Institute of Neuropathology, RWTH Aachen University Hospital, Pauwelsstr. 30, 52074, Aachen, Germany.
Leibniz-Institut für Analytische Wissenschaften-ISAS e.V, Otto-Hahn-Str. 6b, 44227, Dortmund, Germany.
Mol Neurobiol. 2016 Oct;53(8):5527-41. doi: 10.1007/s12035-015-9456-z. Epub 2015 Oct 14.
SIL1 acts as nucleotide exchange factor for the endoplasmic reticulum chaperone BiP. Mutations of SIL1 cause Marinesco-Sjögren syndrome (MSS), a neurodegenerative disorder. Moreover, a particular function of SIL1 for etiopathology of amyotrophic lateral sclerosis (ALS) was highlighted, thus declaring the functional SIL1-BiP complex as a modifier for neurodegenerative disorders. Thereby, depletion of SIL1 was associated with an earlier manifestation and in strengthened disease progression in ALS. Owing to the absence of appropriate in vitro models, the precise cellular pathophysiological mechanisms leading to neurodegeneration in MSS and triggering the same in further disorders like ALS are still elusive. We found that SIL1 depletion in human embryonic kidney 293 (HEK293) cells led to structural changes of the endoplasmic reticulum (ER) including the nuclear envelope and mitochondrial degeneration that closely mimic pathological alterations in MSS and ALS. Functional studies revealed disturbed protein transport, cytotoxicity with reduced proliferation and viability, accompanied by activation of cellular defense mechanisms including the unfolded protein response, ER-associated degradation pathway, proteolysis, and expression of apoptotic and survival factors. Our data moreover indicated that proteins involved in cytoskeletal organization, vesicular transport, mitochondrial function, and neurological processes contribute to SIL1 pathophysiology. Altered protein expression upon SIL1 depletion in vitro could be confirmed in Sil1-deficient motoneurones for paradigmatic proteins belonging to different functional classes. Our results demonstrate that SIL1-depleted HEK293 cells are an appropriate model to identify proteins modulated by SIL1 expression level and contributing to neurodegeneration in MSS and further disorders like ALS. Thereby, our combined results point out that proteins beyond such involved ER-related protein processing are affected by SIL1 depletion.
SIL1 作为内质网伴侣蛋白 BiP 的核苷酸交换因子。SIL1 突变会导致 Marinesco-Sjögren 综合征（MSS），这是一种神经退行性疾病。此外，SIL1 对于肌萎缩侧索硬化症（ALS）的发病机制有特定的作用，从而将功能性 SIL1-BiP 复合物宣布为神经退行性疾病的修饰因子。因此，SIL1 的耗竭与 ALS 中疾病更早发作和更强疾病进展有关。由于缺乏适当的体外模型，导致 MSS 中神经退行性变和引发其他疾病（如 ALS）的精确细胞病理生理机制仍不清楚。我们发现，人胚肾 293（HEK293）细胞中 SIL1 的耗竭导致内质网（ER）的结构变化，包括核膜和线粒体的退化，这与 MSS 和 ALS 中的病理改变非常相似。功能研究显示，蛋白质运输受到干扰，细胞毒性降低，增殖和活力降低，同时激活细胞防御机制，包括未折叠蛋白反应、ER 相关降解途径、蛋白水解和凋亡及存活因子的表达。我们的数据还表明，参与细胞骨架组织、囊泡运输、线粒体功能和神经过程的蛋白质与 SIL1 的病理生理学有关。体外 SIL1 耗竭时涉及不同功能类别的典型蛋白的蛋白质表达改变可以在 Sil1 缺陷的运动神经元中得到证实。我们的结果表明，SIL1 耗竭的 HEK293 细胞是一种合适的模型，可以确定受 SIL1 表达水平调节并有助于 MSS 和其他疾病（如 ALS）神经退行性变的蛋白质。因此，我们的综合结果表明，除了涉及此类 ER 相关蛋白加工的蛋白质之外，SIL1 耗竭还会影响其他蛋白质。
