Biomedical subjects

Kaoru Inokuchi

Publications and source records attributed to Kaoru Inokuchi.

24 records · Page 2Linked to original sources

PubMed2003

Hippocampal LTP is accompanied by enhanced F-actin content within the dendritic spine that is essential for late LTP maintenance in vivo.

The dendritic spine is an important site of neuronal plasticity and contains extremely high levels of cytoskeletal actin. However, the dynamics of the actin cytoskeleton during synaptic plasticity and its in vivo function remain unclear. Here we used an in vivo dentate gyrus LTP model to show that LTP induction is associated with actin cytoskeletal reorganization characterized by a long-lasting increase in F-actin content within dendritic spines. This increase in F-actin content is dependent on NMDA receptor activation and involves the inactivation of actin depolymerizing factor/cofilin. Inhibition of actin polymerization with latrunculin A impaired late phase of LTP without affecting the initial amplitude and early maintenance of LTP. These observations suggest that mechanisms regulating the spine actin cytoskeleton contribute to the persistence of LTP.

Actin Depolymerizing Factors↗

PubMed2003

Differential functional interaction of two Vesl/Homer protein isoforms with ryanodine receptor type 1: a novel mechanism for control of intracellular calcium signaling.

Vesl/Homer proteins physically link proteins that mediate cellular signaling [Curr. Opin. Neurobiol. 10 (2000) 370; Trends Neurosci. 23 (2000) 80; J. Cell Sci. 113 (2000) 1851] and thereby influence cellular function [Nat. Neurosci. 4 (2001) 499; Nature 411 (2001) 962]. A previous study reported that Vesl-1L/Homer-1c (V-1L) controls the gain of the intracellular calcium activated calcium channel ryanodine receptor type 1 (RyR1) channel [J. Biol Chem. 277 (2002) 44722]. Here, we show that the function of RyR1 is differentially regulated by two isoforms of Vesl-1/Homer-1, V-1L and Vesl-1S/Homer-1a (V-1S). V-1L increases the activity of RyR1 while important regulatory functions and pharmacological characteristics are preserved. V-1S alone had no effect on RyR1, even though, like V-1L, it is directly bound to the channel. However, V-1S dose-dependently decreased the effects of V-1L on RyR1, providing a novel mechanism for the regulation of intracellular calcium channel activity and calcium homeostasis by changing expression levels of Vesl/Homer proteins.

Animals↗

PubMed2003

Vesl/Homer proteins regulate ryanodine receptor type 2 function and intracellular calcium signaling.

Cellular signaling proteins such as metabotropic glutamate receptors, Shank, and different types of ion channels are physically linked by Vesl (VASP/Ena-related gene up-regulated during seizure and LTP)/Homer proteins [Curr. Opin. Neurobiol. 10 (2000) 370; Trends Neurosci. 23 (2000) 80; J. Cell Sci. 113 (2000) 1851]. Vesl/Homer proteins have also been implicated in differentiation and physiological adaptation processes [Nat. Neurosci. 4 (2001) 499; Nature 411 (2001) 962; Biochem. Biophys. Res. Commun. 279 (2000) 348]. Here we provide evidence that a Vesl/Homer subtype, Vesl-1L/Homer-1c (V-1L), reduces the function of the intracellular calcium channel ryanodine receptor type 2 (RyR2). In contrast, Vesl-1S/Homer-1a (V-1S) had no effect on RyR2 function but reversed the effects of V-1L. In live cells, in calcium release studies and in single-channel electrophysiological recordings of RyR2, V-1L reduced RyR2 activity. Important physiological functions and pharmacological properties of RyR2 are preserved in the presence of V-1L. Our findings demonstrate that a protein-protein interaction between V-1L and RyR2 is not only necessary for organizing the structure of intracellular calcium signaling proteins [Curr. Opin. Neurobiol. 10 (2000) 370; Trends Neurosci. 23(2000)80; J. Cell Sci. 113 (2000) 1851; Nat Neurosci. 4 (2001) 499; Nature 411 (2001) 962; Biochem. Biophys. Res. Commun. 279 (2000) 348; Nature 386 (1997) 284], but that V-1L also directly regulates RyR2 channel activity by changing its biophysical properties. Thereby it may control cellular calcium homeostasis. These observations suggest a novel mechanism for the regulation of RyR2 and calcium-dependent cellular functions.

Aniline Compounds↗

PubMed2003

Homer-1a/Vesl-1S enhances hippocampal synaptic transmission.

Homer/Vesl proteins are involved in regulating metabotropic glutamate receptors, synaptogenesis, dendritic spine development and axonal pathfinding. We investigated the potential modulation of glutamatergic synaptic transmission by the immediate early gene product Homer-1a/Vesl-1S and by the constitutively expressed long-form Homer-1c/Vesl-1L in CA1 pyramidal cells from cultured rat hippocampal slices. Semliki Forest virus vector-mediated overexpression of Homer-1a enhanced alpha-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid (AMPA) receptor function, but did not detectably affect N-methyl-d-aspartate (NMDA) receptor function and presynaptic glutamate release. Overexpression of Homer-1c, by contrast, did not alter synaptic transmission. To corroborate our electrophysiological results obtained in slice cultures, we performed quantitative immunocytochemistry in cultures of dissociated hippocampal neurons. Homer-1a also increased synaptic clustering of AMPA but not NMDA receptors, whereas Homer-1c had no detectable effect. Our results show that Homer-1a potentiates synaptic AMPA receptor function, supporting a critical role for Homer-1a in hippocampal synaptic plasticity.

Animals↗

PubMed2003

Functional analysis of basic transcription element binding protein by gene targeting technology.

Basic transcription element binding protein (BTEB) is a transcription factor with a characteristic zinc finger motif and is most remarkably enhanced by thyroid hormone T(3) treatment (R. J. Denver et al., J. Biol. Chem. 272:8179-8188, 1997). To investigate the function of BTEB per se and to touch on the effects of T(3) (3,5,3'-triiodothyronine) on mouse development, we generated BTEB-deficient mice by gene knockout technology. Homologous BTEB(-/-) mutant mice were bred according to apparently normal Mendelian genetics, matured normally, and were fertile. Mutant mice could survive for at least 2 years without evident pathological defects. From the expression of lacZ, which was inserted into the reading frame of the BTEB gene, BTEB showed a characteristic tissue-specific expression profile during the developmental process of brain and bone. Dramatically increased expression of BTEB was observed in Purkinje cells of the cerebellum and pyramidal cell layers of the hippocampus at P7 when synapses start to form in the brain. Although general behavioral activities such as locomotion, rearing, and speed of movement were not so much affected in the BTEB(-/-) mutant mice, they showed clearly reduced activity levels in rotorod and contextual fear-conditioning tests; this finding was probably due to defective functions of the cerebellum, hippocampus, and amygdala.

Amygdala↗

PubMed2003

Estrogen protects the inner retina from apoptosis and ischemia-induced loss of Vesl-1L/Homer 1c immunoreactive synaptic connections.

PURPOSE: Protective effects of estrogen on nerve cells including retinal neurons have been described previously. However, subcellular effects on synaptic connectivity in mild ischemia more closely resembling ischemic conditions found in diabetic or sickle cell retinopathy and stenosis of the carotid artery have not been identified. The present study quantitatively analyzed effects of estrogen administration on synaptic connections of neurons in the ganglion cell layer (GCL) of the retina. METHODS: Staining of Vesl-1L/Homer 1c (V-1L) immunoreactivity and TUNEL cytochemistry were used to quantify neuroprotective effects at the synaptic level in a model of mild retinal ischemia induced by temporary middle cerebral artery occlusion in the adult rat. RESULTS: V-1L immunoreactivity was found in both synaptic layers, postsynaptic to glutamatergic ribbon synapses. Mild retinal ischemia led to a significantly higher percentage reduction in the number of V-1L-positive synapses in the inner plexiform layer (IPL) compared with the percentage of TUNEL-positive apoptotic neurons in the GCL. Estrogen prevented ischemia-induced loss of V-1L-immunoreactive synapses in the IPL and apoptosis of cells in the GCL. CONCLUSIONS: Immunoreactivity for V-1L can be used as a synaptic marker for early changes before more severe neurodegenerative events. The present results suggest that estrogen protects neurons in the GCL including RGCs from both apoptosis and early changes in synaptic connections associated with ischemia and potentially preceding apoptosis.

Animals↗