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A complex interaction between Wnt signaling and TNF-? in nucleus pulposus cells.

ABSTRACT: INTRODUCTION: Increased expression of the proinflammatory cytokine TNF-? in intervertebral discs (IVDs) leads to inflammation, which results in progressive IVD degeneration. We have previously reported that activation of Wnt-?-catenin (hereafter called Wnt) signaling suppresses the proliferation of nucleus pulposus cells and induces cell senescence, suggesting that Wnt signaling triggers the process of degeneration of the IVD. However, it is not known whether cross talk between TNF-? and Wnt signaling plays a role in the regulation of nucleus pulposus cells. The goal of the present study was to examine the effect of the interaction between Wnt signaling and the proinflammatory cytokine TNF-? in nucleus pulposus cells. METHODS: Cells isolated from rat nucleus pulposus regions of IVDs were cultured in monolayers, and the expression and promoter activity of Wnt signaling and TNF-? were evaluated. We also examined whether the inhibition of Wnt signaling using cotransfection with Dickkopf (DKK) isoforms and Sclerostin (SOST) could block the effects of pathological TNF-? expression in nucleus pulposus cells. RESULTS: TNF-? stimulated the expression and promoter activity of Wnt signaling in nucleus pulposus cells. In addition, the activation of Wnt signaling by 6-bromoindirubin-3'-oxime (BIO), which is a selective inhibitor of glycogen synthase kinase 3 (GSK-3) activity that activates Wnt signaling, increased TNF-? expression and promoter activity. Conversely, the suppression of TNF-? promoter activity using a ?-catenin small interfering RNA was evident. Moreover, transfection with DKK-3, DKK-4, or SOST, which are inhibitors of Wnt signaling, blocked Wnt signaling-mediated TNF-? activation; these effects were not observed for DKK-1 or DKK-2. CONCLUSIONS: Here, we have demonstrated that Wnt signaling regulates TNF-? and that Wnt signaling and TNF-? form a positive-feedback loop in nucleus pulposus cells. The results of the present study provide in vitro evidence that activation of Wnt signaling upregulates the TNF-? expression and might cause the degeneration of nucleus pulposus cells. We speculate that blocking this pathway might protect nucleus pulposus cells against degeneration.

SUBMITTER: Hiyama A

PROVIDER: S-EPMC3978705 | biostudies-literature | 2013

REPOSITORIES: biostudies-literature

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A complex interaction between Wnt signaling and TNF-α in nucleus pulposus cells.

Hiyama Akihiko A Yokoyama Katsuya K Nukaga Tadashi T Sakai Daisuke D Mochida Joji J

Arthritis research & therapy 20131114 6

<h4>Introduction</h4>Increased expression of the proinflammatory cytokine TNF-α in intervertebral discs (IVDs) leads to inflammation, which results in progressive IVD degeneration. We have previously reported that activation of Wnt-β-catenin (hereafter called Wnt) signaling suppresses the proliferation of nucleus pulposus cells and induces cell senescence, suggesting that Wnt signaling triggers the process of degeneration of the IVD. However, it is not known whether cross talk between TNF-α and ...[more]

PMID: 24286133

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Project description:BackgroundThe aims of this study were to investigate the gene expression of CCN family members in rat intervertebral disc (IVD) cells and to examine whether Wnt-β-catenin signaling regulates the expression of CCN family 2 (CCN2)/connective tissue growth factor (CTGF) in rat nucleus pulposus (NP) cells.MethodsThe gene expression of CCN family members were assessed in rat IVD cells using real-time reverse transcription polymerase chain reaction (RT-PCR). The expression pattern of CCN2 was also assessed in rat IVD cells using western blot and immunohistochemical analyses. Gain-of-function and loss-of-function experiments were performed to identify the mechanisms by which Wnt-β-catenin signaling influences the activity of the CCN2 promoter. To further determine if the mitogen-activated protein kinase (MAPK) pathway is required for the Wnt-β-catenin signaling-induced regulation of CCN2 expression in the NP cells, CCN2 expression was analyzed by reporter assay, RT-PCR and western blot analysis.ResultsCCN2 messenger RNA (mRNA) and protein were expressed in rat IVDs. Expression of CCN2 was significantly higher than for mRNA of other CCN family members in both rat NP and annulus fibrosus (AF) cells. The relative activity of the CCN2 promoter decreased 24 h after treatment with 6-bromoindirubin-3'-oxime (1.0 μM) (0.773 (95% 0.735, 0.812) P = 0.0077) in NP cells. In addition, treatment with the WT-β-catenin vector (500 ng) significantly decreased CCN2 promoter activity (0.688 (95% 0.535, 0.842) P = 0.0063), whereas β-catenin small interfering RNA (500 ng) significantly increased CCN2 promoter activity (1.775 (95% 1.435, 2.115) P < 0.001). Activation of Wnt-β-catenin signaling decreased the expression of CCN2 mRNA and protein by NP cells. Regulation of CCN2 by Wnt-β-catenin signaling involved the MAPK pathway in rat NP cells.ConclusionsThis study shows that Wnt-β-catenin signaling regulates the expression of CCN2 through the MAPK pathway in NP cells. Understanding the balance between Wnt-β-catenin signaling and CCN2 is necessary for developing therapeutic alternatives for the treatment of IVD degeneration.

Project description:Background contextLow back pain, affecting nearly 40% of adults, mainly results from intervertebral disc degeneration (IVDD), while the pathogenesis of IVDD is still not fully elucidated. Recently, some researches have revealed that necroptosis, a programmed necrosis, participated in the progression of IVDD, nevertheless, the underlying mechanism remains unclear.PurposeTo study the mechanism of necroptosis of Nucleus Pulposus (NP) cells in IVDD, focusing on the role of MyD88 signaling.Study designThe expression and co-localization of necroptotic indicators and MyD88 were examined in vivo, and MyD88 inhibitor was applied to determine the role of MyD88 signaling in necroptosis of NP cells in vitro.MethodsHuman disc specimens were collected from patients receiving diskectomy for lumbar disc herniation (LDH) or traumatic lumbar fractures after MRI scanning. According to the Pfirrmann grades, they were divided into normal (Grades 1, 2) and degenerated groups (4, 5). Tissue slides were prepared for immunofluorescence to assess the co-localization of necroptotic indicators (RIP3, MLKL, p-MLKL) and MyD88 histologically. The combination of TNFα, LPS and Z-VAD-FMK was applied to induce necroptosis of NP cells. Level of ATP, reactive oxygen species (ROS), live-cell staining and electron microscope study were employed to study the role of MyD88 signaling in necroptosis of NP cells.ResultsIn vivo, the increased expression and co-localization of necroptotic indicators (RIP3, MLKL, p-MLKL) and MyD88 were found in NP cells of degenerated disc, while very l low fluorescence intensity in tissue of traumatic lumbar fractures. In vitro, the MyD88 inhibitor effectively rescued the necroptosis of NP cells, accompanied by increased viability, ATP level, and decreased ROS level. The effect of MyD88 inhibition on necroptosis of NP cells was further confirmed by ultrastructure of mitochondria shown by Transmission Electron Microscope (TEM).ConclusionOur results indicated that the involvement of MyD88 signaling in the necroptosis of NP cells in IVDD, which will replenish the pathogenesis of IVDD and provide a novel potential therapeutic target for IVDD.

Project description:BackgroundAccelerated cellular senescence within the nucleus pulposus (NP) region is a common feature of disc degeneration. Our previous work indicated that TNF-α promoted NP cell senescence. Although the intervertebral disc has been reported to be an estrogen-sensitive tissue, it is unclear whether estrogen can inhibit premature senescence of NP cells.ObjectiveTo investigate whether 17beta-estradiol (E2) can attenuate TNF-α-induced premature senescence of NP cells and the potential mechanism behind this regulatory process.MethodsIsolated NP cells and intact intervertebral discs from healthy rats were cultured with or without TNF-α, E2 or their combination. The pan estrogen receptor (ER) antagonist ICI 182780 was used to investigate the role of ER. Direct and indirect indicators including cell proliferation, SA-β-Gal activity, telomerase activity, cell cycle, and the expression of matrix macromolecules (aggrecan and collagen II) and senescence markers (p16 and p53) were used to evaluate the premature senescence of NP cells. Additionally, intracellular reactive oxygen species (ROS) and NF-κB/p65 activity were also detected in the NP cell cultures.ResultsIn the NP cell cultures, E2 significantly increased cell proliferation potency, telomerase activity and the expression of matrix macromolecules but attenuated SA-β-Gal activity, senescence marker (p53 and p16) expression and G1 cycle arrest in TNF-α-treated NP cells. Furthermore, E2 inhibited ROS generation and phospho-NF-κB/p65 expression in the TNF-α-treated NP cells. However, the ER antagonist ICI 182780 abolished the effects of E2 on TNF-α-treated NP cells. In the disc organ cultures, E2 also significantly increased matrix synthesis, whereas it decreased senescence marker (p53 and p16) expression, which could be abolished by the ER antagonist ICI 182780.ConclusionThe interaction between E2 and ER can attenuate TNF-α-induced premature senescence of rat NP cells through interfering with the ROS/NF-κB pathway.

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A complex interaction between Wnt signaling and TNF-? in nucleus pulposus cells.

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A complex interaction between Wnt signaling and TNF-α in nucleus pulposus cells.

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