Down-regulation of Homer1b/c attenuates glutamate-mediated excitotoxicity through endoplasmic reticulum and mitochondria pathways in rat cortical neurons

• Published in: Free radical biology & medicine 2012-01, Vol.52 (1), p.208-217
• Main Authors: Chen, Tao, Fei, Fei, Jiang, Xiao-fan, Zhang, Lei, Qu, Yan, Huo, Kai, Fei, Zhou
• Format: Article
• Language: English
• Subjects: Animals; Apoptosis; calcium; Calcium (intracellular); Carrier Proteins - genetics; Carrier Proteins - metabolism; Caspase 12 - genetics; Caspase 12 - metabolism; caspase-12; Cell survival; Cell Survival - drug effects; Central nervous system; central nervous system diseases; Cerebral Cortex - cytology; Cerebral Cortex - drug effects; Cerebral Cortex - metabolism; Cortex; cytochrome c; Down-Regulation; eIF-2 Kinase - genetics; eIF-2 Kinase - metabolism; Endoplasmic reticulum; Endoplasmic Reticulum - drug effects; Endoplasmic Reticulum - metabolism; Excitotoxicity; gene expression; Gene Expression - drug effects; gene expression regulation; glutamic acid; Glutamic Acid - adverse effects; Glutamic acid receptors; Glutamic acid receptors (metabotropic); Heat-Shock Proteins - genetics; Heat-Shock Proteins - metabolism; Homer; Homer protein; Homer Scaffolding Proteins; Initiation factor eIF-2; Injuries; Inositol 1,4,5-Trisphosphate Receptors - genetics; Inositol 1,4,5-Trisphosphate Receptors - metabolism; Intracellular signalling; membrane potential; Membrane Potential, Mitochondrial; Mitochondria; Mitochondria - drug effects; Mitochondria - metabolism; mitochondrial membrane; neurons; Neurons - cytology; Neurons - drug effects; Neurons - metabolism; neuroprotective effect; Neurotoxicity; Primary Cell Culture; Protein Isoforms - genetics; Protein Isoforms - metabolism; Protein-Serine-Threonine Kinases - genetics; Protein-Serine-Threonine Kinases - metabolism; Proto-Oncogene Proteins c-bcl-2 - genetics; Proto-Oncogene Proteins c-bcl-2 - metabolism; Rats; Reactive oxygen species; Reactive Oxygen Species - metabolism; scaffolding proteins; Signal transduction; Signal Transduction - drug effects; siRNA; small interfering RNA; Transcription Factor CHOP - genetics; Transcription Factor CHOP - metabolism; Transfection
• ISSN: 0891-5849; 1873-4596
• DOI: 10.1016/j.freeradbiomed.2011.10.451

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. [Display omitted] ► Glutamate-induced neurotoxicity involves Ca2+-dependent ROS production. ► Down-regulation of Homer 1b/c attenuates glutamate-induced neurotoxicity. ► Down-regulation of Homer1b/c inhibits glutamate-induced release of ER Ca2+. ► Down-regulation of Homer1b/c reduces glutamate-induced ER stress. ► Down-regulation of Homer1b/c improves mitochondria function.