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Soluble iron accumulation induces microglial glutamate release in the spinal cord of sporadic amyotrophic lateral sclerosis
Author(s) -
NiidaKawaguchi Motoko,
Kakita Akiyoshi,
Noguchi Noriko,
Kazama Miku,
Masui Kenta,
Kato Yoichiro,
Yamamoto Tomoko,
Sawada Tatsuo,
Kitagawa Kazuo,
Watabe Kazuhiko,
Shibata Noriyuki
Publication year - 2020
Publication title -
neuropathology
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.701
H-Index - 61
eISSN - 1440-1789
pISSN - 0919-6544
DOI - 10.1111/neup.12632
Subject(s) - glutamate receptor , blot , amyotrophic lateral sclerosis , glutaminase , microglia , ferritin , glutamine , spinal cord , tumor necrosis factor alpha , astrocyte , chemistry , western blot , intracellular , ferroportin , glutamate aspartate transporter , endocrinology , medicine , microbiology and biotechnology , hepcidin , biochemistry , biology , central nervous system , inflammation , metabotropic glutamate receptor , neuroscience , amino acid , receptor , disease , gene
Previous studies on sporadic amyotrophic lateral sclerosis (SALS) demonstrated iron accumulation in the spinal cord and increased glutamate concentration in the cerebrospinal fluid. To clarify the relationship between the two phenomena, we first performed quantitative and morphological analyses of substances related to iron and glutamate metabolism using spinal cords obtained at autopsy from 12 SALS patients and 12 age‐matched control subjects. Soluble iron content determined by the Ferrozine method as well as ferritin (Ft) and glutaminase C (GLS‐C) expression levels on Western blots were significantly higher in the SALS group than in the control group, while ferroportin (FPN) levels on Western blots were significantly reduced in the SALS group as compared to the control group. There was no significant difference in aconitase 1 (ACO1) and tumor necrosis factor‐alpha (TNFα)‐converting enzyme (TACE) levels on Western blots between the two groups. Immunohistochemically, Ft, ACO1, TACE, TNFα, and GLS‐C were proven to be selectively expressed in microglia. Immunoreactivities for FPN and hepcidin were localized in neuronal and glial cells. Based on these observations, it is predicted that soluble iron may stimulate microglial glutamate release. To address this issue, cell culture experiments were carried out on a microglial cell line (BV‐2). Treatment of BV‐2 cells with ferric ammonium citrate (FAC) brought about significant increases in intracellular soluble iron and Ft expression levels and conditioned medium glutamate and TNFα concentrations. Glutamate concentration was also significantly increased in conditioned media of TNFα‐treated BV‐2 cells. While the FAC‐driven increases in glutamate and TNFα release were completely canceled by pretreatment with ACO1 and TACE inhibitors, respectively, the TNFα‐driven increase in glutamate release was completely canceled by GLS‐C inhibitor pretreatment. Moreover, treatment of BV‐2 cells with hepcidin resulted in a significant reduction in FPN expression levels on Western blots of the intracellular total protein extracts. The present results provide in vivo and in vitro evidence that microglial glutamate release in SALS spinal cords is enhanced by intracellular soluble iron accumulation‐induced activation of ACO1 and TACE and by increased extracellular TNFα‐stimulated GLS‐C upregulation, and suggest a positive feedback mechanism to maintain increased intracellular soluble iron levels, involving TNFα, hepcidin, and FPN.