Synapse Engulfment by Oligodendrocyte Precursor Cells: A New Mechanism of Circuit Refinement in the Developing Brain

项目摘要 在大脑发育过程中，突触连接的建立涉及到一个神经元的最初形成。 过剩的突触，然后是一个细化过程，其中一些突触被保留下来 而另一些则被淘汰。过量突触的精确消除是由感觉经验驱动的， 出生后早期生命的关键时期。感觉依赖性突触消除的损伤有助于 神经发育障碍，如自闭症，强调了这一过程的重要性，为适当的 神经回路的发育和功能。然而，尽管神经发育障碍在美国越来越多， 由于其发病率以惊人的速度增长，治疗它们的治疗策略很少，部分原因是缺乏了解 健康大脑中控制突触消除的因素。该提案的一个关键目标是揭示 新的细胞和分子机制消除突触下游的经验， 从而为治疗出生后大脑发育障碍的新治疗方法奠定基础。 对小鼠视觉系统的研究表明，非神经元脑细胞，主要是 小胶质细胞和星形胶质细胞，协调突触消除之前的视觉经验发作的吞噬作用 多余的突触然而，数据表明，这些细胞可能不是突触消除的主要调节者 在由视觉经验协调的发展后期。相反，我们最近 发现了一种不太清楚的神经胶质细胞，少突胶质前体细胞（OPCs）在 通过突触吞噬作用消除突触以响应经验。这一结果符合 广泛流传的猜测，OPC，而主要赞赏他们的分化成成熟的 少突胶质细胞在脑中除了髓鞘形成之外还起着关键作用。根据这种可能性，我们的数据表明， OPCs在大脑成熟过程中对形成功能性神经回路至关重要。 在这个应用程序中，我们提出了一个多学科的战略来测试的假设， OPCs对突触的作用是感觉依赖性功能性突触消除的核心机制 在发育中的大脑中。在目标1中，我们将采用病毒和转基因工具来表征时空 使用体内双光子显微镜观察OPC的突触吞噬的动力学和活性依赖性基础。在 目的二，我们将应用生理和行为学的分析来确定突触吞噬的后果 对大脑功能的影响。在目标3中，我们将合并无偏转录组学和CRISPR- 基于筛选技术的候选人为基础的方法集中在吞噬受体Lrp 1，以揭示 OPCs吞噬突触的分子途径。总之，我们希望这些研究能够 OPCs对突触的吞噬作用是一种将经验与神经回路发育联系起来的新机制， 并为将来的研究奠定基础，以修改OPC功能作为潜在的治疗方法。 治疗神经发育障碍的策略。

PROJECT SUMMARY The establishment of synaptic connectivity during brain development involves the initial formation of an overabundance of synapses followed by a refinement process in which some of these synapses are maintained while others are eliminated. The precise elimination of excess synapses is driven by sensory experience during critical periods of early postnatal life. Impairments in sensory-dependent synapse elimination contribute to neurodevelopmental disorders such as autism, underscoring the importance of this process for the proper development and function of neural circuits. However, although neurodevelopmental disorders are growing in prevalence at an alarming rate, therapeutic strategies for treating them are scarce in part due to a lack of insight into the factors that control synapse elimination in the healthy brain. A key goal of this proposal is to uncover novel cellular and molecular mechanisms underlying the elimination of synapses downstream of experience, thereby laying the groundwork for new therapeutic approaches to treat disorders of postnatal brain development. Work in the visual system of the mouse has revealed that non-neuronal brain cells, predominantly microglia and astrocytes, coordinate synapse elimination before the onset of visual experience by phagocytosing excess synapses. However, data suggest that these cells may not be major regulators of synapse elimination during late phases of development that are coordinated by visual experience. On the contrary, we recently discovered a key role for a less well understood class of glia, oligodendrocyte precursor cells (OPCs), in eliminating synapses in response to experience through synaptic phagocytosis. This result is consistent with wide-spread speculation that OPCs, while predominantly appreciated for their differentiation into mature oligodendrocytes, play key roles in the brain beyond myelination. In line with this possibility, our data suggest that OPCs are essential for shaping functional neural circuits during the maturation of the brain. In this application, we propose a multi-disciplinary strategy to test the hypothesis that the engulfment of synapses by OPCs is a core mechanism underlying the sensory-dependent elimination of functional synapses in the developing brain. In Aim 1, we will employ viral and transgenic tools to characterize the spatio-temporal dynamics and activity-dependent basis of synaptic engulfment by OPCs using in vivo two-photon microscopy. In Aim 2, we will apply physiological and behavioral assays to determine the consequences of synaptic engulfment by OPCs on brain function in the intact animal. In Aim 3, we will merge unbiased transcriptomic and CRISPR- based screening techniques with a candidate-based approach focused on the phagocytic receptor Lrp1 to reveal molecular pathways underlying the engulfment of synapses by OPCs. Altogether, we expect these studies to establish synapse engulfment by OPCs as a new mechanism linking experience to neural circuit development, and to lay the foundation for future studies geared toward modifying OPC function as a potential therapeutic strategy for treating neurodevelopmental disorders.