Suppression of endogenous bcl-2 expression by antisense treatment exacerbates ischemic neuronal death

Previous studies have shown that overexpression of bcl-2 in transgenic mice or by viral vectors protects the brain against cerebral ischemia. However, it is not known whether bcl-2, which is endogenously expressed in response to ischemia, exerts a protective effect. To address this question, the aut hors blocked the endogenous expression of bcl-2 after ischemia using antise nse oligodeoxynucleotides (ODN). Antisense, sense, scrambled ODN, or vehicl es were infused in the lateral ventricle of the rat for 24 hours after 30 m inutes of temporary middle cerebral artery occlusion. Twenty-four hours lat er the brains were removed and bcl-2 protein expression was assayed by West ern blot. Antisense ODN, but not sense or scrambled ODN treatment, signific antly inhibited bcl-2 protein expression after ischemia. Bcl-2 protein expr ession was also studied 24 hours after 60 minutes of temporary middle cereb ral artery occlusion in vehicle and antisense ODN-treated rats. After 60 mi nutes of ischemia and vehicle treatment, bcl-2 was expressed in many neuron s in the ventral cortical mantle and the medial striatum. After antisense O DN treatment there were few neurons in this region expressing bcl-2, instea d most neurons TUNEL labeled. Treatment with the antisense ODN, but not sen se ODN, increased infarction volume as determined by cresyl violet staining 72 hours after ischemia compared with vehicle controls. These results sugg ested that endogenously expressed bcl-2 promoted survival in ischemic neuro ns and was not simply an epiphenomenon in neurons already destined to live or die.