Le microbiote intestinal module la balance homéostasie / plaisir régulant la prise alimentaire chez le rat

National audienceIntroduction et but de l’étude : Les troubles du comportement alimentaire résultent d’un déséquilibre entre régulation homéostatique et plaisir contrôlant la prise alimentaire. Chez le rongeur soumis brutalement à un régime hyper-lipidique (HF), une première phase d’hyperphagie liée à l’activation des noyaux de la récompense et du plaisir est observée pendant un jour et est suivie d’un remodelage hypothalamique sous-tendant un retour à un ingéré normal en 2 ou 3 jours. Notre objectif était d’évaluer le rôle du microbiote intestinal dans les adaptations du comportement alimentaire lors de cette exposition à un régime HF.Matériel et méthodes : Des rats Wistars conventionnels ont été soumis à un régime HF et euthanasiés après 0, 2h, 1J, 2J ou 4J (n= 6 à 9) afin d’évaluer les changements au niveau du microbiote intestinal (16s) et de l’hypothalamus (métabolomique) concomitants à l’adaptation du comportement alimentaire. L’impact du microbiote sur le comportement alimentaire et l’adaptation hypothalamique ont été étudiés avec des rats Fischer axéniques (Ax, n=9) ou conventionnels (Cv, n=10) soumis à un régime HF ou contrôle (C) pendant 2J.Résultats et Analyse statistique : Chez les rats Wistars, le passage au régime HF a entrainé une modification rapide du microbiote caecal : diminution de la richesse (Chao1) et de la diversité (Shannon) dès 1J de régime HF (P<0.0001), modification de la diversité-β (P<0.001, ACP sous contrainte de l’indice de Bray Curtis). Une forte baisse de l’abondance de Prevotellaceae et des genres Lactobacillus, Lachnospiraceae NK4A136, Anaerovax, Bacteroidales S24, Enterohabdus et une forte augmentation des genres Lactococcus, Desulfovibrio, Escherichia/Shigella et Alloprevotella étaient observées dès 1J. A l’inverse le microbiote iléal était peu impacté par le changement de régime. Au niveau hypothalamique, une analyse métabolomique a révélé des modifications très rapides du système redox, du métabolisme du tryptophane ainsi que des phénomènes de remodelage membranaire. Les rats Ax soumis au régime HF, ont présenté une augmentation moins importante de leur ingéré énergétique à 1J et 2J que les rats Cv-HF (P<0.0001). Ceci était dû à une absence totale d’augmentation de consommation diurne chez les rats Ax par rapport aux rats Cv dont la prise alimentaire augmente dès la présentation du régime HF (P=0.035) et à une plus faible consommation nocturne des rats Ax-HF par rapport aux rats Cv-HF (P=0.04 à J1). Au niveau hypothalamique, le statut microbiologique impactait fortement l’expression des gènes impliqués dans la plasticité cellulaire. De plus l’expression d’AgrP était deux fois plus importante chez les rats Ax-C que chez les rats Cv-C et elle diminuait de 40% chez les rats Ax après 2J de régime HF. Cette diminution n’était pas observée chez les rats Cv-HF.Conclusion : L’écosystème intestinal s’adapte très rapidement au changement d’aliment, en parallèle d’un profond remodelage hypothalamique. L’absence de microbiote modifie l’adaptation du comportement alimentaire au régime HF, à la fois dans la phase d’activation du système de la récompense et dans celle de remodelage du système oréxigène, suggérant un rôle du microbiote et de l’axe intestin-cerveau dans ces phénomènes

Differential metal sensing and metal‐dependent degradation of the broad spectrum root metal transporter <scp>IRT1</scp>

SUMMARYIron is an essential micronutrient for plant growth and development. Under low iron conditions, Arabidopsis plants take up soil iron using the root iron transporter IRT1. In addition to iron, IRT1 also transports others divalent metals, including cadmium, which consequently accumulates into plant tissues and enters the food chain. IRT1 expression was shown to be regulated at the transcriptional and post‐translational levels by its essential metal substrates to maximize iron uptake while limiting the accumulation of zinc, manganese, or cobalt. Here, we characterized the regulation of IRT1 by cadmium. A short‐term exposure to cadmium decreased the cell surface levels of IRT1 through endocytosis and degradation, but with a lower efficiency than observed for other IRT1 metal substrates. We demonstrated that IRT1 endocytosis in response to cadmium is mediated through the direct binding of cadmium to histidine residues within the regulatory loop of IRT1. However, we revealed that the affinity of the metal sensing motif is much lower for cadmium compared to other metal substrates of IRT1. Finally, we proved that cadmium‐induced IRT1 degradation takes place through ubiquitin‐mediated endocytosis driven by the UBC35/36 E2 ubiquitin‐conjugating enzymes and the IDF1 E3 ubiquitin ligase. Altogether, this work sheds light on the mechanisms of cadmium‐mediated downregulation of IRT1 and provides an additional molecular basis for cadmium accumulation and toxicity in plants.</jats:p

Characterization of a uranium-tolerant green microalga with high potential for the remediation of metal-polluted waters

Uranium (U) pollution of terrestrial and aquatic ecosystems poses a significant threat to the environment and human health because this radionuclide is chemotoxic. Characterization of organisms that tolerate and accumulate U is critical to decipher the mechanisms evolved to cope with the radionuclide and to propose new effective strategies for bioremediation of U-contaminated environments. We isolated a unicellular green microalga that is much more tolerant to U than Chlamydomonas reinhardtii and Chlorella vulgaris. The isolated microalga is able to accumulate U very rapidly and, then, progressively release it into the medium, behaving as an excluder to limit the toxic effects of U. The U-tolerant microalga is able to grow, maintain high photosynthesis and capture 25-55% of U from natural metal-contaminated waters from a reclaimed U mine. The isolated microalga is very promising for the remediation of polluted waters with valorization of algal biomass that accumulates neutral lipids

Characterization of a uranium-tolerant green microalga with high potential for the remediation of metal-polluted waters

Uranium (U) pollution of terrestrial and aquatic ecosystems poses a significant threat to the environment and human health because this radionuclide is chemotoxic. Characterization of organisms that tolerate and accumulate U is critical to decipher the mechanisms evolved to cope with the radionuclide and to propose new effective strategies for bioremediation of U-contaminated environments. We isolated a unicellular green microalga that is much more tolerant to U than Chlamydomonas reinhardtii and Chlorella vulgaris. The isolated microalga is able to accumulate U very rapidly and, then, progressively release it into the medium, behaving as an excluder to limit the toxic effects of U. The U-tolerant microalga is able to grow, maintain high photosynthesis and capture 25-55% of U from natural metal-contaminated waters from a reclaimed U mine. The isolated microalga is very promising for the remediation of polluted waters with valorization of algal biomass that accumulates neutral lipids

Calcium-permeable cation channels are involved in uranium uptake in Arabidopsis thaliana

International audienc

Uranium-tolerant soil bacteria protect Arabidopsis thaliana seedling growth in a uranium pollution context

We investigated the impact of uranium (U) on Arabidopsis thaliana seed germination and on the early stages of seedling development. Using an in vitro device, we demonstrated that uranyl ion had a very low impact on Arabidopsis seed germination but had a drastic effect on the development of Arabidopsis seedlings. We showed that the two soil bacterial strains Microbacterium sp. ViU2A and Stenotrophomonas bentonitica BII-R7, which are able to tolerate high concentrations of U, strongly reduced the toxic effects of the metal on the seedling development. This protective effect is specific to these soil bacteria, as E. coli was not able to protect seedlings. The analysis of the distribution of U between Arabidopsis seedlings and soil bacteria showed that the protective effect of the bacteria was due to their ability to sequester U either by biosorption at the level of the cell surface and/or by intracellular or extracellular biomineralization.This study reveals that these bacteria are very good candidates for use in phytoremediation strategies in the case of phytostabilisation of U-polluted soils. They would be also useful to limit the contamination of the food chain by U because they would limit the entry of this toxic element in crop plants

Rôle du dialogue entre le tissu adipeux et l’intestin dans le maintien de l’homéostasie intestinale

National audienc

Characterization of a uranium-tolerant green microalga of the genus Coelastrella with high potential for the remediation of metal-polluted waters

International audienceUranium (U) contamination of terrestrial and aquatic ecosystems poses a significant threat to the environment and human health due to the chemotoxicity of this actinide. The characterization of organisms that tolerate and accumulate U is crucial to decipher the mechanisms evolved to cope with the radionuclide and to propose new effective strategies for the bioremediation of U-contaminated environments. Here, we isolated a unicellular green microalga of the genus Coelastrella from U-contaminated wastewater. We showed that Coelastrella sp. PCV is much more tolerant to U than Chlamydomonas reinhardtii and Chlorella vulgaris. Coelastrella sp. PCV is able to accumulate U very rapidly and then gradually release it into the medium, behaving as an excluder to limit the toxic effects of U. The ability of Coelastrella sp. PCV to accumulate U is remarkably high, with up to 240 mg of tightly bound U per g of dry biomass. Coelastrella sp. PCV is able to grow and maintain high photosynthesis in natural metal-contaminated waters from a wetland near a reclaimed U mine. In a single one-week growth cycle, Coelastrella sp. PCV is able to capture 25-55% of the U from the contaminated waters and shows lipid droplet accumulation. Coelastrella sp. PCV is a very promising microalga for the remediation of polluted waters with valorization of algal biomass that accumulates lipids

Lipo-protein emulsion structure in the diet affects protein digestion kinetics, intestinal mucosa parameters and microbiota composition

SCOPE: Food structure is a key factor controlling digestion and nutrient absorption. We tested the hypothesis that protein emulsion structure in the diet may affect digestive and absorptive processes. METHODS & RESULTS: Rats (n = 40) were fed for 3 weeks two diets chemically identical but based on lipid-protein liquid-fine (LFE) or gelled-coarse (GCE) emulsions that differ at the macro- and micro-structure levels. After an overnight fasting, they ingested a 15 N-labeled LFE or GCE test meal and were euthanized 0, 15min, 1h and 5h later. 15 N enrichment in intestinal contents and 15 N blood fate were measured. Gastric emptying, protein digestion kinetics, 15 N absorption and incorporation in blood protein and urea were faster with LFE than GCE. At 15min timepoint, LFE group showed higher increase in GIP portal levels than GCE. Three weeks of dietary adaptation led to higher expression of cationic amino acid-transporters in ileum of LFE compared to GCE. LFE diet raised cecal butyrate and isovalerate proportion relative to GCE, suggesting increased protein fermentation. LFE diet increased fecal Parabacteroides relative abundance but decreased Bifidobacterium, Sutterella, Parasutterella genera, and Clostridium cluster XIV abundance. CONCLUSION: Protein emulsion structure regulates digestion kinetics and gastrointestinal physiology, and could be targeted to improve food health value