Department of Neuroscience Rita Levi Montalcini, University of Turin, 10124, Turin, Italy.
Institute of Pharmacology and Toxicology, University of Zurich, Winterthurerstrasse 190, 8057, Zurich, Switzerland.
Brain Struct Funct. 2017 Dec;222(9):4149-4161. doi: 10.1007/s00429-017-1462-7. Epub 2017 Jun 22.
Perisomatic GABAergic synapses onto hippocampal pyramidal cells arise from two populations of basket cells with different neurochemical and functional properties. The presence of the dystrophin-glycoprotein complex in their postsynaptic density (PSD) distinguishes perisomatic synapses from GABAergic synapses on dendrites and the axon-initial segment. Targeted deletion of neuroligin 2 (NL2), a transmembrane protein interacting with presynaptic neurexin, has been reported to disrupt postsynaptic clustering of GABA receptors (GABAR) and their anchoring protein, gephyrin, at perisomatic synapses. In contrast, targeted deletion of Gabra2 disrupts perisomatic clustering of gephyrin, but not of α1-GABAR, NL2, or dystrophin/dystroglycan. Unexpectedly, conditional deletion of Dag1, encoding dystroglycan, selectively prevents the formation of perisomatic GABAergic synapses from basket cells expressing cholecystokinin. Collectively, these observations suggest that multiple mechanisms regulate formation and molecular composition of the GABAergic PSD at perisomatic synapses. Here, we further explored this issue by investigating the effect of targeted deletion of Gabra1 and NL2 on the dystrophin-glycoprotein complex and on perisomatic synapse formation, using immunofluorescence analysis with a battery of GABAergic pre- and postsynaptic markers. We show that the absence of α1-GABAR increases GABAergic synapses containing the α2 subunit, without affecting the clustering of dystrophin and NL2; in contrast, the absence of NL2 produces highly variable effects postsynaptically, not restricted to perisomatic synapses and being more severe for the GABAR subunits and gephyrin than dystrophin. Altogether, the results confirm the importance of NL2 as organizer of the GABAergic PSD and unravel distinct roles for α1- and α2-GABARs in the formation of GABAergic circuits in close interaction with the dystrophin-glycoprotein complex.
体旁 GABA 能突触起源于具有不同神经化学和功能特性的两类 basket 细胞。其突触后密度（PSD）中存在肌营养不良糖蛋白复合物（dystrophin-glycoprotein complex）将其与树突和轴起始段上的 GABA 能突触区分开来。已有研究报道，跨膜蛋白神经连接蛋白 2（neurexin）的相互作用蛋白 neuroligin 2（NL2）的靶向缺失会破坏体旁突触上 GABA 受体（GABAR）及其锚定蛋白 gephyin 的突触后聚集。相比之下，Gabra2 的靶向缺失会破坏 gephyin，但不会破坏 α1-GABAR、NL2 或 dystrophin/dystroglycan 的体旁聚集。出乎意料的是，编码 dystroglycan 的 Dag1 的条件缺失选择性地阻止了表达胆囊收缩素的 basket 细胞形成体旁 GABA 能突触。总的来说，这些观察结果表明，多种机制调节体旁 GABA 能 PSD 的形成和分子组成。在这里，我们使用一系列 GABA 能突触前和突触后标志物的免疫荧光分析，进一步研究了靶向缺失 Gabra1 和 NL2 对肌营养不良糖蛋白复合物和体旁突触形成的影响，以探讨这个问题。我们发现，α1-GABAR 的缺失会增加含有 α2 亚基的 GABA 能突触，而不会影响 dystrophin 和 NL2 的聚集；相比之下，NL2 的缺失会产生高度可变的突触后效应，不仅限于体旁突触，并且对 GABAR 亚基和 gephyin 的影响比 dystrophin 更严重。总的来说，这些结果证实了 NL2 作为 GABA 能 PSD 组织者的重要性，并揭示了 α1-和 α2-GABAR 在与肌营养不良糖蛋白复合物密切相互作用的 GABA 能回路形成中的不同作用。
