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(27) A DECREASE IN THE RATE OF MITOCHONDRIAL PROTEIN IMPORT IS AN EARLY EVENT DURING THE INITIATION OF NEURONAL APOPTOSIS J. Wadia1
and L.R. Mills2
Growing evidence suggests that mitochondria are involved in the initiation and progression of apoptosis and that mitochondrial changes are related to the onset of several neuropathological diseases. We propose that alterations in the import of nuclear-encoded mitochondrial proteins, independent of their expression, may account for some of the long-term, progressive loss of neurons during physiological apoptotic cell death. Factors which affect mitochondrial protein import have been previously shown to cause profound changes in mitochondrial morphology, the function of the mitochondrial respiratory chain enzymes, and increase mitochondrial permeability. To study this phenomenon we constructed a stable PC12 cell line which expresses an inducible, mitochondrially-targeted GFP fusion protein (GFPmt). We have found that during trophic withdrawal (TW) induced apoptosis of neuronal PC12 cells there is a marked decrease in the import of GFPmt into mitochondria by 1h (30% of control). Treatment of PC12 cells with either Beta-AP or the Parkinson toxin MPP+, for 24h, was able to induce a similar dose-dependent decrease in the rate of mitochondrial import. The drop in mitochondrial import following TW occurred before the drop in mitochondrial potential and the rise in oxidative radicals and could not be blocked by pretreatment with the permeability transition inhibitor cyclosporine A. Caspase-3 activation occurred following the drop in protein import and treatment of the cells with the caspase inhibitor ZVAD.FMK was not sufficient to attenuate the decrease. However, there appears to be a relationship between mitochondrial import and the oxidative state of the cell as treatment of the cells with H2O2 causes a rapid drop in import.
For further information contact...Carmen Mannella: carmen@wadsworth.org |
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