| Stroke has been considered to be a vital disease to human being. The fate of ischemic neurons is determined by the balance of neuronal damage and its pretection. Therefore, much more attention has been paid on how to augment neuronal protection and alleviate neuronal damage. Vascular endothelial growth factor (VEGF), an important neurotrophic factor, could be up-regulated in ischemic brain. It has been proved that exogenous VEGF has neuroprotective role. However, it is still unclear whether ischemia-induced endogenous VEGF expression plays a neuroprotective role. In the present study, we investigate whether the induction of endogenous VEGF plays neuroprotective role in ischemic neurons and whether it associates with DNA repair. On the other hand, more and more evidences showed that neurogenesis exists in adult mammalian brain. Ischemia could stimulate neurogenesis in the cerebral cortex and hippocampus which is considered as a very important neuronal protection mechanism. Therefore, in the second part of this study, we further evaluate whether ischemia could induce neurogenesis in the striatum, the most commonly ischemic area; if so, where newborn neurons in the striatum come from and whether electric stimulation could enhance neurogenesis in ischemic injured brain.The first part: The neuroprotective roles and mechanisms of endogenous VEGF in ischemia-injured brainVascular endothelial growth factor (VEGF), an important neural trophic factor, could be up-regulated in ischemic brain. Studies have shown the exogenous VEGF protects neurons against ischemia-reperfusion injury, whose protective mechanism may be related to neoangiogenesis or vessel protection. On the other hand, VEGF may play direct cytoprotective role through its receptor-coupled phosphatidylinositol 3'-kinase (PI3-K)/Akt signal transduction system. Activation of PI3-K/Akt pathway can upregulate antiapoptotic proteins and downregulate activated caspase-3. It's still unknown whether the ischemia-induced endogenous VEGF expression has the same neuroprotective role as the exogenous one does.The cascade of events following cerebral ischemia could induce neuronal DNA damage. Incomplete repair or nonrepair of DNA damage would induce ischemic neuronal death and further contribute to the expansion of the ischemic lesion. At the same time, cerebral ischemia can activate a complex network of DNA repair tocounteract neuronal DNA damage. Nucleotide excision repair (NER) is the most important and best studied among the DNA repair pathway. In NER, the transcribed strand of transcriptionally active gene is repaired more preferentially and efficiently than the nontranscribed one. ERCC6 has been confirmed to be a transcription-repair coupling factor and to play a crucial role in preferential transcription-repair coupling of NER. Also, several studies have demonstrated that the induction of ERCC6 in ischemic injured neurons contributes to cytoprotection against ischemic neuronal DNA damage.In the first part of study, we used VEGF antisense oligodeoxynucleotide (ODN) to specially knockdown VEGF induction in ischemic neurons, then analyzed the changes of infarct volume, ischemia-induced TUNEL and ERCC6 mRNA expression to elucidate whether the induced endogenous VEGF plays neuroprotective role probably associated with the expression of ERCC6 mRNA.RESULTS:1. Immunostaining was used to examine the expression of VEGF to prove the validity of VEGF antisense ODN. Compared with random ODN treatment, VEGF antisense reduced the number of VEGF positive neurons in the ipsilateral striatum and frontoparietal cortex at 3 d reperfusion after ischemia. Cresyl violet staining and image processing and analysis system were used to determine the infarct volume. They showd that VEGF antisense ODN significantly increased infarct volume at 3 d reperfusion after ischemia.2. In situ TUNEL staining was used to detect DNA double-strand breaks in the ischemic brains. TUNEL positive cells were found in ipsilateral striatum and frontoparietal cortex, but not in... |
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