Targeting NMNAT1 to Axons and Synapses Transforms Its Neuroprotective Potency In Vivo
Targeting NMNAT1 to Axons and Synapses Transforms Its Neuroprotective Potency In Vivo
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DOI：
10.1523/jneurosci.1189-10.2010
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发表时间：
2010-10-06
影响因子：
5.3
通讯作者：
Coleman, Michael P.
中科院分区：
文献类型：
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作者：
Babetto, Elisabetta;Beirowski, Bogdan;Coleman, Michael P.
轴突和突触退变是许多神经退行性疾病的常见组成部分，对其进行挽救对于有效的神经保护至关重要。嵌合的沃勒变性缓慢蛋白（Wld(S)）呈剂量依赖性地保护轴突，但其作用机制仍不清楚。我们最近发现Wld(S)在非核位置发挥作用且存在于轴突中。这一发现以及其他近期的报道支持一种模型，即Wld(S)通过其核内的烟酰胺单核苷酸腺苷酰转移酶1（NMNAT1）部分的核外再分布来发挥保护作用。然而，细胞质中的NMNAT1是在轴突和突触局部发挥作用，还是在细胞体的非核位点发挥作用，仍不清楚。非核NMNAT1相对于Wld(S)的轴突保护效力也需要在体内确定。由于Wld(S)的N末端部分（N70）定位于轴突，我们假设它介导NMNAT1部分的运输。为了验证这一点，我们用源自淀粉样前体蛋白的轴突靶向肽替代N70，并将其与核靶向被破坏的NMNAT1融合。在转基因小鼠中，这种改造后的NMNAT1从一种即使在高表达水平下也无法抑制沃勒变性的分子，转变成一种比Wld(S)更有效的蛋白质，能够在检测不到的表达水平下将受损轴突保存数周。阻止NMNAT1向轴突的运输会消除其保护作用。轴突靶向的NMNAT1定位于囊泡结构，与核外的Wld(S)共定位，并且至少部分与线粒体共同运输。我们得出结论，NMNAT活性的轴突靶向对于延迟沃勒变性既是必要的也是充分的，并且促进轴突和突触运输可大大提高其有效性。
Axon and synapse degeneration are common components of many neurodegenerative diseases, and their rescue is essential for effective neuroprotection. The chimeric Wallerian degeneration slow protein (Wld(S)) protects axons dose dependently, but its mechanism is still elusive. We recently showed that Wld(S) acts at a non-nuclear location and is present in axons. This and other recent reports support a model in which Wld(S) protects by extranuclear redistribution of its nuclear NMNAT1 portion. However, it remains unclear whether cytoplasmic NMNAT1 acts locally in axons and synapses or at a non-nuclear site within cell bodies. The potency of axon protection by non-nuclear NMNAT1 relative to Wld(S) also needs to be established in vivo. Because the N-terminal portion of Wld(S) (N70) localized to axons, we hypothesized that it mediates the trafficking of the NMNAT1 portion. To test this, we substituted N70 with an axonal targeting peptide derived from amyloid precursor protein, and fused this to NMNAT1 with disrupted nuclear targeting. In transgenic mice, this transformed NMNAT1 from a molecule unable to inhibit Wallerian degeneration, even at high expression levels, into a protein more potent than Wld(S), able to preserve injured axons for several weeks at undetectable expression levels. Preventing NMNAT1 axonal delivery abolished its protective effect. Axonally targeted NMNAT1 localized to vesicular structures, colocalizing with extranuclear Wld(S), and was cotransported at least partially with mitochondria. We conclude that axonal targeting of NMNAT activity is both necessary and sufficient to delay Wallerian degeneration, and that promoting axonal and synaptic delivery greatly enhances the effectiveness.