Chromogranins as molecular coordinators at the crossroads between hormone aggregation and secretory granule biogenesis

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Nouvelles raisons d’agir des acteurs de la pêche et de l’agriculture

Les acteurs de la pêche et de l’agriculture (professionnels, institutions d'enseignement, techniciens, organisations professionnelles et syndicales, politiques et législateurs, chercheurs, consommateurs…) font l'expérience de l’évolution des techniques et des droits à produire et à prélever la ressource vivante. Les agriculteurs et les pêcheurs se questionnent sur les raisons de faire leur métier, de s’y maintenir et de le transformer par de nouveaux modes de transmission, de débat et par de nouvelles solidarités. Les auteurs, des chercheurs en sciences sociales et des professionnels des deux filières, examinent les situations les plus propices au développement de nouvelles raisons d'agir et de nouveaux savoirs : débats sur la gestion des ressources renouvelables, décisions relatives au contenu du métier et à sa transmission, mutations professionnelles ou encore nouvelle division du travail. Les situations présentées permettent un éclairage contrasté des secteurs de la pêche et de l'agriculture, et plus particulièrement : – de l’évolution des raisons d’agir et des savoirs des professionnels, des scientifiques, des législateurs mais aussi des nouveaux arrivants, notamment dans leur rapport à l’écologie. Comment de nouvelles raisons d’agir et de nouveaux savoirs émergent-ils des divisions et des conflits ? – des transformations du travail et de la formation professionnelle dans les deux secteurs. Comment les référentiels de formation et les pratiques didactiques modifient-ils les enjeux cognitifs, environnementaux, économiques et sociaux des activités de pêche et d’agriculture ? Ces questions majeures intéresseront à la fois les pêcheurs et les agriculteurs, les concepteurs de politiques publiques et les scientifiques

Effects of eight neuropsychiatric copy number variants on human brain structure

Many copy number variants (CNVs) confer risk for the same range of neurodevelopmental symptoms and psychiatric conditions including autism and schizophrenia. Yet, to date neuroimaging studies have typically been carried out one mutation at a time, showing that CNVs have large effects on brain anatomy. Here, we aimed to characterize and quantify the distinct brain morphometry effects and latent dimensions across 8 neuropsychiatric CNVs. We analyzed T1-weighted MRI data from clinically and non-clinically ascertained CNV carriers (deletion/duplication) at the 1q21.1 (n = 39/28), 16p11.2 (n = 87/78), 22q11.2 (n = 75/30), and 15q11.2 (n = 72/76) loci as well as 1296 non-carriers (controls). Case-control contrasts of all examined genomic loci demonstrated effects on brain anatomy, with deletions and duplications showing mirror effects at the global and regional levels. Although CNVs mainly showed distinct brain patterns, principal component analysis (PCA) loaded subsets of CNVs on two latent brain dimensions, which explained 32 and 29% of the variance of the 8 Cohen’s d maps. The cingulate gyrus, insula, supplementary motor cortex, and cerebellum were identified by PCA and multi-view pattern learning as top regions contributing to latent dimension shared across subsets of CNVs. The large proportion of distinct CNV effects on brain morphology may explain the small neuroimaging effect sizes reported in polygenic psychiatric conditions. Nevertheless, latent gene brain morphology dimensions will help subgroup the rapidly expanding landscape of neuropsychiatric variants and dissect the heterogeneity of idiopathic conditions

Study of the molecular mechanisms governing neuroendocrine secretion : role of the interaction between chromogranin A and phosphatidic acid in the formation and exocytosis of secretory granules

L’exocytose régulée des cellules neuroendocrines est un mécanisme biologique fondamental finement contrôlé, régissant la libération des hormones dans le milieu extracellulaire suite à la fusion des granules de sécrétion à cœur dense (GSCD) avec la membrane plasmique. Ces organites, générés par bourgeonnement de la membrane du réseau trans-golgien (TGN), contiennent des hormones et des neuropeptides ainsi que des glycoprotéines solubles, les granines, et sont donc des acteurs essentiels de l’homéostasie cellulaire. Parmi les granines, la chromogranine A (CgA) joue un rôle majeur dans la biogénèse des GSCD mais les mécanismes moléculaires sous-jacents ne sont pas clairement identifiés. Avant mon arrivée, mon équipe d’accueil démontra que l’expression de la CgA dans des cellules non-endocrines COS7 (dépourvues de GSCD et donc d’exocytose régulée) induit la formation de vésicules ayant les caractéristiques des GSCD et que la délétion des extrémités terminales de la CgA organisées en hélice réduit significativement la formation de ces vésicules. Les hélices conférant aux protéines la capacité d’interagir avec les membranes biologiques, nous nous sommes intéressés durant ma thèse à l’interaction entre la CgA et les phospholipides membranaires. Nous avons montré tout d’abord que la CgA interagit spécifiquement avec l’acide phosphatidique (PA), un lipide conique ayant un rôle clé dans la sécrétion régulée neuroendocrine. Ensuite, à l’aide de la spectrométrie de masse LC-MS/MS, nous avons (i) identifié les formes de PA prédominantes (PA (36 : 1) et (40 : 6)) et observé qu’elles sont communes dans les membranes golgiennes et granulaires, et (ii) démontré que la CgA interagit avec ces formes de PA incluses dans des modèles de membranes artificielles, entraînant la déformation/le remaniement de la membrane de ces modèles. Par ailleurs, une analyse in silico de la séquence de la CgA a révélé la présence d’un domaine de liaison au PA (PABD) au niveau de la région C-terminale. Nous avons alors observé que la délétion de cette région altère significativement la liaison de la CgA aux formes de PA préalablement identifiées, ainsi que la formation des GSCD au sein des cellules neuroendocrines. Enfin, l’inhibition génétique ou pharmacologique de la PLD, enzyme responsable de la synthèse du PA au sein de la voie de sécrétion régulée, entraîne une diminution significative du nombre de GSCD formés. Ces travaux montrent pour la première fois l’importance de l’interaction CgA/PA dans la courbure de la membrane du TGN et la formation consécutive des GSCD. Par ailleurs, l’analyse de l’exocytose des GSCD contenant la CgA-GFP à l’aide de la microscopie à ondes évanescentes (TIRFM) ayant révélé une persistance de fluorescence à la membrane plasmique après exocytose, nous avons recherché la présence de la CgA au niveau des sites de fusion des GSCD et l’implication de l‘interaction CgA/PA dans le contrôle de l’exocytose régulée. Nous avons ainsi d’ores et déjà montré (i) que la stimulation des cellules chromaffines entraîne la présence d’une partie des molécules de CgA au niveau des sites de fusion des GSCD et (ii) que l’inhibition de la synthèse du PA produit par la PLD diminue la sécrétion régulée de CgA et des catécholamines. L’ensemble de ces données obtenues dans le cadre de ma thèse suggère que l’interaction entre la CgA et le PA a un rôle fondamental dans la dynamique des membranes au cours de la biogenèse des GSCD, et ainsi dans la sécrétion des cellules neuroendocrines.Regulated exocytosis of neuroendocrine cells is a finely controlled fundamental biological mechanism governing the release of hormones into the extracellular medium following the fusion of dense-core secretory granules (DCSG) with the plasma membrane. These organelles, generated by budding from the trans-golgian network (TGN) membrane, contain hormones and neuropeptides as well as soluble glycoproteins, granins, and are therefore essential actors of cell homeostasis. Among granins, chromogranin A (CgA) plays a major role in DCSG biogenesis, but the underlying molecular mechanisms are not clearly identified. Previously, my team demonstrated that CgA expression in non-endocrine COS7 cells (devoid of DCSG and therefore of regulated exocytosis) induces the formation of vesicles with DCSG characteristics and that the deletion of CgA -helix terminal regions significantly reduce the formation of these vesicles. Since helices ensure that proteins interact with biological membranes, we were interested in the interaction between CgA and membrane phospholipids during my thesis. We first showed that CgA interacts specifically with phosphatidic acid (PA), a conical lipid with a key role in the regulated neuroendocrine secretion. Then, using LC-MS/MS mass spectrometry, we (i) identified PA predominant forms (PA (36: 1) and (40: 6)) and observed that they are common in Golgi and granular membranes, (ii) demonstrated that CgA interacts with those PA forms inserted in artificial membrane models, leading to the deformation/remodeling of these membrane models. Furthermore, in silico analysis of the CgA sequence revealed the presence of a PA-binding domain (PABD) at the level of its C-terminal region. Then, we observed that the deletion of this region significantly alters CgA binding to PA forms previously identified, as well as the formation of DCSG within neuroendocrine cells. Finally, the genetic or pharmacological inhibition of PLD, the enzyme involved in PA synthesis within the regulated secretory pathway, results in a significant decrease of the DCSG number. This work shows for the first time the importance of CgA/PA interaction in the curvature of the TGN membrane and the resulting DCSG biogenesis. Furthermore, the analysis of the exocytosis of CgA-GFP containing DCSG using Total Internal Reflection Fluorescence Microscopy (TIRFM) showing a persistent fluorescence at the plasma membrane after exocytosis, we looked for the presence of CgA at DCSG fusion sites and the involvement of CgA/PA interaction in the control of regulated exocytosis. Thus, we have already shown (i) that chromaffin cell stimulation leads to the presence of CgA molecules at the level of DCSG fusion sites and (ii) that the inhibition of PA synthesis through PLD decreases the regulated secretion of CgA and catecholamines

Pu multi-recycling scenarios towards a PWR fleet for a stabilization of spent fuel inventories in France

Nuclear scenario studies are performed to explore the impact of possible evolutions of nuclear fleets. The nuclear fuel cycle simulation tool COSI, developed by CEA, is used to model these dynamic scenarios and to evaluate them with respect to uranium and plutonium management, fuel reprocessing and waste production. In recent years, scenarios have focused on transitions from the current nuclear French fleet to a deployment of SFR. However, the French Multi-annual Energy Planning has recently postponed the deployment of this technology to the second half of the 21st century. Alternative solutions of plutonium management in PWR are investigated to stabilize total inventories of spent nuclear fuels. The MIX concept is based on homogeneous fuel assemblies where fuel rods are composed of plutonium blended with enriched uranium. In this study, a transition from the current French fleet to an EPR™ fleet is simulated. Two power capacities of the future EPR™ fleet are considered. A progressive deployment of fuel multi-recycling in the EPR™ fleet is implemented to enable stabilization of all spent fuels and plutonium inventories. Natural uranium consumption is also minimized thanks to ERU fuel batches in EPR™. Results are compared with plutonium and uranium mono-recycling in a PWR fleet

Chromogranins as molecular coordinators at the crossroads between hormone aggregation and secretory granule biogenesis

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A new tool for the simulation of different nuclear fleets at equilibrium

Scenario simulations are the main tool for studying the impact of a nuclear reactor fleet on the related fuel cycle facilities. This equilibrium preliminary study aims to present the functionalities of a new tool and to show the wide variety of reactors/cycles/strategies that can be studied in steady state conditions and validated with more details thanks to dynamic code. Different types of scenario simulation tools have been developed at CEA over the years, this study focuses on dynamic and equilibrium codes. Dynamic fuel cycle simulation code models the ingoing and outgoing material flow in all the facilities of a nuclear reactor fleet and their evolutions through the different nuclear processes over a given period of time. Equilibrium fuel cycle simulation code models advanced nuclear fuel cycles in equilibrium conditions, i.e. in conditions which stabilize selected nuclear inventories such as spent nuclear fuel constituents, plutonium or some minor actinides. The principle of this work is to analyze different nuclear reactors (PWR, AMR) and several fuel types (UOX, MOX, ERU, MIX) to simulate advanced nuclear fleet with partial and fully plutonium and uranium multi-recycling strategies at equilibrium. At this first stage, selected results are compared with COSI6 simulations in order to evaluate the precision of this new tool, showing a significant general agreement

Myosin 1b and F-actin are involved in the control of secretory granule biogenesis

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Myosin 1b and F-actin are involved in the control of secretory granule biogenesis

Hormone secretion relies on secretory granules which store hormones in endocrine cells and release them upon cell stimulation. The molecular events leading to hormone sorting and secretory granule formation at the level of the TGN are still elusive. Our proteomic analysis of purified whole secretory granules or secretory granule membranes uncovered their association with the actomyosin components myosin 1b, actin and the actin nucleation complex Arp2/3. We found that myosin 1b controls the formation of secretory granules and the associated regulated secretion in both neuroendocrine cells and chromogranin A-expressing COS7 cells used as a simplified model of induced secretion. We show that F-actin is also involved in secretory granule biogenesis and that myosin 1b cooperates with Arp2/3 to recruit F-actin to the Golgi region where secretory granules bud. These results provide the first evidence that components of the actomyosin complex promote the biogenesis of secretory granules and thereby regulate hormone sorting and secretion.This work was supported by Institut National de la Santé et de la Recherche Médicale, the University of Rouen Normandy, the Conseil Régional de Normandie and the Ministère de l’Enseignement Supérieur et de la RecherchePeer Reviewe

Chromogranin A preferential interaction with Golgi phosphatidic acid induces membrane deformation and contributes to secretory granule biogenesis

International audienceChromogranin A (CgA) is a key luminal actor of secretory granule biogenesis at the trans‐Golgi network (TGN) level but the molecular mechanisms involved remain obscure. Here, we investigated the possibility that CgA acts synergistically with specific membrane lipids to trigger secretory granule formation. We show that CgA preferentially interacts with the anionic glycerophospholipid phosphatidic acid (PA). In accordance, bioinformatic analysis predicted a PA‐binding domain (PABD) in CgA sequence that effectively bound PA (36:1) or PA (40:6) in membrane models. We identified PA (36:1) and PA (40:6) as predominant species in Golgi and granule membranes of secretory cells, and we found that CgA interaction with these PA species promotes artificial membrane deformation and remodeling. Furthermore, we demonstrated that disruption of either CgA PABD or phospholipase D (PLD) activity significantly alters secretory granule formation in secretory cells. Our findings show for the first time the ability of CgA to interact with PLD‐generated PA, which allows membrane remodeling and curvature, key processes necessary to initiate secretory granule budding