Lyn inhibits osteoclast differentiation by interfering with PLCgamma1-mediated Ca2+ signaling.

Osteoclasts differentiate from macrophage-lineage cells to become specialized for bone resorption function. By a proteomics approach, we found that Lyn was down-regulated by the osteoclast differentiation factor, receptor activator of NF-kappaB ligand (RANKL). The forced reduction of Lyn caused a striking increase in the RANKL-induced PLCgamma1, Ca(2+), and NFATc1 responses during differentiation. These data suggest that Lyn plays a negative role in osteoclastogenesis by interfering with the PLCgamma1-mediated Ca(2+) signaling that leads to NFATc1 activation. Consistent with the in vitro results, in vivo injection of Lyn specific siRNA into mice calvariae provoked a fulminant bone resorption. Our study provides the first evidence of the involvement of Lyn in the negative regulation of osteoclastogenesis by RANKL.