PubMed Health⌕ Search

Biomedical subjects

Yuko Sekino

Publications and source records attributed to Yuko Sekino.

13 recordsLinked to original sources
PubMed2006

Nitric oxide serves as an endogenous regulator of neuronal adenosine A1 receptor expression.

Nitric oxide (NO) radicals are produced during normal cellular function, after tissue injury, and in response to immune system activation during infection. The transformation of NO to peroxynitrite is essential for mediating some of its physiological and/or cytotoxic actions. As the expression of the adenosine A1 receptor (A1AR) is regulated by oxidative stress, we evaluated the role of NO in the regulation of A1AR expression, a G protein-coupled receptor involved in cytoprotection in the central nervous system. Administration of the NO donor, S-nitrosylpenicillamine (SNAP), to pheochromocytoma 12 (PC12) cells increased A1AR protein in a time- and dose-dependent manner, with maximal induction observed with 20 microm SNAP at 24 h. The response to SNAP was attenuated by the NO scavenger 2-(4-carboxyphenyl)-4,4,5,5-tetramethylimidazoline-1-oxyl-3 oxide (C-PTIO), and by the inhibition of nuclear factor-kappaB (NF-kappaB), implicating this transcription factor in the regulatory process. In addition SNAP also increased the degradation of Inhibitory kappaB-alpha (IkappaB-alpha), a marker of NF-kappaB activation. Furthermore, the induction of inducible nitric oxide synthase (iNOS) by lipopolysaccharide increased A1AR in PC12 cells and in mice, whereas the inhibition of NOS activity suppressed this response. We conclude that NO, via the activation of NF-kappaB, serves as an endogenous regulator of A1AR, and speculate that the induction of the A1AR could counteract the cytotoxicity of NO.

Adenosine Deaminase↗
PubMed2005

Activation of N-methyl-D-aspartate receptor induces a shift of drebrin distribution: disappearance from dendritic spines and appearance in dendritic shafts.

Drebrin is a major actin-filament-binding protein localized in mature dendritic spines. A recent in vivo immunoelectron microscopic study suggests that drebrin content at each dendritic spine is regulated by some unknown mechanisms. In the present in vitro study, we examined whether glutamate stimulation alters drebrin content in dendritic spines. Glutamate stimulation induced disappearance of drebrin immunostaining from dendritic spines but led to appearance of drebrin immunostaining in dendritic shafts and somata. The glutamate-induced shift of drebrin immunostaining was blocked by an NMDA receptor antagonist. Immunoblot analyses showed that both the total and the cytosolic drebrin remained unchanged and revealed that the drebrin shift was not due to drebrin degradation. These findings indicate that NMDA receptor activation induces a shift in subcellular distribution of drebrin associated with actin filaments, and that the shift might be a molecular basis for actin reorganization accompanied with synaptic plasticity.

Actin Cytoskeleton↗
PubMed2005

Induction of adenosine A1 receptor expression by pertussis toxin via an adenosine 5'-diphosphate ribosylation-independent pathway.

Pertussis toxin ADP ribosylates G(i) and G(o) transducing proteins and functionally uncouples adenosine A(1) receptor (A(1)AR) from its effectors. We hypothesized that this loss in receptor coupling could lead to de novo A(1)AR synthesis by the cell in a futile attempt to re-establish normal receptor function. To test this hypothesis, we used hamster ductus deferens tumor (DDT(1) MF-2) cells, a cell culture model for studying A(1)AR, and showed that pertussis toxin (100 ng/ml) produced a time-dependent loss in A(1)AR-G(i) interaction and abolished A(1)AR activation of extracellular signal-regulated kinase 1/2. Interestingly, pertussis toxin increased the expression of A(1)AR, as measured by real-time polymerase chain reaction, immunocytochemistry, and [(3)H]cyclopentyl-1,3-dipropylxanthine (DPCPX) binding, suggesting a compensatory response to G(i) protein inactivation. DDT(1) MF-2 cells exposed to pertussis toxin demonstrated nuclear factor kappaB (NF-kappaB) activation within 30 min of exposure, a time point that preceded the loss of function of the A(1)AR. Inhibition of NF-kappaB attenuated the increase in A(1)AR induced by pertussis toxin. Cells exposed to B-oligomer subunit of pertussis toxin, devoid of significant ADP ribosyltransferase activity, showed increased A(1)AR protein expression, preceded by activation of NF-kappaB. B-Oligomer increased intracellular Ca(2+) in DDT(1) MF-2 cells. Chelation of intracellular Ca(2+) with 1,2-bis(2-aminophenoxy)ethane-N,N,N',N'-tetraacetic acid or inhibition of protein kinase C (PKC) with bisindolylmaleimide hydrochloride reduced the activation of NF-kappaB and [(3)H]DPCPX binding. We conclude that pertussis toxin promotes de novo A(1)AR synthesis by activating NF-kappaB through an ADP ribosylation-independent mechanism involving intracellular Ca(2+) release and PKC activation.

Adenosine Diphosphate Ribose↗
PubMed2005

Drebrin A is a postsynaptic protein that localizes in vivo to the submembranous surface of dendritic sites forming excitatory synapses.

Drebrin A is a neuron-specific, actin binding protein. Evidence to date is from in vitro studies, consistently supporting the involvement of drebrin A in spinogenesis and synaptogenesis. We sought to determine whether drebrin A arrives at the plasma membrane of neurons, in vivo, in time to orchestrate spinogenesis and synaptogenesis. To this end, a new antibody was used to locate drebrin A in relation to electron microscopically imaged synapses during early postnatal days. Western blotting showed that drebrin A emerges at postnatal day (PNd) 6 and becomes progressively more associated with F-actin in the pellet fraction. Light microscopy showed high concentrations of drebrin A in the synaptic layers of the hippocampus and cortex. Electron microscopy revealed that drebrin A in these regions is located exclusively in dendrites both neonatally and in adulthood. In adulthood, nearly all of the synaptic drebrin A is within spines forming asymmetric excitatory synapses, verified by gamma-aminobutyric acid (GABA) negativity. At PNd7, patches of drebrin A immunoreactivity were discretely localized to the submembranous surfaces of dendrites forming slight protrusions-protospines. The drebrin A sites exhibited only thin postsynaptic densities and lacked axonal associations or were contacted by axons that contained only a few vesicles. Yet, because of their immunoreactivity to the NR2B subunit of N-methyl-D-aspartate receptors and immunonegativity of axon terminals to GABA, these could be presumed to be nascent, excitatory synapses. Thus, drebrin A may be involved in organizing the dendritic pool of actin for the formation of spines and of axospinous excitatory synapses during early postnatal periods.

Age Factors↗
PubMed2005

Overexpression of drebrin A in immature neurons induces the accumulation of F-actin and PSD-95 into dendritic filopodia, and the formation of large abnormal protrusions.

Drebrin A is a neuron-specific F-actin binding protein, and plays a pivotal role in the spine formation. In this study, we expressed drebrin A tagged with green fluorescent protein (GFP-DA) in hippocampal neurons at 7-9 days in vitro when presynaptic terminals are not fully maturated. GFP-DA was accumulated in dendritic protrusions and formed large abnormal structures. Since these structures were similar to filopodia in terms of lack of MAP2 immunostaining, we named them "megapodia" meaning large dendritic filopodia. F-actin and PSD-95 were also accumulated in megapodia, and their amounts were significantly correlated with that of GFP-DA. However, the expression of GFP-DA did not result in the promotion of the morphological change from filopodia into spines. These results demonstrate that drebrin A accumulates spine-resident proteins via protein-protein interaction in filopodia, and suggest that the spine formation requires the concurrence of the increase of drebrin-A expression and the functional presynaptic contact.

Actins↗
PubMed2005

Overexpression of drebrin A in immature neurons induces the accumulation of F-actin and PSD-95 into dendritic filopodia, and the formation of large abnormal protrusions.

Drebrin A is a neuron-specific F-actin binding protein, and plays a pivotal role in the spine formation. In this study, we expressed drebrin A tagged with green fluorescent protein (GFP-DA) in hippocampal neurons at 7-9 days in vitro when presynaptic terminals are not fully maturated. GFP-DA was accumulated in dendritic protrusions and formed large abnormal structures. Since these structures were similar to filopodia in terms of lack of MAP2 immunostaining, we named them "megapodia" meaning large dendritic filopodia. F-actin and PSD-95 were also accumulated in megapodia, and their amounts were significantly correlated with that of GFP-DA. However, the expression of GFP-DA did not result in the promotion of the morphological change from filopodia into spines. These results demonstrate that drebrin A accumulates spine-resident proteins via protein-protein interaction in filopodia, and suggest that the spine formation requires the concurrence of the increase of drebrin-A expression and the functional presynaptic contact.

Actins↗
PubMed2004

Osmotic diuretics induce adenosine A1 receptor expression and protect renal proximal tubular epithelial cells against cisplatin-mediated apoptosis.

Osmotic diuretics are used successfully to alleviate acute tubular necrosis (ATN) produced by chemotherapeutic agents and aminoglycoside antibiotics. The beneficial action of these agents likely involves rapid elimination of the nephrotoxic agents from the kidney by promoting diuresis. Adenosine A1 receptor (A1AR) subtype present on renal proximal tubular epithelial and cortical collecting duct cells mediates the antidiuretic and cytoprotective actions of adenosine. These receptors are induced by activation of nuclear factor (NF)-kappaB, a transcription factor reported to mediate hyperosmotic stress-induced cytoprotection in renal medullary cells. In this study, we tested the hypothesis that induction of the A1AR in renal proximal tubular cells by NF-kappaB contributes to the cytoprotection afforded by osmotic diuretics. Exposure of porcine renal proximal tubular epithelial (LLC-PK1) cells to mannitol or NaCl produced a significant increase in A1AR. This increase was preceded by adenosine release and NF-kappaB activation. Expression of an IkappaB-alpha mutant, which acts as a superrepressor of NF-kappaB, abrogated the increase in A1AR. Cells exposed to mannitol demonstrated increased reactive oxygen species (ROS) generation, which was attenuated by inhibiting xanthine oxidase with allopurinol. Allopurinol attenuated both the increase in A1AR expression and NF-kappaB activation produced by osmotic diuretics, indicating a role of adenosine metabolites in these processes. Treatment of LLC-PK1 cells with cisplatin (8 microm) resulted in apoptosis, which was attenuated by mannitol but exacerbated by selective A1AR blockade. Administration of mannitol to mice increases A1AR expression and activation of NF-kappaB in renal cortical sections. Taken together, these data provide novel mechanisms of nephroprotection by osmotic diuretics, involving both activation and induction of the A1AR, the latter mediated through activation of a xanthine oxidase pathway leading to ROS generation and promoting activation of NF-kappaB.

Allopurinol↗
PubMed2004

Antisense knockdown of drebrin A, a dendritic spine protein, causes stronger preference, impaired pre-pulse inhibition, and an increased sensitivity to psychostimulant.

Drebrin located in dendritic spines regulates their morphological changes and plays a role in the synaptic plasticity via spine function. Reduced drebrin has been found in the brain of patients with Alzheimer's disease or Down's syndrome. To examine whether the down-regulation of drebrin protein levels causes deficits in higher brain function, such as memory or cognition, we performed antisense-induced knockdown of drebrin A expression in rat brain using an hemagglutinating virus of Japan (HVJ)-liposome gene transfer technique. We investigated the effects of drebrin in vivo knockdown on spatial memory in a water-maze task, sensorimotor gating in a pre-pulse-inhibition test, adaptive behaviors in an open-field test, and sensitivity to psychostimulant in an amphetamine-induced locomotor response. Rats with drebrin A in vivo knockdown displayed a stronger preference for a previous event due to perseverative behavior, impaired pre-pulse inhibition (PPI), increased locomotor activity, anxiety-like behavior, and an increased sensitivity to psychostimulant, suggesting behaviors related to schizophrenia. These findings indicated that decreased drebrin produces deficits in cognitive function but not in spatial memory, probably via hypofunction of dendritic spines.

Adaptation, Psychological↗
PubMed2004

[Synaptic development and abnormality at protein level].

A pyramidal neuron in the adult brain has numerous dendritic spines, which are typical postsynaptic structures. The shapes of spines are abnormal in the case of mental retardation, epilepsy, or Fragile X syndrome. Since the spine is thought to be a fundamental element in synaptic function, the abnormal shape of the spine is thought to be directly associated with brain dysfunction in the above diseases. Spine shape is regulated by each cytoskeletal protein. Over-expression of drebrin, a major actin-binding protein in the spine, elongates the spine. In the brain of Alzheimer's disease and Down syndrome, drebrin is greatly reduced. This indicates the structural abnormality of the spine as pathogenesis in the dementia. Now the spine morphogenesis comes into the spotlight. Although spines are thought to be formed from dendritic filopodia, the conversion mechanism of filopodia to spines has not been fully elucidated. We have recently demonstrated that cluster formation of drebrin-actin complex in filopodia is a key step for this conversion. When the cluster formation is inhibited, PSD-95 is not accumulated at postsynaptic sites. Since the drebrin-A isoform is necessary for the cluster formation, the regulation of drebrin A expression is now a focus in the field of spine formation.

Dementia↗
PubMed2003

Drebrin-dependent actin clustering in dendritic filopodia governs synaptic targeting of postsynaptic density-95 and dendritic spine morphogenesis.

Dendritic spines have two major structural elements: postsynaptic densities (PSDs) and actin cytoskeletons. PSD proteins are proposed to regulate spine morphogenesis. However, other molecular mechanisms should govern spine morphogenesis, because the initiation of spine morphogenesis precedes the synaptic clustering of these proteins. Here, we show that synaptic clustering of drebrin, an actin-binding protein highly enriched in dendritic spines, governs spine morphogenesis. We immunocytochemically analyzed developing hippocampal neurons of low-density cultures. Filopodia-like dendritic protrusions were classified into two types: diffuse-type filopodia, which have diffuse distribution of drebrin, and cluster-type filopodia, which have drebrin clusters with filamentous actin (F-actin). Most cluster-type filopodia were synaptic filopodia. Postsynaptic drebrin clusters were found in both most synaptic filopodia and spines. Postsynaptic PSD-95 clusters, however, were found in only one-half of synaptic filopodia but in most spines. These data indicate that cluster-type filopodia are not mature spines but their precursors. Suppression of the upregulation of drebrin adult isoform (drebrin A) by antisense oligonucleotides against it attenuated synaptic clustering of PSD-95, as well as clustering of drebrin and F-actin. Furthermore, the restoration of drebrin A expression by injection of the expression vectors of drebrin A tagged with green fluorescent protein into the neurons treated with the antisense oligonucleotides induced synaptic reclustering of PSD-95 on clusters of the labeled drebrin A. These data indicated that the synaptic clustering of drebrin is necessary for that of PSD-95 in developing neurons. Together, these data suggest that synaptic clustering of drebrin is an essential step for spine morphogenesis.

Actins↗
PubMed2002

A novel, brain-specific mouse drebrin: cDNA cloning, chromosomal mapping, genomic structure, expression, and functional characterization.

Drebrin A, a major neuronal actin-binding protein, regulates the dendritic spine shapes of neurons. Here, we have cloned and characterized a novel mouse cDNA clone encoding a truncated form of drebrin A, named s-drebrin A. Analysis of the genomic organization of the mouse drebrin gene (Dbn1), which mapped to the central portion of chromosome 13, revealed that isoforms including s-drebrin A are generated by alternative splicing from a single drebrin gene. The s-drebrin A mRNA was expressed in the brain, but not in non-neuronal tissues. The s-drebrin A expression was barely detected in the embryonic brain, but was upregulated during postnatal development of the brain. Overexpression of GFP-tagged s-drebrin A in fibroblasts showed it to be associated with actin filaments and with changes in actin cytoskeleton organization. These findings suggest that s-drebrin A has a role in spine morphogenesis, possibly by competing the actin-binding activity with drebrin A.

Actins↗