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      Alzheimer's disease: the amyloid hypothesis and the Inverse Warburg effect

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          Abstract

          Epidemiological and biochemical studies show that the sporadic forms of Alzheimer's disease (AD) are characterized by the following hallmarks: (a) An exponential increase with age; (b) Selective neuronal vulnerability; (c) Inverse cancer comorbidity. The present article appeals to these hallmarks to evaluate and contrast two competing models of AD: the amyloid hypothesis (a neuron-centric mechanism) and the Inverse Warburg hypothesis (a neuron-astrocytic mechanism). We show that these three hallmarks of AD conflict with the amyloid hypothesis, but are consistent with the Inverse Warburg hypothesis, a bioenergetic model which postulates that AD is the result of a cascade of three events—mitochondrial dysregulation, metabolic reprogramming (the Inverse Warburg effect), and natural selection. We also provide an explanation for the failures of the clinical trials based on amyloid immunization, and we propose a new class of therapeutic strategies consistent with the neuroenergetic selection model.

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          Most cited references58

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          Glutamate uptake into astrocytes stimulates aerobic glycolysis: a mechanism coupling neuronal activity to glucose utilization.

          Glutamate, released at a majority of excitatory synapses in the central nervous system, depolarizes neurons by acting at specific receptors. Its action is terminated by removal from the synaptic cleft mostly via Na(+)-dependent uptake systems located on both neurons and astrocytes. Here we report that glutamate, in addition to its receptor-mediated actions on neuronal excitability, stimulates glycolysis--i.e., glucose utilization and lactate production--in astrocytes. This metabolic action is mediated by activation of a Na(+)-dependent uptake system and not by interaction with receptors. The mechanism involves the Na+/K(+)-ATPase, which is activated by an increase in the intracellular concentration of Na+ cotransported with glutamate by the electrogenic uptake system. Thus, when glutamate is released from active synapses and taken up by astrocytes, the newly identified signaling pathway described here would provide a simple and direct mechanism to tightly couple neuronal activity to glucose utilization. In addition, glutamate-stimulated glycolysis is consistent with data obtained from functional brain imaging studies indicating local nonoxidative glucose utilization during physiological activation.
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            Ageing and neuronal vulnerability.

            Everyone ages, but only some will develop a neurodegenerative disorder in the process. Disease might occur when cells fail to respond adaptively to age-related increases in oxidative, metabolic and ionic stress, thereby resulting in the accumulation of damaged proteins, DNA and membranes. Determinants of neuronal vulnerability might include cell size and location, metabolism of disease-specific proteins and a repertoire of signal transduction pathways and stress resistance mechanisms. Emerging evidence on protein interaction networks that monitor and respond to the normal ageing process suggests that successful neural ageing is possible for most people, but also cautions that cures for neurodegenerative disorders are unlikely in the near future.
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              The bioenergetic and antioxidant status of neurons is controlled by continuous degradation of a key glycolytic enzyme by APC/C-Cdh1.

              Neurons are known to have a lower glycolytic rate than astrocytes and when stressed they are unable to upregulate glycolysis because of low Pfkfb3 (6-phosphofructo-2-kinase/fructose-2, 6-bisphosphatase-3) activity. This enzyme generates fructose-2,6-bisphosphate (F2,6P(2)), the most potent activator of 6-phosphofructo-1-kinase (Pfk1; ref. 4), a master regulator of glycolysis. Here, we show that Pfkfb3 is absent from neurons in the brain cortex and that Pfkfb3 in neurons is constantly subject to proteasomal degradation by the action of the E3 ubiquitin ligase, anaphase-promoting complex/cyclosome (APC/C)-Cdh1. By contrast, astrocytes have low APC/C-Cdh1 activity and therefore Pfkfb3 is present in these cells. Upregulation of Pfkfb3 by either inhibition of Cdh1 or overexpression of Pfkfb3 in neurons resulted in the activation of glycolysis. This, however, was accompanied by a marked decrease in the oxidation of glucose through the pentose phosphate pathway (a metabolic route involved in the regeneration of reduced glutathione) resulting in oxidative stress and apoptotic death. Thus, by actively downregulating glycolysis by APC/C-Cdh1, neurons use glucose to maintain their antioxidant status at the expense of its utilization for bioenergetic purposes.
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                Author and article information

                Contributors
                Journal
                Front Physiol
                Front Physiol
                Front. Physiol.
                Frontiers in Physiology
                Frontiers Media S.A.
                1664-042X
                18 September 2014
                14 January 2015
                2014
                : 5
                : 522
                Affiliations
                [1] 1Department of Organismic and Evolutionary Biology, Harvard University Cambridge, MA, USA
                [2] 2Max Planck Institute for Molecular Genetics Berlin, Germany
                [3] 3Division of Biological and Environmental Sciences and Engineering, King Abdullah University of Science and Technology Thuwal, Saudi Arabia
                [4] 4Laboratory of Neuroenergetics and Cellular Dynamics, Brain Mind Institute, Ecole Polytechnique Fédérale de Lausanne Lausanne, Switzerland
                [5] 5Laboratory of Neuroenergetics, Department of Physiology, University of Lausanne Lausanne, Switzerland
                Author notes

                Edited by: Rafael Tabarés-Seisdedos, University of Valencia, Spain

                Reviewed by: Anshu Bhardwaj, Council of Scientific and Industrial Research, India; Jane A. Driver, VA Boston Medical Center, USA

                *Correspondence: Luc Pellerin, Department of Physiology, University of Lausanne, 7 Rue du Bugnon, 1005 Lausanne, Switzerland e-mail: luc.pellerin@ 123456unil.ch

                This article was submitted to Systems Biology, a section of the journal Frontiers in Physiology.

                Article
                10.3389/fphys.2014.00522
                4294122
                25642192
                c1464ee8-d209-4157-8348-5bcd5efbccd4
                Copyright © 2015 Demetrius, Magistretti and Pellerin.

                This is an open-access article distributed under the terms of the Creative Commons Attribution License (CC BY). The use, distribution or reproduction in other forums is permitted, provided the original author(s) or licensor are credited and that the original publication in this journal is cited, in accordance with accepted academic practice. No use, distribution or reproduction is permitted which does not comply with these terms.

                History
                : 14 August 2014
                : 19 December 2014
                Page count
                Figures: 14, Tables: 3, Equations: 7, References: 74, Pages: 20, Words: 13525
                Categories
                Physiology
                Hypothesis and Theory Article

                Anatomy & Physiology
                age-related disease,mitochondrial dysregulation,metabolic alteration,the inverse warburg effect,inverse cancer comorbidity

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