The molecular and functional properties of neurotransmitter receptors, ligand-gated channels and voltage-dependent channels in glial cells were studied, in order to understand their regulation and physiological role in the brain. Studies were carried out to: A. define the physiological role of glutamate receptors (GluRs) and voltage-dependent K+ channels in oligodendrocyte development, B. study expression of noradrenergic receptors in cells of the oligodendrocyte lineage, and define their role in development, C. analyze the role of different 5' upstream DNA elements in the transcriptional regulation of a GluR gene, D. characterize an intronic silencer of this GluR gene and identify the repressor proteins. (A) Physiological role of glutamate receptors in oligodendrocyte development. In cerebellar slice cultures, GluR agonists decreased the number of oligodendrocyte (O-2A) progenitor cells and their proliferation, and the number of differentiated oligodendrocytes. A GluR antagonist had opposite effects. mRNA transcripts of the oligodendrocyte gene 2',3'-cyclic nucleotide 3'-phosphodiesterase were significantly decreased by GluR agonists and increased by the antagonist. (B) Noradrenergic receptors in cells of the oligodendrocyte lineage. Selective activation of beta- adrenergic receptors with isoproterenol (Iso) increased cAMP levels in O-2A cells, inhibited their proliferation and stimulated their differentiation. Long-term treatment of O-2A cells with Iso decreased outward K+ current density and caused a rightward shift in the voltage-dependence of activation. 8-Br-cAMP mimicked all the effects of Iso. (C) Analysis of DNA elements in the 5' upstream region of a glutamate receptor gene. Two Sp1 consensus binding sites and an AP-2 site present in the rat GluR gene GRIK5 promoter region are specifically bound by nuclear proteins extracted from the glial cells. In transgenic mice, 2 kb of GRIK5 upstream region conferred tissue-specific reporter gene expression. The cellular pattern of the transgene in cerebral cortex mimicked that of the endogenous gene. (D) Identification of proteins that act as repressors of transcription of a glutamate receptor gene. A silencer present in intron 1 of the GRIK5 gene was characterized as two consensus direct repeats of AGGTCA. By using the one-hybrid system, several cDNAs corresponding to members of the nuclear orphan receptor family were cloned. In vitro translation of these cloned inserts generated products which bind to the direct repeats of intron 1.
| Gallo, V; Ghiani, C A (2000) Glutamate receptors in glia: new cells, new inputs and new functions. Trends Pharmacol Sci 21:252-8 |
| Ghiani, C A; Yuan, X; Eisen, A M et al. (1999) Voltage-activated K+ channels and membrane depolarization regulate accumulation of the cyclin-dependent kinase inhibitors p27(Kip1) and p21(CIP1) in glial progenitor cells. J Neurosci 19:5380-92 |
