Regulation of endoplasmic reticulum stress on autophagy and apoptosis of nucleus pulposus cells in intervertebral disc degeneration and its related mechanisms

Abstract

Abstract Background Intervertebral disc degeneration (IVDD) is a common and frequent disease in orthopedics, which seriously affects the quality of life of patients. Endoplasmic reticulum stress (ERS)-regulated autophagy and apoptosis play an important role in nucleus pulposus (NP) cells in IVDD. Methods and Results Hypoxia and serum deprivation were used to induce NP cells. CCK-8 assay was used to detect cell activity and immunofluorescence (IF) was applied for the appraisement of GRP78 and GFP-LC3. Cell apoptosis was detected by flow cytometry and the expression of LC3II/I was detected by western blot. NP cells under hypoxia and serum deprivation were induced by lipopolysaccharide (LPS), and intervened by ERS inhibitor (4-phenylbutyric acid, 4-PBA) and activator (Thapsigargin, TP). Then, above functional experiments were conducted again and western blot was employed for the evaluation of autophagy-, apoptosis and ERS-related proteins. Finally, NP cells under hypoxia and serum deprivation were stimulated by LPS and intervened using apoptosis inhibitor z-VAD-FMK and autophagy inhibitor 3-MA. CCK-8 assay, IF, flow cytometry and western blot were preformed again. Besides, the levels of inflammatory cytokines were measured with ELISA and the protein expressions of programmed death markers were estimated with western blot. It showed that serum deprivation induces autophagy and apoptosis. ERS was significantly activated by LPS in hypoxic and serum deprivation environment, and autophagy and apoptosis were significantly promoted. Conclusions ERS affects the occurrence and development of IVDD by regulating autophagy, apoptosis and other programmed death.