Pharmaceutical Science Research Division, King's College London, 150 Stamford Street, London, UK.
BMC Neurosci. 2011 Mar 7;12:24. doi: 10.1186/1471-2202-12-24.
The cause of sporadic amyotrophic lateral sclerosis (ALS) is largely unknown but hypotheses about disease mechanisms include oxidative stress, defective axonal transport, mitochondrial dysfunction and disrupted RNA processing. Whereas familial ALS is well represented by transgenic mutant SOD1 mouse models, the mouse mutant wobbler (WR) develops progressive motor neuron degeneration due to a point mutation in the Vps54 gene, and provides an animal model for sporadic ALS. VPS54 protein as a component of a protein complex is involved in vesicular Golgi trafficking; impaired vesicle trafficking might also be mechanistic in the pathogenesis of human ALS.
In motor neurons of homozygous symptomatic WR mice, a massive number of endosomal vesicles significantly enlarged (up to 3 μm in diameter) were subjected to ultrastructural analysis and immunohistochemistry for the endosome-specific small GTPase protein Rab7 and for amyloid precursor protein (APP). Enlarged vesicles were neither detected in heterozygous WR nor in transgenic SOD1(G93A) mice; in WR motor neurons, numerous APP/Rab7-positive vesicles were observed which were mostly LC3-negative, suggesting they are not autophagosomes.
We conclude that endosomal APP/Rab7 staining reflects impaired vesicle trafficking in WR mouse motor neurons. Based on these findings human ALS tissues were analysed for APP in enlarged vesicles and were detected in spinal cord motor neurons in six out of fourteen sporadic ALS cases. These enlarged vesicles were not detected in any of the familial ALS cases. Thus our study provides the first evidence for wobbler-like aetiologies in human ALS and suggests that the genes encoding proteins involved in vesicle trafficking should be screened for pathogenic mutations.
散发性肌萎缩侧索硬化症（ALS）的病因在很大程度上尚不清楚，但关于疾病机制的假说包括氧化应激、轴突运输缺陷、线粒体功能障碍和 RNA 加工紊乱。家族性 ALS 很好地由转突变 SOD1 小鼠模型代表，而 wobbler（WR）小鼠突变体由于 Vps54 基因突变而发展出进行性运动神经元变性，为散发性 ALS 提供了动物模型。VPS54 蛋白作为蛋白复合物的一个组成部分，参与囊泡高尔基体运输；囊泡运输受损也可能是人类 ALS 发病机制中的机制性因素。
在纯合症状 WR 小鼠的运动神经元中，大量的内体囊泡显著增大（直径达 3μm），进行超微结构分析和内体特异性小 GTP 酶蛋白 Rab7 和淀粉样前体蛋白（APP）的免疫组织化学分析。WR 杂合子和转 SOD1(G93A) 小鼠中均未检测到增大的囊泡；在 WR 运动神经元中，观察到大量 APP/Rab7 阳性囊泡，这些囊泡大多数为 LC3 阴性，表明它们不是自噬体。
我们得出结论，内体 APP/Rab7 染色反映了 WR 小鼠运动神经元中囊泡运输受损。基于这些发现，我们分析了人类 ALS 组织中增大的囊泡中的 APP，并在 14 例散发性 ALS 病例中的 6 例脊髓运动神经元中检测到。在任何家族性 ALS 病例中均未检测到这些增大的囊泡。因此，我们的研究首次为人类 ALS 提供了类似于 wobbler 的病因证据，并表明参与囊泡运输的蛋白编码基因应进行致病性突变筛查。
