Apoptotic and necrotic death mechanisms are concomitantly activated in the same cell after cerebral ischemia.

Abstract

Both necrotic and apoptotic cell death mechanisms are activated after cerebral ischemia. However, whether they are concomitantly active in the same cell or in discrete cell populations is not known. We investigated activation of both pathways at the cellular level in mice brains subjected to transient or permanent focal ischemia. Four hours after ischemia, diffuse cathepsin-B spillage into cytoplasm, suggesting lysosomal leakage, was observed within neurons immunoreactive for the active form of caspase-3 (p20). Ischemic neurons with a leaky plasma membrane (positive for propidium iodide) were colabeled with caspase-cleaved actin fragment and exhibited TUNEL-positive nuclei having apoptotic morphology. At 72 hours, up to 27% of cells with caspase activity displayed morphological features suggestive of secondary necrosis. These data, demonstrating an early and concurrent increase in caspase-3 and cathepsin-B activities followed by appearance of caspase-cleavage products, DNA fragmentation, and membrane disintegration, suggest that subroutines of necrotic and apoptotic cell death are concomitantly activated in ischemic neurons and that the dominant cell death phenotype is determined by the relative speed of each process.