Mechanosensitive Ion Channel TMEM63A Gangs Up with Local Macrophages to Modulate Chronic Post-amputation Pain

Abstract

Post-amputation pain causes great suffering to amputees, but still no effective 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 effectively relieves the phantom pain afflicting 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 infiltrated 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 significantly 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 affected in the Tmem63a-/- mice in the naïve state, suggesting the basal pain was not affected. In the inflammatory and post-amputation state, the mechanical allodynia but not the heat hyperalgesia or cold allodynia was significantly decreased in Tmem63a-/- mice. Further study showed that there was severe neuronal injury and macrophage infiltration in the DRG, tibial nerve, residual stump, and the neuroma-like structure of the TNT mouse model, Consistent with this, expression of the pro-inflammatory cytokines TNF-α, IL-6, and IL-1β all increased dramatically in the DRG. Interestingly, the deletion of Tmem63a significantly reduced the macrophage infiltration in the DRG but not in the tibial nerve stump. Furthermore, the ablation of macrophages significantly 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.

To be or not to be an ion channel: cryo-EM structures have a say

“…This "TMCO1-defect syndrome" was then found to share many clinical features with cerebrofaciothoracic dysplasia (CFTD) when more pathogenic variants were characterized from other populations (Caglayan et al , 2013;Yuan et al , 2014;Yan et al , 2019). TMCO1 is a transmembrane protein at the ER and its deficiency resulted in supernormal ER Ca 2+ level, and was therefore proposed to form a Ca 2+ channel that releases Ca 2+ when the ER Ca 2+ store is overfilled (Pu et al , 2022). TMCO1 was proposed to assemble an ion-conducting pore in a tetrameric architecture, and purified TMCO1 proteins were capable to form functional Ca 2+ -selective channels in reconstituted proteoliposomes (Pu et al , 2022).…”

“…TMCO1 is a transmembrane protein at the ER and its deficiency resulted in supernormal ER Ca 2+ level, and was therefore proposed to form a Ca 2+ channel that releases Ca 2+ when the ER Ca 2+ store is overfilled (Pu et al , 2022). TMCO1 was proposed to assemble an ion-conducting pore in a tetrameric architecture, and purified TMCO1 proteins were capable to form functional Ca 2+ -selective channels in reconstituted proteoliposomes (Pu et al , 2022).…”

“…Tmem63c -deficient mice are generally normal and only exhibited morphological changes in brain, heart and liver at late adult stage. A recent study found that TMEM63A is expressed in nociceptors in the dorsal root ganglion of mice and involved in mechanical allodynia (Pu et al , 2022). For TMEM63B, the only physiological function reported so far is its role as a hypo-osmolarity-activated channel regulating survival of cochlear hair cells and by which supports hearing in mice (Du et al , 2020).…”

Expression and localization of the mechanosensitive/osmosensitive ion channel TMEM63B in the mouse urinary tract

“…In Drosophila, the single TMEM63 ortholog is required for the detection of humidity by Or42b neurons and detection of food texture by the md-L neurons that innervate sensory sensilla (Li et al, 2022;Li & Montell, 2021). Intriguingly, TMEM63 in Drosophila and TMEM63A in Neuro-2A cells reportedly function as lysosomal mechanosensors (Li et al, 2024), whereas Tmem63a modulates chronic post-amputation pain (Pu et al, 2023). TMEM63Bdependent osmosensation is required for vertebrate hearing (Du et al, 2020), and TMEM63B is also integral to thirst perception and the detection of hyperosmolarity by neurons in the subfornical organ of the brain (Yang et al, 2024).…”

Transmembrane proteins with unknown function (TMEMs) as ion channels: electrophysiological properties, structure, and pathophysiological roles

“…TMEM63B is required for the survival of outer hair cells and hearing via mediation of Ca 2+ -dependent regulatory volume decrease under hypotonic stress 95 . TMEM63A is abundantly expressed in nonpeptidergic nociceptors and modulates chronic post‑amputation pain in synchrony with local macrophages 96 . TMEM63A is enriched in oligodendrocytes, and heterozygous missense mutations in this gene, such as Gly168Glu, Ile462Asn, and Gly567Ser, lead to infantile disorders that resemble transient hypomyelination 97 .…”