title: Does abnormal glycogen structure contribute to increased susceptibility to seizures in epilepsy?
abstract: Epilepsy is a family of brain disorders with a largely unknown etiology and high percentage of pharmacoresistance. The clinical manifestations of epilepsy are seizures, which originate from aberrant neuronal synchronization and hyperexcitability. Reactive astrocytosis, a hallmark of the epileptic tissue, develops into loss-of-function of glutamine synthetase, impairment of glutamate-glutamine cycle and increase in extracellular and astrocytic glutamate concentration. Here, we argue that chronically elevated intracellular glutamate level in astrocytes is instrumental to alterations in the metabolism of glycogen and leads to the synthesis of polyglucosans. Unaccessibility of glycogen-degrading enzymes to these insoluble molecules compromises the glycogenolysis-dependent reuptake of extracellular K(+) by astrocytes, thereby leading to increased extracellular K(+) and associated membrane depolarization. Based on current knowledge, we propose that the deterioration in structural homogeneity of glycogen particles is relevant to disruption of brain K(+) homeostasis and increased susceptibility to seizures in epilepsy.
authors.affiliation: MARBILab, Museo storico della fisica e Centro di studi e ricerche "Enrico Fermi", Rome, Italy, mauro.dinuzzo@roma1.infn.it.
authors.forename: Mauro
authors.initials: M
authors.lastname: DiNuzzo
authors.forename: Silvia
authors.initials: S
authors.lastname: Mangia
authors.forename: Bruno
authors.initials: B
authors.lastname: Maraviglia
authors.forename: Federico
authors.initials: F
authors.lastname: Giove
mesh_terms: D000818:Animals; D001253:Astrocytes / Q000187:drug effects / Q000378:metabolism; D003292:Convulsants / Q000494:pharmacology; D004198:Disease Susceptibility; D004827:Epilepsy / Q000378:metabolism*; D005911:Gliosis / Q000378:metabolism; D005936:Glucans / Q000378:metabolism; D005974:Glutamate-Ammonia Ligase / Q000037:antagonists & inhibitors / Q000172:deficiency; D005971:Glutamates / Q000378:metabolism; D005973:Glutamine / Q000378:metabolism; D006003:Glycogen / Q000737:chemistry* / Q000378:metabolism; D038362:Glycogen Synthase Kinase 3 / Q000378:metabolism; D006706:Homeostasis; D006801:Humans; D008564:Membrane Potentials; D008717:Methionine Sulfoximine / Q000494:pharmacology; D015394:Molecular Structure; D009474:Neurons / Q000378:metabolism; D011188:Potassium / Q000378:metabolism*; D012640:Seizures / Q000139:chemically induced / Q000209:etiology / Q000378:metabolism; D012890:Sleep / Q000502:physiology; D012892:Sleep Deprivation / Q000503:physiopathology; D013329:Structure-Activity Relationship
chemical_list: D003292:Convulsants; D005936:Glucans; D005971:Glutamates; D005973:Glutamine; D008717:Methionine Sulfoximine; D006003:Glycogen; C083094:polyglucosan; D038362:Glycogen Synthase Kinase 3; D005974:Glutamate-Ammonia Ligase; D011188:Potassium