Softening of POPC membranes by magainin

International audienc

Sustained increase of alpha7 nicotinic receptors and choline-induced improvement of learning deficit in STOP knock-out mice.

International audienceMice deficient in the microtubule stabilizing protein STOP (stable tubule only polypeptide) show synaptic plasticity anomalies in hippocampus, dopamine hyper-reactivity in the limbic system and severe behavioral deficits. Some of these disturbances are alleviated by long-term antipsychotic treatment. Therefore, this mouse line represents a pertinent model for some aspects of schizophrenia symptomatology. Numerous data support dysfunction of nicotinic neurotransmission in schizophrenia and epidemiological studies show increased tobacco use in schizophrenic patients, in whom nicotine has been reported to improve cognitive deficits and impairment in sensory gating. In this study, we examined potential alterations in cholinergic (ACh) and nicotinic components and functions in STOP mutant mice. STOP KO mice displayed no variation of the density of ACh esterase and beta2* nicotinic receptors (nAChRs), large reductions in the density of vesicular ACh transporter and alpha6* nAChRs and marked increases in the density of alpha7 nAChRs, in some brain areas. STOP KO mice were hypersensitive to the stimulating locomotor effect of nicotine and, interestingly, their impaired performance in learning the cued version of the water maze were improved by administration of the preferential alpha7 nAChR agonist choline. Altogether, our data show that the deletion of the ubiquitous STOP protein elicited restricted alterations in ACh components. They also suggest that nicotinic neurotransmission can be deficient in STOP KO mice and that mutant mice can represent a meaningful model to study some nicotinic dysfunctions and therapeutic treatments

Microtubule-associated STOP protein deletion triggers restricted changes in dopaminergic neurotransmission.: Accumbic DA system in STOP KO mice

International audienceThe microtubule-associated stable tubule only polypeptide (STOP) protein plays a key-role in neuron architecture and synaptic plasticity. Recent studies suggest that schizophrenia is associated with alterations in the synaptic connectivity. Mice invalidated for the STOP gene display phenotype reminiscent of some schizophrenic-like symptoms, such as behavioral disturbances, dopamine (DA) hyper-reactivity, and possible hypoglutamatergia, partly improved by antipsychotic treatment. In the present work, we examined potential alterations in some DAergic key proteins and behaviors in STOP knockout mice. Whereas the densities of the DA transporter, the vesicular monoamine transporter and the D(1) receptor were not modified, the densities of the D(2) and D(3) receptors were decreased in some DAergic regions in mutant versus wild-type mice. Endogenous DA levels were selectively decreased in DAergic terminals areas, although the in vivo DA synthesis was diminished both in cell bodies and terminal areas. The DA uptake was decreased in accumbic synaptosomes, but not significantly altered in striatal synaptosomes. Finally, STOP knockout mice were hypersensitive to acute and subchronic locomotor effects of cocaine, although the drug equally inhibited DA uptake in mutant and wild-type mice. Altogether, these data showed that deletion of the ubiquitous STOP protein elicited restricted alterations in DAergic neurotransmission, preferentially in the meso-limbic pathway

N-(Di)icosyl-substituted benzo[a]phenoxazinium chlorides : synthesis and evaluation as near-infrared membrane probes

Five benzo[a]phenoxazinium chlorides containing alkyl chains with twenty carbon atoms on 5- or 9-positions of the tetracyclic ring were efficiently synthesised and characterised by UV/Vis/NIR spectroscopy. The absorption and emission maxima in ethanol lie in the range 627-641 nm and 645-676 nm, respectively, with quantum yields varying from 0.14 to 0.38. Preliminary photophysical studies with these fluorochromophores in zwitterionic (2,3- bis(palmitoyl-oxy)propyl-2-(trimethylammonio)ethyl phosphate, DPPC) and cationic (N,N-dimethyl-N-octadecyloctadecan-1-aminium bromide, DODAB) vesicles were carried out. The results showed that the new benzo[a]phenoxazinium derivatives are able to detect the gel to liquid-crystalline lipid phase transition through variations, either in the H-aggregation extent or in an acid-base equilibrium.Fundação para a Ciência e Tecnologia (FCT) - REDE/1517/RMN/2005Fundo Europeu de Desenvolvimento Regional (FEDER) - POCI 201

Loss of STOP Protein Impairs Peripheral Olfactory Neurogenesis

International audienceIn conclusion, STOP protein seems to be involved in the establishment of synapses in the olfactory glomerulus. Our results indicate that the olfactory system of STOP null mice is a well-suited experimental model (1) for the study of the mechanism of action of STOP protein in synaptic function/plasticity and (2) for pathophysiological studies of the mechanisms of altered neuronal connections in schizophrenia

Ions modulate stress-induced nano-texture in supported fluid lipid bilayers.

Most plasma membranes comprise a large number of different molecules including lipids and proteins. In the standard fluid mosaic model, the membrane function is effected by proteins whereas lipids are largely passive and serve solely in the membrane cohesion. Here we show, using supported 1,2-dioleoyl-sn-glycero-3-phosphocholine lipid bilayers in different saline solutions, that ions can locally induce ordering of the lipid molecules within the otherwise fluid bilayer when the latter is supported. This nanoordering exhibits a characteristic length scale of ∼20 nm, and manifests itself clearly when mechanical stress is applied to the membrane. Atomic force microscopy (AFM) measurements in aqueous solutions containing NaCl, KCl, CaCl2, and Tris buffer show that the magnitude of the effect is strongly ion-specific, with Ca2+ and Tris, respectively, promoting and reducing stress-induced nanotexturing of the membrane. The AFM results are complemented by fluorescence recovery after photobleaching experiments, which reveal an inverse correlation between the tendency for molecular nanoordering and the diffusion coefficient within the bilayer. Control AFM experiments on other lipids and at different temperatures support the hypothesis that the nanotexturing is induced by reversible, localized gel-like solidification of the membrane. These results suggest that supported fluid phospholipid bilayers are not homogenous at the nanoscale, but specific ions are able to locally alter molecular organization and mobility, and spatially modulate the membrane’s properties on a length scale of ∼20 nm. To illustrate this point, AFM was used to follow the adsorption of the membrane-penetrating antimicrobial peptide Temporin L in different solutions. The results confirm that the peptides do not absorb randomly, but follow the ion-induced spatial modulation of the membrane. Our results suggest that ionic effects have a significant impact for passively modulating the local properties of biological membranes, when in contact with a support such as the cytoskeleton

Asthme et environnement intérieur : intérêt des méthodes d'éviction globale sur l'exposition domiciliaire au risque fongique et sur le contrôle de l'asthme

RENNES1-BU Santé (352382103) / SudocSudocFranceF

Propriétés mécaniques de vésicules géantes fluctuantes

Les vésicules géantes sont un modèle des membranes biologiques souvent utilisées pour des études biophysiques, notamment pour étudier les propriétés mécaniques des bicouches lipidiques. Des développements ont été effectués sur le plan théorique avec la mise en place d'une analyse statistique des fluctuations membranaires permettant d'obtenir un module d'élasticité de courbure plus précis, et au niveau méthodologique avec l'amélioration de la méthode d'électroformation permettant de former des vésicules géantes à partir de différents types de liposomes ou protéoliposomes et de plus dans des conditions relevantes physiologiquement. Une première caractérisation des propriétés mécaniques de vésicules géantes dans des conditions physiologiques a été effectuée en étudiant la magainine. Sa présence conduit à un assouplissement de la bicouche par formation localement de régions à forte courbure à sa surface. Les mesures de l'élasticité de courbure peuvent aussi servir d'outil analytique capable de détecter des dégradations membranaires, comme illustré par l'étude de l'impact de différents fluorophores amphiphiles.L'étude des sels de sodium suggère une forte dépendance des propriétés mécaniques des bicouches de POPC avec la composition du solvant et démontre que la rigidité de courbure fait partie des paramètres qui sont perturbés par les solutions salines selon la série d'Hofmeister. Finalement les effets de l'activité de la pompe à sodium-potassium sur les fluctuations membranaires ont été étudiés. Une amplification des fluctuations de la membrane est observée, ce qui se reflète par une forte diminution de la rigidité de courbure. De plus, deux comportements différents des membranes actives semblent être discriminés : un état de pseudo-équilibre et un état très éloigné de l'équilibre .The giant vesicles are a model of biological membranes often used in biophysical studies, for instance to investigate the mechanical properties of lipid bilayers. Improvements have been performed theoretically by use of a statistical analysis of the membrane fluctuations allowing to obtain a bending rigidity which is more precise, and regarding the electroformation method that allows now to form giant vesicles from different types of liposomes and proteoliposomes and furthermore under physiologically relevant conditions. A first characterization of the mechanical properties of GUVs under physiological buffer conditions has been presented with the magainin study. Magainin molecules induce a softening of the lipid bilayer by formation of local regions of high curvature on the membrane surface. The measurements of the bending rigidity can also be considered as an analytical tool enabling to detect membranes degradation, as illustrated by the study of the impact of different amphiphilic fluorophores. The study of sodium salts effects suggest a strong dependence of the mechanical properties of POPC bilayers on the solvent composition and demonstrates that the bending rigidity falls into the category of phenomena, which are perturbed by salt solutions according to the Hofmeister series. Finally the activity effects of the sodium-potassium pump on the membrane fluctuations have been studied. An enhancement of the membrane fluctuations is observed, as suggested by the major decrease of the bending rigidity. Besides, two distinct behaviors of the active membrane seem to be distinguished: a pseudo-equilibrium state and a far-from-equilibrium state.RENNES1-BU Sciences Philo (352382102) / SudocSudocFranceF

Buffers Affect the Bending Rigidity of Model Lipid Membranes

International audienceIn biophysical and biochemical studies of lipid bilayers the influence of the used buffer is often ignored or assumed to be negligible on membrane structure, elasticity, or physical properties. However, we here present experimental evidence, through bending rigidity measurements performed on giant vesicles, of a more complex behavior, where the buffering molecules may considerably affect the bending rigidity of phosphatidylcholine bilayers. Furthermore, a synergistic effect on the bending modulus is observed in the presence of both salt and buffer molecules, which serves as a warning to experimentalists in the data interpretation of their studies, since typical lipid bilayer studies contain buffer and ion molecules