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Iron 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.

Uranium (U) is a non-essential and toxic element that is taken up by plants from the environment. The assimilation pathway of U is still unknown in plants and any other organism. In this study, we provide several evidences that U is taken up by the roots of Arabidopsis thaliana through Ca2+-permeable cation channels. First, we showed that deprivation of Arabidopsis plants with calcium induced a 1.5-fold increase in the capacity of roots to accumulate U, suggesting that calcium deficiency promoted the radionuclide import pathway. Second, we showed that external calcium inhibits U accumulation in roots, suggesting a common route for the uptake of both cations. Third, we found that gadolinium, nifedipine and verapamil inhibit the absorption of U, suggesting that different types of Ca2+-permeable channels serve as a route for U uptake. Last, we showed that U bioaccumulation in Arabidopsis mutants deficient for the Ca2+-permeable channels MCA1 and ANN1 was decreased by 40%. This suggests that MCA1 and ANN1 contribute to the absorption of U in different zones and cell layers of the root. Together, our results describe for the first time the involvement of Ca2+-permeable cation channels in the cellular uptake of U.

Fructose is metabolized in the cytoplasm by the enzyme ketohexokinase (KHK), and excessive consumption may affect bone health. Previous work in calcium-restricted, growing mice demonstrated that fructose disrupted intestinal calcium transport. Thus, we hypothesized that the observed effects on bone were dependent on fructose metabolism and took advantage of a KHK knockout (KO) model to assess direct effects of high plasma fructose on the long bones of growing mice. Four groups (n = 12) of 4-week-old, male, C57Bl/6 background, congenic mice with intact KHK (wild-type, WT) or global knockout of both isoforms of KHK-A/C (KHK-KO), were fed 20% glucose (control diet) or fructose for 8 weeks. Dietary fructose increased by 40-fold plasma fructose in KHK-KO compared to the other three groups (p

International audience; Current fructose consumption levels often overwhelm the intestinal capacity to absorb fructose. We investigated the impact of fructose malabsorption on intestinal endocrine function and addressed the role of the microbiota in this process. To answer this question, a mouse model of moderate fructose malabsorption [ketohexokinase mutant (KHK)-/-] and wild-type (WT) littermate mice were used and received a 20%-fructose (KHK-F and WT-F) or 20%-glucose diet. Cholecystokinin (Cck) mRNA and protein expression in the ileum and cecum, as well as preproglucagon (Gcg) and neurotensin (Nts) mRNA expression in the cecum, increased in KHK-F mice. In KHK-F mice, triple-label immunohistochemistry showed major up-regulation of CCK in enteroendocrine cells (EECs) that were glucagon-like peptide-1 (GLP-1)+/Peptide YY (PYY-) in the ileum and colon and GLP-1-/PYY- in the cecum. The cecal microbiota composition was drastically modified in the KHK-F in association with an increase in glucose, propionate, succinate, and lactate concentrations. Antibiotic treatment abolished fructose malabsorption-dependent induction of cecal Cck mRNA expression and, in mouse GLUTag and human NCI-H716 cells, Cck mRNA expression levels increased in response to propionate, both suggesting a microbiota-dependent process. Fructose reaching the lower intestine can modify the composition and metabolism of the microbiota, thereby stimulating the production of CCK from the EECs possibly in response to propionate.-Zhang, X., Grosfeld, A., Williams, E., Vasiliauskas, D., Barretto, S., Smith, L., Mariadassou, M., Philippe, C., Devime, F., Melchior, C., Gourcerol, G., Dourmap, N., Lapaque, N., Larraufie, P., Blottière, H. M., Herberden, C., Gerard, P., Rehfeld, J. F., Ferraris, R. P., Fritton, J. C., Ellero-Simatos, S., Douard, V. Fructose malabsorption induces cholecystokinin expression in the ileum and cecum by changing microbiota composition and metabolism.

International audience; Background: Early hyperphagia and hypothalamic inflammation encountered after Western diet (WD) are linked to rodent propensity to obesity. Inflammation in several brain structures has been associated with gut dysbiosis. Since gut microbiota is highly sensitive to dietary changes, we hypothesised that immediate gut microbiota adaptation to WD in rats is involved in inflammation-related hypothalamic modifications. Methods: We evaluated short-term impact of WD consumption (2 h, 1, 2 and 4 days) on hypothalamic metabolome and caecal microbiota composition and metabolome. Data integration analyses were performed to uncover potential relationships among these three datasets. Finally, changes in hypothalamic gene expression in absence of gut microbiota were evaluated in germ-free rats fed WD for 2 days. Results: WD quickly and profoundly affected the levels of several hypothalamic metabolites, especially oxidative stress markers. In parallel, WD consumption reduced caecal microbiota diversity, modified its composition towards pro-inflammatory profile and changed caecal metabolome. Data integration identified strong correlations between gut microbiota sub-networks, unidentified caecal metabolites and hypothalamic oxidative stress metabolites. Germ-free rats displayed reduced energy intake and no changes in redox homoeostasis machinery expression or pro-inflammatory cytokines after 2 days of WD, in contrast to conventional rats, which exhibited increased SOD2, GLRX and IL-6 mRNA levels. Conclusion: A potentially pro-inflammatory gut microbiota and an early hypothalamic oxidative stress appear shortly after WD introduction. Tripartite data integration highlighted putative links between gut microbiota sub-networks and hypothalamic oxidative stress. Together with the absence of hypothalamic modifications in germ-free rats, this strongly suggests the involvement of the microbiota-hypothalamus axis in rat adaptation to WD introduction and in energy homoeostasis regulation.

International audience; ScopeFood structure is a key factor controlling digestion and nutrient absorption. We test the hypothesis that protein emulsion structure in the diet may affect digestive and absorptive processes.Methods & ResultsRats (n = 40) are fed for 3 weeks with two diets chemically identical but based on lipid–protein liquid‐fine (LFE) or gelled‐coarse (GCE) emulsions that differ at the macro‐ and microstructure levels. After an overnight fasting, they ingest a 15N‐labeled LFE or GCE test meal and are euthanized 0, 15 min, 1 h, and 5 h later. 15N enrichment in intestinal contents and blood are measured. Gastric emptying, protein digestion kinetics, 15N absorption, and incorporation in blood protein and urea are faster with LFE than GCE. At 15 min time point, LFE group shows higher increase in GIP portal levels than GCE. Three weeks of dietary adaptation leads to higher expression of cationic amino acid transporters in ileum of LFE compared to GCE. LFE diet raises cecal butyrate and isovalerate proportion relative to GCE, suggesting increased protein fermentation. LFE diet increases fecal Parabacteroides relative abundance but decreases Bifidobacterium, Sutterella, Parasutterella genera, and Clostridium cluster XIV abundance.ConclusionProtein emulsion structure regulates digestion kinetics and gastrointestinal physiology, and could be targeted to improve food health value.

Introduction et but de l’etude Les troubles du comportement alimentaire resultent d’un desequilibre entre regulation homeostatique et plaisir controlant la prise alimentaire. Chez le rongeur soumis brutalement a un regime hyper-lipidique (HF), une premiere phase d’hyperphagie liee a l’activation des noyaux de la recompense et du plaisir est observee pendant un jour et est suivie d’un remodelage hypothalamique sous-tendant un retour a un ingere normal en 2 ou 3 jours. Notre objectif etait d’evaluer le role du microbiote intestinal dans les adaptations du comportement alimentaire lors de cette exposition a un regime HF. Materiel et methodes Des rats Wistars conventionnels ont ete soumis a un regime HF et euthanasies apres 0, 2 h, 1j, 2j ou 4j (n = 6 a 9) afin d’evaluer les changements au niveau du microbiote intestinal (16 s) et de l’hypothalamus (metabolomique) concomitants a l’adaptation du comportement alimentaire. L’impact du microbiote sur le comportement alimentaire et l’adaptation hypothalamique ont ete etudies avec des rats Fischer axeniques (Ax, n = 9) ou conventionnels (Cv, n = 10) soumis a un regime HF ou controle (C) pendant 2j. Resultats et analyse statistique Chez les rats Wistars, le passage au regime HF a entraine une modification rapide du microbiote caecal : diminution de la richesse (Chao1) et de la diversite (Shannon) des 1j de regime HF (p Les rats Ax soumis au regime HF, ont presente une augmentation moins importante de leur ingere energetique a 1j et 2j que les rats Cv-HF (p Conclusion L’ecosysteme intestinal s’adapte tres rapidement au changement d’aliment, en parallele d’un profond remodelage hypothalamique. L’absence de microbiote modifie l’adaptation du comportement alimentaire au regime HF, a la fois dans la phase d’activation du systeme de la recompense et dans celle de remodelage du systeme orexigene, suggerant un role du microbiote et de l’axe intestin-cerveau dans ces phenomenes.

Introduction et but de l’etude Il est communement accepte que l’obesite, d’origine genetique ou alimentaire, est liee a une alteration des fonctions de barriere de l’intestin, elle-meme consequence de l’inflammation de cet organe. L’endotoxemie resultant de l’alteration de la barriere intestinale joue un role important dans la mise en place de l’inflammation des tissus peripheriques. Or, des travaux recents ont montre une absence d’effet des regimes tres riches en lipides sur l’inflammation de bas bruit. Ces travaux suggerent egalement un role cle de l’intestin dans la prevention de la mise en place de l’inflammation de bas bruit via l’augmentation de l’expression des proteines a mucus. En parallele, une autre etude a montre que l’inhibition du developpement du tissu adipeux (TA) rendait l’intestin plus susceptible a l’induction de colite experimentale. Notre objectif est de clarifier la relation de causalite entre l’hypertrophie du TA et l’homeostasie intestinale dans le contexte de l’obesite et de determiner le role du microbiote dans ce dialogue. Materiel et methodes Afin de repondre a ces questions, des modeles de rats predisposes (OP) et resistants (OR) a l’obesite ainsi que des rats axeniques ont ete soumis a des regimes contenant des teneurs variables en lipides. Resultats et analyse statistique Soumis a des regimes hyperlipidiques (45 % pendant 2 mois) les rats OP developpent une adiposite 45 % plus elevee que les OR. Neanmoins, dans l’intestin aucune difference d’expression des marqueurs de l’inflammation et de la fonction barriere n’a ete observee. Il a ete montre que la composition du microbiote des OP et OR diverge dans ces conditions. Le transfert de ces microbiotes vers des rats axeniques n’a pas permis de restaurer le phenotype d’obesite chez les rats axeniques conventionnalises OP (rat CV-OP) recevant le meme regime hyper6lipidique pendant 2 mois, mais une augmentation de marqueurs proinflammatoires (IL-1b, TNFa, MCP1, IL-12) a ete observee dans leurs ileon et colon compare aux rats CV-OR. Dans le colon, cette inflammation s’accompagne d’une diminution de l’expression de la mucine MUC2, constituant principal du mucus. En l’absence d’augmentation de l’adiposite, la presence d’un « microbiote predisposant a l’obesite », en association avec un regime obesogene, conduit donc a une alteration des fonctions barriere de l’epithelium intestinal. Afin de confirmer le role du TA sur l’homeostasie intestinale, des rats OP ont ete soumis a des regimes moyennement (10 % : OP10) ou fortement riches en lipides (45 % : OP45). Apres 2 mois, les rats OP45 ont developpe une adiposite 65 % plus elevee que les OP10. Parallelement a l’augmentation de l’adiposite, on observe une forte reduction de l’expression des genes codant pour des marqueurs de l’inflammation (IL-1b, TNFa, MCP1) dans l’ileon et le colon des rats OP45. Cette reduction est egalement associee a une augmentation de l’expression de MUC2 dans le colon des rats OP45 en comparaison aux rat OP10. Conclusion Lors d’une mise sous regime hyper-lipique, le TA peut jouer un role protecteur de l’homeostasie intestinale, prevenant l’effet deletere eventuel d’un microbiote obesogene. Cet effet du TA pourrait etre en partie controle par un renforcement de la couche de mucus via la regulation de MUC2 par certains facteurs adipocytaires.

Obesity has been associated with activation of cellular stress signaling and inflammatory pathways. A key player in this cellular stress response is the endoplasmic reticulum (ER). Thus, this study...

At the request of the INRA, and following an external investigation, the Editors and Publisher have agreed to retract this paper owing to image manipulation. FA Duca, B Langelier, F Devime, H Blottiere, C Delorme, P Renault and M Covasa agree to the retraction of this paper; M Covasa, however, does not agree to the language of this retraction notice. Y Sakar could not be reached to comment on the retraction. See : http://dx.doi.org/doi:10.1038/ijo.2016.118 The corrigendum associated with this article (http://dx.doi.org/10.1038/ijo.2014.54) has also been retracted.; BACKGROUND AND OBJECTIVES:Gut hormones secreted by enteroendocrine cells (EECs) play a major role in energy regulation. Differentiation of EEC is controlled by the expression of basic helix-loop-helix (bHLH) transcription factors. High-fat (HF) feeding alters gut hormone levels; however, the impact of HF feeding on bHLH transcription factors in mediating EEC differentiation and subsequent gut hormone secretion and expression is not known.METHODS:Outbred Sprague-Dawley rats were maintained on chow or HF diet for 12 weeks. Gene and protein expression of intestinal bHLH transcription factors, combined with immunofluorescence studies, were analyzed for both groups in the small intestine and colon. Gut permeability, intestinal lipid and carbohydrate transporters as well as circulating levels and intestinal protein expression of gut peptides were determined.RESULTS:We showed that HF feeding resulted in hyperphagia and increased adiposity. HF-fed animals exhibited decreased expression of bHLH transcription factors controlling EEC differentiation (MATH1, NGN3, NEUROD1) and increased expression of bHLH factors modulating enterocyte expression. Furthermore, HF-fed animals had decreased number of total EECs and L-cells. This was accompanied by increased gut permeability and expression of lipid and carbohydrate transporters, and a decrease in circulating and intestinal gut hormone levels.CONCLUSIONS:Taken together, our results demonstrate that HF feeding caused decreased secretory lineage (that is, EECs) differentiation through downregulation of bHLH transcription factors, resulting in reduced EEC number and gut hormone levels. Thus, impaired EEC differentiation pathways by HF feeding may promote hyperphagia and subsequent obesity.

The lead and corresponding authors wish to retract the above-cited article as an institutional investigation has identified that coauthor Yassine Sakar falsified the data used to produce Fig. 4B, fabricated Fig. 5A, and fabricated the data used to produce Fig. S3(C). The authors regret these errors and apologize for any inconvenience to the readers of the journal.See : https://doi.org/10.2337/db16-rt05The lead and corresponding authors wish to retract the above-cited article as an institutional investigation has identified that coauthor Yassine Sakar falsified the data used to produce Fig. 4B, fabricated Fig. 5A, and fabricated the data used to produce Fig. S3(C). The authors regret these errors and apologize for any inconvenience to the readers of the journal. See : https://doi.org/10.2337/db16-rt05; Aberrations in gut microbiota are associated with metabolic disorders, including obesity. However, whether shifts in the microbiota profile during obesity are a characteristic of the phenotype or a consequence of obesogenic feeding remains elusive. Therefore, we aimed to determine differences in the gut microbiota of obese-prone (OP) and obese-resistant (OR) rats and examined the contribution of this microbiota to the behavioral and metabolic characteristics during obesity. We found that OP rats display a gut microbiota distinct from OR rats fed the same high-fat diet, with a higher Firmicutes-to-Bacteroidetes ratio and significant genera differences. Transfer of OP but not OR microbiota to germ-free (GF) mice replicated the characteristics of the OP phenotype, including reduced intestinal and hypothalamic satiation signaling, hyperphagia, increased weight gain and adiposity, and enhanced lipogenesis and adipogenesis. Furthermore, increased gut permeability through conventionalization resulted in inflammation by proinflammatory nuclear factor (NF)-B/inhibitor of NF-B kinase subunit signaling in adipose tissue, liver, and hypothalamus. OP donor and GF recipient animals harbored specific species from Oscillibacter and Clostridium clusters XIVa and IV that were completely absent from OR animals. In conclusion, susceptibility to obesity is characterized by an unfavorable microbiome predisposing the host to peripheral and central inflammation and promoting weight gain and adiposity during obesogenic feeding.

Impact of high-fat feeding on basic helix–loop–helix transcription factors controlling enteroendocrine cell differentiation