αB-crystallin suppresses oxidative stress-induced astrocyte apoptosis by inhibiting caspase-3 activation

αB-crystallin is a member of the small heat shock proteins, which is abundantly expressed in various vertebrate tissues including the central nervous system. In our previous report, we showed αB-crystallin induction in activated astrocytes in the postischemic brain and in H₂O₂-treated primary astrocyte cultures. To investigate the functional significance of αB-crystallin induction in astrocytes, we generated a stable C6 astroglioma cell line overexpressing αB-crystallin. In these cells, hydrogen peroxide-induced apoptosis was reduced by 60% compared to parent cells. Furthermore, the repression of αB-crystallin expression by αB-crystallin siRNA transfection suppressed this protective effect, indicating that αB-crystallin is responsible for the protection against H₂O₂-induced apoptosis in C6 astroglioma cells. Similar level of aggravation in H₂O₂-induced apoptosis was observed in primary astrocyte cultures when αB-crystallin expression was suppressed by αB-crystallin siRNA transfection, confirming the importance of αB-crystallin. In addition, the induction of caspase-3 activity after H₂O₂ treatment was markedly suppressed in αB-crystallin-overexpressing cells, and immunoprecipitation proved binding between αB-crystallin and partially processed caspase-3 (a p24 intermediate). These results indicate that αB-crystallin confers protection against hydrogen peroxide-induced astrocytes apoptosis in part by inhibiting caspase-3 activation.