La stéatose hépatique chez les palmipèdes : gènes clés, différences entre types génétiques et cinétique postprandiale

In waterfowls, hepatic steatosis is a complex mechanism which involved many factors including genetic background. Indeed, some inter-genotype differences have already been demonstrated between Muscovy, Pekin ducks and their crossbreed the mule ducks (which is used in fatty liver or “foie gras” production). The work of this thesis is enrolled in a comprehensive understanding of the physiological mechanisms underlying the development of hepatic steatosis. The first study “DuckPhy” is interested in intergenotypic differences during overfeeding in the three genotypes particularly at transcriptional level. This experiment leads us to highlight the importance of the hepatic re-uptake of lipid and its possible involvement in the exacerbated development of fatty liver disease in the mule ducks. In fact, the fatty acid transporter Fatty Acid Binding Protein 4 (FABP4) and the receptor of Very Low Density Lipoprotein (VLDLR) present a very large overexpression at the end of the overfeeding period in liver of mule ducks in comparison with the two other genetic types.However, Pekin ducks overexpressed genes related to lipid export and β-oxidation such as Apolipoprotein B (ApoB), Microsomal Triglyceride Transfer Protein (MTTP), but also Carnitine Palmitoyl Transferase 1 (CPT1) leading to a weak hepatic lipid accumulation. Regarding glucose metabolism, Pekin ducks seem to better express GLUcose Transporters (GLUT) in liver and peripheral tissues at the end of the overfeeding period associated with a lower glycemia. The second study “DuckKinetic” allow us to build an expression profile in order to localize their peak of expression and to select the best sampling point after the meal in overfed mule ducks. This study provides a kinetic of expression of genes involves in both lipid and glucid metabolisms. We have observed a precocious expression of glucose transporters in jejunum and a high postprandial regulation of DGAT2 positioning this gene as a key enzyme in lipogenesis. All these data allow to highlight previously unknown mechanisms including hepatic re-uptake of circulating lipids, but also to build a profile of expression for each gene involved in the development of hepatic steatosis.La stéatose hépatique chez les palmipèdes est un processus complexe impliquant de nombreux facteurs notamment le fond génétique. En effet, des différences inter-génotypes ont d’ores et déjà été démontrées entre les canards de Barbarie, Pékin ainsi que leur hybride, le canard mulard (utilisé dans la production de foie gras). Les travaux de cette thèse se sont donc inscrits dans une compréhension globale des mécanismesphysiologiques à l’origine du développement de la stéatose hépatique autrement appelée «foie gras ». La première étude « DuckPhy » s’intéresse particulièrement aux différences intergénotypiques rencontrées au cours du gavage chez les trois types génétiques, notamment du point de vue transcriptionnel. Cette expérimentation a permis de mettre en évidence l’apport important du recaptage des lipides au niveau hépatique et sa possible implication dans le développement exacerbé de la stéatose hépatique chez le canard mulard. En effet, le transporteur d’acides gras Fatty Acid Binding Protein 4 (FABP4) ainsi que le récepteur aux Very Low Density Lipoprotein (VLDLR) présentent une induction très importante de leur expression à la fin du gavage dans le foie du canard mulard en comparaison des deux autres types génétiques. Le canard Pékin, quant à lui, surexprime les gènes en rapport avec l’exportation des lipides et la β-oxydation à savoir, d’une part l’Apolipoprotéine B (ApoB) ainsi que la Microsomal Triglyceride Transfer Protein (MTTP), et d’autre part la Carnitine Palmitoyl Transferase 1 (CPT1), conduisant à une faible accumulation de lipides dans le foie. Concernant le métabolisme glucidique, le canard Pékin semble mieux exprimer les transporteurs de glucose (GLUT), notamment dans le foie et les tissus périphériques en fin de gavage associé à une glycémie plus faible. La seconde étude « DuckKinetic » a permis d’établir un profil d’expression des différents gènes d’intérêt en vue de localiser leurs pics d’expression permettant ainsi de sélectionner le meilleur point de prélèvement postprandial chez le canard mulard gavé. Cette étude fournit un historique d’expression des gènes des enzymes impliquées aussi bien dans le métabolisme lipidique que glucidique avec une expression précoce des transporteurs de glucose dans le jejunum et une forte régulation postprandiale de la DGAT2 la positionnant comme enzyme clé de la lipogenèse. L’ensemble de ces données a permis de mettre enavant des mécanismes jusqu’alors inconnus notamment sur le recaptage hépatique des lipides circulants, mais aussi de construire un historique d’expression pour chaque gène impliqué dans la mise en place de la stéatose

Postprandial consequences of lipid absorption in the onset of obesity: Role of intestinal CD36

International audienceObesity has reached epidemic proportions and its incidence is still increasing. Obesity is an excess of fat, which can have harmful consequences such as inflammation, insulin resistance or dyslipidemia. Taken together, these conditions are known as metabolic syndrome (MetS). More and more studies consider obesity from a postprandial perspective: parameters such as triglyceridemia, endotoxemia or hormone secretion may have deeper postprandial metabolic consequences than during the fasting state. These effects take even more importance when we consider that humans spend more than half of the day in a postprandial state. This review focuses on the postprandial state in a fat-enriched diet and on the consequences of intestinal lipid absorption, putting the intestine in a central place in the development of obesity / MetS. Finally, we describe the crucial role of the lipid receptor cluster of differentiation 36 (CD36) for gut lipid absorption and the alterations that occur in CD36 dysfunction

Kinetics of expression of genes involved in glucose metabolism after the last meal in overfed mule ducks

International audienceIn waterfowls, overfeeding leads to a hepatic steatosis, also called "foie gras." We decided to investigate the role of glucose metabolism in steatosis emergence. For this, we measured the expression of genes during the 12 h following the last meal of the overfeeding period. As expected, it showed that the expression of glucose transporter is more precocious in jejunal mucosa, especially for SGLT1, known to be the major transporter at the apical surface. In the liver, GLUT2 and HK1 are upregulated at the same time and seem to work together to import glucose. In peripherals tissues, such as muscle and subcutaneous adipose tissue (SAT), expression of genes of interest occurs later than the one in jejunum and liver. These results are in accordance with the evolution of glycemia. This study allows us to better understand the kinetic treatment of glucose after a meal in overfed ducks. It also will allow researchers to better target their sampling time knowing the optimal point of expression of each gene

Genes involved in the establishment of hepatic steatosis in Muscovy, Pekin and mule ducks

International audienceOur main objectives were to determine the genes involved in the establishment of hepatic steatosis in three genotypes of palmipeds. To respond to this question, we have compared Muscovy ducks, Pekin ducks and their crossbreed the mule duck fed ad libitum or overfed. We have shown a hepatic overexpression of fatty acid synthase (FAS) and di-acyl glycerol acyl transferase 2 (DGAT2) in overfed individuals, where DGAT2 seemed to be more regulated. This increase in lipogenesis genes is associated with a decrease of lipoprotein formation in Muscovy and mule ducks, especially apolipoprotein B (ApoB) and Microsomal Triglyceride Transfer Protein (MTTP), leading to lipid accumulation in liver. In Pekin ducks, MTTP expression is upregulated suggesting a better hepatic lipids exportation. Regarding lipids re-uptake, fatty acid-binding protein 4 and very-low-density-lipoprotein receptor are overexpressed in liver of mule ducks at the end of the overfeeding period. This phenomenon puts light on a mechanism unknown until today. In fact, mule can incorporate more lipids in liver than the two other genotypes leading to an intensified hepatic steatosis. To conclude, our results confirmed the genotype variability to overfeeding. Furthermore, similar observations are already described in non-alcoholic fatty liver disease in human, and ask if ducks could be an animal model to study hepatic triglyceride accumulation

Pre- and post-prandial expression of genes involved in lipid metabolism at the end of the overfeeding period of mule ducks

In palmipeds, overfeeding leads to hepatic steatosis, also called ‘‘foie gras’’ which is the result of many metabolic mechanisms. In order to understand these mechanisms, we decided to measure the expression of genes implicated in lipid metabolism during 12 hours (h) following the last meal of the overfeeding period. We have shown that there is a precocious expression (within 2 h) of fatty acid synthase and acyl CoA synthetase longchain 1 in liver and muscle of mule ducks in addition with a later peak. Furthermore, di-acyl glycerol acyl transferase presents the highest induction of expression in liver and it is overexpressed quite a long time, positioning this enzyme as a key factor in hepatic steatosis. These observations are quite similar in muscle. Lipoprotein secretion is upregulated later in postprandial period, with an upregulation of apolipoprotein and microsomal triglycerides transfer protein beginning at 5 h in liver or muscle. Regarding hepatic re-uptake of lipid, lesser variations are observed, suggesting that fatty acid binding protein and very low-density lipoprotein receptor (VLDLR) are already at their maximum expression specifically in these tissues. In muscle, VLDLR and LDLR upregulation is observed 5 h after the meal, associated with an overexpression in the adipose tissue of lipase maturation factor 1 involved in the maturation of lipoprotein lipase. These findings will allow us to better understand the kinetic treatment in lipid metabolism after a meal in overfed ducks. This first report on kinetic expression will allow researcher to better target their sampling time knowing the optimal point of expression of each gen

Colonisation bactérienne des colliers d’ambre portés par les nourrissons et enfants : une étude prospective de 27 cas

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Inter genotype differences in expression of genes involved in glucose metabolism in the establishment of hepatic steatosis in Muscovy, Pekin and mule ducks

International audienceIn waterfowls, overfeeding leads to a hepatic steatosis, also called "foie gras". Our main objectives were to determine what is the share of genes involvement of glucose metabolism in the establishment of fatty liver in three genotypes of waterfowls: Muscovy (Cairina moschata), Pekin ducks (Anas platyrhynchos) and their crossbreed, the mule duck. 288 male ducks of Pekin, Muscovy and mule genotypes were reared until weeks 12 and overfed between weeks 12 and 14. We analysed gene expression at the beginning, the middle and the end of the overfeeding period in different tissues. We have shown an upregulation of glucose transporters (GLUT) in peripheral tissues (pectoralis major or adipose tissue) in Pekin ducks. In addition, GLUT2 was not found in jejunal mucosa and another GLUT seems to replace it 3 h after the meal: GLUT3. Mule ducks upregulating GLUT3 earlier compared to Pekin ducks. However, these results need further investigations. In liver, globally, Pekin ducks exhibit the highest expression of GLUT or enzymes implicated in glycolysis. The few significant variations of gene expressions in glucose metabolism between these three genotypes and the momentary specific overexpression of GLUT do not allow us to detect a lot of specific genotype differences. To conclude, the differences in response to overfeeding of Pekin, Muscovy and mule ducks, for the establishment of hepatic steatosis, cannot be only explained by the glucose metabolism at transcriptomic level

Development of a model of neonatal analgesia throughout lactation in rats

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Glucagon-like peptide-1 is associated with poor clinical outcome, lipopolysaccharide translocation and inflammation in patients undergoing cardiac surgery with cardiopulmonary bypass

International audienceIntroduction: Cardiac surgery with cardiopulmonary bypass (CPB) is associated with gut barrier dysfunction. Gut barrier dysfunction might be estimated non-invasively by lipopolysaccharide (LPS) plasma concentration. Glucagon-like peptide-1 (GLP-1) is a gut secreted hormone that is a potential marker of mucosal integrity. Our objective was to evaluate GLP-1 as a peri-operative marker of gut barrier dysfunction in patients undergoing cardiac surgery with CPB.Methods: GLP-1, intestinal fatty acid binding protein (I-FABP) and lipopolysaccharide were assayed: at induction, after CPB and 24 h after admission in the intensive care unit. The primary end-point was peri-operative lipopolysaccharide concentration (LPS concentration at those 3 time points).Results: Seventy-two patients were included in the present analysis. The highest measured post-operative GLP-1 concentration was in the sample taken 24 h after admission to intensive care, which was associated with peri-operative lipopolysaccharide plasma concentration. Patients who had the highest GLP-1 concentrations at 24 h experienced more severe inflammation and worse clinical outcomes.Conclusion: Our study supports that GLP-1 is not only a hormone of glucose metabolism but is also secreted when gut barrier is impaired in cardiac surgery with CPB. The GLP-1 levels measured 24 h after admission to the intensive care unit were associated with LPS concentration, inflammation and clinical outcomes

Increased Phospholipid Transfer Protein Activity Is Associated With Markers of Enhanced Lipopolysaccharide Clearance in Human During Cardiopulmonary Bypass

International audienceIntroduction: Lipopolysaccharide (LPS) is a component of gram-negative bacteria, known for its ability to trigger inflammation. The main pathway of LPS clearance is the reverse lipopolysaccharide transport (RLT), with phospholipid transfer protein (PLTP) and lipoproteins playing central roles in this process in experimental animal models. To date, the relevance of this pathway has never been studied in humans. Cardiac surgery with cardiopulmonary bypass is known to favor LPS digestive translocation. Our objective was to determine whether pre-operative PLTP activity and triglyceride or cholesterol-rich lipoprotein concentrations were associated to LPS concentrations in patients undergoing cardiac surgery with cardiopulmonary bypass. Methods: A post-hoc analysis was conducted on plasma samples obtained from patients recruited in a randomized controlled trial.Total cholesterol, high density lipoprotein cholesterol (HDLc), low density lipoprotein cholesterol (LDLc), triglyceride and PLTP activity were measured before surgery. LPS concentration was measured by mass spectrometry before surgery, at the end of cardiopulmonary bypass and 24 h after admission to the intensive care unit. Results: High PLTP activity was associated with lower LPS concentration but not with inflammation nor post-operative complications. HDLc, LDLc and total cholesterol were not associated with LPS concentration but were lower in patients developing post-operative adverse events. HDLc was negatively associated with inflammation biomarkers (CRP, PCT). Triglyceride concentrations were positively correlated with LPS concentration, PCT and were higher in patients with post-operative complications. Conclusion: Our study supports the role of PLTP in LPS elimination and the relevance of RLT in human. PLTP activity, and not cholesterol rich lipoproteins pool size seemed to be the limiting factor for RLT. PLTP activity was not directly related to post-operative inflammation and adverse events, suggesting that LPS clearance is not the main driver of inflammation in our patients. However, HDLc was associated with lower inflammation and was associated with favorable outcomes, suggesting that HDL beneficial anti-inflammatory effects could be, at least in part independent of LPS clearance