Tetsuhiro Niidome

Primary structure and functional expression of the ω-conotoxin-sensitive N-type calcium channel from rabbit brain

The complete amino acid sequence of a rabbit brain calcium channel (BIII) has been deduced by cloning and sequencing the cDNA. The open reading frame encodes 2339 amino acids, which corresponds to an M(r) of 261,167. A phylogenetic tree representing evolutionary relationships indicates that BIII is grouped together with the other rabbit brain calcium channels, BI and BII, into a subfamily that is distinct from the dihydropyridine-sensitive L-type subfamily. Transient expression in cultured skeletal muscle myotubes derived from muscular dysgenic mice demonstrates that the BIII channel mediates an omega-conotoxin-sensitive calcium current with kinetics and voltage dependence like those previously reported for whole-cell N-type current. Cell-attached patch recordings, with isotonic barium as the charge carrier, revealed distinct single channels with an average slope conductance of 14.3 pS.

Microglia‐derived interleukin‐6 and leukaemia inhibitory factor promote astrocytic differentiation of neural stem/progenitor cells

Neural stem/progenitor cells (NSPCs) proliferate and differentiate depending on their intrinsic properties and local environment. It has been recognized that astrocytes promote neurogenic differentiation of NSPCs, suggesting the importance of cell–cell interactions between glial cells and NSPCs. Recent studies have demonstrated that microglia, one type of glial cells, play an important role in neurogenesis. However, little is known about how activated microglia control the proliferation and differentiation of NSPCs. In this study, we investigated the possibility that microglia‐derived soluble factors regulate the behaviour of NSPCs. To this end, NSPCs and microglial cultures were obtained from rat embryonic day 16 subventricular zone (SVZ) and rat postnatal 1 day cortex, respectively, and the conditioned medium from microglia was prepared. Microglial‐conditioned medium had no significant effect on the proliferation of NSPCs. In contrast, it increased the percentage of cells positive for a marker of astrocytes, glial fibrillary acidic protein (GFAP) during differentiation. The induction of astrocytic differentiation by microglial‐conditioned medium was reduced by the inhibition of the Janus kinase/signal transducer and activation of transcription (JAK/STAT) and mitogen‐activated protein kinase (MAPK) pathways. Furthermore, microglia‐derived interleukin (IL)‐6 and leukaemia inhibitory factor (LIF) were identified as essential molecules for this astrocytic differentiation using neutralizing antibodies and recombinant cytokines. Our results suggest that microglia as well as astrocytes contribute to the integrity of the local environment of NSPCs, and at least IL‐6 and LIF released by activated microglia promote astrocytic differentiation of NSPCs via the activation of the JAK/STAT and MAPK pathways.

Differential nociceptive responses in mice lacking the alpha(1B) subunit of N-type Ca(2+) channels.

The role of N-type Ca(2+) channels in nociceptive transmission was examined in genetically engineered mice lacking the alpha(1B) subunit of N-type channels and in their heterozygote and wild-type littermates. In alpha(1B)-deficient mice, N-type channel activities in dorsal root ganglion neurons and spinal synaptoneurosomes were eliminated without compensation by other types of voltage-dependent Ca(2+) channels. The alpha(1B)-deficient mice showed a diminution in the phase 2 nociceptive responses more extensively than in the phase 1 nociceptive responses of the formalin test. The alpha(1B)-deficient mice exhibited significantly increased thermal nociceptive thresholds in the hot plate test, but failed to increase mechanical nociceptive thresholds in the tail pinch test. These results suggest a crucial role of N-type channels in nociceptive transmission, especially for persistent pain like phase 2 of the formalin test and for nociception induced by thermal stimuli.

Functional disorders of the sympathetic nervous system in mice lacking the α1B subunit (Cav 2.2) of N-type calcium channels

N-type voltage-dependent Ca2+ channels (VDCCs), predominantly localized in the nervous system, have been considered to play an essential role in a variety of neuronal functions, including neurotransmitter release at sympathetic nerve terminals. As a direct approach to elucidating the physiological significance of N-type VDCCs, we have generated mice genetically deficient in the α1B subunit (Cav 2.2). The α1B-deficient null mice, surprisingly, have a normal life span and are free from apparent behavioral defects. A complete and selective elimination of N-type currents, sensitive to ω-conotoxin GVIA, was observed without significant changes in the activity of other VDCC types in neuronal preparations of mutant mice. The baroreflex response, mediated by the sympathetic nervous system, was markedly reduced after bilateral carotid occlusion. In isolated left atria prepared from N-type-deficient mice, the positive inotropic responses to electrical sympathetic neuronal stimulation were dramatically decreased compared with those of normal mice. In contrast, parasympathetic nervous activity in the mutant mice was nearly identical to that of wild-type mice. Interestingly, the mutant mice showed sustained elevation of heart rate and blood pressure. These results provide direct evidence that N-type VDCCs are indispensable for the function of the sympathetic nervous system in circulatory regulation and indicate that N-type VDCC-deficient mice will be a useful model for studying disorders attributable to sympathetic nerve dysfunction.

Molecular cloning and characterization of a novel calcium channel from rabbit brain

The complete amino acid sequence of a novel calcium channel (designated BII) from rabbit brain has been deduced by cloning and sequencing the cDNA. The BII calcium channel is structurally more closely related to the BI calcium channel than to the cardiac and skeletal muscle L‐type calcium channels. Blot hybridization analysis of RNA from different tissues and from different regions of the brain shows that the BII calcium channel is distributed predominantly in the brain, being abundant in the cerebral cortex, hippocampus and corpus striatum.

Flavonols and flavones as BACE-1 inhibitors: Structure–activity relationship in cell-free, cell-based and in silico studies reveal novel pharmacophore features

Generation and accumulation of the amyloid beta peptide (Abeta) following proteolytic processing of the amyloid precursor protein (APP) by BACE-1 (Beta-site APP Cleaving Enzyme-1, beta-secretase) and gamma-secretase is a main causal factor of Alzheimers disease (AD). Consequently, inhibition of BACE-1, a rate-limiting enzyme in the production of Abeta, is an attractive therapeutic approach for the treatment of AD. In this study, we discovered that natural flavonoids act as non-peptidic BACE-1 inhibitors and potently inhibit BACE-1 activity and reduce the level of secreted Abeta in primary cortical neurons. In addition, we demonstrated the calculated docking poses of flavonoids to BACE-1 and revealed the interactions of flavonoids with the BACE-1 catalytic center. We firstly revealed novel pharmacophore features of flavonoids by using cell-free, cell-based and in silico docking studies. These results contribute to the development of new BACE-1 inhibitors for the treatment of AD.

Neuroprotection by donepezil against glutamate excitotoxicity involves stimulation of α7 nicotinic receptors and internalization of NMDA receptors

BACKGROUND AND PURPOSE Glutamate excitotoxicity may be involved in ischaemic injury to the CNS and some neurodegenerative diseases, such as Alzheimers disease. Donepezil, an acetylcholinesterase (AChE) inhibitor, exerts neuroprotective effects. Here we demonstrated a novel mechanism underlying the neuroprotection induced by donepezil.

PI3K/Akt/mTOR signaling regulates glutamate transporter 1 in astrocytes.

Reduction in or dysfunction of glutamate transporter 1 (GLT1) is linked to several neuronal disorders such as stroke, Alzheimers disease, and amyotrophic lateral sclerosis. However, the detailed mechanism underlying GLT1 regulation has not been fully elucidated. In the present study, we first demonstrated the effects of mammalian target of rapamycin (mTOR) signaling on GLT1 regulation. We prepared astrocytes cultured in astrocyte-defined medium (ADM), which contains several growth factors including epidermal growth factor (EGF) and insulin. The levels of phosphorylated Akt (Ser473) and mTOR (Ser2448) increased, and GLT1 levels were increased in ADM-cultured astrocytes. Treatment with a phosphatidylinositol 3-kinase (PI3K) inhibitor or an Akt inhibitor suppressed the phosphorylation of Akt (Ser473) and mTOR (Ser2448) as well as decreased ADM-induced GLT1 upregulation. Treatment with the mTOR inhibitor rapamycin decreased GLT1 protein and mRNA levels. In contrast, rapamycin did not affect Akt (Ser473) phosphorylation. Our results suggest that mTOR is a downstream target of the PI3K/Akt pathway regulating GLT1 expression.

Epigallocatechin-3-gallate and curcumin suppress amyloid beta-induced beta-site APP cleaving enzyme-1 upregulation.

Beta-site APP cleaving enzyme-1 (BACE-1), is a rate-limiting enzyme for &bgr; amyloid production. Beta amyloid induces the production of radical oxygen species and neuronal injury. Oxidative stress plays a key role in various neurological diseases such as ischemia and Alzheimers disease. Recent studies suggest that oxidative stress induces BACE-1 protein upregulation in neuronal cells. Here, we demonstrate that naturally occurring compounds (−)-epigallocatechin-3-gallate and curcumin suppress &bgr; amyloid-induced BACE-1 upregulation. Exposure of &bgr; amyloid 1–42 to neuronal culture increased BACE-1 protein levels. (−)-Epigallocatechin-3-gallate or curcumin significantly attenuated &bgr; amyloid-induced radical oxygen species production and &bgr;-sheet structure formation. These two compounds have novel pharmacological effects that may be beneficial for Alzheimers disease treatment.

Distinct mechanisms underlie distinct polyphenol-induced neuroprotection

Glutamate excitotoxicity is mediated by intracellular Ca2+ overload, caspase‐3 activation, and ROS generation. Here, we show that curcumin, tannic acid (TA) and (+)‐catechin hydrate (CA) all inhibited glutamate‐induced excitotoxicity. Curcumin inhibited PKC activity, and subsequent phosphorylation of NR1 of the NMDA receptor. As a result, glutamate‐mediated Ca2+ influx was reduced. TA attenuated glutamate‐mediated Ca2+ influx only when simultaneously administered, directly interfering with Ca2+. Both curcumin and TA inhibited glutamate‐induced caspase‐3 activation. Although Ca2+ influx was not attenuated by CA, caspase‐3 was reduced by direct inhibition of the enzyme. All polyphenols reduced glutamate‐induced generation of ROS.