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Bcl-2 family members and functional electron transport chain regulate oxygen deprivation-induced cell death
David S McClintock1, Matthew T Santore, Vivian Y Lee
1Division of Pulmonary & Critical Care Medicine, Department of Medicine, Northwestern University Medical School, Chicago, Illinois 60601-3010, USA.
Abstract:
The mechanisms underlying cell death during oxygen deprivation are unknown. We report here a model for oxygen deprivation-induced apoptosis. The death observed during oxygen deprivation involves a decrease in the mitochondrial membrane potential, followed by the release of cytochrome c and the activation of caspase-9. Bcl-X(L) prevented oxygen deprivation-induced cell death by inhibiting the release of cytochrome c and caspase-9 activation. The ability of Bcl-X(L) to prevent cell death was dependent on allowing the import of glycolytic ATP into the mitochondria to generate an inner mitochondrial membrane potential through the F(1)F(0)-ATP synthase. In contrast, although activated Akt has been shown to inhibit apoptosis induced by a variety of apoptotic stimuli, it did not prevent cell death during oxygen deprivation. In addition to Bcl-X(L), cells devoid of mitochondrial DNA (rho degrees cells) that lack a functional electron transport chain were resistant to oxygen deprivation. Further, murine embryonic fibroblasts from bax(-/-) bak(-/-) mice did not die in response to oxygen deprivation. These data suggest that when subjected to oxygen deprivation, cells die as a result of an inability to maintain a mitochondrial membrane potential through the import of glycolytic ATP. Proapoptotic Bcl-2 family members and a functional electron transport chain are required to initiate cell death in response to oxygen deprivation.
Insights
Oxygen deprivation triggers apoptosis via mitochondrial dysfunction. Cell death is prevented by maintaining mitochondrial membrane potential with glycolytic ATP import, highlighting a novel cell death pathway.
Area of Science:
- Cell Biology
- Biochemistry
- Physiology
Background:
- The mechanisms of cell death during oxygen deprivation (hypoxia) are not fully understood.
- Apoptosis, or programmed cell death, is a critical cellular process.
- Mitochondria play a central role in regulating apoptosis.
Purpose of the Study:
- To elucidate the molecular mechanisms of cell death induced by oxygen deprivation.
- To investigate the role of mitochondria and specific proteins in this process.
- To establish a model for oxygen deprivation-induced apoptosis.
Main Methods:
- Utilized a cell culture model for oxygen deprivation.
- Assessed mitochondrial membrane potential and cytochrome c release.
- Investigated the role of Bcl-X(L), Akt, F(1)F(0)-ATP synthase, and electron transport chain.
- Used bax(-/-) bak(-/-) mice embryonic fibroblasts and rho(0) cells.
Main Results:
- Oxygen deprivation induces apoptosis characterized by decreased mitochondrial membrane potential, cytochrome c release, and caspase-9 activation.
- Bcl-X(L) inhibits this cell death pathway by preserving mitochondrial membrane potential via glycolytic ATP import through F(1)F(0)-ATP synthase.
- Activated Akt failed to prevent oxygen deprivation-induced cell death.
- Cells lacking mitochondrial DNA (rho(0) cells) and bax(-/-) bak(-/-) fibroblasts were resistant to oxygen deprivation.
- A functional electron transport chain is required for cell death.
Conclusions:
- Cell death during oxygen deprivation results from impaired mitochondrial membrane potential maintenance due to insufficient glycolytic ATP import.
- Proapoptotic Bcl-2 family members and an intact electron transport chain are essential for initiating cell death under oxygen deprivation.
- This study reveals a novel pathway for hypoxia-induced apoptosis distinct from pathways regulated by Akt.