Nociceptive information is detected and transmitted by neurons in the DRG. Recently, single-cell RNA sequencing has revealed the molecular profile of various cell types, including fibroblasts in the DRG. However, the role of molecules in fibroblasts needs to be elucidated in nociceptive regulation. Here, we found that secreted modular calcium-binding protein 2 (SMOC2) was secreted by fibroblasts to become a component of basement membrane and envelop the unit consisting of DRG neurons and attached satellite glial cells. KO of Smoc2 in both sexes of mice led to increased neuronal clusters and decreased mechanical threshold, but unchanged noxious thermal response. Knockdown of Smoc2 in the DRG phenocopied the behavioral performance by Smoc2 KO in both sexes of mice. In vivo calcium imaging showed that Smoc2 KO increased coupled activation of adjacent DRG neurons induced by nociceptive mechanical stimuli, which was reversed by DRG injection of SMOC2. Importantly, SMOC2 interacted with P2X7 receptor (P2X7R) and suppressed ATP-induced activation in HEK293 cells expressing this receptor. Injection of A740003, an antagonist of P2X7R, to the DRG reduced coupled activation of adjacent DRG neurons induced by nociceptive mechanical stimuli but did not further enhance the SMOC2-inhibited effect. Furthermore, peripheral inflammation resulted in a decreased SMOC2 and increased neuronal clusters. DRG injection of SMOC2 inhibited the neuronal coupling resulted from peripheral inflammation. This study reveals a specific role of fibroblastic SMOC2 in suppressing mechanical nociception through inhibiting the communication of adjacent DRG neurons, which provides an important mechanism of fibroblasts in nociceptive regulation.

SIGNIFICANCE STATEMENT The function of fibroblastic molecules is rarely noticed in the regulation of nociceptive sensation. Here, we reveal that fibroblastic SMOC2 is secreted to be a component of basement membrane and surrounded the unit consisting of DRG neuron and attached satellite glial cells. SMOC2 is required for maintaining the basal mechanical nociceptive threshold in the DRG. Loss of SMOC2 leads to the increased coupled activation of adjacent DRG neurons induced by noxious mechanical stimuli. Peripheral inflammation causes decreased fibroblast cells and SMOC2, which may result in the increase of coupled activation of adjacent DRG neurons. Mechanistically, SMOC2 interacts with and suppresses satellite glial P2X7 receptor to inhibit the coupled activation of adjacent DRG neurons.

伤害感受信息由 DRG 中的神经元检测和传递。最近，单细胞 RNA 测序揭示了各种细胞类型的分子谱，包括 DRG 中的成纤维细胞。然而，分子在成纤维细胞中的作用需要在伤害性调节中加以阐明。在这里，我们发现分泌的模块化钙结合蛋白 2 (SMOC2) 由成纤维细胞分泌，成为基底膜的组成部分，并包裹由 DRG 神经元和附着的卫星神经胶质细胞组成的单元。Smoc2在两性小鼠中的KO导致神经元簇增加和机械阈值降低，但有害的热反应没有改变。DRG 中Smoc2的敲除对Smoc2 的行为表现进行了表型复制在两性小鼠中均发生 KO。体内钙成像显示Smoc2KO 增加了由伤害性机械刺激诱导的相邻 DRG 神经元的耦合激活，这被 DRG 注射 SMOC2 逆转。重要的是，SMOC2 与 P2X7 受体 (P2X7R) 相互作用并抑制表达该受体的 HEK293 细胞中 ATP 诱导的活化。将 P2X7R 的拮抗剂 A740003 注射到 DRG 可减少由伤害性机械刺激诱导的相邻 DRG 神经元的耦合激活，但不会进一步增强 SMOC2 抑制作用。此外，外周炎症导致 SMOC2 减少和神经元簇增加。SMOC2的DRG注射抑制了由外周炎症引起的神经元耦合。这项研究揭示了成纤维细胞 SMOC2 通过抑制相邻 DRG 神经元的通讯来抑制机械伤害感受的特定作用，

意义声明成纤维细胞分子的功能在伤害性感觉的调节中很少被注意到。在这里，我们揭示了成纤维细胞 SMOC2 被分泌为基底膜的一个组成部分，并包围了由 DRG 神经元和附着的卫星神经胶质细胞组成的单元。SMOC2 是维持 DRG 中基础机械伤害性阈值所必需的。SMOC2 的缺失导致由有害机械刺激诱导的相邻 DRG 神经元的耦合激活增加。外周炎症导致成纤维细胞和 SMOC2 减少，这可能导致相邻 DRG 神经元的耦合激活增加。从机制上讲，SMOC2 与卫星神经胶质 P2X7 受体相互作用并抑制它以抑制相邻 DRG 神经元的耦合激活。