Senescent cartilage endplate stem cells-derived exosomes induce oxidative stress injury in nucleus pulposus cells and aggravate intervertebral disc degeneration by regulating FOXO3

Intervertebral disc degeneration (IVDD) is the leading cause of low back pain and associated disability worldwide. The cartilage endplate (CEP) is a critical structure in maintaining the homeostasis of the intervertebral disc, by exosomes (Exos)-mediated intracellular communication between cartilage endplate stem cells (CESCs) and nucleus pulposus cells (NPCs). However, whether the senescence of CESCs influences the functionality of CESCs-derived Exos (CESCs-Exos) and participates in the progress of IVDD remains unclear. In this study, we explored the role and mechanism of the Exos-based intracellular communication between senescent CESCs and NPCs in IVDD. CESCs isolated from aged individuals (S-CESCs) exhibited high levels of senescence compared with CESCs isolated from young individuals (Y-CESCs). Exos from Y-CESCs (Y-Exos) and from S-CESCs (S-Exos) were extracted and identified. Surprisingly, we found that S-Exos lost the therapeutic effects as the Y-Exos exhibited in mitigating IVDD, and even aggravated IVDD by inducing oxidative stress injury in NPCs. MicroRNA-sequencing revealed significant upregulation of miR-29b-3p expression in S-Exos. Through microRNA target prediction, dual luciferase assays, RNA-sequencing, lentivirus-mediated overexpression and suppression, we demonstrated that miR-29b-3p regulates the expression of FOXO3 and downstream antioxidant enzymes to induce oxidative stress injury in NPCs. In vivo experiments further verified that countering miR-29b-3p by antagomir reversed the detrimental effects of S-Exos in exacerbating IVDD. This work elucidates the role and mechanism of senescent CESCs in disrupting redox homeostasis in the nucleus pulposus and exacerbating IVDD by Exos-mediated intracellular communication and offers an experimental foundation for the selection of proper CESCs-Exos to obtain better therapeutic effects in IVDD.