Partenaires et organisations internationales
(Anglais)
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CNR Pisa; Ares-serono (formerly Glaxo-
wellcome, Geneva), University of Paris VI, University of Oxford, Charing cross and Westminster medical school, London
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Résumé des résultats (Abstract)
(Anglais)
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Molecular mechanisms of neuronal death studied in vivo
The overall aim of this project was to identify the cellular mechanisms of axotomy-induced and naturally-occurring neuronal death in vivo. Our experimental model was retinal ganglion cell death in chick embryos, which occurs naturally between embryonic days 12 and 16, and is greatly exacerbated 16-48 hours after a tectal lesion. Our approach was primarily pharmacological, and in most experiments we tested the ability of intraocularly injected agents to modify the extent of retinal ganglion cell death.
In the first two years we studied the roles of the redox status and cell cycle mechanisms, showing that the axotomy-induced neuronal death can be reduced by various antioxidants or by inhibitors of cyclin-dependent kinases.
In the third year we have focused on the effects of the redox-sensitive transcription factor NF-kappaB, which appears to provide a link between the redox status and cell cycle mechanisms. We had previously shown that axotomy-induced cell death is reduced by the intraocular injection of the translational inhibitor cycloheximide (CX). One possible explanation of CX's protection is that the resulting blockade of protein synthesis might increase the level of free amino acids in the cytosol, and hence augment the synthesis of glutathione, leading to improved antioxidant defence. We therefore tested whether partial inhibition of glutathione synthesis by intraocularly injected BSO would eliminate the protective effect of CX. Contrary to expectation, when CX was given 16 h after axotomy, and BSO 8 or 16 h earlier, the BSO increased the protection. Probably, the mild oxidative stress induced by BSO stimulates an increase in the cellular defences. This might involve redoxsensitive transcription factors, so we tested the role of one of these, NF-kappaB. In the absence of other pharmacological agents, inhibitors of NF-kappaB produced a modest neuroprotection. However, in combination with BSO and CX, in precisely the situation where BSO was protective, the NF-kappaB inhibitors greatly increased the cell death. We have developed a model explaining these results including the dual effects of NF-kappaB. According to this model, axotomy (after a delay) and BSO both increase the production of reactive oxygen species, leading to the activation of NF-kappaB, which activates one death pathway but inhibits another.
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