Sensory nerves directly promote osteoclastogenesis by secreting Cyp40

BackgroundGiven the afferent functions, sensors have been found exerting efferent influences and directly alter organ physiology. Sensory nerves have been found critical in osteoclasts and bone resorption. However, the direct evidence of whether sensory nerve efferent influences osteoclast, remains lacking. MethodsWe treated mice with resiniferatoxin (RTX) or complete Freund’s adjuvant (CFA) to induce sensory hypersensitivity. Bone histomorphometry including micro-ct, three-point bending assay, von kossa staining, calcein double labeling, toluidine blue staining, and trap staining were performed to monitor bone quality and bone cells. Multiple virus vectors were applied to trace signals between sensory nerves and osteoclasts. Sensory neurons (SN) and osteoclasts were cocultured to study the effects and mechanisms of the sensory nerves on osteoclasts in vitro. Isobaric tag for relative and absolute quantitation (iTRAQ) was used to identify secreted proteins in the sensory nerve. ResultsHere, we found sensory hypersensitivity significantly increased osteoclast bone resorption; SN directly promote osteoclastogenesis in vitro; and abundant sensory efferent signals transported into osteoclasts. Then our screening identified a novel neuropeptide Peptidyl-prolyl cis-trans isomerase D (Cyp40), is the reverse signal from the sensory nerve and plays a critical role for osteoclastogenesis, via aryl hydrocarbon receptor (AhR)-Ras/Raf-pErk-NFATc1 pathway. The efferent signals from sensory nerves tend to involves in the rapid feedback process: vast majority of sensory efferent signals (87.28%) present in fast-twitch myofibers. ConclusionThis study revealed a novel mechanism of sensory nerves on osteoclasts: the direct promotion of osteoclastogenesis by the Cyp40. This mechanism may represent a direct, and quick response of sensory nerves to the changes in bone. Targeting the Cyp40 could therefore be a strategy to promote bone repair at the early stage of bone injury.