BDNF signaling via astrocyte Trkb.T1 drives morphogenesis and maturation of astrocytes, a dysregulated feature of Rett syndrome

项目总结 星形胶质细胞的形态成熟是中枢神经系统健康发育的关键步骤。不成熟 星形胶质细胞阐述其突起，并以细小的、终末的小叶突起渗入神经纤维层。这些 突起允许细胞与邻近星形胶质细胞的细胞间通讯，血管系统的包膜和 包裹突触，以及星形胶质细胞参与神经递质摄取、突触发育和 稳定状态。星形胶质细胞的形态发生与神经元的成熟和突触发生相一致，这意味着 这两个事件之间的共同机制。脑源性神经营养因子(BDNF)是一种发育 对神经元发育和活性依赖可塑性至关重要的分子。我们的实验室已经证明了BDNF 通过TrkB受体亚型(TrkB.T1)与星形胶质细胞相互作用促进星形胶质细胞形态 成熟。我们发表的工作表明，星形胶质细胞TrkB.T1的缺失导致 星形胶质细胞的体积和分支的复杂性，这一变化一直持续到成年。我们的发现是 与健康相关，因为神经发育障碍(NDD)与BDNF失调有关， 包括X连锁NDD，Rett综合征(RTT)。初步证据表明，RTT中的星形胶质细胞 小鼠模型存在类似TrKB.T1基因敲除的体积缺陷，并伴有基因表达异常。 报告表明，TrkB.T1亚型与一种小的RhoGTP酶抑制剂具有独特的相互作用，尽管其 功能意义相对不为人所知。我们建议评估星形胶质细胞RhoGTPase信号和 体外应用BDNF和潜在治疗性TrkB激活剂对细胞骨架的影响 以及原位遗传、分子和成像技术。此外，我们将评估TrkB疗法是否 挽救RTT星形胶质细胞形态缺陷和基因失调。我的具体目标是：(1)确定 TrkB.T1激活的信号转导和(2)TrkB.T1激活在细胞形态变化中的作用 并通过(3)在相关的NDD模型中评估星形胶质细胞TrkB.T1来扩展我们的发现。 这一建议符合大脑启蒙2.0的优先事项：(1)证明关系之间的因果关系；(2) 确定可观察到的大脑特性的基本原则。

PROJECT SUMMARY Astrocyte morphological maturation is a critical step for healthy central nervous system development. Immature astrocytes elaborate their processes and infiltrate the neuropil with fine, terminal, leaflet processes. These processes allow for cell-cell communication with neighboring astrocytes, ensheathment of the vasculature and enwrapping synapses, and where astrocytes participate in neurotransmitter uptake, synapse development and stabilization. Astrocyte morphogenesis coincides with neuronal maturation and synaptogenesis, implicating a common mechanism between these two events. Brain-derived neurotrophic factor (BDNF) is one developmental molecule crucial for development and activity-dependent plasticity in neurons. Our lab has shown that BDNF interacts with astrocytes through a TrkB receptor isoform (TrkB.T1) to promote astrocyte morphological maturation. Our published work demonstrates astrocyte deletion of TrkB.T1 results in a 25% reduction in astrocyte volume and branching complexity, a change that persists through adulthood. Our discovery is relevant to health, as neurodevelopmental disorders (NDDs) are associated with BDNF dysregulation, including the X-linked NDD, Rett Syndrome (RTT). Preliminary evidence demonstrates that astrocytes in RTT mouse models have volume deficits similar to TrKB.T1 knockout accompanied by dysregulated gene expression. Reports demonstrate that the TrkB.T1 isoform uniquely interacts with a small RhoGTPase inhibitor, though its functional significance is relatively unknown. We propose to evaluate astrocyte RhoGTPase signaling and cytoskeletal dynamics in response to BDNF and potentially therapeutic TrkB activators utilizing in vitro and in situ genetic, molecular, and imaging techniques. Furthermore, we will assess if TrkB therapeutics rescue RTT astrocyte morphology deficits and gene dysregulation. My specific aims seek to (1) determine signaling consequences of TrkB.T1 activation and (2) the role of TrkB.T1 activation on morphological change in astrocytes as well as to expand upon our discovery by (3) evaluating astrocyte TrkB.T1 in a relevant NDD model. This proposal meets the priorities of the BRAIN Initiate 2.0 of (1) demonstrating causality of relationships and (2) identifying fundamental principles of observable brain properties.