How Do Muller Glia Control Circuit-Specific Retinal Synaptogenesis?

突触是中枢神经系统的基本功能单位。突触功能障碍和 突触丢失是包括视网膜变性在内的神经系统疾病的特征。但是，目前有 没有有效的治疗方法可以修复或再生这些突触损伤。因此，我的龙- 学期目标是开发基于细胞和基因的疗法来修复和/或再生这些受损的突触 电路。特别是，我的目标是确定治疗视网膜的新的细胞和分子靶点。 退行性疾病，如老年性黄斑变性和青光眼。 最近的研究表明，神经胶质细胞是突触形成、维持和发育的重要调节者。 大脑的功能。尤其是星形胶质细胞，是大脑中主要的胶质细胞类型，分泌凝血酶敏感蛋白(TSP)家族。 诱导兴奋性突触形成的蛋白质。与脑不同的是，穆勒胶质细胞(MG)是主要的胶质细胞类型。 然而，视网膜中MG如何调节视网膜中的神经元连接仍不清楚。在我的 初步实验发现，MG在视网膜发育早期会分泌TSP1和TSP2 电路。TSP1、TSP2及其突触原受体α-2、δ-1在外丛和内丛中均有丰富分布 视网膜的突触层(分别为OPL和IPL)。缺乏α2δ-1(α2δ-1 KO)的转基因小鼠 IPL中突触的数量显著减少，进一步支持它们参与视网膜回路 发展。特别是，TSP1特异性地定位于IPL内的两个突触亚胺。离体 使用纯化的视网膜神经节细胞(RGC)培养的研究表明，TSP1特异性地促进 开关方向选择性视网膜节细胞(OoDSGCs)的突触形成。TSP1诱导的突触发生受到抑制 通过针对整合素TSP1的功能阻断抗体，β1是TSP1的另一个已知受体，富含 OoDSGCs。另一方面，TSP2诱导所有视网膜节细胞形成突触。 基于这些发现，我推测，在视网膜中，MG分泌的TSP控制着视网膜的不同方面 兴奋性突触的发育通过其共同的受体α2，δ-1。我进一步假设TSP1调节 通过与整合素β1相互作用形成ooDSGCs连接，从而赋予电路特异性。至 验证这些假设，在这里我提出了两个具体的目标：1)确定MG分泌的需求 TSP1和2及其共同的突触源性受体α2δ-1与视网膜突触发育和 功能。2)确定Tsp1/整合素β1相互作用在开关dsGC形成中的作用 特定的电路。拟议的研究将使我们在理解如何 MG以电路特异性的方式控制视网膜突触的发育，也将促进 修复受损突触回路的新治疗策略。 好了！

Synapses are the basic functional units of the central nervous system (CNS). Synaptic dysfunction and synapse loss are hallmarks of neurological disorders including retinal degeneration. However, there currently are no effective therapies that can repair or regenerate these synaptic impairments. Therefore, my long- term goal is to develop cell- and gene-based therapies to repair and/or regenerate these impaired synaptic circuits. In particular, I aim to identify novel cellular and molecular targets for the treatment of retinal degenerative diseases such as age-related macular degeneration and glaucoma. Recent studies have shown that glial cells are important regulators of synapse formation, maintenance and function in the brain. Particularly, astrocytes, major glia cell type in brain, secrete thrombospondin (TSP) family proteins that induce excitatory synapse formation. Unlike brain, Muller glia (MG) are the major glial cell type of the retina, however, how MG regulate neuronal connectivity in the retina remains unclear. In my preliminary experiments, I found that MG secretes TSP1 and TSP2 during early development of the retinal circuitry. TSP1, TSP2 and their synaptogenic receptor α2δ-1 are enriched in the outer and inner plexiform synaptic layers (OPL and IPL, respectively) of the retina. Transgenic mice lacking α2δ-1 (α2δ-1 KO) have dramatically decreased number of synapses in the IPL further supporting their involvements in retinal circuitry development. Particularly, TSP1 is specifically localized at two synaptic sublaminae within the IPL. In vitro studies using purified Retinal Ganglion Cell (RGC) cultures demonstrated that TSP1 specifically promotes synapse formation of On-Off Direction-Selective RGCs (ooDSGCs). TSP1-induced synaptogenesis is inhibited by a function-blocking antibody against Integrin β1, another known receptor of TSP1 that is enriched in ooDSGCs. On the other hand, TSP2 induces formation of synapses onto all RGCs. Based on these findings, I hypothesize that, in the retina, MG-secreted TSPs control different aspects of retinal excitatory synapse development through their common receptor α2δ-1. I further postulate that TSP1 regulates formation of ooDSGCs connectivity through an interaction with Integrin β1 which confers circuit specificity. To test these hypotheses, here I propose two specific aims; 1) To determine the requirement of MG-secreted TSP1 and 2 and their common synaptogenic receptor α2δ-1 for retinal synapse development and function. 2) To determine the role of TSP1/Integrin β1 interaction for the formation of On-Off DSGC specific circuitry. The proposed studies would provide a significant step forward in our understanding of how MG control retinal synaptic development in a circuit specific manner and also would facilitate development of novel therapeutic strategy to repair impaired synaptic circuits. !