Benoit Viollet

Université René Descartes - Paris 5, Lutetia Parisorum, Île-de-France, France

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Publications (331)2049.43 Total impact

  • [Show abstract] [Hide abstract] ABSTRACT: Antihyperglycaemic effects of the hydroxybenzoic acid salicylate might stem from effects of the drug on mitochondrial uncoupling, activation of AMP-activated protein kinase and inhibition of NF-κB signalling. Here, we have gauged the contribution of these effects to control of hepatocyte glucose production, comparing salicylate with inactive hydroxybenzoic acid analogues of the drug. In rat H4IIE hepatoma cells, salicylate was the only drug tested that activated AMPK. Salicylate also reduced mTOR signalling but this property was observed widely amongst the analogues. In a sub-panel of analogues, salicylate alone reduced promoter activity of the key gluconeogenic enzyme glucose 6-phosphatase and suppressed basal glucose production in mouse primary hepatocytes. Both salicylate and 2,6 dihydroxybenzoic acid suppressed TNFα-induced IκB degradation and in genetic knockout experiments we found the effect of salicylate on IκB degradation was AMPK-independent. Previous data also identified AMPK-independent regulation of glucose production but we found that direct inhibition of neither NF-κB nor mTOR signalling suppressed glucose production, suggesting that other factors besides these cell signalling pathways may need to be considered to account for this response to salicylate. We found for example that H4IIE cells were exquisitely sensitive to uncoupling with modest doses of salicylate, which occurred on a similar time course to another antihyperglycaemic uncoupling agent 2,4-dinitrophenol, whilst there was no discernible effect at all of two salicylate analogues which are not anti-hyperglycaemic. This finding supports much earlier literature suggesting that salicylates exert anti-hyperglycaemic effects at least in part through uncoupling.
    No preview · Article · Apr 2016 · Biochimica et Biophysica Acta (BBA) - Molecular Basis of Disease
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    [Show abstract] [Hide abstract] ABSTRACT: Background: Enteroendocrine L-cells synthesise and release the gut hormone glucagon-like peptide-1 (GLP-1) in response to food transit. Deletion of the tumour suppressor kinase LKB1 from proglucagon-expressing cells leads to the generation of intestinal polyps but no change in circulating GLP-1 levels. Here, we explore the role of the downstream kinase AMP-activated protein kinase (AMPK) in these cells. Method: Loss of AMPK from proglucagon-expressing cells was achieved using a preproglucagon promoter-driven Cre (iGluCre) to catalyse recombination of floxed alleles of AMPKα1 and α2. Oral and intraperitoneal glucose tolerance were measured using standard protocols. L-cell mass was measured by immunocytochemistry. Hormone and peptide levels were measured by electrochemical-based luminescence detection or radioimmunoassay. Results: Recombination with iGluCre led to efficient deletion of AMPK from intestinal L- and pancreatic alpha-cells. In contrast to mice rendered null for LKB1 using the same strategy, mice deleted for AMPK displayed an increase (WT: 0.05 ± 0.01, KO: 0.09±0.02%, p<0.01) in L-cell mass and elevated plasma fasting (WT: 5.62 ± 0.800 pg/ml, KO: 14.5 ± 1.870, p<0.01) and fed (WT: 15.7 ± 1.48pg/ml, KO: 22.0 ± 6.62, p<0.01) GLP-1 levels. Oral, but not intraperitoneal, glucose tolerance was significantly improved by AMPK deletion, whilst insulin and glucagon levels were unchanged despite an increase in alpha to beta cell ratio (WT: 0.23 ± 0.02, KO: 0.33 ± 0.03, p<0.01). Conclusion: AMPK restricts L-cell growth and GLP-1 secretion to suppress glucose tolerance. Targeted inhibition of AMPK in L-cells may thus provide a new therapeutic strategy in some forms of type 2 diabetes.
    Preview · Article · Mar 2016 · PLoS ONE
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    [Show abstract] [Hide abstract] ABSTRACT: Biguanides such as metformin have previously been shown to antagonize hepatic glucagon-stimulated cyclic AMP (cAMP) signalling independently of AMP-activated protein kinase (AMPK) via direct inhibition of adenylate cyclase by AMP. Here we show that incubation of hepatocytes with the small-molecule AMPK activator 991 decreases glucagon-stimulated cAMP accumulation, cAMP-dependent protein kinase (PKA) activity and downstream PKA target phosphorylation. Moreover, incubation of hepatocytes with 991 increases the V-max of cyclic nucleotide phosphodiesterase 4B (PDE4B) without affecting intracellular adenine nucleotide concentrations. The effects of 991 to decrease glucagon-stimulated cAMP concentrations and activate PDE4B are lost in hepatocytes deleted for both catalytic subunits of AMPK. PDE4B is phosphorylated by AMPK at three sites, and by site-directed mutagenesis, Ser304 phosphorylation is important for activation. In conclusion, we provide a new mechanism by which AMPK antagonizes hepatic glucagon signalling via phosphorylation-induced PDE4B activation.
    Full-text · Article · Mar 2016 · Nature Communications
  • No preview · Article · Mar 2016
  • [Show abstract] [Hide abstract] ABSTRACT: The AMP-activated protein kinase (AMPK) is an important regulator of cellular energy homeostasis which plays a role in fertility. Complete disruption of the AMPK catalytic subunit α1 gene (α1AMPK KO) in male mice results in a decrease in litter size which is associated with the production of altered sperm morphology and motility. Because of the importance of Sertoli cells in the formation of germ cells, we have chosen to selectively disrupt α1AMPK only in the Sertoli cells in mice (Sc-α1AMPK-KO mice). Specific deletion of the α1AMPK gene in Sertoli cells resulted in a 25% reduction in male fertility associated with abnormal spermatozoa with a thin head. No clear alterations in testis morphology or modification in the number of Sertoli cells in vivo were observed, but a dysregulation in energy metabolism in Sertoli cells occurred. We have reported an increase in lactate production, in lipid droplets, and a reduction in ATP production in Sc-α1AMPK-KO Sertoli cells. These perturbations were associated with lower expression of mitochondrial markers (cytochrome c and PGC1-α). In addition another metabolic sensor, the deacetylase SIRT1, had a reduction in expression which is correlated with a decline in deacetylase activity. Finally, expression and localization of junctions forming the blood-testis barrier between Sertoli cells themselves and with germ cells were deregulated in Sc-α1AMPK-KO. In conclusion, these results suggest that dysregulation of the energy sensing machinery exclusively through disruption of α1AMPK in Sertoli cells translates to a reduction in the quality of germ cells and fertility.
    No preview · Article · Jan 2016 · Molecular and Cellular Endocrinology
  • [Show abstract] [Hide abstract] ABSTRACT: Autophagy is a cellular self-eating process essential for stress response and maintaining tissue homeostasis by lysosomal degradation of unwanted or damaged proteins and organelles. Here we show that cells with defective mitochondria induce autophagy to promote cell survival through activating the AMPK pathway. Loss of mitochondrial complex III protein cytochrome b activates the AMPK signaling and induced autophagy. Inhibiting mitochondria energetics by mitochondria-targeted agents activates the AMPK signaling and induced autophagy. Genetic inhibition of AMPK inhibits autophagy induction in cells with defective mitochondria, while genetic inhibition of autophagy has no effect on AMPK activation. Mitochondria dysfunction has no effect of DNA repair of UV-induced DNA damage. However, mitochondria dysfunction sensitizes cells to apoptosis induced by UV radiation. Genetic inhibition of autophagy or AMPK sensitized cells to apoptosis in cells with defective mitochondria. Our results demonstrate that AMPK and autophagy senses mitochondria dysfunction and serves as a mechanism for survival. Our findings may provide new insights into the interplay between mitochondria function and autophagy process in maintaining tissue homeostasis, and suggest that this interaction may play important roles in diseases such as cancer and neurodegeneration.
    No preview · Article · Jan 2016
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    Full-text · Dataset · Dec 2015
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    [Show abstract] [Hide abstract] ABSTRACT: Rationale: Modulation of breathing by hypoxia accommodates variations in oxygen demand and supply during, for example, sleep and ascent to altitude, yet the precise molecular mechanisms remain controversial. Among those genes influenced by natural selection in high-altitude populations is that for the AMP-activated protein kinase (AMPK) α1 catalytic subunit, which governs cell autonomous adaptations during metabolic stress. Objective: We investigated whether or not AMPK-α1 and/or AMPK-α2 are required for the hypoxic ventilatory response and the mechanism of ventilatory dysfunctions arising from AMPK deficiency. Methods: Experiments utilized plethysmography, electrophysiology, functional magnetic resonance imaging and immediate early gene (cfos) expression to assess the hypoxic ventilatory response of mice with conditional deletion of the AMPK-α1 and/or AMPK-α2 genes in catecholaminergic cells, which comprise the hypoxia-responsive respiratory network from carotid body to brainstem. Measurements and main results: AMPK-α1+α2 deletion virtually abolished the hypoxic ventilatory response, and ventilatory depression during hypoxia was exacerbated under anesthesia. Rather than hyperventilating, mice lacking AMPK-α1+α2 exhibited hypoventilation and apnea during hypoxia, the primary precipitant being loss of AMPK-α1 expression. However, the carotid bodies of AMPK knockouts remained exquisitely sensitive to hypoxia, contrary to the view that the hypoxic ventilatory response is solely determined by increased carotid body afferent input to the brainstem. Regardless, functional magnetic resonance imaging and cfos expression revealed reduced activation by hypoxia of well-defined dorsal and ventral brainstem nuclei. Conclusions: AMPK is required to coordinate the activation by hypoxia of brainstem respiratory networks and deficiencies in AMPK expression precipitate hypoventilation and apnea, even where carotid body afferent input is normal.
    Full-text · Article · Dec 2015 · American Journal of Respiratory and Critical Care Medicine
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    [Show abstract] [Hide abstract] ABSTRACT: Metformin is a biguanide widely prescribed to treat Type II diabetes that has gained interest as an antineoplastic agent. Recent work suggests that metformin directly antagonizes cancer cell growth through its actions on complex I of the mitochondrial electron transport chain (ETC). However, the mechanisms by which metformin arrests cancer cell proliferation remain poorly defined. Here we demonstrate that the metabolic checkpoint kinases AMP-activated protein kinase (AMPK) and LKB1 are not required for the antiproliferative effects of metformin. Rather, metformin inhibits cancer cell proliferation by suppressing mitochondrial-dependent biosynthetic activity. We show that in vitro metformin decreases the flow of glucose- and glutamine-derived metabolic intermediates into the Tricarboxylic Acid (TCA) cycle, leading to reduced citrate production and de novo lipid biosynthesis. Tumor cells lacking functional mitochondria maintain lipid biosynthesis in the presence of metformin via glutamine-dependent reductive carboxylation, and display reduced sensitivity to metformin-induced proliferative arrest. Our data indicate that metformin inhibits cancer cell proliferation by suppressing the production of mitochondrial-dependent metabolic intermediates required for cell growth, and that metabolic adaptations that bypass mitochondrial-dependent biosynthesis may provide a mechanism of tumor cell resistance to biguanide activity.
    Full-text · Article · Dec 2015 · PLoS Biology
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    [Show abstract] [Hide abstract] ABSTRACT: Cancer cells exhibit unique metabolic response and adaptation to the fluctuating microenvironment, yet molecular and biochemical events imprinting this phenomenon are unclear. Here, we show that metabolic homeostasis and adaptation to metabolic stress in cancer cells are primarily achieved by an integrated response exerted by the activation of AMPK. We provide evidence that AMPK-p38-PGC-1α axis, by regulating energy homeostasis, maintains survival in cancer cells under glucose-limiting conditions. Functioning as a molecular switch, AMPK promotes glycolysis by activating PFK2, and facilitates mitochondrial metabolism of non-glucose carbon sources thereby maintaining cellular ATP level. Interestingly, we noted that AMPK can promote oxidative metabolism via increasing mitochondrial biogenesis and OXPHOS capacity via regulating expression of PGC-1α through p38MAPK activation. Taken together, our study signifies the fundamental role of AMPK in controlling cellular bioenergetics and mitochondrial biogenesis in cancer cells.
    Full-text · Article · Nov 2015
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    [Show abstract] [Hide abstract] ABSTRACT: An increase in muscle tissue delivery of glucose and insulin due to insulin-induced vasodilatation of arterioles and the subsequent increase in muscle microvascular perfusion is known to be a requisite response to food intake. An impairment of this physiological response could play a role in the development of both hyperglycemia and hypertension.
    Full-text · Article · Nov 2015
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    Monica Guma · Yun Wang · Benoit Viollet · Ru Liu-Bryan
    [Show abstract] [Hide abstract] ABSTRACT: Objective: AMP-activated protein kinase (AMPK) is a serine/threonine protein kinase critically involved in the regulation of cellular energy homeostasis. It is a central regulator of both lipid and glucose metabolism. Many studies have suggested that AMPK activation exert significant anti-inflammatory and immunosuppressive effects. In this study, we assessed whether targeted activation of AMPK inhibits inflammatory arthritis in vivo. Methods: We tested the effect of A-769662, a specific AMPK agonist (60mg/kg/bid) in mouse models of antigen-induced arthritis (AIA) and passive K/BxN serum-induced arthritis. The passive K/BxN serum-induced arthritis model was also applied to AMPKα1-deficient mice. Joints were harvested and subjected to histological analysis. IL-6 expression was measured in both joint tissues and sera by ELISA. The effect of A-769662 on bone marrow derived macrophage (BMDM) response to stimulation with TLR2 and TLR4 agonists was tested in vitro. Results: AMPK activation by A-769662 reduced inflammatory infiltration and joint damage in both mouse models. IL-6 expression in serum and arthritic joints was significantly decreased in A-769662-treated mice. AMPKα1 deficient mice mildly elicited an increase of clinical arthritis. IL-6 expression at both mRNA and protein levels, phosphorylation of p65 NF-κB and MAPK phosphorylation were inhibited by A-769662 in BMDMs stimulated with either TLR2 or TLR4 agonists. Conclusions: AMPK activation by specific AMPK agonist A-769662 suppressed inflammatory arthritis in mice as well as IL-6 expression in serum and arthritic joints. These data suggest that targeted activation of AMPK has a potential to be an effective therapeutic strategy for IL-6 dependent inflammatory arthritis.
    Full-text · Article · Oct 2015 · PLoS ONE
  • [Show abstract] [Hide abstract] ABSTRACT: Exercise training increases skeletal muscle expression of metabolic proteins improving the oxidative capacity. Adaptations in skeletal muscle by pharmacologically induced activation of 5'AMP-activated protein kinase (AMPK) are dependent on the AMPKα2 subunit. We hypothesized that exercise training-induced increases in exercise capacity and expression of metabolic proteins as well as acute exercise-induced gene regulation would be compromised in AMPKα1 and -α2 muscle-specific double knockout (mdKO) mice. An acute bout of exercise increased skeletal muscle mRNA content of cytochrome C oxidase subunit I, glucose transporter 4 and VEGF in an AMPK-dependent manner, while cluster of differentiation 36 and fatty acid transport protein 1 mRNA content increased similarly in AMPKα wild type (WT) and mdKO mice. During four weeks of voluntary running wheel exercise training, the AMPKα mdKO mice ran less than WT. Maximal running speed was lower in AMPKα mdKO than WT mice, but increased similarly in both genotypes with exercise training. Exercise training increased quadriceps protein content of ubiquinol-cytochrome-C reductase core protein 1 (UQCRC1), cytochrome C, hexokinase II, plasma membrane fatty acid binding protein and citrate synthase activity more in AMPKα WT than mdKO muscle. However, analysis of a subgroup of mice matched for running distance revealed that only UQCRC1 protein content increased more in WT than mdKO mice with exercise training. Thus, AMPKα1 and -α2 subunits are important for acute exercise-induced mRNA responses of some genes and may be involved in regulating basal metabolic protein expression, but seem to be less important in exercise training-induced adaptations in metabolic proteins.
    No preview · Article · Sep 2015 · AJP Endocrinology and Metabolism
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    Xing Fu · Meijun Zhu · Shuming Zhang · Marc Foretz · Benoit Viollet · Min Du
    [Show abstract] [Hide abstract] ABSTRACT: Obesity is increasing rapidly worldwide, accompanied with many complications including impaired muscle regeneration. Obese condition is known to inhibit AMP-activated protein kinase (AMPK) activity in multiple tissues. We hypothesized that the loss of AMPK activity is a major reason for the hampered muscle regeneration in obese subjects. We found that obesity inhibited AMPK activity in regenerating muscle, which was associated with impeded satellite cell activation, and impaired muscle regeneration. To test the mediatory role of AMPKα1, we knocked out AMPKα1 and found that both proliferation and differentiation of satellite cells are reduced following injury and muscle regeneration was severely impeded, reminiscent to hampered muscle regeneration seen in obese subjects. Transplanted satellite cells with AMPKα1 deficiency had severely impaired myogenic capacity in regenerating muscle fibers. Finally, we found attenuated muscle regeneration in obese mice was rescued by AICAR, a drug specifically activating AMPK. On the other hand, AICAR treatment failed to improve muscle regeneration in obese mice with satellite cell-specific AMPKα1 knockout, demonstrating the importance of AMPKα1 in satellite cell activation and muscle regeneration. In summary, AMPKα1 is a key mediator linking obesity and impaired muscle regeneration, providing a convenient drug target to facilitate muscle regeneration in obese populations.
    Full-text · Article · Sep 2015 · Diabetes
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    [Show abstract] [Hide abstract] ABSTRACT: Certain inborn errors of metabolism result from deficiencies in biotin containing enzymes. These disorders are mimicked by dietary absence or insufficiency of biotin, ATP deficit being a major effect, whose responsible mechanisms have not been thoroughly studied. Here we show that in rats and cultured cells it is the result of reduced TCA cycle flow, partly due to deficient anaplerotic biotin-dependent pyruvate carboxylase. This is accompanied by diminished flow through the electron transport chain, augmented by deficient cytochrome c oxidase (complex IV) activity with decreased cytochromes and reduced oxidative phosphorylation. There was also severe mitochondrial damage accompanied by decrease of mitochondria, associated with toxic levels of propionyl CoA as shown by carnitine supplementation studies, which explains the apparently paradoxical mitochondrial diminution in the face of the energy sensor AMPK activation, known to induce mitochondria biogenesis. This idea was supported by experiments on AMPK knockout mouse embryonic fibroblasts (MEFs). The multifactorial ATP deficit also provides a plausible basis for the cardiomyopathy in patients with propionic acidemia, and other diseases. Additionally, systemic inflammation concomitant to the toxic state might explain our findings of enhanced IL-6, STAT3 and HIF-1α, associated with an increase of mitophagic BNIP3 and PINK proteins, which may further increase mitophagy. Together our results imply core mechanisms of energy deficit in several inherited metabolic disorders.
    Full-text · Article · Sep 2015 · Molecular Genetics and Metabolism
  • Benoit Viollet · Marc Foretz
    [Show abstract] [Hide abstract] ABSTRACT: AMP-activated protein kinase (AMPK) is a major energy sensor that regulates cellular and whole-body energy balance. AMPK has critical roles in reprogramming metabolism and regulating growth. This chapter summarizes the recent breakthroughs in AMPK function in the liver, focusing on a number of newly identified downstream effectors. Hence, understanding the control of cellular processes by AMPK could guide us to identify and improve preventive and therapeutic strategies for liver diseases. Recently, AMPK has attracted widespread interest as a potential therapeutic target for metabolic disorders including fatty liver disease and cancer.
    No preview · Article · Aug 2015
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    Full-text · Dataset · Jul 2015
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    Full-text · Dataset · Jul 2015
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    Full-text · Dataset · Jul 2015
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    [Show abstract] [Hide abstract] ABSTRACT: Secretory Phospholipase A2 of type IIA (sPLA2 IIA) plays a crucial role in the production of lipid mediators by amplifying the neointimal inflammatory context of the vascular smooth muscle cells (VSMCs), especially during atherogenesis. Phenformin, a biguanide family member, by its anti-inflammatory properties presents potential for promoting beneficial effects upon vascular cells, however its impact upon the IL-1β-induced sPLA2 gene expression has not been deeply investigated so far. The present study was designed to determine the relationship between phenformin coupling AMP-activated protein kinase (AMPK) function and the molecular mechanism by which the sPLA2 IIA expression was modulated in VSMCs. Here we find that 5-aminoimidazole-4-carboxamide-1-β-D-ribonucleotide (AICAR) treatment strongly repressed IL-1β-induced sPLA2 expression at least at the transcriptional level. Our study reveals that phenformin elicited a dose-dependent inhibition of the sPLA2 IIA expression and transient overexpression experiments of constitutively active AMPK demonstrate clearly that AMPK signaling is involved in the transcriptional inhibition of sPLA2-IIA gene expression. Furthermore, although the expression of the transcriptional repressor B-cell lymphoma-6 protein (BCL-6) was markedly enhanced by phenformin and AICAR, the repression of sPLA2 gene occurs through a mechanism independent of BCL-6 DNA binding site. In addition we show that activation of AMPK limits IL-1β-induced NF-κB pathway activation. Our results indicate that BCL-6, once activated by AMPK, functions as a competitor of the IL-1β induced NF-κB transcription complex. Our findings provide insights on a new anti-inflammatory pathway linking phenformin, AMPK and molecular control of sPLA2 IIA gene expression in VSMCs.
    Preview · Article · Jul 2015 · PLoS ONE

Publication Stats

16k Citations
2,049.43 Total Impact Points

Institutions

  • 2002-2016
    • Université René Descartes - Paris 5
      • Faculté de Médecine
      Lutetia Parisorum, Île-de-France, France
  • 2010-2014
    • Unité Inserm U1077
      Caen, Lower Normandy, France
  • 2012
    • University Pompeu Fabra
      • Department of Experimental and Health Sciences
      Barcino, Catalonia, Spain
  • 2001-2012
    • French National Centre for Scientific Research
      Lutetia Parisorum, Île-de-France, France
  • 2011
    • Università degli Studi di Bari Aldo Moro
      Bari, Apulia, Italy
  • 2004-2011
    • French Institute of Health and Medical Research
      • Cochin Institute
      Lutetia Parisorum, Île-de-France, France
  • 2004-2010
    • Institut Cochin
      Lutetia Parisorum, Île-de-France, France
  • 2008
    • Institut de Génétique et de Biologie Moléculaire et Cellulaire
      Strasburg, Alsace, France
    • University of Bordeaux
      Burdeos, Aquitaine, France
  • 2007
    • University of Toulouse
      Tolosa de Llenguadoc, Midi-Pyrénées, France
    • The Catholic University of America
      Washington, Washington, D.C., United States
  • 2004-2007
    • Université catholique de Louvain
      Лувен-ла-Нев, Wallonia, Belgium
  • 2006
    • Hôpital Bichat - Claude-Bernard (Hôpitaux Universitaires Paris Nord Val de Seine)
      Lutetia Parisorum, Île-de-France, France