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| Christoph Aufenberg |
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Max-Planck-Institute for neurological Research, Gleueler Str. 50, 50931 Cologne, Germany
e-mail: Christoph.Aufenberg@gmx.de |
Poster Presentation: |
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| ATTEMPTS TO UNDERSTAND THE INHIBITION OF PROTEIN SYNTHESIS AFTER TRANSIENT FOCAL CEREBRAL ISCHEMIA. |
| Christoph Aufenberg and Wulf Paschen | |
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Max-Planck-Institute for neurological Research, Gleueler Str. 50, 50931 Cologne, Germany |
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| Background and Purpose:
Transient cerebral ischemia induces a long lasting inhibition of protein synthesis. Protein synthesis is controlled at the initiation step. Many proteins, so-called initiation factors are involved in the initiation. Changes in their protein level and phosphorylation state may play important roles in the pathological process of the inhibition of protein synthesis.
In this study we investigated four factors and their changes following transient occlusion of the middle cerebral artery (MCAO) and different recirculation times. First we analysed eIF2a, which is –in its phosphorylated form- inactivated and therefore inhibiting the protein synthesis. Then we investigated the p70S6-kinase (S6K). S6K phosphorylates the S6 protein of the 40S subunit of the ribosome. This increases the translation of proteins involved in the cell cycle progression. Additionally the phosphorylation pattern and protein level of the initiation factors eIF2Be and eIF4G1 were analysed.
Methods:
Transient cerebral ischemia was induced by occlusion of the middle cerebral artery for 10min, 30min and 1h with recirculation periods of 0, 1, 3 and 6h.
Brains were frozen and processed for evaluation of the energy state (ATP-bioluminescence). Further on tissue samples were taken from striatum and cortex for analysis of protein levels and phosphorylation states (Western Blotting). Ischemia induced changes of cortical blood flow and the extent of reperfusion was assessed by Laser Doppler flowmetry.
Results:
The initiation factor eIF2a was transiently phosphorylated peaking at 1-3h after ischemia independently of duration of ischemia and extent of reperfusion. Ischemia induced an almost complete dephosphorylation of S6K, irrespective of the duration of vascular occlusion. The phosphorylation state recovered after 1h of reperfusion.
In addition we observed a moderate decrease in the protein level of S6K in brains subjected to 1h ischemia exhibiting the worst reperfusion level.
Conclusions:
Changes in protein levels and phosphorylation states observed during or following ischemia were almost identical in animals subjected to 10min and 1h vascular occlusion.
We have shown before that the protein synthesis rate recovers after 10min ischemia, but not after 1h MCAO.
It can be concluded therefore that changes in protein levels and phosphorylation states of the initiation factors in the present study are not directly related to the long-lasting inhibition of protein synthesis triggered by long periods of vascular occlusions. The pattern of the obeserved changes suggest, that it reflects the respones of cells to severe forms of stress induced by a breakdown of energy metabolism during ischemia. Other mechanisms must be involved in the prolonged inhibition of translation after 1h of vascular occlusion.
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