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Caspase-mediated loss of mitochondrial function and generation of reactive oxygen species during apoptosis
Jean-Ehrland Ricci1, Roberta A Gottlieb, Douglas R Green
1Division of Cellular Immunology, La Jolla Institute for Allergy and Immunology, San Diego, CA 92121, USA.
Abstract:
During apoptosis, the permeabilization of the mitochondrial outer membrane allows the release of cytochrome c, which induces caspase activation to orchestrate the death of the cell. Mitochondria rapidly lose their transmembrane potential (Delta Psi m) and generate reactive oxygen species (ROS), both of which are likely to contribute to the dismantling of the cell. Here we show that both the rapid loss of Delta Psi m and the generation of ROS are due to the effects of activated caspases on mitochondrial electron transport complexes I and II. Caspase-3 disrupts oxygen consumption induced by complex I and II substrates but not that induced by electron transfer to complex IV. Similarly, Delta Psi m generated in the presence of complex I or II substrates is disrupted by caspase-3, and ROS are produced. Complex III activity measured by cytochrome c reduction remains intact after caspase-3 treatment. In apoptotic cells, electron transport and oxygen consumption that depends on complex I or II was disrupted in a caspase-dependent manner. Our results indicate that after cytochrome c release the activation of caspases feeds back on the permeabilized mitochondria to damage mitochondrial function (loss of Delta Psi m) and generate ROS through effects of caspases on complex I and II in the electron transport chain.
Insights
Activated caspases damage mitochondria during apoptosis by inhibiting electron transport complexes I and II. This leads to loss of mitochondrial membrane potential and reactive oxygen species generation, contributing to cell death.
Area of Science:
- Cell Biology
- Biochemistry
- Molecular Biology
Background:
- Apoptosis involves mitochondrial outer membrane permeabilization and cytochrome c release.
- Cytochrome c release triggers caspase activation, orchestrating programmed cell death.
- Mitochondria undergo rapid loss of transmembrane potential (Delta Psi m) and generate reactive oxygen species (ROS) during apoptosis.
Purpose of the Study:
- To investigate the role of activated caspases in mitochondrial dysfunction during apoptosis.
- To determine the specific mitochondrial targets of caspases affecting Delta Psi m and ROS production.
Main Methods:
- Assessing oxygen consumption using complex I, II, and IV substrates.
- Measuring mitochondrial transmembrane potential (Delta Psi m) in the presence of caspase-3.
- Evaluating reactive oxygen species (ROS) production.
- Assessing complex III activity via cytochrome c reduction.
Main Results:
- Activated caspase-3 disrupts oxygen consumption linked to mitochondrial electron transport complexes I and II.
- Caspase-3 triggers loss of Delta Psi m and ROS generation when using complex I or II substrates.
- Complex III activity remains unaffected by caspase-3 treatment.
- Electron transport and oxygen consumption dependent on complexes I and II are impaired in apoptotic cells in a caspase-dependent manner.
Conclusions:
- Activated caspases feedback on permeabilized mitochondria post-cytochrome c release.
- Caspases damage mitochondrial function, specifically complexes I and II, leading to Delta Psi m loss and ROS generation.
- These caspase-mediated effects on the electron transport chain contribute to cellular dismantling during apoptosis.