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相关物和临床治疗的唯一靶点，部分原因是 快速而直接地操纵神经元会改变行为。然而，人脑也是由神经胶质细胞组成的， 形态和遗传复杂化是人脑的显著特征。特别是星形胶质细胞， 现在已知它协调许多神经功能，明确了星形胶质细胞直接参与神经功能的可能性。 认知功能和心理健康。然而，由于缺乏对星形胶质细胞的管理规则的了解， 活动及其参与神经回路的能力限制了我们测试这一想法的能力。最近集体工作 表明星形胶质细胞将神经调节信息传递到突触回路上。具体来说，我们发现， 星形胶质细胞上的α7烟碱乙酰胆碱受体（α 7 nAChRs）调节星形胶质细胞递质的释放 D-丝氨酸到突触上。神经调节，特别是胆碱能信号传导，允许行为适应， 环境的变化，其改变与精神分裂症的认知缺陷有关。巧合的是， 在过去的十年中，α 7 nAChR集中了主要的药物开发工作，以恢复认知症状， 精神分裂症患者在这里，我们将利用这种新的基于星形胶质细胞的α 7 nAChR通路来测试 星形胶质细胞在认知功能和促认知干预中的作用，并阐明其机制 神经调节通过其在细胞和分子水平上被星形胶质细胞感知和转导。在 这样做，我们将测试一组一般原则，我们假设支配输入输出保真度星形胶质细胞 （位置耦合）。在目标1中，我们将检验α 7 nAChR位于邻近区域的假设。 的D-丝氨酸池，直接连接Ca 2+内流通过α 7 nAChR通道活性的Ca 2+依赖的D-丝氨酸 解放机械我们将进行荧光Ca 2+成像研究，以了解空间，时间和 α 7 nAChR介导的Ca ~（2+）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 突触周星形胶质细胞突起中α 7 nAChR和D-丝氨酸池的物理联系，使用电子 显微镜此外，我们将进行单粒子跟踪研究，以了解动态 相对于D-丝氨酸池，α 7 nAChR在星形胶质细胞表面的分布受到结合的影响。 内源性和外源性配体。在目标2中，我们将产生细胞特异性敲除小鼠系， 选择性地从星形胶质细胞、大脑中的兴奋性神经元或抑制性神经元中清除α 7 nAChR， 每种细胞类型对α 7 nAChRs支持的特征行为的贡献。我们最近发现， 一种在III期临床试验中测试的α 7 nAChR部分激动剂，用于治疗以下患者的认知缺陷： 精神分裂症，提高小鼠大脑中的D-丝氨酸水平。根据我们的观察， 基于星形胶质细胞的α 7 nAChR信号转导导致D-丝氨酸水平和认知行为的特定改变，我们 然后将测试星形胶质细胞而不是神经元使认知的行为功效的假设， 在临床试验中测试的增强剂，和D-丝氨酸信号是这些效果的电路致动器。

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.