Epigallocatechin gallate protects nerve growth factor differentiated PC12 cells from oxidative-radical-stress-induced apoptosis through its effect on phosphoinositide 3-kinase/Akt and glycogen synthase kinase-3.
The effects of epigallocatechin gallate (EGCG) on the phosphoinositide 3-kinase (PI3K)/Akt and glycogen synthase kinase-3 (GSK-3) pathway during oxidative-stress-induced injury were studied using H2O2-treated PC12 cells, which were differentiated by nerve growth factor (NGF). Following 100 microM H2O2 exposure, the viability of differentiated PC12 cells (EGCG or z-VAD-fmk pretreated vs. not pretreated) was evaluated the number of viable cell with Trypan blue and 3,4,5-dimethylthiazol-2-yl (MTT). Additionally, expression of cytochrome c, caspase-3, poly(ADP-ribose) polymerase (PARP), PI3K/Akt and GSK-3 was examined using Western blot analyses. EGCG or z-VAD-fmk-pretreated PC12 cells showed an increase of viability compared to untreated PC12 cells, and pretreatment of PC12 cells with either agent induced a dose-dependent inhibition of caspase-3 activation and PARP cleavage. However, inhibition of cytochrome c release was only detected in EGCG-pretreated cells. Upon examination of the PI3K/Akt and GSK-3 upstream pathway, Western blots of EGCG pretreated cells showed decreased immunoreactivity (IR) of Akt and GSK-3 and increased IR of p85a PI3K, phosphorylated Akt and phosphorylated GSK-3. In contrast, no changes were seen in z-VAD-fmk-pretreated cells. These results show that EGCG affects the PI3K/Akt, GSK-3 pathway as well as downstream signaling, including the cytochrome c and caspase-3 pathways. Therefore, it is suggested that EGCG-mediated activation of PI3K/Akt and inhibition of GSK-3 could be a new potential therapeutic strategy for neurodegenerative diseases associated with oxidative injury.