Acceleration of bone regeneration by local application of lithium: Wnt signal-mediated osteoblastogenesis and Wnt signal-independent suppression of osteoclastogenesis

Inhibition of glycogen synthase kinase (GSK)-3 and the consequent activation of the Wnt/β-catenin signaling pathway have been reported to increase bone volume. To develop a novel pharmacotherapy for injured bone, we investigated whether GSK-3 inhibitor was effective in promoting bone formation. In in vitro experiments, we examined the effects of GSK-3 inhibitors LiCl and SB216763 on osteoblastogenesis of mesenchymal progenitor C3H10T1/2 cells and osteoclastogenesis of osteoclast precursor RAW-D cells. Both inhibitors promoted osteoblast differentiation, assessed by alkaline phosphatase activity and calcium deposition, stimulating the Wnt/β-catenin signaling pathway and thereby inducing Runx2. On the other hand, the GSK-3 inhibitors suppressed osteoclast differentiation, assessed by tartrate-resistant acid phosphatase staining and number of nuclei in the cells, reducing NFATc1 expression independently of the Wnt/β-catenin signaling pathway. In subsequently performed in vivo studies, we examined the effect of locally administered Li₂CO₃ on the recovery from a partial defect made on the rat tibia. Computerized tomography and bone histomorphometry showed that Li ₂CO₃ accelerated bone regeneration in defect lesion with increased lamellar bone ratio compared with the controls. These results suggested that local application of lithium (or other GSK-3 inhibitors) might effectively facilitate recovery from bone injury by promoting osteoblastogenesis and inhibiting osteoclastogenesis.