title: Osteoclasts play a part in pain due to the inflammation adjacent to bone.
abstract: Bone disorders with increased osteoclastic bone resorption are frequently associated with bone pain and inhibitors of osteoclasts reduce bone pain. Osteoclasts degrade bone minerals by secreting protons through the vacuolar H+-ATPase, creating acidic microenvironments. Because acidosis is a well-known cause of pain, we reasoned that osteoclasts cause pain through proton secretion. We explored this using an animal model in which a single subcutaneous injection of the complete Freund's adjuvant (CFA) in the hind-paw caused inflammatory hyperalgesia (hyper-responsiveness to noxious stimuli). Osteoclastic bone resorption was increased in the metatarsal bones in the CFA-injected hind-paws. CFA-induced hyperalgesia was significantly suppressed by the bisphosphonates, zoledronic acid (ZOL) and alendronate and osteoprotegerin. c-src-deficient mice in which osteoclasts are inherently dysfunctional exhibited reduced CFA-induced hyperalgesia. Repeated subcutaneous injections of parathyroid hormone-related protein into the hind-paw also induced hyperalgesia with increased osteoclastic bone resorption. The hyperalgesia was associated with increased mRNA expression of acid-sensing ion channel (ASIC) 1a, 1b and 3 in the ipsi-lateral dorsal root ganglions (DRGs) by RT-PCR and c-Fos in the ipsi-lateral spinal dorsal horn by immunohistochemistry. Of note, ZOL decreased the ASIC1a mRNA expression and c-Fos. Treatment of the DRG cell line F-11 with acid (pH5.5) increased ASIC1a, 1b and 3 mRNA expression and nuclear c-Fos expression. The ASIC blocker amiloride inhibited acid-induced c-Fos expression in F-11 cells. Moreover, F-11 cells transfected with the transient receptor potential channel vanilloid subfamily member 1 (TRPV1) showed increased acid-induced nuclear c-Fos expression compared with parental F-11 cells. Finally, bafilomycin A1, an inhibitor of the vacuolar H+-ATPase, reversed the hyperalgesia and down-regulated ASIC1a mRNA expression in the DRGs. These results led us to propose that osteoclasts play a part in CFA-induced inflammatory pain through an activation of the acid-sensing receptors including ASICs and TRPV1 by creating acidosis.
authors.affiliation: Department of Biochemistry, Osaka University Graduate School of Dentistry, 1-8 Yamadaoka, Suita, Osaka 565-0871, Japan.
authors.forename: Maho
authors.initials: M
authors.lastname: Nagae
authors.affiliation: Department of Biochemistry, Osaka University Graduate School of Dentistry, 1-8 Yamadaoka, Suita, Osaka 565-0871, Japan.
authors.forename: Toru
authors.initials: T
authors.lastname: Hiraga
authors.affiliation: Department of Biochemistry, Osaka University Graduate School of Dentistry, 1-8 Yamadaoka, Suita, Osaka 565-0871, Japan.
authors.forename: Hiroki
authors.initials: H
authors.lastname: Wakabayashi
authors.affiliation: Department of Biochemistry, Osaka University Graduate School of Dentistry, 1-8 Yamadaoka, Suita, Osaka 565-0871, Japan.
authors.forename: Liyang
authors.initials: L
authors.lastname: Wang
authors.affiliation: Department of Physiology, Nihon University School of Dentistry, 1-8-13, Kanda-Surugadai, Chiyoda-ku, Tokyo 101-8310, Japan; Division of Functional Morphology, Dental Research Center, Nihon University School of Dentistry, 1-8-13, Kanda-Surugadai, Chiyoda-ku, Tokyo 101-8310, Japan.
authors.forename: Koichi
authors.initials: K
authors.lastname: Iwata
authors.affiliation: Department of Biochemistry, Osaka University Graduate School of Dentistry, 1-8 Yamadaoka, Suita, Osaka 565-0871, Japan. Electronic address: tyoneda@dent.osaka-u.ac.jp.
authors.forename: Toshiyuki
authors.initials: T
authors.lastname: Yoneda
mesh_terms: D062565:Acid Sensing Ion Channels; D000818:Animals; D001862:Bone Resorption / Q000139:chemically induced / Q000503:physiopathology / Q000517:prevention & control; D001842:Bone and Bones; D002460:Cell Line; D004164:Diphosphonates / Q000008:administration & dosage / Q000494:pharmacology; D005620:Freund's Adjuvant / Q000008:administration & dosage / Q000633:toxicity; D016391:Genes, src / Q000235:genetics; D006930:Hyperalgesia / Q000139:chemically induced / Q000503:physiopathology* / Q000517:prevention & control; D007249:Inflammation / Q000139:chemically induced / Q000503:physiopathology* / Q000517:prevention & control; D007275:Injections, Intravenous; D007278:Injections, Spinal; D007279:Injections, Subcutaneous; D018942:Macrolides / Q000494:pharmacology; D008297:Male; D008565:Membrane Proteins / Q000235:genetics / Q000378:metabolism; D051379:Mice; D008817:Mice, Mutant Strains; D009419:Nerve Tissue Proteins / Q000235:genetics / Q000378:metabolism; D010010:Osteoclasts / Q000187:drug effects / Q000378:metabolism / Q000502:physiology*; D053244:Osteoprotegerin / Q000008:administration & dosage / Q000494:pharmacology; D010146:Pain; D010281:Parathyroid Hormone / Q000008:administration & dosage / Q000494:pharmacology; D020671:Posterior Horn Cells / Q000187:drug effects / Q000378:metabolism; D020133:Reverse Transcriptase Polymerase Chain Reaction; D015222:Sodium Channels / Q000235:genetics / Q000378:metabolism; D050916:TRPV Cation Channels / Q000235:genetics / Q000378:metabolism; D025262:Vacuolar Proton-Translocating ATPases / Q000378:metabolism
chemical_list: C568267:ASIC1 protein, mouse; D062565:Acid Sensing Ion Channels; D004164:Diphosphonates; D018942:Macrolides; D008565:Membrane Proteins; D009419:Nerve Tissue Proteins; D053244:Osteoprotegerin; D010281:Parathyroid Hormone; D015222:Sodium Channels; D050916:TRPV Cation Channels; C493921:TRPV1 protein, mouse; C040929:bafilomycin A1; D005620:Freund's Adjuvant; D025262:Vacuolar Proton-Translocating ATPases