Telomere biology in human aging and aging syndromes

TERRA and the alternative lengthening of telomeres: a dangerous affair

Eukaryotic telomeres are transcribed into the long noncoding RNA TERRA. A fraction of TERRA remains associated with telomeres by forming RNA:DNA hybrids dubbed telR-loops. TERRA and telR-loops are essential to promote telomere elongation in human cancer cells that maintain telomeres through a homology-directed repair pathway known as alternative lengthening of telomeres or ALT. However, TERRA and telR-loops compromise telomere integrity and cell viability if their levels are not finely tuned. The study of telomere transcription in ALT cells will enormously expand our understanding of the ALT mechanism and of how genome integrity is maintained. Moreover, telomere transcription, TERRA and telR-loops are likely to become exceptionally suited targets for the development of novel anti-cancer therapies.

Electrospun Nanofibers Encapsulated with Natural Products: A Novel Strategy to Counteract Skin Aging

The skin is the primary tissue affected by wounds and aging, significantly impacting its protective function. Natural products are widely used in cosmetics, representing a new approach to preventing age-related damage. Nanomedicine combines nanotechnology and traditional treatments to create innovative drugs. The main targets of nanotechnological approaches are wound healing, regeneration, and rejuvenation of skin tissue. The skin barrier is not easily permeable, and the creation of modern nanodevices is a way to improve the passive penetration of substances. In this study, Helichrysum italicum oil (HO) was combined with different types of electrospun nanofibers to study their protective activity on the skin and to evaluate their future application for topical treatments. In the present research, we used biodegradable polymers, including polyvinyl alcohol (PVA) and polyvinylpyrrolidone (PVP), which were characterized by a scanning electron microscope (SEM). All results show a positive trend in cell proliferation and viability of human skin stem cells (SSCs) and BJ fibroblasts pre-treated with combined nanofibers and then exposed to UV stress. Gene expression analysis revealed the activation of a molecular rejuvenation program in SSCs treated with functionalized nanofibers before UV exposure. Understanding the mechanisms involved in skin changes during aging allows for the future application of nanomaterials combined with HO directly to the patients.

TERT Promoter Methylation Is Oxygen-Sensitive and Regulates Telomerase Activity

Telomere repeats protect linear chromosomes from degradation, and telomerase has a prominent role in their maintenance. Telomerase has telomere-independent effects on cell proliferation, DNA replication, differentiation, and tumorigenesis. TERT (telomerase reverse transcriptase enzyme), the catalytic subunit of telomerase, is required for enzyme activity. TERT promoter mutation and methylation are strongly associated with increased telomerase activation in cancer cells. TERT levels and telomerase activity are downregulated in stem cells during differentiation. The link between differentiation and telomerase can provide a valuable tool for the study of the epigenetic regulation of TERT. Oxygen levels can affect cellular behaviors including proliferation, metabolic activity, stemness, and differentiation. The role of oxygen in driving TERT promoter modifications in embryonic stem cells (ESCs) is poorly understood. We adopted a monolayer ESC differentiation model to explore the role of physiological oxygen (physoxia) in the epigenetic regulation of telomerase and TERT. We further hypothesized that DNMTs played a role in physoxia-driven epigenetic modification. ESCs were cultured in either air or a 2% O2 environment. Physoxia culture increased the proliferation rate and stemness of the ESCs and induced a slower onset of differentiation than in ambient air. As anticipated, downregulated TERT expression correlated with reduced telomerase activity during differentiation. Consistent with the slower onset of differentiation in physoxia, the TERT expression and telomerase activity were elevated in comparison to the air-oxygen-cultured ESCs. The TERT promoter methylation levels increased during differentiation in ambient air to a greater extent than in physoxia. The chemical inhibition of DNMT3B reduced TERT promoter methylation and was associated with increased TERT gene and telomerase activity during differentiation. DNMT3B ChIP (Chromatin immunoprecipitation) demonstrated that downregulated TERT expression and increased proximal promoter methylation were associated with DNMT3B promoter binding. In conclusion, we have demonstrated that DNMT3B directly associates with TERT promoter, is associated with differentiation-linked TERT downregulation, and displays oxygen sensitivity. Taken together, these findings help identify novel aspects of telomerase regulation that may play a role in better understanding developmental regulation and potential targets for therapeutic intervention.

Natural Compounds and PCL Nanofibers: A Novel Tool to Counteract Stem Cell Senescence

Tissue homeostasis mainly depends on the activity of stem cells to replace damaged elements and restore tissue functions. Within this context, mesenchymal stem cells and fibroblasts are essential for maintaining tissue homeostasis in skin, in particular in the dermis. Modifications in collagen fibers are able to affect stem cell features. Skin properties can be significantly reduced after injuries or with aging, and stem cell niches, mainly comprising extracellular matrix (ECM), may be compromised. To this end, specific molecules can be administrated to prevent the aging process induced by UV exposure in the attempt to maintain a youngness phenotype. NanoPCL-M is a novel nanodevice able to control delivery of Mediterranean plant myrtle (Myrtus communis L.) extracts. In particular, we previously described that myrtle extracts, rich in bioactive molecules and nutraceuticals, were able to counteract senescence in adipose derived stem cells. In this study, we analyzed the effect of NanoPCL-M on skin stem cells (SSCs) and dermal fibroblasts in a dynamic cell culture model in order to prevent the effects of UV-induced senescence on proliferation and collagen depot. The BrdU assay results highlight the significantly positive effect of NanoPCL-M on the proliferation of both fibroblasts and SSCs. Our results demonstrate that-M is able to preserve SSCs features and collagen depot after UV-induced senescence, suggesting their capability to retain a young phenotype.

Telomerase Regulation: A Role for Epigenetics

Simple Summary

Maintenance of telomeres is a fundamental step in human carcinogenesis and is primarily regulated by telomerase and the human telomerase reverse transcriptase gene (TERT). Improved understanding of the transcriptional control of this gene may provide potential therapeutic targets. Epigenetic modifications are a prominent mechanism to control telomerase activity and regulation of the TERT gene. TERT-targeting miRNAs have been widely studied and their function explained through pre-clinical in vivo model-based validation studies. Further, histone deacetylase inhibitors are now in pre and early clinical trials with significant clinical success. Importantly, TERT downregulation through epigenetic modifications including TERT promoter methylation, histone deacetylase inhibitors, and miRNA activity might contribute to clinical study design. This review provides an overview of the epigenetic mechanisms involved in the regulation of TERT expression and telomerase activity.

Abstract

Telomerase was first described by Greider and Blackburn in 1984, a discovery ultimately recognized by the Nobel Prize committee in 2009. The three decades following on from its discovery have been accompanied by an increased understanding of the fundamental mechanisms of telomerase activity, and its role in telomere biology. Telomerase has a clearly defined role in telomere length maintenance and an established influence on DNA replication, differentiation, survival, development, apoptosis, tumorigenesis, and a further role in therapeutic resistance in human stem and cancer cells including those of breast and cervical origin. TERT encodes the catalytic subunit and rate-limiting factor for telomerase enzyme activity. The mechanisms of activation or silencing of TERT remain open to debate across somatic, cancer, and stem cells. Promoter mutations upstream of TERT may promote dysregulated telomerase activation in tumour cells but additional factors including epigenetic, transcriptional and posttranscriptional modifications also have a role to play. Previous systematic analysis indicated methylation and mutation of the TERT promoter in 53% and 31%, respectively, of TERT expressing cancer cell lines supporting the concept of a key role for epigenetic alteration associated with TERT dysregulation and cellular transformation. Epigenetic regulators including DNA methylation, histone modification, and non-coding RNAs are now emerging as drivers in the regulation of telomeres and telomerase activity. Epigenetic regulation may be responsible for reversible silencing of TERT in several biological processes including development and differentiation, and increased TERT expression in cancers. Understanding the epigenetic mechanisms behind telomerase regulation holds important prospects for cancer treatment, diagnosis and prognosis. This review will focus on the role of epigenetics in telomerase regulation.

Exosomes and Exosomal MicroRNAs in Age-Associated Stroke

Aging has been considered to be the most important non-modifiable risk factor for stroke and death. Changes in circulation factors in the systemic environment, cellular senescence and artery hypertension during human ageing have been investigated. Exosomes are nanosize membrane vesicles that can regulate target cell functions via delivering their carried bioactive molecules (e.g. protein, mRNA, and microRNAs). In the central nervous system, exosomes and exosomal microRNAs play a critical role in regulating neurovascular function, and are implicated in the initiation and progression of stroke. MicroRNAs are small non-coding RNAs that have been reported to play critical roles in various biological processes. Recently, evidence has shown that microRNAs are packaged into exosomes and can be secreted into the systemic and tissue environment. Circulating microRNAs participate in cellular senescence and contribute to age-associated stroke. Here, we provide an overview of current knowledge on exosomes and their carried microRNAs in the regulation of cellular and organismal ageing processes, demonstrating the potential role of exosomes and their carried microRNAs in age-associated stroke.

Smart Nanofibers with Natural Extracts Prevent Senescence Patterning in a Dynamic Cell Culture Model of Human Skin

Natural cosmetic products have recently re-emerged as a novel tool able to counteract skin aging and skin related damages. In addition, recently achieved progress in nanomedicine opens a novel approach yielding from combination of modern nanotechnology with traditional treatment for innovative pharmacotherapeutics. In the present study, we investigated the antiaging effect of a pretreatment with Myrtus communis natural extract combined with a polycaprolactone nanofibrous scaffold (NanoPCL-M) on skin cell populations exposed to UV. We set up a novel model of skin on a bioreactor mimicking a crosstalk between keratinocytes, stem cells and fibroblasts, as in skin. Beta-galactosidase assay, indicating the amount of senescent cells, and viability assay, revealed that fibroblasts and stem cells pretreated with NanoPCL-M and then exposed to UV are superimposable to control cells, untreated and unexposed to UV damage. On the other hand, cells only exposed to UV stress, without NanoPCL-M pretreatment, exhibited a significantly higher yield of senescent elements. Keratinocyte-based 3D structures appeared disjointed after UV-stress, as compared to NanoPCL-M pretreated samples. Gene expression analysis performed on different senescence associated genes, revealed the activation of a molecular program of rejuvenation in stem cells pretreated with NanoPCL-M and then exposed to UV. Altogether, our results highlight a future translational application of NanoPCL-M to prevent skin aging.

Investigating the cumulative effects of Δ9-tetrahydrocannabinol and repetitive mild traumatic brain injury on adolescent rats

The prevalence of mild traumatic brain injury is highest amongst the adolescent population and can lead to complications including neuroinflammation and excitotoxicity. Also pervasive in adolescents is recreational cannabis use. Δ9-Tetrahydrocannabinol, the main psychoactive component of cannabis, is known to have anti-inflammatory properties and serves as a neuroprotective agent against excitotoxicity. Thus, we investigated the effects of Δ9-tetrahydrocannabinol on recovery when administered either prior to or following repeated mild brain injuries. Male and female Sprague-Dawley rats were randomly assigned to receive Δ9-tetrahydrocannabinol or vehicle either prior to or following the repeated injuries. Rats were then tested on a behavioural test battery designed to measure post-concussive symptomology. The hippocampus, nucleus accumbens and prefrontal cortex were extracted from all animals to examine mRNA expression changes (Bdnf, Cnr1, Comt, GR, Iba-1 and Vegf-2R). We hypothesized that, in both experiments, Δ9-tetrahydrocannabinol administration would provide neuroprotection against mild injury outcomes and confer therapeutic benefit. Δ9-Tetrahydrocannabinol administration following repeated mild traumatic brain injury was beneficial to three of the six behavioural outcomes affected by injury (reducing anxiety and depressive-like behaviours while also mitigating injury-induced deficits in short-term working memory). Δ9-Tetrahydrocannabinol administration following injury also showed beneficial effects on the expression of Cnr1, Comt and Vegf-2R in the hippocampus, nucleus accumbens and prefrontal cortex. There were no notable benefits of Δ9-tetrahydrocannabinol when administered prior to injury, suggesting that Δ9-tetrahydrocannabinol may have potential therapeutic benefit on post-concussive symptomology when administered post-injury, but not pre-injury.

Examining the Progressive Behavior and Neuropathological Outcomes Associated with Chronic Repetitive Mild Traumatic Brain Injury in Rats

While the physical and behavioral symptomologies associated with a single mild traumatic brain injury (mTBI) are typically transient, repetitive mTBIs (RmTBI) have been associated with persisting neurological deficits. Therefore, this study examined the progressive changes in behavior and the neuropathological outcomes associated with chronic RmTBI through adolescence and adulthood in male and female Sprague Dawley rats. Rats experienced 2 mTBIs/week for 15 weeks and were periodically tested for changes in motor behavior, cognitive function, emotional disturbances, and aggression. Brain tissue was examined for neuropathological changes in ventricle size and presentation of Iba1 and GFAP. We did not see progressively worse behavioral impairments with the accumulation of injuries or time, but did find evidence for neurological and functional change (motor disturbance, reduced exploration, reduced aggression, alteration in depressive-like behavior, deficits in short-term working memory). Neuropathological assessment of RmTBI animals identified an increase in ventricle size, prolonged changes in GFAP, and sex differences in Iba1, in the corpus callosum, thalamus, and medial prefrontal cortex. Telomere length reduced exponentially as the injury load increased. Overall, chronic RmTBI did not result in accumulating behavioral impairment, and there is a need to further investigate progressive behavioral changes associated with repeated injuries in adolescence and young adulthood.

Sexually Dimorphic Behavioral and Genetic Outcomes Associated With Administration of TA65 (A Telomerase Activator) Following Repetitive Traumatic Brain Injury: A Pilot Study

Children and adolescents have the highest rates of traumatic brain injury (TBI), with mild TBI (mTBI) accounting for most of these injuries. This demographic also often suffers from post-injury symptomologies that may persist for months. Telomere length (TL) has previously been used as a marker for outcomes following repetitive mild TBI (RmTBI) and it may be possible that telomere elongation can reduce post-traumatic behavioral impairments. Telomerase activator-65 (TA-65) is a telomerase small-molecule activator purified from the root of Chinese herbs that has been anecdotally reported to have anti-aging and life-extending potential. We hypothesized that RmTBI would shorten TL but administration of TA-65 would reverse RmTBI-induced telomere shortening and behavioral deficits. Male and female Sprague-Dawley rats were orally administered TA-65 or a placebo substance for 30 consecutive days [postnatal day (P) 25–55]. Following the injury protocol (mTBIs on P33, 36, and 40), rats went through a behavioral test battery designed to examine symptomologies commonly associated with mTBI (balance and motor coordination, exploratory behavior, short-term working memory, and anxiety- and depressive-like behaviors). TL in ear and brain tissue (prefrontal cortex and hippocampus) and relative expression of TERT and Tep1 via qPCR were assessed 15 days following the last injury. We observed a heterogenous response between males and females, with TA65 administration resulting in increased mRNA expression of TERT and Tep1 in female rats that experienced RmTBI, which was accompanied by some functional recovery on motor behavior and footslips in the beam walk task and depressive-like behavior in the forced swim task.

The need to incorporate aged animals into the preclinical modeling of neurological conditions

Neurological conditions such as traumatic brain injury, stroke, Parkinson's disease, epilepsy, multiple sclerosis, and Alzheimer's disease are serious clinical problems that affect millions of people worldwide. The majority of clinical trials for these common conditions have failed, and there is a critical need to understand why treatments in preclinical animal models do not translate to patients. Many patients with these conditions are middle-aged or older, however, the majority of preclinical studies have used only young-adult animals. Considering that aging involves biological changes that are relevant to the pathobiology of neurological diseases, the lack of aged subjects in preclinical research could contribute to translational failures. This paper details how aging affects biological processes involved in neurological conditions, and reviews aging research in the context of traumatic brain injury, stroke, Parkinson's disease, epilepsy, multiple sclerosis, and Alzheimer's disease. We conclude that aging is an important, but often overlooked, factor that influences biology and outcomes in neurological conditions, and provide suggestions to improve our understanding and treatment of these diseases in aged patients.

Telomere Length of Circulating Cell-Free DNA and Gastric Cancer in a Chinese Population at High-Risk

Background: Telomeres have long been found to be involved in cancer development, while little was known about the dynamic changes of telomere length in carcinogenesis process.

Methods: The present study longitudinally investigated telomere alterations of cell-free DNA (cfDNA) in 86 gastric cancer (GC) subjects recruited through a 16-year prospective cohort with 2–4 serums collected before each GC-diagnosis from baseline and three follow-up time-points (a total of 276 samples). As the control, 86 individual-matched cancer-free subjects were enrolled with 276 serums from the matched calendar year.

Results: In the 73 pairs of baseline serums from GC and control subjects, shortened telomeres showed increased subsequent GC risk [odds ratio (OR) = 9.17, 95% CI: 2.72–31.25 for 1 unit shortening]. In each baseline gastric lesion category, higher risks of GC progression were also found with shortened cfDNA telomeres; ORs per 1 unit shortening were 6.99 (95% CI: 1.63–30.30) for mild gastric lesions, 6.06 (95% CI: 1.89–19.61) for intestinal metaplasia and 15.63 (95% CI: 1.91–125.00) for dysplasia. With all measurements from baseline and follow-up time-points, shortened telomeres also showed significant association with GC risk (OR = 7.37, 95% CI: 2.06–26.32 for 1 unit shortening). In temporal trend analysis, shortened telomeres were found in GC subjects compared to corresponding controls more than 3 years ahead of GC-diagnosis (most P < 0.05), while no significant difference was found between two groups within 3 years approaching to GC-diagnosis.

Conclusion: Our findings suggest that telomere shortening may be associated with gastric carcinogenesis, which supports further etiological study and potential biomarker for risk stratification.

Genetic variants in RTEL1 influencing telomere length are associated with prostate cancer risk

Telomere length measured in lymphocytes has been evaluated as a potential biomarker for prostate cancer (PCa) risk. Identifying genetic variants that affect telomere length and testing their association with disease could clarify any causal role. We therefore investigated associations between genetic variants in three telomere length-related genes and PCa risk in a case-control study. The influence of these variants on the leukocyte telomere lengths was then appraised by real-time PCR. RTEL1 rs2297441 [odds ratio (OR): 1.23; 95% confidence interval (CI): 1.03-1.46, P = 0.021] and rs3208008 (OR: 1.23; 95% CI: 1.03-1.46) were associated with PCa risk. These two risk single nucleotide polymorphisms (SNPs) (OR: 0.59; 95% CI: 0.39-0.89, P = 0.012 and OR: 0.58; 95% CI: 0.38-0.87, P = 0.009, respectively) and another SNP PARP1 rs1136410 (OR: 1.53; 95% CI: 1.01-2.31, P = 0.043) were also associated with leukocyte telomere length. These findings support that genetic determinants of telomere length may influence PCa risk.

A Bump on the Head or Late to Bed: Behavioral and Pathophysiological Effects of Sleep Deprivation after Repetitive Mild Traumatic Brain Injury in Adolescent Rats

An old wives' tale, and strongly held dogma, maintains that one should be kept awake after a mild traumatic brain injury (mTBI) to prevent a coma. This, however, conflicts with the known benefits of sleep: repair and restoration. We therefore sought to examine the effects of sleep deprivation (SD) in the post-traumatic sleep period on post-concussion symptomology (PCS). Adolescent male and female rats were administered repetitive mTBIs (RmTBI) or sham injuries and were then assigned to 5 h of SD or left undisturbed. All animals were then tested using seven behavioral tasks validated to examine PCS, followed by analysis of serum cytokines, and quantitative real-time PCR for messenger RNA (mRNA) expression. Exposure to 3 SD epochs significantly impaired behavior in 4 of 7 of the measures, while RmTBI also produced dysfunction in 5 of 7 tests, but the effects of SD and RmTBI were not cumulative. SD induced long-lasting changes in serum levels of Tnf-α, IL6, and IL-1ß. mRNA expression in the pre-frontal cortex, hippocampus, hypothalamus, and anterior cingulate cortex was modified in response to SD and RmTBI; but similar to the behavioral measures, the mRNA changes were not cumulative. Consequently, we report that SD often produced impairments similar or worse than RmTBI, and sleep hygiene should become a priority for adolescent health.

Significant SNPs Related to Telomere Length and Hepatocellular Carcinoma Risk in Chronic Hepatitis B Carriers

Chronic hepatitis B virus (HBV) infection increases the risk of developing cirrhosis and hepatocellular carcinoma (HCC) with suspected interactions between virus replication and host immune responses. A number of reports have suggested that telomerase function may be involved in chronic hepatitis B (CHB) pathogenesis, but positive or negative associations with HCC risk remain for discussion. Mean telomere length is an indicator of biological aging and it has been reported that reduction in NBV carriers compared to normal individuals. In somatic cells, telomeres contain simple, tandemly repeated G-rich sequences that frequently are reduced by 50 to 200 base pairs at each cell division. Several genome-wide association studies (GWAS) in diverse ethnic populations have revealed eleven single nucleotide polymorphisms (SNPs) linked to telomere length. Two of these, rs398652 and rs621559, have prognostic value and could be used as genetic markers. This review describes current knowledge concerning telomerase activity and telomere length as well as significant polymorphisms in HBV-related HCC patients. In particular, to cast light on genotype-phenotype interactions, we used SNPnexus to evaluate effects of the two SNPs on risk of disease and complex disorders.

Telomere length and advanced diffusion MRI as biomarkers for repetitive mild traumatic brain injury in adolescent rats

Mild traumatic brain injuries (mTBI) are of worldwide concern in adolescents of both sexes, and repeated mTBI (RmTBI) may have serious long-term neurological consequences. As such, the study of RmTBI and discovery of objective biomarkers that can help guide medical decisions is an important undertaking. Diffusion-weighted MRI (DWI), which provides markers of axonal injury, and telomere length (TL) are two clinically relevant biomarkers that have been implicated in a number of neurological conditions, and may also be affected by RmTBI. Therefore, this study utilized the lateral impact injury model of RmTBI to investigate changes in diffusion MRI and TL, and how these changes relate to each other. Adolescent male and female rats received either three mTBIs or three sham injuries. The first injury was given on postnatal day 30 (P30), with the repeated injuries separated by four days each. Seven days after the final injury, a sample of ear tissue was collected for TL analysis. Rats were then euthanized and whole brains were collected and fixated for MRI analyses that included diffusion and high-resolution structural sequences. Compared to the sham-injured group, RmTBI rats had significantly shorter TL at seven days post-injury. Analysis of advanced DWI measures found that RmTBI rats had abnormalities in the corpus callosum and cortex at seven days post-injury. Notably, many of the DWI changes were correlated with TL. These findings demonstrate that TL and DWI measurements are changed by RmTBI and may represent clinically applicable biomarkers for this.

The shortening telomere length of T lymphocytes maybe associated with hyper‑function in servere aplastic anemia

Severe aplastic anemia (SAA) is a primary disorder of severe bone marrow failure characterizing with extreme pancytopenia and a profound diminution of bone marrow progenitor cells, which is associated with T cell hyper‑function. Abnormal telomere shortening of bone marrow mononuclear cell has been reported in AA, which may lead to genomic instability, and result in cell senescence or apoptosis. Notably, certain studies identfieid that lymphocytes of shortening telomere length have undergone apoptosis escape in autoimmune diseases. In order to investigate the association between telomere lengths and function of T lymphocytes in SAA, the relative telomere lengths (RTLs) of different subtypes of T lymphocytes were investigated by flow‑fluorescent in situ hybridization in 30 patients with SAA and 25 healthy controls. Then the levels of expression of cluster of differentiation 28 (CD28), CD158 and CD70 were measured, which represent the function of T lymphocytes. The apoptosis rate and the cell cycle progression of CD8+T lymphocytes, and the level of secretion interferon‑γ and tumor necrosis factor‑α were also measured. Finally, the correlation between telomere length and these functional events of CD8+T lymphocytes was analyzed in patients with SAA. The results showed that RTLs of CD8+T lymphocytes in SAA were significantly shorter compared with those in controls. Furthermore, in patients with SAA, CD8+T lymphocytes are associated with T cell hyper‑function, which is related to the RTL. Thus, the shorter RTLs of CD8+T lymphocytes in SAA may be associated with hyper‑function of these cells, which contribute to the pathogenesis of SAA.

Prospective and longitudinal evaluations of telomere length of circulating DNA as a risk predictor of hepatocellular carcinoma in HBV patients

Prospective and longitudinal epidemiological evidence is needed to assess the association between telomere length and risk of hepatocellular carcinoma (HCC). In 323 cancer-free Korean-American HBV patients with 1-year exclusion window (followed for >1 year and did not develop HCC within 1 year), we measured the relative telomere length (RTL) in baseline serum DNAs and conducted extensive prospective and longitudinal analyses to assess RTL-HCC relationship. We found that long baseline RTL conferred an increased HCC risk compared to short RTL [hazard ratio (HR) = 4.93, P = 0.0005). The association remained prominent when the analysis was restricted to patients with a more stringent 5-year exclusion window (HR = 7.51, P = 0.012), indicating that the association was unlikely due to including undetected HCC patients in the cohort, thus minimizing the reverse-causation limitation in most retrospective studies. Adding baseline RTL to demographic variables increased the discrimination accuracy of the time-dependent receiver operating characteristic analysis from 0.769 to 0.868 (P = 1.0 × 10-5). In a nested longitudinal subcohort of 16 matched cases-control pairs, using a mixed effects model, we observed a trend of increased RTL in cases and decreased RTL in controls along 5 years of follow-up, with a significant interaction of case/control status with time (P for interaction=0.002) and confirmed the association between long RTL and HCC risk [odds ratio [OR] = 3.63, P = 0.016]. In summary, serum DNA RTL may be a novel non-invasive prospective marker of HBV-related HCC. Independent studies are necessary to validate and generalize this finding in diverse populations and assess the clinical applicability of RTL in HCC prediction.

Genetic variants in telomere-maintenance genes are associated with ovarian cancer risk and outcome

Most ovarian cancer patients present at an advanced stage with poor prognosis. Telomeres play a critical role in protecting chromosomes stability. The associations of genetic variants in telomere maintenance genes and ovarian cancer risk and outcome are unclear. We genotyped 137 single nucleotide polymorphisms (SNPs) in telomere-maintenance genes in 417 ovarian cancer cases and 417 matched healthy controls to evaluate their associations with cancer risk, survival and therapeutic response. False discovery rate Q-value was calculated to account for multiple testing. Eleven SNPs from two genes showed nominally significant associations with the risks of ovarian cancer. The most significant SNP was TEP1: rs2228026 with participants carrying at least one variant allele exhibiting a 3.28-fold (95% CI: 1.72-6.29; P < 0.001, Q = 0.028) increased ovarian cancer risk, which remained significant after multiple testing adjusting. There was also suggested evidence for the associations of SNPs with outcome, although none of the associations had a Q < 0.05. Seven SNPs from two genes showed associations with ovarian cancer survival (P < 0.05). The strongest association was found in TNKS gene (rs10093972, hazard ratio = 1.88; 95% CI: 1.20-2.92; P = 0.006, Q = 0.076). Five SNPs from four genes showed suggestive associations with therapeutic response (P < 0.05). In a survival tree analysis, TEP1:rs10143407 was the primary factor contributing to overall survival. Unfavourable genotype analysis showed a cumulative effect of significant SNPs on ovarian cancer risk, survival and therapeutic response. Genetic variations in telomere-maintenance genes may be associated with ovarian cancer risk and outcome.

Association of telomere length in peripheral leukocytes with chronic hepatitis B and hepatocellular carcinoma

BACKGROUND & OBJECTIVES

Telomere plays a critical role in the maintenance of genomic stability in eukaryotic chromosomes. More and more findings have shown that alteration in telomere length may involve in normal somatic cells and some diseases, however, whether the telomere length is associated with the development and/or progression of hepatic diseases remains poorly understood.

METHODS

A case-control study was employed to illustrate the correlation of relative telomere length (RTL) with chronic hepatitis B (CHB) and hepatocellular carcinoma (HCC). In this study, 152 patients with HCC, 212 patients with CHB, and 184 healthy controls were recruited. Genomic deoxyribonucleic acid (DNA) was extracted from the peripheral blood leukocytes, and fluorescence quantitative polymerase chain reaction (FQ-PCR) was used to detect telomere repeated numbers and 36B4 copy numbers. The RTL was calculated by telomere repeat copy number to single-copy gene number ratio in each sample compared with a reference DNA sample.

RESULTS

We found that the RTL in HCC group was the longest, followed by CHB group, and healthy control group was the shortest, showing significant statistical differences. When participants were categorized into longer and shorter group according to medium value in healthy controls, individuals who had longer RTL had a significant increased risk of CHB (odds ratio [OR]: 1.83, 95% confidence interval [CI]: 1.22-2.73) when the healthy control was used as the reference groups; furthermore, longer RTL also showed higher incidence of HCC (OR: 3.22, 95% CI: 2.01-5.17; OR: 1.58, 95% CI:1.03-2.41) when healthy control and CHB were used as the reference groups, respectively. When participants were categorized further into 4 groups according to quartile values of RTL in healthy controls, it showed that the longest RTL was also associated with an increased risk of CHB (OR: 2.09, 95% CI: 1.17-3.74) and HCC (OR: 4.31, 95% CI: 2.18-8.52; OR: 2.86, 95% CI: 1.53-5.34) when control and control/CHB group were used as the reference groups, respectively.

CONCLUSION

Our results suggest that the alteration of telomere length in peripheral leukocytes might be involved in the hepatitis B virus infection and HCC events, and RTL might be a potential useful predictor of CHB and HCC.

Does Reproductive Investment Decrease Telomere Length in Menidia menidia?

Given finite resources, intense investment in one life history trait is expected to reduce investment in others. Although telomere length appears to be strongly tied to age in many taxa, telomere maintenance requires energy. We therefore hypothesize that telomere maintenance may trade off against other life history characters. We used natural variation in laboratory populations of Atlantic silversides (Menidia menidia) to study the relationship between growth, fecundity, life expectancy, and relative telomere length. In keeping with several other studies on fishes, we found no clear dependence of telomere length on age. However, we did find that more fecund fish tended to have both reduced life expectancy and shorter telomeres. This result is consistent with the hypothesis that there is a trade-off between telomere maintenance and reproductive output.

Genome instability biomarkers and blood micronutrient risk profiles associated with mild cognitive impairment and Alzheimer's disease

Successful maintenance of metabolic systems relating to accurate DNA replication and repair is critical for optimal lifelong human health. Should this homeostatic balance become impaired, genomic instability events can arise, compromising the integrity of the genome, which may result in gene expression and human disease. Both genome instability and micronutrient imbalance have been identified and implicated in diseases associated with accelerated ageing which potentially leads to an increased risk for the future development of clinically defined neurodegenerative disorders. Cognitive decline leading to the clinical diagnosis of mild cognitive impairment (MCI) has been shown to predict an increased risk in later life of developing Alzheimer's disease (AD). Knowledge on the impact of dietary factors in relation to MCI and AD risk is improving but incomplete; in particular the role of nutrient combinations (i.e. nutriomes) has not been thoroughly investigated. Currently, there is a need for preventative strategies as well as the identification of robust and reproducible diagnostic biomarkers that will allow identification of those individuals with increased risk for neurodegenerative diseases. Growing evidence suggests cells originating from different somatic tissues derived from individuals that have been clinically diagnosed with neurodegenerative disorders exhibit elevated frequencies of DNA damage compared to tissues of cognitively normal individuals which could be due to malnutrition. The objective of this review is to discuss current evidence and identify knowledge gaps relating to genome instability biomarkers and blood micronutrient profiles from human studies of MCI and AD that may be specific to and contribute to the increased risk of these diseases. This is a vital step in order to create research strategies for the future development of diagnostics that are indicative of dementia risk and to inform preventative therapies.

Stem cell senescence. Effects of REAC technology on telomerase-independent and telomerase-dependent pathways

Decline in the gene expression of senescence repressor Bmi1, and telomerase, together with telomere shortening, underlay senescence of stem cells cultured for multiple passages. Here, we investigated whether the impairment of senescence preventing mechanisms can be efficiently counteracted by exposure of human adipose-derived stem cells to radio electric asymmetrically conveyed fields by an innovative technology, named Radio Electric Asymmetric Conveyer (REAC). Due to REAC exposure, the number of stem cells positively stained for senescence associated β-galactosidase was significantly reduced along multiple culturing passages. After a 90-day culture, REAC-treated cells exhibited significantly higher transcription of Bmi1 and enhanced expression of other stem cell pluripotency genes and related proteins, compared to unexposed cells. Transcription of the catalytic telomerase subunit (TERT) was also increased in REAC-treated cells at all passages. Moreover, while telomere shortening occurred at early passages in both REAC-treated and untreated cells, a significant rescue of telomere length could be observed at late passages only in REAC-exposed cells. Thus, REAC-asymmetrically conveyed radio electric fields acted on a gene and protein expression program of both telomerase-independent and telomerase-dependent patterning to optimize stem cell ability to cope with senescence progression.

Telomere length in peripheral blood leukocytes is associated with risk of colorectal cancer in Chinese population

Background

Human telomeres, tandem repeats of TTAGGG nucleotides at the ends of chromosomes, are essential for maintaining genomic integrity and stability. Results of previous epidemiologic studies about the association of telomere length with risk of colorectal cancer (CRC) have been conflicting.

Methods

A case-control study was conducted in a Han population in Wuhan, central China. The relative telomere length (RTL) was measured in peripheral blood leukocytes (PBLs) using quantitative real-time polymerase chain reaction (PCR) in 628 CRC cases and 1,256 age and sex frequency matched cancer-free controls. Odds ratios (OR) and 95% confidence intervals (95% CI) were calculated using unconditional logistic regression models to evaluate the association between RTL and CRC risk.

Results

Using median RTL in the controls as the cutoff, individuals with shorter RTL were associated with a significantly increased risk of CRC (adjusted OR = 1.27, 95%CI: 1.05–1.55). When participants were further categorized into 3 and 4 groups according to the tertile and quartile RTL values of controls, significant relationships were still observed between shorter RTL and increased CRC risk (OR per tertile = 1.13, 95%CI: 1.00–1.28, P_trend = 0.045; OR per quartile = 1.12, 95%CI: 1.03–1.23, P_trend = 0.012). In stratified analyses, significant association between shorter RTL and increased CRC risk was found in females, individuals younger than 60 years old, never smokers and never drinkers.

Conclusions

This study suggested that short telomere length in PBLs was significantly associated with an increased risk of CRC in Chinese Han population. Further validation in large prospective studies and investigation of the biologic mechanisms are warranted.

Short telomere lengths in peripheral blood leukocytes are associated with an increased risk of oral premalignant lesion and oral squamous cell carcinoma

BACKGROUND

Oral premalignant lesions (OPLs) are precursors of oral squamous cell carcinoma (OSCC). Short telomeres in peripheral blood leukocytes (PBLs) are associated with increased risks of several cancers. However, it is unclear whether short leukocyte telomere length (LTL) predisposes individuals to OPL and OSCC.

METHODS

LTL was measured in PBLs from 266 patients who had a diagnosis of either OPL (N = 174) or OSCC (N = 92) and from 394 age-matched and sex-matched controls. The association between LTL and the risk of OPL or OSCC, as well as the interaction of telomere length, cigarette smoking, and alcohol drinking on the risk of OPL or OSCC, were analyzed.

RESULTS

The age-adjusted relative LTL was shortest in the OSCC group (1.64 ± 0.29), intermediate in the OPL group (1.75 ± 0.43), and longest in the control group (1.82 ± 0.36; Ptrend < .001). When the analysis was dichotomized at the median value in controls, adjusting for age, sex, smoking status, and alcohol drinking status, the odds ratio for the risk of OPL and OSCC associated with short LTL was 2.03 (95% confidence interval, 1.29-3.21) and 3.47 (95% CI, 1.84-6.53), respectively, with significant dose-response effects for both associations. Among 174 patients with OPL, 23 progressed to OSCC, and the mean LTL was shorter in progressors than in nonprogressors (mean ± standard deviation: 1.66 ± 0.35 vs 1.77 ± 0.44, respectively), although the difference did not reach statistical significance (P = .258), probably because of the small number of progressors. An interaction analysis identified short LTL, smoking, and drinking alcohol as independent risk factors for OPL and OSCC.

CONCLUSIONS

Short LTL was associated with increased risks of developing OPL and OSCC. The current results also indicated that short LTL likely predisposes patients to the malignant progression of OPL.

Hepatocellular carcinoma and other malignancies in autoimmune hepatitis

Hepatocellular carcinoma and extrahepatic malignancies can complicate the course of autoimmune hepatitis, and these occurrences may increase in frequency as the survival of patients with cirrhosis is extended and the prospect of new nonstandard immune-modifying intervention is realized. The frequency of hepatocellular carcinoma in patients with autoimmune hepatitis and cirrhosis is 1-9 %, and annual occurrence in patients with cirrhosis is 1.1-1.9 %. The standardized incidence ratio for hepatocellular carcinoma in autoimmune hepatitis is 23.3 (95 % confidence interval (CI) 7.5-54.3) in Sweden, and the standardized mortality ratio for hepatobiliary cancer is 42.3 (95 % CI 20.3-77.9) in New Zealand. The principal risk factor is long-standing cirrhosis, and patients at risk are characterized mainly by cirrhosis for ≥ 10 years, manifestations of portal hypertension, persistent liver inflammation, and immunosuppressive therapy for ≥ 3 years. Multiple molecular disturbances, including the accumulation of senescent hepatocytes because of telomere shortening, step-wise accumulation of chromosomal injuries, and aberrations in transcription factors and genes, may contribute to the risk. Extraheptic malignancies of diverse cell types occur in 5 % in an unpredictable fashion. The standardized incidence ratio is 2.7 (95 % CI 1.8-3.9) in New Zealand, and non-melanoma skin cancers are most common. Outcomes are related to the nature and stage of the tumor at diagnosis. Surveillance recommendations have not been promulgated, but hepatic ultrasonography every six months in patients with cirrhosis is a consideration. Routine health screening measures for other malignancies should be applied diligently.

Recent progress in the discovery of small molecules for the treatment of amyotrophic lateral sclerosis (ALS)

Amyotrophic lateral sclerosis (ALS) is a fatal neurodegenerative disorder with few therapeutic options. While several gene mutations have been implicated in ALS, the exact cause of neuronal dysfunction is unknown and motor neurons of affected individuals display numerous cellular abnormalities. Ongoing efforts to develop novel ALS treatments involve the identification of small molecules targeting specific mechanisms of neuronal pathology, including glutamate excitotoxicity, mutant protein aggregation, endoplasmic reticulum (ER) stress, loss of trophic factors, oxidative stress, or neuroinflammation. Herein, we review recent advances in the discovery and preclinical characterization of lead compounds that may ultimately provide novel drugs to treat patients suffering from ALS.

Long telomeres in peripheral blood leukocytes are associated with an increased risk of soft tissue sarcoma

BACKGROUND

Human telomeres consisting of long, tandem repeats of the nucleotide sequence TTAGGG at the chromosome ends are essential for maintaining chromosomal stability. Previous epidemiologic studies have indicated that shorter telomere length in peripheral blood leukocytes (PBLs) is associated with the development of many cancers. However, the relation between PBL telomere length and the risk of soft tissue sarcoma (STS) has not been investigated.

METHODS

The relative telomere length (RTL) was determined in PBLs using real-time polymerase chain reaction in this case-control study. The study participants included 137 patients with histologically confirmed STS (cases) who had received no prior chemotherapy or radiotherapy and 137 healthy controls who were frequency-matched to cases on age, sex, and ethnicity.

RESULTS

Patients in the case group had significantly longer RTL than controls (1.46 ± 0.42 for cases vs 1.15 ± 0.39 for controls; P < .001). By using median RTL in the controls as a cutoff level, individuals who had long telomere length were associated with a significantly increased risk of STS compared with those who had short telomere length (adjusted odds ratio, 4.71; 95% confidence interval, 2.63-8.44). When participants were categorized further into 3 or 4 groups according to the tertile or quartile RTL values of healthy controls, a significant dose-response relation was observed between longer RTL and increased risks of STS.

CONCLUSIONS

The current results provided the first epidemiologic evidence that longer telomere length in PBLs is associated significantly with an increased risk of STS, potentially suggesting an important role for telomere maintenance in STS development.

Telomere length in circulating serum DNA as a novel non-invasive biomarker for cirrhosis: a nested case-control analysis

BACKGROUND & AIMS

Previous studies have indicated that telomere length is associated with altered risk of various tumours including hepatitis B virus (HBV)-related hepatocellular carcinoma. However, the association between telomere length and the risk of cirrhosis has not been reported.

METHODS

In this nested case-control study, we used real-time quantitative PCR to determine the relative telomere length (RTL) in serum DNA samples from 100 HBV-related cirrhosis cases and 100 frequency-matched HBV controls, and evaluated the associations between RTL and cirrhosis risk by logistic regression analyses.

RESULTS

We found that cirrhotic cases had a significantly longer RTL (median, 0.36; range, 0.08-1.87) than non-cirrhotic controls (median, 0.20; range, 0.05-1.11) (P < 0.0001). Compared with subjects with short RTL, those with long RTL had a significantly increased cirrhosis risk [odds ratio, 2.76, 95% confidence interval, 1.50-5.10; P = 0.001]. Quartile analysis further indicated a dose-response effect for this association. Compared with patients with the lowest quartile of RTL, the cirrhosis risk for those with the second, third and highest quartile of RTL was 2.68 (0.91-7.87, P = 0.073), 3.37 (1.32-10.54, P = 0.013) and 6.64 (2.41-18.32, P < 0.0001) respectively (P(trend) <0.0001). Moreover, the area under the receiver operating characteristic curve increased from 0.60 (epidemiological variables) to 0.72 (epidemiological variables plus RTL), with statistically significant difference assessed by bootstrap analysis.

CONCLUSIONS

Our study presents the first epidemiological evidence that RTL in serum DNA could potentially be used as a simple, inexpensive and non-invasive marker of cirrhosis risk, a finding that warrants further investigations in independent retrospective and prospective populations.

Relative telomere length: a novel non-invasive biomarker for the risk of non-cirrhotic hepatocellular carcinoma in patients with chronic hepatitis B infection

BACKGROUND AND AIMS

Telomere length has emerged as a promising risk predictor of various cancers including hepatocellular carcinoma (HCC). However, the majority of studies in this area measured telomere length in hepatocytes and one in lymphocytes with conflicting results. Moreover, no studies have been reported on using circulating DNA telomere length as a non-invasive HCC biomarker.

METHODS

We conducted a nested case-control study to determine the relative telomere length (RTL) in serum DNA from 140 hepatitis B virus (HBV)-related HCC cases and 280 frequency-matched cancer-free HBV controls.

RESULTS

Cases had a significantly longer RTL (median, 0.31; range, 0.02-2.31) than controls (median, 0.20; range, 0.01-1.60) (P = 0.003). Consistently, longer RTLs conferred a significantly increased HCC risk compared to short RTLs in a univariate logistic regression analysis (odds ratio [OR] = 1.55, 95% confidence interval [CI] = 1.02-2.33, P = 0.038). This association attenuated after multivariate adjustment (OR = 1.40, 95% CI = 0.90-2.19, P = 0.132). In a quartile analysis, a significant dose-response relationship was noted in univariate analysis (P(trend) = 0.017) which was again attenuated in multivariate analysis (P(trend) = 0.079). Further analyses revealed that the significant association between serum RTL and HCC risk was evident in non-cirrhotic (OR = 3.54, 95% CI 1.58-7.93 P = 0.002), but not cirrhotic (OR = 0.95, 95% CI 0.55-1.64, P = 0.860) HBV patients. Moreover, the significantly increased HCC risk conferred by cirrhosis was modulated by RTL with a significant interaction effect (P(interaction) = 0.013).

CONCLUSIONS

RTL in circulating cell-free serum DNA could potentially be used as a novel non-invasive biomarker for non-cirrhotic HCC. Prospective cohort studies are warranted to validate this finding and assess its clinical significance in HCC prevention.

Genetic variants in telomere-maintenance genes and bladder cancer risk

Telomeres are critical in maintaining genomic stability. Genetic variants in telomere pathway genes may affect telomere and telomerase function, and subsequently cancer risk. We evaluated 126 SNPs from 10 genes related to telomere regulation in relation to bladder cancer risk. Five SNPs, 4 from TEP1 gene and 1 from PINX1 gene, were found to be highly significant (P<0.01). Out of these, the most significant association was found in rs2228041 of TEP1 (OR 1.66, 95% CI 1.19–2.31) while rs1469557 of PINX1 had a protective effect (OR 0.75, 95% CI 0.61–0.93). Haplotype analysis showed that a TEP1 haplotype consisting of the variant alleles of 7 SNPs exhibited a 2.28 fold increased risk (95% CI 1.13–4.60). We then performed cumulative analysis of multiple risk variants, as well as Classification and Regression Tree (CART) to look for gene-gene interactions. In cumulative effect analysis, the group with 4–5 risk variants had an OR of 2.57 (95% CI = 1.62–4.09) versus the reference group with 0 risk variants. The CART analysis categorized individuals into five subgroups with different bladder cancer risk profiles based on their distinct genotype background. To our knowledge, this is one of the largest, most comprehensive studies on bladder cancer risk concerning telomere-regulating pathway gene SNPs and our results support that genetic variations of telomere maintenance modulate bladder cancer risk individually and jointly.

A genome-wide association study identifies a locus on chromosome 14q21 as a predictor of leukocyte telomere length and as a marker of susceptibility for bladder cancer

Telomeres play a critical role in maintaining genome integrity. Telomere shortening is associated with the risk of many aging-related diseases. Classic twin studies have shown that genetic components may contribute up to 80% of the heritability of telomere length. In the study we report here that we used a multistage genome-wide association study to identify genetic determinants of telomere length. The mean telomere length in peripheral blood leukocytes was measured by quantitative real-time PCR. We first analyzed 300,000 single-nucleotide polymorphisms (SNPs) in 459 healthy controls, finding 15,120 SNPs associated with telomere length at P < 0.05. We then validated these SNPs in two independent populations comprising 890 and 270 healthy controls, respectively. Four SNPs, including rs398652 on 14q21, were associated with telomere length across all three populations (pooled P values of <10(-5)). The variant alleles of these SNPs were associated with longer telomere length. We then analyzed the association of these SNPs with the risk of bladder cancer in a large case-control study. The variant allele of rs398652 was associated with a significantly reduced risk of bladder cancer (odds ratio = 0.81; 95% confidence interval, 0.67-0.97; P = 0.025), consistent with the correlation of this variant allele with longer telomeres. We then conducted a mediation analysis to examine whether the association between rs398652 and reduced bladder cancer risk is mediated by telomere length, finding that telomere length was a significant mediator of the relationship between rs398652 and bladder cancer (P = 0.013), explaining 14% of the effect. In conclusion, we found that the SNP rs398652 on 14q21 was associated with longer telomere length and a reduced risk of bladder cancer and that a portion of the effect of this SNP on bladder cancer risk was mediated by telomere length.

Telomeres are shortened in acinar-to-ductal metaplasia lesions associated with pancreatic intraepithelial neoplasia but not in isolated acinar-to-ductal metaplasias

Telomeres protect against chromosomal breakage, fusion, and interchromosome bridges during cell division. Shortened telomeres have been observed in the lowest grade of pancreatic intraepithelial neoplasia (PanIN). Genetically engineered mouse models of pancreatic neoplasia develop acinar-to-ductal metaplasia prior to the development of PanIN, suggesting that acinar-to-ductal metaplasias can be an early precursor lesion to pancreatic cancer. Some human PanINs are associated with acinar-to-ductal metaplasias, and it has been suggested that these acinar-to-ductal metaplasias arise as a consequence of growth of adjacent PanINs. As the earliest known genetic lesions of PanINs is shortened telomeres, we compared the telomere lengths of acinar-to-ductal metaplasia lesions, PanINs, and adjacent normal cells of human pancreata to determine whether acinar-to-ductal metaplasias could be precursors to PanIN. We used quantitative fluorescent in situ hybridization to measure the telomere length of cells from pancreatic lesions and adjacent normal pancreata from 22 patients, including 20 isolated acinar-to-ductal metaplasias, 13 PanINs associated with acinar-to-ductal metaplasias, and 12 PanINs. Normalized mean telomere fluorescence was significantly different among the cell types analyzed; 12.6 ± 10.2 units in normal acinar cells, 10.2 ± 6.4 in ductal cells, 8.4 ± 5.9 in fibroblasts, 9.4 ± 7.3 in isolated acinar-to-ductal metaplasias, 4.1 ± 2.9 in PanIN-associated acinar-to-ductal metaplasias, and 1.6 ± 1.9 in PanINs, respectively (P<0.001, ANOVA with randomized block design). Telomeres were significantly shorter in PanIN-associated acinar-to-ductal metaplasias (P<0.05, post hoc Duncan test) and in PanINs (P<0.05), than in normal cells, or isolated acinar-to-ductal metaplasias. Thus, shortened telomeres are found in PanIN-associated acinar-to-ductal metaplasias, but not in isolated acinar-to-ductal metaplasia lesions. These results indicate that isolated acinar-to-ductal metaplasias are not a precursor to PanIN, and support the hypothesis that PanIN-associated acinar-to-ductal metaplasias arise secondary to PanIN lesions.

Role of oxidatively induced DNA lesions in human pathogenesis

Genome stability is essential for maintaining cellular and organismal homeostasis, but it is subject to many threats. One ubiquitous threat is from a class of compounds known as reactive oxygen species (ROS), which can indiscriminately react with many cellular biomolecules including proteins, lipids, and DNA to produce a variety of oxidative lesions. These DNA oxidation products are a direct risk to genome stability, and of particular importance are oxidative clustered DNA lesions (OCDLs), defined as two or more oxidative lesions present within 10 bp of each other. ROS can be produced by exposure of cells to exogenous environmental agents including ionizing radiation, light, chemicals, and metals. In addition, they are produced by cellular metabolism including mitochondrial ATP generation. However, ROS also serve a variety of critical cellular functions and optimal ROS levels are maintained by multiple cellular antioxidant defenses. Oxidative DNA lesions can be efficiently repaired by base excision repair or nucleotide excision repair. If ROS levels increase beyond the capacity of its antioxidant defenses, the cell's DNA repair capacity can become overwhelmed, leading to the accumulation of oxidative DNA damage products including OCDLs, which are more difficult to repair than individual isolated DNA damage products. Here we focus on the induction and repair of OCDLs and other oxidatively induced DNA lesions. If unrepaired, these lesions can lead to the formation of mutations, DNA DSBs, and chromosome abnormalities. We discuss the roles of these lesions in human pathologies including aging and cancer, and in bystander effects.

Telomere attrition and genomic instability in xeroderma pigmentosum type-b deficient fibroblasts under oxidative stress

Xeroderma pigmentosum B (XPB/ERCC3/p89) is an ATP-dependent 3′→5′ directed DNA helicase involved in basal RNA transcription and the nucleotide excision repair (NER) pathway. While the role of NER in alleviating oxidative DNA damage has been acknowledged it remains poorly understood. To study the involvement of XPB in repair of oxidative DNA damage, we utilized primary fibroblasts from a patient suffering from XP with Cockayne syndrome and hydrogen peroxide (H₂O₂) to induce oxidative stress. Mutant cells retained higher viability and cell cycle dysfunction after H₂O₂ exposure. Cytokinesis blocked micronucleus assay revealed increased genome instability induced by H₂O₂. Single cell gel electrophoresis (comet) assay showed that the missense mutation caused a reduced repair capacity for oxidative DNA damage. Mutant fibroblasts also displayed decreased population doubling rate, increased telomere attrition rate and early emergence of senescent characteristics under chronic low dose exposure to H₂O₂. Fibroblasts from a heterozygous individual displayed intermediate traits in some assays and normal traits in others, indicating possible copy number dependence. The results show that a deficiency in functional XPB paradoxically renders cells more sensitive to the genotoxic effects of oxidative stress while reducing the cytotoxic effects. These findings have implications in the mechanisms of DNA repair, mutagenesis and carcinogenesis and ageing in normal physiological systems.

Increased Oral Fibroblast Lifespan Is Telomerase-independent

Oral mucosal wound-healing is characterized by rapid re-epithelialization and remodeling, with minimal scar formation. This may be attributed to the distinct phenotypic characteristics of the resident fibroblasts. To test this hypothesis, we investigated patient-matched oral mucosal and skin fibroblasts. Compared with skin fibroblasts, oral mucosal fibroblasts had longer proliferative lifespans, underwent more population doublings, and experienced senescence later, which was directly related to longer telomere lengths within oral mucosal fibroblasts. The presence of these longer telomeres was independent of telomerase expression, since both oral oral mucosal fibroblasts and skin fibroblasts were negative for active telomerase, as assessed according to the Telomeric Repeat Amplification Protocol. This study has demonstrated that, compared with skin fibroblasts, oral mucosal fibroblasts are ‘younger’, with a more embryonic/fetal-like phenotype that may provide a notable advantage for their ability to repair wounds in a scarless fashion.

Constitutive telomere length and gastric cancer risk: case-control analysis in Chinese Han population

The shortening of telomeres may result in chromosome instability and thus promote tumorigenesis. Previous studies have demonstrated clear involvement of telomere shortening in the carcinogenesis of several malignancies. However, the association between constitutive telomere shortening and gastric cancer development has yet to be established. Therefore, in the present study, we measured average telomere length using quantitative real-time PCR in peripheral blood lymphocytes from a gastric cancer (GC) case-control study consisting of 396 cases and 378 controls. The results showed that GC patients had significantly shorter average telomere length than matched controls (mean +/- SD 0.89 +/- 0.19 vs 1.06 +/- 0.25, P < 0.001). We further categorized telomere length using the 50% value in the controls as a cut-off point and assessed the association between telomere length and GC risk using multivariate logistic regression analysis. We found that short telomere length was associated with a significantly increased GC risk (adjusted odds ratio = 2.14, 95% confidence interval = 1.52-2.93). Quartile stratification revealed a dose-response relationship between telomere shortening and GC risk (P for trend < 0.001). Stratified analysis showed that sex, age, and alcohol drinking, but not smoking and Helicobacter pylori infection, seem to have a modulating effect on the average telomere length in both cases and controls. We also found that telomere shortening and smoking had a significant joint effect on GC risk. Collectively, our findings provide the first evidence linking the short telomere length in peripheral blood lymphocytes to elevated GC risk, which warrants further investigation in other populations.

Constitutive short telomere length of chromosome 17p and 12q but not 11q and 2p is associated with an increased risk for esophageal cancer

Shortened telomere length may cause chromosomal instability in Barrett's esophagus and thus promote tumorigenesis. However, whether short telomere length in all chromosomes or just some of them is associated with increased esophageal cancer (EC) risk is largely unknown. To address this question, we examined the overall and chromosome-specific telomere lengths of 17p, 12q, 2p, and 11q and assessed their associations with EC risk. In a case-control study with 94 EC cases and 94 matched controls, the overall telomere length and the chromosome-specific telomere lengths of 17p, 12q, 2p, and 11q in peripheral blood lymphocytes were determined by a real-time PCR and a modified single telomere length analysis assay, respectively. Multivariate logistic regression analysis was used to assess the association between telomere length and EC risk. Compared with controls, EC patients had significantly shorter overall telomere lengths (P = 0.004) and chromosome-specific telomere lengths of 17p (P = 0.003) and 12q (P = 0.006) but not of 11q (P = 0.632) and 2p (P = 0.972). Furthermore, the multivariate logistic regression analysis showed that the short overall telomere length and chromosome-specific telomere lengths of 17p and 12q were associated with a dose-dependent increase in EC risk. Our study provides the first epidemiologic evidence that short telomere length of 17p and 12q plays an important role in esophageal carcinogenesis, suggesting that short telomere length of specific chromosomes is associated with the etiology of different cancer types.

Is schizophrenia a syndrome of accelerated aging?

Schizophrenia is associated with a number of anatomical and physiological abnormalities outside of the brain, as well as with a decrease in average life span estimated at 20% in the United States. Some studies suggest that this increased mortality is not entirely due to associated causes such as suicide and the use of psychotropic medications. In this article, in order to focus greater attention on the increased mortality associated with schizophrenia, we present a special case of the hypothesis that physiological abnormalities associated with schizophrenia make a contribution to the increased mortality of schizophrenia: specifically, the hypothesis that schizophrenia is a syndrome of accelerated aging. Evidence consistent with this hypothesis comes from several areas. The biological plausibility of the hypothesis is supported by the existence of established syndromes of accelerated aging and by the sharing of risk factors between schizophrenia and other age-related conditions. We propose methods for testing the hypothesis.

Telomere length change in European sea bass (Dicentrarchus labrax)

Telomeres, the repetitive sequences found at the end of chromosomes, are observed to shorten with age in birds and mammals, but to date no investigation on changes of telomere length has been made in long-lived marine fish during ageing. We have measured the telomere length of European sea bass (Dicentrarchus labrax) ranging in age from 12 to 94 months. No overall decrease of telomere length could be detected, but a broad range of intraspecies variation was observed. Telomere length change does not appear to be useful for estimating age in this species, but may prove a useful tool for examining individual fitness and response to stress.

Premature telomere shortening in polymorphonuclear neutrophils from patients with systemic lupus erythematosus is related to the lupus disease activity

We investigated whether premature telomeric loss occurred in peripheral polymorphonuclear neutrophils (PMN) as well as mononuclear cells (MNC) from patients with systemic lupus erythematosus (SLE). We measured the telomere length of MNC and PMN in 60 SLE patients and 26 sex-, race- and age-matched healthy volunteers by Southern blotting with chemiluminescence method. The possible predisposing factors associated with telomere change were also analysed. We found the telomere length of MNC and PMN shortened with age in different degrees in both SLE and control groups. Compared to the control group, the telomere length was shortened in both SLE-MNC (6.08 kb in SLE versus 6.71 kb in control, P = 0.0008) and PMN (6.24 kb in SLE versus 6.75 kb in control, P = 0.0025). The average reduction in telomere length in SLE patients was equivalent to a premature senescence of 16.5 years in MNC and 13.4 years in PMN. In addition, the accelerated telomere shortening was more prominent in SLE patients younger than 45 years old. SLE disease activity (SLEDAI) contributed remarkably to the accelerated telomere erosion, at least in PMN. Moreover, the telomere length of MNC was significantly shorter than PMN in the same SLE patients with leukopenia and lymphopenia. These data suggested that MNC and PMN from patients with SLE displayed premature and accelerated telomere shortening that SLE is an independent factor for it.

Senescent phenotypes of skin fibroblasts from patients with Tangier disease

Tangier disease (TD) is characterized by a deficiency of high density lipoprotein (HDL) in plasma and patients with TD have an increased risk for coronary artery disease (CAD). Recently, we reported that fibroblasts from TD exhibited large and flattened morphology, which is often observed in senescent cells. On the other hand, data have accumulated to show the relationship between cellular senescence and development of atherosclerotic CAD. The aim of the present study was to investigate whether TD fibroblasts exhibited cellular senescence. The proliferation of TD fibroblasts was gradually decreased at population doubling level (PDL) approximately 10 compared with control cells. TD cells practically ceased proliferation at PDL approximately 30. DNA synthesis was markedly decreased in TD fibroblasts. TD cells exhibited a higher positive rate for senescence-associated beta-galactosidase (SA-beta-gal), which is one of the biomarkers of cellular senescence in vitro. These data showed that TD cells reached cellular senescence at an earlier PDL compared with controls. Although, there was no difference in the telomere length of fibroblasts between TD and controls at the earlier passage (PDL 6), the telomere length of TD cells was shorter than that of controls at the late passage (PDL 25). Taken together, the current study demonstrates that the late-passaged TD fibroblasts showed senescent phenotype in vitro, which might be related to the increased cardiovascular manifestations in TD patients.

Progression of astrocytomas and meningiomas: an evaluation in vitro

OBJECTIVES/BACKGROUND

In biological terms, progression means that malignancy increases as genetic mutations accumulate leading to increased proliferation and invasion capacity. By verifying the proliferation capacity, human telomerase reverse transcriptase (hTERT) expression and in vitro invasion, in a group of highly malignant glioblastomas, benign meningiomas and astrocytomas, at the initial stage of progression, we have analysed putative progression in vitro for proliferation and telomerase expression.

MATERIALS AND METHODS

The relative proliferation status (visualized with Ki-67 antibodies) and presence of hTERT protein was analysed in 27 intracranial tumours (6 astrocytomas, 8 glioblastomas and 13 meningiomas) by immunohistochemistry on paraffin-embedded biopsy tissue, as well as on primary tumour-derived cell cultures. A confrontation model was used to analyse invasiveness in vitro.

RESULTS

The mean proliferation indices were 22.3 (SD = 18.1) for glioblastomas and 2.1 (SD = 1.9) for low-grade (LG) astrocytomas. The group of benign meningiomas had a labelling index of 2.2 (SD = 2.7). Mean percentages of staining for hTERT varied between 36.5 (SD = 28.4) for glioblastomas and 10.2 (SD = 8.6) for LG astrocytomas. The group of benign meningiomas had a labelling index of 12.4 (SD = 19.2) for hTERT. A significant difference was seen for Ki-67 (P < 0.05) and hTERT (P < 0.001) in vivo versus in vitro. No difference was seen between the group of invasive and non-invasive tumour-derived cell cultures for the histopathological markers Ki-67 and hTERT (P > 0.05) in vitro.

CONCLUSIONS

The elevated expression of hTERT and Ki-67 in vitro provides a potential prognostic tool for early detection of the progression of brain tumours. As tumour cells require telomerase for continued proliferation, the expression of hTERT may mark immortality, leading to indefinite life span. On the other hand, hTERT expression and cell proliferation are not linked directly to invasion in vitro.

Telomeres, interstitial telomeric repeat sequences, and chromosomal aberrations

Telomeres are specialized nucleoproteic complexes localized at the physical ends of linear eukaryotic chromosomes that maintain their stability and integrity. The DNA component of telomeres is characterized by being a G-rich double stranded DNA composed by short fragments tandemly repeated with different sequences depending on the species considered. At the chromosome level, telomeres or, more properly, telomeric repeats--the DNA component of telomeres--can be detected either by using the fluorescence in situ hybridization (FISH) technique with a DNA or a peptide nucleic acid (PNA) (pan)telomeric probe, i.e., which identifies simultaneously all of the telomeres in a metaphase cell, or by the primed in situ labeling (PRINS) reaction using an oligonucleotide primer complementary to the telomeric DNA repeated sequence. Using these techniques, incomplete chromosome elements, acentric fragments, amplification and translocation of telomeric repeat sequences, telomeric associations and telomeric fusions can be identified. In addition, chromosome orientation (CO)-FISH allows to discriminate between the different types of telomeric fusions, namely telomere-telomere and telomere-DNA double strand break fusions and to detect recombination events at the telomere, i.e., telomeric sister-chromatid exchanges (T-SCE). In this review, we summarize our current knowledge of chromosomal aberrations involving telomeres and interstitial telomeric repeat sequences and their induction by physical and chemical mutagens. Since all of the studies on the induction of these types of aberrations were conducted in mammalian cells, the review will be focused on the chromosomal aberrations involving the TTAGGG sequence, i.e., the telomeric repeat sequence that "caps" the chromosomes of all vertebrate species.

Telomere length versus hormonal and bone mineral status in healthy elderly men

Telomeres, the termini of linear chromosomes, exert a key role in the process of cellular ageing. Progressive telomere shortening is implicated in senescence in vitro and ample evidence exists to support the hypothesis that telomere length is correlated with chronological age and ageing phenotypes in vivo. In this study, we assessed whether mean telomere length of peripheral blood leukocytes predicts age-associated bone loss and/or is related to sex steroid status in an elderly healthy male population (71-86 years). Out of this population, we selected 110 samples for telomere restriction fragment (TRF) length analysis. Fasting blood was analysed for testosterone, estradiol, sex hormone binding globulin and biochemical markers of bone turnover. Also, the bioavailable fractions of sex steroids were calculated. Bone mineral density was measured at baseline and longitudinal follow-up was available for 84 men. We found that mean TRF length was inversely correlated with age (r=-0.19; P=0.049). Although no correlations were found with sex steroids or BMD at baseline, age corrected mean TRF length was associated with longitudinal bone loss for different distal forearm sites (P<0.05). Further studies are required to confirm our results, yet in this study, the predictive value of telomere length for bone loss appears to be substantial, hence underscoring the role of telomere length as a biomarker of ageing phenotypes.