Dose-specific effects of tumor necrosis factor alpha on osteogenic differentiation of mesenchymal stem cells.
ABSTRACT To investigate tumor necrosis factor alpha (TNF-α)-induced changes in osteogenic differentiation from mesenchymal stem cells (MSCs).
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.
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.
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.
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ABSTRACT: There is a major medical need for developing novel and effective approaches for repairing non-union and critical-sized bone defects. Although the mechanisms remain to be determined, it is known that inflammation plays a crucial role in initiating bone repair and regeneration. This study investigated the effect of short-term (three days) preconditioning with tumour necrosis factor-alpha (TNF-α) on proliferation, mobilization and differentiation of adipose tissue-derived mesenchymal stem cells (ASCs). We demonstrated that TNF-α pre-conditioning increased proliferation, mobilization, and osteogenic differentiation of ASCs and up-regulated bone morphogenetic protein-2 (BMP-2) protein levels. BMP-2 silencing by siRNA partially inhibited osteogenic differentiation of ASCs induced by TNF-α; BMP-2 pre-conditioning also significantly increased osteogenic differentiation of ASCs but the effects were significantly smaller than those observed for TNF-α preconditioning. Furthermore, TNF-α treatment promoted extracellular-signal-regulated kinases(Erk)1/2 and p38 mitogen-activated protein kinase (MAPK) signaling pathways, but only Erk1/2 inhibition reduced the BMP-2 levels and osteogenic differentiation induced by TNF-α preconditioning. Together, these results support the hypothesis that inflammation contributes to bone regeneration by promoting proliferation, mobilization, and osteogenic differentiation of ASCs; three days of TNF-α preconditioning, mimicking the short boost of inflammation normally occurring after bone injury, might serve as a feasible approach for directing stem cells into osteogenic differentiation. J. Cell. Physiol. © 2013 Wiley Periodicals, Inc.Journal of Cellular Physiology 01/2013; DOI:10.1002/jcp.24330 · 3.87 Impact Factor
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ABSTRACT: Wear particles are the major cause of osteolysis associated with failure of implant following total joint replacement. During this pathologic process, activated macrophages mediate inflammatory responses to increase osteoclastogenesis, leading to enhanced bone resorption. In osteolysis caused by wear particles, osteoprogenitors present along with macrophages at the implant interface may play significant roles in bone regeneration and implant osteointegration. Although the direct effects of wear particles on osteoblasts have been addressed recently, the role of activated macrophages in regulation of osteogenic activity of osteoblasts has scarcely been studied. In the present study, we examined the molecular communication between macrophages and osteoprogenitor cells that may explain the effect of wear particles on impaired bone forming activity in inflammatory bone diseases. It has been demonstrated that conditioned medium of macrophages challenged with titanium particles (Ti CM) suppresses early and late differentiation markers of osteoprogenitors, including alkaline phosphatase (ALP) activity, collagen synthesis, matrix mineralization and expression of osteocalcin and Runx2. Moreover, bone forming signals such as WNT and BMP signaling pathways were inhibited by Ti CM. Interestingly, TNFα was identified as a predominant factor in Ti CM to suppress osteogenic activity as well as WNT and BMP signaling activity. Furthermore, Ti CM or TNFα induces the expression of sclerostin (SOST) which is able to inhibit WNT and BMP signaling pathways. It was determined that over-expression of SOST suppressed ALP activity, whereas the inhibition of SOST by siRNA partially restored the effect of Ti CM on ALP activity. This study highlights the role of activated macrophages in regulation of impaired osteogenic activity seen in inflammatory conditions and provides a potential mechanism for autocrine regulation of WNT and BMP signaling mediated by TNFα via induction of SOST in osteprogenitor cells.Biomaterials 03/2012; 33(17):4251-63. DOI:10.1016/j.biomaterials.2012.03.005 · 8.31 Impact Factor
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ABSTRACT: Tumor necrosis factor-alpha (TNF-α) is one major inflammatory factor peaking at 24 h after bone fracture in response to injury; its role in bone healing is controversial. The aims of this study were to investigate whether the duration of exposure to TNF-α is crucial for the initiation of bone regeneration and to determine its underlying mechanism(s). We demonstrated that 24 h of TNF-α treatment significantly abrogated osteocalcin gene expression by human primary osteoblasts (HOBs). However, when TNF-α was withdrawn after 24 h, bone sialoprotein and osteocalcin gene expression levels in HOBs at day 7 were significantly up-regulated compared with the HOBs without TNF-α treatment. In contrast, continuous TNF-α treatment down-regulated bone sialoprotein and osteocalcin gene expression. In addition, in an indirect co-culture system, HOBs pretreated with TNF-α for 24 h induced significantly greater osteogenic differentiation of adipose tissue-derived mesenchymal stem cells (ASCs) than the HOBs without TNF-α treatment. TNF-α treatment also promoted endogenous bone morphogenetic protein 2 (BMP-2) production in HOBs, while blocking the BMP-2 signaling pathway with Noggin inhibited osteogenic differentiation of ASCs in the co-culture system. Furthermore, activation of the p38 mitogen-activated protein kinase (MAPK) signaling pathway after TNF-α treatment occurred earlier than BMP-2 protein expression. BMP-2 production by HOBs and osteogenic differentiation of ASCs in the co-culture system with HOBs was significantly decreased when HOBs were pretreated with TNF-α in combination with the p38 MAPK-specific inhibitor (SB203580). Taken together, we provide evidence that exposure duration is a critical element in determining TNF-α's effects on bone regeneration. We also demonstrate that the p38 MAPK signaling pathway regulates the expression of BMP-2 in osteoblasts, which then acts through a paracrine loop, to direct the osteoblast lineage commitment of mesenchymal stem cells.Stem cells and development 03/2012; 21(13):2420-9. DOI:10.1089/scd.2011.0589 · 4.20 Impact Factor