Excess glucocorticoid treatment induces loss of osteoblast differentiation. Post-translational modification of β-catenin reportedly regulates osteogenic activities in bone cells. This study was undertaken to test whether miR-29a signaling regulates the acetylation status of β-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. β-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 β-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 β-catenin deacetylation and ubiquitination and restored nuclear β-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 β-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 β-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.
Pubmed ID: 24096265 RIS Download
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Database of microRNA target predictions and expression profiles. Target predictions are based on a development of the miRanda algorithm which incorporates current biological knowledge on target rules and on the use of an up-to-date compendium of mammalian microRNAs. MicroRNA expression profiles are derived from a comprehensive sequencing project of a large set of mammalian tissues and cell lines of normal and disease origin. This website enables users to explore: * The set of genes that are potentially regulated by a particular microRNA. * The implied cooperativity of multiple microRNAs on a particular mRNA. * MicroRNA expression profiles in various mammalian tissues. The web resource provides users with functional information about the growing number of microRNAs and their interaction with target genes in many species and facilitates novel discoveries in microRNA gene regulation. The microRNA Target Detection Software, miRanda, is an algorithm for finding genomic targets for microRNAs. This algorithm has been written in C and is available as an open-source method under the GPL.
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