Impact of telomerase ablation on organismal viability, aging, and tumorigenesis in mice lacking the DNA repair proteins PARP-1, Ku86, or DNA-PKcs - PubMed (original) (raw)

Impact of telomerase ablation on organismal viability, aging, and tumorigenesis in mice lacking the DNA repair proteins PARP-1, Ku86, or DNA-PKcs

Silvia Espejel et al. J Cell Biol. 2004.

Abstract

The DNA repair proteins poly(ADP-ribose) polymerase-1 (PARP-1), Ku86, and catalytic subunit of DNA-PK (DNA-PKcs) have been involved in telomere metabolism. To genetically dissect the impact of these activities on telomere function, as well as organismal cancer and aging, we have generated mice doubly deficient for both telomerase and any of the mentioned DNA repair proteins, PARP-1, Ku86, or DNA-PKcs. First, we show that abrogation of PARP-1 in the absence of telomerase does not affect the rate of telomere shortening, telomere capping, or organismal viability compared with single telomerase-deficient controls. Thus, PARP-1 does not have a major role in telomere metabolism, not even in the context of telomerase deficiency. In contrast, mice doubly deficient for telomerase and either Ku86 or DNA-PKcs manifest accelerated loss of organismal viability compared with single telomerase-deficient mice. Interestingly, this loss of organismal viability correlates with proliferative defects and age-related pathologies, but not with increased incidence of cancer. These results support the notion that absence of telomerase and short telomeres in combination with DNA repair deficiencies accelerate the aging process without impacting on tumorigenesis.

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Figures

Figure 1.

Telomere length in MEFs derived from successive generations of telomerase-deficient mice lacking PARP-1. Telomere length distribution in primary MEFs from littermate mice of the indicated genotypes. One telomere fluorescence unit (TFU) corresponds to 1 kb of TTAGGG repeats (Zijlmans et al., 1997). The respective genotype, average telomere length, and SD are indicated. Note that SD and not SEM is shown. In addition, the total number of telomeres analyzed and the number of signal-free ends, i.e., telomeres that do not contain any detectable TTAGGG signal as determined by the Q-FISH technique (detection limit is 150 bp), are given. The vertical dashed line is shown to facilitate comparisons between genotypes.

Figure 2.

Effect of Ku86, DNA-PKcs, or PARP-1 deficiency on the life span of successive generations of telomerase-deficient mice. Overall survival of mice with intact telomerase (Terc+/+, circles) and four successive generations of telomerase-deficient (Terc−/−) mice, including G1 (squares), G2 (rhombus), G3 (upward triangles), and G4 (downward triangles), which are either wild-type (solid lines, open symbols) or deficient (dashed lines, closed symbols) for Ku86 (A), DNA-PKcs (B), or PARP-1 (C); n.a. = not analyzed.

Figure 3.

Effect of Ku86, DNA-PKcs, or PARP-1 deficiency on tumorigenesis and tissue atrophies in successive generations of telomerase-deficient mice. Mice with telomerase (Terc+/+) and four successive generations of telomerase-deficient (Terc−/−) mice (G1–G4) that were either wild-type (gray bars) or deficient (black bars) for Ku86 (A–C), DNA-PKcs (D–F), and PARP-1 (G–I) were killed when they showed signs of poor health and were analyzed for the occurrence of tumors (A, D, and G) as well as intestinal (B, E, and H) and testicular atrophy (C, F, and I). The number of animals suffering a given pathology in relation to the total number of animals examined is given above each bar. Significant differences (P < 0.05, Fisher's exact test) between single and double mutant animals are indicated by an asterisk; n.a. = not analyzed.

Figure 4.

Effect of Ku86, DNA-PKcs, or PARP-1 deficiency on morphology, apoptosis, and proliferative potential of the intestinal epithelium in successive generations of telomerase-deficient mice. Representative photomicrographs of paraffin sections of large intestine from 1-yr-old mice of the indicated genotype stained with Harris hematoxylin and eosin (A), immunostained for active caspase-3 (B), and Ki67 (C). Arrowheads indicate examples of positive immunostaining for active caspase-3 and Ki67. ML, muscular layer; C, crypt; F, fold.

Figure 5.

Effect of Ku86, DNA-PKcs, or PARP-1 deficiency on the early onset of age-related pathologies in successive generations of telomerase-deficient mice. Mice with telomerase (Terc+/+) and four successive generations of telomerase-deficient (Terc−/−) mice (G1–G4) that were either wild-type (gray bars) or deficient (black bars) for Ku86 (A), DNA-PKcs (B), and PARP-1 (C) were killed when they showed signs of poor health and analyzed for the occurrence of a variety of age-associated pathologies (see Table S1, available at

http://www.jcb.org/cgi/content/full/jcb.200407178/DC1

). Here, we show the onset of these aging-associated pathologies in animals younger than 1 yr of age in a given mouse group relative to the total number of detected pathologies in that group. The number of senile lesions detected in young animals (<1 yr) in relation to the total number of lesions detected in the respective mouse group is given above each bar; for example, as shown in A, in the Terc+/+/Ku86−/− mouse cohort we detected a total of 21 senile lesions and 11 of them were detected in mice younger than 1 yr of age. Significant differences (P < 0.05, Fisher's exact test) between single and double mutant animals are indicated by an asterisk; n.a. = not analyzed.

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Impact of telomerase ablation on organismal viability, aging, and tumorigenesis in mice lacking the DNA repair proteins PARP-1, Ku86, or DNA-PKcs - PubMed (original) (raw)