Alzheimer’s disease (AD) is characterized by the presence of neurofibrillary tangles made of hyperphosphorylated tau and senile plaques composed of beta-amyloid. These pathognomonic deposits have been implicated in the pathogenesis, although the molecular mechanisms and consequences remain undetermined. UFM1 is an important, but understudied ubiquitin-like protein that is covalently attached to substrates. UFMylation has recently been identified as major modifier of tau aggregation upon seeding in experimental models. However, potential alterations of the UFM1 pathway in human AD brain have not been investigated yet. Here we used frontal and temporal cortex samples from individuals with or without AD to measure the protein levels of the UFMylation pathway in human brain. We used multivariable regression analyses followed by Bonferroni correction for multiple testing to analyze associations of the UFMylation pathway with neuropathological characteristics, primary biochemical measurements of tau and additional biochemical markers from the same cases. We further studied associations of the UFMylation cascade with cellular stress pathways using Spearman correlations with bulk RNAseq expression data and functionally validated these interactions using gene-edited neurons that were generated by CRISPR-Cas9. Compared to controls, human AD brain had increased protein levels of UFM1. Our data further indicates that this increase mainly reflects conjugated UFM1 indicating hyperUFMylation in AD. UFMylation was strongly correlated with pathological tau in both AD-affected brain regions. In addition, we found that the levels of conjugated UFM1 were negatively correlated with soluble levels of the deUFMylation enzyme UFSP2. Functional analysis of UFM1 and/or UFSP2 knockout neurons revealed that the DNA damage response as well as the unfolded protein response are perturbed by changes in neuronal UFM1 signaling. There are marked changes in the UFMylation pathway in human AD brain. These changes are significantly associated with pathological tau, supporting the idea that the UFMylation cascade might indeed act as a modifier of tau pathology in human brain. Our study further nominates UFSP2 as an attractive target to reduce the hyperUFMylation observed in AD brain but also underscores the critical need to identify risks and benefits of manipulating the UFMylation pathway as potential therapeutic avenue for AD.

中文翻译：

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UFMylation 通路在阿尔茨海默病中受损


阿尔茨海默病 （AD） 的特征是存在由过度磷酸化的 tau 组成的神经原纤维缠结和由 β-淀粉样蛋白组成的老年斑。这些特征性沉积物与发病机制有关，但分子机制和后果仍未确定。UFM1 是一种重要但研究不足的泛素样蛋白，它与底物共价连接。UFMylation 最近被确定为实验模型中接种时 tau 聚集的主要修饰物。然而，尚未研究人类 AD 大脑中 UFM1 通路的潜在改变。在这里，我们使用来自患有或没有 AD 的个体的额叶和颞叶皮层样本来测量人脑中 UFMylation 通路的蛋白质水平。我们使用多变量回归分析，然后进行 Bonferroni 校正进行多重测试，以分析 UFMylation 通路与神经病理学特征、tau 的原发性生化测量以及来自相同病例的其他生化标志物的关联。我们使用 Spearman 相关性与大量 RNAseq 表达数据进一步研究了 UFMylation 级联反应与细胞应激通路的关联，并使用 CRISPR-Cas9 生成的基因编辑神经元对这些相互作用进行了功能验证。与对照组相比，人 AD 脑的 UFM1 蛋白水平升高。我们的数据进一步表明，这种增加主要反映了共轭的 UFM1 表明 AD 中的高 UFMylation。UFMylation 与两个受 AD 影响的大脑区域的病理 tau 密切相关。此外，我们发现偶联的 UFM1 水平与去 UFMylation 酶 UFSP2 的可溶性水平呈负相关。 UFM1 和/或 UFSP2 敲除神经元的功能分析显示，DNA 损伤反应以及未折叠的蛋白质反应受到神经元 UFM1 信号传导变化的干扰。人类 AD 大脑中的 UFMylation 通路发生了显著变化。这些变化与病理性 tau 显著相关，支持 UFMylation 级联反应可能确实可以作为人脑中 tau 病理学的修饰物的观点。我们的研究进一步将 UFSP2 提名为减少在 AD 大脑中观察到的超 UFMylation 的有吸引力的靶点，但也强调了确定操纵 UFMylation 途径作为 AD 潜在治疗途径的风险和益处的迫切需求。