DNA damage and aging

Oxidative stress, inflammation and hormesis: The role of dietary and lifestyle modifications on aging

Oxidative stress (OS) is primarily caused by the formation of free radicals and reactive oxygen species; it is considered as one of the prominent factors in slowing down and degrading cellular machinery of an individual, and it eventually leads to aging and age-related diseases by its continuous higher state. The relation between molecular damage and OS should be particularized to understand the beginning of destruction at the cellular levels, extending outwards to affect tissues, organs, and ultimately to the organism. Several OS biomarkers, which are established at the biomolecular level, are useful in investigating the disease susceptibility during aging. Slowing down the aging process is a matter of reducing the rate of oxidative damage to the cellular machinery over time. The breakdown of homeostasis, the mild overcompensation, the reestablishment of homeostasis, and the adaptive nature of the process are the essential features of hormesis, which incorporates several factors, including calorie restriction, nutrition and lifestyle modifications that play an important role in reducing the OS. In the current review, along with the concept and theories of aging (with emphasis on free radical theory), various manifestations of OS with special attention on mitochondrial dysfunction and age-related diseases have been discussed. To alleviate the OS, hormetic approaches including caloric restriction, exercise, and nutrition have also been discussed.

EIF5A2 specifically regulates the transcription of aging-related genes in human neuroblastoma cells

BACKGROUND

Post-transcriptional regulation plays a critical role in controlling biological processes such as aging. Previous studies have shown that eukaryotic initiation factor 5A (EIF5A) might play a crucial role in aging. It is unknown whether EIF5A2, a second isoform of EIF5A, could impact aging through post-transcriptional regulation.

METHODS

In the present study, EIF5A2 overexpression (EIF5A2-OE) was induced in SH-SY5Y cells. RNA-seq, bioinformatics analysis and RT-qPCR validation experiments were then performed to explore the molecular mechanism of EIF5A2-mediated transcriptional regulation. Cell viability, proportion of senescent cells and the cell cycle were respectively determined by Cell Counting Kit-8, SA-β‑galactosidase and flow cytometry to evaluate the cell senescence.

RESULTS

A total of 190 downregulated and 126 upregulated genes related to EIF5A2-OE were identified. Genes closely related to cellular aging processes such as unfolded protein response (UPR), cell adhesion and calcium signaling pathway were under global transcriptional regulation. Moreover, EIF5A2-OE promoted the viability of SH-SY5Y cells and reduced cell senescence in vitro. Among 30 genes with the most significant expression differences in EIF5A2-OE cells, we identified eight genes, including ASNS, ATF3, ATF4, CEBPB, DDIT3, HERPUD1, HSPA5 and XBP1, enriched in the UPR. Through EIF5A2-tanscription factors (TFs)-targets regulation network in EIF5A2-OE cells, we found three TFs, BHLHE40, RHOXF1 and TBX20, that targeted at these eight UPR-related genes. Verification test via the published database of human glial cell tissue showed only BHLHE40 and RHOXF1 were significantly associated with EIF5A2.

CONCLUSIONS

Our findings suggest that EIF5A2 may alleviate cell senescence in vitro and mediate UPR-related genes via specific TFs. Thus, EIF5A2 could function as a regulator of aging via the regulation of transcription, which greatly expands the current understanding of the mechanisms of EIF5A2-mediated gene regulation.

Pathological Nuclear Hallmarks in Dentate Granule Cells of Alzheimer’s Patients: A Biphasic Regulation of Neurogenesis

The dentate gyrus (DG) of the human hippocampus is a complex and dynamic structure harboring mature and immature granular neurons in diverse proliferative states. While most mammals show persistent neurogenesis through adulthood, human neurogenesis is still under debate. We found nuclear alterations in granular cells in autopsied human brains, detected by immunohistochemistry. These alterations differ from those reported in pyramidal neurons of the hippocampal circuit. Aging and early AD chromatin were clearly differentiated by the increased epigenetic markers H3K9me3 (heterochromatin suppressive mark) and H3K4me3 (transcriptional euchromatin mark). At early AD stages, lamin B2 was redistributed to the nucleoplasm, indicating cell-cycle reactivation, probably induced by hippocampal nuclear pathology. At intermediate and late AD stages, higher lamin B2 immunopositivity in the perinucleus suggests fewer immature neurons, less neurogenesis, and fewer adaptation resources to environmental factors. In addition, senile samples showed increased nuclear Tau interacting with aged chromatin, likely favoring DNA repair and maintaining genomic stability. However, at late AD stages, the progressive disappearance of phosphorylated Tau forms in the nucleus, increased chromatin disorganization, and increased nuclear autophagy support a model of biphasic neurogenesis in AD. Therefore, designing therapies to alleviate the neuronal nuclear pathology might be the only pathway to a true rejuvenation of brain circuits.

Understanding the effects of Abhraka Bhasma on genotoxicity and its DNA repair potential in mouse model

BACKGROUND

Metal toxicity is of major concern to human health. The metals may modulate molecular mechanisms of various pathways. Rasashastra, the branch of Ayurveda, narrates the properties, unique preparation, processing techniques, and therapeutic uses of minerals. The use of herbal metallic preparations has evoked concern for their potential to produce toxicity, interest in efficacy as therapeutic agents and safety related issues. Abhraka Bhasma, is one such incinerated herbo-metallic preparation of mica, widely used by traditional medicine practitioners. Although there are reports of Abhraka Bhasma on beneficial effects, clear evidence is lacking on the effect of Abhraka Bhasma on genotoxicity and DNA repair.

OBJECTIVE

The present study aims to understand the effects of Abhraka Bhasma on geno toxicity, DNA repair, and other mechanisms in the mice test model.

MATERIAL AND METHODS

The experiments were conducted in in vivo Swiss albino mice. The acute oral toxicity was performed as per the OECD guidelines. The mice were treated with Abhraka Bhasma (120 or 360 mg/kg body weight) for 7 days. They were then challenged with ethyl methanesulfonate and the DNA repair was analyzed.

RESULTS

The data obtained indicated that the Abhraka Bhasma is not a genotoxic and reproductive toxic formulation. The selected higher concentration of Abhraka Bhasma showed a protective role against ethyl methanesulfonate induced chromosomal damages and enhanced constitutive DNA base excision repair in mice.

CONCLUSION

The anti-oxidant, potentiation of DNA repair and hematinic properties of Abhraka Bhasma may be attributed to the synergistic actions of its bioactive components.

Phospho-Tau and Chromatin Landscapes in Early and Late Alzheimer's Disease

Cellular identity is determined through complex patterns of gene expression. Chromatin, the dynamic structure containing genetic information, is regulated through epigenetic modulators, mainly by the histone code. One of the main challenges for the cell is maintaining functionality and identity, despite the accumulation of DNA damage throughout the aging process. Replicative cells can remain in a senescent state or develop a malign cancer phenotype. In contrast, post-mitotic cells such as pyramidal neurons maintain extraordinary functionality despite advanced age, but they lose their identity. This review focuses on tau, a protein that protects DNA, organizes chromatin, and plays a crucial role in genomic stability. In contrast, tau cytosolic aggregates are considered hallmarks of Alzheimer´s disease (AD) and other neurodegenerative disorders called tauopathies. Here, we explain AD as a phenomenon of chromatin dysregulation directly involving the epigenetic histone code and a progressive destabilization of the tau–chromatin interaction, leading to the consequent dysregulation of gene expression. Although this destabilization could be lethal for post-mitotic neurons, tau protein mediates profound cellular transformations that allow for their temporal survival.

Antigenotoxic and antioxidant potential of medicinal mushrooms (Immune Assist) against DNA damage induced by free radicals-an in vitro study

Immune Assist (IA) is produced from extract of six species of medical mushrooms: Agaricus blazei - Cordyceps sinensis - Grifola frondosa - Ganoderma lucidum - Coriolus versicolor - Lentinula edodes. The genoprotective potential of IA was evaluated for the first time. Significant antigenotoxic effects were detected in human peripheral blood cells against H₂O₂ induced DNA damage, in the pretreatment and in the posttreatment. The most efficient concentration of IA in pretreatment was 500 μg/mL, while in posttreatment it was the concentration of 250 μg/mL. Kinetics of attenuation of H₂O₂ induced DNA damage in posttreatment with the optimal concentration of IA showed significant decrease in the number of damaged cells at all time periods (15-60 min), reaching the greatest reduction after 15 and 45 min. Remarkable ·OH scavenging properties and moderate reducing power, together with the modest DPPH scavenging activity, could be responsible for the great attenuation of DNA damage after 15 min of exposure to IA, while reduction of DNA damage after 45 min could be the result in additional stimulation of the cell's repair machinery. Our results suggest that IA displayed antigenotoxic and antioxidant properties. A broader investigation of its profile in biological systems is needed.

Ionizing Radiation-Induced Cellular Senescence in Normal, Non-transformed Cells and the Involved DNA Damage Response: A Mini Review

Cellular senescence is identified by a living cell in irreversible and persistent cell cycle arrest in response to various cellular stresses. Senescent cells secrete senescence-associated secretory phenotype factors that can amplify cellular senescence and alter the microenvironments. Radiotherapy, via ionizing radiation, serves as an effective treatment for local tumor control with side effects on normal cells, which can induce inflammation and fibrosis in irradiated and nearby regions. Research has revealed that senescent phenotype is observable in irradiated organs. This process starts with DNA damage mediated by radiation, after which a G2 arrest occurs in virtually all eukaryotic cells and a mitotic bypass is possibly necessary to ultimately establish cellular senescence. Within this complex DNA damage response signaling network, ataxia telangiectasia-mutated protein, p53, and p21 stand out as the crucial mediators. Senolytic agents, a class of small molecules that can selectively kill senescent cells, hold great potential to substantially reduce the side effects caused by radiotherapy while reasonably steer clear of carcinogenesis.

Cognitive deficit in hippocampal-dependent tasks in Werner syndrome mouse model

Mammalian aging is often characterized by metabolic disturbances, cognitive declines and DNA repairs deficiency, but the underlying molecular mechanisms are still not well understood. Alterations in DNA repair can significantly exacerbate aging. Mammalian neuronal cells which accumulate unrepaired DNA damage over time could potentially lead to brain functions disorders. Focusing on the ATP-dependent RecQ-type DNA helicase, an enzyme involved in repair of double strand DNA, a mouse model of Werner syndrome (WS) had been proposed as a model of accelerated aging. Until now, no study has investigated the impact of this premature aging syndrome on learning and memory. Spatial memory and cognitive flexibility are particularly affected by the aging process in both men and rodents. Studies have shown that aged mice exhibited similar performance than young adult mice on non-hippocampus dependent memory whereas their performances were decreased in hippocampus-dependent tasks. In this study, we have submitted 3, 5 and 8 month-old WS mice to several behavioral paradigms to evaluate hippocampus-dependent (spatial object location, Morris water maze and fear conditioning) and non hippocampus-dependent (object recognition) memories. No effect on the locomotion activity and anxiety level has been observed in adult WS mice. Interestingly, the 8 month-old WS mice exhibit long-term memory impairment similar to aged mice, suggesting that adult WS mice do develop some aspects of cognitive aging.

DNA repair and aging: the impact of the p53 family

Cells are constantly exposed to endogenous and exogenous factors that threaten the integrity of their DNA. The maintenance of genome stability is of paramount importance in the prevention of both cancer and aging processes. To deal with DNA damage, cells put into operation a sophisticated and coordinated mechanism, collectively known as DNA damage response (DDR). The DDR orchestrates different cellular processes, such as DNA repair, senescence and apoptosis. Among the key factors of the DDR, the related proteins p53, p63 and p73, all belonging to the same family of transcription factors, play multiple relevant roles. Indeed, the members of this family are directly involved in the induction of cell cycle arrest that is necessary to allow the cells to repair. Alternatively, they can promote cell death in case of prolonged or irreparable DNA damage. They also take part in a more direct task by modulating the expression of core factors involved in the process of DNA repair or by directly interacting with them. In this review we will analyze the fundamental roles of the p53 family in the aging process through their multifaceted function in DDR.

Molecular and Cellular Effects of Hydrogen Peroxide on Human Lung Cancer Cells: Potential Therapeutic Implications

Lung cancer has a very high mortality-to-incidence ratio, representing one of the main causes of cancer mortality worldwide. Therefore, new treatment strategies are urgently needed. Several diseases including lung cancer have been associated with the action of reactive oxygen species (ROS) from which hydrogen peroxide (H₂O₂) is one of the most studied. Despite the fact that H₂O₂ may have opposite effects on cell proliferation depending on the concentration and cell type, it triggers several antiproliferative responses. H₂O₂ produces both nuclear and mitochondrial DNA lesions, increases the expression of cell adhesion molecules, and increases p53 activity and other transcription factors orchestrating cancer cell death. In addition, H₂O₂ facilitates the endocytosis of oligonucleotides, affects membrane proteins, induces calcium release, and decreases cancer cell migration and invasion. Furthermore, the MAPK pathway and the expression of genes related to inflammation including interleukins, TNF-α, and NF-κB are also affected by H₂O₂. Herein, we will summarize the main effects of hydrogen peroxide on human lung cancer leading to suggesting it as a potential therapeutic tool to fight this disease. Because of the multimechanistic nature of this molecule, novel therapeutic approaches for lung cancer based on the use of H₂O₂ may help to decrease the mortality from this malignancy.

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

OBJECTIVES

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

MATERIALS AND METHODS

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

RESULTS

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

CONCLUSIONS

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

Methylation of the nonhomologous end joining repair pathway genes does not explain the increase of translocations with aging

Chromosome translocations are especially frequent in human lymphomas and leukemias but are insufficient to drive carcinogenesis. Indeed, several of the so-called tumor specific translocations have been detected in peripheral blood of healthy individuals, finding a higher frequency of some of them with aging. The inappropriate repair of DNA double strand breaks by the nonhomologous end joining (NHEJ) pathway is one of the reasons for a translocation to occur. Moreover, fidelity of this pathway has been shown to decline with age. Although the mechanism underlying this inefficacy is unknown, other repair pathways are inactivated by methylation with aging. In this study, we analyzed the implication of NHEJ genes methylation in the increase of translocations with the age. To this aim, we determined the relationship between translocations and aging in 565 Spanish healthy individuals and correlated these data with the methylation status of 11 NHEJ genes. We found higher frequency of BCL2-JH and BCR-ABL (major) translocations with aging. In addition, we detected that two NHEJ genes (LIG4 and XRCC6) presented age-dependent promoter methylation changes. However, we did not observe a correlation between the increase of translocations and methylation, indicating that other molecular mechanisms are involved in the loss of NHEJ fidelity with aging.

In search of antiaging modalities: evaluation of mTOR- and ROS/DNA damage-signaling by cytometry

This review presents the evidence in support of the IGF-1/mTOR/S6K1 signaling as the primary factor contributing to aging and cellular senescence. Reviewed are also specific interactions between mTOR/S6K1 and ROS-DNA damage signaling pathways. Outlined are critical sites along these pathways, including autophagy, as targets for potential antiaging (gero-suppressive) and/or chemopreventive agents. Presented are applications of flow- and laser scanning- cytometry utilizing phospho-specific Abs, to monitor activation along these pathways in response to the reported antiaging drugs rapamycin, metformin, berberine, resveratrol, vitamin D3, 2-deoxyglucose, and acetylsalicylic acid. Specifically, effectiveness of these agents to attenuate the level of constitutive mTOR signaling was tested by cytometry and confirmed by Western blotting through measuring phosphorylation of the mTOR-downstream targets including ribosomal protein S6. The ratiometric analysis of phosphorylated to total protein along the mTOR pathway offers a useful parameter reporting the effects of gero-suppressive agents. In parallel, their ability to suppress the level of constitutive DNA damage signaling induced by endogenous ROS was measured. While the primary target of each of these agents may be different the data obtained on several human cancer cell lines, WI-38 fibroblasts and normal lymphocytes suggest common downstream mechanism in which the decline in mTOR/S6K1 signaling and translation rate is coupled with a reduction of oxidative phosphorylation and ROS that leads to decreased oxidative DNA damage. The combined assessment of constitutive γH2AX expression, mitochondrial activity (ROS, ΔΨm), and mTOR signaling provides an adequate gamut of cell responses to test effectiveness of gero-suppressive agents. Described is also an in vitro model of induction of cellular senescence by persistent replication stress, its quantitative analysis by laser scanning cytometry, and application to detect the property of the studied agents to attenuate the induction of senescence. Discussed is cytometric analysis of cell size and heterogeneity of size as a potential biomarker used to asses gero-suppressive agents and longevity.

Potential anti-aging agents suppress the level of constitutive mTOR- and DNA damage- signaling

Two different mechanisms are considered to be the primary cause of aging. Cumulative DNA damage caused by reactive oxygen species (ROS), the by-products of oxidative phosphorylation, is one of these mechanisms (ROS concept). Constitutive stimulation of mitogen- and nutrient-sensing mTOR/S6 signaling is the second mechanism (TOR concept). The flow- and laser scanning- cytometric methods were developed to measure the level of the constitutive DNA damage/ROS- as well as of mTOR/S6- signaling in individual cells. Specifically, persistent activation of ATM and expression of γH2AX in untreated cells appears to report constitutive DNA damage induced by endogenous ROS. The level of phosphorylation of Ser235/236-ribosomal protein (RP), of Ser2448-mTOR and of Ser65-4EBP1, informs on constitutive signaling along the mTOR/S6 pathway. Potential gero-suppressive agents rapamycin, metformin, 2-deoxyglucose, berberine, resveratrol, vitamin D3 and aspirin, all decreased the level of constitutive DNA damage signaling as seen by the reduced expression of γH2AX in proliferating A549, TK6, WI-38 cells and in mitogenically stimulated human lymphocytes. They all also decreased the level of intracellular ROS and mitochondrial trans-membrane potential ΔΨm, the marker of mitochondrial energizing as well as reduced phosphorylation of mTOR, RP-S6 and 4EBP1. The most effective was rapamycin. Although the primary target of each on these agents may be different the data are consistent with the downstream mechanism in which the decline in mTOR/S6K signaling and translation rate is coupled with a decrease in oxidative phosphorylation, (revealed by ΔΨm) that leads to reduction of ROS and oxidative DNA damage. The decreased rate of translation induced by these agents may slow down cells hypertrophy and alleviate other features of cell aging/senescence. Reduction of oxidative DNA damage may lower predisposition to neoplastic transformation which otherwise may result from errors in repair of DNA sites coding for oncogenes or tumor suppressor genes. The data suggest that combined assessment of constitutive γH2AX expression, mitochondrial activity (ROS, ΔΨm) and mTOR signaling provides an adequate gamut of cell responses to evaluate effectiveness of gero-suppressive agents.

A high nuclear nm23-H1 expression is associated with a better prognosis in elderly patients with laryngeal carcinoma

CONCLUSIONS

Nuclear nm23-H1 expression may be useful in identifying elderly patients operated for laryngeal squamous cell carcinoma (LSCC) at higher risk of recurrence. Further studies are needed to clarify the biological role of nm23-H1 in elderly patients with LSCC and to determine how to restore nm23-H1 loss of expression/function.

OBJECTIVES

Nowadays more than 50% of cancer cases are elderly patients and this percentage is expected to be 70% by 2030. Despite advances in LSCC diagnosis and treatment, patient survival has not improved in the last two decades. Novel, effective strategies should rely also on receptor-mediated LSCC-targeted therapy. nm23-H1 protein is related to the tumor cells' metastatic potential, and low nm23-H1 expression in carcinomas often correlates with a poor prognosis.

METHODS

Immunohistochemistry and image analysis were used to investigate the prognostic value of nm23-H1 expression and subcellular localization in a series of 54 elderly patients consecutively undergoing primary surgery for LSCC.

RESULTS

On univariate analysis, the disease recurrence rate correlated inversely with nuclear nm23-H1 expression (p = 0.014), and disease-free survival (DFS) was longer in patients whose nuclear nm23-H1 levels were ≥2.0% (p = 0.022). On multivariate analysis, nuclear nm23-H1 expression (hazard ratio (HR) 2.77, p = 0.022) and N stage (HR 3.49, p = 0.007) were prognostically significant in terms of DFS.

Berberine suppresses gero-conversion from cell cycle arrest to senescence

Berberine (BRB), a natural alkaloid, has a long history of medicinal use in both Ayurvedic and old Chinese medicine. Recently, available as a dietary supplement, Berberine is reported to have application in treatment of variety diseases. Previously we observed that BRB inhibited mTOR/S6 signaling concurrently with reduction of the level of endogenous oxidants and constitutive DNA damage response. We currently tested whether Berberine can affect premature, stress-induced cellular senescence caused by mitoxantrone. The depth of senescence was quantitatively measured by morphometric parameters, senescence-associated β-galactosidase, induction of p21WAF1, replication stress (γH2AX expression), and mTOR signaling; the latter revealed by ribosomal S6 protein (rpS6) phosphorylation. All these markers of senescence were distinctly diminished, in a concentration-dependent manner, by Berberine. In view of the evidence that BRB localizes in mitochondria, inhibits respiratory electron chain and activates AMPK, the observed attenuation of the replication stress-induced cellular senescence most likely is mediated by AMPK that leads to inhibition of mTOR signaling. In support of this mechanism is the observation that rhodamine123, the cationic probe targeting mitochondrial electron chain, also suppressed rpS6 phosphorylation. The present findings reveal that: (a) in cells induced to senescence BRB exhibits gero-suppressive properties by means of mTOR/S6 inhibition; (b) in parallel, BRB reduces the level of constitutive DNA damage response, previously shown to report oxidative DNA damage by endogenous ROS; (c) there appears to a causal linkage between the (a) and (b) activities; (d) the in vitro model of premature stress-induced senescence can be used to assess effectiveness of potential gero-suppressive agents targeting mTOR/S6 and ROS signaling; (e) since most of the reported beneficial effects of BRB are in age-relate diseases, it is likely that gero-suppression is the primary activity of this traditional medicine.

HEART AND AGE (PART I): AGEING THEORIES AND MORPHOLOGICAL CHANGES

Heart ageing is a complex process including multiple cellular and molecular-level changes and resulting in different ageing phenotypes within the same biological species. According to the existing ageing theories, the multiple interacting mechanisms of ageing include somatic mutations, telomere shortening, oxidative stress, and mitochondrial defects. The review presents the most accepted ageing theories and discusses morphological characteristics of heart ageing on subcellular, cellular, and organ levels.

ADAR1 protein induces adenosine-targeted DNA mutations in senescent Bcl6 gene-deficient cells

Somatic mutations accumulate in senescent cells. Bcl6, which functions as a transcriptional repressor, has been identified as a potent inhibitor of cell senescence, but a role of Bcl6 in the accumulation of somatic mutations has remained unclear. Ig class-switch recombination simultaneously induces somatic mutations in an IgM class-switch (Ig-Sμ) region of IgG B cells. Surprisingly, mutations were detected in the Ig-Sμ region of Bcl6-deficient IgM B cells without class-switch recombination, and these mutations were mainly generated by conversion of adenosine to guanosine, suggesting a novel DNA mutator in the B cells. The ADAR1 (adenosine deaminase acting on RNA1) gene was overexpressed in Bcl6-deficient cells, and its promoter analysis revealed that ADAR1 is a molecular target of Bcl6. Exogenous ADAR1 induced adenosine-targeted DNA mutations in IgM B cells from ADAR1-transgenic mice and in wild-type mouse embryonic fibroblasts (MEFs). These mutations accumulated in senescent MEFs accompanied with endogenous ADAR1 expression, and the frequency in senescent Bcl6-deficient MEFs was higher than senescent wild-type MEFs. Thus, Bcl6 protects senescent cells from accumulation of adenosine-targeted DNA mutations induced by ADAR1.

Genome protective effect of metformin as revealed by reduced level of constitutive DNA damage signaling

We have shown before that constitutive DNA damage signaling represented by H2AX-Ser139 phosphorylation and ATM activation in untreated normal and tumor cells is a reporter of the persistent DNA replication stress induced by endogenous oxidants, the by-products of aerobic respiration. In the present study we observed that exposure of normal mitogenically stimulated lymphocytes or tumor cell lines A549, TK6 and A431 to metformin, the specific activator of 5'AMP-activated protein kinase (AMPK) and an inhibitor of mTOR signaling, resulted in attenuation of constitutive H2AX phosphorylation and ATM activation. The effects were metformin-concentration dependent and seen even at the pharmacologically pertinent 0.1 mM drug concentration. The data also show that intracellular levels of endogenous reactive oxidants able to oxidize 2',7'-dihydro-dichlorofluorescein diacetate was reduced in metformin-treated cells. Since persistent constitutive DNA replication stress, particularly when paralleled by mTOR signaling, is considered to be the major cause of aging, the present findings are consistent with the notion that metformin, by reducing both DNA replication stress and mTOR-signaling, slows down aging and/or cell senescence processes.

Induction of DNA damage signaling by oxidative stress in relation to DNA replication as detected using "click chemistry"

Induction of DNA damage by oxidants such as H(2) O(2) activates the complex network of DNA damage response (DDR) pathways present in cells to initiate DNA repair, halt cell cycle progression, and prepare an apoptotic reaction. We have previously reported that activation of Ataxia Telangiectasia Mutated protein kinase (ATM) and induction of γH2AX are among the early events of the DDR induced by exposure of cells to H(2) O(2) , and in human pulmonary carcinoma A549 cells, both events were expressed predominantly during S-phase. This study was designed to further explore a correlation between these events and DNA replication. Toward this end, we utilized 5-ethynyl-2'deoxyuridine (EdU) and the "click chemistry" approach to label DNA during replication, followed by exposure of A549 cells to H(2) O(2) . Multiparameter laser scanning cytometric analysis of these cells made it possible to identify DNA replicating cells and directly correlate H(2) O(2) -induced ATM activation and induction of γH2AX with DNA replication on a cell by cell basis. After pulse-labeling with EdU and exposure to H(2) O(2) , confocal microscopy was also used to examine the localization of DNA replication sites ("replication factories") versus the H2AX phosphorylation sites (γH2AX foci) in nuclear chromatin in an attempt to observe the absence or presence of colocalization. The data indicate a close association between DNA replication and H2AX phosphorylation in A549 cells, suggesting that these DNA damage response events may be triggered by stalled replication forks and perhaps also by induction of DNA double-strand breaks at the primary DNA lesions induced by H(2) O(2) .

Addressing the complex etiology of Alzheimer’s disease: the role of p25/Cdk5

Alzheimer’s disease (AD) is an age-related neurodegenerative disorder characterized by the progressive loss of forebrain neurons and the deterioration of learning and memory. Therapies for AD have primarily focused upon either the inhibition of amyloid synthesis or its deposition in the brain, but clinical testing to date has not yet found an effective amelioration of cognitive symptoms. Synaptic loss closely correlates with the degree of dementia in AD patients. However, mouse AD models that target the amyloid-β pathway generally do not exhibit a profound loss of synapses, despite extensive synaptic dysfunction. The increased generation of p25, an activator of the cyclin-dependent kinase 5 (Cdk5) has been found in both human patients and mouse models of neurodegeneration. The current work reviews our knowledge, to date, on the role of p25/Cdk5 in Alzheimer’s disease, with a focus upon the interaction of amyloid-β and p25/Cdk5 in synaptic dysfunction and neuronal loss.

Aging is accompanied by a progressive decrease of expression of the WRN gene in human blood mononuclear cells

The WRN gene encodes DNA helicase participating in genome maintenance. We looked for associations of natural aging with expression and methylation of this gene in blood mononuclear cells and with its common polymorphisms. Analyses were performed in ethnically homogenous Polish Caucasians. The mean level of the WRN messenger RNA was significantly lower in long-living individuals than in young and middle-aged controls (p < .001 and p = .025, respectively). Analysis of the 361 bp WRN promoter CpG island showed that aging might be accompanied by a slight increase of its methylation status; however, it seems to be biologically insignificant. Finally, analysis of the WRN R834C, L1074F, and C1367R polymorphisms showed that the frequencies of the L1074F and C1367R polymorphisms were similar in all age groups tested, whereas the R834C polymorphism was absent from Polish Caucasians. We suggest that age-related decrease of the WRN expression but not its common genetic variants might contribute to human immunosenescence.

Checkpoint kinase phosphorylation in response to endogenous oxidative DNA damage in repair-deficient stationary-phase Saccharomyces cerevisiae

Stationary-phase Saccharomyces cerevisiae can serve as a model for post-mitotic cells of higher eukaryotes. Phosphorylation and activation of the checkpoint kinase Rad53 was observed after more than 2 days of culture if two major pathways of oxidative DNA damage repair, base excision repair (BER) and nucleotide excision repair (NER), are inactive. The wild type showed a low degree of Rad53 phosphorylation when the incubation period was drastically increased. In the ber ner strain, Rad53 phosphorylation can be abolished by inclusion of antioxidants or exclusion of oxygen. Furthermore, this modification and enhanced mutagenesis in extended stationary phase were absent in rho degrees strains, lacking detectable mitochondrial DNA. This checkpoint response is therefore thought to be dependent on reactive oxygen species originating from mitochondrial respiration. There was no evidence for progressive overall telomere shortening during stationary-phase incubation. Since Rad50 (of the MRN complex) and Mec1 (the homolog of ATR) were absolutely required for the observed checkpoint response, we assume that resected random double-strand breaks are the critical lesion. Single-strand resection may be accelerated by unrepaired oxidative base damage in the vicinity of a double-strand break.

Telomere-dependent and telomere-independent origins of endogenous DNA damage in tumor cells

Human tumors and cultured cells contain elevated levels of endogenous DNA damage resulting from telomere dysfunction, replication and transcription errors, reactive oxygen species, and genome instability. However, the contribution of telomere-associated versus telomere-independent endogenous DNA lesions to this damage has never been examined. In this study, we characterized the relative amounts of these two types of DNA damage in five tumor cell lines by noting whether γ-H2AX foci, generally considered to mark DNA double-strand breaks (DSBs), were on chromosome arms or at chromosome ends. We found that while the numbers of non-telomeric DSBs were remarkably similar in these cultures, considerable variation was detected in the level of telomeric damage. The distinct heterogeneity in the numbers of γ-H2AX foci in these tumor cell lines was found to be due to foci associated with uncapped telomeres, and the amount of total telomeric damage also appeared to inversely correlate with the telomerase activity present in these cells. These results indicate that damaged telomeres are the major factor accounting for the variability in the amount of DNA DSB damage in tumor cells. This characterization of DNA damage in tumor cells helps clarify the contribution of non-telomeric DSBs and damaged telomeres to major genomic alterations.

Model of human aging: recent findings on Werner's and Hutchinson-Gilford progeria syndromes

The molecular mechanisms involved in human aging are complicated. Two progeria syndromes, Werner's syndrome (WS) and Hutchinson-Gilford progeria syndrome (HGPS), characterized by clinical features mimicking physiological aging at an early age, provide insights into the mechanisms of natural aging. Based on recent findings on WS and HGPS, we suggest a model of human aging. Human aging can be triggered by two main mechanisms, telomere shortening and DNA damage. In telomere-dependent aging, telomere shortening and dysfunction may lead to DNA damage responses which induce cellular senescence. In DNA damage-initiated aging, DNA damage accumulates, along with DNA repair deficiencies, resulting in genomic instability and accelerated cellular senescence. In addition, aging due to both mechanisms (DNA damage and telomere shortening) is strongly dependent on p53 status. These two mechanisms can also act cooperatively to increase the overall level ofgenomic instability, triggering the onset of human aging phenotypes.

DNA repair by nonhomologous end joining and homologous recombination during cell cycle in human cells

DNA double-strand breaks (DSBs) are dangerous lesions that can lead to potentially oncogenic genomic rearrangements or cell death. The two major pathways for repair of DSBs are nonhomologous end joining (NHEJ) and homologous recombination (HR). NHEJ is an intrinsically error-prone pathway while HR results in accurate repair. To understand the origin of genomic instability in human cells it is important to know the contribution of each DSB repair pathway. Studies of rodent cells and human cancer cell lines have shown that the choice between NHEJ or HR pathways depends on cell cycle stage. Surprisingly, cell cycle regulation of DSB repair has not been examined in normal human cells with intact cell cycle checkpoints. Here we measured the efficiency of NHEJ and HR at different cell cycle stages in hTERT-immortalized diploid human fibroblasts. We utilized cells with chromosomally-integrated fluorescent reporter cassettes, in which a unique DSB is introduced by a rare-cutting endonuclease. We show that NHEJ is active throughout the cell cycle, and its activity increases as cells progress from G1 to G2/M (G1 < S < G2/M). HR is nearly absent in G1, most active in the S phase, and declines in G2/M. Thus, in G2/M NHEJ is elevated, while HR is on decline. This is in contrast to a general belief that NHEJ is most active in G1, while HR is active in S, G2 and M. The overall efficiency of NHEJ was higher than HR at all cell cycle stages. We conclude that human somatic cells utilize error-prone NHEJ as the major DSB repair pathway at all cell cycle stages, while HR is used, primarily, in the S phase.

Adaptive Mutation inSaccharomyces cerevisiae

Adaptive mutation is a generic term for processes that allow individual cells of nonproliferating cell populations to acquire advantageous mutations and thereby to overcome the strong selective pressure of proliferation-limiting environmental conditions. Prerequisites for an occurrence of adaptive mutation are that the selective conditions are nonlethal and that a restart of proliferation may be accomplished by some genetic change in principle. The importance of adaptive mutation is derived from the assumption that it may, on the one hand, result in an accelerated evolution of microorganisms and, on the other, in multicellular organisms may contribute to a breakout of somatic cells from negative growth regulation, i.e., to cancerogenesis. Most information on adaptive mutation in eukaryotes has been gained with the budding yeast Saccharomyces cerevisiae. This review focuses comprehensively on adaptive mutation in this organism and summarizes our current understanding of this issue.

Protective effect of hyaluronate on oxidative DNA damage in WI-38 and A549 cells

Progressive DNA damage in live cells by oxidants is the key factor contributing to cell aging and preconditioning to neoplastic transformation. The strategies to slow aging or prevent cancer rely on protection of DNA from the damage. Since cells reside within intercellular matrix it is of interest to know whether matrix constituents possess properties of modulating oxidative DNA damage. We explored, therefore, the effect of hyaluronate (HA), the ubiquitous component of the matrix, on extent of DNA damage induced by exogenous and endogenously generated oxidants. WI-38 and A549 cells were exposed to 200 microM H2O2 in the absence or presence of HA and induction of histone H2AX phosphorylation and activation of ATM, the reporters of DNA damage, was assessed by multiparameter cytometry. Also explored was effect of HA on constitutive H2AX phosphorylation that reflects DNA damage caused by endogenous oxidants generated during aerobic metabolism. HA of average MW 5.4 million (high MW) and 2 million (medium MW) at 0.1% (w/v) in culture medium totally prevented the H2O2-induced H2AX phosphorylation in both cell types whereas effect of 60,000 average MW (low MW) HA was somewhat less pronounced. Constitutive H2AX phosphorylation in WI-38 cells growing in the presence of 0.1% HA of low MW and medium MW was reduced by about 35 and 30%, respectively; no reduction was observed in A549 cells. The data indicate that HA protected DNA from damage caused by the exogenous oxidant H2O2. In WI-38 fibroblasts, the cells that express the HA-receptor CD44, HA also protected DNA from damage caused by endogenous oxidants. We postulate that expression of CD44 in some cell types such as stem cells may provide the means to internalize HA by endocytosis and one of the functions of the internalized HA may be protection of DNA from oxidants. The mechanism of protective effect of HA may either: i) involve entrapment of iron ions thereby inhibiting the Fenton's reaction that produces secondary oxidative species, and/or: ii) directly scavenging of primary and secondary ROIs, as an antioxidant, resulting in HA degradation. Since no significant degradation of HA upon its exposure in tissue culture medium to H2O2 was detected the scavenging may occur intracellularly.

Accumulation of nuclear DNA damage or neuron loss: molecular basis for a new approach to understanding selective neuronal vulnerability in neurodegenerative diseases

According to a long-standing hypothesis, aging is mainly caused by accumulation of nuclear (n) DNA damage in differentiated cells such as neurons due to insufficient nDNA repair during lifetime. In line with this hypothesis it was until recently widely accepted that neuron loss is a general consequence of normal aging, explaining some degree of decline in brain function during aging. However, with the advent of more accurate procedures for counting neurons, it is currently widely accepted that there is widespread preservation of neuron numbers in the aging brain, and the changes that do occur are relatively specific to certain brain regions and types of neurons. Whether accumulation of nDNA damage and decline in nDNA repair is a general phenomenon in the aging brain or also shows cell-type specificity is, however, not known. It has not been possible to address this issue with the biochemical and molecular-biological methods available to study nDNA damage and nDNA repair. Rather, it was the introduction of autoradiographic methods to study quantitatively the relative amounts of nDNA damage (measured as nDNA single-strand breaks) and nDNA repair (measured as unscheduled DNA synthesis) on tissue sections that made it possible to address this question in a cell-type-specific manner under physiological conditions. The results of these studies revealed a formerly unknown inverse relationship between age-related accumulation of nDNA damage and age-related impairment in nDNA repair on the one hand, and the age-related, selective, loss of neurons on the other hand. This inverse relation may not only reflect a fundamental process of aging in the central nervous system but also provide the molecular basis for a new approach to understand the selective neuronal vulnerability in neurodegenerative diseases, particularly Alzheimer's disease.

HGPS and related premature aging disorders: from genomic identification to the first therapeutic approaches

Progeroid syndromes are heritable human disorders displaying features that recall premature ageing. In these syndromes, premature aging is defined as "segmental" since only some of its features are accelerated. A number of cellular biological pathways have been linked to aging, including regulation of the insulin/growth hormone axis, pathways involving ROS metabolism, caloric restriction, and DNA repair. The number of identified genes associated with progeroid syndromes has increased in recent years, possibly shedding light as well on mechanisms underlying ageing in general. Among these, premature aging syndromes related to alterations of the LMNA gene have recently been identified. This review focuses on Hutchinson-Gilford Progeria syndrome and Restrictive Dermopathy, two well-characterized Lamin-associated premature aging syndromes, pointing out the current knowledge concerning their pathophysiology and the development of possible therapeutic approaches.

Oxidative stress induces cell cycle-dependent Mre11 recruitment, ATM and Chk2 activation and histone H2AX phosphorylation

DNA damage response recruits complex molecular machinery involved in DNA repair, arrest of cell cycle progression, and potentially in activation of apoptotic pathway. Among the first responders is the Mre11- (MRN) complex of proteins (Mre11, Rad50, Nbs1), essential for activation of ATM; the latter activates checkpoint kinase 2 (Chk2) and phosphorylates histone H2AX. In the present study the recruitment of Mre11 and phosphorylation of ATM, Chk2 and H2AX (gammaH2AX) detected immunocytochemically were measured by laser scanning cytometry to assess kinetics of these events in A549 cells treated with H(2)O(2). Recruitment of Mre11 was rapid, peaked at 10 min of exposure to the oxidant, and was of similar extent in all phases of the cell cycle. ATM and Chk2 activation as well as H2AX phosphorylation reached maximum levels after 30 min of treatment with H(2)O(2); the extent of phosphorylation of each was most prominent in S-, less in G(1)-, and the least in G(2)M- phase cells. A strong correlation between activation of ATM and Chk2, measured in the same cells, was seen in all phases of the cycle. In untreated cells activated Chk2 and Mre11 were distinctly present in centrosomes while in interphase cells they had characteristic punctate nuclear localization. The punctate expression of activated Chk2 both in untreated and H(2)O(2) treated cells was accentuated when measured as maximal pixel rather than integrated value of immunofluorescence (IF) per nucleus, and was most pronounced in G(1) cells, likely reflecting the function of Chk2 in activating Cdc25A. Subpopulations of G(1) and G(2)M cells with strong maximal pixel of Chk2-Thr68(P) IF in association with centrosomes were present in untreated cultures. Cytometric multiparameter assessment of the DNA damage response utilizing quantitative image analysis that allows one to measure inhomogeneity of fluorochrome distribution (e.g., maximal pixel) offers unique advantage in studies of the response of different cell constituents in relation to cell cycle position.

Cytometric assessment of DNA damage by exogenous and endogenous oxidants reports aging-related processes

The ongoing DNA damage caused by reactive oxygen species generated during oxidative metabolism is considered a key factor contributing to cell aging as well as preconditioning cells to neoplastic transformation. We postulated before that a significant fraction of constitutive histone H2AX phosphorylation (CHP) and constitutive activation of ATM (CAA) seen in untreated normal and tumor cells occurs in response to such DNA damage. In the present study, we provide further evidence in support of this postulate. The level of ATM activation and H2AX phosphorylation, detected immunocytochemically, has been monitored in WI-38, A549, and TK6 cells treated with H2O2 as well as growing under conditions known or suspected to affect the level of endogenous oxidants. Thirty- to 60-min exposure of cells to 100 or 200 microM H2O2 led to an increase in the level of H2AX phosphorylation and ATM activation, particularly pronounced (nearly fivefold) in S-phase cells. Cell growth for 24-48 h under hypoxic conditions (3% O2) distinctly lowered the level of CHP and CAA while it had minor effect on cell cycle progression. Treatment (4 h) with 0.1 or 0.3 mM 3-bromopyruvate, an inhibitor of glycolysis and mitochondrial oxidative phosphorylation, reduced the level of CHP (up to fourfold) and also decreased the level of CAA. Growth of WI-38 cells in 2% serum concentration for 48 h led to a 25 and 30% reduction in CHP and CHA, respectively, compared with cells growing in 10% serum. The antioxidant vitamin C (2 mM) reduced CHP and CAA by 20-30% after 24 h of treatment, while the COX-2 inhibitor celecoxib (5 microM) had a minor effect on CHP and CAA, though it decreased the level of H2O2-induced H2AX phosphorylation and ATM activation. In contrast, dichloroacetate known to shift metabolism from anaerobic to oxidative glycolysis through its effect on pyruvate dehydrogenase kinase enhanced the level of CHP and CAA. Our present data and earlier observations strongly support the postulate that a large fraction of CHP and CAA occurs in response to DNA damage caused by metabolically generated oxidants. Cytometric analysis of CHP and CAA provides the means to measure the effectiveness of exogenous factors, which either through lowering aerobic metabolism or neutralizing radicals may protect DNA from such damage.

Longevity and resistance to stress correlate with DNA repair capacity in Caenorhabditis elegans

DNA repair is an important mechanism by which cells maintain genomic integrity. Decline in DNA repair capacity or defects in repair factors are thought to contribute to premature aging in mammals. The nematode Caenorhabditis elegans is a good model for studying longevity and DNA repair because of key advances in understanding the genetics of aging in this organism. Long-lived C. elegans mutants have been identified and shown to be resistant to oxidizing agents and UV irradiation, suggesting a genetically determined correlation between DNA repair capacity and life span. In this report, gene-specific DNA repair is compared in wild-type C. elegans and stress-resistant C. elegans mutants for the first time. DNA repair capacity is higher in long-lived C. elegans mutants than in wild-type animals. In addition, RNAi knockdown of the nucleotide excision repair gene xpa-1 increased sensitivity to UV and reduced the life span of long-lived C. elegans mutants. These findings support that DNA repair capacity correlates with longevity in C. elegans.

DNA repair and the immune system: From V(D)J recombination to aging lymphocytes

B and T lymphocytes are exposed to various genotoxic stresses during their life, which originate from programmed molecular mechanisms during their development and maturation or are secondary to cellular metabolism during acute phases of cell proliferation and activation during immune responses. How lymphocytes handle these multiple genomic assault has become a focus of interest over the years, perhaps beginning with the identification of the murine scid model in the early 80s when it was recognized that DNA repair deficiencies had profound consequences on the immune system. In this respect, the immune system represents an ideal model to study DNA damage responses (DDR) and the survey of immune deficiency conditions in humans or the development of specific animal models provided many major contributions in our understanding of the various biochemical pathways at play during DDR in general. Although the role of DNA repair in the early phases of B and T cell development has been analyzed thoroughly, the role of these functions in various aspects of the mature immune system (homeostasis, immunological memory, ageing) is less well understood. Lastly, the analysis of DNA repair in the immune system has provided many insights in the more general understanding of cancer.

Delayed kinetics of DNA double-strand break processing in normal and pathological aging

Accumulation of DNA damage may play an essential role in both cellular senescence and organismal aging. The ability of cells to sense and repair DNA damage declines with age. However, the underlying molecular mechanism for this age-dependent decline is still elusive. To understand quantitative and qualitative changes in the DNA damage response during human aging, DNA damage-induced foci of phosphorylated histone H2AX (gamma-H2AX), which occurs specifically at sites of DNA double-strand breaks (DSBs) and eroded telomeres, were examined in human young and senescing fibroblasts, and in lymphocytes of peripheral blood. Here, we show that the incidence of endogenous gamma-H2AX foci increases with age. Fibroblasts taken from patients with Werner syndrome, a disorder associated with premature aging, genomic instability and increased incidence of cancer, exhibited considerably higher incidence of gamma-H2AX foci than those taken from normal donors of comparable age. Further increases in gamma-H2AX focal incidence occurred in culture as both normal and Werner syndrome fibroblasts progressed toward senescence. The rates of recruitment of DSB repair proteins to gamma-H2AX foci correlated inversely with age for both normal and Werner syndrome donors, perhaps due in part to the slower growth of gamma-H2AX foci in older donors. Because genomic stability may depend on the efficient processing of DSBs, and hence the rapid formation of gamma-H2AX foci and the rapid accumulation of DSB repair proteins on these foci at sites of nascent DSBs, our findings suggest that decreasing efficiency in these processes may contribute to genome instability associated with normal and pathological aging.

DNA damage, cellular senescence and organismal ageing: causal or correlative?

Cellular senescence has long been used as a cellular model for understanding mechanisms underlying the ageing process. Compelling evidence obtained in recent years demonstrate that DNA damage is a common mediator for both replicative senescence, which is triggered by telomere shortening, and premature cellular senescence induced by various stressors such as oncogenic stress and oxidative stress. Extensive observations suggest that DNA damage accumulates with age and that this may be due to an increase in production of reactive oxygen species (ROS) and a decline in DNA repair capacity with age. Mutation or disrupted expression of genes that increase DNA damage often result in premature ageing. In contrast, interventions that enhance resistance to oxidative stress and attenuate DNA damage contribute towards longevity. This evidence suggests that genomic instability plays a causative role in the ageing process. However, conflicting findings exist which indicate that ROS production and oxidative damage levels of macromolecules including DNA do not always correlate with lifespan in model animals. Here we review the recent advances in addressing the role of DNA damage in cellular senescence and organismal ageing.

Multiple-pathway analysis of double-strand break repair mutations in Drosophila

The analysis of double-strand break (DSB) repair is complicated by the existence of several pathways utilizing a large number of genes. Moreover, many of these genes have been shown to have multiple roles in DSB repair. To address this complexity we used a repair reporter construct designed to measure multiple repair outcomes simultaneously. This approach provides estimates of the relative usage of several DSB repair pathways in the premeiotic male germline of Drosophila. We applied this system to mutations at each of 11 repair loci plus various double mutants and altered dosage genotypes. Most of the mutants were found to suppress one of the pathways with a compensating increase in one or more of the others. Perhaps surprisingly, none of the single mutants suppressed more than one pathway, but they varied widely in how the suppression was compensated. We found several cases in which two or more loci were similar in which pathway was suppressed while differing in how this suppression was compensated. Taken as a whole, the data suggest that the choice of which repair pathway is used for a given DSB occurs by a two-stage "decision circuit" in which the DSB is first placed into one of two pools from which a specific pathway is then selected.

8-Hydroxy-2′-deoxyguanosine (8-OH-dG) as a potential survival biomarker in patients with nonsmall-cell lung cancer

BACKGROUND

8-Hydroxy-2'-deoxyguanosine (8-OH-dG) is 1 of the most abundant oxidative products of cellular DNA. Accumulation of impaired 8-OH-dG could lead to increased genomic instability that in turn could lead to a more malignant phenotypic behavior of tumors. Therefore, the effects of 8-OH-dG on survival in 99 resected nonsmall-cell lung cancer (NSCLC) patients was evaluated.

METHODS

The enzyme-linked immunosorbent assay was applied to measure the levels of 8-OH-dG in tumor DNA. The median levels of 8-OH-dG were 6.5 pmol/microg for all study subjects.

RESULTS

Patients with low levels of 8-OH-dG had significantly longer survival times compared with those with high levels of 8-OH-dG (log-rank test: P < .001). In Cox regression analysis, patients with high levels of 8-OH-dG had an over 3-fold increased hazard of death. In addition, a statistically significant correlation between levels of 8-OH-dG and age was noted (rho = 0.206, P = .048). Furthermore, we observed a genotype-phenotype modification between hOGG1 gene polymorphism (Ser326Cys) and levels of 8-OH-dG.

CONCLUSIONS

The results demonstrated that levels of 8-OH-dG could predict survival in resected NSCLC patients. It is postulated that an intact base excision repair mechanism may reduce the accumulation of oxidative DNA damage that is thought to contribute to the tumor's malignant potential and therefore the risk of death.

Age-dependent usage of double-strand-break repair pathways

A DNA double-strand break (DSB) can be repaired by any of several alternative and competing mechanisms. The repaired sequences often differ from the original depending on which mechanism was used so that the cell's "choice" of repair mechanism can have profound genetic consequences. DSBs can accumulate with age , and human diseases that mimic some of the effects of aging, such as increased susceptibility to cancer, are associated with certain defects in DSB repair . The premeiotic germ cells of Drosophila provide a useful model for exploration of the connection between aging and DNA repair because these cells are subject to mortality and other age-related changes , and their DNA repair process is easily quantified. We used Rr3, a repair reporter system in Drosophila, to show that the relative usage of DSB repair mechanisms can change substantially as an organism ages. Homologous repair increased linearly in the male germline from 14% in young individuals to more than 60% in old ones, whereas two other pathways showed a corresponding decrease. Furthermore, the proportion of longer conversion tracts (>156 bp) also increased nearly 2-fold as the flies aged. These findings are relevant to the more general question of how DNA damage and repair are related to aging.

Constitutive histone H2AX phosphorylation and ATM activation, the reporters of DNA damage by endogenous oxidants

DNA in live cells undergoes continuous oxidative damage caused by metabolically generated endogenous as well as external oxidants and oxidant-inducers. The cumulative oxidative DNA damage is considered the key factor in aging and senescence while the effectiveness of anti-aging agents is often assessed by their ability to reduce such damage. Oxidative DNA damage also preconditions cells to neoplastic transformation. Sensitive reporters of DNA damage, particularly the induction of DNA double-strand breaks (DSBs), are activation of ATM, through its phosphorylation on Ser 1981, and phosphorylation of histone H2AX on Ser 139; the phosphorylated form of H2AX has been named gammaH2AX. We review the observations that constitutive ATM activation (CAA) and H2AX phosphorylation (CHP) take place in normal cells as well in the cells of tumor lines untreated by exogenous genotoxic agents. We postulate that CAA and CHP, which have been measured by multiparameter cytometry in relation to the cell cycle phase, are triggered by oxidative DNA damage. This review also presents the findings on differences in CAA and CHP in various cell lines as well as on the effects of several agents and growth conditions that modulate the extent of these histone and ATM modifications. Specifically, described are effects of the reactive oxygen species (ROS) scavenger N-acetyl-L-cysteine (NAC), and the glutathione synthetase inhibitor buthionine sulfoximine (BSO) as well as suppression of cell metabolism by growth at higher cell density or in the presence of the glucose antimetabolite 2-deoxy-D-glucose. Collectively, the reviewed data indicate that multiparameter cytometric measurement of the level of CHP and/or CAA allows one to estimate the extent of ongoing oxidative DNA damage and to measure the DNA protective-effects of antioxidants or agents that reduce or amplify generation of endogenous ROS.

The murmur of old broken heartstrings

Although it has long been hypothesized that gene expression might become more variable or noisy during aging, direct evidence has been scarce so far. A new study reports detection, by PCR analysis of individual cells, of increased cell-to-cell variability in gene expression in aging mouse heart; moreover, a similar variability can be generated in cultured cells using oxidative stress (Bahar et al., 2006).

Abasic sites and survival in resected patients with non-small cell lung cancer

Apurinic/apyrimidinic (AP or abasic) sites are common DNA lesions that arise from spontaneous depurination or by base excision repair (BER) of modified bases. Accumulation of impaired AP sites could lead to increased genomic instability that in turn could lead to a more malignant phenotypic behavior of tumors. We, therefore, evaluated the effects of AP sites on survival in resected non-small cell lung cancer (NSCLC) patients. Resected tumor specimens from 99 patients with NSCLC who underwent surgical resection were collected. The enzyme-linked immunosorbent assay was applied to measure the levels of AP sites in tumor DNA. The median number of AP sites per 10(5) nucleotides was 12.4 for all the study subjects. Patients with low levels of AP site had significantly longer survival time compared with ones with medium or high levels of AP site (log-rank test: P=0.015). In Cox regression analysis, patients with medium or high levels of AP sites had over twofold increased hazard of death. In addition, we found a statistically significant correlation between levels of AP sites and age (rho=0.560, P<0.001). The results of this study demonstrated that levels of AP sites could predict survival in resected NSCLC patients. We postulate that an intact BER mechanism may reduce the accumulation of oxidative DNA damage that are thought to contribute to the tumor's malignant potential and therefore the risk of death.

New insights into structure and function of mitochondria and their role in aging and disease

This review covers some novel findings on mitochondrial biochemistry and discusses diseases due to mitochondrial DNA mutations as a model of the changes occurring during physiological aging. The random collision model of organization of the mitochondrial respiratory chain has been recently challenged on the basis of findings of supramolecular organization of respiratory chain complexes. The source of superoxide in Complex I is discussed on the basis of laboratory experiments using a series of specific inhibitors and is presumably iron sulfur center N2. Maternally inherited diseases due to mutations of structural genes in mitochondrial DNA are surveyed as a model of alterations mimicking those occurring during normal aging. The molecular defects in senescence are surveyed on the basis of the "Mitochondrial Theory of Aging", establishing mitochondrial DNA somatic mutations, caused by accumulation of oxygen radical damage, to be at the basis of cellular senescence. Mitochondrial production of reactive oxygen species increases with aging and mitochondrial DNA mutations and deletions accumulate and may be responsible for oxidative phosphorylation defects. Evidence is presented favoring the mitochondrial theory, with primary mitochondrial alterations, although the problem is made more complex by changes in the cross-talk between nuclear and mitochondrial DNA.

A life-history perspective on short- and long-term consequences of compensatory growth

Compensatory or catch-up growth (CG) is widely observed following periods of resource deprivation. Because of this commonness, it is generally assumed that compensatory growth is adaptive, but most theory to date has explicitly ignored considerations of fitness. Following a period of deprivation, when resources become plentiful again, individuals may not respond at all and continue on a "normal" trajectory from a smaller size at age, may exhibit faster-than-normal growth immediately following the end of the period, or may adopt a growth strategy that involves faster-than-normal growth at some later time. Compensating individuals may also overtake control individuals who have been growing normally throughout. We hypothesize that the key to understanding CG is that growth leads to the accumulation of damage at the cellular level that is expressed (and thus must be modeled) at the level of the organism. We show that a life-history model incorporating the mortality consequences of both size and damage provides a framework for understanding compensatory growth. We use the theory to classify physiological and life-history characteristics for which CG is predicted to be the optimal response to deprivation.

Cancer and ageing: a nexus at several levels

Cancer is largely a disease of older people. With the relatively recent expansive growth within the geriatric population, a number of pressing biological and clinical questions that currently remain unanswered need to be addressed. These include what effect age itself has on the development or growth of cancer, and what are the benefits and risks of cancer prevention and treatment for the older person? New insights into the underlying biological processes of ageing provide a frame of reference for addressing these and other related questions.

Genomic instability in laminopathy-based premature aging

Premature aging syndromes often result from mutations in nuclear proteins involved in the maintenance of genomic integrity. Lamin A is a major component of the nuclear lamina and nuclear skeleton. Truncation in lamin A causes Hutchinson-Gilford progerial syndrome (HGPS), a severe form of early-onset premature aging. Lack of functional Zmpste24, a metalloproteinase responsible for the maturation of prelamin A, also results in progeroid phenotypes in mice and humans. We found that Zmpste24-deficient mouse embryonic fibroblasts (MEFs) show increased DNA damage and chromosome aberrations and are more sensitive to DNA-damaging agents. Bone marrow cells isolated from Zmpste24-/- mice show increased aneuploidy and the mice are more sensitive to DNA-damaging agents. Recruitment of p53 binding protein 1 (53BP1) and Rad51 to sites of DNA lesion is impaired in Zmpste24-/- MEFs and in HGPS fibroblasts, resulting in delayed checkpoint response and defective DNA repair. Wild-type MEFs ectopically expressing unprocessible prelamin A show similar defects in checkpoint response and DNA repair. Our results indicate that unprocessed prelamin A and truncated lamin A act dominant negatively to perturb DNA damage response and repair, resulting in genomic instability which might contribute to laminopathy-based premature aging.