,2 Of all the features associated with aging, a gradual destabilization of genome integrity is perhaps the most fundamental as increased genomic instability may lead to other age-associated phenotypes such as cellular senescence and stem cell exhaustion. Indeed, for the past several decades, numerous studies have indicated that DNA mutations and chromosomal rearrangements gradually accumulate with age.3-6 Of all types of DNA lesions, which may contribute to the gradual loss of genetic information during aging, DNA double-strand breaks (DSBs) are the most hazardous to cells as unrepaired or inappropriately repaired DSBs can cause insertions, deletions and chromosomal rearrangements. Using different analysis approaches, several studies have demonstrated that aging is often associated with the accumulation of DNA DSBs in various organs and tissues in mammals such as mice and humans. [7][8][9][10][11] Moreover, a recent study provides direct evidence that an induction of DNA DSBs in genomes causes aging in mouse livers.12 However, why DNA DSBs accumulate with age remains an open question. A number of studies indicate that it may be a consequence of a progressing imbalance between DNA damage and the efficiency of the molecular machinery that catalyzes DNA repair. 7,9,11 Two major pathways, nonhomologous end joining (NHEJ) and homologous recombination (HR) evolved to repair DNA DSBs. NHEJ is...

A suboptimal maternal diet combined with accelerated postnatal growth results in an altered aging profile in the thymus of male rats

“…It should be also noted that γ-H2ax foci have a robust correlation with replicative telomere shortening (16) as demonstrated by a positive correlation between γ-H2ax expression and thymic telomere shortening in this study. DNA Pkcs , Mre11 and Xrcc4 were also markedly reduced at 12 months, which is consistent with previous findings showing that the NHEJ DNA repair mechanism declines with old age (37), and this has been associated with increased genomic instability (37, 38). …”

Base excision repair but not DNA double‐strand break repair is impaired in aged human adipose‐derived stem cells

“…Here, we successfully obtained 20 eyelid adipose‐derived stem cell (ADSC) lines from two groups of donors (a young group with ages ranging 17–25 years and an old group with ages ranging 50–59 years). Using these ADSCs, we systematically compared the efficiency of base excision repair (BER), nonhomologous end joining (NHEJ), and homologous recombination (HR) repair using our well‐established plasmid reactivation assay based on a GFP gene (Li et al, ; Mao, Jiang, Liu, Seluanov, & Gorbunova, ; Xu et al, ). Surprisingly, we found that BER efficiency but not the other two pathways for repairing DNA DSBs declines with age in human ADSCs.…”

“…We therefore set out to examine whether an impairment in DNA repair capacity contributes to the loss of genome integrity. Since mounting evidence indicates that the efficiency of two DNA DSB repair pathways—NHEJ and HR declines with age in somatic cells in both mice and human beings (Li et al, ; Vaidya et al, ) and that deficiency in NHEJ or HR pathway leads to a phenotype of premature aging (Espejel et al, ; White & Vijg, ), we therefore first examined if NHEJ or HR changed with age in human ADSCs using our well‐characterized, GFP‐based reporter cassettes (Li et al, ; Mao et al, ). We linearized NHEJ or HR reporter cassettes with the restriction enzyme, I‐SceI, in vitro and then transfected the digested NHEJ (0.6 µg) or HR (1.5 µg) reporter constructs together with 0.03 µg pCMV‐DsRed2, for normalizing transfection efficiency, into each exponentially proliferating ADSC line at a concentration of 8 × 10 5 cells/ transfection.…”

“…We therefore set out to examine whether an impairment in DNA repair capacity contributes to the loss of genome integrity. Since mounting evidence indicates that the efficiency of two DNA DSB repair pathways-NHEJ and HR declines with age in somatic cells in both mice and human beings (Li et al, 2016;Vaidya et al, 2014) and that deficiency in NHEJ or HR pathway leads to a phenotype of premature aging (Espejel et al, 2004;White & Vijg, 2016), we therefore first examined if NHEJ or HR changed with age in human ADSCs using our well-characterized, GFP-based reporter cassettes (Li et al, 2016;Mao et al, 2009).…”

Somatic genome alterations in relation to age in lung adenocarcinoma

“…The SI3 associated with failure of DNA double‐strand break‐repair by homologous recombination was as well increasing along patient age in the TP53 ‐mutated subcohort. Recent studies showed that impaired DNA double‐strand break repair contributes to the age‐associated rise of genomic instability in humans . Meanwhile, although present and past smoking is reported in the TP53 wild‐type patients, no correlation between mutational signatures and patient age was detected.…”