Overexpression of the cell death suppressor Bcl-w in ischemic brain: Implications for a neuroprotective role via the mitochondrial pathway

Bcl-w is a newly described cell death suppressor member of the Bcl-2 gene f amily. As these genes may have a role in the outcome of ischemic brain inju ry, the regional expression of Bcl-w protein in rat brain was examined at 6 to 72 hours after 90 minutes of transient middle cerebral artery occlusion . Bcl-w protein, although constitutively expressed at low Levels in nonisch emic brain, was found to be overexpressed in ischemic brain at all time poi nts studied. Up-regulation of Bcl-w protein was particularly abundant in th e penumbral region of the cortex and mainly in cells lacking DNA fragmentat ion. In the cortical penumbra. Bcl-w protein was detected predominantly in neurons and showed mitochondrial localization. as determined using double-l abel immunohistochemistry. Bcl-w expression was also detectable. to a lesse r extent, in reactive astrocytes in the infarct border zone and in microves sel walls in the infarct regions. At the mechanistic level, incubation of i solated brain mitochondria with the addition or recombinant Bax or high con centration of calcium resulted in release of cytochrome c from the mitochon dria. In the presence of recombinant Bcl-w protein, however, the release of cytochrome c induced by Bar or calcium was largely inhibited, Further, rec ombinant Bcl-w protein inhibited calcium-induced loss of mitochondrial tran smembrane potential, indicative of permeability transition, in a dose-depen dent manner. These results suggest that Bcl-w may be an endogenous neuropro tectant against ischemic neuronal death and that, like its analogues such a s Bcl-2 and Bcl-x-long, Bcl-w may achieve this protection via the mitochond rial death-regulatory pathway.