Invalidation et activation du transcepteur des sucres GLUT2 (impacts sur la régulation de la prise alimentaire et la sécrétion d'insuline)

GLUT2 est un transporteur membranaire des sucres exprimé dans de nombreux tissus contribuant au maintien de l homéostasie glucidique dont les cellules b pancréatiques. Notre équipe a montré que GLUT2 est également un détecteur des sucres extracellulaires. Au cours de cette thèse, nous avons montré par une approche de souris transgénique que la détection des sucres par GLUT2 contrôlait la prise alimentaire en régulant l activité de neurones dans l hypothalamus et l expression de neuropetides orexigènes et anorexigènes. Chez l Homme, des mutations de GLUT2 sont associées au syndrome de Fanconi-Bickel (FBS), maladie caractérisée par un dérèglement du métabolisme des carbohydrates. Des mutations de GLUT2 ont été également identifiées chez des patients atteints du syndrome d Hyperinsulinisme Congénital (CHI). Ce syndrome est caractérisé par une hypoglycémie chronique provoquée par une hypersécrétion d insuline. Dans ce travail de thèse, nous avons analysé les conséquences fonctionnelles sur l expression et les capacités cinétiques de GLUT2 de 4 mutations associées au FBS, 3 mutations associées au CHI et 2 SNP. Nous avons confirmé que les mutations de GLUT2 associées au FBS inactivaient soit son expression, soit sa fonction de transporteur. Les mutations de GLUT2 associées au CHI altèrent la fonction de transporteur de GLUT2 et provoquent une sécrétion d insuline basale augmentée. Ces résultats sont compatibles avec une activation constitutive de la fonction de détection des sucres par GLUT2 et revisite le rôle de GLUT2 dans la sécrétion d insuline chez l homme.PARIS-BIUSJ-Biologie recherche (751052107) / SudocSudocFranceF

Metabolic stress impairs pericyte response to optogenetic stimulation in pancreatic islets

Pancreatic islets are highly vascularized micro-organs ensuring whole body glucose homeostasis. Islet vascular cells play an integral part in sustaining adequate insulin release by beta cells. In particular, recent studies have demonstrated that islet pericytes regulate local blood flow velocity and are required for maintenance of beta cell maturity and function. In addition, increased metabolic demand accompanying obesity alters islet pericyte morphology. Here, we sought to explore the effects of metabolic stress on islet pericyte functional response to stimulation in a mouse model of type 2 diabetes, directly in the pancreas in vivo. We found that high fat diet induced islet pericyte hypertrophy without alterations in basal local blood flow. However, optogenetic stimulation of pericyte activity revealed impaired islet vascular responses, despite increased expression of genes encoding proteins directly or indirectly involved in cell contraction. These findings suggest that metabolic stress impinges upon islet pericyte function, which may contribute to beta cell failure during T2D

Mineralogical evolution of a claystone after reaction with iron under thermal gradient

The design of the repository for high-level nuclear waste (HLW) in France consists of a multiple-barrier system including steel canisters in a clay host rock. The system will undergo temperature variations in time and space, the heat source being the HLW within the canisters. The effect of a thermal gradient in space on the Fe-claystone interaction was investigated here by applying a thermal gradient (150-300°C and 80-150°C) to a mix of claystone, Fe, and an aqueous chloride solution over periods of 3 and 6 months. Following the reaction, the starting clay minerals (mostly illite and mixed-layer illite smectite) evolved toward chlorite, Fe-serpentine, Fe-saponite, mixed-layer chlorite-smectite, or mixed-layer serpentine-smectite as a function of temperature. Iron corrosion made the medium basic and reductive. Magnesium enrichment of clay minerals was observed in the hottest part of the experiment due to Mg migration under the thermal gradient. Reaction progress was enhanced at the lowest temperatures, compared to batch experiments

Experimental Study of Pyrite Oxidation at 100 °C: Implications for Deep Geological Radwaste Repository in Claystone

ACLThe oxidation of pyrite is one of the near field processes of the chemical evolution of clay rock planned to host a deep geological radioactive waste repository during operation. Indeed, this process can lead to transitory acidic conditions in the medium (i.e., production of sulphuric acid, carbonic acid) which may influence the corrosion kinetics of the carbon steel components of some disposal cells. In order to improve the geochemical modelling of the long-term disposal, the oxidation of pyrite in contact with clays and carbonates at 100 degrees C must be evaluated. In this study, special attention was paid to the pyrite oxidation rate thanks to an original experimental set-up, involving several pyrite/mineral mixtures and a reactor coupled to a micro gas chromatograph (P-O2 and P-CO2 monitoring). Although thermodynamic modelling expects that hematite is the most stable phase in a pure pyrite heated system (low pH), experiments show the formation of native sulfur as an intermediate product of the reaction. In the presence of calcite, the pH is neutralized and drives the lower reactivity of pyrite in the absence of native sulfur. The addition of clay phases or other detrital silicates from the claystone had no impact on pyrite oxidation rate. The discrepancies between experiments and thermodynamic modelling are explained by kinetic effects. Two laws were deduced at 100 degrees C. The first concerns a pure pyrite system, with the following law: rPy= 10-4.8 center dot PO20.5 center dot t-0.5. The second concerns a pyrite/carbonates system: rPy+Ca= 10-5.1 center dot PO20.5 center dot t-0.5 where P-O2 corresponds to the partial pressure of O-2 (in bar) and t is time in seconds. Different mechanisms are proposed to explain the evolution with time of the O-2 consumption during pyrite oxidation: (i) decrease of the specific or reactive surface area after oxidation of fine grains of pyrite, (ii) decrease of O-2 pressure, (iii) growing up of secondary minerals (Fe-oxides or anhydrite in the presence of calcium in the system) on the surface of pyrite limiting the access of O-2 to the fresh surface of pyrite, and (iv) change in the pH of the solution

Integrin β1 Optimizes Diabetogenic T Cell Migration and Function in the Pancreas

The Supplementary Material for this article can be found online at https://www.frontiersin.org/articles/10.3389/fimmu.2018.01156/full#supplementary-material.International audienceT cell search behavior is dictated by their need to encounter their specific antigen to eliminate target cells. However, mechanisms controlling effector T cell motility are highly tissue-dependent. Specifically, how diabetogenic T cells encounter their target beta cells in dispersed islets throughout the pancreas (PA) during autoimmune diabetes remains unclear. Using intra-vital 2-photon microscopy in a mouse model of diabetes, we found that CXCR3 chemokine downregulated CD8+ T cell motility specifically within islets, promoting effector cell confinement to their target sites. By contrast, T cell velocity and directionality in the exocrine tissue were enhanced along blood vessels and extracellular matrix fibers. This guided migration implicated integrin-dependent interactions, since integrin blockade impaired exocrine T cell motility. In addition, integrin β1 blockade decreased CD4+ T cell effector phenotype specifically in the PA. Thus, we unveil an important role for integrins in the PA during autoimmune diabetes that may have important implications for the design of new therapies

Femtosecond filamentation in turbulent air

International audienceThe influence of air turbulence on femtosecond laser filamentation is studied experimentally and numerically for laser powers of a few critical powers. Air turbulence in the path of the beam prior to filamentation induces a large pointing and formation instability attributed to an increase of the self-focusing distance and higher modulational instability in the presence of turbulence. By contrast, previously formed filaments are robust both in terms of beam pointing accuracy and survival when crossing turbulent air

Detection of extracellular glucose by GLUT2 contributes to hypothalamic control of food intake

International audienceThe sugar transporter GLUT2, present in several tissues of the gut-brain axis, has been reported to be involved in the control of food intake. GLUT2 is a sugar transporter sustaining energy production in the cell, but GLUT2 can also function as a receptor for extracellular glucose. A glucose-signaling pathway is indeed triggered, independently of glucose metabolism, through its large cytoplasmic loop domain. However, it remains to determine the contribution of the receptor function over the transporter function of GLUT2 in the control of food intake. Thus, we generated transgenic mice that express a GLUT2-loop domain, blocking the detection of glucose, but leaving GLUT2-dependent glucose transport unaffected. Inhibiting GLUT2-mediated glucose detection augmented daily food intake by a mechanism that increased the meal size but not the number of meals. Peripheral hormones (ghrelin, insulin, leptin) were unaffected, leading to a focus on central aspects of feeding behavior. We found defects in c-Fos activation by glucose in the arcuate nucleus, and changes in the amounts of TRH and orexin neuropeptide mRNA, which are relevant to poorly controlled meal size. Our data provide evidence that glucose detection by GLUT2 contributes to the control of food intake by the hypothalamus. The sugar transporter-receptor, i.e. 'transceptor' GLUT2, may constitute a drug target to treat eating disorders and associated metabolic diseases, particularly by modulating its receptor function without affecting vital sugar provision by its transporter function

video_1_Integrin β1 Optimizes Diabetogenic T Cell Migration and Function in the Pancreas.mp4

<p>T cell search behavior is dictated by their need to encounter their specific antigen to eliminate target cells. However, mechanisms controlling effector T cell motility are highly tissue-dependent. Specifically, how diabetogenic T cells encounter their target beta cells in dispersed islets throughout the pancreas (PA) during autoimmune diabetes remains unclear. Using intra-vital 2-photon microscopy in a mouse model of diabetes, we found that CXCR3 chemokine downregulated CD8⁺ T cell motility specifically within islets, promoting effector cell confinement to their target sites. By contrast, T cell velocity and directionality in the exocrine tissue were enhanced along blood vessels and extracellular matrix fibers. This guided migration implicated integrin-dependent interactions, since integrin blockade impaired exocrine T cell motility. In addition, integrin β1 blockade decreased CD4⁺ T cell effector phenotype specifically in the PA. Thus, we unveil an important role for integrins in the PA during autoimmune diabetes that may have important implications for the design of new therapies.</p

video_3_Integrin β1 Optimizes Diabetogenic T Cell Migration and Function in the Pancreas.mp4

<p>T cell search behavior is dictated by their need to encounter their specific antigen to eliminate target cells. However, mechanisms controlling effector T cell motility are highly tissue-dependent. Specifically, how diabetogenic T cells encounter their target beta cells in dispersed islets throughout the pancreas (PA) during autoimmune diabetes remains unclear. Using intra-vital 2-photon microscopy in a mouse model of diabetes, we found that CXCR3 chemokine downregulated CD8⁺ T cell motility specifically within islets, promoting effector cell confinement to their target sites. By contrast, T cell velocity and directionality in the exocrine tissue were enhanced along blood vessels and extracellular matrix fibers. This guided migration implicated integrin-dependent interactions, since integrin blockade impaired exocrine T cell motility. In addition, integrin β1 blockade decreased CD4⁺ T cell effector phenotype specifically in the PA. Thus, we unveil an important role for integrins in the PA during autoimmune diabetes that may have important implications for the design of new therapies.</p

Structure-Activity Relationship Studies of Retro-1 Analogues Against Shiga Toxin

The Retro-1 molecule was identified in a high-throughput screening as an inhibitor of ricin and Shiga toxins by diminishing their intracellular trafficking via the retrograde route, from early endosomes to the Golgi apparatus. In order to improve the activity of Retro-1, a SAR study was undertaken yielding an analog that possesses roughly 70-fold better EC50 against Shiga toxin cytotoxicity measured in a cell protein synthesis assay. </p