Dose-specific effects of tumor necrosis factor alpha on osteogenic differentiation of mesenchymal stem cells

Objectives: To investigate tumor necrosis factor alpha (TNF‐α)‐induced changes in osteogenic differentiation from mesenchymal stem cells (MSCs). Materials and methods: Blockade of nuclear factor‐κB (NF‐κB) was achieved in ST2 murine MSCs via overexpression of the NF‐κB inhibitor, IκBα. Osteogenic differentiation was induced in IκBα‐overexpressing ST2 cells and normal ST2 cells when these cells were treated with TNF‐α at various concentrations. Expression levels of bone marker genes were determined using real time RT‐PCR and ALP activity assay. In vitro mineralization was performed to determine long‐term exposure to TNF‐α on mineral nodule formation. MTT assay was used to determine the changes in cell proliferation/survival. Results: Levels of Runx2, Osx, OC and ALP were up‐regulated in cell cultures treated with TNF‐α at lower concentrations, while down‐regulated in cell cultures treated with TNF‐α at higher concentrations. Blockade of NF‐κB signaling reversed the inhibitory effect observed in cell cultures treated with TNF‐α at higher concentrations, but showed no effect on cell cultures treated with TNF‐α at lower concentrations. In contrast, long‐term treatment of TNF‐α at all concentrations induced inhibitory effects on in vitro mineral nodule formation. MTT assay showed that TNF‐α inhibits proliferation/survival of mesenchymal stem cells when the NF‐κB signaling pathway is blocked. Conclusions: The binding of TNF‐α to its receptors results in the activation of multiple signaling pathways, which actively interact with each other to regulate the differentiation, proliferation, survival and apoptosis of MSCs.