58 research outputs found
Antagonistic control of muscle cell size by AMPK and mTORC1.
7 pages (2640-2646)International audienceNutrition and physical activity have profound effects on skeletal muscle metabolism and growth. Regulation of muscle mass depends on a thin balance between growth-promoting and growth-suppressing factors. Over the past decade, the mammalian target of rapamycin (mTOR) kinase has emerged as an essential factor for muscle growth by mediating the anabolic response to nutrients, insulin, insulin-like growth factors and resistance exercise. As opposed to the mTOR signaling pathway, the AMP-activated protein kinase (AMPK) is switched on during starvation and endurance exercise to upregulate energy-conserving processes. Recent evidence indicates that mTORC1 (mTOR Complex 1) and AMPK represent two antagonistic forces governing muscle adaption to nutrition, starvation and growth stimulation. Animal knockout models with impaired mTORC1 signaling showed decreased muscle mass correlated with increased AMPK activation. Interestingly, AMPK inhibition in p70S6K-deficient muscle cells restores cell growth and sensitivity to nutrients. Conversely, muscle cells lacking AMPK have increased mTORC1 activation with increased cell size and protein synthesis rate. We also demonstrated that the hypertrophic action of MyrAkt is enhanced in AMPK-deficient muscle, indicating that AMPK acts as a negative feedback control to restrain muscle hypertrophy. Our recent results extend this notion by showing that AMPKα1, but not AMPKα2, regulates muscle cell size through the control of mTORC1 signaling. These results reveal the diverse functions of the two catalytic isoforms of AMPK, with AMPKα1 playing a predominant role in the control of muscle cell size and AMPKα2 mediating muscle metabolic adaptation. Thus, the crosstalk between AMPK and mTORC1 signaling is a highly regulated way to control changes in muscle growth and metabolic rate imposed by external cues
PRKAA1/AMPKα1 is required for autophagy-dependent mitochondrial clearance during erythrocyte maturation
AMP-activated protein kinase α1 knockout (prkaa1â/â) mice manifest splenomegaly and anemia. The underlying molecular mechanisms, however, remain to be established. In this study, we tested the hypothesis that defective autophagy-dependent mitochondrial clearance in prkaa1â/â mice exacerbates oxidative stress, thereby enhancing erythrocyte destruction. The levels of ULK1 phosphorylation, autophagical flux, mitochondrial contents, and reactive oxygen species (ROS) were examined in human erythroleukemia cell line, K562 cells, as well as prkaa1â/â mouse embryonic fibroblasts and erythrocytes. Deletion of Prkaa1 resulted in the inhibition of ULK1 phosphorylation at Ser555, prevented the formation of ULK1 and BECN1- PtdIns3K complexes, and reduced autophagy capacity. The suppression of autophagy was associated with enhanced damaged mitochondrial accumulation and ROS production. Compared with wild-type (WT) mice, prkaa1â/â mice exhibited a shortened erythrocyte life span, hemolytic destruction of erythrocytes, splenomegaly, and anemia, all of which were alleviated by the administration of either rapamycin to activate autophagy or Mito-tempol, a mitochondria-targeted antioxidant, to scavenge mitochondrial ROS. Furthermore, transplantation of WT bone marrow into prkaa1â/â mice restored mitochondrial removal, reduced intracellular ROS levels, and normalized hematologic parameters and spleen size. Conversely, transplantation of prkaa1 â/â bone marrow into WT mice recapitulated the prkaa1â/â mouse phenotypes. We conclude that PRKAA1-dependent autophagy-mediated clearance of damaged mitochondria is required for erythrocyte maturation and homeostasis
Targeting the AMPK pathway for the treatment of Type 2 diabetes.
International audienceType 2 diabetes is one of the fastest growing public health problems worldwide, resulting from both genetic factors and inadequate adaptation to environmental changes. It is characterized by abnormal glucose and lipid metabolism due in part to resistance to the actions of insulin in skeletal muscle, liver and fat. AMP-activated protein kinase (AMPK), a phylogenetically conserved serine/threonine protein kinase, acts as an integrator of regulatory signals monitoring systemic and cellular energy status. The growing realization that AMPK regulates the coordination of anabolic and catabolic metabolic processes represents an attractive concept for type 2 diabetes therapy. Recent findings showing that pharmacological activation of AMPK improves blood glucose homeostasis, lipid profile and blood pressure in insulin-resistant rodents suggest that this kinase could be a novel therapeutic target in the treatment of type 2 diabetes. Consistent with these results, physical exercise and major classes of antidiabetic drugs have recently been reported to activate AMPK. In the present review, we update these topics and discuss the concept of targeting the AMPK pathway for the treatment of type 2 diabetes
Metformin inhibits hepatic gluconeogenesis in mice independently of the LKB1/AMPK pathway via a decrease in hepatic energy state.
pages 1-15International audienceMetformin is widely used to treat hyperglycemia in individuals with type 2 diabetes. Recently the LKB1/AMP-activated protein kinase (LKB1/AMPK) pathway was proposed to mediate the action of metformin on hepatic gluconeogenesis. However, the molecular mechanism by which this pathway operates had remained elusive. Surprisingly, here we have found that in mice lacking AMPK in the liver, blood glucose levels were comparable to those in wild-type mice, and the hypoglycemic effect of metformin was maintained. Hepatocytes lacking AMPK displayed normal glucose production and gluconeogenic gene expression compared with wild-type hepatocytes. In contrast, gluconeogenesis was upregulated in LKB1-deficient hepatocytes. Metformin decreased expression of the gene encoding the catalytic subunit of glucose-6-phosphatase (G6Pase), while cytosolic phosphoenolpyruvate carboxykinase (Pepck) gene expression was unaffected in wild-type, AMPK-deficient, and LKB1-deficient hepatocytes. Surprisingly, metformin-induced inhibition of glucose production was amplified in both AMPK- and LKB1-deficient compared with wild-type hepatocytes. This inhibition correlated in a dose-dependent manner with a reduction in intracellular ATP content, which is crucial for glucose production. Moreover, metformin-induced inhibition of glucose production was preserved under forced expression of gluconeogenic genes through PPARgamma coactivator 1alpha (PGC-1alpha) overexpression, indicating that metformin suppresses gluconeogenesis via a transcription-independent process. In conclusion, we demonstrate that metformin inhibits hepatic gluconeogenesis in an LKB1- and AMPK-independent manner via a decrease in hepatic energy state
Reducing two-level system dissipations in 3D superconducting Niobium resonators by atomic layer deposition and high temperature heat treatment
Superconducting qubits have arisen as a leading technology platform for
quantum computing which is on the verge of revolutionizing the world's
calculation capacities. Nonetheless, the fabrication of computationally
reliable qubit circuits requires increasing the quantum coherence lifetimes,
which are predominantly limited by the dissipations of two-level system (TLS)
defects present in the thin superconducting film and the adjacent dielectric
regions. In this paper, we demonstrate the reduction of two-level system losses
in three-dimensional superconducting radio frequency (SRF) niobium resonators
by atomic layer deposition (ALD) of a 10 nm aluminum oxide Al2O3 thin films
followed by a high vacuum (HV) heat treatment at 650 {\deg}C for few hours. By
probing the effect of several heat treatments on Al2O3-coated niobium samples
by X-ray photoelectron spectroscopy (XPS) plus scanning and conventional high
resolution transmission electron microscopy (STEM/HRTEM) coupled with electron
energy loss spectroscopy (EELS) and (EDX) , we witness a dissolution of niobium
native oxides and the modification of the Al2O3-Nb interface, which correlates
with the enhancement of the quality factor at low fields of two 1.3 GHz niobium
cavities coated with 10 nm of Al2O3
Ătude de fiabilitĂ© dâun instrument dâobservation des comportements de lâĂ©lĂšve en classe
AprĂšs avoir dĂ©crit lâinstrument et le schĂšme utilisĂ©s pour lâobservation des comportements de lâĂ©lĂšve en classe, on prĂ©sente les rĂ©sultats de lâanalyse statistique effectuĂ©e pour sâassurer de la fiabilitĂ© des donnĂ©es. Pour chacun des trois comportements observĂ©s, un coefficient dâentente inter-juges a Ă©tĂ© calculĂ© pour Ă©valuer dans quelle mesure la mĂ©sentente inter-juges pouvait limiter la fiabilitĂ© des donnĂ©es et un coefficient de fiabilitĂ© a Ă©tĂ© calculĂ© pour mesurer la fiabilitĂ© avec laquelle les comportements des Ă©lĂšves pouvaient ĂȘtre observĂ©s. Les valeurs du coefficient dâentente inter-juges se sont montrĂ©es trĂšs Ă©levĂ©es alors que les valeurs du coefficient de fiabilitĂ© se sont montrĂ©es trĂšs faibles. Ce faible coefficient est expliquĂ© en grande partie par lâinstabilitĂ© des comportements de lâĂ©lĂšve dâoccasion en occasion : câest-Ă -dire par la trop grande variabilitĂ© des donnĂ©es intra-Ă©lĂšve par rapport Ă la variabilitĂ© inter-Ă©lĂšves. Les auteurs concluent de lâimportance des situations homogĂšnes dâapprentissage dans lâobservation des comportements des Ă©lĂšves en classe
La mesure des comportements dans un systÚme d'enseignement individualisé /
Cet article prĂ©sente la nature et les rĂ©sultats dâune Ă©tude dont le but Ă©tait de juger de la pertinence de lâutilisation de lâinstrument dâobservation de la classe (Stanford Research Institute Classroom Observation Instrument) pour Ă©valuer, dans un systĂšme individualisĂ© dâenseignement, les variables suivantes : indĂ©pendance, coopĂ©ration et persistance au travail de lâĂ©tudiant. En un premier temps, trois observateurs se sont entraĂźnĂ©s Ă maĂźtriser lâinstrument pour arriver Ă un niveau dâentente suffisant et pour apprĂ©cier la validitĂ© de lâinstrument. En un second temps, lâinstrument a Ă©tĂ© utilisĂ© pour mesurer les variables indiquĂ©es ci-dessus en comparant deux groupes dâĂ©tudiants, lâun situĂ© dans un contexte dâenseignement collectif, lâautre dans un contexte dâenseignement individualisĂ©
AMPK Activation Promotes Tight Junction Assembly in Intestinal Epithelial Caco-2 Cells
International audienceThe AMP-activated protein kinase (AMPK) is principally known as a major regulator of cellular energy status, but it has been recently shown to play a key structural role in cell-cell junctions. The aim of this study was to evaluate the impact of AMPK activation on the reassembly of tight junctions in intestinal epithelial Caco-2 cells. We generated Caco-2 cells invalidated for AMPK α1/α2 (AMPK dKO) by CRISPR/Cas9 technology and evaluated the effect of the direct AMPK activator 991 on the reassembly of tight junctions following a calcium switch assay. We analyzed the integrity of the epithelial barrier by measuring the trans-epithelial electrical resistance (TEER), the paracellular permeability, and quantification of zonula occludens 1 (ZO-1) deposit at plasma membrane by immunofluorescence. Here, we demonstrated that AMPK deletion induced a delay in tight junction reassembly and relocalization at the plasma membrane during calcium switch, leading to impairments in the establishment of TEER and paracellular permeability. We also showed that 991-induced AMPK activation accelerated the reassembly and reorganization of tight junctions, improved the development of TEER and paracellular permeability after calcium switch. Thus, our results show that AMPK activation ensures a better recovery of epithelial barrier function following injury
: AMPK controls muscle cell size
7 pagesInternational audienceSkeletal muscle mass is regulated by signaling pathways that govern protein synthesis and cell proliferation, and the mammalian target of rapamycin (mTOR) plays a key role in these processes. Recent studies suggested the crucial role of AMP-activated protein kinase (AMPK) in the inhibition of protein synthesis and cell growth. Here, we address the role of AMPK in the regulation of muscle cell size in vitro and in vivo. The size of AMPK-deficient myotubes was 1.5-fold higher than for controls. A marked increase in p70S6K Thr(389) and rpS6 Ser-235/236 phosphorylation was observed concomitantly with an up-regulation of protein synthesis rate. Treatment with rapamycin prevented p70S6K phosphorylation and rescued cell size control in AMPK-deficient cells. Importantly, myotubes lacking AMPK were resistant to further cell size increase beyond AMPK deletion alone, as MyrAkt-induced hypertrophy was absent in these cells. Moreover, in skeletal muscle-specific deficient AMPKalpha1/alpha2 KO mice, soleus muscle showed a higher mass with myofibers of larger size and was associated with increased p70S6K and rpS6 phosphorylation. Our results uncover the role of AMPK in the maintenance of muscle cell size control and highlight the crosstalk between AMPK and mTOR/p70S6K signaling pathways coordinating a metabolic checkpoint on cell growth
Cellular and molecular mechanisms of metformin: an overview.
8 pagesInternational audienceConsiderable efforts have been made since the 1950s to better understand the cellular and molecular mechanisms of action of metformin, a potent antihyperglycaemic agent now recommended as the first-line oral therapy for T2D (Type 2 diabetes). The main effect of this drug from the biguanide family is to acutely decrease hepatic glucose production, mostly through a mild and transient inhibition of the mitochondrial respiratory chain complex I. In addition, the resulting decrease in hepatic energy status activates AMPK (AMP-activated protein kinase), a cellular metabolic sensor, providing a generally accepted mechanism for the action of metformin on hepatic gluconeogenesis. The demonstration that respiratory chain complex I, but not AMPK, is the primary target of metformin was recently strengthened by showing that the metabolic effect of the drug is preserved in liver-specific AMPK-deficient mice. Beyond its effect on glucose metabolism, metformin has been reported to restore ovarian function in PCOS (polycystic ovary syndrome), reduce fatty liver, and to lower microvascular and macrovascular complications associated with T2D. Its use has also recently been suggested as an adjuvant treatment for cancer or gestational diabetes and for the prevention in pre-diabetic populations. These emerging new therapeutic areas for metformin will be reviewed together with recent findings from pharmacogenetic studies linking genetic variations to drug response, a promising new step towards personalized medicine in the treatment of T2D
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