Implications for the Amgen aborted study?

http://www.eurekalert.org/pub_releas...-ntf071608.php
Neuronal Death Path
Li-ying Yu, Mart Saarma, and Urmas Arumäe

Programmed cell death pathways are generally divided into two broad categories: the intrinsic pathway, in which cellular stress (e.g., oxidative stress) leads to release of cytochrome c from mitochondria, which leads to activation of caspase-9, which activates effector caspases that degrade cellular proteins; and the extrinsic pathway, in which extracellular ligands bind to death receptors, which activate Fas-activated death domain (FADD) protein, which leads to activation of caspase-8, which activates effector caspases. This week, Yu et al. describe the apoptosis pathway activated by withdrawal of GDNF and BDNF from cultured midbrain dopaminergic neurons. The normal intrinsic pathway was not involved, because cytochrome c was not released from mitochondria. Nonetheless, caspase-9 was involved. Death-receptor pathways were also involved, because blocking FADD or caspase-8 prevented apoptosis. Interestingly, this apoptosis pathway is different than that induced by withdrawal of GDNF from sympathetic neurons.