Tabatadze Nino, McGonigal Rhona, Neve Rachel L, Routtenberg Aryeh
Department of Neurobiology, Northwestern University, Evanston, Illinois.
Hippocampus. 2014 Apr;24(4):455-65. doi: 10.1002/hipo.22239. Epub 2014 Jan 9.
Wnt proteins have emerged as transmembrane signaling molecules that regulate learning and memory as well as synaptic plasticity at central synapses (Inestrosa and Arenas (2010) Nat Rev Neurosci 11:77-86; Maguschak and Ressler (2011) J Neurosci 31:13057-13067; Tabatadze et al. (2012) Hippocampus 22: 1228-1241; Fortress et al. (2013) J Neurosci 33:12619-12626). For example, there is both a training-selective and Wnt isoform-specific increase in Wnt 7 levels in hippocampus seven days after spatial learning in rats (Tabatadze et al. (2012) Hippocampus 22: 1228-1241). Despite growing interest in Wnt signaling pathways in the adult brain, intracellular distribution and release of Wnt molecules from synaptic compartments as well as their influence on synaptic strength and connectivity remain less well understood. As a first step in such an analysis, we show here that Wnt 7 levels in primary hippocampal cells are elevated by potassium or glutamate activation in a time-dependent manner. Subsequent Wnt 7 elevation in dendrites suggests selective somato-dendritic trafficking followed by transport from dendrites to their spines. Wnt 7 elevation is also TTX-reversible, establishing that its elevation is indeed an activity-dependent process. A second stimulation given 6 h after the first significantly reduces Wnt 7 levels in dendrites 3 h later as compared to non-stimulated controls suggesting activity-dependent Wnt 7 release from dendrites and spines. In a related experiment designed to mimic the release of Wnt 7, exogenous recombinant Wnt 7 increased the number of active zones in presynaptic terminals as indexed by bassoon. This suggests the formation of new presynaptic release sites and/or presynaptic terminals. Wnt signaling inhibitor sFRP-1 completely blocked this Wnt 7-induced elevation of bassoon cluster number and cluster area. We suggest that Wnt 7 is a plasticity-related protein involved in the regulation of presynaptic plasticity via a retrograde signaling mechanism as previously proposed (Routtenberg (1999) Trends in Neuroscience 22:255-256). These findings provide support for this proposal, which offers a new perspective on the synaptic tagging mechanism (Redondo and Morris (2011) Nat Rev Neurosci 12:17-30).
Wnt蛋白已成为跨膜信号分子，可调节学习、记忆以及中枢突触处的突触可塑性（伊内斯特罗萨和阿雷纳斯（2010年）《自然神经科学综述》11:77 - 86；马古沙克和雷斯勒（2011年）《神经科学杂志》31:13057 - 13067；塔巴塔泽等人（2012年）《海马体》22: 1228 - 1241；福里斯特等人（2013年）《神经科学杂志》33:12619 - 12626）。例如，在大鼠进行空间学习七天后，海马体中Wnt 7水平会出现训练选择性和Wnt亚型特异性增加（塔巴塔泽等人（2012年）《海马体》22: 1228 - 1241）。尽管成年大脑中Wnt信号通路的研究兴趣日益浓厚，但Wnt分子在突触区室的细胞内分布和释放，以及它们对突触强度和连接性的影响仍不太清楚。作为此类分析的第一步，我们在此表明，原代海马体细胞中的Wnt 7水平会因钾离子或谷氨酸激活而呈时间依赖性升高。随后树突中Wnt 7的升高表明存在选择性的胞体 - 树突运输，随后从树突运输到其棘突。Wnt 7的升高也是TTX可逆的，这表明其升高确实是一个活动依赖性过程。在第一次刺激6小时后给予的第二次刺激，与未刺激的对照组相比，3小时后显著降低了树突中Wnt 7的水平，这表明Wnt 7从树突和棘突的释放是活动依赖性的。在一项旨在模拟Wnt 7释放的相关实验中，外源性重组Wnt 7增加了以巴松管为指标的突触前终末活性区的数量。这表明形成了新的突触前释放位点和/或突触前终末。Wnt信号抑制剂sFRP - 1完全阻断了这种Wnt 7诱导的巴松管簇数量和簇面积的升高。我们认为，Wnt 7是一种与可塑性相关的蛋白质，如先前所提出的，它通过逆行信号机制参与突触前可塑性的调节（劳滕伯格（1999年）《神经科学趋势》22:255 - 256）。这些发现为这一观点提供了支持，该观点为突触标记机制提供了一个新的视角（雷东多和莫里斯（2011年）《自然神经科学综述》12:17 - 30）。
