Preclinical assessment of GCPII inhibitors for cognition and tau pathology

这项拟议中的研究将测试一种保护高级认知和减少tau蛋白的新机制 磷酸化在老化的皮质，基于新进化的联合皮质的独特需求， 神经元在阿尔茨海默病（AD）中最脆弱。这些电路被前馈有力地调制， cAMP-PKA-钙信号传导，随着年龄的增长而变得失调，导致：1）过度 K+通道开放，减少神经元放电并损害认知，和2）tau的磷酸化。早期 PKA导致的tau蛋白磷酸化的阶段可以在老年大鼠联合皮层中看到，而更高级的阶段 在老年猴皮质中观察到，包括AT 8抗体标记的原纤维化tau蛋白和伴随的Aβ 表情这项拟议的研究将测试一种调节cAMP-PKA-钙信号传导以减少AD的策略。 就像通过放大大脑对谷氨酸代谢的自然保护作用来研究衰老皮质的病理学一样 受体3型（mGluR 3）。mGluR 3对星形胶质细胞具有神经保护作用， 对神经元的作用。新的数据显示，前额叶联合皮层（PFC）中的突触后mGluR 3， 调节cAMP-PKA-钙信号传导。这项研究将通过其对mGluR 3的刺激来增强mGluR 3的刺激。 内源性配体，NAAG（N-乙酰基-谷氨酸），通过抑制破坏NAAG的酶， 谷氨酸羧肽酶II。GCPII抑制剂正在开发中，用于治疗炎症 在I期人体试验中，这些药物具有优异的耐受性和最小的副作用。我们将观察是否 mGluR 3被定位以调节灵长类动物内嗅皮层（ERC）中tau的cAMP-PKA磷酸化 和PFC电路在AD中最脆弱，以及GCPII抑制是否可以恢复神经元放电，改善 认知功能，抑制tau的磷酸化，并减少老年大鼠和猴子的神经炎症。 这项工作将证实和扩展两种结构不同的GCPII抑制剂，2-MPPA和2- PMPA，由约翰霍普金斯药物发现小组开发。目的1将使用双免疫电子 显微镜检查以确认mGluR 3正确定位以调节tau的cAMP-PKA磷酸化 （pS214 Tau）和AT 8标记的tau蛋白在老化的ERC和PFC突触中的表达。目标2将测试是否 急性给予2-MPPA或2-PMPA增强衰老猴记忆相关PFC神经元放电 通过调节K+通道的cAMP-PKA开放，以及系统给药是否可以改善认知 在老年大鼠和猴子身上进行，副作用最小。目标3将测试慢性治疗是否具有最佳的 剂量的2-MPPA产生工作记忆的持续改善，并减少tau蛋白磷酸化， 老年大鼠和猴联合皮质的神经炎症。我们将有难得的机会看看是否 在老年猴中的慢性2-MPPA治疗降低了原纤维化的AT 8标记的tau和Aβ表达。 初步数据表明，这些药物在认知方面产生了非常强大的改善，没有证据表明， 副作用，鼓励具有可行的转化应用的治疗策略。

The proposed research will test a novel mechanism for protecting higher cognition and reducing tau phosphorylation in the aging cortex, based on the unique needs of the newly evolved association cortical neurons most vulnerable in Alzheimer's Disease (AD). These circuits are powerfully modulated by feedforward, cAMP-PKA-calcium signaling, which becomes dysregulated with advancing age, leading to: 1) excessive opening of K+ channels, reducing neuronal firing and impairing cognition, and 2) phosphorylation of tau. Early stages of tau phosphorylation by PKA can be seen in aged rat association cortex, while more advanced stages are seen in aged monkey cortex, including fibrillated tau labeled by the AT8 antibody, and accompanying Aβ expression. The proposed research will test a strategy to regulate cAMP-PKA-calcium signaling to reduce AD- like pathology in the aging cortex by amplifying the brain's natural protective actions at glutamate metabotropic receptors type 3 (mGluR3). mGluR3 have neuroprotective actions on astrocytes, and additional, regulatory actions on neurons. New data have revealed post-synaptic mGluR3 in prefrontal association cortex (PFC) that regulate cAMP-PKA-calcium signaling. The proposed research will enhance stimulation of mGluR3 by its endogenous ligand, NAAG (N-acetylaspartyl-glutamic acid), via inhibition of the enzyme that destroys NAAG, GCPII (glutamate carboxypeptidase II). GCPII inhibitors are under development for treating inflammatory disorders, with excellent tolerability and minimal side effects in phase I human testing. We will observe whether mGluR3 are positioned to regulate cAMP-PKA phosphorylation of tau in the primate entorhinal cortex (ERC) and PFC circuits most vulnerable in AD, and whether GCPII inhibition can restore neuronal firing, improve cognitive function, inhibit phosphorylation of tau, and reduce neuroinflammation in aged rats and monkeys. This work will confirm and extend the efficacy of two structurally distinct GCPII inhibitors, 2-MPPA and 2- PMPA, under development by the Johns Hopkins Drug Discovery group. Aim 1 will use dual immunoelectron microscopy to confirm that mGluR3 are correctly positioned to regulate cAMP-PKA phosphorylation of tau (pS214Tau) and AT8-labeled tau in aging ERC and PFC glutamatergic synapses. Aim 2 will test whether acute administration of 2-MPPA or 2-PMPA enhances memory-related PFC neuronal firing in aging monkeys by regulating cAMP-PKA opening of K+ channels, and whether systemic administration can improve cognition in aged rats and monkeys with minimal side effects. Aim 3 will test whether chronic treatment with an optimal dose of 2-MPPA produces sustained improvement in working memory, and reduces tau phosphorylation and neuroinflammation in aged rat and monkey association cortex. We will have the rare opportunity to see if chronic 2-MPPA treatment in aged monkeys reduces both fibrillated AT8-labeled tau, and Aβ expression. Preliminary data indicate that these agents produce very robust improvements in cognition with no evidence of side effects, encouraging a therapeutic strategy with feasible translational application.