MicroRNA-29a ameliorates glucocorticoid-induced suppression of osteoblast differentiation by regulating β-catenin acetylation

Excess glucocorticoid treatment induces loss of osteoblast differentiation. Post-translational modification of beta-catenin reportedly regulates osteogenic activities in bone cells. This study was undertaken to test whether miR-29a signaling regulates the acetylation status of beta-catenin in the glucocorticoid-mediated osteoblast dysfunction. Murine osteoblast cultures were incubated under osteogenic conditions with or without supraphysiological glucocorticoid, miR-29a precursor, antisense oligonucleotides or histone deacetylase 4 (HDAC4) RNA interferences. Osteoblast differentiation was determined by alkaline phosphatase activity, calcium deposition, and von Kossa stain. beta-Catenin acetylation and miR-29a transcription were detected by immunoblotting, chromatin immunoprecipitation and quantitative PCR Protein interaction was detected by fluorescence protein ligation assay. Supraphysiological glucocorticoid treatment repressed osteoblast differentiation and induced loss of miR-29a expression and acetylated beta-catenin levels in osteoblast cultures. Gain of miR-29a function attenuated the deleterious effects of glucocorticoid on osteogenic gene expression and mineralized nodule formation, whereas knockdown of miR-29a signaling accelerated loss of osteoblast differentiation capacity. miR-29a reduced HDAC4 signaling and attenuated the glucocorticoid-mediated beta-catenin deacetylation and ubiquitination and restored nuclear beta-catenin levels. Glucocorticoid-induced loss of miR-29a signaling occurred through transcriptional and translational regulation. Interruption of HDAC4 signaling attenuated the glucocorticoid-induced hypoacetylation of histone H3 at lysine 9 (H3K9Ac) and restored the enrichment of H3K9Ac in miR-29a proximal promoter region and miR-29a transcription in cell cultures. Taken together, excess glucocorticoid-induced loss of miR-29a signaling accelerates beta-catenin deacetylation and ubiquitination that impairs osteogenic activities of osteoblast cultures. miR-29a and HDAC4 reciprocal regulation of H3K9 acetylation contributes to the acetylation status of beta-catenin and miR-29a expression. Enhancement of miR-29a signaling is an alternative strategy for protecting against the adverse actions of excess glucocorticoid on differentiation capacity of osteogenic cells. (C) 2013 Elsevier Inc. All rights reserved.