Physiologic osteoclasts are not sufficient to induce skeletal pain in mice

Abstract

Background: Increased bone resorption is driven by augmented osteoclast activity in pathological states of the bone, including osteoporosis, fracture and metastatic bone cancer. Pain is a frequent co-morbidity in bone pathologies and adequate pain management is necessary for symptomatic relief. Bone cancer is associated with severe skeletal pain and dysregulated bone remodelling, while increased osteoclast activity and bone pain are also observed in osteoporosis and during fracture repair. However, the effects of altered osteoclast activity and bone resorption on nociceptive processing of bone afferents remain unclear. Methods: This study investigates whether physiologic osteoclasts and resulting changes in bone resorption can induce skeletal pain. We first assessed correlation between changes in bone microarchitecture (through µCT) and skeletal pain using standardized behavioural phenotyping assays in a mouse model of metastatic bone cancer. We then investigated whether increased activity of physiologic osteoclasts, and the associated bone resorption, is sufficient to induce skeletal pain using mouse models of localized and widespread bone resorption following administration of exogenous receptor activator of nuclear factor kappa-B ligand (RANKL). Results: Our data demonstrates that mice with bone cancer exhibit progressive pain behaviours that correlate with increased bone resorption at the tumour site. Systemic RANKL injections enhance osteoclast activity and associated bone resorption, without producing any changes in motor function or pain behaviours at both early and late timepoints. Conclusion: These findings suggest that activation of homeostatic osteoclasts alone is not sufficient to induce skeletal pain in mice. Significance statement: The role of osteoclasts in peripheral sensitization of sensory neurones is not fully understood. This study reports on the direct link between oestrogen-independent osteoclast activation and skeletal pain. Administration of exogenous receptor activator of nuclear factor kappa-B ligand (RANKL) increases bone resorption, but does not produce pro-nociceptive changes in behavioural pain thresholds. Our data demonstrates that physiologic osteoclasts are not essential for skeletal pain behaviours. This is an open access article under the terms of the Creat ive Commo ns Attri bution License, which permits use, distribution and reproduction in any medium, provided the original work is properly cited.

Antibody-induced pain-like behavior and bone erosion: links to subclinical inflammation, osteoclast activity, and acid-sensing ion channel 3–dependent sensitization

“…Interestingly, induction of osteoclastogenesis by local or systemic administration of RANKL does not produce pain-related behaviors in mice, suggesting that enhanced osteoclast activity in the absence of other local changes is not pain-inducing. 16 Thus, the exact role of osteoclasts and how they contribute to sensitization of nociceptors are not fully understood yet.…”

Mechanisms of cancer pain

“…Rodents exhibit pain-like behaviours within 2–3 weeks of intrafemoral inoculation with cancer cells in a dose-dependent manner ( 30 , 36 , 37 ). Non-evoked pain behaviours include reduced use of the affected limb, which can be quantified using a limb score, as well as a reduction in weight borne on the affected limb when tested by an incapacitance tester ( 30 , 36 – 38 ).…”

“…The occurrence of SREs in CIBP provides the rationale for bone targeting agents to manage CIBP and to reduce the occurrence of SREs by reducing bone resorption ( 210 ). Besides bone cancer, other painful syndromes such as osteoporosis and fracture repair are also associated with increased bone resorption ( 37 ). Bisphosphonates and Denosumab are osteoclast targeting molecules that inhibit bone resorption.…”

Sensitization of Cutaneous Primary Afferents in Bone Cancer Revealed by In Vivo Calcium Imaging

“…The progression of CIBP was assessed by limb use score and a cut-off of 2 or 1 (i.e., significant limping) was used as the endpoint for cancer animals, as previously described [33]. Deficits in static weight bearing were assessed using an Incapacitance Meter as previously described [70]. Mechanical sensitivity of the ipsilateral hindpaw was measured using the von Frey up-down method [71] and Randall-Selitto apparatus [72].…”

“…Mechanical sensitivity of the tumour-surrounding tissue was determined by non-noxious palpation of the distal femur head [44]. Thermal nociception was assessed on the hot-plate test at 50 • C as previously described [70]. Limb use score and weight bearing was performed on all animals.…”