Activation of G Proteins by Aluminum Fluoride Enhances RANKL-Mediated Osteoclastogenesis

Receptor activator of NF-κB ligand (RANKL)-induced osteoclastogenesis is accompanied by intracellular Ca(2+) mobilization in a form of oscillations, which plays essential roles by activating sequentially Ca(2+)/calmodulin-dependent protein kinase, calcineurin and NFATc1, necessary in the osteoclast differentiation. However, it is not known whether Ca(2+) mobilization which is evoked in RANKL-independent way induces to differentiate into osteoclasts. In present study, we investigated Ca(2+) mobilization induced by aluminum fluoride (AlF4 (-)), a G-protein activator, with or without RANKL and the effects of AlF4 (-) on the osteoclastogenesis in primary cultured mouse bone marrow-derived macrophages (BMMs). We show here that AlF4 (-) induces intracellular Ca(2+) concentration ([Ca(2+)]i) oscillations, which is dependent on extracellular Ca(2+) influx. Notably, co-stimulation of AlF4 (-) with RANKL resulted in enhanced NFATc1 expression and formation of tartrate-resistant acid phosphatase (TRAP) positive multinucleated cells. Additionally, we confirmed that mitogen-activated protein kinase (MAPK) is also activated by AlF4 (-). Taken together, these results demonstrate that G-protein would be a novel modulator responsible for [Ca(2+)]i oscillations and MAPK activation which lead to enhancement of RANKL-mediated osteoclastogenesis.