The molecular and functional properties of neurotransmitter ligand-gated ion channels in glial cells were studied, in order to understand their regulation and function in the brain. Studies were carried out to: A. identify the growth factors that regulate glutamate receptor expression in glia, B. characterize the physiological role of glutamate-gated ion channels in glial development, and C. clone a glutamate receptor gene and determine the role of 5' upstream and intragenic DNA elements in the transcriptional regulation of this gene. A. Effects of growth factors on glutamate receptor gene expression. Primary cultures of rat oligodendrocyte progenitors (O-2A) were used as a model system. Kainate-and AMPA-preferring glutamate receptors are co-expressed in O-2A cells. Platelet-derived and basic fibroblast growth factors selectively up-regulated GluR1 mRNA and protein, through an increase in the gene transcription rate. This corresponded to an increase in AMPA receptor density and an increased number of glutamate-gated channels that did not contain the subunit GluR2. B. Physiological properties and functional role. AMPA receptor activation inhibits O-2A cell proliferation and prevents lineage progression at early developmental stages. These effects are due to a Na+--dependent block of voltage-dependent K= channels. AMPA and muscarinic receptors trigger intracellular Ca2+ transients in O-2A cells and stimulate Ca2+ -dependent phosphorylation of the transcription factor CREB. Growth factors promote CREB phosphorylation independently of extracellular Ca2+. The MAP Kinase/RSK was identified as the intracellular pathway of CREB phosphorylation in O-2A cells. C. Glutamate receptor genes and analysis of their 5' regulatory region. Genes encoding kainate receptor subunits are highly expressed in cells of the oligodendrocyte lineage. The cloning of the entire rat GRIK5 gene, which encodes the kainate preferring subunit KA2 was completed, including 4 kb of its upstream region. The intron-exon organization of this gene was determined, and a negative regulatory DNA element residing within intron 1 was partially characterized. The transcriptional potential of 2kb of GRIK5 upstream region was analyzed in transgenic mice and found to be sufficient to confer tissue-specific reporter gene expression.
| 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 |
