The accumulation of phosphorylated tau protein (pTau) in the entorhinal cortex (EC) is the earliest tau pathology in Alzheimer's disease (AD). Tau tubulin kinase-1 (TTBK1) is a neuron-specific tau kinase and expressed in the EC and hippocampal regions in both human and mouse brains. Here we report that collapsin response mediator protein-2 (CRMP2), a critical mediator of growth cone collapse, is a new downstream target of TTBK1 and is accumulated in the EC region of early stage AD brains. TTBK1 transgenic mice show severe axonal degeneration in the perforant path, which is exacerbated by crossing with Tg2576 mice expressing Swedish familial AD mutant of amyloid precursor protein (APP). TTBK1 mice show accumulation of phosphorylated CRMP2 (pCRMP2), in the EC at 10 months of age, whereas age-matched APP/TTBK1 bigenic mice show pCRMP2 accumulation in both the EC and hippocampal regions. Amyloid-β peptide (Aβ) and TTBK1 suppress the kinetics of microtubule polymerization and TTBK1 reduces the neurite length of primary cultured neurons in Rho kinase-dependent manner in vitro. Silencing of TTBK1 or expression of dominant-negative Rho kinase demonstrates that Aβ induces CRMP2 phosphorylation at threonine 514 in a TTBK1-dependent manner, and TTBK1 enhances Aβ-induced CRMP2 phosphorylation in Rho kinase-dependent manner in vitro. Furthermore, TTBK1 expression induces pCRMP2 complex formation with pTau in vitro, which is enhanced upon Aβ stimulation in vitro. Finally, pCRMP2 forms a complex with pTau in the EC tissue of TTBK1 mice in vivo, which is exacerbated in both the EC and hippocampal tissues in APP/TTBK1 mice. These results suggest that TTBK1 and Aβ induce phosphorylation of CRMP2, which may be causative for the neurite degeneration and somal accumulation of pTau in the EC neurons, indicating critical involvement of TTBK1 and pCRMP2 in the early AD pathology.

中文翻译：

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在阿尔茨海默病小鼠模型中，Tau-微管蛋白激酶 1 和淀粉样蛋白-β 肽诱导塌陷蛋白反应介质蛋白 2 的磷酸化并增强神经突退化。

在内嗅皮质 (EC) 中磷酸化 tau 蛋白 (pTau) 的积累是阿尔茨海默病 (AD) 中最早的 tau 病理学。Tau 微管蛋白激酶-1 (TTBK1) 是一种神经元特异性 tau 激酶，在人和小鼠大脑的 EC 和海马区均有表达。在这里，我们报告了生长锥塌陷的关键介质 collapsin response mediator protein-2 (CRMP2) 是 TTBK1 的新下游靶标，并在早期 AD 大脑的 EC 区域中积累。TTBK1 转基因小鼠在穿孔路径中表现出严重的轴突变性，与表达淀粉样前体蛋白 (APP) 的瑞典家族性 AD 突变体的 Tg2576 小鼠杂交会加剧这种情况。TTBK1 小鼠在 10 个月大时在 EC 中显示出磷酸化 CRMP2 (pCRMP2) 的积累，而年龄匹配的 APP/TTBK1 基因小鼠在 EC 和海马区域均显示 pCRMP2 积累。淀粉样蛋白-β 肽 (Aβ) 和 TTBK1 抑制微管聚合的动力学，TTBK1 在体外以 Rho 激酶依赖性方式减少原代培养神经元的神经突长度。TTBK1 的沉默或显性失活 Rho 激酶的表达表明 Aβ 在体外以 TTBK1 依赖性方式诱导 CRMP2 在苏氨酸 514 处的磷酸化，而 TTBK1 在体外以 Rho 激酶依赖性方式增强 Aβ 诱导的 CRMP2 磷酸化。此外，TTBK1 表达在体外诱导 pCRMP2 复合物与 pTau 形成，在体外 Aβ 刺激后增强。最后，pCRMP2 在体内 TTBK1 小鼠的 EC 组织中与 pTau 形成复合物，这在 APP/TTBK1 小鼠的 EC 和海马组织中都加剧了。