Altération métabolique et déficit synaptique dans la maladie d'Alzheimer : rôle de la PHGDH astrocytaire

An early alteration of both cerebral glucose metabolism and synaptic activity has been consistently described in Alzheimer's disease (AD) patients. Metabolism of glucose via glycolysis and the citric acid cycle produces ATP that is essential for synaptic activity and plasticity. In the brain, glucose is predominantly processed glycolytically into astrocytes and not by neurons. Beyond ATP production, a major function of aerobic glycolysis is to provide precursors to support macromolecular synthesis. L-serine, generated from glucose through diversion of the glycolytic intermediate 3-phosphoglycerate (3PG) into the phosphorylated pathway, is only produced in astrocytes by 3-phosphoglycerate dehydrogenase (PHGDH), selectively expressed in those glial cells. L-serine is the precursor of D-serine, the main co-agonist of synaptic NMDAR, required for synaptic activity and plasticity. We used 3xTg-AD mice, which develop a progressive pathology, to investigate whether a defective production of L-/D-serine contributes to early synaptic deficits in AD. We found that 3xTg-AD mice display early in vivo alterations of glucose metabolism, synaptic deficits (LTP) in the CA1 region and also lower concentration of L-serine. The local expression of PHGDH was significantly altered. Exogenous D-serine completely rescued LTP in 3xTg-AD mice. These data support the hypothesis that a deficit of L-serine synthesis by astrocytes likely mediated by a decreased glycolytic flux may be responsible for the synaptic alteration mediated by NMDAR in the hippocampus of 3xTg-AD mice.Les patients atteints de la MA souffrent d'altérations métaboliques et synaptiques précoces. Via la glycolyse et le cycle de Krebs, le métabolisme du glucose permet la production d'ATP, essentielle à l'activité et la plasticité synaptique. Contrairement aux neurones, les astrocytes utilisent majoritairement la glycolyse pour métaboliser le glucose. En plus de la production d'énergie, la glycolyse fournit les précurseurs indispensables à la synthèse de biomolécules comme la L-sérine. Cet acide aminé est produit à partir du glucose par la déviation du 3-phosphoglycérate (3PG), un intermédiaire glycolytique, via l'enzyme 3-phosphoglycérate déshydrogénase (PHGDH), exprimée spécifiquement dans les astrocytes. La L-sérine est le précurseur de la D-sérine, le principal co-agoniste des NMDAR nécessaires à l'activité et la plasticité synaptique.Nous avons utilisé des souris 3xTg-AD, un modèle développant une MA progressive, afin d'étudier si une altération de la production de L-/D-sérine pouvait contribuer à des déficits synaptiques.A 6 mois, lorsque les souris 3xTg-AD ne possèdent pas encore de plaques amyloïdes dans l'hippocampe, nous avons observé in vivo une diminution du métabolisme du glucose, de la concentration de L-sérine et des déficits synaptiques (LTP). L'expression locale de la PHGDH est aussi altérée. L'application de D-sérine restaure complètement les déficits de LTP chez les souris 3xTg-AD.Ces données supportent l'hypothèse qu'un déficit de production de L-sérine par les astrocytes médié par une diminution du flux glycolytique serait responsable de l'altération synaptique observée dans l'hippocampe des souris 3xTg-AD

Astrocytic 3-phosphoglycerate dehydrogenase links energy metabolism and LTP deficits in a mouse model of Alzheimer's Disease

Les patients atteints de la MA souffrent d'altérations métaboliques et synaptiques précoces. Via la glycolyse et le cycle de Krebs, le métabolisme du glucose permet la production d'ATP, essentielle à l'activité et la plasticité synaptique. Contrairement aux neurones, les astrocytes utilisent majoritairement la glycolyse pour métaboliser le glucose. En plus de la production d'énergie, la glycolyse fournit les précurseurs indispensables à la synthèse de biomolécules comme la L-sérine. Cet acide aminé est produit à partir du glucose par la déviation du 3-phosphoglycérate (3PG), un intermédiaire glycolytique, via l'enzyme 3-phosphoglycérate déshydrogénase (PHGDH), exprimée spécifiquement dans les astrocytes. La L-sérine est le précurseur de la D-sérine, le principal co-agoniste des NMDAR nécessaires à l'activité et la plasticité synaptique.Nous avons utilisé des souris 3xTg-AD, un modèle développant une MA progressive, afin d'étudier si une altération de la production de L-/D-sérine pouvait contribuer à des déficits synaptiques.A 6 mois, lorsque les souris 3xTg-AD ne possèdent pas encore de plaques amyloïdes dans l'hippocampe, nous avons observé in vivo une diminution du métabolisme du glucose, de la concentration de L-sérine et des déficits synaptiques (LTP). L'expression locale de la PHGDH est aussi altérée. L'application de D-sérine restaure complètement les déficits de LTP chez les souris 3xTg-AD.Ces données supportent l'hypothèse qu'un déficit de production de L-sérine par les astrocytes médié par une diminution du flux glycolytique serait responsable de l'altération synaptique observée dans l'hippocampe des souris 3xTg-AD.An early alteration of both cerebral glucose metabolism and synaptic activity has been consistently described in Alzheimer's disease (AD) patients. Metabolism of glucose via glycolysis and the citric acid cycle produces ATP that is essential for synaptic activity and plasticity. In the brain, glucose is predominantly processed glycolytically into astrocytes and not by neurons. Beyond ATP production, a major function of aerobic glycolysis is to provide precursors to support macromolecular synthesis. L-serine, generated from glucose through diversion of the glycolytic intermediate 3-phosphoglycerate (3PG) into the phosphorylated pathway, is only produced in astrocytes by 3-phosphoglycerate dehydrogenase (PHGDH), selectively expressed in those glial cells. L-serine is the precursor of D-serine, the main co-agonist of synaptic NMDAR, required for synaptic activity and plasticity. We used 3xTg-AD mice, which develop a progressive pathology, to investigate whether a defective production of L-/D-serine contributes to early synaptic deficits in AD. We found that 3xTg-AD mice display early in vivo alterations of glucose metabolism, synaptic deficits (LTP) in the CA1 region and also lower concentration of L-serine. The local expression of PHGDH was significantly altered. Exogenous D-serine completely rescued LTP in 3xTg-AD mice. These data support the hypothesis that a deficit of L-serine synthesis by astrocytes likely mediated by a decreased glycolytic flux may be responsible for the synaptic alteration mediated by NMDAR in the hippocampus of 3xTg-AD mice

Astrocytic 3-phosphoglycerate dehydrogenase links energy metabolism and LTP deficits in a mouse model of Alzheimer's Disease

Les patients atteints de la MA souffrent d'altérations métaboliques et synaptiques précoces. Via la glycolyse et le cycle de Krebs, le métabolisme du glucose permet la production d'ATP, essentielle à l'activité et la plasticité synaptique. Contrairement aux neurones, les astrocytes utilisent majoritairement la glycolyse pour métaboliser le glucose. En plus de la production d'énergie, la glycolyse fournit les précurseurs indispensables à la synthèse de biomolécules comme la L-sérine. Cet acide aminé est produit à partir du glucose par la déviation du 3-phosphoglycérate (3PG), un intermédiaire glycolytique, via l'enzyme 3-phosphoglycérate déshydrogénase (PHGDH), exprimée spécifiquement dans les astrocytes. La L-sérine est le précurseur de la D-sérine, le principal co-agoniste des NMDAR nécessaires à l'activité et la plasticité synaptique.Nous avons utilisé des souris 3xTg-AD, un modèle développant une MA progressive, afin d'étudier si une altération de la production de L-/D-sérine pouvait contribuer à des déficits synaptiques.A 6 mois, lorsque les souris 3xTg-AD ne possèdent pas encore de plaques amyloïdes dans l'hippocampe, nous avons observé in vivo une diminution du métabolisme du glucose, de la concentration de L-sérine et des déficits synaptiques (LTP). L'expression locale de la PHGDH est aussi altérée. L'application de D-sérine restaure complètement les déficits de LTP chez les souris 3xTg-AD.Ces données supportent l'hypothèse qu'un déficit de production de L-sérine par les astrocytes médié par une diminution du flux glycolytique serait responsable de l'altération synaptique observée dans l'hippocampe des souris 3xTg-AD.An early alteration of both cerebral glucose metabolism and synaptic activity has been consistently described in Alzheimer's disease (AD) patients. Metabolism of glucose via glycolysis and the citric acid cycle produces ATP that is essential for synaptic activity and plasticity. In the brain, glucose is predominantly processed glycolytically into astrocytes and not by neurons. Beyond ATP production, a major function of aerobic glycolysis is to provide precursors to support macromolecular synthesis. L-serine, generated from glucose through diversion of the glycolytic intermediate 3-phosphoglycerate (3PG) into the phosphorylated pathway, is only produced in astrocytes by 3-phosphoglycerate dehydrogenase (PHGDH), selectively expressed in those glial cells. L-serine is the precursor of D-serine, the main co-agonist of synaptic NMDAR, required for synaptic activity and plasticity. We used 3xTg-AD mice, which develop a progressive pathology, to investigate whether a defective production of L-/D-serine contributes to early synaptic deficits in AD. We found that 3xTg-AD mice display early in vivo alterations of glucose metabolism, synaptic deficits (LTP) in the CA1 region and also lower concentration of L-serine. The local expression of PHGDH was significantly altered. Exogenous D-serine completely rescued LTP in 3xTg-AD mice. These data support the hypothesis that a deficit of L-serine synthesis by astrocytes likely mediated by a decreased glycolytic flux may be responsible for the synaptic alteration mediated by NMDAR in the hippocampus of 3xTg-AD mice

Complex I assembly into supercomplexes determines differential mitochondrial ROS production in neurons and astrocytes

Neurons depend on oxidative phosphorylation for survival, whereas astrocytes do not. Mitochondrial respiratory chain (MRC) complexes can be organized in higher structures called supercomplexes, which dictate MRC electron flux and energy efficiency. Whether the specific metabolic shapes of neurons and astrocytes are determined by the specific organization of MRC complexes is unknown. Here, we found that, in astrocytes, most complex I is free, resulting in poor mitochondrial respiration but high reactive oxygen species (ROS) production. In contrast, neurons show complex I to be mostly embedded into supercomplexes, thus resulting in high mitochondrial respiration and low ROS production. Thus, MRC organization dictates different bioenergetics preferences of neurons and astrocytes impacting on ROS production, possibly playing a role in neurodegenerative diseases.J.P.B. is funded by the Ministry of Economy and Competitiveness (SAF2013-41177-R), Instituto de Salud Carlos III (RD12/0043/0021), European Union (EU) SP3-People-MC-ITN Programme (608381), EU BATCure Grant 666918, and NIH/National Institute on Drug Abuse Grant 1R21DA037678-01. A.A. is funded by Instituto de Salud Carlos III (PI12/00685 and RD12/0014/0007).Peer Reviewe

Supragranular Pyramidal Cells Exhibit Early Metabolic Alterations in the 3xTg-AD Mouse Model of Alzheimer’s Disease

International audienceThe impairment of cerebral glucose utilization is an early and predictive biomarker of Alzheimer's disease (AD) that is likely to contribute to memory and cognition disorders during the progression of the pathology. Yet, the cellular and molecular mechanisms underlying these metabolic alterations remain poorly understood. Here we studied the glucose metabolism of supragranular pyramidal cells at an early presymptomatic developmental stage in non-transgenic (non-Tg) and 3xTg-AD mice, a mouse model of AD replicating numerous hallmarks of the disease. We performed both intracellular glucose imaging with a genetically encoded fluorescence resonance energy transfer (FRET)-based glucose biosensor and transcriptomic profiling of key molecular elements of glucose metabolism with single-cell multiplex RT-PCR (scRT-mPCR). We found that juvenile pyramidal cells exhibit active glycolysis and pentose phosphate pathway at rest that are respectively enhanced and impaired in 3xTg-AD mice without alteration of neuronal glucose uptake or transcriptional modification. Given the importance of glucose metabolism for neuronal survival, these early alterations could initiate or at least contribute to the later neuronal dysfunction of pyramidal cells in AD

NX210c Peptide Promotes Glutamatergic Receptor-Mediated Synaptic Transmission and Signaling in the Mouse Central Nervous System

NX210c is a disease-modifying dodecapeptide derived from the subcommissural organ-spondin that is under preclinical and clinical development for the treatment of neurological disorders. Here, using whole-cell patch-clamp recordings, we demonstrate that NX210c increased α-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid receptor (AMPAR)- and GluN2A-containing N-methyl-D-aspartate receptor (GluN2A-NMDAR)-mediated excitatory postsynaptic currents in the brain. Accordingly, using extracellular field excitatory postsynaptic potential recordings, an enhancement of synaptic transmission was shown in the presence of NX210c in two different neuronal circuits. Furthermore, the modulation of synaptic transmission and GluN2A-NMDAR-driven signaling by NX210c restored memory in mice chronically treated with the NMDAR antagonist phencyclidine. Overall, by promoting glutamatergic receptor-related neurotransmission and signaling, NX210c represents an innovative therapeutic opportunity for patients suffering from CNS disorders, injuries, and states with crippling synaptic dysfunctions

The cAMP pathway regulates mRNA decay through phosphorylation of the RNA-binding protein TIS11b/BRF1

International audienceTPA-inducible sequence 11b/butyrate response factor 1 (TIS11b/BRF1) belongs to the tristetraprolin (TTP) family of zinc-finger proteins, which bind to mRNAs containing AU-rich elements in their 3'-untranslated region and target them for degradation. Regulation of TTP family function through phosphorylation by p38 MAP kinase and Akt/protein kinase B signaling pathways has been extensively studied. In contrast, the role of cAMP-dependent protein kinase (PKA) in the control of TTP family activity in mRNA decay remains largely unknown. Here we show that PKA activation induces TIS11b gene expression and protein phosphorylation. Site-directed mutagenesis combined with kinase assays and specific phosphosite immunodetection identified Ser-54 (S54) and Ser-334 (S334) as PKA target amino acids in vitro and in vivo. Phosphomimetic mutation of the C-terminal S334 markedly increased TIS11b half-life and, unexpectedly, enhanced TIS11b activity on mRNA decay. Examination of protein-protein interactions between TIS11b and components of the mRNA decay machinery revealed that mimicking phosphorylation at S334 enhances TIS11b interaction with the decapping coactivator Dcp1a, while preventing phosphorylation at S334 potentiates its interaction with the Ccr4-Not deadenylase complex subunit Cnot1. Collectively our findings establish for the first time that cAMP-elicited phosphorylation of TIS11b plays a key regulatory role in its mRNA decay-promoting function

New paradigm to assess brain cell morphology by diffusion-weighted MR spectroscopy in vivo

International audienceThe brain is one of the most complex organs, and tools are lacking to assess its cellular morphology in vivo. Here we combine original diffusion-weighted magnetic resonance (MR) spectroscopy acquisition and novel modeling strategies to explore the possibility of quantifying brain cell morphology noninvasively. First, the diffusion of cell-specific metabolites is measured at ultra-long diffusion times in the rodent and primate brain in vivo to observe how cell long-range morphology constrains metabolite diffusion. Massive simulations of particles diffusing in synthetic cells parameterized by morphometric statistics are then iterated to fit experimental data. This method yields synthetic cells (tentatively neurons and astrocytes) that exhibit striking qualitative and quantitative similarities with histol-ogy (e.g., using Sholl analysis). With our approach, we measure major interspecies difference regarding astrocytes, whereas den-dritic organization appears better conserved throughout species. This work suggests that the time dependence of metabolite diffusion coefficient allows distinguishing and quantitatively characterizing brain cell morphologies noninvasively. cell morphology | noninvasive histology | diffusion-weighted NMR spectroscopy | numerical simulations | metabolites T he brain is one of the most complex organs, and it has defined an inexhaustible field of research over the last centuries. Unfortunately , brain's complexity is paralleled by the difficulty in examining it noninvasively