title: Ryanodine receptor-mediated Ca(2+) release underlies iron-induced mitochondrial fission and stimulates mitochondrial Ca(2+) uptake in primary hippocampal neurons.
abstract: Mounting evidence indicates that iron accumulation impairs brain function. We have reported previously that addition of sub-lethal concentrations of iron to primary hippocampal neurons produces Ca(2) (+) signals and promotes cytoplasmic generation of reactive oxygen species. These Ca(2) (+) signals, which emerge within seconds after iron addition, arise mostly from Ca(2) (+) release through the redox-sensitive ryanodine receptor (RyR) channels present in the endoplasmic reticulum. We have reported also that addition of synaptotoxic amyloid-β oligomers to primary hippocampal neurons stimulates RyR-mediated Ca(2) (+) release, generating long-lasting Ca(2) (+) signals that activate Ca(2) (+)-sensitive cellular effectors and promote the disruption of the mitochondrial network. Here, we describe that 24 h incubation of primary hippocampal neurons with iron enhanced agonist-induced RyR-mediated Ca(2) (+) release and promoted mitochondrial network fragmentation in 43% of neurons, a response significantly prevented by RyR inhibition and by the antioxidant agent N-acetyl-L-cysteine. Stimulation of RyR-mediated Ca(2) (+) release by a RyR agonist promoted mitochondrial Ca(2) (+) uptake in control neurons and in iron-treated neurons that displayed non-fragmented mitochondria, but not in neurons with fragmented mitochondria. Yet, the global cytoplasmic Ca(2) (+) increase induced by the Ca(2) (+) ionophore ionomycin prompted significant mitochondrial Ca(2) (+) uptake in neurons with fragmented mitochondria, indicating that fragmentation did not prevent mitochondrial Ca(2) (+) uptake but presumably decreased the functional coupling between RyR-mediated Ca(2) (+) release and the mitochondrial Ca(2) (+) uniporter. Taken together, our results indicate that stimulation of redox-sensitive RyR-mediated Ca(2) (+) release by iron causes significant neuronal mitochondrial fragmentation, which presumably contributes to the impairment of neuronal function produced by iron accumulation.
authors.affiliation: Center for Molecular Studies of the Cell, Institute of Biomedical Sciences, Faculty of Medicine, Universidad de Chile Santiago, Chile ; Biomedical Neuroscience Institute, Faculty of Medicine, Universidad de Chile Santiago, Chile.
authors.forename: Carol D
authors.initials: CD
authors.lastname: Sanmartín
authors.affiliation: Center for Molecular Studies of the Cell, Institute of Biomedical Sciences, Faculty of Medicine, Universidad de Chile Santiago, Chile ; Biomedical Neuroscience Institute, Faculty of Medicine, Universidad de Chile Santiago, Chile ; Institute for Research in Dental Sciences, Faculty of Dentistry, Universidad de Chile Santiago, Chile.
authors.forename: Andrea C
authors.initials: AC
authors.lastname: Paula-Lima
authors.affiliation: Biomedical Neuroscience Institute, Faculty of Medicine, Universidad de Chile Santiago, Chile.
authors.forename: Alejandra
authors.initials: A
authors.lastname: García
authors.affiliation: Biomedical Neuroscience Institute, Faculty of Medicine, Universidad de Chile Santiago, Chile.
authors.forename: Pablo
authors.initials: P
authors.lastname: Barattini
authors.affiliation: Biomedical Neuroscience Institute, Faculty of Medicine, Universidad de Chile Santiago, Chile ; Laboratory of Scientific Image Processing, Anatomy and Developmental Biology Program, Institute of Biomedical Sciences, Faculty of Medicine, Universidad de Chile Santiago, Chile.
authors.forename: Steffen
authors.initials: S
authors.lastname: Hartel
authors.affiliation: Department of Biology, Faculty of Sciences and Research Ring on Oxidative Stress in the Nervous System, Universidad de Chile Santiago, Chile.
authors.forename: Marco T
authors.initials: MT
authors.lastname: Núñez
authors.affiliation: Center for Molecular Studies of the Cell, Institute of Biomedical Sciences, Faculty of Medicine, Universidad de Chile Santiago, Chile ; Biomedical Neuroscience Institute, Faculty of Medicine, Universidad de Chile Santiago, Chile ; Physiology and Biophysics Program, Institute of Biomedical Sciences, Faculty of Medicine, Universidad de Chile Santiago, Chile.
authors.forename: Cecilia
authors.initials: C
authors.lastname: Hidalgo
keywords: Drp-1; cellular redox state; endoplasmic reticulum; mitochondrial calcium; mitochondrial network; reactive oxygen species