Melatonin attenuates oxidative stress–induced ferroptosis of nucleus pulposus cells and intervertebral disc degeneration via PI3K/AKT-mTOR pathway

BACKGROUND: Intervertebral disc degeneration (IVDD) is a leading cause of low back pain and disability. Ferroptosis, an iron-dependent form of regulated cell death driven by oxidative stress, plays a critical role in IVDD pathogenesis. Melatonin, a neurohormone with antioxidative properties, has shown potential protective effects, but its precise mechanism of action remains unclear. METHODS: This study integrated multi-omics analyses, human NP specimens, cultured human NP cells, and a rat IVDD model induced by tert-butyl hydroperoxide (TBHP). Ferroptosis, oxidative stress, mitochondrial injury, and ECM metabolism were evaluated using histological staining, flow cytometry, ELISA, immunofluorescence, and western blotting. The involvement of melatonin receptors and PI3K/AKT-mTOR signaling was examined using pharmacological activation/blockade. Computational structural modeling was additionally employed to assess interactions between mTOR and ferroptosis-related proteins. RESULTS: Melatonin significantly inhibited TBHP-induced ferroptosis in NP cells by restoring GSH levels, reducing Fe2⁺ accumulation and ROS generation, preserving mitochondrial morphology, and upregulating SLC7A11 and GPX4. Melatonin also ameliorated ECM metabolic imbalance by increasing collagen II, aggrecan, and osteonectin, while suppressing MMP-9 and ADAMTS5. These protective effects were abolished by MT1/MT2 receptor antagonism or AKT phosphorylation inhibition, indicating pathway dependence. In vivo, melatonin attenuated disc degeneration, reduced apoptosis, restored ECM components, and normalized ferroptosis-related markers. Multi-omics datasets and structural modeling further supported that melatonin regulates ferroptosis through MT1/2-mediated activation of the PI3K/AKT-mTOR axis. CONCLUSIONS: Melatonin mitigates IVDD by suppressing ferroptosis and preserving ECM homeostasis through melatonergic receptor (MT1/MT2)-dependent activation of the PI3K/AKT-mTOR pathway. Notably, clinical and protein-level evidence suggests that MT1 may represent the predominant therapeutic target, supporting melatonin as a promising, low-toxicity candidate for delaying IVDD progression.