Glutamate-stimulated production of inositol phosphates is mediated by Ca2+ influx in oligodendrocyte progenitors
Introduction
Glutamate, the major excitatory neurotransmitter in the mammalian central nervous system, binds to two groups of receptors classified into ionotropic and metabotropic receptors. Ionotropic receptors are ligand-gated ion channels which further subdivide into N-methyl-d-aspartate (NMDA), α-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid (AMPA), and kainate receptors according to their agonist selectivity. Activation of ionotropic receptors opens ion channels permeable to Na+, K+ and Ca2+. Glutamate also activates metabotropic receptors coupled through G-proteins to second messenger pathways. Their activation increases phospholipase C activity which hydrolyses phosphatidylinositol-4,5-bisphosphate (PIP2) into inositol 1,4,5-trisphosphate (IP3) and diacylglycerol. IP3 mobilizes intracellular Ca2+ ([Ca2+]i) while diacylglycerol activates protein kinase C. Recent cloning and expression studies have identified several genes encoding glutamate receptor subunits that are expressed extensively in central nervous system neurons and glia (for review, see Hollmann and Heinemann, 1994; Gallo et al., 1995).
It is well established that cells of the oligodendrocyte lineage express glutamate-gated ion channels both in culture and in situ (for review, see Gallo and Russell, 1995). Glutamate and related agonists depolarize oligodendrocytes and their progenitors through ionotropic non-NMDA (AMPA/kainate) receptors (Barres et al., 1990; Wyllie et al., 1991; Borges et al., 1994; Gallo et al., 1994b; Holzwarth et al., 1994). The analysis of glutamate receptor currents in single cells revealed different desensitization kinetics and affinity for agonists, suggesting the co-expression of functional AMPA- and kainate-preferring receptors (Gallo et al., 1994b; Patneau et al., 1994). Furthermore, molecular analysis of glutamate receptors in oligodendrocyte progenitors has demonstrated the expression of AMPA- and kainate-preferring subunit mRNAs and proteins (Jensen and Chiu, 1993; Gallo et al., 1994a, Gallo et al., 1994b; Holzwarth et al., 1994; Patneau et al., 1994; Yoshioka et al., 1995; Garcia-Barcina and Matute, 1996). Ca2+-imaging experiments, in antigenically identified cultured oligodendrocyte progenitors, further supported the electrophysiological studies showing that activation of AMPA or kainate receptors produced large and transient increases in [Ca2+]i (Holzwarth et al., 1994; Holtzclaw et al., 1995; Pende et al., 1994; Meucci et al., 1996). More recent studies have also provided evidence for the presence of metabotropic (Holtzclaw et al., 1995) and NMDA (Wang et al., 1996) receptors in oligodendrocyte progenitors obtained from cortical and neurohypophysial cultures, respectively.
The potential functions of glutamate receptors in oligodendrocyte progenitors are beginning to be elucidated. Thus, NMDA receptors in neurohypophysial explant cultures play a critical role in oligodendrocyte progenitor migration and regulate polysialic acid-neural cell adhesion molecule expression (Wang et al., 1996). On the other hand, prolonged activation of kainate-responsive non-NMDA receptors mediates excitotoxicity in cells of the oligodendroglial lineage when exposed to millimolar concentrations of the agonist (Yoshioka et al., 1995). We and others have recently shown that glutamate, at concentrations which are not toxic to the cells, inhibited proliferation through activation of AMPA or kainate receptors, suggesting a role in cellular development (Liu and Almazan, 1995; Gallo et al., 1996). In addition, activation of AMPA or kainate receptors increased the expression of the immediate early genes NGFI-A (Gallo et al., 1994b; Pende et al., 1994) and c-fos (Pende et al., 1994; Liu and Almazan, 1995). Since glutamate-induced c-fos expression was dependent both on extracellular calcium influx and downstream protein kinase C activation (Liu and Almazan, 1995), it was of interest to further elucidate the molecular events linking receptor activation to gene expression. The objective of the present study was to determine whether phospholipase C participates in the signaling cascade initiated by glutamate in oligodendrocyte progenitors and the role of extracellular calcium.
We have found that stimulation of AMPA receptors causes activation of phospholipase C through a mechanism that requires influx of calcium from the extracellular milieu. Cyclothiazide, an agent which blocks desensitization of the AMPA receptors, in combination with AMPA or kainate produced a large increase in a2+ uptake and potentiated the effects of the agonists on PI hydrolysis.
Section snippets
Materials
l-glutamic acid, (±)-α-amino-3-hydroxy-5-methyl-isoxazole-4-propionic acid (AMPA), kainic acid, trans-(1S,3R)-1-amino-1,3-cyclopentanedicarboxylic acid (ACPD), N-methyl-d-aspartic acid (NMDA), quisqualate, (5R,10S)-(+)-5-methyl-10,11-dihydro-5H-dibenzo[a,d]cyclo-hepten-5,10-imine (MK-801), 6-cyano-7-nitro-quinoxaline-2,3-dione (CNQX), R(−)-3-(2-carboxypiperazin-4-yl)-propyl-1-phosphonic acid (CPP), l(+)-2-amino-3-phosphono-propanoic acid (l-AP3), GYKI 52466, α-methyl-4-carboxyphenylglycine
Effects of glutamate agonists on [3H]IPs accumulation: Concentration and time-dependency
Exposure of progenitors to glutamate at a range of concentrations from 1 to 1000 μM for 15 min caused a concentration-dependent increase in the accumulation of []IP3 (Fig. 1) as well as other inositol phosphate metabolites including []IP1, []IP2 and []IP4 (data not shown). Glutamate was the most potent activator of phosphoinositide hydrolysis (EC50 =27 μM), causing a maximal increase in []IP3 formation at 1 mM (315% of basal level); it was followed by AMPA (EC50 =34 μM) which achieved
Discussion
In this paper we report that (1) activation of AMPA receptors in cultured oligodendrocyte progenitors leads to the formation of []inositol phosphates (IPs) in a time- and concentration-dependent manner, (2) the increases in []IPs are dependent on extracellular Ca2+ influx, (3) cyclothiazide strongly potentiates the AMPA- and kainate-stimulated formation of []IPs as well as 2+ uptake and (4) both voltage-dependent Ca2+ channels and the Na+/Ca2+ exchanger are implicated in AMPA
Acknowledgements
The present study was funded by a grant from the Medical Research Council of Canada to G.A. H.N.L. was supported by a studentship from the Multiple Sclerosis Society of Canada. E.M.H. was supported by a postdoctoral fellowship from the Ministry of Education and Science of Spain. We thank Dr. W.E. Mushynski for edition of the manuscript. 3,4-Dichlorobenzamil was provided by Research Biochemicals International as part of the Chemical Synthesis Program of the National Institute of Mental Health,
References (53)
- et al.
Ion channel expression by white matter glia: The oligodendrocyte glial progenitor cell
Neuron
(1990) - et al.
AMPA/kainate receptor activation in murine oligodendrocyte precursor cells leads to activation of a cation conductance, calcium influx and blockade of delayed rectifying K+ channels
Neuroscience
(1994) - et al.
Carbachol stimulates c-fos expression and proliferation in oligodendrocyte progenitors
Mol. Brain Res.
(1996) - et al.
The calcium response to the excitotoxin kainate is amplified by subsequent reduction of extracellular sodium
Neuroscience
(1995) - et al.
Intracellular Ca2+ activates phospholipase C
Trends Neurosci.
(1988) - et al.
Glutamate impairs neuronal calcium extrusion while reducing sodium gradient
Neuron
(1994) - et al.
Glial cells of the oligodendrocyte lineage express both kainate- and AMPA-preferring subtypes of glutamate receptor
Neuron
(1994) - et al.
Further characterization of excitatory amino acid receptors coupled to phosphoinositide metabolism in astrocytes
Neurosci. Lett.
(1990) - et al.
Selective antagonism of AMPA receptors unmasks kainate receptor-mediated responses in hippocampal neurons
Neuron
(1995) - et al.
Protein kinases mediate basic fibroblast growth factor's stimulation of proliferation and c-fos induction in oligodendrocyte progenitors
Mol. Brain Res.
(1994)
Calcium signalling in glial cells
Trends Neurosci.
Phosphorylation and disruption of intermediate filament proteins in oligodendrocyte precursor cultures treated with calyculin A
J. Neurosci. Res.
Activation of mitogen-activated protein kinase in oligodendrocyte progenitors by muscarinic or AMPA/KA receptor activation
Am. Soc. Neurochem.
Increased intracellular calcium stimulates -inositol polyphosphate accumulation in rat cerebral cortical slices
J. Neurochem.
AMPA-type glutamate receptors in glial precursor cells of the rat corpus callosum: Ionic and pharmacological properties
Glia
Changes in the levels of inositol phosphates after agonist-dependent hydrolysis of membrane phosphoinositides
Biochem. J.
Cooperation between two growth factors promotes extended self-renewal and inhibits differentiation of oligodendrocyte-type-2-astrocyte (O-2A) progenitor cells
Proc. Natl. Acad. Sci. USA
Blockade of K+ channels induced by AMPA/kainate receptor activation in mouse oligodendrocyte precursor cells is mediated by Na+ entry
J. Neurosci. Res.
Calcium- versus G protein-mediated phosphoinositide hydrolysis in rat cerebral cortical synaptoneurosomes
J. Neurochem.
Rat oligodendrocytes express muscarinic receptors coupled to phosphoinositide hydrolysis and adenylyl cyclase
Eur. J. Neurosci.
Regulation of phosphoinositide phospholipases by hormones, neurotransmitters, and other agonists linked to G proteins
Annu. Rev. Pharmacol. Toxicol.
Visualization of O-2A progenitor cells in developing and adult rat optic nerve by quisqualate-stimulated cobalt uptake
J. Neurosci.
Expression and regulation of a glutamate receptor subunit by bFGF in oligodendrocyte progenitors
Glia
Excitatory amino acid receptors in glial progenitor cells: Molecular and functional properties
Glia
Excitatory amino acid receptors in glia: Different subtypes for distinct functions?
J. Neurosci. Res.
Expression and regulation of kainate and AMPA receptors in uncommitted and committed neural progenitors
Neurochem. Res.
Cited by (33)
Neuron-glial interactions and neurotransmitter signaling to cells of the oligodendrocyte lineage
2020, Patterning and Cell Type Specification in the Developing CNS and PNS: Comprehensive Developmental Neuroscience, Second EditionAgonist-induced down-regulation of AMPA receptors in oligodendrocyte progenitors
2014, NeuropharmacologyNeuron-Glial Interactions: Neurotransmitter Signaling to Cells of the Oligodendrocyte Lineage
2013, Comprehensive Developmental Neuroscience: Patterning and Cell Type Specification in the Developing CNS and PNSIon channels in autoimmune neurodegeneration
2011, FEBS LettersCitation Excerpt :By means of electron microscopy, these α1B-subunits were found to be located in the axonal membrane and thus might mediate an increased neuronal calcium influx. Based on these findings and together with the fact that calcium channels are present on oligodendrocytes [57] and axons [58] – both key targets in autoimmune demyelination –, EAE mice were treated with two different calcium channel blockers, bepridil and nitrendipine. Both drugs, although different in many structural and functional respects, block calcium influx through L-type calcium channels (Cav1.2, Cav1.3, Cav1.4).
Calcium and glial cell death
2005, Cell CalciumCalcium channel blockers ameliorate disease in a mouse model of multiple sclerosis
2004, Experimental Neurology