No description available.

Obesity is associated with greater rates of cardiovascular disease, dyslipidemia and dysfunctional lipid metabolism. Exercise may provide an effective therapeutic tool to ameliorate dyslipidemia. However, how exercise attenuates dyslipidemia with obesity is not fully understood. Additionally, whether acute exercise or exercise training is the primary driver of such changes in this population is unknown. Furthermore, mechanisms mediating these exercise responses are not elucidated. The peroxisome proliferator-activated receptors (PPARs) provide a likely mechanism through enhanced expression of oxidative metabolism and cholesterol transport proteins augmenting fatty acid oxidation and cholesterol transport. Study one describes blood lipid and lipoprotein responses to acute aerobic exercise and exercise training in obese men and women. The primary measured effects include: increased HDL-C in men following 12 wks exercise training, and a shift from HDL3-C to HDL2-C, with concomitantly reduced HDL-C mean density and LDL3-C in women. Acute exercise of 400 kcal duration performed before and after training, yielded a decreased TC: HDL-C ratio in men, which was unaffected by training. Thus, the primary exercise-based treatment for dyslipidemia with obesity appears to be exercise training. In study two, PPARδ and PGC-1α content were significantly enhanced after acute exercise, whereas PPARα and AMPKα content were augmented only after training. These effects were seen with concomitantly increased content of target proteins involved in oxidative and lipoprotein metabolism including lipoprotein lipase, CPT-I, COX-IV, and FAT/CD36. PPARδ expression was correlated with total and LDL-cholesterol concentrations. AMPKα expression was correlated with the concentration of HDL-C and its subfractions, suggesting regulation of blood cholesterols by PPARδ and AMPKα. Study three demonstrates comparative responses to high volume resistance exercise (RE) in lean and obese Zucker rats. RE enhanced PPARδ expression regardless of phenotype, but PGC-1α in obese only. Mitochondrial biogenesis was enhanced in lean animals only, indicating PPARδ and PGC-1α content is disconnected from mitochondrial biogenesis with obesity. These studies enhance our understanding of exercise as a therapeutic tool in treating dyslipidemia and dysregulated lipid metabolism often associated with obesity. They further demonstrate the necessity for exercise training to attenuate dyslipidemia, while illustrating PPAR-mediated augmentations in oxidative and lipoprotein metabolism following exercise with obesity.

Mitochondria not only supply the energy for cell function, but also take part in cell signaling. This review describes the dysfunctions of mitochondria in aging and neurodegenerative diseases, and the signaling pathways leading to mitochondrial biogenesis (including PGC-1 family proteins, SIRT1, AMPK) and mitophagy (parkin-Pink1 pathway). Understanding the regulation of these mitochondrial pathways may be beneficial in finding pharmacological approaches or lifestyle changes (caloric restrict or exercise) to modulate mitochondrial biogenesis and/or to activate mitophagy for the removal of damaged mitochondria, thus reducing the onset and/or severity of neurodegenerative diseases.

The purpose of this study was to investigate the effects of hydroxytyrosol (HT) supplementation on markers of mitochondrial biogenesis, aerobic capacity, and endurance exercise performance in recreationally active men. Sixty-one (n = 61) subjects (21.46 ± 0.22 yrs, 179.46 ± 0.79 cm, 78.91 ± 1.19 kg) consumed either a high dose (HI) HT supplement (150 mg HT), a low dose (LO) HT supplement (50 mg HT), or a placebo (PLA) every day for 6 weeks. Muscle biopsies from the vastus lateralis were obtained at baseline and after 6 weeks of supplement consumption and analyzed for markers of mitochondrial biogenesis: succinate dehydrogenase (SDH), citrate synthase (CS), and peroxisome proliferator-activated receptor ɣ coactivator (PGC)-1α. Subjects completed exercise testing on a bicycle ergometer at baseline and after 3 and 6 weeks of supplement consumption to measure changes in maximal aerobic power (VO2MAX), lactate threshold, respiratory exchange ratio (RER), substrate utilization, and endurance exercise performance on a 20 km time trial course. The primary findings were that HT supplementation increased muscle oxidative enzyme activity suggesting increased oxidative capacity. HT also increased time trial performance at midpoint and endpoint and this corresponded with an improvement in lactate threshold and a lower RER for the LO HT treatment. Time trial performance was also improved at endpoint for PLA, however, unlike LO an HI HT, this was accompanied by a significant increase in rating of perceived exercise (RPE) and not associated with improvements in muscle oxidative capacity. Our results indicate that HT ranging from 50 to 150 mg/day for 6 weeks can improve muscle oxidative capacity and aerobic performance, and suggests that HT may be used chronically to improve mitochondrial function. HT may be used as an effective means to increase mitochondria to improve exercise performance, and limit diseases associated with mitochondrial dysfunction such as cardiovascular disease, type II diabetes, and some cancers. / text

Oxidative and nitrosative stress are deleterious physiological processes caused by an imbalance between reactants such as reactive oxygen and nitrogen species and antioxidants. Due to the links between oxidative and nitrosative stress and disease, there is much interest in accurately quantifying these in biological and physiological samples. There are numerous methods to quantify the in vivo oxidative and nitrosative damage to lipids, DNA and proteins however they are generally time-consuming, expensive and difficult. Furthermore, due to the complex nature of oxidative and nitrosative stress it would be appropriate to measure a number of different biomarkers, however this is rarely done. The first section of this thesis contains research aimed at developing a bioassay to simultaneously detect markers of oxidative and nitrosative stress. This includes; 1) a review of the studies investigating the ability of these biomarkers to predict the onset of disease, 2) a description of the attempts to develop the bioassay, 3) a study designed to test the sensitivity of the bioassay to detect changes in oxidative stress. Unfortunately, the attempts to develop the bioassay were not as successful as hoped and, in the interests of completing the PhD in the time allowed, the PhD changed focus to look at the effects of oxidant:antioxidant balance on mitochondrial biogenesis. The second section of the thesis contains a review of the literature on this topic and two original investigations. It is well documented that oxidative and nitrosative stress contributes to the progression of many diseases including; cardiovascular disease, type 2 diabetes, Alzheimer’s disease, kidney disease and cancer. To determine which biomarkers would have the greatest efficacy in the bioassay, a comprehensive review was undertaken. The aim of the review was to investigate studies which have measured oxidative and nitrosative biomarkers to determine whether they are independent predictors of cardiovascular events (Chapter two). From the review, fifty-one studies were identified with twenty-six of these measuring oxidised (Ox)-LDL, fifteen assessing myeloperoxidase (MPO), seven using lipid peroxidation measures and three quantifying protein oxidation in plasma/serum. The recommendation of the review was that all areas require further investigation, however, it was determined that Ox-LDL and MPO would be beneficial for inclusion in the bio-assay. Other biomarkers considered for the bio-assay were nitrotyrosine, superoxide dismutase and glutathione peroxidase. Chapter three outlines method development used to measure the oxidative and nitrosative markers simultaneously. Recent technology allows multiple analytes to be detected simultaneously from the one sample. The Mulit-plex system is used to detect analytes that have been sandwiched between primary capture and secondary biotinylated detection antibodies. The secondary antibody attaches to streptavidin-phycoerythrin and is used by the Mulit-plex analyser to quantify the analyte. During development of the bio-assay, clumping of microspheres, high background, no detection of standard curve or samples, matrix effects, mislabeling of antibodies by manufacturers and lack of commercial available antibodies were obstacles that limited the success of this method. MPO was the only biomarker that was successful. Chapter four contains a study that investigated the sensitivity of the MPO mulitplex bio-assay. Nine highly trained cyclists underwent an extensive exercise protocol designed to induce dehydration by 4 % body mass, rehydration of 150 % fluid loss and a performance time-trial. Plasma samples were taken at five time points; baseline, post dehydration, post rehydration, pre time-trial and post time-trial and analysed using the mulitplex bio-assay. The results showed that there was a significant increase in MPO post dehydration and post time-trial compared with all other time points (P<0.05), thereby demonstrating that the mulitplex bio-assay is sensitive to detect changes in exercise and appropriate rehydration reduces oxidative stress. The MPO mulitplex bio-assay requires further testing on patients with diseases to further validate its future applications. As mentioned above, due to time constraints it was decided to stop the attempts to create a multi-analyte bioassay and focus on another important area of cellular oxidative stress. Currently, there is much interest in the involvement of oxidant:antioxidant balance in mitochondrial biogenesis. The increase of mitochondrial content within the skeletal muscle, termed mitochondrial biogenesis, provides an increased capacity to generate ATP during exercise and is recognized as one of major cellular adaptations to exercise. Reactive oxygen species are produced during exercise and have been shown to induce mitochondrial biogenesis. One of the key instigators of mitochondrial biogenesis is peroxisome proliferator activated receptor gamma coactivator-1α (PGC-1α). PGC-1α is central to the transcription of mitochondrial and nuclear encoded genes, which regulate downstream pathways such as oxidative phosphorylation and fatty acid oxidation. Antioxidant supplementation is common among athletes and healthy individuals; however, antioxidant supplements suppress reactive oxygen species and could therefore could hinder mitochondrial biogenesis and the positive adaptations associated with exercise. To establish whether antioxidant supplementation reduced mitochondrial biogenesis in skeletal muscle, male Wistar rats were supplemented with α-tocopherol and α-lipoic acid for fourteen weeks (Chapter six). Animals were separated into four groups: 1) sedentary control diet, 2) sedentary antioxidant diet, 3) exercise control diet and 4) exercise antioxidant diet. The exercise animals were trained 5 days/week for 14 weeks. Consistent with increased mitochondrial biogenesis and antioxidant defences following training, there were significant increases in PGC-1α mRNA and protein, COX IV and Cyt C protein abundance, citrate synthase activity, Nfe2l2 and SOD2 protein (P<0.05). Antioxidant supplementation reduced PGC-1α mRNA, PGC-1α and COX IV protein, and citrate synthase enzyme activity (P<0.05) in both sedentary and exercise-trained rats. In summary, antioxidants α-tocopherol and -lipoic acid supplementation suppresses beneficial adaptations in skeletal muscle such as markers of mitochondrial biogenesis and mitochondrial proteins, regardless of training status. The reduction in mitochondrial biogenesis may affect exercise training adaptations and reduce the ability of healthy individuals to attain optimal exercise adaptations. The last investigation (Chapter seven) studied the effect of reduced glutathione, through diethyl maleate (DEM) administration, on upstream regulators of mitochondrial biogenesis, markers of mitochondrial biogenesis and downstream signalling. Glutathione is a key antioxidant that reduces the amount of hydrogen peroxide. Male Wistar rats were divided into six groups 1) sedentary control, 2) sedentary DEM, 3) post-exercise control, 4) post-exercise DEM, 5) exercise-recovery and 6) exercise-recovery DEM. After an exercise bout to fatigue, animals were euthanized directly after exercise (post-exercise) or four hours post exercise (exercise-recovery). Exercising animals given DEM had significantly (P<0.05) decreased glutathione in skeletal muscle and had a significantly (P<0.05) greater increase in PGC-1α gene expression. There were also main interaction effects between exercise and DEM administration on SOD2 activity. Exercise altered the gene expression of GPx and the phosphorylation of p38 MAPK. Glutathione depletion decreased GPX activity and oxidised glutathione levels. These novel findings represent important in vivo evidence of the involvement of glutathione and oxidant:antioxidant balance in mitochondrial biogenisis. Overall this thesis has provided 1) the first comprehensive review on the prognostic ability of oxidative stress biomarkers to predict the onset of cardiovascular disease, 2) detailed information to assist in the further development of a multi-analyte bioassay to quantify oxidative and nitrosative stress, 3) data indicating that the MPO Mulit-plex bioassay is sensitive to detect physiological perturbations to oxidative stress, 4) evidence that antioxidant supplementation suppresses mitochondrial biogenesis and 5) proof that glutathione is important in the regulation of exercise-induced mitochondrial biogenesis.

Yes / Organelle biogenesis is concomitant to organelle inheritance during cell division. It is necessary that organelles double their size and divide to give rise to two identical daughter cells. Mitochondrial biogenesis occurs by growth and division of pre-existing organelles and is temporally coordinated with cell cycle events [1]. However, mitochondrial biogenesis is not only produced in association with cell division. It can be produced in response to an oxidative stimulus, to an increase in the energy requirements of the cells, to exercise training, to electrical stimulation, to hormones, during development, in certain mitochondrial diseases, etc. [2]. Mitochondrial biogenesis is therefore defined as the process via which cells increase their individual mitochondrial mass [3]. Recent discoveries have raised attention to mitochondrial biogenesis as a potential target to treat diseases which up to date do not have an efficient cure. Mitochondria, as the major ROS producer and the major antioxidant producer exert a crucial role within the cell mediating processes such as apoptosis, detoxification, Ca2+ buffering, etc. This pivotal role makes mitochondria a potential target to treat a great variety of diseases. Mitochondrial biogenesis can be pharmacologically manipulated. This issue tries to cover a number of approaches to treat several diseases through triggering mitochondrial biogenesis. It contains recent discoveries in this novel field, focusing on advanced mitochondrial therapies to chronic and degenerative diseases, mitochondrial diseases, lifespan extension, mitohormesis, intracellular signaling, new pharmacological targets and natural therapies. It contributes to the field by covering and gathering the scarcely reported pharmacological approaches in the novel and promising field of mitochondrial biogenesis.

Maintaining energy organismal homeostasis under changing physiological and environmental conditions is vital, and requires constant adjustments of the energy metabolism. Central to meeting energy demands is the regulation of mitochondrial oxidative capacity. When demands increase, animals can increase mitochondrial content/enzymes, known as mitochondrial biogenesis. Central to mammalian mitochondrial biogenesis is the transcriptional master regulator PPARγ (peroxisome proliferator-activated receptor γ) coactivator-1α (PGC-1α), and the network of DNA-binding proteins it coactivates (e.g. nuclear respiratory factor 1 and 2 [NRF-1, NRF-2], estrogen-related receptor α [ERRα], thyroid receptor α [TRα-1], retinoid X receptor α [RXRα]). However, the mechanisms by which mitochondrial content in lower vertebrates such as fish is controlled are less studied. In my study I investigate underlying mechanisms of the phenomenon that many fish species alter mitochondrial enzyme activities, such as cytochrome c oxidase (COX) in response to low temperatures. In particular, I investigated (i) if the phenomenon of mitochondrial biogenesis during cold-acclimation is related to fish phylogeny, (ii) what role PGC-1α and other transcription factors play in mitochondrial biogenesis in fish, and (iii) if mRNA decay rates are important in the transcriptional control of a multimeric protein like COX. This study shows that mitochondrial biogenesis does not follow a phylogenetic pattern: while distantly related species displayed the same response to low temperatures, closely related species showed opposite responses. In species exhibiting mitochondrial biogenesis, little evidence was found for PGC-1α as a master regulator, whereas NRF-1 is supported to be an important regulator in mitochondrial biogenesis in fish. Further, there was little support for other transcription factors (NRF-2, ERRα, TRα-1, RXRα) to be part of the regulatory network. Lastly, results on the post-transcriptional control mechanism of mRNA decay indicate that this mechanism is important in the regulation of COX under mitochondrial biogenesis: it accounts for up to 30% of the change in subunit transcript levels. In summary, there is no simple temperature-dependent mitochondrial response ubiquitous in fish. Further, the pathways controlling mitochondrial content in fish differ from mammals in the important master regulator PGC-1α, however, NRF-1 is important in regulating cold-induced mitochondrial biogenesis in fish. Lastly, COX subunit mRNA decay rates seem to have a part in controlling COX amounts during mitochondrial biogenesis. / Thesis (Ph.D, Biology) -- Queen's University, 2013-10-21 09:53:59.46

The Hap2/3/4/5 complex is a heme-activated, CCAATT binding, global transcriptional activator of genes involved in respiration and mitochondrial biogenesis in the yeast species Saccharomyces cerevisiae. Hap4 is the regulatory subunit of the complex and its levelsdetermine the activity of the complex. Hap4 is known to play a signaling role in response toenvironmental conditions; however, little is known about the regulation of Hap4 levels or how it responses to a cell’s functional state. The activity of the Hap2-5 complex is known to be reduced in respiratory-deficient cells. In Liu Lab, it has previously been found that a link between Hap4 stability, mediated through 26S proteasome-dependent degradation, and dependence on mitochondrial functional state plays a regulatory role on downstream targets of the Hap complex. However, the mechanism behind this regulation is still largely unknown. In normally functioning yeast cells, Hap4 is a highly unstable protein with a half-life of ~10 min. We have observed that loss of mitochondrial DNA in respiratory deficient rho 0 cells has a role in the further destabilization of Hap4 to a half-life of ~4 min through the ubiquitin-proteasome pathway. Through the screening of a collection of mutants defective in E2 ubiquitin-conjugating enzymes, we show that Hap4 is greatly stabilized in ubc1Δubc4Δ double mutant cells. We also show that Hap4 stabilization in the ubc1Δubc4Δ mutant leads to increased activity of the Hap2-5 complex, indicating that mitochondrial biogenesis in yeast is regulated by the functional state of mitochondria through ubiquitin/proteasome-dependent degradation of Hap4. Furthermore, studies on Hap4 mutants involving two highly conserved cysteine residues led to a proposed mechanism behind the regulation of Ubc4 activity towards Hap4 in response to changes in the cellular redox state.

La maladie de Parkinson (MP) est caractérisée par une dégénérescence des neurones dopaminergiques de la substance noire. Elle est le plus souvent sporadique mais des formes familiales monogéniques existent, notamment dues à des mutations de PARK2 et de PINK1. Ces gènes codent pour l'ubiquitine-protéine ligase cytosolique Parkine et la sérine/thréonine kinase mitochondriale PINK1, deux acteurs majeurs du contrôle de qualité mitochondrial. Ce travail étudie le rôle de leur interaction au niveau de la membrane mitochondriale externe dans la régulation de l'homéostasie mitochondriale.Nous avons montré que l'association de PINK1 et Parkine au complexe d'import mitochondrial TOM lors d'un stress mitochondrial permet l'import de la grande majorité des protéines adressées à la mitochondrie ; que déstabiliser ce complexe suffit à initier la mitophagie ; et que l'activation de Parkine par PINK1 facilite l'import de son substrat HSD17?10. Nous avons développé un biosenseur moléculaire inductible, permettant d'étudier la voie d'import classique des protéines à pré-séquence. Nous avons également montré, dans un modèle neuronal, qu'un stress mitochondrial, en présence de Parkine, induit une forte augmentation de l'expression de gènes clés de la biogenèse mitochondriale ; et que ces gènes sont up-régulés de façon basale dans les neurones PARK2-/-, indiquant une possible altération de la réponse aigüe au stress.Ces résultats approfondissent notre connaissance de la physiopathologie des formes autosomiques récessives de MP en soulignant l'importance de la voie PINK1/Parkine dans l'import et la biogenèse mitochondriaux. / Parkinson’s disease (PD) is linked to a specific loss of dopaminergic neurons of the substancia nigra. The disease is most often sporadic but familial monogenic forms exist, for example due to mutations in PARK2 or PINK1. Those genes encore the cytosolic ubiquitin-protein ligase Parkin and the mitochondrial serine/threonine kinase PINK1, both essential for mitochondrial quality control. This work studies the role of their interaction at the outer mitochondrial membrane in the regulation of mitochondrial homeostasis. We found that the association of PINK1 and Parkin to the mitochondrial import TOM complex during mitochondrial stress induces the import of most proteins targeted to mitochondria; that destabilizing this complex is sufficient to initiate mitophagy; and that Parkin activation by PINK1 facilitates the import of its substrate, HSD17β10. We developed an inducible BRET-based molecular biosensor to study the classical pre-sequence import pathway. We also found, in a neuronal model, that mitochondrial stress induced a strong increase in the expression of mitochondrial biogenesis key genes, in the presence of Parkin; and that these genes are basally up-regulated in PARK2-/- neurons, possibly reflecting an alteration of acute stress response. These results increase our understanding of the pathophysiology of autosomal recessive forms of PD, underlining the importance of the PINK1/Parkin pathway in mitochondrial import and biogenesis.

La dynamique mitochondriale est impliquée dans la maintenance et la fonction des mitochondries. Dans les graines sèches tout les processus cellulaires sont arrêtés du fait de la faible teneur en eau des tissues, et la transition développementale que représente la germination requiert la réactivation de la dynamique cellulaire. Une approche de bio-imagerie sur la plante modèle Arabidopsis a été utilisée afin d’étudier la réactivation des mitochondries nécessaire à la germination. La réactivation bioénergétique des mitochondries, mesurée par la présence du potentiel membranaire, intervient dès le début de l’hydratation des tissus. Cependant les mitochondries restent statiques et la dynamique mitochondriale ne reprend que plus tardivement. La réactivation des mitochondries provoque une réorganisation du chondriome impliquant la biogenèse de membranes et une fusion massive menant à la formation de structures réticulaires et périnucléaires, qui permet le mélange des nucléoïdes d’ADNmt précédemment isolés en unités discrètes. La mitophagie, un indicateur de la qualité mitochondriale, est réactivée de manière concomitante à la dynamique, alors qu’elle est réprimée durant la biogenèse des mitochondries. La fin de la germination coïncide avec la fragmentation du chondriome tubulaire, menant au doublement du nombre de mitochondrie et à une redistribution hétérogène des nucléoïdes dans le chondriome, générant une population de mitochondrie adaptée à la croissance des plantules. Cette thèse met en évidence l’imbrication des processus de dynamique mitochondriale, de biogenèse et de contrôle qualité des mitochondries requis pour la germination et pour la transition vers l’autotrophie. / Mitochondrial dynamics underpin their function and maintenance. In dry seeds, all cellular processes are in stasis due to a low water content. Thus, the developmental switch leading to germination necessarily involves a reactivation of cellular dynamics. In order tobetter understand the role played by mitochondrial dynamics during germination we used Arabidopsis as a model for a bioimaging approach to investigate the rapid reactivation of mitochondria that is required in order to provide ATP to support germination. Bioenergetic reactivation, visualised as the presence of a mitochondrial membrane potential, is almost immediate upon rehydration. However, the reactivation of mitochondrial dynamics only occurs after several hours of rehydration. The reactivation of mitochondrialbioenergetics and dynamics lead to a dramatic reorganisation of the chondriome involving massive fusion and membrane biogenesis to form a perinuclear tubuloreticular structure enabling mixing of previously discrete mtDNA nucleoids. Mitophagy, an indicator of mitochondrial quality, is reactivated concomitant with a reactivation of mitochondrial dynamics, but is repressed at time of mitochondrial biogenesis. The end of germination coincides with fragmentation of the tubular chondriome leading to a doubling of mitochondrialnumber and heterogeneous redistribution of the nucleoids amongst the mitochondria, generating a population of mitochondria tailored to seedling growth. This thesis provides strong evidence for the tight interweaving of mitochondrial dynamics, mitochondrialbiogenesis and mitochondrial quality control that is required to ensure effective germination and the transition to autotrophy.