Li Ning, Wu Hao, Yang Sufang, Chen Dexi
Department of Medicine, Beijing Youan Hospital, Capital University of Medical Science, Beijing 100054, China.
DNA Repair (Amst). 2007 Sep 1;6(9):1297-306. doi: 10.1016/j.dnarep.2007.02.027. Epub 2007 Apr 6.
Neuronal protection induced by ischemic preconditioning has an important role in the reduction of stroke volume and attenuation of neuronal cell death. Ischemic injury is associated with increased oxidative DNA damage, and failure to efficiently repair these oxidatively damaged lesions results in the accumulation of mutations and neuronal cell death. Although the effects of ischemic tolerance can have profound implications, the precise mechanisms mediating this phenomenon remain unclear. The base excision repair (BER) pathway has a major role in the repair of oxidative DNA base damage after ischemic injury. Using a rat model of ischemic preconditioning, we now report that the neuronal protection observed after induction of ischemic tolerance is associated with increased BER. In situ detection of single-strand breaks and apurinic/apyrimidinic sites reduced to baseline levels after reperfusion following ischemic preconditioning. By contrast, no change was seen in the quantity of in situ lesions after reperfusion in non-ischemic preconditioned brain. Induction of the BER proteins XRCC1, DNA polymerase-beta, and DNA ligase III was seen after reperfusion in ischemically conditioned brain. Moreover, an increase in binding between XRCC1 and DNA polymerase-beta was seen under these conditions, as might be expected during formation of functional BER complexes. Using in vitro BER oligonucleotides, we directly demonstrated an increase in total BER capacity of nuclear extracts prepared from ischemic-conditioned brain after reperfusion compared with sham-operated brain. These findings provide direct evidence that increased BER is associated with the neuroprotection induced after ischemic preconditioning, and provides important new mechanistic insight into the important biologic pathways that protect neurons against irreversible ischemic injury.
缺血预处理诱导的神经元保护在减少脑血流量和减轻神经元细胞死亡方面具有重要作用。缺血性损伤与氧化性DNA损伤增加相关，而未能有效修复这些氧化性损伤的病变会导致突变积累和神经元细胞死亡。尽管缺血耐受的影响可能具有深远意义，但其介导这一现象的精确机制仍不清楚。碱基切除修复（BER）途径在缺血性损伤后氧化性DNA碱基损伤的修复中起主要作用。利用缺血预处理的大鼠模型，我们现在报告，诱导缺血耐受后观察到的神经元保护与BER增加有关。缺血预处理后再灌注时，单链断裂和无嘌呤/无嘧啶位点的原位检测降至基线水平。相比之下，非缺血预处理脑再灌注后原位损伤数量未见变化。缺血预处理脑再灌注后可见BER蛋白XRCC1、DNA聚合酶β和DNA连接酶III的诱导。此外，在这些条件下，XRCC1与DNA聚合酶β之间的结合增加，这在功能性BER复合物形成过程中可能是预期的。使用体外BER寡核苷酸，我们直接证明，与假手术脑相比，缺血预处理脑再灌注后制备的核提取物的总BER能力增加。这些发现提供了直接证据，表明BER增加与缺血预处理后诱导的神经保护有关，并为保护神经元免受不可逆缺血性损伤的重要生物学途径提供了重要的新机制见解。
