Telomere dysfunction in genome instability syndromes

Integration of RNA molecules data with prior-knowledge driven Joint Deep Semi-Negative Matrix Factorization for heart failure study

Heart failure (HF) is the main manifestation of cardiovascular disease. Recent studies have shown that various RNA molecules and their complex connections play an essential role in HF’s pathogenesis and pathological progression. This paper aims to mine key RNA molecules associated with HF. We proposed a Prior-knowledge Driven Joint Deep Semi-Negative Matrix Factorization (PD-JDSNMF) model that uses a hierarchical nonlinear feature extraction method that integrates three types of data: mRNA, lncRNA, and miRNA. The PPI information is added to the model as prior knowledge, and the Laplacian constraint is used to help the model resist the noise in the genetic data. We used the PD-JDSNMF algorithm to identify significant co-expression modules. The elements in the module are then subjected to bioinformatics analysis and algorithm performance analysis. The results show that the PD-JDSNMF algorithm can robustly select biomarkers associated with HF. Finally, we built a heart failure diagnostic model based on multiple classifiers and using the Top 13 genes in the significant module, the AUC of the internal test set was up to 0.8714, and the AUC of the external validation set was up to 0.8329, which further confirmed the effectiveness of the PD-JDSNMF algorithm.

Exposure to hypomethylating 5-aza-2'-deoxycytidine (decitabine) causes rapid, severe DNA damage, telomere elongation and mitotic dysfunction in human WIL2-NS cells

BACKGROUND

5-aza-2'-deoxycytidine (5azadC, decitabine) is a DNA hypomethylating agent used in the treatment of myelodysplastic syndromes. Due to cytotoxic side effects dose optimization is essential. The aim of this study was to define and quantify the effects of 5azadC on biomarkers of chromosomal stability, and telomere length, in human lymphoblastoid cell line, WIL2-NS, at clinically relevant dosages.

METHODS

Human WIL2-NS cells were maintained in complete medium containing 0, 0.2 or 1.0 μM 5azadC for four days, and analysed daily for telomere length (flow cytometry), chromosomal stability (cytokinesis-block micronucleus cytome (CBMN-cyt) assay), and global methylation (%5me-C).

RESULTS

DNA methylation decreased significantly in 1.0 μM 5azadC, relative to control (p < 0.0001). Exposure to 1.0 μM 5azadC resulted in 1.7-fold increase in telomere length (p < 0.0001), in parallel with rapid increase in biomarkers of DNA damage; (micronuclei (MN, 6-fold increase), nucleoplasmic bridges (NPB, a 12-fold increase), and nuclear buds (NBud, a 13-fold increase) (all p < 0.0001). Fused nuclei (FUS), indicative of mitotic dysfunction, showed a 5- and 13-fold increase in the 0.2 μM and 1.0 μM conditions, respectively (p = 0.001) after 4 days.

CONCLUSIONS

These data show that (i) clinically relevant concentrations of 5azadC are highly genotoxic; (ii) hypomethylation was associated with increased TL and DNA damage; and (iii) longer TL was associated with chromosomal instability. These findings suggest that lower doses of 5azdC may be effective as a hypomethylating agent, while potentially reducing DNA damage and risk for secondary disease.

Three-Dimensional Nuclear Telomere Profiling as a Biomarker for Recurrence in Oligodendrogliomas: A Pilot Study

Mechanisms of recurrence in oligodendrogliomas are poorly understood. Recurrence might be driven by telomere dysfunction-mediated genomic instability. In a pilot study, we investigated ten patients with oligodendrogliomas at the time of diagnosis (first surgery) and after recurrence (second surgery) using three-dimensional nuclear telomere analysis performed with quantitative software TeloView^® (Telo Genomics Corp, Toronto, Ontario, Canada). 1p/19q deletion status of each patient was determined by fluorescent in situ hybridization on touch preparation slides. We found that a very specific 3D telomeric profile was associated with two pathways of recurrence in oligodendrogliomas independent of their 1p/19q status: a first group of 8 patients displayed significantly different 3D telomere profiles between both surgeries (p < 0.0001). Their recurrence happened at a mean of 231.375 ± 117.42 days and a median time to progression (TTP) of 239 days, a period defined as short-term recurrence; and a second group of three patients displayed identical 3D telomere profiles between both surgery samples (p > 0.05). Their recurrence happened at a mean of 960.666 ± 86.19 days and a median TTP of 930 days, a period defined as long-term recurrence. Our results suggest a potential link between nuclear telomere architecture and telomere dysfunction with time to recurrence in oligodendrogliomas, independently of the 1p/19q status.

The telomere length of gastric mucosal samples and peripheral blood lymphocytes in patients who have undergone Billroth II distal gastrectomy

INTRODUCTION

Telomeres play an important role in maintaining chromosomal integrity. Functional loss of telomeres increases the risk of cancer by causing genomic instability. Telomere length abnormalities have been reported in several precancerous lesions. There is no study that evaluates telomere length in Billroth II distal gastrectomy, which is known as a risk factor for gastric stump carcinogenesis, in the literature. The aim of this study was to assess the relationship between the telomere length of residual gastric mucosal samples, peripheral blood lymphocytes, and other clinicopathological parameters of patients who had undergone Billroth II distal gastrectomy.

MATERIAL AND METHODS

There were two groups: a control group (n = 15) and a patient group (n = 15). In all cases, upper gastrointestinal endoscopy was performed, and biopsies were taken during endoscopy. Telomere lengths were measured by qRT-PCR.

RESULTS

It was observed that the lengths of the telomeres were shortened as the time of postoperative period increased in the patient group (r = -0.126) (p > 0.05). Also, the lengths of the telomeres were shortened in chronic inflammation, neutrophil activity, glandular atrophy, and intestinal metaplasia.

CONCLUSIONS

The telomere length was shortened as the time of postoperative period increased in the patient group. The telomeres were also shorter in chronic inflammation, neutrophil activity, intestinal metaplasia, and glandular atrophy, in all of the study groups. Telomere length abnormalities in gastric stump carcinogenesis process may be a guide for early diagnosis and treatment.

Flow cytometric measurement of absolute telomere length

The length of the end of chromosomes – telomeres is a dynamic and constant characterizes cellular aging process. Measurement of telomere length (TL) and its connection with the diagnosis, course, prognosis and treatment of a number of diseases in recent years, is of great interest for researchers. The methods used for this are varied and are primarily by molecular biological. Variability of methodological approaches, the lack of a common standard of measurement TL measurements in absolute and relative terms: all this leads to results that cannot be compared with each other. The aim of this work is the development of data conversion algorithm is obtained by flow cytometry in absolute telomere length, expressed in kilobases (kb). The study was conducted from venous blood of children 2–3 years of age (8 healthy children and 3 patients with dyskeratosis congenita). As control material used cell line 1301 (ATCC, UK). Determination of relative telomere length was performed by using a set FlowFISH Telomere PNA Kit / FITC (DakoCytomation, Glostrup, Denmark). RTL code and the absolute length of telomeres were calculated for each study participant. Data on the length of patients telomere were compared with data on TL healthy children of appropriate age. RTL average value for healthy children 2–3 years was 30.1, and an absolute telomere length – 15.56 kb. Telomere length patients with dyskeratosis congenita was significantly shorter (RTL 1.4–4.3, the absolute value of TL 0.3–2.4 kb). The algorithm conversion molecular fluorescence equivalent in absolute TL is universal and can be used in any laboratory equipped with a flow cytometer. The resulting data TL can be compared with the data expressed in absolute units and obtained by any other method.

From cellular morphology to molecular and epigenetic anomalies of myelodysplastic syndromes

Myelodysplastic syndromes (MDSs) are a myeloid neoplasm with a propensity for natural evolution or transformation to acute leukemias (AL) over time. Mechanisms for MDS transformation to AL remain poorly understood but are related to genomic instability, which affects the production of the different cell lineages. Genomic instability is also generated by dysfunctional telomeres. Indeed telomeres, the protective ends of chromosomes are the backbone of genome stability. Nuclear telomere remodeling is an early indicator of nuclear remodeling preceding the onset of genomic instability and MDS. This review aims to revisit the pathogenesis and pathophysiology of MDS from morphology and cytogenetics to molecular and epigenetic mechanisms. Furthermore, this review will highlight and discuss recent breakthroughs in dysfunctional telomeres and nuclear telomere architecture roles in the pathogenesis and physiopathology of MDS in the global context of genomic instability.

Association between statin drug use and peripheral blood leukocyte telomere length in the National Health and Nutrition Examination Survey 1999-2002: a cross-sectional study

PURPOSE

To evaluate the association between statin drug use and peripheral blood leukocyte telomere length in a U.S. nationally representative sample of adults.

METHODS

We conducted a cross-sectional analysis of data from National Health and Nutrition Examination Survey 1999-2002, representative of the noninstitutionalized U.S.

POPULATION

The analytic study population included 3496 men and women aged 40-84 years without a history of cancer and who had information of telomere length and statin use.

RESULTS

Compared with nonusers, statin users were more likely to be former smokers, older, white, male, and had more comorbidities. Statin users did not have longer telomeres than nonusers after age (coefficient -0.013, p = .30) and multivariable (0.0003, p = .98) adjustment. After multivariable adjustment, log-transformed telomere length nonstatistically significantly increased with increasing duration of use (0.003, p-trend = .11), which did not differ by number of comorbidities (p-interaction = 0.18). Compared with nonuse, more than 5 years of use had an odds ratio of telomere length above the 75th percentile of 1.62 (95% confidence interval 0.90-2.92; p-trend = .10).

CONCLUSIONS

Although telomere length appeared to be longer with longer duration of use of a statin, this association was not statistically significant, and we could not rule out bias as the explanation.

Organ reserve, excess metabolic capacity, and aging

"Organ reserve" refers to the ability of an organ to successfully return to its original physiological state following repeated episodes of stress. Clinical evidence shows that organ reserve correlates with the ability of older adults to cope with an added workload or stress, suggesting a role in the process of aging. Although organ reserve is well documented clinically, it is not clearly defined at the molecular level. Interestingly, several metabolic pathways exhibit excess metabolic capacities (e.g., bioenergetics pathway, antioxidants system, plasticity). These pathways comprise molecular components that have an excess of quantity and/or activity than that required for basic physiological demand in vivo (e.g., mitochondrial complex IV or glycolytic enzymes). We propose that the excess in mtDNA copy number and tandem DNA repeats of telomeres are additional examples of intrinsically embedded structural components that could comprise excess capacity. These excess capacities may grant intermediary metabolism the ability to instantly cope with, or manage, added workload or stress. Therefore, excess metabolic capacities could be viewed as an innate mechanism of adaptability that substantiates organ reserve and contributes to the cellular defense systems. If metabolic excess capacities or organ reserves are impaired or exhausted, the ability of the cell to cope with stress is reduced. Under these circumstances cell senescence, transformation, or death occurs. In this review, we discuss excess metabolic and structural capacities as integrated metabolic pathways in relation to organ reserve and cellular aging.

Targeting telomerase and telomeres to enhance ionizing radiation effects in in vitro and in vivo cancer models

One of the hallmarks of cancer consists in the ability of tumor cells to divide indefinitely, and to maintain stable telomere lengths throughout the activation of specific telomere maintenance mechanisms (TMM). Therefore in the last fifteen years, researchers proposed to target telomerase or telomeric structure in order to block limitless replicative potential of cancer cells providing a fascinating strategy for a broad-spectrum cancer therapy. In the present review, we report in vitro and in vivo evidence regarding the use of chemical agents targeting both telomerase or telomere structure and showing promising antitumor effects when used in combination with ionizing radiation (IR). RNA interference, antisense oligonucleotides (e.g., GRN163L), non-nucleoside inhibitors (e.g., BIBR1532) and nucleoside analogs (e.g., AZT) represent some of the most potent strategies to inhibit telomerase activity used in combination with IR. Furthermore, radiosensitizing effects were demonstrated also for agents acting directly on the telomeric structure such as G4-ligands (e.g., RHPS4 and Telomestatin) or telomeric-oligos (T-oligos). To date, some of these compounds are under clinical evaluation (e.g., GRN163L and KML001). Advantages of Telomere/Telomerase Targeting Compounds (T/TTCs) coupled with radiotherapy may be relevant in the treatment of radioresistant tumors and in the development of new optimized treatment plans with reduced dose adsorbed by patients and consequent attenuation of short- end long-term side effects. Pros and cons of possible future applications in cancer therapy based on the combination of T/TCCs and radiation treatment are discussed.

Common Chemical Inductors of Replication Stress: Focus on Cell-Based Studies

DNA replication is a highly demanding process regarding the energy and material supply and must be precisely regulated, involving multiple cellular feedbacks. The slowing down or stalling of DNA synthesis and/or replication forks is referred to as replication stress (RS). Owing to the complexity and requirements of replication, a plethora of factors may interfere and challenge the genome stability, cell survival or affect the whole organism. This review outlines chemical compounds that are known inducers of RS and commonly used in laboratory research. These compounds act on replication by direct interaction with DNA causing DNA crosslinks and bulky lesions (cisplatin), chemical interference with the metabolism of deoxyribonucleotide triphosphates (hydroxyurea), direct inhibition of the activity of replicative DNA polymerases (aphidicolin) and interference with enzymes dealing with topological DNA stress (camptothecin, etoposide). As a variety of mechanisms can induce RS, the responses of mammalian cells also vary. Here, we review the activity and mechanism of action of these compounds based on recent knowledge, accompanied by examples of induced phenotypes, cellular readouts and commonly used doses.

Repair activity of oxidatively damaged DNA and telomere length in human lung epithelial cells after exposure to multi-walled carbon nanotubes

One type of carbon nanotubes (CNTs) (MWCNT-7, from Mitsui) has been classified as probably carcinogenic to humans, however insufficient data does not warrant the same classification for other types of CNTs. Experimental data indicate that CNT exposure can result in oxidative stress and DNA damage in cultured cells, whereas these materials appear to induce low or no mutagenicity. Therefore, the present study aimed to investigate whether in vitro exposure of cultured airway epithelial cells (A549) to multi-walled CNTs (MWCNTs) could increase the DNA repair activity of oxidatively damaged DNA and drive the cells toward replicative senescence, assessed by attrition of telomeres. To investigate this, H₂O₂ and KBrO₃ were used to induce DNA damage in the cells and the effect of pre-exposure to MWCNT tested for a change in repair activity inside the cells or in the extract of treated cells. The effect of MWCNT exposure on telomere length was investigated for concentration and time response. We report a significantly increased repair activity in A549 cells exposed to MWCNTs compared to non-exposed cells, suggesting that DNA repair activity may be influenced by exposure to MWCNTs. The telomere length was decreased at times longer than 24h, but this decrease was not concentration dependent. The results suggest that the seemingly low mutagenicity of CNTs in cultured cells may be associated with an increased DNA repair activity and a replicative senescence, which may counteract the manifestation of DNA lesions to mutations.

Association Between Human Telomerase Reverse Transcriptase Gene Variations and Risk of Developing Breast Cancer

BACKGROUND

Despite a reduction in the number of deaths from cancers made possible by the development of early detection tests, improvements in treatment, changes in the age distribution of the population, and changes of personal behaviors as a result of awareness, breast cancer remains a major health problem worldwide. Breast cancer is the most common cancer and second leading cause of cancer death in women. Several genetic and environmental factors are known to be involved in breast cancer pathogenesis, but its exact etiology is complicated and is not clearly identified. The structure and integrity of telomeres are pivotal for genome stability, and telomere length is maintained by the expression of the telomerase enzyme. The human telomerase reverse transcriptase (hTERT) gene is a principal functional subunit of the telomerase. Several recent studies have provided evidence that hTERT gene variants may have an important role in cancer development.

METHODS

Three hTERT variants (rs2736100, rs2736098, and rs2853669) were genotyped for 107 breast cancer patients and 110 healthy controls to determine their effect on breast cancer susceptibility.

RESULTS

It was observed that hTERT rs2736098 was associated with breast cancer risk (odds ratio [OR] = 1.88; p = 0.034), while rs2736100 and rs2853669 did not significantly differ between the groups.

CONCLUSIONS

These findings are the first description of hTERT allele distributions in the Turkish population and may contribute to our understanding of breast cancer development. Nevertheless, further large-scale population studies are needed to understand the role of the hTERT polymorphisms and haplotypes in the development of breast cancer.

Telomerase Reverse Transcriptase (TERT) Gene Variations and Susceptibility of Colorectal Cancer

AIM

Colorectal cancer is the third most common cause of cancer-related mortality. Previous studies demonstrated increased telomerase activity in colorectal cancer tissue and suggested a prognostic value for patients with colorectal carcinoma. Telomerase reverse transcriptase (TERT), one of the main functional subunits of the telomerase, is an important factor in modulating telomerase activity, telomere length, and genomic stability. However, there are few studies that have addressed the association between genetic variation at TERT and the risk of colorectal cancer.

METHOD

We evaluated the influence of three common single-nucleotide polymorphisms (SNPs) of the TERT gene (rs2853669, rs2736100, rs2736098) on susceptibility to colorectal cancer in 104 patients and 135 controls in a Turkish population.

RESULTS

We observed that rs2736098 was significantly associated with increased risk of colorectal cancer (OR = 2.53; 95% CI = 1.26-5.10; p = 0.008). On the other hand, rs2736100 and rs2853669 showed no association with colorectal cancer (p ≥ 0.128).

CONCLUSION

These findings are the first results of TERT allele distributions in the Turkish population and also provide increased understanding with respect to colorectal cancer etiology.

Strong association between long and heterogeneous telomere length in blood lymphocytes and bladder cancer risk in Egyptian

Although it is widely recognized that telomere dysfunction plays an important role in cancer, the relationship between telomere function and bladder cancer risk is not well defined. In a case-control study of bladder cancer in Egypt, we examined relationships between two telomere features and bladder cancer risk. Telomere fluorescent in situ hybridization was used to measure telomere features using short-term cultured blood lymphocytes. Logistic regression was used to estimate the strength of association between telomere features and the risk of urothelial carcinoma of the bladder. High telomere length variation (TLV) across all chromosomal ends was significantly associated with an increased risk of bladder cancer [adjusted odds ratios (OR) = 2.22, 95% confidence interval (CI) = 1.48-3.35], as was long average telomere length (OR = 3.19, 95% CI = 2.07, 4.91). Further, TLV and average telomere length jointly affected bladder cancer risk: when comparing individuals with long telomere length and high TLV to those with short telomere length and low TLV, the adjusted OR was 14.68 (95% CI: 6.74-31.98). These associations were stronger among individuals who are 60 years of age or younger. In summary, long and heterogeneous telomere length in blood lymphocytes was strongly associated with an increased bladder cancer risk in Egyptian and the association was modulated by age.

Telomere length variation: A potential new telomere biomarker for lung cancer risk

OBJECTIVES

In this report the associations between telomere length variation (TLV), mean telomere length in blood lymphocytes and lung cancer risk were examined.

MATERIALS AND METHODS

The study design is case-control. Cases (N=191) were patients newly diagnosed with histologically confirmed non-small cell lung cancer. Controls (N=207) were healthy individuals recruited from the same counties as cases and matched to cases on age and gender. Telomere fluorescent in situ hybridization was used to measure telomere features using short-term cultured blood lymphocytes. Logistic regression was used to estimate the strength of association between telomere features and lung cancer risk.

RESULTS

Telomere length variation across all chromosomal ends was significantly associated with lung cancer risk; adjusted odds ratios 4.67 [95% confidence interval (CI): 1.46-14.9] and 0.46 (95% CI: 0.25-0.84) for younger (age≤60) and older (age>60) individuals, respectively. TLV and mean telomere length jointly affected lung cancer risk: when comparing individuals with short telomere length and high TLV to those with long telomere length and low TLV, adjusted odd ratios were 8.21 (95% CI: 1.71-39.5) and 0.33 (95% CI: 0.15-0.72) for younger and older individuals, respectively.

CONCLUSIONS

TLV in blood lymphocytes is significantly associated with lung cancer risk and the associations were modulated by age. TLV in combination with mean telomere length might be useful in identifying high risk population for lung cancer computerized tomography screening.

Plasma micronutrient levels and telomere length in children

OBJECTIVE

Telomeres are long hexamer (TTAGGG) repeats at the ends of chromosomes, and contribute to maintenance of chromosomal stability. Telomere shortening has been linked to cancers and other chronic diseases in adults, although evidence for causal associations is limited. The aim of this study was to determine whether nutritional factors are associated with telomere length (TL) in children.

METHODS

We conducted a cross-sectional study of nutritional factors and TL in 437 children between 2009 and 2011. Healthy children ages 3, 6, and 9 y provided blood samples, and their parents completed a food frequency questionnaire and a telephone interview about relevant environmental exposures. TL and blood micronutrient levels were measured, and genotyping at 10 loci was undertaken. Associations between the micronutrients and other variables were assessed using linear regression.

RESULTS

No significant main or interactive effects of age or sex were seen. After adjustment for age, sex, parental education, and month of blood collection, TL was inversely associated with plasma zinc, and shorter in children with the homozygous mutant genotype of the RFC G80A (rs1051266) polymorphism.

CONCLUSIONS

To the best of our knowledge, this is the first investigation of the association between telomere length and micronutrients in healthy children. The reason for the inverse relationship of TL with zinc is unknown but could be the result of an increase in telomere sequence deletions caused by labile zinc induction of oxidative stress. These findings should be corroborated in other studies before nutritional recommendations might be considered.

Correlation between terminal restriction fragments and flow-FISH measures in samples over wide range telomere lengths

OBJECTIVES

Terminal restriction fragment (TRF) analysis of human telomeres was used to calibrate flow-fluorescence in situ hybridization (FF) measures of telomere lengths to expand the range of measures and increase power of resolution of our previously published protocol. TRF data used as the gold standard should be obtained by electrophoresis with suitable resolution applied to appropriately isolated genomic DNA. When we considered TRF attained by correct methods, we found our method to be insufficiently accurate, thus we have reviewed our previously published FF protocol to obtain the best coefficient of determination (r(2)) between our experimental results and valid TRF lengths.

MATERIALS AND METHODS

Using human telomere-specific PNA probe, Cy5-OO-(CCCTAA)3 , we measured telomere lengths of continuous cell line and of peripheral blood lymphocytes by FF. We modified hybridization, stringency, negative control handling, stoichiometric DNA staining and telomere fluorescence assessment of the protocol.

RESULTS

We realized a procedure with increased power of resolution, improved TRF versus FF r(2) values that allowed simultaneous analysis of DNA and telomere duplication. Notwithstanding multiple steps in formamide sampling, recovery was satisfactory.

DISCUSSION

The reviewed FF protocol appeared at least as suitable as the TRF method. Measures obtained by TRF can be affected by chromosome end variability, DNA fragmentation, incomplete digestion and unsuitable electrophoresis. In contrast, the FF technique analyses telomeric sequences confined to preserved nuclei thus overcome most previous limitations. As yet, however, the FF telomere measure cannot be performed together with immunophenotyping and/or generation study by the dye dilution method.

Genomic instability in newborn with short telomeres

Telomere length is considered to be a risk factor in adults due to its proved association with cancer incidence and mortality. Since newborn present a wide interindividual variation in mean telomere length, it is relevant to demonstrate if these differences in length can act also as an early risk indicator. To answer this question, we have measured the mean telomere length of 74 samples of cord blood from newborns and studied its association with the basal genetic damage, measured as the frequency of binucleated cells carrying micronuclei. In addition, we have challenged the cells of a subgroup of individuals (N = 35) against mitomycin-C (MMC) to establish their sensitivity to induced genomic instability. Results indicate that newborn with shorter telomeres present significantly higher levels of genetic damage when compared to those with longer telomeres. In addition, the cellular response to MMC was also significantly higher among those samples from subjects with shorter telomeres. Independently of the causal mechanisms involved, our results show for the first time that telomere length at delivery influence both the basal and induced genetic damage of the individual.

Impact

Individuals born with shorter telomeres may be at increased risk, especially for those biological processes triggered by genomic instability as is the case of cancer and other age-related diseases.

Elevated plasma magnesium and calcium may be associated with shorter telomeres in older South Australian women

Telomeres are structures that cap the ends of chromosomes. The integrity of the telomere structure and its DNA hexamer (TTAGGG)n repeat sequence is critical for protecting the ends of chromosomes from degradation and in maintaining overall chromosomal stability. Currently, there are limited data on the influence that nutrition has on telomere length. Recent studies have suggested that micronutrients may influence telomere length. Here we examined the relationship between telomere length in lymphocytes and plasma calcium, magnesium, selenium and zinc status in a healthy cohort of younger and older adults. We report a negative association between telomere length and both plasma calcium and magnesium levels, (r=-0.47, P=0.03 and r=-0.61, P=0.001 respectively), in older females; Intriguingly Ca/Mg ratio was positively associated with telomere length (r=0.55, P=0.007). These relationships were not observed in the younger adults, nor in the older males. In conclusion, our study provides preliminary evidence suggesting that levels of plasma magnesium and calcium may impact on telomere length in lymphocytes in older women.

Radiation-induced telomere length variations in normal and in Nijmegen Breakage Syndrome cells

PURPOSE

The meiotic recombination protein 11 (MRE11), radiation sensitive 50 (RAD50) and nibrin (NBN) are members of the MRE11/RAD50/NBN (MRN) complex which plays a fundamental role in the double-strand break damage response, including DNA damage sensing, signalling and repair after exposure to ionizing radiations. In addition the MRN complex is involved in the mechanisms regulating telomere length maintenance. Based on our previous results indicating that, in contrast to X-rays, high linear energy transfer (LET) radiations were able to elongate telomeres, we investigated the behavior of cells mutated in components of the MRN complex after exposure either to 62 MeV carbon-ions (50 keV/μm, at cell surface) or X-rays.

MATERIALS AND METHODS

Epstein Barr Virus (EBV)-transformed lymphoblastoid cell lines (LCL) established from normal, heterozygous for the NBN gene, homozygous for either mutant/deleted NBN, RAD50 or ataxia telangiectasia mutated (ATM) genes were irradiated with 4 Gy, with telomere length being evaluated 24 h later or in time course-experiments up to 15 days later. The induction of telomeric sister chromatid exchanges (T-SCE) was measured as a hallmark of homologous directed recombinational repair.

RESULTS

NBN and RAD50 mutated cells failed to elongate telomeres that instead occurred in the remaining cell lines as a response only to high-LET irradiation. Also, a kinetic study with 0.5-4 Gy up to 15 days from irradiation confirmed that NBN gene was indispensable for telomere elongation. Furthermore, such an elongation, was accompanied by an increased frequency of sister chromatid exchanges at telomeres (T-SCE). In contrast, the induction of genomic sister chromatid exchanges (G-SCE) occurred for carbon-ions irrespective of NBN gene status.

CONCLUSIONS

We speculate that the MRN is necessary to process a subclass of high-LET radiation-induced complex DNA damage through a recombinational-repair mediated mechanism which in turn is responsible for telomere elongation.

Genetic variations in TERT-CLPTM1L locus are associated with risk of lung cancer in Chinese population

Recent genome-wide association studies (GWAS) have reported multiple genetic variations at 5p15.33 (TERT-CLPTM1L) associated with risk of lung cancer. However, most of the associated variations identified by GWAS thus far are unlikely to be the actual causal variants, but may be mostly marker-single nucleotide polymorphisms tagging functional variations that influence gene expression. This study aimed to explore the function-validated and potentially functional variations in TERT-CLPTM1L locus conferring susceptibility to lung cancer. A case-control study including 502 cases and 502 controls in Chinese Han population was firstly conducted. Bioinformatic approaches are applied to prioritize genetic variations based on their potential functionality. In the logistic regression analysis, TERT-rs2853669, rs2736108, and CLPTM1L-rs31490 were significant associated with increased risk of lung cancer (OR = 1.46, 95% CI = 1.22-1.75; OR = 1.22, 95% CI = 1.00-1.49 and OR = 1.74, 95% CI = 1.35-2.23 under additive model, respectively). The significant associations were observed in non-small-cell lung cancer but not-in-small-cell lung cancer, and more prominent in adenocarcinoma. Haplotype analysis presented a significant allele-dose effect of haplotypes in increasing risk of lung cancer (P for trend = 1.894 × 10(-6)). Moreover, significant multiplicative interactions were observed between smoking and these three polymorphisms of TERT-rs2853669, rs2736108, and CLPTM1L-rs31490, even after bonferroni correction for multiple comparisons (Pinteraction = 1.316 × 10(-9), 3.912 × 10(-4), and 2.483 × 10(-5), respectively). These findings indicated that the function-validated and potentially functional variations in TERT-CLPTM1L locus, modified by smoking, may play a substantial role in the susceptibility to lung cancer.

Telomere length modulation in human astroglial brain tumors

Background

Telomeres alteration during carcinogenesis and tumor progression has been described in several cancer types. Telomeres length is stabilized by telomerase (h-TERT) and controlled by several proteins that protect telomere integrity, such as the Telomere Repeat-binding Factor (TRF) 1 and 2 and the tankyrase-poli-ADP-ribose polymerase (TANKs-PARP) complex.

Objective

To investigate telomere dysfunction in astroglial brain tumors we analyzed telomeres length, telomerase activity and the expression of a panel of genes controlling the length and structure of telomeres in tissue samples obtained in vivo from astroglial brain tumors with different grade of malignancy.

Materials and Methods

Eight Low Grade Astrocytomas (LGA), 11 Anaplastic Astrocytomas (AA) and 11 Glioblastoma Multiforme (GBM) samples were analyzed. Three samples of normal brain tissue (NBT) were used as controls. Telomeres length was assessed through Southern Blotting. Telomerase activity was evaluated by a telomere repeat amplification protocol (TRAP) assay. The expression levels of TRF1, TRF2, h-TERT and TANKs-PARP complex were determined through Immunoblotting and RT-PCR.

Results

LGA were featured by an up-regulation of TRF1 and 2 and by shorter telomeres. Conversely, AA and GBM were featured by a down-regulation of TRF1 and 2 and an up-regulation of both telomerase and TANKs-PARP complex.

Conclusions

In human astroglial brain tumours, up-regulation of TRF1 and TRF2 occurs in the early stages of carcinogenesis determining telomeres shortening and genomic instability. In a later stage, up-regulation of PARP-TANKs and telomerase activation may occur together with an ADP-ribosylation of TRF1, causing a reduced ability to bind telomeric DNA, telomeres elongation and tumor malignant progression.

Shorter telomere length - A potential susceptibility factor for HIV-associated neurocognitive impairments in South African women [corrected]

The neuropathogenesis of the human immunodeficiency virus (HIV) may manifest as various neurocognitive impairments (NCI). HIV-positive individuals also have significantly shorter telomere length (TL) in peripheral blood mononuclear cells (PBMCs) and CD8+ T cells compared to HIV-negative individuals. Additionally, reduced TL has been found to be associated with chronic psychological stress. This study focused on the effects of HIV-infection and chronic stress associated with childhood trauma on telomere length, and investigated whether leukocyte TL (LTL), in particular, represents a risk factor for NCI. Eighty-three HIV-positive and 45 HIV-negative women were assessed for childhood trauma and were subjected to detailed neurocognitive testing. Blood from each participant was used to extract Deoxyribonucleic acid (DNA). Relative LTL were determined by performing real time quantitative PCR reactions as described by Cawthon et al. (2002). As expected, relative LTL in the HIV-positive individuals was significantly shorter than that of HIV-negative individuals (F = 51.56, p = <0.01). Notably, a significant positive correlation was evident between relative LTL and learning performance in the HIV-positive group. In addition, a significant negative correlation was observed between relative LTL and verbal fluency, but this association was only evident in HIV-positive individuals who had experienced trauma. Our results suggest that reduced LTL is associated with worse learning performance in HIV-positive individuals, indicating that TL could act as a susceptibility factor in increasing neurocognitive decline in HIV-infected individuals.

The impact of voluntary exercise on relative telomere length in a rat model of developmental stress

Background

Exposure to early adverse events can result in the development of later psychopathology, and is often associated with cognitive impairment. This may be due to accelerated cell aging, which can be catalogued by attritioned telomeres. Exercise enhances neurogenesis and has been proposed to buffer the effect of psychological stress on telomere length. This study aimed to investigate the impact of early developmental stress and voluntary exercise on telomere length in the ventral hippocampus (VH) and prefrontal cortex (PFC) of the rat. Forty-five male Sprague–Dawley rats were categorised into four groups: maternally separated runners (MSR), maternally separated non-runners (MSnR), non-maternally separated runners (nMSR) and non-maternally separated non-runners (nMSnR). Behavioural analyses were conducted to assess anxiety-like behaviour and memory performance in the rats, after which relative telomere length was measured using qPCR.

Results

Maternally separated (MS) rats exhibited no significant differences in either anxiety levels or memory performance on the elevated-plus maze and the open field compared to non-maternally separated rats at 49 days of age. Exercised rats displayed increased levels of anxiety on the day that they were removed from the cages with attached running wheels, as well as improved spatial learning and temporal recognition memory compared to non-exercised rats. Exploratory post-hoc analyses revealed that maternally separated non-exercised rats exhibited significantly longer telomere length in the VH compared to those who were not maternally separated; however, exercise appeared to cancel this effect since there was no difference in VH telomere length between maternally separated and non-maternally separated runners.

Conclusions

The increased telomere length in the VH of maternally separated non-exercised rats may be indicative of reduced cellular proliferation, which could, in turn, indicate hippocampal dysfunction. This effect on telomere length was not observed in exercised rats, indicating that voluntary exercise may buffer against the progressive changes in telomere length caused by alterations in maternal care early in life. In future, larger sample sizes will be needed to validate results obtained in the present study and obtain a more accurate representation of the effect that psychological stress and voluntary exercise have on telomere length.

Telomere length and LINE1 methylation is associated with chromosomal aberrations in peripheral blood

The frequency of chromosomal aberrations in peripheral blood predicts a probable cancer risk. The individual telomere length and methylation of repetitive elements may be susceptibility factors for chromosomal aberrations. A cohort of healthy Norwegian men (N = 364) recruited during 1980-1999 were analyzed for chromosomal aberrations in phytohemagglutinin-stimulated lymphocytes from peripheral blood. Chromosome-type or chromatid-type aberrations were scored. DNA was extracted from slides cytogenetically analyzed and relative average telomere length and methylation of LINE1 repeats were determined by quantitative polymerase chain reaction and bisulfite pyrosequencing, respectively. Information about individuals with malignant tumors (N = 49) diagnosed after chromosomal aberrations testing until end of 2008 was obtained and two matched controls per case were used in a nested case-control analysis. Shorter relative telomere length and higher methylation of LINE1 were associated with higher frequency of total chromosomal aberrations (β = -0.76, P = 0.022; and β = 0.042, P = 0.048, respectively; age-adjusted ordinal regression). The telomere length was stronger associated with chromosome-type (β = -1.00, P = 0.006) than with chromatid-type aberrations (β = -0.49, P = 0.115). The LINE1 methylation was stronger associated with chromatid-type (β = 0.062, P = 0.003) than with chromosome-type aberrations (β = 0.018, P = 0.41). Telomere length [individuals with short telomeres odds ratio (OR) = 0.87, 95% confidence interval (CI) 0.38-2.0], LINE1 (individuals with high methylation OR = 1.04, 95% CI 0.43-2.5) and chromosomal aberrations (individuals with high frequency OR = 1.6, 95% CI 0.63-3.9) at baseline did not predict cancer risk, but the conclusions were hampered by low statistical precision. The results suggest that shorter telomere length and higher LINE1 methylation in peripheral blood lymphocytes are predisposition factors for increased frequency of chromosomal aberrations.

Role of MRE11 in cell proliferation, tumor invasion, and DNA repair in breast cancer

BACKGROUND

Previous studies have shown that altered forms of MRE11, a protein known to play a vital role in DNA double-strand break repair, DNA replication, and telomere maintenance are associated with cancer outcomes. We investigated the role of MRE11 in breast cancer in both clinical and in vitro settings.

METHODS

We examined MRE11 expression in tumor tissues from invasive ductal carcinoma breast cancer patients (n = 254) by immunohistochemistry, and associations with clinicopathological characteristics and overall survival were assessed using Cox proportional hazards regression models and Kaplan-Meier survival curves. Effect of MRE11 overexpression and knockdown on cell proliferation, invasion, and radioresistance was assessed in vitro using breast cancer cell lines (MCF-7 and MDA-MB-231). We also investigated the mechanisms involved. Effect of MRE11 overexpression on tumor growth was assessed in an orthotopic xenograft model (n = 8 mice per group). All statistical tests were two-sided.

RESULTS

Of the 254 tissue samples, 69.3% and 30.7% showed high and low MRE11 expression, respectively. High MRE11 expression was statistically significantly associated with malignant cancer behavior compared with low MRE11 expression (eg, stages III and IV vs stage I, P = .004; poor overall survival, P = .005). MRE11 overexpression in breast cancer cell lines promoted cell proliferation through STAT3, cell cycle entry, invasion and migration, and radioresistance via enhanced DNA repair activity and also inhibited apoptosis; knockdown of MRE11 had the opposite effect. In xenograft tumor-bearing mice (n = 8 per group), increased tumor growth was observed in the MRE11-overexpressing group compared with the control group (tumor volume at week 8, control vs MRE11-overexpressing tumor originating from MCF-7 cells, mean = 280.4 mm(3), 95% confidence interval [CI] = 62.4 to 498.4 mm(3) vs mean = 631.0 mm(3), 95% CI = 296.9 to 965.0 mm(3), P = .043).

CONCLUSION

High MRE11 expression was associated with a more malignant behavior in breast cancer. MRE11 may be a novel oncoprotein and may therefore serve as a new therapeutic intervention against breast cancer.

The role of zinc in genomic stability

Zinc (Zn) is an essential trace element required for maintaining both optimal human health and genomic stability. Zn plays a critical role in the regulation of DNA repair mechanisms, cell proliferation, differentiation and apoptosis involving the action of various transcriptional factors and DNA or RNA polymerases. Zn is an essential cofactor or structural component for important antioxidant defence proteins and DNA repair enzymes such as Cu/Zn SOD, OGG1, APE and PARP and may also affect activities of enzymes such as BHMT and MTR involved in methylation reactions in the folate-methionine cycle. This review focuses on the role of Zn in the maintenance of genome integrity and the effects of deficiency or excess on genomic stability events and cell death.

Profiling three-dimensional nuclear telomeric architecture of myelodysplastic syndromes and acute myeloid leukemia defines patient subgroups

PURPOSE

Myelodysplastic syndromes (MDS) are a group of disorders characterized by cytopenias, with a propensity for evolution into acute myeloid leukemias (AML). This transformation is driven by genomic instability, but mechanisms remain unknown. Telomere dysfunction might generate genomic instability leading to cytopenias and disease progression.

EXPERIMENTAL DESIGN

We undertook a pilot study of 94 patients with MDS (56 patients) and AML (38 patients). The MDS cohort consisted of refractory cytopenia with multilineage dysplasia (32 cases), refractory anemia (12 cases), refractory anemia with excess of blasts (RAEB)1 (8 cases), RAEB2 (1 case), refractory anemia with ring sideroblasts (2 cases), and MDS with isolated del(5q) (1 case). The AML cohort was composed of AML-M4 (12 cases), AML-M2 (10 cases), AML-M5 (5 cases), AML-M0 (5 cases), AML-M1 (2 cases), AML-M4eo (1 case), and AML with multidysplasia-related changes (1 case). Three-dimensional quantitative FISH of telomeres was carried out on nuclei from bone marrow samples and analyzed using TeloView.

RESULTS

We defined three-dimensional nuclear telomeric profiles on the basis of telomere numbers, telomeric aggregates, telomere signal intensities, nuclear volumes, and nuclear telomere distribution. Using these parameters, we blindly subdivided the MDS patients into nine subgroups and the AML patients into six subgroups. Each of the parameters showed significant differences between MDS and AML. Combining all parameters revealed significant differences between all subgroups. Three-dimensional telomeric profiles are linked to the evolution of telomere dysfunction, defining a model of progression from MDS to AML.

CONCLUSIONS

Our results show distinct three-dimensional telomeric profiles specific to patients with MDS and AML that help subgroup patients based on the severity of telomere dysfunction highlighted in the profiles.

A qPCR-based assay to quantify oxidized guanine and other FPG-sensitive base lesions within telomeric DNA

Telomere shortening is an important risk factor for cancer and accelerated aging. However, it is becoming evident that oxidatively damaged DNA within the telomere sequence may also cause telomere dysfunction. Here we describe a reliable, cost-effective quantitative PCR (qPCR)-based method to measure the amount of oxidized residues within telomeric DNA that are recognized and excised by formamidopyridine DNA glycosylase (FPG). We also report that in an in vitro model of oxidative stress oxidized base lesions measured using this method are more prevalent within telomeric sequences. Furthermore, this method is sufficiently sensitive to detect changes in oxidative stress induced by zinc deficiency and hydrogen peroxide within the physiological range.

Investigation of telomere length and psychological stress in rape victims

BACKGROUND

Women are at an increased risk of depression and other mental health problems following rape. Various etiological factors for depression, including predisposing genetic factors, have been identified. Telomeres are repetitive nucleoprotein structures located at chromosomal ends that protect them from premature degradation. Telomeres reduce in length with each cell division, resulting in cellular senescence and apoptosis.

METHODS

Relative quantification of telomeric repeats using qPCR was performed to investigate whether shorter relative leukocyte telomere length (LTL) in a cohort of 64 rape victims was associated with resilience, the development of rape trauma-related major depressive disorder (MDD) or the development of posttraumatic stress disorder (PTSD) after 3 months.

RESULTS

Out of the 64 participants, 23 participants were diagnosed with MDD at baseline and 31 after 3 months. Nine participants were diagnosed with PTSD (MDD and PTSD specifically related to the trauma). No significant associations were observed between relative LTL and resilience or the development of MDD at either baseline or after 3 months in this cohort. However, a marginally significant association was evident between relative LTL and PTSD status.

CONCLUSIONS

The significant association between relative LTL and PTSD suggests that shorter relative LTL might have acted as a predisposing factor in the development of PTSD after a severely traumatic event. The results of this study indicate that telomere shortening may be an important marker of PTSD risk, with implications for early intervention and timely treatment, and as such warrant replication in a larger cohort.

Colonocyte telomere shortening is greater with dietary red meat than white meat and is attenuated by resistant starch

BACKGROUND & AIMS

Population studies indicate that greater red meat consumption increases colorectal cancer risk while dietary fibre is protective. Previous work in rats showed that diets high in protein, including red meat, increase colonocyte DNA strand breaks and that this effect is attenuated by resistant starches (RS). Telomeres are long hexamer repeats that protect against spontaneous DNA damage which would lead to chromosomal instability. Telomere shortening is associated with greater risk of colorectal cancer. The current study aimed to determine the effects of cooked red and white meat intake on colonocyte telomere length in rats and whether dietary RS modified their effects.

METHODS

After four weeks of feeding cooked beef or chicken at 15, 25 and 35% of diet with or without RS, colonocyte telomere length was measured.

RESULTS

Telomere length decreased in proportion to red meat content of the diet. A similar trend was observed in the white meat group. Colonocyte telomere shortening due to increased dietary meat was attenuated by the inclusion of RS.

CONCLUSION

These data support previous findings of increased colonocyte DNA damage with greater red and white meat intake and also the protective effect of dietary fibre.

Zinc deficiency or excess within the physiological range increases genome instability and cytotoxicity, respectively, in human oral keratinocyte cells

Zinc (Zn) is an essential component of Zn-finger proteins and acts as a cofactor for enzymes required for cellular metabolism and in the maintenance of DNA integrity. The study investigated the genotoxic and cytotoxic effects of Zn deficiency or excess in a primary human oral keratinocyte cell line and determined the optimal concentration of two Zn compounds (Zn Sulphate (ZnSO(4)) and Zn Carnosine (ZnC)) to minimise DNA damage. Zn-deficient medium (0 μM) was produced using Chelex treatment, and the two Zn compounds ZnSO(4) and ZnC were tested at concentrations of 0.0, 0.4, 4.0, 16.0, 32.0 and 100.0 μM. Cell viability was decreased in Zn-depleted cells (0 μM) as well as at 32 μM and 100 μM for both Zn compounds (P < 0.0001) as measured via the MTT assay. DNA strand breaks, as measured by the comet assay, were found to be increased in Zn-depleted cells compared with the other treatment groups (P < 0.05). The Cytokinesis Block Micronucleus Cytome assay showed a significant increase in the frequency of both apoptotic and necrotic cells under Zn-deficient conditions (P < 0.05). Furthermore, elevated frequencies of micronuclei (MNi), nucleoplasmic bridges (NPBs) and nuclear buds (NBuds) were observed at 0 and 0.4 μM Zn, whereas these biomarkers were minimised for both Zn compounds at 4 and 16 μM Zn (P < 0.05), suggesting these concentrations are optimal to maintain genome stability. Expression of PARP, p53 and OGG1 measured by western blotting was increased in Zn-depleted cells indicating that DNA repair mechanisms are activated. These results suggest that maintaining Zn concentrations within the range of 4-16 μM is essential for DNA damage prevention in cultured human oral keratinocytes.

Topographical analysis of telomere length and correlation with genomic instability in whole mount prostatectomies

BACKGROUND

Many critical events in prostatic carcinogenesis appear to relate to the emergence of genomic instability. Characteristic genomic abnormalities such as 8p loss, 8q gain, trisomy 7, and PTEN microdeletions may provide selective advantages to increase neoplastic transformation. Evidence suggests that telomere dysfunction is a plausible mechanism for some of these abnormalities on the basis of the break-fusion-bridge cycle that can lead to manifestations of genomic instability.

METHODS

In this study, we correlate telomere length measured by quantitative FISH in various prostatic histologies with markers of genomic instability and immunohistochemical measures of proliferation and oxidative stress.

RESULTS

We find that telomere shortening is correlated with abnormalities on chromosome 8, but not with trisomy 7 or abnormalities of the PTEN locus. There are associations with C-MYC aberrations in stroma with greater proximity to cancer and a correlation between telomere length in a number of prostatic histologies and the adjacent stroma, suggesting the importance of microenvironmental effects on telomere maintenance in the prostate. This finding was also supported by the finding of the correlation between telomere attrition and the levels of oxidative stress as measured by malondialdehyde staining in HPIN lesions close to cancer.

CONCLUSIONS

Telomere attrition in the prostate gland is associated with particular genomic aberrations that contribute to the genomic instability characteristic of prostatic carcinogenesis. Correlations between various histologies and adjacent stroma telomere length suggest it is also may reveal microenvironmental effects within the prostate gland. Oxidative stress may contribute to telomere attrition in HPIN close to cancer.

The effect of zinc sulphate and zinc carnosine on genome stability and cytotoxicity in the WIL2-NS human lymphoblastoid cell line

Zinc (Zn) is an essential cofactor required by numerous enzymes that are essential for cell metabolism and the maintenance of DNA integrity. We investigated the effect of Zn deficiency or excess on genomic instability events and determined the optimal concentration of two Zn compounds that minimize DNA-damage events. The effects of Zn sulphate (ZnSO(4)) and Zn carnosine (ZnC) on cell proliferation were investigated in the WIL2-NS human lymphoblastoid cell line. DNA damage was determined by the use of both the comet assay and the cytokinesis-block micronucleus cytome (CBMN-Cyt) assay. Zn-deficient medium (0μM) was produced using Chelex treatment, and the two Zn compounds (i.e. ZnSO(4) and ZnC) were tested at concentrations of 0.0, 0.4, 4.0, 16.0, 32.0 and 100.0μM. Results from an MTT assay showed that cell growth and viability were decreased in Zn-depleted cells (0μM) as well as at 32μM and 100μM for both Zn compounds (P<0.0001). DNA strand-breaks, as measured by the comet assay, were found to be increased in Zn-depleted cells compared with the other treatment groups (P<0.05). The CBMN-Cyt assay showed a significant increase in the frequency of both apoptotic and necrotic cells under Zn-deficient conditions (P<0.0001). Elevated frequencies of micronuclei (MNi), nucleoplasmic bridges (NPBs) and nuclear buds (NBuds) were induced in Zn-depleted cells (P<0.0001), whereas genome damage was reduced in supplemented cultures for both Zn compounds at 4μM and 16μM, possibly suggesting that these concentrations may be optimal for genome stability. The potential protective effect of ZnSO(4) and ZnC was also investigated following exposure to 1.0Gy γ-radiation. Culture in medium containing these compounds at 4-32μM prior to irradiation displayed significantly reduced frequencies of MNi, NPBs and NBuds compared with cells maintained in 0μM medium (P<0.0001). Expression of γ-H2AX and 8-oxoguanine glycosylase measured by western blotting was increased in Zn-depleted cells. These results suggest that Zn plays important role in genomic stability and that the optimal Zn concentration-range for prevention of DNA damage and cytotoxicity in vitro lies between 4 and 16μM.

Fanconi anemia protein FANCD2 inhibits TRF1 polyADP-ribosylation through tankyrase1-dependent manner

Background

Fanconi anemia (FA) is a rare autosomal recessive syndrome characterized by developmental abnormalities, progressive bone marrow failure, and predisposition to cancer. The key FA protein FANCD2 crosstalks with members of DNA damage and repair pathways that also play a role at telomeres. Therefore, we investigated whether FANCD2 has a similar involvement at telomeres.

Results

We reveal that FANCD2 may perform a novel function separate to the FANCD2/BRCA pathway. This function includes FANCD2 interaction with one of the telomere components, the PARP family member tankyrase-1. Moreover, FANCD2 inhibits tankyrase-1 activity in vitro. In turn, FANCD2 deficiency increases the polyADP-ribosylation of telomere binding factor TRF1.

Conclusions

FANCD2 binding and inhibiting tankyrase-1PARsylation at telomeres may provide an additional step within the FA pathway for the regulation of genomic integrity.

A quantitative PCR method for measuring absolute telomere length

We describe a simple and reproducible method to measure absolute telomere length (aTL) using quantitative real-time polymerase chain reaction (qPCR). This method is based on the Cawthon method for relative measurement of telomere length (TL) but modified by introducing an oligomer standard to measure aTL. The method describes the oligomer standards, the generation of the standard curve and the calculations required to calculate aTL from the qPCR data. The necessary controls and performance characteristics of the assay are described in detail and compared relative to other methods for measuring TL. Typical results for this assay for a variety of human tissue samples are provided as well as a troubleshooting schedule. This method allows high throughput measurement of aTL using small amounts of DNA making it amenable for molecular epidemiological studies. Compared to the traditional relative TL qPCR assays, the aTL method described in this protocol enables a more direct comparison of results between experiments within and between laboratories.

Role of progerin-induced telomere dysfunction in HGPS premature cellular senescence

Hutchinson-Gilford Progeria Syndrome (HGPS) is a premature-aging syndrome caused by a dominant mutation in the gene encoding lamin A, which leads to an aberrantly spliced and processed protein termed progerin. Previous studies have shown that progerin induces early senescence associated with increased DNA-damage signaling and that telomerase extends HGPS cellular lifespan. We demonstrate that telomerase extends HGPS cellular lifespan by decreasing progerin-induced DNA-damage signaling and activation of p53 and Rb pathways that otherwise mediate the onset of premature senescence. We show further that progerin-induced DNA-damage signaling is localized to telomeres and is associated with telomere aggregates and chromosomal aberrations. Telomerase amelioration of DNA-damage signaling is relatively rapid, requires both its catalytic and DNA-binding functions, and correlates in time with the acquisition by HGPS cells of the ability to proliferate. All of these findings establish that HGPS premature cellular senescence results from progerin-induced telomere dysfunction.

A non-empirical chromophoric interpretation of CD spectra of DNA G-quadruplex structures

G-quadruplex DNA (G4-DNA) structures are four-stranded helical DNA (or RNA) structures, comprising stacks of G-tetrads, which are the outcome of planar association of four guanines in a cyclic Hoogsteen hydrogen-bonding arrangement. In the last decade the number of publications where CD spectroscopy has been used to study G4-DNAs, is extremely high. However, with very few exceptions, these investigations use an empirical interpretation of CD spectra. In this interpretation two basic types of CD spectra have been associated to a single specific difference in the features of the strand folding, i.e. the relative orientation of the strands, "parallel" (all strands have the same 5' to 3' orientation) or "antiparallel". Different examples taken from the literature where the empirical interpretation is not followed or is meaningless are presented and discussed. Furthermore, the case of quadruplexes formed by monomeric guanosine derivatives, where there is no strand connecting the adjacent quartets and the definition parallel/antiparallel strands cannot apply, will be discussed. The different spectral features observed for different G-quadruplexes is rationalised in terms of chromophores responsible for the electronic transitions. A simplified exciton coupling approach or more refined QM calculations allow to interpret the different CD features in terms of different stacking orientation (head-to-tail, head-to-head, tail-to-tail) between adjacent G-quartets irrespectively of the relative orientation of the stands (parallel/antiparallel).

Three-dimensional nuclear telomere architecture is associated with differential time to progression and overall survival in glioblastoma patients

The absence of biological markers allowing for the assessment of the evolution and prognosis of glioblastoma (GBM) is a major impediment to the clinical management of GBM patients. The observed variability in patients' treatment responses and in outcomes implies biological heterogeneity and the existence of unidentified patient categories. Here, we define for the first time three GBM patient categories with distinct and clinically predictive three-dimensional nuclear-telomeric architecture defined by telomere number, size, and frequency of telomeric aggregates. GBM patient samples were examined by three-dimensional fluorescent in situ hybridization of telomeres using two independent three-dimensional telomere-measurement tools (TeloView program [P(1)] and SpotScan system [P(2)]). These measurements identified three patients categories (categories 1-3), displaying significant differences in telomere numbers/nucleus (P(1) = .0275; P(2) <or= .0001), telomere length (P(1) and P(2) = .0275), and number of telomeric aggregates (P(1) = .0464; P(2) <or= .0001). These categories corresponded to patients with long-term, intermediate, and short-term survival, respectively (P = .0393). The time to progression analyses showed significant differences between the three categories (P = .0167). There was a correlation between time to progression, median survival, and nuclear telomere architecture. Our study suggests a link between patient outcome and three-dimensional nuclear-telomere organization and highlights the potential clinical power of telomere signatures as a new prognostic, predictive, and potentially pharmacodynamic biomarker in GBM. Furthermore, novel automated three-dimensional high-throughput scanning as developed here permits to obtain data from 300 nuclei in 20 minutes. This method is applicable to any cell type and scanning application.

Telomere length in lymphocytes of older South Australian men may be inversely associated with plasma homocysteine

Deficiencies in folate (FOL) and vitamin B12 (B12) result in increased chromosomal aberrations, a validated biomarker of cancer risk. Telomeres, the regions of DNA that cap the ends of each chromosome, are critical for maintaining chromosomal stability but the impact of micronutrients on telomere structure and function remains unclear. We hypothesized that telomere length maintenance might be compromised if the status of FOL and B12 was inadequate and plasma homocysteine (HCY) was increased. We investigated the relationship between telomere length in peripheral blood lymphocytes and plasma FOL, B12, and HCY status, and tested whether any such relationship was dependent on age, gender, body mass index, and common polymorphisms in folate metabolism genes. A single blood sample was collected from 43 younger (18-32 years) and 47 older (65-83 years) adults in South Australia. The younger cohort consisted of 18 males and 25 females, whereas the older group included 24 males and 23 females. Telomere length was determined in lymphocytes by flow cytometry. Telomere length in the younger cohort was 11.52% greater than in the older cohort (p = 0.015). In the older cohort, telomere length in females was 12.5% greater than in males (p = 0.028). In older males, there was a significant inverse correlation between telomere length and HCY (r = -0.57, p = 0.004), but this effect was not observed in the younger cohort or in the older female group. These results provide evidence that telomere length of lymphocytes in older men may be adversely affected by HCY in vivo.

Radiation sensitivity increases with proliferation-associated telomere dysfunction in nontransformed human epithelial cells

Epidemiological studies have demonstrated age differences among human adults in susceptibility to radiation, with cancer cases attributable to radiation being more frequent for older individuals at time of exposure. In addition to the notion that susceptibility increases because of progressive decline in DNA monitoring and immunosurveillance, telomere function is now emerging as a new and important factor in modulating cellular and organism sensitivity to ionizing radiation. The link between telomeres and radiosensitivity is well-documented in humans, but the causal events remain elusive. In this paper, it is shown that irradiated human epithelial cells with short dysfunctional telomeres derived from normal mammary gland display elevated DNA damage. An approach identifying the specific chromosomes with critically shortened telomeres in each donor has allowed us to conclude that short dysfunctional telomeres in human epithelial cells join radiation-induced DNA broken ends, thus interfering with their efficient repair. These findings argue against telomeres participating as sensors or transducers of DNA damage, as previously suggested. Rather, our current findings give support to the idea that dysfunctional telomeres, by acting as an additional joining option, reduce the repair fidelity of DNA broken-ends induced by radiation throughout the genome. In the mammary gland, age-dependent telomere attrition due to epithelial turnover, together with the accretion of checkpoint deficiencies, might render the accumulation of short dysfunctional telomeres. This implies that the risks associated with mammography screening could be higher than previously assumed. Our results have the possibility of imprinting a temporal dimension onto radiation sensitivity, namely, that shortened telomeres in aged cells may more easily compromise normal tissue function in the elderly.

Genotype-phenotype correlations in Fanconi anemia

Although still incomplete, we now have a remarkably detailed and nuanced picture of both phenotypic and genotypic components of the FA spectrum. Initially described as a combination of pancytopenia with a limited number of physical anomalies, it was later recognized that additional features were compatible with the FA phenotype, including a form without detectable malformations (Estren-Dameshek variant). The discovery of somatic mosaicism extended the boundaries of the FA phenotype to cases even without any overt hematological manifestations. This clinical heterogeneity was augmented by new conceptualizations. There was the realization of a constant risk for the development of myelodysplasia and certain malignancies, including acute myelogenous leukemia and squamous cell carcinoma, and there was the emergence of a distinctive cellular phenotype. A striking degree of genetic heterogeneity became apparent with the delineation of at least 12 complementation groups and the identification of their underlying genes. Although functional genetic insights have fostered the interpretation of many phenotypic features, surprisingly few stringent genotype-phenotype connections have emerged. In addition to myriad genetic alterations, less predictable influences are likely to modulate the FA phenotype, including modifier genes, environmental factors and chance effects. In reviewing the current status of genotype-phenotype correlations, we arrive at a unifying hypothesis to explain the remarkably wide range of FA phenotypes. Given the large body of evidence that genomic instability is a major underlying mechanism of accelerated ageing phenotypes, we propose that the numerous FA variants can be viewed as differential modulations and compression in time of intrinsic biological ageing.

Telomere length, oxidative damage, antioxidants and breast cancer risk

Telomeres play a critical role in maintaining the integrity and stability of the genome, and are susceptible to oxidative damage after telomere shortening to a critical length. In the present study, we explored the role of white blood cell DNA telomere length on breast cancer risk, and examined whether urinary 15-F(2)-isoprostanes (15-F(2t)-IsoP) and 8-oxo-7,8-dihydrodeoxyguanosine (8-oxodG) or dietary antioxidant intake modified the relationship between telomere length and breast cancer risk. A population-based case-control study-the Long Island Breast Cancer Study Project-was conducted among 1,067 cases and 1,110 controls. Telomere length was assessed by quantitative PCR. Overall, the mean levels of telomere length (T/S ratio), 15-F(2t)-IsoP and 8-oxodG were not significantly different between cases and controls. Among premenopausal women only, carrying shorter telomeres (Q3 and Q4), as compared with the longest (Q1), was associated with significantly increased breast cancer risk. Age-adjusted OR and 95% CI were 1.71 (1.10-2.67) and 1.61 (1.05-2.45). The 5-F(2t)-IsoP and 8-oxodG biomarkers did not modify the telomere-breast cancer association. A moderate increase in breast cancer risk was observed among women with the shortest telomeres (Q4) and lower dietary and supplemental intake of beta-carotene, vitamin C or E intake [OR (95% CI) = 1.48 (1.08-2.03), 1.39 (1.01-1.92) and 1.57 (1.14-2.18), respectively], although the trend test exhibited statistical significance only within the lower vitamin E intake subgroup (p(trend) = 0.01). These results provided the strongest evidence to date that breast cancer risk may be affected by telomere length among premenopausal women or women with low dietary intake of antioxidants or antioxidant supplements.

Accelerated senescence: an emerging role in tumor cell response to chemotherapy and radiation

Treatment of malignancies with chemotherapeutic drugs and/or radiotherapy is designed to eliminate the disease by depriving the tumor cell of its reproductive potential. Frequently, the desired effect of cell killing is achieved through the promotion of apoptosis; however, accumulating evidence suggests that apoptosis may not be the exclusive or even primary mechanism whereby tumor cells lose their self-renewal capacity after radiation or drug treatment, particularly in the case of solid tumors. While failure to undergo apoptosis in response to chemotherapeutic drugs or radiation may represent a mechanism of drug and radiation resistance, particularly in the case of leukemias and lymphomas, it is gradually being recognized that in the case of solid tumors, loss of reproductive capacity can occur through alternative pathways including reproductive cell death or mitotic catastrophe, through autophagic cell death, and as described below, through a terminally arrested state similar to replicative senescence. Studies building upon the phenomenon of replicative senescence in normal cells approaching the limit of their reproductive potential have identified a comparable senescence-like arrest as a component of the tumor cell response to chemotherapeutic drugs and radiation. This response, which has been termed "premature senescence", "senescence-like growth arrest", "stress-induced premature senescence", and "accelerated senescence", can also result from supraphysiological mitogenic signaling, sub-optimal culture conditions, and ectopic expression of oncogenes. Here, we will use the term "accelerated senescence" in our consideration of the morphological, biochemical, and molecular aspects of treatment-induced senescence, its relationship to classical replicative senescence, its prevalence in clinical specimens and the implications of accelerated senescence for the outcome of cancer therapy.

A regulatory SNP of the BICD1 gene contributes to telomere length variation in humans

Telomeres are repetitive sequences of variable length at the ends of chromosomes involved in maintaining their integrity. Telomere dysfunction is associated with increased risk of cancer and other age-related diseases. Telomere length is an important determinant of telomere function and has a strong genetic basis. We previously carried out a genome-wide linkage analysis of mean leukocyte telomere length, and identified a 12 cm quantitative-trait locus affecting telomere length on human chromosome 12. In the present study we confirmed linkage to this locus in an extended sample (380 families, 520 sib-pairs, maximum LOD score 4.3). Fine-mapping identified a 51 kb region of association within intron 1 of the Bicaudal-D homolog 1 (BICD1, MIM 602204) gene. The strongest association (P = 1.9 x 10(-5)) was with SNP rs2630578 where the minor allele C (frequency 0.21) was associated with telomeres that were shorter by 604 (+/-204) base pairs, equivalent to approximately 15-20 years of age-related attrition in telomere length. Subjects carrying the C allele for rs2630778 had 44% lower BICD1 mRNA levels in their leukocytes compared with GG homozygotes (P = 0.004). BICD1 is involved in Golgi-to-endoplasmic reticulum vacuolar transport. Previous studies have implicated vacuolar genes in telomere length homeostasis in yeast. Our study indicates that BICD1 plays a similar role in humans.

Genome-health nutrigenomics and nutrigenetics: nutritional requirements or ‘nutriomes’ for chromosomal stability and telomere maintenance at the individual level

It is becoming increasingly evident that (a) risk for developmental and degenerative disease increases with more DNA damage, which in turn is dependent on nutritional status, and (b) the optimal concentration of micronutrients for prevention of genome damage is also dependent on genetic polymorphisms that alter the function of genes involved directly or indirectly in the uptake and metabolism of micronutrients required for DNA repair and DNA replication. The development of dietary patterns, functional foods and supplements that are designed to improve genome-health maintenance in individuals with specific genetic backgrounds may provide an important contribution to an optimum health strategy based on the diagnosis and individualised nutritional prevention of genome damage, i.e. genome health clinics. The present review summarises some of the recent knowledge relating to micronutrients that are associated with chromosomal stability and provides some initial insights into the likely nutritional factors that may be expected to have an impact on the maintenance of telomeres. It is evident that developing effective strategies for defining nutrient doses and combinations or ‘nutriomes’ for genome-health maintenance at the individual level is essential for further progress in this research field.

Telomere length, telomeric proteins and genomic instability during the multistep carcinogenic process

Telomeres form specialized structures at the ends of eukaryotic chromosomes, preventing them from being wrongly recognized as DNA damage. The human telomere DNA sequence is a tandem repetition of the sequence TTAGGG. In normal cells, the DNA replication machinery is unable to completely duplicate the telomeric DNA; thus, telomeres are shortened after every cell division. Having reached a critical length, telomeres may be recognized as double strand break DNA lesions, and cells eventually enter senescence. Carcinogenesis is a multistep process involving multiple mutations and chromosomal aberrations. One of the most prevalent aberrations in pre-cancerous lesions is telomere shortening and telomerase activation. We discuss the role and homeostasis of telomeres in normal cells and their implication in the early steps of carcinogenesis. We also discuss various techniques used, and their limitations, in the study of telomeres and genome instability and their role in carcinogenesis and related genomic modifications.