miR-365 Ameliorates Dexamethasone-Induced Suppression of Osteogenesis in MC3T3-E1 Cells by Targeting HDAC4

Glucocorticoid administration is the leading cause of secondary osteoporosis. In this study, we tested the hypotheses that histone deacetylase 4 (HDAC4) is associated with glucocorticoid-induced bone loss and that HDAC4 dependent bone loss can be ameliorated by miRNA-365. Our previous studies showed that miR-365 mediates mechanical stimulation of chondrocyte proliferation and differentiation by targeting HDAC4. However, it is not clear whether miR-365 has an effect on glucocorticoid-induced osteoporosis. We have shown that, in MC3T3-E1 osteoblasts, dexamethasone (DEX) treatment decreased the expression of miR-365, which is accompanied by the decrease of cell viability in a dose-dependent manner. Transfection of miR-365 ameliorated DEX-induced inhibition of MC3T3-E1 cell viability and alkaline phosphatase activity, and attenuated the suppressive effect of DEX on runt-related transcription factor 2 (Runx2), osteopontin (OPN), and collagen 1a1 (Col1a1) osteogenic gene expression. In addition, miR-365 decreased the expression of HDAC4 mRNA and protein by direct targeting the 3'-untranslated regions (3'-UTR) of HDAC4 mRNA in osteoblasts. MiR-365 increased Runx2 expression and such stimulatory effect could be reversed by HDAC4 over-expression in osteoblasts. Collectively, our findings indicate that miR-365 ameliorates DEX-induced suppression of cell viability and osteogenesis by regulating the expression of HDAC4 in osteoblasts, suggesting miR-365 might be a novel therapeutic agent for treatment of glucocorticoid-induced osteoporosis.