title: Neuronal depolarization controls brain-derived neurotrophic factor-induced upregulation of NR2C NMDA receptor via calcineurin signaling.
abstract: In the developing cerebellum, switching of subunit composition of NMDA receptors occurs in granule cells from NR2B subunit-containing receptors to NR2C subunit-containing receptors. This switching of subunit composition plays an important role in the establishment of functional mossy fiber-granule cell synaptic transmission in the mature cerebellar network. The mechanism underlying NR2C upregulation in developing granule cells, however, has to date remained to be determined. In granule cells cultured in low (5 mm) KCl, brain-derived neurotrophic factor (BDNF) upregulated NR2C mRNA via the TrkB-extracellular signal-regulated kinase (ERK) 1/2 cascade and promoted the formation of an NR2C-containing NMDA receptor complex. In granule cells cultured in high (25 mm) KCl, depolarization stimulated voltage-sensitive Ca2+ channels. The resultant increase in intracellular Ca2+ activated Ca2+/calmodulin-dependent calcineurin phosphatase and blocked NR2C mRNA upregulation. Interestingly, the depolarization-induced Ca2+ increase simultaneously upregulated BDNF mRNA via Ca2+/calmodulin-dependent protein kinase (CaMK). Consequently, when calcineurin was inhibited by its inhibitor FK506 under the depolarizing condition, the CaMK-mediated increase in BDNF became a stimulatory signal, and the endogenous BDNF autocrine system was capable of upregulating NR2C mRNA via the common TrkB-ERK cascade. The importance of the BDNF-TrkB pathway was further supported by a significant reduction in NR2C in normally migrated granule cells of TrkB(-/-) knock-out mice in vivo. The convergent mechanism of the BDNF and Ca2+ signaling cascades thus plays an important regulatory role in NR2C induction in granule cells during cerebellar development.
authors.affiliation: Department of Molecular and Systems Biology, Graduate School of Biostudies, Faculty of Medicine, Kyoto University, Kyoto 606-8501, Japan.
authors.forename: Kazunori
authors.initials: K
authors.lastname: Suzuki
authors.forename: Masaaki
authors.initials: M
authors.lastname: Sato
authors.forename: Yosuke
authors.initials: Y
authors.lastname: Morishima
authors.forename: Shigetada
authors.initials: S
authors.lastname: Nakanishi
mesh_terms: D000818:Animals; D019208:Brain-Derived Neurotrophic Factor / Q000502:physiology*; D019703:Calcineurin / Q000235:genetics / Q000502:physiology*; D002478:Cells, Cultured; D066298:In Vitro Techniques; D051379:Mice; D018345:Mice, Knockout; D009474:Neurons / Q000187:drug effects / Q000502:physiology*; D012333:RNA, Messenger / Q000096:biosynthesis / Q000235:genetics; D016194:Receptors, N-Methyl-D-Aspartate / Q000096:biosynthesis* / Q000235:genetics; D015398:Signal Transduction / Q000187:drug effects / Q000502:physiology*; D016559:Tacrolimus / Q000494:pharmacology; D015854:Up-Regulation / Q000187:drug effects / Q000502:physiology*
chemical_list: D019208:Brain-Derived Neurotrophic Factor; C432823:NR2C NMDA receptor; D012333:RNA, Messenger; D016194:Receptors, N-Methyl-D-Aspartate; D019703:Calcineurin; D016559:Tacrolimus