Metabolic Compartmentation – A System Level Property of Muscle Cells: Real Problems of Diffusion in Living Cells

Problems of quantitative investigation of intracellular diffusion and compartmentation of metabolites are analyzed. Principal controversies in recently published analyses of these problems for the living cells are discussed. It is shown that the formal theoretical analysis of diffusion of metabolites based on Fick's equation and using fixed diffusion coefficients for diluted homogenous aqueous solutions, but applied for biological systems in vivo without any comparison with experimental results, may lead to misleading conclusions, which are contradictory to most biological observations. However, if the same theoretical methods are used for analysis of actual experimental data, the apparent diffusion constants obtained are orders of magnitude lower than those in diluted aqueous solutions. Thus, it can be concluded that local restrictions of diffusion of metabolites in a cell are a system-level properties caused by complex structural organization of the cells, macromolecular crowding, cytoskeletal networks and organization of metabolic pathways into multienzyme complexes and metabolons. This results in microcompartmentation of metabolites, their channeling between enzymes and in modular organization of cellular metabolic networks. The perspectives of further studies of these complex intracellular interactions in the framework of Systems Biology are discussed

Metabolic Compartmentation – A System Level Property of Muscle Cells

Problems of quantitative investigation of intracellular diffusion and compartmentation of metabolites are analyzed. Principal controversies in recently published analyses of these problems for the living cells are discussed. It is shown that the formal theoretical analysis of diffusion of metabolites based on Fick’s equation and using fixed diffusion coefficients for diluted homogenous aqueous solutions, but applied for biological systems in vivo without any comparison with experimental results, may lead to misleading conclusions, which are contradictory to most biological observations. However, if the same theoretical methods are used for analysis of actual experimental data, the apparent diffusion constants obtained are orders of magnitude lower than those in diluted aqueous solutions. Thus, it can be concluded that local restrictions of diffusion of metabolites in a cell are a system-level properties caused by complex structural organization of the cells, macromolecular crowding, cytoskeletal networks and organization of metabolic pathways into multienzyme complexes and metabolons. This results in microcompartmentation of metabolites, their channeling between enzymes and in modular organization of cellular metabolic networks. The perspectives of further studies of these complex intracellular interactions in the framework of Systems Biology are discussed

Transformation des OPCA au fil des réformes récentes : vers un nouveau modèle économique ?

Marseille : Céreq, Coll. Céreq études, n° 18, 93 p.La réforme de la formation professionnelle de 2014 est venue bouleverser le modèle économique des OPCA (Organismes paritaires collecteurs agréés), dont l'épicentre était pour l'essentiel constitué jusqu’alors par des contributions obligatoires versées par les entreprises au titre du plan de formation, largement mutualisées (qui correspondaient au 0,9 % de la masse salariale brute). La quasi-disparition de cette obligation pour un grand nombre d’entreprises (celles de plus de 50 salariés) ne s’est vue que partiellement compensée par les versements issus d'accords conventionnels de branche sur la formation dont la faiblesse est patente (40 % des accords de branche ne prévoient pas de contributionconventionnelle). Ces versements conventionnels correspondent à moins de la moitié du montant des versements libres, qui eux-mêmes représentent, pour l’ensemble des OPCA, la moitié des fonds totaux fléchés « plan de formation » (1,2 milliard d’euros sur 2,4 milliards).La recherche de compléments de financement, provenant d’une part des versements volontaires d'entreprises, et d’autre part de co-financements adossés à des dispositifs et des programmes de politiques publiques sur l’emploi et la formation (nationaux et européens), est alors devenue pour les OPCA un enjeu économique de premier ordre qui oriente leurs nouvelles stratégies. Ces stratégies ont de nombreux effets, tant sur l’équilibre organisationnel des OPCA, entre logique de services publics et comportements de nature commerciale, que sur le renouvellement en profondeur de l’offre de services avec une variété de niveaux, de conditions d’accès, et d’agencement des prestations et desfinancements. Cette segmentation en niveaux et qualités de services s’est imposée pour attirer les contributions volontaires des entreprises prévues par la loi de 2014, et qui dépendent elles-mêmes de leur sensibilisation aux enjeux de la formation, de l’appréhension de leurs besoins en compétences et de leur capacité de financement (ou de co-financement)

Defensive medicine among antibiotic stewards: the international ESCMID AntibioLegalMap survey

International audienceObjectives:To investigate fear of legal claims and defensive behaviours among specialists in infectious diseases (ID) and clinical microbiology (CM) and to identify associated demographic and professional characteristics.Methods:AntibioLegalMap was an international cross-sectional internet-based survey targeting specialists in ID and CM. Three variables were explored: fear of legal liability in antibiotic prescribing/advising on antibiotic prescription; defensive behaviours in antibiotic prescribing; and defensive behaviours in advising. A multivariable logistic regression analysis was performed to identify factors significantly associated with each of the three variables.Results:Eight hundred and thirty individuals from 74 countries participated. Only 0.4% (3/779) had any kind of condemnation for malpractice related to antibiotic prescription. Concerning the fear of liability, 21.2% (164/774) of respondents said they never worried, 45.1% (349/774) sometimes worried and 28.6% (221/774) frequently worried when prescribing/advising on antibiotic prescription. Being female, younger than or equal to 35 years and aware of previous cases of litigation were independently associated with fear. Most respondents (85.0%, 525/618) reported some defensive behaviour in antibiotic prescribing. These behaviours were independently associated with being younger than or equal to 35 years and sometimes or often worried about liability. Similarly, 76.4% (505/661) reported defensive behaviours in advising. These behaviours were associated with being sometimes or often worried about liability. The preferred measures to reduce fear and defensive behaviours were having local guidelines and sharing decisions through teamwork.Conclusions:A significant proportion of specialists in ID and CM reported some form of defensive behaviour in prescribing or advising to prescribe antibiotics. Defensive medicine should be considered when implementing antibiotic stewardship programmes

Mitochondrial dynamics in heart cells: very low amplitude high frequency fluctuations in adult cardiomyocytes and flow motion in non beating Hl-1 cells.

International audienceThe arrangement and movement of mitochondria were quantitatively studied in adult rat cardiomyocytes and in cultured continuously dividing non beating (NB) HL-1 cells with differentiated cardiac phenotype. Mitochondria were stained with MitoTracker Green and studied by fluorescent confocal microscopy. High speed scanning (one image every 400 ms) revealed very rapid fluctuation of positions of fluorescence centers of mitochondria in adult cardiomyocytes. These fluctuations followed the pattern of random walk movement within the limits of the internal space of mitochondria, probably due to transitions between condensed and orthodox configurational states of matrix and inner membrane. Mitochondrial fusion or fission was seen only in NB HL-1 cells but not in adult cardiomyocytes. In NB HL-1 cells, mitochondria were arranged as a dense tubular network, in permanent fusion, fission and high velocity displacements of approximately 90 nm/s. The differences observed in mitochondrial dynamics are related to specific structural organization and mitochondria-cytoskeleton interactions in these cells

Structure–function relationships in feedback regulation of energy fluxes in vivo in health and disease: Mitochondrial Interactosome

AbstractThe aim of this review is to analyze the results of experimental research of mechanisms of regulation of mitochondrial respiration in cardiac and skeletal muscle cells in vivo obtained by using the permeabilized cell technique. Such an analysis in the framework of Molecular Systems Bioenergetics shows that the mechanisms of regulation of energy fluxes depend on the structural organization of the cells and interaction of mitochondria with cytoskeletal elements. Two types of cells of cardiac phenotype with very different structures were analyzed: adult cardiomyocytes and continuously dividing cancerous HL-1 cells. In cardiomyocytes mitochondria are arranged very regularly, and show rapid configuration changes of inner membrane but no fusion or fission, diffusion of ADP and ATP is restricted mostly at the level of mitochondrial outer membrane due to an interaction of heterodimeric tubulin with voltage dependent anion channel, VDAC. VDAC with associated tubulin forms a supercomplex, Mitochondrial Interactosome, with mitochondrial creatine kinase, MtCK, which is structurally and functionally coupled to ATP synthasome. Due to selectively limited permeability of VDAC for adenine nucleotides, mitochondrial respiration rate depends almost linearly upon the changes of cytoplasmic ADP concentration in their physiological range. Functional coupling of MtCK with ATP synthasome amplifies this signal by recycling adenine nucleotides in mitochondria coupled to effective phosphocreatine synthesis. In cancerous HL-1 cells this complex is significantly modified: tubulin is replaced by hexokinase and MtCK is lacking, resulting in direct utilization of mitochondrial ATP for glycolytic lactate production and in this way contributing in the mechanism of the Warburg effect. Systemic analysis of changes in the integrated system of energy metabolism is also helpful for better understanding of pathogenesis of many other diseases

Comparative analysis of the bioenergetics of adult cardiomyocytes and nonbeating HL-1 cells: respiratory chain activities, glycolytic enzyme profiles, and metabolic fluxes.

International audienceComparative analysis of the bioenergetic parameters of adult rat cardiomyocytes (CM) and HL-1 cells with very different structure but similar cardiac phenotype was carried out with the aim of revealing the importance of the cell structure for regulation of its energy fluxes. Confocal microscopic analysis showed very different mitochondrial arrangement in these cells. The cytochrome content per milligram of cell protein was decreased in HL-1 cells by a factor of 7 compared with CM. In parallel, the respiratory chain complex activities were decreased by 4-8 times in the HL-1 cells. On the contrary, the activities of glycolytic enzymes, hexokinase (HK), and pyruvate kinase (PK) were increased in HL-1 cells, and these cells effectively transformed glucose into lactate. At the same time, the creatine kinase (CK) activity was significantly decreased in HL-1 cells. In conclusion, the results of this study comply with the assumption that in contrast to CM in which oxidative phosphorylation is a predominant provider of ATP and the CK system is a main carrier of energy from mitochondria to ATPases, in HL-1 cells the energy metabolism is based mostly on the glycolytic reactions coupled to oxidative phosphorylation through HK