Age-associated damage in mitochondrial DNA in human hearts

Current Perspective of Hydrogen Sulfide as a Novel Gaseous Modulator of Oxidative Stress in Glaucoma

Glaucoma is a group of diseases characterized by the progressive loss of retinal ganglion cells and their axons. Elevated intraocular pressure (IOP) is the main clinical manifestation of glaucoma. Despite being in the focus of the studies for decades, the characteristic and the exact pathology of neurodegeneration in glaucoma remains unclear. Oxidative stress is believed to be one of the main risk factors in neurodegeneration, especially its damage to the retinal ganglion cells. Hydrogen sulfide (H₂S), the recently recognized gas signaling molecule, plays a pivotal role in the nervous system, vascular system, and immune system. It has also shown properties in regulating oxidative stress through different pathways in vivo. In this review, we summarize the distribution and the properties of H₂S within the eye with an emphasis on its role in modulating oxidative stress in glaucoma.

Mitochondrial Markers in Aging and Primary Open-Angle Glaucoma

This review focuses on recent progress in understanding the role of mitochondrial markers in the context of mitochondrial dysfunction in glaucoma and discussing new therapeutic approaches to modulate mitochondrial function and potentially lead to improved outcomes in glaucoma.

Mitochondrial DNA Damage Does Not Determine C. elegans Lifespan

The mitochondrial free radical theory of aging (mFRTA) proposes that accumulation of oxidative damage to macromolecules in mitochondria is a causative mechanism for aging. Accumulation of mitochondrial DNA (mtDNA) damage may be of particular interest in this context. While there is evidence for age-dependent accumulation of mtDNA damage, there have been only a limited number of investigations into mtDNA damage as a determinant of longevity. This lack of quantitative data regarding mtDNA damage is predominantly due to a lack of reliable assays to measure mtDNA damage. Here, we report adaptation of a quantitative real-time polymerase chain reaction (qRT-PCR) assay for the detection of sequence-specific mtDNA damage in C. elegans and apply this method to investigate the role of mtDNA damage in the aging of nematodes. We compare damage levels in old and young animals and also between wild-type animals and long-lived mutant strains or strains with modifications in ROS detoxification or production rates. We confirm an age-dependent increase in mtDNA damage levels in C. elegans but found that there is no simple relationship between mtDNA damage and lifespan. MtDNA damage levels were high in some mutants with long lifespan (and vice versa). We next investigated mtDNA damage, lifespan and healthspan effects in nematode subjected to exogenously elevated damage (UV- or γ-radiation induced). We, again, observed a complex relationship between damage and lifespan in such animals. Despite causing a significant elevation in mtDNA damage, γ-radiation did not shorten the lifespan of nematodes at any of the doses tested. When mtDNA damage levels were elevated significantly using UV-radiation, nematodes did suffer from shorter lifespan at the higher end of exposure tested. However, surprisingly, we also found hormetic lifespan and healthspan benefits in nematodes treated with intermediate doses of UV-radiation, despite the fact that mtDNA damage in these animals was also significantly elevated. Our results suggest that within a wide physiological range, the level of mtDNA damage does not control lifespan in C. elegans.

Pandora's Box: mitochondrial defects in ischaemic heart disease and stroke

Ischaemic heart disease and stroke are vascular events with serious health consequences worldwide. Recent genetic and epigenetic techniques have revealed many genetic determinants of these vascular events and simplified the approaches to research focused on ischaemic heart disease and stroke. The pathogenetic mechanisms of ischaemic heart disease and stroke are complex, with mitochondrial involvement (partially or entirely) recently gaining substantial support. Not only can mitochondrial reactive oxygen species give rise to ischaemic heart disease and stroke by production of oxidised low-density lipoprotein and induction of apoptosis, but the impact on pericytes contributes directly to the pathogenesis. Over the past two decades, publications implicate the causative role of nuclear genes in the development of ischaemic heart disease and stroke, in contrast to the potential role of mitochondrial DNA (mtDNA) in the pathophysiology of the disorders, which is much less understood, although recent studies do demonstrate that the involvement of mitochondria and mtDNA in the development of ischaemic heart disease and stroke is likely to be larger than originally thought, with the novel discovery of links among mitochondria, mtDNA and vascular events. Here we explore the molecular events and mtDNA alterations in relation to the role of mitochondria in ischaemic heart disease and stroke.

Hydroferrate fluid, MRN-100, provides protection against chemical-induced gastric and esophageal cancer in Wistar rats

In the current study, we examined the protective effect of hydroferrate fluid MRN-100 against the carcinogen methylnitronitrosoguanidine (MNNG)-induced gastric and esophageal cancer in rats. MRN-100 is an iron-based compound composed of bivalent and trivalent ferrates. At 33 weeks post treatment with MNNG, rats were killed and examined for the histopathology of esophagus and stomach; liver, spleen, and total body weight; and antioxidant levels in the blood and stomach tissues. Results showed that 17/20 (85%) gastroesophageal tissues from carcinogen MNNG-treated rats developed dysplasia and cancer, as compared to 8/20 (40%) rats treated with MNNG plus MRN-100. In addition, MRN-100 exerted an antioxidant effect in both the blood and stomach tissues by increasing levels of GSH, antioxidant enzymes SOD, CAT, and GPx, and total antioxidant capacity (TAC) level. This was accompanied by a reduction in the total free-radical and malondialdehyde levels. Furthermore, MRN-100 protected against body and organ weight loss. Thus, MRN-100 exhibited significant cancer chemopreventive activity by protecting tissues against oxidative damage in rats, which may suggest its effectiveness as an adjuvant for the treatment of gastric/esophageal carcinoma.

Cardiac aging and insulin resistance: could insulin/insulin-like growth factor (IGF) signaling be used as a therapeutic target?

Intrinsic cardiac aging is an independent risk factor for cardiovascular disease and is associated with structural and functional changes that impede cardiac responses to stress and to cardio-protective mechanisms. Although systemic insulin resistance and the associated risk factors exacerbate cardiac aging, cardiac-specific insulin resistance without confounding systemic alterations, could prevent cardiac aging. Thus, strategies aimed to reduce insulin/insulin-like growth factor (IGF) signaling in the heart prevent cardiac aging in lower organisms and in mammals but the mechanisms underlying this protection are not fully understood. In this review, we describe the impact of aging on the cardiovascular system and discuss the mounting evidence that reduced insulin/IGF signaling in the heart could alleviate age-associated alterations and preserve cardiac performance.

Mitochondria, oxidative DNA damage, and aging

Protection from reactive oxygen species (ROS) and from mitochondrial oxidative damage is well known to be necessary to longevity. The relevance of mitochondrial DNA (mtDNA) to aging is suggested by the fact that the two most commonly measured forms of mtDNA damage, deletions and the oxidatively induced lesion 8-oxo-dG, increase with age. The rate of increase is species-specific and correlates with maximum lifespan. It is less clear that failure or inadequacies in the protection from reactive oxygen species (ROS) and from mitochondrial oxidative damage are sufficient to explain senescence. DNA containing 8-oxo-dG is repaired by mitochondria, and the high ratio of mitochondrial to nuclear levels of 8-oxo-dG previously reported are now suspected to be due to methodological difficulties. Furthermore, MnSOD -/+ mice incur higher than wild type levels of oxidative damage, but do not display an aging phenotype. Together, these findings suggest that oxidative damage to mitochondria is lower than previously thought, and that higher levels can be tolerated without physiological consequence. A great deal of work remains before it will be known whether mitochondrial oxidative damage is a "clock" which controls the rate of aging. The increased level of 8-oxo-dG seen with age in isolated mitochondria needs explanation. It could be that a subset of cells lose the ability to protect or repair mitochondria, resulting in their incurring disproportionate levels of damage. Such an uneven distribution could exceed the reserve capacity of these cells and have serious physiological consequences. Measurements of damage need to focus more on distribution, both within tissues and within cells. In addition, study must be given to the incidence and repair of other DNA lesions, and to the possibility that repair varies from species to species, tissue to tissue, and young to old.

Mitochondrial DNA sequence variation is associated with free-living activity energy expenditure in the elderly

The decline in activity energy expenditure underlies a range of age-associated pathological conditions, neuromuscular and neurological impairments, disability, and mortality. The majority (90%) of the energy needs of the human body are met by mitochondrial oxidative phosphorylation (OXPHOS). OXPHOS is dependent on the coordinated expression and interaction of genes encoded in the nuclear and mitochondrial genomes. We examined the role of mitochondrial genomic variation in free-living activity energy expenditure (AEE) and physical activity levels (PAL) by sequencing the entire (~16.5 kilobases) mtDNA from 138 Health, Aging, and Body Composition Study participants. Among the common mtDNA variants, the hypervariable region 2 m.185G>A variant was significantly associated with AEE (p=0.001) and PAL (p=0.0005) after adjustment for multiple comparisons. Several unique nonsynonymous variants were identified in the extremes of AEE with some occurring at highly conserved sites predicted to affect protein structure and function. Of interest is the p.T194M, CytB substitution in the lower extreme of AEE occurring at a residue in the Qi site of complex III. Among participants with low activity levels, the burden of singleton variants was 30% higher across the entire mtDNA and OXPHOS complex I when compared to those having moderate to high activity levels. A significant pooled variant association across the hypervariable 2 region was observed for AEE and PAL. These results suggest that mtDNA variation is associated with free-living AEE in older persons and may generate new hypotheses by which specific mtDNA complexes, genes, and variants may contribute to the maintenance of activity levels in late life.

Age-related decline in mitochondrial bioenergetics: does supercomplex destabilization determine lower oxidative capacity and higher superoxide production?

Mitochondrial decay plays a central role in the aging process. Although certainly multifactorial in nature, defective operation of the electron transport chain (ETC) constitutes a key mechanism involved in the age-associated loss of mitochondrial energy metabolism. Primarily, mitochondrial dysfunction affects the aging animal by limiting bioenergetic reserve capacity and/or increasing oxidative stress via enhanced electron leakage from the ETC. Even though the important aging characteristics of mitochondrial decay are known, the molecular events underlying inefficient electron flux that ultimately leads to higher superoxide appearance and impaired respiration are not completely understood. This review focuses on the potential role(s) that age-associated destabilization of the macromolecular organization of the ETC (i.e. supercomplexes) may be important for development of the mitochondrial aging phenotype, particularly in post-mitotic tissues.

Mitochondrial-nuclear epistasis: implications for human aging and longevity

There is substantial evidence that mitochondria are involved in the aging process. Mitochondrial function requires the coordinated expression of hundreds of nuclear genes and a few dozen mitochondrial genes, many of which have been associated with either extended or shortened life span. Impaired mitochondrial function resulting from mtDNA and nuclear DNA variation is likely to contribute to an imbalance in cellular energy homeostasis, increased vulnerability to oxidative stress, and an increased rate of cellular senescence and aging. The complex genetic architecture of mitochondria suggests that there may be an equally complex set of gene interactions (epistases) involving genetic variation in the nuclear and mitochondrial genomes. Results from Drosophila suggest that the effects of mtDNA haplotypes on longevity vary among different nuclear allelic backgrounds, which could account for the inconsistent associations that have been observed between mitochondrial DNA (mtDNA) haplogroups and survival in humans. A diversity of pathways may influence the way mitochondria and nuclear-mitochondrial interactions modulate longevity, including: oxidative phosphorylation; mitochondrial uncoupling; antioxidant defenses; mitochondrial fission and fusion; and sirtuin regulation of mitochondrial genes. We hypothesize that aging and longevity, as complex traits having a significant genetic component, are likely to be controlled by nuclear gene variants interacting with both inherited and somatic mtDNA variability.

A potential impact of DNA repair on ageing and lifespan in the ageing model organism Podospora anserina: decrease in mitochondrial DNA repair activity during ageing

The free radical theory of ageing states that ROS play a key role in age-related decrease in mitochondrial function via the damage of mitochondrial DNA (mtDNA), proteins and lipids. In the sexually reproducing ascomycete Podospora anserina ageing is, as in other eukaryotes, associated with mtDNA instability and mitochondrial dysfunction. Part of the mtDNA instabilities may arise due to accumulation of ROS induced mtDNA lesions, which, as previously suggested for mammals, may be caused by an age-related decrease in base excision repair (BER). Alignments of known BER protein sequences with the P. anserina genome revealed high homology. We report for the first time the presence of BER activities in P. anserina mitochondrial extracts. DNA glycosylase activities decrease with age, suggesting that the increased mtDNA instability with age may be caused by decreased ability to repair mtDNA damage and hence contribute to ageing and lifespan control in this ageing model. Additionally, we find low DNA glycosylase activities in the long-lived mutants grisea and DeltaPaCox17::ble, which are characterized by low mitochondrial ROS generation. Overall, our data identify a potential role of mtDNA repair in controlling ageing and life span in P. anserina, a mechanism possibly regulated in response to ROS levels.

Regulating the age-related oxidative damage, mitochondrial integrity, and antioxidative enzyme activity in Fischer 344 rats by supplementation of the antioxidant epigallocatechin-3-gallate

In this study, epigallocatechin-3-gallate (EGCG) was examined for the first time for its anti-aging effect on middle-aged male Fischer 344 rats as a dietary supplement at 50 (low dose) and 500 (high dose) mg/kg/day over a 6-month period. Such levels of EGCG concentration were well-tolerated by rats without causing tissue damage or dysfunction in the liver and kidney, as evaluated by histopathological and biochemical observations. Compared to the rats in the low-dose and control groups, rats fed with high-dose EGCG showed a significant decline in the concentration of 8-hydroxy-2'-deoxyguanosine in the plasma while maintaining a better mitochondrial potential in the peripheral lymphocytes and preventing the deletion of ND4 region from mitochondrial DNA in the liver. The protective effects of high-dose EGCG against oxidative stress were comparable with the effects of caloric restriction, a well-established dietary intervention that retards aging. However, the supplementation of EGCG influenced merely the antioxidative enzyme activities and their gene expressions in rats, suggesting that EGCG may either function as an antioxidant itself or regulate other bioprocesses, including energy metabolism, biosynthesis, and stress response, as shown in the gene profiling analysis of microarray data. Thus, the present study provides preliminary information on the anti-aging property of EGCG in male Fischer 344 rats.

Mitochondrial DNA repair in aging and disease

Mitochondria are organelles which, according to the endosymbiosis theory, evolved from purpurbacteria approximately 1.5 billion years ago. One of the unique features of mitochondria is that they have their own genome. Mitochondria replicate and transcribe their DNA semiautonomously. Like nuclear DNA, mitochondrial DNA (mtDNA) is constantly exposed to DNA damaging agents. Regarding the repair of mtDNA, the prevailing concept for many years was that mtDNA molecules suffering an excess of damage would simply be degraded to be replaced by newly generated successors copied from undamaged genomes. However, evidence now clearly shows that mitochondria contain the machinery to repair the damage to their genomes caused by certain endogenous or exogenous damaging agents. The link between mtDNA damage and repair to aging, neurodegeneration, and carcinogenesis-associated processes is the subject of this review.

Mitochondrial cascade hypothesis of Alzheimer's disease: myth or reality?

Mitochondria are recognized to play a pivotal role in neuronal cell survival or death because they are regulators of both energy metabolism and apoptotic pathways. Morphologic, biochemical, and molecular genetic studies suggest that mitochondria might be a convergence point for neurodegeneration, including Alzheimer's disease (AD). The functions and properties of mitochondria might render subsets of selectively vulnerable neurons intrinsically susceptible to cellular aging and stress. However, the question, "Is mitochondrial dysfunction a necessary step in neurodegeneration?" is still unanswered. This review presents the ways in which malfunctioning mitochondria and oxidative stress might contribute to neuronal death in AD.

Formation of elongated giant mitochondria in DFO-induced cellular senescence: Involvement of enhanced fusion process through modulation of Fis1

Enlarged or giant mitochondria have often been documented in aged tissues although their role and underlying mechanism remain unclear. We report here how highly elongated giant mitochondria are formed in and related to the senescent arrest. The mitochondrial morphology was progressively changed to a highly elongated form during deferoxamine (DFO)-induced senescent arrest of Chang cells, accompanied by increase of intracellular ROS level and decrease of mtDNA content. Interestingly, under exposure to subcytotoxic doses of H2O2 (200 microM), about 65% of Chang cells harbored elongated mitochondria with senescent phenotypes whereas ethidium bromide (EtBr) (50 ng/ml) only reformed the cristae structure. Elongated giant mitochondria were also observed in TGF beta1- or H2O2-induced senescent Mv1Lu cells and in old human diploid fibroblasts (HDFs). In all senescent progresses employed in this study Fis1 protein, a mitochondrial fission modulator, was commonly downexpressed. Overexpression of YFP-Fis1 reversed both mitochondrial elongation and appearance of senescent phenotypes induced by DFO, implying its critical involvement in the arrest. Finally, we found that direct induction of mitochondrial elongation by blocking mitochondrial fission process with Fis1-DeltaTM or Drp1-K38A was sufficient to develop senescent phenotypes with increased ROS production. These data suggest that mitochondrial elongation may play an important role as a mediator in stress-induced premature senescence.

Gene expression profile in dilated cardiomyopathy caused by elevated frequencies of mitochondrial DNA mutations in the mouse heart

BACKGROUND

Elevated mitochondrial DNA (mtDNA) mutations are associated with aging and age-related diseases, but their pathogenic potential is unclear.

METHODS

We performed expression profiling using an Incyte cDNA array of a mouse model of elevated mtDNA mutations wherein random mutations accumulate specifically in the heart. At frequencies of about 1 mutation/10,000 base pairs, these mice show apoptosis of cardiomyocytes and development of four-chamber dilated cardiomyopathy.

RESULTS

Significant Analysis of Microarrays (SAM) revealed that 117 genes were altered in their expression in the transgenic (Tg) heart at a threshold of less than one false positive, of which 34 were up-regulated and 83 were down-regulated. Some of the changes were confirmed by Northern and Western blots. By classification of these genes into functional categories, we identified changes that reflected cardiac pathology. The results indicated that cardiomyopathy caused by mtDNA mutations was largely characterized by gene expression changes indicative of increased fibrosis and cardiac remodeling of the extracellular matrix. Few changes were observed, suggesting an alteration in either mitochondrial energy production or generation of increased oxidative stress.

CONCLUSIONS

Elevated frequencies of mtDNA mutations in the mouse heart lead to gene expression changes that are associated with remodeling of the extracellular matrix. Because cardiomyocytic death by apoptosis is also a feature of the dilated cardiomyopathy evident in these mice, extracellular remodeling may be a response to apoptotic signaling originating from the mitochondria with mtDNA mutations.

Mitochondrial DNA and aging

Among the numerous theories that explain the process of aging, the mitochondrial theory of aging has received the most attention. This theory states that electrons leaking from the ETC (electron transfer chain) reduce molecular oxygen to form O2•− (superoxide anion radicals). O2•−, through both enzymic and non-enzymic reactions, can cause the generation of other ROS (reactive oxygen species). The ensuing state of oxidative stress results in damage to ETC components and mtDNA (mitochondrial DNA), thus increasing further the production of ROS. Ultimately, this ‘vicious cycle’ leads to a physiological decline in function, or aging. This review focuses on recent developments in aging research related to the role played by mtDNA. Both supportive and contradictory evidence is discussed.

Oxidative DNA damage and disease: induction, repair and significance

The generation of reactive oxygen species may be both beneficial to cells, performing a function in inter- and intracellular signalling, and detrimental, modifying cellular biomolecules, accumulation of which has been associated with numerous diseases. Of the molecules subject to oxidative modification, DNA has received the greatest attention, with biomarkers of exposure and effect closest to validation. Despite nearly a quarter of a century of study, and a large number of base- and sugar-derived DNA lesions having been identified, the majority of studies have focussed upon the guanine modification, 7,8-dihydro-8-oxo-2'-deoxyguanosine (8-OH-dG). For the most part, the biological significance of other lesions has not, as yet, been investigated. In contrast, the description and characterisation of enzyme systems responsible for repairing oxidative DNA base damage is growing rapidly, being the subject of intense study. However, there remain notable gaps in our knowledge of which repair proteins remove which lesions, plus, as more lesions identified, new processes/substrates need to be determined. There are many reports describing elevated levels of oxidatively modified DNA lesions, in various biological matrices, in a plethora of diseases; however, for the majority of these the association could merely be coincidental, and more detailed studies are required. Nevertheless, even based simply upon reports of studies investigating the potential role of 8-OH-dG in disease, the weight of evidence strongly suggests a link between such damage and the pathogenesis of disease. However, exact roles remain to be elucidated.

Mitochondria play a critical role in cardioprotection

BACKGROUND

There is increasing evidence documenting the capacity of myocardial cells exposed to a variety of insults to mount a cardioprotective response. Although this cardioprotection has been most well characterized with respect to ischemic preconditioning, other chemical and metabolic stressors have been shown to share features of the ischemic preconditioning model, including the involvement of mitochondria in the triggering, signaling, and mediation of the cardioprotective response.

METHODS

In this article, we review the evidence showing that mitochondria play a critical role in cardioprotection from multiple (often interrelated) standpoints: its primary function in producing the cellular bioenergetic supply, its control over events in apoptosis, its contribution to myocardial signal transducing processes, and its role in producing reactive oxidative species and in providing an appropriate antioxidant response to a variety of cellular insults.

CONCLUSIONS

Although our understanding of cytoprotection has increased substantially within the last few years, the mechanisms mediating mitochondrial resistance to insults leading to cardiac protection remain to be fully delineated, and represents a significant approach in the clinical treatment of heart disease.

Mitochondrial enzyme activities as biochemical markers of aging

The decrease of neurological performance in normal aging is directly related to brain oxidative stress and inversely related to lifespan. Male mice lifespan was increased by 8-10% (median and maximal lifespan, respectively) in mice with high spontaneous neurological activity, by 21-15% after moderate exercise; and by 25-20% after supplementation with vitamin E. Oxidative stress markers, TBARS and protein carbonyl content, were found increased on aging; a higher content of oxidation products is considered an effective aging factor, specially in the brain, with a majority of postmitotic cells. Mitochondrial enzyme activities, mitochondrial nitric oxide synthase (mtNOS), NADH dehydrogenase and cytochrome oxidase, behaved as markers of brain aging. The decrease in enzyme activities was directly related to the content of oxidation products and to the loss of neurological function in aged mice, this latter was determined in the tighrope and the T-maze tests. The above mentioned conditions that increased mice lifespan were effective to decrease the level of oxidative stress markers, and to retard the decreases in mitochondrial enzyme activities and neurological function associated to aging. The activities of mtNOS, NADH dehydrogenase and cytochrome oxidase may be used as indicators of the effectiveness of antiaging treatments.

MtDNA mutations in aging and apoptosis

There is considerable evidence that the oxidative phosphorylation capacity of human mitochondria declines in various tissues with aging. However, the genetic basis of this phenomenon has not yet been clarified. The occurrence of large deletions in mtDNA from brain, skeletal, and heart muscles and other tissues of old subjects at relatively low levels has been well documented. We discuss their possible functional relevance for the aging processes. On the contrary, until very recently, only inconclusive and often discordant evidence was available for the accumulation of mtDNA point mutations in old individuals. In the past few years, however, an aging-dependent large accumulation of mtDNA point mutations has been demonstrated in the majority of individuals above a certain age. These mutations occur in the mtDNA main control region at critical sites for mtDNA replication in fibroblasts and skeletal muscles. The extraordinary tissue specificity and nucleotide selectivity of these mutations strongly support the idea of their being functionally relevant. Evidence in agreement with this conclusion has been provided by the very recent observation that an mtDNA mutation occurring in blood leukocytes near an origin of replication, which causes a remodeling of this origin, occurs at a strikingly higher frequency in centenarians and monozygotic and dizygotic twins than in the control populations, strongly pointing to its survival value. The present article reviews another area of active research and discussion, namely, the role of pathogenic mtDNA mutations in causing programmed cell death. The available evidence has clearly shown that mtDNA and respiration are not essential for the process of apoptosis. However, the limited and sometimes contradictory data indicate that the absence or impaired function of mtDNA can influence the rate of this process, most probably by regulating the production of reactive oxygen species or the lack thereof.

Protective action of copper (II) complex of a Schiff base against DNA damage induced by m-chloroperbenzoic acid using a novel DNA unwinding technique

DNA strand breaks can be detected with great sensitivity by exposing calf thymus DNA to alkaline solutions and monitoring the rate of strand unwinding. Fluorometric analysis of DNA unwinding (FADU) is a reliable method for detecting single-strand DNA breaks as an index of DNA damage induced by photosensitizer.m-Chloroperbenzoic acid (CPBA) was used as a photosensitizer in the photodamage of calf thymus DNA. When DNA is exposed to ionizing radiation, the radicals produced in the irradiated sample modify the base-pair regions of the double strands. The protective action of copper salt, Schiff base [ethylene diamine with ethyl acetate](L) and its Cu(II) complex (Cu(7) L Cl(14)) against DNA damage photoinduced by CPBA was studied using ethidium bromide as a fluorescent probe. Treatment of DNA with 5, 10, 50, 100, or 200 microM CPBA produced 75%, 48%, 38%, 32% and 30% double-stranded DNA remaining, respectively after 30 min of alkaline treatment at 15 degrees C. Treatment of calf thymus DNA irradiated with CPBA with a dose of 1 mM [Cu(7) L Cl(14)] produced 96% double-stranded remaining protection under the same conditions compared with irradiated DNA without addition of Cu(II) complex of Schiff base.

Age-related mitochondrial DNA deletion in human heart: its relationship with cardiovascular diseases

BACKGROUND AND AIMS

Accumulation of damage to mitochondrial DNA (mtDNA) occurs in myocardial tissue with advancing age. However, despite higher incidence of cardiac diseases in the elderly, little attempt has been made to detect deletions of mtDNA in the myocardial tissue of aged individuals. The aim of the present study was to clarify the relationship between aging, mtDNA deletion and cardiovascular (CV) diseases.

METHODS

We examined 163 autopsy cases, aged 60 years or older, using two different kinds of polymerase chain reaction (PCR): highly sensitive PCR to detect a common 4977-bp deletion and long-PCR for multiple deletions, which could be detected in case that deleted mtDNA accounted for more than several percents in total mtDNA.

RESULTS

The common 4977-bp deletion was detected in 156 cases (95.7%), showing no significant difference among these age groups and no relation to CV diseases. By long-PCR, multiple deletions in cardiac mtDNA were found in 33 (20.2%) of 163 cases. The proportion of the mtDNA deletion in the nineties (46.2%) was significantly higher than those in the younger (15.3%, p < 0.05). Female predominance was significantly found in the group with the mtDNA deletion (p < 0.05). Multiple deletions of mtDNA were not significantly related to ischemic change, valvular diseases, left ventricular hypertrophy, congestive heart failure, coronary sclerosis, or heart weight except for right ventricular hypertrophy.

CONCLUSIONS

These findings suggest that there is a close relationship between aging and deletion of mtDNA, and that the ratio of deleted mtDNA to total mtDNA increases with advancing age. Age-related deletion of mtDNA may have little influence on CV diseases except for right ventricular hypertrophy.

From the Hayflick mosaic to the mosaics of ageing. Role of stress-induced premature senescence in human ageing

The Hayflick limit-senescence of proliferative cell types-is a fundamental feature of proliferative cells in vitro. Various human proliferative cell types exposed in vitro to many types of subcytotoxic stresses undergo stress-induced premature senescence (SIPS) (also called stress-induced premature senescence-like phenotype, according to the definition of senescence). The known mechanisms of appearance the main features of SIPS are reviewed: senescent-like morphology, growth arrest, senescence-related changes in gene expression, telomere shortening. Long before telomere-shortening induces senescence, other factors such as culture conditions or lack of 'feeder cells' can trigger either SIPS or prolonged reversible G(0) phase of the cell cycle. In vivo, 'proliferative' cell types of aged individuals are likely to compose a mosaic made of cells irreversibly growth arrested or not. The higher level of stress to which these cells have been exposed throughout their life span, the higher proportion of the cells of this mosaic will be in SIPS rather than in telomere-shortening dependent senescence. All cell types undergoing SIPS in vivo, most notably the ones in stressful conditions, are likely to participate in the tissular changes observed along ageing. For instance, human diploid fibroblasts (HDFs) exposed in vivo and in vitro to pro-inflammatory cytokines display biomarkers of senescence and might participate in the degradation of the extracellular matrix observed in ageing.

Behavioral dysfunction, brain oxidative stress, and impaired mitochondrial electron transfer in aging mice

Behavioral tests, tightrope success, and exploratory activity in a T maze were conducted with male and female mice for 65 wk. Four groups were defined: the lower performance slow males and slow females and the higher performance fast males and fast females. Fast females showed the longest life span and the highest performance, and slow males showed the lowest performance and the shortest life span. Oxidative stress and mitochondrial electron transfer activities were determined in brain of young (28 wk), adult (52 wk), and old (72 wk) mice in a cross-sectional study. Brain thiobarbituric acid reactive substances (TBARS) were increased by 50% in old mice and were approximately 15% higher in males than in females and in slow than in fast mice. Brain Cu,Zn-superoxide dismutase (SOD) activity was increased by 52% and Mn-SOD by 108% in old mice. The activities of mitochondrial enzymes NADH-cytochrome c reductase, cytochrome oxidase, and citrate synthase were decreased by 14-58% in old animals. The cumulative toxic effects of oxyradicals are considered the molecular mechanism of the behavioral deficits observed on aging.

Mouse models for mitochondrial disease

Mutations in mitochondrial genes encoded by both mitochondrial DNA (mtDNA) and nuclear DNA (nDNA) genes have been implicated in a wide range of neuromuscular diseases. MtDNA base substitution and rearrangement mutations generally inactivate one or more tRNA or rRNA genes and can cause myopathy, cardiomyopathy, cataracts, growth retardation, diabetes, etc. nDNA mutations can cause Leigh syndrome, cardiomyopathy, and nephropathy, due to defects in oxidative phosphorylation (OXPHOS) enzyme complexes; cartilage-hair hypoplasia (CHH) and mtDNA depletion syndrome, through defects in mitochondrial nucleic acid metabolism; and ophthalmoplegia with multiple mtDNA deletions, caused by adenine nucleotide translocator-1 (ANT1) mutations. Mouse models have been prepared that recapitulate a number of these diseases. The mtDNA 16S rRNA chloramphenicol (CAP) resistance mutation was introduced into the mouse female germline and caused cataracts and rod and cone abnormalities in chimeras and neonatal lethal myopathy and cardiomyopathy in mutant animals. A mtDNA deletion was introduced into the mouse germline and caused myopathy, cardiomyopathy, and nephropathy. Conditional inactivation of the nDNA mitochondrial transcription factor (Tfam) gene in the heart resulted in neonatal lethal cardiomyopathy, while its inactivation in the pancreatic beta-cells caused diabetes. The ATP/ADP ratio was implicated in mitochondrial diabetes through transgenic modification of the beta-cell ATP-sensitive K(+) channel (K(ATP)). Mutational inactivation of the mouse Ant1 gene resulted in myopathy, cardiomyopathy, and multiple mtDNA deletions in association with elevated reactive oxygen species (ROS) production. Inactivation of uncoupler proteins (Ucp) 1-3 revealed that mitochondrial Delta Psi regulated ROS production. The role of mitochondrial ROS toxicity in disease and aging was confirmed by inactivating glutathione peroxidase (GPx1), resulting in growth retardation, and by total and partial inactivation of Mn superoxide dismutase (MnSOD; Sod2), resulting in neonatal lethal dilated cardiomyopathy and accelerated apoptosis in aging, respectively. The importance of mitochondrial ROS in degenerative diseases and aging was confirmed by treating Sod2 -/- mice and C. elegans with catalytic antioxidant drugs.

Regulation of intracellular localization of human MTH1, OGG1, and MYH proteins for repair of oxidative DNA damage

In mammalian cells, more than one genome has to be maintained throughout the entire life of the cell, one in the nucleus and the other in mitochondria. It seems likely that the genomes in mitochondria are highly exposed to reactive oxygen species (ROS) as a result of their respiratory function. Human MTH1 (hMTH1) protein hydrolyzes oxidized purine nucleoside triphosphates, such as 8-oxo-dGTP, 8-oxo-dATP, and 2-hydroxy (OH)-dATP, thus suggesting that these oxidized nucleotides are deleterious for cells. Here, we report that a single-nucleotide polymorphism (SNP) in the human MTH1 gene alters splicing patterns of hMTH1 transcripts, and that a novel hMTH1 polypeptide with an additional mitochondrial targeting signal is produced from the altered hMTH1 mRNAs; thus, intracellular location of hMTH1 is likely to be affected by a SNP. These observations strongly suggest that errors caused by oxidized nucleotides in mitochondria have to be avoided in order to maintain the mitochondrial genome, as well as the nuclear genome, in human cells. Based on these observations, we further characterized expression and intracellular localization of 8-oxoG DNA glycosylase (hOGG1) and 2-OH-A/adenine DNA glycosylase (hMYH) in human cells. These two enzymes initiate base excision repair reactions for oxidized bases in DNA generated by direct oxidation of DNA or by incorporation of oxidized nucleotides. We describe the detection of the authentic hOGG1 and hMYH proteins in mitochondria, as well as nuclei in human cells, and how their intracellular localization is regulated by alternative splicing of each transcript.

Mitochondrial defects in neurodegenerative disease

Over the past 12 years, a wide variety of neurodegenerative diseases has been linked to mutations in mitochondrial genes located in either the mitochondrial DNA (mtDNA) or the nuclear DNA (nDNA). These disorders encompass an array of unorthodox inheritance patterns and a plethora of symptoms ranging from lethal neonatal multi-symptom disorders to later onset myopathies, cardiomyopathies, movement disorders, and dementias. The bases for the genetic and phenotypic variability of mitochondrial diseases lie in the multiplicity of the mitochondria genes dispersed across the human genome and the variety of cellular pathways and functions in which the mitochondria play a central role.

Accumulation of oxidative DNA damage, 8-oxo-2'-deoxyguanosine, and change of repair systems during in vitro cellular aging of cultured human skin fibroblasts

Effects of in vitro cellular aging on the content of 8-oxo-2'-deoxyguanosine, a typical oxidation product of DNA bases, were examined in cultured human skin fibroblasts. The 8-oxo-2'-deoxyguanosine content in the DNA of TIG-3S cells established from skin tissues of a fetal donor increased immediately before the cessation of proliferation. TIG-114 and TIG-104 cells established from skin tissues of adult and aged donors, respectively, showed similar changes in 8-oxo-2'-deoxyguanosine content during in vitro cellular aging. The accumulation of 8-oxo-2'-deoxyguanosine in late-passage cells was dependent on the number of cell divisions, and not on the cultivation time. Increases in the activities of superoxide dismutase and glutathione peroxidase were observed prior to the increase in 8-oxo-2'-deoxyguanosine content, while the catalase activity decreased gradually during in vitro cellular aging at late-passage. Furthermore, the activities of 8-oxo-2'-deoxyguanosine endonuclease and DNA polymerases decreased with the progression of proliferation. These results indicate that defense systems against oxidative stress in late-passage cells remain sufficiently active before the cessation of cell division, but that repair systems against oxidative damage decay at late-passage. Oxidative stress beyond the antioxidant capacity and/or repair activity seems to result in an accumulation of 8-oxo-2'-deoxyguanosine in late-passage cells.

Mitochondrial DNA deletion mutations colocalize with segmental electron transport system abnormalities, muscle fiber atrophy, fiber splitting, and oxidative damage in sarcopenia

The in vivo cellular impact of age-associated mitochondrial DNA mutations is unknown. We hypothesized that mitochondrial DNA deletion mutations contribute to the fiber atrophy and loss that cause sarcopenia, the age-related decline of muscle mass and function. We examined 82,713 rectus femoris muscle fibers from Fischer 344 x Brown Norway F1 hybrid rats of ages 5, 18, and 38 months through 1000 microns by serial cryosectioning and histochemical staining for cytochrome c oxidase and succinate dehydrogenase. Between 5 and 38 months of age, the rectus femoris muscle in the hybrid rat demonstrated a 33% decrease in mass concomitant with a 30% decrease in total fibers at the muscle mid-belly. We observed significant increases in the number of mitochondrial abnormalities with age from 289 +/- 8 ETS abnormal fibers in the entire 5-month-old rectus femoris to 1094 +/- 126 in the 38-month-old as calculated from the volume density of these abnormalities. Segmental mitochondrial abnormalities contained mitochondrial DNA deletion mutations as revealed by laser capture microdissection and whole mitochondrial genome amplification. Muscle fibers harboring mitochondrial deletions often displayed atrophy, splitting and increased steady-state levels of oxidative nucleic damage. These data suggest a causal role for age-associated mitochondrial DNA deletion mutations in sarcopenia.

Cloning of neuronal mtDNA variants in cultured cells by synaptosome fusion with mtDNA-less cells

Synaptosome cybrids were used to confirm the presence of heteroplasmic mtDNA sequence variants in the human brain. Synaptosomes contain one to several mitochondria, and when fused to mtDNA-deficient (rho degrees ) mouse or human cell lines result in viable cybrid cell lines. The brain origin of mouse synaptosome cybrid mtDNAs was confirmed using sequence polymorphisms in the mtDNA COIII, ND3 and tRNA(Arg)genes. The brain origin of the human synaptosome cybrids was confirmed using a rare mtDNA Mbo I polymorphism. Fusion of synaptosomes from the brain of a 35-year-old woman resulted in 71 synaptosome cybrids. Sequencing the mtDNA control region of these cybrid clones revealed differences in the number of Cs in a poly C track between nucleotide pairs (nps) 301 and 309. Three percent of the cybrid clones had mtDNAs with 10 Cs, 76% had nine, 18% had eight and 3% had seven Cs. Comparable results were obtained by PCR amplification, cloning and sequencing of mtDNA control regions directly from the patient's brain tissue, but not when the control region was amplified and cloned from a synaptosome cybrid homoplasmic for a mtDNA with nine Cs. Thus, we have clonally recovered mtDNA control region length variants from an adult human brain without recourse to PCR, and established the variant mtDNAs within living cultured cells. This confirms that some mtDNA heteroplasmy can exist in human neurons, and provides the opportunity to study its functional significance.

Very rare complementation between mitochondria carrying different mitochondrial DNA mutations points to intrinsic genetic autonomy of the organelles in cultured human cells

In the present work, a large scale investigation was done regarding the capacity of cultured human cell lines (carrying in homoplasmic form either the mitochondrial tRNA(Lys) A8344G mutation associated with the myoclonic epilepsy and ragged red fiber (MERRF) encephalomyopathy or a frameshift mutation, isolated in vitro, in the gene for the ND4 subunit of NADH dehydrogenase) to undergo transcomplementation of their recessive mitochondrial DNA (mtDNA) mutations after cell fusion. The presence of appropriate nuclear drug resistance markers in the two cell lines allowed measurements of the frequency of cell fusion in glucose-containing medium, non-selective for respiratory capacity, whereas the frequency of transcomplementation of the two mtDNA mutations was determined by growing the same cell fusion mixture in galactose-containing medium, selective for respiratory competence. Transcomplementation of the two mutations was revealed by the re-establishment of normal mitochondrial protein synthesis and respiratory activity and by the relative rates synthesis of two isoforms of the ND3 subunit of NADH dehydrogenase. The results of several experiments showed a cell fusion frequency between 1.4 and 3.4% and an absolute transcomplementation frequency that varied between 1.2 x 10(-5) and 5.5 x 10(-4). Thus, only 0.3-1.6% of the fusion products exhibited transcomplementation of the two mutations. These rare transcomplementing clones were very sluggish in developing, grew very slowly thereafter, and showed a substantial rate of cell death (22-28%). The present results strongly support the conclusion that the capacity of mitochondria to fuse and mix their contents is not a general intrinsic property of these organelles in mammalian cells, although it may become activated in some developmental or physiological situations.

Expression and differential intracellular localization of two major forms of human 8-oxoguanine DNA glycosylase encoded by alternatively spliced OGG1 mRNAs

We identified seven alternatively spliced forms of human 8-oxoguanine DNA glycosylase (OGG1) mRNAs, classified into two types based on their last exons (type 1 with exon 7: 1a and 1b; type 2 with exon 8: 2a to 2e). Types 1a and 2a mRNAs are major in human tissues. Seven mRNAs are expected to encode different polypeptides (OGG1-1a to 2e) that share their N terminus with the common mitochondrial targeting signal, and each possesses a unique C terminus. A 36-kDa polypeptide, corresponding to OGG1-1a recognized only by antibodies against the region containing helix-hairpin-helix-PVD motif, was copurified from the nuclear extract with an activity introducing a nick into DNA containing 8-oxoguanine. A 40-kDa polypeptide corresponding to a processed form of OGG1-2a was detected in their mitochondria using antibodies against its C terminus. Electron microscopic immunocytochemistry and subfractionation of the mitochondria revealed that OGG1-2a locates on the inner membrane of mitochondria. Deletion mutant analyses revealed that the unique C terminus of OGG1-2a and its mitochondrial targeting signal are essential for mitochondrial localization and that nuclear localization of OGG1-1a depends on the NLS at its C terminus.

Age-associated change in mitochondrial DNA damage

There is an age-associated decline in the mitochondrial function of the Wistar rat heart. Previous reports from this lab have shown a decrease in mitochondrial cytochrome c oxidase (COX) activity associated with a reduction in COX gene and protein expression and a similar decrease in the rate of mitochondrial protein synthesis. Damage to mitochondrial DNA may contribute to this decline. Using the HPLC-Coularray system (ESA, USA), we measured levels of nuclear and mitochondrial 8-oxo-2'-deoxyguanosine (8-oxodG) from 6-month (young) and 23-month-old (senescent) rat liver DNA. We measured the sensitivity of the technique by damaging calf thymus DNA with photoactivated methylene blue for 30s up to 2h. The levels of damage were linear over the entire time course including the shorter times which showed levels comparable to those expected in liver. For the liver data, 8-oxodG was reported as a fraction of 2-deoxyguanosine (2-dG). There was no change in the levels of 8-oxodG levels in the nuclear DNA from 6 to 23-months of age. However, the levels of 8-oxodG increased 2.5-fold in the mitochondrial DNA with age. At 6 months, the level of 8-oxodG in mtDNA was 5-fold higher than nuclear and increased to approximately 12-fold higher by 23 months of age. These findings agree with other reports showing an age-associated increase in levels of mtDNA damage; however, the degree to which it increases is smaller. Such damage to the mitochondrial DNA may contribute to the age-associated decline in mitochondrial function.

Reduced mitochondrial DNA transcription in senescent rat heart

We studied the effect of senescence on mitochondrial DNA (mtDNA) transcription with an in organello system using intact isolated rat heart mitochondria. A comparison of the electrophoretic patterns of mtDNA transcription products in young, adult and senescent rats showed an age-related reduction in newly-synthesized mitochondrial RNAs that reflects a decrease in the synthesis rate. These results correlate with the enzyme activities of the oxidative phosphorylation complexes I and IV, that are partially encoded by the mitochondrial genome. In addition, an age-related increase in the protein carbonyl content of the mitochondrial membranes was observed in senescent mitochondria suggesting an accumulation of mitochondrial oxidative damage. This reduction in the mtDNA transcriptional rate in the heart of senescent animals suggests that this could be one of the molecular bases underlying senescence of the myocardium.

Mitochondrial DNA mutations and age

Apopotic cell death is reported to be prominent in the stable tissues of the failing heart, in cardiomyopathies (CM), in the sinus node of complete heart block, in B cells of diabetes mellitus, and in neurodegenerative diseases. Recently, mitochondrial (mt) control of nuclear apoptosis was demonstrated in the cell-free system. The mt bioenergetic crisis induced by exogenously added factors such as respiratory inhibitors leads to the collapse of mt transmembrane potential, to the opening of the inner membrane pore, to the release of the apoptotic protease activating factors into cytosol, and subsequently to nuclear DNA fragmentation. However, the endogenous factor for the mt bioenegertic crisis in naturally occurring cell death under the physiological conditions without vascular involvement has remained unknown. Recently devised, the total detection system for deletion demonstrates the extreme fragmentation of mtDNA in the cardiac myocytes of senescence, and mt CM harboring maternally inherited point mutations in mtDNA and on the cultured cell line with or without mtDNA disclosed that mtDNA is unexpectedly fragile to hydroxyl radial damage and hence to oxygen stress. The great majority of wild-type mtDNA fragmented into over two hundreds types of deleted mtDNA related to oxidative damage, resulting in pleioplasmic defects in the mt energy transducing system. The mtDNA fragmentation to this level is demonstrated in cardiac myocytes of normal subjects over age 80, of an mtCM patient who died at age 20 and one who died at age 19, of a recipient of heart transplantation at age 7 with severe mtCM, and in mtDNA of a cultured cell line under hyperbaric oxygen stress for two days, leading a majority of cells to apoptotic death on the third day. The extreme fragility of mtDNA could be the missing link in the apoptosis cascade that is the physiological basis of aging and geriatrics of such stable tissues as nerve and muscle.

Coenzyme Q10 treatment improves the tolerance of the senescent myocardium to pacing stress in the rat

OBJECTIVE

In elderly patients the results of cardiac interventions are inferior to those in the young. A possible contributing factor is an age-related reduction in cellular energy transduction during the intervention which may induce aerobic or ischemic stress. To investigate whether coenzyme Q10 (CoQ10) improves the response to aerobic stress, functional recoveries of senescent and young rat hearts after rapid pacing were compared with or without CoQ10.

METHODS

Young (4.8 +/- 0.1 months) and senescent (35.3 +/- 0.2 months) rats were given daily intraperitoneal injections of CoQ10 (4 mg/kg) or vehicle for 6 weeks. Their isolated hearts were rapidly paced at 510 beats per minute for 120 min to induce aerobic stress without ischemia.

RESULTS

In senescent hearts pre-pacing cardiac work was 74% and oxygen consumption (MVO2) 66% of that in young hearts. CoQ10 treatment abolished these differences. After pacing, the untreated senescent hearts, compared to young, showed reduced recovery of pre-pacing work, (16.8 +/- 4.3 vs. 44.5 +/- 7.4%; P < 0.01). CoQ10 treatment in senescent hearts improved recovery of work, (48.1 +/- 4.1 vs. 16.8 +/- 4.3%; P < 0.0001) and MVO2 (82.1 +/- 2.8 vs. 61.3 +/- 4.0%; P < 0.01) in treated versus untreated hearts respectively. Post-pacing levels of these parameters in CoQ10 treated senescent hearts were as high as in young hearts.

CONCLUSIONS

(1) Senescent rat hearts have reduced baseline function and reduced tolerance to aerobic stress compared to young hearts. (2) Pre-treatment with CoQ10 improves baseline function of the senescent myocardium and its tolerance to aerobic stress.

Increased mitochondrial DNA deletion in the brain of SAMP8, a mouse model for spontaneous oxidative stress brain

Oxidative stress is considered to be closely correlated with degenerative brain abnormalities. In this study, the plausibility of a SAMP8 strain mouse showing memory deterioration and short life span as an oxidative stress brain model was evaluated. Mitochondrial DNA deletions were detected using polymerase chain reaction (PCR) as cumulative spontaneous oxidative stress. In the 4-8-week-old SAMP8 brain, multiple mitochondrial DNA (mtDNA) deletions were already found and the contents were significantly higher than those of SAMR1 or ddY controls. Enzyme activity studies indicated that electron transport was disturbed at the lower site of the chain and the electronegativity of the upper site might be increased, a cause of radical production and therefore oxidative stress.

Role of mitochondria in oxidative stress and ageing

Mitochondria are deeply involved in the production of reactive oxygen species through one-electron carriers in the respiratory chain; mitochondrial structures are also very susceptible to oxidative stress as evidenced by massive information on lipid peroxidation, protein oxidation, and mitochondrial DNA (mtDNA) mutations. Oxidative stress can induce apoptotic death, and mitochondria have a central role in this and other types of apoptosis, since cytochrome c release in the cytoplasm and opening of the permeability transition pore are important events in the apoptotic cascade. The discovery that mtDNA mutations are at the basis of a number of human pathologies has profound implications: maternal inheritance of mtDNA is the basis of hereditary mitochondrial cytopathies; accumulation of somatic mutations of mtDNA with age has represented the basis of the mitochondrial theory of ageing, by which a vicious circle is established of mtDNA damage, altered oxidative phosphorylation and overproduction of reactive oxygen species. Experimental evidence of respiratory chain defects and of accumulation of multiple mtDNA deletions with ageing is in accordance with the mitochondrial theory, although some other experimental findings are not directly ascribable to its postulates.