ChREBP et le contrôle de la lipogenèse hépatique (interrelation avec les récepteurs nucléaires et la signalisation insulinique)

Ce travail a porté sur le facteur de transcription ChREBP, un régulateur clef de la synthèse d acides gras à partir du glucose, ou lipogenèse. Cette voie métabolique est stimulée par un signal glucose, via ChREBP, et par l insuline, via les facteurs LXR et SREBP-1c. L expression adénovirale d une forme constitutivement active de ChREBP (ChREBPCA) dans le foie de souris suffit à stimuler la lipogenèse et l accumulation de triglycérides hépatiques (stéatose), même en l absence de SREBP-1c (souris insulinopéniques traitées à la streptozotocine STZ) ou de LXR et de SREBP1c (souris LXR / KO). Bien que la stéatose soit bégnine, elle est la première étape d un spectre de maladies hépatiques délétères. Chez les souris STZ, ChREBPCA permet de restaurer la voie de signalisation insulinique hépatique et stimule le stockage de glucose. A moyen terme, ces souris présentent une amélioration de la glycémie due probablement à la stimulation par ChREBPCA de FGF21, une hépatokine bénéfique pour l homéostasie énergétique. L expression de ChREBPCA est en revanche néfaste chez les souris LXR / KO. La stéatose s accompagne dans ce cas d une inflammation et d une importante apoptose. ChREBPCA diminue l expression du régulateur CAR et perturbe la voie de détoxification des acides biliaires. Ceux-ci s accumulent dans le foie et causent des dommages importants chez les souris LXR / KO mais pas les sauvages, soulignant ainsi le rôle protecteur du récepteur nucléaire LXR. Ces données révèlent le rôle ambivalent de ChREBP dans la physiologie hépatique, et apportent des éléments nouveaux sur les mécanismes qui gouvernent la transition de la stéatose simple à l apparition des dommages hépatiquesThis work focused on ChREBP, a master regulator of fatty acid synthesis (lipogenesis) from glucose. This metabolic pathway is stimulated by a glucose signal, via ChREBP, and by an insulin signal, via transcription factors LXR and SREBP-1c. Adenoviral expression of a constitutive active form of ChREBP (ChREBPCA) in liver was sufficient to promote lipogenesis and triglyceride accumulation (steatosis) even in a situation of SREBP-1c deficiency (insulinopenic streptozotocin (STZ) treated mice) or synergistic LXR and SREBP-1c deficiency (LXR / KO mice). Hepatic steatosis, by itself, is benign, but represents the first step of a spectrum of deleterious liver diseases (NAFLD). In STZ mice, ChREBPCA rescued the hepatic insulin signaling pathway and led to enhanced hepatic glucose storage under the form of glycogen and lipids. These mice also displayed improved glycemia, probably due to the stimulation by ChREBPCA of the insulin-sensitizer circulating factor FGF21. In contrast, expression of ChREBPCA in liver of LXR / KO mice was deleterious. Steatosis in this model was linked to inflammatory markers and to hepatocyte apoptosis. In addition, ChREBPCA, by downregulating the expression of the nuclear receptor CAR, led to an alteration in the bile acid and bilirubin detoxification pathway. In turn, accumulation of these toxic components in liver caused critical alterations in liver of LXR / KO but not in wild type mice, underlining the protective role of LXR against stressed-induced damages. These results provide novel insights on the ambivalent role of ChREBP in liver physiology, as well as on the mechanisms triggering simple steatosis transition toward more severe liver damagesPARIS-BIUSJ-Biologie recherche (751052107) / SudocSudocFranceF

Cross-regulation of hepatic glucose metabolism ChREBP and Nuclear Receptors

International audienceThere is a worldwide epidemic of obesity and type 2 diabetes, two major public health concerns associated with alterations in both insulin and glucose signaling pathways. Glucose is not only an energy source but also controls the expression of key genes involved in energetic metabolism, through the glucose-signaling transcription factor, Carbohydrate Responsive Element Binding Protein (ChREBP). ChREBP has emerged as a central regulator of fatty acid synthesis (lipogenesis) in response to glucose under both physiological and physiopathological conditions. Glucose activates ChREBP by regulating its entry from the cytosol to the nucleus, thereby promoting its binding to carbohydrate responsive element (ChoRE) in the promoter regions of glycolytic (L-PK) and lipogenic genes (ACC and FAS). We have previously reported that the inhibition of ChREBP in liver of obese ob/ob mice improves the metabolic alterations linked to obesity, fatty liver and insulin-resistance. Therefore, regulating ChREBP activity could be an attractive target for lipid-lowering therapies in obesity and diabetes. However, before this is possible, a better understanding of the mechanism(s) regulating its activity is needed. In this review, we summarize recent findings on the role and regulation of ChREBP and particularly emphasize on the cross-regulations that may exist between key nuclear receptors (LXR, TR, HNF4α) and ChREBP for the control of hepatic glucose metabolism. These novel molecular cross-talks may open the way to new pharmacological opportunities

Le facteur de transcription ChREBP

International audienc

Water Regimes Questioned from the ‘Global South’ : Agents, Practices And Knowledge: Proceedings of Conference held on January 15-17, 2016 at New Delhi

This working paper presents the proceedings of an international workshop on water policies, held on January 2016 in (Delhi) and brought together 25 participants. It was supported by a number of partners (Centre for Policy Research, Centre de Sciences Humaines, Institut Français of Pondicherry, UMI i-GLOBES CNRS/University of Arizona, ANR ENGIND, ANR BLUEGRASS, Indo French Water Network et Institut de recherche pour le Développement). The research focused on comparisons between different case studies in a range of countries (USA, Kenya, South Africa, Morocco, Mexico, France and India), adopting an approach situated at the crossroads of geography and sociology. This international dimension proves particularly appropriate for a study of ‘water regimes’ as is consubstantial to their development: beyond the models often identified as “national’, from the 19th century onwards, we can identify rationales of transfer involving knowledge, expertise, skills and trained agents. From the beginning of the 20th century these models have to be included in the complexity of potential circulations: North-South transfers, as well as South-North and South-South transfers. The workshop covered the following topics: water regime transformations, situations where dominant doxa is challenged, the socio-historic transformations of the ‘Hydrocracies’ with emergence of a new generation of water professionals

Perinatal Hypercholesterolemia Exacerbates Atherosclerosis Lesions in Offspring by Altering Metabolism of Trimethylamine-N-Oxide and Bile Acids

International audienceObjective-Experimental studies suggest that maternal hypercholesterolemia may be relevant for the early onset of cardiovascular disease in offspring. We investigated the effect of perinatal hypercholesterolemia on the atherosclerosis development in the offspring of apolipoprotein E-deficient mice and the underlying mechanism. Approach and Results-Atherosclerosis and related parameters were studied in adult male or female apolipoprotein E-deficient mice offspring from either normocholesterolemic or hypercholesterolemic mothers and normocholesterolemic fathers. Female born to hypercholesterolemic mothers had more aortic root lesions than female born to normocholesterolemic mothers. Lesions in whole aorta did not differ between groups. Higher trimethylamine-N-oxide levels and Fmo3 hepatic gene expression were higher in female born to hypercholesterolemic mothers offspring compared with female born to normocholesterolemic mothers and male. Trimethylamine-N-oxide levels were correlated with the size of atherosclerotic root lesions. Levels of hepatic cholesterol and gallbladder bile acid were greater in male born to hypercholesterolemic mothers compared with male born to normocholesterolemic mothers. At 18 weeks of age, female born to hypercholesterolemic mothers showed lower hepatic Scarb1 and Cyp7a1 but higher Nr1h4 gene expression compared with female born to normocholesterolemic mothers. Male born to hypercholesterolemic mothers showed an increase in Scarb1 and Ldlr gene expression compared with male born to normocholesterolemic mothers. At 25 weeks of age, female born to hypercholesterolemic mothers had lower Cyp7a1 gene expression compared with female born to normocholesterolemic mothers. DNA methylation of Fmo3, Scarb1, and Ldlr promoter regions was slightly modified and may explain the mRNA expression modulation. Conclusions-Our findings suggest that maternal hypercholesterolemia may exacerbate the development of atherosclerosis in female offspring by affecting metabolism of trimethylamine-N-oxide and bile acids. These data could be explained by epigenetic alterations

Systemic Delivery of siRNA Down Regulates Brain Prion Protein and Ameliorates Neuropathology in Prion Disorder

International audienceOne of the main challenges for neurodegenerative disorders that are principally incurable is the development of new therapeutic strategies, which raises important medical, scientific and societal issues. Creutzfeldt-Jakob diseases are rare neurodegenerative fatal disorders which today remain incurable. The objective of this study was to evaluate the efficacy of the down-regulation of the prion protein (PrP) expression using siRNA delivered by, a water-in-oil microemulsion, as a therapeutic candidate in a preclinical study. After 12 days rectal mucosa administration of Aonys/PrP-siRNA in mice, we observed a decrease of about 28% of the brain PrP(C) level. The effect of Aonys/PrP-siRNA was then evaluated on prion infected mice. Several mice presented a delay in the incubation and survival time compared to the control groups and a significant impact was observed on astrocyte reaction and neuronal survival in the PrP-siRNA treated groups. These results suggest that a new therapeutic scheme based an innovative delivery system of PrP-siRNA can be envisioned in prion disorders

In vivo PrP^C expression in AONYS/siRNA-treated mice.

<p>Panel A. Brain homogenates of mice treated for 12(see <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0088797#pone-0088797-t001" target="_blank">Table 1</a>) with two doses of PrP^C siRNA (Aonys/siPrP 300 (L) and 600 µg/kg), the vehicle only and scrambled-siRNA, were analysed for PrP^C accumulation by Western blot. The C+ lane corresponds to a brain homogenate of untreated mice. A decrease of PrP^C was apparent in siPrP treated mice. However there was a relative variability in detection in relation with the low linearity of the western blot. Panel B. Samples in A were analysed using ELISA for quantitation of PrP^C. Graphic results of normalized PrP^C were presented as medians and interquartile ranges. Statistical analysis (Kruskal-Wallis test) was used to evaluate the significance of the difference between the groups. The siPrP group (600 µg/kg) presents a significant reduction of PrP^C levels. Panels C and D. Additional experiments were carried out (10 mice/groups) in which mice were treated or not with Aonys/PrP^C siRNA at 600 µg/kg. Panel C. PrP^C ELISA. Panel D. RT-Q-PCR quantitation (light Cycler) of PrP and GAPDH in Graphic results were presented as medians and interquartile ranges. Statistical analysis (Kruskal-Wallis test) was used to evaluate the significance of the difference between the groups. The siPrP group presents a significant reduction of both PrP^C protein and RNA levels.</p

Histological and Immunohistolochemical illustration.

<p>Panel A. PrP^Sc immunostaining was observed in all the mice (arrow). Panel B. Vacuolar lesions revealed after Hematoxylin & Eosin staining were apparent in all conditions. Immunohistochemical detections of the GFAP astrocyte marker (Panel C) and the neuronal marker NeuN were also performed (Panel D).</p

Impact of siRNA on incubation and survival time.

<p>Panel A. The incubation time in scrapie infected mice based on the presence of at least three clinical signs (among: waddling gait, flattened back, rough coat, sticky eye discharge, weight loss, very jumpy, hunched, incontinence) was plotted as medians and interquartile ranges in the three groups: Aonys/PrP^C siRNA (siPrP 600 µg/kg), Aonys vehicle only and Aonys/scrambled-siRNA. The survival times of the three groups of infected mice were plotted as medians and interquartile ranges (Panel B.) and Kaplan-Meier survival curves (Panel C.). No statistical difference was observed between each group neither for the incubation period nor the survival time.</p