Glucocorticoid inhibits cell proliferation in differentiating osteoblasts by microRNA-199a targeting of WNT signaling

The inhibition of osteoblast proliferation by glucocorticoids (GCs) is very important in the etiology of GC-induced osteoporosis. The mechanisms of this process are still not fully understood. The results of recent studies have indicated an important role for microRNAs in GC-mediated responses in various cellular processes, including cell proliferation and apoptosis. Therefore, we developed the hypothesis that these regulatory molecules might be involved in GC-decreased osteoblast proliferation. Western blotting, quantitative realtime PCR, cell proliferation assays, and luciferase assays were employed to investigate the role of miRNAs in GC-inhibited osteoblast proliferation. microRNA-199a-5p was significantly increased in osteoblasts treated with dexamethasone (Dex). To delineate the role of microRNA-199a-5p, we silenced and overexpressed microRNA-199a-5p in osteoblasts. We found that overexpressing microRNA-199a-5p remarkably increased the inhibition effect of Dex on osteoblast proliferation, and depleting microRNA-199a-5p significantly attenuated Dex-inhibited osteoblast proliferation. Results of mechanistic studies indicated that microRNA-199a-5p inhibited FZD4 and WNT2 expression through a microRNA-199a-5p binding site within the 3'-UTR of FZD4 and WNT2. The post-transcriptional repression of FZD4 and WNT2 were further confirmed by luciferase reporter assay. These results indicated that microRNA-199a-5p may play a significant role in GC-inhibited osteoblast proliferation by regulating the WNT signaling pathway.