Elucidation of the neuronal toxicity mechanism by TDP-43 based on dysfunction of the nucleocytoplasmic shuttling

TDP-43是一种核RNA结合蛋白，定位改变和异常沉积到神经元的细胞质中是肌萎缩侧索硬化症(ALS)和额颞叶变性(FTLD)的特征。我们假设TDP-43的沉积可能干扰了TDP-43蛋白向轴突的特定mRNA转运，从而形成ALS/FTLD，并利用我们的皮质神经元隔室培养系统鉴定了与蛋白质翻译相关的mRNA，包括核糖体蛋白作为TDP-43转运到轴突的候选靶点。靶基因和TDP-43在神经突起中共定位并表现出相同的运动方式。在神经突起中，用局部蛋白质翻译刺激物BDNF刺激后，靶基因的翻译增加。此外，通过下调TDP-43的表达，减少了靶基因在神经突起中的翻译，从而导致了局部蛋白质翻译的减少，抑制了神经突起的生长。提示神经突起中TDP-43功能丧失可能是导致ALS/FTLD神经退行性变的原因之一。

Altered localization and abnormal deposition of TDP-43, a nuclear RNA-binding protein, into the cytoplasm of neurons are hallmarks of amyotrophic lateral sclerosis (ALS) and frontotemporal lobar degeneration (FTLD). We hypothesized that deposition of TDP-43 may disturb the particular mRNA transport by the protein to neurites to develop ALS/FTLD, and identified mRNA associated with protein translation including that of ribosomal proteins as candidate targets transported to neurites by TDP-43 using our compartment culture system of cortical neurons. The target mRNA and TDP-43 co-localized and showed the same movement in neurites. Translation of the target mRNA was increased by stimulation with a local protein translation stimulator, BDNF, in neurites. Moreover, translation of the target mRNA in neurites was decreased by down-regulation of TDP-43 expression, which caused the decrease of overall protein translation at the site and the inhibition of neurite outgrowth. It indicates that the failure of local protein translation may occur by loss-of-function of TDP-43 in neurites, which may be a factor of the neurodegeneration in ALS/FTLD.