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V. Necrapoptosis and the mitochondrial permeability transition: shared pathways to necrosis and apoptosis
1Department of Cell Biology & Anatomy, University of North Carolina, Chapel Hill, North Carolina 27799-7090, USA.
Abstract:
Opening of a high-conductance pore conducting solutes of molecular mass <1,500 Da causes onset of the mitochondrial permeability transition (MPT). Cyclosporin A blocks this pore and prevents acute necrotic cell death in several models. Confocal microscopy directly visualizes onset of the MPT during acute cytotoxicity from the movement of the green-fluorescing fluorophore, calcein, into the mitochondria from the cytosol. The MPT also plays a causative role in tumor necrosis factor-alpha-induced apoptosis in hepatocytes. Progression to apoptosis or necrosis after the MPT may depend on the presence or absence, respectively, of ATP. Often, features of both apoptotic and necrotic cell death develop after death signals and toxic stresses. The term "necrapoptosis" is introduced to emphasize the shared pathways leading to both forms of cell death.
Insights
The mitochondrial permeability transition (MPT) pore opening causes cell death, but cyclosporin A can block it. Visualizing MPT with calcein shows its role in apoptosis and necrosis, with ATP levels determining the cell death pathway.
Area of Science:
- Mitochondrial biophysics and cell death mechanisms.
- Molecular biology of cell death pathways.
- Toxicology and drug discovery.
Background:
- The mitochondrial permeability transition (MPT) involves opening of a high-conductance pore, allowing solutes <1,500 Da to pass.
- This pore opening is a critical event in initiating cell death.
- Cyclosporin A is known to inhibit this pore, offering potential therapeutic benefits.
Purpose of the Study:
- To directly visualize the onset of MPT during acute cytotoxicity.
- To investigate the role of MPT in both apoptosis and necrosis.
- To explore the influence of ATP levels on cell death outcomes following MPT.
Main Methods:
- Utilizing confocal microscopy to track the movement of the fluorophore calcein into mitochondria.
- Employing cell models to study acute cytotoxicity and tumor necrosis factor-alpha-induced apoptosis in hepatocytes.
- Analyzing the impact of ATP levels on cell fate after MPT induction.
Main Results:
- Confocal microscopy successfully visualized MPT onset via calcein influx into mitochondria during cytotoxicity.
- MPT was confirmed to play a causative role in tumor necrosis factor-alpha-induced apoptosis in hepatocytes.
- Cellular ATP levels were found to influence whether cells undergo apoptosis or necrosis after MPT.
Conclusions:
- The opening of the MPT pore is a key event leading to cell death, which can be inhibited by cyclosporin A.
- MPT contributes to both apoptotic and necrotic cell death pathways, with ATP levels modulating the outcome.
- The study introduces the term 'necrapoptosis' to describe the shared pathways underlying these cell death forms.