Frontotemporal dementia and amyotrophic lateral sclerosis proteins in neurite health and dysfunction
Frontotemporal dementia and amyotrophic lateral sclerosis proteins in neurite health and dysfunction
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额颞叶痴呆和肌萎缩性侧索硬化症蛋白在神经突健康和功能障碍中的作用
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发表时间：
2018
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通讯作者：
R. Atkinson
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作者：
R. Atkinson
已鉴定出许多与额颞叶痴呆（FTD）和肌萎缩侧索硬化症（ALS）在病理上和/或遗传上相关的蛋白质。 C9ORF72 基因非编码区的六核苷酸重复扩增是与 FTD 和 ALS 相关的最大遗传因素。此外，大约 50% 的 FTD 病例和 90% 的 ALS 病例的大脑中发现了 TDP-43 蛋白的病理性内含物。然而，这两种蛋白质的正常功能以及其与疾病中神经元退化的关系尚不清楚。越来越多的证据表明这两种蛋白质可能与神经元细胞骨架有关。由于在死后病例中观察到显着的轴突病理学和损失，细胞骨架在 FTD/ALS 中特别令人感兴趣。众所周知，细胞骨架通常是许多神经退行性疾病中轴突完整性变化的关键效应器。本论文通过使用小鼠原代细胞培养物、完整小鼠大脑的组织学分析以及小鼠视网膜模型中病毒介导的感兴趣蛋白的表达，研究了 TDP-43 和 C9ORF72 的正常功能及其与细胞骨架的联系。
TDP-43 是一种主要的核蛋白，人们对其在 DNA 和 RNA 结合以及转录和翻译调节中的核作用非常了解。有证据表明，TDP-43 对于神经突生长、重塑也很重要，并且可以调节神经元细胞骨架的许多组成部分。检查了原代皮质神经元中 TDP-43 过表达的影响，并证明了肌动蛋白相关细胞过程的明显改变，包括神经突分支和生长锥形态，以及这些细胞蛋白质组中肌动蛋白结合蛋白的下调。为了检查体内 TDP-43 致病性改变的影响，通过眼内注射病毒，使用 AAV2 病毒介导野生型人类 TDP-43 和具有核定位信号 (NLS) 突变的人类 TDP-43 在小鼠视网膜神经节细胞中的表达。这些变化引起了视神经的轴突病理，表明由于细胞器积累的存在而扰乱了轴突运输。
已经描述了 C9ORF72 中非编码重复序列扩展如何导致疾病的几种机制，但对 C9ORF72 蛋白的正常功能和表达模式知之甚少。本论文描述了三种报道的小鼠 C9ORF72 亚型在细胞培养物和体内的表达模式和细胞定位，并证明 C9ORF72 存在于突触体和富含肌动蛋白的神经元结构中。
总之，这些结果表明 C9ORF72 和 TDP-43 可能与神经元细胞骨架，特别是肌动蛋白细胞骨架有联系。神经元细胞骨架的调节是为脆弱的细胞成分（例如轴突）提供治疗保护的一个引人注目的目标。本论文中描述的研究可能有助于了解 TDP-43 和 C9ORF72 相关的 FTD/ALS 是否适合这些类型的干预措施。
A number of proteins have been identified which are pathologically and/or genetically associated with both frontotemporal dementia (FTD) and amyotrophic lateral sclerosis (ALS). A hexanucleotide repeat expansion in the non-coding region of the C9ORF72 gene is the largest genetic factor associated with FTD and ALS. Additionally, pathological inclusions of the TDP-43 protein are found in brains of approximately 50% of FTD cases and 90% of ALS cases. However, the normal function of these two proteins and how this relates to the degeneration of neurons in disease are not yet well understood. Accumulating evidence suggests that both proteins may have involvement with the neuronal cytoskeleton. The cytoskeleton is of particular interest in FTD/ALS due to significant axon pathology and loss observed in post mortem cases. It is known that the cytoskeleton is often a key effector to changes in axon integrity in many neurodegenerative diseases. This thesis examined the normal functions of TDP-43 and C9ORF72, and their links with the cytoskeleton through use of mouse primary cell culture, histological analysis of intact mouse brain, and viral-mediated expression of proteins of interest in a retina model in the mouse.
TDP-43 is a predominantly nuclear protein, with much known about its nuclear roles in DNA and RNA binding, and regulation of transcription and translation. Evidence suggests that TDP-43 is also important for neurite outgrowth, remodelling and can regulate many components of the neuronal cytoskeleton. The effects of overexpression of TDP-43 in primary cortical neurons were examined and demonstrated distinct alterations to actin-associated cellular processes including neurite branching and growth cone morphology, as well as down-regulation of actin-binding proteins in the proteome of these cells. To examine the effect of pathogenic alterations to TDP-43 in vivo AAV2 virus was used to mediate the expression of wildtype human TDP-43 and human TDP-43 with a mutation to the nuclear localisation signal (NLS) in mouse retinal ganglion cells, through intraocular injection of the virus. These changes induced axon pathology in the optic nerve, with indications of perturbed axonal transport due to presence of organelle accumulation.
Several mechanisms for how the non-coding repeat expansion in C9ORF72 may lead to disease have been described, however little is known about the normal function and the expression pattern of the C9ORF72 protein. This thesis characterized the expression pattern and cellular localisation of the three reported mouse isoforms of C9ORF72 in cell culture and in vivo, and demonstrated that C9ORF72 was present in synaptosomes and within actin-rich structures of neurons.
In summary, these results indicate that both C9ORF72 and TDP-43 may have links to the neuronal cytoskeleton, and in particular the actin cytoskeleton. Modulation of the neuronal cytoskeleton is a compelling target for providing therapeutic protection to vulnerable cellular components, such as the axon. Studies such as those described in this thesis may provide insight for whether TDP-43- and C9ORF72-related FTD/ALS are candidates for these types of interventions.