MOE Key Laboratory of Laser Life Science and Institute of Laser Life Science, South China Normal University, Guangzhou, China.
J Neurosci Res. 2011 Nov;89(11):1723-36. doi: 10.1002/jnr.22725. Epub 2011 Aug 8.
The mammalian nicotinamide-adenine dinucleotide (NAD)-dependent deacetylase Sirt1 impacts different processes involved in the maintenance of brain integrity and in the pathogenic pathways associated with several neurodegenerative disorders, including Alzheimer's disease. Here we used human Sirt1 transgenic mice to demonstrate that neuron-specific Sirt1 overexpression promoted neurite outgrowth and improved cell viability under normal and nutrient-limiting conditions in primary culture systems and that Sirt1-overexpressing neurons exhibited higher tolerance to cell death or degeneration induced by amyloid-β1-42 oligomers. Coincidentally, we found that enhanced Sirt1 expression in neurons downregulated the mammalian target of rapamycin (mTOR) protein levels and its phosphorylation without changes in its mRNA levels, which was accompanied by concomitant inhibition of the mTOR downstream signaling activity as revealed by decreased p70S6 kinase (p70S6K) phosphorylation at Thr389. Consistently with this, using a Sirt1 siRNA transfection approach, we observed that reduction of endogenous mouse Sirt1 led to increased levels of mTOR and phosphorylation of itself and p70S6K as well as impaired cell survival and neurite outgrowth in wild-type mouse primary neurons, corroborating a suppressing effect of mTOR by Sirt1. Correspondingly, the mTOR inhibitor rapamycin markedly improved neuronal cell survival in response to nutrient deprivation and significantly enhanced neurite outgrowth in wild-type mouse neurons. The protective effect of rapamycin was extended to neurons even with Sirt1 siRNA knockdown that displayed developmental abnormalities compared with siRNA control-treated cells. Collectively, our findings suggest that Sirt1 may act to promote growth and survival of neurons in the central nervous system via its negative modulation of mTOR signaling.
哺乳动物烟酰胺腺嘌呤二核苷酸（NAD）依赖性去乙酰化酶 Sirt1 影响维持大脑完整性的不同过程，以及与几种神经退行性疾病相关的致病途径，包括阿尔茨海默病。在这里，我们使用人类 Sirt1 转基因小鼠证明，神经元特异性 Sirt1 过表达可促进原代培养系统中神经突起生长，并在正常和营养限制条件下提高细胞活力，而过表达 Sirt1 的神经元对淀粉样β1-42 寡聚体诱导的细胞死亡或变性表现出更高的耐受性。巧合的是，我们发现神经元中增强的 Sirt1 表达下调了哺乳动物雷帕霉素靶蛋白（mTOR）蛋白水平及其磷酸化，而其 mRNA 水平没有变化，这伴随着 mTOR 下游信号活性的同时抑制，如 p70S6 激酶（p70S6K）在 Thr389 处的磷酸化降低所揭示的那样。与此一致，使用 Sirt1 siRNA 转染方法，我们观察到减少内源性小鼠 Sirt1 会导致 mTOR 及其自身和 p70S6K 的磷酸化水平增加，以及野生型小鼠原代神经元的细胞存活和神经突起生长受损，证实了 Sirt1 对 mTOR 的抑制作用。相应地，mTOR 抑制剂雷帕霉素可显著改善营养剥夺后神经元的细胞存活，并显著增强野生型小鼠神经元的神经突起生长。雷帕霉素的保护作用甚至扩展到即使 Sirt1 siRNA 敲低的神经元，与 siRNA 对照处理的细胞相比，其显示出发育异常。总之，我们的研究结果表明，Sirt1 可能通过其对 mTOR 信号的负调控来促进中枢神经系统中神经元的生长和存活。
