Pathogenic Roles for Microtubule Stabilization Pathways in Alzheimer's Disease

总结 与阿尔茨海默病（AD）相关的两个主要神经病理学标志是β淀粉样蛋白斑块 以及由微管结合的过度磷酸化变体组成的细胞内神经元缠结 tau蛋白。这些沉积物导致异常的细胞结构和突触的丧失，这两者都强烈影响 行为和记忆。然而，触发这些沉积物形成的致病机制和 早期突触功能障碍仍然知之甚少，缺乏这方面的知识是发展的障碍 有效的治疗策略。微管蛋白经历许多翻译后修饰（PTM）， 影响微管稳定性和相关蛋白，包括tau和微管依赖性马达。的 微管蛋白酪氨酸/去酪氨酸（Tyr/deTyr）循环发生在α-微管蛋白的C-末端酪氨酸驻留在 微管被间歇性地切割，然后通过微管蛋白酪氨酸连接酶（TTL）返回。重要的是， 脱酪氨酸微管蛋白可以通过羧肽酶1/4/6不可逆地转化为δ 2微管蛋白（D2）， 谷氨酸的倒数第二个氨基酸的断裂。该变更将D2从循环中永久删除。 因此，D2积累是微管寿命的标志，尽管它对微管稳定性的影响， tau过度磷酸化和突触毒性是完全未知的。 该提议旨在检验抑制微管蛋白再酪氨酸化 D2的积累影响微管动力学，是tau蛋白的分子驱动因子 过度磷酸化，轴突运输缺陷和线粒体功能障碍，伴有严重的直接 对神经传递的影响。我们提出的研究是新颖的和非常重要的，因为他们将 研究了Tyr/deTyr微管蛋白循环失调在促进tau蛋白过度磷酸化中的新作用， 原代海马神经元、小鼠和人类家族性AD模型中的AD病理学。这个假设依赖于 我们的初步数据显示：1）微管蛋白重新酪氨酸化缺陷与AD进展和tau蛋白相关 在散发性和家族性AD中的过度磷酸化; 2）微管蛋白再酪氨酸化的丧失促进 应激感受器与tau激酶AMPK、tau蛋白过度磷酸化和突触损伤; 3）突触动态MT 在突触和结构可塑性中起着关键作用。 这项建议依赖于多学科的努力，以检查体外和体内的机制， 过早的微管蛋白寿命可驱动tau过度磷酸化和AD相关的突触功能障碍。工作 有可能确定新的目标，可能是在药物治疗，旨在挽救认知调节 减少散发性和家族性AD。

Summary The two main neuropathological hallmarks associated with Alzheimer’s disease (AD) are amyloid beta plaques and intracellular neurofibrillary tangles comprised of hyperphosphorylated variants of the microtubule binding protein tau. These deposits lead to abnormal cellular structure and loss of synapses, both of which strongly affect behavior and memory. However, the pathogenic mechanisms that trigger the formation of these deposits and early synaptic dysfunction are still poorly understood and lack of this knowledge is a hurdle for the development of effective therapeutic strategies. Tubulin undergoes numerous post-translational modifications (PTMs) that affect both microtubule stability and associated proteins, including tau and microtubule-dependent motors. The tubulin tyrosination/detyrosination (Tyr/deTyr) cycle occurs when the C-terminal tyrosine of α-tubulin residing in a microtubule is episodically cleaved and then returned by a tubulin-tyrosine-ligase (TTL). Importantly, detyrosinated tubulin can be irreversibly converted by carboxypeptidases 1/4/6 to delta 2 tubulin (D2) by cleavage of the penultimate amino acid of glutamic acid. This change permanently removes D2 from the cycle. D2 accumulation is therefore a hallmark of microtubule longevity, although its effects on microtubule stability, tau hyperphosphorylation and synaptotoxicity are completely unknown. This proposal is designed to test the central hypothesis that inhibition of tubulin re-tyrosination and accumulation of D2 affect microtubule dynamics and are molecular drivers of tau hyperphosphorylation, defective axonal transport and mitochondria dysfunction, with severe direct consequences on neurotransmission. Our proposed studies are novel and highly significant, as they will examine a new role for dysregulation of the Tyr/deTyr tubulin cycle in promoting tau hyperphosphorylation and AD pathology in primary hippocampal neurons, mice and a human model of familial AD. The hypothesis relies on our preliminary data showing that: 1) defects in tubulin re-tyrosination correlate with AD progression and tau hyperphosphorylation in sporadic and familial AD; 2) loss of tubulin re-tyrosination promotes activation of the stress sensor and tau kinase AMPK, tau hyperphosphorylation and synaptic injury; 3) synaptic dynamic MTs play critical roles in synaptic and structural plasticity. This proposal relies on a multidisciplinary effort to examine the in vitro and in vivo mechanisms by which premature tubulin longevity may drive tau hyperphosphorylation and AD-related synaptic dysfunction. The work has the potential to identify novel targets that may be modulated in drug therapies aimed at rescuing cognitive decline in sporadic and familial forms of AD.