A reliable assessment of 8-oxo-2-deoxyguanosine levels in nuclear and mitochondrial DNA using the sodium iodide method to isolate DNA

The thioredoxin system determines CHK1 inhibitor sensitivity via redox-mediated regulation of ribonucleotide reductase activity

Checkpoint kinase 1 (CHK1) is critical for cell survival under replication stress (RS). CHK1 inhibitors (CHK1i's) in combination with chemotherapy have shown promising results in preclinical studies but have displayed minimal efficacy with substantial toxicity in clinical trials. To explore combinatorial strategies that can overcome these limitations, we perform an unbiased high-throughput screen in a non-small cell lung cancer (NSCLC) cell line and identify thioredoxin1 (Trx1), a major component of the mammalian antioxidant-system, as a determinant of CHK1i sensitivity. We establish a role for redox recycling of RRM1, the larger subunit of ribonucleotide reductase (RNR), and a depletion of the deoxynucleotide pool in this Trx1-mediated CHK1i sensitivity. Further, the TrxR inhibitor auranofin, an approved anti-rheumatoid arthritis drug, shows a synergistic interaction with CHK1i via interruption of the deoxynucleotide pool. Together, we show a pharmacological combination to treat NSCLC that relies on a redox regulatory link between the Trx system and mammalian RNR activity.

Quantitation of oxidized nuclear and mitochondrial DNA in plasma samples of patients with abdominal aortic aneurysm

There is accumulating evidence that pro-inflammatory features are inherent to mitochondrial DNA and oxidized DNA species. 8-oxo-7,8-dihydro-2'-deoxyguanosine (8-oxodGuo) is the most frequently studied oxidatively generated lesion. Modified DNA reaches the circulation upon cell apoptosis, necrosis or neutrophil extracellular trap (NET) formation. Standard chromatography-based techniques for the assessment of 8-oxodGuo imply degradation of DNA to a single base level, thus precluding the attribution to a nuclear or mitochondrial origin. We therefore aimed to establish a protocol for the concomitant assessment of oxidized mitochondrial and nuclear DNA from human plasma samples. We applied immunoprecipitation (IP) for 8-oxodGuo to separate oxidized from non-oxidized DNA species and subsequent quantitative polymerase chain reaction (qPCR) to assign them to their subcellular source. The IP procedure failed when applied directly to plasma samples, i.e. isotype control precipitated similar amounts of DNA as the specific 8-oxodGuo antibody. In contrast, DNA isolation from plasma prior to the IP process provided assay specificity with little impact on DNA oxidation status. We further optimized sensitivity and efficiency of qPCR analysis by reducing amplicon length and targeting repetitive nuclear DNA elements. When the established protocol was applied to plasma samples of abdominal aortic aneurysm (AAA) patients and control subjects, the AAA cohort displayed significantly elevated circulating non-oxidized and total nuclear DNA and a trend for increased levels of oxidized mitochondrial DNA. An enrichment of mitochondrial versus nuclear DNA within the oxidized DNA fraction was seen for AAA patients. Regarding the potential source of circulating DNA, we observed a significant correlation of markers of neutrophil activation and NET formation with nuclear DNA, independent of oxidation status. Thus, the established method provides a tool to detect and distinguish the release of oxidized nuclear and mitochondrial DNA in human plasma and offers a refined biomarker to monitor disease conditions of pro-inflammatory cell and tissue destruction.

Sterile inflammation in liver transplantation

Sterile inflammation is the immune response to damage-associated molecular patterns (DAMPs) released during cell death in the absence of foreign pathogens. In the setting of solid organ transplantation, ischemia-reperfusion injury results in mitochondria-mediated production of reactive oxygen and nitrogen species that are a major cause of uncontrolled cell death and release of various DAMPs from the graft tissue. When properly regulated, the immune response initiated by DAMP-sensing serves as means of damage control and is necessary for initiation of recovery pathways and re-establishment of homeostasis. In contrast, a dysregulated or overt sterile inflammatory response can inadvertently lead to further injury through recruitment of immune cells, innate immune cell activation, and sensitization of the adaptive immune system. In liver transplantation, sterile inflammation may manifest as early graft dysfunction, acute graft failure, or increased risk of immunosuppression-resistant rejection. Understanding the mechanisms of the development of sterile inflammation in the setting of liver transplantation is crucial for finding reliable biomarkers that predict graft function, and for development of therapeutic approaches to improve long-term transplant outcomes. Here, we discuss the recent advances that have been made to elucidate the early signs of sterile inflammation and extent of damage from it. We also discuss new therapeutics that may be effective in quelling the detrimental effects of sterile inflammation.

Defining the nuanced nature of redox biology in post-traumatic stress disorder

Post-traumatic stress disorder (PTSD) is a mental health disorder that arises after experiencing or witnessing a traumatic event. Despite affecting around 7% of the population, there are currently no definitive biological signatures or biomarkers used in the diagnosis of PTSD. Thus, the search for clinically relevant and reproducible biomarkers has been a major focus of the field. With significant advances of large-scale multi-omic studies that include genomic, proteomic, and metabolomic data, promising findings have been made, but the field still has fallen short. Amongst the possible biomarkers examined, one area is often overlooked, understudied, or inappropriately investigated: the field of redox biology. Redox molecules are free radical and/or reactive species that are generated as a consequence of the necessity of electron movement for life. These reactive molecules, too, are essential for life, but in excess are denoted as "oxidative stress" and often associated with many diseases. The few studies that have examined redox biology parameters have often utilized outdated and nonspecific methods, as well as have reported confounding results, which has made it difficult to conclude the role for redox in PTSD. Herein, we provide a foundation of how redox biology may underlie diseases like PTSD, critically examine redox studies of PTSD, and provide future directions the field can implement to enhance standardization, reproducibility, and accuracy of redox assessments for the use of diagnosis, prognosis, and therapy of this debilitating mental health disorder.

The multi-tissue landscape of somatic mtDNA mutations indicates tissue-specific accumulation and removal in aging

Accumulation of somatic mutations in the mitochondrial genome (mtDNA) has long been proposed as a possible mechanism of mitochondrial and tissue dysfunction that occurs during aging. A thorough characterization of age-associated mtDNA somatic mutations has been hampered by the limited ability to detect low-frequency mutations. Here, we used Duplex Sequencing on eight tissues of an aged mouse cohort to detect >89,000 independent somatic mtDNA mutations and show significant tissue-specific increases during aging across all tissues examined which did not correlate with mitochondrial content and tissue function. G→A/C→T substitutions, indicative of replication errors and/or cytidine deamination, were the predominant mutation type across all tissues and increased with age, whereas G→T/C→A substitutions, indicative of oxidative damage, were the second most common mutation type, but did not increase with age regardless of tissue. We also show that clonal expansions of mtDNA mutations with age is tissue- and mutation type-dependent. Unexpectedly, mutations associated with oxidative damage rarely formed clones in any tissue and were significantly reduced in the hearts and kidneys of aged mice treated at late age with elamipretide or nicotinamide mononucleotide. Thus, the lack of accumulation of oxidative damage-linked mutations with age suggests a life-long dynamic clearance of either the oxidative lesions or mtDNA genomes harboring oxidative damage.

Detection of Oxidatively Modified Base Lesion(s) in Defined DNA Sequences by FLARE Quantitative PCR

Assessment of DNA base and strand damage can be determined using a quantitative PCR assay that is based on the concept that damage blocks the progression of a thermostable polymerase thus resulting in decreased amplification. However, some of the mutagenic DNA base lesions cause little or no distortion in Watson-Crick base pairing. One of the most abundant such lesion is 8-oxo-7,8-dihydro-2'-deoxyguanosine (8-oxo(d)Gua), although it affects the thermodynamic stability of the DNA, duplex 8-oxo(d)Gua does not inhibit DNA synthesis or arrest most of DNA or RNA polymerases during replication and transcription. When unrepaired, it is a pre-mutagenic base as it pairs with adenine in anti-syn conformation. Recent studies considered 8-oxo(d)Gua as an epigenetic-like mark and along with 8-oxoguanine DNA glycosylase1 (OGG1) and apurinic/apyrimidinic endonuclease1 (APE1) has roles in gene expression via nucleating transcription factor's promoter occupancy. Here, we introduce its identification through fragment length analysis with repair enzyme (FLARE)-coupled quantitative (q)-PCR. One of the strengths of the assay is that 8-oxo(d)Gua can be identified within short stretches of nuclear and mitochondrial DNA in ng quantities. Bellow we describe the benefits and limits of using FLARE qPCR to assess DNA damage in mammalian cells and provide a detailed protocol of the assay.

Targeting the PANoptosome with 3,4-Methylenedioxy-β-Nitrostyrene, Reduces PANoptosis and Protects the Kidney against Renal İschemia-Reperfusion Injury

OBJECTIVES

The objectives of this study were a) to investigate the effect of targeting the PANoptosome with 3,4-methylenedioxy-β-nitrostyrene (MNS) on PANoptosis in the Renal ischemia-reperfussion (RIR) model b) to investigate the kidney protective effect of MNS toward RIR injury.

METHODS

Thirty-two rats were divided into four groups randomly. The groups were assigned as Control, Sham, DMSO (dimethyl sulfoxide) and MNS groups. The rats in the MNS group were intraperitoneally given 20 mg/kg of MNS 30 minutes before reperfusion. 2% DMSO solvent that dissolves MNS were given to the rats in DMSO group. Left nephrectomy was performed on the rats under anesthesia at the 6th hour after reperfusion. Glutathione peroxidase (GPx), malondialdehyde (MDA), catalase (CAT), superoxide dismutase (SOD) and 8-Okso-2'-deoksiguanozin (8-OHdG) levels were measured. Immunohistochemical analysis, electron microscopic and histological examinations were carried out in the tissues.

RESULTS

Total tubular injury score was lower in the MNS group (p < 0.001). Caspase-3, Gasdermin D and MLK (Mixed Lineage Kinase Domain Like Pseudokinase) expressions were considerably decreased in the MNS group (p < 0.001). Apoptotic index (AI) was found to be low in the MNS group (p < 0.001). CAT and SOD levels were higher in the MNS Group (p = 0.006, p = 0.0004, respectively). GPx, MDA, and 8-OH-dG levels were similar (p > 0.05) in all groups. MNS considerably improved the tissue structure, based on the electron microscopic analysis.

CONCLUSIONS

Our results suggested that MNS administrated before the reperfusion reduces pyroptosis, apoptosis and necroptosis. These findings suggest that MNS significantly protects the kidney against RIR injury by reducing PANoptosis as a result of specific inhibition of Nod-like receptor pyrin domain-containing 3 (NLRP 3), one of the PANoptosome proteins.

Dynamic features of human mitochondrial DNA maintenance and transcription

Mitochondria are the primary sites for cellular energy production and are required for many essential cellular processes. Mitochondrial DNA (mtDNA) is a 16.6 kb circular DNA molecule that encodes only 13 gene products of the approximately 90 different proteins of the respiratory chain complexes and an estimated 1,200 mitochondrial proteins. MtDNA is, however, crucial for organismal development, normal function, and survival. MtDNA maintenance requires mitochondrially targeted nuclear DNA repair enzymes, a mtDNA replisome that is unique to mitochondria, and systems that control mitochondrial morphology and quality control. Here, we provide an overview of the current literature on mtDNA repair and transcription machineries and discuss how dynamic functional interactions between the components of these systems regulate mtDNA maintenance and transcription. A profound understanding of the molecular mechanisms that control mtDNA maintenance and transcription is important as loss of mtDNA integrity is implicated in normal process of aging, inflammation, and the etiology and pathogenesis of a number of diseases.

8-oxoguanine and 8-oxodeoxyguanosine Biomarkers of Oxidative DNA Damage: A Review on HPLC-ECD Determination

Reactive oxygen species (ROS) are continuously produced in living cells due to metabolic and biochemical reactions and due to exposure to physical, chemical and biological agents. Excessive ROS cause oxidative stress and lead to oxidative DNA damage. Within ROS-mediated DNA lesions, 8-oxoguanine (8-oxoG) and its nucleotide 8-oxo-2'-deoxyguanosine (8-oxodG)-the guanine and deoxyguanosine oxidation products, respectively, are regarded as the most significant biomarkers for oxidative DNA damage. The quantification of 8-oxoG and 8-oxodG in urine, blood, tissue and saliva is essential, being employed to determine the overall effects of oxidative stress and to assess the risk, diagnose, and evaluate the treatment of autoimmune, inflammatory, neurodegenerative and cardiovascular diseases, diabetes, cancer and other age-related diseases. High-performance liquid chromatography with electrochemical detection (HPLC-ECD) is largely employed for 8-oxoG and 8-oxodG determination in biological samples due to its high selectivity and sensitivity, down to the femtomolar range. This review seeks to provide an exhaustive analysis of the most recent reports on the HPLC-ECD determination of 8-oxoG and 8-oxodG in cellular DNA and body fluids, which is relevant for health research.

Effects of prenatal testosterone on cumulative markers of oxidative damage to organs of young adult zebra finches (Taeniopygia guttata)

We tested the hypothesis that exposure of avian embryos to androgens in ovo entails long-term costs in the form of oxidative damage to vital cells and organs in adulthood. We injected zebra finch eggs with testosterone (T), monitored postnatal growth, and analyzed markers of oxidative damage in heart and liver in mature birds. We measured 8-oxo-2'-deoxyguanosine and isoprostanes, markers of oxidative damage to DNA and membrane lipids, respectively. T treatment (1) reduced growth rates of female but not male nestlings vs. controls; (2) resulted in less accumulation of 8-oxo-dG, but not IsoPs, in liver tissue of 60-day-old females, but not males; and (3) a trend toward elevated 8-oxo-dG levels in heart tissue of males and females at 60 and 180 days old combined. These results generally support the testosterone oxidative damage hypothesis, in that embryonic exposure to higher T resulted in damage to DNA of heart tissue in both sexes. They also suggest that sex-specific effects of androgens on early growth rates may carry over as differences in some forms of oxidative damage in adults. This supports a basic tenet of evolutionary aging theory that developmental influences early in life can be linked to costs later on.

DNA Methylation and Establishing Memory

A single event can cause a life-long memory. Memories physically reside in neurons, and changes in neuronal gene expression are considered to be central to memory. Early models proposed that specific DNA methylations of cytosines in neuronal DNA encode memories in a stable biochemical form. This review describes recent research that elucidates the molecular mechanisms used by the mammalian brain to form DNA methylcytosine encoded memories. For example, neuron activation initiates cytosine demethylation by stimulating DNA topoisomerase II beta (TOP2B) protein to make a temporary DNA double-strand break (repaired within about 2 hours) at a promoter of an immediate early gene, EGR1, allowing expression of this gene. The EGR1 proteins then recruit methylcytosine dioxygenase TET1 proteins to initiate demethylation at several hundred genes, facilitating expression of those genes. Initiation of demethylation of cytosine also occurs when OGG1 localizes at oxidized guanine in a methylated CpG site and recruits TET1 for initiation of demethylation at that site. DNMT3A2 is another immediate early gene upregulated by synaptic activity. DNMT3A2 protein catalyzes de novo DNA methylations. These several mechanisms convert external experiences into DNA methylations and initiated demethylations of neuronal DNA cytosines, causing changes in gene expression that are the basis of long-term memories.

Expression of miR-200c corresponds with increased reactive oxygen species and hypoxia markers after transient focal ischemia in mice

Embolic stroke results in a necrotic core of cells destined to die, but also a peri-ischemic, watershed penumbral region of potentially salvageable brain tissue. Approaches to effectively differentiate between the ischemic and peri-ischemic zones is critical for novel therapeutic discovery to improve outcomes in survivors of stroke. MicroRNAs are a class of small non-coding RNAs regulating gene translation that have region- and cell-specific expression and responses to ischemia. We have previously reported that global inhibition of cerebral microRNA-200c after experimental stroke in mice is protective, however delineating the post-stroke sub-regional and cell-type specific patterns of post-stroke miR-200c expression are necessary to minimize off-target effects and advance translational application. Here, we detail a novel protocol to visualize regional miR-200c expression after experimental stroke, complexed with visualization of regional ischemia and markers of oxidative stress in an experimental stroke model in mice. In the present study we demonstrate that the fluorescent hypoxia indicator pimonidazole hydrochloride, the reactive-oxygen-species marker 8-hydroxy-deoxyguanosine, neuronal marker MAP2 and NeuN, and the reactive astrocyte marker GFAP can be effectively complexed to determine regional differences in ischemic injury as early as 30 min post-reperfusion after experimental stroke, and can be effectively used to distinguish ischemic core from surrounding penumbral and unaffected regions for targeted therapy. This multi-dimensional post-stroke immunofluorescent imaging protocol enables a greater degree of sub-regional mechanistic investigation, with the ultimate goal of developing more effective post-stroke pharmaceutical therapy.

How Robust is the Evidence for a Role of Oxidative Stress in Autism Spectrum Disorders and Intellectual Disabilities?

Growing interest in the pathogenesis of autism spectrum disorders (ASDs) and other intellectual and developmental disabilities (IDD) has led to emerging evidence implicating a role for oxidative stress. However, understanding the strength of this association is made challenging by the use of a variety of purported biomarkers of oxidative stress, many of which have either uncertain specificity or flawed methods of analysis. This review aims to address this issue, which is widespread in the ASD and IDD literature, by providing readers with information concerning the strengths and limitations of the choice and analysis of biomarkers of oxidative stress. We highlight that biomarkers and assays should be specific, sensitive, reproducible, precise, robust, and chosen with careful consideration. Future studies should be sufficiently powered and address sample collection, processing, and storage which are, additionally, poorly considered, sources of bad practice, and potential errors. Only with these issues considered, will the data lead to conclusions as to the precise role of oxidative stress in ASDs and IDD.

The involvement of nucleotide excision repair proteins in the removal of oxidative DNA damage

The six major mammalian DNA repair pathways were discovered as independent processes, each dedicated to remove specific types of lesions, but the past two decades have brought into focus the significant interplay between these pathways. In particular, several studies have demonstrated that certain proteins of the nucleotide excision repair (NER) and base excision repair (BER) pathways work in a cooperative manner in the removal of oxidative lesions. This review focuses on recent data showing how the NER proteins, XPA, XPC, XPG, CSA, CSB and UV-DDB, work to stimulate known glycosylases involved in the removal of certain forms of base damage resulting from oxidative processes, and also discusses how some oxidative lesions are probably directly repaired through NER. Finally, since many glycosylases are inhibited from working on damage in the context of chromatin, we detail how we believe UV-DDB may be the first responder in altering the structure of damage containing-nucleosomes, allowing access to BER enzymes.

SIRT1 Activation Using CRISPR/dCas9 Promotes Regeneration of Human Corneal Endothelial Cells through Inhibiting Senescence

Human corneal endothelial cells (hCECs) are restricted in proliferative capacity in vivo. Reduction in the number of hCEC leads to persistent corneal edema requiring corneal transplantation. This study demonstrates the functions of SIRT1 in hCECs and its potential for corneal endothelial regeneration. Cell morphology, cell growth rates and proliferation-associated proteins were compared in normal and senescent hCECs. SIRT1 was activated using the CRISPR/dCas9 activation system (SIRT1a). The plasmids were transfected into CECs of six-week-old Sprague–Dawley rats using electroporation and cryoinjury was performed. Senescent cells were larger, elongated and showed lower proliferation rates and lower SIRT1 levels. SIRT1 activation promoted the wound healing of CECs. In vivo transfection of SIRT1a promoted the regeneration of CECs. The proportion of the S-phase cells was lower in senescent cells and elevated upon SIRT1a activation. SIRT1 regulated cell proliferation, proliferation-associated proteins, mitochondrial membrane potential, and oxidative stress levels. In conclusion, corneal endothelial senescence is related with a decreased SIRT1 level. SIRT1a promotes the regeneration of CECs by inhibiting cytokine-induced cell death and senescence. Gene function activation therapy using SIRT1a may serve as a novel treatment strategy for hCEC diseases.

Bioactive Plasma Mitochondrial DNA Is Associated With Disease Progression in Scleroderma-Associated Interstitial Lung Disease

OBJECTIVE

Systemic sclerosis-associated interstitial lung disease (SSc-ILD) is characterized by variable clinical outcomes, activation of innate immune pattern-recognition receptors (PRRs), and accumulation of α-smooth muscle actin (α-SMA)-expressing myofibroblasts. The aim of this study was to identify an association between these entities and mitochondrial DNA (mtDNA), an endogenous ligand for the intracellular DNA-sensing PRRs Toll-like receptor 9 (TLR-9) and cyclic GMP-AMP synthase/stimulator of interferon genes (cGAS/STING), which has yet to be determined.

METHODS

Human lung fibroblasts (HLFs) from normal donors and SSc-ILD explants were treated with synthetic CpG DNA and assayed for α-SMA expression and extracellular mtDNA using quantitative polymerase chain reaction for the human MT-ATP6 gene. Plasma MT-ATP6 concentrations were evaluated in 2 independent SSc-ILD cohorts and demographically matched controls. The ability of SSc-ILD and control plasma to induce TLR-9 and cGAS/STING activation was evaluated with commercially available HEK 293 reporter cells. Plasma concentrations of type I interferons (IFNs), interleukin-6 (IL-6), and oxidized DNA were measured using electrochemiluminescence and enzyme-linked immunosorbent assay-based methods. Extracellular vesicles (EVs) precipitated from plasma were evaluated for MT-ATP6 concentrations and proteomics via liquid chromatography mass spectrometry.

RESULTS

Normal HLFs and SSc-ILD fibroblasts developed increased α-SMA expression and MT-ATP6 release following CpG stimulation. Plasma mtDNA concentrations were increased in the 2 SSc-ILD cohorts, reflective of ventilatory decline, and were positively associated with both TLR-9 and cGAS/STING activation as well as type I IFN and IL-6 expression. Plasma mtDNA was not oxidized and was conveyed by EVs displaying a proteomics profile consistent with a multicellular origin.

CONCLUSION

These findings demonstrate a previously unrecognized connection between EV-encapsulated mtDNA, clinical outcomes, and intracellular DNA-sensing PRR activation in SSc-ILD. Further study of these interactions could catalyze novel mechanistic and therapeutic insights into SSc-ILD and related disorders.

Mitochondrial DNA damage as a potential biomarker of LRRK2 kinase activity in LRRK2 Parkinson's disease

Leucine-rich repeat kinase 2 (LRRK2) is a promising therapeutic target for the treatment of Parkinson's disease (PD) and LRRK2 kinase inhibitors are currently being tested in early phase clinical trials. In order to ensure the highest chance of success, a biomarker-guided entry into clinical trials is key. LRRK2 phosphorylation, and phosphorylation of the LRRK2 substrate Rab10, have been proposed as target engagement biomarkers for LRRK2 kinase inhibition. However, a pharmacodynamic biomarker to demonstrate that a biological response has occurred is lacking. We previously discovered that the LRRK2 G2019S mutation causes mitochondrial DNA (mtDNA) damage and is LRRK2 kinase activity-dependent. Here, we have explored the possibility that measurement of mtDNA damage is a "surrogate" for LRRK2 kinase activity and consequently of kinase inhibitor activity. Mitochondrial DNA damage was robustly increased in PD patient-derived immune cells with LRRK2 G2019S mutations as compared with controls. Following treatment with multiple classes of LRRK2 kinase inhibitors, a full reversal of mtDNA damage to healthy control levels was observed and correlated with measures of LRRK2 dephosphorylation. Taken together, assessment of mtDNA damage levels may be a sensitive measure of altered kinase activity and provide an extended profile of LRRK2 kinase modulation in clinical studies.

Understanding the Functional Impact of VOC-Ozone Mixtures on the Chemistry of RNA in Epithelial Lung Cells

Introduction

Ambient air pollution is associated with premature death caused by heart disease, stroke, chronic obstructive pulmonary disease (COPD), and lung cancer. Recent studies have suggested that ribonucleic acid (RNA) oxidation is a sensitive environment-related biomarker that is implicated in pathogenesis.

Aims and Methods

We used a novel approach that integrated RNA-Seq analysis with detection by immunoprecipitation techniques of the prominent RNA oxidative modification 8-oxo-7,8-dihydroguanine (8-oxoG). Our goal was to uncover specific messenger RNA (mRNA) oxidation induced by mixtures of volatile organic compounds (VOCs) and ozone in healthy human epithelial lung cells. To this end, we exposed the BEAS-2B human epithelial lung cell line to the gas- and particle-phase products formed from reactions of 790 ppb acrolein (ACR) and 670 ppb methacrolein (MACR) with 4 ppm ozone.

Results

Using this approach, we identified 222 potential direct targets of oxidation belonging to previously described pathways, as well as uncharacterized pathways, after air pollution exposures. We demonstrated the effect of our VOC-ozone mixtures on the morphology and actin cytoskeleton of lung cells, suggesting the influence of selective mRNA oxidation in members of pathways regulating physical components of the cells. In addition, we observed the influence of the VOC-ozone mixtures on metabolic cholesterol synthesis, likely implicated as a result of the incidence of mRNA oxidation and the deregulation of protein levels of squalene synthase (farnesyl-diphosphate farnesyltransferase 1 [FDFT1]), a key enzyme in endogenous cholesterol biosynthesis.

Conclusions

Overall, our findings indicate that air pollution influences the accumulation of 8-oxoG in transcripts of epithelial lung cells that largely belong to stress-induced signaling and metabolic and structural pathways. A strength of the study was that it combined traditional transcriptome analysis with transcriptome-wide 8-oxoG mapping to facilitate the discovery of underlying processes not characterized by earlier approaches. Investigation of the processes mediated by air pollution oxidation of RNA molecules in primary cells and animal models needs to be explored in future studies. Our research has thus opened new avenues to further inform the relationship between atmospheric agents on the one hand and cellular responses on the other that are implicated in diseases.

Thioredoxin overexpression in mitochondria showed minimum effects on aging and age-related diseases in male C57BL/6 mice

Objective:

In this study, the effects of overexpression of thioredoxin 2 (Trx2) on aging and age-related diseases were examined using Trx2 transgenic mice [Tg(TXN2]^+/0]. Because our previous studies demonstrated that thioredoxin (Trx) overexpression in the cytosol (Trx1) did not extend maximum lifespan, this study was conducted to test if increased Trx2 expression in mitochondria shows beneficial effects on aging and age-related pathology.

Methods:

Trx2 transgenic mice were generated using a fragment of the human genome containing the TXN2 gene. Effects of Trx2 overexpression on survival, age-related pathology, oxidative stress, and redox-sensitive signaling pathways were examined in male Tg(TXN2)^+/0 mice.

Results:

Trx2 levels were significantly higher (approximately 1.6- to 5-fold) in all of the tissues we examined in Tg(TXN2)^+/0 mice compared to wild-type (WT) littermates, and the expression levels were maintained during aging (up to 22-24 months old). Trx2 overexpression did not alter the levels of Trx1, glutaredoxin, glutathione, or other major antioxidant enzymes. Overexpression of Trx2 was associated with reduced reactive oxygen species (ROS) production from mitochondria and lower isoprostane levels compared to WT mice. When we conducted the survival study, male Tg(TXN2)^+/0 mice showed a slight extension (approximately 8-9%] of mean, median, and 10th percentile lifespans; however, the survival curve was not significantly different from WT mice. Cross-sectional pathological analysis (22-24 months old) showed that Tg(TXN2)^+/0 mice had a slightly higher severity of lymphoma; however, tumor burden, disease burden, and severity of glomerulonephritis and inflammation were similar to WT mice. Trx2 overexpression was also associated with higher c-Jun and c-Fos levels; however, mTOR activity and levels of NFκB p65 and p50 were similar to WT littermates.

Conclusions:

Our findings suggest that the increased levels of Trx2 in mitochondria over the lifespan in Tg(TXN2)^+/0 mice showed a slight life-extending effect, reduced ROS production from mitochondria and oxidative damage to lipids, but showed no significant effects on aging and age-related diseases.

Oxidative Stress in Cognitive and Epigenetic Aging: A Retrospective Glance

Brain aging is the critical and common factor among several neurodegenerative disorders and dementia. Cellular, biochemical and molecular studies have shown intimate links between oxidative stress and cognitive dysfunction during aging and age-associated neuronal diseases. Brain aging is accompanied by oxidative damage of nuclear as well as mitochondrial DNA, and diminished repair. Recent studies have reported epigenetic alterations during aging of the brain which involves reactive oxygen species (ROS) that regulates various systems through distinct mechanisms. However, there are studies which depict differing roles of reactive oxidant species as a major factor during aging. In this review, we describe the evidence to show how oxidative stress is intricately linked to age-associated cognitive decline. The review will primarily focus on implications of age-associated oxidative damage on learning and memory, and the cellular events, with special emphasis on associated epigenetic machinery. A comprehensive understanding of these mechanisms may provide a perspective on the development of potential therapeutic targets within the oxidative system.

Helicobacter pylori severely reduces expression of DNA repair proteins PMS2 and ERCC1 in gastritis and gastric cancer

Gastric cancers are the third leading cause of cancer mortality in the world. Helicobacter pylori causes over 60 % of all stomach cancers. Colonization of the gastric mucosa by H. pylori results in increased DNA damage. Repair of DNA damage may also be reduced by H. pylori infection. Reduced DNA repair in combination with increased DNA damage can cause carcinogenic mutations. During progression to gastric cancer, gastric epithelium goes through stages of increasing pathology. Determining the levels of DNA repair enzymes during progression to gastric cancer could illuminate treatment approaches. Our aim is to determine the level of gastric expression of DNA repair proteins ERCC1 (a nucleotide excision repair enzyme) and PMS2 (a mismatch repair enzyme) in the presence of H. pylori infection at successive stages of gastric pathology and in gastric cancers. We analyzed gastric tissues of 300 individuals, including 30 without dyspepsia, 200 with dyspepsia and 70 with gastric cancers. The presence of H. pylori, gastric pathology and expression of DNA repair proteins ERCC1 and PMS2 were evaluated. Infection by H. pylori carrying the common cagA gene reduced median nuclear expression of ERCC1 and PMS2 to less than 20 % and 15 % of normal, respectively, in all pathologic stages preceding cancer. ERCC1 and PMS2 nuclear expression was 0-5 % of normal in gastric cancers. H. pylori can cause deficiency of ERCC1 and PMS2 protein expression. These deficiencies are associated with gastric pathology and cancer. This reduction in DNA repair likely causes carcinogenic mutations. Substantially reduced ERCC1 and PMS2 expression appears to be an early step in progression to H. pylori-induced gastric cancer.

DNA damage accumulates and responses are engaged in human ALS brain and spinal motor neurons and DNA repair is activatable in iPSC-derived motor neurons with SOD1 mutations

DNA damage is implicated in the pathogenesis of amyotrophic lateral sclerosis (ALS). However, relationships between DNA damage accumulation, DNA damage response (DDR), and upper and lower motor neuron vulnerability in human ALS are unclear; furthermore, it is unknown whether epigenetic silencing of DNA repair pathways contributes to ALS pathogenesis. We tested the hypotheses that DNA damage accumulates in ALS motor neurons along with diminished DDR, and that DNA repair genes undergo hypermethylation. Human postmortem CNS tissue was obtained from ALS cases (N = 34) and age-matched controls without neurologic disease (N = 15). Compared to age-matched controls, abasic sites accumulated in genomic DNA of ALS motor cortex and laser capture microdissection-acquired spinal motor neurons but not in motor neuron mitochondrial DNA. By immunohistochemistry, DNA damage accumulated significantly in upper and lower motor neurons in ALS cases as single-stranded DNA and 8-hydroxy-deoxyguanosine (OHdG) compared to age-matched controls. Significant DDR was engaged in ALS motor neurons as evidenced by accumulation of c-Abl, nuclear BRCA1, and ATM activation. DNA damage and DDR were present in motor neurons at pre-attritional stages and throughout the somatodendritic attritional stages of neurodegeneration. Motor neurons with DNA damage were also positive for activated p53 and cleaved caspase-3. Gene-specific promoter DNA methylation pyrosequencing identified the DNA repair genes Ogg1, Apex1, Pnkp and Aptx as hypomethylated in ALS. In human induced-pluripotent stem cell (iPSC)-derived motor neurons with familial ALS SOD1 mutations, DNA repair capacity was similar to isogenic control motor neurons. Our results show that vulnerable neurons in human ALS accumulate DNA damage, and contrary to our hypothesis, strongly activate and mobilize response effectors and DNA repair genes. This DDR in ALS motor neurons involves recruitment of c-Abl and BRCA1 to the nucleus in vivo, and repair of DNA double-strand breaks in human ALS motor neurons with SOD1 mutations in cell culture.

Interplay of Guanine Oxidation and G-Quadruplex Folding in Gene Promoters

Living in an oxygen atmosphere demands an ability to thrive in the presence of reactive oxygen species (ROS). Aerobic organisms have successfully found solutions to the oxidative threats imposed by ROS by evolving an elaborate detoxification system, upregulating ROS during inflammation, and utilizing ROS as messenger molecules. In this Perspective, recent studies are discussed that demonstrate ROS as signaling molecules for gene regulation by combining two emergent properties of the guanine (G) heterocycle in DNA, namely, oxidation sensitivity and a propensity for G-quadruplex (G4) folding, both of which depend upon sequence context. In human gene promoters, this results from an elevated 5'-GG-3' dinucleotide frequency and GC enrichment near transcription start sites. Oxidation of DNA by ROS drives conversion of G to 8-oxo-7,8-dihydroguanine (OG) to mark target promoters for base excision repair initiated by OG-glycosylase I (OGG1). Sequence-dependent mechanisms for gene activation are available to OGG1 to induce transcription. Either OGG1 releases OG to yield an abasic site driving formation of a non-canonical fold, such as a G4, to be displayed to apurinic/apyrimidinic 1 (APE1) and stalling on the fold to recruit activating factors, or OGG1 binds OG and facilitates activator protein recruitment. The mechanisms described drive induction of stress response, DNA repair, or estrogen-induced genes, and these pathways are novel potential anticancer targets for therapeutic intervention. Chemical concepts provide a framework to discuss the regulatory or possible epigenetic potential of the OG modification in DNA, in which DNA "damage" and non-canonical folds collaborate to turn on or off gene expression. The next steps for scientific discovery in this growing field are discussed.

The genomics of oxidative DNA damage, repair, and resulting mutagenesis

Reactive oxygen species are a constant threat to DNA as they modify bases with the risk of disrupting genome function, inducing genome instability and mutation. Such risks are due to primary oxidative DNA damage and also mediated by the repair process. This leads to a delicate decision process for the cell as to whether to repair a damaged base at a specific genomic location or better leave it unrepaired. Persistent DNA damage can disrupt genome function, but on the other hand it can also contribute to gene regulation by serving as an epigenetic mark. When such processes are out of balance, pathophysiological conditions could get accelerated, because oxidative DNA damage and resulting mutagenic processes are tightly linked to ageing, inflammation, and the development of multiple age-related diseases, such as cancer and neurodegenerative disorders. Recent technological advancements and novel data analysis strategies have revealed that oxidative DNA damage, its repair, and related mutations distribute heterogeneously over the genome at multiple levels of resolution. The involved mechanisms act in the context of genome sequence, in interaction with genome function and chromatin. This review addresses what we currently know about the genome distribution of oxidative DNA damage, repair intermediates, and mutations. It will specifically focus on the various methodologies to measure oxidative DNA damage distribution and discuss the mechanistic conclusions derived from the different approaches. It will also address the consequences of oxidative DNA damage, specifically how it gives rise to mutations, genome instability, and how it can act as an epigenetic mark.

Role of Oxidative Stress and Metal Toxicity in the Progression of Alzheimer's Disease

Alzheimer's disease (AD) is one of the life-threatening neurodegenerative disorders in the elderly (>60 years) and incurable across the globe to date. AD is caused by the involvement of various genetic, environmental and lifestyle factors that affect neuronal cells to degenerate over the period of time. The oxidative stress is engaged in the pathogenesis of various disorders and its key role is also linked to the etiology of AD. AD is attributed by neuronal loss, abnormal accumulation of Amyloid-β (Aβ) and neurofibrillary tangles (NFTs) with severe memory impairments and other cognitive dysfunctions which lead to the loss of synapses and neuronal death and eventual demise of the individual. Increased production of reactive oxygen species (ROS), loss of mitochondrial function, altered metal homeostasis, aberrant accumulation of senile plaque and mitigated antioxidant defense mechanism all are indulged in the progression of AD. In spite of recent advances in biomedical research, the underlying mechanism of disruption of redox balance and the actual source of oxidative stress is still obscure. This review highlights the generation of ROS through different mechanisms, the role of some important metals in the progression of AD and free radical scavenging by endogenous molecule and supplementation of nutrients in AD.

Honey as an antioxidant therapy to reduce cognitive ageing

This paper reviews the potential role of honey as a therapeutic antioxidant to reduce oxidative stress and improve cognitive ageing. All articles indexed to PubMed Central (PMC) were searched using the following key words: honey, antioxidant, memory and ageing. Honey is a natural insect-derived product with therapeutic, medicinal and nutritional values. Antioxidant properties of honey quench biologically-circulating reactive oxygen species (ROS) and counter oxidative stress while restoring the cellular antioxidant defense system. Antioxidant properties of honey may complement its nootropic effects to reduce cognitive ageing.

Measurement of Oxidatively Induced DNA Damage in Caenorhabditis elegans with High-Salt DNA Extraction and Isotope-Dilution Mass Spectrometry

Caenorhabditis elegans is used extensively as a medical and toxicological model organism. However, little is known about background levels of oxidatively induced DNA damage in the nematode or how culturing methods affect DNA damage levels. The tough C. elegans cuticle makes it challenging to extract genomic DNA without harsh procedures that can artifactually increase DNA damage. Therefore, a mild extraction protocol based on enzymatic digestion of the C. elegans cuticle with high-salt phase-separation of DNA has been developed and optimized. This method allows for efficient extraction of >50 μg DNA using a minimum of 250000 nematodes grown in liquid culture. The extracted DNA exhibited acceptable RNA levels (<10% contamination), functionality in polymerase chain reaction assays, and reproducible DNA fragmentation. Gas chromatography/tandem mass spectrometry (GC-MS/MS) with isotope-dilution measured lower lesion levels in high-salt extracts than in phenol extracts. Phenolic extraction produced a statistically significant increase in 8-hydroxyguanine, a known artifact, and additional artifactual increases in 2,6-diamino-4-hydroxy-5-formamidopyrimidine, 4,6-diamino-5-formamidopyrimidine, and 8-hydroxyadenine. The high-salt DNA extraction procedure utilizes green solvents and reagents and minimizes artifactual DNA damage, making it more suitable for molecular and toxicological studies in C. elegans. This is, to our knowledge, the first use of GC-MS/MS to measure multiple 8,5'-cyclopurine-2'-deoxynucleosides in a toxicologically important terrestrial organism.

Pyrimidine Ring-Opened Product from Oxidative DNA Damage of 5-Formyl-2'-deoxyuridine

After thymidine (dT) was treated with a Fenton-type reagent and further incubated for a long period (6 days) under physiological conditions (37 °C, pH 7.4), a new product, named dT*, was detected by HPLC in addition to the free thymine base and the known oxidative dT damage, 5-formyl-2'-deoxyuridine (f⁵dU). dT* was found to be formed from f⁵dU. The structure of dT* was determined to be 3-amino-2-carbamoyl-2-propenal-N³-2'-deoxyriboside, a pyrimidine ring-opened product from f⁵dU, on the basis of ¹H- and ¹³C NMR analyses and mass spectra. From the model compound 1-methyl-5-formyluracil, a similar ring-opened product was formed after the incubation. dT* was also detected in DNA treated with a Fenton-type reagent or γ-rays, followed by the prolonged incubation. dT* will be a new promising marker of oxidative DNA damage. The possible role of this product in oxy-radical-induced mutagenesis is discussed.

Measurement of the Oxidative DNA Lesion 8-Oxoguanine (8-oxoG) by ELISA or by High-Performance Liquid Chromatography (HPLC) with Electrochemical Detection

Reactive oxygen species (ROS) can oxidize cellular macromolecules like DNA, causing DNA damage. The most common form of DNA damage is the 8-oxoguanine (8-oxoG) lesion, typically repaired by the base excision repair (BER) pathway, which is initiated by the enzyme oxoguanine glycosylase 1 (OGG1). ROS are produced endogenously and can be enhanced by environmental factors, such as xenobiotics, radiation, and microbial pathogens. As a commonly used biomarker of oxidative damage, 8-oxoG can be measured in two different ways described herein. Commercially available ELISA kits allow for easy detection of the 8-oxoG lesion, while more difficult HPLC assays with UV and electrochemical detection allow for a more definitive identification and quantification of 8-oxoG.

Heteroplasmy Shifting as Therapy for Mitochondrial Disorders

Mitochondrial disease can arise due to pathogenic sequence variants in the mitochondrial DNA (mtDNA) that prevent cells from meeting their energy demands. Mitochondrial diseases are often fatal and currently there are no treatments directed towards the underlying cause of disease. Pathogenic variants in mtDNA often exist in a state of heteroplasmy, with coexistence of pathogenic and wild type mtDNA. The load of heteroplasmy, defined as the relative amount of pathogenic mtDNA to wild type mtDNA, corresponds to timing and symptom severity. Thus, changing the heteroplasmy load may lead to a shift in disease onset and symptom severity. Here we review techniques aimed at preventing inheritance of pathogenic mtDNA via mitochondrial replacement therapy (MRT) and strategies geared toward shifting of heteroplasmy in individuals with active mitochondrial disease. MRT strategies seek to create embryos with the nuclear genetic makeup of the intended parents and wild type mtDNA from a donor in order to avoid known maternal pathogenic variants. Heteroplasmy shift approaches in patients are of two categories: nuclease dependent and nuclease independent strategies. Despite initial success in mouse models and patient cells, these techniques have not reached clinical use. Translational attempts in this area are urgently needed to improve therapies for a currently untreatable set of disorders.

Genomic landscape of oxidative DNA damage and repair reveals regioselective protection from mutagenesis

BACKGROUND

DNA is subject to constant chemical modification and damage, which eventually results in variable mutation rates throughout the genome. Although detailed molecular mechanisms of DNA damage and repair are well understood, damage impact and execution of repair across a genome remain poorly defined.

RESULTS

To bridge the gap between our understanding of DNA repair and mutation distributions, we developed a novel method, AP-seq, capable of mapping apurinic sites and 8-oxo-7,8-dihydroguanine bases at approximately 250-bp resolution on a genome-wide scale. We directly demonstrate that the accumulation rate of apurinic sites varies widely across the genome, with hot spots acquiring many times more damage than cold spots. Unlike single nucleotide variants (SNVs) in cancers, damage burden correlates with marks for open chromatin notably H3K9ac and H3K4me2. Apurinic sites and oxidative damage are also highly enriched in transposable elements and other repetitive sequences. In contrast, we observe a reduction at chromatin loop anchors with increased damage load towards inactive compartments. Less damage is found at promoters, exons, and termination sites, but not introns, in a seemingly transcription-independent but GC content-dependent manner. Leveraging cancer genomic data, we also find locally reduced SNV rates in promoters, coding sequence, and other functional elements.

CONCLUSIONS

Our study reveals that oxidative DNA damage accumulation and repair differ strongly across the genome, but culminate in a previously unappreciated mechanism that safeguards the regulatory and coding regions of genes from mutations.

The Comparative Biology of Mitochondrial Function and the Rate of Aging

The mitochondrial hypothesis of aging evolved from the rate-of-living theory. That theory posited that the rate of aging was largely determined by the rate of energy expenditure. The mechanistic link between energy expenditure and aging was hypothesized to be oxidative stress. As both energy expenditure and reactive oxygen species (ROS) centered on the mitochondria that organelle became a central focus of aging research. Until about the turn of the 21st century available evidence largely supported the efficiency of mitochondrial function as a key contributor to aging. However as methods for investigating mitochondrial oxidant production and tissue level oxidative damage improved, evidentiary support for the theory weakened. Recently, direct disruption of mitochondrial function has been shown not to shorten life or health as expected, but in many cases in multiple laboratory species disrupted mitochondrial function has lengthened life, sometimes without apparent tradeoffs. Does this mean that mitochondrial function plays no role in aging as had been posited for many years? One key consideration is that experiments under laboratory conditions can be misleading about physiological processes that occur in the uncertain conditions of nature. Before we discard the mitochondrial hypothesis of aging, more field experiments targeted at that hypothesis need to be performed. Fortunately, emerging technology is making such experiment more possible than ever before.

DNA polymerase β: A missing link of the base excision repair machinery in mammalian mitochondria

Mitochondrial genome integrity is fundamental to mammalian cell viability. Since mitochondrial DNA is constantly under attack from oxygen radicals released during ATP production, DNA repair is vital in removing oxidatively generated lesions in mitochondrial DNA, but the presence of a strong base excision repair system has not been demonstrated. Here, we addressed the presence of such a system in mammalian mitochondria involving the primary base lesion repair enzyme DNA polymerase (pol) β. Pol β was localized to mammalian mitochondria by electron microscopic-immunogold staining, immunofluorescence co-localization and biochemical experiments. Extracts from purified mitochondria exhibited base excision repair activity that was dependent on pol β. Mitochondria from pol β-deficient mouse fibroblasts had compromised DNA repair and showed elevated levels of superoxide radicals after hydrogen peroxide treatment. Mitochondria in pol β-deficient fibroblasts displayed altered morphology by electron microscopy. These results indicate that mammalian mitochondria contain an efficient base lesion repair system mediated in part by pol β and thus pol β plays a role in preserving mitochondrial genome stability.

MMS19 localizes to mitochondria and protects the mitochondrial genome from oxidative damage

MMS19 localizes to the cytoplasmic and nuclear compartments involved in transcription and nucleotide excision repair (NER). However, whether MMS19 localizes to mitochondria, where it plays a role in maintaining mitochondrial genome stability, remains unknown. In this study, we provide the first evidence that MMS19 is localized in the inner membrane of mitochondria and participates in mtDNA oxidative damage repair. MMS19 knockdown led to mitochondrial dysfunctions including decreased mtDNA copy number, diminished mtDNA repair capacity, and elevated levels of mtDNA common deletion after oxidative stress. Immunoprecipitation - mass spectrometry analysis identified that MMS19 interacts with ANT2, a protein associated with mitochondrial ATP metabolism. ANT2 knockdown also resulted in a decreased mtDNA repair capacity after oxidative damage. Our findings suggest that MMS19 plays an essential role in maintaining mitochondrial genome stability.

Simple and fast quantification of DNA damage by real-time PCR, and its application to nuclear and mitochondrial DNA from multiple tissues of aging zebrafish

We describe a real-time (rt) PCR-based method of quantifying DNA damage, adapted from the long-run rtPCR method of DNA damage quantification (LORD-Q) developed by Lehle et al. (Nucleic Acids Res 42(6):e41, 2014). We show that semi-long run rtPCR, which generates amplicons half the length of those generated in LORD-Q, provides equivalent sensitivity for detecting low lesion frequencies, and better sensitivity for detecting high frequencies. The smaller amplicon size greatly facilitates PCR optimization and allows greater flexibility in the use of detection dyes, and a modified data analysis method simplifies the calculation of lesion frequency. The method was used to measure DNA damage in the nuclear and mitochondrial genomes of different tissues in zebrafish of different ages. We find that nuclear DNA damage generally increases with age, and that the amount of mitochondrial DNA damage varies substantially between tissues, increasing with age in liver and brain but not in heart or skeletal muscle, the latter having the highest levels of damage irrespective of age.

The m6A methylation perturbs the Hoogsteen pairing-guided incorporation of an oxidized nucleotide

This study describes the structural implications and properties of m⁶A in reducing the incorporation of an oxidized nucleotide into DNA.

Natural nucleic acid bases can form Watson–Crick (WC) or Hoogsteen (HG) base pairs. Importantly, 8-oxo-2′-deoxyguanosine (8-oxo-dG) in DNA or 8-oxo-dG 5′-triphosphate (8-oxo-dGTP) favors a syn conformation because of the steric repulsion between O8 and O4′ of the deoxyribose ring. 8-oxo-dGTP can be incorporated into DNA opposite the templating adenine (A) using HG pairing as the dominant mechanism. Both RNA and DNA can be methylated at the N6 position of A to form N⁶-methyladenine (m⁶A). It has been found that certain viral infections may trigger an increase in the production of both 8-oxo-dGTP and m⁶A. The current study aims to systematically explore the effects of m⁶A methylation on HG base pairs and the consequent nucleotide incorporation. Our thermodynamic melting study shows that the m⁶A·8-oxo-dG is significantly less stable than the A·8-oxo-dG base pair in the paired region of a DNA duplex. Moreover, we have used pre-steady-state kinetics to examine the incorporation of 8-oxo-dGTP opposite m⁶A relative to A by a variety of reverse transcriptase (RT) enzymes and DNA polymerase (DNA pol) enzymes such as the human immunodeficiency virus type 1 (HIV-1) RT and human DNA pol β. The results demonstrate that all of these enzymes incorporate 8-oxo-dGTP less efficiently opposite m⁶A relative to A. Considering the steric bulk of the purine–purine pair between 8-oxo-dG and A, m⁶A methylation may affect the HG pairing to a great extent. Hence, it will be unfavorable to incorporate 8-oxo-dGTP into the growing strand opposite m⁶A. Moreover, the impeded incorporation of 8-oxo-dGTP opposite m⁶A has been extended to determine m⁶A at pre-defined positions in human rRNA. Our study may provide new insights into the roles of m⁶A in reducing the mutagenic potential of cellular 8-oxo-dGTP.

A new role for oxidative stress in aging: The accelerated aging phenotype in Sod1-/- mice is correlated to increased cellular senescence

In contrast to other mouse models that are deficient in antioxidant enzymes, mice null for Cu/Zn-superoxide dismutase (Sod1^−/− mice) show a major decrease in lifespan and several accelerated aging phenotypes. The goal of this study was to determine if cell senescence might be a contributing factor in the accelerated aging phenotype observed in the Sod1^−/− mice. We focused on kidney because it is a tissue that has been shown to a significant increase in senescent cells with age. The Sod1^−/− mice are characterized by high levels of DNA oxidation in the kidney, which is attenuated by DR. The kidney of the Sod1^−/− mice also have higher levels of double strand DNA breaks than wild type (WT) mice. Expression (mRNA and protein) of p16 and p21, two of the markers of cellular senescence, which increased with age, are increased significantly in the kidney of Sod1^−/− mice as is β-gal staining cells. In addition, the senescence associated secretory phenotype was also increased significantly in the kidney of Sod1^−/− mice compared to WT mice as measured by the expression of transcripts for IL-6 and IL-1β. Dietary restriction of the Sod1^−/− mice attenuated the increase in DNA damage, cellular senescence, and expression of IL-6 and IL-1β. Interestingly, the Sod1^−/− mice showed higher levels of circulating cytokines than WT mice, suggesting that the accelerated aging phenotype shown by the Sod1^−/− mice could result from increased inflammation arising from an accelerated accumulation of senescent cells. Based on our data with Sod1^−/− mice, we propose that various bouts of increased oxidative stress over the lifespan of an animal leads to the accumulation of senescent cells. The accumulation of senescent cells in turn leads to increased inflammation, which plays a major role in the loss of function and increased pathology that are hallmark features of aging.

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Sod1^−/− mice have high levels of oxidative damage and DNA double strand breaks.

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Sod1^−/− mice show increased cellular senescence, e.g., p16, p21 and β-gal+ cells.

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Sod1^−/− mice showed an increase in the senescence associated secretory phenotype.

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Dietary restriction attenuated cellular senescence and inflammation in Sod1^−/− mice.

Metabolic Damage and Premature Thymus Aging Caused by Stromal Catalase Deficiency

T lymphocytes are essential mediators of immunity that are produced by the thymus in proportion to its size. The thymus atrophies rapidly with age, resulting in progressive diminution of new T cell production. This decreased output is compensated by duplication of existing T cells, but it results in gradual dominance by memory T cells and decreased ability to respond to new pathogens or vaccines. Here, we show that accelerated and irreversible thymic atrophy results from stromal deficiency in the reducing enzyme catalase, leading to increased damage by hydrogen peroxide generated by aerobic metabolism. Genetic complementation of catalase in stromal cells diminished atrophy, as did chemical antioxidants, thus providing a mechanistic link between antioxidants, metabolism, and normal immune function. We propose that irreversible thymic atrophy represents a conventional aging process that is accelerated by stromal catalase deficiency in the context of an intensely anabolic (lymphoid) environment.

Mechanisms linking mtDNA damage and aging

In the past century, considerable efforts were made to understand the role of mitochondrial DNA (mtDNA) mutations and of oxidative stress in aging. The classic mitochondrial free radical theory of aging, in which mtDNA mutations cause genotoxic oxidative stress, which in turn creates more mutations, has been a central hypothesis in the field for decades. In the past few years, however, new elements have discredited this original theory. The major sources of mitochondrial DNA mutations seem to be replication errors and failure of the repair mechanisms, and the accumulation of these mutations as observed in aged organisms seems to occur by clonal expansion and not to be caused by a reactive oxygen species-dependent vicious cycle. New hypotheses of how age-associated mitochondrial dysfunction may lead to aging are based on the role of reactive oxygen species as signaling molecules and on their role in mediating stress responses to age-dependent damage. Here, we review the changes that mtDNA undergoes during aging and the past and most recent hypotheses linking these changes to the tissue failure observed in aging.

XPD localizes in mitochondria and protects the mitochondrial genome from oxidative DNA damage

Xeroderma pigmentosum group D (XPD/ERCC2) encodes an ATP-dependent helicase that plays essential roles in both transcription and nucleotide excision repair of nuclear DNA, however, whether or not XPD exerts similar functions in mitochondria remains elusive. In this study, we provide the first evidence that XPD is localized in the inner membrane of mitochondria, and cells under oxidative stress showed an enhanced recruitment of XPD into mitochondrial compartment. Furthermore, mitochondrial reactive oxygen species production and levels of oxidative stress-induced mitochondrial DNA (mtDNA) common deletion were significantly elevated, whereas capacity for oxidative damage repair of mtDNA was markedly reduced in both XPD-suppressed human osteosarcoma (U2OS) cells and XPD-deficient human fibroblasts. Immunoprecipitation-mass spectrometry analysis was used to identify interacting factor(s) with XPD and TUFM, a mitochondrial Tu translation elongation factor was detected to be physically interacted with XPD. Similar to the findings in XPD-deficient cells, mitochondrial common deletion and oxidative damage repair capacity in U2OS cells were found to be significantly altered after TUFM knock-down. Our findings clearly demonstrate that XPD plays crucial role(s) in protecting mitochondrial genome stability by facilitating an efficient repair of oxidative DNA damage in mitochondria.

The paradoxical role of thioredoxin on oxidative stress and aging

In spite of intensive study, there is still controversy about the free radical or oxidative stress theory of aging, particularly in mammals. Our laboratory has conducted the first detailed studies on the role of thioredoxin (Trx) in the cytosol (Trx1) and in mitochondria (Trx2) on oxidative stress and aging using unique mouse models either overexpressing or down-regulating Trx1 or Trx2. The results generated from our lab and others indicate that: (1) oxidative stress and subsequent changes in signaling pathways could have different pathophysiological impacts at different stages of life; (2) changes in redox-sensitive signaling controlled by levels of oxidative stress and redox state could play more important roles in pathophysiology than accumulation of oxidative damage; (3) changes in oxidative stress and redox state in different cellular compartments (cytosol, mitochondria, or nucleus) could play different roles in pathophysiology during aging, and their combined effects show more impact on aging than changes in either oxidative stress or redox state alone; and (4) the roles of oxidative stress and redox state could have different pathophysiological consequences in different organs/tissues/cells or pathophysiological conditions. To critically test the role of oxidative stress on aging and investigate changes in redox-sensitive signaling pathways, further study is required.

Cellular response to the genotoxic insult: the question of threshold for genotoxic carcinogens

Maintenance of cellular integrity is crucial for its physiological function, which is constantly threatened by DNA damage arising from numerous intrinsic and environmental sources.

Expression of airway remodeling proteins in mast cell activated by TGF-β released in OVA-induced allergic responses and their inhibition by low-dose irradiation or 8-oxo-dG

Allergic asthma is characterized by chronic airway remodeling, which is associated with the expression of extracellular matrix proteins (ECM) by TGF-β. However, to date there are no reports demonstrating that structural proteins are directly expressed in mast cells. This study aimed to investigate whether ECM proteins are expressed in mast cells activated with antigen/antibody reaction, and whether the resolution effects of irradiation or 8-oxo-dG may contribute to allergic asthma prevention. Bone marrow-derived mast cells (BMMCs) were activated with DNP-HSA/anti-DNP IgE antibody (act-BMMCs). C57BL/6 mice were sensitized and challenged with ovalbumin (OVA) to induce allergic asthma. Mice were treated orally with 8-oxo-dG or exposed to whole body irradiation (using (137)Cs gamma ray at a dose of 0.5 Gy) for three consecutive days 24 h after OVA challenge. Expression of extracellular matrix (ECM) proteins, TGF-β signaling molecules and NF-κB/AP-1 was determined in the BMMCs, bronchoalveolar lavage (BAL) cells or lung tissues using Western blot, polymerase chain reaction (PCR) and electrophoretic mobility shift assay (EMSA), respectively. Act-BMMCs increased expression of ECM proteins, TGF-β/TGF-β receptor I, TGF-β signaling molecules and cytokines; and increased both NF-κB and AP-1 activity. In addition, the population of mast cells; expression of mast cell markers, TGF-β signaling molecules, ECM proteins/amounts; OVA-specific serum IgE level; numbers of goblet cells; airway hyperresponsiveness; cytokines/chemokines were increased in BAL cells and lung tissues of OVA-challenged mice. All of the above end points were reduced by irradiation or 8-oxo-dG in vitro and in vivo, respectively. The data suggest that mast cells induce expression of ECM proteins through TGF-β produced in inflammatory cells of OVA mice and that post treatment of irradiation or 8-oxo-dG after OVA-challenge may reduce airway remodeling through down-regulating mast cell re-activation by TGF-β/Smad signals.

Formation and repair of oxidative damage in the mitochondrial DNA

The mitochondrial DNA (mtDNA) encodes for only 13 polypeptides, components of 4 of the 5 oxidative phosphorylation complexes. But despite this apparently small numeric contribution, all 13 subunits are essential for the proper functioning of the oxidative phosphorylation circuit. Thus, accumulation of lesions, mutations and deletions/insertions in the mtDNA could have severe functional consequences, including mitochondrial diseases, aging and age-related diseases. The DNA is a chemically unstable molecule, which can be easily oxidized, alkylated, deaminated and suffer other types of chemical modifications, throughout evolution the organisms that survived were those who developed efficient DNA repair processes. In the last two decades, it has become clear that mitochondria have DNA repair pathways, which operate, at least for some types of lesions, as efficiently as the nuclear DNA repair pathways. The mtDNA is localized in a particularly oxidizing environment, making it prone to accumulate oxidatively generated DNA modifications (ODMs). In this article, we: i) review the major types of ODMs formed in mtDNA and the known repair pathways that remove them; ii) discuss the possible involvement of other repair pathways, just recently characterized in mitochondria, in the repair of these modifications; and iii) address the role of DNA repair in mitochondrial function and a possible cross-talk with other pathways that may potentially participate in mitochondrial genomic stability, such as mitochondrial dynamics and nuclear-mitochondrial signaling. Oxidative stress and ODMs have been increasingly implicated in disease and aging, and thus we discuss how variations in DNA repair efficiency may contribute to the etiology of such conditions or even modulate their clinical outcomes.

Tissue specific oxidative stress profile in relation to glycaemic regulation in mice

BACKGROUND

Diabetes mellitus is a metabolic disorder characterized by hyperglycaemia resulting from uncontrolled glucose regulation. Reactive oxygen species are recognized as one link between hyperglycaemia and diabetic complications. Studies have shown that diabetes mellitus is associated with decreases in antioxidant potential and increased formation of free radicals leading to oxidative stress. The present study was undertaken because an unequivocal demonstration that control of hyperglycaemia can reduce oxidative stress is still lacking.

METHODS

In the present study, we investigated oxidative stress profile of normal, streptozotocin-induced diabetic, insulin-treated and untreated diabetic animals. On the one hand, oxidative damage caused to lipids, proteins and DNA was measured. On other hand, antioxidant defense was measured in terms of specific activities of antioxidant enzymes (AOEs) and antioxidant molecules.

RESULTS

It was observed that the damage to lipids, proteins and DNA caused by free radicals increased in diabetic animals compared with that in controls. In diabetic animals not treated with insulin, damage to all biological molecules increased further significantly (p ≤ 0.005). Changes in AOEs from different tissues were complex depicting a varied AOE level in different tissues. Insulin treatment significantly improved the oxidative stress profile in all tissues studies.

CONCLUSIONS

The control of hyperglycaemia improves oxidative stress profile, that is, the ability of cells to cope up with oxidative stress.

Updating the mitochondrial free radical theory of aging: an integrated view, key aspects, and confounding concepts

An updated version of the mitochondrial free radical theory of aging (MFRTA) and longevity is reviewed. Key aspects of the theory are emphasized. Another main focus concerns common misconceptions that can mislead investigators from other specialties, even to wrongly discard the theory. Those different issues include (i) the main reactive oxygen species (ROS)-generating site in the respiratory chain in relation to aging and longevity: complex I; (ii) the close vicinity or even contact between that site and the mitochondrial DNA, in relation to the lack of local efficacy of antioxidants and to sub-cellular compartmentation; (iii) the relationship between mitochondrial ROS production and oxygen consumption; (iv) recent criticisms on the MFRTA; (v) the widespread assumption that ROS are simple "by-products" of the mitochondrial respiratory chain; (vi) the unnecessary postulation of "vicious cycle" hypotheses of mitochondrial ROS generation which are not central to the free radical theory of aging; and (vii) the role of DNA repair concerning endogenous versus exogenous damage. After considering the large body of data already available, two general characteristics responsible for the high maintenance degree of long-lived animals emerge: (i) a low generation rate of endogenous damage: and (ii) the possession of tissue macromolecules that are highly resistant to oxidative modification.

Involvement of redox state in the aging of Drosophila melanogaster

SIGNIFICANCE

The main objective of this review was to provide an exposition of investigations, conducted in Drosophila melanogaster, on the role of reactive oxygen species and redox state in the aging process. While early transgenic studies did not clearly support the validity of the oxidative stress hypothesis of aging, predicated on the accumulation of structural damage, they spawned a broader search for redox-related effects that might impact the aging process.

RECENT ADVANCES

Initial evidence implicating the thiol redox state as a possible causative factor in aging has been obtained in Drosophila. Overexpression of genes, such as GCL, G6PD, Prx2, and Prx5, which are involved in the maintenance of thiol redox homeostasis, has strong positive effects on longevity. Further, the depletion of peroxiredoxin activity in the mitochondria through the double knockdown of Prx5 and Prx3 not only results in a redox crisis but also elicits a rapid aging phenotype.

CRITICAL ISSUES

Herein, we summarize the present status of knowledge about the main components of the machinery controlling thiol redox homeostasis and describe how age-related redox fluctuations might impact aging more acutely through disruption of the redox-sensitive signaling mechanisms rather than via the simple accumulation of structural damage.

FUTURE DIRECTIONS

Based on these initial insights into the plausible impact of redox fluctuations on redox signaling, future studies should focus on the pathways that have been explicitly implicated in aging, such as insulin signaling, TOR, and JNK/FOXO, with particular attention to elements that are redox sensitive.

Comparative analysis of four oxidized guanine lesions from reactions of DNA with peroxynitrite, singlet oxygen, and γ-radiation

Oxidative damage to DNA has many origins, including irradiation, inflammation, and oxidative stress, but the chemistries are not the same. The most oxidizable base in DNA is 2-deoxyguanosine (dG), and the primary oxidation products are 8-oxodG and 2-amino-imidazolone. The latter rapidly converts to 2,2-diamino-oxazolone (Ox), and 8-oxodG is further oxidized to spiroiminodihydantoin (Sp) and guanidinohydantoin (Gh). In this study, we have examined the dose–response relationship for the formation of the above four products arising in calf thymus DNA exposed to gamma irradiation, photoactivated rose bengal, and two sources of peroxynitrite. In order to carry out these experiments, we developed a chromatographic system and synthesized isotopomeric internal standards to enable accurate and precise analysis based upon selected reaction monitoring mass spectrometry. 8-OxodG was the most abundant products in all cases, but its accumulation was highly dependent on the nature of the oxidizing agent and the subsequent conversion to Sp and Gh. Among the other oxidation products, Ox was the most abundant, and Sp was formed in significantly greater yield than Gh.