Kir4.1 in satellite glial cells contributes to trigeminal neuropathic pain

Abstract text (incl. figure legends and references)

Question: Astrocyte Kir4.1 emerged as a novel therapeutic target for nervous system diseases, such as depression and pain. However, the role and mechanism of Kir4.1 in satellite glial cells (SGCs) in trigeminal neuropathic pain remain unknown. Methods: In vivo, chronic constriction injury of the infraorbital nerve (CCI-ION) and Von-Frey tests were used. The ATF3, GFAP, and Kir4.1 were detected by immunofluorescence in the trigeminal ganglion (TG). The AAV2/8 aimed at Kir4.1 was delivered to TG in WT and Kir4.1^f/f mice to knockdown or overexpress Kir4.1. In vitro, cultured SGCs were transfected with siRNA to knock down Kir4.1. The expression of Kir4.1 and its potential downstream cellular signalings were measured by RT-qPCR, western blot (WB), and/or ELISA. Results: Firstly, CCI-ION induced orofacial mechanical hypersensitivity. The increased ATF3 confirmed trigeminal nerve injury and increased GFAP indicated SGCs activation. Kir4.1 was expressed on SGCs of TG. RT-qPCR and WB showed that CCI-ION decreased Kir4.1 expression but increased the expression of GFAP, brain-derived neurotrophic factor (BDNF), and glial cell-derived neurotrophic factor (GDNF) in TG. Secondly, knockdown of Kir4.1 in mice evoked orofacial mechanical hypersensitivity and upregulated GFAP, BDNF, and GDNF expression in TG. Overexpression of Kir4.1 alleviated CCI-ION-induced mechanical hypersensitivity and GFAP, BDNF, and GDNF production. In vitro, Kir4.1-siRNA treated SGCs increased GFAP, BDNF, and GDNF expression. Thirdly, phosphorylated extracellular signal-regulated kinase 1/2 (ERK1/2) was increased in TG after CCI-ION, knockdown of Kir4.1 mice, and Kir4.1-siRNA treated SGCs, which also were reduced by Kir4.1 rescue. Furthermore, the inhibitors of ERK1/2 (U0126) decreased these above upregulated BDNF and GDNF. Conclusions: This study indicated that Kir4.1 in SGCs contributed to trigeminal neuropathic pain by regulating BDNF and GDNF production via ERK signaling pathway and SGCs activation.