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-3 beta (GSK-3 beta) signaling reportedly participates in bone remodeling. This Study investigated whether GSK-3 beta 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-3 beta mutant and 6-bromoindirubin-3'-oxim (BIO) and then exposed to 1 mu M 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 Ser-9-GSK-3 beta and beta-catenin in osteoblast Cultures. Kinase-inactive GSK-3 beta mutant and BIO treatments attenuated dexamethasone-induced inhibition of beta-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-3 beta and beta-catenin immunostaining following BIO treatment. Significance: Inhibition of GSK-3 beta abrogated glucocorticoid-induced bone loss by increasing beta-catenin- and Runx2-mediated osteoblast differentiation. Controlling GSK-3 beta signaling in bone cells may be a strategy for preventing glucocorticoid-induced osteopenia. (C) 2009 Elsevier Inc. All rights reserved.