Regulation of N-Myc downstream regulated gene 2 by bile acids

Here we report that bile acid chenodeoxycholic acid (CDCA) and synthetic farnesoid X receptor (FXR) agonist GW4064 robustly induced tumor suppressor N-Myc downstream regulated gene 2 (NDRG2) expression in human hepatoma cells and primary hepatocytes. Knockdown of FXR abolished the induction by CDCA, whereas overexpre ssion of a constitutively active form of FXR increased NDRG2 expression. A FXR-response element was identified within intronic regions of human and murine genes. Moreover, mice given GW4064 exhib it an increase of Ndrg2 expression in liver and kidney, where both NDRG2 and FXR are enriched. The identification of NDRG2 as a bile acid regulated gene may provide novel knowledge toward the understanding of NDRG2 physiological function and the link between metabolism and cancer

A polyphenol-rich plant extract prevents hypercholesterolemia and modulates gut microbiota in western diet-fed mice

IntroductionTotum-070 is a combination of five plant extracts enriched in polyphenols to target hypercholesterolemia, one of the main risk factors for cardiovascular diseases. The aim of this study was to investigate the effects of Totum-070 on cholesterol levels in an animal model of diet-induced hypercholesterolemia.MethodsC57BL/6JOlaHsd male mice were fed a Western diet and received Totum-070, or not, by daily gavage (1g/kg and 3g/kg body weight) for 6 weeks.ResultsThe Western diet induced obesity, fat accumulation, hepatic steatosis and increased plasma cholesterol compared with the control group. All these metabolic perturbations were alleviated by Totum-070 supplementation in a dose-dependent manner. Lipid excretion in feces was higher in mice supplemented with Totum-070, suggesting inhibition of intestinal lipid absorption. Totum-070 also increased the fecal concentration of short chain fatty acids, demonstrating a direct effect on intestinal microbiota.DiscussionThe characterization of fecal microbiota by 16S amplicon sequencing showed that Totum-070 supplementation modulated the dysbiosis associated with metabolic disorders. Specifically, Totum-070 increased the relative abundance of Muribaculum (a beneficial bacterium) and reduced that of Lactococcus (a genus positively correlated with increased plasma cholesterol level). Together, these findings indicate that the cholesterol-lowering effect of Totum-070 bioactive molecules could be mediated through multiple actions on the intestine and gut microbiota

Métabolisme du cholestérol et function β-cellulaire

Le diabète de type 2 est fréquemment associé à une dyslipidémie mixte, ainsi qu’à une lipotoxicité caractérisée par une augmentation du contenu en triglycérides dans plusieurs types cellulaires. Au niveau de la cellule β-pancréatique, cette lipotoxicité conduit à un défaut d’insulinosécrétion et à une apoptose. Plus récemment, de nouvelles données suggèrent l’existence d’un lien entre le métabolisme du cholestérol et la fonction des cellules β. Ainsi, l’accumulation de cholestérol dans les îlots pancréatiques altère la sécrétion d’insuline. Sur le plan moléculaire, le transporteur ABCA1 (ATP-binding cassette transporter, member 1) et le récepteur des LDL (low density lipoproteins) apparaissent comme des médiateurs majeurs du métabolisme du cholestérol dans l’îlot. Le cholestérol intracellulaire semble réguler à la fois l’organisation des microdomaines membranaires et la sécrétion d’insuline en réponse au glucose. Enfin, les différentes classes de lipoprotéines ont des effets propres sur l’apoptose et la prolifération des cellules β-pancréatiques (protection des HDL et effet délétère des LDL)

Implication de PCSK9 dans les maladies métaboliques (régulation par les acides biliaires et rôle fonctionnel dans le pancréas)

PCSK9 (proprotein convertase subtilisin kexin type 9) est le 3ème gène impliqué dans l'hypercholestérolémie familiale dominante, après les mutations des gènes codant pour le récepteur aux LDL (LDLR) et pour son ligand l apo-B. PCSK9 agit comme un inhibiteur de l'expression hépatique du LDLR par un mécanisme post-traductionnel. En se liant au domaine extracellulaire du LDLR à la surface des membranes plasmiques, PCSK9 induit l'internalisation du LDLR et sa dégradation dans les lysosomes. Ainsi les mutations de PCSK9 associées à l'hypercholestérolémie sont des mutations gain de fonction. A l'inverse, les mutations perte de fonction de PCSK9 induisent une hypocholestérolémie et une protection contre les maladies cardiovasculaires. Le développement d'inhibiteurs de PCSK9 est donc un enjeu thérapeutique majeur dans la prise en charge des hypercholestérolémies. Dans ce contexte, la 1ère partie de ma thèse a consisté à étudier la régulation transcriptionnelle de PCSK9 par les acides biliaires et le récepteur nucléaire FXR (Farnesoid X Receptor). De nombreux gènes du métabolisme lipidique sont régulés par FXR et l activation de FXR a des effets bénéfiques dans les troubles métaboliques. Les résultats obtenus dans des lignées d'hépatocytes humains montrent que l'activation de FXR réprime l'expression de PCSK9, ce qui s'accompagne d'une augmentation de l'activité du LDLR mesurée in vitro. Ceci suggère que l'utilisation d agoniste de FXR pour réprimer PCSK9 et ainsi potentialiser l'action des statines pourrait être utile dans le traitement de l'hypercholestérolémie. On sait à présent que le métabolisme du cholestérol intervient dans la régulation de la sécrétion d insuline par les cellules b du pancréas et pourrait ainsi jouer un rôle dans la physiopathologie du diabète de type 2. La 2nde partie de ma thèse s'est intéressée au rôle de PCSK9 dans la fonction insulino-sécrétrice des cellules b. A partir d ilots isolés du pancréas humains et de souris, je démontre que PCSK9 est exprimée dans les cellulesdelta. Par ailleurs, PCSK9 diminue l'expression du LDLR au sein des ilots de Langerhans, probablement via une action endocrine En revanche, l'invalidation de PCSK9 chez la souris ne semble pas perturber l'homéostasie du glucose ex vivo et in vivo, ni la survie des cellules b en réponse à un traitement par la streptozotocine.PCSK9 (proprotein convertase subtilisin kexin type 9) is the 3rd gene implicated in autosomic familial hypercholesterolemia with the LDL Receptor (LDLR) gene and its ligand apo-B. PCSK9 acts as a post-transcriptional inhibitor of hepatic LDLR expression. Gain of function mutations of PCSK9 are associated with hypercholesterolemia. By contrast, loss of function mutations of PCSK9 induce hypocholesterolemia and a protection against cardiovascular diseases. Therefore, development of PCSK9 inhibitors is a promising therapeutical approach to treat hypercholesterolemia. In this context, the 1st part of my thesis consisted of studying transcriptional regulation of PCSK9 by bile acids and the nuclear receptor FXR (Farnesoid X Receptor). FXR regulates many genes involved in lipid metabolism, and FXR activation may have beneficial effects in metabolic diseases. My results in human hepatocytes cell lines show that FXR activation represses PCSK9 expression. Such PCSK9 repression is correlated with the induction of LDLR activity in vitro. These findings suggest that FXR agonists may be used in combination with statins to amplify their hypocholestrolemic action in hyperlipidemic patients .It is now admitted that cholesterol metabolism modulates insulin secretion by pancreatic b cells and might interfere with the development of type 2 diabetes. The 2nd part of my thesis focussed on the role of PCSK9 in the b cells function. Using isolated pancreatic islets from humans and mice, I show that PCSK9 is expressed in delta cells of islets of Langehrans. PCSK9 is able to downregulate LDLR expression in the whole islet, probably acting in an endocrine manner. However, PCSK9-deficiency does not alter glucose homeostasis ex vivo and in vivo in mice, as well as b cell survival upon streptozotocin treatment.NANTES-BU Médecine pharmacie (441092101) / SudocSudocFranceF

Regulation of human class I alcohol dehydrogenases by bile acids

Class I alcohol dehydrogenases (ADH1s) are the rate-limiting enzymes for ethanol and vitamin A (retinol) metabolism in the liver . Because previous studies have shown that human ADH1 enzymes may participate in bile acid metabolism, we investigated whether the bile acid-activated nuclear receptor farnesoid X receptor (FXR) regulates ADH1 genes. In human hepatocytes, both the endogenous FXR ligand chenodeoxycholic acid and synthetic FXR-specific agonist GW4064 increased ADH1 mRNA, protein, and activity. Moreover, overexpression of a constitutively active form of FXR induced ADH1A and ADH1B expression, whereas silencing of FXR abolished the effects of FXR agonists on ADH1 expression and activity. Transient transfection studies and electrophoretic mobility shift assays revealed functional FXR response elements in the ADH1A and ADH1B proximal promoters, thus indicating that both genes are direct targets of FXR. These findings provide the first evidence for direct connection of bile acid signaling and alcohol metabolism

Regulation of N-Myc downstream regulated gene 2 by bile acids

Here we report that bile acid chenodeoxycholic acid (CDCA) and synthetic farnesoid X receptor (FXR) agonist GW4064 robustly induced tumor suppressor N-Myc downstream regulated gene 2 (NDRG2) expression in human hepatoma cells and primary hepatocytes. Knockdown of FXR abolished the induction by CDCA, whereas overexpre ssion of a constitutively active form of FXR increased NDRG2 expression. A FXR-response element was identified within intronic regions of human and murine genes. Moreover, mice given GW4064 exhib it an increase of Ndrg2 expression in liver and kidney, where both NDRG2 and FXR are enriched. The identification of NDRG2 as a bile acid regulated gene may provide novel knowledge toward the understanding of NDRG2 physiological function and the link between metabolism and cancer

Regulation of human class I alcohol dehydrogenases by bile acids

Class I alcohol dehydrogenases (ADH1s) are the rate-limiting enzymes for ethanol and vitamin A (retinol) metabolism in the liver . Because previous studies have shown that human ADH1 enzymes may participate in bile acid metabolism, we investigated whether the bile acid-activated nuclear receptor farnesoid X receptor (FXR) regulates ADH1 genes. In human hepatocytes, both the endogenous FXR ligand chenodeoxycholic acid and synthetic FXR-specific agonist GW4064 increased ADH1 mRNA, protein, and activity. Moreover, overexpression of a constitutively active form of FXR induced ADH1A and ADH1B expression, whereas silencing of FXR abolished the effects of FXR agonists on ADH1 expression and activity. Transient transfection studies and electrophoretic mobility shift assays revealed functional FXR response elements in the ADH1A and ADH1B proximal promoters, thus indicating that both genes are direct targets of FXR. These findings provide the first evidence for direct connection of bile acid signaling and alcohol metabolism

Inhibitory Potential of α-Amylase, α-Glucosidase, and Pancreatic Lipase by a Formulation of Five Plant Extracts: TOTUM-63

International audienceControlling post-prandial hyperglycemia and hyperlipidemia, particularly by regulating the activity of digestive enzymes, allows managing type 2 diabetes and obesity. The aim of this study was to assess the effects of TOTUM-63, a formulation of five plant extracts (Olea europaea L., Cynara scolymus L., Chrysanthellum indicum subsp. afroamericanum B.L.Turner, Vaccinium myrtillus L., and Piper nigrum L.), on enzymes involved in carbohydrate and lipid absorption. First, in vitro inhibition assays were performed by targeting three enzymes: α-glucosidase, α-amylase, and lipase. Then, kinetic studies and binding affinity determinations by fluorescence spectrum changes and microscale thermophoresis were performed. The in vitro assays showed that TOTUM-63 inhibited all three digestive enzymes, particularly α-glucosidase (IC50 of 13.1 µg/mL). Mechanistic studies on α-glucosidase inhibition by TOTUM-63 and molecular interaction experiments indicated a mixed (full) inhibition mechanism, and higher affinity for α-glucosidase than acarbose, the reference αglucosidase inhibitor. Lastly, in vivo data using leptin receptor-deficient (db/db) mice, a model of obesity and type 2 diabetes, indicated that TOTUM-63 might prevent the increase in fasting glycemia and glycated hemoglobin (HbA1c) levels over time, compared with the untreated group. These results show that TOTUM-63 is a promising new approach for type 2 diabetes management via αglucosidase inhibition