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Mitochondria are selectively eliminated from eukaryotic cells after blockade of caspases during apoptosis
L Xue1, G C Fletcher, A M Tolkovsky
1Department of Biochemistry, University of Cambridge, Cambridge CB2 1QW, United Kingdom.
Abstract:
Pan caspase inhibitors are potentially powerful cell-protective agents that block apoptosis in response to a wide variety of insults that cause tissue degeneration. In many conditions, however, the blockade of apoptosis by caspase inhibitors does not permit long-term cell survival, but the reasons are not entirely clear. Here we show that the blockade of apoptosis by Boc.Aspartyl(O-methyl)CH2F can result in the highly selective elimination of the entire cohort of mitochondria, including mitochondrial DNA, from both neurons and HeLa cells, irrespective of the stimulus used to trigger apoptosis. In cells that lose their mitochondria, the nuclear DNA, Golgi apparatus, endoplasmic reticulum, centrioles, and plasma membrane remain undamaged. The capacity to remove mitochondria is both specific and regulated since mitochondrial loss in neurons is completely prevented by the expression of the antiapoptotic protein Bcl-2 and partially suppressed by the autolysosomal inhibitor bafilomycin. Cells without mitochondria are more tolerant to an anaerobic environment but are essentially irreversibly committed to death. Prevention of mitochondrial loss may be crucial for the long-term regeneration of tissues emerging from an apoptotic episode in which death was prevented by caspase blockade.
Insights
Pan caspase inhibitors block apoptosis but can cause mitochondria loss, leading to cell death. Preventing this mitochondrial elimination may be key for tissue regeneration after apoptosis blockade.
Area of Science:
- Cell Biology
- Biochemistry
- Neuroscience
Background:
- Pan caspase inhibitors are explored as cell-protective agents against tissue degeneration by blocking apoptosis.
- However, long-term cell survival is often not achieved despite apoptosis blockade, with unclear underlying mechanisms.
Purpose of the Study:
- To investigate the reasons behind limited long-term cell survival when apoptosis is inhibited by caspase inhibitors.
- To elucidate the specific cellular events triggered by caspase inhibition that impact cell viability.
Main Methods:
- Utilized a pan caspase inhibitor (Boc.Aspartyl(O-methyl)CH2F) in neuronal and HeLa cell models.
- Assessed cellular integrity, mitochondrial DNA, and organelle status post-inhibition.
- Investigated the role of Bcl-2 and bafilomycin in modulating mitochondrial loss.
Main Results:
- Caspase inhibition selectively eliminated all mitochondria, including mitochondrial DNA, in both neurons and HeLa cells.
- Nuclear DNA and other organelles remained intact during mitochondrial loss.
- Mitochondrial removal was regulated, inhibited by Bcl-2 and partially by bafilomycin.
- Cells lacking mitochondria showed increased tolerance to anaerobic conditions but were committed to irreversible death.
Conclusions:
- Blockade of apoptosis by pan caspase inhibitors can lead to selective mitochondrial elimination, not long-term cell survival.
- Prevention of mitochondrial loss is critical for tissue regeneration following apoptosis-inhibited episodes.