Chemokine CCL12 in trigeminal ganglion contributes to CFA-induced mechanical allodynia in mice

Abstract

Chemokines are known to play a role in the nervous system, involving a wide range of functions including the development of chronic pain. The C–C motif chemokine ligand 12 (CCL12) and its receptor CCR2 have been implicated in the pathophysiology of chronic pian. However, the precise mechanisms by which CCL12 influences the development and persistence of pain remain unclear. In this study, we aim to investigate the roles of CCL12 in chronic inflammatory pain at the primary sensory ganglion level. A mouse model of orofacial pain was established by subcutaneous injection of complete Freud’s adjuvant (CFA) into the right whisker pad. Mechanical allodynia was assessed using the von Frey test. The expression of CCL12 in the trigeminal ganglion (TG) was markedly upregulated at 7 days post-injection (dpi). Immunofluorescence and single-cell RNA-sequencing (scRNA-seq) data revealed that CCR2 was predominantly expressed in macrophages in the TG following CFA injection. To specifically target CCL12, an interfering adeno-associated virus (AAV) was administered intraganglionically into the right TG. Knockdown of Ccl12 in the TG significantly alleviated mechanical allodynia and c-Fos expression in the spinal trigeminal nucleus caudalis (SpVc) of CFA mice. Additionally, the infiltration of macrophages and the levels of IL-6 and TNF-α in the TG were significantly increased at 7 dpi and were attenuated by Ccl12 knockdown. These findings suggest that CCL12 contributes to CFA-induced orofacial allodynia by promoting macrophage infiltration and the production of IL-6 and TNF-α in the TG.