Publications by authors named "Takashi Maejima"

32 Publications

GABA from vasopressin neurons regulates the time at which suprachiasmatic nucleus molecular clocks enable circadian behavior.

Proc Natl Acad Sci U S A 2021 Feb;118(6)

Department of Integrative Neurophysiology, Graduate School of Medical Sciences, Kanazawa University, 920-8640 Ishikawa, Japan;

The suprachiasmatic nucleus (SCN), the central circadian pacemaker in mammals, is a network structure composed of multiple types of γ-aminobutyric acid (GABA)-ergic neurons and glial cells. However, the roles of GABA-mediated signaling in the SCN network remain controversial. Here, we report noticeable impairment of the circadian rhythm in mice with a specific deletion of the vesicular GABA transporter in arginine vasopressin (AVP)-producing neurons. These mice showed disturbed diurnal rhythms of GABA receptor-mediated synaptic transmission in SCN neurons and marked lengthening of the activity time in circadian behavioral rhythms due to the extended interval between morning and evening locomotor activities. Synchrony of molecular circadian oscillations among SCN neurons did not significantly change, whereas the phase relationships between SCN molecular clocks and circadian morning/evening locomotor activities were altered significantly, as revealed by PER2::LUC imaging of SCN explants and in vivo recording of intracellular Ca in SCN AVP neurons. In contrast, daily neuronal activity in SCN neurons in vivo clearly showed a bimodal pattern that correlated with dissociated morning/evening locomotor activities. Therefore, GABAergic transmission from AVP neurons regulates the timing of SCN neuronal firing to temporally restrict circadian behavior to appropriate time windows in SCN molecular clocks.
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http://dx.doi.org/10.1073/pnas.2010168118DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC8017960PMC
February 2021

RGS2 drives male aggression in mice via the serotonergic system.

Commun Biol 2019 11;2:373. Epub 2019 Oct 11.

1Department of General Zoology and Neurobiology, Ruhr-University Bochum, 44780 Bochum, Germany.

Aggressive behavior in our modern, civilized society is often counterproductive and destructive. Identifying specific proteins involved in the disease can serve as therapeutic targets for treating aggression. Here, we found that overexpression of RGS2 in explicitly serotonergic neurons augments male aggression in control mice and rescues male aggression in mice, while anxiety is not affected. The aggressive behavior is directly correlated to the immediate early gene induction in the dorsal raphe nuclei and ventrolateral part of the ventromedial nucleus hypothalamus, to an increase in spontaneous firing in serotonergic neurons and to a reduction in the modulatory action of G and G coupled 5HT and adrenergic receptors in serotonergic neurons of -expressing mice. Collectively, these findings specifically identify that RGS2 expression in serotonergic neurons is sufficient to drive male aggression in mice and as a potential therapeutic target for treating aggression.
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http://dx.doi.org/10.1038/s42003-019-0622-0DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC6789038PMC
May 2020

The coronavirus macrodomain is required to prevent PARP-mediated inhibition of virus replication and enhancement of IFN expression.

PLoS Pathog 2019 05 16;15(5):e1007756. Epub 2019 May 16.

Department of Microbiology and Immunology, University of Iowa, Iowa City, IA, United States of America.

ADP-ribosylation is a ubiquitous post-translational addition of either monomers or polymers of ADP-ribose to target proteins by ADP-ribosyltransferases, usually by interferon-inducible diphtheria toxin-like enzymes known as PARPs. While several PARPs have known antiviral activities, these activities are mostly independent of ADP-ribosylation. Consequently, less is known about the antiviral effects of ADP-ribosylation. Several viral families, including Coronaviridae, Togaviridae, and Hepeviridae, encode for macrodomain proteins that bind to and hydrolyze ADP-ribose from proteins and are critical for optimal replication and virulence. These results suggest that macrodomains counter cellular ADP-ribosylation, but whether PARPs or, alternatively, other ADP-ribosyltransferases cause this modification is not clear. Here we show that pan-PARP inhibition enhanced replication and inhibited interferon production in primary macrophages infected with macrodomain-mutant but not wild-type coronavirus. Specifically, knockdown of two abundantly expressed PARPs, PARP12 and PARP14, led to increased replication of mutant but did not significantly affect wild-type virus. PARP14 was also important for the induction of interferon in mouse and human cells, indicating a critical role for this PARP in the regulation of innate immunity. In summary, these data demonstrate that the macrodomain is required to prevent PARP-mediated inhibition of coronavirus replication and enhancement of interferon production.
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http://dx.doi.org/10.1371/journal.ppat.1007756DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC6521996PMC
May 2019

A Study into the ADP-Ribosylome of IFN-γ-Stimulated THP-1 Human Macrophage-like Cells Identifies ARTD8/PARP14 and ARTD9/PARP9 ADP-Ribosylation.

J Proteome Res 2019 04 21;18(4):1607-1622. Epub 2019 Mar 21.

Center for Interdisciplinary Cardiovascular Sciences, Division of Cardiovascular Medicine, Department of Medicine , Brigham Women's Hospital, Harvard Medical School , Boston , Massachusetts 02115 , United States.

ADP-ribosylation is a post-translational modification that, until recently, has remained elusive to study at the cellular level. Previously dependent on radioactive tracers to identify ADP-ribosylation targets, several advances in mass spectrometric workflows now permit global identification of ADP-ribosylated substrates. In this study, we capitalized on two ADP-ribosylation enrichment strategies, and multiple activation methods performed on the Orbitrap Fusion Lumos, to identify IFN-γ-induced ADP-ribosylation substrates in macrophages. The ADP-ribosyl binding protein, Af1521, was used to enrich ADP-ribosylated peptides, and the antipoly-ADP-ribosyl antibody, 10H, was used to enrich ADP-ribosylated proteins. ADP-ribosyl-specific mass spectra were further enriched by an ADP-ribose product ion triggered EThcD and HCD activation strategy, in combination with multiple acquisitions that segmented the survey scan into smaller ranges. HCD and EThcD resulted in overlapping and unique ADP-ribosyl peptide identifications, with HCD providing more peptide identifications but EThcD providing more reliable ADP-ribosyl acceptor sites. Our acquisition strategies also resulted in the first ever characterization of ADP-ribosyl on three poly-ADP-ribose polymerases, ARTD9/PARP9, ARTD10/PARP10, and ARTD8/PARP14. IFN-γ increased the ADP-ribosylation status of ARTD9/PARP9, ARTD8/PARP14, and proteins involved in RNA processes. This study therefore summarizes specific molecular pathways at the intersection of IFN-γ and ADP-ribosylation signaling pathways.
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http://dx.doi.org/10.1021/acs.jproteome.8b00895DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC6456868PMC
April 2019

Glutamatergic neurons in the medial prefrontal cortex mediate the formation and retrieval of cocaine-associated memories in mice.

Addict Biol 2020 01 7;25(1):e12723. Epub 2019 Feb 7.

Laboratory of Molecular Pharmacology, Institute of Medical, Pharmaceutical and Health Sciences, Kanazawa University, Kanazawa, Japan.

In drug addiction, environmental stimuli previously associated with cocaine use readily elicit cocaine-associated memories, which persist long after abstinence and trigger cocaine craving and consumption. Although previous studies suggest that the medial prefrontal cortex (mPFC) is involved in the expression of cocaine-addictive behaviors, it remains unclear whether excitatory and inhibitory neurons in the mPFC are causally related to the formation and retrieval of cocaine-associated memories. To address this issue, we used the designer receptors exclusively activated by designer drugs (DREADD) technology combined with a cocaine-induced conditioned place preference (CPP) paradigm. We suppressed mPFC neuronal activity in a cell-type- and timing-dependent manner. C57BL/6J wild-type mice received bilateral intra-mPFC infusion of an adeno-associated virus (AAV) expressing inhibitory DREADD (hM4Di) under the control of CaMKII promotor to selectively suppress mPFC pyramidal neurons. GAD67-Cre mice received bilateral intra-mPFC infusion of a Cre-dependent AAV expressing hM4Di to specifically silence GABAergic neurons. Chemogenetic suppression of mPFC pyramidal neurons significantly attenuated both the acquisition and expression of cocaine CPP, while suppression of mPFC GABAergic neurons affected neither the acquisition nor expression of cocaine CPP. Moreover, chemogenetic inhibition of mPFC glutamatergic neurons did not affect the acquisition and expression of lithium chloride-induced conditioned place aversion. These results suggest that the activation of glutamatergic, but not GABAergic, neurons in the mPFC mediates both the formation and retrieval of cocaine-associated memories.
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http://dx.doi.org/10.1111/adb.12723DOI Listing
January 2020

Uremic Toxin Indoxyl Sulfate Promotes Proinflammatory Macrophage Activation Via the Interplay of OATP2B1 and Dll4-Notch Signaling.

Circulation 2019 01;139(1):78-96

Center for Excellence in Vascular Biology (T.N., S.K., M.C., D.V.S.P., A.S.T.K., R.K.K., W.S.G., M.S.B., G.C.G., E.A., M.A.), Brigham and Women's Hospital, Harvard Medical School, Boston, MA.

Background: Chronic kidney disease (CKD) increases cardiovascular risk. Underlying mechanisms, however, remain obscure. The uremic toxin indoxyl sulfate is an independent cardiovascular risk factor in CKD. We explored the potential impact of indoxyl sulfate on proinflammatory activation of macrophages and its underlying mechanisms.

Methods: We examined in vitro the effects of clinically relevant concentrations of indoxyl sulfate on proinflammatory responses of macrophages and the roles of organic anion transporters and organic anion transporting polypeptides (OATPs). A systems approach, involving unbiased global proteomics, bioinformatics, and network analysis, then explored potential key pathways. To address the role of Delta-like 4 (Dll4) in indoxyl sulfate-induced macrophage activation and atherogenesis in CKD in vivo, we used 5/6 nephrectomy and Dll4 antibody in low-density lipoprotein receptor-deficient (Ldlr-/-) mice. To further determine the relative contribution of OATP2B1 or Dll4 to proinflammatory activation of macrophages and atherogenesis in vivo, we used siRNA delivered by macrophage-targeted lipid nanoparticles in mice.

Results: We found that indoxyl sulfate-induced proinflammatory macrophage activation is mediated by its uptake through transporters, including OATP2B1, encoded by the SLCO2B1 gene. The global proteomics identified potential mechanisms, including Notch signaling and the ubiquitin-proteasome pathway, that mediate indoxyl sulfate-triggered proinflammatory macrophage activation. We chose the Notch pathway as an example of key candidates for validation of our target discovery platform and for further mechanistic studies. As predicted computationally, indoxyl sulfate triggered Notch signaling, which was preceded by the rapid induction of Dll4 protein. Dll4 induction may result from inhibition of the ubiquitin-proteasome pathway, via the deubiquitinating enzyme USP5. In mice, macrophage-targeted OATP2B1/Slco2b1 silencing and Dll4 antibody inhibited proinflammatory activation of peritoneal macrophages induced by indoxyl sulfate. In low-density lipoprotein receptor-deficient mice, Dll4 antibody abolished atherosclerotic lesion development accelerated in Ldlr-/- mice. Moreover, coadministration of indoxyl sulfate and OATP2B1/Slco2b1 or Dll4 siRNA encapsulated in macrophage-targeted lipid nanoparticles in Ldlr-/- mice suppressed lesion development.

Conclusions: These results suggest that novel crosstalk between OATP2B1 and Dll4-Notch signaling in macrophages mediates indoxyl sulfate-induced vascular inflammation in CKD.
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http://dx.doi.org/10.1161/CIRCULATIONAHA.118.034588DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC6311723PMC
January 2019

Monoamines Inhibit GABAergic Neurons in Ventrolateral Preoptic Area That Make Direct Synaptic Connections to Hypothalamic Arousal Neurons.

J Neurosci 2018 07 18;38(28):6366-6378. Epub 2018 Jun 18.

International Institute for Integrative Sleep Medicine, University of Tsukuba, Tsukuba, Ibaraki 305-8575, Japan,

The hypothalamus plays an important role in the regulation of sleep/wakefulness states. While the ventrolateral preoptic nucleus (VLPO) plays a critical role in the initiation and maintenance of sleep, the lateral posterior part of the hypothalamus contains neuronal populations implicated in maintenance of arousal, including orexin-producing neurons (orexin neurons) in the lateral hypothalamic area (LHA) and histaminergic neurons in the tuberomammillary nucleus (TMN). During a search for neurons that make direct synaptic contact with histidine decarboxylase-positive (HDC+), histaminergic neurons (HDC neurons) in the TMN and orexin neurons in the LHA of male mice, we found that these arousal-related neurons are heavily innervated by GABAergic neurons in the preoptic area including the VLPO. We further characterized GABAergic neurons electrophysiologically in the VLPO (GABA neurons) that make direct synaptic contact with these hypothalamic arousal-related neurons. These neurons (GABA or GABA neurons) were both potently inhibited by noradrenaline and serotonin, showing typical electrophysiological characteristics of sleep-promoting neurons in the VLPO. This work provides direct evidence of monosynaptic connectivity between GABA neurons and hypothalamic arousal neurons and identifies the effects of monoamines on these neuronal pathways. Rabies-virus-mediated tracing of input neurons of two hypothalamic arousal-related neuron populations, histaminergic and orexinergic neurons, showed that they receive similar distributions of input neurons in a variety of brain areas, with rich innervation by GABAergic neurons in the preoptic area, including the ventrolateral preoptic area (VLPO), a region known to play an important role in the initiation and maintenance of sleep. Electrophysiological experiments found that GABAergic neurons in the VLPO (GABA neurons) that make direct input to orexin or histaminergic neurons are potently inhibited by noradrenaline and serotonin, suggesting that these monoamines disinhibit histamine and orexin neurons. This work demonstrated functional and structural interactions between GABA neurons and hypothalamic arousal-related neurons.
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http://dx.doi.org/10.1523/JNEUROSCI.2835-17.2018DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC6596100PMC
July 2018

Orexin modulates behavioral fear expression through the locus coeruleus.

Nat Commun 2017 11 20;8(1):1606. Epub 2017 Nov 20.

International Institute for Integrative Sleep Medicine (WPI-IIIS), University of Tsukuba, 1-1-1 Tennodai Tsukuba, Ibaraki, 305-8575, Japan.

Emotionally salient information activates orexin neurons in the lateral hypothalamus, leading to increase in sympathetic outflow and vigilance level. How this circuit alters animals' behavior remains unknown. Here we report that noradrenergic neurons in the locus coeruleus (NA neurons) projecting to the lateral amygdala (LA) receive synaptic input from orexin neurons. Pharmacogenetic/optogenetic silencing of this circuit as well as acute blockade of the orexin receptor-1 (OX1R) decreases conditioned fear responses. In contrast, optogenetic stimulation of this circuit potentiates freezing behavior against a similar but distinct context or cue. Increase of orexinergic tone by fasting also potentiates freezing behavior and LA activity, which are blocked by pharmacological blockade of OX1R in the LC. These findings demonstrate the circuit involving orexin, NA and LA neurons mediates fear-related behavior and suggests inappropriate excitation of this pathway may cause fear generalization sometimes seen in psychiatric disorders, such as PTSD.
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http://dx.doi.org/10.1038/s41467-017-01782-zDOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC5694764PMC
November 2017

Serotonin neurons in the dorsal raphe mediate the anticataplectic action of orexin neurons by reducing amygdala activity.

Proc Natl Acad Sci U S A 2017 04 10;114(17):E3526-E3535. Epub 2017 Apr 10.

Department of Molecular Neuroscience and Integrative Physiology, Graduate School of Medical Sciences, Kanazawa University, Kanazawa 920-8640, Japan;

Narcolepsy is a sleep disorder caused by the loss of orexin (hypocretin)-producing neurons and marked by excessive daytime sleepiness and a sudden weakening of muscle tone, or cataplexy, often triggered by strong emotions. In a mouse model for narcolepsy, we previously demonstrated that serotonin neurons of the dorsal raphe nucleus (DRN) mediate the suppression of cataplexy-like episodes (CLEs) by orexin neurons. Using an optogenetic tool, in this paper we show that the acute activation of DRN serotonin neuron terminals in the amygdala, but not in nuclei involved in regulating rapid eye-movement sleep and atonia, suppressed CLEs. Not only did stimulating serotonin nerve terminals reduce amygdala activity, but the chemogenetic inhibition of the amygdala using designer receptors exclusively activated by designer drugs also drastically decreased CLEs, whereas chemogenetic activation increased them. Moreover, the optogenetic inhibition of serotonin nerve terminals in the amygdala blocked the anticataplectic effects of orexin signaling in DRN serotonin neurons. Taken together, the results suggest that DRN serotonin neurons, as a downstream target of orexin neurons, inhibit cataplexy by reducing the activity of amygdala as a center for emotional processing.
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http://dx.doi.org/10.1073/pnas.1614552114DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC5410844PMC
April 2017

Direct evidence for pitavastatin induced chromatin structure change in the KLF4 gene in endothelial cells.

PLoS One 2014 5;9(5):e96005. Epub 2014 May 5.

Research Center for Advanced Science and Technology, The University of Tokyo, Meguro-ku, Tokyo, Japan; Radioisotope Center, The University of Tokyo, Bunkyo-ku, Tokyo, Japan.

Statins exert atheroprotective effects through the induction of specific transcriptional factors in multiple organs. In endothelial cells, statin-dependent atheroprotective gene up-regulation is mediated by Kruppel-like factor (KLF) family transcription factors. To dissect the mechanism of gene regulation, we sought to determine molecular targets by performing microarray analyses of human umbilical vein endothelial cells (HUVECs) treated with pitavastatin, and KLF4 was determined to be the most highly induced gene. In addition, it was revealed that the atheroprotective genes induced with pitavastatin, such as nitric oxide synthase 3 (NOS3) and thrombomodulin (THBD), were suppressed by KLF4 knockdown. Myocyte enhancer factor-2 (MEF2) family activation is reported to be involved in pitavastatin-dependent KLF4 induction. We focused on MEF2C among the MEF2 family members and identified a novel functional MEF2C binding site 148 kb upstream of the KLF4 gene by chromatin immunoprecipitation along with deep sequencing (ChIP-seq) followed by luciferase assay. By applying whole genome and quantitative chromatin conformation analysis {chromatin interaction analysis with paired end tag sequencing (ChIA-PET), and real time chromosome conformation capture (3C) assay}, we observed that the MEF2C-bound enhancer and transcription start site (TSS) of KLF4 came into closer spatial proximity by pitavastatin treatment. 3D-Fluorescence in situ hybridization (FISH) imaging supported the conformational change in individual cells. Taken together, dynamic chromatin conformation change was shown to mediate pitavastatin-responsive gene induction in endothelial cells.
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http://journals.plos.org/plosone/article?id=10.1371/journal.pone.0096005PLOS
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC4010393PMC
June 2015

Cross-enhancement of ANGPTL4 transcription by HIF1 alpha and PPAR beta/delta is the result of the conformational proximity of two response elements.

Genome Biol 2014 Apr 10;15(4):R63. Epub 2014 Apr 10.

Background: Synergistic transcriptional activation by different stimuli has been reported along with a diverse array of mechanisms, but the full scope of these mechanisms has yet to be elucidated.

Results: We present a detailed investigation of hypoxia-inducible factor (HIF) 1 dependent gene expression in endothelial cells which suggests the importance of crosstalk between the peroxisome proliferator-activated receptor (PPAR) β/δ and HIF signaling axes. A migration assay shows a synergistic interaction between these two stimuli, and we identify angiopoietin-like 4 (ANGPTL4) as a common target gene by using a combination of microarray and ChIP-seq analysis. We profile changes of histone marks at enhancers under hypoxia, PPARβ/δ agonist and dual stimulations and these suggest that the spatial proximity of two response elements is the principal cause of the synergistic transcription induction. A newly developed quantitative chromosome conformation capture assay shows the quantitative change of the frequency of proximity of the two response elements.

Conclusions: To the best of our knowledge, this is the first report that two different transcription factors cooperate in transcriptional regulation in a synergistic fashion through conformational change of their common target genes.
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http://dx.doi.org/10.1186/gb-2014-15-4-r63DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC4053749PMC
April 2014

Vertebrate cone opsins enable sustained and highly sensitive rapid control of Gi/o signaling in anxiety circuitry.

Neuron 2014 Mar;81(6):1263-1273

Department of General Zoology and Neurobiology, ND7/31, Ruhr-University Bochum, Universitätsstrasse 150, 44780 Bochum, Germany. Electronic address:

G protein-coupled receptors (GPCRs) coupling to Gi/o signaling pathways are involved in the control of important physiological functions, which are difficult to investigate because of the limitation of tools to control the signaling pathway with precise kinetics and specificity. We established two vertebrate cone opsins, short- and long-wavelength opsin, for long-lasting and repetitive activation of Gi/o signaling pathways in vitro and in vivo. We demonstrate for both opsins the repetitive fast, membrane-delimited, ultra light-sensitive, and wavelength-dependent activation of the Gi/o pathway in HEK cells. We also show repetitive control of Gi/o pathway activation in 5-HT1A receptor domains in the dorsal raphe nucleus (DRN) in brain slices and in vivo, which is sufficient to modulate anxiety behavior in mice. Thus, vertebrate cone opsins represent a class of tools for understanding the role of Gi/o-coupled GPCRs in health and disease.
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http://dx.doi.org/10.1016/j.neuron.2014.01.041DOI Listing
March 2014

Modulation of firing and synaptic transmission of serotonergic neurons by intrinsic G protein-coupled receptors and ion channels.

Front Integr Neurosci 2013 23;7:40. Epub 2013 May 23.

Department of Zoology and Neurobiology, Ruhr-University Bochum Bochum, Germany.

Serotonergic neurons project to virtually all regions of the central nervous system and are consequently involved in many critical physiological functions such as mood, sexual behavior, feeding, sleep/wake cycle, memory, cognition, blood pressure regulation, breathing, and reproductive success. Therefore, serotonin release and serotonergic neuronal activity have to be precisely controlled and modulated by interacting brain circuits to adapt to specific emotional and environmental states. We will review the current knowledge about G protein-coupled receptors and ion channels involved in the regulation of serotonergic system, how their regulation is modulating the intrinsic activity of serotonergic neurons and its transmitter release and will discuss the latest methods for controlling the modulation of serotonin release and intracellular signaling in serotonergic neurons in vitro and in vivo.
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http://dx.doi.org/10.3389/fnint.2013.00040DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC3661940PMC
June 2013

Postnatal loss of P/Q-type channels confined to rhombic-lip-derived neurons alters synaptic transmission at the parallel fiber to purkinje cell synapse and replicates genomic Cacna1a mutation phenotype of ataxia and seizures in mice.

J Neurosci 2013 Mar;33(12):5162-74

Department of Zoology and Neurobiology, Ruhr University Bochum, D-44780 Bochum, Germany.

Ataxia, episodic dyskinesia, and thalamocortical seizures are associated with an inherited loss of P/Q-type voltage-gated Ca(2+) channel function. P/Q-type channels are widely expressed throughout the neuraxis, obscuring identification of the critical networks underlying these complex neurological disorders. We showed recently that the conditional postnatal loss of P/Q-type channels in cerebellar Purkinje cells (PCs) in mice (purky) leads to these aberrant phenotypes, suggesting that intrinsic alteration in PC output is a sufficient pathogenic factor for disease initiation. The question arises whether P/Q-type channel deletion confined to a single upstream cerebellar synapse might induce the pathophysiological abnormality of genomically inherited P/Q-type channel disorders. PCs integrate two excitatory inputs, climbing fibers from inferior olive and parallel fibers (PFs) from granule cells (GCs) that receive mossy fiber (MF) input derived from precerebellar nuclei. In this study, we introduce a new mouse model with a selective knock-out of P/Q-type channels in rhombic-lip-derived neurons including the PF and MF pathways (quirky). We found that in quirky mice, PF-PC synaptic transmission is reduced during low-frequency stimulation. Using focal light stimulation of GCs that express optogenetic light-sensitive channels, channelrhodopsin-2, we found that modulation of PC firing via GC input is reduced in quirky mice. Phenotypic analysis revealed that quirky mice display ataxia, dyskinesia, and absence epilepsy. These results suggest that developmental alteration of patterned input confined to only one of the main afferent cerebellar excitatory synaptic pathways has a significant role in generating the neurological phenotype associated with the global genomic loss of P/Q-type channel function.
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http://dx.doi.org/10.1523/JNEUROSCI.5442-12.2013DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC3641643PMC
March 2013

Optogenetic control of motor coordination by Gi/o protein-coupled vertebrate rhodopsin in cerebellar Purkinje cells.

J Biol Chem 2011 Jul 31;286(29):25848-58. Epub 2011 May 31.

Department of Zoology and Neurobiology, ND7/31, Ruhr-University Bochum, Bochum, Germany.

G protein-coupled receptors are involved in the modulation of complex neuronal networks in the brain. To investigate the impact of a cell-specific G(i/o) protein-mediated signaling pathway on brain function, we created a new optogenetic mouse model in which the G(i/o) protein-coupled receptor vertebrate rhodopsin can be cell-specifically expressed with the aid of Cre recombinase. Here we use this mouse model to study the functional impact of G(i/o) modulation in cerebellar Purkinje cells (PCs). We show that in vivo light activation of vertebrate rhodopsin specifically expressed in PCs reduces simple spike firing that is comparable with the reduction in firing observed for the activation of cerebellar G(i/o)-coupled GABA(B) receptors. Notably, the light exposure of the cerebellar vermis in freely moving mice changes the motor behavior. Thus, our studies directly demonstrate that spike modulation via G(i/o)-mediated signaling in cerebellar PCs affects motor coordination and show a new promising approach for studying the physiological function of G protein-coupled receptor-mediated signaling in a cell type-specific manner.
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http://dx.doi.org/10.1074/jbc.M111.253674DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC3138296PMC
July 2011

Pitavastatin increases ABCA1 expression by dual mechanisms: SREBP2-driven transcriptional activation and PPARα-dependent protein stabilization but without activating LXR in rat hepatoma McARH7777 cells.

J Pharmacol Sci 2011 27;116(1):107-15. Epub 2011 Apr 27.

Tokyo New Drug Research Laboratories, Kowa Company, Ltd., Higashimurayama, Tokyo 189-0022, Japan.

Hepatic ATP-binding cassette transporter A1 (ABCA1) plays a key role in high-density lipoprotein (HDL) production by apolipoprotein A-I (ApoA-I) lipidation. 3-Hydroxy-3-methylglutaryl coenzyme A (HMG-CoA) reductase inhibitors, statins, increase ABCA1 mRNA levels in hepatoma cell lines, but their mechanism of action is not yet clear. We investigated how statins increase ABCA1 in rat hepatoma McARH7777 cells. Pitavastatin, atorvastatin, and simvastatin increased total ABCA1 mRNA levels, whereas pravastatin had no effect. Pitavastatin also increased ABCA1 protein. Hepatic ABCA1 expression in rats is regulated by both liver X receptor (LXR) and sterol regulatory element-binding protein (SREBP2) pathways. Pitavastatin repressed peripheral type ABCA1 mRNA levels and its LXR-driven promoter, but activated the liver-type SREBP-driven promoter, and eventually increased total ABCA1 mRNA expression. Furthermore, pitavastatin increased peroxisome proliferator-activated receptor α (PPARα) and its downstream gene expression. Knockdown of PPARα attenuated the increase in ABCA1 protein, indicating that pitavastatin increased ABCA1 protein via PPARα activation, although it repressed LXR activation. Furthermore, the degradation of ABCA1 protein was retarded in pitavastatin-treated cells. These data suggest that pitavastatin increases ABCA1 protein expression by dual mechanisms: SREBP2-mediated mRNA transcription and PPARα-mediated ABCA1 protein stabilization, but not by the PPAR-LXR-ABCA1 pathway. [Supplementary Figures: available only at http://dx.doi.org/10.1254/jphs.10241FP].
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http://dx.doi.org/10.1254/jphs.10241fpDOI Listing
September 2011

Delayed postnatal loss of P/Q-type calcium channels recapitulates the absence epilepsy, dyskinesia, and ataxia phenotypes of genomic Cacna1a mutations.

J Neurosci 2011 Mar;31(11):4311-26

Department of Zoology and Neurobiology, ND7/31, Ruhr-University Bochum, D-44780 Bochum, Germany.

Inherited loss of P/Q-type calcium channel function causes human absence epilepsy, episodic dyskinesia, and ataxia, but the molecular "birthdate" of the neurological syndrome and its dependence on prenatal pathophysiology is unknown. Since these channels mediate transmitter release at synapses throughout the brain and are expressed early in embryonic development, delineating the critical circuitry and onset underlying each of the emergent phenotypes requires targeted control of gene expression. To visualize P/Q-type Ca(2+) channels and dissect their role in neuronal networks at distinct developmental stages, we created a novel conditional Cacna1a knock-in mouse by inserting the floxed green fluorescent protein derivative Citrine into the first exon of Cacna1a and then crossed it with a postnatally expressing PCP2-Cre line for delayed Purkinje cell (PC) gene deletion within the cerebellum and sparsely in forebrain (purky). PCs in purky mice lacked P/Q-type calcium channel protein and currents within the first month after birth, displayed altered spontaneous firing, and showed impaired neurotransmission. Unexpectedly, adult purky mice exhibited the full spectrum of neurological deficits seen in mice with genomic Cacna1a ablation. Our results show that the ataxia, dyskinesia, and absence epilepsy caused by inherited disorders of the P/Q-type channel arise from signaling defects beginning in late infancy, revealing an early window of opportunity for therapeutic intervention.
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http://dx.doi.org/10.1523/JNEUROSCI.5342-10.2011DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC3065835PMC
March 2011

Pet-1 is required across different stages of life to regulate serotonergic function.

Nat Neurosci 2010 Oct 5;13(10):1190-8. Epub 2010 Sep 5.

Case Western Reserve University, School of Medicine, Department of Neurosciences, Cleveland, Ohio, USA.

Transcriptional cascades are required for the specification of serotonin (5-HT) neurons and behaviors modulated by 5-HT. Several cascade factors are expressed throughout the lifespan, which suggests that their control of behavior might not be temporally restricted to programming normal numbers of 5-HT neurons. We used new mouse conditional targeting approaches to investigate the ongoing requirements for Pet-1 (also called Fev), a cascade factor that is required for the initiation of 5-HT synthesis, but whose expression persists into adulthood. We found that Pet-1 was required after the generation of 5-HT neurons for multiple steps in 5-HT neuron maturation, including axonal innervation of the somatosensory cortex, expression of appropriate firing properties, and the expression of the Htr1a and Htr1b autoreceptors. Pet-1 was still required in adult 5-HT neurons to preserve normal anxiety-related behaviors through direct autoregulated control of serotonergic gene expression. These findings indicate that Pet-1 is required across the lifespan of the mouse and that behavioral pathogenesis can result from both developmental and adult-onset alterations in serotonergic transcription.
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http://dx.doi.org/10.1038/nn.2623DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC2947586PMC
October 2010

Substitution of 5-HT1A receptor signaling by a light-activated G protein-coupled receptor.

J Biol Chem 2010 Oct 19;285(40):30825-36. Epub 2010 Jul 19.

Department of Neurosciences, School of Medicine, Case Western Reserve University, Cleveland, Ohio 44106, USA.

Understanding serotonergic (5-HT) signaling is critical for understanding human physiology, behavior, and neuropsychiatric disease. 5-HT mediates its actions via ionotropic and metabotropic 5-HT receptors. The 5-HT(1A) receptor is a metabotropic G protein-coupled receptor linked to the G(i/o) signaling pathway and has been specifically implicated in the pathogenesis of depression and anxiety. To understand and precisely control 5-HT(1A) signaling, we created a light-activated G protein-coupled receptor that targets into 5-HT(1A) receptor domains and substitutes for endogenous 5-HT(1A) receptors. To induce 5-HT(1A)-like targeting, vertebrate rhodopsin was tagged with the C-terminal domain (CT) of 5-HT(1A) (Rh-CT(5-HT1A)). Rh-CT(5-HT1A) activates G protein-coupled inward rectifying K(+) channels in response to light and causes membrane hyperpolarization in hippocampal neurons, similar to the agonist-induced responses of the 5-HT(1A) receptor. The intracellular distribution of Rh-CT(5-HT1A) resembles that of the 5-HT(1A) receptor; Rh-CT(5-HT1A) localizes to somatodendritic sites and is efficiently trafficked to distal dendritic processes. Additionally, neuronal expression of Rh-CT(5-HT1A), but not Rh, decreases 5-HT(1A) agonist sensitivity, suggesting that Rh-CT(5-HT1A) and 5-HT(1A) receptors compete to interact with the same trafficking machinery. Finally, Rh-CT(5-HT1A) is able to rescue 5-HT(1A) signaling of 5-HT(1A) KO mice in cultured neurons and in slices of the dorsal raphe showing that Rh-CT(5-HT1A) is able to functionally compensate for native 5-HT(1A). Thus, as an optogenetic tool, Rh-CT(5-HT1A) has the potential to directly correlate in vivo 5-HT(1A) signaling with 5-HT neuron activity and behavior in both normal animals and animal models of neuropsychiatric disease.
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http://dx.doi.org/10.1074/jbc.M110.147298DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC2945576PMC
October 2010

Induction of paranodal myelin detachment and sodium channel loss in vivo by Campylobacter jejuni DNA-binding protein from starved cells (C-Dps) in myelinated nerve fibers.

J Neurol Sci 2010 Jan 31;288(1-2):54-62. Epub 2009 Oct 31.

Department of Neurology, Neurological Institute, Graduate School of Medical Sciences, Kyushu University, Fukuoka 812-8582, Japan.

In an axonal variant of Guillain-Barré syndrome (GBS) associated with Campylobacter jejuni (C. jejuni) enteritis, the mechanism underlying axonal damage is obscure. We purified and characterized a DNA-binding protein from starved cells derived from C. jejuni (C-Dps). This C-Dps protein has significant homology with Helicobacter pylori neutrophil-activating protein (HP-NAP), which is chemotactic for human neutrophils through binding to sulfatide. Because sulfatide is essential for paranodal junction formation and for the maintenance of ion channels on myelinated axons, we examined the in vivo effects of C-Dps. First, we found that C-Dps specifically binds to sulfatide by ELISA and immunostaining of thin-layer chromatograms loaded with various glycolipids. Double immunostaining of peripheral nerves exposed to C-Dps with anti-sulfatide antibody and anti-C-Dps antibody revealed co-localization of them. When C-Dps was injected into rat sciatic nerves, it densely bound to the outermost parts of the myelin sheath and nodes of Ranvier. Injection of C-Dps rapidly induced paranodal myelin detachment and axonal degeneration; this was not seen following injection of PBS or heat-denatured C-Dps. Electron microscopically, C-Dps-injected nerves showed vesiculation of the myelin sheath at the nodes of Ranvier. Nerve conduction studies disclosed a significant reduction in compound muscle action potential amplitudes in C-Dps-injected nerves compared with pre-injection values, but not in PBS-, heat-denatured C-Dps-, or BSA-injected nerves. However, C-Dps did not directly affect Na(+) currents in dissociated hippocampal neurons. Finally, when C-Dps was intrathecally infused into rats, it was deposited in a scattered pattern in the cauda equina, especially in the outer part of the myelin sheath and the nodal region. In C-Dps-infused rats, but not in BSA-infused ones, a decrease in the number of sodium channels, vesiculation of the myelin sheath, axonal degeneration and infiltration of Iba-1-positive macrophages were observed. Thus, we consider that C-Dps damages myelinated nerve fibers, possibly through interference with paranodal sulfatide function, and may contribute to the axonal pathology seen in C. jejuni-related GBS.
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http://dx.doi.org/10.1016/j.jns.2009.10.007DOI Listing
January 2010

Pharmacological evidence for the involvement of diacylglycerol lipase in depolarization-induced endocanabinoid release.

Neuropharmacology 2008 Jan 22;54(1):58-67. Epub 2007 Jun 22.

Department of Neurophysiology, Graduate School of Medicine, Osaka University, Suita 565-0871, Japan.

Depolarization-induced suppression of inhibition (DSI) or excitation (DSE) is a well-known form of endocannabinoid-mediated short-term plasticity that is induced by postsynaptic depolarization. It is generally accepted that DSI/DSE is triggered by Ca(2+) influx through voltage-gated Ca(2+) channels. It is also demonstrated that DSI/DSE is mediated by 2-arachidonoylglycerol (2-AG). However, how Ca(2+) induces 2-AG production is still unclear. In the present study, we investigated molecular mechanisms underlying the Ca(2+)-driven 2-AG production. Using cannabinoid-sensitive inhibitory synapses of cultured hippocampal neurons, we tested several inhibitors for enzymes that are supposed to be involved in 2-AG metabolism. The chemicals we tested include inhibitors for phospholipase C (U73122 and ET-18), diacylglycerol kinase (DGK inhibitor 1), phosphatidic acid phosphohydrolase (propranolol), and diacylglycerol lipase (DGL; RHC-80267 and tetrahydrolipstatin (THL)). However, unfavorable side effects were observed with these inhibitors, except for THL. Furthermore, we found that RHC-80267 hardly inhibited the endocannabinoid release driven by G(q/11)-coupled receptors, which is thought to be DGL-dependent. By contrast, THL exhibited no side effects as long as we tested, and was confirmed to inhibit the DGL-dependent process. Using THL as a DGL inhibitor, we demonstrated that DGL is involved in both hippocampal DSI and cerebellar DSE. To test a possible involvement of PLCdelta in DSI, we examined hippocampal DSI in PLCdelta1, delta3 and delta4-knockout mice. However, there was no significant difference in the DSI magnitude between these knockout mice and wild-type mice. The present study clearly shows that DGL is a prerequisite for DSI/DSE. The enzymes yielding DG remain to be determined.
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http://dx.doi.org/10.1016/j.neuropharm.2007.06.002DOI Listing
January 2008

Cooperative interaction between hepatocyte nuclear factor 4 alpha and GATA transcription factors regulates ATP-binding cassette sterol transporters ABCG5 and ABCG8.

Mol Cell Biol 2007 Jun 2;27(12):4248-60. Epub 2007 Apr 2.

Laboratory of Systems Biology and Medicine, Research Center for Advanced Science and Technology, University of Tokyo, 4-6-1 Komaba, Meguro, Tokyo, Japan.

Cholesterol homeostasis is maintained by coordinate regulation of cholesterol synthesis and its conversion to bile acids in the liver. The excretion of cholesterol from liver and intestine is regulated by ATP-binding cassette half-transporters ABCG5 and ABCG8. The genes for these two proteins are closely linked and divergently transcribed from a common intergenic promoter region. Here, we identified a binding site for hepatocyte nuclear factor 4alpha (HNF4alpha) in the ABCG5/ABCG8 intergenic promoter, through which HNF4alpha strongly activated the expression of a reporter gene in both directions. The HNF4alpha-responsive element is flanked by two conserved GATA boxes that were also required for stimulation by HNF4alpha. GATA4 and GATA6 bind to the GATA boxes, coexpression of GATA4 and HNF4alpha leads to a striking synergistic activation of both the ABCG5 and the ABCG8 promoters, and binding sites for HNF4alpha and GATA were essential for maximal synergism. We also show that HNF4alpha, GATA4, and GATA6 colocalize in the nuclei of HepG2 cells and that a physical interaction between HNF4alpha and GATA4 is critical for the synergistic response. This is the first demonstration that HNF4alpha acts synergistically with GATA factors to activate gene expression in a bidirectional fashion.
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http://dx.doi.org/10.1128/MCB.01894-06DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC1900057PMC
June 2007

Expression of liver X receptor alpha in rat fetal tissues at different developmental stages.

J Histochem Cytochem 2007 Jun 6;55(6):641-9. Epub 2007 Mar 6.

Division of Cellular and Molecular Pathology, Department of Cellular Function, Niigata University Graduate School of Medical and Dental Sciences, Asahimachi-dori 1-757, 951-8510, Niigata, Japan.

The liver X receptor (LXR) is a nuclear receptor that acts as a sterol sensor and metabolic regulator of cholesterol and lipid homeostasis. Using a novel LXRalpha-specific antibody for immunohistochemistry, we evaluated cellular expression of LXRalpha in fetal rat tissues. In the fetal liver, LXRalpha-positive macrophages appeared at 12 days and their number peaked at 18 days of gestation. In contrast, hepatocytes expressed LXRalpha during the later stage of gestation, suggesting the functional development of the liver during ontogeny. Later, macrophages in spleen and thymus expressed LXRalpha, and some mononuclear cells in the vascular lumen compatible to primitive/fetal macrophages in the fetal circulation were found to express LXRalpha. In vitro, rat monocytes did not express LXRalpha, but monocyte-derived macrophages cultured in the presence of macrophage-colony stimulating factor revealed the distinct expression of LXRalpha in nucleoli. These findings suggest that LXRalpha plays a role in the differentiation of fetal macrophages, particularly hepatic macrophages, in rat development.
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http://dx.doi.org/10.1369/jhc.6A7120.2007DOI Listing
June 2007

Influence of 3-hydroxy-3-methylglutaryl coenzyme A reductase inhibitors on ubiquinone levels in rat skeletal muscle and heart: relationship to cytotoxicity and inhibitory activity for cholesterol synthesis in human skeletal muscle cells.

J Atheroscler Thromb 2006 Dec;13(6):295-307

Tokyo New Drug Research Laboratories I, Pharmaceutical Division, Kowa, Co. Ltd, Japan.

Although statins are prescribed as relatively safe and effective drugs for hypercholesterolemic patients, it has been reported that a significant side effect, myopathy, occurs infrequently during medication. Moreover, because statins decrease cardiac ubiquinone levels, the risk of cardiac dysfunction has been suggested. This study sought to evaluate and compare the cytotoxicity of statins (cerivastatin, pitavastatin, fluvastatin, simvastatin, atorvastatin and pravastatin) in cultured human skeletal muscle cells (HSkMCs) and the effects on ubiquinone levels in statin-treated rat skeletal muscle and heart. Cerivastatin, the most potent inhibitor of HMG-CoA reductase, showed the strongest cytotoxicity (over 10-fold) among the statins examined, while the effects of the others were in a similar range. In rat experiments, neither pitavastatin nor cerivastatin decreased ubiquinone levels in skeletal muscle, but both dose-dependently lowered ubiquinone levels in the heart. As the rates of reduction by pitavastatin (9.6% at 30 mg/kg) and cerivastatin (9.7% at 0.3 mg/kg) were almost equal, it was estimated that cerivastatin reduced ubiquinone levels in the rat heart approximately 100-fold more strongly than pitavastatin, based on the effective doses. We found that cerivastatin showed the most potent cytotoxicity in HSkMCs and strongly lowered ubiquinone levels in the rat heart.
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http://dx.doi.org/10.5551/jat.13.295DOI Listing
December 2006

The CB1 cannabinoid receptor is the major cannabinoid receptor at excitatory presynaptic sites in the hippocampus and cerebellum.

J Neurosci 2006 Mar;26(11):2991-3001

Department of Cellular Neuroscience, Graduate School of Medicine, Osaka University, Suita 565-0871, Japan.

Endocannabinoids work as retrograde messengers and contribute to short-term and long-term modulation of synaptic transmission via presynaptic cannabinoid receptors. It is generally accepted that the CB1 cannabinoid receptor (CB1) mediates the effects of endocannabinoid in inhibitory synapses. For excitatory synapses, however, contributions of CB1, "CB3," and some other unidentified receptors have been suggested. In the present study we used electrophysiological and immunohistochemical techniques and examined the type(s) of cannabinoid receptor functioning at hippocampal and cerebellar excitatory synapses. Our electrophysiological data clearly demonstrate the predominant contribution of CB1. At hippocampal excitatory synapses on pyramidal neurons the cannabinoid-induced synaptic suppression was reversed by a CB1-specific antagonist, N-(piperidin-1-yl)-5-(4-iodophenyl)-1-(2,4-dichlorophenyl)-4-methyl-1H-pyrazole-3-carboxamide (AM251), and was absent in CB1 knock-out mice. At climbing fiber (CF) and parallel fiber (PF) synapses on cerebellar Purkinje cells the cannabinoid-dependent suppression was absent in CB1 knock-out mice. The presence of CB1 at presynaptic terminals was confirmed by immunohistochemical experiments with specific antibodies against CB1. In immunoelectron microscopy the densities of CB1-positive signals in hippocampal excitatory terminals and cerebellar PF terminals were much lower than in inhibitory terminals but were clearly higher than the background. Along the long axis of PFs, the CB1 was localized at a much higher density on the perisynaptic membrane than on the extrasynaptic and synaptic regions. In contrast, CB1 density was low in CF terminals and was not significantly higher than the background. Despite the discrepancy between the electrophysiological and morphological data for CB1 expression on CFs, these results collectively indicate that CB1 is responsible for cannabinoid-dependent suppression of excitatory transmission in the hippocampus and cerebellum.
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http://dx.doi.org/10.1523/JNEUROSCI.4872-05.2006DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC6673964PMC
March 2006

SOX6 attenuates glucose-stimulated insulin secretion by repressing PDX1 transcriptional activity and is down-regulated in hyperinsulinemic obese mice.

J Biol Chem 2005 Nov 7;280(45):37669-80. Epub 2005 Sep 7.

Laboratory for Systems Biology and Medicine, Research Center for Advanced Science and Technology, University of Tokyo, Japan.

In obesity-related insulin resistance, pancreatic islets compensate for insulin resistance by increasing secretory capacity. Here, we report the identification of sex-determining region Y-box 6 (SOX6), a member of the high mobility group box superfamily of transcription factors, as a co-repressor for pancreatic-duodenal homeobox factor-1 (PDX1). SOX6 mRNA levels were profoundly reduced by both a long term high fat feeding protocol in normal mice and in genetically obese ob/ob mice on a normal chow diet. Interestingly, we show that SOX6 is expressed in adult pancreatic insulin-producing beta-cells and that overexpression of SOX6 decreased glucose-stimulated insulin secretion, which was accompanied by decreased ATP/ADP ratio, Ca(2+) mobilization, proinsulin content, and insulin gene expression. In a complementary fashion, depletion of SOX6 by small interfering RNAs augmented glucose-stimulated insulin secretion in insulinoma mouse MIN6 and rat INS-1E cells. These effects can be explained by our mechanistic studies that show SOX6 acts to suppress PDX1 stimulation of the insulin II promoter through a direct protein/protein interaction. Furthermore, SOX6 retroviral expression decreased acetylation of histones H3 and H4 in chromatin from the promoter for the insulin II gene, suggesting that SOX6 may decrease PDX1 stimulation through changes in chromatin structure at specific promoters. These results suggest that perturbations in transcriptional regulation that are coordinated through SOX6 and PDX1 in beta-cells may contribute to the beta-cell adaptation in obesity-related insulin resistance.
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http://dx.doi.org/10.1074/jbc.M505392200DOI Listing
November 2005

Calcium signaling and synaptic modulation: regulation of endocannabinoid-mediated synaptic modulation by calcium.

Cell Calcium 2005 Sep-Oct;38(3-4):369-74

Department of Cellular Neurophysiology, Graduate School of Medical Science, Kanazawa University, 13-1 Takara-machi, Kanazawa 920-8640, Japan.

Postsynaptic Ca2+ signal influences synaptic transmission through multiple mechanisms. Some of them involve retrograde messengers that are released from postsynaptic neurons in a Ca2+-dependent manner and modulate transmitter release through activation of presynaptic receptors. Recent studies have revealed essential roles of endocannabinoids in retrograde modulation of synaptic transmission. Endocannabinoid release is induced by either postsynaptic Ca2+ elevation alone or activation of postsynaptic Gq/11-coupled receptors with or without Ca2+ elevation. The former pathway is independent of phospholipase Cbeta (PLCbeta) and requires a large Ca2+ elevation to a micromolar range. The latter pathway requires PLCbeta and is facilitated by a moderate Ca2+ elevation to a submicromolar range. This facilitation is caused by Ca2+-dependency of receptor-driven PLCbeta activation. The released endocannabinoids then activate presynaptic cannabinoid receptor type 1 (CB1), and suppress transmitter release from presynaptic terminals. Both CB1 receptors and Gq/11-coupled receptors are widely distributed in the brain. Thus, the endocannabinoid-mediated retrograde modulation may be an important and widespread mechanism in the brain, by which postsynaptic events including Gq/11-coupled receptor activation and Ca2+ elevation can retrogradely influence presynaptic function.
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http://dx.doi.org/10.1016/j.ceca.2005.06.014DOI Listing
May 2008

Synaptically driven endocannabinoid release requires Ca2+-assisted metabotropic glutamate receptor subtype 1 to phospholipase Cbeta4 signaling cascade in the cerebellum.

J Neurosci 2005 Jul;25(29):6826-35

Department of Cellular Neurophysiology, Graduate School of Medical Science, Kanazawa University, Kanazawa 920-8640, Japan.

Endocannabinoids mediate retrograde signaling and modulate synaptic transmission in various regions of the CNS. Depolarization-induced elevation of intracellular Ca2+ concentration causes endocannabinoid-mediated suppression of excitatory/inhibitory synaptic transmission. Activation of G(q/11)-coupled receptors including group I metabotropic glutamate receptors (mGluRs) also causes endocannabinoid-mediated suppression of synaptic transmission. However, precise mechanisms of endocannabinoid production initiated by physiologically relevant synaptic activity remain to be determined. To address this problem, we made whole-cell recordings from Purkinje cells (PCs) in mouse cerebellar slices and examined their excitatory synapses arising from climbing fibers (CFs) and parallel fibers (PFs). We first characterized three distinct modes to induce endocannabinoid release by analyzing CF to PC synapses. The first mode is strong activation of mGluR subtype 1 (mGluR1)-phospholipase C (PLC) beta4 cascade without detectable Ca2+ elevation. The second mode is Ca2+ elevation to a micromolar range without activation of the mGluR1-PLCbeta4 cascade. The third mode is the Ca2+-assisted mGluR1-PLCbeta4 cascade that requires weak mGluR1 activation and Ca2+ elevation to a submicromolar range. By analyzing PF to PC synapses, we show that the third mode is essential for effective endocannabinoid release from PCs by excitatory synaptic activity. Furthermore, our biochemical analysis demonstrates that combined weak mGluR1 activation and mild depolarization in PCs effectively produces 2-arachidonoylglycerol (2-AG), a candidate of endocannabinoid, whereas either stimulus alone did not produce detectable 2-AG. Our results strongly suggest that under physiological conditions, excitatory synaptic inputs to PCs activate the Ca2+-assisted mGluR1-PLCbeta4 cascade, and thereby produce 2-AG, which retrogradely modulates synaptic transmission to PCs.
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http://dx.doi.org/10.1523/JNEUROSCI.0945-05.2005DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC6725357PMC
July 2005

Phospholipase Cbeta serves as a coincidence detector through its Ca2+ dependency for triggering retrograde endocannabinoid signal.

Neuron 2005 Jan;45(2):257-68

Department of Cellular Neurophysiology, Graduate School of Medical Science, Kanazawa University, Kanazawa 920-8640, Japan.

Endocannabinoids mediate retrograde signal and modulate transmission efficacy at various central synapses. Although endocannabinoid release is induced by either depolarization or activation of G(q/11)-coupled receptors, it is markedly enhanced by the coincidence of depolarization and receptor activation. Here we report that this coincidence is detected by phospholipase Cbeta1 (PLCbeta1) in hippocampal neurons. By measuring cannabinoid-sensitive synaptic currents, we found that the receptor-driven endocannabinoid release was dependent on physiological levels of intracellular Ca(2+) concentration ([Ca(2+)](i)), and markedly enhanced by depolarization-induced [Ca(2+)](i) elevation. Furthermore, we measured PLC activity in intact neurons by using exogenous TRPC6 channel as a biosensor for the PLC product diacylglycerol and found that the receptor-driven PLC activation exhibited similar [Ca(2+)](i) dependence to that of endocannabinoid release. Neither endocannabinoid release nor PLC activation was induced by receptor activation in PLCbeta1 knockout mice. We therefore conclude that PLCbeta1 serves as a coincidence detector through its Ca(2+) dependency for endocannabinoid release in hippocampal neurons.
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http://dx.doi.org/10.1016/j.neuron.2005.01.004DOI Listing
January 2005

Effect of pitavastatin on apolipoprotein A-I production in HepG2 cell.

Biochem Biophys Res Commun 2004 Nov;324(2):835-9

Tokyo New Drug Research Laboratories I, Kowa Company Ltd., Tokyo, Japan.

There are few reports describing the mechanism of HDL-elevating action of HMG-CoA reductase inhibitors (statins). As it is considered that the key step of HDL production is the secretion of apolipoprotein A-I (apoA-I), we investigated the effect of statins on apoA-I synthesis and secretion by HepG2 cell to elucidate the mechanism of the action. Each statin induced apoA-I expression (mRNA and protein) dose-dependently: the rank order of the apoA-I induction pitavastatin (3 microM)>simvastatin (10 microM)>atorvastatin (30 microM). The induction of apoA-I by statins disappeared with addition of mevalonate, which indicates that the effect is HMG-CoA reductase inhibition-dependent. Based on HMG-CoA reductase inhibition, pitavastatin-induced apoA-I more efficiently than simvastatin and atorvastatin. Further study revealed that pitavastatin increased ABCA1 mRNA in HMG-CoA reductase-dependent manner and that Rho and Rho kinase inhibitor (C3T and Y27632) increased apoA-I production in the HepG2 cells. These results suggest that pitavastatin efficiently increases apoA-I in the culture medium of HepG2 cells by promoting apoA-I production through inhibition of HMG-CoA reductase and suppression of Rho activity and by protecting apoA-I from catabolism through ABCA1 induction and lipidation of apoA-I.
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http://dx.doi.org/10.1016/j.bbrc.2004.09.122DOI Listing
November 2004