Thyroid hormones influence the astroglial plasticity : changes in the expression of glial fibrillary acidic protein (GFAP) and of its encoding message

Normal development of the brain requires the presence of thyroid hormones. To progress in the understanding of the contribution of astrocytes to brain pathophysiology we investigated the effect of T3, on the astroglial plasticity through the expression of two astroglial proteins: the Glial fibrillary acidic protein (GFAP) and the glutamine synthetase (GS). Western and northern blots were performed using astroglial primary cultures initiated from neocortex and cerebellum of new-born mice. Treatment with T3 caused a decrease of GFAP and of its encoding message level in both areas, suggesting a transcriptional regulation of its expression, whereas it had no apparent effect on GS expression. This reduction in GFAP expression was developmentally regulated; it was significant in proliferating but not in more mature astrocytes. T3 effect on astrocytes was higher in the cerebellum compared to the neocortex, suggesting the presence of astroglial subpopulations differing by their sensitivity to T3. The astroglial specific response to T3, corresponds to a precise, targetted and regulated adaptation of the cell. Factors of the microenvironment may modulate this specific astroglial response in vivo.