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 authors blocked the endogenous expression of bcl-2 after ischemia using antisense oligodeoxynucleotides (ODN). Antisense, sense, scrambled ODN, or vehicles were infused in the lateral ventricle of the rat for 24 hours after 30 minutes of temporary middle cerebral artery occlusion. Twenty-four hours later the brains were removed and bcl-2 protein expression was assayed by Western blot. Antisense ODN, but not sense or scrambled ODN treatment, significantly inhibited bcl-2 protein expression after ischemia. Bcl-2 protein expression was also studied 24 hours after 60 minutes of temporary middle cerebral artery occlusion in vehicle and antisense ODN-treated rats. After 60 minutes of ischemia and vehicle treatment, bcl-2 was expressed in many neurons in the ventral cortical mantle and the medial striatum. After antisense ODN treatment there were few neurons in this region expressing bcl-2, instead most neurons TUNEL labeled. Treatment with the antisense ODN, but not sense ODN, increased infarction volume as determined by cresyl violet staining 72 hours after ischemia compared with vehicle controls. These results suggested that endogenously expressed bcl-2 promoted survival in ischemic neurons and was not simply an epiphenomenon in neurons already destined to live or die.