title: Ca2+and calpain mediate capsaicin-induced ablation of axonal terminals expressing transient receptor potential vanilloid 1.
abstract: Capsaicin is an ingredient in spicy peppers that produces burning pain by activating transient receptor potential vanilloid 1 (TRPV1), a Ca2+-permeable ion channel in nociceptors. Capsaicin has also been used as an analgesic, and its topical administration is approved for the treatment of certain pain conditions. The mechanisms underlying capsaicin-induced analgesia likely involve reversible ablation of nociceptor terminals. However, the mechanisms underlying these effects are not well understood. To visualize TRPV1-lineage axons, a genetically engineered mouse model was used in which a fluorophore is expressed under the TRPV1 promoter. Using a combination of these TRPV1-lineage reporter mice and primary afferent cultures, we monitored capsaicin-induced effects on afferent terminals in real time. We found that Ca2+influx through TRPV1 is necessary for capsaicin-induced ablation of nociceptive terminals. Although capsaicin-induced mitochondrial Ca2+uptake was TRPV1-dependent, dissipation of the mitochondrial membrane potential, inhibition of the mitochondrial transition permeability pore, and scavengers of reactive oxygen species did not attenuate capsaicin-induced ablation. In contrast, MDL28170, an inhibitor of the Ca2+-dependent protease calpain, diminished ablation. Furthermore, overexpression of calpastatin, an endogenous inhibitor of calpain, or knockdown of calpain 2 also decreased ablation. Quantitative assessment of TRPV1-lineage afferents in the epidermis of the hind paws of the reporter mice showed that EGTA and MDL28170 diminished capsaicin-induced ablation. Moreover, MDL28170 prevented capsaicin-induced thermal hypoalgesia. These results suggest that TRPV1/Ca2+/calpain-dependent signaling plays a dominant role in capsaicin-induced ablation of nociceptive terminals and further our understanding of the molecular mechanisms underlying the effects of capsaicin on nociceptors.
authors.affiliation: Department of Neural and Pain Sciences, School of Dentistry, Program in Neuroscience, Center to Advance Chronic Pain Research, University of Maryland, Baltimore, Maryland 21201.
authors.forename: Sheng
authors.initials: S
authors.lastname: Wang
authors.affiliation: Department of Neural and Pain Sciences, School of Dentistry, Program in Neuroscience, Center to Advance Chronic Pain Research, University of Maryland, Baltimore, Maryland 21201.
authors.forename: Sen
authors.initials: S
authors.lastname: Wang
authors.affiliation: Department of Neural and Pain Sciences, School of Dentistry, Program in Neuroscience, Center to Advance Chronic Pain Research, University of Maryland, Baltimore, Maryland 21201.
authors.forename: Jamila
authors.initials: J
authors.lastname: Asgar
authors.affiliation: Department of Neural and Pain Sciences, School of Dentistry, Program in Neuroscience, Center to Advance Chronic Pain Research, University of Maryland, Baltimore, Maryland 21201.
authors.forename: John
authors.initials: J
authors.lastname: Joseph
authors.affiliation: Department of Neural and Pain Sciences, School of Dentistry, Program in Neuroscience, Center to Advance Chronic Pain Research, University of Maryland, Baltimore, Maryland 21201.
authors.forename: Jin Y
authors.initials: JY
authors.lastname: Ro
authors.affiliation: Department of Neural and Pain Sciences, School of Dentistry, Program in Neuroscience, Center to Advance Chronic Pain Research, University of Maryland, Baltimore, Maryland 21201.
authors.forename: Feng
authors.initials: F
authors.lastname: Wei
authors.affiliation: Centrexion, Baltimore, Maryland 21202.
authors.forename: James N
authors.initials: JN
authors.lastname: Campbell
authors.affiliation: Department of Neural and Pain Sciences, School of Dentistry, Program in Neuroscience, Center to Advance Chronic Pain Research, University of Maryland, Baltimore, Maryland 21201. Electronic address: mchung@umaryland.edu.
authors.forename: Man-Kyo
authors.initials: MK
authors.lastname: Chung
mesh_terms: D000818:Animals; D001369:Axons / Q000378:metabolism*; D002118:Calcium / Q000378:metabolism*; D020013:Calcium Signaling / Q000187:drug effects; D002154:Calpain / Q000235:genetics / Q000378:metabolism*; D002211:Capsaicin / Q000494:pharmacology*; D004151:Dipeptides / Q000494:pharmacology; D005786:Gene Expression Regulation / Q000187:drug effects*; D051379:Mice; D008822:Mice, Transgenic; D008928:Mitochondria / Q000235:genetics / Q000378:metabolism; D009619:Nociceptors / Q000378:metabolism*; D050916:TRPV Cation Channels / Q000235:genetics / Q000378:metabolism*
chemical_list: D004151:Dipeptides; D050916:TRPV Cation Channels; C493921:TRPV1 protein, mouse; D002154:Calpain; C570925:Capn2 protein, mouse; D002211:Capsaicin; D002118:Calcium; C058076:calpain inhibitor III
keywords: analgesia; calcium; calpain; capsaicin; dorsal root ganglia; nociceptors; pain; transient receptor potential channels (TRP channels)