title: Iron depletion increases manganese uptake and potentiates apoptosis through ER stress.
abstract: Iron deficiency is a risk factor for manganese (Mn) accumulation. Excess Mn promotes neurotoxicity but the mechanisms involved and whether iron depletion might affect these pathways is unknown. To study Mn intoxication in vivo, iron deficient and control rats were intranasally instilled with 60mg MnCl2/kg over 3 weeks. TUNEL staining of olfactory tissue revealed that Mn exposure induced apoptosis and that iron deficiency potentiated this effect. In vitro studies using the dopaminergic SH-SY5Y cell line confirmed that Mn-induced apoptosis was enhanced by iron depletion using the iron chelator desferrioxamine. Mn has been reported to induce apoptosis through endoplasmic reticulum stress. In SH-SY5Y cells, Mn exposure induced the ER stress genes glucose regulated protein 94 (GRP94) and C/EBP homologous protein (CHOP). Increased phosphorylation of the eukaryotic translation initiation factor 2α (phospho-eIF2α) was also observed. These effects were accompanied by the activation of ER resident enzyme caspase-12, and the downstream apoptotic effector caspase-3 was also activated. All of the Mn-induced responses were enhanced by DFO treatment. Inhibitors of ER stress and caspases significantly blocked Mn-induced apoptosis and its potentiation by DFO, indicating that ER stress and subsequent caspase activation underlie cell death. Taken together, these data reveal that Mn induces neuronal cell death through ER stress and the UPR response pathway and that this apoptotic effect is potentiated by iron deficiency most likely through upregulation of DMT1.
authors.affiliation: Department of Genetics & Complex Diseases, Harvard School of Public Health, Boston, MA 02115, United States; Department of Nutrition, Harvard School of Public Health, Boston, MA 02115, United States.
authors.forename: Young Ah
authors.initials: YA
authors.lastname: Seo
authors.forename: Yuan
authors.initials: Y
authors.lastname: Li
authors.forename: Marianne
authors.initials: M
authors.lastname: Wessling-Resnick
mesh_terms: D000818:Animals; D017209:Apoptosis / Q000187:drug effects*; D053454:Caspase 12 / Q000378:metabolism; D053148:Caspase 3 / Q000378:metabolism; D002460:Cell Line; D002470:Cell Survival / Q000187:drug effects; D003676:Deferoxamine / Q000494:pharmacology; D059865:Endoplasmic Reticulum Stress / Q000187:drug effects*; D015852:Eukaryotic Initiation Factor-2 / Q000378:metabolism; D018840:HSP70 Heat-Shock Proteins / Q000378:metabolism; D006801:Humans; D007501:Iron / Q000378:metabolism; D000090463:Iron Deficiencies; D008345:Manganese / Q000378:metabolism* / Q000633:toxicity*; D008565:Membrane Proteins / Q000378:metabolism; D051381:Rats; D051742:Transcription Factor CHOP / Q000378:metabolism
chemical_list: C497251:Ddit3 protein, rat; D015852:Eukaryotic Initiation Factor-2; D018840:HSP70 Heat-Shock Proteins; D008565:Membrane Proteins; C018551:glucose-regulated proteins; D051742:Transcription Factor CHOP; D008345:Manganese; D007501:Iron; D053454:Caspase 12; D053148:Caspase 3; D003676:Deferoxamine
keywords: DMT1; Endoplasmic reticulum; Iron deficiency; SH-SY5Y cells