L-type Ca2+ channel agonist inhibits RANKL-induced osteoclast formation via NFATc1 down-regulation

Aims BayK 8644 is an L-type Ca 2+ channel agonist that enhances Ca 2+ influx and elevates cytosolic Ca 2+ . As intracellular calcium plays a key role in osteoclast formation, we investigated the effects of BayK 8644 in cultures of bone marrow-derived precursor cells with macrophage colony-stimulating factor (M-CSF) and receptor activator of nuclear factor kappaB ligand (RANKL). Main methods We performed an osteoclast formation assay, a pit formation assay, real-time PCR, and Western blot analysis. Key findings BayK 8644 concentration-dependently suppressed osteoclastogenesis, as well as the expression of osteoclastic marker genes. It also decreased osteoclastic bone resorption on a dentine slice. While the RANKL-stimulated induction of IL-1β and IL-6 was not affected, TNF-α induction was reduced by BayK 8644 treatment. In addition, BayK 8644 blocked IκB degradation and the induction of nuclear factor of activated T cells c1 (NFATc1), the master regulator of osteoclast differentiation, following RANKL stimulation. Finally, forced expression of NFATc1 reversed the inhibitory effect of BayK 8644 on osteoclastogenesis, suggesting that NFATc1 is a downstream target for the anti-osteoclastogenic action of BayK 8644. Taken together, our data suggest that BayK 8644 has an anti-osteoclastogenic effect by inhibiting RANKL-induced activation of NF-κB pathways, thereby suppressing the gene expression of NFATc1 in osteoclast precursors. Significance Our results provide a molecular understanding of the inhibitory effect of the L-type Ca 2+ channel agonist, BayK 8644, on osteoclastogenesis.