Rôle de la sirtuine 1 dans la modulation de la réponse des cardiomyocytes au stress RE et à l’apoptose

Impairment of physiological functions of the endoplasmic reticulum (ER) induces the so-called ER stress. ER stress has been implicated in many cardiovascular diseases including ischemic heart, hypertrophy and heart failure. To overcome the deleterious effect of ER stress, an evolutionarily conserved adaptive response known as Unfolded Protein Response (UPR) is activated in order to restore ER homeostasis and promote cell survival. Nevertheless, in the case of prolonged or severe ER stress, apoptotic cell death is ultimately activated to eliminate stressed cells, thus contributing to the development of the pathology. The modulation of ER stress response, in order to reduce cardiomyocyte apoptosis, thus appears as a promising therapeutic strategy for such pathologies. During my Ph.D thesis, I studied the modification that occur during ER stress response in the heart and the role of the sirtuine 1 (SIRT1) in the modulation of this response. SIRT1 is a deacetylase activated in response to many cardiac stresses to promote cell survival. First, we showed that ER stress induces important structural modifications of cardiomyocytes and in particular an increase in contact sites between ER and mitochondria associated with an alteration of the mitochondrial function. Secondly, using a cell line (H9c2), freshly isolated adult rat ventricular cardiomyocytes and SIRT1-KO mice, we demonstrated in vitro and in vivo (i) that SIRT1 is activated and plays a cardioprotective role in ER stress response, (ii) that SIRT1 attenuates the UPR by specifically regulating the PERK pathway, and (iii) that SIRT1 modulates PERK axis by deacetylating the translation initiation factor, eIF2on two lysine residues. Collectively, our results provide the first evidence that SIRT1 modulates ER stress-induced apoptosis in the heart and suggest that this deacetylase may represent a therapeutic target to prevent apoptosis in cardiac pathologies associated to ER stress.Des altérations de fonctions physiologiques du réticulum endoplasmique (RE) induisent un processus appelé stress RE. Dans le domaine cardiovasculaire, plusieurs travaux ont montré que le stress RE contribue au développement de la majorité des pathologies cardiaques. En réponse au stress RE, la réponse UPR (Unfolded Protein Response) est activée afin de restaurer l’homéostasie du RE et de permettre la survie de la cellule. Néanmoins, dans le cas d’un stress RE excessif ou prolongé, les altérations ne pouvant plus être compensées, la cellule est éliminée par apoptose contribuant au développement de la pathologie cardiaque. Une thérapie prometteuse pour lutter contre ce type de pathologie consisterait donc à moduler la réponse au stress RE afin d’inhiber l’apoptose des cardiomyocytes. Au cours de ma thèse, je me suis intéressé aux modifications induites en réponse au stress RE dans le cœur et au rôle de la sirtuine 1 (SIRT1) dans la modulation de cette réponse. SIRT1 est une déacétylase activée par différents stress cardiaques et connue pour favoriser la survie cellulaire. D’une part, j’ai mis en évidence que le stress RE induit une modification importante de l’architecture des cardiomyocytes et en particulier une augmentation des contacts RE/mitochondries associée à une altération de la fonction mitochondriale. D’autre part, en utilisant une lignée cellulaire (H9c2), des cardiomyocytes de rat adulte et des souris invalidées pour SIRT1, j’ai démontré in vitro et in vivo (i) que SIRT1 est activée et joue un rôle cardioprotecteur en réponse au stress RE, (ii) que SIRT1 limite la réponse UPR en régulant spécifiquement la voie PERK, et (iii) que SIRT1 régule la voie PERK en déacétylant le facteur d’initiation de la traduction, eIF2 sur deux résidus lysine. Ces résultats montrent donc pour la première fois que SIRT1 est impliquée dans la régulation de la réponse apoptotique au stress RE des cardiomyocytes et suggèrent que cette déacétylase serait une cible thérapeutique intéressante pour prévenir l’apoptose dans les pathologies cardiaques liées au stress RE

Simultaneous adsorption of Cd2+ and reactive dye on mesoporous nanocarbons

High-surface-area mesoporous MgO-templated nanocarbons made with reinforcing fibres from scrap tyres and a bituminous waste as carbon precursors were employed for the simultaneous adsorption of Cd2+ and reactive Cibacron Brilliant Yellow 3G-P dye. A commercial activated carbon (AC) Darco KB-WJ was also used for comparison purposes. The effect of the pH of the solution was studied to establish whether acidic pH favours the adsorption of reactive dye and alkaline pH improves the removal of Cd2+. Because the surface chemistry of the three adsorbents was similar, the focus in this study was directed towards their textural characteristics. It was found that the larger the SBET, the greater the amount of dye removal. The adsorption isotherms corresponding to the commercial AC fitted to the Langmuir-Freundlich model, whereas in the case of the nanocarbons the Langmuir model provided the best fit. The results obtained show that Cd2+ is successfully adsorbed in the presence of the dye due to the ion exchange between the Na+ from the dye and the Cd2+. It was also found that a high total and mesopore volume, and a high SBET played a determinant role in the simultaneous adsorption

Hypothalamic AgRP-neurons control peripheral substrate utilization and nutrient partitioning

Obesity-related diseases such as diabetes and dyslipidemia result from metabolic alterations including the defective conversion, storage and utilization of nutrients, but the central mechanisms that regulate this process of nutrient partitioning remain elusive. As positive regulators of feeding behaviour, agouti-related protein (AgRP) producing neurons are indispensible for the hypothalamic integration of energy balance. Here, we demonstrate a role for AgRP-neurons in the control of nutrient partitioning. We report that ablation of AgRP-neurons leads to a change in autonomic output onto liver, muscle and pancreas affecting the relative balance between lipids and carbohydrates metabolism. As a consequence, mice lacking AgRP-neurons become obese and hyperinsulinemic on regular chow but display reduced body weight gain and paradoxical improvement in glucose tolerance on high-fat diet. These results provide a direct demonstration of a role for AgRP-neurons in the coordination of efferent organ activity and nutrient partitioning, providing a mechanistic link between obesity and obesity-related disorders

Mitochondrial physiology

As the knowledge base and importance of mitochondrial physiology to evolution, health and disease expands, the necessity for harmonizing the terminology concerning mitochondrial respiratory states and rates has become increasingly apparent. The chemiosmotic theory establishes the mechanism of energy transformation and coupling in oxidative phosphorylation. The unifying concept of the protonmotive force provides the framework for developing a consistent theoretical foundation of mitochondrial physiology and bioenergetics. We follow the latest SI guidelines and those of the International Union of Pure and Applied Chemistry (IUPAC) on terminology in physical chemistry, extended by considerations of open systems and thermodynamics of irreversible processes. The concept-driven constructive terminology incorporates the meaning of each quantity and aligns concepts and symbols with the nomenclature of classical bioenergetics. We endeavour to provide a balanced view of mitochondrial respiratory control and a critical discussion on reporting data of mitochondrial respiration in terms of metabolic flows and fluxes. Uniform standards for evaluation of respiratory states and rates will ultimately contribute to reproducibility between laboratories and thus support the development of data repositories of mitochondrial respiratory function in species, tissues, and cells. Clarity of concept and consistency of nomenclature facilitate effective transdisciplinary communication, education, and ultimately further discovery

Mitochondrial physiology

As the knowledge base and importance of mitochondrial physiology to evolution, health and disease expands, the necessity for harmonizing the terminology concerning mitochondrial respiratory states and rates has become increasingly apparent. The chemiosmotic theory establishes the mechanism of energy transformation and coupling in oxidative phosphorylation. The unifying concept of the protonmotive force provides the framework for developing a consistent theoretical foundation of mitochondrial physiology and bioenergetics. We follow the latest SI guidelines and those of the International Union of Pure and Applied Chemistry (IUPAC) on terminology in physical chemistry, extended by considerations of open systems and thermodynamics of irreversible processes. The concept-driven constructive terminology incorporates the meaning of each quantity and aligns concepts and symbols with the nomenclature of classical bioenergetics. We endeavour to provide a balanced view of mitochondrial respiratory control and a critical discussion on reporting data of mitochondrial respiration in terms of metabolic flows and fluxes. Uniform standards for evaluation of respiratory states and rates will ultimately contribute to reproducibility between laboratories and thus support the development of data repositories of mitochondrial respiratory function in species, tissues, and cells. Clarity of concept and consistency of nomenclature facilitate effective transdisciplinary communication, education, and ultimately further discovery

Rôle de la sirtuine 1 dans la modulation de la réponse des cardiomyocytes au stress RE et à l’apoptose

Impairment of physiological functions of the endoplasmic reticulum (ER) induces the so-called ER stress. ER stress has been implicated in many cardiovascular diseases including ischemic heart, hypertrophy and heart failure. To overcome the deleterious effect of ER stress, an evolutionarily conserved adaptive response known as Unfolded Protein Response (UPR) is activated in order to restore ER homeostasis and promote cell survival. Nevertheless, in the case of prolonged or severe ER stress, apoptotic cell death is ultimately activated to eliminate stressed cells, thus contributing to the development of the pathology. The modulation of ER stress response, in order to reduce cardiomyocyte apoptosis, thus appears as a promising therapeutic strategy for such pathologies. During my Ph.D thesis, I studied the modification that occur during ER stress response in the heart and the role of the sirtuine 1 (SIRT1) in the modulation of this response. SIRT1 is a deacetylase activated in response to many cardiac stresses to promote cell survival. First, we showed that ER stress induces important structural modifications of cardiomyocytes and in particular an increase in contact sites between ER and mitochondria associated with an alteration of the mitochondrial function. Secondly, using a cell line (H9c2), freshly isolated adult rat ventricular cardiomyocytes and SIRT1-KO mice, we demonstrated in vitro and in vivo (i) that SIRT1 is activated and plays a cardioprotective role in ER stress response, (ii) that SIRT1 attenuates the UPR by specifically regulating the PERK pathway, and (iii) that SIRT1 modulates PERK axis by deacetylating the translation initiation factor, eIF2on two lysine residues. Collectively, our results provide the first evidence that SIRT1 modulates ER stress-induced apoptosis in the heart and suggest that this deacetylase may represent a therapeutic target to prevent apoptosis in cardiac pathologies associated to ER stress.Des altérations de fonctions physiologiques du réticulum endoplasmique (RE) induisent un processus appelé stress RE. Dans le domaine cardiovasculaire, plusieurs travaux ont montré que le stress RE contribue au développement de la majorité des pathologies cardiaques. En réponse au stress RE, la réponse UPR (Unfolded Protein Response) est activée afin de restaurer l’homéostasie du RE et de permettre la survie de la cellule. Néanmoins, dans le cas d’un stress RE excessif ou prolongé, les altérations ne pouvant plus être compensées, la cellule est éliminée par apoptose contribuant au développement de la pathologie cardiaque. Une thérapie prometteuse pour lutter contre ce type de pathologie consisterait donc à moduler la réponse au stress RE afin d’inhiber l’apoptose des cardiomyocytes. Au cours de ma thèse, je me suis intéressé aux modifications induites en réponse au stress RE dans le cœur et au rôle de la sirtuine 1 (SIRT1) dans la modulation de cette réponse. SIRT1 est une déacétylase activée par différents stress cardiaques et connue pour favoriser la survie cellulaire. D’une part, j’ai mis en évidence que le stress RE induit une modification importante de l’architecture des cardiomyocytes et en particulier une augmentation des contacts RE/mitochondries associée à une altération de la fonction mitochondriale. D’autre part, en utilisant une lignée cellulaire (H9c2), des cardiomyocytes de rat adulte et des souris invalidées pour SIRT1, j’ai démontré in vitro et in vivo (i) que SIRT1 est activée et joue un rôle cardioprotecteur en réponse au stress RE, (ii) que SIRT1 limite la réponse UPR en régulant spécifiquement la voie PERK, et (iii) que SIRT1 régule la voie PERK en déacétylant le facteur d’initiation de la traduction, eIF2 sur deux résidus lysine. Ces résultats montrent donc pour la première fois que SIRT1 est impliquée dans la régulation de la réponse apoptotique au stress RE des cardiomyocytes et suggèrent que cette déacétylase serait une cible thérapeutique intéressante pour prévenir l’apoptose dans les pathologies cardiaques liées au stress RE

Role of the sirtuine 1 in the modulation of endoplasmic reticulum stress response and apoptosis in cardiomyocytes

Des altérations de fonctions physiologiques du réticulum endoplasmique (RE) induisent un processus appelé stress RE. Dans le domaine cardiovasculaire, plusieurs travaux ont montré que le stress RE contribue au développement de la majorité des pathologies cardiaques. En réponse au stress RE, la réponse UPR (Unfolded Protein Response) est activée afin de restaurer l’homéostasie du RE et de permettre la survie de la cellule. Néanmoins, dans le cas d’un stress RE excessif ou prolongé, les altérations ne pouvant plus être compensées, la cellule est éliminée par apoptose contribuant au développement de la pathologie cardiaque. Une thérapie prometteuse pour lutter contre ce type de pathologie consisterait donc à moduler la réponse au stress RE afin d’inhiber l’apoptose des cardiomyocytes. Au cours de ma thèse, je me suis intéressé aux modifications induites en réponse au stress RE dans le cœur et au rôle de la sirtuine 1 (SIRT1) dans la modulation de cette réponse. SIRT1 est une déacétylase activée par différents stress cardiaques et connue pour favoriser la survie cellulaire. D’une part, j’ai mis en évidence que le stress RE induit une modification importante de l’architecture des cardiomyocytes et en particulier une augmentation des contacts RE/mitochondries associée à une altération de la fonction mitochondriale. D’autre part, en utilisant une lignée cellulaire (H9c2), des cardiomyocytes de rat adulte et des souris invalidées pour SIRT1, j’ai démontré in vitro et in vivo (i) que SIRT1 est activée et joue un rôle cardioprotecteur en réponse au stress RE, (ii) que SIRT1 limite la réponse UPR en régulant spécifiquement la voie PERK, et (iii) que SIRT1 régule la voie PERK en déacétylant le facteur d’initiation de la traduction, eIF2 sur deux résidus lysine. Ces résultats montrent donc pour la première fois que SIRT1 est impliquée dans la régulation de la réponse apoptotique au stress RE des cardiomyocytes et suggèrent que cette déacétylase serait une cible thérapeutique intéressante pour prévenir l’apoptose dans les pathologies cardiaques liées au stress RE.Impairment of physiological functions of the endoplasmic reticulum (ER) induces the so-called ER stress. ER stress has been implicated in many cardiovascular diseases including ischemic heart, hypertrophy and heart failure. To overcome the deleterious effect of ER stress, an evolutionarily conserved adaptive response known as Unfolded Protein Response (UPR) is activated in order to restore ER homeostasis and promote cell survival. Nevertheless, in the case of prolonged or severe ER stress, apoptotic cell death is ultimately activated to eliminate stressed cells, thus contributing to the development of the pathology. The modulation of ER stress response, in order to reduce cardiomyocyte apoptosis, thus appears as a promising therapeutic strategy for such pathologies. During my Ph.D thesis, I studied the modification that occur during ER stress response in the heart and the role of the sirtuine 1 (SIRT1) in the modulation of this response. SIRT1 is a deacetylase activated in response to many cardiac stresses to promote cell survival. First, we showed that ER stress induces important structural modifications of cardiomyocytes and in particular an increase in contact sites between ER and mitochondria associated with an alteration of the mitochondrial function. Secondly, using a cell line (H9c2), freshly isolated adult rat ventricular cardiomyocytes and SIRT1-KO mice, we demonstrated in vitro and in vivo (i) that SIRT1 is activated and plays a cardioprotective role in ER stress response, (ii) that SIRT1 attenuates the UPR by specifically regulating the PERK pathway, and (iii) that SIRT1 modulates PERK axis by deacetylating the translation initiation factor, eIF2on two lysine residues. Collectively, our results provide the first evidence that SIRT1 modulates ER stress-induced apoptosis in the heart and suggest that this deacetylase may represent a therapeutic target to prevent apoptosis in cardiac pathologies associated to ER stress

Cardiolipin Alterations during Obesity: Exploring Therapeutic Opportunities

Cardiolipin is a specific phospholipid of the mitochondrial inner membrane that participates in many aspects of its organization and function, hence promoting proper mitochondrial ATP production. Here, we review recent data that have investigated alterations of cardiolipin in different tissues in the context of obesity and the related metabolic syndrome. Data relating perturbations of cardiolipin content or composition are accumulating and suggest their involvement in mitochondrial dysfunction in tissues from obese patients. Conversely, cardiolipin modulation is a promising field of investigation in a search for strategies for obesity management. Several ways to restore cardiolipin content, composition or integrity are emerging and may contribute to the improvement of mitochondrial function in tissues facing excessive fat storage. Inversely, reduction of mitochondrial efficiency in a controlled way may increase energy expenditure and help fight against obesity and in this perspective, several options aim at targeting cardiolipin to achieve a mild reduction of mitochondrial coupling. Far from being just a victim of the deleterious consequences of obesity, cardiolipin may ultimately prove to be a possible weapon to fight against obesity in the future

Cardiolipin Alterations during Obesity: Exploring Therapeutic Opportunities

Cardiolipin is a specific phospholipid of the mitochondrial inner membrane that participates in many aspects of its organization and function, hence promoting proper mitochondrial ATP production. Here, we review recent data that have investigated alterations of cardiolipin in different tissues in the context of obesity and the related metabolic syndrome. Data relating perturbations of cardiolipin content or composition are accumulating and suggest their involvement in mitochondrial dysfunction in tissues from obese patients. Conversely, cardiolipin modulation is a promising field of investigation in a search for strategies for obesity management. Several ways to restore cardiolipin content, composition or integrity are emerging and may contribute to the improvement of mitochondrial function in tissues facing excessive fat storage. Inversely, reduction of mitochondrial efficiency in a controlled way may increase energy expenditure and help fight against obesity and in this perspective, several options aim at targeting cardiolipin to achieve a mild reduction of mitochondrial coupling. Far from being just a victim of the deleterious consequences of obesity, cardiolipin may ultimately prove to be a possible weapon to fight against obesity in the future