scRNAseq analysis of mouse L4 whole dorsal root ganglions with and without sciatic nerve crush injury

Peripheral sensory neurons with cell body in dorsal root ganglia (DRG) switch to a regenerative state after nerve injury to enable axon regeneration and functional recovery. Studies of nerve injury responses in sensory neurons have revealed signaling and transcriptional mechanisms that increase their intrinsic regenerative capacity. However, the extent to which satellite glial cells (SGC), which completely surround the neuronal soma contribute to these responses remains unexplored. Using single cell RNA-seq, we defined the transcriptional profile of SGC in naive and injured conditions and identified Fabp7, also known as BLBP, as a novel marker of SGC. We report that nerve injury elicits gene expression changes in SGC, which are mostly related to lipid metabolism, specifically fatty acid synthesis and the peroxisome proliferator-activated receptor (PPAR) signaling. Conditional deletion of Fatty acid synthase (Fasn), the key enzyme in de novo fatty acid synthesis, specifically in SGC, impairs axon regeneration. Treatment with fenofibrate, a PPARa agonist, rescues the impaired regeneration, suggesting that PPRAa, which belongs to a family of lipid regulated transcription factors, functions downstream of fatty acid synthesis in SGC to promote axon regeneration. These results unravel fatty acid synthesis in SGC as a fundamental novel mechanism mediating axon regeneration in mature peripheral nerves. We have applied the high-throughput single-cell mRNA sequencing technique, using the Chromium Single Cell Gene Expression Solution (10x Genomics) to mouse L4 DRG in naive and injured conditions (3 days post sciatic nerve crush injury), 2 biological replicates for each sample.胞体位于背根神经节（dorsal root ganglia, DRG）的外周感觉神经元，在神经损伤后会切换至再生状态，以支持轴突再生与功能恢复。针对感觉神经元神经损伤应答的研究，已揭示了可提升其内在再生能力的信号转导与转录调控机制。然而，完全包裹神经元胞体的卫星胶质细胞（satellite glial cells, SGC）在这些应答中发挥的作用程度仍未被探明。本研究借助单细胞RNA测序（single cell RNA-seq），明确了卫星胶质细胞在未处理与损伤状态下的转录组特征，并鉴定出脂肪酸结合蛋白7（Fabp7，亦称BLBP）可作为卫星胶质细胞的新型标记物。本研究发现，神经损伤会引发卫星胶质细胞的基因表达变化，这些变化主要与脂质代谢相关，具体涉及脂肪酸合成及过氧化物酶体增殖物激活受体（peroxisome proliferator-activated receptor, PPAR）信号通路。特异性在卫星胶质细胞中条件性敲除脂肪酸合酶（Fatty acid synthase, Fasn）——这是从头脂肪酸合成过程中的关键酶——会损伤轴突再生能力。使用PPARα激动剂非诺贝特（fenofibrate）处理可挽救受损的再生能力，这表明属于脂质调控转录因子家族的PPARα，在卫星胶质细胞中位于脂肪酸合成的下游发挥作用，以促进轴突再生。上述研究结果揭示，卫星胶质细胞中的脂肪酸合成是介导成熟外周神经轴突再生的全新核心机制。本研究采用高通量单细胞mRNA测序技术，借助Chromium单细胞基因表达解决方案（10x Genomics），对未处理及损伤状态下的小鼠L4背根神经节进行了测序（损伤模型为坐骨神经压榨损伤后3天），每个样本设置2个生物学重复。