Institute of Clinical Neurobiology, University Hospital of Wuerzburg, Wuerzburg, Germany.
Max Planck Institute of Biochemistry, Martinsried, Germany.
Nat Neurosci. 2016 Dec;19(12):1610-1618. doi: 10.1038/nn.4407. Epub 2016 Oct 10.
Intronic hexanucleotide expansions in C9ORF72 are common in amyotrophic lateral sclerosis (ALS) and frontotemporal dementia, but it is unknown whether loss of function, toxicity by the expanded RNA or dipeptides from non-ATG-initiated translation are responsible for the pathophysiology. We determined the interactome of C9ORF72 in motor neurons and found that C9ORF72 was present in a complex with cofilin and other actin binding proteins. Phosphorylation of cofilin was enhanced in C9ORF72-depleted motor neurons, in patient-derived lymphoblastoid cells, induced pluripotent stem cell-derived motor neurons and post-mortem brain samples from ALS patients. C9ORF72 modulates the activity of the small GTPases Arf6 and Rac1, resulting in enhanced activity of LIM-kinases 1 and 2 (LIMK1/2). This results in reduced axonal actin dynamics in C9ORF72-depleted motor neurons. Dominant negative Arf6 rescues this defect, suggesting that C9ORF72 acts as a modulator of small GTPases in a pathway that regulates axonal actin dynamics.
C9ORF72 基因中的内含子六核苷酸扩展在肌萎缩侧索硬化症（ALS）和额颞叶痴呆中很常见，但尚不清楚功能丧失、扩展 RNA 的毒性还是非 ATG 起始翻译产生的二肽导致了病理生理学的发生。我们确定了运动神经元中 C9ORF72 的互作组，发现 C9ORF72 与丝切蛋白和其他肌动蛋白结合蛋白存在于一个复合物中。在 C9ORF72 耗尽的运动神经元、患者来源的淋巴母细胞、诱导多能干细胞衍生的运动神经元和来自 ALS 患者的死后脑组织样本中，丝切蛋白的磷酸化增强。C9ORF72 调节小 GTPase Arf6 和 Rac1 的活性，导致 LIM 激酶 1 和 2（LIMK1/2）的活性增强。这导致 C9ORF72 耗尽的运动神经元中的轴突肌动蛋白动力学减少。显性负性 Arf6 挽救了这一缺陷，表明 C9ORF72 作为小 GTPase 的调节剂，在调节轴突肌动蛋白动力学的途径中发挥作用。
