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

Objectives: To investigate tumor necrosis factor alpha (TNF-alpha)-induced changes in osteogenic differentiation from mesenchymal stem cells (MSCs). Materials and methods: Blockade of nuclear factor-kappa B (NF-kappa B) was achieved in ST2 murine MSCs via overexpression of the NF-kappa B inhibitor, I kappa B alpha. Osteogenic differentiation was induced in I kappa B alpha-overexpressing ST2 cells and normal ST2 cells when these cells were treated with TNF-alpha 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-alpha 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-alpha at lower concentrations, while down-regulated in cell cultures treated with TNF-alpha at higher concentrations. Blockade of NF-kappa B signaling reversed the inhibitory effect observed in cell cultures treated with TNF-alpha at higher concentrations, but showed no effect on cell cultures treated with TNF-alpha at lower concentrations. In contrast, long-term treatment of TNF-alpha at all concentrations induced inhibitory effects on in vitro mineral nodule formation. MTT assay showed that TNF-alpha inhibits proliferation/survival of mesenchymal stem cells when the NF-kappa B signaling pathway is blocked. Conclusions: The binding of TNF-alpha 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.