Gadd45b Enhances Neurogenesis In The SVZ Of Rats After Ischemia Stroke

Objective: Ischemia stroke is a common cause of mortality and disability. The adult SVZ neurogenesis after ischemia stroke may contribute to stroke outcome. Therefore, enhancing neurogenesis may be a future therapeutic target for stroke. Continual audlt neurogenesis has been detected mainly in the SVZ of the lateral ventricles and the subgranular zone(SGZ) of the dentate gyrus(DG).Environmental Enrichment(EE) has been reported to increase neurogenesis after stroke, and may facilitate functional recovery from injury. Growth arrest and DNA-damage-inducible protein 45 beta(Gadd45b) has recently been demonstrated to can be induced by neuronal activity and required for activity-induced neurogenesis in the adult hippocampus of mice. In this study, we examine the role of Gadd45 b in adult SVZ neurogenesis after stroke and detect whether Gadd45 b plays a role in EE-induced SVZ neurogenesis in models of focal cerebral ischemia.Methods: Adult male Sprague Dawley(SD) rats were randomly divided into five groups: MCAO(single ischemia), LV-shGadd45b(MCAOplus LV-shGadd45b), LV-control(MCAO plus LV-control), EE(MCAO plus Environmental Enrichment), EE+LV-shGadd45b(MCAO plus Environmental Enrichment and LV-shGadd45b). Middle cerebral artery occlusion(MCAO) was established, followed with reperfusion 90 min later.Gadd45 b expression was knockdown by lentiviral with RNA interference(RNAi). Double immunofluorescent labeling for Gadd45 b and a few phenotype-specific markers(NeuN, GFAP, DCX and Nestin) were performed to determine the localization of Gadd45 b after stroke. Edu staining and immunofluorescence assay with several makers(DCX, GFAP and MAP2) were performed to detect cell proliferation in the SVZ and differentiation in the peri-infarction region. In addition, Gadd45 b expression was investigated by Western Blot and Q-PCR analysis. BDNF expression was detected by western blot analysis and IHC staining.Results: We found that most of Gadd45 b immunoreactive cells in ischemia hemisphere were colabeled with NeuN but not GFAP. In the SVZ,Gadd45 b was also detected on Nestin positive type C cells. Edu staining and immunofluorescent staining showed that the number of Edu+cells,DCX+/Edu+ and MAP-2+/Edu+ cells of LV-shGadd45 b were pronouncedly decreased in the ipsilateral SVZ compared with MCAO and LV-control 7d after stroke. Rats received administration of EE exhibited an obvious increase of EdU+cells, DCX+/Edu+ and MAP-2+/Edu+ cells in the ipsilateral SVZ compared with MCAO on 7d of reperfusion. There wasno statistical difference between EE+ LV-shGadd45 b, MCAO and LV-control in the ipsilateral SVZ. The expression of Gadd45 b and BDNF significantly decreased in LV-shGadd45 b compared with MCAO. EE clearly increased the expression of Gadd45 b and BDNF compared with MCAO. No significant difference was found between EE+ LV-shGadd45 b and MCAO.Conclusion: We found that Gadd45b-RNAi after MCAO reduced proliferation in the ipsilateral SVZ and differentiation in peri-infarct regions after ischemic injury, accompanied with a decrease in Brain-derived neurotrophic factor(BDNF) expression. These data indicate that Gadd45 b is indispensable in SVZ neurogenesis after ischemia stroke,and Gadd45 b may enhance SVZ neurogenesis by up-regulating the expression of BDNF. Treatment with EE after ischemia stroke up-regulated Gadd45 b and BDNF expression and increased the SVZ neurogenesis.Inhibition of Gadd45 b almost counteracted the increased neurogenesis and BDNF expression induced by EE, indicating that EE can promote neurogenesis in the SVZ probably by up-regulating Gadd45 b expression and Gadd45 b expression and Gadd45 b should be one of the upstream regulators to BDNF in the EE-induced neurogenesis after cerebral ischemia.All together, our results indicate that Gadd45 b is a beneficial molecule for SVZ neurogenesis after ischemia stroke and EE can promote neurogenesis in the SVZ probably by up-regulating Gadd45b expression.