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Distinct alterations in mitochondrial mass and function characterize different models of apoptosis
S Camilleri-Broët1, H Vanderwerff, E Caldwell
1Division of Clinical Research and Molecular Medicine, Fred Hutchinson Cancer Research Center, Seattle, Washington 98109, USA.
Abstract:
Recent studies have shown that reduction in mitochondrial membrane potential (delta psi m) and generation of reactive oxygen species are early events in apoptosis. In this study, we present two different models of apoptotic cell death, Chinese hamster ovary (CHO) cells treated with aphidicolin and dexamethasone-treated 2B4 T-cell hybridoma cells, which display opposing mitochondrial changes. CHO cells arrested at G1/S with aphidicolin have a progressive increase in mitochondria mass and number, assessed by flow cytometry and fluorescent microscopy with mitochondria-specific probes. The increase in mitochondrial mass was not accompanied by a gain in net cellular mitochondrial membrane potential, consistent with an accumulation of relatively depolarized mitochondria. Fluorescent microscopy demonstrated an increased content of low delta psi m mitochondria in aphidicolin-treated CHO cells, but high delta psi m mitochondria were also present and remained stable in number. Mitochondrial mass correlated with decreased clonogenicity of aphidicolin-treated CHO cells. Cycloheximide prevented both the proliferation of mitochondria and subsequent cell death. In contrast, dexamethasone treatment of 2B4 T-cell hybridoma cells caused a decrease in delta psi m without mitochondrial proliferation. Cycloheximide and Bcl-2 overexpression inhibited the loss of delta psi m, as well as apoptosis. In both models, cell death was associated with a decrease in mitochondrial potential relative to mitochondrial mass, suggesting that an accumulation of damaged or dysfunctional mitochondria had occurred.
Insights
Mitochondrial changes during apoptosis vary by cell type. Some cells increase mitochondrial mass with decreased membrane potential, while others show reduced potential without proliferation, indicating dysfunctional mitochondria contribute to cell death.
Area of Science:
- Cell Biology
- Biochemistry
- Molecular Biology
Background:
- Apoptosis involves early events like reduced mitochondrial membrane potential (Δψm) and reactive oxygen species generation.
- Mitochondrial dynamics are crucial in regulating cell death pathways.
Purpose of the Study:
- To investigate distinct mitochondrial alterations in two models of apoptosis.
- To correlate mitochondrial mass and membrane potential changes with cell death.
Main Methods:
- Utilized Chinese hamster ovary (CHO) cells and 2B4 T-cell hybridoma cells.
- Induced apoptosis using aphidicolin (CHO) and dexamethasone (2B4 T-cells).
- Assessed mitochondrial mass, number, and membrane potential (Δψm) via flow cytometry and fluorescent microscopy.
Main Results:
- Aphidicolin-treated CHO cells showed increased mitochondrial mass and number, but accumulated depolarized mitochondria, correlating with reduced clonogenicity.
- Dexamethasone-treated 2B4 T-cells exhibited decreased Δψm without mitochondrial proliferation.
- Cycloheximide and Bcl-2 inhibited mitochondrial proliferation and/or Δψm loss, preventing cell death in respective models.
Conclusions:
- Apoptotic cell death involves diverse mitochondrial responses depending on the cellular context.
- Cell death is linked to a decreased ratio of mitochondrial potential to mitochondrial mass, suggesting accumulation of dysfunctional mitochondria.