Transforming growth factor-β1-regulated Fas/FasL pathway activation suppresses nucleus pulposus cell apoptosis in an inflammatory environment

Background: During disc degeneration, inflammatory cytokine tumor necrosis factor (TNF)-alpha is correlated with nucleus pulposus (NP) cell apoptosis. Transforming growth factor (TGF)-beta 1 has the potential to regenerate degenerative disc. Objective: To investigate the protective role of TGF-beta 1 against TNF-alpha-mediated NP cell apoptosis and the underlying mechanism. Methods: Rat NP cells were treated with TNF-alpha (100 ng/ml) for 48 h. TGF-beta 1 was added into the culture medium to investigate its protective effects against TNF-alpha-induced NP cell apoptosis. Exogenous FasL was used to investigate the potential role of the Fas/FasL pathway in this process. Flow cytometry assay was used to analyze NP cell apoptosis. Real-time PCR and Western blotting were used to analyze gene and protein expression of apoptosis-related molecules. Results: In TNF-alpha-treated NP cells, TGF-beta 1 significantly decreased NP cell apoptosis, declined caspase-3 and -8 activity, and decreased expression of Bax and caspase-3 (cleaved-caspase-3) but increased expression of Bcl-2. However, exogenous FasL partly reversed these effects of TGF-beta 1 in NP cells treated with TNF-alpha. Additionally, expression of Fas and FasL in TNF-alpha-treated NP cells partly decreased by TGF-beta 1, whereas exogenous FasL increased expression of Fas and FasL in NP cells treated with TGF-beta 1 and TNF-alpha. Conclusion: TGF-beta 1 helps to inhibit TNF-alpha-induced NP cell apoptosis and the Fas/FasL pathway may be involved in this process. The present study suggests that TGF-beta 1 may be effective to retard inflammation-mediated disc degeneration.