8-Nitro-cGMP is a promoter of osteoclast differentiation induced by RANKL

Abstract Osteoclastsare multinucleated giant cells differentiatedfrom monocyte-macrophage-lineage cells under stimulation of receptor activator of nuclear factor κ-B ( RANK) ligand( RANKL) produced by osteoblasts and osteocytes. Although it has been reported that nitric oxide (NO) and reactive oxygen species (ROS) are involved in this process, the mechanism by which these labile molecules promote osteoclast differentiationare not fully understood. In this study, we investigated the formation and function of 8- nitro-cGMP, a downstream molecule of NO and ROS, in the process of osteoclast differentiationin vitro . 8- Nitro-cGMP was detected in mouse bone marrow macrophages and osteoclasts differentiatedfrom macrophages in the presence of RANKL. Inhibition of NO synthase suppressed the formation of 8- nitro-cGMP as well as RANKL-induced osteoclast differentiationfrom macrophages. On the other hand, RANKL-induced osteoclast differentiationwas promoted by addition of 8- nitro-cGMP to the cultures. In addition, 8- nitro-cGMP enhanced the mRNA expression of RANK, the receptor for RANKL. However, 8-bromo-cGMP, a membrane-permeable derivative of cGMP, did not have an effect on either RANKL-induced osteoclast differentiationor expression of the RANK gene. These results suggest that 8- nitro-cGMP is a novel positive regulator of osteoclast differentiation, which might help to explain the roles of NO and ROS in osteoclast differentiation.