Ultrastructural study of mitochondria in the spinal cord of transgenic mice with a G93A mutant SOD1 gene
Ultrastructural study of mitochondria in the spinal cord of transgenic mice with a G93A mutant SOD1 gene
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DOI：
10.1007/s00401-004-0837-z
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发表时间：
2004-05-01
影响因子：
12.7
通讯作者：
Iwata, M
中科院分区：
文献类型：
--
作者：
Sasaki, S;Warita, H;Iwata, M
本研究的目的是研究在我们自己的实验室通过电子和免疫电镜从症状前阶段产生的一个相对低的转基因拷贝数（基因拷贝10）表达的G93 A突变的人铜/锌超氧化物歧化酶（SOD 1）的转基因小鼠的脊髓线粒体的变化。在每个阶段，将非转基因小鼠作为对照。在超微结构上，在早期presympathy阶段，许多大的有髓轴突中的线粒体表现出肿胀，嵴的数量增加，并在基质，嵴或两者，在前根出口区，前根，并在前角的腹侧部分的神经髓鞘孔小空泡。在症状前晚期，在与前一阶段相同的区域观察到各种大小的液泡（包括大的）。线粒体膜间隙空泡化。在晚期空泡化的线粒体中，空泡空间充满颗粒状或无定形物质。在症状阶段，在症状前期晚期观察到的线粒体空泡化持续存在，尽管程度较轻。这些空泡化的线粒体主要见于轴突中，但在任何阶段的正常神经元或树突的胞体中均未见到，这与其他报道中所描述的不同。非转基因同窝仔偶尔表现出空泡的前角轴突的变化。然而，它们在大小和数量上都小于转基因小鼠。通过免疫电子显微镜使用免疫金标记方法，在症状前和症状阶段，SOD 1和泛素决定簇定位于空泡化线粒体，特别是在大空泡的颗粒状或无定形物质中，但在大多数正常出现的线粒体中未检测到。SOD 1免疫反应性线粒体只观察到的轴突，而不是在近端树突或胞体。这些发现表明突变SOD 1的毒性直接影响轴突中的线粒体，并随着疾病的进展而增加。因此，突变的SOD 1毒性可能破坏神经元活力所需底物的轴突运输，导致运动神经元变性。泛素和SOD 1在空泡化线粒体中的定位表明，泛素-蛋白酶体系统的蛋白质降解也可能被几种病理机制破坏，例如由于线粒体功能或蛋白酶体功能受损而导致的泛素化蛋白质加工减少，这两者都是由突变SOD 1引起的。此外，巨大的线粒体空泡几乎占据了整个轴突口径，可能是运动神经元变性的另一个促成因素，因为它们可以物理地阻断轴突运输。
The purpose of this study was to examine mitochondrial changes in the spinal cord of transgenic mice of a relatively low transgenic copy number (gene copy 10) expressing a G93A mutant human Cu/Zn superoxide dismutase (SOD1) that were generated in our own laboratories by electron and immunoelectron microscopy from presymptomatic to symptomatic stages. Age-matched non-transgenic mice served as controls at each stage. Ultrastructurally, at the early presymptomatic stage, many mitochondria in large myelinated axons exhibited swelling with an increased number of cristae, and bore small vacuoles in the matrix, cristae or both, in the anterior root exit zone, anterior root, and in the neuropils of the ventral portion of the anterior horn. At the late presymptomatic stage, vacuoles of various sizes (including large ones) were observed in the same regions as in the previous stage. The intermembrane space of mitochondria was also vacuolated. In mitochondria with advanced vacuolation, the vacuolar space was filled with a granular or amorphous substance. At the symptomatic stage, mitochondrial vacuolation seen in the late presymptomatic stage persisted, although to a lesser extent. These vacuolated mitochondria were predominantly seen in the axons, but not in the somata of normal-looking neurons or dendrites at any stage, which differs from that described in other reports. Non-transgenic littermates occasionally exhibited vacuolar changes in the axons of anterior horns. However, they were smaller both in size and number than those in transgenic mice. By immunoelectron microscopy using an immunogold labeling method, at the presymptomatic and symptomatic stages both SOD1 and ubiquitin determinants were localized in vacuolated mitochondria, particularly in the granular or amorphous substance of large vacuoles, but were not detected in most normal-appearing mitochondria. The SOD1-immunoreactive mitochondria were exclusively observed in the axons, and not in proximal dendrites or somata. These findings suggest that the toxicity of mutant SOD1 directly affects mitochondria in the axons and increases with the disease progression. Thus, the mutant SOD1 toxicity might disrupt axonal transport of substrates needed for neuronal viability, leading to motor neuron degeneration. The localization of both ubiquitin and SOD1 in vacuolated mitochondria indicates that protein degradation by ubiquitin-proteasomal system may be also disrupted by several pathomechanisms, such as decreased processing of ubiquitinated proteins due to impairment of mitochondrial function or of proteasomal function, both of which are caused by mutant SOD1. Moreover, giant mitochondrial vacuoles occupying almost the entire axonal caliber could be another contributing factor in motor neuron degeneration, in that they could physically block axonal transport.