Osteoblasts induce Ca²⁺ oscillation-independent NFATc1 activation during osteoclastogenesis

Intercellular cross-talk between osteoblasts and osteoclasts is important for controlling bone remolding and maintenance. However, the precise molecular mechanism by which osteoblasts regulate osteoclastogenesis is still largely unknown. Here, we show that osteoblasts can induce Ca²⁺ oscillation-independent osteoclastogenesis. We found that bone marrow-derived monocyte/macrophage precursor cells (BMMs) lacking inositol 1,4,5-trisphosphate receptor type2 (IP₃R2)did not exhibit Ca²⁺ oscillation or differentiation into multinuclear osteoclasts in response to recombinant receptor activator of NF-κB Ligand/macrophage colony-stimulating factor stimulation. IP₃R2 knockout BMMs, however, underwent osteoclastogenesis when they were cocultured with osteoblasts or in vivo in the absence of Ca²⁺ oscillation. Furthermore, we found that Ca ²⁺ oscillation-independent osteoclastogenesis was insensitive to FK506, a calcineurin inhibitor. Taken together, we conclude that both Ca ²⁺ oscillation/calcineurin-dependent and -independent signaling pathways contribute to NFAT1 activation, leading to efficient osteoclastogenesis in vivo.