Caractérisation géochimique du kérogène associé à l'argile Oligocène de Boom (Mol, Belgique) et évolution sous divers stress thermiques

La formation argileuse de Boom, en Belgique, a été choisie comme site d'étude pour l'enfouissement en profondeur des déchets radioactifs de hautes activités. Un important programme de recherche a été entrepris pour appréhender les différentes variations engendrées par le stockage de tels colis: par exemple augmentation de la température et des contraintes physiques. La matière organique (MO) sédimentaire, qui se trouve principalement sous forme de macromolécule insoluble appelée kérogène, est sensible au stress thermique. Il est connu que sous un tel stress les kérogènes donnent naissance à un grand nombre de composés gazeux et liquides. Cette production pourrait avoir des conséquences physico-chimiques importantes, tels des changements locaux de pH et des processus de fracturation. Par ailleurs, certains des composés ainsi formés, en particulier les composés polaires, seraient susceptibles de complexer les radionucléides. L'ensemble de ces phénomènes pourrait ainsi influencer la capacité de confinement de la barrière géologique. Les échantillons étudiés au cours de cette thèse ont été prélevés au niveau du laboratoire souterrain de Mol, situé à 223 m de profondeur. Ils ont été analysés en détail par des méthodes géochimiques (pyrolyse Rock-Eval, analyse élémentaire et microscopies électronique à balayage et à transmission couplées à des analyses EDS), spectroscopiques (IRTF, RMN 13C à l'état solide, Raman) et pyrolytiques ("off-line", "on-line" et en tube scellés, combinées avec des analyses par couplage CG/SM). L'étude d'un échantillon représentatif de la formation a permis d'obtenir la caractérisation à l'échelle moléculaire de cette MO et donc des informations détaillées sur la nature de ses organismes sources, les mécanismes de sa fossilisation et la nature des produits organiques piégés au sein du kérogène. La MO de l'argile de Boom provient principalement de matériel phytoplanctonique, avec une contribution de matériel terrestre et bactérien importante. La dégradation-recondensation a joué un rôle prédominant dans la préservation de cette MO mais la présence de nombreuses molécules oxygénées implique que l'incorporation oxydative est également intervenue dans cette préservation. Enfin divers produits (hydrocarbures, composés polaires oxygénés et azotés) piégés, en quantité significative, au sein de la structure macromoléculaire, sont libérés sous un stress thermique relativement faible. Par ailleurs, sous un stress thermique, la MO libére de nombreuses petites molécules organiques polaires qui peuvent donc jouer un rôle dans la rétention et/ou la migration des radioéléments dans la barrière géologique. - 12 - Résumé L'étude de l'évolution de cette MO sous divers stress thermiques est essentielle dans l'optique du stockage. Pour cela, nous avons tout d'abord examiné un échantillon ayant subi un stress thermique in situ de 80°C pendant cinq ans durant l'expérience CERBERUS. La comparaison du kérogène de cet échantillon avec le kérogène de l'échantillon de référence non chauffé, analysé en première partie du travail, a montré que le stress thermique (80°C/5 ans) n'a pas induit de changement important dans la structure du kérogène. Des expériences de simulation en laboratoire ont été ensuite effectuées par chauffage en tube scellé pour différents couples températures/temps. Des stress thermiques croissants ont ainsi été approximativement simulés, le stress CERBERUS et les stress 100°C/10000 ans et 150°C/1000 ans. Les résultats préliminaires obtenus concernant la nature et l'abondance des produits ainsi formés montrent (i) une production significative de composés gazeux et solubles dès le stress le plus faible (simulant le stress de CERBERUS) et (ii) la prédominance de composés polaires, en particulier les acides carboxyliques, dans les composés solubles formés sous un tel stress

Caractérisation géochimique du kérogène associé à l'argile oligocène de Boom (Mol, Belgique) et évolution sous divers stress thermiques

PARIS-BIUSJ-Thèses (751052125) / SudocPARIS-BIUSJ-Physique recherche (751052113) / SudocSudocFranceF

Asymmetric Synthesis of 2-Heteroaryl Cyclic Amines: Total Synthesis of (-)-Anabasine

International audienc

Activation of Wnt/beta-catenin signaling increases insulin sensitivity through a reciprocal regulation of Wnt10b and SREBP-1c in skeletal muscle cells.

Intramyocellular lipid accumulation is strongly related to insulin resistance in humans, and we have shown that high glucose concentration induced de novo lipogenesis and insulin resistance in murin muscle cells. Alterations in Wnt signaling impact the balance between myogenic and adipogenic programs in myoblasts, partly due to the decrease of Wnt10b protein. As recent studies point towards a role for Wnt signaling in the pathogenesis of type 2 diabetes, we hypothesized that activation of Wnt signaling could play a crucial role in muscle insulin sensitivity.Here we demonstrate that SREBP-1c and Wnt10b display inverse expression patterns during muscle ontogenesis and regeneration, as well as during satellite cells differentiation. The Wnt/beta-catenin pathway was reactivated in contracting myotubes using siRNA mediated SREBP-1 knockdown, Wnt10b over-expression or inhibition of GSK-3beta, whereas Wnt signaling was inhibited in myoblasts through silencing of Wnt10b. SREBP-1 knockdown was sufficient to induce Wnt10b protein expression in contracting myotubes and to activate the Wnt/beta-catenin pathway. Conversely, silencing Wnt10b in myoblasts induced SREBP-1c protein expression, suggesting a reciprocal regulation. Stimulation of the Wnt/beta-catenin pathway i) drastically decreased SREBP-1c protein and intramyocellular lipid deposition in myotubes; ii) increased basal glucose transport in both insulin-sensitive and insulin-resistant myotubes through a differential activation of Akt and AMPK pathways; iii) restored insulin sensitivity in insulin-resistant myotubes.We conclude that activation of Wnt/beta-catenin signaling in skeletal muscle cells improved insulin sensitivity by i) decreasing intramyocellular lipid deposition through downregulation of SREBP-1c; ii) increasing insulin effects through a differential activation of the Akt/PKB and AMPK pathways; iii) inhibiting the MAPK pathway. A crosstalk between these pathways and Wnt/beta-catenin signaling in skeletal muscle opens the exciting possibility that organ-selective modulation of Wnt signaling might become an attractive therapeutic target in regenerative medicine and to treat obese and diabetic populations

Characterization of organic matter in the Oligocene (Chattian) turbiditic fine grained deposits, offshore Angola

Variations in the abundance and gross composition of the organic matter (OM) content of fine grained turbiditic Chattian sediments off Angola were explored with Rock-Eval pyrolysis of 216 core samples from 4 wells. The study revealed that the OM of the sediments is immature but is present in sufficient abundance [> 1 % total organic carbon (TOC)] and with a good enough quality [hydrogen index (HI) around 185 mg hydrocarbon/g TOC on average] to constitute a potential source rock. A deeper insight into the composition of the OM was provided by the extraction and analysis of the kerogen from 15 samples. These kerogen samples were submitted to visual inspection and the counting of organic particles under the microscope (palynofacies analysis), elemental analysis and pyrolysis-gas chromatographymass spectrometry. Although individually the various observations did not provide evidence clearly diagnostic of the origin of the OM, they confirm that it has a mixed marine-terrestrial origin, a notable part of the terrestrial contribution very probably originating from leaves. The good buoyancy of the OM and its richness in lipid components might explain the spreading of terrestrial OM over a large area and its relatively good oil potential

Glycosaminoglycan mimetics trigger IP3-dependent intracellular calcium release in myoblasts.

International audienceGlycosaminoglycans (GAG) are sulfated polysaccharides that play an important role in regulating cell functions. GAG mimetics called RGTAs (for ReGeneraTing Agents) have been shown to stimulate tissue repair. In particular they accelerate myogenesis, in part via their heparin-mimetic property towards growth factors. RGTAs also increase activity of calcium-dependent intracellular protease suggesting an effect on calcium cellular homeostasis. This effect was presently investigated on myoblasts in vitro using one member of the RGTA family molecule named OTR4120. We have shown that OTR4120 or heparin induced transient increases of intracellular calcium concentration ([Ca(2+)]i) in pre-fusing myoblasts from both mouse SolD7 cell line and rat skeletal muscle satellite cells grown in primary culture by mobilising sarcoplasmic reticulum store. This [Ca(2+)]i was not mediated by ryanodine receptors but instead resulted from stimulation of the Inositol-3 phosphate-phospholipase C activation pathway. OTR4120-induced calcium transient was not mediated through an ATP, nor a tyrosine kinase, nor an acetylcholine receptor but principally through serotonin 5-HT2A receptor. This original finding shows that the GAG mimetic can induce calcium signal through serotonin receptors and the IP3 pathway may be relevant to its ability to favour myoblast differentiation. It supports a novel and unexpected function of GAGs in the regulation of calcium homeostasis

Activation of Wnt signaling in contracting myotubes.

<p>(<b>A</b>) Over-expression of Wnt10b cDNA down-regulated SREBP-1c protein. Myotubes were transfected with a plasmid encoding the mouse Wnt10b cDNA, then treated or not with 10 nM insulin for 24 hours. Western blot analysis of cytoplasmic (left panel) and nuclear (right panel) protein extracts showing the down-regulation of precursor and mature forms of SREBP-1c following the activation of the Wnt/β-catenin pathway. Wnt10b over-expression induced the nuclear accumulation of active β-catenin and MyoD. Blots were normalized using antibodies raised against the cytoplasmic protein GAPDH or the nuclear protein Lamin A/C. (<b>B</b>) Myotubes were submitted to a 48 hour-treatment with 1 µM BIO, then 10 nM insulin was added for 24 hours. BIO-mediated activation of the Wnt/β-catenin pathway induced SREBP-1c down-regulation, even in the presence of insulin.</p

Wnt10b and SREBP-1c are also inversely expressed in cultured satellite cells.

<p>(<b>A</b>) Western blot analysis showing an inverse expression pattern between Wnt10b and SREBP-1c proteins according to the differentiation stage. In contrast, Wnt3 remained almost unchanged throughout differentiation. SREBP-1c induced the up-regulation of the lipogenic enzyme FAS in myotubes. (<b>B</b>) Wnt10b knockdown was sufficient to up-regulate SREBP-1c and PPARγ mRNAs, whereas Wnt10b over-expression down-regulated their expression. RT-PCR was performed on myoblasts transfected with a scrambled siRNA (lane 1), a pool of 3 Wnt10b siRNAs (lane 2), or a plasmid encoding the mouse Wnt10 cDNA (lane 3) as described in <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0008509#s4" target="_blank">Material and Methods</a>. (<b>C</b>) SREBP-1 knockdown stimulated Wnt signaling in contracting myotubes. Myotubes were transfected with SREBP-1 siRNAs or a scrambled siRNA, then treated or not with 10 nM insulin for 24 hours. SREBP-1 knockdown was sufficient to induce Wnt10b protein expression in myotubes, particularly in the presence of insulin, and to activate the Wnt/β-catenin pathway, as shown by GSK-3β and β-catenin activities. (<b>D</b>) Wnt10b knockdown induced SREBP-1c protein expression in myoblasts. Myoblasts were transfected with 30 pmoles or 60 pmoles of a pool of 3 Wnt10b siRNAs, or with a scrambled siRNA as a control. Silencing Wnt10b was sufficient to induce SREBP-1c protein expression in myoblasts through the inhibition of Wnt/β-catenin signaling. The blots are representative of 3 independent experiments.</p

Differential expression of SREBP-1c and Wnt proteins during skeletal muscle ontogenesis and regeneration.

<p>(<b>A</b>) Western blot analysis showing inverse expression patterns between Wnt10b and SREBP-1c during ontogenesis. The developmental stages are underlined using antibodies against developmental (MyHC-Dev) and fast (MyHC-2) myosin heavy chains. (<b>B</b>) Western blot analysis of Wnt10b and SREBP-1c protein levels in regenerating (R) adult EDL muscles at 2, 8, and 30 days after crush injury as compared to contralateral control (C) EDL. The down-regulation of SREBP-1c was concomitant with the up-regulation of Wnt10b throughout regeneration. The blots are representative of 3 independent experiments.</p

Effect of BIO on intramyocellular lipid accumulation.

<p>Oil red O staining of intramyocellular lipids in myotubes cultured in 5 mM glucose (<b>A</b>) 25 mM glucose (<b>B</b>) or 25 mM glucose in the presence of 1 µM BIO for 5 days (<b>C</b>). Phase-contrast microphotographs of the same myotubes cultured in 5 mM glucose (<b>D</b>), or 25 mM glucose in the absence (<b>E</b>) or presence (<b>F</b>) of BIO. BIO totally abolished intramyocellular lipid deposition. Scale bar 20 µm.</p