Shaofeng Pu1 • Yiyang Wu1 • Fang Tong2 • Wan‑Jie Du2 • Shuai Liu2 • Huan Yang2 • Chen Zhang2 • Bin Zhou2 • Ziyue Chen2 • Xiaomeng Zhou2 • Qingjian Han2 • Dongping Du1

1 Pain Management Center, Shanghai Jiao Tong University Afliated Sixth People’s Hospital, Shanghai 200233, China

2 State Key Laboratory of Medical Neurobiology and MOE Frontier Center for Brain Science, Institutes of Brain Science, Fudan University, Shanghai 200032, China

 

Abstract

    Post-amputation pain causes great sufering to amputees, but still no efective drugs are available due to its elusive mechanisms. Our previous clinical studies found that surgical removal or radiofrequency treatment of the neuroma at the axotomized nerve stump efectively relieves the phantom pain aficting patients after amputation. This indicated an essential role of the residual nerve stump in the formation of chronic post-amputation pain (CPAP). However, the molecular mechanism by which the residual nerve stump or neuroma is involved and regulates CPAP is still a mystery. In this study, we found that nociceptors expressed the mechanosensitive ion channel TMEM63A and macrophages infltrated into the dorsal root ganglion (DRG) neurons worked synergistically to promote CPAP. Histology and qRT-PCR showed that TMEM63A was mainly expressed in mechanical pain-producing non-peptidergic nociceptors in the DRG, and the expression of TMEM63A increased signifcantly both in the neuroma from amputated patients and the DRG in a mouse model of tibial nerve transfer (TNT). Behavioral tests showed that the mechanical, heat, and cold sensitivity were not afected in the Tmem63a-/- mice in the naïve state, suggesting the basal pain was not afected. In the infammatory and post-amputation state, the mechanical allodynia but not the heat hyperalgesia or cold allodynia was signifcantly decreased in Tmem63a-/- mice. Further study showed that there was severe neuronal injury and macrophage infltration in the DRG, tibial nerve, residual stump, and the neuromalike structure of the TNT mouse model, Consistent with this, expression of the pro-infammatory cytokines TNFα, IL-6, and IL-1β all increased dramatically in the DRG. Interestingly, the deletion of Tmem63a signifcantly reduced the macrophage infltration in the DRG but not in the tibial nerve stump. Furthermore, the ablation of macrophages signifcantly reduced both the expression of Tmem63a and the mechanical allodynia in the TNT mouse model, indicating an interaction between nociceptors and macrophages, and that these two factors gang up together to regulate the formation of CPAP. This provides a new insight into the mechanisms underlying CPAP and potential drug targets its treatment.

 

 

Keywords

    Mechanosensitive ion channel; TMEM63A; Post-amputation pain; Tibial nerve transfer; Macrophage

 

 

[SpringerLink]