Intercellular TWEAK/Fn14 Cytokine Signaling in Sensory-Dependent Circuit Refinement

在出生后的大脑发育过程中，新组装的神经回路通过突触连接子集的加强和其他突触连接的同时消除而得到完善。突触完善的过程首先由生命早期内在产生的神经活动协调，然后在出生后发育的后期阶段由感觉经验驱动。人们认为，感觉依赖性精化的损伤会导致多种神经发育障碍，这与环境风险因素（如免疫挑战）对其病理生理的影响是一致的。然而，旨在纠正这种损伤的治疗策略受到了限制，因为从根本上缺乏对感觉输入改善发育回路的分子和细胞机制的了解。本研究的重点是更全面地了解在发育过程中感觉经验改善突触连接的基本细胞和分子机制，并确定这些机制的损伤如何导致神经发育疾病。在初步研究中，申请人应用新开发的单细胞转录组学方法鉴定了Fn14是一种由兴奋性神经元的视觉体验转录诱导的基因，并编码一种细胞因子受体，该受体是发育中的大脑中感觉依赖性改进所必需的。该提案包含一个全面的培训和研究计划，以这些发现为基础，在短期内通过实验解决剩余的知识差距，并通过促进建立一个创新的多学科研究计划，长期专注于解决这些问题。在Aim 1中，申请人将学习并应用专门的急性层电生理学技术来测试假设，即TWEAK， Fn14的促炎细胞因子配体，是通过小胶质细胞到神经元信号轴驱动感觉依赖性改善的必要和充分的。在Aim 2中，申请人将结合电生理学和生物信息学的新方法来确定在母体免疫激活（MIA）小鼠异常脑发育模型中，升高的TWEAK/Fn14信号是否导致突触过度精细。在Aim 3中，申请人将验证TWEAK/Fn14信号通过促进未成熟突触棘向成熟棘的转化而介导功能完善的假设。这些技术培训活动将得到几位非常成功的科学家的重点指导，他们致力于帮助申请人在哈佛医学院充满活力和协作的培训环境中获得专业和智力技能。这些活动有望促进申请人成功过渡到学术机构的独立研究职位。

During postnatal brain development, newly assembled neural circuits are refined through the strengthening of a subset of synaptic connections and the concurrent elimination of others. This process of synaptic refinement is first coordinated by intrinsically generated neural activity early in life and then driven by sensory experience during a later phase of postnatal development. Impairments in sensory-dependent refinement are thought to contribute to a heterogeneous array of neurodevelopmental disorders, consistent with the contribution of environmental risk factors, such as immune challenge, to their pathophysiology. Yet, therapeutic strategies aimed at correcting such impairments have been limited by a fundamental lack of insight into the molecular and cellular mechanisms through which sensory input refines developing circuits. The key focus of the proposed research is to obtain a more comprehensive understanding of the basic cellular and molecular mechanisms by which sensory experience refines synaptic connections in the course of development, and to determine how impairments in these mechanisms may contribute to neurodevelopmental disease. In preliminary studies, the applicant applied newly developed single-cell transcriptomic methods to identify Fn14 as a gene that is transcriptionally induced by visual experience in excitatory neurons and encodes a cytokine receptor that is required for sensory-dependent refinement in the developing brain. This proposal contains a comprehensive training and research plan to build upon these findings by addressing the remaining gaps in knowledge experimentally in the short-term, and by facilitating the establishment of an innovative and multidisciplinary research program focused on addressing these questions in the long-term. In Aim 1, the applicant will learn and apply specialized acute slice electrophysiology techniques to test the hypothesis that TWEAK, the pro-inflammatory cytokine ligand of Fn14, is necessary and sufficient to drive sensory-dependent refinement via a microglia-to-neuron signaling axis. In Aim 2, the applicant will combine electrophysiology with newly learned methods in bioinformatics to determine whether heightened TWEAK/Fn14 signaling contributes to excessive synaptic refinement in the maternal immune activation (MIA) mouse model of aberrant brain development. In Aim 3, the applicant will test the hypothesis that TWEAK/Fn14 signaling mediates functional refinement by promoting the conversion of immature synaptic spines to mature spines. These technical training activities will be augmented by focused mentorship from several highly successful scientists who are committed to aiding in the applicant's acquisition of professional and intellectual skills in the highly energetic and collaborative training environment at Harvard Medical School. These activities are expected to facilitate the successful transition of the applicant into an independent research position at an academic institution.