Osteoclasts play a part in pain due to the inflammation adjacent to bone.
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.
Nagae
Maho
M
Department of Biochemistry, Osaka University Graduate School of Dentistry, 1-8 Yamadaoka, Suita, Osaka 565-0871, Japan.
Hiraga
Toru
T
Department of Biochemistry, Osaka University Graduate School of Dentistry, 1-8 Yamadaoka, Suita, Osaka 565-0871, Japan.
Wakabayashi
Hiroki
H
Department of Biochemistry, Osaka University Graduate School of Dentistry, 1-8 Yamadaoka, Suita, Osaka 565-0871, Japan.
Wang
Liyang
L
Department of Biochemistry, Osaka University Graduate School of Dentistry, 1-8 Yamadaoka, Suita, Osaka 565-0871, Japan.
Iwata
Koichi
K
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.
Yoneda
Toshiyuki
T
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.
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
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