2023, Vol. 27 ›› Issue (2): 223-229

Effect of nucleus pulposus cells-derived exosomes under cyclic mechanical tension on endplate chondrocytes

Zhang Weiye1, Zhan Jiawen1, 2, Zhu Liguo2, 3, Wang Shangquan1, 2, Chen Ming1, 2, Wei Xu2, 4, Feng Minshan3, 4, Yu Jie3, 4, Han Tao1, 4, Cai Chuhao1, Zhou Shuaiqi1, Shao Chenchen1   

Abstract: BACKGROUND: Endplate chondrocytes are regulated by many factors in the microenvironment of the intervertebral disc and the influence of microenvironmental changes inside the intervertebral disc caused by abnormal stress on endplate chondrocytes still needs to be explored.
OBJECTIVE: To observe the exosome secretion of nucleus pulposus cells under cyclic mechanical tension conditions and the effect of exosomes on endplate chondrocytes under this condition.
METHODS: Nucleus pulposus cells were isolated and cultured from the nucleus pulposus of patients undergoing lumbar surgery in vitro. The cells were loaded with cyclic mechanical tension by FX-5000T system. Exosomes secreted from nucleus pulposus cells under stress and non-stress conditions were extracted by magnetic bead method. Purity and concentration of nucleus pulposus cells-derived exosomes were identified by flow cytometry. The exosomes were labeled with PKH67 fluorescent dye and incubated with endplate chondrocytes for 24 hours. Endplate chondrocytes cultured alone were used as control. The uptake of exosomes by endplate chondrocytes was observed under inverted fluorescence microscope. Then the apoptosis and activity of endplate chondrocytes were observed. Type II collagen, depolymerized protein like metalloproteinase 5, matrix metalloproteinase 3, bone morphogenetic protein 2, and β-catenin mRNA expression were detected.
RESULTS AND CONCLUSION: Under certain cyclic mechanical tension conditions, nucleus pulposus cells could be promoted to secrete exosomes, and the particle concentration of nucleus pulposus cells-derived exosomes was higher than that under non-stress conditions. Under the inverted fluorescence microscope, both stress and non-stress nucleus pulposus cells-derived exosomes could be ingested by endplate chondrocytes. Compared with the control group, the viability of endplate chondrocytes decreased significantly (P < 0.05) and the apoptosis rate increased in the stress group (P < 0.05). Compared with the control group, the mRNA expression of matrix metalloproteinase 3 and bone morphogenetic protein 2 in endplate chondrocytes decreased significantly in the non-stress group (P < 0.05). Compared with the control group, the mRNA expression of type I collagen decreased significantly in the stress group (P < 0.05), while the mRNA expression of depolymerized protein like metalloproteinase 5, matrix metalloproteinase 3 and β-catenin increased significantly in the stress group (P < 0.05). Compared with the non-stress group, the mRNA expression of type II collagen decreased significantly in the stress group, while the mRNA expression of depolymerized protein like metalloproteinase 5, matrix metalloproteinase 3 and bone morphogenetic protein 2 increased significantly in the stress group (P < 0.05). Therefore, abnormal stress could promote the exosome secretion of nucleus pulposus cells, and the exosomes under this condition could inhibit the viability of endplate chondrocytes and cause the disorder of cell matrix synthesis and catabolism.
Key words: cyclic mechanical tension, nucleus pulposus cell, exosome, endplate chondrocyte, microenvironment, intervertebral disc, degeneration, abnormal stress