Alteration of mitochondrial oxidative phosphorylation in aged skeletal muscle involves modification of adenine nucleotide translocator

AbstractThe process of skeletal muscle aging is characterized by a progressive loss of muscle mass and functionality. The underlying mechanisms are highly complex and remain unclear. This study was designed to further investigate the consequences of aging on mitochondrial oxidative phosphorylation in rat gastrocnemius muscle, by comparing young (6 months) and aged (21 months) rats. Maximal oxidative phosphorylation capacity was clearly reduced in older rats, while mitochondrial efficiency was unaffected. Inner membrane properties were unaffected in aged rats since proton leak kinetics were identical to young rats. Application of top-down control analysis revealed a dysfunction of the phosphorylation module in older rats, responsible for a dysregulation of oxidative phosphorylation under low activities close to in vivo ATP turnover. This dysregulation is responsible for an impaired mitochondrial response toward changes in cellular ATP demand, leading to a decreased membrane potential which may in turn affect ROS production and ion homeostasis. Based on our data, we propose that modification of ANT properties with aging could partly explain these mitochondrial dysfunctions

Improved Energy Supply Regulation in Chronic Hypoxic Mouse Counteracts Hypoxia-Induced Altered Cardiac Energetics

Hypoxic states of the cardiovacular system are undoubtedly associated with the most frequent diseases of modern time. Therefore, understanding hypoxic resistance encountered after physiological adaptation such as chronic hypoxia, is crucial to better deal with hypoxic insult. In this study, we examine the role of energetic modifications induced by chronic hypoxia (CH) in the higher tolerance to oxygen deprivation.P-NMR), and to describe the integrated changes in cardiac energetics regulation by using Modular Control Analysis (MoCA). Oxygen reduction induced a concomitant decrease in RPP (−46%) and in [PCr] (−23%) in Control hearts while CH hearts energetics was unchanged. MoCA demonstrated that this adaptation to hypoxia is the direct consequence of the higher responsiveness (elasticity) of ATP production of CH hearts compared with Controls (−1.88±0.38 vs −0.89±0.41, p<0.01) measured under low oxygen perfusion. This higher elasticity induces an improved response of energy supply to cellular energy demand. The result is the conservation of a healthy control pattern of contraction in CH hearts, whereas Control hearts are severely controlled by energy supply.As suggested by the present study, the mechanisms responsible for this increase in elasticity and the consequent improved ability of CH heart metabolism to respond to oxygen deprivation could participate to limit the damages induced by hypoxia

Microglia in Close Vicinity of Glioma Cells: Correlation Between Phenotype and Metabolic Alterations

Microglia are immune cells within the central nervous system. In brain-developing tumors, gliomas are able to silence the defense and immune functions of microglia, a phenomenon which strongly contributes to tumor progression and treatment resistance. Being activated and highly motile, microglia infiltrate tumors and secrete macrophagic chemoattractant factors. Thereafter, the tumor cells shut down their immune properties and stimulate the microglia to release tumor growth-promoting factors. The result of such modulation is that a kind of symbiosis occurs between microglia and tumor cells, in favor of tumor growth. However, little is known about microglial phenotype and metabolic modifications in a tumoral environment. Co-cultures were performed using CHME5 microglia cells grown on collagen beads or on coverslips and placed on monolayer of C6 cells, limiting cell/cell contacts. Phagocytic behavior and expression of macrophagic and cytoskeleton markers were monitored. Respiratory properties and energetic metabolism were also studied with regard to the activated phenotype of microglia. In co-cultures, transitory modifications of microglial morphology and metabolism were observed linked to a concomitant transitory increase of phagocytic properties. Therefore, after 1 h of co-culture, microglia were activated but when longer in contact with tumor cells, phagocytic properties appear silenced. Like the behavior of the phenotype, microglial respiration showed a transitory readjustment although the mitochondria maintained their perinuclear relocation. Nevertheless, the energetic metabolism of the microglia was altered, suggesting a new energetic steady state. The results clearly indicate that like the depressed immune properties, the macrophagic and metabolic status of the microglia is quickly driven by the glioma environment, despite short initial phagocytic activation. Such findings question the possible contribution of diffusible tumor factors to the microglial metabolism

Chronic hypoxia aggravates monocrotaline-induced pulmonary arterial hypertension: a rodent relevant model to the human severe form of the disease

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Analyse intégrative de l'adaptation de l'énergétique cardiaque à l'hypoxie chronique

La compréhension des mécanismes physiologiques mis en jeu en réponse à l hypoxie aigüe et chronique ainsi que leur retentissement global sur l énergétique cardiaque nécessite l application d approches globales. L approche intégrative développée par notre équipe, l Analyse Modulaire du Contrôle (MoCA) permet une description quantitative de l ensemble des interactions au sein d un système biologique complexe décomposé en différents modules liés par des intermédiaires communs, ce qui en fait un outil puissant pour l étude des interactions au sein de l énergétique cardiaque, normale ou pathologique. Dans cette thèse, MoCA a été appliquée sur des coeurs isolés de souris contrôles et de souris soumises à une hypoxie chronique de 21 jours, perfusés en conditions d oxygénation normale ou avec un milieu dont la concentration en oxygène dans le milieu a été réduite. Après exposition à l hypoxie chronique, les coeurs sont caractérisés par une réponse (élasticité) plus importante des processus d apport en énergie face à une variation des intermédiaires énergétiques (PCr, ATP, Pi), et ceci malgré une diminution de la masse mitochondriale. De plus, contrairement aux coeurs sains, aucune modi?cation de l activité contractile et de la concentration d intermédiaires énergétiques n a été mesurée sur les coeurs hypoxiques après diminution de la concentration en oxygène dans le milieu de perfusion. Ces résultats suggèrent une adaptation fonctionnelle de l ensemble de la bioénergétique cardiaque après exposition à l hypoxie chronique, l augmentation de l élasticité des processus d apport en énergie permettant de compenser en partie les altérations énergétiques induites par un dé?cit en oxygène.An important issue in the comprehension of the link between molecular events developed in pathologies such as chronic hypoxia adaptation, is the development of new experimental strategies aimed at the study of the integrated organ physiology. Our Modular Control Analysis (MoCA), gives quantitative information on the internal control and regulation of integrated heart energetics on the basis of a supply-demand system and is therefore of particular interest to better understand the overall effect as well as the relative importance of the various modi?cations developed during pathologies. In this thesis, MoCA was applied on isolated hearts of control and chronic hypoxic mice perfused with high or low oxygen in the medium. Despite a severe mitochondrial alteration after chronic hypoxia exposure, a surprizing higher response of energy supply (elasticity) to energetic intermediates changes (PCr, ATP, Pi) was detected in chronic hypoxic hearts. Moreover, chronic hypoxic hearts energetics was unchanged by oxygen reduction while a strong concomitant decrease in heart contractile activity and in PCr concentration, was measured in control hearts. As suggested by these results, this increase in energy-supply elasticity could be considered as an adaptive mechanism developed after chronic hypoxia counteracting hypoxia-induced altered cardiac energetics.BORDEAUX2-Bib. électronique (335229905) / SudocSudocFranceF

An old medicine as a new drug to prevent mitochondrial complex I from producing oxygen radicals.

FindingsHere, we demonstrate that OP2113 (5-(4-Methoxyphenyl)-3H-1,2-dithiole-3-thione, CAS 532-11-6), synthesized and used as a drug since 1696, does not act as an unspecific antioxidant molecule (i.e., as a radical scavenger) but unexpectedly decreases mitochondrial reactive oxygen species (ROS/H2O2) production by acting as a specific inhibitor of ROS production at the IQ site of complex I of the mitochondrial respiratory chain. Studies performed on isolated rat heart mitochondria also showed that OP2113 does not affect oxidative phosphorylation driven by complex I or complex II substrates. We assessed the effect of OP2113 on an infarct model of ex vivo rat heart in which mitochondrial ROS production is highly involved and showed that OP2113 protects heart tissue as well as the recovery of heart contractile activity.Conclusion / significanceThis work represents the first demonstration of a drug authorized for use in humans that can prevent mitochondria from producing ROS/H2O2. OP2113 therefore appears to be a member of the new class of mitochondrial ROS blockers (S1QELs) and could protect mitochondrial function in numerous diseases in which ROS-induced mitochondrial dysfunction occurs. These applications include but are not limited to aging, Parkinson's and Alzheimer's diseases, cardiac atrial fibrillation, and ischemia-reperfusion injury

Quantitative studies of enzyme-substrate compartmentation, functional coupling and metabolic channelling in muscle cells

International audienceSome historical aspects of development of the concepts of functional coupling, metabolic channelling, compartmentation and energy transfer networks are reviewed. Different quantitative approaches, including kinetic and mathematical modeling of energy metabolism, intracellular energy transfer and metabolic regulation of energy production and fluxes in the cells in vivo are analyzed. As an example of the system with metabolic channelling, thermodynamic aspects of the functioning the mitochondrial creatine kinase functionally coupled to the oxidative phosphorylation are considered. The internal thermodynamics of the mitochondrial creatine kinase reaction is similar to that for other isoenzymes of creatine kinase, and the oxidative phosphorylation process specifically influences steps of association and dissociation of MgATP with the enzyme due to channelling of ATP from adenine nucleotide translocase. A new paradigm of muscle bioenergetics - the paradigm of energy transfer and feedback signaling networks based on analysis of compartmentation phenomena and structural and functional interactions in the cell is described. Analysis of the results of mathematical modeling of the compartmentalized energy transfer leads to conclusion that both calcium and ADP, which concentration changes synchronously in contraction cycle, may simultaneously activate oxidative phosphorylation in the muscle cells in vivo. The importance of the phosphocreatine circuit among other pathways of intracellular energy transfer network is discussed on the basis of the recent data published in the literature, with some experimental demonstration. The results of studies of perfused rat hearts with completely inhibited creatine kinase show significantly decreased work capacity and respectively, energy fluxes, in these hearts in spite of significant activation of adenylate kinase system (Dzeja et al. this volume). These results, combined with those of mathematical analysis of the energy metabolism of hearts of transgenic mice with switched off creatine kinase isoenzymes confirm the importance of phosphocreatine pathway for energy transfer for cell function and energetics in mature heart and many other types of cells, as one of major parts of intracellular energy transfer network and metabolic regulation

Thermodynamical Fluxes for the Modeling of Cardiac Mitochondrial Calcium Handling

International audienceIt is known that mitochondria play a crucial role in the handling of calcium by cardiac cells during the excitation-contraction cycle. However, the precise characterization of this role is still under debate. With this intent, a collection of mathematical models have been developed, but they generally show a level of complexity that is not compatible with inverse problem techniques required for calibration with experimental data. Their large number of equations and parameters can also lead to transcription mistakes that can be found in the literature. In this paper we apply a similar methodology as Bertram et al.in [1] to propose a simple model that is derived from the base equations that constitute the origin of most mitochondrial models [2]. Our model describes the main features of the mitochon-drial activity with 6 equations and ∼30 parameters, which we will eventually reduce in a forthcoming sensitivity analysis

Parameter estimation in modeling phosphocreatine recovery in human skeletal muscle

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