Differential promotion of glutamate transporter expression and function by glucocorticoids in astrocytes from various brain regions

Zschocke J, Bayatti N, Clement AM, Witan H, Figiel M, Engele J and Behl C
Source: J Biol Chem
Publication Date: (2005)
Issue: 280(41): 34924-34932
Research Area:
Cells used in publication:
Astrocyte, rat
Species: rat
Tissue Origin: brain
Nucleofector® I/II/2b
Steroids that activate glucocorticoid receptors (GRs) and mineralocorticoid receptors (MRs) have important regulatory effects on neural development, plasticity and the body's stress response. Here, we investigated the role of corticosteroids in regulating the expression of the glial glutamate transporters GLT-1 and GLAST in rat primary astrocytes. The synthetic glucocorticoid dexamethasone provoked a marked increase of GLT-1 transcription and protein levels in cortical astrocytes, whereas GLAST expression remained unaffected. Up-regulation of GLT-1 expression was accompanied by an enhanced glutamate uptake, which could be blocked by the specific GLT-1-inhibitor dihydro-kainate. The promoting effect of dexamethasone on GLT-1 gene expression and function was abolished by the GR antagonist mifepristone. A predominent role of the GR was further supported by the observation that corticosterone could elevate GLT-1 expression in a dose dependent manner, whereas aldosterone, the physiological ligand of the MR, exerted only weak effects even when applied at high concentrations. Moreover, we monitored brain region-specific differences since all corticosteroids used in this study failed to alter the expression of GLT-1 in midbrain and cerebellar glia, although expression levels of both corticosteroid receptor subtypes were similar in all brain regions analyzed. Dexamethasone, however, modestly enhanced GLT-1 expression in cerebellar glia in combination with the DNA methyltransferase inhibitor 5-aza-deoxycytidine, suggesting that suppression of GLT-1 expression in cerebellar cultures may at least in part be epigenetically mediated by a DNA methylation-dependent process. Taken together, our data highlight a potential role for glucocorticoids in regulating GLT-1 gene expression during CNS development or pathophysiogical processes including stress.