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Velázquez-Flores MÁ, Sánchez-Chávez G, Morales-Lázaro SL, Ruiz Esparza-Garrido R, Canizales-Ontiveros A, Salceda R. Streptozotocin-Induced Diabetic Rats Showed a Differential Glycine Receptor Expression in the Spinal Cord: A GlyR Role in Diabetic Neuropathy. Neurochem Res 2024; 49:684-691. [PMID: 38017313 PMCID: PMC10884118 DOI: 10.1007/s11064-023-04058-9] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/13/2023] [Revised: 10/24/2023] [Accepted: 10/26/2023] [Indexed: 11/30/2023]
Abstract
In the spinal cord, attenuation of the inhibitory action of glycine is related to an increase in both inflammatory and diabetic neuropathic pain; however, the glycine receptor involvement in diabetic neuropathy has not been reported. We determined the expression of the glycine receptor subunits (α1-α3 and β) in streptozotocin-induced diabetic Long-Evans rats by qPCR and Western blot. The total mRNA and protein expression (whole spinal cord homogenate) of the α1, α3, and β subunits did not change during diabetes; however, the α2 subunit mRNA, but not the protein, was overexpressed 45 days after diabetes induction. By contrast, the synaptic expression of the α1 and α2 subunits decreased in all the studied stages of diabetes, but that of the α3 subunit increased on day 45 after diabetes induction. Intradermal capsaicin produced higher paw-licking behavior in the streptozotocin-induced diabetic rats than in the control animals. In addition, the nocifensive response was higher at 45 days than at 20 days. During diabetes, the expression of the glycine receptor was altered in the spinal cord, which strongly suggests its involvement in diabetic neuropathy.
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Affiliation(s)
- Miguel Ángel Velázquez-Flores
- Noncoding RNAs Laboratory, Unit of Medical Research on Human Genetics, Children's Hospital "Silvestre Frenk Freund", National Medical Center Century XXI, Mexican Institute of Social Security, Mexico City, Mexico
| | - Gustavo Sánchez-Chávez
- División de Neurociencias, Instituto de Fisiología Celular, Universidad Nacional Autónoma de México, Mexico City, Mexico
| | - Sara L Morales-Lázaro
- División de Neurociencias, Instituto de Fisiología Celular, Universidad Nacional Autónoma de México, Mexico City, Mexico
| | - Ruth Ruiz Esparza-Garrido
- Unit of Medical Research on Human Genetics, Children's Hospital "Silvestre Frenk Freund", National Medical Center Century XXI, Mexican Institute of Social Security, Mexico City, Mexico
| | - Alejandro Canizales-Ontiveros
- División de Neurociencias, Instituto de Fisiología Celular, Universidad Nacional Autónoma de México, Mexico City, Mexico
| | - Rocío Salceda
- División de Neurociencias, Instituto de Fisiología Celular, Universidad Nacional Autónoma de México, Mexico City, Mexico.
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2
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Rabbani N, Thornalley PJ. Hexokinase-linked glycolytic overload and unscheduled glycolysis in hyperglycemia-induced pathogenesis of insulin resistance, beta-cell glucotoxicity, and diabetic vascular complications. Front Endocrinol (Lausanne) 2024; 14:1268308. [PMID: 38292764 PMCID: PMC10824962 DOI: 10.3389/fendo.2023.1268308] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Figures] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 07/27/2023] [Accepted: 12/12/2023] [Indexed: 02/01/2024] Open
Abstract
Hyperglycemia is a risk factor for the development of insulin resistance, beta-cell glucotoxicity, and vascular complications of diabetes. We propose the hypothesis, hexokinase-linked glycolytic overload and unscheduled glycolysis, in explanation. Hexokinases (HKs) catalyze the first step of glucose metabolism. Increased flux of glucose metabolism through glycolysis gated by HKs, when occurring without concomitant increased activity of glycolytic enzymes-unscheduled glycolysis-produces increased levels of glycolytic intermediates with overspill into effector pathways of cell dysfunction and pathogenesis. HK1 is saturated with glucose in euglycemia and, where it is the major HK, provides for basal glycolytic flux without glycolytic overload. HK2 has similar saturation characteristics, except that, in persistent hyperglycemia, it is stabilized to proteolysis by high intracellular glucose concentration, increasing HK activity and initiating glycolytic overload and unscheduled glycolysis. This drives the development of vascular complications of diabetes. Similar HK2-linked unscheduled glycolysis in skeletal muscle and adipose tissue in impaired fasting glucose drives the development of peripheral insulin resistance. Glucokinase (GCK or HK4)-linked glycolytic overload and unscheduled glycolysis occurs in persistent hyperglycemia in hepatocytes and beta-cells, contributing to hepatic insulin resistance and beta-cell glucotoxicity, leading to the development of type 2 diabetes. Downstream effector pathways of HK-linked unscheduled glycolysis are mitochondrial dysfunction and increased reactive oxygen species (ROS) formation; activation of hexosamine, protein kinase c, and dicarbonyl stress pathways; and increased Mlx/Mondo A signaling. Mitochondrial dysfunction and increased ROS was proposed as the initiator of metabolic dysfunction in hyperglycemia, but it is rather one of the multiple downstream effector pathways. Correction of HK2 dysregulation is proposed as a novel therapeutic target. Pharmacotherapy addressing it corrected insulin resistance in overweight and obese subjects in clinical trial. Overall, the damaging effects of hyperglycemia are a consequence of HK-gated increased flux of glucose metabolism without increased glycolytic enzyme activities to accommodate it.
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Affiliation(s)
| | - Paul J. Thornalley
- College of Health and Life Sciences, Hamad Bin Khalifa University, Doha, Qatar
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3
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Nag TC, Sharma B, Gorla S. Glycogen in retinal horizontal cells of the African mud catfish Clarias gariepinus (Burchell, 1822) and its physiological significance. Tissue Cell 2023; 83:102140. [PMID: 37329686 DOI: 10.1016/j.tice.2023.102140] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/17/2023] [Revised: 06/09/2023] [Accepted: 06/10/2023] [Indexed: 06/19/2023]
Abstract
This paper reports on glycogen store in the retinal horizontal cells (HC) of the African mud catfish Clarias gariepinus, as seen by histochemical reaction with periodic acid Schiff (PAS) and transmission electron microscopy in light- as well as dark-adapted state. Glycogen is abundant in the large somata and less in their axons, characterised ultrastructurally by many microtubules and extensive gap junctions interconnecting them. There was no apparent difference in glycogen content in HC somata between light- and dark adaptation, but the axons clearly showed absence of glycogen in dark condition. The HC somata (presynaptic) make synapses with dendrites in the outer plexiform layer. Müller cell inner processes, which contain more densely packed glycogen, invest the HC. Other cells of the inner nuclear layer do not show any appreciable content of glycogen. Rods, but not cones, contain abundant glycogen in their inner segments and synaptic terminals. It is likely that glycogen is used as energy substrate in hypoxia for this species that dwell muddy aquatic environment with low oxygen content. They appear to have high energy demand, and a high glycogen content in HC could act as a ready source to fulfil physiological processes, like microtubule-based transport of cargo from the large somata to axons and the maintenance of electrical activities across the gap junctions between the axonal processes. It is also likely that they can supplement glucose to the neighbouring inner nuclear layer neurons, which are clearly devoid of glycogen.
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Affiliation(s)
- Tapas C Nag
- Department of Anatomy, All India Institute of Medical Sciences, New Delhi, India.
| | - Bhaskar Sharma
- Department of Anatomy, All India Institute of Medical Sciences, New Delhi, India
| | - Shilpa Gorla
- Department of Anatomy, All India Institute of Medical Sciences, New Delhi, India
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Albert-Garay JS, Riesgo-Escovar JR, Sánchez-Chávez G, Salceda R. Retinal Nrf2 expression in normal and early streptozotocin-diabetic rats. Neurochem Int 2021; 145:105007. [PMID: 33675841 DOI: 10.1016/j.neuint.2021.105007] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Key Words] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/24/2020] [Revised: 01/14/2021] [Accepted: 02/25/2021] [Indexed: 12/30/2022]
Abstract
Diabetic retinopathy is the most common cause of vision loss among diabetic patients. Although hyperglycemia produces retinal oxidative stress in long-standing diabetes, the pathogenesis mechanism is unknown. The Nuclear factor erythroid 2-related factor 2 (Nrf2) plays a central role in cell responses against oxidative damage. We used adult Long Evans rats where diabetes was induced by streptozotocin. Normal and treated rats were sacrificed at 7, 20, and 45 days after streptozotocin injection. We analyzed Nrf2 and Keap1 expression in retinal homogenates, cytoplasmic, and nuclear retinal fractions. Normal retina showed Nrf2 expression in all retina nuclear layers. We found a transitory decrease of Nrf2 mRNA and protein expression at 7 and 20 days after the streptozotocin injection that recovered later on: moreover, the protein level increased after 45 days. Keap1 immunoprecipitation revealed similar levels as Nrf2 in normal and diabetic rat retinas, indicating that the diabetic condition did not lead to dissociation of the Keap1-Nrf2 complex. Indeed, glutathione levels and superoxide dismutase activity were not altered in the treated rat retinas. These results do not support oxidative stress in the retina shortly after diabetes induction.
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Affiliation(s)
- Jesús Silvestre Albert-Garay
- Instituto de Fisiología Celular, Departamento de Neurodesarrollo y Fisiología, Universidad Nacional Autónoma de México, CDMX, Mexico.
| | - Juan Rafael Riesgo-Escovar
- Instituto de Neurobiología, Campus UNAM Juriquilla, Universidad Nacional Autónoma de México, Querétaro, Mexico
| | - Gustavo Sánchez-Chávez
- Instituto de Fisiología Celular, Departamento de Neurodesarrollo y Fisiología, Universidad Nacional Autónoma de México, CDMX, Mexico
| | - Rocío Salceda
- Instituto de Fisiología Celular, Departamento de Neurodesarrollo y Fisiología, Universidad Nacional Autónoma de México, CDMX, Mexico
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5
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Ramírez-Pérez G, Sánchez-Chávez G, Salceda R. Mitochondrial bound hexokinase type I in normal and streptozotocin diabetic rat retina. Mitochondrion 2020; 52:212-217. [DOI: 10.1016/j.mito.2020.04.004] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/15/2019] [Revised: 02/24/2020] [Accepted: 04/07/2020] [Indexed: 12/19/2022]
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Duran J, Gruart A, López-Ramos JC, Delgado-García JM, Guinovart JJ. Glycogen in Astrocytes and Neurons: Physiological and Pathological Aspects. ADVANCES IN NEUROBIOLOGY 2019; 23:311-329. [PMID: 31667813 DOI: 10.1007/978-3-030-27480-1_10] [Citation(s) in RCA: 21] [Impact Index Per Article: 4.2] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 01/01/2023]
Abstract
Brain glycogen is stored mainly in astrocytes, although neurons also have an active glycogen metabolism. Glycogen has gained relevance as a key player in brain function. In this regard, genetically modified animals have allowed researchers to unravel new roles of this polysaccharide in the brain. Remarkably, mice in which glycogen synthase is abolished in the brain, and thus devoid of brain glycogen, are viable, thereby indicating that the polysaccharide in this organ is not a requirement for survival. While there was growing evidence supporting a role of glycogen in learning and memory, these animals have now confirmed that glycogen participates in these two processes.The association of epilepsy with brain glycogen has also attracted attention. Analysis of genetically modified mice indicates that the relation between brain glycogen and epilepsy is complex. While the formation of glycogen aggregates clearly underlies epilepsy, as in Lafora Disease (LD), the absence of glycogen also favors the occurrence of seizures.LD is a rare genetic condition that affects children. It is characterized by epileptic seizures and neurodegeneration, and it develops rapidly until finally causing death. Research into this disease has unveiled new aspects of glycogen metabolism. Animal models of LD accumulate polyglucosan bodies formed by aberrant glycogen aggregates, called Lafora bodies (LBs). The abolition of glycogen synthase (GS) prevents the formation of LBs and the development of LD, thereby indicating that glycogen accumulation underlies this disease and the associated symptoms, and thus establishing a clear relation between the accumulation of glycogen aggregates and the incidence of seizures.Although it was initially accepted that LBs were essentially neuronal, it is now evident that astrocytes also accumulate polyglucosan aggregates in LD. However, the appearance and composition of these deposits differs from that observed in neurons. Of note, the astrocytic aggregates in LD models show remarkable similarities with corpora amylacea (CA), a type of polyglucosan aggregate observed in the brains of aged mice and humans. The abolition of GS in mice also impedes the formation of CA with age and at the same time prevents the formation of a number of protein aggregates associated with aging. Therefore CA may play a role in age-related neurological decline.
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Affiliation(s)
- Jordi Duran
- Institute for Research in Biomedicine (IRB Barcelona), Barcelona Institute of Science and Technology, Barcelona, Spain
- Centro de Investigación Biomédica en Red de Diabetes y Enfermedades Metabólicas Asociadas (CIBERDEM), Madrid, Spain
| | - Agnès Gruart
- Division of Neurosciences, Pablo de Olavide University, Seville, Spain
| | | | | | - Joan J Guinovart
- Institute for Research in Biomedicine (IRB Barcelona), Barcelona Institute of Science and Technology, Barcelona, Spain.
- Centro de Investigación Biomédica en Red de Diabetes y Enfermedades Metabólicas Asociadas (CIBERDEM), Madrid, Spain.
- Department of Biochemistry and Molecular Biomedicine, University of Barcelona, Barcelona, Spain.
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7
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Morales-Calixto E, Velázquez-Flores MÁ, Sánchez-Chávez G, Ruiz Esparza-Garrido R, Salceda R. Glycine receptor is differentially expressed in the rat retina at early stages of streptozotocin-induced diabetes. Neurosci Lett 2019; 712:134506. [DOI: 10.1016/j.neulet.2019.134506] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/12/2019] [Revised: 08/21/2019] [Accepted: 09/16/2019] [Indexed: 02/06/2023]
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8
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Pederson BA. Structure and Regulation of Glycogen Synthase in the Brain. ADVANCES IN NEUROBIOLOGY 2019; 23:83-123. [PMID: 31667806 DOI: 10.1007/978-3-030-27480-1_3] [Citation(s) in RCA: 7] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 01/20/2023]
Abstract
Brain glycogen synthesis is a regulated, multi-step process that begins with glucose transport across the blood brain barrier and culminates with the actions of glycogen synthase and the glycogen branching enzyme to elongate glucose chains and introduce branch points in a growing glycogen molecule. This review focuses on the synthesis of glycogen in the brain, with an emphasis on glycogen synthase, but draws on salient studies in mammalian muscle and liver as well as baker's yeast, with the goal of providing a more comprehensive view of glycogen synthesis and highlighting potential areas for further study in the brain. In addition, deficiencies in the glycogen biosynthetic enzymes which lead to glycogen storage diseases in humans are discussed, highlighting effects on the brain and discussing findings in genetically modified animal models that recapitulate these diseases. Finally, implications of glycogen synthesis in neurodegenerative and other diseases that impact the brain are presented.
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Öz G, DiNuzzo M, Kumar A, Moheet A, Khowaja A, Kubisiak K, Eberly LE, Seaquist ER. Cerebral glycogen in humans following acute and recurrent hypoglycemia: Implications on a role in hypoglycemia unawareness. J Cereb Blood Flow Metab 2017; 37:2883-2893. [PMID: 27834283 PMCID: PMC5536796 DOI: 10.1177/0271678x16678240] [Citation(s) in RCA: 25] [Impact Index Per Article: 3.6] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 01/08/2023]
Abstract
Supercompensated brain glycogen levels may contribute to the development of hypoglycemia-associated autonomic failure (HAAF) following recurrent hypoglycemia (RH) by providing energy for the brain during subsequent periods of hypoglycemia. To assess the role of glycogen supercompensation in the generation of HAAF, we estimated the level of brain glycogen following RH and acute hypoglycemia (AH). After undergoing 3 hyperinsulinemic, euglycemic and 3 hyperinsulinemic, hypoglycemic clamps (RH) on separate occasions at least 1 month apart, five healthy volunteers received [1-13C]glucose intravenously over 80+ h while maintaining euglycemia. 13C-glycogen levels in the occipital lobe were measured by 13C magnetic resonance spectroscopy at ∼8, 20, 32, 44, 56, 68 and 80 h at 4 T and glycogen levels estimated by fitting the data with a biophysical model that takes into account the tiered glycogen structure. Similarly, prior 13C-glycogen data obtained following a single hypoglycemic episode (AH) were fitted with the same model. Glycogen levels did not significantly increase after RH relative to after euglycemia, while they increased by ∼16% after AH relative to after euglycemia. These data suggest that glycogen supercompensation may be blunted with repeated hypoglycemic episodes. A causal relationship between glycogen supercompensation and generation of HAAF remains to be established.
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Affiliation(s)
- Gülin Öz
- 1 Department of Radiology, University of Minnesota, Minneapolis, USA
| | - Mauro DiNuzzo
- 2 Faculty of Health and Medical Sciences, University of Copenhagen, Copenhagen, Denmark
| | - Anjali Kumar
- 3 Department of Medicine, University of Minnesota, Minneapolis, USA
| | - Amir Moheet
- 3 Department of Medicine, University of Minnesota, Minneapolis, USA
| | - Ameer Khowaja
- 3 Department of Medicine, University of Minnesota, Minneapolis, USA
| | - Kristine Kubisiak
- 4 Division of Biostatistics, University of Minnesota, Minneapolis, USA
| | - Lynn E Eberly
- 4 Division of Biostatistics, University of Minnesota, Minneapolis, USA
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10
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Technical and experimental features of Magnetic Resonance Spectroscopy of brain glycogen metabolism. Anal Biochem 2017; 529:117-126. [DOI: 10.1016/j.ab.2016.12.023] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/20/2016] [Revised: 08/31/2016] [Accepted: 12/23/2016] [Indexed: 01/20/2023]
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11
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Sánchez-Chávez G, Hernández-Ramírez E, Osorio-Paz I, Hernández-Espinosa C, Salceda R. Potential Role of Endoplasmic Reticulum Stress in Pathogenesis of Diabetic Retinopathy. Neurochem Res 2015; 41:1098-106. [PMID: 26721508 DOI: 10.1007/s11064-015-1798-4] [Citation(s) in RCA: 12] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/09/2015] [Revised: 12/09/2015] [Accepted: 12/09/2015] [Indexed: 01/23/2023]
Abstract
Diabetes mellitus is a metabolic disease that leads to several complications which include retinopathy. Multiple biochemical abnormalities have been proposed to explain the development of retinopathy, including oxidative stress. Although the existence of oxidative stress has been established in the retina from long standing diabetic animals, pathogenesis and progression of retinopathy remain unclear. In order to gain insight into the pathogenesis of diabetic retinopathy, we analyzed the levels of different oxidative stress biomarkers in the retina at early stages during the progress of streptozotocin-induced diabetes. No significant changes in glutathione content, expression of NADPH-oxidase, levels of lipid peroxidation, nor production of free radicals were observed in the retina up to 45 days of diabetes induction. Likewise, a transient decrease in aconitase activity, parallel to an increase in the superoxide dismutase activity was observed at 20 days of hyperglycemia, suggesting a high capacity of retina to maintain its redox homeostasis, at least at early stages of diabetes. Nonetheless, we found an early and time-dependent increase in the levels of oxidized proteins, which was not affected by the administration of the antioxidant quercetin. Also, positive immunoreactivity to the reticulum stress protein CHOP was found in glial Müller cells of diabetic rat retinas. These findings suggest the occurrence of endoplasmic reticulum stress as a primary event in retina pathogenesis in diabetes.
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Affiliation(s)
- Gustavo Sánchez-Chávez
- División de Neurociencias, Departamento de Neurodesarrollo y Fisiología, Instituto de Fisiología Celular, Universidad Nacional Autónoma de México, Apdo. Postal 70-253, CP 04510, Mexico, D. F., Mexico
| | - Ernesto Hernández-Ramírez
- División de Neurociencias, Departamento de Neurodesarrollo y Fisiología, Instituto de Fisiología Celular, Universidad Nacional Autónoma de México, Apdo. Postal 70-253, CP 04510, Mexico, D. F., Mexico
| | - Ixchel Osorio-Paz
- División de Neurociencias, Departamento de Neurodesarrollo y Fisiología, Instituto de Fisiología Celular, Universidad Nacional Autónoma de México, Apdo. Postal 70-253, CP 04510, Mexico, D. F., Mexico
| | - Claudia Hernández-Espinosa
- División de Neurociencias, Departamento de Neurodesarrollo y Fisiología, Instituto de Fisiología Celular, Universidad Nacional Autónoma de México, Apdo. Postal 70-253, CP 04510, Mexico, D. F., Mexico
| | - Rocío Salceda
- División de Neurociencias, Departamento de Neurodesarrollo y Fisiología, Instituto de Fisiología Celular, Universidad Nacional Autónoma de México, Apdo. Postal 70-253, CP 04510, Mexico, D. F., Mexico.
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12
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Duarte JMN. Metabolic Alterations Associated to Brain Dysfunction in Diabetes. Aging Dis 2015; 6:304-21. [PMID: 26425386 DOI: 10.14336/ad.2014.1104] [Citation(s) in RCA: 61] [Impact Index Per Article: 6.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/15/2014] [Accepted: 11/04/2014] [Indexed: 12/13/2022] Open
Abstract
From epidemiological studies it is known that diabetes patients display increased risk of developing dementia. Moreover, cognitive impairment and Alzheimer's disease (AD) are also accompanied by impaired glucose homeostasis and insulin signalling. Although there is plenty of evidence for a connection between insulin-resistant diabetes and AD, definitive linking mechanisms remain elusive. Cerebrovascular complications of diabetes, alterations in glucose homeostasis and insulin signalling, as well as recurrent hypoglycaemia are the factors that most likely affect brain function and structure. While difficult to study in patients, the mechanisms by which diabetes leads to brain dysfunction have been investigated in experimental models that display phenotypes of the disease. The present article reviews the impact of diabetes and AD on brain structure and function, and discusses recent findings from translational studies in animal models that link insulin resistance to metabolic alterations that underlie brain dysfunction. Such modifications of brain metabolism are likely to occur at early stages of neurodegeneration and impact regional neurochemical profiles and constitute non-invasive biomarkers detectable by magnetic resonance spectroscopy (MRS).
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Affiliation(s)
- João M N Duarte
- Laboratory for Functional and Metabolic Imaging (LIFMET), École Polytechnique Fédérale de Lausanne (EPFL), Lausanne, Switzerland
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13
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Osorio-Paz I, Uribe-Carvajal S, Salceda R. In the Early Stages of Diabetes, Rat Retinal Mitochondria Undergo Mild Uncoupling due to UCP2 Activity. PLoS One 2015; 10:e0122727. [PMID: 25951172 PMCID: PMC4423783 DOI: 10.1371/journal.pone.0122727] [Citation(s) in RCA: 18] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/19/2014] [Accepted: 02/12/2015] [Indexed: 01/04/2023] Open
Abstract
In order to maintain high transmembrane ionic gradients, retinal tissues require a large amount of energy probably provided by a high rate of both, glycolysis and oxidative phosphorylation. However, little information exists on retinal mitochondrial efficiency. We analyzed the retinal mitochondrial activity in ex vivo retinas and in isolated mitochondria from normal rat retina and from short-term streptozotocin-diabetic rats. In normal ex vivo retinas, increasing glucose concentrations from 5.6mM to 30mM caused a four-fold increase in glucose accumulation and CO2 production. Retina from diabetic rats accumulated similar amounts of glucose. However, CO2 production was not as high. Isolated mitochondria from normal rat retina exhibited a resting rate of oxygen consumption of 14.6 ± 1.1 natgO (min.mg prot)-1 and a respiratory control of 4.0. Mitochondria from 7, 20 and 45 days diabetic rats increased the resting rate of oxygen consumption and the activity of the electron transport complexes; under these conditions the mitochondrial transmembrane potential decreased. In spite of this, the ATP synthesis was not modified. GDP, an UCP2 inhibitor, increased mitochondrial membrane potential and superoxide production in controls and at 45 days of diabetes. The role of UCP2 is discussed. The results suggest that at the early stage of diabetes we studied, retinal mitochondria undergo adaptations leading to maintain energetic requirements and prevent oxidative stress.
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Affiliation(s)
- Ixchel Osorio-Paz
- Departamento de Neurodesarrollo y Fisiología, Instituto de Fisiología Celular, Universidad Nacional Autónoma de México, México Distrito Federal, México
| | - Salvador Uribe-Carvajal
- Departamento de Genética Molecular, Instituto de Fisiología Celular, Universidad Nacional Autónoma de México, México Distrito Federal, México
| | - Rocío Salceda
- Departamento de Neurodesarrollo y Fisiología, Instituto de Fisiología Celular, Universidad Nacional Autónoma de México, México Distrito Federal, México
- * E-mail:
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Sickmann HM, Waagepetersen HS. Effects of diabetes on brain metabolism--is brain glycogen a significant player? Metab Brain Dis 2015; 30:335-43. [PMID: 24771109 DOI: 10.1007/s11011-014-9546-z] [Citation(s) in RCA: 20] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 03/13/2014] [Accepted: 04/10/2014] [Indexed: 10/25/2022]
Abstract
Brain glycogen, being an intracellular glucose reservoir, contributes to maintain energy and neurotransmitter homeostasis under physiological as well as pathological conditions. Under conditions with a disturbance in systemic glucose metabolism such as in diabetes, the supply of glucose to the brain may be affected and have important impacts on brain metabolism and neurotransmission. This also implies that brain glycogen may serve an essential role in the diabetic state to sustain appropriate brain function. There are two main types of diabetes; type 1 and type 2 diabetes and both types may be associated with brain impairments e.g. cognitive decline and dementia. It is however, not clear how these impairments on brain function are linked to alterations in brain energy and neurotransmitter metabolism. In this review, we will illuminate how rodent diabetes models have contributed to a better understanding of how brain energy and neurotransmitter metabolism is affected in diabetes. There will be a particular focus on the role of brain glycogen to support glycolytic and TCA cycle activity as well as glutamate-glutamine cycle in type 1 and type 2 diabetes.
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Affiliation(s)
- Helle M Sickmann
- Dept. of Drug Design and Pharmacology, Faculty of Health and Medical Sciences, University of Copenhagen, Jagtvej 160, 2100, Copenhagen, Denmark,
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15
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Hernández C, Garcia-Ramírez M, García-Rocha M, Saez-López C, Valverde ÁM, Guinovart JJ, Simó R. Glycogen storage in the human retinal pigment epithelium: a comparative study of diabetic and non-diabetic donors. Acta Diabetol 2014; 51:543-52. [PMID: 24458975 DOI: 10.1007/s00592-013-0549-8] [Citation(s) in RCA: 13] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 11/18/2013] [Accepted: 12/18/2013] [Indexed: 01/18/2023]
Abstract
Liver and muscle glycogen content is reduced in diabetic patients but there is no information on the effect of diabetes on the glycogen content in the retinal pigment epithelium (RPE). The main aim of the study was to compare the glycogen content in the RPE between diabetic and non-diabetic human donors. Glycogen synthase (GS) and glycogen phosphorylase (GP), the key enzymes of glycogen metabolism, as well as their isoforms, were also assessed. For this purpose, 44 human postmortem eye cups were included (22 from 11 type 2 diabetic and 22 from 11 non-diabetic donors matched by age). Human RPE cells cultured in normoglycemic and hyperglycemic conditions were also analyzed. Glycogen content as well as the mRNA, protein content and enzyme activity of GS and GP were determined. In addition, GS and GP isoforms were characterized. In the RPE from diabetic donors, as well as in RPE cells grown in hyperglycemic conditions, the glycogen content was increased. The increase in glycogen content was associated with an increase in GS without changes in GP levels. In RPE form human donors, the muscle GS isoform but not the liver GS isoform was detected. Regarding GP, the muscle and brain isoform of GP but not the liver GP isoform were detected. We conclude that glycogen storage is increased in the RPE of diabetic patients, and it is associated with an increase in GS activity. Further studies aimed at determining the role of glycogen deposits in the pathogenesis of diabetic retinopathy are warranted.
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Affiliation(s)
- Cristina Hernández
- Diabetes and Metabolism Research Unit, Vall d'Hebron Research Institute, Universitat Autònoma de Barcelona, Pg. Vall d'Hebron 119-129, 08035, Barcelona, Spain,
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Insulin stimulated-glucose transporter Glut 4 is expressed in the retina. PLoS One 2012; 7:e52959. [PMID: 23285235 PMCID: PMC3528717 DOI: 10.1371/journal.pone.0052959] [Citation(s) in RCA: 24] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/30/2012] [Accepted: 11/26/2012] [Indexed: 11/19/2022] Open
Abstract
The vertebrate retina is a very metabolically active tissue whose energy demands are normally met through the uptake of glucose and oxygen. Glucose metabolism in this tissue relies upon adequate glucose delivery from the systemic circulation. Therefore, glucose transport depends on the expression of glucose transporters. Here, we show retinal expression of the Glut 4 glucose transporter in frog and rat retinas. Immunohistochemistry and in situ hybridization studies showed Glut 4 expression in the three nuclear layers of the retina: the photoreceptor, inner nuclear and ganglionar cell layers. In the rat retina immunoprecipitation and Western blot analysis revealed a protein with an apparent molecular mass of 45 kDa. ¹⁴C-glucose accumulation by isolated rat retinas was significantly enhanced by physiological concentrations of insulin, an effect blocked by inhibitors of phosphatidyl-inositol 3-kinase (PI3K), a key enzyme in the insulin-signaling pathway in other tissues. Also, we observed an increase in ³H-cytochalasin binding sites in the presence of insulin, suggesting an increase in transporter recruitment at the cell surface. Besides, insulin induced phosphorylation of Akt, an effect also blocked by PI3K inhibition. Expression of Glut 4 was not modified in retinas of a type 1 diabetic rat model. To our knowledge, our results provide the first evidence of Glut4 expression in the retina, suggesting it as an insulin- responsive tissue.
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Control of glycogen content in retina: allosteric regulation of glycogen synthase. PLoS One 2012; 7:e30822. [PMID: 22363495 PMCID: PMC3281881 DOI: 10.1371/journal.pone.0030822] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/29/2011] [Accepted: 12/26/2011] [Indexed: 02/03/2023] Open
Abstract
Retinal tissue is exceptional because it shows a high level of energy metabolism. Glycogen content represents the only energy reserve in retina, but its levels are limited. Therefore, elucidation of the mechanisms controlling glycogen content in retina will allow us to understand retina response under local energy demands that can occur under normal and pathological conditions. Thus, we studied retina glycogen levels under different experimental conditions and correlated them with glucose-6-phosphate (G-6-P) content and glycogen synthase (GS) activity. Glycogen and G-6-P content were studied in ex vivo retinas from normal, fasted, streptozotocin-treated, and insulin-induced hypoglycemic rats. Expression levels of GS and its phosphorylated form were also analyzed. Ex vivo retina from normal rats showed low G-6-P (14±2 pmol/mg protein) and glycogen levels (43±3 nmol glycosyl residues/mg protein), which were increased 6 and 3 times, respectively, in streptozotocin diabetic rats. While no changes in phosphorylated GS levels were observed in any condition tested, a positive correlation was found between G-6-P levels with GS activity and glycogen content. The results indicated that in vivo, retina glycogen may act as an immediately accessible energy reserve and that its content was controlled primarily by G-6-P allosteric activation of GS. Therefore, under hypoglycemic situations retina energy supply is strongly compromised and could lead to the alterations observed in type 1 diabetes.
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Santiago AR, Garrido MJ, Cristóvão AJ, Duarte JMN, Carvalho RA, Ambrósio AF. Evaluation of the Impact of Diabetes on Retinal Metabolites by NMR Spectroscopy. Curr Eye Res 2010; 35:992-1001. [DOI: 10.3109/02713683.2010.500113] [Citation(s) in RCA: 11] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/25/2022]
Affiliation(s)
- A. R. Santiago
- Center for Neuroscience and Cell Biology, Department of Zoology, University of Coimbra, Coimbra, Portugal
- Center of Ophthalmology and Visual Sciences, IBILI, Faculty of Medicine, University of Coimbra, Coimbra, Portugal
| | - M. J. Garrido
- Center for Neuroscience and Cell Biology, Department of Zoology, University of Coimbra, Coimbra, Portugal
| | - A. J. Cristóvão
- Center for Neuroscience and Cell Biology, Department of Zoology, University of Coimbra, Coimbra, Portugal
- Department of Zoology, University of Coimbra, Coimbra, Portugal
| | - J. M. N. Duarte
- Center for Neuroscience and Cell Biology, Institute of Biochemistry, Faculty of Medicine, University of Coimbra, Coimbra, Portugal
| | - R. A. Carvalho
- Center for Neuroscience and Cell Biology, Department of Zoology, University of Coimbra, Coimbra, Portugal
- Department of Life Sciences, Faculty of Sciences and Technology, University of Coimbra, Coimbra, Portugal
| | - A. F. Ambrósio
- Center for Neuroscience and Cell Biology, Department of Zoology, University of Coimbra, Coimbra, Portugal
- Center of Ophthalmology and Visual Sciences, IBILI, Faculty of Medicine, University of Coimbra, Coimbra, Portugal
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Obesity and type 2 diabetes in rats are associated with altered brain glycogen and amino-acid homeostasis. J Cereb Blood Flow Metab 2010; 30:1527-37. [PMID: 20424632 PMCID: PMC2949239 DOI: 10.1038/jcbfm.2010.61] [Citation(s) in RCA: 71] [Impact Index Per Article: 5.1] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 11/08/2022]
Abstract
Obesity and type 2 diabetes have reached epidemic proportions; however, scarce information about how these metabolic syndromes influence brain energy and neurotransmitter homeostasis exist. The objective of this study was to elucidate how brain glycogen and neurotransmitter homeostasis are affected by these conditions. [1-(13)C]glucose was administered to Zucker obese (ZO) and Zucker diabetic fatty (ZDF) rats. Sprague-Dawley (SprD), Zucker lean (ZL), and ZDF lean rats were used as controls. Several brain regions were analyzed for glycogen levels along with (13)C-labeling and content of glutamate, glutamine, GABA, aspartate, and alanine. Blood glucose concentrations and (13)C enrichment were determined. (13)C-labeling in glutamate was lower in ZO and ZDF rats in comparison with the controls. The molecular carbon labeling (MCL) ratio between alanine and glutamate was higher in the ZDF rats. The MCL ratios of glutamine and glutamate were decreased in the cerebellum of the ZO and the ZDF rats. Glycogen levels were also lower in this region. These results suggest that the obese and type 2 diabetic models were associated with lower brain glucose metabolism. Glucose metabolism through the TCA cycle was more decreased than glycolytic activity. Furthermore, reduced glutamate-glutamine cycling was also observed in the obese and type 2 diabetic states.
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