Etude des mécanismes de l'action des oestrogènes et des glucocorticoïdes dans différents modèles de mort neuronale in vitro

CAEN-BU Sciences et STAPS (141182103) / SudocSudocFranceF

Dexamethasone enhances glutamine synthetase activity and reduces N-methyl-D-aspartate neurotoxicity in mixed cultures of neurons and astrocytes

Astrocytes are claimed to protect neurons against excitotoxicity by clearing glutamate from the extracellular space and rapidly converting it into glutamine. Glutamine, is then released into the extracellular medium, taken up by neurons and transformed back into glutamate which is then stored into synaptic vesicles. Glutamine synthetase (GS), the key enzyme that governs this glutamate/glutamine cycle, is known to be upregulated by glucocorticoids. In the present work we have thus studied in parallel the effects of dexamethasone on glutamine synthetase activity and NMDA-induced neuronal death in cultures derived from the brain cortex of murine embryos. We showed that dexamethasone was able to markedly enhance GS activity in cultures of astrocytes but not in near pure neuronal cultures. The pharmacological characteristics of the dexamethasone action strongly suggest that it corresponds to a typical receptor-mediated effect. We also observed that long lasting incubation (72 h) of mixed astrocyte-neuron cultures in the presence of 100 nM dexamethasone significantly reduced the toxicity of NMDA treatment. Furthermore we demonstrated that methionine sulfoximine, a selective inhibitor of GS, abolished the dexamethasone-induced increase in GS activity and also markedly potentiated NMDA toxicity. Altogether these results suggest that dexamethasone may promote neuroprotection through a stimulation of astrocyte glutamine synthetase

Estrogen receptor alpha mediates neuronal differentiation and neuroprotection in PC12 cells: critical role of the A/B domain of the receptor.

International audienceNumerous studies, both in vivo and in vitro, have reported neuronal differentiating and neuroprotective actions of estrogens. Most of these estrogenic effects are mediated through specific receptors termed estrogen receptors. The aim of this study was to assess the importance of the N-terminal A/B domain of the estrogen receptor-alpha (ER alpha) in its neuronal aspects. Consequently, estrogen effects on (i) the transcriptional activity of target genes, (ii) neuronal differentiation and (iii) neuroprotection in PC12 cells transfected with either a full length form of ER alpha or an A/B domain truncated form (ER alphaCF), have been studied. We demonstrate that the maximal estrogen-induced transcriptional activity of reporter genes requires a full length ER alpha, especially when cells are differentiated. Precisely, the transcriptional activity of ER alpha in differentiated cells relies, predominantly, on the activation function AF-1, located in the A/B domain. Furthermore, in PC12 cells stably expressing ER alpha, 17beta-estradiol markedly enhances the neurite outgrowth triggered by treatment with nerve growth factor and protects cells from oxidative shocks induced by depletion of glutathione. These estrogenic effects are not observed in non-transfected cells and in cells transfected with the truncated ER, devoid of the A/B domain. Altogether, these results underline the importance of the A/B domain of ER alpha in both the differentiating and the neuroprotective effects of estrogens