Mitochondria in organismal aging and degeneration

High-Intensity Interval Training Improves Glycemic Control, Cellular Apoptosis, and Oxidative Stress of Type 2 Diabetic Patients

Background and Objectives: Physical exercise is an important therapeutic modality for treating and managing diabetes. High-intensity interval training (HIIT) is considered one of the best non-drug strategies for preventing and treating type 2 diabetes mellitus (T2DM) by improving mitochondrial biogenesis and function. This study aimed to determine the effects of 12 weeks of HIIT training on the expression of tumor suppressor protein-p53, mitochondrial cytochrome c oxidase (COX), and oxidative stress in patients with T2DM. Methods: A total of thirty male sedentary patients aged (45-60 years) were diagnosed with established T2DM for more than five years. Twenty healthy volunteers, age- and sex-matched, were included in this study. Both patients and control subjects participated in the HIIT program for 12 weeks. Glycemic control variables including p53 (U/mL), COX (ng/mL), total antioxidant capacity (TAC, nmole/µL), 8-hydroxy-2'-deoxyguanosine (8-OHdG, ng/mL), as well as genomic and mitochondrial DNA content were measured in both the serum and muscle tissues of control and patient groups following exercise training. Results: There were significant improvements in fasting glucose levels. HbA1c (%), HOMA-IR (mUmmol/L2), fasting insulin (µU/mL), and C-peptide (ng/mL) were reported in T2DM and healthy controls. A significant decrease was also observed in p53 protein levels. COX, 8-OhdG, and an increase in the level of TAC were reported in T2DM following 12 weeks of HIIT exercise. Before and after exercise, p53; COX, mt-DNA content, TAC, and 8-OhdG showed an association with diabetic control parameters such as fasting glucose (FG), glycated hemoglobin (HbA1C, %), C-peptide, fasting insulin (FI), and homeostatic model assessment for insulin resistance (HOMA-IR) in patients with T2DM. These findings support the positive impact of HIIT exercise in improving regulation of mitochondrial biogenesis and subsequent control of diabetes through anti-apoptotic and anti-oxidative pathways. Conclusions: A 12-week HIIT program significantly improves diabetes by reducing insulin resistance; regulating mitochondrial biogenesis; and decreasing oxidative stress capacity among patients and healthy controls. Also; p53 protein expression; COX; 8-OhdG; and TAC and mt-DNA content were shown to be associated with T2DM before and after exercise training.

The Potential Role of Peripheral Oxidative Stress on the Neurovascular Unit in Amyotrophic Lateral Sclerosis Pathogenesis: A Preliminary Report from Human and In Vitro Evaluations

Oxidative stress, the alteration of mitochondrial function, and changes in the neurovascular unit (NVU) could play a role in Amyotrophic Lateral Sclerosis (ALS) pathogenesis. Our aim was to analyze the plasma redox system and nitric oxide (NO) in 25 ALS new-diagnosed patients and five healthy controls and the effects of plasma on the peroxidation/mitochondrial function in human umbilical cord-derived endothelial vascular cells (HUVEC) and astrocytes. In plasma, thiobarbituric acid reactive substances (TBARS), glutathione (GSH), and nitric oxide (NO) were analyzed by using specific assays. In HUVEC/astrocytes, the effects of plasma on the release of mitochondrial reactive oxygen species (mitoROS) and NO, viability, and mitochondrial membrane potential were investigated. In the plasma of ALS patients, an increase in TBARS and a reduction in GSH and NO were found. In HUVEC/astrocytes treated with a plasma of ALS patients, mitoROS increased, whereas cell viability and mitochondrial membrane potential decreased. Our results show that oxidative stress and NVU play a central role in ALS and suggest that unknown plasma factors could be involved in the disease pathogenesis. Quantifiable changes in ALS plasma related to redox state alterations can possibly be used for early diagnosis.

Strategies to protect against age-related mitochondrial decay: Do natural products and their derivatives help?

Mitochondria serve vital roles critical for overall cellular function outside of energy transduction. Thus, mitochondrial decay is postulated to be a key factor in aging and in age-related diseases. Mitochondria may be targets of their own decay through oxidative damage. However, treating animals with antioxidants has been met with only limited success in rejuvenating mitochondrial function or in increasing lifespan. A host of nutritional strategies outside of using traditional antioxidants have been devised to promote mitochondrial function. Dietary compounds are under study that induce gene expression, enhance mitochondrial biogenesis, mitophagy, or replenish key metabolites that decline with age. Moreover, redox-active compounds may now be targeted to mitochondria which improve their effectiveness. Herein we review the evidence that representative dietary effectors modulate mitochondrial function by stimulating their renewal or reversing the age-related loss of key metabolites. While in vitro evidence continues to accumulate that many of these compounds benefit mitochondrial function and/or prevent their decay, the results using animal models and, in some instances human clinical trials, are more mixed and sometimes even contraindicated. Thus, further research on optimal dosage and age of intervention are warranted before recommending potential mitochondrial rejuvenating compounds for human use.

Stressed mitochondria: A target to intrude alzheimer's disease

Alzheimer's disease (AD) is the inoperable, incapacitating, neuropsychiatric, and degenerative manifestation that drastically affects human life quality. The current medications target extra-neuronal senile plaques, oxidative stress, neuroinflammation, intraneuronal neurofibrillary tangles, cholinergic deficits, and excitotoxicity. Among novel pathways and targets, bioenergetic and resultant mitochondrial dysfunction has been recognized as essential factors that decide the neuronal fate and consequent neurodegeneration in AD. The crucial attributes of mitochondria, including bioenergesis, signaling, sensing, integrating, and transmitting biological signals contribute to optimum networking of neuronal dynamics and make them indispensable for cell survival. In AD, mitochondrial dysfunction and mitophagy are a preliminary and critical event that aggravates the pathological cascade. Stress is known to promote and exaggerate the neuropathological alteration during neurodegeneration and metabolic impairments, especially in the cortico-limbic system, besides adversely affecting the normal physiology and mitochondrial dynamics. Stress involves the allocation of energy resources for neuronal survival. Chronic and aggravated stress response leads to excessive release of glucocorticoids by activation of the hypothalamic-pituitaryadrenal (HPA) axis. By acting through their receptors, glucocorticoids influence adverse mitochondrial changes and alter mtDNA transcription, mtRNA expression, hippocampal mitochondrial network, and ultimately mitochondrial physiology. Chronic stress also affects mitochondrial dynamics by changing metabolic and neuro-endocrinal signalling, aggravating oxidative stress, provoking inflammatory mediators, altering tropic factors, influencing gene expression, and modifying epigenetic pathways. Thus, exploring chronic stress-induced glucocorticoid dysregulation and resultant bio-behavioral and psychosomatic mitochondrial alterations may be a feasible narrative to investigate and unravel the mysterious pathobiology of AD.

High-Intensity Interval Training Restores Glycolipid Metabolism and Mitochondrial Function in Skeletal Muscle of Mice With Type 2 Diabetes

High-intensity interval training has been reported to lower fasting blood glucose and improve insulin resistance of type 2 diabetes without clear underlying mechanisms. The purpose of this study was to investigate the effect of high-intensity interval training on the glycolipid metabolism and mitochondrial dynamics in skeletal muscle of high-fat diet (HFD) and one-time 100 mg/kg streptozocin intraperitoneal injection-induced type 2 diabetes mellitus (T2DM) mice. Our results confirmed that high-intensity interval training reduced the body weight, fat mass, fasting blood glucose, and serum insulin of the T2DM mice. High-intensity interval training also improved glucose tolerance and insulin tolerance of the T2DM mice. Moreover, we found that high-intensity interval training also decreased lipid accumulation and increased glycogen synthesis in skeletal muscle of the T2DM mice. Ultrastructural analysis of the mitochondria showed that mitochondrial morphology and quantity were improved after 8 weeks of high-intensity interval training. Western blot analysis showed that the expression of mitochondrial biosynthesis related proteins and mitochondrial dynamics related proteins in high-intensity interval trained mice in skeletal muscle were enhanced. Taken together, these data suggest high-intensity interval training improved fasting blood glucose and glucose homeostasis possibly by ameliorating glycolipid metabolism and mitochondrial dynamics in skeletal muscle of the T2DM mice.

The Effects of APOE4 on Mitochondrial Dynamics and Proteins in vivo

This study examined the effects of apolipoprotein E4 (APOE4), the most prevalent genetic risk factor for Alzheimer's disease (AD), on proteins involved in mitochondrial dynamics and autophagy, in the hippocampus of targeted replacement mice. Immunohistochemical measurements revealed that the levels of the mitochondrial fusion-mediating protein, MFN1, were higher, whereas those of corresponding fission-regulating protein, DRP-1, were lower in the hippocampus of ApoE4 mice than in the corresponding ApoE3 mice, indicating that APOE4 is associated with increased mitochondrial fusion and decreased fission. A similar ApoE4-driven decrease in DRP-1 was also observed in AD brains. The levels of the mitochondrial proteins COX1 and Tom40, were higher in the ApoE4 mice, which is consistent with the increased fusion. Measurements of the levels of cleaved PINK1 and parkin, which mark and target mitochondria for mitophagic degradation, revealed lower levels of cleaved PINK1, suggesting reduced mitochondrial membrane potential, and higher levels of parkin in the hippocampus of ApoE4 compared with the ApoE3 mice, indicating altered mitophagy. The levels of the ubiquitin-binding scaffold protein, p62/SQSTM1, which directs selected cargo to the autophagosomes, were also higher in the ApoE4 mice. These findings suggest that APOE4 is associated with enhanced mitochondrial fusion and decreased fission. Additionally, the results indicate that mitophagy/autophagy is reduced in ApoE4 mice, resulting in higher levels of proteins such as parkin and p62, which are normally degraded during this process. Taken together, these results suggest a novel mechanism that may underlie the pathological effects of APOE4 and indicate that use of APOE4 genotyping could pave the way for identification of novel APOE4-related therapeutic targets.

Zmynd17 controls muscle mitochondrial quality and whole-body metabolism

Muscle mitochondria are crucial for systemic metabolic function, yet their regulation remains unclear. The zinc finger MYND domain-containing protein 17 (Zmynd17) was recently identified as a muscle-specific gene in mammals. Here, we investigated the role of Zmynd17 in mice. We found Zmynd17 predominantly expressed in skeletal muscle, especially in fast glycolytic muscle. Genetic Zmynd17 inactivation led to morphologic and functional abnormalities in muscle mitochondria, resulting in decreased respiratory function. Metabolic stress induced by a high-fat diet upregulated Zmynd17 expression and further exacerbated muscle mitochondrial morphology in Zmynd17-deficient mice. Strikingly, Zmynd17 deficiency significantly aggravated metabolic stress-induced hepatic steatosis, glucose intolerance, and insulin resistance. Furthermore, middle-aged mice lacking Zmynd17 exhibited impaired aerobic exercise performance, glucose intolerance, and insulin resistance. Thus, our results indicate that Zmynd17 is a metabolic stress-inducible factor that maintains muscle mitochondrial integrity, with its deficiency profoundly affecting whole-body glucose metabolism.-Fujita, R., Yoshioka, K., Seko, D., Suematsu, T., Mitsuhashi, S., Senoo, N., Miura, S., Nishino, I., Ono, Y. Zmynd17 controls muscle mitochondrial quality and whole-body metabolism.

Alzheimer's Disease: From Mitochondrial Perturbations to Mitochondrial Medicine

Age-related neurodegenerative diseases such as Alzheimer's disease (AD) are distressing conditions causing countless levels of suffering for which treatment is often insufficient or inexistent. Considered to be the most common cause of dementia and an incurable, progressive neurodegenerative disorder, the intricate pathogenic mechanisms of AD continue to be revealed and, consequently, an effective treatment needs to be developed. Among the diverse hypothesis that have been proposed to explain AD pathogenesis, the one concerning mitochondrial dysfunction has raised as one of the most discussed with an actual acceptance in the field. It posits that manipulating mitochondrial function and understanding the deficits that result in mitochondrial injury may help to control and/or limit the development of AD. To achieve such goal, the concept of mitochondrial medicine places itself as a promising gathering of strategies to directly manage the major insidious disturbances of mitochondrial homeostasis as well as attempts to directly or indirectly manage its consequences in the context of AD. The aim of this review is to summarize the evolution that occurred from the establishment of mitochondrial homeostasis perturbation as masterpieces in AD pathogenesis up until the development of mitochondrial medicine. Following a brief glimpse in the past and current hypothesis regarding the triad of aging, mitochondria and AD, this manuscript will address the major mechanisms currently believed to participate in above mentioned events. Both pharmacological and lifestyle interventions will also be reviewed as AD-related mitochondrial therapeutics.

Skeletal muscle mitochondria as a target to prevent or treat type 2 diabetes mellitus

Low levels of physical activity and the presence of obesity are associated with mitochondrial dysfunction. In addition, mitochondrial dysfunction has been associated with the development of insulin resistance and type 2 diabetes mellitus (T2DM). Although the evidence for a causal relationship between mitochondrial function and insulin resistance is still weak, emerging evidence indicates that boosting mitochondrial function might be beneficial to patient health. Exercise training is probably the most recognized promoter of mitochondrial function and insulin sensitivity and hence is still regarded as the best strategy to prevent and treat T2DM. Animal data, however, have revealed several new insights into the regulation of mitochondrial metabolism, and novel targets for interventions to boost mitochondrial function have emerged. Importantly, many of these targets seem to be regulated by factors such as nutrition, ambient temperature and circadian rhythms, which provides a basis for nonpharmacological strategies to prevent or treat T2DM in humans. Here, we will review the current evidence that mitochondrial function can be targeted therapeutically to improve insulin sensitivity and to prevent T2DM, focusing mainly on human intervention studies.

Dietary fatty acids affect mitochondrial phospholipid compositions and mitochondrial gene expression of rainbow trout liver at different ages

Mitochondria are among the first responders to various stressors that challenge the homeostasis of cells and organisms. Mitochondrial decay is generally associated with impairment in the organelle bioenergetics function and increased oxidative stress, and it appears that deterioration of mitochondrial inner membrane phospholipids (PL), particularly cardiolipin (CL), and accumulation of mitochondrial DNA (mtDNA) mutations are among the main mechanisms involved in this process. In the present study, liver mitochondrial membrane PL compositions, lipid peroxidation, and mtDNA gene expression were analyzed in rainbow trout fed three diets with the same base formulation but with lipid supplied either by fish oil (FO), rapeseed oil (RO), or high DHA oil (DHA) during 6 weeks. Specifically, two feeding trials were performed using fish from the same population of two ages (1 and 3 years), and PL class compositions of liver mitochondria, fatty acid composition of individual PL classes, TBARS content, and mtDNA expression were determined. Dietary fatty acid composition strongly affected mitochondrial membrane composition from trout liver but observed changes did not fully reflect the diet, particularly when it contained high DHA. The changes were PL specific, CL being particularly resistant to changes in DHA. Some significant differences observed in expression of mtDNA with diet may suggest long-term dietary effects in mitochondrial gene expression which could affect electron transport chain function. All the changes were influenced by fish age, which could be related to the different growth rates observed between 1- and 3-year-old trout but that could also indicate age-related changes in the ability to maintain structural homeostasis of mitochondrial membranes.

Evolution of aging and death: what insights bacteria can provide

Several unresolved issues, paradoxes, and information voids characterize the field of evolution of aging. The recent discovery of aging-like phenomenon in Escherichia coli, marked by asymmetric segregation of damaged components, particularly protein aggregates, has created a number of new possibilities that remain underexplored. Bacterial systems can potentially throw light on issues such as: whether evolution of aging and evolution of death are different phenomena; whether aging is inevitable for life or is an evolved strategy; whether there could be selection for aging or aging is a pleiotropic effect of some other selection; what are the possible mechanisms of antagonistic pleiotropy, if any; and whether there are mechanisms of aging that are conserved throughout the hierarchy of life. Bacterial aging itself is underexplored and least understood as of now, but even scratching the surface appears to reveal things that may compel us to revise some of the classical concepts about evolution of aging. This warrants more focused and innovative inquiry into aging-like processes in bacteria.

Apoptosis in differentiating C2C12 muscle cells selectively targets Bcl-2-deficient myotubes

Muscle cell apoptosis accompanies normal muscle development and regeneration, as well as degenerative diseases and aging. C2C12 murine myoblast cells represent a common model to study muscle differentiation. Though it was already shown that myogenic differentiation of C2C12 cells is accompanied by enhanced apoptosis in a fraction of cells, either the cell population sensitive to apoptosis or regulatory mechanisms for the apoptotic response are unclear so far. In the current study we characterize apoptotic phenotypes of different types of C2C12 cells at all stages of differentiation, and report here that myotubes of differentiated C2C12 cells with low levels of anti-apoptotic Bcl-2 expression are particularly vulnerable to apoptosis even though they are displaying low levels of pro-apoptotic proteins Bax, Bak and Bad. In contrast, reserve cells exhibit higher levels of Bcl-2 and high resistance to apoptosis. The transfection of proliferating myoblasts with Bcl-2 prior to differentiation did not protect against spontaneous apoptosis accompanying differentiation of C2C12 cells but led to Bcl-2 overexpression in myotubes and to significant protection from apoptotic cell loss caused by exposure to hydrogen peroxide. Overall, our data advocate for a Bcl-2-dependent mechanism of apoptosis in differentiated muscle cells. However, downstream processes for spontaneous and hydrogen peroxide induced apoptosis are not completely similar. Apoptosis in differentiating myoblasts and myotubes is regulated not through interaction of Bcl-2 with pro-apoptotic Bcl-2 family proteins such as Bax, Bak, and Bad.

The influence of dietary lipid composition on skeletal muscle mitochondria from mice following eight months of calorie restriction

Calorie restriction (CR) has been shown to decrease reactive oxygen species (ROS) production and retard aging in a variety of species. It has been proposed that alterations in membrane saturation are central to these actions of CR. As a step towards testing this theory, mice were assigned to 4 dietary groups (control and 3 CR groups) and fed AIN-93G diets at 95 % (control) or 60 % (CR) of ad libitum for 8 months. To manipulate membrane composition, the primary dietary fats for the CR groups were soybean oil (also used in the control diet), fish oil or lard. Skeletal muscle mitochondrial lipid composition, proton leak, and H(2)O(2) production were measured. Phospholipid fatty acid composition in CR mice was altered in a manner that reflected the n-3 and n-6 fatty acid profiles of their respective dietary lipid sources. Dietary lipid composition did not alter proton leak kinetics between the CR groups. However, the capacity of mitochondrial complex III to produce ROS was decreased in the CR lard compared to the other CR groups. The results of this study indicate that dietary lipid composition can influence ROS production in muscle mitochondria of CR mice. It remains to be determined if lard or other dietary oils can maximize the CR-induced decreases in ROS production.

Maintenance of mitochondrial morphology by autophagy and its role in high glucose effects on chronological lifespan of Saccharomyces cerevisiae

In Saccharomyces cerevisiae, mitochondrial morphology changes when cells are shifted between nonfermentative and fermentative carbon sources. Here, we show that cells of S. cerevisiae grown in different glucose concentrations display different mitochondrial morphologies. The morphology of mitochondria in the cells growing in 0.5% glucose was similar to that of mitochondria in respiring cells. However, the mitochondria of cells growing in higher glucose concentrations (2% and 4%) became fragmented after growth in these media, due to the production of acetic acid; however, the fragmentation was not due to intracellular acidification. From a screen of mutants involved in sensing and utilizing nutrients, cells lacking TOR1 had reduced mitochondrial fragmentation, and autophagy was found to be essential for this reduction. Mitochondrial fragmentation in cells grown in high glucose was reversible by transferring them into conditioned medium from a culture grown on 0.5% glucose. Similarly, the chronological lifespan of cells grown in high glucose medium was reduced, and this phenotype could be reversed when cells were transferred to low glucose conditioned medium. These data indicate that chronological lifespan seems correlated with mitochondrial morphology of yeast cells and that both phenotypes can be influenced by factors from conditioned medium of cultures grown in low glucose medium.

Pathways related to mitochondrial dysfunction in cartilage of endemic osteoarthritis patients in China

In this paper, we present the first evidence of differences in the mitochondria-related gene expression profiles of adult articular cartilage derived from patients with Kashin-Beck disease and normal controls. The expression of 705 mitochondria-related genes was analyzed by mitochondria-related gene expression analysis and ingenuity pathways analysis. Mitochondria-related gene expression analysis identified 9 up-regulated genes in Kashin-Beck disease based on their average expression ratio. Three canonical pathways involved in oxidative phosphorylation, apoptosis signaling and pyruvate metabolism were identified, which indicate the involvement of mitochondrial dysfunction in the pathogenesis of Kashin-Beck disease.

Organochalcogens inhibit mitochondrial complexes I and II in rat brain: possible implications for neurotoxicity

Organochalcogens, such as organoselenium and organotellurium compounds, can be neurotoxic to rodents. Since mitochondrial dysfunction plays a pivotal role in neurological disorders, the present study was designed to test the hypothesis that rat brain mitochondrial complexes (I, II, I-III, II-III and IV) could be molecular targets of organochalcogens. The results show that organochalcogens caused statistically significant inhibition of mitochondrial complex I activity, which was prevented by preincubation with NADH and fully blunted by reduced glutathione (GSH). Mitochondrial complex II activity remained unchanged in response to (PhSe)₂ treatment. Ebs and (PhTe)₂ caused a significant concentration-dependent inhibition of complex II that was also blunted by GSH. Mitochondrial complex IV activity was not modified by organochalcogens. Collectively, Ebs, (PhSe)₂ and (PhTe)₂ were more effective inhibitors of brain mitochondrial complex I than of complex II, whereas they did not affect complex IV. These observations are consistent with organochalcogens inducing mitochondrial complex I and II inhibition via their thiol-oxidase-like activity, with Ebs, (PhSe)₂ and (PhTe)₂ effectively oxidising critical thiol groups of these complexes.

Superoxide dismutase deficiency enhances superoxide levels in brain tissues during oxygenation and hypoxia-reoxygenation

To determine whether the mitochondria or cytoplasm produces superoxide during ischemia-reperfusion of the brain, we analyzed lucigenine-enhanced chemiluminescence emission in slices of brain tissue prepared from manganese-superoxide dismutase (Mn-SOD)-deficient (Sod2-deficient) and copper and zinc-superoxide dismutase (Cu,Zn-SOD)-deficient (Sod1-deficient) mice during oxygenation and hypoxia-reoxygenation. The steady-state level of chemiluminescence under oxygenated conditions was significantly enhanced by a lack of either Sod. We hypothesize that the enhanced chemiluminescence produced by Sod2 and Sod1 deficiency reflects in situ superoxide generation in the mitochondria and cytoplasm, respectively. Based on this hypothesis, the major site of intracellular superoxide generation was assumed to be the cytoplasm. However, mitochondria occupy less cellular space than the cytoplasm. In terms of volume, the superoxide concentration is assumed to be higher in mitochondria than in the cytoplasm. Mn-SOD activity was 18% of the Cu,Zn-SOD activity observed in the wild-type mouse brain. However, when mitochondrial SOD activity was expressed as per volume, it was assumed to be equal to that observed in the cytoplasm. This imbalance between superoxide and SOD activity is expected to cause mitochondrial oxidative damage. The chemiluminescence intensity increased significantly during reoxygenation and was enhanced by Sod2 deficiency but was not significantly affected by Sod1 deficiency. The superoxide concentration in the reoxygenated brain would be higher in the mitochondria than in the cytoplasm. The present study indicated that the major site of intracellular superoxide generation in the brain during oxygenation is the cytoplasm, whereas it is the mitochondria during reoxygenation.

Ginkgo biloba extract EGb761 protects against aging-associated mitochondrial dysfunction in platelets and hippocampi of SAMP8 mice

Standardized Ginkgo biloba extract, EGb761, has been shown to possess polyvalent properties, such as anti-oxidation, anti-apoptosis and anti-inflammation. Recently, it has also been proposed to have direct protective effects on mitochondria. The effects of EGb761 make it a potential anti-aging drug. Despite that, the 'anti-aging' effect of EGb761, particularly its effect on the central nervous system, is still inconclusive. Using two age groups (3-week-old and 40-week-old) of SAMP8 mice (a senescence-accelerated strain of mice), the effects of EGb761 on mitochondrial function in platelets and hippocampi were investigated in this study. It was found that mitochondrial functions, evaluated as cytochrome c oxidase (COX) activity, mitochondrial ATP (adenosine-5'-triphosphate) content and mitochondrial glutathione (GSH) content, decreased with age. EGb761 protected against mitochondrial dysfunction in platelets of young and old mice, suggesting a peripheral effect of this herb in the prevention and treatment of age-associated degeneration. In contrast, in hippocampi, protective effects of EGb761 were observed only in the old mice, probably due to an age-associated increase in the permeability of the blood brain barrier (BBB). Therefore, while EGb761 has a potential anti-aging effect, its central effect can be affected by in vivo factors such as the BBB permeability. A better understanding of the in vivo pharmacological actions of EGb761 may contribute to a better understanding of the effectiveness and complexity of this drug.

8-Oxo-7,8-dihydroguanine: links to gene expression, aging, and defense against oxidative stress

The one-electron oxidation product of guanine, 8-oxo-7,8-dihydroguanine (8-oxoG), is an abundant lesion in genomic, mitochondrial, and telomeric DNA and RNA. It is considered to be a marker of oxidative stress that preferentially accumulates at the 5' end of guanine strings in the DNA helix, in guanine quadruplexes, and in RNA molecules. 8-OxoG has a lower oxidation potential compared to guanine; thus it is susceptible to oxidation/reduction and, along with its redox products, is traditionally considered to be a major mutagenic DNA base lesion. It does not change the architecture of the DNA double helix and it is specifically recognized and excised by 8-oxoguanine DNA glycosylase (OGG1) during the DNA base excision repair pathway. OGG1 null animals accumulate excess levels of 8-oxoG in their genome, yet they do not have shorter life span nor do they exhibit severe pathological symptoms including tumor formation. In fact they are increasingly resistant to inflammation. Here we address the rarely considered significance of 8-oxoG, such as its optimal levels in DNA and RNA under a given condition, essentiality for normal cellular physiology, evolutionary role, and ability to soften the effects of oxidative stress in DNA, and the harmful consequences of its repair, as well as its importance in transcriptional initiation and chromatin relaxation.

Loss of estrogen receptor beta decreases mitochondrial energetic potential and increases thrombogenicity of platelets in aged female mice

Platelets derived from aged (reproductively senescent) female mice with genetic deletion of estrogen receptor beta (betaER) are more thrombogenic than those from age-matched wild-type (WT) mice. Intracellular processes contributing to this increased thrombogenicity are not known. Experiments were designed to identify subcellular localization of estrogen receptors and evaluate both glycolytic and mitochondrial energetic processes which might affect platelet activation. Platelets and blood from aged (22-24 months) WT and estrogen receptor beta knockout (betaERKO) female mice were used in this study. Body, spleen weight, and serum concentrations of follicle-stimulating hormone and 17beta-estradiol were comparable between WT and betaERKO mice. Number of spontaneous deaths was greater in the betaERKO colony (50% compared to 30% in WT) over the course of 24 months. In resting (nonactivated) platelets, estrogen receptors did not appear to colocalize with mitochondria by immunostaining. Lactate production and mitochondrial membrane potential of intact platelets were similar in both groups of mice. However, activities of NADH dehydrogenase, cytochrome bc ( 1 ) complex, and cytochrome c oxidase of the electron transport chain were reduced in mitochondria isolated from platelets from betaERKO compared to WT mice. There were a significantly higher number of phosphatidylserine-expressing platelet-derived microvesicles in the plasma and a greater thrombin-generating capacity in betaERKO compared to WT mice. These results suggest that deficiencies in betaER affect energy metabolism of platelets resulting in greater production of circulating thrombogenic microvesicles and could potentially explain increased predisposition to thromboembolism in some elderly females.

Patterns of persistent DNA damage associated with sun exposure and the glutathione S-transferase M1 genotype in melanoma patients

Solar radiation can lead to changes affecting DNA metabolism resulting in loss of DNA integrity. Skin specimens obtained from melanoma patients treated at the Memorial Sloan-Kettering Cancer Center were used to study patterns of DNA fragmentation using the comet assay and levels of deletions in mitochondrial DNA (mtDNA) using real-time PCR. Skin specimens were classified according to the glutathione S-transferase M1 (GSTM1) genotype (either wild type [WT] or null) and patient sunburn history. GSTM1 null individuals with a sunburn history showed increased levels of both DNA fragmentation by comet assays and mtDNA deletions relative to GSTM1 WT patients with little or no sunburn history. Microarray analyses identified a number of genes whose expression was upregulated >or=5-fold in cells from GSTM1-null patients or from those reporting histories of sunburn. These genes encoded small molecule transporters, various growth factor/chemokine receptors, transcription factors and tumor suppressors. Of 17 genes directly involved in DNA repair, three DNA ligases were highly upregulated while the RAD23 UV excision repair gene and the Growth Arrest and DNA Damage gene (GADD45) were downregulated. These findings support the idea that exposure to solar radiation early in life may induce long-term cellular changes that lead to persistent DNA damage and altered patterns of gene expression.

Selective mtDNA mutation accumulation results in beta-cell apoptosis and diabetes development

To test the hypothesis that somatic mitochondrial (mt)DNA mutation accumulation predisposes mice to beta-cell loss and diabetes development, transgenic mice expressing a proofreading-deficient mtDNA polymerase-gamma under the control of the rat insulin-1 promoter were generated. At 6 wk of age, mtDNA mutations reached 0.01% (1.05 mutations/10,000 bp) in islets isolated from transgenic mice. This mutational burden is associated with impaired glucose tolerance and a diabetes prevalence of 52% in male transgenic mice. Female transgenic mice maintain slightly elevated fasting glucose levels, mild glucose intolerance, and a diabetes prevalence of 14%. Diabetes in transgenic animals is associated with insulin insufficiency that results from a significant reduction in beta-cell mass. Importantly, apoptosis of beta-cells is increased 7-fold in female and 11-fold in male transgenic mice compared with littermate controls. These results are consistent with a causative role of somatic mtDNA mutation accumulation in the loss of beta-cell mass and diabetes development.

Mitochondrial protection by low doses of insulin-like growth factor-Iin experimental cirrhosis

AIM: To characterize the mitochondrial dysfunction in experimental cirrhosis and to study whether insulin-like growth factor-I(IGF-I) therapy (4 wk) is able to induce beneficial effects on damaged mitochondria leading to cellular protection.

METHODS: Wistar rats were divided into three groups: Control group, untreated cirrhotic rats and cirrhotic rats treated with IGF-Itreatment (2 &mgr;g/100 g bw/d). Mitochondrial function was analyzed by flow cytometry in isolated hepatic mitochondria, caspase 3 activation was assessed by Western blot and apoptosis by TUNEL in the three experimental groups.

RESULTS: Untreated cirrhotic rats showed a mitochondrial dysfunction characterized by a significant reduction of mitochondrial membrane potential (in status 4 and 3); an increase of intramitochondrial reactive oxigen species (ROS) generation and a significant reduction of ATPase activity. IGF-Itherapy normalized mitochondrial function by increasing the membrane potential and ATPase activity and reducing the intramitochondrial free radical production. Activity of the electron transport complexes Iand III was increased in both cirrhotic groups. In addition, untreated cirrhotic rats showed an increase of caspase 3 activation and apoptosis. IGF-Itherapy reduced the expression of the active peptide of caspase 3 and resulted in reduced apoptosis.

CONCLUSION: These results show that IGF-Iexerts a mitochondrial protection in experimental cirrhosis leading to reduced apoptosis and increased ATP production.

Low doses of insulin-like growth factor-I induce mitochondrial protection in aging rats

Serum IGF-I levels decline with age. We have recently reported that in aging rats the exogenous administration of IGF-I restores IGF-I circulating levels and age related-changes, improving glucose and lipid metabolisms, increasing testosterone levels and serum total antioxidant capability, and reducing oxidative damage in the brain and liver associated with a normalization of antioxidant enzyme activities. Understanding that mitochondria are one of the most important cellular targets of IGF-I, the aims of this study were to characterize mitochondrial dysfunction and study the effect of IGF-I therapy on mitochondria, leading to cellular protection in the following experimental groups: young controls, untreated old rats, and aging rats treated with IGF-I. Compared with young controls, untreated aging rats showed an increase of oxidative damage in isolated mitochondria with a mitochondrial dysfunction characterized by: depletion of membrane potential with increased proton leak rates and intramitochondrial free radical production, and a significant reduction of ATPase and complex IV activities. In addition, mitochondrial respiration from untreated aging rats was atractyloside insensitive, suggesting that the adenine nucleotide translocator was uncoupled. The adenine nucleotide translocator has been shown to be one of the most sensitive locations for pore opening. Accordingly, untreated aging rats showed a significant overexpression of the active fragment of caspases 3 and 9. IGF-I therapy corrected these parameters of mitochondrial dysfunction and reduced caspase activation. In conclusion, these results show that the cytoprotective effect of IGF-I is closely related to a mitochondrial protection, leading to reduce free radical production, oxidative damage, and apoptosis, and to increased ATP production.

Decreased susceptibility to antifungals in respiratory-deficient Kluyveromyces lactis mutants

Decreased susceptibility of K. lactis mutants impaired in the function of cytochrome c, cytochrome c1 and cytochrome-c oxidase to fluconazole, bifonazole and amphotericin B in comparison with the isogenic wild-type strain was observed. Flow cytometry with rhodamine 6G did not show any changes in the accumulation of the dye in the mutant cells compared with the corresponding wild-type strain. Sterol analysis showed similar overall amount of sterols in both wild-type and mutant cells. Taking into account the increased amphotericin B resistance and significantly diminished susceptibility of mutant cells to lyticase digestion, the cell wall structure and/or composition may probably be responsible for the observed changes in the susceptibility of mutants to the antifungal compounds used.

Effects of ageing and Alzheimer's disease on mitochondrial function of human platelets

Mitochondrial dysfunction may play an important role in the pathogenesis of ageing and age-neurodegenerative diseases such as Alzheimer's disease (AD). Platelet mitochondrial membrane potential (reflected by measurement of JC-1 fluorescence ratio) and adenosine 5'-triphosphate (ATP) contents of 24 moderate probable AD patients, 20 age-matched control subjects and 20 young control subjects were measured. Also, a beta-amyloid peptide (Abeta)-induced damage model of platelets was established. After the addition of Abeta, platelet JC-1 fluorescence ratio and ATP content of platelets were measured in 16 AD patients, 20 aged and 20 young control subjects. Young control subjects had higher JC-1 fluorescence ratio than both AD patients and aged control subjects. No significant differences in platelet ATP contents were found among AD patients, aged and young control subjects. After the addition of Abeta, platelet JC-1 fluorescence ratio and ATP content of aged and young control subjects lowered markedly, but no obvious decrease of platelet JC-1 fluorescence ratio of AD patients was found compared with those of aged and young control subjects. Decrease of platelet JC-1 fluorescence ratio of aged control subjects was lower than that of young control subjects following the addition of Abeta. These results indicated that mitochondrial dysfunction may occur during ageing and platelet mitochondria of AD patients and aged subjects showed a tolerance to Abeta-induced damage. Therefore, blood platelets might serve as a biomarker for detection of mitochondrial function and age-related disease.

Molecular mechanisms of life- and health-span extension: role of calorie restriction and exercise intervention

The aging process results in a gradual and progressive structural deterioration of biomolecular and cellular compartments and is associated with many pathological conditions, including cardiovascular disease, stroke, Alzheimer's disease, osteoporosis, sarcopenia, and liver dysfunction. Concomitantly, each of these conditions is associated with progressive functional decline, loss of independence, and ultimately disability. Because disabled individuals require care in outpatient or home care settings, and in light of the social, emotional, and fiscal burden associated with caring for an ever-increasing elderly population, research in geriatric medicine has recently focused on the biological mechanisms that are involved in the progression towards functional decline and disability to better design treatment and intervention strategies. Although not completely understood, the mechanisms underlying the aging process may partly involve inflammatory processes, oxidative damage, mitochondrial dysfunction, and apoptotic tissue degeneration. These hypotheses are based on epidemiological evidence and data from animal models of aging, as well as interventional studies. Findings from these studies have identified possible strategies to decrease the incidence of age-related diseases and delay the aging process. For example, lifelong exercise is known to extend mean life-span, whereas calorie restriction (CR) increases both mean and maximum life-span in a variety of species. Optimal application of these intervention strategies in the elderly may positively affect health-related outcomes and possibly longevity. Therefore, the scope of this article is to (i) provide an interpretation of various theories of aging from a "health-span" perspective; (ii) describe interventional testing in animals (CR and exercise); and (iii) provide a translational interpretation of these data.

Modulation of age-induced apoptotic signaling and cellular remodeling by exercise and calorie restriction in skeletal muscle

Aging is inevitably associated with a progressive loss of muscle mass and strength, a condition also known as sarcopenia of aging. Although the precise mechanisms underlying this syndrome have not been completely elucidated, recent studies point toward several key cellular mechanisms that could contribute to age-associated muscle loss. Among these, mitochondrial dysfunction and deregulation of apoptotic signaling have emerged as critical players in the onset and progression of sarcopenia. Interestingly, calorie restriction, a well-known antiaging intervention, and, more recently, exercise training have been shown to beneficially affect both mitochondrial function and apoptotic signaling in skeletal muscle from young and old animals. Preliminary observations also indicate that even a small (8%) reduction in food intake may still provide protective effects against sarcopenia and cellular remodeling in aging skeletal muscle, with the advantage of being more applicable to human subjects than the traditional 30-40% restriction regimen. The most recent evidence on the relevance of skeletal muscle apoptosis to sarcopenia, as well as its modulation by calorie restriction and exercise, is reviewed.

The role of mitochondria in aging of skeletal muscle

Aging can be characterized as a time dependent decline of maximal functionality that affects tissues and organs of the whole body. Such is induced by the progressive loss of redundant components and leads to an increased susceptibility to disease and risk of death. Regarding the aging of skeletal muscle, it has been pointed out that mitochondria is a key factor behind the loss of redundancy and functionality, since this organelle has a major role in cellular homeostasis particularly at the level of the bioenergetic status. Decreased activities of the mitochondrial electron transport chain complexes and an increased release of reactive oxygen species from mitochondria are well documented with age; it is suggested that the mitochondrial loss of function results from the increased oxidative damage to proteins, lipids, and DNA of this organelle. However, it is important to be aware that the mitochondrial loss of function could also be a consequence, rather than a cause, of the cellular deterioration with age, which compromises mitochondrial biogenesis, mitochondrial protein turnover and autophagocytosis of damaged mitochondria. In this review several topics will be addressed regarding the age-related loss of skeletal muscle redundancy associated with mitochondrial dysfunction, emphasizing hypotheses for underlying mechanisms. In addition, we discuss some of the cellular mechanisms that can be pointed out as being responsible for the age-related mitochondrial dysfunction.

Mitochondrial dysfunction: the first domino in brain aging and Alzheimer's disease?

With the increasing average life span of humans and with decreasing cognitive function in elderly individuals, age-related cognitive disorders including dementia have become a major health problem in society. Aging-related mitochondrial dysfunction underlies many common neurodegenerative disorders diseases, including Alzheimer's disease (AD). AD is characterized by two major histopathological hallmarks, initially intracellular and with the progression of the disease extracellular accumulation of oligomeric and fibrillar beta-amyloid (Abeta) peptides and intracellular neurofibrillary tangles (NFT) composed of hyperphosphorylated tau protein. In this review, the authors focus on the latest findings in AD animal models indicating that these histopathological alterations induce deficits in the function of the complexes of the respiratory chain and therefore consecutively result in mitochondrial dysfunction. This parameter is intrinsically tied to oxidative stress. Both are early events in aging and especially in the pathogenesis of aging-related severe neurodegeneration. Ginkgo biloba extract seems to be of therapeutic benefit in the treatment of mild to moderate dementia of different etiology, although the data are quite heterogeneous. Herein, the authors suggest that mitochondrial protection and subsequent reduction of oxidative stress are important components of the neuroprotective activity of Ginkgo biloba extract.

Purinergic receptor-stimulated IP3-mediated Ca2+ release enhances neuroprotection by increasing astrocyte mitochondrial metabolism during aging

Astrocytes play an essential role in the maintenance and protection of the brain, which we reported was diminished with age. Here, we demonstrate that activation of a purinergic receptor (P2Y-R) signaling pathway, in astrocytes, significantly increases the resistance of astrocytes and neurons to oxidative stress. Interestingly, P2Y-R activation in old astrocytes increased their resistance to oxidative stress to levels that were comparable with stimulated young astrocytes. P2Y-R enhanced neuroprotection was blocked by oligomycin and by Xestospongin C, inhibitors of the ATP synthase and of inositol (1,4,5) triphosphate (IP3) binding to the IP3 receptor, respectively. Treatment of astrocytes with a membrane permeant analog of IP3 also protected astrocytes against oxidative stress. These data indicate that P2Y-R enhanced astrocyte neuroprotection is mediated by a Ca2+-dependent increase in mitochondrial metabolism. These data also reveal a signaling pathway that can rapidly respond to central energy needs throughout the aging process.

Mechanisms of mitochondrial dysfunction and energy deficiency in Alzheimer's disease

Several studies have demonstrated aberrations in the Electron Transport Complexes (ETC) and Krebs (TCA) cycle in Alzheimer's disease (AD) brain. Optimal activity of these key metabolic pathways depends on several redox active centers and metabolites including heme, coenzyme Q, iron-sulfur, vitamins, minerals, and micronutrients. Disturbed heme metabolism leads to increased aberrations in the ETC (loss of complex IV), dimerization of APP, free radical production, markers of oxidative damage, and ultimately cell death all of which represent key cytopathologies in AD. The mechanism of mitochondrial dysfunction in AD is controversial. The observations that Abeta is found both in the cells and in the mitochondria and that Abeta binds with heme may provide clues to this mechanism. Mitochondrial Abeta may interfere with key metabolites or metabolic pathways in a manner that overwhelms the mitochondrial mechanisms of repair. Identifying the molecular mechanism for how Abeta interferes with mitochondria and that explains the established key cytopathologies in AD may also suggest molecular targets for therapeutic interventions. Below we review recent studies describing the possible role of Abeta in altered energy production through heme metabolism. We further discuss how protecting mitochondria could confer resistance to oxidative and environmental insults. Therapies targeted at protecting mitochondria may improve the clinical outcome of AD patients.

Mitochondrial dysfunction in platelets and hippocampi of senescence-accelerated mice

Senescence-accelerated mice (SAM) strains are useful models to understand the mechanisms of age-dependent degeneration. In this study, measurements of the mitochondrial membrane potential (Deltapsi(m)) of platelets and the Adenosine 5(')-triphosphate (ATP) content of hippocampi and platelets were made, and platelet mitochondria were observed in SAMP8 (faster aging mice) and SAMR1 (aging resistant control mice) at 2, 6 and 9 months of age. In addition, an Abeta-induced (Amyloid beta-protein) damage model of platelets was established. After the addition of Abeta, the Deltapsi(m) of platelets of SAMP8 at 1 and 6 months of age were measured. We found that platelet Deltapsi(m), and hippocampal and platelet ATP content of SAMP8 mice decreased at a relatively early age compared with SAMR1. The platelets of 6 month-old SAMP8 showed a tolerance to Abeta-induced damages. These results suggest that mitochondrial dysfunction might be one of the mechanisms leading to age-associated degeneration in SAMP mice at an early age and the platelets could serve as a biomarker for detection of mitochondrial function and age related disease.

ESCI Award 2006. Mitochondrial function and endocrine diseases

Mitochondria are fundamental for oxidative energy production and impairment of their functionality can lead to reduced ATP synthesis and contribute to initiation of apoptosis. Endocrine tissues critically rely on oxidative phosphorylation so that mitochondrial abnormalities may either be causes or consequences of diminished hormone production or action. Abnormalities typical for diseases caused by mitochondrial DNA mutations such as Kearns-Sayre syndrome or mitochondrial encephalomyopathy, lactic acidosis, and stroke-like episodes syndrome are also seen in certain endocrine diseases. Lack or excess of thyroid hormones, major ubiquitous regulators of mitochondrial content and activity, cause muscular abnormalities and multisystem disorders. Mitochondria are a further prerequisite for steroidogenesis as well as insulin secretion and action. Recent studies showed that reduced mitochondrial ATP synthesis in skeletal muscle is a feature of certain hereditary and acquired forms of insulin resistance and diabetes mellitus. Finally, ageing is not only accompanied by various degrees of hormonal deficiency and insulin resistance but is also associated with a progressive decline of mitochondrial number and function. Future research is needed to examine whether mitochondrial abnormalities are the cause or consequence of ageing and frequent metabolic diseases such as obesity and type 2 diabetes mellitus, and to address mitochondria as a target for novel therapeutic regimes.

Molecular bases of hearing loss in multi-systemic mitochondrial cytopathy

PURPOSE

Hearing loss is a common clinical feature in classic mitochondrial syndromes. The purpose of this study was to evaluate the diverse molecular etiologies and natural history of hearing loss in multi-systemic mitochondrial cytopathies and the possible correlation between degree of hearing loss and neurological phenotype.

METHODS

In this retrospective study we evaluated the clinical features and molecular bases of hearing loss associated with multi-systemic mitochondrial cytopathy. Forty-five patients with sensorineural hearing loss and definite diagnosis of mitochondrial cytopathy according to the published diagnostic criteria were studied.

RESULTS

The sensorineural hearing loss was progressive and for the most part symmetrical with involvement of the higher frequencies. Both cochlear and retrocochlear involvement were found in this cohort. No correlation was found between the degree of hearing loss and the number and severity of neurological manifestations. Deleterious mtDNA point mutations of undisputed pathogenicity were identified in 18 patients. The A3243G mutation was the most frequently encountered among this group. MtDNA depletion, over-replication, and multiple deletions were found in further 11 cases.

CONCLUSION

This study reveals an expanding spectrum of mtDNA abnormalities associated with hearing loss. No correlation was found between the degrees of hearing loss and the severity of neurological manifestations.

New insights into the regulation of cardiolipin biosynthesis in yeast: implications for Barth syndrome

Recent studies have revealed an array of novel regulatory mechanisms involved in the biosynthesis and metabolism of the phospholipid cardiolipin (CL), the signature lipid of mitochondria. CL plays an important role in cellular and mitochondrial function due in part to its association with a large number of mitochondrial proteins, including many which are unable to function optimally in the absence of CL. New insights into the complexity of regulation of CL provide further evidence of its importance in mitochondrial and cellular function. The biosynthesis of CL in yeast occurs via three enzymatic steps localized in the mitochondrial inner membrane. Regulation of this process by general phospholipid cross-pathway control and factors affecting mitochondrial development has been previously established. In this review, novel regulatory mechanisms that control CL biosynthesis are discussed. A unique form of inositol-mediated regulation has been identified in the CL biosynthetic pathway, independent of the INO2-INO4-OPI1 regulatory circuit that controls general phospholipid biosynthesis. Inositol leads to decreased activity of phosphatidylglycerolphosphate (PGP) synthase, which catalyzes the committed step of CL synthesis. Reduced enzymatic activity does not result from alteration of expression of the structural gene, but is instead due to increased phosphorylation of the enzyme. This is the first demonstration of phosphorylation in response to inositol and may have significant implications in understanding the role of inositol in other cellular regulatory pathways. Additionally, synthesis of CL has been shown to be dependent on mitochondrial pH, coordinately controlled with synthesis of mitochondrial phosphatidylethanolamine (PE), and may be regulated by mitochondrial DNA absence sensitive factor (MIDAS). Further characterization of these regulatory mechanisms holds great potential for the identification of novel functions of CL in mitochondrial and cellular processes.

Histological recurrent hepatitis C after liver transplantation: Outcome and role of retransplantation

Impact of hepatitis C virus (HCV) recurrence on long-term outcome after orthotopic liver transplantation (OLT) is highly variable, and the role of retransplantation is still debated. From 1996 to 2003, 131 OLT with histologically proven HCV recurrence and 6 months of follow-up were retrospectively reviewed. One and 5-yr overall survivals were 90.7 and 81.3%, respectively. The mean time of HCV recurrence was 10.1 +/- 6.2 months in patients whose donor's age was less than 70 yr old, and 6.6 +/- 4.7 in patients whose donor's age was more than 70 (P < 0.01). The mean time between OLT and HCV recurrence was 10.7 +/- 8.2 months among patients still alive, and 5 +/- 4.2 among the 20 who died (P = 0.02). In 16 (12.2%) patients, retransplantation was required for severe HCV recurrence; 5 are still alive and 11 (68.7%) died. The mean survival time was 16.2 +/- 6 months if re-OLT was performed within 12 months from first OLT, and it was 45.9 +/- 10 months if re-OLT was performed later (P < 0.01). In conclusion, donors older than 70 yr are at high risk of early HCV recurrence; expectancy of life is significantly reduced in case of histologically proven recurrence within 6 months. Outcome is quite dismal in patients with early HCV recurrence requiring retransplantation within 1 yr of first OLT.

A low dose of ethidium bromide leads to an increase of total mitochondrial DNA while higher concentrations induce the mtDNA 4997 deletion in a human neuronal cell line

Ethidium bromide (EtBr) is widely used to deplete mitochondrial DNA (mtDNA) and produce mitochondrial DNA-less cell lines. However, it frequently fails to deplete mtDNA in mouse cells. In this study we show by using a highly sensitive real-time PCR, that low doses of EtBr (10 microM) did lead to a three-fold increase of the total amount of mitochondrial DNA in a human neuronal cell line (Ntera 2). A higher dose of EtBr (25 microM) led to the expected decrease of mtDNA until day 22 when the cells almost died. Cell growth and mtDNA content could be restored after additional 22 days of non-EtBr treatment. The highest concentration of 50 microM also led to a significant increase of mtDNA. The cells died when they had only about 10% of mtDNA left, indicating a mtDNA threshold for cell survival. Additionally, the so-called common 4977 bp deletion could be induced by prolonged exposure to ethidium bromide. Whereas the higher doses led to significant higher amounts of deleted mtDNA.

Mitochondrial DNA and ageing

The accumulation of mitochondrial DNA mutations has been proposed as a potential mechanism in the physiological processes of ageing and age-related disease. Although mitochondria have long been anticipated as a perpetrator of ageing, there was little experimental evidence to link these changes directly with the cellular pathology of ageing. Recently, considerable progress in understanding basic mitochondrial genetics and in identifying acquired mtDNA mutations in ageing has been made. Furthermore, the creation of mtDNA-mutator mice has provided the first direct evidence that accelerating the mtDNA mutation rate can result in premature ageing, consistent with the view that loss of mitochondrial function is a major causal factor in ageing. This review will, therefore, focus on recent developments in ageing research related to the role played by mtDNA.

Frataxin, iron-sulfur clusters, heme, ROS, and aging

A deficiency in mitochondrial frataxin causes an increased generation of mitochondrial reactive oxygen species (ROS), which may contribute to the cell degenerative features of Friedreich's ataxia. In this work the authors demonstrate mitochondrial iron-sulfur cluster (ISC) defects and mitochondrial heme defects, and suggest how both may contribute to increased mitochondrial ROS in lymphoblasts from human patients. Mutant cells are deficient in the ISC-requiring mitochondrial enzymes aconitase and succinate dehydrogenase, but not in the non-ISC mitochondrial enzyme citrate synthase; also, the mitochondrial iron-sulfur scaffold protein IscU2 co-immunoprecipitates with frataxin in vivo. Presumably as a consequence of the iron-sulfur cluster defect, cytochrome c heme is deficient in mutants, as well as heme-dependent Complex IV. Mitochondrial superoxide is elevated in mutants, which may be a consequence of cytochrome c deficiency. Hydrogen peroxide, glutathione peroxidase activity, and oxidized glutathione (GSSG) are each elevated in mutants, consistent with activation of the glutathione peroxidase pathway. Mutant status blunted the effects of Complex III and IV inhibitors, but not a Complex I inhibitor, on superoxide production. This suggests that heme defects late in the electron transport chain of mutants are responsible for increased mutant superoxide. The impact of ISC and heme defects on ROS production with age are discussed.

Effect of antioxidant diets on mitochondrial gene expression in rat brain during aging

Age-related increase of reactive oxygen species (ROS) is particularly detrimental in postmitotic tissues. Calorie restriction (CR) has been shown to exert beneficial effects, consistent with reduced ROS generation by mitochondria. Many antioxidant compounds also mimic such effects. N-acetyl cysteine (NAC) provides thiol groups to glutathione and to mitochondrial respiratory chain proteins; thus, it may counteract both ROS generation and effects. In the present study we investigated, in different rat brain areas during aging (6, 12, and 28 months), the effect of 1-year treatment with CR and dietary supplementation with NAC on the expression of subunit 39 kDa and ND-1 (mitochondrial respiratory complex I), subunit IV (complex IV), subunit alpha of F0F1-ATP synthase (complex V) and of adenine nucleotide translocator, isoform 1 (ANT-1). The observed age-related changes of expression were prevented by the dietary treatments. The present study provides further evidence for the critical role of mitochondria in the aging process.

Ca2+ signaling, mitochondria and sensitivity to oxidative stress in aging astrocytes

Age-related changes in astrocytes that could potentially affect neuroprotection have been largely unexplored. To test whether astrocyte function was diminished during the aging process, we examined cell growth, Ca2+ signaling, mitochondrial membrane potential (DeltaPsi) and neuroprotection of NGF-differentiated PC12 cells. We observed that cell growth was significantly slower for astrocytes cultured from old (26-29 months) mice as compared to young (4-6 months) mice. DeltaPsis in old astrocytes were also more depolarized (lower) than in young astrocytes and old astrocytes showed greater sensitivity to the oxidant tert-butyl hydrogen peroxide (t-BuOOH). ATP-induced Ca2+ responses in old astrocytes were consistently larger in amplitude and more frequently oscillatory than in young astrocytes, which may be attributable to lower mitochondrial Ca2+ sequestration. Finally, NGF-differentiated PC12 cells that were co-cultured with old astrocytes were significantly more sensitive to t-BuOOH treatment than co-cultures of NGF-differentiated PC12 cells with young astrocytes. Together, these data demonstrate that astrocyte physiology is significantly altered during the aging process and that the astrocyte's ability to protect neurons is compromised.