Alternating metabolic pathways in NGF-deprived sympathetic neurons affect caspase-independent death

Mitochondrial release of cytochrome c in apoptotic cells activates caspases, which execute apoptotic cell death. However, the events themselves that culminate in caspase activation can have deleterious effects because caspase inhibitor–saved cells ultimately die in a caspase-independent manner. To determine what events may underlie this form of cell death, we examined bioenergetic changes in sympathetic neurons deprived of NGF in the presence of a broad-spectrum caspase inhibitor, boc-aspartyl-(OMe)-fluoromethylketone. Here, we report that NGF-deprived, boc-aspartyl-(OMe)-fluoromethylketone–saved neurons rely heavily on glycolysis for ATP generation and for survival. Second, the activity of F₀F₁ contributes to caspase-independent death, but has only a minor role in the maintenance of mitochondrial membrane potential, which is maintained primarily by electron transport. Third, permeability transition pore inhibition by cyclosporin A attenuates NGF deprivation–induced loss of mitochondrial proteins, suggesting that permeability transition pore opening may have a function in regulating the degradation of mitochondria after cytochrome c release. Identification of changes in caspase inhibitor–saved cells may provide the basis for rational strategies to augment the effectiveness of the therapeutic use of postmitochondrial interventions.