DNA甲基转移酶在低氧预适应小鼠脑保护中作用研究

Hypoxia/Ischemia is one of the important factors in center nerve system(CNS) injury. Hypoxia preconditioning is defined as a period of sublethal hypoxia insult, which can induce a protection from an otherwise lethal period, and is believed to trigger endogenous cellular adaptation. Many studies reported that the expression levels of some molecules may be one of the molecular mechanisms of hypoxic preconditioning. It is well known that DNA methylation catalized by DNA methyltransferase(DNMT) can regulate the changes of gene expression, but the role of DNA methylation and DNMT have been not reported in hypoxia preconditioning. It is reported that DnmtS/1 mice are resistant to mild ischemic damage, suggesting that DNMT should play an important role in ischemia/hypoxia tolerance. So it is essential to reveal the protection role of DNMT in hypoxia preconditioning. Using hypoxic preconditioning mouse model which was treated with 5-Aza,we want to investigate the role of DNMT in the neuroprotection of hypoxic preconditioning mice. In order to further clarify the mechanism of DNMT in hypoxia preconditioning，its effect was also supported by cell culture in which three kinds of DNA methyltransferase were over-expressed or knocked-down. This study is important for understanding the mechanisms of neuroprotection of hypoxia preconditioning. This study may provide a new strategy for clinical treatment in CNS impairment caused by cerebral hypoxia/ischemia.

低氧/缺血是导致中枢神经系统损伤的重要因素之一，低氧预适应是通过亚致死性低氧刺激使机体产生内源性保护。研究显示一些分子表达改变是低氧预适应分子机制之一，DNA甲基化可以调节基因表达变化，催化DNA甲基化的是DNA甲基转移酶（DNMT），而DNA甲基化和DNMT在低氧预适应中的作用国内外尚未见报道。有报道DnmtS/1小鼠可以降低缺血引起的神经损伤，提示DNMT在神经的缺血/低氧耐受中有重要作用。因此有必要对DNMT在低氧预适应中的基因表达调控的分子机制进行研究。本研究拟利用低氧预适应小鼠，利用DNMT的抑制剂5-Aza，探讨DNMT调节DNA甲基化作为一种分子机制参与对低氧/缺血的神经保护的可能。本研究辅以体外培养细胞，通过过量和下调表达3种DNMTs，进一步明确其作用机理及机制。将对深入了解低氧预适应神经保护机制有重要意义，还可为临床上脑低氧/缺血后脑损伤防治提供新策略和科学理论依据。

低氧/缺血是导致中枢神经系统损伤的重要因素之一，低氧预适应是通过亚致死性低氧刺激使机体产生内源性保护。研究显示一些分子表达改变是低氧预适应分子机制之一，DNA甲基化可以调节基因表达变化，催化DNA甲基化的是DNA甲基转移酶（DNMT），而DNA甲基化和DNMT在低氧预适应中的作用国内外尚未见报道。有报道DnmtS/1小鼠可以降低缺血引起的神经损伤，提示DNMT在神经的缺血/低氧耐受中有重要作用。因此有必要对DNMT在低氧预适应中的基因表达调控的分子机制进行研究。本研究使用低氧预适应小鼠，利用DNMT的抑制剂5-Aza，通过分子生物学手段发现低氧预适应在早期项可以降低DNMT3A和DNMT3B的表达及DNMTs的活力。研究0-4天小鼠海马组织中DNMTs,VEGF,VEGFR,EPO,EPOR的表达变化，发现低氧预适应可以降低DNMT1，DNMT3A和DNMT3B的表达，低氧预适应可改变VEGF,VEGFR,EPO,EPOR的表达。小鼠侧脑室注射探讨5-Aza 后，对DNMTs以及VEGF,VEGFR,EPO,EPOR的表达均有影响。体外细胞实验进一步验证了体内实验结果。我们得出低氧预适应脑保护涉及DNA甲基化变化的结论。本研究对深入了解低氧预适应神经保护机制有重要意义，还可为临床上脑低氧/缺血后脑损伤防治提供新策略和科学理论依据。