Role of astrocyte-based cholinergic neuromodulation in cognition and in the treatment of cognitive disorders

摘要 神经元被视为认知的细胞关联，也是临床治疗的唯一目标，部分原因是 快速而直接地操纵神经元可以改变行为。然而，人类的大脑也是由胶质细胞组成的，它 形态和遗传的复杂化是人脑的一个显著特征。尤其是星形胶质细胞， 现在已知协调许多神经功能，明确了星形胶质细胞直接贡献的可能性 认知功能和心理健康。然而，由于缺乏对星形胶质细胞规则的理解 活动和它们对神经回路的参与限制了我们测试这一想法的能力。最近的集体工作 表明星形胶质细胞将神经调节信息传递到突触回路。具体来说，我们发现， 星形胶质细胞上α7烟碱型乙酰胆碱受体(α7nAChRs)调节星形胶质细胞递质的释放 D-丝氨酸进入突触。神经调节，特别是胆碱能信号，允许行为适应 环境的变化，以及它的变化与精神分裂症的认知缺陷有关。巧合的是， α7nAChR在过去十年中专注于主要药物开发努力，以恢复 精神分裂症患者。在这里，我们将利用这一基于星形胶质细胞的新的α7nAChR途径来测试 星形胶质细胞在认知功能和前认知干预中的作用，并阐明其机制 通过它，星形胶质细胞在细胞和分子水平上感受和传递神经调节。在……里面 这样做，我们将测试一组我们假设的支配星形胶质细胞输入输出保真度的一般原则 (位置联轴器)。在目标1中，我们将检验α7nAChRs位于邻近区域的假设 在D-丝氨酸库中，通过α7nAChR通道活性将钙内流直接连接到钙依赖的D-丝氨酸 释放机械。我们将进行荧光钙成像研究，以了解空间，时间和 α7nAChR介导的钙信号的分子规律及其与D-丝氨酸释放的关系然后，我们将绘制 突触周围星形细胞突起中α7nAChR和D-丝氨酸池的物理联系 显微镜。此外，我们将进行单粒子跟踪研究，以了解 α7nAChR在星形胶质细胞表面相对于D-丝氨酸池的分布受结合的影响 内源和外源配体。在目标2中，我们将生成细胞特异性基因敲除小鼠系来 选择性消融星形胶质细胞、脑内兴奋性神经元或抑制性神经元和画布中的α7nAChR 每种细胞类型对α7nAChRs支持的特征行为的贡献。我们最近展示了 一种α7nAChR部分激动剂在第三阶段临床试验中用于治疗慢性阻塞性肺疾病患者的认知障碍 精神分裂症，会提高小鼠大脑中D-丝氨酸的水平。根据我们的观察，灭活 基于星形胶质细胞的α7nAChR信号导致D-丝氨酸水平和认知行为的特定变化 然后将检验这一假设，即星形胶质细胞，而不是神经元，使认知的行为效能 增强剂在临床试验中进行了测试，D-丝氨酸信号是这些效应的电路执行器。

ABSTRACT Neurons are viewed as the cellular correlate of cognition and only target of clinical therapeutics, in part because manipulating neurons rapidly and directly alters behavior. Yet, the human brain is also made of glial cells, which morphological and genetic complexification is a striking feature of the human brain. Astrocytes, in particular, are now known to orchestrate many neural functions, crystalizing the possibility of a direct astrocyte contribution to cognitive functions and mental health. However, a lack of understanding of the rules that govern astrocytes activity and their involvement in neural circuits has limited our ability to test this idea. Collective work recently showed that astrocytes transduce neuromodulatory information onto synaptic circuits. Specifically, we found that α7 nicotinic acetylcholine receptors (α7nAChRs) on astrocytes regulate the release of the astrocyte transmitter D-serine onto synapses. Neuromodulation, in particular cholinergic signaling, permits behavioral adaptations to changes in the environment, and its alteration is linked to cognitive deficits in schizophrenia. Coincidently, the α7nAChR has focalized major drug development efforts in the past decade to restore the cognitive symptoms of patients with schizophrenia. Here, we will take advantage of this new astrocyte-based α7nAChR pathway to test the role of astrocytes in cognitive functions and pro-cognitive interventions, and elucidate the mechanisms through which neuromodulation is sensed and transduced by astrocytes at the cellular and molecular levels. In doing so, we will test a set of general principles which we hypothesize govern input output fidelity in astrocytes (positional coupling). In Aim 1, we will test the hypothesis that α7nAChRs are located in the immediate vicinity of D-serine pools, directly linking Ca2+ influx through α7nAChR channel activity to the Ca2+-dependent D-serine release machinery. We will conduct fluorescence Ca2+ imaging studies to understand the spatial, temporal and molecular rules of α7nAChR-mediated Ca2+ signals and their relation to D-serine release. We will then map the physical association of α7nAChR and D-serine pools in perisynaptic astrocytic processes, using electron microscopy. In addition, we will conduct single-particle tracking studies to understand how the dynamic distribution of α7nAChR at the surface of astrocytes, with respect to D-serine pools, is influenced by the binding of endogenous and exogenous ligands. In Aim 2, we will generate cell-specific knockout mouse lines to selectively ablate α7nAChR from astrocytes, excitatory neurons or inhibitory neurons in the brain, and canvas the contribution of each cell-types to characteristic behaviors supported by α7nAChRs. We recently showed that an α7nAChR partial agonist tested in Phase-III clinical trials for the treatment of cognitive deficits in patients with schizophrenia, elevates D-serine levels in the mouse brain. Based on our observations that inactivating astrocyte-based α7nAChR signaling leads to specific alterations in D-serine levels and cognitive behavior, we will then test the hypothesis that astrocytes, but not neurons, enable the behavioral efficacy of cognitive enhancers tested in clinical trials, and that D-serine signaling is the circuit actuator of these effects.