Bcl-2 Overexpression Protects Against Neuron Loss in Peri-infarct Regions Following Experimental Stroke
Purpose: Bcl-2 protects against both apoptotic and necrotic death induced by various insults, including cerebral ischemia. Ischemic injury with and without reperfusion may occur by different mechanisms, and protective strategies may be effective against one, but not the other. Here, we determine whether Bcl-2 protects against 2 different forms of focal cerebral ischemic injury within cortical penumbra in a model of experimental stroke. Methods: Bipromoter defective herpes simplex viral (HSV) vectors expressing Bcl-2 plus β-galactosidase (β-gal) as the reporter or β-gal only (control vector)were stereotaxically injected into left and right cortices using coordinates corresponding to the infarct border. 12 h later, focal ischemia was induced by occluding the middle cerebral artery (MCA) and both common carotid arteries (CCA). For the permanent occlusion model, the MCA was left occluded, but the CCAs were reopened after 2 h. For the reperfusion model, all 3 vessels were reopened after 2 h. 2 days later, brains were harvested and sections were reacted with X-gal followed by cresyl violet. X-gal positive neurons were counted in each hemisphere and expressed as the ratio of positive neurons in the ischemic side compared to the non-ischemic side. Results: Bcl-2 overexpression resulted in significantly improved cortical neuron survival within penumbral regions compared to control vector in both cases. Following reperfusion, Bcl-2 injected animals had 74±14%(n=5) survival compared to control 26±3% (n=6)(P<0.05). Following permanent MCA occlusion, Bcl-2 injected animals had 92±9%(n=5)survival vs.control, 45±5%(n=7)(P<0.05). The extent of survival from the 2 different paradigms suggest that Bcl-2 mediated protection was greater in the ischemia with permanent occlusion compared to reperfusion group. Conclusion: Bcl-2 overexpression protects against experimental stroke with and without reperfusion. The extent of protection appears to be greater for ischemia with permanent MCA occlusion. Furthermore, we show that gene transfer to penumbral zones is possible, suggesting a potential therapeutic strategy for clinical application.