Mitochondrial biogenesis and mitochondrial DNA maintenance of mammalian cells under oxidative stress

QPCR: a tool for analysis of mitochondrial and nuclear DNA damage in ecotoxicology

The quantitative PCR (QPCR) assay for DNA damage and repair has been used extensively in laboratory species. More recently, it has been adapted to ecological settings. The purpose of this article is to provide a detailed methodological guide that will facilitate its adaptation to additional species, highlight its potential for ecotoxicological and biomonitoring work, and critically review the strengths and limitations of this assay. Major strengths of the assay include very low (nanogram to picogram) amounts of input DNA; direct comparison of damage and repair in the nuclear and mitochondrial genomes, and different parts of the nuclear genome; detection of a wide range of types of DNA damage; very good reproducibility and quantification; applicability to properly preserved frozen samples; simultaneous monitoring of relative mitochondrial genome copy number; and easy adaptation to most species. Potential limitations include the limit of detection (approximately 1 lesion per 10(5) bases); the inability to distinguish different types of DNA damage; and the need to base quantification of damage on a control or reference sample. I suggest that the QPCR assay is particularly powerful for some ecotoxicological studies.

Mitochondrial turnover and aging of long-lived postmitotic cells: the mitochondrial-lysosomal axis theory of aging

It is now generally accepted that aging and eventual death of multicellular organisms is to a large extent related to macromolecular damage by mitochondrially produced reactive oxygen species, mostly affecting long-lived postmitotic cells, such as neurons and cardiac myocytes. These cells are rarely or not at all replaced during life and can be as old as the whole organism. The inherent inability of autophagy and other cellular-degradation mechanisms to remove damaged structures completely results in the progressive accumulation of garbage, including cytosolic protein aggregates, defective mitochondria, and lipofuscin, an intralysosomal indigestible material. In this review, we stress the importance of crosstalk between mitochondria and lysosomes in aging. The slow accumulation of lipofuscin within lysosomes seems to depress autophagy, resulting in reduced turnover of effective mitochondria. The latter not only are functionally deficient but also produce increased amounts of reactive oxygen species, prompting lipofuscinogenesis. Moreover, defective and enlarged mitochondria are poorly autophagocytosed and constitute a growing population of badly functioning organelles that do not fuse and exchange their contents with normal mitochondria. The progress of these changes seems to result in enhanced oxidative stress, decreased ATP production, and collapse of the cellular catabolic machinery, which eventually is incompatible with survival.

eNOS plays a major role in adiponectin synthesis in adipocytes

Nitric oxide (NO) stimulates mitochondrial biogenesis. We recently reported that adiponectin synthesis is regulated by mitochondrial function in adipocytes. This study was undertaken to test the hypothesis that endothelial NO synthase (eNOS) plays an important role in adiponectin synthesis by producing NO and enhancing mitochondrial function in adipocytes. We examined the effects of eNOS knockdown on adiponectin synthesis in 3T3-L1 adipocytes and also examined plasma adiponectin levels and the mitochondria in adipose tissue of eNOS knockout (eNOS(-/-)) mice with and without chronic administration of a NO donor. In cultured 3T3-L1 adipocytes, eNOS siRNA decreased rosiglitazone-induced adiponectin secretion, which was associated with decreases in mitochondrial proteins and biogenesis factors. Plasma adiponectin concentrations were reduced in adult eNOS(-/-) mice compared with age-matched wild-type mice. Mitochondrial contents in adipose tissue were reduced in eNOS(-/-) mice, and this was associated with decreased expression of mitochondrial biogenesis factors, increased levels of 8-hydroxyguanosine, a biomarker of oxidative stress, and morphological abnormalities in mitochondria. Rosiglitazone-induced increases in adiponectin expression and mitochondrial content were also reduced significantly in eNOS(-/-) mice. Chronic administration of a NO donor reversed mitochondrial abnormalities and increased adiponectin expression in adipose tissue of eNOS(-/-) mice. eNOS plays an important role in adiponectin synthesis in adipocytes by increasing mitochondrial biogenesis and enhancing mitochondrial function.

Diabetes regulates mitochondrial biogenesis and fission in mouse neurons

AIMS/HYPOTHESIS

Normal mitochondrial activity is a critical component of neuronal metabolism and function. Disruption of mitochondrial activity by altered mitochondrial fission and fusion is the root cause of both neurodegenerative disorders and Charcot-Marie-Tooth type 2A inherited neuropathy. This study addressed the role of mitochondrial fission in the pathogenesis of diabetic neuropathy.

METHODS

Mitochondrial biogenesis and fission were assayed in both in vivo and in vitro models of diabetic neuropathy. Gene, protein, mitochondrial DNA and ultrastructural analyses were used to assess mitochondrial biogenesis and fission.

RESULTS

There was greater mitochondrial biogenesis in dorsal root ganglion neurons from diabetic compared with non-diabetic mice. An essential step in mitochondrial biogenesis is mitochondrial fission, regulated by the mitochondrial fission protein dynamin-related protein 1 (DRP1). Evaluation of diabetic neurons in vivo indicated small, fragmented mitochondria, suggesting increased fission. In vitro studies revealed that short-term hyperglycaemic exposure increased levels of DRP1 protein. The influence of hyperglycaemia-mediated mitochondrial fission on cell viability was evaluated by knockdown of Drp1 (also known as Dnm1l). Knockdown of Drp1 resulted in decreased susceptibility to hyperglycaemic damage.

CONCLUSIONS/INTERPRETATION

We propose that: (1) mitochondria undergo biogenesis in response to hyperglycaemia, but the increased biogenesis is insufficient to accommodate the metabolic load; (2) hyperglycaemia causes an excess of mitochondrial fission, creating small, damaged mitochondria; and (3) reduction of aberrant mitochondrial fission increases neuronal survival and indicates an important role for the fission-fusion equilibrium in the pathogenesis of diabetic neuropathy.

Resveratrol attenuates radiation damage in Caenorhabditis elegans by preventing oxidative stress

Resveratrol, a member of a class of polyphenolic compounds known as flavonols, has been extensively studied for its anticancer, antiviral, anti-inflammatory, and neuroprotective roles. Caenorhabidits elegans is a well-established animal for investigating responses to radiation. We found that resveratrol may provide protection against hazardous radiation. Pre-treatment with resveratrol extended both the maximum and mean life span of irradiated C. elegans. Resveratrol acted as a strong radical scavenger and regulated superoxide dismutase (SOD) expression. In addition, resveratrol was shown to be capable of alleviating gamma-ray radiation exposure-induced reduction in mitochondrial SOD expression. Ultimately, a correlation may exist between dietary intake of trace amounts of resveratrol and anti-aging effects. A specific response mechanism may be activated after the administration of resveratrol in irradiated animals. Our results suggest the protective effect of resveratrol is due to its strong ability to protect from oxidative stress and protective effects in mitochondria. Therefore, resveratrol is potentially an effective protecting agent against irradiative damage.

Mitochondrial DNA variants in the pathogenesis of type 2 diabetes - relevance of asian population studies

Mitochondrial dysfunction involves defective insulin secretion by pancreatic beta-cells, and insulin resistance in insulin-sensitive tissues such as muscle and adipose tissue. Mitochondria are recognized as the most important cellular source of energy, and the major generator of intracellular reactive oxygen species (ROS). Intracellular antioxidative systems have been developed to cope with increased oxidative damage. In case of minor oxidative stress, the cells may increase the number of mitochondria to produce more energy. A mechanism called mitochondrial biogenesis, involving several transcription factors and regulators, controls the quantity of mitochondria. When oxidative damage is advanced beyond the repair capacity of antioxidative systems, then oxidative stress can lead to cell death. Therefore, this organelle is central to cell life or death. Available evidence increasingly shows genetic linkage between mitochondrial DNA (mtDNA) alterations and type 2 diabetes (T2D). Based on previous studies, the mtDNA 16189 variant is associated with metabolic syndrome, higher fasting insulin concentration, insulin resistance index and lacunar cerebral infarction. These data support the involvement of mitochondrial genetic variation in the pathogenesis of T2D. Importantly, phylogeographic studies of the human mtDNAs have revealed that the human mtDNA tree is rooted in Africa and radiates into different geographic regions and can be grouped as haplogroups. The Asian populations carry very different mtDNA haplogroups as compared to European populations. Therefore, it is critically important to determine the role of mtDNA polymorphisms in T2D.

Redox regulation of adaptive responses in skeletal muscle to contractile activity

Skeletal muscle is a highly malleable tissue that responds to changes in its pattern of activity or the mechanical and environmental stresses placed upon it. The signaling pathways involved in these multiple adaptations are increasingly well described, but there is a lack of information on the factors responsible for initiating these processes. Reactive oxygen species (ROS) are produced at various sites in skeletal muscle and there is increasing evidence that these species play targeted roles in modulating redox-sensitive signaling pathways that are important to the muscle for making adaptations. This review will outline some of the processes involved and the types of experimental approaches that seem necessary to fully evaluate these redox signaling systems in muscle. To understand how labile, highly reactive ROS can play a role in cell signaling that is discrete and yet regulated to prevent oxidative damage, an increased knowledge of the subcellular localization and compartmentalization of both ROS generation and the redox-sensitive targets of ROS activity is required. It seems likely that application of this increased knowledge will lead to new approaches to manipulating muscle metabolism to maintain health and prevent loss of muscle function in age-related diseases.

Antiapoptotic cardioprotective effect of hypothermia treatment against oxidative stress injuries

OBJECTIVES

The effect of hypothermia on cardiomyocyte injury induced by oxidative stress remains unclear. The authors investigated the effects of hypothermia on apoptosis and mitochondrial dysfunction in cardiomyocytes exposed to oxidative stress.

METHODS

Cardiomyocytes (H9c2) derived from embryonic rat heart cell culture were exposed to either normothermic (37 degrees C) or hypothermic (31 degrees C) environments before undergoing oxidative stress via treatment with hydrogen peroxide (H(2)O(2)). The degree of apoptosis was determined by annexin V and terminal deoxynucleotidyl transferase (TUNEL) staining. The amount of reactive oxygen species (ROS) was compared after H(2)O(2) exposure between normo- and hypothermic-pretreated groups. Mitochondrial dysfunction in both groups was measured by differential reductase activity and transmembrane potential (DeltaPsim).

RESULTS

Hydrogen peroxide induced significant apoptosis in both normothermic and hypothermic cardiomyocytes. Hypothermia ameliorated apoptosis as demonstrated by decreased annexin V staining (33 +/- 1% vs. 49 +/- 4%; p < 0.05) and TUNEL staining (27 +/- 17% vs. 80 +/-25%; p < 0.01). The amount of intracellular ROS increased after H(2)O(2) treatment and was higher in the hypothermic group than that in the normothermic group (237.9 +/- 31.0% vs. 146.6 +/- 20.6%; p < 0.05). In the hypothermic group, compared with the normothermic group, after H(2)O(2) treatment mitochondrial reductase activity was greater (72.0 +/- 17.9% vs. 27.0 +/- 13.3%; p < 0.01) and the mitochondria DeltaPsim was higher (101.0 +/- 22.6% vs. 69.7 +/- 12.9%; p < 0.05). Pretreatment of cardiomyocytes with the antioxidant ascorbic acid diminished the hypothermia-induced increase in intracellular ROS and prevented the beneficial effects of hypothermia on apoptosis and mitochondrial function.

CONCLUSIONS

Hypothermia at 31 degrees C can protect cardiomyocytes against oxidative stress-induced injury by decreasing apoptosis and mitochondrial dysfunction through intracellular ROS-dependent pathways.

Selective apoptosis induction by the cancer chemopreventive agent N-(4-hydroxyphenyl)retinamide is achieved by modulating mitochondrial bioenergetics in premalignant and malignant human prostate epithelial cells

Prostate tumorigenesis is coupled with an early metabolic switch in transformed prostate epithelial cells that effectively increases their mitochondrial bioenergetic capacity. The synthetic retinoid N-(4-hydroxyphenyl)retinamide (4HPR) inhibits prostate cancer development in vivo, and triggers reactive oxygen species (ROS)-dependent prostate cancer cell apoptosis in vitro. The possibility that 4HPR-induced ROS production is associated with mitochondrial bioenergetics and required for apoptosis induction in transformed prostate epithelial cells in vitro would advocate a prospective mechanistic basis for 4HPR-mediated prostate cancer chemoprevention in vivo. We investigated this tenet by comparing and contrasting 4HPR's effects on premalignant PWR-1E and malignant DU-145 human prostate epithelial cells. 4HPR promoted a dose- and/or time-dependent apoptosis induction in PWR-1E and DU-145 cells, which was preceded by and dependent on an increase in mitochondrial ROS production. In this regard, the PWR-1E cells were more sensitive than the DU-145 cells, and they consumed roughly twice as much oxygen as the DU-145 cells suggesting oxidative phosphorylation was higher in the premalignant cells. Interestingly, increasing the [Ca(2+)] in the culture medium of the PWR-1E cells attenuated their proliferation as well as their mitochondrial bioenergetic capacity and 4HPR's cytotoxic effects. Correspondingly, the respiration-deficient derivatives (i.e., rho(0) cells lacking mitochondrial DNA) of DU-145 cells were markedly resistant to 4HPR-induced ROS production and apoptosis. Together, these observations implied that the reduction of mitochondrial bioenergetics protected PWR-1E and DU-145 cells against the cytotoxic effects of 4HPR, and support the concept that oxidative phosphorylation is an essential determinant in 4HPR's apoptogenic signaling in transformed human prostate epithelial cells.

Overexpression of Tfam protects mitochondria against beta-amyloid-induced oxidative damage in SH-SY5Y cells

There is strong evidence that beta-amyloid (Abeta) causes oxidative stress and induces mitochondrial dysfunction in the pathogenesis of Alzheimer's disease. Mitochondrial transcription factor A (Tfam) has multiple roles in the maintenance of mtDNA. To study the protective roles of Tfam against amyloid neurotoxicity, we established SH-SY5Y cell lines stably overexpressing Tfam and exposed them to 10 microm Abeta1-42 for 24 h. We found that Tfam overexpression attenuated Abeta1-42-induced cell viability damage and apoptosis. In addition, Tfam overexpression significantly suppressed the increase in excess reactive oxygen species and reversed the reduction in cytochrome c oxidase activity and ATP production induced by Abeta1-42. Furthermore, overexpression of DeltaC-Tfam, which has no functional domain for stimulating mtDNA transcription but can still maintain the mtDNA nucleoid formation and mtDNA copy number, also exhibited protective effects against Abeta1-42 cytotoxicity in SH-SY5Y cells. Together, our data suggest that Tfam overexpression protects mitochondria against Abeta-induced oxidative damage in SH-SY5Y cells. These beneficial effects may be attributable to the roles of Tfam in maintaining mtDNA nucleoid formation and mtDNA copy number.

Variations in mouse mitochondrial DNA copy number from fertilization to birth are associated with oxidative stress

Mitochondria are inherited maternally via the oocyte, which in the mouse contains 150-250 x 10(3) copies of mitochondrial DNA (mtDNA). The number of mtDNA copies/embryo is thought to be stable during cleavage, being progressively diluted/cell with each round of cell division, until replication begins at an undefined time post-implantation. Post-natally, tissues differ in copy number of mtDNA/cell, but when and how these differences arise is unclear. A ratiometric quantitative real-time polymerase chain reaction assay of the levels of a single mitochondrial gene against a single copy nuclear gene was used to estimate the average copy value of mtDNA/per cell from zygote to birth. A novel Bayesian statistical model was used to identify day 5.15-6.15 as the time at which replication recommences, consistent with the viability patterns of embryos carrying mitochondrial mutations. Mitochondrial DNA copy number/cell in a range of post-day 9.5 fetal and placental tissues showed tissue-specific temporal expression patterns. Western blotting was used to quantify post-day 9.5 tissue markers for oxidative stress and manganese superoxide dismutase, and revealed correlations with the changes in mtDNA copy number. These findings have potential implications for fetal programming, in-vitro embryo culture, and the mechanism underlying the mitochondrial bottleneck.

OXPHOS gene expression and control in mitochondrial disorders

The cellular consequences of deficiencies of the mitochondrial OXPHOS system include a variety of direct and secondary changes in metabolite homeostasis, such as ROS, Ca(2+), ADP/ATP, and NAD/NADH. The adaptive responses to these changes include the transcriptional responses of nuclear and mitochondrial genes that are mediated by these metabolites, control of the mitochondria permeability transition pore, and a great variety of secondary signalling elements. Among the transcriptional responses reported over more than a decade using material harboring mtDNA mutations, deletions, or depletions, nuclear and mitochondrial DNA OXPHOS genes have mostly been up-regulated. However, it is evident from the limited data in a variety of disease models that expression responses are highly diverse and inconsistent. In this article, the mechanisms and controlling elements of these transcriptional responses are reviewed. In addition, the elements that need to be evaluated, in order to gain an improved perspective of the manner in which OXPHOS genes respond and impact on mitochondrial disease expression, are highlighted.

The CREB/CRE transcriptional pathway: protection against oxidative stress-mediated neuronal cell death

Formation of reactive oxygen and nitrogen species is a precipitating event in an array of neuropathological conditions. In response to excessive reactive oxygen species (ROS) levels, transcriptionally dependent mechanisms drive the up-regulation of ROS scavenging proteins which, in turn, limit the extent of brain damage. Here, we employed a transgenic approach in which cAMP-response element binding protein (CREB)-mediated transcription is repressed (via A-CREB) to examine the contribution of the CREB/cAMP response element pathway to neuroprotection and its potential role in limiting ROS toxicity. Using the pilocarpine-evoked repetitive seizure model, we detected a marked enhancement of cell death in A-CREB transgenic mice. Paralleling this, there was a dramatic increase in tyrosine nitration (a marker of reactive species formation) in A-CREB transgenic mice. In addition, inducible expression of peroxisome proliferator-activated receptor gamma coactivator-1alpha was diminished in A-CREB transgenic mice, as was activity of complex I of the mitochondrial electron transport chain. Finally, the neuroprotective effect of brain-derived neurotrophic factor (BDNF) against ROS-mediated cell death was abrogated by disruption of CREB-mediated transcription. Together, these data both extend our understanding of CREB functionality and provide in vivo validation for a model in which CREB functions as a pivotal upstream integrator of neuroprotective signaling against ROS-mediated cell death.

Mitochondrial DNA instability and metabolic shift in human cancers

A shift in glucose metabolism from oxidative phosphorylation to glycolysis is one of the biochemical hallmarks of tumor cells. Mitochondrial defects have been proposed to play an important role in the initiation and/or progression of various types of cancer. In the past decade, a wide spectrum of mutations and depletion of mtDNA have been identified in human cancers. Moreover, it has been demonstrated that activation of oncogenes or mutation of tumor suppressor genes, such as p53, can lead to the upregulation of glycolytic enzymes or inhibition of the biogenesis or assembly of respiratory enzyme complexes such as cytochrome c oxidase. These findings may explain, at least in part, the well documented phenomena of elevated glucose uptake and mitochondrial defects in cancers. In this article, we review the somatic mtDNA alterations with clinicopathological correlations in human cancers, and their potential roles in tumorigenesis, cancer progression, and metastasis. The signaling pathways involved in the shift from aerobic metabolism to glycolysis in human cancers are also discussed.

Interactions between coexisting intracellular genomes: mitochondrial density and Wolbachia infection

Many arthropods are infected with maternally transmitted microorganisms, leading to the coexistence of several intracellular genomes within the host cells, including their own mitochondria. As these genomes are cotransmitted, their patterns of evolution have been intimately linked, with possible consequences for the diversity and evolution of the host mitochondrial DNA. The evolutionary aspects of the situation have been thoroughly investigated, especially the selective sweep on the mitochondria as a result of Wolbachia invasion, whereas direct interactions between mitochondria and intracellular symbionts within the host cells or body have received little attention. Since endosymbionts exploit host resources but mitochondria supply energy to meet the bioenergetic demands of organisms, an unanswered question concerns the correlation between their densities. Here, we investigated the influence of Wolbachia symbiosis on mitochondrial density in two parasitic wasps of Drosophila species, both of which are naturally infected by three Wolbachia strains, but they differ in their degree of dependency on these bacteria. In Leptopilina heterotoma, all Wolbachia strains are facultative, whereas Asobara tabida requires a strain of Wolbachia for oogenesis to occur. In both species, Wolbachia infections are stable and well regulated, since the density of each strain does not depend on the presence or absence of other strains. Using lines that harbor various Wolbachia infection statuses, we found that mitochondrial density was not affected by the infection regardless of the sex and age of the host, which is strongly reminiscent of the independent regulation of specific Wolbachia strains and suggest that the protagonists coexist independently of each other as the result of a long-term coevolutionary interaction.

Interactions between ROS and AMP kinase activity in the regulation of PGC-1alpha transcription in skeletal muscle cells

Reactive oxygen species (ROS) play an important role in cellular function via the activation of signaling cascades. ROS have been shown to affect mitochondrial biogenesis, morphology, and function. Their beneficial effects are likely mediated via the upregulation of transcriptional regulators such as peroxisome proliferator-activated receptor-gamma coactivator-1 protein-alpha (PGC-1alpha). However, the ROS signals that regulate PGC-1alpha transcription in skeletal muscle are not understood. Here we examined the effect of H2O2 on the regulation of PGC-1alpha expression, and its relationship to AMPK activation. We demonstrate that 24 h of exogenous H2O2 treatment increased PGC-1alpha promoter activity and mRNA expression. Both effects were blocked with the addition of N-acetylcysteine, a ROS scavenger. These effects were mediated, in part, via upstream stimulatory factor-1/Ebox DNA binding and involved 1) interactions with downstream sequences and 2) the activation of AMPK. Elevated ROS led to the activation of AMPK, likely via a decline in ATP levels. The activation of AMPK using 5-aminoimidazole-4-carboxamide-1-beta-d-ribofuranoside increased PGC-1alpha promoter activity and mRNA levels but reduced ROS production. Thus the net effect of AMPK activation on PGC-1alpha expression was a result of increased transcriptional activation, counterbalanced by reduced ROS production. The effects of H2O2 on PGC-1alpha expression differed depending on the level of ROS within the cell. Low levels of ROS result in reduced PGC-1alpha mRNA in the absence of an effect on PGC-1alpha promoter activation. In contrast, elevated levels of H2O2 induce PGC-1alpha transcription indirectly, via AMPK activation. These data identify unique interactions between ROS and AMPK activation on the expression of PGC-1alpha in muscle cells.

Effects of oxygen on mouse embryonic stem cell growth, phenotype retention, and cellular energetics

Most embryonic stem (ES) cell research is performed with a gas phase oxygen partial pressure (pO(2)) of 142 mmHg, whereas embryonic cells in early development are exposed to pO(2) values of 0-30 mmHg. To understand effects of these differences, we studied murine ES (mES) growth, maintenance of stem cell phenotype, and cell energetics over a pO(2) range of 0-285 mmHg, in the presence or absence of differentiation-suppressing leukemia inhibitory factor (LIF). With LIF, growth rate was sensitive to pO(2) but constant with time, and expression of self-renewal transcription factors decreased at extremes of pO(2). Subtle morphological changes suggested some early differentiation, but cells retained the ability to differentiate into derivatives of all three germ layers at low pO(2). Without LIF, growth rate decreased with time, and self-renewal transcription factor mRNA decreased further. Gross morphological changes occurred, and overt differentiation occurred at all pO(2). These findings suggested that hypoxia in the presence of LIF promoted limited early differentiation. ES cells survived oxygen starvation with negligible cell death by increasing anaerobic metabolism within 48 h of anoxic exposure. Decreasing pO(2) to 36 mmHg or lower decreased oxygen consumption rate and increased lactate production rate. The fraction of ATP generated aerobically was 60% at or above 142 mmHg and decreased to 0% under anoxia, but the total ATP production rate remained nearly constant at all pO(2). In conclusion, undifferentiated ES cells adapt their energy metabolism to proliferate at all pO(2) between 0 and 285 mmHg. Oxygen has minimal effects on undifferentiated cell growth and phenotype, but may exert more substantial effects under differentiating conditions.

Mitochondrial biogenesis and healthy aging

Aging is associated with an overall loss of function at the level of the whole organism that has origins in cellular deterioration. Most cellular components, including mitochondria, require continuous recycling and regeneration throughout the lifespan. Mitochondria are particularly susceptive to damage over time as they are the major bioenergetic machinery and source of oxidative stress in cells. Effective control of mitochondrial biogenesis and turnover, therefore, becomes critical for the maintenance of energy production, the prevention of endogenous oxidative stress and the promotion of healthy aging. Multiple endogenous and exogenous factors regulate mitochondrial biogenesis through the peroxisome proliferator-activated receptor gamma coactivator-1alpha (PGC-1alpha). Activators of PGC-1alpha include nitric oxide, CREB and AMPK. Calorie restriction (CR) and resveratrol, a proposed CR mimetic, also increase mitochondrial biogenesis through activation of PGC-1alpha. Moderate exercise also mimics CR by inducing mitochondrial biogenesis. Negative regulators of PGC-1alpha such as RIP140 and 160MBP suppress mitochondrial biogenesis. Another mechanism involved in mitochondrial maintenance is mitochondrial fission/fusion and this process also involves an increasing number of regulatory proteins. Dysfunction of either biogenesis or fission/fusion of mitochondria is associated with diseases of the neuromuscular system and aging, and a greater understanding of the regulation of these processes should help us to ultimately control the aging process.

Chemotoxicity recovery of mitochondria in non-Hodgkin lymphoma resulting in minimal residual disease

BACKGROUND

The mechanisms responsible for resistant disease or recurrence of non-Hodgkin lymphoma (NHL) in children cover a wide spectrum from drug resistance to genetic mutations. A unique mechanism suggesting the role of mitochondria as the key energy source is studied following a clinical observation where pediatric Burkitt lymphoma (BL) specimens from patients on therapy were found to have increased copies of mitochondria DNA (mtDNA) in specimens which were shown to be positive for minimal residual disease and/or persistent disease (MRD/PD). This study hypothesized that the mitochondria play an important role in a cell's recovery from toxicity via a compensatory increase in mtDNA.

PROCEDURE

BL specimens with MRD/PD were assayed for mtDNA. An in vitro model was then designed using Ramos cell lines by exposing the lymphoma cells to varying concentrations of doxorubicin and vincristine for 1 hr; and allowing for recovery in culture over 7 days. DNA was extracted from aliquots over several days to determine mtDNA copy numbers by real-time polymerase chain reaction (PCR).

RESULTS

Increased mtDNA copy numbers were found in clinical specimens with MRD/PD as well as in recovering Ramos cells from chemotoxicity.

CONCLUSIONS

The recovering lymphoma cells from the chemotoxic effects appeared to compensate by increasing mtDNA content, which may contribute to the clinical residual or resistant disease in some cases of childhood BL.

Association between mitochondrial DNA copy number, blood cell counts, and occupational benzene exposure

Benzene is a recognized hematotoxicant and carcinogen that produces genotoxic damage. Benzene metabolites can produce reactive oxidative species. Mitochondrial DNA (mtDNA) copy number may be increased in response to oxidative stress to compensate for damaged mitochondria. We carried out a cross-sectional study of 40 benzene-exposed workers and 40 controls to evaluate the association between benzene exposure and mtDNA copy number. Copy number of mtDNA in leukocyte DNA was determined by real-time PCR. Compared with controls, the copy number of mtDNA increased by 4% and by 15% in workers exposed to < or =10 ppm (n = 20) and >10 ppm (n = 20) benzene, respectively. After adjusting for recent infection, the factor that was significantly correlated with mtDNA, the increase of mtDNA was statistically significant in the high exposed group (P = 0.016) with a significant linear trend (P = 0.024). To our best knowledge, this is the first report that benzene exposure was associated with increased mitochondria DNA copy number. Benzene exposure may induce mtDNA amplification, possibly in response to oxidative stress caused by benzene. The finding needs to be replicated by other studies.

PINK1 is necessary for long term survival and mitochondrial function in human dopaminergic neurons

Parkinson's disease (PD) is a common age-related neurodegenerative disease and it is critical to develop models which recapitulate the pathogenic process including the effect of the ageing process. Although the pathogenesis of sporadic PD is unknown, the identification of the mendelian genetic factor PINK1 has provided new mechanistic insights. In order to investigate the role of PINK1 in Parkinson's disease, we studied PINK1 loss of function in human and primary mouse neurons. Using RNAi, we created stable PINK1 knockdown in human dopaminergic neurons differentiated from foetal ventral mesencephalon stem cells, as well as in an immortalised human neuroblastoma cell line. We sought to validate our findings in primary neurons derived from a transgenic PINK1 knockout mouse. For the first time we demonstrate an age dependent neurodegenerative phenotype in human and mouse neurons. PINK1 deficiency leads to reduced long-term viability in human neurons, which die via the mitochondrial apoptosis pathway. Human neurons lacking PINK1 demonstrate features of marked oxidative stress with widespread mitochondrial dysfunction and abnormal mitochondrial morphology. We report that PINK1 plays a neuroprotective role in the mitochondria of mammalian neurons, especially against stress such as staurosporine. In addition we provide evidence that cellular compensatory mechanisms such as mitochondrial biogenesis and upregulation of lysosomal degradation pathways occur in PINK1 deficiency. The phenotypic effects of PINK1 loss-of-function described here in mammalian neurons provides mechanistic insight into the age-related degeneration of nigral dopaminergic neurons seen in PD.

Alterations in hepatic mitochondrial compartment in a model of obesity and insulin resistance

The objective of this paper is to evaluate adaptations in hepatic mitochondrial protein mass, function and efficiency in a rat model of high-fat diet-induced obesity and insulin resistance that displays several correlates to human obesity. Adult male rats were fed a high-fat diet for 7 weeks. Mitochondrial state 3 and state 4 respiratory capacities were measured in liver homogenate and isolated mitochondria by using nicotinamide adenine dinucleotide, flavin adenine dinucleotide and lipid substrates. Mitochondrial efficiency was evaluated by measuring proton leak kinetics. Mitochondrial mass was assessed by ultrastructural observations and citrate synthase (CS) activity measurements. Mitochondrial oxidative damage and antioxidant defence were also considered by measuring lipid peroxidation, aconitase and superoxide dismutase (SOD) specific activity. Whole body metabolic characteristics were obtained by measuring 24-h oxygen consumption (VO2), carbon dioxide production (VCO2), respiratory quotient (RQ) and nonprotein respiratory quotient (NPRQ), using indirect calorimetry with urinary nitrogen analysis. Whole body glucose homeostasis was assessed by measuring plasma insulin and glucose levels after a glucose load. Adult rats fed a high-fat diet for 7 weeks, exhibit not only obesity, insulin resistance and hepatic steatosis, but also reduced respiratory capacity and increased oxidative stress in liver mitochondria. Our present results indicate that alterations in the mitochondrial compartment induced by a high-fat diet are associated with the development of insulin resistance and ectopic fat storage in the liver. Our results thus fit in with the emerging idea that mitochondrial dysfunction can led to the development of metabolic diseases, such as obesity, type 2 diabetes mellitus and nonalcoholic steatohepatitis.

Review: mitochondrial defects in breast cancer

Mitochondria play important roles in cellular energy metabolism, free radical generation, and apoptosis. Mitochondrial DNA has been proposed to be involved in carcinogenesis because of its high susceptibility to mutations and limited repair mechanisms in comparison to nuclear DNA. Breast cancer is the most frequent cancer type among women in the world and, although exhaustive research has been done on nuclear DNA changes, several studies describe a variety of mitochondrial DNA alterations present in breast cancer. In this review article, we to provide a summary of the mitochondrial genomic alterations reported in breast cancer and their functional consequences.

Deficient mitochondrial biogenesis in critical illness: cause, effect, or epiphenomenon?

Recent studies indicate that mitochondrial dysfunction plays a role in the pathogenesis of a number of disease states. The importance of these organelles in shock and multiple organ dysfunction is of particular interest to those caring for the critically ill. Mitochondria have their own unique DNA (mtDNA) that encodes 13 essential subunits of electron transport chain enzymes, two ribosomal RNAs and 22 transfer RNAs. Importantly, mtDNA is especially susceptible to deletions, rearrangements and mutations because it is not bound by histones and lacks the extensive repair machinery present in the nucleus. The study by Côté et al. in this issue of Critical Care examines changes in mtDNA in critically ill patients. The results support further investigation into the role of mtDNA in the critically ill.

Sustained hypoxia modulates mitochondrial DNA content in the neonatal rat brain

The effects of placental insufficiency and preterm birth on neurodevelopment can be modeled in experimental settings of neonatal hypoxia in rodents. Here, rat pups were reared in reduced oxygen (9.5%) for 11 days, starting on postnatal day 3 (P3). This led to a significant reduction in brain and body weight gain in hypoxic pups compared to age-matched normoxia-reared controls, plausibly reflecting an inability to fulfill the energetic needs of normal growth and development. Adaptive processes designed to augment energetic capacity in eukaryotes include stimulation of mitochondrial biogenesis. We show that after 11 days of sustained hypoxia, the levels of nuclear respiratory factor-1 and mitochondrial transcription factor A are elevated and the content of mitochondrial DNA (mtDNA) is greater in the hypoxic P14 pup brain compared to normoxic conditions. Corresponding immunohistochemical analyses reveal increased density of mtDNA in large cortical neurons. In contrast, no changes in mtDNA content are observed in the brain of pups reared for 24 h (P3-P4) under hypoxic conditions. Together, these data suggest that prolonged inadequate oxygenation may trigger a compensatory increase in neuronal mitochondrial DNA content to partially mitigate compromised energy homeostasis and reduced energetic capacity in the developing hypoxic brain.

Thyroid hormone effects on mitochondrial energetics

Thyroid hormones are the major endocrine regulators of metabolic rate, and their hypermetabolic effects are widely recognized. The cellular mechanisms underlying these metabolic effects have been the subject of much research. Thyroid hormone status has a profound impact on mitochondria, the organelles responsible for the majority of cellular adenosine triphosphate (ATP) production. However, mechanisms are not well understood. We review the effects of thyroid hormones on mitochondrial energetics and principally oxidative phosphorylation. Genomic and nongenomic mechanisms have been studied. Through the former, thyroid hormones stimulate mitochondriogenesis and thereby augment cellular oxidative capacity. Thyroid hormones induce substantial modifications in mitochondrial inner membrane protein and lipid compositions. Results are consistent with the idea that thyroid hormones activate the uncoupling of oxidative phosphorylation through various mechanisms involving inner membrane proteins and lipids. Increased uncoupling appears to be responsible for some of the hypermetabolic effects of thyroid hormones. ATP synthesis and turnover reactions are also affected. There appear to be complex relationships between mitochondrial proton leak mechanisms, reactive oxygen species production, and thyroid status. As the majority of studies have focused on the effects of thyroid status on rat liver preparations, there is still a need to address fundamental questions regarding thyroid hormone effects in other tissues and species.

Sequence variations of mitochondrial DNA D-loop region are highly frequent events in familial breast cancer

Mitochondrial DNA (mtDNA) is known for its high frequencies of polymorphisms and mutations. The non-coding displacement (D)-loop, especially a mononucleotide repeat (poly-C) between 303 and 315 nucleotides (D310), has been recently identified as a frequent hotspot of mutations in human neoplasia, including breast cancer. To further explore the sequence variations of mitochondrial D-loop region in familial breast cancer and their possible associations with breast cancer risk, PCR-SSCP and direct DNA sequencing methods were used to detect the variants of the mtDNA D-Loop in 23 familial breast cancer patients as well as three high-risk cancer families. Compared to that in sporadic breast tumors (53.3%, 16/30) and healthy blood donors (6.7%, 2/30), we identified a total of 126 sequence alterations in 23/23 (100%) of familial breast cancer patients, including eight novel nucleotide variants. Among these changes, A to G at nt.263, T to C at nt.489, T to C at nt.310, TC insertion at nt.311, CA deletion at nt.522, and C to G at nt.527 were highly frequent ones. In addition, among three high-risk cancer families, we found that individuals affected with breast cancer harbored more mtDNA sequence variants in mtDNA D310 area than other affected family members. Together, our data indicate that sequence variants within the mtDNA D-Loop region are frequent events in Chinese familial breast cancer patients. Some of these nucleotide abnormalities, particularly those in D310 segment, might be involved in the breast carcinogenesis and could be included in a panel of molecular biomarkers for cancer susceptibility early-detection strategy.

Stimulation of mitochondrial biogenesis and autophagy by lipopolysaccharide in the neonatal rat cardiomyocyte protects against programmed cell death

Adult rat cardiomyocytes in culture respond to sub-lethal doses of lipopolysaccharides (LPS) by activation of pathways including the production of TNF-alpha and increased apoptosis. We and others have demonstrated a protective phenotype for neonatal rat cardiomyocytes to LPS. Concentrations of LPS far exceeding those necessary to induce TNF-alpha release do not induce apoptosis in the neonatal cells, although these cells are fully capable or inducing apoptosis in response to multiple other stimuli. In neonatal cells, we demonstrate that LPS treatment leads to a loss of mitochondrial membrane potential (Deltapsi) which is temporally associated with an increase in the level of uncoupling protein 3 (UCP3). Cells remain viable with no measurable increase in apoptotic or necrotic cell death. Many markers of mitochondrial biogenesis are also activated. LPS treatment stimulates an increase in the (i) transcription of mitochondrial transcription factor A (Tfam), (ii) nuclear accumulation of redox-sensitive nuclear respiratory factor 1 (NRF-1), and (iii) expression of peroxisome proliferator-activated receptor gamma co-activator 1 (PGC-1). We also observed that LPS increased intracellular autophagy. Autophagy was assessed by monitoring the levels of a mammalian protein specifically associated with autophagosomes, microtubule-associated light chain 3 (LC3). Furthermore, inhibition of autophagy in the presence of LPS stimulates markers of apoptosis. Our data suggest that the protective response of neonatal cells to LPS is multi-faceted at the level of the mitochondrion. Viable cells replace dysfunctional mitochondria by mitochondrial biogenesis and the extent of the damage limited by the rapid removal of damaged organelles by the stimulation of autophagy.

Treating neurodegeneration by modifying mitochondria: potential solutions to a "complex" problem

Mitochondria function differently in aged brains than they do in young brains. Consistently reported changes include reduced electron transport chain (ETC) enzyme activities, reduced phosphorylation of ADP, and increased reactive oxygen species (ROS) production. Various neurodegenerative diseases are also associated with changes in mitochondrial function, and these changes both recapitulate and extend those seen in "normal" aging. Unfortunately, attempts to treat neurodegenerative diseases by treating mitochondria-related pathology have thus far minimally impacted affected patients. A better understanding of how mitochondrial function changes in aging and neurodegenerative diseases, though, now suggests new approaches to mitochondrial therapy may prove more efficacious. Increasing ETC capacity, increasing oxidative phosphorylation, or decreasing mitochondrial ROS may yet prove useful for the treatment of brain aging and neurodegenerative diseases, and accomplishing this seems increasingly feasible. This review will discuss the role of mitochondrial function and dysfunction in aging and neurodegenerative diseases, and will focus on potential treatment strategies.

Gene expression profile of the PDAPP mouse model for Alzheimer's disease with and without Apolipoprotein E

The APOE epsilon 4 allele is a strong risk factor for Alzheimer's disease (AD). However, the molecular basis for this effect remains unclear. We examined expression of approximately 12,000 genes and expressed sequence tags in the hippocampus and cortex of PDAPP (APP(V717)) mice modeling AD that show extensive amyloid beta (A beta) deposition, and in PDAPP mice lacking murine APOE expression, which show marked attenuation of A beta deposition in the brain. Wild type and APOE knockout animals were also examined. Expression levels were determined at the initial stage of A beta deposition, as well as in older animals showing extensive neuropathological changes. Fifty-four transcripts were identified using our statistical analysis as differentially regulated between the PDAPP and PDAPP/APOE ko mice, whereas 31 transcripts were classified as differentially regulated among PDAPP mice and WT animals, and seven transcripts were identified as regulated between the PDAPP/APOE ko animals and the APOE ko animals. Interestingly, many of the differentially regulated genes we detected can be related to biological processes previously shown to be important in AD pathophysiology, including inflammation, calcium homeostasis, cholesterol transport and uptake, kinases and phosphatases involved in tau phosphorylation and dephosphorylation, mitochondrial energy metabolism, protein degradation, neuronal growth, endoplasmic reticulum (ER) stress related proteins, antioxidant activity, cytoskeletal organization, and presenilin binding proteins. Regulated genes also included some not directly associated with AD in the past but likely to be involved in known AD pathophysiologic mechanisms, and others that may represent completely novel factors in the pathogenesis of AD. These results provide a global molecular profile of hippocampal and cortical gene expression during the initial and intermediate stages Abeta deposition, and the effects of APOE deletion on this process.

Mitochondrial fission and fusion mediators, hFis1 and OPA1, modulate cellular senescence

The number and morphology of mitochondria within a cell are precisely regulated by the mitochondrial fission and fusion machinery. The human protein, hFis1, participates in mitochondrial fission by recruiting the Drp1 into the mitochondria. Using short hairpin RNA, we reduced the expression levels of hFis1 in mammalian cells. Cells lacking hFis1 showed sustained elongation of mitochondria and underwent significant cellular morphological changes, including enlargement, flattening, and increased cellular granularity. In these cells, staining for acidic senescence-associated beta-galactosidase activity was elevated, and the rate of cell proliferation was greatly reduced, indicating that cells lacking hFis1 undergo senescence-associated phenotypic changes. Reintroduction of the hFis1 gene into hFis1-depleted cells restored mitochondrial fragmentation and suppressed senescence-associated beta-galactosidase activity. Moreover, depletion of both hFis1 and OPA1, a critical component of mitochondrial fusion, resulted in extensive mitochondrial fragmentation and markedly rescued cells from senescence-associated phenotypic changes. Intriguingly, sustained elongation of mitochondria was associated with decreased mitochondrial membrane potential, increased reactive oxygen species production, and DNA damage. The data indicate that sustained mitochondrial elongation induces senescence-associated phenotypic changes that can be neutralized by mitochondrial fragmentation. Thus, one of the key functions of mitochondrial fission might be prevention of the sustained extensive mitochondrial elongation that triggers cellular senescence.

Increased oxidative damage and mitochondrial abnormalities in the peripheral blood of Huntington's disease patients

Increased oxidative stress and mitochondrial abnormalities contribute to neuronal dysfunction in Huntington's disease (HD). We investigated whether these pathological changes in HD brains may also be present in peripheral tissues. Leukocyte 8-hydroxydeoxyguanosine (8-OHdG) and plasma malondialdehyde (MDA) were elevated, and activities of erythrocyte Cu/Zn-superoxide dismutase (Cu/Zn-SOD) and glutathione peroxidase (GPx) reduced in 16 HD patients when compared to 36 age- and gender-matched controls. Deleted and total mitochondrial DNA (mtDNA) copy numbers were increased, whereas the mRNA expression levels of mtDNA-encoded mitochondrial enzymes are not elevated in HD leukocytes compared to the normal controls. Plasma MDA levels also significantly correlated with HD disease severity. These results indicate means to suppress oxidative damage or to restore mitochondrial functions may be beneficial to HD patients. Plasma MDA may be used as a potential biomarker to test treatment efficacy in the future, if confirmed in a larger, longitudinal study.

Enhanced oxidative stress and aberrant mitochondrial biogenesis in human neuroblastoma SH-SY5Y cells during methamphetamine induced apoptosis

Methamphetamine (METH) is an abused drug that may cause psychiatric and neurotoxic damage, including degeneration of monoaminergic terminals and apoptosis of non-monoaminergic cells in the brain. The cellular and molecular mechanisms underlying these METH-induced neurotoxic effects remain to be clarified. In this study, we performed a time course assessment to investigate the effects of METH on intracellular oxidative stress and mitochondrial alterations in a human dopaminergic neuroblastoma SH-SY5Y cell line. We characterized that METH induces a temporal sequence of several cellular events including, firstly, a decrease in mitochondrial membrane potential within 1 h of the METH treatment, secondly, an extensive decline in mitochondrial membrane potential and increase in the level of reactive oxygen species (ROS) after 8 h of the treatment, thirdly, an increase in mitochondrial mass after the drug treatment for 24 h, and finally, a decrease in mtDNA copy number and mitochondrial proteins per mitochondrion as well as the occurrence of apoptosis after 48 h of the treatment. Importantly, vitamin E attenuated the METH-induced increases in intracellular ROS level and mitochondrial mass, and prevented METH-induced cell death. Our observations suggest that enhanced oxidative stress and aberrant mitochondrial biogenesis may play critical roles in METH-induced neurotoxic effects.

Gene Expression in Breast Muscle and Duodenum from Low and High Feed Efficient Broilers

This study was conducted to evaluate messenger RNA (mRNA) expression of genes that are involved in energy metabolism and mitochondrial biogenesis: avian adenine nucleotide translocator (avANT), cytochrome oxidase III (COX III), inducible nitric oxide synthase (iNOS), peroxisome proliferator-activated receptor-gamma (PPAR-gamma), avian PPAR-gamma coactivator-1alpha (avPGC-1alpha), and avian uncoupling protein in breast muscle and duodenum of broilers with low and high feed efficiency (FE). Total RNA was extracted from snap-frozen tissues from male broilers with low (0.55 +/- 0.01) and high (0.72 +/- 0.01) FE (n = 8 per group). Total RNA was reverse-transcribed using oligo(dT), random primers, or both followed by real-time reverse transcription-PCR. Protein oxidation, measured as protein carbonyls, was also evaluated in duodenal mucosa. Protein carbonyls were higher in low FE mucosa in tissue homogenate and mitochondrial fraction. The mRNA expression of iNOS and PPAR-gamma in the duodenum was lower in the low FE broilers, with no differences in avANT, COX III, and avPGC-1alpha. In contrast, expression of avANT and COX III mRNA in breast muscle was lower in low FE broilers with no differences in iNOS, PPAR-gamma, and avPGC-1alpha. The avian uncoupling protein in breast muscle was higher in low FE birds (P = 0.068). These results indicate that there are differences in the expression of mRNA encoding for mitochondrial transcription factors and proteins in breast muscle and duodenal tissue between low and high FE birds. The differences that were observed may also reflect inherent metabolic and gene regulation differences between tissues.

Pathways and genes differentially expressed in the motor cortex of patients with sporadic amyotrophic lateral sclerosis

BACKGROUND

Amyotrophic lateral sclerosis (ALS) is a fatal disorder caused by the progressive degeneration of motoneurons in brain and spinal cord. Despite identification of disease-linked mutations, the diversity of processes involved and the ambiguity of their relative importance in ALS pathogenesis still represent a major impediment to disease models as a basis for effective therapies. Moreover, the human motor cortex, although critical to ALS pathology and physiologically altered in most forms of the disease, has not been screened systematically for therapeutic targets.

RESULTS

By whole-genome expression profiling and stringent significance tests we identify genes and gene groups de-regulated in the motor cortex of patients with sporadic ALS, and interpret the role of individual candidate genes in a framework of differentially expressed pathways. Our findings emphasize the importance of defense responses and cytoskeletal, mitochondrial and proteasomal dysfunction, reflect reduced neuronal maintenance and vesicle trafficking, and implicate impaired ion homeostasis and glycolysis in ALS pathogenesis. Additionally, we compared our dataset with publicly available data for the SALS spinal cord, and show a high correlation of changes linked to the diseased state in the SALS motor cortex. In an analogous comparison with data for the Alzheimer's disease hippocampus we demonstrate a low correlation of global changes and a moderate correlation for changes specifically linked to the SALS diseased state.

CONCLUSION

Gene and sample numbers investigated allow pathway- and gene-based analyses by established error-correction methods, drawing a molecular portrait of the ALS motor cortex that faithfully represents many known disease features and uncovers several novel aspects of ALS pathology. Contrary to expectations for a tissue under oxidative stress, nuclear-encoded mitochondrial genes are uniformly down-regulated. Moreover, the down-regulation of mitochondrial and glycolytic genes implies a combined reduction of mitochondrial and cytoplasmic energy supply, with a possible role in the death of ALS motoneurons. Identifying candidate genes exclusively expressed in non-neuronal cells, we also highlight the importance of these cells in disease development in the motor cortex. Notably, some pathways and candidate genes identified by this study are direct or indirect targets of medication already applied to unrelated illnesses and point the way towards the rapid development of effective symptomatic ALS therapies.

Building the mitochondrial proteome

Mitochondria are essential organelles for cellular homeostasis. A variety of pathologies including cancer, myopathies, diabetes, obesity, aging and neurodegenerative diseases are linked to mitochondrial dysfunction. Therefore, mapping the different components of mitochondria is of particular interest to gain further understanding of such diseases. In recent years, proteomics-based approaches have been developed in attempts to determine the complete set of mitochondrial proteins in yeast, plants and mammals. In addition, proteomics-based methods have been applied not only to the analysis of protein function in the organelle, but also to identify biomarkers for diagnosis and therapeutic targets of specific pathologies associated with mitochondria. Altogether, it is becoming clear that proteomics is a powerful tool not only to identify currently unknown components of the mitochondrion, but also to study the different roles of the organelle in cellular homeostasis.

Expression of mitochondrial biogenesis-signaling factors in brown adipocytes is influenced specifically by 17beta-estradiol, testosterone, and progesterone

Control of mitochondrial biogenesis in brown adipose tissue (BAT), as part of the thermogenesis program, is a complex process that requires the integration of multiple transcription factors to orchestrate mitochondrial and nuclear gene expression. Despite the knowledge of the role of sex hormones on BAT physiology, little is known about the effect of these hormones on the mitochondrial biogenic program. The aim of this study was to determine the effect of testosterone, 17beta-estradiol, and progesterone on the expression of nuclear factors involved in the control of mitochondrial biogenesis and thermogenic function such as ppargamma, pgc1alpha, nrf1, gabpa, and tfam, and also an inhibitor of PI3K-Akt pathway, recently found to be involved in the control of mitochondrial recruitment (pten). For this purpose, an in vitro assay using cell-cultured brown adipocytes was used to address the role of steroid hormones, progesterone, testosterone, and 17beta-estradiol on the mRNA expression of these factors by real-time PCR. Thus 17beta-estradiol seemed to exert a dual effect, activating the PI3K-Akt pathway by inhibiting pten mRNA expression and also inhibiting nrf1 and tfam mRNA expression. Progesterone seemed to positively stimulate mitochondriogenesis and BAT differentiation by increasing the mRNA expression of the gabpa-tfam axis and ppargamma, respectively, but also exerted a negative output by increasing pten mRNA levels. Finally, testosterone inhibited the transcription of pgc1alpha, the master factor involved in UCP1 expression and mitochondrial biogenesis. In conclusion, our results support the idea that sex hormones have direct effects on different mediators of the mitochondriogenesis program.

Gestation linked radical oxygen species fluxes and vitamins and trace mineral deficiencies in the ruminant

In mammals, radical oxygen species (ROS) are essential factors of cell replication, differentiation and growth (oxidative signal), notably during gestation, but are also potentially damaging agents. In Women, ROS play a role in remodeling of uterine tissues, implantation of the embryo, settlement of the villi and development of blood vessels characteristic of gestation. The body stores of vitamins and minerals of gestating females are used to keep ROS fluxes at a level corresponding to oxidative signals and to prevent an imbalance between their production and scavenging (oxidative stress), which would be detrimental to the mother and fetus. There is some evidence that, although based on different regulatory mechanisms, most of the effects of ROS reported in humans also occur in pregnant ruminant females, some of which have been actually reported. Many vitamins and trace elements have dual effects in the organism of mammals: (a) they are involved in the control of metabolic pathways or/and gene expression, (b) but most of the time they also display ROS trapping activity or their deficiencies induce high rates of ROS production. Deficiencies induce different disorders of gestation and can be induced by different kinds of stress. An example is given, corresponding to the decreased contents of cobalt of forages, when exposed to sustained heavy rains, so that the supply of vitamins B12 to the organism of the ruminant that grazes them is reduced and failure of gestation is induced. Outdoor exposure of ruminants to adverse climatic conditions by itself can increase the vitamin and trace element requirements. Adaptation of production systems taking into account these interactions between gestation and sources of stress or change of the quality of feeding stuffs as well as further developments of knowledge in that field is necessary to promote sustainable agricultural practices.

Differences in reactive oxygen species production explain the phenotypes associated with common mouse mitochondrial DNA variants

Common mitochondrial DNA (mtDNA) haplotypes in humans and mice have been associated with various phenotypes, including learning performance and disease penetrance. Notably, no influence of mtDNA haplotype in cell respiration has been demonstrated. Here, using cell lines carrying four different common mouse mtDNA haplotypes in an identical nuclear background, we show that the similar level of respiration among the cell lines is only apparent and is a consequence of compensatory mechanisms triggered by different production of reactive oxygen species. We observe that the respiration capacity per molecule of mtDNA in cells with the NIH3T3 or NZB mtDNA is lower than in those with the C57BL/6J, CBA/J or BALB/cJ mtDNA. In addition, we have determined the genetic element underlying these differences. Our data provide insight into the molecular basis of the complex phenotypes associated with common mtDNA variants and anticipate a relevant contribution of mtDNA single nucleotide polymorphisms to phenotypic variability in humans.

Nitric oxide/redox-based signalling as a therapeutic target for penile disorders

Oxidative and/or nitrosative stress is implicated in the pathogeneses of assorted penile disorders of clinical significance, notably erectile dysfunction, priapism and penile fibrosis. It is becoming increasingly recognised that the generation and activity of reactive oxygen and nitrogen species in the penis influence vascular homeostasis of this organ, with adverse effects exerted at cellular and molecular levels. Furthermore, these elements may interact with molecular signalling pathways operating in the penis, modulating their functional roles. This interaction in particular suggests that by accessing molecular targets associated with oxidative/nitrosative stress in the penis, new pharmacotherapeutic approaches may be developed to promote normal erectile ability and preserve erectile tissue health. This notion pertains to, but also extends beyond, interventions which predictably target components of the nitric oxide-based signal transduction pathway for the on-demand treatment of erectile dysfunction. The next line of pharmaceuticals for disorders of the penis, in general, may well spawn from an integrative understanding of the complex regulatory interactions influenced by, as well as influencing nitric oxide signalling in this organ.

Increased relative mitochondrial DNA content in leucocytes of patients with NAION

AIM

To investigate possible changes in relative mitochondrial DNA (mtDNA) content in patients with non-arteritic anterior ischaemic optic neuropathy (NAION).

METHODS

19 patients with NAION were compared to 32 controls matched for age, sex distribution, and ethnicity. DNA was extracted from leucocytes and competitive multiplex polymerase chain reaction was carried out with two primer pairs (one pair for mtDNA ND1 gene and the other pair for beta actin nuclear gene) in the presence of a fluorescent dye.

RESULTS

The mean relative mtDNA content in controls (0.93 (SD 0.11); 95% CI 0.89 to 0.97) was significantly less than in NAION patients (2.40 (1.05); 95% CI 1.90 to 2.91; p < 0.001). Relative mtDNA content was negatively correlated with Snellen visual acuity (Spearman's rho; r = -0.37; p = 0.022).

CONCLUSION

Increased relative mtDNA content in NAION patients may imply a response to oxidative stress, possibly in part because of mitochondrial respiratory chain defects. Significantly more non-synonymous mtDNA nucleotide changes, significantly increased relative mtDNA content, and a significant association between relative mtDNA content and visual acuity all imply that mitochondrial abnormalities may be a risk factor for NAION.

Energy metabolism and oxidative stress: impact on the metabolic syndrome and the aging process

Aging can be defined as a progressive decline in the ability of the organism to resist stress, damage, and disease. Although there are currently over 300 theories to explain the aging phenomenon, it is still not well understood why organisms age and why the aging process can vary so much in speed and quality from individual to individual. The oxidative stress hypothesis is one of the prevailing theories of aging. This theory states that free radicals produced during cellular respiration damage lipids, proteins, and DNA thereby accelerating the aging process and increasing disease risk. Under normal conditions, the electron transport chain is the primary producer of the superoxide anion, which is precursor to other highly reactive species such as hydrogen peroxide and the hydroxyl radical. Oxidative stress accumulates when prooxidants overwhelm the antioxidant defense mechanisms. This is dependent on a number of factors including free radical production, susceptibility of tissue to stress, and strength of the defense and repair system. Oxidative stress has been implicated in a number of chronic disease states usually grouped under the umbrella of the metabolic syndrome and is thought to contribute to the aging process. It has been hypothesized that the production of free radicals is dependent on resting metabolic rate and this may have an impact on the aging process. However, other factors, such as mitochondrial function, may be important in the production of free radicals and the subsequent effect on aging and disease states.

The role of oxidative stress in the dysregulation of gene expression and protein metabolism in neurodegenerative disease

There are few examples for which the genetic basis for neurodegenerative disease has been identified. For the majority of these disorders, the key to their understanding lies in knowledge of the molecular changes that contribute to altered gene expression and the translational modification of the protein products. Environmental factors play a role in the development and chronicity of neurodegenerative disorders. Environmental stimuli such as hypoxia, toxins, or heavy metals, increase production of reactive oxygen species and lower energy reserves. Chronic exposure to oxidative radicals can adversely affect gene expression and proteolysis. This review summarizes what is currently known about some of the changes in gene expression and protein metabolism that occur after oxidative stress which contribute to neurodegeneration, and reveals areas where more research is clearly needed.

Mitochondrial biogenesis in mtDNA-depleted cells involves a Ca2+-dependent pathway and a reduced mitochondrial protein import

Alterations in mitochondrial activity resulting from defects in mitochondrial DNA (mtDNA) can modulate the biogenesis of mitochondria by mechanisms that are still poorly understood. In order to study mitochondrial biogenesis in cells with impaired mitochondrial activity, we used rho-L929 and rho(0)143 B cells (partially and totally depleted of mtDNA, respectively), that maintain and even up-regulate mitochondrial population, to characterize the activity of major transcriptional regulators (Sp1, YY1, MEF2, PPARgamma, NRF-1, NRF-2, CREB and PGC-1alpha) known to control the expression of numerous nuclear genes encoding mitochondrial proteins. Among these regulators, cyclic AMP-responsive element binding protein (CREB) activity was the only one to be increased in mtDNA-depleted cells. CREB activation mediated by a calcium-dependent pathway in these cells also regulates the expression of cytochrome c and the abundance of mitochondrial population as both are decreased in mtDNA-depleted cells that over-express CREB dominant negative mutants. Mitochondrial biogenesis in mtDNA-depleted cells is also dependent on intracellular calcium as its chelation reduces mitochondrial mass. Despite a slight increase in mitochondrial mass in mtDNA-depleted cells, the mitochondrial protein import activity was reduced as shown by a decrease in the import of radiolabeled matrix-targeted recombinant proteins into isolated mitochondria and by the reduced mitochondrial localization of ectopically expressed HA-apoaequorin targeted to the mitochondria. Decrease in ATP content, in mitochondrial membrane potential as well as reduction in mitochondrial Tim44 abundance could explain the lower mitochondrial protein import in mtDNA-depleted cells. Taken together, these results suggest that mitochondrial biogenesis is stimulated in mtDNA-depleted cells and involves a calcium-CREB signalling pathway but is associated with a reduced mitochondrial import for matrix proteins.