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

在一些神经退行性疾病，如肌萎缩性侧索硬化症、脱髓鞘疾病、外源性神经丝基因过表达的小鼠以及包括人类在内的老年动物中，可以看到神经丝（NF）在神经元体细胞和/或轴突中的异常积累。过表达NF基因的转基因小鼠出现神经退行性变，提示NF的异常积累与NF基因的突变或改变有关。为了阐明NF积累的机制，我们制作了缺乏NF各亚基基因的敲除小鼠，并用生化和形态学方法对其进行了分析。我们还制作了敲入小鼠，其中NF- m， NF- h或两个基因被替换以删除其羧基末端尾部结构域，以了解缺少交叉桥如何影响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室中检测到。NF-L基因敲除小鼠NF-M和NF-M mrna表达增加，但NF-M蛋白表达减少，导致nf缺失和轴突直径减少，微管密度增加。NF-M敲除小鼠NF-L蛋白表达降低，nf数量减少且不规则。NF- h敲除小鼠的NF组织基本不变，但NF- M蛋白含量增加。虽然NF- m尾的选择性缺失对NF组织没有明显的影响，但NF- h尾的类似缺失会显著减少交叉桥和增加核心丝的压实。两条尾巴的缺失表明轴突直径减少，轴浆组织明显改变，即核心丝不规则，完全没有交叉桥，有时被膜结合细胞器占据，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均增加。综上所述，NF基因治疗可以预防神经元中NF的异常积累。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