Human Molecular Genetics

This Article Abstract FREE Full Text (PDF) Alert me when this article is cited Alert me if a correction is posted Services Email this article to a friend Similar articles in this journal Similar articles in ISI Web of Science Similar articles in PubMed Alert me to new issues of the journal Add to My Personal Archive Download to citation manager Search for citing articles in: ISI Web of Science (44) Request Permissions Google Scholar Articles by Tchirkov, A. Articles by Lansdorp, P. M. Search for Related Content PubMed PubMed Citation Articles by Tchirkov, A. Articles by Lansdorp, P. M. Social Bookmarking          What's this?

Human Molecular Genetics, 2003, Vol. 12, No. 3 227-232
© 2003 Oxford University Press

Role of oxidative stress in telomere shortening in cultured fibroblasts from normal individuals and patients with ataxia–telangiectasia

Andrei Tchirkov^1, and Peter M. Lansdorp^1,2,*

¹The Terry Fox Laboratory, BC Cancer Agency, Vancouver, BC, Canada V5Z 1L3 and ²Department of Medicine, University of British Columbia, Vancouver, BC, Canada V5Z 4E3

Received August 21, 2002; Accepted November 26, 2002

	ABSTRACT

TOP ABSTRACT INTRODUCTION RESULTS DISCUSSION MATERIALS AND METHODS REFERENCES

 
Cells from patients with the autosomal recessive disorder ataxia–telangiectasia (A–T) display accelerated telomere shortening upon culture in vitro. It has been suggested that A–T cells are in a chronic state of oxidative stress, which could contribute to their enhanced telomere shortening. In order to examine this hypothesis, we monitored the changes in telomere length in A–T homozygous, heterozygous and control fibroblasts cultured in vitro under various conditions of oxidative stress using quantitative fluorescent in situ hybridization. Compared with normal cells, the rate of telomere shortening was 1.5-fold increased under ‘normal’ levels of oxidative stress in A–T heterozygous cells and 2.4–3.2-fold in A–T homozygous cells. Mild chronic oxidative stress induced by hydrogen peroxide increased the rate of telomere shortening in A–T cells but not in normal fibroblasts and the telomere shortening rate decreased in both normal and A–T fibroblasts if cultures were supplemented with the anti-oxidant phenyl-butyl-nitrone. Increased telomere shortening upon oxidative stress in A–T cells was associated with a significant increase in the number of extra-chromosomal fragments of telomeric DNA and chromosome ends without detectable telomere repeats. We propose that the ATM (A–T mutated) protein has a role in the prevention or repair of oxidative damage to telomeric DNA and that enhanced sensitivity of telomeric DNA to oxidative damage in A–T cells results in accelerated telomere shortening and chromosomal instability.

	INTRODUCTION

TOP ABSTRACT INTRODUCTION RESULTS DISCUSSION MATERIALS AND METHODS REFERENCES

 
Ataxia–telangiectasia (A–T) is an autosomal recessive disorder involving cerebellar degeneration, oculocutaneous telangiectasia, immunodeficiency, premature senescence, radiosensitivity, and a strong predisposition to cancer (1). In most cases, mutations of the ATM (for ataxia–telangiectasia mutated gene), account for this pleiotropic phenotype (2). ATM encodes a protein kinase that is activated in the response to DNA strand breaks and is thought to be essential for maintaining chromosomal stability and telomere integrity (reviewed in 3). Telomeres protect the end of the chromosome against degradation, inappropriate recombination and fusion events (4). Telomeric sequences are lost with cell division and from other causes including oxidative stress (5). Telomere shortening may eventually compromise the stability of chromosomes, with implications for aging and oncogenesis (reviewed in 6).

Cells from patients with A–T and from mice with a defective ATM gene show prominent signs of telomere dysfunction including an accelerated rate of telomere loss with cell division, chromosome end-to-end fusions and the presence of extrachromosomal fragments of telomeric DNA (7–11). However, the impaired function of telomeres in the absence of functional ATM is not fully understood.

Several lines of evidence point to the possibility that the ATM protein may have a role in activating of defense mechanisms against oxidative stress (reviewed in 12). Because it is known that telomeres shorten prematurely under enhanced oxidative stress (5,13), we wanted to explore the possible linkage between telomere malfunction and enhanced oxidative stress in ATM-deficient cells. In order to do this, we monitored the changes in telomere length using quantitative fluorescent in situ hybridization (Q-FISH) in A–T homozygous and heterozygous as well as normal fibroblast strains grown in vitro under varied conditions of oxidative stress. For this purpose, the fluorescence intensity of directly labeled (CCCTAA)₃ peptide nucleic acid probe hybridized to metaphase chromosomes of at least 10–15 cells (resulting in >2000 data points per measurement) was measured as described (14–16). Results of Q-FISH are expressed in telomere fluorescence units (TFU) with each TFU corresponding to 1 kb of telomere repeats (15). The results of our study indicate an enhanced sensitivity of telomeric DNA to oxidative stress in A–T cells. We propose that defective maintenance or repair of telomeric DNA in cells from patients with A–T is a major contributing factor to the chromosomal breakage and genetic instability in such cells.

	RESULTS

TOP ABSTRACT INTRODUCTION RESULTS DISCUSSION MATERIALS AND METHODS REFERENCES

 
The changes in average telomere length in A–T and normal fibroblasts grown under variable conditions of oxidative stress were monitored using Q-FISH, from early passages to replicative senescence (Fig. 1). Linear regression was used to analyze the relationship between the mean telomere length and PD number. For all cultures, the relationship was highly significant (at the 0.01 level or better) with r= 0.98–0.99. The slopes of the regressions, which can be directly interpreted as rates of telomere shortening, were then compared between different cultures using t-statistics (17). In untreated cultures, the rate of telomere shortening was increased 3.2-fold in A–T homozygous AG 04405 cells (t=-13.26, d.f.=10, P<0.0001) and 2.4-fold in AG 03058 cells (t=-6.18, d.f.=8, P<0.0003) compared with normal BJ cells. A–T heterozygous cells displayed an intermediate rate of telomere shortening which was 1.5-fold higher than in normal fibroblasts (t=-5.2, d.f.=9, P=0.0006) but lower than in A–T cells (AG 04405; t=-10.45, d.f.=7, P<0.0001).

View larger version (30K): [in this window] [in a new window]   Figure 1. Telomere length dynamics in cultured normal and A–T fibroblasts at different levels of oxidative stress: ‘normal’ (cultures in atmospheric oxygen levels), increased (cultures with 20 µM hydrogen peroxide), and decreased (cultures with 400 µM of the spin trap agent PBN). Values of slopes (m= rate of telomere shortening per PD) are shown for each regression line. The indicated levels of significance correspond to the comparisons of the rates of telomere shortening in the presence of H2O2or PBN with the ‘normal’ rate in untreated cultures.

 
The treatment with H₂O₂, inducing an excess of oxidative radicals, significantly accelerated the rate of telomere shortening in ATM-deficient strains (homozygous and heterozygous) but not in the normal fibroblasts (Fig. 1). In contrast, the protection of cells from oxidative radicals using PBN, a spin-trap agent, significantly reduced the rate of telomere shortening in both A–T and normal fibroblasts. However, the rate of telomere shortening under anti-oxidant protection was yet substantially accelerated in A–T cells compared with untreated normal cells (AG 04405: t=-8.94, d.f.=10, P<0.0001 and AG 03058: t=-2.8, d.f.=9, P<0.02).

Table 1 shows that ATM-deficient cells from H₂O₂-treated cultures accumulated significant proportions of short telomeres, i.e. those having a telomere length of 1.5 TFU or less, which could be a threshold value for maintaining a functional telomere (18). Normal cells did not show such a pronounced increase in the number of short telomeres under exposure to H₂O₂. The PBN treatment slowed down the accumulation of short telomeres both in normal and A–T fibroblasts. Overall, a reduced mean telomere length was associated with an increased fraction of short telomeres as expected.

View this table: [in this window] [in a new window]   Table 1. Telomere characteristics of early- and late-passage normal and A–T fibroblasts cultured at different levels of oxidative stress

 
In addition, we studied the yield of extra-chromosomal telomeric DNA fragments after a single high-dose (200 µM) H₂O₂ treatment. We have previously reported that the spontaneous incidence of such fragments was significantly higher in A–T cells than in normal fibroblasts (11). Although the average number of extra-chromosomal telomeres was increased after treatment in all cell strains, the frequency of fragments was significantly higher in ATM-deficient cells than in normal cells (Fig. 2). Occasionally, very high numbers of extra-chromosomal telomere fragments were observed in A–T cells following high dose H₂O₂ treatment (Fig. 3).

View larger version (30K): [in this window] [in a new window]   Figure 2. Frequency distribution of extra-chromosomal telomeric DNA fragments in normal and ATM-deficient fibroblasts from untreated cultures and from cultures treated with a high-dose of hydrogen peroxide. Note a significant increase in the average frequency of the fragments after treatment, which was more pronounced in ATM-deficient cells than in normal cells (*P<0.05 in the Mann–Whitney rank sum test). At the time of experiment, the cultures were at the following population doublings (PD): the normal strain BU was at 39.3 PD, the A–T heterozygote AG 03059 at 22.5 PD, the A–T homozygote AG 04405 at 20.5 PD, and the A–T homozygote AG 03058 at 17.8 PD.

 

View larger version (113K): [in this window] [in a new window]   Figure 3. Multiple extra-chromosomal telomeric DNA fragments in an A–T metaphase cell from a culture exposed to a high-dose hydrogen peroxide (some of the fragments are indicated by arrows). Also the presence of chromosomal ends without detectable telomeric probe signals (some of which are indicated by asterisks).

 

	DISCUSSION

TOP ABSTRACT INTRODUCTION RESULTS DISCUSSION MATERIALS AND METHODS REFERENCES

 
The aim of this study was to examine the potential role of oxidative stress in the markedly increased telomere shortening in A–T cells. Using Q-FISH, we evaluated the dynamics of telomere length in A–T and normal fibroblasts cultured in vitro under variable levels of oxidative stress. In agreement with previous studies (8,11), ATM-deficient cells were found to lose telomeric sequences at significantly higher rates than normal BJ cells under ‘normal’ levels of free oxygen radicals. The rate of telomere shortening was increased 1.5 fold in an A–T heterozygote and 2.4–3.2-fold in A–T homozygotes compared with normal cells. A chronic oxidative stress induced by low-dose hydrogen peroxide significantly increased the rate of telomere shortening in ATM-deficient cells but not in BJ cells, which are characterized by a good antioxidant capacity (19). In contrast, culture of cells in the presence of the anti-oxidant PBN decreased the rate of telomere shortening not only in normal fibroblasts in agreement with previous observations (20), but also in A–T cells. However, PBN treatment did not completely ‘normalize’ the telomere loss in A–T cells, as telomeres in A–T cells continued to decrease in length more rapidly than in normal untreated cells. These observations indicate an enhanced sensitivity of telomeric DNA to oxidative damage in ATM-deficient cells. Additional studies with normal as well as ATM deficient cells are needed to delineate the variation in the degree of accelerated telomere shortening in response to oxidative damage in relation to functional levels of ATM protein.

In addition to loss of telomeric DNA with replication, oxidative damage of telomeric DNA is an important cause of the telomere shortening in normal human somatic cells (reviewed in 13). An increased production of reactive oxygen species was shown to accelerate telomere shortening in replicating fibroblasts in vitro (5). This acceleration was attributed to the enhanced induction of telomeric single strand breaks by free radicals, leading to the loss of the distal fragments of telomeric DNA following replication (21). Other studies have shown that telomeric DNA is a preferential target for oxidative damage (22,23) and accelerated telomere shortening has been detected in cells from patients with mutations in mitochondrial DNA that are characterized by an increased production of reactive oxygen species (24).

Problems at telomeres related to enhanced sensitivity to oxidative damage may be exacerbated because lesions in telomeric DNA are repaired less efficiently than in other regions in the genome (25,26). We observed that ATM-deficient fibroblasts were strikingly sensitive to oxidative radicals generated by hydrogen peroxide treatment, displaying not only an enhanced telomere loss but also the presence of multiple extra-chromosomal fragments of telomeric DNA. A single high-dose hydrogen peroxide treatment induced in A–T cells such fragments of telomeric DNA at considerably higher rates than in BJ fibroblasts. Taken together, our findings suggest that the loss of ATM function results in problems specifically at telomeres. One possibility is that ATM has a role in the repair of DNA lesions at terminal positions in telomeric DNA for example in nucleotide excision repair pathways that involve a switch in the template for DNA polymerases. Such mechanisms may fail when the replication fork reaches the very end of the chromosome and the physical linkage between sister chromatids is lost before DNA damage signaling pathways can arrest progression of the replication fork. Deficient DNA damage signaling in A–T cells could compromise the efficiency of such nucleotide excision repair pathways specifically at telomeres by allowing ‘premature’ separation of sister chromatids. The net result of such deficiency would be lesions that are not repaired which could lead to accelerated telomere shortening.

The ATM protein has been hypothesized to activate defense mechanisms against oxidative stress. Cells from A–T patients are thought to be defective in a general cellular response to oxidative stress that may be explained by lower antioxidative capacity and impaired repair of oxidative DNA damage (reviewed in 12). The combination of two deficiencies may have a synergistic adverse effect on the telomere maintenance in A–T cells. Accelerated loss of telomeric sequences and resulting telomere dysfunction appears to be prominent in A–T homozygous cells and, to a lower degree, in A–T heterozygous cells. The function of ATM in the repair of oxidative damage to telomeric DNA appears to be essential for maintaining telomere integrity and telomere abnormalities could be of crucial importance in the phenotype A–T.

	MATERIALS AND METHODS

TOP ABSTRACT INTRODUCTION RESULTS DISCUSSION MATERIALS AND METHODS REFERENCES

 
Cell strains, culture and treatments
The A–T homozygous human fibroblast strains AG 04405 (male, 7 years) and AG 03058 (female, 14 years) and a heterozygous strain AG 03059 (male, 47 years) were obtained from the National Institute of Aging Cell Culture Repository (Camden, NJ, USA). The neonatal human foreskin fibroblast cell strain BJ was a kind gift from Dr J. Smith, Houston, Texas. Fibroblasts were grown in HAM's F10 medium supplemented with 5–10% fetal bovine serum and, in parallel with untreated cultures, either in the presence of 20 µM hydrogen peroxide (H₂O₂, Sigma, Oakville, Canada) or 400 µM phenyl-butyl-nitrone (PBN, Sigma). As the H₂O₂ concentration diminishes quickly in the culture media in the presence of cells and serum (27), the medium with hydrogen peroxide was changed more frequently. Cells were split at a ratio of 1:4 or 1:8 at early passage or at a ratio of 1:2 in later passages. Population doubling (PD) number was calculated as PD=log₂(N_f/N₀), where N_f is the final cell number and N₀ is the initial number of seeded cells. Senescence was defined as failure to double cell numbers over a period of 4 weeks. In untreated cultures, ATM-deficient cells senesced prematurely, A–T homozygous fibroblasts after 23–26 PD and A–T heterozygous fibroblasts after 33.5 PD. For comparison, normal BJ fibroblasts reached 69 PD.

The effect of acute oxidative stress on telomeres was studied by exposing confluent fibroblast cultures to a single high-dose treatment with 200 µM H₂O₂ in a serum-free medium for 1 h at 37°C. Cells were then washed, trypsinized and cultured at 1:2 or 1:4 density and harvested 48 h later.

Chromosome preparations and quantitative fluorescence in situ hybridization
The fibroblast cultures were treated with 0.1 µg/ml of Colcemid (Gibco) for the last 6–12 h of incubation to accumulate mitotic cells which were harvested according to standard cytogenetic procedures. After hypotonic swelling in KCl buffer for 30 min at 37°C, cells were fixed three times in methanol/acetic acid (3:1), dropped onto clean wet slides, and dried overnight. In situ hybridization with a telomere Cy-3-conjugated (C₃TA₂)₃ peptide nucleic acid (PNA) probe (PBIO/Biosearch Product, Bedford, MA, USA) was performed as described previously (14–16). The chromosome preparations were counterstained with 4',6-diamidino-2-phenylindole (DAPI).

Quantitative image analysis
Digital images were recorded with a MicroImager MI1400–12 camera (Xillix) on an Axioplan fluorescence microscope (Zeiss). Microscope control and image acquisition was performed with the dedicated software (SSM, Xillix). An analysis of integrated fluorescence intensities of telomere hybridization signals was carried out using the computer program ‘TFLTELO’ (16). A total of 62 analyses were performed, with a median of 1460 telomeres from 15–20 metaphases evaluated per test. Values of fluorescence intensity for each telomere were converted into the number of TFU using special calibration curves, as described (15). One TFU corresponds to 1 kb of telomeric repetitive sequences.

	ACKNOWLEDGEMENTS

 
We thank Viktoriya Dobrovinska and Elizabeth Chavez for expert technical assistance. This work was supported by a grant from the Canadian Institute of Health Research.

	FOOTNOTES

 
^* To whom correspondence should be addressed at: Terry Fox Laboratory, BC Cancer Agency, 601 West 10th Avenue, Vancouver, BC, Canada V5Z 1L3. Tel: +1 6048776070, ext. 3026; Fax: +1 6048770712; E-mail: plansdor{at}bccancer.bc.ca

Present address: Département de Radiothérapie, Centre Jean Perrin, Clermont-Ferrand 63011, France.

	REFERENCES

TOP ABSTRACT INTRODUCTION RESULTS DISCUSSION MATERIALS AND METHODS REFERENCES

 

1. Sedgwick, R.P. and Boder, E. (1991) Ataxia–telangiectasia. In Vilken, P.J., Bruyn, G.W. and Klamans, H.L. (eds), Handbook of Clinical Neurology. Elsevier Science, Amsterdam, pp. 347–423.

2. Savitsky, K., Bar-Shira, A., Gilad, S., Rotman, G., Ziv, Y., Vanagaite, L., Tagle, D.A., Smith, S., Uziel, T. and Sfez, S. (1995) A single ataxia telangiectasia gene with a product similar to PI-3 kinase. Science, 268, 1749–1753.[Abstract/Free Full Text]

3. Rotman, G. and Shiloh, Y. (1999) ATM: a mediator of multiple responses to genotoxic stress. Oncogene, 18, 6135–6144.[CrossRef][Web of Science][Medline]

4. Blackburn, E.H. (2001) Switching and signaling at the telomere. Cell, 106, 661–673.[CrossRef][Web of Science][Medline]

5. von Zglinicki, T., Saretzki, G., Docke, W. and Lotze, C. (1995) Mild hyperoxia shortens telomeres and inhibits proliferation of fibroblasts: a model for senescence? Exp. Cell Res., 220, 186–193.[CrossRef][Web of Science][Medline]

6. Collins, K. and Mitchell, J.R. (2002) Telomerase in the human organism. Oncogene, 21, 564–579.[CrossRef][Web of Science][Medline]

7. Pandita, T.K., Pathak, S. and Geard, C.R. (1995) Chromosome end associations, telomeres and telomerase activity in ataxia telangiectasia cells. Cytogenet. Cell Genet., 71, 86–93.[Web of Science][Medline]

8. Metcalfe, J.A., Parkhill, J., Campbell, L., Stacey, M., Biggs, P., Byrd, P.J. and Taylor, M.R. (1996) Accelerated telomere shortening in ataxia telangiectasia. Nat. Genet., 13, 350–353.[CrossRef][Web of Science][Medline]

9. Xia, S.J., Shammas, M.A. and Shmookler reis, R.J. (1996) Reduced telomere length in ataxia–telangiectasia fibroblasts. Mutat. Res., 364, 1–11.[Web of Science][Medline]

10. Vaziri, H., West, M.D., Allsopp, R.C., Davison, T.S., Wu, Y.S., Arrowsmith, C.H., Poirier, G.G. and Benchimol, S. (1997) ATM-dependent telomere loss in aging human diploid fibroblasts and DNA damage lead to the post-translational activation of p53 protein involving poly(ADP-ribose) polymerase. EMBO J., 16, 6018–6033.[CrossRef][Web of Science][Medline]

11. Hande, M.P., Balajee, A.S., Tchirkov, A., Wynshaw-Boris, A. and Lansdorp, P.M. (2001) Extra-chromosomal telomeric DNA in cells from Atm^-/- mice and patients with ataxia–telangiectasia. Hum. Mol. Genet., 10, 519–528.[Abstract/Free Full Text]

12. Rotman, G. and Shiloh, Y. (1997) Ataxia–telangiectasia: is ATM a sensor of oxidative damage and stress? Bioessays, 19, 911–917.[CrossRef][Web of Science][Medline]

13. Saretzki, G. and von Zglinicki, T. (2002) Replicative aging, telomeres, and oxidative stress. Ann. NY Acad Sci, 959, 24–29.[Web of Science][Medline]

14. Lansdorp, P.M., Verwoerd, N.P., van de Rijke, F.M., Dragowska, V., Little, M.-T., Dirks, R.W., Raap, A.K. and Tanke, H.J. (1996) Heterogeneity in telomere length of human chromosomes. Hum. Mol. Genet., 5, 685–691.[Abstract/Free Full Text]

15. Martens, U.M., Zijlmans, J.M.J.M., Poon, S.S.S., Dragowska, W., Yui, J., Chavez, E.A., Ward, R.K. and Lansdorp, P.M. (1998) Short telomeres on human chromosome 17p. Nat. Genet., 18, 76–80.[CrossRef][Web of Science][Medline]

16. Poon, S.S.S., Martens, U.M., Ward, R.K. and Lansdorp, P.M. (1999) Telomere length measurements using digital fluorescence microscopy. Cytometry, 36, 267–278.[CrossRef][Web of Science][Medline]

17. Armitage, P. and Berry, G. (1987) Statistical Methods in Medical Research. Blackwell Scientific, Oxford.

18. Martens, U.M., Chavez, E.A., Poon, S.S.S., Schmoor, C. and Lansdorp, P.M. (2000) Accumulation of short telomeres in human fibroblasts prior to replicative senescence. Exp. Cell Res., 256, 291–299.[CrossRef][Web of Science][Medline]

19. Lorenz, M., Saretzki, G., Sitte, N., Metzkow, S. and von Zglinicki, T. (2001) BJ fibroblasts display high antioxidant capacity and slow telomere shortening independent of hTERT transfection. Free Radic. Biol. Med., 31, 824–831.[CrossRef][Web of Science][Medline]

20. von Zglinicki, T., Pilger, R. and Sitte, N. (2000) Accumulation of single-strand breaks is the major cause of telomere shortening in human fibroblasts. Free Radic. Biol. Med., 28, 64–74.[CrossRef][Web of Science][Medline]

21. Sitte, N., Saretzki, G. and von Zglinicki, T. (1998) Accelerated telomere shortening in fibroblasts after extended periods of confluency. Free Radic. Biol. Med., 24, 885–893.[CrossRef][Web of Science][Medline]

22. Henle, E.S., Han, Z., Tang, N., Rai, P., Luo, Y. and Linn, S. (1999) Sequence-specific DNA cleavage by Fe²⁺-mediated fenton reactions has possible biological implications. J. Biol. Chem., 274, 962–971.[Abstract/Free Full Text]

23. Oikawa, S. and Kawanishi, S. (1999) Site-specific DNA damage at GGG sequence by oxidative stress may accelerate telomere shortening. FEBS Lett., 453, 365–368.[CrossRef][Web of Science][Medline]

24. Oexle, K. and Zwirner, A. (1997) Advanced telomere shortening in respiratory chain disorders. Hum. Mol. Genet., 6, 905–908.[Abstract/Free Full Text]

25. Kruk, P.A., Rampino, N.J. and Bohr, V.A. (1995) DNA damage and repair in telomeres: Relation to aging. Proc. Natl Acad. Sci. USA, 92, 258–262.[Abstract/Free Full Text]

26. Petersen, S., Saretzki, G. and von Zglinicki, T. (1998) Preferential accumulation of single-stranded regions in telomeres of human fibroblasts. Exp. Cell Res., 239, 152–160.[CrossRef][Web of Science][Medline]

27. Gille, J.J. and Joenje, H. (1992) Cell culture models for oxidative stress: superoxide and hydrogen peroxide versus normobaric hyperoxia. Mutat. Res., 275, 405–414.[CrossRef][Web of Science][Medline]

CiteULike    Connotea    Del.icio.us    What's this?

This article has been cited by other articles:

				R. C. Kaplan, A. L. Fitzpatrick, M. N. Pollak, J. P. Gardner, N. S. Jenny, A. P. McGinn, L. H. Kuller, H. D. Strickler, M. Kimura, B. M. Psaty, et al. Insulin-Like Growth Factors and Leukocyte Telomere Length: The Cardiovascular Health Study J Gerontol A Biol Sci Med Sci, November 1, 2009; 64A(11): 1103 - 1106. [Abstract] [Full Text] [PDF]

				H. M. Salomons, G. A. Mulder, L. van de Zande, M. F. Haussmann, M. H. K. Linskens, and S. Verhulst Telomere shortening and survival in free-living corvids Proc R Soc B, September 7, 2009; 276(1670): 3157 - 3165. [Abstract] [Full Text] [PDF]

				C. Sebastian, C. Herrero, M. Serra, J. Lloberas, M. A. Blasco, and A. Celada Telomere Shortening and Oxidative Stress in Aged Macrophages Results in Impaired STAT5a Phosphorylation J. Immunol., August 15, 2009; 183(4): 2356 - 2364. [Abstract] [Full Text] [PDF]

				M. Hills, K. Lucke, E. A. Chavez, C. J. Eaves, and P. M. Lansdorp Probing the mitotic history and developmental stage of hematopoietic cells using single telomere length analysis (STELA) Blood, June 4, 2009; 113(23): 5765 - 5775. [Abstract] [Full Text] [PDF]

				A. Aviv, W. Chen, J. P. Gardner, M. Kimura, M. Brimacombe, X. Cao, S. R. Srinivasan, and G. S. Berenson Leukocyte Telomere Dynamics: Longitudinal Findings Among Young Adults in the Bogalusa Heart Study Am. J. Epidemiol., February 1, 2009; 169(3): 323 - 329. [Abstract] [Full Text] [PDF]

				J. A. Lemon, C. D. Rollo, and D. R. Boreham Elevated DNA damage in a mouse model of oxidative stress: impacts of ionizing radiation and a protective dietary supplement Mutagenesis, November 1, 2008; 23(6): 473 - 482. [Abstract] [Full Text] [PDF]

				I. Spyridopoulos, Y. Erben, T. H. Brummendorf, J. Haendeler, K. Dietz, F. Seeger, C. K. Kissel, H. Martin, J. Hoffmann, B. Assmus, et al. Telomere Gap Between Granulocytes and Lymphocytes Is a Determinant for Hematopoetic Progenitor Cell Impairment in Patients With Previous Myocardial Infarction Arterioscler Thromb Vasc Biol, May 1, 2008; 28(5): 968 - 974. [Abstract] [Full Text] [PDF]

				J. L. Yanowitz Genome Integrity Is Regulated by the Caenorhabditis elegans Rad51D Homolog rfs-1 Genetics, May 1, 2008; 179(1): 249 - 262. [Abstract] [Full Text] [PDF]

				L. F. Cherkas, J. L. Hunkin, B. S. Kato, J. B. Richards, J. P. Gardner, G. L. Surdulescu, M. Kimura, X. Lu, T. D. Spector, and A. Aviv The Association Between Physical Activity in Leisure Time and Leukocyte Telomere Length Arch Intern Med, January 28, 2008; 168(2): 154 - 158. [Abstract] [Full Text] [PDF]

				M. Muftuoglu, H. K. Wong, S. Z. Imam, D. M. Wilson III, V. A. Bohr, and P. L. Opresko Telomere Repeat Binding Factor 2 Interacts with Base Excision Repair Proteins and Stimulates DNA Synthesis by DNA Polymerase {beta} Cancer Res., January 1, 2006; 66(1): 113 - 124. [Abstract] [Full Text] [PDF]

				P. L. Opresko, J. Fan, S. Danzy, D. M. Wilson III, and V. A. Bohr Oxidative damage in telomeric DNA disrupts recognition by TRF1 and TRF2 Nucleic Acids Res., February 24, 2005; 33(4): 1230 - 1239. [Abstract] [Full Text] [PDF]

				I. Spyridopoulos, J. Haendeler, C. Urbich, T. H. Brummendorf, H. Oh, M. D. Schneider, A. M. Zeiher, and S. Dimmeler Statins Enhance Migratory Capacity by Upregulation of the Telomere Repeat-Binding Factor TRF2 in Endothelial Progenitor Cells Circulation, November 9, 2004; 110(19): 3136 - 3142. [Abstract] [Full Text] [PDF]

				D. J. Kurz, S. Decary, Y. Hong, E. Trivier, A. Akhmedov, and J. D. Erusalimsky Chronic oxidative stress compromises telomere integrity and accelerates the onset of senescence in human endothelial cells J. Cell Sci., May 1, 2004; 117(11): 2417 - 2426. [Abstract] [Full Text] [PDF]

				Y. Bai and J. P. Murnane Telomere Instability in a Human Tumor Cell Line Expressing NBS1 With Mutations at Sites Phosphorylated by ATM Mol. Cancer Res., December 1, 2003; 1(14): 1058 - 1069. [Abstract] [Full Text] [PDF]

This Article Abstract FREE Full Text (PDF) Alert me when this article is cited Alert me if a correction is posted Services Email this article to a friend Similar articles in this journal Similar articles in ISI Web of Science Similar articles in PubMed Alert me to new issues of the journal Add to My Personal Archive Download to citation manager Search for citing articles in: ISI Web of Science (44) Request Permissions Google Scholar Articles by Tchirkov, A. Articles by Lansdorp, P. M. Search for Related Content PubMed PubMed Citation Articles by Tchirkov, A. Articles by Lansdorp, P. M. Social Bookmarking          What's this?

Online ISSN 1460-2083 - Print ISSN 0964-6906

Copyright © 2009 Oxford University Press

Oxford Journals Oxford University Press

• Site Map
• Privacy Policy
• Frequently Asked Questions

Other Oxford University Press sites: Oxford University Press Oxford Journals China Oxford Journals Japan American National Biography Booksellers' Information Service Children's Fiction and Poetry Children's Reference Corporate & Special Sales Dictionaries Dictionary of National Biography Digital Reference English Language Teaching Higher Education Textbooks Humanities International Education Unit Law Medicine Music Online Products Oxford English Dictionary Reference Rights and Permissions Science School Books Social Sciences Very Short Introductions World's Classics