Endoplasmic Reticulum Stress Facilitates the Survival and Proliferation of Nucleus Pulposus Cells in TNF-α Stimulus by Activating Unfolded Protein Response

Intervertebral disc (IVD) degeneration is closely related to inflammatory cytokines, such as tumor necrosis factor alpha (TNF-). The endoplasmic reticulum (ER) serves several important cell functions, which are essential for normal cell metabolism and survival. This study aims to clarify the role of ER stress and unfolded protein response (UPR) in TNF--induced biological changes in rat nucleus pulposus cells (NPCs) and IVD degeneration. In our research, rat NPCs were cultured with different concentrations of TNF- in the presence or absence of ER stress inhibitors. Related genes and proteins were measured by immunofluorescence staining, quantitative real-time PCR, and Western blot analyses to monitor ER stress. Cell proliferation was evaluated by CCK-8 assay and cyclin D1 expression. Apoptosis was detected by flow cytometry and Western blot analyses. Our results showed that TNF- induced the apoptosis of some NPCs in the early stage and then accelerated the proliferation of surviving cells. In addition, TNF- stimulus upregulated ER stress markers and initiated UPR. However, these effects could be reversed by inhibitors, thereby reducing cell proliferation and enhancing apoptosis. In conclusion, ER stress reinforces the survival and proliferation of NPCs in TNF- stimulus by activating UPR signaling, which could be an important therapeutic target in the future.