Activation of TRPV1 mediates calcitonin gene-related peptide release, which excites trigeminal sensory neurons and is attenuated by a retargeted botulinum toxin with anti-nociceptive potential.
Excessive release of inflammatory/pain mediators from peripheral sensory afferents renders nerve endings hyper-responsive, causing central sensitization and chronic pain. Herein, the basal release of proinflammatory calcitonin gene-related peptide (CGRP) was shown to increase the excitability of trigeminal sensory neurons in brainstem slices via CGRP1 receptors because the effect was negated by an antagonist, CGRP8-37. This excitatory action could be prevented by cleaving synaptosomal-associated protein of M(r) 25,000 (SNAP-25) with botulinum neurotoxin (BoNT) type A, a potent inhibitor of exocytosis. Strikingly, BoNT/A proved unable to abolish the CGRP1 receptor-mediated effect of capsaicin, a nociceptive TRPV1 stimulant, or its elevation of CGRP release from trigeminal ganglionic neurons (TGNs) in culture. Although the latter was also not susceptible to BoNT/E, apparently attributable to a paucity of its acceptors (glycosylated synaptic vesicle protein 2 A/B), this was overcome by using a recombinant chimera (EA) of BoNT/A and BoNT/E. It bound effectively to the C isoform of SV2 abundantly expressed in TGNs and cleaved SNAP-25, indicating that its /A binding domain (H(C)) mediated uptake of the active /E protease. The efficacy of /EA is attributable to removal of 26 C-terminal residues from SNAP-25, precluding formation of SDS-resistant SNARE complexes. In contrast, exocytosis could be evoked after deleting nine of the SNAP-25 residues with /A but only on prolonged elevation of [Ca(2+)](i) with capsaicin. This successful targeting of /EA to nociceptive neurons and inhibition of CGRP release in vitro and in situ highlight its potential as a new therapy for sensory dysmodulation and chronic pain.
International Centre for Neurotherapeutics, Dublin City University, Glasnevin, Dublin 9, Ireland.
Jianghui
J
Meng
Saak V
SV
Ovsepian
Jiafu
J
Wang
Mark
M
Pickering
Astrid
A
Sasse
K Roger
KR
Aoki
Gary W
GW
Lawrence
J Oliver
JO
Dolly
D000700:Analgesics / Q000008:administration & dosage*; D000818:Animals; D001905:Botulinum Toxins / Q000008:administration & dosage*; D015740:Calcitonin Gene-Related Peptide / Q000378:metabolism*; D002478:Cells, Cultured; D016503:Drug Delivery Systems / Q000379:methods*; D051381:Rats; D017207:Rats, Sprague-Dawley; D011984:Sensory Receptor Cells / Q000378:metabolism*; D050916:TRPV Cation Channels / Q000378:metabolism* / Q000502:physiology; D012668:Trigeminal Ganglion / Q000187:drug effects / Q000378:metabolism*
D000700:Analgesics; D050916:TRPV Cation Channels; C493922:Trpv1 protein, rat; D001905:Botulinum Toxins; D015740:Calcitonin Gene-Related Peptide