TrkB.T1 signaling in astrocytes

星形胶质细胞中的 TrkB.T1 信号传导

• 批准号: 10319180
• 负责人: Michelle L Olsen
• 金额: $ 31.92万
• 依托单位: VIRGINIA POLYTECHNIC INST AND ST UNIV
• 依托单位国家: 美国
• 财政年份: 2020
• 资助国家: 美国
• 起止时间: 2020-12-15 至 2025-11-30
• 项目状态: 未结题
• 来源: https://reporter.nih.gov/project-details/10319180
• 关键词: Actins; Astrocytes; Behavioral; Binding; Brain-Derived Neurotrophic Factor; Cells; Cellular Morphology; Central Nervous System Diseases; Code; Cytoskeletal Modeling; Cytoskeletal Proteins; Cytoskeleton; Data; Data Set; Development; Distal; Electrophysiology (science); Elements; Evaluation; Genes; Genetic; Glutamates; Home; Human; Image; In Vitro; Ions; Knockout Mice; Length; Link; Maintenance; Mediating; Membrane; Mining; Molecular; Morphology; Mus; NTRK2 gene; Names; Nervous System Physiology; Neuraxis; Neurodevelopmental Disorder; Neuroglia; Neuronal Dysfunction; Neurons; Neurotransmitters; Neurotrophic Tyrosine Kinase Receptor Type 2; Pathway interactions; Peripheral; Phenotype; Population; Process; Property; Protein Isoforms; Proteins; Publishing; Receptor Signaling; Regulation; Research; Resources; Role; Sensory; Signal Pathway; Signal Transduction; Somatosensory Cortex; Structure; Synapses; Testing; Tyrosine Kinase Domain; Vertebral column; Vibrissae; Work; cell motility; cell type; density; experience; experimental study; in vivo; nervous system disorder; neurotrophic factor; novel; receptor; reconstruction; recruit; response; rho; rho GTP-Binding Proteins; synaptic function; synaptogenesis; transcriptome sequencing; uptake

Astrocytes contribute to many facets of ‘normal’ central nervous system (CNS) physiology, including regulation of neurotransmitters and K+ ions concentration, synaptic development, and synapse stabilization. These functions are largely mediated at distal, fine, peripheral astrocyte processes (PAPs). It is at these processes that astrocytes communicate with their neighbors, regulate ion and neurotransmitter levels and contribute to synapse development and stabilization. Despite decades of research indicating astrocytes enwrap or contact excitatory and inhibitory synaptic elements, with increased coverage of mature synapses, there is little known regarding signals that recruit astrocyte PAPs to synaptic structures. RNA sequencing data we have generated (and confirmed using multiple public resources) indicate astrocytes express very high levels of the BDNF receptor, TrkB. Isoform specific identification demonstrates astrocytes predominately express the truncated form, TrkB.T1. In cortex, TrkB.T1 is found almost exclusively in astrocytes. Global and astrocyte specific genetic deletion of TrkB.T1 results in astrocytes with significantly reduced volume and branching complexities. Astrocytes lacking TrkB.T1 show dysregulated expression of both perisynaptic genes associated with mature astrocyte function and pro-synaptogenic genes. In vitro and in vivo we observed that TrkB.T1 KO astrocytes do not support normal excitatory synaptogenesis or function as assessed by evaluation of pre and post synaptic excitatory elements and neuronal mEPSC analysis. Preliminary in vitro data also indicate that TrkB.T1 KO astrocytes fail to enwrap glutamatergic synapses, a phenotype we readily observe in WT astrocytes. In the current proposal we test the hypothesis that BDNF signaling through the astrocytic TrkB.T1 receptor serves as a key signaling pathway in recruiting astrocyte perisynaptic processes to glutamatergic synapses thus facilitating actin mediated structural plasticity. In the current work we use ultrastructural imaging in WT and astrocyte specific TrkB.T1 KO mice to determine if BDNF/TrkB.T1 signaling in astrocytes is necessary for astrocyte structural plasticity and function at glutamatergic synapses (Aim 1). We evaluate the loss of astrocyte TrkB.T1 on neuronal synapse development and function (Aim 2) and we use a combination of in vitro and in vivo approaches to identify the key signaling mechanisms by which BDNF binding to astrocyte TrkB.T1 receptors engage downstream signaling mechanisms, providing a molecular mechanistic framework linking astrocyte BDNF/TrkB.T1 signaling to actin cytoskeletal reorganization, morphological refinement, process outgrowth and synapse enwrapment. These studies identify a completely novel signaling pathway in astrocyte structural plasticity and have the potential to significantly advance our understanding of astrocyte-synapse interactions. While disrupted BDNF/TrkB signaling is implicated in many CNS disorders the relevance of BDNF/astrocytic TrkB.T1 signaling has not been considered.

星形胶质细胞对“正常”中枢神经系统（CNS）生理学的许多方面都有贡献，包括调节 神经递质和 K+ 离子浓度、突触发育和突触稳定性的影响。这些 功能主要由远端、精细、外周星形胶质细胞过程（PAP）介导。正是在这些过程中 星形胶质细胞与其邻居沟通，调节离子和神经递质水平并促进突触 发展和稳定。尽管数十年的研究表明星形胶质细胞包裹或接触兴奋性 和抑制性突触元件，随着成熟突触覆盖范围的增加，关于 将星形胶质细胞 PAP 招募到突触结构的信号。我们生成的 RNA 测序数据（以及 使用多个公共资源证实）表明星形胶质细胞表达非常高水平的 BDNF 受体， TrkB。同种型特异性鉴定表明星形胶质细胞主要表达截短形式 TrkB.T1。 在皮质中，TrkB.T1 几乎只存在于星形胶质细胞中。全局和星形胶质细胞特异性基因缺失 TrkB.T1 导致星形胶质细胞的体积和分支复杂性显着降低。星形胶质细胞缺乏 TrkB.T1 显示与成熟星形胶质细胞功能相关的两个突触周围基因的表达失调 和促突触基因。在体外和体内我们观察到 TrkB.T1 KO 星形胶质细胞不支持正常 通过评估突触前和后兴奋性元件来评估兴奋性突触发生或功能 和神经元 mEPSC 分析。初步体外数据还表明，TrkB.T1 KO 星形胶质细胞未能包裹 谷氨酸能突触，我们很容易在 WT 星形胶质细胞中观察到的一种表型。在当前的提案中，我们测试了 假设 BDNF 信号通过星形细胞 TrkB.T1 受体作为关键信号通路 将星形胶质细胞突触周围过程募集到谷氨酸能突触，从而促进肌动蛋白介导的结构 可塑性。在目前的工作中，我们使用 WT 和星形胶质细胞特异性 TrkB.T1 KO 小鼠的超微结构成像来 确定星形胶质细胞中的 BDNF/TrkB.T1 信号传导对于星形胶质细胞的结构可塑性和功能是否是必需的 谷氨酸能突触（目标 1）。我们评估星形胶质细胞 TrkB.T1 的丢失对神经元突触发育的影响 和功能（目标 2），我们结合使用体外和体内方法来识别关键信号传导 BDNF 与星形胶质细胞 TrkB.T1 受体结合的机制参与下游信号机制， 提供将星形胶质细胞 BDNF/TrkB.T1 信号传导与肌动蛋白细胞骨架联系起来的分子机制框架 重组、形态细化、过程生长和突触包裹。这些研究确定 星形胶质细胞结构可塑性中一个全新的信号通路，并有可能显着 增进我们对星形胶质细胞-突触相互作用的理解。虽然 BDNF/TrkB 信号传导被破坏 BDNF/星形细胞 TrkB.T1 信号传导与许多 CNS 疾病有关，但尚未被考虑。