EZH2 inhibits senescence-associated inflammation and attenuates intervertebral disc degeneration by regulating the cGAS/STING pathway via H3K27me3

Objective: Senescent nucleus pulposus mesenchymal stem cells (NPMSCs) are key instigators of local chronic inflammation and disruptions in nucleus pulposus tissue repair in intervertebral disc degeneration (IVDD). This study aimed to investigate the interplay between EZH2 and NPMSCs senescence-associated inflammation. Methods: Nucleus pulposus samples were collected from IVDD patients (n = 15, F/M = 7/8, average age 47.9 (21−72) year-old). Multiplex immunohistochemistry was conducted to detect the expression of EZH2 and the cGAS/STING pathway. Subsequently, NPMSCs were isolated from 7 patients (n = 7, F/M = 4/3, average age 49.4 (36−68) year-old). After treatment with tert-butyl hydroperoxide and lentivirus-overexpression-EZH2 (Lv-OE-EZH2), real time fluorescent quantitative PCR, immunofluorescence, western blot, and ChIP were used to detect the expression of EZH2 and the cGAS/STING pathway. Micro-CT, magnetic resonance imaging, and histological staining were performed to assess the therapeutic effects of Lv-OE-EZH2 and a STING inhibitor on rat IVDD. All experiment designs were independent. Results: In both human nucleus pulposus tissues and an in vitro cell model, EZH2 expression decreased while the cGAS/STING pathway became activated in senescent NPMSCs. ChIP assays and Lv-OE-EZH2 experiments validated that EZH2 epigenetically inhibited STING expression via H3K27me3, thereby impairing the cGAS/STING pathway and attenuating senescence-associated inflammation. Moreover, overexpression of EZH2 (Pfirrmann grade means difference −1.375, p = 0.0089) and inhibition of STING effectively attenuated rat IVDD. Conclusion: The decreased expression of EZH2 in senescent NPMSCs promotes senescence-associated inflammation and the progression of IVDD, possibly by relieving the transcriptional inhibition of STING and enabling the activation of the cGAS/STING pathway.