Investigating Syngap1 as a regulator of striatal synaptic function

项目总结 Syngap1相关的智能障碍是一种神经发育障碍，由基因突变引起 SYNGAP1基因。Syngap1编码SynGAP，是一种高度丰富的蛋白质，存在于细胞内。 兴奋性突触的突触密度。在突触，SynGAP起到抑制下游NMDAR的作用 通过抑制小的GTP酶的信号和AMPAR的贩运。SynGAP的移位 突触后密度是允许NMDAR依赖的长时程增强(LTP)所必需的 神经元。在没有SynGAP的情况下，NMDAR依赖的可塑性不受限制，从而导致改变 在突触强度、脊柱结构和可塑性方面。虽然SynGAP的功能一直很好- 在大脑皮层和海马区的研究中，纹状体也表现出高水平的SynGAP表达。 纹状体投射神经元是覆盖着密集的树突阵列的GABA能神经元，它 接受来自大脑皮层的兴奋性输入。因此，SynGAP定位为在选通中发挥关键作用 纹状体突触的传递和可塑性。尽管如此，SynGAP在纹状体神经元中的功能 尚未定义。重要的是，SYNGAP1紊乱的几个主要症状很可能 涉及纹状体活动的改变，包括运动发育延迟、重复和限制性 行为，以及其他行为问题。 在这个项目中，我们将阐明SynGAP缺失对纹状体突触功能的影响 并确定纹状体神经元中SynGAP的缺失是否足以引起行为改变 与SYNGAP1障碍相关。具体地说，我们将确定SynGAP的丢失如何影响纹状体 突触的发育、传递和可塑性。此外，我们将使用成像方法来 研究SynGAP缺乏如何影响脊柱发生、脊柱数量和形态。要确定 纹状体神经元中Syngap1的缺失是否足以改变疾病相关行为，我们将 研究细胞类型特异性基因敲除小鼠Syngap1单倍体缺失对运动功能的影响， 习惯学习和行为灵活性。最后，我们将测试Syngap1的表达是否恢复 选择性地在纹状体投射神经元可以改善突触和行为异常 救援策略。总之，这项工作将1)加深我们对SynGAP在纹状体中的功能的理解 突触，2)确定与SYNGAP1障碍的表现最相关的纹状体细胞类型(S)， 以及3)确定疾病相关表型的发病和抢救的关键时期。

PROJECT SUMMARY SYNGAP1-related intellectual disability is a neurodevelopmental disorder caused by mutations in the SYNGAP1 gene. SYNGAP1 encodes SynGAP, which is a highly abundant protein in the post- synaptic density of excitatory synapses. At synapses, SynGAP functions to repress downstream NMDAR signaling and AMPAR trafficking through its inhibition of small GTPases. Translocation of SynGAP out of the post-synaptic density is required to allow NMDAR-dependent long-term potentiation (LTP) in cultured neurons. In the absence of SynGAP, NMDAR-dependent plasticity is unrestrained leading to alterations in synapse strength, spine structure, and plasticity. While the functions of SynGAP have been well- studied in the cortex and hippocampus, the striatum also exhibits high levels of SynGAP expression. Striatal projection neurons are GABA-ergic neurons covered in a dense array of dendritic spines, which receive excitatory inputs from the cortex. SynGAP is therefore positioned to play a key role in gating transmission and plasticity at striatal synapses. Despite this, SynGAP’s functions in striatal neurons have not yet been defined. Importantly, several of the major symptoms of SYNGAP1 disorder are likely to involve alterations in striatal activity including motor developmental delay, repetitive and restrictive behaviors, and other behavioral problems. In this project, we will elucidate the consequences of SynGAP loss on striatal synaptic function and determine whether loss of SynGAP from striatal neurons is sufficient to induce behavioral alterations relevant for SYNGAP1 disorder. Specifically, we will determine how loss of SynGAP impacts striatal synaptic development, transmission and plasticity. In addition, we will use imaging approaches to investigate how SynGAP deficiency affects spinogenesis, spine number and morphology. To determine whether deletion of Syngap1 from striatal neurons is sufficient to alter disease-relevant behaviors, we will investigate how haploinsufficiency of Syngap1 in cell type-specific knock-out mice affects motor function, habit learning, and behavioral flexibility. Finally, we will test whether restoration of Syngap1 expression selectively in striatal projection neurons can improve synaptic and behavioral abnormalities using genetic rescue strategies. Together, this work will 1) further our understanding of SynGAP’s functions at striatal synapses, 2) identify the striatal cell type(s) most relevant for the manifestations of SYNGAP1 disorder, and 3) define critical periods for the onset and rescue of disease-related phenotypes.