bcl-xl over-expression in transgenic mice reduces cerebral ischemia/reperfusion injury

BACKGROUND: Basal cell lymphoma-extra large (bcl-xl) can inhibit neuronal apoptosis by stabilizing the mitochondrial membrane and suppressing cytochrome C release into the cytoplasm. OBJECTIVE: This study aimed to further investigate the cascade reaction pathway of cellular apoptosis. We established an ischemia/dreperfusion model by middle cerebral artery occlusion (MCAO) in transgenic and wild-type mice, and observed changes in the number and distribution of apoptotic neural cells, differences in cerebral infarct volume, in neurological function score, and in cytochrome C expression in the ischemic cerebral cortex, at different time points, DESIGN AND SETTING: The present gene engineering and cell biology experiment was performed at the Laboratory of Biology, Hubei Academy of Agricultural Sciences and at the Laboratory of Immunology, Tongji Medical College, Huazhong University of Science and Technology. MATERIALS: Male bcl-xl over-expression Kunming mice aged 8 weeks and age-matched male wild-type mice were used for this study. Terminal deoxynucleotidyl transferase biotin-dUTP nick end labeling (TUNEL) kits were purchased from Boliman, France. Cytochrome C antibody and Bcl-x immunohistochemical kit were purchased from PharMingen, USA and Santa Cruz Biotechnology, USA, respectively. METHODS: Following MCAO and reperfusion, apoptosis in the ischemic cerebral cortex was detected by the TUNEL assay. Prior to MCAO and 3 hours after reperfusion, the Bcl-xl protein level in the ischemic cerebral cortex was measured by immunohistochemistry. At 3, 6, 12 and 24 hours after reperfusion, the level of cytochrome C in the ischemic cerebral cortex was examined by western blot analysis. Subsequent to MCAO, cerebral infarct volume measurement and neurological examination were performed. MAIN OUTCOME MEASURES: Neural cell apoptosis and cytochrome C expression in the ischemic cerebral cortex; cerebral infarct volume and neurological function score. RESULTS: Twenty-four hours after reperfusion, cerebral infarct volume was reduced by 30% in bcl-xl transgenic mice compared with wild-type mice. Simultaneously, the number of apoptotic cells in the ischemic cerebral cortex was significantly less in the transgenic mice compared with the wild-type mice. Overall, the number of apoptotic cells in the transgenic mice remained at a relatively low level. Prior to and subsequent to cerebral ischemia/reperfusion, transgenic mice exhibited markedly higher Bcl-xl protein levels compared with wild-type mice. In addition, after reperfusion, the level of Bcl-xl protein was increased in both transgenic and wild-type mice, but there was no significant difference (P > 0.05) between the two groups. The level of cytochrome C in the transgenic mice was low in the first 24 hours after reperfusion and increased thereafter but was still lower compared with wild-type mice. Neurological function scores demonstrated that transgenic mice exhibited milder neurological function impairment compared with wild-type mice. CONCLUSION: bcl-xl over-expression can inhibit cytochrome C release and result in an inhibitory effect on neural cell apoptosis, thereby alleviating neural cell injury. This is likely to occur due to exogenous over-expression of bcl-xl rather than endogenous production of bcl-xl.