Single Synapse Indicators of Impaired Glutamate Clearance Derived from Fast iGluu Imaging of Cortical Afferents in the Striatum of Normal and Huntington (Q175) Mice
Single Synapse Indicators of Impaired Glutamate Clearance Derived from Fast iGluu Imaging of Cortical Afferents in the Striatum of Normal and Huntington (Q175) Mice
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DOI：
10.1523/jneurosci.2865-18.2019
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发表时间：
2019-05-15
影响因子：
5.3
通讯作者：
Grantyn, Rosemarie
中科院分区：
文献类型：
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作者：
Dvorzhak, Anton;Helassa, Nordine;Grantyn, Rosemarie
谷氨酸释放和摄取平衡的改变可能刺激突触重组甚至突触丢失。在神经退行性变的情况下，星形胶质细胞摄取谷氨酸和突触前谷氨酸释放之间的不匹配，如果在单突触水平上独立评估这两个参数，可以检测到。由于一种新的基因编码超快谷氨酸传感器iGlu(u)的成像分析，这已经成为可能。我们报告了从bb10 - 1岁的雌雄小鼠急性切片中单个皮质纹状体突触的发现。短期可塑性和大小标准的对比模式确定了两类终端，可能对应于先前定义的IT（脑内）和PT（锥体束）突触。后者表现出更高程度的频率增强/残余Glu积累，并被选择用于我们在Q175小鼠（亨廷顿病（HD）模型）中进行的首次iGlu(u)单突触研究。在HD小鼠中，作为摄取指标的突触周围谷氨酸浓度（TauD）的衰减时间常数和作为释放指标的谷氨酸峰值(u)振幅分别延长和降低。用星形细胞谷氨酸摄取阻滞剂TFB-TBOA （100 nM）处理WT制剂可以模拟纯合子中TauD的变化。考虑到WT中遇到的最大TauD值，Q175杂合子中测试的约40%的PT突触可归类为功能障碍。此外，HD突触的TauD值与iGlu峰幅呈正相关，而WT突触的TauD值与iGlu峰幅呈正相关。最后，兴奋性氨基酸转运蛋白2 （EAAT2）在皮质纹状体末端的免疫反应性降低。因此，星形细胞谷氨酸转运仍然是治疗干预的一个有希望的目标。
Changes in the balance between glutamate (Glu) release and up take may stimulate synaptic reorganization and even synapse loss. In the case of neurodegeneration, a mismatch between astroglial Glu uptake and presynaptic Glu release could be detected if both parameters were assessed independently and at a single-synapse level. This has now become possible due to a new imaging assay with the genetically encoded ultrafast Glu sensor iGlu(u). We report findings from individual corticostriatal synapses in acute slices prepared from mice of either sex that were > 1 year of age. Contrasting patterns of short-term plasticityanda size criterion identified two classes of terminals, presumably corresponding to the previously defined IT (intratelencephalic) and PT (pyramidal tract) synapses. The latter exhibited a higher degree of frequency potentiation/residual Glu accumulation and were selected for our first iGlu(u) single-synapse study in Q175 mice, a model of Huntington's disease (HD). In HD mice, the decay time constant of the perisynaptic Glu concentration (TauD), as an indicator of uptake, and the peak iGlu(u) amplitude, as an indicator of release, were prolonged and reduced, respectively. Treatment of WT preparations with the astrocytic Glu uptake blocker TFB-TBOA (100 nM) mimicked the TauD changes in homozygotes. Considering the largest TauD values encountered in WT, similar to 40% of PT synapses tested in Q175 heterozygotes can be classified as dysfunctional. Moreover, HD but not WT synapses exhibited a positive correlation between TauD and the peak amplitude of iGlu(u). Finally, EAAT2 (excitatory amino acid transport protein 2) immunoreactivity was reduced next to corticostriatal terminals. Thus, astrocytic Glu transport remains a promising target for therapeutic intervention.