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Activation of Erk1/2 and Akt in astrocytes under ischemia

Authors Zhang, Yun
Issue Date 2002
Summary Astrocytes have the capacity for reducing ischemic injury to other cells in the central nervous system (CNS). Understanding of intracellular signaling systems triggered by ischemic injury in astrocytes is of great clinical significance. In this study, we investigate the activities of two cell-proliferation-and-survival-related kinases, extracellular signal-regulated kinase1/2 (Erk1/2) and serine threonine kinase (Akt) in primary culture of astrocytes under in vitro ischemia model. Western blots shows that Erk1/2 and Akt are both activated in astrocytes under ischemia. The level of phosphorylated Erk1/2 (p-Erk1/2) in astrocytes begins to increase at 1 hour of ischemia, reaches to the highest level at 4 hour of ischemia, and then declines at 5 and 6 hour of ischemia. Though it is not increased as early as that of Erk1/2, the level of phosphorylated Akt (p-Akt) also goes up significantly at 4 hour of ischemia and drops afterwards. U0126 and LY294002 are used to block the activation of Erk1/2 and Akt, respectively. Hoechst nucleic staining and lactate dehydrogenase (LDH) assay indicate that U0126 promotes ischemia-induced cell death of astrocytes, whereas LY294002 delays the cell death. Western blot showed that, in U0126 treated astrocytes, the expression level of Bc1-2 is down-regulated at 4 and 6 hour ischemia. In LY294002 treated astrocytes, however, the expression level of Bc1-2 is up-regulated. The expression level of Bc1-XL remains unchanged in both cases. We then investigate the activation of Erk1/2 and Akt in astrocytes of different developmental stage, since previous study found that young culture of astrocytes had stronger capability to tolerate ischemic injury. By western blot experiments, we find that the expression levels of p-Erk1/2 and p-Akt are both decreased, which may reflect the different tolerance of developmental astrocytes to ischemic injury. In addition, Erk1/2 and Akt are both activated by glial cell line-derived neurotrophic factor (GDNF) pre-treatment in astrocytes under 5 hour of ischemia. At this time point, GDNF is found to have the protective effect on astrocytes, as shown by Hoechst nucleic staining and LDH assay. Western blot results demonstrate that the protein level of Bcl-2 expression is increased, while the level of Bc1-XL expression is not affected. These findings suggest that activation of MEK/Erk1/2 pathway may protect astrocytes from ischemic injury, but activation of PI3K/Akt pathway may not. They may both exert their effects by regulating protein expression of Bc1-2, not Bc1-XL. Besides, GDNF protects astrocytes against ischemic injury, possibly through regulating Bc1-2. Erk1/2 and Akt activation may be also involved in this protective effect.
Note Thesis (M.Phil.)--Hong Kong University of Science and Technology, 2002
Language English
Format Thesis
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