The role of NMDA receptor subunit GluN3A in age and Alzheimer's disease-related dementia

摘要 痴呆症和阿尔茨海默病(AD)在美国和世界范围内影响着数亿人， 经过几十年的深入研究，这些与年龄相关的疾病的临床治疗仍然非常困难 有限的。先前使用建立在淀粉样β蛋白(Aβ)和Tau假说基础上的动物模型的研究 有助于获得关于AD相关痴呆的病理特征和进展的广泛知识。 不幸的是，到目前为止，直接针对Aβ和Tau病理的临床试验未能成功临床转化。在……上面 另一方面，N-甲基-D-天冬氨酸受体(NMDAR)的过度激活被认为是一个关键 阿尔茨海默病的病理和发病机制。NMDAR拮抗剂美金刚是为数不多的 对中/重度阿尔茨海默病和痴呆症患者显示出一些治疗效果。事实上, 药物抑制谷氨酸能活动已成为延缓Aβ的重要策略 诱导神经元损伤和AD进展。然而，对NMDAR法规的研究一直是 主要关注NMDAR亚基GluN1和GluN2，目前还没有关于GluN3A在 广告相关机制。作为NMDAR的唯一抑制亚基，GluN3保持紧张性NMDAR活性，并 生理范围内的慢性钙稳态。基因敲除小鼠中GluN3A的缺失 导致成年后神经细胞死亡和焦虑行为增强。我们的初步数据显示， 随着年龄的增长，GluN3A KO小鼠经历了AD样病理和认知障碍的自发演变， 这可以通过从发病前阶段开始每天服用小剂量美金刚来预防。在这 R21调查，我们将以年龄依赖的方式验证GluN3A的致病作用。具体目标1将 老年性痴呆的病理特征及其与阿尔茨海默病的关系 疾病。在不同年龄的GluN3A KO和WT小鼠中，我们将检测Aβ空斑、NFT、磷酸化 Tau蛋白、突触结构和海马区和皮质中的细胞死亡。炎症反应 包括反应性星形胶质细胞、小胶质细胞/巨噬细胞和炎症因子。具体目标2 将描述GluN3A在AD相关进展中所起作用的关键时间窗口 病理生理学。我们将在不同的条件下进行条件GluN3A基因敲除的功能丧失实验 年龄，以了解是否存在启动年龄相关进化的关键时间点 痴呆与阿尔茨海默病的病理生理学。这项R21调查是第一次努力揭示一种调节/致病 NMDAR亚单位GluN3A在老年性痴呆和可能的散发性AD小鼠模型中的作用。这 探索性研究将使我们能够对GluN3A调节的基因进行循证的系统研究 痴呆症的发病机制与AD的病理。我们的最终目标是确定GluN3A是一种新的治疗方法 针对并制定早期遗传和药物干预措施，以实现最优的NMDAR调节 延缓甚至预防渐进性痴呆和AD病理生理学的进展。

Summary Dementia and Alzheimer’s disease (AD) affect hundreds of millions of people in the US and worldwide, after several decades of intensive investigations clinical treatments of these age-related disorders are still very limited. Previous investigations using animal models established on the amyloid beta (Aβ) and Tau hypothesis have helped to gain extensive knowledge on the pathological features and progression of AD related dementia. Unfortunately, clinical trials directly targeting Aβ and Tau pathology have so far failed clinical translation. On the other hand, hyperactivation of N-Methyl-D-aspartate receptors (NMDARs) has been identified as a key mechanism contributing to AD pathology and pathogenesis. The NMDAR antagonist memantine is one of few treatments showing some therapeutic benefits for moderate/severe AD and dementia patients. In fact, pharmacological suppression of glutamatergic activities has become an important strategy in postponing Aβ- induced neuronal damage and AD progression. The research in NMDAR regulations, however, has been heavily focused on the NMDAR subunits GluN1 and GluN2, there is no information about the role of GluN3A in AD related mechanism. As a unique inhibitory subunit of NMDARs, GluN3 keeps the tonic NMDAR activity and chronic Ca2+ homeostasis within the physiological range. Deletion of GluN3A in the knockout (KO) mouse resulted in enhanced neuronal cell death and anxiety behaviors at adult ages. Our preliminary data show that GluN3A KO mice undergo spontaneous evolvement of AD-like pathology and cognitive deficits with aging, which can be prevented by daily treatments of low-dose memantine initiated from the pre-onset stage. In this R21 investigation, we will verify the pathogenic role of GluN3A in age-dependent manners. Specific Aim 1 will characterize the pathological features of the age-dependent dementia and the relation to Alzheimer’s disease. In GluN3A KO and WT mice of different ages, we will examine Aβ plagues, NFT, phosphorylation of Tau protein, synaptic structures and cell death in the hippocampus and cortex. Inflammatory reactions including reactive astrocytes, microglia/microphage, and inflammatory factors will be measure. Specific Aim 2 will delineate the critical time window for the role of GluN3A in progression of AD-associated pathophysiology. We will perform loss-of-function experiments of conditional GluN3A knockout at different ages to understand whether there is a critical time point for initiating the age-dependent evolvement of dementia and AD pathophysiology. This R21 investigation is the first effort in revealing a regulatory/pathogenic role of the NMDAR subunit GluN3A in age-related dementia and possibly a sporadic AD mouse model. This exploratory study will allow us to develop an evidence-based systematic investigation on the GluN3A-regulated mechanism of dementia and AD pathology. Our ultimate goal is to identify GluN3A as a novel therapeutic target and develop early genetic and pharmacological interventions for an optimal NMDAR regulation in order to delay or even prevent the gradually evolved dementia and the progression of AD pathophysiology.