Axonal Eif5a hypusination controls local translation and mitigates defects in FUS-ALS

Local protein synthesis is vital for neuronal function, but its dysregulation in neurodegenerative diseases remains poorly defined. Here we applied spatial transcriptomics to adult mouse motor nerve axons and cell bodies to enable subcellular mapping. Among transcripts found in mature axons, the most enriched biological process is protein translation, and localization of translation machinery was confirmed using multiplexed single-molecule spatial transcriptomics combined with immunofluorescence. Amyotrophic lateral sclerosis (ALS)-associated mutations in the RNA-binding protein fused in sarcoma (FUS), which suppress local translation, disrupt the compartment-specific RNA signatures, including components of the translation machinery. In particular, eukaryotic initiation factor 5a (Eif5a), a translation factor involved in elongation and termination, is found to be locally impaired in mutant FUS axons with reduced levels of its active hypusinated form. Axon-specific treatment with polyamine spermidine restores Eif5a hypusination and ameliorates mutant FUS-dependent neuronal defects, including suppression of local protein synthesis. Finally, in vivo spermidine treatment reduces ALS-related toxicity in mutant FUS and TDP-43 Drosophila models, which may have implications for therapy development.局部蛋白质合成（local protein synthesis）对神经元功能至关重要，但神经退行性疾病中其失调机制仍未得到充分阐明。本研究将空间转录组学（spatial transcriptomics）应用于成年小鼠运动神经轴突与细胞体，以实现亚细胞水平的图谱绘制。在成熟轴突中检出的转录本里，富集程度最高的生物学过程为蛋白质翻译；研究结合多重单分子空间转录组学与免疫荧光（immunofluorescence）技术，验证了翻译装置的定位情况。肌萎缩侧索硬化症（ALS）相关的RNA结合蛋白肉瘤融合蛋白（FUS）突变会抑制局部蛋白质合成，并破坏区域特异性RNA特征，包括翻译装置的组分。具体而言，参与翻译延伸与终止过程的真核起始因子5a（Eif5a），在突变型FUS轴突中出现局部功能受损，其活性形式——羟丁氨酸修饰型Eif5a的水平显著降低。通过轴突特异性给药多胺亚精胺（spermidine），可恢复Eif5a的羟丁氨酸修饰水平，并改善突变型FUS介导的神经元缺陷，包括局部蛋白质合成的抑制。最后，体内给予亚精胺可降低突变型FUS与TDP-43果蝇模型中ALS相关的毒性，该发现可为治疗开发提供参考。