Tau is a microtubule-associated protein, which promotes neuronal microtubule assembly and stability. Accumulation of tau into insoluble aggregates known as neurofibrillary tangles (NFTs) is a pathological hallmark of several neurodegenerative diseases. The current hypothesis is that small, soluble oligomeric tau species preceding NFT formation cause toxicity. However, thus far, visualizing the spatial distribution of tau monomers and oligomers inside cells under physiological or pathological conditions has not been possible. Here, using single-molecule localization microscopy, we show that tau forms small oligomers on microtubules ex vivo. These oligomers are distinct from those found in cells exhibiting tau aggregation and could be precursors of aggregated tau in pathology. Furthermore, using an unsupervised shape classification algorithm that we developed, we show that different tau phosphorylation states are associated with distinct tau aggregate species. Our work elucidates tau’s nanoscale composition under nonaggregated and aggregated conditions ex vivo.

Tau 是一种微管相关蛋白，可促进神经元微管组装和稳定性。tau 蛋白聚集成不溶性聚集体，称为神经原纤维缠结 (NFT)，是多种神经退行性疾病的病理标志。目前的假设是，在 NFT 形成之前的小的可溶性寡聚 tau 物种会导致毒性。然而，到目前为止，在生理或病理条件下可视化细胞内 tau 单体和寡聚体的空间分布是不可能的。在这里，使用单分子定位显微镜，我们表明 tau 在离体微管上形成小寡聚体。这些寡聚体不同于在表现出 tau 聚集的细胞中发现的寡聚体，并且可能是病理学中聚集的 tau 的前体。此外，使用我们开发的无监督形状分类算法，我们表明不同的 tau 磷酸化状态与不同的 tau 聚集体种类相关。我们的工作阐明了 tau 在离体非聚集和聚集条件下的纳米级组成。