Mechanism of apoptosis and DNA methylation during development and aging of neuronal cells

5-氮杂胞苷(5-azacytidine，5AzC)是一种胞苷类似物，嘧啶环上的5个碳原子被氮原子取代。5-AzC进入Prymidine环可能导致5位不能甲基化，导致某个基因的启动子区域去甲基化。新产生的一种未知的凋亡相关蛋白(S)可能参与了5-AzC诱导的细胞凋亡。本研究分离了这种凋亡相关基因(S)/蛋白(S)，并阐明了该基因(S)被激活的机制。结果表明，5AzC诱导的神经元组织或细胞的凋亡与脱甲基化密切相关。此外，5AzC作用于PC12细胞(来源于大鼠嗜铬细胞瘤)后，核糖体蛋白L4(RpL4)基因在细胞凋亡前表达增加，并且rpL4基因也可诱导细胞凋亡。因此，rpL4基因的表达是神经细胞凋亡的关键事件。最近，狗和猫等伴生动物的寿命延长。随着寿命的延长，更多的老年狗会患上痴呆症。我们证明，脑细胞凋亡的数量与痴呆样疾病的进展密切相关。本研究还试图揭示老年犬脑内细胞凋亡相关基因与痴呆的关系。直到目前为止还没有得到足够的结果，进一步的研究将澄清两者之间的关系。

5-Azacytidine (5AzC) is a cytidine analogue and the number 5 carbon atom of the pyrimidine ring is replaced by a nitrogen atom. Intake of 5AzC into the prymidine ring may render the 5 position unable to be methylated, leading activation of a certain gene with demethylated promotor region. An unknown apoptosis-related protein(s) newly produced would be involved in the 5AzC-induced apoptosis. The present study is performed to isolate such apoptosis-related gene(s)/protein(s) and to clarify the mechanism through which the gene(s) would be activated.The results clarified that 5AzC-induced apoptosis in the neuronal tissue or cells is closely involved in DNA demethylation. In addition, the increased expression of ribosomal protein L4 (rpL4) gene was demonstrated before apoptosis in PC12 cells (originated from rat pheochromocytoma) treated with 5AzC.Furthermore, apoptosis was also induced in cells transfected with rpL4 gene. Therefore, it was revealed that the expression of rpL4 gene is an crucial event for neuronal apoptosis.Recently, the life span of companion animals such as dogs and cats is expanded. As the life span elongates, more aged dogs suffer from dementia-like condition. We demonstrated that the number of apoptotic brain cells were closely related to progression of the dementia-like condition. In the present study, we also tried to reveal the relation between apoptosis-related genes and dementia in the brain of aged dogs. Not enough results are obtained until the present and further studies will clarify the relations.