Mammalian telomeres and telomerase

The interaction between ageing and Alzheimer's disease: insights from the hallmarks of ageing

Ageing is a crucial risk factor for Alzheimer's disease (AD) and is characterised by systemic changes in both intracellular and extracellular microenvironments that affect the entire body instead of a single organ. Understanding the specific mechanisms underlying the role of ageing in disease development can facilitate the treatment of ageing-related diseases, such as AD. Signs of brain ageing have been observed in both AD patients and animal models. Alleviating the pathological changes caused by brain ageing can dramatically ameliorate the amyloid beta- and tau-induced neuropathological and memory impairments, indicating that ageing plays a crucial role in the pathophysiological process of AD. In this review, we summarize the impact of several age-related factors on AD and propose that preventing pathological changes caused by brain ageing is a promising strategy for improving cognitive health.

TERT transcription and translocation into mitochondria regulate benzo[a]pyrene/BPDE-induced senescence and mitochondrial damage in mouse spermatocytes

Telomere and mitochondria may be the targets of Benzo[a]pyrene (BaP) -induced male reproductive damage, and further elucidation of the toxic molecular mechanisms is necessary. In this study, we used in vivo and in vitro exposure models to explore the molecular mechanisms of TERT regulation in BaP-induced telomere and mitochondrial damage in spermatocytes. The results showed that the treatment of benzo[a]pyrene-7,8-dihydrodiol-9,10-epoxide (BPDE), the active metabolite of BaP, caused telomere dysfunction in mouse spermatocyte-derived GC-2 cells, resulting in S-phase arrest and increased senescence-associated secretory phenotype (SASP). These effects were significantly alleviated by telomerase agonist (ABG) pretreatment in GC-2 cells. SIRT1, FOXO3a, or c-MYC overexpressing GC-2 cell models were established to demonstrate that BPDE inhibited TERT transcriptional expression through the SIRT1/FOXO3a/c-MYC pathway, leading to telomere dysfunction. We also observed that BPDE induced mitochondrial compromise, including complex I damage, accompanied by reduced mitochondrial TERT expression. Based on this, we constructed wild-type TERT-overexpressing (OE-TERTwt) and mitochondria targeting TERT-overexpressing (OE-TERTmst) GC-2 cell models and found that OE-TERTmst GC-2 cells improved mitochondrial function better than OE-TERTwt GC-2 cells. Finally, ICR mice were given BaP by intragastric administration for 35 days, which verified the results of the in vitro study. The results shown that BaP exposure can lead to spermatogenesis disturbance, which is related to the telomere and mitochondrial damage in spermatocytes. In conclusion, our results suggest that BPDE causes telomere and mitochondrial damage in spermatocytes by inhibiting TERT transcription and mitochondrial TERT expression. This study elucidates the molecular mechanism of male reproductive toxicity due to environmental pollutant BaP, and also provides a new perspective for the exploration of interventions and protective measures against male reproductive damage by BaP.

An intercellular transfer of telomeres rescues T cells from senescence and promotes long-term immunological memory

The common view is that T lymphocytes activate telomerase to delay senescence. Here we show that some T cells (primarily naïve and central memory cells) elongated telomeres by acquiring telomere vesicles from antigen-presenting cells (APCs) independently of telomerase action. Upon contact with these T cells, APCs degraded shelterin to donate telomeres, which were cleaved by the telomere trimming factor TZAP, and then transferred in extracellular vesicles at the immunological synapse. Telomere vesicles retained the Rad51 recombination factor that enabled telomere fusion with T-cell chromosome ends lengthening them by an average of ~3,000 base pairs. Thus, there are antigen-specific populations of T cells whose ageing fate decisions are based on telomere vesicle transfer upon initial contact with APCs. These telomere-acquiring T cells are protected from senescence before clonal division begins, conferring long-lasting immune protection.

Molecular Mechanisms of Alveolar Epithelial Stem Cell Senescence and Senescence-Associated Differentiation Disorders in Pulmonary Fibrosis

Pulmonary senescence is accelerated by unresolved DNA damage response, underpinning susceptibility to pulmonary fibrosis. Recently it was reported that the SARS-Cov-2 viral infection induces acute pulmonary epithelial senescence followed by fibrosis, although the mechanism remains unclear. Here, we examine roles of alveolar epithelial stem cell senescence and senescence-associated differentiation disorders in pulmonary fibrosis, exploring the mechanisms mediating and preventing pulmonary fibrogenic crisis. Notably, the TGF-β signalling pathway mediates alveolar epithelial stem cell senescence by mechanisms involving suppression of the telomerase reverse transcriptase gene in pulmonary fibrosis. Alternatively, telomere uncapping caused by stress-induced telomeric shelterin protein TPP1 degradation mediates DNA damage response, pulmonary senescence and fibrosis. However, targeted intervention of cellular senescence disrupts pulmonary remodelling and fibrosis by clearing senescent cells using senolytics or preventing senescence using telomere dysfunction inhibitor (TELODIN). Studies indicate that the development of senescence-associated differentiation disorders is reprogrammable and reversible by inhibiting stem cell replicative senescence in pulmonary fibrosis, providing a framework for targeted intervention of the molecular mechanisms of alveolar stem cell senescence and pulmonary fibrosis. Abbreviations: DPS, developmental programmed senescence; IPF, idiopathic pulmonary fibrosis; OIS, oncogene-induced replicative senescence; SADD, senescence-associated differentiation disorder; SALI, senescence-associated low-grade inflammation; SIPS, stress-induced premature senescence; TERC, telomerase RNA component; TERT, telomerase reverse transcriptase; TIFs, telomere dysfunction-induced foci; TIS, therapy-induced senescence; VIS, virus-induced senescence.

Assessment of Peripheral Blood Mononuclear Cells Senescence and Endothelial Dysfunction among Adults with High Cardiovascular Risk

BACKGROUND

Cardiovascular diseases (CVD) are one of the leading causes of mortality and morbidity worldwide. Biological aging has been associated with the occurrence of adverse cardiovascular outcomes; however, the underlying mechanism of this process remains unknown.

OBJECTIVES

This study sought to evaluate if peripheral blood mononuclear cell (PBMC) senescence and endothelial biomarkers could influence cardiovascular (CV) risk and be suitable markers for the early detection of cardiovascular diseases in adults.

METHODS

In this cross-sectional study patients free of CVD were classified as lower (n=32) and higher Interheart Risk (IHR) scores (n=28). PBMC senescence was assessed by estimating the telomerase activity (TA) and detecting the presence of senescent cells and endothelial dysfunction by estimating the concentration of nitrite and nitrate and of total antioxidant capacity (TAC). Statistical analysis was performed with SPSS version 16.0 (SPSS Inc., Chicago, IL). All p-values <0.05 were considered statistically significant.

RESULTS

PBMC senescence 0.95 [p-value = 0.0001; 95% CI (0.874-1.026)] was a significant predictor of patients with higher IHR scores with a cut-off value of 21.65 with a sensitivity and specificity of 92% and 88% respectively. PBMC senescence, nitrite and nitrate and TA were found to be independently associated with high IHR scores.

CONCLUSION

PBMC senescence, TA and nitrite, and nitrate status are suitable measures to predict high cardiovascular risk in adults with CV risk. Nevertheless, long-term follow-up studies are needed to confirm these findings. (Arq Bras Cardiol. 2021; 116(1):37-47).

Origin matters: spontaneous DNA-RNA hybrids do not form in trans as a source of genome instability

Multiple exogenous and endogenous genotoxic agents threaten the integrity of the genome, but one major source of spontaneous DNA damage is the formation of unscheduled DNA-RNA hybrids. These can be genetically detected by their ability to induce recombination. The origin of spontaneous hybrids has been mainly attributed to the nascent RNA formed co-transcriptionally in cis invading its own DNA template. However, it was unclear whether hybrids could also be spontaneously generated by RNA produced in a different locus (in trans). Using new genetic systems in the yeast Saccharomyces cerevisiae, we recently tested whether hybrids could be formed in trans and compromise genome integrity. Whereas we detected recombinogenic DNA-RNA hybrids in cis and in a Rad51-independent manner, we found no evidence for recombinogenic DNA-RNA hybrids to be formed with RNAs produced in trans. Here, we further discuss the implications in the field for the origin of genetic instability and the threats coming from RNAs.

Robustness during Aging-Molecular Biological and Physiological Aspects

Understanding the process of aging is still an important challenge to enable healthy aging and to prevent age-related diseases. Most studies in age research investigate the decline in organ functionality and gene activity with age. The focus on decline can even be considered a paradigm in that field. However, there are certain aspects that remain surprisingly stable and keep the organism robust. Here, we present and discuss various properties of robust behavior during human and animal aging, including physiological and molecular biological features, such as the hematocrit, body temperature, immunity against infectious diseases and others. We examine, in the context of robustness, the different theories of how aging occurs. We regard the role of aging in the light of evolution.

Harmful DNA:RNA hybrids are formed in cis and in a Rad51-independent manner

DNA:RNA hybrids constitute a well-known source of recombinogenic DNA damage. The current literature is in agreement with DNA:RNA hybrids being produced co-transcriptionally by the invasion of the nascent RNA molecule produced in cis with its DNA template. However, it has also been suggested that recombinogenic DNA:RNA hybrids could be facilitated by the invasion of RNA molecules produced in trans in a Rad51-mediated reaction. Here, we tested the possibility that such DNA:RNA hybrids constitute a source of recombinogenic DNA damage taking advantage of Rad51-independent single-strand annealing (SSA) assays in the yeast Saccharomyces cerevisiae. For this, we used new constructs designed to induce expression of mRNA transcripts in trans with respect to the SSA system. We show that unscheduled and recombinogenic DNA:RNA hybrids that trigger the SSA event are formed in cis during transcription and in a Rad51-independent manner. We found no evidence that such hybrids form in trans and in a Rad51-dependent manner.

The Role of Telomerase in Radiation-Induced Genomic Instability

Findings from previous studies have suggested that the telomerase system is involved in radiation-induced genomic instability. In this study, we investigated the involvement of telomerase in the development and processing of chromosomal damage at different cell cycle stages after irradiation of human fibroblasts. Several response criteria were investigated, including cell survival, chromosomal damage (using the micronucleus assay), G₂-induced chromatid aberrations (using the conventional G₂ assay as well as a chemically-induced premature chromosome condensation assay) and DNA double-strand breaks (DSBs; using γ-H2AX, 53BP1 and Rad51) in an isogenic pair of cell lines: BJ human foreskin fibroblasts and BJ1-hTERT, a telomerase-immortalized BJ cell line. To distinguish among G₁, S and G₂ phase, cells were co-immunostained for CENP-F and cyclin A, which are tightly regulated proteins in the cell cycle. After X-ray irradiation at doses in the range of 0.1-6 Gy, the results showed that for cell survival and micronuclei induction, where the overall effect is dominated by the cells in G₁ and S phase, no difference was observed between the two cell types; in contrast, when radiation sensitivity at the G₂ stage of the cell cycle was analyzed, a significantly higher number of chromatid-type aberrations (breaks and exchanges), and higher levels of γ-H2AX and of Rad51 foci were observed for the BJ cells compared to the BJ1-hTERT cells. Therefore, it can be concluded that telomerase appears to be involved in DNA DSB repair processes, mainly in the G₂ phase. These data, taken overall, reinforce the notion that hTERT or other elements of the telomere/telomerase system may defend chromosome integrity in human fibroblasts by promoting repair in G₂ phase of the cell cycle.

Effects of 3-hydroxy-3-methylglutaryl coenzyme A reductase inhibitors on ageing: Molecular mechanisms

Human ageing is determined by degenerative alterations and processes with different manifestations such as gradual organ dysfunction, tissue function loss, increased population of aged (senescent) cells, incapability of maintaining homeostasis and reduced repair capacity, which collectively lead to an increased risk of diseases and death. The inhibitors of HMG-CoA reductase (statins) are the most widely used lipid-lowering agents, which can reduce cardiovascular morbidity and mortality. Accumulating evidence has documented several pleiotropic effects of statins in addition to their lipid-lowering properties. Recently, several studies have highlighted that statins may have the potential to delay the ageing process and inhibit the onset of senescence. In this review, we focused on the anti-ageing mechanisms of statin drugs and their effects on cardiovascular and non-cardiovascular diseases.

Neural Stem Cells of the Subventricular Zone as the Origin of Human Glioblastoma Stem Cells. Therapeutic Implications

Human glioblastoma is the most aggressive type of primary malignant brain tumors. Standard treatment includes surgical resection followed by radiation and chemotherapy but it only provides short-term benefits and the prognosis of these brain tumors is still very poor. Glioblastomas contain a population of glioma stem cells (GSCs), with self-renewal ability, which are partly responsible for the tumor resistance to therapy and for the tumor recurrence after treatment. The human adult subventricular zone contains astrocyte-like neural stem cells (NSCs) that are probably reminiscent of the radial glia present in embryonic brain development. There are numerous molecules involved in the biology of subventricular zone NSCs that are also instrumental in glioblastoma development. These include cytoskeletal proteins, telomerase, tumor suppressor proteins, transcription factors, and growth factors. Interestingly, genes encoding these molecules are frequently mutated in glioblastoma cells. Indeed, it has been recently shown that NSCs in the subventricular zone are a potential cell of origin that contains the driver mutations of human glioblastoma. In this review we will describe common features between GSCs and subventricular zone NSCs, and we will discuss the relevance of this important finding in terms of possible future therapeutic strategies.

Regulation of human and mouse telomerase genes by genomic contexts and transcription factors during embryonic stem cell differentiation

Differential regulation of telomerase reverse transcriptase (TERT) genes contribute to distinct aging and tumorigenic processes in humans and mice. To study TERT regulation, we generated mouse embryonic stem cell (ESC) lines containing single-copy bacterial artificial chromosome (BAC) reporters, covering hTERT and mTERT genes and their neighboring loci, via recombinase-mediated BAC targeting. ESC lines with chimeric BACs, in which two TERT promoters were swapped, were also generated. Using these chromatinized BACs, we showed that hTERT silencing during differentiation to embryoid bodies (EBs) and to fibroblast-like cells was driven by the human-specific genomic context and accompanied by increases of repressive epigenetic marks, H3K9me3 and H3K27me3, near its promoter. Conversely, the mouse genomic context did not repress TERT transcription until late during differentiation. The hTERT promoter was more active than its mouse counterpart when compared in the same genomic contexts. Mutations of E-box and E2F consensus sites at the promoter had little effect on hTERT transcription in ESCs. However, the mutant promoters were rapidly silenced upon EB differentiation, indicating that transcription factors (TFs) bound to these sites were critical in maintaining hTERT transcription during differentiation. Together, our study revealed a dynamic hTERT regulation by chromatin environment and promoter-bound TFs during ESC differentiation.

Analyses of Selenotranscriptomes and Selenium Concentrations in Response to Dietary Selenium Deficiency and Age Reveal Common and Distinct Patterns by Tissue and Sex in Telomere-Dysfunctional Mice

Background: The hierarchies of tissue selenium distribution and selenotranscriptomes are thought to critically affect healthspan and longevity.Objective: We determined selenium status and selenotranscriptomes in response to long-term dietary selenium deficiency and age in tissues of male and female mice.Methods: Weanling telomerase RNA component knockout C57BL/6 mice were fed a selenium-deficient (0.03 mg Se/kg) Torula yeast-based AIN-93G diet or a diet supplemented with sodium selenate (0.15 mg Se/kg) until age 18 or 24 mo. Plasma, hearts, kidneys, livers, and testes were collected to assay for selenotranscriptomes, selected selenoproteins, and tissue selenium concentrations. Data were analyzed with the use of 2-factor ANOVA (diet × age) in both sexes.Results: Dietary selenium deficiency decreased (P ≤ 0.05) selenium concentrations (65-72%) and glutathione peroxidase (GPX) 3 (82-94%) and selenoprotein P (SELENOP) (17-41%) levels in the plasma of both sexes of mice and mRNA levels (9-68%) of 4, 4, and 12 selenoproteins in the heart, kidney, and liver of males, respectively, and 5, 16, and 14 selenoproteins, respectively, in females. Age increased selenium concentrations and SELENOP levels (27% and 30%, respectively; P ≤ 0.05) in the plasma of males only but decreased (12-46%; P < 0.05) mRNA levels of 1, 5, and 13 selenoproteins in the heart, kidney, and liver of males, respectively, and 6, 5, and 0 selenoproteins, respectively, in females. Among these mRNAs, selenoprotein H (Selenoh), selenoprotein M (Selenom), selenoprotein W (Selenow), methionine-R-sulfoxide reductase 1 (MsrB1), Gpx1, Gpx3, thioredoxin reductase 1 (Txnrd1), Txnrd2, selenoprotein S (Selenos), selenoprotein F (Selenof), and selenoprotein O (Selenoo) responded in parallel to dietary selenium deficiency and age in ≥1 tissue or sex, or both. Dietary selenium deficiency upregulated (40-160%; P ≤ 0.05) iodothyronine deiodinase 2 (Dio2) and selenoprotein N (Selenon) in the kidneys of males. Age upregulated (11-44%; P < 0.05) Selenon in the kidneys of males, selenoprotein K (Selenok) and selenoprotein I (Selenoi) in the kidneys of females, and Selenof and Selenok in the testes.Conclusions: These results illustrate tissue-specific sexual dimorphisms of selenium status and selenotranscriptomes because of dietary selenium deficiency and age.

Single Stem Cell Imaging and Analysis Reveals Telomere Length Differences in Diseased Human and Mouse Skeletal Muscles

Muscle stem cells (MuSCs) contribute to muscle regeneration following injury. In many muscle disorders, the repeated cycles of damage and repair lead to stem cell dysfunction. While telomere attrition may contribute to aberrant stem cell functions, methods to accurately measure telomere length in stem cells from skeletal muscles have not been demonstrated. Here, we have optimized and validated such a method, named MuQ-FISH, for analyzing telomere length in MuSCs from either mice or humans. Our analysis showed no differences in telomere length between young and aged MuSCs from uninjured wild-type mice, but MuSCs isolated from young dystrophic mice exhibited significantly shortened telomeres. In corroboration, we demonstrated that telomere attrition is present in human dystrophic MuSCs, which underscores its importance in diseased regenerative failure. The robust technique described herein provides analysis at a single-cell resolution and may be utilized for other cell types, especially rare populations of cells.

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MuQ-FISH is a telomere analysis assay of mouse and human muscle stem cells

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Highly sensitive telomere analysis on small numbers of cells

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Detection of both telomere length and number of telomere foci with MuQ-FISH assay

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Telomere analysis is now possible in quiescent and/or cycling stem cells

Multiple therapeutic effect of endothelial progenitor cell regulated by drugs in diabetes and diabetes related disorder

BACKGROUND

Reduced levels of endothelial progenitor cells (EPCs) counts have been reported in diabetic mellitus (DM) patients and other diabetes-related disorder. EPCs are a circulating, bone marrow-derived cell population that appears to participate in vasculogenesis, angiogenesis and damage repair. These EPC may revert the damage caused in diabetic condition. We aim to identify several existing drugs and signaling molecule, which could alleviate or improve the diabetes condition via mobilizing and increasing EPC number as well as function.

MAIN BODY

Accumulated evidence suggests that dysregulation of EPC phenotype and function may be attributed to several signaling molecules and cytokines in DM patients. Hyperglycemia alone, through the overproduction of reactive oxygen species (ROS) via eNOS and NOX, can induce changes in gene expression and cellular behavior in diabetes. Furthermore, reports suggest that EPC telomere shortening via increased oxidative DNA damage may play an important role in the pathogenesis of coronary artery disease in diabetic patients. In this review, different type of EPC derived from different sources has been discussed along with cell-surface marker. The reduced number and immobilized EPC in diabetic condition have been mobilized for the therapeutic purpose via use of existing, and novel drugs have been discussed. Hence, evidence list of all types of drugs that have been reported to target the same pathway which affect EPC number and function in diabetes has been reviewed. Additionally, we highlight that proteins are critical in diabetes via polymorphism and inhibitor studies. Ultimately, a lucid pictorial explanation of diabetic and normal patient signaling pathways of the collected data have been presented in order to understand the complex signaling mystery underlying in the diseased and normal condition.

CONCLUSION

Finally, we conclude on eNOS-metformin-HSp90 signaling and its remedial effect for controlling the EPC to improve the diabetic condition for delaying diabetes-related complication. Altogether, the review gives a holistic overview about the elaborate therapeutic effect of EPC regulated by novel and existing drugs in diabetes and diabetes-related disorder.

Telomere Biology-Insights into an Intriguing Phenomenon

Bacteria and viruses possess circular DNA, whereas eukaryotes with typically very large DNA molecules have had to evolve into linear chromosomes to circumvent the problem of supercoiling circular DNA of that size. Consequently, such organisms possess telomeres to cap chromosome ends. Telomeres are essentially tandem repeats of any DNA sequence that are present at the ends of chromosomes. Their biology has been an enigmatic one, involving various molecules interacting dynamically in an evolutionarily well-trimmed fashion. Telomeres range from canonical hexameric repeats in most eukaryotes to unimaginably random retrotransposons, which attach to chromosome ends and reverse-transcribe to DNA in some plants and insects. Telomeres invariably associate with specialised protein complexes that envelop it, also regulating access of the ends to legitimate enzymes involved in telomere metabolism. They also transcribe into repetitive RNA which also seems to be playing significant roles in telomere maintenance. Telomeres thus form the intersection of DNA, protein, and RNA molecules acting in concert to maintain chromosome integrity. Telomere biology is emerging to appear ever more complex than previously envisaged, with the continual discovery of more molecules and interplays at the telomeres. This review also includes a section dedicated to the history of telomere biology, and intends to target the scientific audience new to the field by rendering an understanding of the phenomenon of chromosome end protection at large, with more emphasis on the biology of human telomeres. The review provides an update on the field and mentions the questions that need to be addressed.

Role of Resveratrol (RES) in Regenerative Medicine

Within the last quarter century, technology has been a major catalyst of the advancement in various fields of scientific knowledge, particularly medical research. This new enlightenment has spurred the exploration of alternative treatment methods to some of society's most problematic diseases. One such innovative treatment is the use of Resveratrol (RES) to treat a number of pathophysiological conditions. RES is a natural polyphenolic compound found in the skin(s) of blueberries, red grapes (a major constituent of red wine), some vegetables, and even peanuts. The compound has a number of potent regenerative properties, which include: anti-aging, anti-inflammatory, and antioxidative. Research has confirmed both in vivo and in vitro RES's beneficial applications to numerous diseases. This chapter centers on its unique healing powers and beneficial applications against myriad debilitating conditions.

Can Leukocyte Telomere Length Predict Survival Time in Heart Transplant Recipients over a Minimal Follow-Up of 20 years?

In humans, leukocyte telomere length (LTL) reduces with age and is reported to be inversely associated with ageing-related diseases. We measured LTL in leukocyte DNA using a quantitative PCR-based method from 127 blood samples of heart recipients (107 males, 20 females, age 44.1 ± 10.5), followed for up to 30 years. Patients with coronary artery disease survived for a shorter time and also had shorter LTL (both P < 0.05 after adjustment for age and sex) than subjects with dilated cardiomyopathy. Patients with non-cardiac causes of death had shorter LTL than patients with cardiac causes (P < 0.05 after adjustment for age). An inverse correlation between LTL and age (P < 0.03) was observed in patients with non-cardiac causes of death only. Most importantly, LTL was not associated with general survival time in patients after heart transplantation. However, shorter LTL was a marker of non-cardiac causes of death. Different LTLs and survival times were determined in association with aetiology of heart failure (HF).

Therapeutic targeting of replicative immortality

One of the hallmarks of malignant cell populations is the ability to undergo continuous proliferation. This property allows clonal lineages to acquire sequential aberrations that can fuel increasingly autonomous growth, invasiveness, and therapeutic resistance. Innate cellular mechanisms have evolved to regulate replicative potential as a hedge against malignant progression. When activated in the absence of normal terminal differentiation cues, these mechanisms can result in a state of persistent cytostasis. This state, termed "senescence," can be triggered by intrinsic cellular processes such as telomere dysfunction and oncogene expression, and by exogenous factors such as DNA damaging agents or oxidative environments. Despite differences in upstream signaling, senescence often involves convergent interdependent activation of tumor suppressors p53 and p16/pRB, but can be induced, albeit with reduced sensitivity, when these suppressors are compromised. Doses of conventional genotoxic drugs required to achieve cancer cell senescence are often much lower than doses required to achieve outright cell death. Additional therapies, such as those targeting cyclin dependent kinases or components of the PI3K signaling pathway, may induce senescence specifically in cancer cells by circumventing defects in tumor suppressor pathways or exploiting cancer cells' heightened requirements for telomerase. Such treatments sufficient to induce cancer cell senescence could provide increased patient survival with fewer and less severe side effects than conventional cytotoxic regimens. This positive aspect is countered by important caveats regarding senescence reversibility, genomic instability, and paracrine effects that may increase heterogeneity and adaptive resistance of surviving cancer cells. Nevertheless, agents that effectively disrupt replicative immortality will likely be valuable components of new combinatorial approaches to cancer therapy.

Downregulation of telomerase activity by diclofenac and curcumin is associated with cell cycle arrest and induction of apoptosis in colon cancer

Uncontrolled cell proliferation is the hallmark of cancer, and cancer cells have typically acquired damage to genes that directly regulate their cell cycles. The synthesis of DNA onto the end of chromosome during the replicative phase of cell cycle by telomerase may be necessary for unlimited proliferation of cells. Telomerase, a ribonucleoprotein enzyme is considered as a universal therapeutic target of cancer because of its preferential expression in cancer cells and its presence in 90 % of tumors. We studied the regulation of telomerase and telomerase reverse transcriptase catalytic subunit (TERT) by diclofenac and curcumin, alone and also in combination, in 1, 2-dimethylhydrazine dihydrochloride-induced colorectal cancer in rats. The relationship of telomerase activity with tumors suppressor proteins (p51, Rb, p21), cell cycle machinery, and apoptosis was also studied. Telomerase is highly expressed in DMH group and its high activity is associated with increased TERT expression. However, telomerase is absent or is present at lower levels in normal tissue. CDK4, CDK2, cyclin D1, and cyclin E are highly expressed in DMH as assessed by RT-PCR, qRT-PCR, Western blot, and immunofluorescence analysis. Diclofenac and curcumin overcome these carcinogenic effects by downregulating telomerase activity, diminishing the expression of TERT, CDK4, CDK2, cyclin D1, and cyclin E. The anticarcinogenic effects shown after the inhibition of telomerase activity by diclofenac and curcumin may be associated with upregulation of tumor suppressor proteins p51, Rb, and p21, whose activation induces the cells cycle arrest and apoptosis.

Differential sensitivity of telomerase from human hematopoietic stem cells and leukemic cell lines to mild hyperthermia

We have investigated the effects of hyperthermia (HT) on cell proliferation and telomerase activity of human hematopoietic stem cells (HSCs) and compared with human leukemic cell lines (TF-1, K562 and HL-60). The cells were exposed to HT at 42 and 43 °C up to 120 min. The cells were incubated at 37 °C for 96 h. Then the cells were collected and assayed for cell proliferation, viability, telomerase activity, and terminal restriction fragment (TRF) lengths. The enzyme activity from HSCs was decreased up to 68.6 at 42 and 85.1 % at 43 °C for 120 min. This inhibition in leukemic cells was up to 28.9 and 53.6 % in TF-1; 53 and 63.9 % in K562; 45.2 and 61.1 % in HL-60 cells. The treated cells showed TRF lengths about 5.3 kb for control HL-60 cells, 5.0 kb for HL-60 cells treated at 42 and 4.5 kb at 43 °C for 120 min. In HSCs, the TRF length was about 4.5 kb for untreated cells and 4.0-4.5 kb for treated cells at 42 and 43 °C for 120 min. The time response curves indicated that, inhibition of the enzyme activity in leukemic cells was dependent to the time of exposure to HT. But in HSCs, the inhibition was reached to steady state at 15 min exposure to 43 °C heat stress. TRF length was constant at treated two types of cells, which implies that in cells subjected to mild HT no telomere shortening was observed.

PinX1, a telomere repeat-binding factor 1 (TRF1)-interacting protein, maintains telomere integrity by modulating TRF1 homeostasis, the process in which human telomerase reverse Transcriptase (hTERT) plays dual roles

TRF1, a telomere-binding protein, is important for telomere protection and homeostasis. PinX1 interacts with TRF1, but the physiological consequences of their interaction in telomere protection are not yet understood. Here we investigated PinX1 function on TRF1 stability in HeLa cells. PinX1 overexpression stabilized TRF1, but PinX1 depletion by siRNA led to TRF1 degradation, TRF1 ubiquitination, and less TRF1 telomere association. The depletion also induced DNA damage responses at telomeres and chromosome instability. These telomere dysfunctional phenotypes were in fact due to TRF1 deficiency. We also report that hTERT, a catalytic component of telomerase, plays dual roles in the TRF1 steady state pathway. PinX1-mediated TRF1 stability was not observed in hTERT-negative immortal cells, but was pronounced when hTERT was ectopically expressed in the cells, suggesting that hTERT may be needed in the PinX1-mediated TRF1 stability pathway. Interestingly, the knockdown of both PinX1 and hTERT in HeLa cells stabilized TRF1, suppressed DNA damage response activation, and restored chromosome stability. In summary, our findings suggested that PinX1 may maintain telomere integrity by regulating TRF1 stability and that hTERT may act as both a positive and a negative regulator of TRF1 homeostasis in a PinX1-dependent manner.

Role of telomerase reverse transcriptase in glial scar formation after spinal cord injury in rats

The study aims to determine the expression of telomerase reverse transcriptase (TERT) in the glial scar following spinal cord injury in the rat, and to explore its relationship with glial scar formation. A total of 120 Sprague–Dawley rats were randomly divided into three groups: SCI only group (without TERT interference), TERT siRNA group (with TERT interference), and sham group. The TERT siRNA and SCI only groups received spinal cord injury induced by the modified Allen’s weight drop method. In the sham group, the vertebral plate was opened to expose the spinal cord, but no injury was modeled. Five rats from each group were sacrificed under anesthesia at days 1, 3, 5, 7, 14, 28, 42, and 56 after spinal cord injury. Specimens were removed for observation of glial scar formation using hematoxylin-eosin staining and immunofluorescence detection. mRNA and protein expressions of TERT and glial fibrillary acidic protein (GFAP) were detected by reverse-transcription (RT)-PCR and western blotting, respectively. Hematoxylin-eosin staining showed evidence of gliosis and glial scarring in the spinal cord injury zone of the TERT siRNA and SCI only groups, but not in the sham group. Immunofluorescence detection showed a significant increase in GFAP expression at all time points after spinal cord injury in the SCI only group (81 %) compared with the TERT siRNA group (67 %) and sham group (2 %). In contrast, the expression of neurofilament protein 200 (NF-200) was gradually reduced and remained at a stable level until 28 days in the SCI only group. There were no NF-200-labeled cells in the spinal cord glial scar and cavity at day 56 after spinal cord injury. NF-200 expression at each time point was significantly lower in the SCI only group than the TERT siRNA group, while there was no change in the sham group. Western blotting showed that TERT and GFAP protein expressions changed dynamically and showed a linear relationship in the SCI only group (r = 0.765, P < 0.01), while there was no obvious linear relationship in the sham group (r = 0.208, P = 0.121). RT-PCR results showed a dynamic expression of TERT and GFAP mRNA in the SCI only group, exhibiting a linear relationship (r = 0.722, P < 0.01), while there was no linear relationship in the sham group (r = 0.206, P = 0.180). Our data indicate that TERT has a dynamic expression in the spinal cord glial scar, which positively correlates to GFAP expression, and may be important for promoting glial scar formation.

Inter-telomeric recombination is present in telomerase-positive human cells

Immortal cells require a mechanism of telomere length control in order to divide infinitely. One mechanism is telomerase, an enzyme that compensates the loss of telomeric DNA. The second mechanism is the alternative lengthening of telomeres (ALT) pathway. In ALT pathway cells, homologous recombination between telomeric DNA is the mechanism by which telomere homeostasis is achieved. We developed a novel homologous recombination reporter system that is able to measure inter-telomeric recombination in a sensitive manner. We asked the fundamental question if homologous recombination between different telomeres is present in telomerase-positive cells. In this in vitro study, we showed that homologous recombination between telomeres is detectable in ALT cells with the same frequency as in cells that utilize the telomerase pathway. We further described an ALT cell clone that showed peaks of recombination which were not detected in telomerase-positive clones. In telomerase-positive cells the frequency of inter-telomeric recombination was not increased by shortened telomeres or by a fragile telomere phenotype induced with aphidicolin. ALT cells, in contrast, responded to aphidicolin with an increase in the frequency of recombination. Our results indicate that inter-telomeric recombination is present in both pathways of telomere length control, but the factors that increase recombination are different in ALT and telomerase-positive cells.

Targeting homologous recombination and telomerase in Barrett's adenocarcinoma: impact on telomere maintenance, genomic instability and tumor growth

Homologous recombination (HR), a mechanism to accurately repair DNA in normal cells, is deregulated in cancer. Elevated/deregulated HR is implicated in genomic instability and telomere maintenance, which are critical lifelines of cancer cells. We have previously shown that HR activity is elevated and significantly contributes to genomic instability in BAC. The purpose of this study was to evaluate therapeutic potential of HR inhibition, alone and in combination with telomerase inhibition, in BAC. We demonstrate that telomerase inhibition in BAC cells increases HR activity, RAD51 expression, and association of RAD51 to telomeres. Suppression of HR leads to shorter telomeres as well as markedly reduced genomic instability in BAC cells over time. Combination of HR suppression (whether transgenic or chemical) with telomerase inhibition, causes a significant increase in telomere attrition and apoptotic death in all BAC cell lines tested, relative to either treatment alone. A subset of treated cells also stain positive for β-galactosidase, indicating senescence. The combined treatment is also associated with decline in S-phase and a strong G2/M arrest, indicating massive telomere attrition. In a subcutaneous tumor model, the combined treatment resulted in the smallest tumors, which were even smaller (P=0.001) than those resulted from either treatment alone. Even the tumors removed from these mice had significantly reduced telomeres and evidence of apoptosis. We therefore conclude that although telomeres are elongated by telomerase, elevated RAD51/HR assist in their maintenance/stabilization in BAC cells. Telomerase inhibitor prevents telomere elongation but induces RAD51/HR, which contribute to telomere maintenance/stabilization and prevention of apoptosis, reducing the efficacy of treatment. Combining HR inhibition with telomerase, makes telomeres more vulnerable to degradation and significantly increases/expedites their attrition, leading to apoptosis. We therefore demonstrate that a therapy, targeting HR and telomerase, has potential to prevent both the tumor growth and genomic evolution in BAC.

Interaction study of ciprofloxacin with human telomeric DNA by spectroscopy and molecular docking

The interaction of ciprofloxacin (CIP) with human telomeric DNA was studied in vitro using multi-spectroscopy and molecular modeling methods. The hypochromic effect with a red shift in ultraviolet (UV) absorption indicated the occurrence of the interaction between CIP and DNA. The fluorescence quenching of CIP was observed with the addition of DNA and was proved to be the static quenching. The binding constant was found to be 9.62×10(4) L mol(-1). Electrospray ionization mass spectrometry (ESI-MS) result further confirmed the formation of 1:1 non-covalent complex between DNA and CIP. Combined with the UV melting results, circular dichroism (CD) results confirmed the existence of groove binding mode, as well as conformational changes of DNA. Molecular docking studies illustrated the visual display of the CIP binding to the GC region in the minor groove of DNA. Specific hydrogen bonds and van der Waals forces were demonstrated as main acting forces between CIP and guanine bases of DNA.

Structure-based design, synthesis and evaluation of novel anthra[1,2-d]imidazole-6,11-dione derivatives as telomerase inhibitors and potential for cancer polypharmacology

A series of anthra[1,2-d]imidazole-6,11-dione derivatives were synthesized and evaluated for telomerase inhibition, hTERT expression and suppression of cancer cell growth in vitro. All of the compounds tested, except for compounds 4, 7, 16, 24, 27 and 28 were selected by the NCI screening system. Among them, compounds 16, 39, and 40 repressed hTERT expression without greatly affecting cell growth, suggesting for the selectivity toward hTERT expression. Taken together, our findings indicated that the analysis of cytotoxicity and telomerase inhibition might provide information applicable for further developing potential telomerase and polypharmacological targeting strategy.

Thymosin β4 reduces senescence of endothelial progenitor cells via the PI3K/Akt/eNOS signal transduction pathway

We previously demonstrated that thymosin β4 (Tβ4) regulates a variety of endothelial progenitor cell (EPC) functions, including cell migration, proliferation, survival and angiogenesis. However, the effect of Tβ4 on the senescence of circulating EPCs remains unclear. In the present study, the effect of Tβ4 on EPC senescence and the signal transduction pathways involved in this process was investigated. Circulating EPCs isolated from healthy volunteers were cultured in the absence or presence of Tβ4 and various signal cascade inhibitors. Tβ4 inhibited EPC senescence in a concentration‑dependent manner. In addition, Tβ4 increased telomerase activity and expression of telomerase reverse transcriptase mRNA in EPCs. Tβ4 also regulated the expression of p21, p27 and cyclin D1. The effects of Tβ4 on EPC senescence were eliminated by the phosphoinositide 3'‑kinase (PI3K) inhibitor, wortmannin and the endothelial nitric oxide synthase inhibitor, L‑nitroarginine methyl ester hydrochloride (L‑NAME). In conclusion, the inhibitory effect on EPC senescence mediated by Tβ4 may be attributed, at least in part, to activation of the PI3K‑Akt‑eNOS signaling pathway.

Aging, cellular senescence, and cancer

For most species, aging promotes a host of degenerative pathologies that are characterized by debilitating losses of tissue or cellular function. However, especially among vertebrates, aging also promotes hyperplastic pathologies, the most deadly of which is cancer. In contrast to the loss of function that characterizes degenerating cells and tissues, malignant (cancerous) cells must acquire new (albeit aberrant) functions that allow them to develop into a lethal tumor. This review discusses the idea that, despite seemingly opposite characteristics, the degenerative and hyperplastic pathologies of aging are at least partly linked by a common biological phenomenon: a cellular stress response known as cellular senescence. The senescence response is widely recognized as a potent tumor suppressive mechanism. However, recent evidence strengthens the idea that it also drives both degenerative and hyperplastic pathologies, most likely by promoting chronic inflammation. Thus, the senescence response may be the result of antagonistically pleiotropic gene action.

Modulating telomerase activity in tumor patients by targeting dyskerin binding site for hTR

Telomeres shortening, which leads to apoptosis, is prevented by telomerase adding small repeated segments of DNA to the telomeres. The telomerase level has been correlated with progression of several cancer types, including acute leukemia, breast, prostate, lung cancer and melanoma. Suppression of telomerase activity was found to reduce metastatic potential but could have serious side effects in normal proliferative cells. One of the proteins stabilizing the telomerase complex called dyskerin reduces the maximum telomerase activity. We suggest a possible therapeutic agent which would disable the interaction of dyskerin and telomerase, but would not completely inhibit telomerase activity.

HeT-A_pi1, a piRNA target sequence in the Drosophila telomeric retrotransposon HeT-A, is extremely conserved across copies and species

The maintenance of the telomeres in Drosophila species depends on the transposition of the non-LTR retrotransposons HeT-A, TAHRE and TART. HeT-A and TART elements have been found in all studied species of Drosophila suggesting that their function has been maintained for more than 60 million years. Of the three elements, HeT-A is by far the main component of D. melanogaster telomeres and, unexpectedly for an element with an essential role in telomere elongation, the conservation of the nucleotide sequence of HeT-A is very low. In order to better understand the function of this telomeric retrotransposon, we studied the degree of conservation along HeT-A copies. We identified a small sequence within the 3′ UTR of the element that is extremely conserved among copies of the element both, within D. melanogaster and related species from the melanogaster group. The sequence corresponds to a piRNA target in D. melanogaster that we named HeT-A_pi1. Comparison with piRNA target sequences from other Drosophila retrotransposons showed that HeT-A_pi1 is the piRNA target in the Drosophila genome with the highest degree of conservation among species from the melanogaster group. The high conservation of this piRNA target in contrast with the surrounding sequence, suggests an important function of the HeT-A_pi1 sequence in the co-evolution of the HeT-A retrotransposon and the Drosophila genome.

Differentiation of human umbilical cord mesenchymal stem cells into hepatocyte-like cells by hTERT gene transfection in vitro

The availability of a large quantity of MSCs (mesenchymal stem cells) would greatly advance liver-directed cell therapies. However, MSCs have a limited lifespan in vitro. Therefore we tested whether hUCMSCs (human umbilical cord MSCs) could be immortalized by transduction with a lentiviral vector carrying the hTERT (human telomerase reverse transcriptase) catalytic subunit gene, and investigated their differentiation potential. Transfected hUCMSCs overexpressed the hTERT gene and up-regulated their telomerase activity. The transfected hUCMSCs maintained their typical morphology and MSC-specific markers, and vigorously proliferated, undergoing more than 100 PDs (population doublings) to date. Following incubation with hepatogenic agents, the transfected hUCMSCs differentiated into hepatocyte-like cells, and expressed hepatic markers, such as albumin, AFP (α-fetoprotein) and CK-18 (cytokeratin-18). Transfected hUCMSCs showed no transformation into tumours in nude mice. In conclusion, telomerization of hUCMSCs by hTERT overexpression extends their replicative lifespan without influencing their hepatogenic differentiation potential. This offers opportunities for obtaining sufficient quantities of cells for liver-directed therapies.

Chemical and biological consequences of oxidatively damaged guanine in DNA

Of the four native nucleosides, 2'-deoxyguanosine (dGuo) is most easily oxidized. Two lesions derived from dGuo are 8-oxo-7,8-dihydro-2'-deoxyguanosine (8-oxodGuo) and 2,6-diamino-4-hydroxy-5-formamidopyrimidine (Fapy)∙dGuo. Furthermore, while steady-state levels of 8-oxodGuo can be detected in genomic DNA, it is also known that 8-oxodGuo is more easily oxidized than dGuo. Thus, 8-oxodGuo is susceptible to further oxidation to form several hyperoxidized dGuo products. This review addresses the structural impact, the mutagenic and genotoxic potential, and biological implications of oxidatively damaged DNA, in particular 8-oxodGuo, Fapy∙dGuo, and the hyperoxidized dGuo products.

Telomeres and the nucleus

Telomeres are crucial for the maintenance of genome stability through "capping" of chromosome ends to prevent their recognition as double-strand breaks, thus avoiding end-to-end fusions or illegitimate recombination [1-3]. Similar to other genomic regions, telomeres participate to the nuclear architecture while being highly mobile. The interaction of telomeres with nuclear domains or compartments greatly differs not only between organisms but also between cells within the same organism. It is also expected that biological processes like replication, repair or telomere elongation impact the distribution of chromosome extremities within the nucleus, as they probably do with other regions of the genome. Pathological processes such as cancer induce profound changes in the nuclear architecture, which also affects telomere dynamics and spatial organization. Here we will expose our present knowledge on the relationship between telomeres and nuclear architecture and on how this relationship is affected by normal or abnormal telomere metabolisms.

Anthracyclines disrupt telomere maintenance by telomerase through inducing PinX1 ubiquitination and degradation

Telomere maintenance is essential for cancer growth. Induction of telomere dysfunction, for example, by inhibition of telomeric proteins or telomerase, has been shown to strongly enhance cancer cells' sensitivity to chemotherapies. However, it is not clear whether modulations of telomere maintenance constitute cancer cellular responses to chemotherapies. Furthermore, the manner in which anti-cancer drugs affect telomere function remains unknown. In this study, we show that anthracyclines, a class of anti-cancer drugs widely used in clinical cancer treatments, have an active role in triggering telomere dysfunction specifically in telomerase-positive cancer cells. Anthracyclines interrupt telomere maintenance by telomerase through the downregulation of PinX1, a protein factor responsible for targeting telomerase onto telomeres, thereby inhibiting telomerase association with telomeres. We further demonstrate that anthracyclines downregulate PinX1 by inducing this protein degradation through the ubiquitin-proteasome-dependent pathway. Our data not only reveal a novel action for anthracyclines as telomerase functional inhibitors but also provide a clue for the development of novel anti-cancer drugs based on telomerase/telomere targeting, which is actively investigated by many current studies.

Telomere length and cardiovascular disease

Telomeres are structures composed of deoxyribonucleic acid repeats that protect the end of chromosomes, but shorten with each cell division. They have been the subject of many studies, particularly in the field of oncology, and more recently their role in the onset, development and prognosis of cardiovascular disease has generated considerable interest. It has already been shown that these structures may deteriorate at the beginning of the atherosclerotic process, in the onset and development of arterial hypertension or during myocardial infarction, in which their length may be a predictor of outcome. As telomere length by its nature is a marker of cell senescence, it is of particular interest when studying the lifespan and fate of endothelial cells and cardiomyocytes, especially so because telomere length seems to be regulated by various factors notably certain cardiovascular risk factors, such as smoking, sex and obesity that are associated with high levels of oxidative stress. To gain insights into the links between telomere length and cardiovascular disease, and to assess the usefulness of telomere length as a new marker of cardiovascular risk, it seems essential to review the considerable amount of data published recently on the subject.

Epigenetic regulation of telomere chromatin integrity in pluripotent embryonic stem cells

Telomeres are protective chromosomal structures highly conserved from primitive organisms to humans. The evolutionary conservation of telomere DNA implicates the importance of telomeric structure for basic cellular functions. Loss of telomere function causes chromosomal fusion, activation of DNA damage checkpoint responses, genome instability and impaired stem cell function. In human cells, the telomeric chromatin consists of TTAGGG repeats associated with a complex of proteins known as Shelterin. It is also organized in nucleosomes enriched with epigenetic modifications of ‘closed’ or ‘silenced’ chromatin states, including DNA hypermethylation and trimethylation of H3K9 and H4K20. These heterochromatin marks serve as a higher-order level of control of telomere length and structural integrity. Recent studies have shown that the telomere nucleosome in pluripotent embryonic stem cells is characterized by a more ‘open’ chromatin state that switches to become more repressive during differentiation. Conversely, the reprogramming of adult somatic cells into induced pluripotent cells results in the switch in telomeric chromatin from a repressive to a more open embryonic stem cell-like state, coupled with the restoration of telomere length. These findings indicate that telomeric chromatin is dynamic and reprogrammable, and has a fundamental role in the maintenance of embryonic stem cell pluripotency.

Tobacco GTBP1, a homolog of human heterogeneous nuclear ribonucleoprotein, protects telomeres from aberrant homologous recombination

Telomeres are nucleoprotein complexes essential for the integrity of eukaryotic chromosomes. Cellular roles of single-stranded telomeric DNA binding proteins have been extensively described in yeast and animals, but our knowledge about plant single-strand telomeric factors is rudimentary. Here, we investigated Nicotiana tabacum G-strand-specific single-stranded telomere binding proteins (GTBPs), homologs of a human heterogeneous nuclear ribonucleoprotein. GTBPs bound specifically to the plant single-stranded (TTTAGGG)(4) telomeric repeat element in vitro and were associated with telomeric sequences in tobacco BY-2 suspension cells. Transgenic plants (35S:RNAi-GTBP1), in which GTBP1 was suppressed, exhibited severe developmental anomalies. In addition, the chromosomes of 35S:RNAi-GTBP1 cells displayed elongated telomeres, frequent formation of extrachromosomal telomeric circles, and numerous abnormal anaphase bridges, indicating that GTBP1 knockdown tobacco plants experienced genome instability. GTBP1 inhibited strand invasion, an initial step in interchromosomal homologous recombination. We propose that GTBP1 plays a critical role in telomere structure and function by preventing aberrant interchromosomal telomeric homologous recombination in tobacco.

Downregulation of mitochondrial telomerase reverse transcriptase induced by H2O2 is Src kinase dependent

Telomerase with its catalytic subunit telomerase reverse transcriptase (TERT) prevents telomere erosion in the nucleus. In addition, telomerase has also telomere-independent functions in protection from apoptosis. Unexpectedly, TERT was found in the mitochondria. However, its regulation in this organelle is completely unknown. Here, we demonstrate that mitochondrial TERT is downregulated by exposure to H(2)O(2) in primary human endothelial cells. This depletion is dependent on the Src phosphorylation site within TERT, tyrosine 707. In accordance with this finding, we also detected Src in the mitochondria and demonstrated that Src is activated upon H(2)O(2) treatment. This regulation of mitochondrial TERT is reminiscent of the situation in the nucleus from where TERT is exported under conditions of oxidative stress in a Src kinase dependent manner. In addition, Akt1 was also found in the mitochondria and H(2)O(2) treatment led to reduced active Akt1 in these organelles, suggesting that similar regulatory mechanisms operate in mitochondria and the nucleus.

Influence of the growth factors PDGF-BB, TGF-beta1 and bFGF on the replicative aging of human articular chondrocytes during in vitro expansion

Decreasing replicative potential and dedifferentiation of articular chondrocytes during expansion in cell culture are essential limitations for tissue engineering and cell therapy approaches. Telomeres and telomerase play a key role in cell development, aging, and tumorigenesis. There is evidence that growth factors are involved in regulating telomerase activity. Therefore, the objective was to evaluate the effect of selected growth factors on telomere biology of serially passaged chondrocytes. Human articular chondrocytes were isolated from cartilage of three patients undergoing total knee arthroplasty. The chondrocytes were cultured in monolayer with the growth factors PDGF-BB, TGF-beta1, and bFGF. Telomere length was measured by telomere restriction fragment length assay, and telomerase activity was determined by quantifying the gene expression of its catalytic subunit hTERT by rtPCR. Chondrocytes cultured with PDGF-BB and TGF-beta1 showed a significantly higher proliferation rate than control cells. None of the growth factor cultures revealed an accelerated rate of telomere shortening. Telomerase was not expressed in significant amounts in any of the chondrocyte cultures. Growth factor treatment of chondrocyte cell cultures for cell therapy purposes can be regarded as safe in terms of telomere biology.

Chromatin and epigenetic regulation of the telomerase reverse transcriptase gene

Telomerase expression and telomere maintenance are critical for long-term cell proliferation and survival, and they play important roles in development, aging, and cancer. Cumulating evidence has indicated that regulation of the rate-limiting subunit of human telomerase reverse transcriptase gene (hTERT) is a complex process in normal cells and many cancer cells. In addition to a number of transcriptional activators and repressors, the chromatin environment and epigenetic status of the endogenous hTERT locus are also pivotal for its regulation in normal human somatic cells and in tumorigenesis.

Telomeres and telomerase in chronic myeloid leukaemia: impact for pathogenesis, disease progression and targeted therapy

Telomeres are specialized structures localized at the end of human chromosomes. Due to the end replication problem, each cell division results in a loss of telomeric repeats in normal somatic cells. In germ line and stem cells, the multicomponent enzyme telomerase maintains the length of telomere repeats. However, elevated telomerase activity has also been reported in the majority of solid tumours as well as in acute and chronic leukaemia. Chronic myeloid leukaemia (CML) serves as a model disease to study telomere biology in clonal myeloproliferative disorders. In CML, telomere shortening correlates with disease stage, duration of chronic phase (CP), prognosis measured by the Hasford risk score and the response to disease-modifying therapeutics such as the tyrosine kinase inhibitor Imatinib. In addition, telomerase activity (TA) is already increased in CP CML and further upregulated with disease progression to accelerated phase and blast crisis (BC). Furthermore, a correlation of TA with increased genetic instability as well as a shorter survival of the patients has been reported. Here, we review the current state of knowledge of the role of telomere and telomerase biology in CML and discuss the possible impact of novel treatment approaches.

Mitochondrial telomerase reverse transcriptase binds to and protects mitochondrial DNA and function from damage

OBJECTIVE

The enzyme telomerase and its catalytic subunit the telomerase reverse transcriptase (TERT) are important for maintenance of telomere length in the nucleus. Recent studies provided evidence for a mitochondrial localization of TERT. Therefore, we investigated the exact localization of TERT within the mitochondria and its function.

METHODS AND RESULTS

Here, we demonstrate that TERT is localized in the matrix of the mitochondria. TERT binds to mitochondrial DNA at the coding regions for ND1 and ND2. Binding of TERT to mitochondrial DNA protects against ethidium bromide-induced damage. TERT increases overall respiratory chain activity, which is most pronounced at complex I and dependent on the reverse transcriptase activity of the enzyme. Moreover, mitochondrial reactive oxygen species are increased after genetic ablation of TERT by shRNA. Mitochondrially targeted TERT and not wild-type TERT revealed the most prominent protective effect on H(2)O(2)-induced apoptosis. Lung fibroblasts from 6-month-old TERT(-/-) mice (F2 generation) showed increased sensitivity toward UVB radiation and heart mitochondria exhibited significantly reduced respiratory chain activity already under basal conditions, demonstrating the protective function of TERT in vivo.

CONCLUSIONS

Mitochondrial TERT exerts a novel protective function by binding to mitochondrial DNA, increasing respiratory chain activity and protecting against oxidative stress-induced damage.

Positive regulation of human telomerase reverse transcriptase gene expression and telomerase activity by DNA methylation in pancreatic cancer

AIM

We sought to determine the role of telomerase and its catalytic subunit hTERT in pancreatic cancer and evaluate the epigenetic regulation of hTERT by promoter methylation.

METHODS

Thirty paired samples of pancreatic ductal adenocarcinomas and adjacent normal tissue and 12 chronic pancreatitis samples were studied. Reverse transcriptase polymerase chain reaction, telomeric repeat amplification protocol assay, and methylation-specific polymerase chain reaction were performed to analyze hTERT expression, telomerase activity, and methylation status of gene promoters, respectively.

RESULT

hTERT and telomerase activity were upregulated in pancreatic cancer compared with paired normal tissues and samples of pancreatitis. hTERT expression correlated with telomerase activity (P \ .05) and in turn correlated positively with hTERT promoter methylation (P \ .001) and p16 promoter methylation. hTERT transcript expression and telomerase activity both conferred a worse outcome by univariate and multivariate analysis (P \ .05).

CONCLUSION

hTERT expression and telomerase activity are predictors of poor outcome in pancreatic cancer. hTERT gene expression is positively regulated by promoter methylation.

Trypanosoma brucei spliced leader RNA maturation by the cap 1 2'-O-ribose methyltransferase and SLA1 H/ACA snoRNA pseudouridine synthase complex

Kinetoplastid flagellates attach a 39-nucleotide spliced leader (SL) upstream of protein-coding regions in polycistronic RNA precursors through trans splicing. SL modifications include cap 2'-O-ribose methylation of the first four nucleotides and pseudouridine (psi) formation at uracil 28. In Trypanosoma brucei, TbMTr1 performs 2'-O-ribose methylation of the first transcribed nucleotide, or cap 1. We report the characterization of an SL RNA processing complex with TbMTr1 and the SLA1 H/ACA small nucleolar ribonucleoprotein (snoRNP) particle that guides SL psi(28) formation. TbMTr1 is in a high-molecular-weight complex containing the four conserved core proteins of H/ACA snoRNPs, a kinetoplastid-specific protein designated methyltransferase-associated protein (TbMTAP), and the SLA1 snoRNA. TbMTAP-null lines are viable but have decreased SL RNA processing efficiency in cap methylation, 3'-end maturation, and psi(28) formation. TbMTAP is required for association between TbMTr1 and the SLA1 snoRNP but does not affect U1 small nuclear RNA methylation. A complex methylation profile in the mRNA population of TbMTAP-null lines indicates an additional effect on cap 4 methylations. The TbMTr1 complex specializes the SLA1 H/ACA snoRNP for efficient processing of multiple modifications on the SL RNA substrate.