Sussex Neuroscience, School of Life Sciences, University of Sussex UK; Biomedical Science Research and Training Centre, Yobe State University, Nigeria. Electronic address: https://twitter.com/mahmoudbukar.
Sussex Neuroscience, School of Life Sciences, University of Sussex UK; Chemistry Department, College of Sciences, Mustansiriyah University, Baghdad, Iraq.
J Mol Biol. 2022 Oct 15;434(19):167785. doi: 10.1016/j.jmb.2022.167785. Epub 2022 Aug 9.
A characteristic hallmark of Alzheimer's Disease (AD) is the pathological aggregation and deposition of tau into paired helical filaments (PHF) in neurofibrillary tangles (NFTs). Oxidative stress is an early event during AD pathogenesis and is associated with tau-mediated AD pathology. Oxidative environments can result in the formation of covalent dityrosine crosslinks that can increase protein stability and insolubility. Dityrosine cross-linking has been shown in Aβ plaques in AD and α-synuclein aggregates in Lewy bodies in ex vivo tissue sections, and this modification may increase the insolubility of these aggregates and their resistance to degradation. Using the PHF-core tau fragment (residues 297 - 391) as a model, we have previously demonstrated that dityrosine formation traps tau assemblies to reduce further elongation. However, it is unknown whether dityrosine crosslinks are found in tau deposits in vivo in AD and its relevance to disease mechanism is unclear. Here, using transmission electron microscope (TEM) double immunogold-labelling, we reveal that neurofibrillary NFTs in AD are heavily decorated with dityrosine crosslinks alongside tau. Single immunogold-labelling TEM and fluorescence spectroscopy revealed the presence of dityrosine on AD brain-derived tau oligomers and fibrils. Using the tau (297-391) PHF-core fragment as a model, we further showed that prefibrillar tau species are more amenable to dityrosine crosslinking than tau fibrils. Dityrosine formation results in heat and SDS stability of oxidised prefibrillar and fibrillar tau assemblies. This finding has implications for understanding the mechanism governing the insolubility and toxicity of tau assemblies in vivo.
阿尔茨海默病（AD）的一个特征性标志是tau 蛋白病理性聚集并沉积为双螺旋丝（PHF），形成神经原纤维缠结（NFT）。氧化应激是 AD 发病机制中的早期事件，与 tau 介导的 AD 病理学有关。氧化环境会导致形成共价二酪氨酸交联，从而增加蛋白质的稳定性和不溶性。在 AD 的 Aβ 斑块和路易体中的α-突触核蛋白聚集体中已经观察到二酪氨酸交联，这种修饰可能会增加这些聚集体的不溶性及其对降解的抵抗力。我们之前使用 PHF-核心 tau 片段（残基 297-391）作为模型，证明了二酪氨酸的形成会困住 tau 组装体，从而阻止其进一步延伸。然而，目前尚不清楚 AD 患者体内 tau 沉积物中是否存在二酪氨酸交联，以及其与疾病机制的相关性。在这里，我们使用透射电子显微镜（TEM）双重免疫金标记，揭示了 AD 中的神经原纤维 NFT 被大量二酪氨酸交联所修饰，同时也被 tau 蛋白修饰。单免疫金标记 TEM 和荧光光谱学显示 AD 脑源性 tau 寡聚体和纤维中存在二酪氨酸。我们进一步使用 tau（297-391）PHF-核心片段作为模型，表明预纤维状 tau 物种比 tau 纤维更容易发生二酪氨酸交联。二酪氨酸的形成导致氧化的预纤维状和纤维状 tau 组装体具有热稳定性和 SDS 稳定性。这一发现对于理解体内 tau 组装体不溶性和毒性的调控机制具有重要意义。
