Coevolution of Non-Homologous End Joining efficiency and encephalization

Double strand breaks, the most difficult to repair DNA damage, are mainly repaired by Non-Homologous End-Joining (NHEJ) or Homologous Recombination (HR). Previous studies seem to indicate that primates, and particularly humans, have a better NHEJ system. A distinctive feature of the primate lineage (beside longevity) is encephalization, i.e. the expansion of brain relative to body mass. Using existing transcriptome data from 34 mammalian species, we investigated the possible correlations between the expression of genes involved in NHEJ and encephalization, body mass and longevity. The same was done also for genes involved in the HR pathway. We found that, while HR gene expression is better correlated with longevity, NHEJ gene expression is strongly (and better) correlated with encephalization. Since the brain is composed of post-mitotic cells, double-strand breaks repair should be mainly performed by NHEJ in this organ. Therefore, we interpret the correlation we found as an indication that NHEJ efficiency coevolved with encephalization.

Effects of p53 and ATRX inhibition on telomeric recombination in aging fibroblasts

In order to avoid replicative senescence, tumor cells must acquire a telomere maintenance mechanism. Beside telomerase activation, a minority of tumors employs a recombinational mechanism called Alternative Lengthening of Telomeres (ALT). Several studies have investigated the potential ALT stimulation by inactivation of ATRX in tumor cells, obtaining contrasting results. Differently, since ALT can be viewed as a mechanism to overcome telomere shortening-mediated replicative senescence, we have investigated the effects of the inhibition of ATRX and p53 in aging primary fibroblasts. We observed that senescence leads to a phenotype that seems permissive for ALT activity, i.e. high levels of ALT-associated PML bodies (APB), telomeric damage and telomeric cohesion. On the other hand, RAD51 is highly repressed and thus telomeric recombination, upon which the ALT machinery relies, is almost absent. Silencing of ATRX greatly increases telomeric recombination in young cells, but is not able to overcome senescence-induced repression of homologous recombination. Conversely, inhibition of both p53 and ATRX leads to a phenotype reminiscent of some aspects of ALT activity, with a further increase of APB, a decrease of telomere shortening (and increased proliferation) and, above all, an increase of telomeric recombination.

X-ray and DNA Damage: Limitations of the Dose as a Parameter for In Vitro Studies

A century of studies has demonstrated that the magnitude of a radiation dose determines the extent of its biological effect. However, different types of radiation show different levels of effectiveness. Although all types of X-rays are usually considered to be equivalent, several authors have demonstrated an inverse relationship between photon energy and the biological effectiveness of the X-ray. Nonetheless, the differences among 50-100 keV X-rays are usually considered absent. However, comparing different types of X-rays with different energies is not easy since they are often used with different dose rates, and the latter can be a confounding factor. We compared the biological effectiveness of X-rays with different photon energies but with the same dose rate. Moreover, we also studied X-ray with different dose rates but the same photon energy. Biological effectiveness was assessed measuring DNA damage and cell survival. We confirmed that both the dose rate and photon energy influence the effectiveness of an X-ray. Moreover, we observed that differences in the 50-100 keV range are detectable after controlling for dose-rate variations. Our results, confirming those of previous studies in a more consistent way (and accompanied by hypotheses on the importance of the number of incident photons), underline the limitations of using the dose as the sole parameter for in vitro studies.

Drug repositioning strategy for the identification of novel telomere-damaging agents: A role for NAMPT inhibitors

Drug repositioning strategy represents a valid tool to accelerate the pharmacological development through the identification of new applications for already existing compounds. In this view, we aimed at discovering molecules able to trigger telomere-localized DNA damage and tumor cell death. By applying an automated high-content spinning-disk microscopy, we performed a screening aimed at identifying, on a library of 527 drugs, molecules able to negatively affect the expression of TRF2, a key protein in telomere maintenance. FK866, resulting from the screening as the best candidate hit, was then validated at biochemical and molecular levels and the mechanism underlying its activity in telomere deprotection was elucidated both in vitro and in vivo. The results of this study allow us to discover a novel role of FK866 in promoting, through the production of reactive oxygen species, telomere loss and deprotection, two events leading to an accumulation of DNA damage and tumor cell death. The ability of FK866 to induce telomere damage and apoptosis was also demonstrated in advanced preclinical models evidencing the antitumoral activity of FK866 in triple-negative breast cancer-a particularly aggressive breast cancer subtype still orphan of targeted therapies and characterized by high expression levels of both NAMPT and TRF2. Overall, our findings pave the way to the development of novel anticancer strategies to counteract triple-negative breast cancer, based on the use of telomere deprotecting agents, including NAMPT inhibitors, that would rapidly progress from bench to bedside.

Inhibition of p53 and ATRX increases telomeric recombination in primary fibroblasts

Telomere length can be maintained either by the telomerase enzyme or by alternative lengthening of telomeres (ALT), which is based on telomeric recombination. However, both mechanisms are inactive in most human somatic cells. ATRX has been previously identified as an ALT repressor gene. Nonetheless, TP53 is also deficient in most ALT cell lines, and previous works showed that it is an inhibitor of homologous recombination (HR). Despite this, the role of p53 as an ALT repressor has not been previously examined. Therefore, we investigated the effects of p53 and ATRX inhibition on normal human fibroblasts (devoid of any mutation), in the presence or absence of X-ray-induced telomeric damage. Performing immunofluorescence with antibodies for RAD51, H2AX, and TRF1 (for studying HR-mediated DNA damage repair) and CO-FISH (for telomeric sister chromatid exchanges), we observed that HR is a normal mechanism for the repair of telomeric damage, present also in noncancer cells. Moreover, we discovered that telomeric HR, as for HR in general, is significantly inhibited by p53. Indeed, we observed that inhibition of p53 drastically increases telomeric sister chromatid exchanges. We also confirmed that ATRX inhibition increases telomeric recombination. In particular, we observed an increase in crossover products, but a much higher increase in noncrossover products.

PARP1 allows proper telomere replication through TRF1 poly (ADP-ribosyl)ation and helicase recruitment

Telomeres are nucleoprotein structures at eukaryotic chromosome termini. Their stability is preserved by a six-protein complex named shelterin. Among these, TRF1 binds telomere duplex and assists DNA replication with mechanisms only partly clarified. Here we found that poly (ADP-ribose) polymerase 1 (PARP1) interacts and covalently PARylates TRF1 in S-phase modifying its DNA affinity. Therefore, genetic and pharmacological inhibition of PARP1 impairs the dynamic association of TRF1 and the bromodeoxyuridine incorporation at replicating telomeres. Inhibition of PARP1 also affects the recruitment of WRN and BLM helicases in TRF1 containing complexes during S-phase, triggering replication-dependent DNA-damage and telomere fragility. This work unveils an unprecedented role for PARP1 as a "surveillant" of telomere replication, which orchestrates protein dynamics at proceeding replication fork.

TERT Extra-Telomeric Roles: Antioxidant Activity and Mitochondrial Protection

Telomerase reverse transcriptase (TERT) is the catalytic subunit of telomerase holoenzyme, which adds telomeric DNA repeats on chromosome ends to counteract telomere shortening. In addition, there is evidence of TERT non-canonical functions, among which is an antioxidant role. In order to better investigate this role, we tested the response to X-rays and H₂O₂ treatment in hTERT-overexpressing human fibroblasts (HF-TERT). We observed in HF-TERT a reduced induction of reactive oxygen species and an increased expression of the proteins involved in the antioxidant defense. Therefore, we also tested a possible role of TERT inside mitochondria. We confirmed TERT mitochondrial localization, which increases after oxidative stress (OS) induced by H₂O₂ treatment. We next evaluated some mitochondrial markers. The basal mitochondria quantity appeared reduced in HF-TERT compared to normal fibroblasts and an additional reduction was observed after OS; nevertheless, the mitochondrial membrane potential and morphology were better conserved in HF-TERT. Our results suggest a protective function of TERT against OS, also preserving mitochondrial functionality.

Many Functions of Telomerase Components: Certainties, Doubts, and Inconsistencies

A growing number of studies have evidenced non-telomeric functions of "telomerase". Almost all of them, however, investigated the non-canonical effects of the catalytic subunit TERT, and not the telomerase ribonucleoprotein holoenzyme. These functions mainly comprise signal transduction, gene regulation and the increase of anti-oxidative systems. Although less studied, TERC (the RNA component of telomerase) has also been shown to be involved in gene regulation, as well as other functions. All this has led to the publication of many reviews on the subject, which, however, are often disseminating personal interpretations of experimental studies of other researchers as original proofs. Indeed, while some functions such as gene regulation seem ascertained, especially because mechanistic findings have been provided, other ones remain dubious and/or are contradicted by other direct or indirect evidence (e.g., telomerase activity at double-strand break site, RNA polymerase activity of TERT, translation of TERC, mitochondrion-processed TERC). In a critical study of the primary evidence so far obtained, we show those functions for which there is consensus, those showing contradictory results and those needing confirmation. The resulting picture, together with some usually neglected aspects, seems to indicate a link between TERT and TERC functions and cellular stemness and gives possible directions for future research.

Analysis of short term and stable DNA damage in patients with differentiated thyroid cancer treated with 131I in hypothyroidism or with rhTSH for remnant ablation

It is well known that ionizing radiations can induce genetic damage and that oxidative stress is a major factor inducing it. Our aim was to investigate whether thyroid remnant ablation with low activities of ¹³¹I (1850 MBq), is associated with DNA damage by evaluating Comet assay, micronuclei and chromosome aberrations with multicolor fluorescent in situ hybridization (M-FISH). Methods: we studied 62 patients prepared with rhTSH or by thyroid hormone withdrawal (THW). In both groups we analyzed stable and unstable genetic alterations before ¹³¹I therapy and 1 week and 3 months after ¹³¹I administration. We also correlated the genetic damage with several variables, including the degree of radiation-induced oxidative stress, genetic polymorphisms of enzymes involved in DNA-repair and anti-oxidative stress. Results: we found comparable amount of DNA breaks evaluated by Comet assay and micronuclei test in both groups of patients at different time points, but a significant increase of stable chromosome aberrations evaluated by M-FISH (breaks and translocations) in patients prepared with THW. Overall, high chromosome damage was associated with higher retained body radioactivity and unfavorable gene polymorphism. A high level of free oxygen radicals and a low level of anti-oxidants was found in all patients at any time point. In particular, patients prepared with THW, at 3 months, had significantly higher levels of free oxygen radicals than those prepared with rhTSH. Conclusion: an increase of stable chromosome aberrations respect to baseline is detectable after administration of low doses of ¹³¹I in patients prepared with THW but not in patients prepared with rhTSH. The clinical significance of these chromosomal alterations remains to be determined.

An integrated approach for chemical water quality assessment of an urban river stretch through Effect-Based Methods and emerging pollutants analysis with a focus on genotoxicity

The impact of emerging chemical pollutants, on both status and functionality of aquatic ecosystems is worldwide recognized as a relevant issue of concern that should be assessed and managed by researchers, policymakers, and all relevant stakeholders. In Europe, the Reach Regulation has registered more than 100.000 chemical substances daily released in the environment. Furthermore, the effects related to the mixture of substances present in aquatic ecosystems may not be predictable on the basis of chemical analyses alone. This evidence, coupled with the dramatic effects of climate changes on water resources through water scarcity and flooding, makes urgent the application of innovative, fast and reliable monitoring methods. In this context, Effect-Based Methods (EBMs) have been applied in the urban stretch of the Tiber River (Central Italy) with the aim of understanding if detrimental pressures affect aquatic environmental health. In particular, different eco-genotoxicological assays have been used in order to detect genotoxic activity of chemicals present in the river, concurrently characterized by chemical analysis. Teratogenicity and embryo-toxicity have been studied in order to cover additional endpoints. The EBMs have highlighted the presence of diffuse chemical pollution and ecotoxicological effects in the three sampling stations, genotoxicological effects have been also detected through the use of different tests and organisms. The chemical analyses confirmed that in the aquatic ecosystems there is a diffuse presence, even at low concentrations, of emerging contaminants such as pharmaceuticals, not routinely monitored pesticides, personal care products, PFAS. The results of this study can help to identify an appropriate battery of EBMs for future studies and the application of more appropriate measures in order to monitor, mitigate or eliminate chemical contamination and remediate its adverse/detrimental effects on the ecosystem health.

How direct measurements of worker eyes with a Scheimpflug camera can affect lensdose coefficients in interventional radiology

The 2013/59/Euratom Directive reduced the occupational exposure limits for the lens. Since it has become crucial to estimate the dose absorbed by the lens, we have studied the individual variability of exposed workers' ocular conformations with respect to the data estimated from their personal dosimetry. The anterior eye conformations of 45 exposed workers were acquired using Scheimpflug imaging and classified according to their sight conditions (emmetropia, myopia or hypermetropia). Three eye models were computed, with two lens reconstructions, and implemented in an interventional radiology scenario using Monte Carlo code. The models were dosimetrically analysed by simulating setup A, a theoretical monoenergetic and isotropic photon source (10-150 keV) and setup B, a more realistic interventional setting with an angiographic x-ray unit (50, 75, 100 kV peak). Scheimpflug imaging provided an average anterior chamber depth of (6.4 ± 0.5) mm and a lens depth of (3.9 ± 0.3) mm, together with a reconstructed equatorial lens length of (7.1-10.1) mm. Using these data for model reconstruction, dose coefficients (DCs) were simulated for all ocular structures. Regardless of the eye model used, the DCs showed a similar trend with radiation energy, which highlighted that for the same energy and setup, no significant dependence on ocular morphology and workers' visual conditions was observed. The maximum difference obtained did not exceed 1% for all eye models or structures analysed. Therefore, the individual variabilities of worker ocular anatomy do not require any additional correction, compared to the personal dosimetry data measured with a dedicated lens dosimeter. To estimate the dose absorbed by the other eye structures, it is, instead, essential to know the spectrum of the source that has generated the irradiation, since there are differences between monoenergetic sources and more realistic angiographic units.

Growing and aging of hematopoietic stem cells

In the hematopoietic system, a small number of stem cells produce a progeny of several distinct lineages. During ontogeny, they arise in the aorta-gonad-mesonephros region of the embryo and the placenta, afterwards colonise the liver and finally the bone marrow. After this fetal phase of rapid expansion, the number of hematopoietic stem cells continues to grow, in order to sustain the increasing blood volume of the developing newborn, and eventually reaches a steady-state. The kinetics of this growth are mirrored by the rates of telomere shortening in leukocytes. During adulthood, hematopoietic stem cells undergo a very small number of cell divisions. Nonetheless, they are subjected to aging, eventually reducing their potential to produce differentiated progeny. The causal relationships between telomere shortening, DNA damage, epigenetic changes, and aging have still to be elucidated.

Functional analysis of POLD1 p.ser605del variant: the aging phenotype of MDPL syndrome is associated with an impaired DNA repair capacity

Mandibular hypoplasia, Deafness and Progeroid features with concomitant Lipodystrophy define a rare systemic disorder, named MDPL Syndrome, due to almost always a de novo variant in POLD1 gene, encoding the DNA polymerase δ. We report a MDPL female heterozygote for the recurrent p.Ser605del variant. In order to deepen the functional role of the in frame deletion affecting the polymerase catalytic site of the protein, cellular phenotype has been characterised. MDPL fibroblasts exhibit in vitro nuclear envelope anomalies, accumulation of prelamin A and presence of micronuclei. A decline of cell growth, cellular senescence and a blockage of proliferation in G0/G1 phase complete the aged cellular picture. The evaluation of the genomic instability reveals a delayed recovery from DNA induced-damage. Moreover, the rate of telomere shortening was greater in pathological cells, suggesting the telomere dysfunction as an emerging key feature in MDPL. Our results suggest an alteration in DNA replication/repair function of POLD1 as a primary pathogenetic cause of MDPL. The understanding of the mechanisms linking these cellular characteristics to the accelerated aging and to the wide spectrum of affected tissues and clinical symptoms in the MDPL patients may provide opportunities to develop therapeutic treatments for progeroid syndromes.

DNA damage in lens epithelial cells exposed to occupationally-relevant X-ray doses and role in cataract formation

The current framework of radiological protection of occupational exposed medical workers reduced the eye-lens equivalent dose limit from 150 to 20 mSv per year requiring an accurate dosimetric evaluation and an increase understanding of radiation induced effects on Lens cells considering the typical scenario of occupational exposed medical operators. Indeed, it is widely accepted that genomic damage of Lens epithelial cells (LEC) is a key mechanism of cataractogenesis. However, the relationship between apoptosis and cataractogenesis is still controversial. In this study biological and physical data are combined to improve the understanding of radiation induced effects on LEC. To characterize the occupational exposure of medical workers during angiographic procedures an INNOVA 4100 (General Electric Healthcare) equipment was used (scenario A). Additional experiments were conducted using a research tube (scenario B). For both scenarios, the frequencies of binucleated cells, micronuclei, p21-positive cells were assessed with different doses and dose rates. A Monte-Carlo study was conducted using a model for the photon generation with the X-ray tubes and with the Petri dishes considering the two different scenarios (A and B) to reproduce the experimental conditions and validate the irradiation setups to the cells. The simulation results have been tallied using the Monte Carlo code MCNP6. The spectral characteristics of the different X-ray beams have been estimated. All irradiated samples showed frequencies of micronuclei and p21-positive cells higher than the unirradiated controls. Differences in frequencies increased with the delivered dose measured with Gafchromic films XR-RV3. The spectrum incident on eye lens and Petri, as estimated with MCNP6, was in good agreement in the scenario A (confirming the experimental setup), while the mean energy spectrum was higher in the scenario B. Nevertheless, the response of LEC seemed mainly related to the measured absorbed dose. No effects on viability were detected. Our results support the hypothesis that apoptosis is not responsible for cataract induced by low doses of X-ray (i.e. 25 mGy) while the induction of transient p21 may interfere with the disassembly of the nuclear envelop in differentiating LEC, leading to cataract formation. Further studies are needed to better clarify the relationship we suggested between DNA damage, transient p21 induction and the inability of LEC enucleation.

Human Fibroblasts In Vitro Exposed to 2.45 GHz Continuous and Pulsed Wave Signals: Evaluation of Biological Effects with a Multimethodological Approach

The increasing exposure to radiofrequency electromagnetic fields (RF-EMF), especially from wireless communication devices, raises questions about their possible adverse health effects. So far, several in vitro studies evaluating RF-EMF genotoxic and cytotoxic non-thermal effects have reported contradictory results that could be mainly due to inadequate experimental design and lack of well-characterized exposure systems and conditions. Moreover, a topic poorly investigated is related to signal modulation induced by electromagnetic fields. The aim of this study was to perform an analysis of the potential non-thermal biological effects induced by 2.45 GHz exposures through a characterized exposure system and a multimethodological approach. Human fibroblasts were exposed to continuous (CW) and pulsed (PW) signals for 2 h in a wire patch cell-based exposure system at the specific absorption rate (SAR) of 0.7 W/kg. The evaluation of the potential biological effects was carried out through a multimethodological approach, including classical biological markers (genotoxic, cell cycle, and ultrastructural) and the evaluation of gene expression profile through the powerful high-throughput next generation sequencing (NGS) RNA sequencing (RNA-seq) approach. Our results suggest that 2.45 GHz radiofrequency fields did not induce significant biological effects at a cellular or molecular level for the evaluated exposure parameters and conditions.

G-quadruplex Stabilization Fuels the ALT Pathway in ALT-positive Osteosarcoma Cells

Most human tumors maintain telomere lengths by telomerase, whereas a portion of them (10–15%) uses a mechanism named alternative lengthening of telomeres (ALT). The telomeric G-quadruplex (G4) ligand RHPS4 is known for its potent antiproliferative effect, as shown in telomerase-positive cancer models. Moreover, RHPS4 is also able to reduce cell proliferation in ALT cells, although the influence of G4 stabilization on the ALT mechanism has so far been poorly investigated. Here we show that sensitivity to RHPS4 is comparable in ALT-positive (U2OS; SAOS-2) and telomerase-positive (HOS) osteosarcoma cell lines, unlinking the telomere maintenance mechanism and RHPS4 responsiveness. To investigate the impact of G4 stabilization on ALT, the cardinal ALT hallmarks were analyzed. A significant induction of telomeric doublets, telomeric clusterized DNA damage, ALT-associated Promyelocytic Leukaemia-bodies (APBs), telomere sister chromatid exchanges (T-SCE) and c-circles was found exclusively in RHPS4-treated ALT cells. We surmise that RHPS4 affects ALT mechanisms through the induction of replicative stress that in turn is converted in DNA damage at telomeres, fueling recombination. In conclusion, our work indicates that RHPS4-induced telomeric DNA damage promotes overactivation of telomeric recombination in ALT cells, opening new questions on the therapeutic employment of G4 ligands in the treatment of ALT positive tumors.

Alternative Lengthening of Telomeres and Chromatin Status

Telomere length is maintained by either telomerase, a reverse transcriptase, or alternative lengthening of telomeres (ALT), a mechanism that utilizes homologous recombination (HR) proteins. Since access to DNA for HR enzymes is regulated by the chromatin status, it is expected that telomere elongation is linked to epigenetic modifications. The aim of this review is to elucidate the epigenetic features of ALT-positive cells. In order to do this, it is first necessary to understand the telomeric chromatin peculiarities. So far, the epigenetic nature of telomeres is still controversial: some authors describe them as heterochromatic, while for others, they are euchromatic. Similarly, ALT activity should be characterized by the loss (according to most researchers) or formation (as claimed by a minority) of heterochromatin in telomeres. Besides reviewing the main works in this field and the most recent findings, some hypotheses involving the role of telomere non-canonical sequences and the possible spatial heterogeneity of telomeres are given.

Quantitative relationships between acentric fragments and micronuclei: new models and implications for curve fitting

Purpose: To examine the phenomena governing the quantitative relationships between acentric fragments and micronuclei and understand which formulas are useful for curve-fitting of experimental data of micronuclei.Materials and methods: A stochastic model, including the phenomena of inclusion, coalescence and culling out, was developed and applied to experimental data.Results: Probabilities for inclusion/exclusion of acentric fragments into daughter nuclei and for coalescence of many fragments into a single micronucleus were found to be not cell type-specific. The biological basis for this result is explained with the lack of DNA damage checkpoints between metaphase (when acentric fragments are scored) and telophase (when micronuclei are formed). The phenomenon of "culling out" cells with high numbers of acentric fragments is also described, along with its proposed biological mechanism.Conclusions: Apart from complex formulas that describe these phenomena, we discuss which simple formulas can best approximate them and when is the case to use them for curve fitting of micronuclei data.

Epigallocatechin-3-gallate induces telomere shortening and clastogenic damage in glioblastoma cells

Epigallocatechingallate (EGCG) is the major polyphenol in green tea, to which many anticancer features, such as antioxidative, antigenotoxic, and antiangiogenetic properties, are attributed. Moreover, it is also well known as a telomerase inhibitor. In this work, we have chronically treated U251 glioblastoma cells with low, physiologically realistic concentrations, of EGCG, in order to investigate its effects both on telomeres and on genome integrity. Inhibition of telomerase activity caused telomere shortening, ultimately leading to senescence and telomere dysfunction at 98 days. Remarkably, we have observed DNA damage through an increase of phosphorylation of γ-H2AX histone and micronuclei also with doses and at timepoints when telomere shortening was not present. Therefore, we concluded that this DNA damage was not correlated with telomere shortening and that EGCG treatment induced not only an increase of telomere-shortening-induced senescence but also telomere-independent genotoxicity. This study questions the common knowledge about EGCG properties, but confirms the few works that indicated the clastogenic properties of this molecule, probably due to DNA reductive damage and topoisomerase II poisoning. Environ. Mol. Mutagen., 60:683-692, 2019. © 2019 Wiley Periodicals, Inc.

Establishment and characterization of induced pluripotent stem cells (iPSCs) from central nervous system lupus erythematosus

Involvement of the central nervous system (CNS) is an uncommon feature in systemic lupus erythematosus (SLE), making diagnosis rather difficult and challenging due to the poor specificity of neuropathic symptoms and neurological symptoms. In this work, we used human‐induced pluripotent stem cells (hiPSCs) derived from CNS‐SLE patient, with the aim to dissect the molecular insights underlying the disease by gene expression analysis and modulation of implicated pathways. CNS‐SLE‐derived hiPSCs allowed us to provide evidence of Erk and Akt pathways involvement and to identify a novel cohort of potential biomarkers, namely CHCHD2, IDO1, S100A10, EPHA4 and LEFTY1, never reported so far. We further extended the study analysing a panel of oxidative stress‐related miRNAs and demonstrated, under normal or stress conditions, a strong dysregulation of several miRNAs in CNS‐SLE‐derived compared to control hiPSCs. In conclusion, we provide evidence that iPSCs reprogrammed from CNS‐SLE patient are a powerful useful tool to investigate the molecular mechanisms underlying the disease and to eventually develop innovative therapeutic approaches.

Aberrant Function of the C-Terminal Tail of HIST1H1E Accelerates Cellular Senescence and Causes Premature Aging

Histones mediate dynamic packaging of nuclear DNA in chromatin, a process that is precisely controlled to guarantee efficient compaction of the genome and proper chromosomal segregation during cell division and to accomplish DNA replication, transcription, and repair. Due to the important structural and regulatory roles played by histones, it is not surprising that histone functional dysregulation or aberrant levels of histones can have severe consequences for multiple cellular processes and ultimately might affect development or contribute to cell transformation. Recently, germline frameshift mutations involving the C-terminal tail of HIST1H1E, which is a widely expressed member of the linker histone family and facilitates higher-order chromatin folding, have been causally linked to an as-yet poorly defined syndrome that includes intellectual disability. We report that these mutations result in stable proteins that reside in the nucleus, bind to chromatin, disrupt proper compaction of DNA, and are associated with a specific methylation pattern. Cells expressing these mutant proteins have a dramatically reduced proliferation rate and competence, hardly enter into the S phase, and undergo accelerated senescence. Remarkably, clinical assessment of a relatively large cohort of subjects sharing these mutations revealed a premature aging phenotype as a previously unrecognized feature of the disorder. Our findings identify a direct link between aberrant chromatin remodeling, cellular senescence, and accelerated aging.

In vitro effects of 1-MHz ultrasound on the mitotic spindle

The effects of ultrasound on the cytoskeleton, comprising microtubules, had been studied decades ago. Nonetheless, very little attention has been paid to the effects of ultrasound on the mitotic spindle, which is also formed by microtubules. In this study, we treated human fibroblasts and human cancer cells (HeLa and MCF-7) with 1-MHz ultrasound at low intensities (70, 140, and 300 mW/cm² ). In all cell lines, 5 min after the end of sonication, we found an intensity-dependent increase of mitotic abnormalities (including multipolar spindles). Two hours after sonication, these abnormalities were present, but at much lower frequencies. Twenty-four hours after sonication, mitotic abnormalities were at the same level of untreated samples, suggesting a transient effect due to ultrasound. Beside abnormalities of the mitotic spindle, we also observed an increase of metaphases with nonaligned chromosomes. The mitotic index of fibroblasts and HeLa cells, two hours after sonication, showed an intensity-dependent decrease; this was not observed in MCF-7 cells. In agreement with this last result, ultrasound-induced growth inhibition (which was also intensity-dependent) was more marked in fibroblasts and HeLa cells compared to MCF-7 cells. This work indicates that therapeutic ultrasound, even at intensities below the cavitation threshold, can affect genome integrity, showing the need to increase the knowledge of the potential risks of ultrasound to human health. Environ. Mol. Mutagen. 2019. © 2019 Wiley Periodicals, Inc.

Rates of erythropoiesis in mammals and their relationship with lifespan and hematopoietic stem cells aging

Investigations on possible links between hematological parameters and longevity are nearly absent. We tested the hypothesis that a fast rate of erythropoiesis, causing an earlier aging of the hematopoietic stem cells pool, contributes to a shorter lifespan. With this aim, we employed a new quantity, daily produced red blood cells per gram of body mass, as a measure of mass-specific rate of erythropoiesis. We found that among mammals rate of erythropoiesis and maximum lifespan are significantly correlated, independently from mass residuals. This seems to be confirmed also by intra-species comparisons and, although with limited data, by the significant correlation of rate of erythropoiesis and rate of telomere shortening in leukocytes (a proxy for hematopoietic stem cell telomere shortening). In our view, this may give a link of causality between rate of erythropoiesis and maximum lifespan. Further studies could test a similar hypothesis also for other kinds of stem cells.

Oxidative Stress Induces Telomere Dysfunction and Senescence by Replication Fork Arrest

Oxidative DNA damage, particularly 8-oxoguanine, represents the most frequent DNA damage in human cells, especially at the telomeric level. The presence of oxidative lesions in the DNA can hinder the replication fork and is able to activate the DNA damage response. In this study, we wanted to understand the mechanisms by which oxidative damage causes telomere dysfunction and senescence in human primary fibroblasts. After acute oxidative stress at telomeres, our data demonstrated a reduction in TRF1 and TRF2, which are involved in proper telomere replication and T-loop formation, respectively. Furthermore, we observed a higher level of γH2AX with respect to 53BP1 at telomeres, suggesting a telomeric replication fork stall rather than double-strand breaks. To confirm this finding, we studied the replication of telomeres by Chromosome Orientation-FISH (CO-FISH). The data obtained show an increase in unreplicated telomeres after hydrogen peroxide treatment, corroborating the idea that the presence of 8-oxoG can induce replication fork arrest at telomeres. Lastly, we analyzed the H3K9me3 histone mark after oxidative stress at telomeres, and our results showed an increase of this marker, most likely inducing the heterochromatinization of telomeres. These results suggest that 8-oxoG is fundamental in oxidative stress-induced telomeric damage, principally causing replication fork arrest.

AGO2 promotes telomerase activity and interaction between the telomerase components TERT and TERC

Telomerase reverse transcriptase (TERT) and telomerase RNA component (TERC) constitute the core telomerase enzyme that maintains the length of telomeres. Telomere maintenance is affected in a broad range of cancer and degenerative disorders. Taking advantage of gain- and loss-of-function approaches, we show that Argonaute 2 (AGO2) promotes telomerase activity and stimulates the association between TERT and TERC AGO2 depletion results in shorter telomeres as well as in lower proliferation rates in vitro and in vivo We also demonstrate that AGO2 interacts with TERC and with a newly identified sRNA (terc-sRNA), arising from the H/ACA box of TERC Notably, terc-sRNA is sufficient to enhance telomerase activity when overexpressed. Analyses of sRNA-Seq datasets show that terc-sRNA is detected in primary human tissues and increases in tumors as compared to control tissues. Collectively, these data uncover a new layer of complexity in the regulation of telomerase activity by AGO2 and might lay the foundation for new therapeutic targets in tumors and telomere diseases.

Correction to: Structural modeling of a novel TERC variant in a patient with aplastic anemia and short telomeres

The original version of this article contained a mistake in the affiliation of E. Bellacchio. Correct affiliation is presented here.

Naphthalene diimide-derivatives G-quadruplex ligands induce cell proliferation inhibition, mild telomeric dysfunction and cell cycle perturbation in U251MG glioma cells

In the present paper, the biological effects of three different naphthalene diimides (NDIs) G-quadruplex (G4) ligands (H-NDI-Tyr, H-NDI-NMe2, and tetra-NDI-NMe2) were comparatively evaluated to those exerted by RHPS4, a well-characterized telomeric G4-ligand, in an in vitro model of glioblastoma. Data indicated that NDIs were very effective in blocking cell proliferation at nanomolar concentrations, although displaying a lower specificity for telomere targeting compared to RHPS4. In addition, differently from RHPS4, NDIs failed to enhance the effect of ionizing radiation, thus suggesting that additional targets other than telomeres could be involved in the strong NDI-mediated anti-proliferative effects. In order to test telomeric off-target action of NDIs, a panel of genes involved in tumor progression, DNA repair, telomere maintenance, and cell-cycle regulation were evaluated at transcriptional and translational level. Specifically, the compounds were able to cause a marked reduction of TERT and BCL2 amounts as well as to favor the accumulation of proteins involved in cell cycle control. A detailed cytofluorimetric analysis of cell cycle progression by means of bromodeoxyuridine (BrdU) incorporation and staining of phospho-histone H3 indicated that NDIs greatly reduce the progression through S-phase and lead to G1 accumulation of BrdU-positive cells. Taken together, these data indicated that, besides effects on telomeres and oncogenes such as Tert and Bcl2, nanomolar concentrations of NDIs determined a sustained block of cell proliferation by slowing down cell cycle progression during S-phase. In conclusion, our data indicate that NDIs G4-ligands are powerful antiproliferative agents, which act through mechanisms that ultimately lead to altered cell-cycle control.

Genotoxic Effects in Human Fibroblasts Exposed to Microwave Radiation

In the last decades, technological development has led to an increasing use of devices and systems based on microwave radiation. The increased employment of these devices has elicited questions about the potential long-term health consequences associated with microwave radiation exposure. From this perspective, biological effects of microwave radiation have been the focus of many studies, but the reported scientific data are unclear and contradictory. The aim of this study is to evaluate the potential genotoxic and cellular effects associated with in vitro exposure of human fetal and adult fibroblasts to microwave radiation at the frequency of 25 GHz. For this purpose, several genetic and biological end points were evaluated. Results obtained from comet assay, phosphorylation of H2AX histone, and antikinetochore antibody (CREST)-negative micronuclei frequency excluded direct DNA damage to human fetal and adult fibroblasts exposed to microwaves. No induction of apoptosis or changes in prosurvival signalling proteins were detected. Moreover, CREST analysis showed for both the cell lines an increase in the total number of micronuclei and centromere positive micronuclei in exposed samples, indicating aneuploidy induction due to chromosome loss.

Study of the effects of 0.15 terahertz radiation on genome integrity of adult fibroblasts

The applications of Terahertz (THz) technologies have significantly developed in recent years, and the complete understanding of the biological effects of exposure to THz radiation is becoming increasingly important. In a previous study, we found that THz radiation induced genomic damage in fetal fibroblasts. Although these cells demonstrated to be a useful model, exposure of human foetuses to THz radiation is highly improbable. Conversely, THz irradiation of adult dermal tissues is cause of possible concern for some professional and nonprofessional categories. Therefore, we extended our study to the investigation of the effects of THz radiation on adult fibroblasts (HDF). In this work, the effects of THz exposure on HDF cells genome integrity, cell cycle, cytological ultrastructure and proteins expression were assessed. Results of centromere-negative micronuclei frequencies, phosphorylation of H2AX histone, and telomere length modulation indicated no induction of DNA damage. Concordantly, no changes in the expression of proteins associated with DNA damage sensing and repair were detected. Conversely, our results showed an increase of centromere-positive micronuclei frequencies and chromosomal nondisjunction events, indicating induction of aneuploidy. Therefore, our results indicate that THz radiation exposure may affect genome integrity through aneugenic effects, and not by DNA breakage. Our findings are compared to published studies, and possible biophysical mechanisms are discussed. Environ. Mol. Mutagen. 59:476-487, 2018. © 2018 Wiley Periodicals, Inc.

The G-quadruplex-stabilizing ligand RHPS4 enhances sensitivity of U251MG glioblastoma cells to clinical carbon ion beams

The pentacyclic acridine RHPS4 is a highly potent and specific G-quadruplex (G4) ligand, which binds and stabilizes telomeric G4 leading to the block of the replication forks at telomeres and consequently to telomere dysfunctionalization. In turn, the cell recognizes unprotected telomeres as DNA double-strand breaks with consequent activation of DNA repair response at telomeres, cellular growth impairment, and death. Data from the literature showed the capability of this compound to sensitize U251MG glioblastoma radioresistant cell line to X-rays sparsely ionizing radiations. In the present paper, it was investigated whether RHPS4 is also able to increase the effect of clinical carbon ion beams (cells irradiated in the middle of a spread-out Bragg peak, in the energy range of 246-312 MeV·μm^-1 and a dose-averaged linear energy transfer of 46 keV·μm^-1 ). Interestingly, also for charged particles whose damage inflicted to DNA is more complex than that of sparsely ionizing radiations and results in higher Relative Biological Effectiveness (RBE), RHPS4 significantly potentiated the radiation effect in terms of cell killing, delayed rejoining of DNA double-strand breaks (γ-H2AX and 53BBP1 immunofluorescence staining), chromosome aberrations (pan-centromeric/telomeric FISH and multicolor FISH), and G₂ /M-phase accumulation in GBM cells. Overall, the results provide the first evidence that the combined administration of the G4-ligand RHPS4 with charged particles interfere with cellular processes involved in cell survival leading to radiosensitization of highly radioresistant tumor cells.

Telomere Length Maintenance in Cancer: At the Crossroad between Telomerase and Alternative Lengthening of Telomeres (ALT)

Eukaryotic cells undergo continuous telomere shortening as a consequence of multiple rounds of replications. During tumorigenesis, cells have to acquire telomere DNA maintenance mechanisms (TMMs) in order to counteract telomere shortening, to preserve telomeres from DNA damage repair systems and to avoid telomere-mediated senescence and/or apoptosis. For this reason, telomere maintenance is an essential step in cancer progression. Most human tumors maintain their telomeres expressing telomerase, whereas a lower but significant proportion activates the alternative lengthening of telomeres (ALT) pathway. However, evidence about the coexistence of ALT and telomerase has been found both in vivo in the same cancer populations and in vitro in engineered cellular models, making the distinction between telomerase- and ALT-positive tumors elusive. Indeed, after the development of drugs able to target telomerase, the capability for some cancer cells to escape death, switching from telomerase to ALT, was highlighted. Unfortunately, to date, the mechanism underlying the possible switching or the coexistence of telomerase and ALT within the same cell or populations is not completely understood and different factors could be involved. In recent years, different studies have tried to shed light on the complex regulation network that controls the transition between the two TMMs, suggesting a role for embryonic cancer origin, epigenetic modifications, and specific genes activation—both in vivo and in vitro. In this review, we examine recent findings about the cancer-associated differential activation of the two known TMMs and the possible factors implicated in this process. Furthermore, some studies on cancers are also described that did not display any TMM.

Genomic damage induced by 1-MHz ultrasound in vitro

Genotoxic effects of therapeutic ultrasound are poorly documented, when compared with the wide use of this physical agent. The aim of this work was to investigate the clastogenic and aneugenic potential of 1 MHz ultrasound, employing intensities (200 and 300 mW/cm² ) above the cavitational threshold, but in the range of those normally used in therapeutics. Both normal fibroblasts (AG01522) and tumoral cells (MCF-7) were sonicated. While no effects on viability were noted, significant increases of CREST-negative micronuclei (indicative of clastogenesis) and CREST-positive micronuclei (indicative of aneuploidy) were detected. Clastogenesis was confirmed by increases of γ-H2AX foci, while increases of spindle anomalies confirmed the induction of aneuploidy. Our results confirm previous works that showed ultrasound-induced DNA breakage. Moreover, our experiments show that the known effect of ultrasound-induced damage to microtubules is also able to damage the mitotic spindle and induce aneuploidy. On the overall, this work highlights the importance to further investigate the potential risks related to therapeutics US. Environ. Mol. Mutagen. 59:60-68, 2018. © 2017 Wiley Periodicals, Inc.

Two sides of the same coin? Unraveling subtle differences between human embryonic and induced pluripotent stem cells by Raman spectroscopy

BACKGROUND

Human pluripotent stem cells, including embryonic stem cells and induced pluripotent stem cells, hold enormous promise for many biomedical applications, such as regenerative medicine, drug testing, and disease modeling. Although induced pluripotent stem cells resemble embryonic stem cells both morphologically and functionally, the extent to which these cell lines are truly equivalent, from a molecular point of view, remains controversial.

METHODS

Principal component analysis and K-means cluster analysis of collected Raman spectroscopy data were used for a comparative study of the biochemical fingerprint of human induced pluripotent stem cells and human embryonic stem cells. The Raman spectra analysis results were further validated by conventional biological assays.

RESULTS

Raman spectra analysis revealed that the major difference between human embryonic stem cells and induced pluripotent stem cells is due to the nucleic acid content, as shown by the strong positive peaks at 785, 1098, 1334, 1371, 1484, and 1575 cm^-1, which is enriched in human induced pluripotent stem cells.

CONCLUSIONS

Here, we report a nonbiological approach to discriminate human induced pluripotent stem cells from their native embryonic stem cell counterparts.

Synthetic lethal genetic interactions between Rad54 and PARP-1 in mouse development and oncogenesis

Mutations in DNA repair pathways are frequent in human cancers. Hence, gaining insights into the interaction of DNA repair genes is key to development of novel tumor-specific treatment strategies. In this study, we tested the functional relationship in development and oncogenesis between the homologous recombination (HR) factor Rad54 and Parp-1, a nuclear enzyme that plays a multifunctional role in DNA damage signaling and repair. We introduced single or combined Rad54 and Parp-1 inactivating germline mutations in Ptc1 heterozygous mice, a well-characterized model of medulloblastoma, the most common malignant pediatric brain tumor. Our study reveals that combined inactivation of Rad54 and Parp-1 causes a marked growth delay culminating in perinatallethality, providing for the first time evidence of synthetic lethal interactions between Rad54 and Parp-1 in vivo. Although the double mutation hampered investigation of Rad54 and Parp-1 interactions in cerebellum tumorigenesis, insights were gained by showing accumulation of endogenous DNA damage and increased apoptotic rate in granule cell precursors (GCPs). A network-based approach to detect differential expression of DNA repair genes in the cerebellum revealed perturbation of p53 signaling in Rad54-/-/Parp-1-/-/Ptc1+/-, and MEFs from combined Rad54/Parp-1 mutants showed p53/p21-dependent typical senescent features. These findings help elucidate the genetic interplay between Rad54 and Parp-1 by suggesting that p53/p21-mediated apoptosis and/or senescence may be involved in synthetic lethal interactions occurring during development and inhibition of tumor growth.

Regular exercise participation improves genomic stability in diabetic patients: an exploratory study to analyse telomere length and DNA damage

Physical activity has been demonstrated to be effective in the prevention and treatment of different chronic conditions, including type 2 diabetes (T2D). In particular, several studies highlighted how the beneficial effects of physical activity may be related to the stability of the DNA molecule, such as longer telomeric ends. Here we analyze the effect of exercise training on telomere length, spontaneous and H₂O₂-induced DNA damage, as well as the apoptosis level in leukocytes from untrained or trained T2D patients vs. age-matched control subjects (CS) (57–66 years). Moreover, expression analysis of selected genes belonging to DNA repair systems, cell cycle control, antioxidant and defence systems was performed. Subjects that participated in a regular exercise program showed a longer telomere sequence than untrained counterparts. Moreover, ex vivo treatment of leukocytes with H₂O₂ highlighted that: (1) oxidative DNA damage induced similar telomere attrition in all groups; (2) in T2D subjects, physical activity seemed to prevent a significant increase of genomic oxidative DNA damage induced by chronic exposure to pro-oxidant stimulus, and (3) decreased the sensitivity of leukocytes to apoptosis. Finally, the gene expression analysis in T2D subjects suggested an adaptive response to prolonged exercise training that improved the response of specific genes.

Transient ALT activation protects human primary cells from chromosome instability induced by low chronic oxidative stress

Cells are often subjected to the effect of reactive oxygen species (ROS) as a result of both intracellular metabolism and exposure to exogenous factors. ROS-dependent oxidative stress can induce 8-oxodG within the GGG triplet found in the G-rich human telomeric sequence (TTAGGG), making telomeres highly susceptible to ROS-induced oxidative damage. Telomeres are nucleoprotein complexes that protect the ends of linear chromosomes and their dysfunction is believed to affect a wide range of cellular and/or organismal processes. Acute oxidative stress was shown to affect telomere integrity, but how prolonged low level oxidative stress, which may be more physiologically relevant, affects telomeres is still poorly investigated. Here, we explored this issue by chronically exposing human primary fibroblasts to a low dose of hydrogen peroxide. We observed fluctuating changes in telomere length and fluctuations in the rates of chromosome instability phenotypes, such that when telomeres shortened, chromosome instability increased and when telomeres lengthened, chromosome instability decreased. We found that telomere length fluctuation is associated with transient activation of an alternative lengthening of telomere (ALT) pathway, but found no evidence of cell death, impaired proliferation, or cell cycle arrest, suggesting that ALT activation may prevent oxidative damage from reaching levels that threaten cell survival.

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

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

Long-term genotoxic effects in the hematopoietic system of prenatally X-irradiated mice

PURPOSE

To investigate the genotoxic effects of prenatal X-irradiation in mice and the possible presence of late genomic instability.

MATERIALS AND METHODS

Pregnant mice were exposed to 0, 1 or 2 Gy at embryonic day 11.5. Blood smears were obtained from pups at birth and on post-natal day 11, 21, 42 and 140. Hematological data (diameter of erythrocytes, percentage of reticulocytes and Granulocyte-to-Lymphocyte ratio [GLR]) and genotoxicity (micronucleated erythrocytes, micronucleated reticulocytes, CREST-positive and negative micronuclei) were assessed.

RESULTS

Prenatal irradiation caused perinatal reticulocytosis (which ended on postnatal day 11) and a dose-dependent increase of GLR (indicative of myeloid skewing) on postnatal days 42 and 140. Two temporally distinct genotoxic effects were observed: an early, acute damage (still detectable at birth and soon after) and a late, long-term damage.

CONCLUSIONS

Increases in micronuclei frequencies and GLR observed from day 42 on are both ascribable to DNA damage. Time of appearance of this late effect may be linked to the shift of hematopoiesis from spleen to bone marrow and to cell-extrinsic factor such as the microenvironment. This study confirms that ionizing radiation can induce long-term genotoxic effects in the hematopoietic system and shows that prenatal irradiation determines genomic instability in blood-forming tissues of adult mice.

Genotoxic sensitivity of the developing hematopoietic system

Genotoxic sensitivity seems to vary during ontogenetic development. Animal studies have shown that the spontaneous mutation rate is higher during pregnancy and infancy than in adulthood. Human and animal studies have found higher levels of DNA damage and mutations induced by mutagens in fetuses/newborns than in adults. This greater susceptibility could be due to reduced DNA repair capacity. In fact, several studies indicated that some DNA repair pathways seem to be deficient during ontogenesis. This has been demonstrated also in murine hematopoietic stem cells. Genotoxicity in the hematopoietic system has been widely studied for several reasons: it is easy to assess, deals with populations cycling also in the adults and may be relevant for leukemogenesis. Reviewing the literature concerning the application of the micronucleus test (a validated assay to assess genotoxicity) in fetus/newborns and adults, we found that the former show almost always higher values than the latter, both in animals treated with genotoxic substances and in those untreated. Therefore, we draw the conclusion that the genotoxic sensitivity of the hematopoietic system is more pronounced during fetal life and decreases during ontogenic development.

Genotoxicity Induced by Foetal and Infant Exposure to Magnetic Fields and Modulation of Ionising Radiation Effects

Background

Few studies have investigated the toxicity and genotoxicity of extremely low frequency magnetic fields (ELF-MF) during prenatal and neonatal development. These phases of life are characterized by cell proliferation and differentiation, which might make them sensitive to environmental stressors. Although in vitro evidences suggest that ELF-MF may modify the effects of ionizing radiation, no research has been conducted so far in vivo on the genotoxic effects of ELF-MF combined with X-rays.

Aim and methods

Aim of this study was to investigate in somatic and germ cells the effects of chronic ELF-MF exposure from mid gestation until weaning, and any possible modulation produced by ELF-MF exposure on ionizing radiation-induced damage. Mice were exposed to 50 Hz, 65 μT magnetic field, 24 hours/day, for a total of 30 days, starting from 12 days post-conception. Another group was irradiated with 1 Gy X-rays immediately before ELF-MF exposure, other groups were only X-irradiated or sham-exposed. Micronucleus test on blood erythrocytes was performed at multiple times from 1 to 140 days after birth. Additionally, 42 days after birth, genotoxic and cytotoxic effects on male germ cells were assessed by comet assay and flow cytometric analysis.

Results

ELF-MF exposure had no teratogenic effect and did not affect survival, growth and development. The micronucleus test indicated that ELF-MF induced a slight genotoxic damage only after the maximum exposure time and that this effect faded away in the months following the end of exposure. ELF-MF had no effects on ionizing radiation (IR)-induced genotoxicity in erythrocytes. Differently, ELF–MF appeared to modulate the response of male germ cells to X-rays with an impact on proliferation/differentiation processes. These results point to the importance of tissue specificity and development on the impact of ELF-MF on the early stages of life and indicate the need of further research on the molecular mechanisms underlying ELF-MF biological effects.

mFISH analysis of irradiated human fibroblasts: a comparison among radiations with different quality in the low-dose range

The present investigation aimed to characterise the shape of dose-response curve and determining the frequency distribution of various aberration types as a function of dose and radiation quality in AG01522 primary human fibroblasts in the 0.1- to 1-Gy dose range. For this purpose, the cells were irradiated with 7.7 and 28.5 keV µm(-1) low-energy protons, 62 keV µm(-1 4)He(2+) ions (LNL Radiobiology facility) or X rays and samples collected for 24-colour mFISH analysis. X rays and 7.7 keV µm(-1) protons displayed a quadratic dose-response curve solely for total and simple exchanges, whereas for high-linear energy transfer radiations, a linear dose-response curve was observed for all the aberration categories, with the exception of complex exchanges.

Micronucleus test on Triturus carnifex as a tool for environmental biomonitoring

The amphibian micronucleus test has been widely used during the last 30 years to test the genotoxic properties of several chemicals and as a tool for ecogenotoxic monitoring. The vast majority of these studies were performed on peripheral blood of urodelan larvae and anuran tadpoles and to a lesser extent adults were also used. In this study, we developed protocols for measuring micronuclei in adult shed skin cells and larval gill cells of the Italian crested newt (Triturus carnifex). Amphibians were collected from ponds in two protected areas in Italy that differed in their radon content. Twenty-three adult newts and 31 larvae were captured from the radon-rich pond, while 20 adults and 27 larvae were taken from the radon-free site. The animals were brought to the laboratory and the micronucleus test was performed on peripheral blood and shed skins taken from the adults and on larval gills. Samples from the radon-rich site showed micronucleus frequencies higher than those from the radon-free site and the difference was statistically significant in gill cells (P < 0.00001). Moreover, the larval gills seem to be more sensitive than the adult tissues. This method represents an easy (and noninvasive in the case of the shed skin) application of the micronucleus assay that can be useful for environmental studies in situ.

The G-quadruplex-stabilising agent RHPS4 induces telomeric dysfunction and enhances radiosensitivity in glioblastoma cells

G-quadruplex (G4) interacting agents are a class of ligands that can bind to and stabilise secondary structures located in genomic G-rich regions such as telomeres. Stabilisation of G4 leads to telomere architecture disruption with a consequent detrimental effect on cell proliferation, which makes these agents good candidates for chemotherapeutic purposes. RHPS4 is one of the most effective and well-studied G4 ligands with a very high specificity for telomeric G4. In this work, we tested the in vitro efficacy of RHPS4 in astrocytoma cell lines, and we evaluated whether RHPS4 can act as a radiosensitising agent by destabilising telomeres. In the first part of the study, the response to RHPS4 was investigated in four human astrocytoma cell lines (U251MG, U87MG, T67 and T70) and in two normal primary fibroblast strains (AG01522 and MRC5). Cell growth reduction, histone H2AX phosphorylation and telomere-induced dysfunctional foci (TIF) formation were markedly higher in astrocytoma cells than in normal fibroblasts, despite the absence of telomere shortening. In the second part of the study, the combined effect of submicromolar concentrations of RHPS4 and X-rays was assessed in the U251MG glioblastoma radioresistant cell line. Long-term growth curves, cell cycle analysis and cell survival experiments, clearly showed the synergistic effect of the combined treatment. Interestingly the effect was greater in cells bearing a higher number of dysfunctional telomeres. DNA double-strand breaks rejoining after irradiation revealed delayed repair kinetics in cells pre-treated with the drug and a synergistic increase in chromosome-type exchanges and telomeric fusions. These findings provide the first evidence that exposure to RHPS4 radiosensitizes astrocytoma cells, suggesting the potential for future therapeutic applications.