Inhibition of glycogen synthase kinase-3β attenuates glucocorticoid-induced bone loss

Aims: Long-term glucocorticoid administration is known to induce bone deterioration. Glycogen synthase kinase-3β (GSK-3β) signaling reportedly participates in bone remodeling. This study investigated whether GSK-3β inhibitor could regulate glucocorticoid-induced inhibition of osteoblast differentiation in vitro or bone mass in vivo. Main methods: MC3T3-E1 osteoblasts were treated with kinase-inactive GSK-3β mutant and 6-bromoindirubin-3′-oxim (BIO) and then exposed to 1 μM dexamethasone. Survival and osteoblast differentiation of cell cultures were assessed by terminal deoxynucleotidyl transferase-mediated deoxyuridine triphosphate-biotin nick end-labeling, quantitative RT-PCR, and von Kossa staining. Mineral density, biomechanical properties and microenvironments of BIO- and glucocorticoid-treated rat bone tissues were analyzed using dual-energy X-ray absorptiometry, material testing, and histomorphometry, respectively. Key findings: Glucocorticoid decreased levels of phosphorylated Ser9-GSK-3β and β-catenin in osteoblast cultures. Kinase-inactive GSK-3β mutant and BIO treatments attenuated dexamethasone-induced inhibition of β-catenin, Runx2 abundance, and osteoblast differentiation but suppressed glucocorticoid-induced apoptosis of cell cultures. Exogenous BIO treatment alleviated methylprednisolone-induced impairment of mineral density, biomechanical strength, trabecular bone volume, osteoblast surface, and bone formation rate of rat bone tissue. BIO treatment also attenuated glucocorticoid-induced promotion of osteoclast surface and marrow adipocyte volume in bone tissue. Bone cells adjacent to glucocorticoid-stressed bone tissue displayed strong phosphorylated Ser9-GSK-3β and β-catenin immunostaining following BIO treatment. Significance: Inhibition of GSK-3β abrogated glucocorticoid-induced bone loss by increasing β-catenin- and Runx2-mediated osteoblast differentiation. Controlling GSK-3β signaling in bone cells may be a strategy for preventing glucocorticoid-induced osteopenia.