Éditeur(s) : HAL CCSD Wiley
Résumé : International audience
The easy-to-use in vivo model, zebrafish larva, is being increasingly used to screen chemical-induced hepatotoxicity, with a good predictivity for various mechanisms of liver injury. However, nothing is known about its applicability in exploring the mechanism called membrane remodeling, depicted as changes in membrane fluidity or lipid raft properties. The aim of this study was, therefore, to substantiate the zebrafish larva as a suitable in vivo model in this context. Ethanol was chosen as a prototype toxicant because it is largely described, both in hepatocyte cultures and in rodents, as capable of inducing a membrane remodeling leading to hepatocyte death and liver injury. The zebrafish larva model was demonstrated to be fully relevant as membrane remodeling was maintained even after a 1-week exposure without any adaptation as usually reported in rodents and hepatocyte cultures. It was also proven to exhibit a high sensitivity as it discriminated various levels of cytotoxicity depending on the extent of changes in membrane remodeling. In this context, its sensitivity appeared higher than that of WIF-B9 hepatic cells, which is suited for analyzing this kind of hepatotoxicity. Finally, the protection afforded by a membrane stabilizer, ursodeoxycholic acid (UDCA), or by a lipid raft disrupter, pravastatin, definitely validated zebrafish larva as a reliable model to quickly assess membrane remodeling involvement in chemical-induced hepatotoxicity. In conclusion, this model, compatible with a high throughput screening, might be adapted to seek hepatotoxicants via membrane remodeling, and also drugs targeting membrane features to propose new preventive or therapeutic strategies in chemical-induced liver diseases.
ISSN: 0260-437X

hal-01526425
https://hal-univ-rennes1.archives-ouvertes.fr/hal-01526425
https://hal-univ-rennes1.archives-ouvertes.fr/hal-01526425/document
https://hal-univ-rennes1.archives-ouvertes.fr/hal-01526425/file/Zebrafish%20larva%20as%20a%20reliable%20model-Podechard%20JAT%202016%20revised.pdf
DOI : 10.1002/jat.3421

Éditeur(s) : HAL CCSD Humana Press
Résumé : International audience
The sodium-proton exchanger 1 (NHE-1) is a membrane transporter that exchanges Na(+) for H(+) ion across the membrane of eukaryotic cells. It is cooperatively activated by intracellular protons, and this allosteric regulation is modulated by the biophysical properties of the plasma membrane and related lipid environment. Consequently, NHE-1 is a mechanosensitive transporter that responds to osmotic pressure, and changes in membrane composition. The purpose of this study was to develop the relationship between membrane surface tension, and the allosteric balance of a mechanosensitive transporter such as NHE-1. In eukaryotes, the asymmetric composition of membrane leaflets results in a difference in surface tensions that is involved in the creation of a reservoir of intracellular vesicles and membrane buds contributing to buffer mechanical constraints. Therefore, we took this phenomenon into account in this study and developed a set of relations between the mean surface tension, membrane asymmetry, fluid phase endocytosis and the allosteric equilibrium constant of the transporter. We then used the experimental data published on the effects of osmotic pressure and membrane modification on the NHE-1 allosteric constant to fit these equations. We show here that NHE-1 mechanosensitivity is more based on its high sensitivity towards the asymmetry between the bilayer leaflets compared to mean global membrane tension. This compliance to membrane asymmetry is physiologically relevant as with their slower transport rates than ion channels, transporters cannot respond as high pressure-high conductance fast-gating emergency valves.
ISSN: 1085-9195

inserm-00871709
http://www.hal.inserm.fr/inserm-00871709
http://www.hal.inserm.fr/inserm-00871709/document
http://www.hal.inserm.fr/inserm-00871709/file/art_3A10.1007_2Fs12013-012-9340-7.pdf
DOI : 10.1007/s12013-012-9340-7

Éditeur(s) : HAL CCSD
Résumé : International audience
Objective Oxidative stress, excess production of reactive oxygen species (ROS) and intense colonization of the respiratory tract by microorganisms are described in CF patients, leading to an influx in macrophages. This results in activation of NADPH oxidase that yields ROS, initiating the oxidative burst responsible for pathogen destruction. We showed that phagocytosis was altered in CF macrophages, yet oxidative status in this cell was not defined. The objective of this study is to draw a link between oxidative stress and plasma membrane integrity in CF macrophages, since lipid peroxidation is known to alter cell membrane. Methods Peripheral blood monocytes-derived macrophages were obtained from CF patients and healthy subjects. Plasma membrane fluidity was assessed with di4-ANEPPDHQ and oxidative status was measured with ROS indicating probes. Results In CF macrophages, membrane fluidity was increased whereas lipid peroxidation was diminished. Surprisingly, general oxidative status remained similar to the one observed in non-CF macrophages. Also, CF macrophages did not abolish chemically induced-oxidative stress. In non-CF macrophages, treatment with cholesterol slightly increased membrane fluidity whereas LPS treatment had no effect. Conclusion CF macrophages displayed an increased membrane fluidity associated with a decreased lipid peroxidation. This raises the hypothesis that membrane alteration in CF macrophages may be due to other mechanism than oxidative stress. Nevertheless, since the killing capacity of CF macrophage is defective, a deregulation of O•−2 production is very likely, suggesting alteration of NADPH oxidase or mitochondrial dysfunction
the 38th European Cystic Fibrosis Conference
Vienne, Austria

hal-01162769
https://hal-univ-rennes1.archives-ouvertes.fr/hal-01162769
DOI : 10.1016/S1569-1993(15)30217-4

Éditeur(s) : HAL CCSD Elsevier
Résumé : International audience
Recently it has become clear that exposure to xenobiotics may result in various forms of cell death; not only passive cell deaths like necrosis, or programmed cell deaths such as apoptosis, but also regulated necrosis, autophagy, senescence, or mitotic catastrophe. Complex cell signaling networks influence the processing of cell death. Furthermore, recent research has revealed early complex molecular interactions between organelles prior to the final triggering of cell death. The plasma membrane may play an important role in the early cell death signaling events. Regarding this latter aspect, drugs and environmental pollutants have been reported to affect plasma membrane characteristics which may further affect cell fate. Changes in membrane fluidity or in composition and function of specialized membrane microdomains (plasma membrane remodeling) have been proven to be involved in the regulation of many important physiological signaling pathways, including cell death. Furthermore, it has been suggested that a crosstalk between chemical-induced cellular membrane effects and other organelles may be of vital importance to explain the final outcome of chemical exposure. Here, we review the effects of plasma membrane remodeling on cell survival and cell death; we describe how the cell signaling pathways activated by changes in plasma membrane characteristics may influence cell fate. Since plasma membrane function plays an important role in the regulation of a number of cellular responses, it has been implicated in the development or progress of several diseases. A better knowledge of the effects of various chemicals on plasma membrane remodeling may be important for understanding the pathogenesis of major diseases, and may assist in developing new therapeutic strategies.
ISSN: 0300-483X

inserm-00818916
http://www.hal.inserm.fr/inserm-00818916
DOI : 10.1016/j.tox.2012.12.014
PUBMED : 23287390

Éditeur(s) : HAL CCSD Elsevier
Résumé : International audience
Several epidemiologic studies have shown an interactive effect of heavy smoking and heavy alcohol drinking on the development of hepatocellular carcinoma. It has also been recently described that chronic hepatocyte death can trigger excessive compensatory proliferation resulting later in the formation of tumors in mouse liver. As we previously demonstrated that both benzo[a]pyrene (B[a]P), an environmental agent found in cigarette smoke, and ethanol possess similar targets, especially oxidative stress, to trigger death of liver cells, we decided to study here the cellular and molecular mechanisms of the effects of B[a]P/ethanol coexposure on cell death. After an 18-h incubation with 100nM B[a]P, primary rat hepatocytes were supplemented with 50mM ethanol for 5 or 8h. B[a]P/ethanol coexposure led to a greater apoptotic cell death that could be linked to an increase in lipid peroxidation. Plasma membrane remodeling, as depicted by membrane fluidity elevation and physicochemical alterations in lipid rafts, appeared to play a key role, because both toxicants acted with specific complementary effects. Membrane remodeling was shown to induce an accumulation of lysosomes leading to an important increase in low-molecular-weight iron cellular content. Finally, ethanol metabolism, but not that of B[a]P, by providing reactive oxygen species, induced the ultimate toxic process. Indeed, in lysosomes, ethanol promoted the Fenton reaction, lipid peroxidation, and membrane permeabilization, thereby triggering cell death. To conclude, B[a]P exposure, by depleting hepatocyte membrane cholesterol content, would constitute a favorable ground for a later toxic insult such as ethanol intoxication. Membrane stabilization of both plasma membrane and lysosomes might be a potential target for further investigation considering cytoprotective strategies.
ISSN: 0891-5849

hal-01018147
https://hal-univ-rennes1.archives-ouvertes.fr/hal-01018147
https://hal-univ-rennes1.archives-ouvertes.fr/hal-01018147/document
https://hal-univ-rennes1.archives-ouvertes.fr/hal-01018147/file/Cooperative-interaction_final.pdf
PUBMED : 24681337

Éditeur(s) : HAL CCSD American Society for Microbiology
Résumé : International audience
: We investigated the in vitro effects of four alkyl-galactofuranoside derivatives, i.e. octyl-β-D-galactofuranoside (1), 6-amino-β-D-galactofuranoside (2), 6-N-acetamido-β-D-galactofuranoside (3), and 6-azido-β-D-galactofuranoside (4) on Leishmania donovani. Their mechanism of action was explored using electron paramagnetic resonance spectroscopy (EPR) and nuclear magnetic resonance (NMR), and ultrastructural alterations by transmission electron microscopy (TEM). Compound 1 showed the most promising effects by inhibiting promastigote growth at IC50 8.96 ± 2.5 μM. All compounds exhibit low toxicity towards human macrophages. Compound 1 had a higher selectivity index than the comparative molecule used, i.e. miltefosine (159.7 versus 37.9, respectively). EPR showed that compound 1 significantly reduced membrane fluidity, compared to control promastigotes and to compound 3. The furanose ring was shown to support this effect since the isomer galactopyranose had no effect on parasite membrane fluidity or growth. NMR showed a direct interaction of all compounds (1>2>3>4) with the promastigote membrane, as well as with octyl-galactopyranose and octanol, providing evidence that the n-octyl chain was primarily involved in the anchoring with the parasite membrane, followed by the putative crucial role of furanose ring in the anti-leishmanial activity. A morphologic analysis of compound 1-treated promastigotes by TEM revealed profound alterations on parasite membrane and organelles, but not with compound 3. Quantification of annexinV binding by flow cytometry confirmed that compound 1 induced apoptosis in >90% promastigotes. The effect of compound 1 was also assessed on intra-macrophagic amastigotes, and showed a reduction in amastigote growth associated with an increase of ROS production, thus validating its promising effect.
ISSN: 0066-4804

hal-00941772
https://hal.archives-ouvertes.fr/hal-00941772
PUBMED : 24468785
DOI : 10.1128/AAC.01350-13

Éditeur(s) : HAL CCSD Elsevier
Résumé : International audience
: Previously, we demonstrated that eicosapentaenoic acid enhanced ethanol-induced oxidative stress and cell death in primary rat hepatocytes via an increase in membrane fluidity and lipid raft clustering. In this context, another n-3 polyunsaturated fatty acid, docosahexaenoic acid (DHA), was tested with a special emphasis on physical and chemical alteration of lipid rafts. Pretreatment of hepatocytes with DHA reduced significantly ethanol-induced oxidative stress and cell death. DHA protection could be related to an alteration of lipid rafts. Indeed, rafts exhibited a marked increase in membrane fluidity and packing defects leading to the exclusion of a raft protein marker, flotillin. Furthermore, DHA strongly inhibited disulfide bridge formation, even in control cells, thus suggesting a disruption of protein-protein interactions inside lipid rafts. This particular spatial organization of lipid rafts due to DHA subsequently prevented the ethanol-induced lipid raft clustering. Such a prevention was then responsible for the inhibition of phospholipase C-γ translocation into rafts, and consequently of both lysosome accumulation and elevation in cellular low-molecular-weight iron content, a prooxidant factor. In total, the present study suggests that DHA supplementation could represent a new preventive approach for patients with alcoholic liver disease based upon modulation of the membrane structures.
ISSN: 0278-6915

hal-00860153
https://hal-univ-rennes1.archives-ouvertes.fr/hal-00860153
https://hal-univ-rennes1.archives-ouvertes.fr/hal-00860153/document
https://hal-univ-rennes1.archives-ouvertes.fr/hal-00860153/file/Sergent-et-al-incl-figures-accepted.pdf
DOI : 10.1016/j.fct.2013.07.061

Éditeur(s) : HAL CCSD Nature Publishing Group
Résumé : International audience
Epithelial-to-mesenchymal transition (EMT) promotes cell motility, which is important for the metastasis of malignant cells, and blocks CD95-mediated apoptotic signaling triggered by immune cells and chemotherapeutic regimens. CD95L, the cognate ligand of CD95, can be cleaved by metalloproteases and released as a soluble molecule (cl-CD95L). Unlike transmembrane CD95L, cl-CD95L does not induce apoptosis but triggers cell motility. Electron paramagnetic resonance was used to show that EMT and cl-CD95L treatment both led to augmentation of plasma membrane fluidity that was instrumental in inducing cell migration. Compaction of the plasma membrane is modulated, among other factors, by the ratio of certain lipids such as sphingolipids in the membrane. An integrative analysis of gene expression in NCI tumor cell lines revealed that expression of ceramide synthase-6 (CerS6) decreased during EMT. Furthermore, pharmacological and genetic approaches established that modulation of CerS6 expression/activity in cancer cells altered the level of C16-ceramide, which in turn influenced plasma membrane fluidity and cell motility. Therefore, this study identifies CerS6 as a novel EMT-regulated gene that has a pivotal role in the regulation of cell migration.Oncogene advance online publication, 17 March 2014; doi:10.1038/onc.2014.55.
ISSN: 0950-9232

hal-01063558
https://hal.archives-ouvertes.fr/hal-01063558
https://hal.archives-ouvertes.fr/hal-01063558/file/Down-regulation%20of%20ceramide_accepted.pdf
DOI : 10.1038/onc.2014.55
PUBMED : 24632610

Éditeur(s) : HAL CCSD Elsevier Masson
Résumé : On the basis of an existing multiparameter borehole fluid sensor(p, T Cw, pH, Eh), a new downhole tool designed for 200 bars and 75 degrees C was developed to measure the spontaneous electrical potential in situ with great precision (better than a mu V). To this end, the new sensor is based on the use of unpolarizable Pb/PbCl2 electrodes either at the surface or downhole. In situ testing has demonstrated a capacity to identify several subsurface sources of natural electrical potential such as diffusion ones (membrane potential in the presence of clays, Fickian processes due to pore fluid salinity gradients), or else the electrokinetic mechanisms with gradients in pore fluid pressure. As a consequence, Multi-Sensors Electrical Tool (MuSET) might be used as an "electrical flow meter" sensitive to both horizontal and vertical fluid flow in a vertical borehole.
ISSN: 1631-0713

hal-00445251
https://hal.archives-ouvertes.fr/hal-00445251
DOI : 10.1016/j.crte.2009.07.009

Éditeur(s) : HAL CCSD American Association of Petroleum Geologists
Résumé : International audience
Determination of the membrane seal capacity of deformation bands is critical for managing geologic reservoirs in porous sandstones. In this study, we have analyzed a cataclastic shear-band network developed in uncemented porous sandstone in Provence, France. Geometrical analyses of the bands show significant differences between three types of bands (single strand, multistrand, and band cluster), sorted by their number of strands, their amount of shear displacement, and their thicknesses. At the microscopic scale, the image-analysis porosities and the grain-size distributions allow definition of three different types of microstructural deformation: damage zone, protocataclastic, and cataclastic. Whereas damage zone and protocataclastic deformations are observed in each type of band, cataclastic strands are observed in clusters and, sometimes, in multistrands. Cataclastic strands are characterized by a porosity reduction of 10 to 25% and a permeability reduction of three to five orders of magnitude compared to the host rock. Field observations of iron hydroxide precipitations around the bands suggest that cataclastic strands were membrane seals to water flow under vadose condition. This study therefore highlights the importance of the degree of cataclasis in shear bands as membrane seals to subsurface fluid flows in sandstone reservoirs.
ISSN: 0149-1423

hal-00766557
https://hal.archives-ouvertes.fr/hal-00766557
DOI : 10.1306/04051211097

Éditeur(s) : HAL CCSD
Résumé : The ecological success of cnidarian-dinoflagellate symbiosis mainly relies on nutrient recycling. Environmental changes, such as global warming or pollution, often result to symbiosis breakdown, also called cnidarian bleaching. The understanding of mechanisms regulating the symbiosis establishment, maintenance and breakdown is essential to prevent massive bleaching phenomena. In this respect, my PhD project focused on the characterization of chemical mediators expressed in the sea anemone Anemonia viridis, their localization and their modulation by stress conditions. A comparative study was first conducted to characterize the chemical mediators and analyze their distribution within the symbiotic sea anemone. We described a great abundance and diversity of lipids in A. viridis tissues. From these results, we proposed possible transfers of FAs between the symbiotic partners. A thermal stress and a chemical stress have also been applied in laboratory-controlled conditions in order to induce symbiosis breakdown and bleaching of the sea anemones, in order to correlate A. viridis metabolome to its symbiotic status. A mapping of these metabolites has been performed by MALDI-MSI of tentacle cross-sections, as well as their evolution following stress. Some betaine lipids have thus been proposed as short-term indicators of stress. A. viridis stress response has also been evaluated with a lipidomic approach, and allowed to identify 3 lipid indicators of early stress response based on membrane fluidity markers. Overall, this study provides insight on key chemical mediators that may regulate the symbiosis maintenance, and may contribute to the symbiosis breakdown.
Le succès évolutif des Cnidaires symbiotiques réside en grande partie dans leurs échanges trophiques établis avec les Dinoflagellés du genre Symbiodinium. Cependant, le réchauffement climatique global ainsi que les pollutions ont un impact fort sur les écosystèmes coralliens, notamment en conduisant à la rupture de la symbiose, phénomène appelé blanchissement. La compréhension des mécanismes qui régissent l’établissement, le maintien et la rupture de la symbiose est essentielle à la prévention des épisodes de blanchissement massif. Dans ce contexte, les objectifs de mon projet de thèse sont de caractériser les médiateurs chimiques de l’anémone de mer Anemonia viridis, de les localiser, et d’analyser leur réponse face à un stress. Parmi les composés caractérisés, les lipides et les bétaïnes sont les plus abondants et présentent une grande diversité. Certains sont transférés des symbiotes vers l’hôte. Des anémones de mer ont ensuite été traitées en laboratoire afin de provoquer la rupture de la symbiose et le blanchissement des individus. Une étude cinétique a été menée par une approche globale comparative identique à celle réalisée sur l’anémone symbiotique. Par ailleurs, une cartographie de l’évolution de composés clé a été réalisée par MALDI-MSI. La réponse au stress a été évaluée et a permis d’identifier des lipides de bétaïne et trois indicateurs lipidiques comme marqueurs de réponse précoce au stress. L’ensemble de ces résultats apporte de nouveaux éléments de réponse concernant le rôle des médiateurs chimiques clés dans le maintien de la symbiose, ainsi que leur influence sur sa rupture.
https://tel.archives-ouvertes.fr/tel-01310668

NNT : 2015NICE4108
tel-01310668
https://tel.archives-ouvertes.fr/tel-01310668
https://tel.archives-ouvertes.fr/tel-01310668/document
https://tel.archives-ouvertes.fr/tel-01310668/file/2015NICE4108.pdf

Éditeur(s) : HAL CCSD Geological Society of America
Résumé : International audience
Porous sandstones tend to deform by the formation of low-permeability deformation bands that influence fluid flow in reservoir settings. The bands may be distributed or localized into clusters, and limited recent data suggest that tectonic regime may exert control on their distribution and clustering. In order to explore this suggestion, we performed a synthetic analysis based of 73 sets of bands, including 22 new sets measured for a reverse Andersonian regime that fill the important gap in data for this context. We find a surprisingly strong correlation between clustering and tectonic regime, where bands clearly are more distributed in the reverse regime compared to the normal regime. Together with the observed band distributions, capillary pressure data show evidence that efficient membrane seals are expected for extension, whereas pervasive permeability anisotropy is expected for contraction. Such a basic new rule concerning tectonic regime is very useful for assessment of reservoir properties where deformation bands are common but below seismic resolution.
ISSN: 0091-7613

hal-01355925
https://hal.archives-ouvertes.fr/hal-01355925
DOI : 10.1130/G37585.1