The Autophagic Flux Inhibitor Bafilomycine A1 Affects the Expression of Intermediary Metabolism-Related Genes in Trout Hepatocytes

Autophagy is an evolutionarily conserved process of cellular self-eating which emerged these last years as a major adaptive metabolic response to various stresses such as fasting, hypoxia, or environmental pollutants. However, surprisingly very few data is currently available on its role in fish species which are directly exposed to frequent environmental perturbations. Here, we report that the treatment of fasted trout hepatocytes with the autophagy inhibitor Bafilomycine A1 lowered the mRNA levels of many of the gluconeogenesis-related genes and increased those of genes involved in intracellular lipid stores. Concurrently, intracellular free amino acid levels dropped and the expression of the main genes involved in the endoplasmic reticulum (ER) stress exhibited a sharp increase in autophagy inhibited cells. Together these results highlight the strong complexity of the crosstalk between ER, autophagy and metabolism and support the importance of considering this function in future studies on metabolic adaptation of fish to environmental stresses

La stéatose hépatique chez le canard mulard : étude cinétique du métabolisme intermédiaire, stress cellulaire, autophagie et nouvelle approche par les microARNs

The main objective of this thesis was to continue the investigations carried out on the mechanisms underlying the development of foie gras in mule ducks. This process, known as hepatic steatosis and induced by overfeeding, needs to be further studied in order to contribute to overfeeding optimization.A kinetic study of the expression of genes related to hepatic steatosis, intermediate metabolism and cellular stress in mule ducks highlighted firstly the strong mobilization of carbohydrate and lipid metabolisms. Secondly a significant induction of the insulin / mTOR signalling pathway and the activation of various cellular protection mechanisms in hepatocytes were observed allowing them to fight against the increased intake of starch brought by the overfeeding. Among these are various protective mechanisms, autophagy has been the subject of extensive study in overfed ducks whose steatosis has been barely induced compared to non-overfed ducks. Autophagic flux measurements (LC3-II) showed that overfeeding induced inhibition of the autophagic process in mule ducks’ hepatocytes from the early stage of hepatic steatosis. This same study found that the mechanisms associated with cellular stress such as oxidative stress, endoplasmic reticulum stress or apoptosis did not occur early in the development of hepatic steatosis but much later. The same is true for the impact of overfeeding on mTOR signalling pathway.In addition, the kinetic study also revealed the significant induction of cholesterol metabolism correlated with the liver weight gain of ducks during overfeeding. These results aroused the interest of investigating plasma biomarkers for the development of hepatic steatosis related to cholesterol metabolism among microRNAs. Thus, duck's plasmatic miRNome was sequenced and it allowed to define the most differentially expressed microRNAs in the plasma of mule ducks but also to detect microRNAs (miR-122, miR-107 and mi-R194) as potential biomarkers that could be used for monitoring the development of fatty liver.All of this work contributes to the advancement of research on understanding the mechanisms of establishment of hepatic steatosis in mule ducks.L’objectif principal de cette thèse était de poursuivre les investigations menées sur les mécanismes sous-jacents au développement du foie gras chez le canard mulard. Ce processus appelé stéatose hépatique et induit par le gavage nécessite d’être davantage étudié afin de contribuer à l’optimisation du gavage. Une étude cinétique de l’expression des gènes en lien avec la stéatose hépatique, le métabolisme intermédiaire et le stress cellulaire chez le canard mulard a permis de mettre en évidence, outre la forte mobilisation des métabolismes glucidique et lipidique, une induction significative de la voie de signalisation de l’insuline mTOR et l’activation de mécanismes de protection cellulaire au sein des hépatocytes leur permettant de lutter contre l’apport accru d’amidon apporté par le gavage. Parmi ces différents mécanismes protecteurs, l’autophagie a fait l’objet d’une étude poussée chez des canards gavés dont la stéatose a été à peine induite comparés à des canards non gavés. Les mesures de flux autophagique (LC3-II) ont montré que le gavage induisait une inhibition du processus autophagique dans les hépatocytes de canards mulards dès la phase précoce du développement de la stéatose hépatique. Cette même étude a permis de constater que les mécanismes associés au stress cellulaires tels que le stress oxydant, le stress du réticulum endoplasmique ou encore l’apoptose ne se sont pas induits dès le début du développement de la stéatose hépatique mais bien plus tardivement. Il en est de même pour l’impact du gavage sur la voie mTOR. Par ailleurs, l’étude cinétique a également permis de mettre en évidence l’induction significative du métabolisme du cholestérol corrélé au gain de poids de foie des canards au cours du gavage. Ces résultats ont suscité l’intérêt de rechercher des biomarqueurs plasmatiques du développement de la stéatose hépatique en lien avec le métabolisme du cholestérol parmi les microARNs. Ainsi, le miRNome plasmatique du canard a été séquencé et a permis de définir les microARNs les plus différentiellement exprimés dans le plasma des canards mulards mais également de déceler des microARNs (miR-122, miR-107 et miR-194) candidats comme potentiels biomarqueurs utilisables pour le suivi du développement du foie gras.L’ensemble de ces travaux contribuent à l’avancée de la recherche sur la compréhension des mécanismes de l’établissement de la stéatose hépatique chez le canard mulard

Hepatic steatosis in mule ducks : kinetic study of intermediate metabolism, cellular stress, autophagy and new approach by microRNAs

L’objectif principal de cette thèse était de poursuivre les investigations menées sur les mécanismes sous-jacents au développement du foie gras chez le canard mulard. Ce processus appelé stéatose hépatique et induit par le gavage nécessite d’être davantage étudié afin de contribuer à l’optimisation du gavage. Une étude cinétique de l’expression des gènes en lien avec la stéatose hépatique, le métabolisme intermédiaire et le stress cellulaire chez le canard mulard a permis de mettre en évidence, outre la forte mobilisation des métabolismes glucidique et lipidique, une induction significative de la voie de signalisation de l’insuline mTOR et l’activation de mécanismes de protection cellulaire au sein des hépatocytes leur permettant de lutter contre l’apport accru d’amidon apporté par le gavage. Parmi ces différents mécanismes protecteurs, l’autophagie a fait l’objet d’une étude poussée chez des canards gavés dont la stéatose a été à peine induite comparés à des canards non gavés. Les mesures de flux autophagique (LC3-II) ont montré que le gavage induisait une inhibition du processus autophagique dans les hépatocytes de canards mulards dès la phase précoce du développement de la stéatose hépatique. Cette même étude a permis de constater que les mécanismes associés au stress cellulaires tels que le stress oxydant, le stress du réticulum endoplasmique ou encore l’apoptose ne se sont pas induits dès le début du développement de la stéatose hépatique mais bien plus tardivement. Il en est de même pour l’impact du gavage sur la voie mTOR. Par ailleurs, l’étude cinétique a également permis de mettre en évidence l’induction significative du métabolisme du cholestérol corrélé au gain de poids de foie des canards au cours du gavage. Ces résultats ont suscité l’intérêt de rechercher des biomarqueurs plasmatiques du développement de la stéatose hépatique en lien avec le métabolisme du cholestérol parmi les microARNs. Ainsi, le miRNome plasmatique du canard a été séquencé et a permis de définir les microARNs les plus différentiellement exprimés dans le plasma des canards mulards mais également de déceler des microARNs (miR-122, miR-107 et miR-194) candidats comme potentiels biomarqueurs utilisables pour le suivi du développement du foie gras.L’ensemble de ces travaux contribuent à l’avancée de la recherche sur la compréhension des mécanismes de l’établissement de la stéatose hépatique chez le canard mulard.The main objective of this thesis was to continue the investigations carried out on the mechanisms underlying the development of foie gras in mule ducks. This process, known as hepatic steatosis and induced by overfeeding, needs to be further studied in order to contribute to overfeeding optimization.A kinetic study of the expression of genes related to hepatic steatosis, intermediate metabolism and cellular stress in mule ducks highlighted firstly the strong mobilization of carbohydrate and lipid metabolisms. Secondly a significant induction of the insulin / mTOR signalling pathway and the activation of various cellular protection mechanisms in hepatocytes were observed allowing them to fight against the increased intake of starch brought by the overfeeding. Among these are various protective mechanisms, autophagy has been the subject of extensive study in overfed ducks whose steatosis has been barely induced compared to non-overfed ducks. Autophagic flux measurements (LC3-II) showed that overfeeding induced inhibition of the autophagic process in mule ducks’ hepatocytes from the early stage of hepatic steatosis. This same study found that the mechanisms associated with cellular stress such as oxidative stress, endoplasmic reticulum stress or apoptosis did not occur early in the development of hepatic steatosis but much later. The same is true for the impact of overfeeding on mTOR signalling pathway.In addition, the kinetic study also revealed the significant induction of cholesterol metabolism correlated with the liver weight gain of ducks during overfeeding. These results aroused the interest of investigating plasma biomarkers for the development of hepatic steatosis related to cholesterol metabolism among microRNAs. Thus, duck's plasmatic miRNome was sequenced and it allowed to define the most differentially expressed microRNAs in the plasma of mule ducks but also to detect microRNAs (miR-122, miR-107 and mi-R194) as potential biomarkers that could be used for monitoring the development of fatty liver.All of this work contributes to the advancement of research on understanding the mechanisms of establishment of hepatic steatosis in mule ducks

Highlighting the role of autophagy in metabolic adaptation of trout hepatocytes to fasting

RésuméRésuméHighlighting the role of autophagy in metabolic adaptation of trout hepatocytes to fasting. 13. International Congress on the Biology of Fis

The autophagic flux inhibitor bafilomycine A1 affects the expression of intermediary metabolism-related genes in trout hepatocytes

Autophagy is an evolutionarily conserved process of cellular self-eating which emerged these last years as a major adaptive metabolic response to various stresses such as fasting, hypoxia, or environmental pollutants. However, surprisingly very few data is currently available on its role in fish species which are directly exposed to frequent environmental perturbations. Here, we report that the treatment of fasted trout hepatocytes with the autophagy inhibitor Bafilomycine A1 lowered the mRNA levels of many of the gluconeogenesis-related genes and increased those of genes involved in intracellular lipid stores. Concurrently, intracellular free amino acid levels dropped and the expression of the main genes involved in the endoplasmic reticulum (ER) stress exhibited a sharp increase in autophagy inhibited cells. Together these results highlight the strong complexity of the crosstalk between ER, autophagy and metabolism and support the importance of considering this function in future studies on metabolic adaptation of fish to environmental stresses

Impacts of Embryonic Thermal Programming on the Expression of Genes Involved in Foie gras Production in Mule Ducks

International audienceEmbryonic thermal programming has been shown to improve foie gras production in overfed mule ducks. However, the mechanisms at the origin of this programming have not yet been characterized. In this study, we investigated the effect of embryonic thermal manipulation (+1°C, 16 h/24 h from embryonic (E) day 13 to E27) on the hepatic expression of genes involved in lipid and carbohydrate metabolisms, stress, cell proliferation and thyroid hormone pathways at the end of thermal manipulation and before and after overfeeding (OF) in mule ducks. Gene expression analyses were performed by classic or high throughput real-time qPCR. First, we confirmed well-known results with strong impact of OF on the expression of genes involved in lipid and carbohydrates metabolisms. Then we observed an impact of OF on the hepatic expression of genes involved in the thyroid pathway, stress and cell proliferation. Only a small number of genes showed modulation of expression related to thermal programming at the time of OF, and only one was also impacted at the end of the thermal manipulation. For the first time, we explored the molecular mechanisms of embryonic thermal programming from the end of heat treatment to the programmed adult phenotype with optimized liver metabolism

Ontogeny of hepatic metabolism in mule ducks highlights different gene expression profiles between carbohydrate and lipid metabolic pathways

International audienceBackground: The production of foie gras involves different metabolic pathways in the liver of overfed ducks suchas lipid synthesis and carbohydrates catabolism, but the establishment of these pathways has not yet beendescribed with precision during embryogenesis. The early environment can have short- and long-term impacts onthe physiology of many animal species and can be used to influence physiological responses that is calledprogramming. This study proposes to describe the basal hepatic metabolism at the level of mRNA in mule duckembryos in order to reveal potential interesting programming windows in the context of foie gras production. To this end, a kinetic study was designed to determine the level of expression of selected genes involved in steatosis-related liver functions throughout embryogenesis.The livers of 20 mule duck embryos were collected every 4 days from the 12th day of embryogenesis (E12) until 4days after hatching (D4), and gene expression analysis was performed. The expression levels of 50 mRNAs werequantified for these 7 sampling points and classified into 4 major cellular pathways.Results: Interestingly, most mRNAs involved in lipid metabolism are overexpressed after hatching (FASN, SCD1,ACOX1), whereas genes implicated in carbohydrate metabolism (HK1, GAPDH, GLUT1) and development (HGF, IGF,FGFR2) are predominantly overexpressed from E12 to E20. Finally, regarding cellular stress, gene expression appears quite stable throughout development, contrasting with strong expression after hatching (CYP2E1, HSBP1, HSP90AA1).Conclusion: For the first time we described the kinetics of hepatic ontogenesis at mRNA level in mule ducks and highlighted different expression patterns depending on the cellular pathway. These results could be particularly usefulin the design of embryonic programming for the production of foie gras

Impact d'une manipulation thermique pendant l'embryogénèse sur la production de foie gras des canards mulards

RésuméPrevious studies have shown that very early life events could have programming effects on adult physiology. Exposing poultry embryos to higher incubation temperatures improve their survival capacity to thermal challenge in adulthood. Recently, embryonic thermal manipulation (TM) has been shown to impact muscle development and hepatic metabolism in Pekin ducks. In this study, we aimed to test whether rising incubation temperature has an impact on development, growth and zootechnical performances in mule ducks, mainly used for fatty liver production. Different thermal incubation conditions were applied during embryogenesis on mule duck eggs with three TM groups and one control, for which the temperature was maintained stable throughout. A faster embryonic and growth development was observed for all TM groups. Significant changes in body temperature and body weight were measured at hatching time and throughout the breeding period. Finally, overfeeding induced significant increase of live body weight, leg muscle, fat, and liver weights in all groups, while embryonic TM significantly increased abdominal fat and liver weights compared to control overfed group.These results suggest that embryonic TM can improve fatty liver production in male mule ducks, nevertheless potential deleterious effects on eclosability need to be explored further.Différentes études ont montré que des événements survenus très tôt dans la vie d’un animal pouvaient avoir des effets de « programmation » sur la physiologie de l’adulte. L'exposition d'embryons de volaille à des températures d'incubation élevées améliore leur capacité de survie lors de pics de chaleur à l'âge adulte.Récemment, il a été démontré que la manipulation thermique embryonnaire (MT) avait un impact sur le développement musculaire et le métabolisme hépatique chez les canards Pékin. Dans cette étude, notre objectif était de mesurer l’impact d’une élévation de la température d'incubation sur le développement, la croissance et les performances des canards mulards, principalement utilisés pour la production de foie gras.Nous avons testé trois modalités expérimentales d’augmentation de la température dans l’incubateur sur des embryons de canards mulards, parallèlement un groupe témoin était maintenu à température constante tout au long de l’embryogenèse. Une éclosion plus précoce a été observée pour tous les groupes soumis à une MT (1 jour d’avance en moyenne). Des changements significatifs de la température et du poids corporels ont été mesurés à l'éclosion et tout au long de l’élevage. Enfin, le gavage a entraîné une augmentation significative du poids vif , des muscles de la cuisse, du tissu adipeux et du foie dans tous les groupes traités, tandis qu’une MT embryonnaire augmentait de manière significative le poids de graisse abdominale (jusqu’à +13,3% ; P=0,0001)et du foie (jusqu’à +16,9% ; P<0,0001), par rapport au groupe contrôle (sans MT) gavé.Ces résultats suggèrent que la MT embryonnaire peut améliorer la production de foie gras chez le canard mulard, mais ses effets potentiels sur l’éclosabilité doivent être approfondis

Positive impact of thermal manipulation during embryogenesis on foie gras production in mule ducks

Animal studies have shown that very early life events may have programing effects on adult metabolism and health. In this study, we aim, for the first, time to elucidate the effects of embryonic thermal manipulation (TM) on the performance of overfed mule ducks, in particular for the production of foie gras (fatty liver). We designed threeembryonic TMs with different protocols for increasing the incubation temperature during the second part of embryogenesis, to determine whether hepatic metabolism could be “programed” to improve its fattening response to overfeeding at the age of three months. Initial results confirm that an increase in the incubation temperature leads to faster development (observed for all treated groups compared to the control group), and a decrease in the body surface temperature at birth. Thereafter, in a very innovative way, we showed that the three TM conditions specifically increased liver weights, as well as liver lipid content after overfeeding compared to the non-TM control group. These results demonstrate that embryonic TM effectively “programs” the metabolic response to thechallenge of force-feeding, resulting in increased hepatic steatosis. Finally, our goal of improving foie gras production has been achieved with three different embryonic thermal stimuli, demonstrating the high reproducibility of the method. However, this repeatability was also perceptible in the adverse effects observed on two groups treated with exactly the same cumulative temperature rise leading to a reduction in hatchability (75 and 76% vs. 82% in control), in addition to an increase in the melting rate after cooking.These results suggest that embryonic thermal programing could be an innovative and inexpensive technique for improving foie gras production, although the specific protocol (duration, level or period of temperature increase), remains to be elucidated in order to avoid adverse effect