Inhibitory effect of CGRP on osteoclast formation by isoproterenol

Objectives: The present study was designed to elucidate the mode of action of isoproterenol (adrenergic β-agonist) and to characterize the effect of calcitonin gene-related peptide (CGRP; sensory neuropeptide) on osteoclast formation induced by isoproterenol in a mouse bone marrow culture system. Method: Mouse bone marrow cells were obtained from tibiae of 6- to 8-week-old ddY male mice. We added isoproterenol to the culture medium with or without osteoprotegerin (OPG) at the beginning of cultures and each change of medium. To estimate the osteoclast formation induced by isoproterenol, tartrate-resistant acid phosphatase-positive multinuclear cells (TRAP-positive MNCs) and the capability of resorbing bone on dentine slices were calculated. Receptor activator of NF-κB ligand (RANKL) and OPG production by isoproterenol and/or CGRP were quantified by ELISA system. Results: Treatment of mouse bone marrow cells with isoproterenol generated TRAP-positive MNCs, being capable of excavating resortive pits on dentine slices, and caused an increase of RANKL and decrease of OPG production. CGRP inhibited osteoclast formation by isoproterenol or soluble RANKL. CGRP had no influence on RANKL and OPG production in bone marrow cells treated with isoproterenol. Conclusion: These results suggest that CGRP inhibits the osteoclast formation by interfering with the action of RANKL produced in bone marrow cells treated with isoproterenol, without affecting RANKL and OPG synthesis. This in vitro evidence may suggest the physiological interaction of sympathetic and sensory nerves in osteoclastgenesis in vivo.