The genotype 3-specific hepatitis C virus core protein residue phenylalanine 164 increases steatosis in an in vitro cellular model.: HCV genotype 3-specific steatosis

International audienceBackground and aims: The prevalence and severity of liver steatosis are higher in patients infected with genotype 3 hepatitis C virus (HCV) than in patients infected with other genotypes. HCV core protein is known to affect lipid metabolism, inducing lipid droplet accumulation both in vitro and in vivo. We used an in vitro cellular model to investigate whether an HCV core protein with residues specific to genotype 3 increased this phenomenon. Methods: Sequence comparisons for HCV core protein domain II, which is known to interact with lipid droplets, identified the phenylalanine (F) residue at position 164 as the only residue specific to genotype 3. We compared the area covered by lipid droplets in sections of cells producing a wild-type genotype 1a HCV core protein with that in cells producing a Y164F mutant protein. Results: Cumulative lipid droplet area was significantly greater in sections of cells producing the Y164F mutant HCV core protein than in cells producing the wild-type protein (p<0.001). The frequency of cell sections containing more than 3 μm2 of lipid droplets, in particular, was higher for the mutant than for the wild-type protein. Conclusion: Our data provide a molecular explanation for HCV genotype 3-specific lipid accumulation. This difference between genotypes may be due to phenylalanine having a higher affinity for lipids than tyrosine (Y). These observations provide useful information for further studies of the mechanisms involved in HCV-induced steatosis

Oxidation of Porphyrins in the Presence of Nucleophiles: From the Synthesis of Multisubstituted Porphyrins to the Electropolymerization of the Macrocycles

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Viral sequence variation in chronic carriers of hepatitis C virus has a low impact on liver steatosis.: HCV variability and steatosis

International audienceMost clinical studies suggest that the prevalence and severity of liver steatosis are higher in patients infected with hepatitis C virus (HCV) genotype 3 than in patients infected with other genotypes. This may reflect the diversity and specific intrinsic properties of genotype 3 virus proteins. We analyzed the possible association of particular residues of the HCV core and NS5A proteins known to dysregulate lipid metabolism with steatosis severity in the livers of patients chronically infected with HCV. We used transmission electron microscopy to quantify liver steatosis precisely in a group of 27 patients, 12 of whom were infected with a genotype 3 virus, the other 15 being infected with viruses of other genotypes. We determined the area covered by lipid droplets in liver tissues and analyzed the diversity of the core and NS5A regions encoded by the viral variants circulating in these patients. The area covered by lipid droplets did not differ significantly between patients infected with genotype 3 viruses and those infected with other genotypes. The core and NS5A protein sequences of the viral variants circulating in patients with mild or severe steatosis were evenly distributed throughout the phylogenic trees established from all the collected sequences. Thus, individual host factors seem to play a much greater role than viral factors in the development of severe steatosis in patients chronically infected with HCV, including those infected with genotype 3 viruses

Identification of stiffness and damping properties of thin isotropic vibrating plates using the virtual fields method: theory and simulations

The present paper proposes a novel procedure to derive both stiffness and damping parameters from forced vibrating isotropic plates. The key feature is that displacement and curvature fields can be measured at different times over the whole surface of the plate by a suitable optical technique. As a consequence, the virtual fields method (VFM) provides sets of equations relating the stiffness and damping parameters to these measured fields and to geometric and excitation (frequency, amplitude) parameters. First, the theory of the VFM is exposed and, then, validation is performed on simulated full-field displacement and curvature data. Calculations are performed in the case of isotropic plates with low and high damping, at resonance and out of resonance. It is shown that the procedure is valid and robust to noise, except on the damping parameters when the damping is low. Future work necessary to develop the method is described as a conclusion.<br/

La réponse en fréquence comme signature d'usinabilité

L'article propose une méthodologie basée sur une procédure expérimentale originale utilisant le comportement vibratoire du système de coupe pour dégager des indicateurs d'usinabilité de matériaux. Elle est appliquée à un outil de tournage en opération de chariotage. Le bridage de l'outil et les phénomènes liés à la coupe définissent les conditions aux limites de l'outil assimilé à une structure vibrante. Toute variation des conditions de coupe se répercute sur le comportement vibratoire de l'outil. Ce comportement peut être représenté par les fonctions de réponse en fréquence de l'outil déterminées pendant l'usinage. Ces dernières sont calculées à partir d'excitations percussionnelles et des réponses vibratoires de l'outil mesurées pendant les opérations de coupe. Un dispositif spécifique d'excitation est utilisé. Sa conception et sa validation sont présentées. Un dépouillement particulier issu des techniques d'analyse modale expérimentale est appliqué à des mesures exploratoires. Les résultats présentés montrent la sensibilité de la méthode. Des perspectives de développement sont avancées

Réactivité électrochimique des cations pyridinium en réduction (Rôle modulateur de la porphyrine dans les systèmes mixtes pyridinium-porphyrine)

De nombreuses études de la réduction électrochimique des cations pyridinium ont été réalisées, leurs produits de réduction étant d'un intérêt primordial dans la compréhension des mécanismes de stress oxydatif des cellules et dans la modélisation des maladies neurodégénératives. Nous proposons une étude originale qui examine des systèmes inédits par rapport à ceux décrits dans la littérature. Nous avons préparé et étudié, par voie électrochimique, des systèmes mixtes pyridinium-porphyrine dans lesquels le cation pyridinium est substitué en position 1 par une porphyrine. Ce macrocycle est lié au cation pyridinium directement sur sa position 1, permettant de moduler l'activité redox de ce cation. Nous présentons les résultats comparés des études électrochimiques effectuées sur les systèmes du type MOEP-m-Py+ et MOEP-m-Py44+ montrant que la position du substituant porphyrine sur le cation pyridinium (1 ou 4) modifie considérablement ses propriétés redox. Nous avons également montré que les systèmes du type MTPP-b-(4-R-Py+) (M = H2, Zn, Cu, Ni, Pd, Au) présentent un comportement similaire à ceux pour lesquels le groupement pyridinium est porté par la position méso de la porphyrine. L'étude de ces systèmes a permis de discriminer les sites des différents transferts de charge et d'appréhender le mécanisme de réduction du groupement pyridinium. Le comportement redox varie selon la nature de la porphyrine. Nous avons ainsi constaté que l'évolution du potentiel de réduction du cation pyridinium est fonction de l'électronégativité du métal de la porphyrine. La nette différence de comportement observée dans le cas des bases libres a été interprétée sur la base des délocalisations de densité électronique. Les étapes de réduction sont également fonction de la substitution de la position 4. Enfin, l'étude du système AuIIITPP-b-Py+ a permis de quantifier l'effet électroattracteur du cation pyridinium sur les valeurs des potentiels de réduction des porphyrines en série TPP.La coulométrie exhaustive au potentiel de réduction du cation pyridinium montre un nombre d'électrons échangés égal à 2. Ainsi, lors d'électrolyses préparatives de ZnTPP-b-bPy+ et ZnTPP-b-Py+, il a été possible de séparer un des produits de réduction, ZnTPP-b-N(CH3)2, qui montre que la liaison C-N est conservée et que le noyau pyridinique est rompu.Numerous of studies have been dedicated to the electrochemical reduction of pyridinium cations because their reduction products are involved in the mechanism of oxidative stress in cells. These molecules are also used in the modeling of neurodegenerative diseases such as the Parkinson's disease.Our study is original because our systems are new compared to those previously examined. We prepared and studied electrochemically mixed systems formed by a pyridinium cation bearing a porphyrin at the 1 position. This macrocycle is able to modulate the redox behavior of the cation. We present the results of the electrochemical studies of the systems MOEP-m-Py+ and MOEP-m-Py44+ compared to thise of the literature. We observed that the substitution position of the porphyrin on the pyridinium cation (1 or 4) drastically changes its redox properties. We also showed that the MTPP-b-(4-R-Py+) systems (M = H2, Zn, Cu, Ni, Pd, Au) are similar to the MOEP-b-(4-R-Py+) compounds, as far as the electrochemical behavior is concerned.The study of these molecules allowed us to discriminate the sites of the different charge transfers (pyridinium cation or porphyrin) and to propose a mechanism for the primary electrochemical reduction of the pyridinium cation. The redox behavior is a fonction of the porphyrin nature (free base or metaled with several metals) and we were able to correlate the electronegativity of the metal with the reduction potential of the pyridinium cation. The different behavior observed for the free base was explained by the differences existing in the electronic densities in the systems. The electron transfers are also dependent on the substitution of the 4 position.Then, the study of AuIIITPP-b-Py+ allowed us to quantify the electroattractor effet of the TPP (0.165 V to 0.255 V).Exhaustive coulometry at the reduction potential of the pyridinium cation showed that two electrons were exchanged. By preparative coulométries of ZnTPP-b-bPy+ and ZnTPP-b-Py+, one reduction product, namely ZnTPP-b-N(CH3)2, could be isolated, allowing us to show that the C-N bond is kept whereas the pyridinium ring is broken.STRASBOURG-Sc. et Techniques (674822102) / SudocSudocFranceF

An alternative to modal analysis for material stiffness and damping identification from vibrating plates

This paper presents an alternative to modal analysis to extract stiffness and damping parameters from thin vibrating plates. Full-field slope measurements are performed through a deflectometry technique on a plate vibrating at a given frequency. Images are recorded in phase and at ?/2 lag from the excitation. From this information, deflection fields are computed by integration and curvature fields are obtained by differentiation. This information is then input into the principle of virtual work to extract both stiffness and damping parameters. This procedure, known as the Virtual Fields Method, is detailed in the paper and the notion of special optimized virtual fields is extended to the present problem. Validation on simulated data is performed before moving to experimental data. One of the main advantages of this technique is that it is completely insensitive to the damping coming from the boundary conditions. This is illustrated experimentally on two tests where a viscoelastic layer and rubber washers are added in the experimental set u