Biology and Bioengineering, Caltech, Pasadena, CA 91125, USA.
Zilkha Neurogenetic Institute, Keck School of Medicine of USC, Los Angeles, CA 90089, USA.
Neurobiol Dis. 2021 Nov;159:105517. doi: 10.1016/j.nbd.2021.105517. Epub 2021 Sep 24.
Huntington's disease (HD) is a genetically inherited neurodegenerative disorder caused by expansion of a polyglutamine (polyQ) repeat in the exon-1 of huntingtin protein (HTT). The expanded polyQ enhances the amyloidogenic propensity of HTT exon 1 (HTTex1), which forms a heterogeneous mixture of assemblies with a broad neurotoxicity spectrum. While predominantly intracellular, monomeric and aggregated mutant HTT species are also present in the cerebrospinal fluids of HD patients, however, their biological properties are not well understood. To explore the role of extracellular mutant HTT in aggregation and toxicity, we investigated the uptake and amplification of recombinant HTTex1 assemblies in cell culture models. We find that small HTTex1 fibrils preferentially enter human neurons and trigger the amplification of neurotoxic assemblies; astrocytes or epithelial cells are not permissive. The amplification of HTTex1 in neurons depletes endogenous HTT protein with non-pathogenic polyQ repeat, activates apoptotic caspase-3 pathway and induces nuclear fragmentation. Using a panel of novel monoclonal antibodies and genetic mutation, we identified epitopes within the N-terminal 17 amino acids and proline-rich domain of HTTex1 to be critical in neural uptake and amplification. Synaptosome preparations from the brain homogenates of HD mice also contain mutant HTT species, which enter neurons and behave similar to small recombinant HTTex1 fibrils. These studies suggest that amyloidogenic extracellular mutant HTTex1 assemblies may preferentially enter neurons, propagate and promote neurodegeneration.
亨廷顿病（HD）是一种遗传性神经退行性疾病，由亨廷顿蛋白（HTT）外显子 1 中的多聚谷氨酰胺（polyQ）重复扩展引起。扩展的 polyQ 增强了 HTT 外显子 1（HTTex1）的淀粉样形成倾向，HTTex1 形成具有广泛神经毒性谱的异质组装混合物。虽然主要是细胞内的，但单体和聚集的突变 HTT 物种也存在于 HD 患者的脑脊液中，但其生物学特性尚未得到很好的理解。为了探索细胞外突变 HTT 在聚集和毒性中的作用，我们研究了重组 Httx1 组装在细胞培养模型中的摄取和扩增。我们发现小 Httx1 原纤维优先进入人类神经元，并引发神经毒性组装的扩增；星形胶质细胞或上皮细胞不可渗透。神经元中 Httx1 的扩增会耗尽具有非致病性 polyQ 重复的内源性 HTT 蛋白，激活凋亡 caspase-3 途径并诱导核碎裂。使用一系列新的单克隆抗体和基因突变，我们确定了 Httx1 的 N 端 17 个氨基酸和脯氨酸丰富结构域内的表位对于神经摄取和扩增至关重要。来自 HD 小鼠脑匀浆的突触体制剂也含有突变 HTT 物种，这些物质进入神经元并表现得类似于小重组 Httx1 原纤维。这些研究表明，淀粉样形成的细胞外突变 Httx1 组装可能优先进入神经元，进行传播并促进神经退行性变。
