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

Chang LK, Schmidt RE, Johnson EM - J. Cell Biol. (2003)

Bottom Line: 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.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.

View Article: PubMed Central - PubMed

Affiliation: Washington 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.

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Related in: MedlinePlus

Proposed events that account for the protective effect of oligomycin and CsA in neurons subsequent to cytochromecrelease by the “mitochondrial hit.” In NGF-maintained sympathetic neurons (A), electron transport generates ΔΨm, which is used by the ΔΨm ATPase to generate ATP. In NGF-deprived, BAF-saved cells (B), mitochondrial cytochrome c (Cc) is lost by permeabilization of the outer mitochondrial membrane, possibly by a channel that includes the proapoptotic Bcl-2 family member BAX. Despite this, electron transport continues, at least through complexes I and III, contributing to ΔΨm. Oxidation of electron transport intermediates could be mediated by residual mitochondrial cytochrome c, or by the generation of reactive oxygen species (ROS), which could themselves be detrimental. Reverse operation of F0F1 also contributes to ΔΨm by hydrolyzing ATP. The importance of the permeability transition pore (PTP), which is composed of the voltage-dependent anion channel (VDAC), adenine nucleotide translocase (ANT), and cyclophilin D (CyD), is evidenced by the ability of CsA to inhibit caspase-independent death (Chang and Johnson, 2002; Fig. 4). Although precisely how PTP opening contributes to caspase-independent cell death is not known, it is possible, but purely speculative, that the opening of the PTP could allow the F0F1 to hydrolyze cytosolic ATP generated by glycolysis, on which the cell depends for survival. Although this model can account for inhibition of caspase-independent death by both oligomycin and CsA, it supposes that mechanisms to equilibrate adenine nucleotides are compromised in NGF-deprived, BAF-saved cells.
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fig8: Proposed events that account for the protective effect of oligomycin and CsA in neurons subsequent to cytochromecrelease by the “mitochondrial hit.” In NGF-maintained sympathetic neurons (A), electron transport generates ΔΨm, which is used by the ΔΨm ATPase to generate ATP. In NGF-deprived, BAF-saved cells (B), mitochondrial cytochrome c (Cc) is lost by permeabilization of the outer mitochondrial membrane, possibly by a channel that includes the proapoptotic Bcl-2 family member BAX. Despite this, electron transport continues, at least through complexes I and III, contributing to ΔΨm. Oxidation of electron transport intermediates could be mediated by residual mitochondrial cytochrome c, or by the generation of reactive oxygen species (ROS), which could themselves be detrimental. Reverse operation of F0F1 also contributes to ΔΨm by hydrolyzing ATP. The importance of the permeability transition pore (PTP), which is composed of the voltage-dependent anion channel (VDAC), adenine nucleotide translocase (ANT), and cyclophilin D (CyD), is evidenced by the ability of CsA to inhibit caspase-independent death (Chang and Johnson, 2002; Fig. 4). Although precisely how PTP opening contributes to caspase-independent cell death is not known, it is possible, but purely speculative, that the opening of the PTP could allow the F0F1 to hydrolyze cytosolic ATP generated by glycolysis, on which the cell depends for survival. Although this model can account for inhibition of caspase-independent death by both oligomycin and CsA, it supposes that mechanisms to equilibrate adenine nucleotides are compromised in NGF-deprived, BAF-saved cells.

Mentions: The polarity of the F0F1 ATPase in the inner mitochondrial membrane dictates that it can only hydrolyze ATP within the mitochondrial matrix. Under normal conditions, ATP and ADP are freely exchanged between the mitochondrial matrix and the cytosol via the adenine nucleotide translocase (ANT). However, this may not hold true during cell death, as ANT function is compromised in lymphocytes undergoing growth factor deprivation–induced apoptosis (Vander Heiden et al., 1999). If adenine nucleotide equilibration is compromised in NGF-deprived, BAF-saved sympathetic neurons, it is possible that opening of the PTP renews the pool of ATP within the mitochondrial matrix by providing equilibration of ATP levels between the cytosol and the matrix, schematized in Fig. 8. In such a scenario, PTP opening allows the F0F1 ATPase access to ATP that has been generated in the cytosol by glycolysis, which is required by these cells for survival (Fig. 3 B). Thus, inhibiting PTP opening with CsA or directly inhibiting ATP hydrolysis by reverse operation of F0F1 with oligomycin limits the deleterious effects of the mitochondrial hit by preserving glycolytic ATP. Consistent with this hypothesis, CsA and oligomycin inhibited Commitment 2 to virtually the same degree (Fig. 4 B). Although purely speculative at this point, because it rests on the supposition that adenine nucleotide transport is altered in NGF-deprived, BAF-saved cells, we favor this model because it accounts for the similarity in protection against caspase-independent death of both oligomycin and CsA.


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

Chang LK, Schmidt RE, Johnson EM - J. Cell Biol. (2003)

Proposed events that account for the protective effect of oligomycin and CsA in neurons subsequent to cytochromecrelease by the “mitochondrial hit.” In NGF-maintained sympathetic neurons (A), electron transport generates ΔΨm, which is used by the ΔΨm ATPase to generate ATP. In NGF-deprived, BAF-saved cells (B), mitochondrial cytochrome c (Cc) is lost by permeabilization of the outer mitochondrial membrane, possibly by a channel that includes the proapoptotic Bcl-2 family member BAX. Despite this, electron transport continues, at least through complexes I and III, contributing to ΔΨm. Oxidation of electron transport intermediates could be mediated by residual mitochondrial cytochrome c, or by the generation of reactive oxygen species (ROS), which could themselves be detrimental. Reverse operation of F0F1 also contributes to ΔΨm by hydrolyzing ATP. The importance of the permeability transition pore (PTP), which is composed of the voltage-dependent anion channel (VDAC), adenine nucleotide translocase (ANT), and cyclophilin D (CyD), is evidenced by the ability of CsA to inhibit caspase-independent death (Chang and Johnson, 2002; Fig. 4). Although precisely how PTP opening contributes to caspase-independent cell death is not known, it is possible, but purely speculative, that the opening of the PTP could allow the F0F1 to hydrolyze cytosolic ATP generated by glycolysis, on which the cell depends for survival. Although this model can account for inhibition of caspase-independent death by both oligomycin and CsA, it supposes that mechanisms to equilibrate adenine nucleotides are compromised in NGF-deprived, BAF-saved cells.
© Copyright Policy
Related In: Results  -  Collection

Show All Figures
getmorefigures.php?uid=PMC2172806&req=5

fig8: Proposed events that account for the protective effect of oligomycin and CsA in neurons subsequent to cytochromecrelease by the “mitochondrial hit.” In NGF-maintained sympathetic neurons (A), electron transport generates ΔΨm, which is used by the ΔΨm ATPase to generate ATP. In NGF-deprived, BAF-saved cells (B), mitochondrial cytochrome c (Cc) is lost by permeabilization of the outer mitochondrial membrane, possibly by a channel that includes the proapoptotic Bcl-2 family member BAX. Despite this, electron transport continues, at least through complexes I and III, contributing to ΔΨm. Oxidation of electron transport intermediates could be mediated by residual mitochondrial cytochrome c, or by the generation of reactive oxygen species (ROS), which could themselves be detrimental. Reverse operation of F0F1 also contributes to ΔΨm by hydrolyzing ATP. The importance of the permeability transition pore (PTP), which is composed of the voltage-dependent anion channel (VDAC), adenine nucleotide translocase (ANT), and cyclophilin D (CyD), is evidenced by the ability of CsA to inhibit caspase-independent death (Chang and Johnson, 2002; Fig. 4). Although precisely how PTP opening contributes to caspase-independent cell death is not known, it is possible, but purely speculative, that the opening of the PTP could allow the F0F1 to hydrolyze cytosolic ATP generated by glycolysis, on which the cell depends for survival. Although this model can account for inhibition of caspase-independent death by both oligomycin and CsA, it supposes that mechanisms to equilibrate adenine nucleotides are compromised in NGF-deprived, BAF-saved cells.
Mentions: The polarity of the F0F1 ATPase in the inner mitochondrial membrane dictates that it can only hydrolyze ATP within the mitochondrial matrix. Under normal conditions, ATP and ADP are freely exchanged between the mitochondrial matrix and the cytosol via the adenine nucleotide translocase (ANT). However, this may not hold true during cell death, as ANT function is compromised in lymphocytes undergoing growth factor deprivation–induced apoptosis (Vander Heiden et al., 1999). If adenine nucleotide equilibration is compromised in NGF-deprived, BAF-saved sympathetic neurons, it is possible that opening of the PTP renews the pool of ATP within the mitochondrial matrix by providing equilibration of ATP levels between the cytosol and the matrix, schematized in Fig. 8. In such a scenario, PTP opening allows the F0F1 ATPase access to ATP that has been generated in the cytosol by glycolysis, which is required by these cells for survival (Fig. 3 B). Thus, inhibiting PTP opening with CsA or directly inhibiting ATP hydrolysis by reverse operation of F0F1 with oligomycin limits the deleterious effects of the mitochondrial hit by preserving glycolytic ATP. Consistent with this hypothesis, CsA and oligomycin inhibited Commitment 2 to virtually the same degree (Fig. 4 B). Although purely speculative at this point, because it rests on the supposition that adenine nucleotide transport is altered in NGF-deprived, BAF-saved cells, we favor this model because it accounts for the similarity in protection against caspase-independent death of both oligomycin and CsA.

Bottom Line: 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.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.

View Article: PubMed Central - PubMed

Affiliation: Washington 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.

Show MeSH
Related in: MedlinePlus