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Polyamines directly induce release of cytochrome c from heart mitochondria
C Stefanelli1, I Stanic', M Zini
1Dipartimento di Biochimica 'G. Moruzzi', Università di Bologna, Via Irnerio, 48. I-40126 Bologna, Italy. cstefan@biocfarm.unibo.it
Abstract:
Cytochrome c release from mitochondria to the cytosol represents a critical step in apoptosis, correlated to the activation of the caspase cascade. In this report, we show that addition of micromolar concentrations of polyamines to isolated rat heart mitochondria induces the release of cytochrome c. Spermine, which is effective at concentrations of 10-100 microM, is more potent than spermidine, whereas putrescine has no effect up to 1 mM. The release of cytochrome c caused by spermine is a rapid, saturable and selective process that is independent of mitochondria damage. Spermine, unlike polylysine, is able to release a discrete amount of cytochrome c from intact, functional mitochondria. The cytochrome c-releasing power of spermine is not affected by cyclosporin A, differently from the effect of permeability transition inducers. In a cardiac cell-free model of apoptosis, the latent caspase activity of cytosolic extracts from cardiomyocytes could be activated by cytochrome c released from spermine-treated heart mitochondria. These data indicate a novel mechanism of cytochrome c release from the mitochondrion, and suggest that prolonged and sustained elevation of polyamines, characteristic of some pathologies such as heart hypertrophy, could be involved in the development of apoptosis.
Insights
Polyamines like spermine can trigger cytochrome c release from mitochondria, initiating apoptosis. This discovery suggests elevated polyamine levels in conditions like heart hypertrophy may drive programmed cell death.
Area of Science:
- Molecular Biology
- Cell Biology
- Biochemistry
Background:
- Cytochrome c release from mitochondria is a key event in apoptosis, activating the caspase cascade.
- The precise mechanisms regulating cytochrome c release, especially in response to cellular stimuli, are areas of ongoing research.
Purpose of the Study:
- To investigate the role of polyamines in inducing cytochrome c release from isolated mitochondria.
- To elucidate the mechanism and specificity of polyamine-induced cytochrome c release.
- To explore the implications of polyamine-mediated cytochrome c release in a cardiac cell-free apoptosis model.
Main Methods:
- Isolated rat heart mitochondria were treated with varying concentrations of polyamines (spermine, spermidine, putrescine).
- Cytochrome c release was measured, and the process was characterized for its speed, saturation, selectivity, and dependence on mitochondrial integrity.
- Effects of cyclosporin A and comparison with polylysine were assessed.
- A cardiac cell-free system was used to evaluate the activation of caspase activity by released cytochrome c.
Main Results:
- Micromolar concentrations of spermine and spermidine, but not putrescine, induced cytochrome c release from isolated mitochondria.
- Spermine was more potent than spermidine and induced rapid, saturable, and selective release of cytochrome c from intact mitochondria, independent of mitochondrial damage.
- Spermine-induced release was not affected by cyclosporin A, distinguishing it from the mitochondrial permeability transition.
- Cytochrome c released by spermine treatment activated latent caspase activity in cardiomyocyte cytosolic extracts.
Conclusions:
- Polyamines, particularly spermine, represent a novel class of molecules capable of inducing cytochrome c release from mitochondria.
- This mechanism offers a new perspective on apoptosis regulation, distinct from classical inducers of the mitochondrial permeability transition.
- Sustained elevation of polyamines, observed in pathologies like heart hypertrophy, may contribute to the development of cardiac apoptosis.