Pathogenic Roles for Microtubule Stabilization Pathways in Alzheimer's Disease

摘要 与阿尔茨海默病(AD)相关的两个主要神经病理特征是淀粉样β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原纤维缠结 蛋白质tau。这些沉积导致细胞结构异常和突触丢失，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。微管蛋白经历了许多翻译后修饰(PTM)， 影响微管稳定性和相关蛋白，包括tau和微管依赖的马达。这个 微管蛋白酪氨酸化/去酪氨酸化(Tyr/deTyr)循环发生在α-微管蛋白的C端酪氨酸驻留在 微管被间歇性地裂解，然后由微管蛋白酪氨酸连接酶(TTL)返回。重要的是 去酪氨酸化的微管蛋白可以被羧肽酶1/4/6不可逆地转化为增量2微管蛋白(D2)。 谷氨酸的倒数第二个氨基酸的裂解。此更改将D2从循环中永久移除。 因此，D2的积累是微管寿命的标志，尽管它对微管的稳定性有影响， Tau蛋白过度磷酸化和突触毒性是完全未知的。 这一提议旨在检验中心假说，即抑制微管蛋白再酪氨酸化 和D2的积累影响微管动力学，是tau的分子驱动因素 过度磷酸化，轴突运输缺陷和线粒体功能障碍，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有意义的，因为它们将 研究Tyr/deTyr微管蛋白循环失调在促进tau过度磷酸化和 家族性阿尔茨海默病原代海马神经元、小鼠和人类模型的AD病理学。这一假设依赖于 根据我们的初步数据显示：1)微管蛋白酪氨酸化缺陷与AD进展和tau相关 散发性和家族性阿尔茨海默病的过度磷酸化；2)微管蛋白再酪氨酸化的丢失促进 应激感受器与tau激酶AMPK、tau蛋白过度磷酸化与突触损伤；3)突触动态MTS 在突触和结构可塑性中起关键作用。 这一建议依赖于多学科的努力来检查体外和体内机制，通过这些机制 过早的微管蛋白寿命可能导致tau过度磷酸化和AD相关的突触功能障碍。这项工作 有可能识别可能在旨在挽救认知能力的药物疗法中调节的新靶点 散发性和家族性阿尔茨海默病的下降。

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.