Neuropathic pain remains a therapeutic challenge because of its complicated mechanisms. Mas‐related GPCR D (MrgprD) is specifically expressed in small‐diameter, nociceptive neurons of dorsal root ganglia (DRGs) and is implicated in pain modulation. However, the underlying mechanism of MrgprD involved in neuropathic pain remains elusive. In this study, we used behavioral experiments and physiologic examination methods to investigate the role of MrgprD in chronic constriction injury (CCI)–induced neuropathic pain. We found that MrgprD is necessary for the initiation of mechanical hypersensitivity and cold allodynia, but not for heat allodynia. Moreover, we demonstrated that transient receptor potential cation channel (TRP)‐A1 was the ion channel downstream of MrgprD, and the β‐alanine–induced calcium signal was attributed mostly to TRP‐A1 function. We further showed that PKA serves as a downstream mediator of β‐alanine–activated MrgprD signaling to activate TRP‐A1 in DRG neurons and in human embryonic kidney 293 cells, to coexpress MrgprD and TRP‐A1 plasmids. Finally, we found that the β‐alanine–induced pain behavior was increased, whereas the itching behavior was unchanged in CCI models compared with sham‐injured animals. Knockout of TRPA1 also attenuated the β‐alanine–induced pain behavior in CCI models. In conclusion, MrgprD is essential in cold allodynia in CCI‐induced neuropathic pain through the PKA–TRP‐A1 pathway. TRP‐A1 facilitates MrgprD to development of neuropathic pain. Our findings reveal a novel mechanism of neuropathic pain formation and highlight MrgprD as a promising drug target for the treatment of neuropathic pain.—Wang, C., Gu, L., Ruan, Y., Geng, X., Xu, M., Yang, N., Yu, L., Jiang, Y., Zhu, C., Yang, Y., Zhou, Y., Guan, X., Luo, W., Liu, Q., Dong, X., Yu, G., Lan, L., Tang, Z. Facilitation of MrgprD by TRP‐A1 promotes neuropathic pain. FASEB J. 33, 1360–1373 (2019). www.fasebj.org

Neuropathic pain is a chronic pain and reduces the life quality of patients substantially. Transient receptor potential vanilloid channel 1 (TRPV1), a nonselective cation channel, has been shown to play a crucial role in neuropathic pain. Although TRPV1 plays an important role in neuropathic pain, the mechanism of how TRPV1 was regulated in neuropathic pain remains unclear. Pirt is a membrane protein and binds to TRPV1 to enhance its activity. It was suggested that Pirt should also be involved in neuropathic pain. In this study, we investigated the role of Pirt in neuropathic pain (CCI model); the results show that mechanical allodynia and thermal hyperalgesia were alleviated in Pirt^−/− mice in CCI models. TRPV1 expression was increased by immunofluorescence and real-time PCR experiments. The increase in TRPV1 expression was less in Pirt knockout mice in CCI models. Moreover, the number of capsaicin-responding neurons and the magnitude of evoked calcium response were attenuated in DRG neurons from Pirt^−/− mice in CCI models. Finally, we found that the pain behavior attenuated in dysfunction of both Pirt and TRPV1 was much stronger than in dysfunction of Pirt or TRPV1 only in a CCI model in vitro study. Taken together, Pirt together with TRPV1 is involved in CCI-induced neuropathic pain.