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

5-氮杂胞苷（5AzC）是一种胞苷类似物，嘧啶环的5号碳原子被氮原子取代。将5AzC引入到嘧啶环中可以使5位不能被甲基化，从而导致具有去甲基化启动子区的特定基因的激活。一种新产生的未知的凋亡相关蛋白可能参与了5AzC诱导的细胞凋亡。本研究旨在分离这些凋亡相关基因/蛋白，并阐明这些基因/蛋白被激活的机制，结果表明5AzC诱导的神经组织或细胞凋亡与DNA去甲基化密切相关。此外，5 AzC处理后PC 12细胞凋亡前核糖体蛋白L4（rpL 4）基因表达增加，rpL 4基因转染的PC 12细胞也出现凋亡。因此，rpL 4基因的表达是神经元凋亡的关键事件。近年来，宠物如狗和猫的寿命延长。随着寿命的延长，更多的老年狗患有痴呆症。我们证明了凋亡脑细胞的数量与痴呆样疾病的进展密切相关。在本研究中，我们还试图揭示痴呆相关基因与老年犬脑痴呆的关系。到目前为止，还没有得到足够的结果，进一步的研究将澄清的关系。

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.