Dm. Jiang et al., Caspase 3 inhibition attenuates hydrogen peroxide-induced DNA fragmentation but not cell death in neuronal PC12 cells, J NEUROCHEM, 76(6), 2001, pp. 1745-1755
Exposure of neurons to H2O2 results in both necrosis and apoptosis. Caspase
s play a pivotal role in apoptosis, but exactly how they are involved in H2
O2-mediated cell death is unknown. We examined H2O2-induced toxicity in neu
ronal PG12 cells and the effects of inducible overexpression of the H2O2-sc
avenging enzyme catalase on this process. H2O2 caused cell death in a time-
and concentration-dependent manner. Cell death induced by H2O2 was found t
o be mediated in part through an apoptotic pathway as H2O2-treated cells ex
hibited cell shrinkage, nuclear condensation and marked DNA fragmentation.
H2O2 also triggered activation of caspase 3. Genetic up-regulation of catal
ase not only significantly reduced cell death but also suppressed caspase 3
activity and DNA fragmentation. While the caspase 3 inhibitor DEVD inhibit
ed both caspase 3 activity and DNA fragmentation induced by H2O2 it did not
prevent cell death. Treatment with the general caspase inhibitor ZVAD, how
ever, resulted in complete attenuation of H2O2-mediated cellular toxicity.
These results suggest that DNA fragmentation induced by H2O2 is attributabl
e to caspase 3 activation and that H2O2 may be critical for signaling leadi
ng to apoptosis. However, unlike inducibly increased catalase expression an
d general caspase inhibition both of which protect cells from cytotoxicity,
caspase 3 inhibition alone did not improve cell survival suggesting that p
revention of DNA fragmentation is insufficient to prevent H2O2-mediated cel
l death.