Élaboration de nouveaux biopolyesters bactériens fonctionnalisés pour des applications dans le domaine biomédical

Les poly(3-hydroxyalcanoate)s ou PHAs sont des biopolyesters linéaires biodégradables et biocompatibles synthétisés par des microorganismes bactériens en tant que réserve de carbone et d'énergie. Ils sont synthétisés par des bactéries à partir de ressources renouvelables et la diversité de leurs structures possibles se traduit par un large éventail de polymères ayant des propriétés mécaniques très différentes. Nous avons tout d'abord testé les capacités de production de PHAs de nouvelles souches bactériennes marines provenant de tapis microbiens de Polynésie française, en utilisant, entre autres, des substrats naturels comme l'huile de coprah, le glucose et l'acide oléique. Nous avons notamment montré que la souche Pseudomonas guezennei est capable de produire des PHAs avec des taux d'insaturation contrôlés et de masse molaire très élevée. Puis, des oligomères de PHAs fonctionnalisés de structures contrôlées portant des fonctions terminales alcynes ou alcènes ont été préparés par transestérification. Ces oligomères ont ensuite été utilisés pour l'élaboration par chimie click de copolymères amphiphiles greffés EPS-g-PHA avec des exopolysaccharides (EPS) bactériens. Enfin la dernière partie de ces travaux a consisté en la réalisation d'un support de croissance pour le développement de cellules souches pour l'ingénierie tissulaire combinant les propriétés mécaniques des PHAs et les propriétés hydrophiles et bioactives des EPSPoly(3-hydroxyalkanoate)s, or PHAs, are linear biodegradable and biocompatible biopolyesters synthesized by bacterial microorganisms as energy and carbon supply. They are synthesized by bacteria from renewable resources and the diversity of the achievable structures leads to a large range of mechanical properties. First, we studied the PHAs production ability of several new marine bacteria strains, isolated from microbial mats from French Polynesia, using, among others, natural substrates such as coprah oil, glucose and oleic acid. We showed particularly that the strain Pseudomonas guezennei was able to produce PHAs with controlled amounts of insaturations and high molar masses. Then, we prepared functionalized PHAs oligomers with controlled structure and bearing a terminal alkyne or alkene function. Following that, these oligomers were used to elaborate amphiphilic by click chemistry graft copolymers EPS-g-PHA with bacterial exopolysaccharide (EPS). Finally, the last part of this work was the making of a scaffold for stem cell culture for tissue engineering which combined the mechanical properties of PHAs and the hydrophilicity and bioactive properties of EPSPARIS-EST-Université (770839901) / SudocSudocFranceF

Élaboration de copolymères amphiphiles à base de poly (3-hydroxyalcanoate)s

Les poly (3-hydroxyalcanoates) (PHAs) sont des polyesters aliphatiques produits et accumulés par des bactéries en tant que réserve de carbone et d'énergie. Ils sont constitués d'unités b-hydroxyesters et possèdent des chaînes latérales de longueur variable, pouvant être fonctionnalisées. Ils possèdent des propriétés de biodégradabilité et de biocompatibilité; ceci leur confère de vastes possibilités d'utilisation dans le domaine biomédical, notamment pour la mise au point de systèmes de libération contrôlée de principes actifs. Dans cette optique, nous nous sommes intéressés à la synthèse de copolymères amphiphiles de différentes architectures à base de PHAs, ainsi qu'à l'étude de leurs propriétés d'auto-association en milieu aqueux. Une méthode simple et efficace permettant le greffage d'oligomères de poly (éthylène glycol) (PEG) a tout d'abord été mise au point grâce à l'utilisation de la chimie click . Une série de copolymères diblocs bien définis PHA-b-PEG a ainsi pu être synthétisée par cycloaddition de Huisgen catalysée par le cuivre (CuAAC). Les copolymères diblocs à base de PHAs à moyennes chaînes latérales (PHA-mcl) ont montré leur capacité à s'auto-associer en milieu aqueux et à former des micelles monodisperses présentant une concentration micellaire critique très faible. Par la suite des copolymères de type greffés PHOU-g-PEG ont été synthétisés par addition thiol-ène. Les analyses par cryo microscopie électronique à transmission (cryo-TEM) ont montré que dans ce cas les copolymères s'auto-associaient en structures vésiculaires, ou polymersomes. Enfin, la synthèse de copolymères amphiphiles greffés porteurs de chaînes perfluorées PHOU-g-(F;PEG) a permis l'obtention de structures auto-associées plus complexes. Le cryo-TEM a en effet révélé la formation de micelles multicompartimentées, c'est à dire possédant un coeur présentant une séparation de phase entre les domaines hydrophobes et les domaines fluorés. Des tests biologiques préliminaires ont montré la cytocompatibilité de ces micellesPoly (3-hydroxyalkanoates) are natural aliphatic polyesters produced and accumulated by many bacteria as carbon and energy supply. They consist of b-hydroxy ester units, with pendant side chains of different lengths that can be functionalized. Thanks to their biodegradability and biocompatibility, they are promising polymers for biomedical applications, especially for controlled drug delivery systems. In this context, we aimed to synthesize PHA-based amphiphilic copolymers with different molecular architectures, and to study their self-assembly in water. First, a simple and straightforward method using click chemistry has been used to graft poly(ethylene glycol) (PEG) oligomers. A series of well-defined diblock copolymers PHA-b-PEG has thus been synthesized using copper-catalyzed azide-alkyne cycloaddition (CuAAC). Medium chain length PHA-based diblock copolymers have shown their ability to self-assemble into stable micelles having very low critical micelle concentrations. Afterwards, amphiphilic graft copolymers PHOU-g-PEG have been synthesized using thiol-ene addition. In this case, cryo-electron microscopy (cryo-TEM) analysis revealed that graft copolymers self-assembled into vesicular morphologies, i.e. in polymersomes. Finally, the synthesis of amphiphilic graft copolymers bearing perfluorinated chains PHOU-g-(F;PEG) was performed. After aqueous self-assembly, cryo-TEM shown the formation of multicompartment micelles, i.e. with a core displaying segregated hydrophobic and fluorophilic domains. Moreover, these multicompartment micelles have shown their cytocompatibilityPARIS-EST-Université (770839901) / SudocSudocFranceF

Memory for public events in mild cognitive impairment and Alzheimer’s disease : the importance of rehearsal

Ribot’s law refers to the better preservation of remote memories compared with recent ones that presumably characterizes retrograde amnesia. Even if Ribot-type temporal gradient has been extensively studied in retrograde amnesia, particularly in Alzheimer’s disease (AD), this pattern has not been consistently found. One explanation for these results may be that rehearsal frequency rather than remoteness accounts for the better preservation of these memories. Thus, the aim of present study was to address this question by studying retrograde semantic memory in subjects with amnestic mild cognitive impairment (aMCI) (n = 20), mild AD (n = 20) and in healthy older controls (HC; n = 19). In order to evaluate the impact of repetition as well as the impact of remoteness, we used a test assessing memory for enduring and transient public events that occurred in the recent and remote past. Results show no clear temporal gradient across time periods (1960–1975; 1976–1990; 1991–2005; 2006–2011), but a better performance was observed in all three groups for enduring compared with transient events. Moreover, although deficits were globally found in both patients groups compared with HC, more specific analyses revealed that aMCI patients were only impaired on transient events while AD patients were impaired on both transient and enduring events. Exploratory analyses also revealed a tendency suggesting preservation of remote transient events in aMCI. These findings are discussed with regards to memory consolidation models

Expression of Viral Antigen by the Liver Leads to Chronic Infection Through the Generation of Regulatory T Cells

Referred to by David E. Kaplan " Does Massive Antigen Burden Allow Hepatic Viruses to Induce Regulatory T Cells and Their Tolerance and Persistence?" CMGH Cellular and Molecular Gastroenterology and Hepatology, Volume 1, Issue 3, May 2015, Pages 259-261International audienceThe constant exposure of the liver to food and bacterial antigens through the mesenteric circulation requires it to maintain tolerance while preserving the ability to mount an effective immune response against pathogens. We investigated the contribution of the liver's tolerogenic nature on the establishment of chronic viral infections. Methods: TTR-NP mice, which express the nucleoprotein (NP) of lymphocytic choriomeningitis virus (LCMV) specifically in hepatocytes under control of a modified transthyretin (TTR) promoter, were infected with the Armstrong (Arm) or WE acute strains of LCMV. Results: The infection persisted for at least 147 days in TTR-NP mice. Expression of NP by the liver induced a strong peripheral tolerance against NP that was mediated by interleukin-10-secreting CD4+ regulatory T cells, leading to high PD-1 (programmed death-1) expression and reduced effector function of virus-specific T cells. Despite an active immune response against LCMV, peripheral tolerance against a single viral protein was sufficient to induce T-cell exhaustion and chronic LCMV Armstrong (Arm) or WE infection by limiting the antiviral T-cell response in an otherwise immunocompetent host. Regulatory T-cell depletion of chronically infected TTR-NP mice led to functional restoration of LCMV-specific CD4+ and CD8+ Tcell responses and viral clearance. Conclusions: Expression of a viral antigen by hepatocytes can induce a state of peripheral tolerance mediated by regulatory Tcells that can lead to the establishment of a chronic viral infection. Strategies targeting regulatory T cells in patients chronically infected with hepatotropic viruses could represent a promising approach to restore functional antiviral immunity and clear infection

Impact of crude oil and the dispersant CorexitTM EC9500A on capelin (Mallotus villosus) embryo development

publishedVersionPaid Open Acces

The impact of time and repeated exposure on famous person knowledge in amnestic Mild cognitive impairment and Alzheimer’s disease

Objective: Famous people knowledge has been shown to be impaired early in Alzheimer’s disease (AD) and amnestic mild cognitive impairment (aMCI). However, the question of whether recently acquired knowledge is more impaired than remotely acquired knowledge remains a matter of debate. The aim of this study was to investigate the patterns of semantic memory impairment in aMCI and AD by investigating two factors that may influence the retrieval of such knowledge, namely remoteness and frequency of repetition of information over time. Method: Three groups (19 controls, 20 aMCI and 20 AD patients) were compared on a test assessing general and specific biographical knowledge about famous people, where the period of acquired fame (remote vs recent) and the type of fame (enduring vs transient) were controlled for. Results: Global performance of aMCI and AD patients was significantly poorer than that of controls. However, different patterns of recall were observed as a function of time and type of fame. A temporal gradient was found in both patient groups for enduring names but not for transient ones, whereby knowledge about remote enduring famous persons was better recalled. Patients were more impaired at questions assessing specific biographical knowledge (unique to an individual) than more general knowledge. Conclusions: Tests of famous people knowledge offer a unique opportunity to investigate semantic deficits in aMCI and AD, because they make it possible to estimate the time at which memories were acquired, as well as the type of fame. Results are discussed in light of memory consolidation models. Keywords

L’évaluation de la mémoire rétrograde dans la population québécoise âgée: Le PUB-40 et le PUB-12

L’évaluation de la mémoire représente une partie importante du travail des neuropsychologues cliniciens œuvrant en gériatrie. En effet, au Canada, environ le tiers des aînés rapporte une plainte mnésique dont les causes sont variées. Selon l’étiologie, différentes composantes du système mnésique peuvent être atteintes, toutefois, l’évaluation de la mémoire rétrograde non autobiographique (publique ou sémantique) n’est souvent effectuée que de manière superficielle, puisqu’aucun outil d’évaluation fiable, valide et standardisé n’est disponible pour la population québécoise vieillissante. Les objectifs de cette recherche étaient donc (1) d’élaborer un protocole d’évaluation de la mémoire rétrograde non autobiographique spécifiquement adapté à cette population, le PUB-40, (2) de recueillir des données de référence auprès de 105 participants âgés sains et (3) de développer une version abrégée à partir des items permettant de discriminer un groupe de 20 patients atteints de troubles cognitifs légers de type amnésique (TCLa) des participants âgés sains

Bioaccumulation and physiological responses of the turtle Chelydra serpentina exposed to polychlorinated biphenyls during early life stages.

Despite the North American production ban of polychlorinated biphenyls (PCBs), PCBs are ubiquitous in the environment and in wildlife tissues. Chelydra serpentina serpentina (common snapping turtle) have been used as environmental indicators of PCB pollution upwards of 40 years given their high site fidelity and high trophic position. Despite their long use as indicators of PCB contamination, the effects of PCBs in reptiles remain largely unknown. In this study, we performed two experiments to assess i) bioaccumulation and ii) toxicity of PCBs to 1-month-old C. s. serpentina, to aid in interpretation of PCB burdens. Food pellets were spiked at an environmentally relevant concentration (0.45 μg/g) of the PCB mixture Aroclor 1254 to model hepatic bioaccumulation and depuration, through feeding, for 31 days and clean food for 50 days, respectively. No significant differences in PCB concentrations were observed in liver tissue over the course of the experiment, suggesting that juvenile turtles can likely metabolize low environmentally occurring concentrations of PCBs. Additionally, a dose-response experiment, performed to determine hepatic toxicity and bioaccumulation in juvenile C. s. serpentina, showed a 1.8-fold increase in hepatic expression of cyp1a when fed A1254-spiked pellets (12.7 μg/g; range 0–12.7 μg/g). This gene induction correlates with the significant increase of group 3 PCB congeners measured in the turtle liver, which are known to be metabolized by CYP1A. This study indicates that C. s. serpentina may be a good environmental indicator for PCBs, while more research is needed to assess the effects of body burdens in wild C. s. serpentina

Chronic Exposure to Two Gestagens Differentially Alters Morphology and Gene Expression in Silurana tropicalis.

Gestagens are active ingredients in human and veterinary drugs with progestogenic activity. Two gestagens—progesterone (P4), and the synthetic P4 analogue, melengestrol acetate (MGA)—are approved for use in beef cattle agriculture in North America. Both P4 and MGA have been measured in surface water receiving runoff from animal agricultural operations. This project aimed to assess the morphometric and molecular consequences of chronic exposures to P4, MGA, and their mixture during Western clawed frog metamorphosis. Chronic exposure (from embryo to metamorphosis) to MGA (1.7 µg/L) or P4 + MGA (0.22 µg/L P4 + 1.5 µg/L MGA) caused a considerable dysregulation of metamorphic timing, as evidenced by an inhibition of growth, narrower head, and lack of forelimb emergence in all animals. Molecular analysis revealed that chronic exposure to the mixture induced an additive upregulation of neurosteroid-related (GABAA receptor subunit α6 (gabra6) and steroid 5-alpha reductase 1 (srd5α1) gene expression in brain tissue. Chronic P4 exposure (0.26 µg/L P4) induced a significant upregulation of the expression hypothalamic–pituitary–gonadal (HPG)-related genes (ipgr, erα) in the gonadal mesonephros complex (GMC). Our data suggest that exposure to P4, MGA, and their mixture induces multiple endocrine responses and adverse effects in larval Western clawed frogs. This study helps to better our understanding of the consequences of chronic gestagen exposure and suggests that the implications and risk of high gestagen use in beef cattle feeding operations may extend to the aquatic environment