title: NR2A induction and NMDA receptor-dependent neuronal death by neurotrophin-4/5 in cortical cell culture.
abstract: We have previously shown that prolonged exposure to neurotrophins induces oxidative neuronal death. In the present study, we further examined the cascades involved in neurotrophin-4/5 (NT-4/5)-induced neuronal death. Exposure of mature cortical cultures for 48 h to NT-4/5 induced neuronal death through TrkB activation. The NT-4/5-induced neuronal death was largely attenuated by addition of MK-801, indicating a critical role for NMDA receptors. Western blots revealed the induction of NR2A by NT-4/5. In addition, levels of phospho-NR2A and 2B increased, suggesting the upregulation of the NMDA receptor function. Whereas glutamate levels in the media changed little, levels of D-serine and L-glycine, co-agonists at NMDA receptors, increased significantly following NT-4/5 treatment. Exposure to NT-4/5 resulted in the activation of Src and extracellular signal-regulated kinase-1/2 (Erk-1/2). Their inhibitors blocked NR2A induction and phosphorylation as well as neuronal death induced by NT-4/5. In addition, Egr-1 was induced in an Src- and Erk-1/2-dependent manner. Anti-sense oligodeoxynucleotides to egr-1 attenuated NR2A induction as well as neuronal death. Although induction of NADPH oxidase and neuronal nitric oxide synthase (nNOS) contributes to NT-4/5-induced neuronal death, inhibition of their activity did not reduce NR2A induction. Conversely, blockade of NMDA receptors did not attenuate induction of NADPH oxidase or nNOS. These results indicate that two events are largely independent of each other. Our results demonstrate that the signaling cascade of TrkB leads to increase in NMDA receptor activity. Whereas this cascade may play an important role in the modulation of NMDA receptors in physiologic conditions, in the context of TrkB overactivation, it may contribute to neuronal death.
authors.affiliation: National Creative Research Initiative Center for the Study of CNS Zinc, University of Ulsan College of Medicine, Songpa-Gu, Seoul, Korea.
authors.forename: So-Young
authors.initials: SY
authors.lastname: Choi
authors.forename: Jung Jin
authors.initials: JJ
authors.lastname: Hwang
authors.forename: Jae-Young
authors.initials: JY
authors.lastname: Koh
mesh_terms: D000818:Animals; D016923:Cell Death / Q000187:drug effects / Q000502:physiology; D002478:Cells, Cultured; D002540:Cerebral Cortex / Q000166:cytology* / Q000187:drug effects / Q000378:metabolism; D051379:Mice; D009414:Nerve Growth Factors / Q000494:pharmacology*; D009474:Neurons / Q000166:cytology* / Q000187:drug effects / Q000378:metabolism; D020794:Receptor Protein-Tyrosine Kinases / Q000037:antagonists & inhibitors; D016194:Receptors, N-Methyl-D-Aspartate / Q000096:biosynthesis* / Q000235:genetics / Q000502:physiology*
chemical_list: C120997:NR2A NMDA receptor; D009414:Nerve Growth Factors; D016194:Receptors, N-Methyl-D-Aspartate; C071951:neurotrophin 5; D020794:Receptor Protein-Tyrosine Kinases; C073922:neurotrophin 4