Crosstalk Between Brain-Derived Neurotrophic Factor And N-Methyl-D-Aspartate Receptor Signaling In Neurons

Glutamate is the major excitatory neurotransmitter in brain exerting prosurvival effect on neurons via N-methyl-D-aspartate receptor (NMDAR) signaling under physiological conditions. However in pathological circumstances such as ischemia, NMDARs might have proapoptotic excitotoxic activity. In contrast brain-derived neurotrophic factor (BDNF) signaling via TrkB receptors has been largely considered to promote neuronal differentiation, plasticity and survival during normal development, and protect neurons in pathophysiological conditions antagonizing the NMDAR-mediated excitotoxic cell death. In this review we summarize recent evidence for the existent crosstalk and positive feedback loops between the BDNF and NMDAR signaling and point out some of the important specific features of each signaling pathway

Crosstalk between brain-derived neurotrophic factor and N-methyl-D-aspartate receptor signaling in neurons

Glutamate is the major excitatory neurotransmitter in brain exerting prosurvival effect on neurons via N-methyl-D-aspartate receptor (NMDAR) signaling under physiological conditions. However in pathological circumstances such as ischemia, NMDARs might have proapoptotic excitotoxic activity. In contrast brain-derived neurotrophic factor (BDNF) signaling via tropomyosinrelated receptor kinase B (TrkB) has been largely considered to promote neuronal differentiation, plasticity and survival during normal development, and protect neurons in pathophysiological conditions antagonizing the NMDAR-mediated excitotoxic cell death. In this review we summarize recent evidence for the existent crosstalk and positive feedback loops between the BDNF and NMDAR signaling and point out some of the important specific features of each signaling pathway.Biomedical Reviews 2008; 19: 17-27

Modulation by static magnetism of neuronal activity

In neurons, the signal propagation involves both the conduction mediated by local electric currents through voltage-sensitive cation channels in axons and the transmission mediated by the exocytotic release of neurotransmitters from nerve endings into synaptic clefts. A great number of desperate efforts have been dedicated to biochemical, pharmacological and molecular biological studies on the elucidation of mechanisms underlying the neurotransmission at synapses, while relatively little attention has been paid to the comprehensive evaluation of the conduction except for local anesthetics. According to a physical theorem, exposure to magnetism should lead to the generation of a certain mechanical force in neurons with concomitant electric currents in a particular situation. In particular, repetitive transcranial magnetic stimulation is beneficial for the treatment of selected patients suffering from depression, bipolar affective disorder and schizophrenia as a possible alternative to the electroconvulsive therapy for refractory depression. In this review, therefore, we will summarize our recent advances made on the neurochemical and molecular biological elucidation in cultured rat hippocampal neurons toward better understanding by the readers of different disciplines of mechanisms associated with the modulation by magnetism of the neuronal activity in the brain.Biomedical Reviews 2004; 15: 21-35

Possible expression of functional glutamate transporters in the rat testis

Neither expression nor functionality is clear in peripheral tissues with the molecular machineries required for excitatory neurotransmitter signaling by L-glutamate (Glu) in the central nervous system, while a recent study has shown that several Glu receptors are functionally expressed in the rat testis. This fact prompted us to explore the possible functional expression in the rat testis of the Glu transporters usually responsible for the regulation of extracellular Glu concentrations in the brain. RT-PCR revealed the expression, in the rat testis, of mRNA for five different subtypes of Glu transporters, in addition to that for particular subtypes of ionotropic and metabotropic Glu receptors. Glutamate transporter-1 (GLT-1) was different in the brain from that in the testis in terms of molecular sizes on Northern and Western blot analyses. In situ hybridization as well as immunohistochemical analysis showed localized expression of glutamate aspartate transporter at interstitial spaces and GLT-1 at elongated spermatids in the rat testis respectively. The expression of mRNA was localized for excitatory amino acid transporter-5 at the basal compartment of the seminiferous tubule in the rat testis. [3H]Glu was accumulated in testicular crude mitochondrial fractions in a temperature-and sodium-dependent saturable manner with pharmacological profiles similar to those shown in brain crude mitochondrial fractions. These results suggested that particular subtypes of central Glu transporters for the regulation of extracellular Glu concentrations in the rat testis could be constitutively and functionally expressed. © 2004 Society for Endocrinology

Synthesis of a Novel Pyrazine-Pyridone Biheteroaryl-Based Fluorescence Sensor and Detection of Endogenous Labile Zinc Ions in Lung Cancer Cells

A small extent of endogenous labile zinc is involved in many vital physiological roles in living systems. However, its detailed functions have not been fully elucidated. In this study, we developed a novel biheteroaryl-based low molecular weight fluorescent sensor, 3-(phenylsulfonyl)-pyrazine-pyridone (5b), and applied it for the detection of endogenous labile zinc ions from lung cancer cells during apoptosis. The electron-withdrawing property of the sulfonyl group between the phenyl ring as an electron donor and the pyridone ring as a fluorophore inhibited the intramolecular charge transfer state, and the background fluorescence of the sensor was decreased in aqueous media. From the structure-fluorescence relationship analysis of the substituent effects with/without Zn 2+ , compound 5b acting as a sensor possessed favorable properties, including a longer emission wavelength, a large Stokes shift (over 100 nm),a large fluorescence enhancement in response to Zn 2+ under physical conditions, and good cell membrane permeability in living cells. Fluorescence imaging studies of human lung adenocarcinoma cells (A549) undergoing apoptosis revealed that compound 5b could detect endogenous labile zinc ions. These experiments suggested that the low molecular weight compound 5b is a potential fluorescence sensor for Zn 2+ toward understanding its functions in living systems

Activator protein-1 responsive to the group II metabotropic glutamate receptor subtype in association with intracellular calcium in cultured rat cortical neurons

金沢大学大学院自然科学研究科分子作用学Activation of ionotropic glutamate (Glu) receptors, such as N-methyl-d-aspartate receptors, is shown to modulate the gene transcription mediated by the transcription factor activator protein-1 (AP1) composed of Fos and Jun family proteins in the brain, while little attention has been paid to the modulation of AP1 expression by metabotropic Glu receptors (mGluRs). In cultured rat cortical neurons, where constitutive expression was seen with all groups I, II and III mGluR subtypes, a significant and selective increase was seen in the DNA binding activity of AP1 120 min after the brief exposure to the group II mGluR agonist (2S,2′R,3′R)-2-(2′,3′-dicarboxycyclopropyl)glycine (DCG-IV) for 5 min. In cultured rat cortical astrocytes, by contrast, a significant increase was induced by a group I mGluR agonist, but not by either a group II or III mGluR agonist. The increase by DCG-IV was significantly prevented by a group II mGluR antagonist as well as by either an intracellular Ca2+ chelator or a voltage-sensitive Ca2+ channel blocker, but not by an intracellular Ca2+ store inhibitor. Moreover, DCG-IV significantly prevented the increase of cAMP formation by forskolin in cultured neurons. Western blot analysis revealed differential expression profiles of Fos family members in neurons briefly exposed to DCG-IV and NMDA. Prior or simultaneous exposure to DCG-IV led to significant protection against neuronal cell death by NMDA. These results suggest that activation of the group II mGluR subtype would modulate the gene expression mediated by AP1 through increased intracellular Ca2+ levels in cultured rat cortical neurons. © 2007

神経細胞死の制御機構

金沢大学自然科学研究科Necdin遺伝子は15番染色体のPrader-Willi症候群欠損領域に存在し、主要な原因遺伝子と考えられている。Prader-Willi症候群は、視床下部ニューロンの異常が原因と考えられているが、Necdin遺伝子欠損マウスでは、視床下部においてホルモン産生ニューロンの減少が報告されている。Necdin結合蛋白質についていくつか報告してきたが、その中でもNecdinは転写因子E2F1やp53と結合し、その転写活性を抑制し、E2F1やp53によって誘導される細胞死を保護する。Necdinは、MAGEファミリーに属するが、その中でMAGE-D1は、p75NTR(p75 neurotrophin receptor)と結合して神経細胞死を誘導することが報告されている。MAGEファミリーには、MAGE homology domainが共通して存在し、このdomainを介していくつかの結合蛋白質が共通して結合する。Necdinもまた、p75NTRと結合するがその作用の違いについて検討を行った。p75NTRは、NGF(nerve growth factor)受容体であるTrkAとheterodimerを形成するが、MAGE-D1の発現によってこの両者の結合が解離するのに対して、Necdinの発現によっては両者の結合の増強が認められた。次に、NecdinあるいはMAGE-D1同士のhomoの結合が報告されていることから、NecdinとMAGE-D1のheteroの結合について検討を行った。さまざまなMAGE-D1欠損変異体を大腸菌で発現させ、Necdinとのpull-down assayを行ってところ、MAGE homology domainを介して、NecdinとMAGE-D1が結合することが認められた。MAGE-D1は、interspersed hexapeptide repeat domainを介して、homeobox型転写因子であるMsxと結合するが、Necdinは、MAGE-D1との結合を介してMsxとも相互作用することが明らかとなった。このようなNecdinとMAGE-D1の相互作用の結果、NGFの受容体への親和性を変化させ神経細胞死あるいは生存を制御していると考えられた。Necdin is a 325-amino acid protein encoded in a cDNA clone isolated from a subtraction library of neurally differentiated mouse embryonal carcinoma cells. The mouse necdin gene is expressed predominantly in postmitotic cells such as neuron and skeletal muscle. The human necdin gene is mapped to chromosome 15q11-q12, a region deleted in Prader-Willi syndrome (PWS). Disruption of the mouse necdin gene results in early postnatal lethality, reduction in specific groups of hypothalamic neurons, and be-havioral alterations, which are characteristics of the PWS phenotype. Necdin shows a significant homology to MAGE family proteins, the remarkable feature of which is a large central region termed MAGE homology domain (MHD). We tested the interactions of necdin and MAGE-D1 (a MAGE family protein) with p75NTR (a neurotrophin receptor) by co-immunoprecipitation assay. Both of necdin and MAGE-D1 bound to the intracellular domain of p75NTR. Necdin protects the E2F1-induced cell death using N1E-115 neuroblastoma cells. While MACE-D1 enhances the p75NTR-induced cell death, co-expression of p75NTR significantly abrogated the necdin induced suppression of cell death through the dissociation of the binding between necdin and E2F1. Furthermore, MAGE-D1 dissociated the interaction of TrkA and p75NTR, necdin enhanced the binding. We next investigated the direct interaction of necdin and MAGE-D1. Necdin bound to MACE-D1 through the MAGE homology domain by pull-down assay in vitro and co-immunoprecipitation analysis in vivo. We also demonstrated that necdin interacted with Msx homeoprotein via MAGE-D1. These findings suggest that necdin and MAGE-D1 regulate the neural cell death via the interaction with neurotrophin receptors.研究課題/領域番号:15500256, 研究期間(年度):2003 – 2004出典：「神経細胞死の制御機構」研究成果報告書　課題番号15500256（KAKEN：科学研究費助成事業データベース（国立情報学研究所））（https://kaken.nii.ac.jp/ja/report/KAKENHI-PROJECT-15500256/155002562004kenkyu_seika_hokoku_gaiyo/)を加工して作