Browsing by Subject "nociceptors"

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    Bone pain induced by multiple myeloma is reduced by targeting V-ATPase and ASIC3
    (AACR Publications, 2017-03-15) Hiasa, Masahiro; Okui, Tatsuo; Allette, Yohance M; Ripsch, Matthew S; Sun-Wada, Ge-Hong; Wakabayashi, Hiroki; Roodman, G David; White, Fletcher A.; Yoneda, Toshiyuki; Medicine, School of Medicine
    Multiple myeloma (MM) patients experience severe bone pain (MMBP) that is undertreated and poorly understood. In this study, we studied MMBP in an intratibial mouse xenograft model which employs JJN3 human MM cells. In this model, mice develop MMBP associated in bone with increased sprouting of calcitonin gene-related peptide-positive (CGRP+) sensory nerves and in dorsal root ganglia (DRG) with upregulation of phosphorylated ERK1/2 (pERK1/2) and pCREB, two molecular indicators of neuron excitation. We found that JJN3 cells expressed a vacuolar proton pump (V-ATPase) that induced an acidic bone microenvironment. Inhibition of JJN3-colonized bone acidification by a single injection of the selective V-ATPase inhibitor, bafilomycin A1, decreased MMBP, CGRP+ SN sprouting, and pERK1/2 and pCREB expression in DRG. CGRP+ sensory nerves also expressed increased levels of the acid-sensing nociceptor ASIC3. Notably, a single injection of the selective ASIC3 antagonist APETx2 dramatically reduced MMBP in the model. Mechanistic investigations in primary DRG neurons co-cultured with JJN3 cells showed increased neurite outgrowth and excitation inhibited by bafilomycin A1 or APETx2. Further, combining APETx2 with bafilomycin A1 reduced MMBP to a greater extent than either agent alone. Lastly, combining bafilomycin A1 with the osteoclast inhibitor zoledronic acid was sufficient to ameliorate MMBP which was refractory to zoledronic acid. Overall, our results show that osteoclasts and MM cooperate to induce an acidic bone microenvironment that evokes MMBP as a result of the excitation of ASIC3-activated sensory neurons. Further, they present a mechanistic rationale for targeting ASIC3 on neurons along with the MM-induced acidic bone microenvironment as a strategy to relieve MMBP in patients.
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    NEUROFIBROMIN, NERVE GROWTH FACTOR AND RAS: THEIR ROLES IN CONTROLLING THE EXCITABILITY OF MOUSE SENSORY NEURONS
    (2007-01-03T18:34:09Z) Wang, Yue; Nicol, Grant D.; Vasko, Michael R.; Clapp, D. Wade; Cummins, Theodore R.
    ABSTRACT Yue Wang Neurofibromin, nerve growth factor and Ras: their roles in controlling the excitability of mouse sensory neurons Neurofibromin, the product of the Nf1 gene, is a guanosine triphosphatase activating protein (GAP) for p21ras (Ras) that accelerates the conversion of active Ras-GTP to inactive Ras-GDP. It is likely that sensory neurons with reduced levels of neurofibromin have augmented Ras-GTP activity. In a mouse model with a heterozygous mutation of the Nf1 gene (Nf1+/-), the patch-clamp recording technique is used to investigate the role of neurofibromin in controlling the state of neuronal excitability. Sensory neurons isolated from adult Nf1+/- mice generate more APs in response to a ramp of depolarizing current compared to Nf1+/+ mice. In order to elucidate whether the activation of Ras underlies this augmented excitability, sensory neurons are exposed to nerve growth factor (NGF) that activates Ras. In Nf1+/+ neurons, exposure to NGF increases the production of APs. To examine whether activation of Ras contributes to the NGF-induced sensitization in Nf1+/+ neurons, an antibody that neutralizes Ras activity is internally perfused into neurons. The NGF-mediated augmentation of excitability is suppressed by the Ras-blocking antibody in Nf1+/+ neurons, suggesting the NGF-induced sensitization in Nf1+/+ neurons depends on the activation of Ras. Surprisingly, the excitability of Nf1+/- neurons is not altered by the blocking antibody, suggesting that this enhanced excitability may depend on previous activation of downstream effectors of Ras. To determine the mechanism giving rise to augmented excitability of Nf1+/- neurons, isolated membrane currents are examined. Consistent with the enhanced excitability of Nf1+/- neurons, the peak current density of tetrodotoxin-resistant (TTX-R) and TTX-sensitive (TTX-S) sodium currents (INa) are significantly larger than in Nf1+/+ neurons. Although the voltage for half-maximal activation (V0.5) is not different, there is a significant depolarizing shift in the V0.5 for steady-state inactivation of INa in Nf1+/- neurons. In summary, these results demonstrate that the enhanced production of APs in Nf1+/- neurons results from a larger current amplitude and a depolarized voltage dependence of steady-state inactivation of INa that leads to more sodium channels being available for the subsequent firing of APs. My investigation supports the idea that regulation of channels by the Ras cascade is an important determinant of neuronal excitability. Grant D. Nicol, Ph.D, Chair