Calcitonin Gene-related Peptide Inhibits Osteoclast Differentiation by Inducing the Negative Regulators MafB and Bcl6

Calcitonin gene-related peptide (CGRP), a neuropeptide derived from sensory nerves, suppresses osteoclast dif-ferentiation; however, the detailed mechanism is unknown. Therefore, in this study, we investigated the mechanism under-lying the CGRP-mediated suppression of osteoclast differentiation using a model in which mouse monocyte/macrophage RAW264.7 cells were induced to differentiate into osteoclasts with recombinant mouse soluble receptor activator of nuclear factor-kappa B ligand (s-RANKL). RAW264.7 cells were cultured with s-RANKL in the presence or absence of CGRP for 24???72 h and then quantitative real-time PCR was performed. The mRNA expression of the positive regulators of osteoclast differentiation [i.e., nuclear factor of activated T-cells 1 (Nfatc1) and B lymphocyte-induced maturation protein-1 (Blimp1)], as well as that of the negative regulators of osteoclast differentiation [i.e., MAF bZIP transcription factor B (MafB), B-cell lymphoma 6 (Bcl6), and interferon regulatory factor-8 (Irf)], was analyzed. In RAW264.7 cells treated with s-RANKL, CGRP significantly suppressed Nfatc1 and Blimp1 mRNA expression at 24 and 48 h. On the contrary, CGRP significantly increased the mRNA expression of MafB at 24 and 48 h of culture and of Bcl6 at 48 and 72 h of culture. However, CGRP did not affect Irf mRNA expression. In s-RANKL-untreated RAW264.7 cells, MafB mRNA expression significantly in-creased from 2 to 8 h, whereas Bcl6 mRNA expression significantly increased from 4 to 24 h of culture. These results sug-gest that CGRP inhibits osteoclast differentiation by increasing the mRNA expression of MafB and Bcl6, which are negative regulators of osteoclast differentiation.

Automated summary

In this study, the mechanism behind CGRP-mediated suppression of osteoclast differentiation was investigated. It was found that CGRP inhibits osteoclast differentiation by increasing the mRNA expression of negative regulators MafB and Bcl6.