Antioxidant Proline Carbon Dot-Composited Poly(L-methionine) Hydrogel Restores Mitophagy to Alleviate Cellular Senescence in Intervertebral Disc Degeneration.

The senescence of nucleus pulposus cells (NPCs) is a hallmark pathological feature of intervertebral disc degeneration. Senescent NPCs exhibit mitochondrial dysfunction and impaired mitophagy, thus compromising mitochondrial turnover and quality control. Current therapeutic strategies predominantly target external risk factors but do not restore mitophagy. In this study, a proline carbon dot-composited poly(L-methionine) (EG45M25/Pro-CD) hydrogel is developed and employed to re-establish the impaired mitophagy pathway. Expression levels of Parkin and phosphorylated Parkin increase, indicating successful activation of the mitophagy pathway. Restoration of mitochondrial function markedly reduces oxidative stress and the senescence-associated secretory phenotype in NPCs. The levels of type II collagen and aggrecan recover to 84.63% and 77.31% of their normal ones, respectively. In an animal model, the administration of Pro-CD in a thermo-sensitive and injectable hydrogel effectively preserves the water content and height of intervertebral discs while maintaining the structural integrity and functional activity of NPCs. The mean Pfirrmann grade improves from 5.00 in the Control group to 3.33 after treatment, whereas the disc height index recovers to 82.06% of the physiological value. Collectively, our findings demonstrate that the EG45M25/Pro-CD composite hydrogel has therapeutic potential to promote endogenous disc regeneration by enhancing mitophagy, re-establishing redox homeostasis, and alleviating NPC senescence.