Inactivation of Glycogen Synthase Kinase-3β Is Required for Osteoclast Differentiation

Glycogen synthase kinase-3 beta (GSK-3 beta is a serine/threonine kinase originally identified as a regulator of glycogen deposition. Although the role of GSK-3 beta in osteoblasts is well characterized as a negative regulator of beta-catenin, its effect on osteoclast formation remains largely unidentified. Here, we show that the GSK-3 beta inactivation upon receptor activator of NF-kappa B ligand (RANKL) stimulation is crucial for osteoclast differentiation. Regulation of GSK-3 beta activity in bone marrow macrophages by retroviral expression of the constitutively active GSK-3 beta (GSK3 beta-S9A) mutant inhibits RANKL-induced osteoclastogenesis, whereas expression of the catalytically inactive GSK-3 beta (GSK3 beta-K85R) or small interfering RNA (siRNA)-mediated GSK-3 beta silencing enhances osteoclast formation. Pharmacological inhibition of GSK-3 beta further confirmed the negative role of GSK-3 beta in osteoclast formation. We also show that overexpression of the GSK3 beta-S9A mutant in bone marrow macrophages inhibits RANKL-mediated NFATc1 induction and Ca2+ oscillations. Remarkably, transgenic mice expressing the GSK3 beta-S9A mutant show an osteopetrotic phenotype due to impaired osteoclast differentiation. Further, osteoclast precursor cells from the transgenic mice show defects in expression and nuclear localization of NFATc1. These findings demonstrate a novel role for GSK-3 beta in the regulation of bone remodeling through modulation of NFATc1 in RANKL signaling.