MULTIPLE PATHWAYS OF NEURONAL DEATH INDUCED BY DNA-DAMAGING AGENTS, NGF DEPRIVATION, AND OXIDATIVE STRESS

Here, we compare the pathways by which DNA-damaging agents, NGF depriv ation, and superoxide dismutase 1 (SOD1) depletion evoke apoptosis of sympathetic neurons. Previous work raised the hypothesis that cell cyc le signaling plays a required role in neuronal apoptosis elicited by N GF deprivation and the DNA-damaging agent camptothecin. To test this h ypothesis, we extended our investigation of DNA-damaging agents to cyt osine arabinoside (AraC) and UV irradiation. As with NGF deprivation a nd camptothecin treatment, the cyclin-dependent kinase inhibitors flav opiridol and olomoucine protected neurons from apoptosis induced by Ar aC and UV treatment. These observations support the model that camptot hecin, AraC, and UV treatment cause DNA damage, which leads to apoptos is by a mechanism that, as in the case of NGF deprivation, includes ac tivation of cell cycle components. Flavopiridol and olomoucine, howeve r, had no effect on death induced by SOD1 depletion, suggesting that C DKs do not play a role in this paradigm of neuronal death. To compare further the mechanisms of death evoked by NGF withdrawal, SOD1 depleti on, and DNA-damaging agents, we investigated their responses to inhibi tors of cysteine aspartases, elements of apoptotic pathways. The V-ICE inh and BAF, two peptide inhibitors of cysteine aspartases, protected neurons in all three death paradigms. in contrast, the cysteine aspart ase inhibitory peptide zVAD-fmk conferred protection from NGF withdraw al and SOD1 depletion, but not DNA-damaging agents, whereas acYVAD-cmk protected only from SOD1 depletion. Taken together, these findings in dicate that three different apoptotic Stimuli activate separate pathwa ys of death in the same neuron type.