Glutamine synthetase (GS) expression is reduced in senile dementia of the Alzheimer type.

Glutamine synthetase (GS), a metabolic marker of the mature astrocyte, was investigated in the temporal neocortex of postmortem brain samples of 8 cases, either not demented or affected by senile dementia of the Alzheimer type. A negative correlation between the GS protein level and the density of both classical beta A4 deposits and senile plaques was evidenced. Such a correlation for GS underlies a dysfunction of the astroglial metabolism and particularly of the glutamate and ammonia neutralization. Since GS is sensitive to oxidative lesioning, the changes in GS level that were observed, occurring at the posttranslational stage, might reflect oxidative damage and have severe consequences on the pathological cascade of events.

Expression of glial fibrillary acidic protein and glutamine synthetase genes in the natural scrapie of sheep.

Gene expression of two astroglial markers, glial fibrillary acidic protein (GFAP) and glutamine synthetase (GS), was investigated in cerebellum and brainstem from scrapie-affected sheep. The GFAP and GFAP-mRNA concentrations were increased in the two cerebral regions studied in the scrapie-affected animals as compared to the controls. The good correlation between the increase in GFAP and GFAP-mRNA concentrations found in scrapie-affected sheep indicates a significant de novo synthesis of GFAP in this pathology. In contrast to these results, in scrapie no significant differences in GS-mRNA content appeared in either brain area from scrapie-affected sheep as compared to the controls. This fact could suggest some specificity of GFAP expression changes in this pathology. The overexpression of GFAP gene could be related to a possible interaction between GFAP and scrapie infectious agent in astrocytes. The relative increase in the GFAP and its encoding message in affected animals was higher in the cerebellum than in the brainstem, which would suggest regional comparative differences in the effect here described.

Long-term astroglial reaction to serotonergic fiber degeneration.

Glial fibrillary acidic protein (GFAP) and glutamine synthetase (GS) expression were analysed by Western and Northern blotting in the hippocampus, the frontal and occipital cortex, and the cerebellum of the adult rat, as a manifestation of the astroglial reaction, 2 and 3 months after 5,7-dihydroxytryptamine injection into the lateral ventricule. 5HT injury stimulated GFAP and GS expression in a temporally and regionally specific fashion. At 2 months postlesion, the GFAP-mRNA and GFAP levels appeared enhanced but returned to control levels at 3 months. The GFAP-mRNA and GS-mRNA levels increased in the frontal cortex at 3 months. Such a delayed astroglial reactivity might implicate astrocytes in neurodegenerative disorders.

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.

Alterations of glial fibrillary acidic protein mRNA level in the aging brain and in senile dementia of the Alzheimer type.

The GFAP mRNA levels were compared to the density of the senile plaques (SP) in postmortem brain samples of 8 cases, either non-demented or affected by senile dementia of the Alzheimer type. In the frontal neocortex, the GFAP mRNA level is not affected, even if SP are present. In the temporal neocortex, a positive correlation between GFAP mRNA level and SP density was highly significant. This shows that in this area, astrocytes are altered at transcriptional or post-transcriptional levels, or both. The different responses of this astrogliosis marker in each area may be related to the loss of specific neurotransmitter system.

DBcAMP effect on the expression of GFAP and of its encoding mRNA in astroglial primary cultures.

Short term and chronic dBcAMP effects on the expression of glial fibrillary acidic protein (GFAP) in astroglial primary cultures are investigated. Short (48 h) and long (more than 7 days) treatments with the cAMP derivative induce both cell shape changes and an increase in GFAP immunolabelling. Such effects are only associated with an increase in GFAP and in GFAP-mRNA levels in the long term treatment. These results suggest that the short term effect of dBcAMP induces post-translational modifications of the protein whereas the long term effect is associated with an increase in GFAP mRNA transcription and/or stability.

GFAP turnover during astroglial proliferation and differentiation.

The expression and turnover of the glial fibrillary acidic protein (GFAP) were studied in astroglial primary cultures during postnatal proliferation and maturation. 1. Immunocytochemical studies demonstrated that in immature proliferating astrocytes. GFAP was expressed as a filamentous organized crown around the nucleus whereas in the maturating cells, a GFAP labelled network began to radiate throughout the cytoplasm and GFAP was highly expressed in the astroglial processes. 2. GFAP turnover was studied at 3 periods of culture. The decay of radioactivity from prelabelled GFAP was followed from day 4-12 (immature stage), 11-19 (maturing stage) and 21-29 (morphologically differentiated stage). GFAP displayed a biphasic decay kinetic at each considered period. Two pools of GFAP distinctly appeared. The first one was a fast decaying pool with a half life of 16-18 h and of 5-6 days for the stable one. The unstable pool decreased from 70% to 30% of the total incorporated radioactivity from the proliferating stage to the most mature stage, whereas the stable pool increased proportionally.

Neuron-glia interactions: effect of serotonin on the astroglial expression of GFAP and of its encoding message.

The trophic effect of serotonin on the glial fibrillary acidic protein (GFAP) expression was investigated in rat brainstem astrocytes in primary culture. GFAP immunolabelling decreased and gliofilaments appeared localized in the cytoplasm periphery. GFAP protein level decreased in parallel with a decrease in its encoding message. Serotonin may act as an inhibitor of GFAP expression either on the transcription or on the stability of the GFAP-mRNA.

Expression of tubulin, GFAP and of their encoding mRNAs during the proliferation and differentiation of cultured astrocytes.

The expression of tubulin, of glial fibrillary acidic protein of their encoding mRNAs were studied in primary cultures of mouse astrocytes. The effects of dibutyryl cyclic AMP on these parameters were also analyzed. (1) The concentration of both ?- and ?-tubulin chains markedly increased (3-fold) between 7 and 12 days of culture and then remained at the same high value at later stages. In contrast ?-tubulin mRNA concentration remained constant throughout the same culture period. (2) Glial fibrillary acidic protein concentration increased steadily reaching a 4-fold higher value at the end of the same culture period. The glial fibrillary acidic protein mRNA increased 3-fold during the first 2 weeks of culture, leveled off at day 18 and then decreased steadily returning to low values (3-fold decrease) at later stages. (3) Addition for 2 days, at day 5 or 19 of the culture, of either dibutyryl cyclic AMP or forskolin remained without effect on tubulin concentration whereas a 50% decrease in ?-tubulin mRNA was observed. In the same conditions the effects of these drugs on glial fibrillary acidic protein and its mRNA were not significant. These results suggest that the increase in tubulin concentration seen between days 7 and 12, as well as that of glial fibrillary acidic protein observed during the last weeks of the culture, are not secondary to an increase either of the rate of transcription or of the stability of their encoding mRNAs.