Role of hypoxia-induced Bax translocation and cytochrome c release in reoxygenation injury

We investigated mechanisms of cell death during hypoxia/reoxygenation of cu ltured kidney cells. During glucose-fret hypoxia, cell ATP levels declined steeply resulting in the translocation of Bas from cytosol to mitochondria. Concurrently, there was cytochrome c release and caspase activation. Cells that leaked cytochrome c underwent apoptosis after reoxygenation, ATP depl etion induced by a mitochondrial uncoupler resulted in similar alterations even in the presence of oxygen. Moreover, inclusion of glucose during hypox ia prevented protein translocations and reoxygenation injury by maintaining intracellular ATP, Thus, ATP depletion, rather than hypoxia per se, was th e cause of protein translocations. Overexpression of Bcl-2 prevented cytoch rome c release and reoxygenation injury without ameliorating ATP depletion or Bas translocation, On the other hand, caspase inhibitors did not prevent protein translocations, but inhibited apoptosis during reoxygenation, Neve rtheless, they could not confer long-term viability, since mitochondria had been damaged. Omission of glucose during reoxygenation resulted in continu ed failure of ATP production, and cell death,vith necrotic morphology. In c ontrast, cells expressing Bcl-2 had functional mitochondria and remained vi able during reoxygenation even,without glucose. Therefore, Bas translocatio n during hypoxia is a molecular trigger for cell death during reoxygenation . If ATP is available during reoxygenation, apoptosis develops; otherwise, death occurs by necrosis. By preserving mitochondrial integrity, BCL-2 prev ents both forms of cell death and ensures cell viability.