TNF‑α treatment increases DKK1 protein levels in primary osteoblasts via upregulation of DKK1 mRNA levels and downregulation of miR‑335‑5p.

Elucidation of the underlying mechanisms governing osteogenic differentiation is of significant importance to the improvement of therapeutics for bone‑related inflammatory diseases. Tumor necrosis factor‑α (TNF‑α) is regarded as one of the major agents during osteogenic differentiation in an inflammatory environment. miR‑335‑5p post‑transcriptionally downregulates the Dickkopf WNT signaling pathway inhibitor 1 (DKK1) protein level by specifically binding to the DKK1 3'UTR and activating Wnt signaling. The role of miR‑335‑5p in TNF‑α‑induced post‑transcriptional regulation of DKK1 remains to be elucidated. In the present study, the mRNA and protein levels of DKK1 and the level of miR‑335‑5p were determined in MC3T3‑E1 cells and the primary calvarial osteoblasts treated with or without TNF‑α. The role of NF‑κB signaling in TNF‑α‑induced post‑transcriptional regulation of DKK1 was also evaluated. The present study determined that although TNF‑α treatment exhibited cell‑specific effects on DKK1 mRNA expression, the stimulation of TNF‑α time‑ and concentration‑dependently upregulated the protein levels of DKK1. In primary calvarial osteoblasts, the decreased miR‑335‑5p level induced by TNF‑α‑activated NF‑κB signaling served an important role in mediating the post‑transcriptional regulation of DKK1 by TNF‑α treatment. In MC3T3‑E1 cells, the post‑transcriptional regulation of DKK1 by TNF‑α treatment was more complicated and involved other molecular signaling pathways in addition to the NF‑κB signaling. In conclusion, TNF‑α treatment served an important role in the post‑transcriptional regulation of DKK1 expression, which requires further investigation. The results of the present study not only provided new insights into the regulatory effects of miR‑335‑5p on osteogenic differentiation in an inflammatory microenvironment, but may also promote the development of potential therapeutic strategies for the treatment of bone‑related inflammatory diseases.