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

项目总结 在大脑发育过程中建立突触连通性涉及到最初的形成 大量的突触伴随着一个精细化的过程，其中一些突触被维持着 当其他人被淘汰的时候。过度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。感觉依赖型突触消除的损害有助于 神经发育障碍，如自闭症，强调了这一过程对适当的 神经回路的发展和功能。然而，尽管神经发育障碍在 以惊人的速度流行，治疗它们的治疗策略很少，部分原因是缺乏洞察力 在健康的大脑中控制突触消除的因素。这项提案的一个关键目标是揭示 经验下游突触消除的新的细胞和分子机制， 从而为治疗出生后大脑发育障碍的新的治疗方法奠定了基础。 对小鼠视觉系统的研究表明，非神经性脑细胞，主要是 小胶质细胞和星形胶质细胞在视觉体验开始前通过吞噬来协调突触消除 突触过多。然而，数据表明，这些细胞可能不是突触消除的主要调节因素 在开发的后期阶段，通过视觉体验进行协调。相反，我们最近 发现了一类不太为人所知的神经胶质细胞，少突胶质前体细胞(OPC)，在 通过突触吞噬作用消除突触以回应经验。这一结果与 广泛的猜测认为，OPC虽然主要是因为它们分化为成熟的 少突胶质细胞在脑髓鞘形成之外的大脑中发挥着关键作用。与这种可能性一致，我们的数据表明 在大脑成熟的过程中，OPC对于形成功能神经回路是必不可少的。 在这个应用中，我们提出了一个多学科策略来检验吞噬的假设 OPC的突触是功能性突触感觉依赖性消除的核心机制 在发育中的大脑中。在目标1中，我们将使用病毒和转基因工具来描述时空 用活体双光子显微镜研究突触被OPC吞噬的动力学和活性依赖基础。在……里面 目的2，我们将应用生理和行为分析来确定突触吞噬的后果 OPC对完好动物大脑功能的影响。在目标3中，我们将合并无偏见的转录和CRISPR- 以吞噬细胞受体LRP1为重点的基于候选的筛选技术揭示 突触被OPC吞噬的分子途径。总而言之，我们预计这些研究将 建立突触被OPC吞噬作为一种将经验与神经回路发育联系起来的新机制， 并为未来旨在改变OPC功能作为一种潜在治疗手段的研究奠定基础 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.