GABA-receptive microglia selectively sculpt developing inhibitory circuits

Microglia, the resident immune cells of the brain, have emerged as crucial regulators of synaptic refinement and therefore wiring precision. However, whether the remodeling of distinct synapses during development is mediated by specialized microglia is unknown. Here, using in vivo two-photon imaging, we show that GABA-receptive microglia selectively interact with inhibitory synapses during a critical window of mouse postnatal development. GABA initiates a transcriptional synapse remodeling program within these specialized microglia, which in turn sculpt inhibitory connectivity without impacting excitatory synapses. Ablation of GABAB receptors within microglia impairs this process and leads to stereotyped repetitive behavior and hyperactivity. These findings demonstrate that distinct microglia differentially engage with specific synapse types during development. We performed single cell RNA sequencing (scRNA-seq) of microglia isolated from the somatosensory cortex of postnatal day 15 mice of the following genotypes: wild-type (Cx3cr1+/+; GABAB1Rfl/fl; N = 12; 3 females and 9 males; 2 replicates), Cre-Het controls (Cx3cr1Cre/+; GABAB1R+/+; N = 10; 8 females and 2 males; 1 replicate) and GABAB1R cKO (Cx3cr1Cre/+; GABAB1Rfl/fl; N = 13; 9 females and 4 males; 2 replicates). Single-cell RNA-seq libraries were prepared on the 10x Genomics platform and sequenced using the Nova-Seq 100 cycle kit (Illumina).小胶质细胞（Microglia）作为脑内驻留免疫细胞，现已被证实是突触重塑乃至神经环路精准构建的关键调控因子。然而，发育过程中不同类型突触的重塑是否由特化的小胶质细胞介导，目前仍不清楚。本研究借助活体双光子成像（in vivo two-photon imaging）技术，证实小鼠出生后发育关键窗口期内，GABA感受性小胶质细胞会选择性地与抑制性突触发生相互作用。GABA可在这些特化小胶质细胞中触发转录层面的突触重塑程序，进而精准塑造抑制性神经环路连接，且不会对兴奋性突触产生任何影响。敲除小胶质细胞内的GABAB受体（GABAB receptor）会破坏这一调控过程，并引发刻板重复行为与多动症状。上述研究结果表明，发育阶段的不同小胶质细胞亚群会差异性地靶向特定类型的突触。 我们对出生后第15天的小鼠躯体感觉皮层分离得到的小胶质细胞开展了单细胞RNA测序（single-cell RNA sequencing, scRNA-seq），实验小鼠分为以下三种基因型：野生型（Cx3cr1+/+; GABAB1Rfl/fl；N=12，含3只雌性、9只雄性，设置2个生物学重复）、Cre杂合对照（Cx3cr1Cre/+; GABAB1R+/+；N=10，含8只雌性、2只雄性，设置1个生物学重复）以及GABAB1R条件性敲除（Cx3cr1Cre/+; GABAB1Rfl/fl；N=13，含9只雌性、4只雄性，设置2个生物学重复）。 单细胞RNA测序文库均基于10x Genomics平台构建，并使用Illumina Nova-Seq 100循环测序试剂盒完成测序。