title: Reduction of TRPV1 expression in the trigeminal system by botulinum neurotoxin type-A.
abstract: Botulinum neurotoxin type-A (BoNT-A) is clinically used for patients with pain disorders and dystonia. The precise mechanism whereby BoNT-A controls pain remains elusive. Here, we studied how BoNT-A affects the expression of the transient receptor potential vanilloid subfamily member 1 (TRPV1), a cation channel critically implicated in nociception, in the trigeminal system. Histological studies revealed that subcutaneous BoNT-A injection (0.25, 0.5, or 5 ng/kg) into the face targeted the ophthalmic division of trigeminal ganglion (TG) neurons and decreased TRPV1-immunoreactive neurons in the TG and TRPV1-immunoreactive fibers in rat trigeminal terminals. Of note, TG neurons that received projections from the dura mater, a principal site of headache generation, had reduced TRPV1 expression. BoNT-A-induced cleavage of SNAP25 (synaptosomal-associated protein of 25-kDa) in the TG became obvious 2 days after BoNT-A administration and persisted for at least 14 days. Quantitative real-time RT-PCR (reverse transcription-polymerase chain reaction) data indicated that the TRPV1-decreasing effects of BoNT-A were not mediated by transcriptional downregulation. By employing a surface protein biotin-labeling assay, we demonstrated that BoNT-A inhibited TRPV1 trafficking to the plasma membrane in primary TG neurons. Moreover, Y200F-mutated TRPV1, which is incapable of trafficking to the plasma membrane, was expressed in PC12 cells by transfection, and pharmacological studies revealed that TRPV1 in the cytoplasm was more predisposed to proteasome-mediated proteolysis than plasma membrane-located TRPV1. We conclude that the mechanism by which BoNT-A reduces TRPV1 expression involves the inhibition of TRPV1 plasma membrane trafficking and proteasome-mediated degradation in the cytoplasm. This paradigm seems to explain how BoNT-A alleviates TRPV1-mediated pain. Our data reveal a likely molecular mechanism whereby BoNT-A treatment reduces TRPV1 expression in the trigeminal system and provide important clues to novel therapeutic measures for ameliorating craniofacial pain.
authors: Department of Neurology, School of Medicine, Keio University, 35 Shinanomachi, Shinjuku-ku, Tokyo, 160-8582, Japan. shimizu-toshi@umin.ac.jp
authors: Toshihiko
authors: T
authors: Shimizu
authors: Mamoru
authors: M
authors: Shibata
authors: Haruki
authors: H
authors: Toriumi
authors: Tatsuo
authors: T
authors: Iwashita
authors: Megumi
authors: M
authors: Funakubo
authors: Hitoshi
authors: H
authors: Sato
authors: Toshiya
authors: T
authors: Kuroi
authors: Taeko
authors: T
authors: Ebine
authors: Kenzo
authors: K
authors: Koizumi
authors: Norihiro
authors: N
authors: Suzuki
mesh_terms: D000818:Animals; D015153:Blotting, Western; D019274:Botulinum Toxins, Type A / Q000494:pharmacology*; D007150:Immunohistochemistry; D008297:Male; D009465:Neuromuscular Agents / Q000494:pharmacology*; D009474:Neurons / Q000187:drug effects* / Q000378:metabolism*; D016716:PC12 Cells; D010146:Pain / Q000188:drug therapy / Q000378:metabolism; D021381:Protein Transport / Q000187:drug effects; D051381:Rats; D017207:Rats, Sprague-Dawley; D020133:Reverse Transcriptase Polymerase Chain Reaction; D050916:TRPV Cation Channels / Q000096:biosynthesis*; D014162:Transfection; D012668:Trigeminal Ganglion / Q000187:drug effects / Q000378:metabolism
chemical_list: D009465:Neuromuscular Agents; D050916:TRPV Cation Channels; C493922:Trpv1 protein, rat; D019274:Botulinum Toxins, Type A