Role of atlastin-1 in axonal development and degeneration of human neurons

描述（由申请人提供）：轴突发育和变性受损与许多衰弱性疾病有关，如遗传性痉挛性截瘫（HSP）、肌萎缩性侧索硬化和周围神经病。HSP是由涉及最长皮质脊髓束轴突的远端轴突病变引起的，导致下肢痉挛和无力。HSP最常见的早发性形式SPG 3A是由atlastin-1基因突变引起的。该基因编码atlastin-1蛋白，其是动力蛋白相关的大GT3超家族的成员。atlastin-1在体外培养的大鼠皮层神经元中的敲低抑制 轴突生长和伸长。然而，atlastin-1活性的改变如何导致轴突缺陷以及HSP患者中特定轴突退化的原因在很大程度上尚不清楚。本研究的目的是建立SPG 3A的人类神经元模型，以阐明HSP轴突缺陷的机制。这项研究的假设是，atlastin突变导致轴突缺陷选择性皮质投射神经元（皮质PNs），这种影响主要是由失调的骨形态发生蛋白（BMP）信号转导介导。该假设将通过追求以下两个目标来测试：1）检查源自SPG 3A患者和正常个体（作为对照）产生的iPSC的皮质PN中的轴突生长和运输; 2）描绘BMP信号传导在SPG 3A中的轴突缺陷中的作用。通过比较来自对照和SPG 3A iPSCs的皮质PN、皮质中间神经元和脊髓运动神经元中的轴突缺陷、atlastin-1活性和BMP信号转导改变，本研究将能够描绘HSP中的细胞类型特异性缺陷及其潜在机制。将通过敲低野生型（WT）神经元中的atlastin-1和通过在SPG 3A iPSC中表达WT atlastin-1来确认atlastin功能丧失与轴突表型之间的因果关系。此外，救援实验将进行，以确定潜在的方法拯救轴突病理，如过度表达的atlastin或治疗与BMP拮抗剂。总之，这项研究将提供有价值的见解atlastin-1和BMP信号转导在HSP病理学中的作用，并开发新的治疗方法来挽救HSP的轴突变性。

DESCRIPTION (provided by applicant): Impaired axonal development and degeneration are implicated in many debilitating disorders, such as hereditary spastic paraplegia (HSP), amyotrophic lateral sclerosis, and periphery neuropathy. HSP is caused by distal axonopathy involving the longest corticospinal tract axons, leading to spasticity and weakness of the lower extremities. The most common early-onset form of HSP, SPG3A, is caused by mutations in the atlastin-1 gene. This gene encodes atlastin-1 protein, which is a member of the dynamin-related large GTPase superfamily. Knockdown of atlastin-1 in rat cortical neuron in vitro cultures inhibits the axonal outgrowth and elongation. However, how altered atlastin-1 activity leads to axonal defects and why specific axons degenerate in HSP patients are largely unclear. The goal of this proposed study is to establish human neuronal models of SPG3A to delineate the mechanisms underlying the axonal defects in HSP. This study's hypothesis is that atlastin mutations result in axonal defects selectively in cortical projection neurons (cortical PNs), and this effect is mediated mainly by dysregulated bone morphogenetic protein (BMP) signaling. This hypothesis will be tested by pursuing the following two aims: 1) to examine the axonal outgrowth and transport in cortical PNs derived from iPSCs that are generated from SPG3A patients and normal individuals (as controls); 2) to delineate the role of BMP signaling in the axonal defects in SPG3A. By comparing the axonal defects, atlastin-1 activity, and BMP signaling alterations in cortical PNs, cortical interneurons, and spinal motor neurons derived from control and SPG3A iPSCs, this study will be able to delineate the cell type-specific defects in HSP and the underlying mechanisms. The cause-effect relationship between loss of atlastin function and axonal phenotypes will be confirmed by knocking down atlastin-1 in wild-type (WT) neurons and by expressing WT atlastin-1 in SPG3A iPSCs. Moreover, rescue experiments will be performed to identify the potential approaches for rescuing the axonal pathology, such as overexpression of atlastin or treatment with BMP antagonists. Together, this study will provide valuable insights into the roles of atlastin-1 and BMP signaling in HSP pathology and developing new therapeutics for rescuing the axonal degeneration in HSP.