Transient oxidative stress in SH-SY5Y human neuroblastoma cells results incaspase dependent and independent cell death and tau proteolysis

The effects of an oxidative insult on cell survival and tau metabolism were investigated in human neuroblastoma SH-SY5Y cells. In this treatment parad igm cells were exposed to the membrane permeant oxidant tert-butylhydropero xide (tBHP) for 40 min, returned to fresh media and cell survival/death was monitored during the post-treatment period. Cell viability decreased signi ficantly by 6 hr after tBHP exposure, and by 24 hr lactate dehydrogenase (L DH) release was 40.1 +/- 8.8% in tBHP treated cells compared to 8.1 +/- 4.7 % in control cells. This oxidative stress paradigm also resulted in signifi cant activation of caspase-3 by 2 hr post-treatment and nuclear apoptotic m orphology. Furthermore, tBHP treatment also resulted in delayed tau proteol ysis that was first evident 2 hr post-treatment. Treatment of the cells wit h the general caspase inhibitor Boc-Asp(OMe)-Fluoromethylketone (BAF) compl etely inhibited caspase-3 activation in response to tBHP, and delayed, but did not prevent cell death. BAF treatment also decreased tau proteolysis. I n vitro, recombinant tau was readily proteolyzed by active recombinant casp ase-3 into a stable breakdown product. Further tau in the cell lysates was cleaved by active recombinant caspase-3 at a rate, and to an extent similar to that observed for the well-established caspase-3 substrate poly(ADP-rib ose)polymerase (PARP). These results suggest that oxidative stress-induced cell death occurs through both caspase-dependent and-independent pathways, and that tau is likely an in situ substrate of caspase-3. (C) 2000 Wiley-Li ss, Inc.