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Alternating metabolic pathways in NGF-deprived sympathetic neurons affect caspase-independent death
Louis K Chang1, Robert E Schmidt, Eugene M Johnson
1Washington University School of Medicine, Saint Louis, MO 63110, USA.
Abstract:
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.
Insights
Even when caspases are inhibited, nerve cells deprived of NGF die. These cells depend on glycolysis for energy and survival, and mitochondrial changes contribute to this caspase-independent cell death.
Area of Science:
- Neuroscience
- Cell Biology
- Biochemistry
Background:
- Mitochondrial cytochrome c release triggers caspases, initiating apoptosis.
- Caspase inhibition can lead to cell death through caspase-independent pathways.
- Understanding these alternative death mechanisms is crucial for therapeutic interventions.
Purpose of the Study:
- To investigate the bioenergetic changes in NGF-deprived sympathetic neurons when caspases are inhibited.
- To elucidate the mechanisms underlying caspase-independent cell death in these neurons.
Main Methods:
- Sympathetic neurons were deprived of NGF and treated with a caspase inhibitor (boc-aspartyl-(OMe)-fluoromethylketone).
- Bioenergetic parameters, including ATP generation, mitochondrial membrane potential, and protein loss, were analyzed.
- The role of F0F1 activity and permeability transition pore (PTP) opening was assessed using specific inhibitors like cyclosporin A.
Main Results:
- NGF-deprived neurons treated with caspase inhibitors relied heavily on glycolysis for ATP production and survival.
- F0F1 activity contributed to caspase-independent death but had a minor role in maintaining mitochondrial membrane potential, which was primarily supported by electron transport.
- Cyclosporin A inhibited the permeability transition pore, attenuating the loss of mitochondrial proteins after cytochrome c release.
Conclusions:
- NGF deprivation induces a shift towards glycolysis for survival in caspase-inhibited neurons.
- Mitochondrial F0F1 activity and permeability transition pore opening play significant roles in caspase-independent cell death and mitochondrial integrity.
- These findings offer insights into therapeutic strategies targeting post-mitochondrial interventions.