Hyperphosphorylation of the microtubule associated protein tau (tau) is inextricably linked to several neurodegenerative diseases, collectively termed tauopathies, in which synapse dysfunction occurs through largely unidentified mechanisms. Our research aimed to uncover molecular mechanisms by which phosphorylation of tau (pTau) affects synapse function. Using combined molecular and electrophysiological analysis with in vitro genetic knock-in of phosphorylation mutant human tau in male rat CA1 hippocampal neurons, we show an interplay between tau and protein kinase C and casein kinase substrate in neurons protein 1 (PACSIN1) that regulates synapse function. pTau at serine residues 396/404 decreases tau:PACSIN1 binding and evokes PACSIN1-dependent functional and structural synapse weakening. Knock-down of tau or PACSIN1 increases AMPA receptor (AMPAR)-mediated current at extrasynaptic regions, supporting a role for these proteins in affecting AMPAR trafficking. The pTau-induced PACSIN1 dissociation may represent a pathophysiological regulator of synapse function that underlies tauopathy-associated synapse defects.

SIGNIFICANCE STATEMENT Knowledge is still lacking for how hyperphosphorylation of tau and its effectors lead to synaptic and neuronal dysfunction. Our results provide crucial insight for this mechanistic understanding; we show that specific tau phosphorylation events modulate its protein interaction with PACSIN1 and thus elicits synapse weakening likely through PACSIN1-dependent regulation of AMPA receptor (AMPAR) trafficking. These findings develop our understanding of molecular events that may be relevant to cellular changes underpinning tauopathy-associated neurodegenerative diseases.

微管相关蛋白 tau (tau) 的过度磷酸化与几种神经退行性疾病密不可分，统称为 tauopathies，其中突触功能障碍的发生主要通过不明机制。我们的研究旨在揭示 tau (pTau) 磷酸化影响突触功能的分子机制。使用联合分子和电生理学分析以及体外基因敲入雄性大鼠 CA1 海马神经元中磷酸化突变体人类 tau，我们展示了 tau 和蛋白激酶 C 以及调节突触功能的神经元蛋白 1 (PACSIN1) 中酪蛋白激酶底物之间的相互作用. 丝氨酸残基 396/404 处的 pTau 降低 tau:PACSIN1 结合并引起 PACSIN1 依赖性功能和结构突触减弱。tau 或 PACSIN1 的敲低增加了突触外区域的 AMPA 受体 (AMPAR) 介导的电流，支持这些蛋白质在影响 AMPAR 运输中的作用。pTau 诱导的 PACSIN1 解离可能代表了突触功能的病理生理调节剂，它是 tau 蛋白病相关突触缺陷的基础。

重要性声明关于 tau 及其效应物的过度磷酸化如何导致突触和神经元功能障碍的知识仍然缺乏。我们的结果为这种机制的理解提供了重要的见解；我们表明，特定的 tau 磷酸化事件调节其与 PACSIN1 的蛋白质相互作用，从而可能通过 PACSIN1 依赖性调节 AMPA 受体（AMPAR）运输引起突触减弱。这些发现加深了我们对可能与支持 tau 蛋白病相关神经退行性疾病的细胞变化相关的分子事件的理解。