Guest displacement in silicon clathrates

We study both theoretically and experimentally the structure of the doped silicon clathrate II NaxSi34. We find that contrary to published works, the sodium atoms do not retain the T-d symmetry inside the Si-28 cages and move about 1 A away from the center of the cage. This displacement, in conjunction with that of a sodium atom in an adjacent Si-28 cage, leads to a "dimerization" of sodium atoms. As a consequence, Rietveld refinements of x-ray diffraction spectra and transport, vibrational, and electronic properties must be revisited

Protein kinase C inhibitors stimulate arachidonic and docosahexaenoic acids release from uterine stromal cells through a Ca2+-independent pathway1Enzymes: Phospholipase A2 (EC 3.1.1.4).1

AbstractThe mechanisms underlying arachidonic acid (AA) release by uterine stromal (UIII) cells were studied. Stimulation of AA release by calcium ionophore and PMA are inhibited by various PKC inhibitors and by calcium deprivation. These results suggest the involvement of an AA-specific cPLA2 as the release of docosahexaenoic acid (DHA) from prelabelled cells is much lower than the release of AA. The results also show a more original stimulation of AA and DHA release induced by PKC inhibitors, which is insensitive to calcium deprivation. This stimulation is not due to acyltransferase inhibition, suggesting the participation of a Ca2+-independent PLA2 (iPLA2). However, iPLA2 activity measured in UIII cells is inhibited by the specific iPLA2 inhibitor, BEL, and is not stimulated by PKC inhibitors, in contrast with the AA and DHA release. It seems therefore that this iPLA2 cannot be involved in this mechanism. The participation of another iPLA2, BEL-insensitive, is discussed

Study of small distorsions in Bi12MO20 oxides by simple exafs transmission technics

International audienceIn some Bi12 [A+xα B+yβ]O20 sillenite type phases the interatomic distances between oxygen and A or B cations located in tetrahedral sites of the lattice can be determined by EXAFS despite difficult recording conditions due to relatively low concentrations of A and B species in presence of strong absorbing bismuth

Phospholipase D protects ECV304 cells against TNFα-induced apoptosis

AbstractTumor necrosis factor α (TNFα), a pleiotropic cytokine, activates both apoptotic and pro-survival signals depending on the cell model. Using ECV304 cells, which can be made TNFα-sensitive by cycloheximide (CHX) co-treatment, we evaluated the potential roles of ceramide and phospholipase D (PLD) in TNFα-induced apoptosis. TNFα/CHX induced a robust increase in ceramide levels after 16h of treatment when cell death was maximal. PLD activity was increased at early time point (1h) whereas both PLD activity and PLD1 protein were strongly decreased after 24h. TNFα/CHX-induced cell death was significantly lowered by exogenous bacterial PLD and phoshatidic acid, and in cells overexpressing PLD1. Conversely, cells depleted in PLD proteins by small interference RNA (siRNA) treatment exhibited higher susceptibility to apoptosis. These results show that PLD exerts a protective role against TNFα-induced cell death

The cAMP-specific Phosphodiesterase PDE4D3 Is Regulated by Phosphatidic Acid Binding CONSEQUENCES FOR cAMP SIGNALING PATHWAY AND CHARACTERIZATION OF A PHOSPHATIDIC ACID BINDING SITE

Hormones and growth factors induce in many cell types the production of phosphatidic acid (PA), which has been proposed to play a role as a second messenger. We have previously shown in an acellular system that PA selectively stimulates certain isoforms of type 4 cAMP-phosphodiesterases (PDE4). Here we studied the effect of endogenous PA on PDE activity of transiently transfected MA10 cells overexpressing the PA-sensitive isoform PDE4D3. Cell treatment with inhibitors of PA degradation, including propranolol, induced an accumulation of endogenous PA accompanied by a stimulation of PDE activity and a significant decrease in both cAMP levels and protein kinase A activity. Furthermore, in FRTL5 cells, which natively express PDE4D3, pretreatment with compounds inducing PA accumulation prevented both cAMP increase and cAMP-responsive element-binding protein phosphorylation triggered by thyroid-stimulating hormone. To determine the mechanism of PDE stimulation by PA, endogenous phospholipids were labeled by preincubating MA10 cells overexpressing PDE4D3 with [(32)P]orthophosphate. Immuno- precipitation experiments showed that PA was specifically bound to PDE4D3, supporting the hypothesis that PDE4D3 activation occurs through direct binding of PA to the protein. PA binding site on PDE4D3 was characterized by engineering deletions of selected regions in the N-terminal regulatory domain of the enzyme. Deletion of amino acid residues 31-59 suppressed both PA-activating effect and PA binding, suggesting that this region rich in basic and hydrophobic residues contains the PA binding site. These observations strongly suggest that endogenous PA can modulate cAMP levels in intact cells, through a direct activation of PDE4D3

Can the Mangombe forest plantation contribute to restore and conserve biodiversity?

This research, conducted in the tropical rainforest, is focused on restoration of tree diversity through natural regeneration mechanism in the 49 year-old Mangombe forest plantation. 12 plots were surveyed, 6 with large transects and the 6 others under regrowth. In each plot, two subplots with 400 m² each were demarcated for the inventory of all stems with diameter greater than 2.5 cm. A total of 2239 stems comprising 107 species distributed in 93 genera and 42 families were identified over 9600 m². There was a slight difference between species richness of plots with large transect (79 species, 72 genera and 35 families) and regrowth plots (85 species, 76 genera and 38 families) while the basal area in the plots with large transects (10.76 m²/ha) was significantly greater than that of regrowth (8.65 m²/ha). Species with high important value index have an affinity with forest undergrowth such as: Tabernaemontana pachysiphon, T. crassa, Mallotus oppositifolius and Heinsia crinita. The undergrowth is diversified with different life feature and a high number of small size trees indicating a vigorous regeneration. This can be favoured by: microclimate undergrowth, canopy gaps, abundance of litter fall that brings humus to the soil, type and age of plots, planted species and the complexity of spatial and vertical structure of the stand.© 2016 International Formulae Group. All rights reserved.Keywords: Mangombé – Cameroon, Natural regeneration, dense humid forest, tree plantation, biodiversit

Models of red giants in the CoRoT asteroseismology fields combining asteroseismic and spectroscopic constraints

Context. The availability of asteroseismic constraints for a large sample of red giant stars from the CoRoT and Kepler missions paves the way for various statistical studies of the seismic properties of stellar populations. Aims. We use the first detailed spectroscopic study of 19 CoRoT red-giant stars (Morel et al 2014) to compare theoretical stellar evolution models to observations of the open cluster NGC 6633 and field stars. Methods. In order to explore the effects of rotation-induced mixing and thermohaline instability, we compare surface abundances of carbon isotopic ratio and lithium with stellar evolution predictions. These chemicals are sensitive to extra-mixing on the red-giant branch. Results. We estimate mass, radius, and distance for each star using the seismic constraints. We note that the Hipparcos and seismic distances are different. However, the uncertainties are such that this may not be significant. Although the seismic distances for the cluster members are self consistent they are somewhat larger than the Hipparcos distance. This is an issue that should be considered elsewhere. Models including thermohaline instability and rotation-induced mixing, together with the seismically determined masses can explain the chemical properties of red-giants targets. However, with this sample of stars we cannot perform stringent tests of the current stellar models. Tighter constraints on the physics of the models would require the measurement of the core and surface rotation rates, and of the period spacing of gravity-dominated mixed modes. A larger number of stars with longer times series, as provided by Kepler or expected with Plato, would help for ensemble asteroseismology.Comment: Accepted 03/05/201

The Mechanism of Docosahexaenoic Acid-induced Phospholipase D Activation in Human Lymphocytes Involves Exclusion of the Enzyme from Lipid Rafts

Docosahexaenoic acid (DHA), an n-3 polyunsaturated fatty acid that inhibits T lymphocyte activation, has been shown to stimulate phospholipase D (PLD) activity in stimulated human peripheral blood mononuclear cells (PBMC). To elucidate the mechanisms underlying the DHA-induced PLD activation, we first characterized the PLD expression pattern of PBMC. We show that these cells express PLD1 and PLD2 at the protein and mRNA level and are devoid of oleate-dependent PLD activity. DHA enrichment of PBMC increased the DHA content of cell phospholipids, which was directly correlated with the extent of PLD activation. The DHA-induced PLD activation was independent of conventional protein kinase C but inhibited by brefeldin A, which suggests ADP-ribosylation factor (ARF)-dependent mechanism. Furthermore, DHA enrichment dose-dependently stimulated ARF translocation to cell membranes. Whereas 50% of the guanosine 5'-3-O-(thio)triphosphate plus ARF-dependent PLD activity and a substantial part of PLD1 protein were located to the detergent-insoluble membranes, so-called rafts, of non-enriched PBMC, DHA treatment strongly displaced them toward detergent-soluble membranes where ARF is present. Collectively, these results suggest that the exclusion of PLD1 from lipid rafts, due to their partial disorganization by DHA, and its relocalization in the vicinity of ARF, is responsible for its activation. This PLD activation might be responsible for the immunosuppressive effect of DHA because it is known to transmit antiproliferative signals in lymphoid cells

Docosahexaenoic acid-containing choline phospholipid modulates LPS-induced neuroinflammation in vivo and in microglia in vitro

BACKGROUND: Neuroinflammatory processes are considered a double-edged sword, having both protective and detrimental effects in the brain. Microglia, the brain's resident innate immune cells, are a key component of neuroinflammatory response. There is a growing interest in developing drugs to target microglia and control neuroinflammatory processes. In this regard, docosahexaenoic acid (DHA), the brain's n-3 polyunsaturated fatty acid, is a promising molecule to regulate pro-inflammatory microglia and cytokine production. Several works reported that the bioavailability of DHA to the brain is higher when DHA is acylated to phospholipid. In this work, we analyzed the anti-inflammatory activity of DHA-phospholipid, either acetylated at the sn-1 position (AceDoPC, a stable form thought to have superior access to the brain) or acylated with palmitic acid at the sn-1 position (PC-DHA) using a lipopolysaccharide (LPS)-induced neuroinflammation model both in vitro and in vivo. METHODS: In vivo, adult C57Bl6/J mice were injected intravenously (i.v.) with either AceDoPC or PC-DHA 24 h prior to LPS (i.p.). For in vitro studies, immortalized murine microglia cells BV-2 were co-incubated with DHA forms and LPS. AceDoPC and PC-DHA effect on brain or BV-2 PUFA content was assessed by gas chromatography. LPS-induced pro-inflammatory cytokines interleukin IL-1β, IL-6, and tumor necrosis factor (TNF) α production were measured by quantitative PCR (qPCR) or multiplex. IL-6 receptors and associated signaling pathway STAT3 were assessed by FACS analysis and western-blot in vitro. RESULTS: In vivo, a single injection of AceDoPC or PC-DHA decreased LPS-induced IL-6 production in the hippocampus of mice. This effect could be linked to their direct effect on microglia, as revealed in vitro. In addition, AceDoPC or PC-DHA reduced IL-6 receptor while only AceDoPC decreased IL-6-induced STAT3 phosphorylation. CONCLUSIONS: These results highlight the potency of administered DHA-acetylated to phospholipids-to rapidly regulate LPS-induced neuroinflammatory processes through their effect on microglia. In particular, both IL-6 production and signaling are targeted by AceDoPC in microglia.Metabolism in human of a structured phospholipid from marine origin and neural effec