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Context Mammalian target of rapamycin complex 1 (mTORC1) is an essential sensor that regulates fundamental biological processes like cell growth, proliferation and energy metabolism. The treatment of disease by sirolimus, a mTORC1 inhibitor, causes adverse effects, such as female fertility disorders. Aims The objective of the study was to decipher the reproductive consequences of a downregulation of mTORC1 in the hypothalamus. Methods The reduced expression of mTORC1 was induced after intracerebroventricular injection of lentivirus expressing a short hairpin RNA (shRNA) against regulatory associated protein of TOR (raptor) in adult female mice (ShRaptor mice). Key results The ShRaptor mice were fertile and exhibited a 15% increase in the litter size compared with control mice. The histological analysis showed an increase in antral, preovulatory follicles and ovarian cysts. In the hypothalamus, the GnRH mRNA and FSH levels in ShRaptor mice were significantly elevated. Conclusions These results support the hypothesis that mTORC1 in the central nervous system participates in the regulation of female fertility and ovarian function by influencing the GnRH neuronal activity. Implications These results suggest that a lower mTORC1 activity directly the central nervous system leads to a deregulation in the oestrous cycle and an induction of ovarian cyst development.

International audience; Prokineticins are family of small proteins involved in many important biological processes including food intake and control of energy balance. The prokineticin 2 (PROK2) is expressed in several peripheral tissues and areas in the central nervous system. PROK2 activates G protein-coupled receptors, namely, prokineticin receptor 1 (PROKR1) and prokineticin receptor 2 (PROKR2). Preclinical models exhibiting disturbances of the PROK2 pathway (at the level of PROK2 or its receptors) are characterized by changes in food intake, feeding behavior and insulin sensitivity related to a dysfunction of the energy balance control. In Humans, mutations of PROK2 and PROKR2 genes are associated to the Kallmann syndrome (KS) that affects both the hormonal reproductive axis and the sense of smell and may also lead to obesity. Moreover, plasma PROK2 concentration has been correlated with various cardiometabolic risk factors and type 2 diabetes (T2D). The present review summarizes knowledge on PROK2 structure, signaling and function focusing on its role in control of food intake and energy homeostasis. (c) 2021 Elsevier B.V. and Soci & eacute;t & eacute; Fran & ccedil;aise de Biochimie et Biologie Mol & eacute;culaire (SFBBM). All rights reserved.

Background Bariatric surgery is an effective treatment for type 2 diabetes. Early post-surgical enhancement of insulin secretion is key for diabetes remission. The full complement of mechanisms responsible for improved pancreatic beta cell functionality after bariatric surgery is still unclear. Our aim was to identify pathways, evident in the islet transcriptome, that characterize the adaptive response to bariatric surgery independently of body weight changes. Methods We performed entero-gastro-anastomosis (EGA) with pyloric ligature in leptin-deficient ob/ob mice as a surrogate of Roux-en-Y gastric bypass (RYGB) in humans. Multiple approaches such as determination of glucose tolerance, GLP-1 and insulin secretion, whole body insulin sensitivity, ex vivo glucose-stimulated insulin secretion (GSIS) and functional multicellular Ca2+-imaging, profiling of mRNA and of miRNA expression were utilized to identify significant biological processes involved in pancreatic islet recovery. Findings EGA resolved diabetes, increased pancreatic insulin content and GSIS despite a persistent increase in fat mass, systemic and intra-islet inflammation, and lipotoxicity. Surgery differentially regulated 193 genes in the islet, most of which were involved in the regulation of glucose metabolism, insulin secretion, calcium signaling or beta cell viability, and these were normalized alongside changes in glucose metabolism, intracellular Ca2+ dynamics and the threshold for GSIS. Furthermore, 27 islet miRNAs were differentially regulated, four of them hubs in a miRNA-gene interaction network and four others part of a blood signature of diabetes resolution in ob/ob mice and in humans. Interpretation Taken together, our data highlight novel miRNA-gene interactions in the pancreatic islet during the resolution of diabetes after bariatric surgery that form part of a blood signature of diabetes reversal. Funding European Union's Horizon 2020 research and innovation programme via the Innovative Medicines Initiative 2 Joint Undertaking (RHAPSODY), INSERM, Societe Francophone du Diabete, Institut Benjamin Delessert, Wellcome Trust Investigator Award (212625/Z/18/Z), MRC Programme grants (MR/R022259/1, MR/J0003042/1, MR/L020149/1), Diabetes UK (BDA/11/0004210, BDA/15/0005275, BDA 16/0005485) project grants, National Science Foundation (310030–188447), Fondation de l'Avenir.

Background: The role of the type 2 diabetes risk gene SLC30A8, encoding ZnT8, in the control of glucagon secretion is not clearly established. Results: Inactivation of ZnT8 in a subset of α-cells leads to increased glucagon secretion in vivo and in vitro. Conclusion: ZnT8 is involved in normal glucagon release. Significance: SLC30A8 diabetes risk alleles may influence glucagon secretion., SLC30A8 encodes a zinc transporter ZnT8 largely restricted to pancreatic islet β- and α-cells, and responsible for zinc accumulation into secretory granules. Although common SLC30A8 variants, believed to reduce ZnT8 activity, increase type 2 diabetes risk in humans, rare inactivating mutations are protective. To investigate the role of Slc30a8 in the control of glucagon secretion, Slc30a8 was inactivated selectively in α-cells by crossing mice with alleles floxed at exon 1 to animals expressing Cre recombinase under the pre-proglucagon promoter. Further crossing to Rosa26:tdRFP mice, and sorting of RFP+: glucagon+ cells from KO mice, revealed recombination in ∼30% of α-cells, of which ∼50% were ZnT8-negative (14 ± 1.8% of all α-cells). Although glucose and insulin tolerance were normal, female αZnT8KO mice required lower glucose infusion rates during hypoglycemic clamps and displayed enhanced glucagon release (p < 0.001) versus WT mice. Correspondingly, islets isolated from αZnT8KO mice secreted more glucagon at 1 mm glucose, but not 17 mm glucose, than WT controls (n = 5; p = 0.008). Although the expression of other ZnT family members was unchanged, cytoplasmic (n = 4 mice per genotype; p < 0.0001) and granular (n = 3, p < 0.01) free Zn2+ levels were significantly lower in KO α-cells versus control cells. In response to low glucose, the amplitude and frequency of intracellular Ca2+ increases were unchanged in α-cells of αZnT8KO KO mice. ZnT8 is thus important in a subset of α-cells for normal responses to hypoglycemia and acts via Ca2+-independent mechanisms.

Aims/Hypothesis: Glucagon release from pancreatic alpha cells is required for normal glucose homoeostasis and is dysregulated in both Type 1 and Type 2 diabetes. The tumour suppressor LKB1 (STK11) and the downstream kinase AMP-activated protein kinase (AMPK), modulate cellular metabolism and growth, and AMPK is an important target of the anti-hyperglycaemic agent metformin. While LKB1 and AMPK have emerged recently as regulators of beta cell mass and insulin secretion, the role of these enzymes in the control of glucagon production in vivo is unclear. Methods: Here, we ablated LKB1 (aLKB1KO), or the catalytic alpha subunits of AMPK (aAMPKdKO, -a1KO, -a2KO), selectively in w45% of alpha cells in mice by deleting the corresponding flox’d alleles with a preproglucagon promoter (PPG) Cre. Results: Blood glucose levels in male aLKB1KO mice were lower during intraperitoneal glucose, aminoimidazole carboxamide ribonucleotide (AICAR) or arginine tolerance tests, and glucose infusion rates were increased in hypoglycemic clamps (p < 0.01). aLKB1KO mice also displayed impaired hypoglycemia-induced glucagon release. Glucose infusion rates were also elevated (p < 0.001) in aAMPKa1 null mice, and hypoglycemia-induced plasma glucagon increases tended to be lower (p ¼ 0.06). Glucagon secretion from isolated islets was sensitized to the inhibitory action of glucose in aLKB1KO, aAMPKdKO, and -a1KO, but not -a2KO islets. Conclusions/Interpretation: An LKB1-dependent signalling cassette, involving but not restricted to AMPKa1, is required in pancreatic alpha cells for the control of glucagon release by glucose. 2015 Published by Elsevier GmbH. This is an open access article under the CC BY license (http://creativecommons.org/licenses/by/3.0/).

24 p.-6 fig.-1 tab.-1 graph. abst., Autophagy facilitates the adaptation to nutritional stress. Here, we show that short-term starvation of cultured cells or mice caused the autophagy-dependent cellular release of acyl-CoA-binding protein (ACBP, also known as diazepam-binding inhibitor, DBI) and consequent ACBP-mediated feedback inhibition of autophagy. Importantly, ACBP levels were elevated in obese patients and reduced in anorexia nervosa. In mice, systemic injection of ACBP protein inhibited autophagy, induced lipogenesis, reduced glycemia, and stimulated appetite as well as weight gain. We designed three approaches to neutralize ACBP, namely, inducible whole-body knockout, systemic administration of neutralizing antibodies, and induction of antiACBP autoantibodies in mice. ACBP neutralization enhanced autophagy, stimulated fatty acid oxidation, inhibited appetite, reduced weight gain in the context of a high-fat diet or leptin deficiency, and accelerated weight loss in response to dietary changes. In conclusion, neutralization of ACBP might constitute a strategy for treating obesity and its co-morbidities., G.K. is supported by the Ligue Contre le Cancer (équipe labelisée); Agence National de la Recherche (ANR) – projets blancs; Cancéropôle Île-de-France; Chancelerie Des universités de Paris (Legs Poix); the European Research Council (ERC); Inserm Transfert, Fondation Carrefour; Institut National du Cancer (INCa); Inserm (HTE); Institut Universitaire de France; Leducq Foundation; the Labex immuno-Oncology; the RHU Torino Lumière; the Seattle Foundation; and the SIRICs SOCRATE and CARPEM. C.M. and C.C.-G. are supported by Agence National de la Recherche (ANR-16-CE14-0026, fat4brain proposal); C.L.-O. is supported by “Juan de Madariaga fellowship”; S.B. is supported by the Swedish Research Council Vetenskapsrådet (2015-05468) and the Austrian Science Fund FWF (P27183-B24); and F.M. is supported by the Austrian Science Fund FWF (grants P23490-B20, P29262, P24381, P29203, and P27893), DKplus Metabolic and Cardiovascular Diseases (W1226), Austrian Science Ministry, Karl Franzens University (“Unkonventionelle Forschung” and “flysleep”), NAWI Graz, and BioTechMed-Graz flagship project “EPIAge.” K.C. is supported by ANR MICRO-Obes and AP/HP (PHRC Microbaria). L.G. is supported by an intramural startup from the Department of Radiation Oncology of Weill Cornell Medical College (New York, US) and by Sotio a.c. (Prague, Czech Republic).

Dietary supplement may potentially help to fight obesity and other metabolic disorders such as insulin-resistance and low-grade inflammation. The present study aimed to test whether supplementation with Agaricus blazei murill (ABM) extract could have an effect on diet-induced obesity in rats. Wistar rats were fed with control diet (CD) or high-fat diet (HF) and either with or without supplemented ABM for 20 weeks. HF diet-induced body weight gain and increased fat mass compared to CD. In addition HF-fed rats developed hyperleptinemia and insulinemia as well as insulin resistance and glucose intolerance. In HF-fed rats, visceral adipose tissue also expressed biomarkers of inflammation. ABM supplementation in HF rats had a protective effect against body weight gain and all study related disorders. This was not due to decreased food intake which remained significantly higher in HF rats whether supplemented with ABM or not compared to control. There was also no change in gut microbiota composition in HF supplemented with ABM. Interestingly, ABM supplementation induced an increase in both energy expenditure and locomotor activity which could partially explain its protective effect against diet-induced obesity. In addition a decrease in pancreatic lipase activity is also observed in jejunum of ABM-treated rats suggesting a decrease in lipid absorption. Taken together these data highlight a role for ABM to prevent body weight gain and related disorders in peripheral targets independently of effect in food intake in central nervous system.

The hypothalamus plays a major role in the control of energy balance, by sensing circulating lipids. Several studies conducted over the past decade suggest that disruption of lipid sensing can lead to hypothalamic lipotoxicity, thereby contributing to the development of various diseases, such as obesity and type 2 diabetes.The physiological role of 'lipid sensing' as a regulator of neuronal activity involved in the regulation of energy homeostasis will be reviewed. Next, the emerging evidence that alterations of hypothalamic systems that regulate energy balance during overnutrition can lead to the development of obesity and associated pathologies such as type 2 diabetes will be described.Several studies have highlighted the role of malonyl-CoA and PKCθ and also autophagy within the hypothalamus as signals of nutrient abundance by critical neurons regulating food intake. Besides the physiological role of hypothalamic lipid sensing, it has been shown that overnutrition can also induce hypothalamic lipotoxicity through an inflammatory process. In conclusion, lipid toxicity could be the starting point of perturbations of the central control of energy balance which will favor the appearance of obesity and type 2 diabetes. Lipid sensing in the hypothalamus could be considered as a potential target for anti-obesity/diabetic strategies.

The hypothalamic arcuate nucleus (ARC) is a major integration center for energy and glucose homeostasis that responds to leptin. Resistance to leptin in the ARC is an important component of the development of obesity and type 2 diabetes. Recently, we showed that Endospanin1 (Endo1) is a negative regulator of the leptin receptor (OBR) that interacts with OBR and retains the receptor inside the cell, leading to a decreased activation of the anorectic STAT3 pathway. Endo1 is up-regulated in the ARC of high fat diet (HFD)-fed mice, and its silencing in the ARC of lean and obese mice prevents and reverses the development of obesity. Objective Herein we investigated whether decreased Endo1 expression in the hypothalamic ARC, associated with reduced obesity, could also ameliorate glucose homeostasis accordingly. Methods We studied glucose homeostasis in lean or obese mice silenced for Endo1 in the ARC via stereotactic injection of shRNA-expressing lentiviral vectors. Results We observed that despite being leaner, Endo1-silenced mice showed impaired glucose homeostasis on HFD. Mechanistically, we show that Endo1 interacts with p85, the regulatory subunit of PI3K, and mediates leptin-induced PI3K activation. Conclusions Our results thus define Endo1 as an important hypothalamic integrator of leptin signaling, and its silencing differentially regulates the OBR-dependent functions., Highlights • Endospanin1 interacts with p85, the regulatory subunit of PI3K. • Endospanin1 silencing increases STAT3 but decreases AKT activation mediated by leptin. • Endospanin1 dissociates leptin-regulated body weight and glucose homeostasis. • Endospanin1 differentially regulates leptin signaling and biological functions.

Resume Des neurones sensibles aux nutriments (glucose, acides gras libres [AGL]) ont ete localises dans differentes structures du systeme nerveux central (SNC), notamment l’hypothalamus et le tronc cerebral, regions clefs impliquees dans le controle nerveux du bilan d’energie. Sur la base de modeles precliniques, il a ete montre que les AGL participent au controle nerveux de la prise alimentaire, ainsi que de la secretion et l’action de l’insuline, a la suite de leur effet sur des neurones hypothalamiques et un relais efferent via le systeme nerveux autonome. Ainsi les variations circadiennes de concentration circulante des AGL peuvent etre detectees dans des conditions physiologiques par le SNC et contribuer a la regulation de l’homeostasie energetique. A l’echelon cellulaire, des sous-populations de neurones « excites » ou « inhibes » par les AGL ont donc ete identifiees dans differents noyaux hypothalamiques (arque ou ventromedian). Le metabolisme intracellulaire des AGL semble etre important pour relayer leurs effets mais des donnees recentes indiquent que dans la moitie au moins des neurones sensibles au AGL, le mecanisme implique serait dependant du transporteur membranaire des acides gras (AG), FAT/CD36. En conclusion, les AGL ou leurs metabolites jouent un role important dans la regulation de l’homeostasie energetique via ces neurones hypothalamiques specialises dans la detection des variations quotidiennes de concentration circulante des nutriments. A cote de ces aspects physiologiques, une surcharge en lipides ou une perturbation du metabolisme lipidique pourrait affecter ce systeme central de detection et consecutivement etre un evenement precoce pouvant conduire a une deterioration du controle nerveux du bilan d’energie. Cela pourrait participer, au moins en partie, a la mise en place des maladies metaboliques (obesite/diabete de type 2) chez des sujets predisposes.

Introduction et but de l’etude La Cystathionine Beta Synthase (CBS) catalyse la premiere etape de la voie de trans-sulfuration, qui transforme l’homocysteine en cystathionine. Une deficience en CBS conduit a une maladie chronique, chez l’homme comme chez la souris, appelee hyperhomocysteinemie (HHcy), qui presente des composantes cardiovasculaires, neuropsychiatriques et hepatiques. Cependant, il y a peu d’information sur un lien entre CBS et secretion d’insuline, et une eventuelle susceptibilite des animaux deficients a developper un diabete de type 2 (DT2). Nous avons recemment montre, par une approche multiparametrique chez la souris, que l’expression de la CBS dans l’ilot de Langerhans etait positivement correlee a la secretion d’insuline [1] , c’est pourquoi nous postulons que la deficience en CBS entrainerait un defaut de secretion d’insuline et pourrait predisposer au DT2. Materiel et methodes Nous avons utilise des souris heterozygotes pour la CBS (CBS ± ) qui presentent une HHcy legere [2] , et les avons supplementees en methionine dans l’eau de boisson de facon a augmenter l’HHcy. Nous les avons soumises a un regime hyperlipidique (HL) et avons suivi la prise alimentaire, le poids et la composition corporelle, l’homeostasie glucidique, et avons analyse le foie des animaux en vue de mettre en evidence une dysfonction hepatique. Resultats et analyse statistique Les souris CBS ± sans supplementation en methionine sont intolerantes au glucose et presentent un defaut de secretion d’insuline (basal et en reponse au glucose), elles ont un poids et une composition corporelle identiques aux controles. En revanche, les CBS± supplementees en methionine sont plus minces (p Conclusion Les souris deficientes en CBS et supplementees en methionine sont plus minces que les controles sous regime normal et sont resistantes a la prise de poids sous regime HL, elles presentent un defaut de secretion d’insuline compense par une augmentation de la sensibilite. Le foie exprime une augmentation des marqueurs fibrotiques et une souffrance hepatocytaire. Un lien direct au niveau de la cellule β entre CBS et secretion d’insuline reste encore a etablir (etudes in vitro).

The increase in adiponectin levels in obese patients with untreated dyslipidemia and its mRNA expression in adipose tissue of obese animals are one of the most interesting consequences of rimonabant treatment. Thus, part of rimonabant's metabolic effects could be related to an enhancement of adiponectin secretion and its consequence on the modulation of insulin action, as well as energy homeostasis. The present study investigated the effects of rimonabant in adiponectin knockout mice (Ad−/−) exposed to diet-induced obesity conditions. Six-week-old Ad−/− male mice and their wild-type littermate controls (Ad+/+) were fed a high-fat diet for 7 mo. During the last month, animals were administered daily either with vehicle or rimonabant by mouth (10 mg/kg). High-fat feeding induced weight gain by about 130% in both wild-type and Ad−/− mice. Obesity was associated with hyperinsulinemia and insulin resistance. Treatment with rimonabant led to a significant and similar decrease in body weight in both Ad+/+ and Ad−/− mice compared with vehicle-treated animals. In addition, rimonabant significantly improved insulin sensitivity in Ad+/+ mice compared with Ad+/+ vehicle-treated mice by decreasing hepatic glucose production and increasing glucose utilization index in both visceral and subcutaneous adipose tissue. In contrast, rimonabant failed to improve insulin sensitivity in Ad−/− mice, despite the loss in body weight. Rimonabant's effect on body weight appeared independent of the adiponectin pathway, whereas adiponectin seems required to mediate rimonabant-induced improvement of insulin sensitivity in rodents.

International audience; Unlike the adjustable gastric banding procedure (AGB), Roux-en-Y gastric bypass surgery (RYGBP) in humans has an intriguing effect: a rapid and substantial control of type 2 diabetes mellitus (T2DM). We performed gastric lap-band (GLB) and entero-gastro anastomosis (EGA) procedures in C57Bl6 mice that were fed a high-fat diet. The EGA procedure specifically reduced food intake and increased insulin sensitivity as measured by endogenous glucose production. Intestinal gluconeogenesis increased after the EGA procedure, but not after gastric banding. All EGA effects were abolished in GLUT-2 knockout mice and in mice with portal vein denervation. We thus provide mechanistic evidence that the beneficial effects of the EGA procedure on food intake and glucose homeostasis involve intestinal gluconeogenesis and its detection via a GLUT-2 and hepatoportal sensor pathway.

Resume Outre leur role de substrats energetiques, il est maintenant clairement etabli que les nutriments (glucose, acides gras, acides amines) peuvent jouer le role de molecules informatives. En effet, toute variation de leur concentration plasmatique sera interpretee par l’organisme comme un manque ou un exces d’energie. En ce qui concerne les acides gras libres (AGL), il est a present reconnu que les variations peripheriques de concentration des AGL peuvent etre detectees par des neurones specialises, notamment dans l’hypothalamus et le tronc cerebral. Ainsi, les AGL regulent finement, via leur effet central, le comportement alimentaire, la production hepatique de glucose mais aussi la secretion d’insuline. Des sous-populations de neurones sensibles (inhibes ou excites) aux AGL sont identifiees dans l’hypothalamus. Leur caracterisation moleculaire reste encore a etablir. Plutot que les AGL directement, il semble que ce soit leurs metabolites (acyl-CoA et/ou le malonyl-CoA par exemple) qui sont les principales molecules actives. Par exemple, une elevation de la concentration intracellulaire de malonyl-CoA est un puissant signal satietogene. Physiopathologiquement, un apport excessif chronique d’AGL pourra entrainer un dysfonctionnement du senseur central des AGL et contribuer, chez les sujets predisposes, a l’apparition de maladies metaboliques, telles que l’obesite ou le diabete de type 2.

Adult mammals finely match glucose production to glucose utilization, thus allowing glycaemia to be maintained in a physiological range of 0.8-1.2mg/dl whatever the energetic status of the mammal (i.e. fed or fasted, rested or exercised). To accomplish this, peripheral signals originating from the gut 'inform' the central nervous system, which in turn is able to monitor the status of both peripheral glucose stores and ongoing fuel availability. Indeed, both secretion and action of hormones regulating endogenous glucose production and utilization are regulated by the autonomic nervous system. These gut signals are either hormonal (e.g. glucagon-like peptide-1, ghrelin and cholecystokinine) or neuronal (e.g. afferent vagus nerve fibres). Recent data, combined with the development of incretin analogues for treatment of diabetes, highlight the importance of the gut-brain axis, especially glucagon-like peptide-1 and ghrelin, in the control of glucose homeostasis.

It is now clearly demonstrated that fatty acids (FAs) may modulate neural control of energy homeostasis and specifically affect both insulin secretion and action. Indeed, pancreatic β-cells receive rich neural innervation and FAs induce important changes in autonomic nervous activity. We previously reported that chronic infusion of lipids decreased sympathetic nervous system activity and led to exaggerated glucose-induced insulin secretion (GIIS), as would be expected from the known inhibitory effect of sympathetic splanchnic nerve activity on insulin secretion. Intracarotid infusion of lipids that do not change plasma FA concentrations also lead to increased GIIS. This effect of FAs on GIIS was prevented by inhibition of β-oxidation. It is noteworthy that a single intracarotid injection of oleic acid also induced a transient increase in plasma insulin without any change in plasma glucose, suggesting that FAs per se can regulate neural control of insulin secretion. Finally, using whole cell current clamp recordings in hypothalamic slices and calcium imaging in dissociated hypothalamic neurons, we identified a hypothalamic subpopulation of neurons either excited (13%) or inhibited (6%) by FAs. Thus, FAs per se or their metabolites modulate neuronal activity, as a means of directly monitoring ongoing fuel availability by central nervous system nutrient-sensing neurons involved in the regulation of insulin secretion.

Resume Les endocannabinoides, lipides endogenes, controlent, via leurs recepteurs CB1 et CB2, les reponses comportementales a la douleur ou l’anxiete. Ce sont egalement d’importants stimulateurs de la prise alimentaire et de la lipogenese. Au niveau central, les endocannabinoides stimulent la prise alimentaire, en modulant l’expression de neuropeptides orexigenes et anorexigenes. A la peripherie, ils stimulent la lipogenese dans le foie et le tissu adipeux blanc. Si l’administration d’agonistes des recepteurs aux cannabinoides est aujourd’hui prescrite pour faciliter la prise alimentaire des personnes atteintes du cancer ou du VIH, le developpement d’antagonistes est egalement en plein essor pour le traitement de l’obesite et l’hyperlipidemie. Ainsi, le Rimonabant, antagoniste des recepteurs CB1 developpe par Sanofi-Aventis, est un puissant inhibiteur de la prise alimentaire et un regulateur de l’homeostasie energetique, ouvrant ainsi des perspectives therapeutiques dans le traitement du syndrome metabolique.

We previously created a novel F-DIO rat strain derived by crossing rats selectively bred for the diet-induced obesity (DIO) phenotype with obesity-resistant Fischer F344 rats. The offspring retained the DIO phenotype through 3 backcrosses with F344 rats but also had exaggerated insulin responses to oral glucose before they became obese on a 31% fat high-energy (HE) diet. Here, we demonstrate that chow-fed rats from the subsequent randomly bred progeny required 57% lower glucose infusions to maintain euglycemia during a hyperinsulinemic clamp in association with 45% less insulin-induced hepatic glucose output inhibition and 80% lower insulin-induced glucose uptake than F344 rats. The DIO phenotype and exaggerated insulin response to oral glucose in the nonobese, chow-fed state persisted in the F6 generation. Also, compared with F344 rats, chow-fed F-DIO rats had 68% higher arcuate nucleus proopiomelanocortin mRNA expression which, unlike the increase in F344 rats, was decreased by 26% on HE diet. Further, F-DIO lateral hypothalamic orexin expression was 18% lower than in F344 rats and was increased rather than decreased by HE diet intake. Finally, both maternal obesity and 30% caloric restriction during the third week of gestation produced F-DIO offspring which were heavier and had higher leptin and insulin levels than lean F-DIO dam offspring. Third-gestational week dexamethasone also produced offspring with higher leptin and insulin levels but with lower body weight. Thus F-DIO rats represent a novel and potentially useful model for the study of DIO, insulin resistance, and perinatal factors that influence the development and persistence of obesity.

The foetal testis originates from a proliferation of the mesonephric and the coelomic epithelia which are colonized by the primordial germ cells. In the foetal testis, the development and functions of the three main cell type precursors (Leydig, Sertoli and germ cells) do not depend upon gonadotropins. Numerous intra- and extra-testicular factors are candidates for the control of its development and functions. To study the potential involvement of these factors, we developed an organotypic culture system. In absence of any growth factors or hormone, this system allows a development of the three main cell types which mimics that observed in vivo. The effects of different regulators (gonadotropin-releasing hormone, follicle-stimulating hormone, transforming growth factor-beta, insulin-like growth factor-I, anti-Mullerian hormone, retinoic acid, oestrogens) were tested in this system. Whether or not some of the effects observed in vitro have a physiological relevance was evaluated using appropriate transgenic mice. It is concluded that the foetal testis cannot be considered as an adult mini-testis since it has a specific physiology which largely differs from that of the immature or adult testis.

Addition of 5x10(-2) U/ml recombinant luteinizing hormone (LH) to testes from fetuses at 16.5 day post conception (dpc) cultured for 5 days increased the number of Leydig cells by 34% and the acute LH-stimulated testosterone production by 600%. To determine whether these positive effects of LH in vitro are physiologically relevant in vivo, fetuses were decapitated on days 16.5 pc (before the onset of LH expression in the hypophysis) or 18.5 pc (before the surge of LH in the fetal plasma) and removed at 21.5 dpc. The number of fetal Leydig cells per testis and the acute LH-stimulated testosterone production by the testes ex vivo were unaltered by decapitation. Since, in all groups, the number of Leydig cells doubled between 16.5 and 18.5 dpc and between 18.5 and 21.5 dpc, these results suggest that neither the appearance of new fully differentiated fetal Leydig cells nor the maintenance of differentiated functions in existing fetal Leydig cells depend on LH during late fetal life, although this hormone is present in the plasma. Decapitation reduced the testosterone concentrations in the plasma (-56%) and in the testis in vivo (-67%) and the basal testosterone secretion of the testis ex vivo (-70%). This suggests that LH is required to maintain the physiological activity of the Leydig cell during late fetal life. However, the decrease of the in vivo testosterone production after decapitation was not sufficient to impair the growth of the Wolffian ducts and the lengthening of the anogenital distance. In conclusion, during late fetal life in the rat, Leydig cells are LH-independent for their functional differentiation and LH-dependent for their activity.

International audience; Fatty acid (FA)-sensitive neurons are present in the brain, especially the hypothalamus, and play a key role in the neural control of energy homeostasis. Through neuronal output, FA may modulate feeding behaviour as well as insulin secretion and action. Subpopulations of neurons in the ventromedial and arcuate hypothalamic nuclei are selectively either inhibited or activated by FA. Molecular effectors of these FA effects probably include chloride or potassium ion channels. While intracellular metabolism and activation of the ATP-sensitive K⁺ channel appear to be necessary for some of the signalling effects of FA, at least half of the FA responses in ventromedial hypothalamic neurons are mediated by interaction with FAT/CD36, an FA transporter/receptor that does not require intracellular metabolism to activate downstream signalling. Thus, FA or their metabolites can modulate neuronal activity as a means of directly monitoring ongoing fuel availability by brain nutrient-sensing neurons involved in the regulation of energy and glucose homeostasis. Recently, the role of lipoprotein lipase in FA sensing has also been shown in animal models not only in hypothalamus, but also in hippocampus and striatum. Finally, FA overload might impair neural control of energy homeostasis through enhanced ceramide synthesis and may contribute to obesity and/or type 2 diabetes pathogenesis in predisposed subjects.

Reproductive function is highly dependent on nutritional input. We recently provided evidence that the unsaturated ω6 fatty acid (FA), linoleic acid (linoleic), interferes with transcription and secretion of the gonadotropin LH, highlighting the existence of a lipid sensing in pituitary gonadotropes. Here, we show, using a combination of in vivo and in vitro models, that linoleic differentially regulates Lhb and Fshb expression. Central exposure of rats to linoleic over 7 days was associated with increase of Lhb but not Fshb transcript levels. Consistently, exposure of rat pituitary cells or LβT2 cells to linoleic increased Lhb, whereas it dramatically decreased Fshb transcript levels without affecting its stability. This effect was also induced by ω9 and ω3-polyunsaturated FA but not by saturated palmitic acid. Analysis of the underlying mechanisms in LβT2 cells using small interfering RNA revealed that early growth response protein 1 mediates linoleic stimulation of Lhb expression. Furthermore, we demonstrated that linoleic counteracts activin and bone morphogenetic protein-2 stimulation of Fshb expression. Using Western blotting and Smad-responsive reporter gene assays, linoleic was shown to decrease basal Smad2/3 phosphorylation levels as well as activin- and bone morphogenetic protein-2-dependent activation of Smad, uncovering a new FA-sensitive signaling cascade. Finally, the protein phosphatase magnesium-dependent 1A was shown to mediate linoleic inhibition of basal Smad phosphorylation and Fshb expression, identifying protein phosphatase magnesium-dependent 1A as a new target of FA in gonadotropes. Altogether, this study provides a novel mechanism by which FAs target gene expression and underlines the relevant role of pituitary gonadotropes in mediating the effects of nutritional FA on reproductive function.

Introduction Le diabete de type 2 est rapidement ameliore par la chirurgie bariatrique. Nous avons etudie la masse et la fonctionnalite du pancreas endocrine apres l'entero-gastro-anastomose (EGA) chez la souris Ob. Materiels et Methodes Des souris mâles Ob/ob ont ete operees soit d'une EGA (Ob-EGA) soit d'une chirurgie controle (groupe Ob-Sham) et compares a un groupe de souris Ob traitees par leptine (Ob-Leptine). Pour chaque groupe sont obtenus avant et 30 jours apres les parametres suivants : prise alimentaire, poids et composition corporelle, tolerance orale au glucose (secretion de l'insuline, du C peptide et du GLP-1), tolerance a l'insuline (ITT), flore caecale (analyse 16S). Au sacrifice, les pancreas sont preleves pour une etude immunohistochimique. Resultats Trente jours apres l'intervention, l'EGA n'induisait pas de changement de prise alimentaire ni de poids corporel par rapport aux Ob-sham. Malgre la persistance de cette obesite, la glycemie basale et la tolerance au glucose etaient significativement diminuees dans le groupe Ob-EGA par rapport aux Ob-Sham (glycemie basale : 1,25±0,15g/L vs 2,06 +/0,29g/L, p vs 396±96, p Discussions Notre etude montre que chez la souris Ob, la disparition du diabete apres EGA est liee a l'amelioration de la fonctionnalite du pancreas endocrine par des mecanismes specifiques non reproduits par le traitement par leptine. Cet effet est independant du poids, de la prise alimentaire, de la flore ceacale et de la secretion de GLP-1.

It is currently admitted that Follicle-Stimulating Hormone (FSH) is physiologically involved in the development and function of fetal/neonatal Sertoli cells in the rat but not the mouse. However, FSH is produced by both species from late fetal life onwards. We thus reinvestigated the role of FSH in mouse testis development at day 0 (birth) 6, 8 and 10 post-partum (dpp) by using mice that lack functional FSH receptors (FSH-R(-/-)). At birth, the number and proliferative index of Sertoli cells were significantly lower in FSH-R(-/-) mice than in wild type neonates. Claudin 11 mRNA expression also was significantly reduced in FSH-R(-/-) testes at 0 and 8 dpp, whereas the mRNA levels of other Sertoli cell markers (Transferrin and Desert hedgehog) were comparable in FSH-R(-/-) and wild type testes. Conversely, AMH mRNA and protein levels were higher at birth, comparable at 6 dpp and then significantly lower in FSH-R(-/-) testes at 8-10 dpp in FSH-R(-/-) mice than in controls. Although the plasma concentration of LH and the number of Leydig cells were similar in FSH-R(-/-) and control (wild type), testosterone concentration and P450c17 mRNA expression were significantly increased in FSH-R(-/-) testes at birth. Conversely, at 10 dpp when adult Leydig cells appear, expression of the steroidogenic genes P450scc, P450c17 and StAR was lower in FSH-R(-/-) testes than in controls. In conclusion, our results show that 1) like in the rat, signaling via FSH-R controls Sertoli cell development and function during late fetal life in the mouse as well; 2) paracrine factors produced by Sertoli cells are involved in the FSH-R-dependent regulation of the functions of fetal Leydig cells in late fetal life; and 3) the role of FSH-R signaling changes during the prepubertal period.

Dietary supplement may potentially help to fight obesity and other metabolic disorders such as insulin-resistance and low-grade inflammation. The present study aimed to test whether supplementation with Agaricus blazei murill (ABM) extract could have an effect on diet-induced obesity in rats.Wistar rats were fed with control diet (CD) or high-fat diet (HF) and either with or without supplemented ABM for 20 weeks.HF diet-induced body weight gain and increased fat mass compared to CD. In addition HF-fed rats developed hyperleptinemia and insulinemia as well as insulin resistance and glucose intolerance. In HF-fed rats, visceral adipose tissue also expressed biomarkers of inflammation. ABM supplementation in HF rats had a protective effect against body weight gain and all study related disorders. This was not due to decreased food intake which remained significantly higher in HF rats whether supplemented with ABM or not compared to control. There was also no change in gut microbiota composition in HF supplemented with ABM. Interestingly, ABM supplementation induced an increase in both energy expenditure and locomotor activity which could partially explain its protective effect against diet-induced obesity. In addition a decrease in pancreatic lipase activity is also observed in jejunum of ABM-treated rats suggesting a decrease in lipid absorption.Taken together these data highlight a role for ABM to prevent body weight gain and related disorders in peripheral targets independently of effect in food intake in central nervous system.

Energy homeostasis is kept through a complex interplay of nutritional, neuronal and hormonal inputs that are integrated at the level of the central nervous system (CNS). A disruption of this regulation gives rise to life-threatening conditions that include obesity and type-2 diabetes, pathologies that are strongly linked epidemiologically and experimentally. The hypothalamus is a key integrator of nutrient-induced signals of hunger and satiety, crucial for processing information regarding energy stores and food availability. Much effort has been focused on the identification of hypothalamic pathways that control food intake but, until now, little attention has been given to a potential role for the hypothalamus in direct control of glucose homeostasis and nergy balance. Recent studies have cast a new light on the role of the CNS in regulating peripheral glucose via a hypothalamic fatty acid (FA)-sensing device that detects nutrient availability and relays, through the autonomic nervous system, a negative feedback signal on food intake, insulin sensitivity and insulin secretion. Indeed, accumulating evidences suggest that FA are used in specific areas of CNS not as nutrients, but as cellular messengers which inform “FA sensitive neurons” about the energy status of the whole body (Blouet & Schwartz, 2010; Migrenne et al., 2006; Migrenne et al., 2011). Thus it has been described that up to 70% of hypothalamic arcuate nucleus (ARC) and ventromedian nucleus (VMN) neurons are either excited or inhibited by long chain fatty acids such as oleic acid (Jo et al., 2009; Le Foll et al., 2009; Migrenne et al., 2011). Within the VMN, 90% of the glucosensing neurons also have their activity altered by FA. In a large percentage of these neurons, glucose and FA have opposing effects on neuronal activity, much as they do on intracellular metabolism in many other cells (Randle et al., 1994). Neuronal FA sensing mechanisms include activation of the KATP channel by long chain fatty acid acyl CoA (Gribble et al., 1998) or inactivation by generation of ATP or reactive oxygen species during mitochondrial ┚-oxidation (Jo et al., 2009; Le Foll et al., 2009; Migrenne et al., 2011; Wang et al., 2006). Many fatty acid sensing neurons are activated by interaction of long chain fatty acids with the fatty acid transporter/receptor, FAT/CD36, presumably by activation of store-operated calcium channels by a mechanism that is independent of fatty acid metabolism (Jo et al., 2009). Importantly, most neurons utilize FA primarily for membrane production rather than as a metabolic substrate (Rapoport et al., 2001; Smith & Nagura, 2001) and only nanomolar concentrations of fatty acid are required to

The activity of pituitary gonadotrope cells, crucial for reproductive function, is regulated by numerous factors including signals related to nutritional status. In this work, we demonstrated, for the first time, that in vivo central exposure of rats to lipids intracarotid infusion of a heparinized triglyceride emulsion selectively increases the expression of pituitary LH subunit genes without any alteration of pituitary GnRH receptor and hypothalamic GnRH or Kiss-1 transcript levels. Furthermore, we showed that unsaturated fatty acids (UFA), oleate and linoleate, increase LH release in a dose-dependent manner as well as LHβ mRNA levels in both immortalized LβT2 gonadotrope cell line and rat primary cell cultures. In contrast, the saturated palmitate was ineffective. ACTH or TSH secretion was unaffected by UFA treatment. We demonstrated in LβT2 cells that linoleate effect is mediated neither by activation of membrane fatty acid (FA) receptors GPR40 or GPR120 although we characterized these receptors in LβT2 cells, nor through nuclear peroxisome proliferator-activated receptors. Furthermore, linoleate β-oxidation is not required for its action on LH secretion. In contrast, pharmacological inhibition of protein kinase C (PKC) or ERK pathways significantly prevented linoleate-stimulated LH release. Accordingly, linoleate was shown to activate novel PKC isoforms, PKCε and -θ, as well as ERK1/2 in LβT2 cells. Lastly, unsaturated, but not saturated, FA inhibited GnRH-induced LH secretion in LβT2 cells as well as in pituitary cell cultures. Altogether, these results suggest that the pituitary is a relevant site of FA action and that UFA may influence reproduction by directly interfering with basal and GnRH-dependent gonadotrope activity.

Nutrient sensitive neurons (glucose and fatty acids (FA)) are present in many sites throughout the brain, including the hypothalamus and brainstem, and play a key role in the neural control of energy and glucose homeostasis. Through neuronal output, FA may modulate feeding behaviour as well as both insulin secretion and action. For example, central administration of oleate inhibits food intake and glucose production in rats. This suggests that daily variations in plasma FA concentrations might be detected by the central nervous system as a signal which contributes to the regulation of energy balance. At the cellular level, subpopulations of neurons in the ventromedial and arcuate hypothalamic nuclei are selectively either inhibited or activated by FA. Possible molecular effectors of these FA effects likely include chloride or potassium ion channels. While intracellular metabolism and activation of the ATP-sensitive K(+) channel appear to be necessary for some of the signaling effects of FA, at least half of the FA responses in ventromedial hypothalamic neurons are mediated by interaction with FAT/CD36, a FA transporter/receptor that does not require intracellular metabolism to activate downstream signaling. Thus, FA or their metabolites can modulate neuronal activity as a means of directly monitoring ongoing fuel availability by brain nutrient-sensing neurons involved in the regulation of energy and glucose homeostasis. Besides these physiological effects, FA overload or metabolic dysfunction might impair neural control of energy homeostasis and contribute to obesity and/or type 2 diabetes in predisposed subjects.

Insulin signaling can be modulated by several isoforms of PKC in peripheral tissues. Here, we assessed whether one specific isoform, PKC-theta, was expressed in critical CNS regions that regulate energy balance and whether it mediated the deleterious effects of diets high in fat, specifically palmitic acid, on hypothalamic insulin activity in rats and mice. Using a combination of in situ hybridization and immunohistochemistry, we found that PKC-theta was expressed in discrete neuronal populations of the arcuate nucleus, specifically the neuropeptide Y/agouti-related protein neurons and the dorsal medial nucleus in the hypothalamus. CNS exposure to palmitic acid via direct infusion or by oral gavage increased the localization of PKC-theta to cell membranes in the hypothalamus, which was associated with impaired hypothalamic insulin and leptin signaling. This finding was specific for palmitic acid, as the monounsaturated fatty acid, oleic acid, neither increased membrane localization of PKC-theta nor induced insulin resistance. Finally, arcuate-specific knockdown of PKC-theta attenuated diet-induced obesity and improved insulin signaling. These results suggest that many of the deleterious effects of high-fat diets, specifically those enriched with palmitic acid, are CNS mediated via PKC-theta activation, resulting in reduced insulin activity.

Pharmacological manipulation of fatty acid metabolism in the hypothalamic arcuate nucleus (ARC) alters energy balance and glucose homeostasis. Thus, we tested the hypotheses that distinctive populations of ARC neurons are oleic acid (OA) sensors that exhibit a glucose dependency, independent of whether some of these OA sensors are also glucose-sensing neurons. We used patch-clamp recordings to investigate the effects of OA on ARC neurons in brain slices from 14- to 21-day-old Sprague–Dawley (SD) rats. Additionally, we recorded spontaneous discharge rate in ARC neurons in 8-wk-old fed and fasted SD rats in vivo. Patch-clamp studies showed that in 2.5 mM glucose 12 of 94 (13%) ARC neurons were excited by 2 μM OA (OA-excited or OAE neurons), whereas six of 94 (6%) were inhibited (OA-inhibited2.5or OAI2.5neurons). In contrast, in 0.1 mM glucose, OA inhibited six of 20 (30%) ARC neurons (OAI0.1neurons); none was excited. None of the OAI0.1neurons responded to OA in 2.5 mM glucose. Thus OAI2.5and OAI0.1neurons are distinct. Similarly, in seven of 20 fed rats (35%) the overall response was OAE-like, whereas in three of 20 (15%) it was OAI-like. In contrast, in fasted rats only OAI-like response were observed (three of 15; 20%). There was minimal overlap between OA-sensing neurons and glucose-sensing neurons. In conclusion, OA regulated three distinct subpopulations of ARC neurons in a glucose-dependent fashion. These data suggest that an interaction between glucose and fatty acids regulates OA sensing in ARC neurons.

Although the role of pituitary hormones in fetal Sertoli cell proliferation is well understood, their involvement in fetal Sertoli cell differentiation is poorly documented. In this study, we evaluated rat fetal Sertoli cell function by measuring basal transferrin secretion ex vivo and transferrin and anti-Mullerian hormone (AMH) mRNA levels in vivo. The differentiation state of the Sertoli cells was estimated from the amount of transferrin secreted ex vivo after acute stimulation with FSH. Surprisingly, we found that the amount of transferrin secreted by each Sertoli cell in basal condition and after acute FSH stimulation decreased between 18.5 and 21.5 day post coitum (dpc), which corresponds to the onset of pituitary hormone secretion. All of the Sertoli cell parameters measured (basal and FSH-stimulated transferrin secretion ex vivo, transferrin and AMH mRNA levels in vivo) were higher in 21.5-dpc fetuses that had been decapitated on 16.5 dpc than in control littermates. Furthermore, immunostaining for AMH was strongly increased after decapitation. Taken together, these results suggest that pituitary hormones in the fetus and in the immature or adult rat differently regulate Sertoli cells, which suggests that fetal Sertoli cells have their own particular physiology.

Introduction et but de l’etude La balance energetique est finement regulee par le systeme nerveux central (SNC), au sein duquel le bulbe olfactif (BO), participe activement a l’initiation de la prise alimentaire. Chez l’Homme et l’animal sain, la sensibilite olfactive est augmentee par le jeune et diminuee par la satiation 1 . Les patients obeses ont quant a eux un seuil de detection plus bas pour la reconnaissance des molecules odorantes 2 , qui pourrait expliquer, du moins en partie, la deregulation de leur comportement alimentaire. La Prokineticine-2 (Prok2), est une proteine secretee qui est fortement exprimee dans le SNC, et particulierement dans le BO, ou elle joue un role dans l’etablissement des projections neuronales en direction de l’hypothalamus 3 . Les patients atteints du Syndrome de Kallmann, cause par une mutation du gene PROK2 ou de son recepteur PROKR2, presentent une anosmie, un hypogonadisme hypogonadotrope et dans certains cas, une severe obesite 4 . Chez les rongeurs, il a recemment ete mis en evidence que Prok2 diminue la prise alimentaire via une action hypothalamique 5 . Le but de notre etude est de mettre en lumiere le role de la Prok2 olfacto-bulbaire dans la regulation de la prise alimentaire et de l’homeostasie glucidique. Materiel et methodes Nous avons quantifie les ARNm de Prok2 presents dans le bulbe olfactif de souris C57Bl/6j minces ou rendues obeses grâce a un regime hyperlipidique afin d’evaluer les differences d’expression. Par la suite, nous avons teste une approche pharmacologique en injectant de la proteine recombinante de maniere aigue par stereotaxie, et une approche genetique en injectant un lentivirus contenant un shRNA specifique contre Prok2 ou au contraire, son ADNc, afin d’evaluer les effets physiologiques resultants d’une sous et d’une sur-expression locale. Resultats et Analyse statistique Dans un premier temps, nous avons pu mettre en evidence par RTqPCR que le niveau d’expression de l’ARNm de Prok2 dans le BO des souris minces etait diminue apres un jeune de 24 h et, inversement, il etait significativement augmente dans le BO des souris rendues obeses, compare a l’etat nourri. Cela suggere que l’expression de l’ARNm de Prok2 dans le BO est a la fois dependant des statuts nutritionnel (nourri/ a jeun) et metabolique (mince / obese) des animaux. Afin de determiner si les variations de l’expression de Prok2 dans le BO pouvaient impacter la prise alimentaire, nous avons injecte soit de la Prok2 recombinante, ou un shRNA integre dans un vecteur lentiviral, dans le BO des souris minces et obeses. Une injection aigue de Prok2 recombinante diminue significativement la prise alimentaire 24 h post chirurgie, en comparaison des souris ayant recu le vehicule, quel que soit leur statut metabolique. A contrario , une sous-expression chronique, obtenue grâce au lentivirus contenant le shRNA anti-Prok2, a pour effet d’augmenter significativement la prise alimentaire et de modifier l’homeostasie glucidique des souris minces et obeses. Nos resultats ont ainsi permis de mettre en evidence que la Prok2 olfacto-bulbaire est impliquee dans le controle de la prise alimentaire et de l’homeostasie glucidique, et que son expression est modifiee chez les animaux obeses, ceci suggerant que cette proteine pourrait etre une nouvelle cible pour le traitement des pathologies metaboliques telles que l’obesite et le diabete de type 2. Afin d’aller plus loin, nous avons commence a etudier son expression chez des souris deficiente en leptine (souris Ob/Ob), qui sont hyperphagiques et ont une sensibilite olfactive modifiee par rapport a des souris normales. Les resultats (moyenne +/−SEM) ont ete analyses avec des tests non-parametriques de Mann-Whitney et consideres significatifs si P Conclusion Nos resultats ont montres que la Prok2 olfacto-bulbaire est impliquee dans le controle de la prise alimentaire et de l’homeostasie glucidique et que son expression est modifiee chez la souris obese, suggerant que cette proteine pourrait etre une nouvelle cible a exploiter dans le traitement des maladies metaboliques telles que l’obesite et le diabete de type 2. Afin d’aller plus loin dans les mecanismes d’action de la Prok2 olfacto-bulbaire, nous avons commence a etudier son expression chez des souris mutees pour le gene codant la leptine (Souris Ob/Ob), qui ont un comportement alimentaire hyperphagique tres bien caracterise et qui est associe a une modification de la sensibilite olfactive.

Introduction Des etudes recentes ont montre que l'accumulation de lipides dans l'hypothalamus serait responsable de l'installation d'une lipotoxicite centrale. Ce phenomene pourrait jouer un role dans l'apparition d'une insulinoresistance et du diabete en deregulant le controle nerveux de l'homeostasie glucidique. Il a ete montre que l'accumulation des ceramides joue un role preponderant dans le developpement d'une lipotoxicite au niveau des tissus peripheriques. Nos resultats preliminaires ont montre que la perfusion de saindoux, compose principalement d'acides gras satures, directement dans le cerveau, conduit a une insulino-resistance peripherique associee a une accumulation de ceramides dans l'hypothalamus. Materiels et methodes Afin etudier la chronologie qui existe entre l'installation d'une insulino-resistance centrale et peripherique, nous avons decide d'etudier les effets d'un acide gras sature, le palmitate sur l'insulino-resistance centrale a l'aide d'approches in vitro (cellules hypothalamiques) et in vivo (rat). Resultats Nous avons pu mettre en evidence un phenomene d'insulino-resistance centrale in vitro en reponse au palmitate qui s'accompagne d'une accumulation de ceramides. Certains ARNm codant pour les enzymes de la voie de synthese de novo des ceramides etant augmentes a la suite de ces traitements, nous avons decide d'inhiber cette voie avec la myriocine. En presence de myriocine, ce phenomene d'insulino-resistance centrale est partiellement contrecarre. Chez le rat, nous avons pu observer le meme phenomene d'insulino-resistance centrale en reponse a une perfusion dans la carotide de palmitate. Cette insulino-resistance s'accompagne a son tour d'une accumulation de ceramides dans l'hypothalamus. Conclusion Au final, notre etude revele que les acides gras satures induisent une accumulation de ceramides dans l'hypothalamus. De facon interessante, cette accumulation est responsable de l'installation d'une insulino-resistance hypothalamique. Ces resultats mettent en evidence le role cle du metabolisme des ceramides dans la deregulation du controle nerveux de l'homeostasie glucidique observe au cours de l'obesite.

Introduction La balance energetique est en partie regulee par le systeme nerveux central, au sein duquel le bulbe olfactif (BO) contribue a l’initiation de la prise alimentaire. Chez l’humain et l’animal sain, la sensibilite olfactive est augmentee par le jeune et diminuee par la satiation. Chez l’obese, une perturbation de la detection des odeurs pourrait provoquer une deregulation du comportement alimentaire et en consequence de l’homeostasie energetique. Il a recemment ete montre qu’une proteine, la prokineticine-2 (Prok2) diminue la prise alimentaire via une action hypothalamique. Prok2 est fortement exprimee dans le BO ou elle participe a la mise en place des projections vers l’hypothalamus. Certains patients porteurs de mutations de la voie Prok2 developpent un syndrome de Kallmann caracterise, entre autres, par une anosmie et une obesite. Le but de notre travail a ete de determiner si Prok2 joue un role dans la regulation de la prise alimentaire via un effet dans le BO. Materiels et methodes Le niveau d’expression des ARNm de Prok2 a ete mesure par qPCR dans le BO de souris C57Bl6 sous regime standard (CD) ou hyper-lipidique (HFD). Afin d’evaluer les effets d’une sur- ou d’une sousexpression, la Prok2 recombinante ou un shRNA anti-Prok2 ont ete injectes dans le BO par stereotaxie. Resultats Apres 24 h de jeune, le niveau d’expression des ARNm de Prok2 est diminue dans le BO de souris sous CD et augmente dans celui de souris sous HFD, comparativement a l’etat nourri. L’injection aigue de Prok2 induit une diminution de la prise alimentaire ; l’injection d’un shRNA anti-Prok2 l’augmente. Conclusion Nous avons identifie Prok2 comme une nouvelle cible potentielle de la regulation de la prise alimentaire via son action dans le BO : son niveau d’expression varie en fonction des statuts metabolique et nutritionnel et elle possede un effet anorexigene.

Introduction La carnitine palmitoyltransferase 1 (CPT1) represente le site majeur de controle de l’oxydation des acides gras a chaine longue (AGCL) du fait de sa capacite a etre inhibee par le malonyl-CoA, premier intermediaire de la lipogenese. Dans le foie d’animaux obeses ou diabetiques, l’existence d’une lipogenese accrue conduit a une augmentation du malonyl-CoA qui entraine une diminution de l’oxydation mitochondriale des AGCL. Materiels et methodes Nous avons developpe un nouveau modele de souris transgeniques (Tg-CPT1mt) exprimant specifiquement dans le foie (promoteur de la transthyretine) une CPT1 insensible au malonyl-CoA (CPT1mt). Resultats L’expression homozygote de la CPT1mt entraine une letalite embryonnaire. Chez les souris heterozygotes a l’etat nourri, l’expression de la CPT1mt entraine une diminution de la sensibilite de la CPT1 hepatique vis-a-vis du malonyl-CoA similaire a celle observee apres un jeune chez des souris temoins (WT). A l’âge de 3 mois, les souris Tg-CPT1mt presentent a l’etat nourri des concentrations circulantes de triglycerides et d’acides gras libres significativement plus faibles que chez les souris WT. Chez les souris Tg-CPT1mt âgees de 10 mois, seule la triglyceridemie est diminuee et ceci s’accompagne d’une diminution du poids corporel. Quel que soit leur âge, les souris Tg-CPT1mt ont a l’etat nourri une diminution du poids des tissus adipeux (epididymaire, visceral et sous cutane) et du contenu hepatique en glycogene. De plus, la glycemie des souris Tg-CPT1mt est plus faible a l’etat nourri comme a l’etat a jeun. Seules les souris Tg-CPT1mt âgees de 10 mois ont une tolerance au glucose et une sensibilite a l’insuline ameliorees. Chez ces souris, des experiences de clamp euglycemique-hyperinsulinemique suggerent que la diminution de la glycemie observee ne resulte pas d’une diminution de la production hepatique de glucose, mais d’une amelioration de l’utilisation basale de glucose. Conclusion Ces resultats suggerent que les souris Tg-CPT1mt presentent un phenotype evolutif et constituent un modele pertinent pour l’etude des consequences d’une augmentation de l’oxydation des AGCL dans le foie sur l’obesite, l’insulinoresistance et la steatose hepatique.

But Comprendre pourquoi le by-pass gastrique (BPG) (et non l’anneau gastrique) chez la souris C57Bl6 soumise au regime gras (HFD) provoque une amelioration rapide de la sensibilite a l’insuline et de la secretion d’insuline. Materiels et methodes Nous avions montre que le BPG provoquait une hausse de la concentration plasmatique de GLP-1 observable lors du test de tolerance orale au glucose (OGTT). Pour connaitre la place du GLP-1 dans les modifications metaboliques apres BPG, la prise alimentaire, le poids, la sensibilite a l’insuline et l’OGTT ont ete realisees chez des souris mâles C57Bl6 HFD avant et apres BPG avec ou sans traitement par un antagoniste du GLP-1 (exendine [9-39] amide). Par ailleurs, nous avons teste l’hypothese que les effets du BPG pouvaient s’expliquer en partie par une stimulation de la neoglucogenese intestinale. L’activite de la glucose-6 phosphatase (Glc6Pase) a ete mesuree dans les differents segments intestinaux de souris C57Bl6 HFD temoins (sham operated), BPG et anneau (n = 10 souris par groupe). Dans ces groupes, le flux de glucose portal a egalement ete mesure. Le transporteur GLUT2 a ete suggere comme sensor essentiel de la detection du glucose portal. Nous avons alors realise un BPG chez des souris KOGLUT2 soumises au regime gras. Resultats Nous montrons que l’exendine 9-39 reduit l’insulinosecretion lors de l’OGTT mais ne modifie pas les effets du BPG sur la prise alimentaire et sur sensibilite a l’insuline. Le BPG est la seule situation ou l’on observe une augmentation de l’activite de la Glc6Pase intestinale et une augmentation du flux de glucose portal. Dans ce cas, la neoglucogenese hepatique diminue et la sensibilite a l’insuline hepatique augmente. Enfin, les effets metaboliques du BPG ne sont pas observes chez les souris KOGLUT2. Conclusion Nos resultats suggerent que le GLP-1 a un role crucial dans les modifications de l’insulinosecretion apres BPG alors que les autres modifications metaboliques (prise alimentaire, sensibilite a l’insuline) semblent determinees par la stimulation de la neoglucogenese intestinale.

Aims/hypothesis Per-Arnt-Sim kinase (PASK) is a nutrient-regulated domain-containing protein kinase previously implicated in the control of insulin gene expression and glucagon secretion. Here, we explore the roles of PASK in the control of islet hormone release, by generating mice with selective deletion of the Pask gene in pancreatic beta or alpha cells. Methods Floxed alleles of Pask were produced by homologous recombination and animals bred with mice bearing beta (Ins1Cre; PaskBKO) or alpha (PpgCre [also known as Gcg]; PaskAKO) cell-selective Cre recombinase alleles. Glucose homeostasis and hormone secretion in vivo and in vitro, gene expression and islet cell mass were measured using standard techniques. Results Ins1Cre-based recombination led to efficient beta cell-targeted deletion of Pask. Beta cell mass was reduced by 36.5% (p