17beta-estradiol Attenuates TNF-α-Induced Premature Senescence of Nucleus Pulposus Cells through Regulating the ROS/NF-κB Pathway

Background: Accelerated 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. Objective: To investigate whether 17beta-estradiol (E(2)) can attenuate TNF-α-induced premature senescence of NP cells and the potential mechanism behind this regulatory process. Methods: Isolated NP cells and intact intervertebral discs from healthy rats were cultured with or without TNF-α, E(2 )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. Results: In the NP cell cultures, E(2 )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, E(2) 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 E(2 )on TNF-α-treated NP cells. In the disc organ cultures, E(2) also significantly increased matrix synthesis, whereas it decreased senescence marker (p53 and p16) expression, which could be abolished by the ER antagonist ICI 182780. Conclusion: The interaction between E(2 )and ER can attenuate TNF-α-induced premature senescence of rat NP cells through interfering with the ROS/NF-κB pathway.