Increasing synaptic PSD-95, a neuroprotection approach against Alzheimer's disease

项目摘要/摘要 阿尔茨海默氏症患者大脑的第一个变化是突触丢失，这是该病最好的生物标志物。 一些研究表明PSD-95(突触上的一种主要的支架蛋白)被严重耗尽 在阿尔茨海默病患者的脑组织以及暴露于淀粉样β蛋白(Aβ，一种多肽)的神经元中 导致阿尔茨海默病(AD))。我们的数据表明，升高的PSD-95阻断了β诱导的突触 抑郁症。令人惊讶的是，这种效应似乎独立于突触增强，但受PSD- NMDA受体信号转导的95。此外，我们观察到含有大量PSD-95的大树突棘， 不受A-β影响，较小的脊椎更容易受到PSD-95含量的影响； 这表明内源性PSD-95也具有保护作用。这些发现表明，突触PSD增加- 95保护突触免受β的伤害。突触PSD-95的数量由一个称为 “棕榈酰化”，介导PSD-95插入突触后膜。特定的酶 最近发现了与PSD-95脱氨酶有关的基因，即从突触中移除PSD-95。这个 因此，这项提议的关键焦点是测试一种新的药物靶点PSD-95脱氨丝裂素的潜力 酶，作为治疗阿尔茨海默病的新途径。我们的初步体外和体内结果，使用 一种可商业化的该酶抑制剂(Palmostatin B)非常有希望。体外实验 结果表明，该药可以挽救β诱导的突触抑制和β介导的树突状细胞的作用 脊椎。我们建议研究阿尔茨海默病患者不同脑区的PSD-95棕榈酰化反应 模型小鼠(APP/PS1)和死后人脑样本。这些实验可以解释为什么某些 大脑区域(和个体)更容易受到阿尔茨海默病的影响。在APP/PS1小鼠中，PSD-95棕榈酰化 海马区显著低于WT仔鼠，而总PSD-95水平几乎没有受到影响。 这表明PSD-95棕榈酰化的丧失将发生在PSD-95的减少之前。重要的是 在腹膜腔内注射Palmostatin B以剂量依赖的方式挽救这种效应，这 表明这种药物可以在体内接触到大脑突触。在这个项目中，我们将研究功能 如果在这些APP/PS1小鼠中观察到的缺陷可以通过以下方法改善，那么救援和测试的后果就是 增加突触PSD-95。我们预计抑制PSD-95的脱氨基转移将改善 涉及记忆和挽救这些AD模型小鼠突触生理损伤的行为测试。 总体而言，这一创新项目将描述PSD-95在不同脑区的贩运特征，并测试是否 药理阻断PSD-95脱氨丝裂解酶可修复APP/PS1模型小鼠的缺陷。 最后，增加突触PSD-95应该会使脆弱的突触变得更强大，这将有利于 治疗和预防阿尔茨海默病。

Project Summary/Abstract The first change in the brains of Alzheimer’s patients and the best biomarker of the disease is synaptic loss. Several studies have shown that PSD-95 (a major scaffolding protein at the synapse) is significantly depleted in brain tissue of Alzheimer’s patients as well as in neurons exposed to amyloid beta (Aβ, a peptide thought to cause Alzheimer’s disease (AD)). Our data indicate that elevated PSD-95 blocks Aβ-induced synaptic depression. Surprisingly, this effect appears independent of synaptic potentiation, but to interference by PSD- 95 of NMDA receptor signaling. Moreover, we observed that big dendritic spines, containing a lot of PSD-95, were unaffected by Aβ and that smaller spines, with lower amounts of PSD-95 were more vulnerable; suggesting that endogenous PSD-95 is also protective. These findings indicate that increased synaptic PSD- 95 protects synapses from Aβ. The amount of synaptic PSD-95 is controlled by a process called ‘palmitoylation’ which mediate the insertion of PSD-95 in post-synaptic membranes. The specific enzyme responsible for PSD-95 depalmitoylation, which removes PSD-95 from synapses, was recently identified. The key focus of this proposal is thus to test the potential of a novel drug target, PSD-95 depalmitoylating enzyme, as a new therapeutic avenue against Alzheimer’s. Our preliminary in vitro and in vivo results, using a commercially available inhibitor of that enzyme (Palmostatin B), are very promising. In vitro experiments showed that this drug could rescue Aβ-induced synaptic depression and Aβ-mediated effects on dendritic spines. We propose to study PSD-95 palmitoylation in brain regions differently affected in the disease in AD model mice (APP/PS1) and postmortem human brain samples. These experiments could explain why certain brain regions (and individuals) are more vulnerable to AD. In APP/PS1 mice, PSD-95 palmitoylation in the hippocampus was drastically lower than in WT littermates while total PSD-95 levels were barely affected. This suggests that loss of PSD-95 palmitoylation would happen before reductions in PSD-95. Importantly, Palmostatin B injections in the intraperitoneal cavity rescued that effect in a dose dependent manner, which indicates that this drug can access brain synapses in vivo. In this project, we will investigate the functional consequences of that rescue and test if deficits observed in these APP/PS1 mice can be ameliorated by increasing synaptic PSD-95. We expect that inhibiting PSD-95 depalmitoylation will improve performance in behavioral tests involving memory and rescue synaptic physiology impairments in these AD model mice. Overall, this innovative project will characterize PSD-95 trafficking in different brain regions and test if pharmacological blockade of PSD-95 depalmitoylating enzyme can rescue deficits in APP/PS1 model mice. Finally, increasing synaptic PSD-95 should make vulnerable synapses stronger, which would be beneficial for both treating and preventing AD.