Relationship between neurodegenerative diseases and neurofilaments accumulated in somata and/or axons

神经丝（neurofilament，NF）在神经元胞体和/或轴突中的异常积聚见于一些神经退行性疾病，如肌萎缩性侧索硬化症、脱髓鞘疾病、过表达外源性NF基因的小鼠以及包括人在内的老年动物。过量表达NF基因的转基因小鼠出现神经元变性的事实表明，NF的异常积聚与NF基因的突变或改变有关。为了阐明NF积累的机制，我们制作了缺失每个NF亚基基因的敲除小鼠，并用生化和形态学方法对其进行分析。我们还制作了敲入小鼠，其中NF-M，NF-H或两者基因被替换以删除其羧基末端尾部结构域，以了解横桥的缺乏如何影响NF组织或神经元结构。在所有转基因小鼠中，结构和/或细胞骨架组织的改变主要在轴突隔室中检测到。NF-L基因敲除的小鼠显示， ...更多信息 NF-M和NF-MmRNA的表达减少，但其蛋白的表达几乎不增加，导致NF缺失，轴突直径减少，但微管密度增加。NF-M基因敲除小鼠NF-L蛋白表达减少，其NF数量减少且不规则。NF-H基因敲除小鼠的NF结构基本不变，但NF- M蛋白含量增加。尽管选择性缺失NF-M尾对NF组织没有显著的改变，但类似的NF-H尾的缺失显著减少了横桥和更多的核心丝的致密化。两个尾部的缺失显示轴突口径的减少和轴浆组织的显著变化，即，核心丝是不规则的，完全没有横桥，有时被膜结合的细胞器占据，表明轴突运输受损。当轴突直径减小时，线粒体的大小和密度都增加。总之，NF基因治疗可以防止神经元中NF的异常积聚。少

Abnormal neurofilament (NF) accumulation in neuronal somata and/or axons is seen in some of neurodegenerative diseases, such as amyotrophic lateral sclerosis, in demyelinated diseases, in mice overexpressing exogenous NF gene, and in aged animals including human. The fact that the transgenic mice overexpressing the NF gene show neuronal degeneration suggests that the abnormal NF accumulation is related with the mutation or alteration in the NF genes. To clarify the mechanism of NF accumulation, we made knockout mice devoid of each NF subunit gene and analysed them with biochemical and morphological methods. We also made knockin mice, in which NF-M, NF-H or both genes were replaced to delete their carboxy-terminal tail domains, to know how the absence of crossbridges influence the NF organization or neuronal structure. In all transgenic mice, alterations in structure and/or cytoskeletal organization were detectable predominantly in the axonal compartment. NF-L knockout mice showed expre … More ssions of NF-M and NF-M mRNAs but hardly those of their proteins, resulting in absence of NFs and reduction of axonal calibers, but increase in density of microtubules. NF-M knockout mice showed a reduced expression of NF-L protein, and their NFs were decreased in number and irregular. NF organization was almost unchanged in NF-H knockout mice, in which NF- M protein was increased in amount. Although selective deletion of the NF-M tail had no significant change in NF organization, similar loss of NF-H tail had significant reduction of crossbridges and more compaction of core filaments. Deletion of both tails showed reduction of axonal calibers and significant change in axoplasmic organization, i.e., core filaments were irregular with complete absence of crossbridges, sometimes occupied with membrane-bound organelles, indicating impairment of the axonal transport. There were increases in both size and density of mitochondria when the axonal calibers were reduced. Taken together, abnormal accumulation of NFs in the neurons may be prevented by the NF gene theraphy. Less