Preclinical assessment of GCPII inhibitors for cognition and tau pathology

这项拟议的研究将测试一种保护高级认知和减少tau的新机制。 老化皮层中的磷酸化，基于新进化的皮层联合的独特需求 阿尔茨海默病(AD)中最脆弱的神经元。这些电路由前馈进行强有力的调制， CAMP-PKA-钙信号，随着年龄的增长而变得失调，导致：1)过度 开放K+通道，减少神经元放电，损害认知；2)tau的磷酸化。早些时候 在老年大鼠的联合皮质中，可以看到PKA对tau的磷酸化阶段，而更高级的阶段 在老年猴皮质中可见，包括AT8抗体标记的原纤化tau，并伴随Aβ 表情。这项拟议的研究将测试一种调节cAMP-PKA-钙信号转导以减少AD- 通过放大大脑对谷氨酸代谢的自然保护作用，在老化的皮质中类似于病理学 受体3型(MGluR3)。MGluR3对星形胶质细胞具有神经保护作用，并具有额外的调节作用 对神经元的作用。新的数据显示，突触后前额叶联想皮质(PFC)中的mGluR3 调节cAMP-PKA-钙信号转导。拟议的研究将通过其增强mGluR3的刺激 内源性配体NAAG(N-乙酰天门冬氨酸)，通过抑制破坏NAAG的酶， 谷氨酸羧肽酶II(GCPII)。GCPII抑制剂正在开发中，用于治疗炎症 在第一阶段人体试验中，具有极好的耐受性和最小的副作用。我们将观察是否 MGluR3被定位为调节灵长类内嗅皮层(ERC)中tau的cAMP-PKA磷酸化。 和PFC通路在AD中最脆弱，以及抑制GCPII是否可以恢复神经元的放电，改善 抑制tau的磷酸化，减少老年大鼠和猴子的神经炎症。 这项工作将证实和扩大两种结构上不同的GCPII抑制剂2-MPPA和2-MPPA的有效性。 由约翰·霍普金斯药物发现小组正在开发的PMPA。目标一号将使用双重免疫电子 显微镜确认mGluR3被正确定位以调节tau的cAMP-PKA磷酸化 (PS214Tau)和AT8标记的tau在衰老的ERC和PFC谷氨酸能突触中的作用。Aim 2将测试 急性给予2-MPPA或2-PMPA可增强老龄猴记忆相关的PFC神经元放电 通过调节cAMP-PKA开放K+通道，以及全身用药是否能改善认知 在老年大鼠和猴子身上，副作用最小。目标3将测试慢性治疗是否有最佳的 剂量的2-MPPA可持续改善工作记忆，并减少tau的磷酸化和 老年大鼠和猴联合皮质中的神经炎症。我们将有难得的机会来看看 老年猴子的慢性2-甲氧基苯丙氨酸治疗降低了原纤化的AT8标记的tau和Aβ的表达。 初步数据表明，这些制剂在认知方面产生了非常强劲的改善，没有证据表明 副作用，鼓励一种可行的翻译应用的治疗策略。

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.