Effect of silent information regulator 2 homologue 1 activity on angiogenesis in cerebral ischemia rats

Abstract

Objective To investigate the effect of silent information regulator 2 homologue 1 (SIRT1) activity on angiogenesis in cerebral ischemia rats and its related mechanisms. Methods One hundred and twenty healthy male Sprague-Dawley rats were randomly divided into four groups by random numbers: control group, the cerebral ischemia-reperfusion injury model group (model group), the SIRT1 agonist group (agonist group) and the SIRT1 inhibitor group (inhibitor group), with 30 rats in each group. A model of transient middle cerebral artery occlusion was performed by the suture method. After reperfusion for 24 h, neurological deficit scores were evaluated. Cerebral infarct area after middle cerebral artery occlusion (MCAO) in rats was determined by staining with triphenyltetrazolium chloride. SIRT1 deacetylase activity was detected by ELISA in ischemic brain tissue. By immunohistochemistry, we observed CD34 expression and detected microvascular density (MVD) in ischemic cerebral cortex. Immunoblotting was carried out to evaluate protein levels of SIRT1, vascular endothelial growth factor (VEGF) and erythropoietin (EPO) in ischemic brain tissue. Results Compared with the control group ((13.828±0.828) U/L), SIRT1 deacetylase activity was significantly reduced in ischemic brain in the model group ((7.721±0.581) U/L, t=8.650, P<0.01). Compared with the model group, SIRT1 deacetylase activity was significantly increased in ischemic brain in the agonist group ((26.165±0.971) U/L, t=-26.123, P<0.01). Compared with the agonist group, SIRT1 deacetylase activity was significantly reduced in ischemic brain in the inhibitor group ((17.094±1.012)U/L, t=12.848, P<0.01). Neurological deficit score was 2.667±0.516 in the model group. When SIRT1 was activated in ischemic brain, neurological deficit score was significantly lower (1.333±0.516, t=4.822, P<0.01) than that of the model group. When SIRT1 activity was inhibited, the neurological deficit score increased significantly (2.500±0.548, t=-4.147, P<0.01). The cerebral infarction area was 15.473%±3.049% in the model group. When SIRT1 was activated in ischemic brain, the cerebral infarction area was significantly reduced (9.152%±1.803%, t=3.188, P<0.05). Immunohistochemical results showed that the brown cells in the ischemic cortex were CD34 staining positive cells. When SIRT1 was activated in ischemic brain, the MVD count significantly increased in ischemic cerebral cortex (the agonist group: 8.167±1.941/high power lens, the model group: 3.167±0.753/high power lens, t=-6.864, P<0.01). Immunoblotting demonstrated that the activation of SIRT1 increased the protein expressions of VEGF (the agonist group: 0.568±0.012, the model group: 0.468±0.008, t=-11.034, P<0.01) and EPO (the agonist group: 0.646±0.010, the model group: 0.471±0.013, t=-20.952, P<0.01) in ischemic brain. Conclusions Activation of SIRT1 has neuroprotective effect on cerebral ischemia-reperfusion injury rats. SIRT1 can promote angiogenesis in the early stage of cerebral ischemia reperfusion via directly increasing the expressions of VEGF and EPO in ischemic brain. Key words: Brain ischemia; Reperfusion injury; Silent information regulator 1; Neuroprotective; Angiogenesis; Vascular endothelial growth factor; Erythropoietin