Abstract
BackgroundCellular senescence is a state reached by normal mammalian cells after a finite number of cell divisions and is characterized by morphological and physiological changes including terminal cell-cycle arrest. The limits on cell division imposed by senescence may play an important role in both organismal aging and in preventing tumorigenesis. Cellular senescence and organismal aging are both accompanied by increased DNA damage, seen as the formation of γ-H2AX foci (γ-foci), which may be found on uncapped telomeres or at non-telomeric sites of DNA damage. However, the relative importance of telomere- and non-telomere-associated DNA damage to inducing senescence has never been demonstrated. Here we present a new approach to determine accurately the chromosomal location of γ-foci and quantify the number of telomeric versus non-telomeric γ-foci associated with senescence in both human and mouse cells. This approach enables researchers to obtain accurate values and to avoid various possible misestimates inherent in earlier methods.ResultsUsing combined immunofluorescence and telomere fluorescence in situ hybridization on metaphase chromosomes, we show that human cellular senescence is not solely determined by telomeric DNA damage. In addition, mouse cellular senescence is not solely determined by non-telomeric DNA damage. By comparing cells from different generations of telomerase-null mice with human cells, we show that cells from late generation telomerase-null mice, which have substantially short telomeres, contain mostly telomeric γ-foci. Most notably, we report that, as human and mouse cells approach senescence, all cells exhibit similar numbers of total γ-foci per cell, irrespective of chromosomal locations.ConclusionOur results suggest that the chromosome location of senescence-related γ-foci is determined by the telomere length rather than species differences per se. In addition, our data indicate that both telomeric and non-telomeric DNA damage responses play equivalent roles in signaling the initiation of cellular senescence and organismal aging. These data have important implications in the study of mechanisms to induce or delay cellular senescence in different species.
Highlights
Cellular senescence is a state reached by normal mammalian cells after a finite number of cell divisions and is characterized by morphological and physiological changes including terminal cell-cycle arrest
Human and mouse primary cells show different patterns of senescence-related γ-foci Metaphase chromosome spreads were prepared from cultures of human and mouse cells at low population doubling (PD) times and during the penultimate PD before the onset of senescence
Metaphase chromosomes were stained for γ-H2AX and for telomeric DNA in order to measure the numbers of uncapped telomeres and other types of DNA double-strand breaks (DSBs) (Figure 1A and 1B) [20]
Summary
Cellular senescence is a state reached by normal mammalian cells after a finite number of cell divisions and is characterized by morphological and physiological changes including terminal cell-cycle arrest. We present a new approach to determine accurately the chromosomal location of γ-foci and quantify the number of telomeric versus non-telomeric γ-foci associated with senescence in both human and mouse cells. This approach enables researchers to obtain accurate values and to avoid various possible misestimates inherent in earlier methods. It has been shown that DNA repair proteins, including γ-H2AX [11,12], are localized at uncapped telomeres [13] This telomeric DNA damage response has been shown to be a potential inducer of senescence or cell death [5,6,7], as well as of in vivo aging in both model systems and human pathology [3]. It has been proposed that replicative cellular senescence is induced by telomere dysfunction [5,6,7,14]
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Free) 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a call
