Pooler A M, Guez D H, Benedictus R, Wurtman R J
Department of Brain and Cognitive Sciences, Massachusetts Institute of Technology, 45 Carleton Street, Cambridge, MA 02139, USA.
Neuroscience. 2005;134(1):207-14. doi: 10.1016/j.neuroscience.2005.03.050.
During rapid cell growth the availability of phospholipid precursors like cytidine triphosphate and diacylglycerol can become limiting in the formation of key membrane constituents like phosphatidylcholine. Uridine, a normal plasma constituent, can be converted to cytidine triphosphate in PC12 [corrected] cells and intact brain, and has been shown to produce a resulting increase in phosphatidylcholine synthesis. To determine whether treatments that elevate uridine availability also thereby augment membrane production, we exposed PC12 [corrected] cells which had been differentiated by nerve growth factor to various concentrations of uridine, and measured the numbers of neurites the cells produced. After 4 but not 2 days uridine significantly and dose-dependently increased the number of neurites per cell. This increase was accompanied by increases in neurite branching and in levels of the neurite proteins neurofilament M [corrected] and neurofilament 70. Uridine treatment also increased intracellular levels of cytidine triphosphate, which suggests that uridine may affect neurite outgrowth by enhancing phosphatidylcholine synthesis. Uridine may also stimulate neuritogenesis by a second mechanism, since the increase in neurite outgrowth was mimicked by exposing the cells to uridine triphosphate, and could be blocked by various drugs known to antagonize P2Y receptors (suramin; Reactive Blue 2; pyridoxal-phosphate-6-azophenyl-2',4' disulfonic acid). Treatment of the cells with uridine or uridine triphosphate stimulated their accumulation of inositol phosphates, and this effect was also blocked by pyridoxal-phosphate-6-azophenyl-2',4' disulfonic acid. Moreover, degradation of nucleotides by apyrase blocked the stimulatory effect of uridine on neuritogenesis. Taken together these data indicate that uridine can regulate the output of neurites from differentiating PC12 [corrected] cells, and suggest that it does so in two ways, i.e. both by acting through cytidine triphosphate as a precursor for phosphatidylcholine biosynthesis and through uridine triphosphate as an agonist for P2Y receptors.
在细胞快速生长过程中，磷脂前体（如三磷酸胞苷和二酰基甘油）的可用性在关键膜成分（如磷脂酰胆碱）的形成中可能会成为限制因素。尿苷是血浆中的一种正常成分，在PC12细胞和完整大脑中可转化为三磷酸胞苷，并且已显示会导致磷脂酰胆碱合成增加。为了确定提高尿苷可用性的处理是否也会增加膜的生成，我们将经神经生长因子分化的PC12细胞暴露于不同浓度的尿苷中，并测量细胞产生的神经突数量。4天后而非2天后，尿苷显著且剂量依赖性地增加了每个细胞的神经突数量。这种增加伴随着神经突分支以及神经突蛋白神经丝M和神经丝70水平的增加。尿苷处理还增加了细胞内三磷酸胞苷的水平，这表明尿苷可能通过增强磷脂酰胆碱合成来影响神经突生长。尿苷也可能通过第二种机制刺激神经突生成，因为将细胞暴露于三磷酸尿苷可模拟神经突生长的增加，并且可被已知拮抗P2Y受体的各种药物（苏拉明；活性蓝2；磷酸吡哆醛 - 6 - 偶氮苯基 - 2',4' - 二磺酸）阻断。用尿苷或三磷酸尿苷处理细胞会刺激它们积累肌醇磷酸，并且这种效应也被磷酸吡哆醛 - 6 - 偶氮苯基 - 2',4' - 二磺酸阻断。此外，腺苷三磷酸双磷酸酶对核苷酸的降解阻断了尿苷对神经突生成的刺激作用。综上所述，这些数据表明尿苷可以调节分化中的PC12细胞的神经突输出，并表明它通过两种方式做到这一点，即通过作为磷脂酰胆碱生物合成前体的三磷酸胞苷起作用以及通过作为P2Y受体激动剂的三磷酸尿苷起作用。
