title: Down-regulation of Homer1b/c attenuates glutamate-mediated excitotoxicity through endoplasmic reticulum and mitochondria pathways in rat cortical neurons.
abstract: Glutamate-mediated excitotoxicity is involved in many acute and chronic brain diseases. Homer proteins, a new member of the postsynaptic scaffolding proteins, regulate glutamatergic signaling and intracellular calcium mobilization in the central nervous system. Here we investigated the effects of down-regulating Homer1b/c, a constitutively expressed long form of Homer proteins, on glutamate excitotoxicity-induced neuronal injury. In our in vitro excitotoxic models, we demonstrated that glutamate insults led to a dose-dependent neuronal injury, which was mediated by the intracellular calcium-dependent reactive oxygen species (ROS) production. We found that down-regulation of Homer1b/c with specific small interfering RNA (siRNA) improved neuronal survival, inhibited intracellular ROS production, and reduced apoptotic cell death after neurotoxicity. Homer1b/c knockdown decreased the intracellular calcium overload through inhibition of the group I metabotropic glutamate receptor (mGluR)/inositol 1,4,5-trisphosphate receptor (IP3R)-mediated Ca2+ release from the endoplasmic reticulum (ER) in injured neurons. In addition, Homer1b/c siRNA transfection attenuated the activation of eukaryotic initiation factor 2α (eIF2α), RNA-dependent protein kinase-like ER kinase (PERK) and caspase-12, and inhibited the up-regulation of glucose-regulated protein 78 (GRP78) and C/EBP homologous protein (CHOP) after glutamate treatment. Homer1b/c knockdown also preserved the mitochondrial membrane potential (MMP), reduced cytochrome c (Cyt. c) release, and partly blocked the increase of capase-9 activity and Bax/Bcl-2 ratio. Taken together, these results suggest that down-regulation of Homer1b/c protects cortical neurons against glutamate-induced excitatory damage, and this neuroprotection may be dependent at least in part on the inhibition of calcium-dependent ROS production and the preservation of the ER and mitochondrial function.
authors.affiliation: Department of Neurosurgery, Xijing Institute of Clinical Neuroscience, Xijing Hospital, Fourth Military Medical University, Xi'an, Shaanxi, China.
authors.forename: Tao
authors.initials: T
authors.lastname: Chen
authors.forename: Fei
authors.initials: F
authors.lastname: Fei
authors.forename: Xiao-fan
authors.initials: XF
authors.lastname: Jiang
authors.forename: Lei
authors.initials: L
authors.lastname: Zhang
authors.forename: Yan
authors.initials: Y
authors.lastname: Qu
authors.forename: Kai
authors.initials: K
authors.lastname: Huo
authors.forename: Zhou
authors.initials: Z
authors.lastname: Fei
mesh_terms: D000818:Animals; D002352:Carrier Proteins / Q000235:genetics / Q000378:metabolism*; D053454:Caspase 12 / Q000235:genetics / Q000378:metabolism; D002470:Cell Survival / Q000187:drug effects; D002540:Cerebral Cortex / Q000166:cytology / Q000187:drug effects* / Q000378:metabolism; D015536:Down-Regulation; D004721:Endoplasmic Reticulum / Q000187:drug effects* / Q000378:metabolism; D015870:Gene Expression / Q000187:drug effects; D018698:Glutamic Acid / Q000009:adverse effects*; D006360:Heat-Shock Proteins / Q000235:genetics / Q000378:metabolism; D000072233:Homer Scaffolding Proteins; D053496:Inositol 1,4,5-Trisphosphate Receptors / Q000235:genetics / Q000378:metabolism; D053078:Membrane Potential, Mitochondrial; D008928:Mitochondria / Q000187:drug effects* / Q000378:metabolism; D009474:Neurons / Q000166:cytology / Q000187:drug effects* / Q000378:metabolism; D061251:Primary Cell Culture; D020033:Protein Isoforms / Q000235:genetics / Q000378:metabolism*; D017346:Protein Serine-Threonine Kinases / Q000235:genetics / Q000378:metabolism; D019253:Proto-Oncogene Proteins c-bcl-2 / Q000235:genetics / Q000378:metabolism; D051381:Rats; D017382:Reactive Oxygen Species / Q000378:metabolism; D015398:Signal Transduction / Q000187:drug effects; D051742:Transcription Factor CHOP / Q000235:genetics / Q000378:metabolism; D019892:eIF-2 Kinase / Q000235:genetics / Q000378:metabolism; D000091342:Endoplasmic Reticulum Chaperone BiP
chemical_list: D002352:Carrier Proteins; D053454:Caspase 12; D018698:Glutamic Acid; D006360:Heat-Shock Proteins; D000072233:Homer Scaffolding Proteins; D053496:Inositol 1,4,5-Trisphosphate Receptors; D020033:Protein Isoforms; D017346:Protein Serine-Threonine Kinases; D019253:Proto-Oncogene Proteins c-bcl-2; D017382:Reactive Oxygen Species; D051742:Transcription Factor CHOP; D019892:eIF-2 Kinase; C497251:Ddit3 protein, rat; C051684:GRP78 protein, rat; D000091342:Endoplasmic Reticulum Chaperone BiP