TDP43-WTvNonTg_diffExp.

A key pathological feature of Amyotrophic Lateral Sclerosis (ALS) and Frontotemporal Dementia (FTD) is the loss of nuclear localization and accumulation of cytoplasmic inclusions of TAR-DNA binding protein 43 (TDP-43). TDP-43 is a nucleic acid-binding protein involved in transcriptional repression, mRNA splicing, and the regulation of retrotransposable elements (RTEs) and endogenous retroviruses (ERVs). RTEs/ERVs are mobile virus-like genetic elements that constitute about 45% of our genome and encode the capacity to replicate through an RNA intermediate and insert cDNA copies at de novo chromosomal locations. A causal role of RTEs/ERVs has been demonstrated in Drosophila in mediating both intracellular toxicity of TDP-43 and the intercellular spread of toxicity from glia to neurons. RTEs/ERVs are inappropriately expressed in postmortem tissues from ALS, FTD, and Alzheimer’s Disease (AD) patients, but the role of RTEs/ERVs has not yet been examined in a vertebrate model of TDP-43 pathology. We utilized established transgenic mouse models that overexpress moderate levels of human wild-type TDP-43 or a mutant version with a specific ALS-causal Q331K amino acid substitution, together with a LINE-1-EGFP retrotransposon indicator line. We found that TDP-43 animals exhibit broad expression of RTEs/ERVs with LINE-1 retrotransposition in glia and neurons in the motor cortex. Expression begins with onset of neurological phenotypes, earlier in hTDP-43-Q331K animals and later in hTDP-43-WT. The LINE-1-EGFP retrotransposition reporter transiently labels spatially clustered groups of neurons and glia at the time of onset of motor symptoms, while EGFP-labeled neurons undergo cell death and are therefore lost over time. Unlabeled cells also die as a function of distance from the clusters of LINE-1-EGFP labeled neurons and glial cells. Together, these findings support the hypothesis that TDP-43 pathology triggers RTE/ERV expression in the motor cortex, that such expression marks cells for programmed cell death, with cell non-autonomous effects on nearby neurons and glial cells.肌萎缩侧索硬化症（Amyotrophic Lateral Sclerosis, ALS）与额颞叶痴呆（Frontotemporal Dementia, FTD）的关键病理特征，在于TAR DNA结合蛋白43（TAR-DNA binding protein 43, TDP-43）的核定位丧失，以及其细胞质包涵体的聚集。TDP-43是一类核酸结合蛋白，参与转录抑制、mRNA剪接，以及逆转录转座因子（retrotransposable elements, RTEs）和内源性逆转录病毒（endogenous retroviruses, ERVs）的调控。RTEs/ERVs是可移动的病毒样遗传元件，约占人类基因组的45%，具备通过RNA中间体复制，并将互补DNA（cDNA）拷贝插入全新染色体位点的能力。已有研究在果蝇中证实了RTEs/ERVs的致病作用：其既可介导TDP-43的细胞内毒性，也可介导毒性从胶质细胞向神经元的细胞间传播。在ALS、FTD及阿尔茨海默病（Alzheimer’s Disease, AD）患者的死后脑组织中，RTEs/ERVs存在异常表达，但目前尚未在TDP-43病理的脊椎动物模型中探究其具体作用。本研究采用已构建的转基因小鼠模型，该模型可过表达中等水平的人类野生型TDP-43，或是携带ALS致病Q331K氨基酸替换的突变型TDP-43，并结合LINE-1-EGFP逆转录转座子报告小鼠系开展实验。研究结果显示，TDP-43转基因小鼠的运动皮层胶质细胞与神经元中，可检测到RTEs/ERVs的广泛表达，同时伴随LINE-1逆转录转座事件。该表达随神经表型的出现而启动：在hTDP-43-Q331K小鼠中表达出现更早，而在hTDP-43-WT小鼠中则出现较晚。在运动症状发作时，LINE-1-EGFP逆转录转座报告系统可瞬时标记空间上成簇的神经元与胶质细胞群；随着时间推移，被EGFP标记的神经元会发生细胞死亡并逐渐消失。同时，距离LINE-1-EGFP标记的神经元与胶质细胞簇一定距离的未标记细胞，也会随与簇群的距离变化发生死亡。综上，本研究结果支持以下假说：TDP-43病理可触发运动皮层中RTE/ERV的表达，此类表达可标记发生程序性细胞死亡的细胞，并对邻近的神经元与胶质细胞产生细胞非自主效应。