[Show abstract][Hide abstract] ABSTRACT: Mitochondrial dysfunction and resulting energy impairment have been identified as features of many neurodegenerative diseases. Whether this energy impairment is the cause of the disease or the consequence of preceding impairment(s) is still under discussion, however a recovery of cellular bioenergetics would plausibly prevent or improve the pathology. In this study, we screened different natural molecules for their ability to increase intracellular adenine triphosphate purine (ATP). Among them, epigallocatechin-3-gallate (EGCG), a polyphenol from green tea, presented the most striking results. We found that it increases ATP production in both human cultured astrocytes and neurons with different kinetic parameters and without toxicity.Specifically, we showed that oxidative phosphorylation in human cultured astrocytes and neurons increased at the level of the routine respiration on the cells pre-treated with the natural molecule. Furthermore, EGCG-induced ATP production was only blocked by sodium azide (NaN3) and oligomycin, inhibitors of cytochrome c oxidase (CcO; complex IV) and ATP synthase (complex V) respectively. These findings suggest that the EGCG modulates CcO activity, as confirmed by its enzymatic activity. CcO is known to be regulated differently in neurons and astrocytes. Accordingly, EGCG treatment is acting differently on the kinetic parameters of the two cell types. To our knowledge, this is the first study showing that EGCG promotes CcO activity in human cultured neurons and astrocytes. Considering that CcO dysfunction has been reported in patients having neurodegenerative diseases such as Alzheimer's disease (AD), we therefore suggest that EGCG could restore mitochondrial function and prevent subsequent loss of synaptic function.
[Show abstract][Hide abstract] ABSTRACT: There is a strong association between aging, diet, and immunity. The effects of macronutrients and energy intake on splanchnic
and hepatic lymphocytes were studied in 15 month old mice. The mice were ad-libitum fed 1 of 25 diets varying in the ratios
and amounts of protein, carbohydrate, and fat over their lifetime. Lymphocytes in liver, spleen, Peyers patches, mesenteric
lymph nodes, and inguinal lymph nodes were evaluated using flow cytometry. Low protein intake reversed aging changes in splenic
CD4 and CD8 T cells, CD4:CD8 T cell ratio, memory/effector CD4 T cells and naïve CD4 T cells. A similar influence of total
caloric intake in these ad-libitum fed mice was not apparent. Protein intake also influenced hepatic NK cells and B cells,
while protein to carbohydrate ratio influenced hepatic NKT cells. Hepatosteatosis was associated with increased energy and
fat intake and changes in hepatic Tregs, effector/memory T, and NK cells. Hepatic NK cells were also associated with body
fat, glucose tolerance, and leptin levels while hepatic Tregs were associated with hydrogen peroxide production by hepatic
mitochondria. Dietary macronutrients, particularly protein, influence splanchnic lymphocytes in old age, with downstream associations
with mitochondrial function, liver pathology, and obesity-related phenotype.
Full-text · Article · Oct 2014 · The Journals of Gerontology Series A Biological Sciences and Medical Sciences
[Show abstract][Hide abstract] ABSTRACT: Mitochondria, the energy-generating organelles, play a role in numerous cellular functions including adenosine triphosphate (ATP) production, cellular homeostasis, and apoptosis. Maternal inheritance of mitochondria and mitochondrial DNA (mtDNA) is universally observed in humans and most animals. In general, high levels of mitochondrial heteroplasmy might contribute to a detrimental effect on fitness and disease resistance. Therefore, a disposal of the sperm-derived mitochondria inside fertilized oocytes assures normal preimplantation embryo development. Here we summarize the current research and knowledge concerning the role of autophagic pathway and ubiquitin-proteasome-dependent proteolysis in sperm mitophagy in mammals, including humans. Current data indicate that sperm mitophagy inside the fertilized oocyte could occur along multiple degradation routes converging on autophagic clearance of paternal mitochondria. The influence of assisted reproductive therapies (ART) such as intracytoplasmic sperm injection (ICSI), mitochondrial replacement (MR), and assisted fertilization of oocytes from patients of advanced reproductive age on mitochondrial function, inheritance, and fitness and for the development and health of ART babies will be of particular interest to clinical audiences. Altogether, the study of sperm mitophagy after fertilization has implications in the timing of evolution and developmental and reproductive biology and in human health, fitness, and management of mitochondrial disease.
Preview · Article · Jun 2014 · BioMed Research International
[Show abstract][Hide abstract] ABSTRACT: There is a long-standing prediction that associations with vertically transmitted symbionts evolve towards maximisation of host reproductive success, eventually leading to mutualist symbiosis and coadaptation. Under this scenario, the regulation of symbiont titres in host tissues would be expected to be greater when partners have coevolved for a long time than when they have recently met. Wolbachia pipientis, a common vertically transmitted symbiont of invertebrates, often has the capacity to spread through the host population without being beneficial to the hosts, by means of reducing the hatch rate in crosses between uninfected females and infected males. This manipulation, namely cytoplasmic incompatibility (CI), may exert strong selection on the accuracy of infection transmission from mother to offspring, and therefore, on regulation of symbiont titres in the ova. Here, we examined the symbiont density dynamics in gonads of Drosophila simulans infected with the wMa strain of Wolbachia, known to cause mild CI and likely to be the oldest Wolbachia infection known to this fly species. Further, we compared these results with those obtained for the more recent association between D. simulans and the potent CI-inducer wHa (Correa and Ballard; 2012). We aimed to determine if the regulation of Wolbachia density in fly gonads is greater in the older association, as would be predicted solely by gradual coadaptation, or if the selection exerted by CI on reproductive fitness could also play a role, therefore showing tighter regulation on flies with the stronger CI-inducing strain. We observed that Wolbachia density in gonads of wMa infected flies changed with laboratory adaptation and were disturbed by environmental challenges, which contrasted with the stability of ovarian wHa density to the same treatments. Our observations are in line with the prediction that selection on reproductive fitness influences the evolution symbiont density regulation in Drosophila, and may provide insights into the evolutionary processes involved in the maintenance or loss of Wolbachia.
No preview · Article · May 2014 · Journal of Invertebrate Pathology
[Show abstract][Hide abstract] ABSTRACT: The fundamental questions of what represents a macronutritionally balanced diet and how this maintains health and longevity remain unanswered. Here, the Geometric Framework, a state-space nutritional modeling method, was used to measure interactive effects of dietary energy, protein, fat, and carbohydrate on food intake, cardiometabolic phenotype, and longevity in mice fed one of 25 diets ad libitum. Food intake was regulated primarily by protein and carbohydrate content. Longevity and health were optimized when protein was replaced with carbohydrate to limit compensatory feeding for protein and suppress protein intake. These consequences are associated with hepatic mammalian target of rapamycin (mTOR) activation and mitochondrial function and, in turn, related to circulating branched-chain amino acids and glucose. Calorie restriction achieved by high-protein diets or dietary dilution had no beneficial effects on lifespan. The results suggest that longevity can be extended in ad libitum-fed animals by manipulating the ratio of macronutrients to inhibit mTOR activation.
[Show abstract][Hide abstract] ABSTRACT: Population studies often assume temporally stable and consistent patterns of genetic variability. Violations of this assumption can lead to misrepresentation of the amount and patterns of genetic variability in natural populations, which can be problematic in basic research and environmental monitoring studies that are designed to detect environmental perturbation. We collected two endemic species of amphipods, Melita plumulosa and Melita matilda, in a major eastern Australian waterway between November 2009 and October 2011, and assessed genetic variation at the mitochondrial cytochrome c oxidase subunit I locus. Overall, M. plumulosa was found to be more genetically variable than M. matilda. No distinct temporal trends in levels and patterns of genetic variation were identified in either species. These findings, combined with the published results demonstrating that M. plumulosa has greater sensitivity to a range of sediment-bound metals and organic contaminants, suggests it to be an informative species for environmental monitoring purposes.
No preview · Article · Jan 2014 · Australian Journal of Zoology
[Show abstract][Hide abstract] ABSTRACT: 1. The vast majority of studies employing mtDNA in evolutionary biology and ecology have used it as a means to infer demographic and historical patterns without pondering the underly-ing functional implications. In contrast, the biochemical and medical communities often aim to understand the influence of specific mtDNA mutations on mitochondrial functions, but rarely consider the evolutionary and ecological implications. 2. Ongoing research has shown that mtDNA mutations can profoundly affect mitochondrial function in humans and other animals. If the mutation (or set of mutations) is pathogenic, mitochondrial malfunction may be detected from early age. In nature, however, most muta-tions are not highly deleterious and may exist at intermediate frequency in populations. 3. In this review, we suggest that knowledge of the underlying biochemistry and functions of mitochondria can facilitate a more complete determination of the evolutionary dynamics of mtDNA and its influence on the life-history traits of organisms. With this approach, it is possi-ble to use biochemistry to link the genotype with the phenotype. 4. After reviewing the literature, we conclude that there can be physiological and evolutionary trade-offs in the way that mitochondrial mutations can affect age classes and/or fitness compo-nents and that these effects may depend on the environment. Through these trade-offs, it may be possible for specific mtDNA mutations to have unequal fitness in different nuclear genetic backgrounds and also in different environments.
Full-text · Article · Dec 2013 · Functional Ecology
[Show abstract][Hide abstract] ABSTRACT: Werner syndrome is a progeric syndrome characterized by premature atherosclerosis, diabetes, cancer, and death in humans.
The knockout mouse model created by deletion of the RecQ helicase domain of the mouse Wrn homologue gene (Wrn∆hel/∆hel) is of great interest because it develops atherosclerosis and hypertriglyceridemia, conditions associated with aging liver
and sinusoidal changes. Here, we show that Wrn∆hel/∆hel mice exhibit increased extracellular matrix, defenestration, decreased fenestration diameter, and changes in markers of liver
sinusoidal endothelial cell inflammation, consistent with age-related pseudocapilliarization. In addition, hepatocytes are
larger, have increased lipofuscin deposition, more frequent nuclear morphological anomalies, decreased mitochondria number,
and increased mitochondrial diameter compared to wild-type mice. The Wrn∆hel/∆hel mice also have altered mitochondrial function and altered nuclei. Microarray data revealed that the Wrn∆hel/∆hel genotype does not affect the expression of many genes within the isolated hepatocytes or liver sinusoidal endothelial cells.
This study reveals that Wrn∆hel/∆hel mice have accelerated typical age-related liver changes including pseudocapillarization. This confirms that pseudocapillarization
of the liver sinusoid is a consistent feature of various aging models. Moreover, it implies that DNA repair may be implicated
in normal aging changes in the liver.
Full-text · Article · Oct 2013 · The Journals of Gerontology Series A Biological Sciences and Medical Sciences
[Show abstract][Hide abstract] ABSTRACT: The accumulation and aggregation of alpha-synuclein (alpha-syn) in several tissue including the brain is a major pathological hallmark in Parkinson's disease (PD). In this study, we show that alpha-syn can be taken up by primary human cortical neurons, astrocytes and skin-derived fibroblasts in vitro. Our findings that brain and peripheral cells exposed to alpha-syn can lead to impaired mitochondrial function, leading to cellular degeneration and cell death, provides additional evidence for the involvement of mitochondrial dysfunction as a mechanism of toxicity of alpha-syn in human cells.
No preview · Article · Oct 2013 · Translational Neurodegeneration
[Show abstract][Hide abstract] ABSTRACT: Parkinson's disease (PD) is a multicentred neurodegenerative disorder characterised by the accumulation and aggregation of alpha-synuclein (α-syn) in several parts of the central nervous system. However, it is well established that PD can generate symptoms of constipation and other gastrointestinal problems and α-syn containing lesions have been identified in intestinal nerve cells. In this study, we show that α-syn can be taken up and accumulate in primary human foetal enteric neurons from the gastrointestinal tract and can be transferred between foetal enteric neurons. Impaired proteosomal/lysosomal degradation can promote the uptake and accumulation of α-syn in enteric neurons. Enteric neurons exposed to α-syn can also lead to impaired mitochondrial complex I activity, reduced mitochondrial function, and NAD(+) depletion culminating in cell death via energy restriction. These findings demonstrate neuron-to-neuron transmission of α-syn in enteric neurons, providing renewed evidence for Braak's hypothesis and the aetiology of PD.
No preview · Article · Sep 2013 · Neurotoxicity Research
[Show abstract][Hide abstract] ABSTRACT: The genetic structure of populations is impacted by environmental
factors of both natural and anthropogenic origin. These factors can
affect dispersion, gene flow and selective pressures. We test whether
natural environmental factors or anthropogenic factors influence the
genetic structure of the amphipod, Melita plumulosa (Crustacea:
Melitidae), which serves as an indicator of environmental health in
estuaries along eastern Australia. Sequence data from one mitochondrial
and two nuclear loci were collected and analyzed from eight
geographically distinct populations spanning the known distribution of
this species. We identified two major clades corresponding to the east
and south coasts of Australia, and populations also largely grouped
according to geography within each clade. Population differentiation
indicated all sampling localities to be distinct from one another and
sequence divergences suggested ancient divergence, with the deepest
genetic divergences between the eastern and southern populations.
Reproductive compatibility did not indicate cryptic speciation between
populations. Sequence divergence and population differentiation suggest
historic geographic isolation dating back to the Pleistocene to have
influenced the population biogeography of M. plumulosa.
[Show abstract][Hide abstract] ABSTRACT: The age structure of natural population is of interest in physiological, life history and ecological studies but it is often difficult to determine. One methodological problem is that samples may need to be invasively sampled preventing subsequent taxonomic curation. A second problem is that it can be very expensive to accurately determine the age structure of given population because large sample sizes are often necessary. In this study, we test the effects of temperature (17(o)C, 23(o)C and 26(o)C) and diet (standard cornmeal and low calorie diet) on the accuracy of the non-invasive, inexpensive and high throughput near-infrared spectroscopy (NIRS) technique to determine the age of Drosophila flies. Composite and simplified calibration models were developed for each sex. Independent sets for each temperature and diet treatments with flies not involved in calibration model were then used to validate the accuracy of the calibration models. The composite NIRS calibration model was generated by including flies reared under all temperatures and diets. This approach permits rapid age measurement and age structure determination in large population of flies as less than or equal to 9 days, or more than 9 days old with 85-97% and 64-99% accuracy, respectively. The simplified calibration models were generated by including flies reared at 23(o)C on standard diet. Low accuracy rates were observed when simplified calibration models were used to identify a) Drosophila reared at 17(o)C and 26(o)C and b) 23(o)C with low calorie diet. These results strongly suggest that appropriate calibration models need to be developed in the laboratory before this technique can be reliably used in field. These calibration models should include the major environmental variables that change across space and time in the particular natural population to be studied.
No preview · Article · Jul 2013 · Journal of insect physiology
[Show abstract][Hide abstract] ABSTRACT: Populations subject to anthropogenic contaminants often display altered patterns of genetic variation, including decreased genetic variability. Selective pressures of contaminant exposure are also reflected in differential tolerance between genotypes. An industrial chemical spill in a major eastern Australian waterway in July 2006 resulted in altered patterns of genetic variability in a nearby population of the amphipod, Melita plumulosa for up to one year post-spill, despite the site being declared clean after 48h. Here, we investigate the toxicant response of three mitochondrial lines naturally occurring at the impacted site by comparing survivorship and life-history trait variables following naphthalene exposure. Overall, M. plumulosa demonstrated differential survivorship between mitochondrial lines under exposure to high concentrations of naphthalene. In addition, we identified differential fecundity and frequencies of gravidity in female amphipods between the mitochondrial haplotypes examined. These findings suggest that the patterns of genetic variability previously identified may be linked with differential tolerance and/or reproductive performance between mitochondrial lineages.
[Show abstract][Hide abstract] ABSTRACT: In this study, we examine the dietary protein to carbohydrate ratio (P:C) on the mitochondrial functions of two Drosophila melanogaster mtDNA haplotypes. We investigated multiple physiological parameters on flies fed with either 1:12 P:C or 1:3 P:C diets. Our results provide experimental evidence that a specific haplotype has a reduction of complex I activity when the flies are fed with the 1:12 P:C diet. This study is of particular importance to understand the influence of diet on mitochondrial evolution in invasive and broadly distributed species including humans.
[Show abstract][Hide abstract] ABSTRACT: Although crucial to the success of fertilization and embryogenesis, little is known about the mitochondrial DNA (mtDNA) content of mature spermatozoa and oocytes across taxa and across different fertilization systems. Oocytes are assumed to hold a large population of mtDNAs that populate emerging cells during early embryogenesis, whereas spermatozoa harbor only a limited pool of mtDNAs that is believed to sustain functionality but fails to contribute paternal mtDNA to the zygote. Recent work suggests that mature sperm of the genetic model Drosophila melanogaster lack mtDNA, questioning the significance of zygotic mechanisms for the selective elimination of paternal mtDNA and their necessity for fertilization success. This finding further contradicts previous observations of the inheritance of paternal mtDNA in drosophilids. Using quantitative polymerase chain reaction, we estimate the mtDNA content of several laboratory strains of D. melanogaster and D. simulans to shed light on this discrepancy and to describe the mitochondrial/mtDNA load of gametes within this system. These measurements led to an average estimate of 22.91±4.61 mtDNA molecules/copies per spermatozoon across both species and to 1.07E+07±2.71E+06 molecules/copies per oocyte for D. simulans. As a consequence, the ratio of paternal and maternal mtDNA in the zygote was estimated at 1:4.65E+05.
No preview · Article · May 2013 · Cell and Tissue Research
[Show abstract][Hide abstract] ABSTRACT: Reproduction imposes significant costs and is characterized by an increased energy demand. As a consequence, individuals adjust their cellular structure and function to this physiological constraint. Because mitochondria are central to energy production, changes in their functional properties are likely to occur during reproduction. Such changes could cause adjustments in reactive oxygen species (ROS) production and consequently in oxidative stress levels. In this study, we investigated several mechanisms involved in energy production, including mitochondrial respiration at different steps of the electron transport system (ETS) and related the results to citrate synthase activity in the liver of non-reproductive and reproductive (two and eight pups) female house mice at peak lactation. Whereas we did not find differences between females having different litter sizes, liver mitochondria of reproductive females showed lower ETS activity and an increase in mitochondrial density when compared to the non-reproductive females. Although it is possible that these changes were due to combined processes involved in reproduction and not to the relative investment in lactation, we propose that the mitochondrial adjustment in liver might help to spare substrates and therefore energy for milk production in the mammary gland. Moreover, our results suggest that these changes lead to an increase in ROS production that subsequently up-regulates antioxidant defences activity and decreases oxidative stress.
[Show abstract][Hide abstract] ABSTRACT: Cytochrome c oxidase (COX) of the electron transport system is thought to be the rate-limiting step in cellular respiration and is found mutated in numerous human pathologies. Here, we employ quaternary three-dimensional (3-D) modeling to construct a model for human COX. The model was used to predict the functional consequences of amino-acid mutations based on phylogenetic conservation of amino acids together with volume and/or steric perturbations, participation in subunit-subunit interfaces and non-covalent energy loss or incompatibilities. These metrics were combined and interpreted for potential functional impact. A notable strength of the 3-D model is that it can interpret and predict the structural consequences of amino-acid variation in all 13 protein subunits. Importantly, the influence of compensatory changes can also be modeled. We examine mutations listed in the human mutation database Mitomap, and in 100 older men, and compare the results from the 3-D model against the automated MutPred web application tool. In combination, these comparisons suggest that the 3-D model predicts more functionally significant mutations than does MutPred. We conclude that the model has useful functional prediction capability but may need modification as functional data on specific mutations becomes known.Journal of Human Genetics advance online publication, 10 January 2013; doi:10.1038/jhg.2012.144.
Full-text · Article · Jan 2013 · Journal of Human Genetics
[Show abstract][Hide abstract] ABSTRACT: The aim of this study was to investigate the effect of temperature changes on the functional properties of mitochondria from two sets of D. simulans fly lines harboring the siII and siIII haplotypes in a common nuclear genetic background. We studied four introgressed isofemale lines possessing the mtDNA of siII and the nuclear background of siIII (siII-introgressed) and four lines possessing siIII mitochondria with its native nuclear genome (siIII-controls). We assessed the catalytic capacities of electron transport system (ETS) at four different temperatures (12, 18, 24 and 28 ºC). The impact of temperature on the pyruvate dehydrogenase (PDH) activity, the mitochondrial respiration (coupled and uncoupled respiration), cytochrome c oxidase activity, as well as the excess capacity of complex IV (COX) were evaluated in these two sets of flies. Our results showed that the temperature coefficient values (Q(10)) measured for mitochondrial respiration in the lower range of temperatures (12 to 18 ºC) showed a 2 to 3 fold increase in siII-introgressed when compared to siIII-controls. This result shows that the impact of temperature on mitochondrial function is different between the two mitotypes studied. The Q(10) results seem to be linked to the apparent COX excess capacity of 193 % for siIII-controls that is inexistent for siII-introgressed at 12 ºC. One explanation for these results is that the mitochondria can compensate for the disruption of mito-nuclear interactions at 24 ºC but not at lower temperatures. An alternate explanation would be that siII haplotype confer divergent kinetic properties to the ETS that translate to different temperature sensitivities.
Full-text · Article · Oct 2012 · Journal of Bioenergetics
[Show abstract][Hide abstract] ABSTRACT: Linking the mitochondrial genotype and the organismal phenotype is of paramount importance in evolution of mitochondria. In this study, we determined the differences in catalytic properties of mitochondria dictated by divergences in the siII and siIII haplogroups of Drosophila simulans using introgressions of siII mtDNA type into the siIII nuclear background. We used a novel in situ method (permeabilized fibers) that allowed us to accurately measure the consumption of oxygen by mitochondria in constructed siII-introgressed flies and in siIII-control flies. Our results showed that the catalytic capacity of the electron transport system is not impaired by introgressions, suggesting that the functional properties of mitochondria are tightly related to the mtDNA haplogroup and not to the nuclear DNA or to the mito-nuclear interactions. This is the first study, to our knowledge, that demonstrates a naturally occurring haplogroup can confer specific functional differences in aspects of mitochondrial metabolism. This study illustrates the importance of mtDNA changes on organelle evolution and highlights the potential bioenergetic and metabolic impacts that divergent mitochondrial haplogroups may have upon a wide variety of species including humans.
[Show abstract][Hide abstract] ABSTRACT: Maternal inheritance is one of the hallmarks of animal mitochondrial DNA (mtDNA) and central to its success as a molecular marker. This mode of inheritance and subsequent lack of heterologous recombination allows us to retrace evolutionary relationships unambiguously down the matriline and without the confounding effects of recombinant genetic information. Accumulating evidence of biparental inheritance of mtDNA (paternal leakage), however, challenges our current understanding of how this molecule is inherited. Here, using Drosophila simulans collected from an East African metapopulation exhibiting recurring mitochondrial heteroplasmy, we conducted single fly matings and screened F1 offspring for the presence of paternal mtDNA using allele-specific PCR assays (AS-PCR). In all, 27 out of 4092 offspring were identified as harboring paternal mtDNA, suggesting a frequency of 0.66% paternal leakage in this species. Our findings strongly suggest that recurring mtDNA heteroplasmy as observed in natural populations of Drosophila simulans is most likely caused by repeated paternal leakage. Our findings further suggest that this phenomenon to potentially be an integral part of mtDNA inheritance in these populations and consequently of significance for mtDNA as a molecular marker.Heredity advance online publication, 26 September 2012; doi:10.1038/hdy.2012.60.