Nagae Maho, Hiraga Toru, Wakabayashi Hiroki, Wang Liyang, Iwata Koichi, Yoneda Toshiyuki
Department of Biochemistry, Osaka University Graduate School of Dentistry, 1-8 Yamadaoka, Suita, Osaka 565-0871, Japan.
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.
Bone. 2006 Nov;39(5):1107-1115. doi: 10.1016/j.bone.2006.04.033.
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.
破骨细胞性骨吸收增加的骨疾病常伴有骨痛，而破骨细胞抑制剂可减轻骨痛。破骨细胞通过液泡H⁺-ATP酶分泌质子来降解骨矿物质，从而形成酸性微环境。由于酸中毒是疼痛的一个众所周知的原因，我们推测破骨细胞通过分泌质子导致疼痛。我们使用一种动物模型对此进行了探究，即在后爪单次皮下注射完全弗氏佐剂（CFA）会引起炎症性痛觉过敏（对有害刺激的超敏反应）。注射CFA的后爪跖骨中的破骨细胞性骨吸收增加。双膦酸盐唑来膦酸（ZOL）、阿仑膦酸盐和骨保护素可显著抑制CFA诱导的痛觉过敏。破骨细胞固有功能失调的c-src缺陷小鼠表现出CFA诱导痛觉过敏减轻。向后爪反复皮下注射甲状旁腺激素相关蛋白也会诱导痛觉过敏并增加破骨细胞性骨吸收。通过逆转录聚合酶链反应（RT-PCR）检测，痛觉过敏与同侧背根神经节（DRG）中酸敏感离子通道（ASIC）1a、1b和3的mRNA表达增加以及通过免疫组织化学检测同侧脊髓背角中c-Fos表达增加有关。值得注意的是，ZOL降低了ASIC1a mRNA表达和c-Fos。用酸（pH5.5）处理DRG细胞系F-11会增加ASIC1a、1b和3 mRNA表达以及核c-Fos表达。ASIC阻滞剂阿米洛利抑制F-11细胞中酸诱导的c-Fos表达。此外，与亲本F-11细胞相比，瞬时受体电位香草酸亚型成员1（TRPV1）转染的F-11细胞显示酸诱导的核c-Fos表达增加。最后，液泡H⁺-ATP酶抑制剂巴弗洛霉素A1可逆转痛觉过敏并下调DRG中ASIC1a mRNA表达。这些结果使我们提出，破骨细胞通过产生酸中毒激活包括ASIC和TRPV1在内的酸敏感受体，从而在CFA诱导的炎性疼痛中发挥作用。
