Background & Aims
Antagonists of calcitonin gene related peptide (CGRP) receptor and monoclonal antibodies have been developed against migraine pain. However, the poor blood-brain barrier penetration of these compounds suggests a peripheral contribution to CGRP-mediated migraine pain. CGRP receptor and the transient receptor potential ankyrin 1 (TRPA1), an oxidant-sensitive and proalgesic channel are expressed by Schwann cells (SC). Here we aimed to identify the cellular mechanisms leading to CGRP-mediated TRPA1 activation in SCs.
Methods
Human primary SCs (HSCs), a mouse SCs line IMS32, and primary SCs from sciatic nerves of C57BL/6J, and Trpa1+/+ and Trpa1?/? mice were used. The Ca2+ response after CGRP exposure was monitored by fluorescent microscope. H2O2 was determined by using the Amplex Red assay. The CGRP effect was measured also in the presence of antagonists of CGRP (CGRP8-37 and olcegepant) and TRPA1 (A967079) receptors, and inhibitors of adenylyl cyclase (SQ22536), NOS (L-NAME), PKA (H89), NOX1 (ML171) and a ROS scavenger (PBN).
Results
In HSCs and IMS32 cells, CGRP stimulated a slowly developing yet sustained increase in Ca2+ response and increased H2O2 levels. Olcegepant, CGRP8-37, SQ22536, H89, L-NAME, Ca2+- free medium, PBN or ML171 attenuated Ca2+ responses and H2O2 levels. A967079 inhibited CGRP-stimulated Ca2+ and H2O2 responses but did not affect CGRP-stimulated NO formation. CGRP-evoked Ca2+ responses were reduced in SCs from Trpa1?/? mice.
Conclusions
These results showed that CGRP, by targeting its receptor in SCs, liberates NO, which activates SC TRPA1. Activated TRPA1 promotes a Ca2+-dependent H2O2 production that sustains a feed-forward mechanism comprising TRPA1 channel engagement and ROS release.
References
1 De Logu F. et al. Macrophages and Schwann cell TRPA1 mediate chronic allodynia in a mouse model of complex regional pain syndrome type I. Brain, Behavior, and Immunity, https://doi.org/10.1016/j.bbi.2020.04.037
2 De Logu F. et al. Schwann cell TRPA1 mediates neuroinflammation that sustains macrophage-dependent neuropathic pain in mice. Nat. Commun. 8, 1887. https://doi.org/10.1038/s41467-017-01739-2.