The Role of Astrocyte BMP Signaling in Fragile X Syndrome

项目总结/摘要 本项目旨在探讨星形胶质细胞骨形态发生蛋白（BMP）信号在骨肉瘤发病机制中的作用。 脆性X综合征（FXS）。FXS是最常见的智力残疾和自闭症的遗传形式 谱系障碍（ASD）。FXS是由FMR 1基因启动子中的三核苷酸重复扩增引起的， 转录沉默，和FXS最常与Fmr 1敲除（KO）小鼠建模。虽然 研究表明，有几种途径介导了Fmr 1功能丧失的影响， 治疗在临床试验中失败，并且FXS主要仅通过症状来治疗。大多数 FXS的研究集中在神经元内的内在变化。然而，FXS的新兴研究表明， 星形胶质细胞，特别是通过星形胶质细胞分泌因子。野生型（WT）神经元与星形胶质细胞或 来自Fmr 1 KO小鼠的星形胶质细胞条件培养基（ACM）表现出发育不良的神经突生长，并重现了 在Fmr 1 KO小鼠和人FXS患者体内观察到的未成熟树突棘表型，提供了直接的 星形胶质细胞分泌因子在FXS中的因果作用的证据。FXS星形胶质细胞的初步数据分析 转录和蛋白分泌鉴定了四种蛋白质，它们在mRNA中过表达并且过分泌， 其中BMP 6。此外，WT星形胶质细胞中BMP信号的激活产生了超过三分之一的蛋白质， FXS星形胶质细胞的分泌变化，而FXS星形胶质细胞中BMP信号的消除消除了神经突 过度增长赤字这项提议的目的是检验星形胶质细胞中BMP信号上游的假设 的神经发育FXS赤字在体内，并确定星形胶质细胞分泌的蛋白质，介导这种效果。 将使用组合的遗传和病毒方法来选择性敲除星形胶质细胞中的Bmpr 2或Smad 4， 评估星形胶质细胞BMP信号转导的下调是否可以挽救树突状细胞中的体内FXS异常， 脊柱可塑性和行为星形胶质细胞特异性体内蛋白质组学方法结合特征分析 将鉴定负责FXS缺陷的BMP信号传导下游的蛋白质。这些 实验将确定星形胶质细胞中的BMP信号传导是否介导体内FXS缺陷，并阐明 它发生的机制，从而提供了一个新的见解，以前低估的方面FXS 病理生理学这项拟议中的研究将在索尔克生物研究所的艾伦实验室进行 研究，一个合作的研究环境，提供所有必要的设备和培训。 通过分子神经生物学的理论和实践培训，与各种支持者合作， 研究和临床背景，以及一个致力于指导的研究团队，拟议的研究 培训计划将使严格的教学研究，并奠定了基础，为未来的职业生涯， 独立的物理学家和科学家

Project Summary/Abstract This project addresses the role of astrocyte bone morphogenetic protein (BMP) signaling in the pathogenesis of Fragile X Syndrome (FXS). FXS is the most common inherited form of intellectual disability (ID) and autism spectrum disorder (ASD). FXS is caused by trinucleotide repeat expansion in the FMR1 gene promoter leading to transcriptional silencing, and FXS is most often modeled with the Fmr1 knockout (KO) mouse. Although research has implicated several pathways mediating the effects of the Fmr1 loss of function, most targeted treatments have failed in clinical trials, and FXS is predominantly treated by symptom only. The majority of research in FXS has focused on intrinsic changes within neurons. However, emerging research in FXS implicates astrocytes, specifically through astrocyte-secreted factors. Wild-type (WT) neurons cultured with astrocytes or astrocyte-conditioned media (ACM) from Fmr1 KO mice exhibit stunted neurite outgrowth and recapitulate the immature dendritic spine phenotype observed in vivo in Fmr1 KO mice and human FXS patients, providing direct evidence for a causal role of astrocyte-secreted factors in FXS. Preliminary data profiling FXS astrocyte transcription and protein secretion identified four proteins both overexpressed in mRNA and oversecreted, one of which is BMP6. Furthermore, activation of BMP signaling in WT astrocytes generates over a third of the protein secretion changes of FXS astrocytes, while abrogation of BMP signaling in FXS astrocytes abolishes neurite outgrowth deficits. The goal of this proposal is to test the hypothesis that BMP signaling in astrocytes is upstream of neurodevelopmental FXS deficits in vivo and to identify the astrocyte-secreted proteins that mediate this effect. A combined genetic and viral approach to selective knock out Bmpr2 or Smad4 in astrocytes will be used to assess whether downregulation of astrocyte BMP signaling can rescue in vivo FXS abnormalities in dendritic spines, plasticity, and behavior. An astrocyte-specific in vivo proteomic approach combined with characterization of specific proteins in vitro will identify proteins downstream of BMP signaling responsible for FXS deficits. These experiments will determine if BMP signaling in astrocytes mediates FXS deficits in vivo and elucidate mechanisms by which it occurs, thereby providing new insight into a previously underappreciated aspect of FXS pathophysiology. The proposed research will take place in the Allen Laboratory at the Salk Institute for Biological Studies, a collaborative research environment that provides access to all necessary equipment and training. Through theoretical and practical training in molecular neurobiology, collaboration with supporters of diverse research and clinical backgrounds, and a research team committed to mentorship, the proposed research training plan will enable rigorous instruction in research and lay the foundation for a future career as an independent physician-scientist.