Bestrophin-1 (Best1) is a GABA- and glutamate-permeable, Ca²⁺-activated Cl- channel, which is mainly expressed in astrocytes and localized at the microdomain or perisynaptic junction of the tripartite synapse. Distribution of Best1 is dramatically changed in pathological conditions such as Alzheimer's disease. However, it is still unknown whether Best1 is located at the glutamatergic or GABAergic tripartite synapses. Here, we utilized the Lattice structured illumination microscopy (Lattice SIM) to visualize Best1 expression at the perisynaptic junctions of the tripartite synapses in CA1 of mouse hippocampus. We performed co-labeling with antibodies against 1) Best1 and vesicular glutamate transporter-2 (vGLUT2) or 2) Best1 and vesicular GABA transporter (vGAT) to measure the proximity of Best1-containing perisynapse to glutamatergic or GABAergic presynapse, respectively. In addition, we examined two transgenic mouse lines of 1) APP/PS1 mouse showing high astrocytic MAOB activity and cytosolic GABA and 2) MAOB-KO mouse showing low astrocytic GABA. Lattice SIM images were further processed by Imaris, which allowed 3Drendering and spot identification. We found that astrocytic Best1 was distributed closer to the glutamatergic synapses than GABAergic synapses in the wild-type mice. In APP/PS1 mice, Best1 distribution was significantly changed by moving away from the glutamatergic synapses while moving closer to the GABAergic synapses. On the contrary, in MAOB-KO mice, the Best1 distribution was dramatically changed by moving closer to the glutamatergic synapses and moving far away from the GABAergic synapses. Our findings propose that the proximity of Best1-containing perisynapses to presynapses dynamically changes according to the level of astrocytic cytosolic GABA.

中文翻译：

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晶格结构照明显微镜揭示的 APP/PS1 和 MAOB-KO 小鼠兴奋性和抑制性三联突触中突触周围星形胶质细胞 Best1 的差异接近度。

Bestrophin-1 (Best1) 是一种 GABA 和谷氨酸可渗透的 Ca ²⁺-激活的Cl-通道，主要在星形胶质细胞中表达并定位于三联突触的微区或突触周围连接处。Best1 的分布在阿尔茨海默病等病理条件下发生了显着变化。然而，Best1 是否位于谷氨酸能或 GABA 能三联突触仍是未知数。在这里，我们利用 Lattice 结构照明显微镜（Lattice SIM）来可视化小鼠海马 CA1 中三联突触的突触周围连接处的 Best1 表达。我们使用针对 1) Best1 和囊泡谷氨酸转运蛋白 2 (vGLUT2) 或 2) Best1 和囊泡 GABA 转运蛋白 (vGAT) 的抗体进行共标记，以分别测量含有 Best1 的突触与谷氨酸能或 GABA 能前突触的接近程度。此外，我们检查了两种转基因小鼠品系：1) APP/PS1 小鼠显示高星形胶质细胞 MAOB 活性和胞质 GABA，2) MAOB-KO 小鼠显示低星形胶质细胞 GABA。Imaris 进一步处理了 Lattice SIM 图像，从而实现了 3Drendering 和点识别。我们发现星形胶质细胞 Best1 在野生型小鼠中的分布比 GABA 能突触更靠近谷氨酸能突触。在 APP/PS1 小鼠中，通过远离谷氨酸能突触而靠近 GABA 能突触，Best1 的分布发生了显着变化。相反，在 MAOB-KO 小鼠中，通过靠近谷氨酸能突触和远离 GABA 能突触，Best1 分布发生了显着变化。