Tumor necrosis factor alpha promotes the proliferation of human nucleus pulposus cells via nuclear factor-κB, c-Jun N-terminal kinase, and p38 mitogen-activated protein kinase

Although tumor necrosis factor alpha (TNF-alpha) is known to play a critical role in intervertebral disc (IVD) degeneration, the effect of TNF-alpha on nucleus pulposus (NP) cells has not yet been elucidated. The aim of this study was to explore the effect of TNF-alpha on proliferation of human NP cells. NP cells were treated with different concentrations of TNF-alpha. Cell proliferation was determined by cell counting kit-8 (CCK-8) analysis and Ki67 immunofluorescence staining, and expression of cyclin B1 was studied by quantitative real-time RT-PCR. Cell cycle was measured by flow cytometry and cell apoptosis was analyzed using an Annexin V-fluorescein isothiocyanate (FITC) & propidium iodide (PI) apoptosis detection kit. To identify the mechanism by which TNF-alpha induced proliferation of NP cells, selective inhibitors of major signaling pathways were used and Western blotting was carried out. Treatment with TNF-alpha increased cell viability (as determined by CCK-8 analysis) and expression of cyclin B1 and the number of Ki67-positive and S-phase NP cells, indicating enhancement of proliferation. Consistent with this, NP cell apoptosis was suppressed by TNF-alpha treatment. Moreover, inhibition of NF-kappa B, c-Jun N-terminal kinase (JNK), and p38 mitogen-activated protein kinase (MAPK) blocked TNF-alpha-stimulated proliferation of NP cells. In conclusion, the current findings suggest that the effect of TNF-alpha on IVD degeneration involves promotion of the proliferation of human NP cells via the NF-kappa B, JNK, and p38 MAPK pathways.